Title of Invention	UPLINK CONGESTION DETECTION AND CONTROL BETWEEN NODES IN A RADIO ACCESS NETWORK
Abstract	Congestion in a radio access network (RAN) associated with transporting uplink information originating from one or more mobile terminals is detected. That detected RAN congestion is reduced using any suitable technique (several examples are described) and may be implemented in one or more nodes in the RAN. One advantageous (but non-limiting) application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs).

Title of Invention

UPLINK CONGESTION DETECTION AND CONTROL BETWEEN NODES IN A RADIO ACCESS NETWORK

Abstract

Congestion in a radio access network (RAN) associated with transporting uplink information originating from one or more mobile terminals is detected. That detected RAN congestion is reduced using any suitable technique (several examples are described) and may be implemented in one or more nodes in the RAN. One advantageous (but non-limiting) application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs).

Full Text	TECHNICAL FIELD The technical field relates to mobile data communications, and more particularly, to regulating uplink communications from mobile radio terminals in a radio access network. BACKGROUND There is an ever increasing demand for wireless communication devices to perform a variety of applications. Some of those applications require substantial bandwidth. For example, next generation wireless communication systems may offer high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA) to provide enhanced data rates over the radio interface to support Internet access and multimedia type applications. The enhanced uplink concept currently being considered in the 3rd Generation Project Partnership (3 GPP) intends to introduce substantially higher peak data rates over the radio interface in the uplink direction. Enhanced uplink data communications will likely employ fast scheduling and fast hybrid automatic repeat request (HARQ) with soft combining in the radio base station. Fast scheduling allows the radio base station to control when a wireless terminal is transmitting in the uplink direction and at what data transmission rate. Data transmission rate and transmission power are closely related, and scheduling can thus also be seen as a mechanism to vary the transmission power used by the mobile terminal for transmitting over an enhanced uplink channel. Because neither the amount of uplink data to be transmitted nor the transmission power available in the mobile terminal at the time of transmission is known to the radio base station. As a result, the final selection of data rate will likely be performed in the mobile terminal. But the radio base station can set an upper limit on the data rate and/or transmission power that the mobile terminal may use to transmit over an enhanced uplink data channel. Although the primary focus of enhanced uplink is on the radio interface performance and efficiency, the "bottleneck" may well occur further upstream from the radio interface in the transport of the uplink information between nodes in the radio access network (RAN). For example, the available uplink bit rate over the interface between a radio base station node in the RAN and a radio network controller node in the RAN (referred to as the Iub interface) may be a fraction of the available uplink bit rate over the radio interface. In this situation, high speed uplink packet access may overload the Iub interface between the radio base station and the radio network controller during peak bit rates. Figure 1 illustrates that even though the downlink HSDPA bit rate over the radio interface is higher than the uplink HSUPA bit 2 rate, the available bandwidth for high speed packet access data between the radio network controller and the radio base station is even less than the uplink HSUPA bit rate. The dashed line representing Iub High Speed Packet Access (HSPA) bandwidth limit is lower that the HSDPA and HSUPA bandwidths. Consider the following simple example. A radio base station (sometimes referred to as a "Node B" using 3GPP terminology) controls three cells that have an enhanced uplink data transmission capability. Assume that the radio base station is connected to a radio network controller using one 4 Mbps link to support the enhanced uplink data transmitted from the radio base station and the radio network controller. Assume that the enhanced uplink capability may be up to 4 Mbps per cell. In this situation, enhanced uplink communication data from three cells at or near capacity cannot be transported from the radio base station to the radio network controller over the single 4 Mbps link. The result is a congested or overload situation. This congestion could result in long delays and loss of data, which reduces quality of service. One possible solution to avoid this kind of overload situation would be to "over provision" the bandwidth resources in the radio access network for communications between radio network controllers and radio base stations. But this is inefficient, costly, and in some existing mobile communications networks, not practical. For high speed downlink, an HSDPA flow control algorithm could be employed by the radio base station to reduce the available downlink HSDPA bit rate to a level that suits the Iub interface bandwidth. But this control methodology cannot be employed in the opposite uplink direction because, as explained above, the amount of uplink data to be transmitted from mobile terminals is not known to the radio base station. Should the uplink enhanced bit rate over the radio interface significantly exceed the Iub uplink bandwidth, congestion will likely occur with long delays and possibly lost or otherwise corrupted data frames. What is needed, therefore, is a way to detect and then control an overload or other congested situation in the radio access network as a result of uplink mobile terminal communications being transported between nodes in the radio access network. SUMMARY The technology described herein meets this need as well as other needs. Congestion associated with transporting in the RAN uplink information originating from one or more mobile terminals is detected. That detected congestion is then reduced using any suitable technique(s) and may be implemented in one or more nodes in the RAN. One advantageous 3 (but non-limiting) application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs). Uplink congestion may be detected over an interface between a radio network controller and a radio base station (the Iub interface) and/or an interface between radio network controllers (the Iur interface). Although congestion reduction may be performed in any suitable fashion, one example approach is to reduce a parameter associated with a bit rate at which uplink mobile terminal information is transported through the RAN. For example, where the uplink mobile terminal information is communicated using uplink data flows, the bit rate parameter may be reduced by reducing a bit rate of one or more uplink data flows. It may be appropriate to limit the bit rate of the one or more uplink data flows actually causing the congestion in the RAN; alternatively, the bit rate of one or more lower priority uplink data flows may be reduced. There are a number of different ways that the bit rate parameter may be reduced. For example, a bit rate parameter value may correspond to an absolute bit rate parameter value or a relative bit rate parameter value sent to one or more mobile terminals, e.g., a maximum bit rate or transmission power or a percentage or fraction of a current bit rate or transmission power. Another approach is to reduce the bit rate parameter using a capacity limitation message. If the RNC detects a congested condition in the RAN, it can send a capacity limitation to a radio base station, which then schedules uplink transmissions from mobile terminals to effect that capacity limitation, e.g., by using scheduling grants or credits. In some situations, more drastic measures may be necessary to reduce the bit rate parameter such as dropping one or more frames of one or more uplink mobile terminal communications. In soft/softer handover situations, one or more of the diversity handover links may be released to reduce the bit rate parameter. Another technique employs sending negative acknowledgment messages for received packets back to the mobile terminal causing the mobile terminal to retransmit those negatively acknowledged packets. This effectively reduces the uplink bit rate through the RAN. The congestion control may be implemented by sending control information either over a separate control signaling channel or in a user data plane where the control signaling is sent along with the data over a data channel. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a graph illustrating the high speed packet access bandwidth for both the uplink and downlink directions as compared to the RAN bandwidth; 4 Figure 2 is a block diagram of a mobile communications system including an example radio access network (RAN); Figure 3 is a diagram illustrating various uplink chancels used by mobile terminals for communicating over the radio/air interface with the RAN; Figure 4 is a function block diagram illustrating various interfaces between multiple nodes in a radio access network; Figure 5 is a flow chart diagram illustrating example steps for uplink RAN congestion detection and control; Figure 6 is a function block diagram illustrating one example implementation for uplink RAN congestion detection and control; Figure 7 illustrates a capacity limitation message being sent from the RNC to the radio base station to reduce detected congestion or load in the RAN; and Figure 8 is a diagram illustrating a mobile terminal in soft handover in which a weaker soft handover leg is dropped in order to reduce uplink RAN congestions. DETAILED DESCRIPTION In the following description, for purposes of explanation and non-limitation, specific details are set forth, such as particular nodes, functional entities, techniques, protocols, standards, etc. in order to provide an understanding of the described technology. For example, one advantageous applications is to enhanced uplink communications in accordance with 3GPP specifications. But other applications and other standards may be employed. It will apparent to one skilled in the art that other embodiments may be practiced apart from the specific details disclosed below. In other instances, detailed descriptions of well-known methods, devices, techniques, etc. are omitted so as not to obscure the description with unnecessary detail. Individual function blocks are shown in the figures. Those skilled in the art will appreciate that the functions of those blocks may be implemented using individual hardware circuits, using software programs and data in conjunction with a suitably programmed microprocessor or general purpose computer, using applications specific integrated circuitry (ASIC), and/or using one or more digital signal processors (DSPs). Referring to Figure 2, an example network 10 that supports wireless communications is illustrated. Network 10 may accommodate one or more standard architectures including a universal mobile telecommunications system (UMTS) and other systems based on code division multiple access (CDMA), GPRS/EDGE and other systems based on time division multiple access (TDMA) systems, etc. In CDMA, different wireless channels are 5 distinguished using different channelization codes or sequences, (these distinct codes are used to encode different information streams), which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream or flow for the receive signal using the appropriate code or sequence to decode the received signal. In TDMA, the radio spectrum is divided into time slots. Each time slot allows only one user to transmit and/or receive. TDMA requires precise timing between the transmitter and the receiver so that each user may transmit its information during its allocated time slot. The network 10 includes a radio access network (RAN) 14 and one or more core network(s) 12. One example radio access network is the UMTS terrestrial access network (UTRAN) used in third generation cellular systems. Core network 14 typically supports circuit-based communications as well as packet-based communications. The RAN 14 includes one or more radio network controllers (RNCs) 16. Each RNC is coupled to one or more radio base stations (RBSs) 18 sometimes referred to as Node B's. The communications interface between Node Bs and RNCs is referred to as the Iub interface, and the communications interface between RNCs is referred to as the Iur interface. Transport of information over the Iub and Iur interfaces is typically based on asynchronous transfer mode (ATM) or Internet Protocol (IP). Wireless terminals 20 (referred to hereafter as mobile terminals) communicate over an air or radio interface with the RAN 14. The radio interface is referred to as the Uu interface. The two center mobile terminals are shown communicating with both RBSs 18. Although attention has recently been paid to high speed downlink packet access (HSDPA), there is increasing interest in high speed uplink packet access (HSUPA), also referred to as "enhanced uplink" and as enhanced uplink dedicated channel (E-DCH). Enhanced uplink employs several uplink channels from each mobile terminal with an active uplink connection as illustrated in Figure 3. The enhanced dedicated physical data channel (E-DPDCH) carries enhanced uplink data (at higher bit rates), in addition to the normal dedicated physical data channels (DPDCHs) used for regular uplink data communication. The dedicated physical control channel (DPCCH) carries pilot symbols and out-of-band control signaling. Out-of-band control signaling related to enhanced uplink, e.g., uplink scheduling requests, may be carried on the enhanced dedicated physical control channel (E- DPCCH). 6 As explained above, there is the possibility, particularly with enhanced uplink data communications, that the enhanced uplink bit rate over the air interface exceeds the uplink bandwidth limits for communications between nodes in the radio access network. This point was illustrated in Figure 1. These kinds of bandwidth restrictions between nodes in a radio access network may only become more significant as radio access networks expand or become more complicated. Consider, for example, the radio access network shown in Figure 4 in which multiple RNCs (RNC1, RNC2, ..., RNCn) are coupled to multiple radio base stations (RBS1, RBS2, ..., RBSn) by way of one or more aggregation nodes 22. The aggregation nodes 22 may be, for example, ATM switches, IP routers, etc. and are optional. Each aggregation node (1) aggregates data traffic from the RBSs to the RNCs and (2) splits the data traffic from the RNCs to the individual RBSs. In this more sophisticated radio access network, there are multiple Iur and Iub interfaces which may have limited bandwidth capability. Some type of congestion control should be in place to avoid congestion, delay, and overload situations caused by receiving uplink data over the radio interface at a rate greater than what can be currently transported over any one of these RAN interfaces. Reference is now made to the flowchart in Figure 5 which illustrates an uplink RAN congestion control routine. Congestion is monitored in the RAN that is associated with transporting uplink information through the RAN (step S2). An overload or congestion condition is detected between nodes in the RAN related to uplink information for example by detecting frame (or other data unit) losses (step S4). Frame losses may be detected using a frame sequence number (FSN). Each transport bearer between an RNC and a radio base station has its own sequence number. It is assumed that when a frame sequence number is detected as missing, that the corresponding frame is lost due to congestion. Alternatively, or in addition, delay build-up can be monitored to detect a congestion condition. In transport networks that include large buffers, congestion may not normally result in frame losses, but rather in a build-up of delay time in the buffer before packets are transmitted. Rather than relying on detected frame losses, which may result in severe delays, each user plane frame transmitted from a base station uplink to an RNC includes a field for a real-time stamp, e.g., a control frame number (CFN) plus a subframe number. If the RNC detects a time stamp "drift," meaning that the delay is increasing, the RNC can then determine there is congestion. For example, if uplink frames are delayed more than 30 msec in addition to the delay that is prevailing in non-congested circumstances, this is a good indicator of uplink congestion in the RAN. 7 Returning to Figure 5, once an overload or congestion condition is detected, one or more actions is taken to reduce the detected uplink congestion in the RAN (step S6). There are various techniques and implementations for reducing that detected uplink congestion in the RAN. Some non-limiting examples are described below. Consider the example implementation shown in Figure 6 in which both the radio network controller 16 and the radio base station 18 perform certain tasks in reducing uplink RAN congestion. The RNC 16 includes an uplink RAN congestion detector 30 and uplink RAN congestion controller 32, and a handover controller 34. The RNC 16 includes other functional entities which are not pertinent to this description and therefore are not shown. The radio base station 18 includes an uplink RAN congestion controller 40, an automatic repeat request (ARQ) controller 42, (which in a preferred implementation is a hybrid ARQ (HARQ) controller), a mobile terminal uplink scheduler 44, and radio circuitry 46. The radio base station 18 has other entities and circuitry for performing the functions not pertinent to the description and therefore are not shown. The uplink RAN congestion detector 30 monitors and detects uplink RAN congestion using, for example, frame loss detection or delay build-up detection as described above. Other techniques may be employed. The uplink RAN congestion controller 32 processes congestion detection information provided by detector 30, and based on certain characteristics of one or more congested uplink flows, the uplink RAN congestion controller 32 may decide to limit the uplink load in the RAN using any suitable methodology. For example, the congestion controller 32 may limit a maximum data rate/transmission power grant that the mobile terminal uplink scheduler 44 is allowed to assign to a particular mobile terminal or to a mobile terminal uplink data flow. The mobile terminal subjected to this maximum data rate/power restriction can be the same mobile terminal or data flow which is experiencing the congestion on one or more flows, or it may be a different mobile terminal or data flow, perhaps with a lower priority. Alternatively, the uplink RAN congestion controller 32 may limit the maximum data rate/transmission power that the uplink scheduler 44 is allowed to assign to a group of mobile terminals. The uplink RAN congestion controller 32 may communicate the maximum data rate/transmission power to the radio base station 18 using a CAPACITY LIMITATION message, as illustrated in Figure 7. The CAPACITY LIMITATION notification message includes the maximum bit rate/power that the uplink scheduler 44 may assign to one or more mobile terminal uplink flows. The CAPACITY LIMITATION message may also include a 8 time interval over which the maximum bit rate/power restriction applies. On the other hand, the limits may remain in effect until a new capacity limitation message is received. The uplink CAPACITY LIMITATION notification may be sent either in the RAN "user plane" using a control frame embedded with the data or in the RAN "control plane" using control signaling over an explicit control channel. Example control signaling protocols includes Node B Application Part (NBAP) /RNS Application Part/RNSAP). The maximum bit rate/power may be expressed, for example, as an absolute limit, such as 200 Kbps, or as a prohibition from using a transport format indicator (TFI) exceeding a particular value, such as TFI 12. An example in terms of an absolute transmission power might be a maximum allowed transmission power offset, and an example of a relative limit might be a percentage by which to reduce the current bit rate/power, e.g., 50%. Again, the load may be reduced with respect to the affected mobile terminal, an affected uplink flow, an aggregated load of multiple mobile terminals, or different mobile terminals or different flows that are less prioritized than the affected one(s). Alternatively, when the uplink RAN congestion controller 40 in the radio base station 18 receives a capacity limitation notification on the uplink RAN congestion controller 32, the congestion controller 40 may limit the scheduling grants assigned to a particular mobile terminal or group of mobile terminals. In a RAN supporting soft-handover, a mobile terminal can be connected to multiple cells controlled by one or several radio base stations. Of the cells in this "active set," the strongest (in terms of a pilot signal) is typically chosen as the "serving cell" responsible for the primary control of the mobile terminal. Via this serving cell, the radio base station can assign absolute grants limiting the maximum bit-rate/power of the mobile terminal. In order to control the, inter-cell interference, the radio base stations can also send relative grants via non-serving cells. Relative grants indicate if one or a group of mobile terminals should increase, hold, or decrease their current bit-rate/power. Any of these grants can be based on scheduling requests sent in the uplink from the mobile terminal to the radio base-stations. Such scheduling requests typically include, e.g., the desired bit-rate or the present buffer fill-levels in the mobile terminal. In the situation where the radio base station controls the serving cell of the mobile terminal, the uplink RAN congestion controller 40 limits the absolute grant of that mobile terminal; alternatively, the uplink RAN congestion controller 40 assigns relative grants (up/hold/down) so that the RNC capacity limitation is fulfilled. The uplink scheduler 44 can provide scheduling information to the mobile terminal to control the upper limit of the mobile 9 terminal transmission data rate/transmission power. The "absolute grant channel" may carry an absolute scheduling grant on a shared channel which includes (a) the identity of the mobile terminal (or a group of mobile terminals) for which the grant is valid and (b) the maximum resources that this mobile terminal (or group of mobile terminals) may use. A "relative grant channel" carries a relative scheduling grant on a dedicated channel and includes at least one bit that registers an incremental up/hold/down. The absolute grant channel is read from the serving cell. The relative grant channel may be read from additional cells, e.g., in the case of soft handover, from all cells in the active set. If a mobile terminal is assigned to read the relative grant channel from a set of cells, the mobile terminal must not increase its data rate or power offset if any cell in the active set signals a hold. Similarly, if any of the cells relative grants is set to down, the mobile terminal must decrease the rate or power offset with some predefined step size. When the radio base station does not control the mobile terminal serving cell, the uplink RAN congestion controller 40 assigns relative grant indications (up/hold/down) to fulfill the RNC capacity limitation. As another alternative already explained above, the uplink RAN congestion controller 40 may discard RAN data frames so that the RAN capacity limitation assigned by the RNC is fulfilled without affecting scheduling grants. Rather than discarding frames, the uplink RAN congestion controller 40 may instruct the H/ARQ controller 42 to send a NACK message for each received and discarded data unit back to the mobile terminal. NACKing the discarded data frames from a non-serving cell triggers re-transmission of those discarded data frames, unless some other link has received those data frames correctly. The effect is reduced pressure on the RAN transport. It is possible that the sending of capacity limitation control frames to inform the uplink RAN congestion controller 40 to lower the bit rate/transmission power relative to the normal bit rate/transmission power per HSUPA flow will result in the following behavior. If the uplink scheduler 44, which controls the HSUPA flow bit rates, lowers the flow bit rate from one of the mobile terminals by modifying its scheduling grants, it is likely that the uplink scheduler 44 will schedule another mobile terminals to transmit in its place. Moreover, it is likely that the mobile terminal associated with RAN congestion has excellent uplink radio/air interface performance. Therefore, scheduling another mobile instead of the congested mobile to transmit in the uplink should reduce the congestion of the uplink RAN congested flows. 10 After recovery from a congestion condition, as detected by the uplink RAN congestion detector 30, the uplink RAN congestion controller 32 may restore the original data rate or transmission power by sending notification to the radio base station. Alternatively, and as explained above, a configurable or predefined period of time may be set after which the temporary restriction on the uplink scheduler 44 is released. This latter approach may be preferred because explicit signaling from the RNC is not required. Consider a situation in which the mobile terminal 20 that is subject to RAN congestion is in soft handover, as illustrated in Figure 8. In this example, mobile terminal 20 has three soft handover links LI, L2, and L3 to three base stations RBS1, RBS2, and RBS3, respectively. Assume that the congested radio link L3 is not the "serving" handover link. Typically, the serving link is the strongest one of the handover links based on detected signal strength measurements. The uplink RAN congestion controller 32 may decide to release the weaker handover radio link L3, which is subject to congestion in the RAN, and leave links LI and L2. This congestion reduction approach has the benefit of not affecting the bit rate over the radio interface. Any capacity loss associated with loss of macro-diversity over the air interface is less impacting than the RAN congestion associated with link L3. The RAN Iub and Iur interfaces each likely have a maximum total uplink bandwidth. A certain, relatively small amount of each maximum bandwidth is allocated for control signaling. The rest of the remaining bandwidth may be divided as desired between uplink dedicated data channels (X) and enhanced uplink dedicated data channels (Y), where the remaining bandwidth = (X + Y). When the RNC detects uplink congestion over one of the interfaces, it sends a message to the RBS to reduce the enhanced uplink dedicated data channels bandwidth by a certain percentage selected to reduce the congestion without impacting the enhanced uplink services too much. When the congestion condition is alleviated or after a predetermined time period, the enhanced uplink dedicated data channels bandwidth may be restored to Y. The above technology solves the problem of uplink RAN congestion without having to over-provision the RAN transport network. The RAN congestion is reduced by adapting the uplink mobile transmissions load to the current uplink RAN resource situation. In other words, the data frame bit rate in the RAN can be adapted to present RAN bandwidth restrictions. As a result, the data frame delays and losses can be minimized even where the uplink radio interface could provide higher bit rates than what the RAN transport network can offer. 11 Although various embodiments have been shown and described in detail, the claims are not limited to any particular embodiment. None of the above description should be read as implying that any particular element, step, range, or function is essential such that it must be included in the claims scope. The scope of patented subject matter is defined only by the claims. The extent of legal protection is defined by the words recited in the allowed claims and their equivalents. No claim is intended to invoke paragraph 6 of 35 USC §112 unless the words "means for" are used. 12 WE CLAIM: 1. A method for managing an overload or congestion condition between nodes in a radio access network (RAN) (14) transporting data received from one or more mobile terminals (20), characterized by: monitoring for congestion in the RAN associated with transporting uplink information from one or more mobile terminals through the RAN; detecting congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN; and reducing the detected congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. 2. The method in claim 1, wherein the mobile terminals transmit information to the RAN using high speed uplink packet access (HSUPA) or using one or more enhanced uplink dedicated channels (E-DCHs). 3. The method in claim 1, wherein the RAN includes a radio network controller (16) coupled to a radio base station (18), and wherein the radio network controller detects uplink congestion over an interface between the radio network controller and the radio base station. 4. The method in claim 3, wherein the RAN includes the first radio network controller coupled to a second radio network controller, and wherein one of the radio network controllers detects uplink congestion over an interface between the first and second radio network controllers. 5. The method in claim 3, wherein the reducing includes taking an action to reduce a parameter associated with a bit rate at which uplink mobile terminal information is transported through the RAN. 6. The method in claim 5, wherein the uplink mobile terminal information is communicated using uplink data flows, and wherein the bit rate parameter is reduced by reducing a bit rate of one or more uplink data flows. 13 7. The method in claim 5, wherein the bit rate parameter is reduced based on an absolute bit rate parameter value or on a relative bit rate parameter value. 8. The method in claim 7, wherein the absolute bit rate parameter value corresponds to a maximum bit rate or transmission power and the relative bit rate parameter value corresponds to a percentage or fraction of a current bit rate or transmission power. 9. The method in claim 5, wherein the bit rate parameter is reduced by sending control information in a control plane or in a user data plane. 10. The method in claim 5, wherein the bit rate parameter is reduced using scheduling grants or credits for uplink mobile terminal communications. 11. The method in claim 5, wherein the bit rate parameter is reduced by dropping one or more frames of one or more uplink mobile terminal communications. 12. The method in claim 5, wherein the bit rate parameter is reduced by releasing one or more diversity handover radio links. 13. The method in claim 5, wherein the bit rate parameter is reduced using negative acknowledgement messages. 14. The method in claim 3, wherein first amount of bandwidth allocated to uplink dedicated channels and a second amount of bandwidth is allocated to enhanced uplink dedicated channels, and wherein the radio network controller sends a message to the radio base station to reduce the second amount of bandwidth when uplink congestion is detected in the RAN. 15. Apparatus for use in managing an overload or congestion condition between nodes in a radio access network (RAN) (14) transporting data received from one or more mobile terminals (20), characterized by: 14 a congestion detector (30) for monitoring and detecting congestion in the RAN associated with transporting information uplink from one or more mobile terminals through the RAN, and a congestion controller (32) for reducing the detected congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. 16. The apparatus in claim 15, wherein the RAN is configured to receive mobile terminal information using high speed uplink packet access (HSUPA) or using one or more enhanced uplink dedicated channels (E-DCHs). 17. The apparatus in claim 15, wherein the RAN includes a radio network controller (16) coupled to a radio base station (16), and wherein the apparatus is implemented in the radio network controller. 18. The apparatus in claim 17, wherein the RAN includes the first radio network controller coupled to a second radio network controller, and wherein one of the radio network controllers is configured to detect uplink congestion over an interface between the first and second radio network controllers. 19. The apparatus in claim 17, wherein the congestion controller is configured to reduce a parameter associated with a bit rate at which mobile terminal information is transported through the RAN. 20. The apparatus in claim 19, wherein the uplink mobile terminal information is communicated using uplink data flows, and wherein the congestion controller is configured to send a signal to the radio base station to reduce a bit rate of one or more uplink data flows. 21. The apparatus in claim 19, wherein the congestion controller is configured to send an absolute bit rate parameter value or a relative bit rate parameter value for use by the radio base station to reduce a bit ratp or power of one or more uplink mobile terminal transmissions. 15 22. The apparatus in claim 19, wherein the congestion controller is configured to reduce the bit rate parameter by sending control information in a control plane or in a user data plane to the radio base station. 23. The apparatus in claim 19, wherein the congestion controller is configured to send a signal to the radio base station to restrict scheduling of one or more uplink transmission grants or credits. 24. The apparatus in claim 15, wherein the congestion controller is configured to release one or more diversity handover radio links to reduce the detected congestion. 25. The apparatus in claim 15, wherein a first amount of bandwidth allocated to uplink dedicated channels and a second amount of bandwidth is allocated to enhanced uplink dedicated channels, and wherein the radio network controller is configured to send a message to the radio base station to reduce the second amount of bandwidth when uplink congestion is detected in the RAN. 26. Apparatus for use in managing an overload or congestion condition in a radio access network (RAN) (14) associated with transporting information uplink from one or more mobile terminals (20) through the RAN, characterized by: a scheduler (44) for scheduling uplink transmissions from one or more mobile terminals, and a congestion controller (40), coupled to the scheduler, for reducing congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. 27. The apparatus in claim 26, wherein the congestion controller is configured to receive one or more messages from a radio network controller in the RAN including information associated with reducing congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. 16 28. The apparatus in claim 27, wherein the congestion controller is configured to instruct the scheduler to restrict uplink transmission grants or credits provided to the one or more mobile terminals. 29. The apparatus in claim 27, wherein the congestion controller is configured to drop one or more frames associated with one or more uplink mobile terminal communications. 30. The apparatus in claim 27, wherein the congestion controller is configured to reduce a bit rate or power associated with one or more uplink mobile terminal communications using negative acknowledgement messages. Dated this 9th day of August 2007 WO 2006/075951 PCT/SE2006/000032 1 UPLINK CONGESTION DETECTION AND CONTROL BETWEEN NODES IN A RADIO ACCESS NETWORK TECHNICAL FIELD [0001] The technical field relates to mobile data communications, and more particularly, to regulating uplink communications from mobile radio terminals in a radio access network. BACKGROUND [0002] There is an ever increasing demand for wireless communication devices to perform a variety of applications. Some of those applications require substantial bandwidth. For example, next generation wireless communication systems may offer high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA) to provide enhanced data rates over the radio interface to support Internet access and multimedia type applications. [0003] The enhanced uplink concept currently being considered in the 3rd Generation Project Partnership (3GPP) intends to introduce substantially higher peak data rates over the radio interface in the uplink direction. Enhanced uplink data communications will likely employ fast scheduling and fast hybrid automatic repeat request (HARQ) with soft combining in the radio base station. Fast scheduling allows the radio base station to control when a wireless terminal is transmitting in the uplink direction and at what data transmission rate. Data transmission rate and transmission power are closely related, and scheduling can thus also be seen as a mechanism to vary the transmission power used by the mobile terminal for transmitting over an enhanced uplink channel. Because neither the amount of uplink data to be transmitted nor the transmission power available in the mobile terminal at the time of transmission is known to the radio base station. As a result, the final selection of data rate will likely be performed in the mobile terminal. But the radio base station can set an upper limit on the data rate and/or transmission power that the mobile terminal may use to transmit over an enhanced uplink data channel. [0004] Although the primary focus of enhanced uplink is on the radio interface performance and efficiency, the "bottleneck" may well occur further upstream from the radio interface in the transport of the uplink information between nodes in the radio access network (RAN). For example, the available uplink bit rate over the interface between a radio base station node in the RAN and a radio network controller node in the RAN (referred to as the Iub WO 2006/075951 PCT/SE2006/000032 2 interface) may be a fraction of the available uplink bit rate over the radio interface. In this situation, high speed uplink packet access may overload the Iub interface between the radio base station and the radio network controller during peak bit rates. Figure 1 illustrates that even though the downlink HSDPA bit rate over the radio interface is higher than the uplink HSUPA bit rate, the available bandwidth for high speed packet access data between the radio network controller and the radio base station is even less than the uplink HSUPA bit rate. The dashed line representing Iub High Speed Packet Access (HSPA) bandwidth limit is lower that the HSDPA and HSUPA bandwidths. [0005] Consider the following simple example. A radio base station (sometimes referred to as a "Node B" using 3GPP terminology) controls three cells that have an enhanced uplink data transmission capability. Assume that the radio base station is connected to a radio network controller using one 4 Mbps link to support the enhanced uplink data transmitted from the radio base station and the radio network controller. Assume that the enhanced uplink capability may be up to 4 Mbps per cell. In this situation, enhanced uplink communication data from three cells at or near capacity cannot be transported from the radio base station to the radio network controller over the single 4 Mbps link. The result is a congested or overload situation. This congestion could result in long delays and loss of data, which reduces quality of service. [0006] One possible solution to avoid this kind of overload situation would be to "over provision" the bandwidth resources in the radio access network for communications between radio network controllers and radio base stations. But this is inefficient, costly, and in some existing mobile communications networks, not practical. For high speed downlink, an HSDPA flow control algorithm could be employed by the radio base station to reduce the available downlink HSDPA bit rate to a level that suits the Iub interface bandwidth. But this control methodology cannot be employed in the opposite uplink direction because, as explained above, the amount of uplink data to be transmitted from mobile terminals is not known to the radio base station. Should the uplink enhanced bit rate over the radio interface significantly exceed the Iub uplink bandwidth, congestion will likely occur with long delays and possibly lost or otherwise corrupted data frames. What is needed, therefore, is a way to detect and then control an overload or other congested situation in the radio access network as a result of uplink mobile terminal communications being transported between nodes in the radio access network. WO 2006/075951 PCT/SE2006/000032 3 SUMMARY [0007] The technology described herein meets this need as well as other needs. Congestion associated with transporting in the RAN uplink information originating from one or more mobile terminals is detected. That detected congestion is then reduced using any suitable technique(s) and may be implemented in one or more nodes in the RAN. One advantageous (but non-limiting) application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs). Uplink congestion may be detected over an interface between a radio network controller and a radio base station (the Iub interface) and/or an interface between radio network controllers (the Iur interface). [0008] Although congestion reduction may be performed in any suitable fashion, one example approach is to reduce a parameter associated with a bit rate at which uplink mobile terminal information is transported through the RAN. For example, where the uplink mobile terminal information is communicated using uplink data flows, the bit rate parameter may be reduced by reducing a bit rate of one or more uplink data flows. It may be appropriate to limit the bit rate of the one or more uplink data flows actually causing the congestion in the RAN; alternatively, the bit rate of one or more lower priority uplink data flows may be reduced. [0009] There are a number of different ways that the bit rate parameter may be reduced. For example, a bit rate parameter value may correspond to an absolute bit rate parameter value or a relative bit rate parameter value sent to one or more mobile terminals, e.g., a maximum bit rate or transmission power or a percentage or fraction of a current bit rate or transmission power. Another approach is to reduce the bit rate parameter using a capacity limitation message. If the RNC detects a congested condition in the RAN, it can send a capacity limitation to a radio base station, which then schedules uplink transmissions from mobile terminals to effect that capacity limitation, e.g., by using scheduling grants or credits. [0010] In some situations, more drastic measures may be necessary to reduce the bit rate parameter such as dropping one or more frames of one or more uplink mobile terminal communications. In soft/softer handover situations, one or more of the diversity handover links may be released to reduce the bit rate parameter. Another technique employs sending negative acknowledgment messages for received packets back to the mobile terminal causing the mobile terminal to retransmit those negatively acknowledged packets. This effectively reduces the uplink bit rate through the RAN. WO 2006/075951 PCT/SE2006/000032 4 [0011] The congestion control may be implemented by sending control information either over a separate control signaling channel or in a user data plane where the control signaling is sent along with the data over a data channel. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIGURE 1 is a graph illustrating the high speed packet access bandwidth for both the uplink and downlink directions as compared to the RAN bandwidth; [0013] Figure 2 is a block diagram of a mobile communications system including an example radio access network (RAN); [0014] Figure 3 is a diagram illustrating various uplink chancels used by mobile terminals for communicating over the radio/air interface with the RAN; [0015] Figure 4 is a function block diagram illustrating various interfaces between multiple nodes in a radio access network; [0016] Figure 5 is a flow chart diagram illustrating example steps for uplink RAN congestion detection and control; [0017] Figure 6 is a function block diagram illustrating one example implementation for uplink RAN congestion detection and control; [0018] Figure 7 illustrates a capacity limitation message being sent from the RNC to the radio base station to reduce detected congestion or load in the RAN; and [0019] Figure 8 is a diagram illustrating a mobile terminal in soft handover in which a weaker soft handover leg is dropped in order to reduce uplink RAN congestions. DETAILED DESCRIPTION [0020] In the following description, for purposes of explanation and non-limitation, specific details are set forth, such as particular nodes, functional entities, techniques, protocols, standards, etc. in order to provide an understanding of the described technology. For example, one advantageous applications is to enhanced uplink communications in accordance with 3GPP specifications. But other applications and other standards may be employed. It will apparent to one skilled in the art that other embodiments may be practiced apart from the specific details disclosed below. In other instances, detailed descriptions of well-known methods, devices, techniques, etc. are omitted so as not to obscure the description with unnecessary detail. Individual function blocks are shown in the figures. Those skilled in the art will appreciate that the functions of those blocks may be implemented using individual WO 2006/075951 PCT/SE2006/000032 5 hardware circuits, using software programs and data in conjunction with a suitably programmed microprocessor or general purpose computer, using applications specific integrated circuitry (ASIC), and/or using one or more digital signal processors (DSPs). [0021] Referring to Figure 2, an example network 10 that supports wireless communications is illustrated. Network 10 may accommodate one or more standard architectures including a universal mobile telecommunications system (UMTS) and other systems based on code division multiple access (CDMA), GPRS/EDGE and other systems based on time division multiple access (TDMA) systems, etc. In CDMA, different wireless channels are distinguished using different channelization codes or sequences, (these distinct codes are used to encode different information streams), which may then be modulated at one or more different carrier frequencies for simultaneous transmission. A receiver may recover a particular stream or flow for the receive signal using the appropriate code or sequence to decode the received signal. In TDMA, the radio spectrum is divided into time slots. Each time slot allows only one user to transmit and/or receive. TDMA requires precise timing between the transmitter and the receiver so that each user may transmit its information during its allocated time slot. [0022] The network 10 includes a radio access network (RAN) 14 and one or more core network(s) 12. One example radio access network is the UMTS terrestrial access network (UTRAN) used in third generation cellular systems. Core network 14 typically supports circuit-based communications as well as packet-based communications. The RAN 14 includes one or more radio network controllers (RNCs) 16. Each RNC is coupled to one or more radio base stations (RBSs) 18 sometimes referred to as Node B's. The communications interface between Node Bs and RNCs is referred to as the lub interface, and the communications interface between RNCs is referred to as the Iur interface. Transport of information over the lub and Iur interfaces is typically based on asynchronous transfer mode (ATM) or Internet Protocol (IP). Wireless terminals 20 (referred to hereafter as mobile terminals) communicate over an air or radio interface with the RAN 14. The radio interface is referred to as the Uu interface. The two center mobile terminals are shown communicating with both RBSs 18. [0023] Although attention has recently been paid to high speed downlink packet access (HSDPA), there is increasing interest in high speed uplink packet access (HSUPA), also referred to as "enhanced uplink" and as enhanced uplink dedicated channel (E-DCH). Enhanced uplink employs several uplink channels from each mobile terminal with an active uplink connection as illustrated in Figure 3. The enhanced dedicated physical data channel (E- WO 2006/075951 PCT/SE2006/000032 6 DPDCH) carries enhanced uplink data (at higher bit rates), in addition to the normal dedicated physical data channels (DPDCHs) used for regular uplink data communication. The dedicated physical control channel (DPCCH) carries pilot symbols and out-of-band control signaling. Out-of-band control signaling related to enhanced uplink, e.g., uplink scheduling requests, may be carried on the enhanced dedicated physical control channel (E-DPCCH). [0024] As explained above, there is the possibility, particularly with enhanced uplink data communications, that the enhanced uplink bit rate over the air interface exceeds the uplink bandwidth limits for communications between nodes in the radio access network. This point was illustrated in Figure 1. These lands of bandwidth restrictions between nodes in a radio access network may only become more significant as radio access networks expand or become more complicated. Consider, for example, the radio access network shown in Figure 4 in which multiple RNCs (RNC1, RNC2, ..., RNCn) are coupled to multiple radio base stations (RBS1, RBS2, ..., RBSn) by way of one or more aggregation nodes 22. The aggregation nodes 22 may be, for example, ATM switches, IP routers, etc. and are optional. Each aggregation node (1) aggregates data traffic from the RBSs to the RNCs and (2) splits the data traffic from the RNCs to the individual RBSs. In this more sophisticated radio access network, there are multiple Iur and Iub interfaces which may have limited bandwidth capability. Some type of congestion control should be in place to avoid congestion, delay, and overload situations caused by receiving uplink data over the radio interface at a rate greater than what can be currently transported over any one of these RAN interfaces. [0025] Reference is now made to the flowchart in Figure 5 which illustrates an uplink RAN congestion control routine. Congestion is monitored in the RAN that is associated with transporting uplink information through the RAN (step S2). An overload or congestion condition is detected between nodes in the RAN related to uplink information for example by detecting frame (or other data unit) losses (step S4). Frame losses may be detected using a frame sequence number (FSN). Each transport bearer between an RNC and a radio base station has its own sequence number. It is assumed that when a frame sequence number is detected as missing, that the corresponding frame is lost due to congestion. [0026] Alternatively, or in addition, delay build-up can be monitored to detect a congestion condition. In transport networks that include large buffers, congestion may not normally result in frame losses, but rather in a build-up of delay time in the buffer before packets are transmitted. Rather than relying on detected frame losses, which may result in severe delays, each user plane frame transmitted from a base station uplink to an RNC includes WO 2006/075951 PCT/SE2006/000032 7 a field for a real-time stamp, e.g., a control frame number (CFN) plus a subframe number. If the RNC detects a time stamp "drift," meaning that the delay is increasing, the RNC can then determine there is congestion. For example, if uplink frames are delayed more than 30 msec in addition to the delay that is prevailing in non-congested circumstances, this is a good indicator of uplink congestion in the RAN. [0027] Returning to Figure 5, once an overload or congestion condition is detected, one or more actions is taken to reduce the detected uplink congestion in the RAN (step S6). There are various techniques and implementations for reducing that detected uplink congestion in the RAN. Some non-limiting examples are described below. [0028] Consider the example implementation shown in Figure 6 in which both the radio network controller 16 and the radio base station 18 perform certain tasks in reducing uplink RAN congestion. The RNC 16 includes an uplink RAN congestion detector 30 and uplink RAN congestion controller 32, and a handover controller 34. The RNC 16 includes other functional entities which are not pertinent to this description and therefore are not shown. The radio base station 18 includes an uplink RAN congestion controller 40, an automatic repeat request (ARQ) controller 42, (which in a preferred implementation is a hybrid ARQ (HARQ) controller), a mobile terminal uplink scheduler 44, and radio circuitry 46. The radio base station 18 has other entities and circuitry for performing the functions not pertinent to the description and therefore are not shown. [0029] The uplink RAN congestion detector 30 monitors and detects uplink RAN congestion using, for example, frame loss detection or delay build-up detection as described above. Other techniques may be employed. The uplink RAN congestion controller 32 processes congestion detection information provided by detector 30, and based on certain characteristics of one or more congested uplink flows, the uplink RAN congestion controller 32 may decide to limit the uplink load in the RAN using any suitable methodology. For example, the congestion controller 32 may limit a maximum data rate/transmission power grant that the mobile terminal uplink scheduler 44 is allowed to assign to a particular mobile terminal or to a mobile terminal uplink data flow. The mobile terminal subjected to this maximum data rate/power restriction can be the same mobile terminal or data flow which is experiencing the congestion on one or more flows, or it may be a different mobile terminal or data flow, perhaps with a lower priority. [0030] Alternatively, the uplink RAN congestion controller 32 may limit the maximum data rate/transmission power that the uplink scheduler 44 is allowed to assign to a group of WO 2006/075951 PCT/SE2006/000032 8 mobile terminals. The uplink RAN congestion controller 32 may communicate the maximum data rate/transmission power to the radio base station 18 using a CAPACITY LIMITATION message, as illustrated in Figure 7. The CAPACITY LIMITATION notification message includes the maximum bit rate/power that the uplink scheduler 44 may assign to one or more mobile terminal uplink flows. The CAPACITY LIMITATION message may also include a time interval over which the maximum bit rate/power restriction applies. On the other hand, the limits may remain in effect until a new capacity limitation message is received. The uplink CAPACITY LIMITATION notification may be sent either in the RAN "user plane" using a control frame embedded with the data or in the RAN "control plane" using control signaling over an explicit control channel. Example control signaling protocols includes Node B Application Part (NBAP) /RNS Application Part/RNSAP). [0031] The maximum bit rate/power may be expressed, for example, as an absolute limit, such as 200 Kbps, or as a prohibition from using a transport format indicator (TFI) exceeding a particular value, such as TFI 12. An example in terms of an absolute transmission power might be a maximum allowed transmission power offset, and an example of a relative limit might be a percentage by which to reduce the current bit rate/power, e.g., 50%. Again, the load may be reduced with respect to the affected mobile terminal, an affected uplink flow, an aggregated load of multiple mobile terminals, or different mobile terminals or different flows that are less prioritized than the affected one(s). [0032] Alternatively, when the uplink RAN congestion controller 40 in the radio base station 18 receives a capacity limitation notification on the uplink RAN congestion controller 32, the congestion controller 40 may limit the scheduling grants assigned to a particular mobile terminal or group of mobile terminals. In a RAN supporting soft-handover, a mobile terminal can be connected to multiple cells controlled by one or several radio base stations. Of the cells in this "active set," the strongest (in terms of a pilot signal) is typically chosen as the "serving cell" responsible for the primary control of the mobile terminal. Via this serving cell, the radio base station can assign absolute grants limiting the maximum bit-rate/power of the mobile terminal. In order to control the inter-cell interference, the radio base stations can also send relative grants via non-serving cells. Relative grants indicate if one or a group of mobile terminals should increase, hold, or decrease their current bit-rate/power. Any of these grants can be based on scheduling requests sent in the uplink from the mobile terminal to the radio base-stations. Such scheduling requests typically include, e.g., the desired bit-rate or the present buffer fill-levels in the mobile terminal. WO 2006/075951 PCT/SE2006/000032 9 [0033] In the situation where the radio base station controls the serving cell of the mobile terminal, the uplink RAN congestion controller 40 limits the absolute grant of that mobile terminal; alternatively, the uplink RAN congestion controller 40 assigns relative grants (up/hold/down) so that the RNC capacity limitation is fulfilled. The uplink scheduler 44 can provide scheduling information to the mobile terminal to control the upper limit of the mobile terminal transmission data rate/transmission power. The "absolute grant channel" may carry an absolute scheduling grant on a shared channel which includes (a) the identity of the mobile terminal (or a group of mobile terminals) for which the grant is valid and (b) the maximum resources that this mobile terminal (or group of mobile terminals) may use. A "relative grant channel" carries a relative scheduling grant on a dedicated channel and includes at least one bit that registers an incremental up/hold/down. The absolute grant channel is read from the serving cell. The relative grant channel may be read from additional cells, e.g., in the case of soft handover, from all cells in the active set. If a mobile terminal is assigned to read the relative grant channel from a set of cells, the mobile terminal must not increase its data rate or power offset if any cell in the active set signals a hold. Similarly, if any of the cells relative grants is set to down, the mobile terminal must decrease the rate or power offset with some predefined step size. When the radio base station does not control the mobile terminal serving cell, the uplink RAN congestion controller 40 assigns relative grant indications (up/hold/down) to fulfill the RNC capacity limitation. [0034] As another alternative already explained above, the uplink RAN congestion controller 40 may discard RAN data frames so that the RAN capacity limitation assigned by the RNC is fulfilled without affecting scheduling grants. Rather than discarding frames, the uplink RAN congestion controller 40 may instruct the H/ARQ controller 42 to send a NACK message for each received and discarded data unit back to the mobile terminal. NACKing the discarded data frames from a non-serving cell triggers re-transmission of those discarded data frames, unless some other link has received those data frames correctly. The effect is reduced pressure on the RAN transport. [0035] It is possible that the sending of capacity limitation control frames to inform the uplink RAN congestion controller 40 to lower the bit rate/transmission power relative to the normal bit rate/transmission power per HSUPA flow will result in the following behavior. If the uplink scheduler 44, which controls the HSUPA flow bit rates, lowers the flow bit rate from one of the mobile terminals by modifying its scheduling grants, it is likely that the uplink scheduler 44 will schedule another mobile terminals to transmit in its place. Moreover, it is WO 2006/075951 PCT/SE2006/000032 10 likely that the mobile terminal associated with RAN congestion has excellent uplink radio/air interface performance. Therefore, scheduling another mobile instead of the congested mobile to transmit in the uplink should reduce the congestion of the uplink RAN congested flows. [0036] After recovery from a congestion condition, as detected by the uplink RAN congestion detector 30, the uplink RAN congestion controller 32 may restore the original data rate or transmission power by sending notification to the radio base station. Alternatively, and as explained above, a configurable or predefined period of time may be set after which the temporary restriction on the uplink scheduler 44 is released. This latter approach may be preferred because explicit signaling from the RNC is not required. [0037] Consider a situation in which the mobile terminal 20 that is subject to RAN congestion is in soft handover, as illustrated in Figure 8. In this example, mobile terminal 20 has three soft handover links LI, L2, and L3 to three base stations RBS1, RBS2, and RBS3, respectively. Assume that the congested radio link L3 is not the "serving" handover link. Typically, the serving link is the strongest one of the handover links based on detected signal strength measurements. The uplink RAN congestion controller 32 may decide to release the weaker handover radio link L3, which is subject to congestion in the RAN, and leave links LI and L2. This congestion reduction approach has the benefit of not affecting the bit rate over the radio interface. Any capacity loss associated with loss of macro-diversity over the air interface is less impacting than the RAN congestion associated with link L3. [0038] The RAN Iub and Iur interfaces each likely have a maximum total uplink bandwidth. A certain, relatively small amount of each maximum bandwidth is allocated for control signaling. The rest of the remaining bandwidth may be divided as desired between uplink dedicated data channels (X) and enhanced uplink dedicated data channels (Y), where the remaining bandwidth = (X + Y). When the RNC detects uplink congestion over one of the interfaces, it sends a message to the RBS to reduce the enhanced uplink dedicated data channels bandwidth by a certain percentage selected to reduce the congestion without impacting the enhanced uplink services too much. When the congestion condition is alleviated or after a predetermined time period, the enhanced uplink dedicated data channels bandwidth may be restored to Y. [0039] The above technology solves the problem of uplink RAN congestion without having to over-provision the RAN transport network. The RAN congestion is reduced by adapting the uplink mobile transmissions load to the current uplink RAN resource situation. In other words, the data frame bit rate in the RAN can be adapted to present RAN bandwidth WO 2006/075951 PCT/SE200fi/000032 11 restrictions. As a result, the data frame delays and losses can be minimized even where the uplink radio interface could provide higher bit rates than what the RAN transport network can offer. [0040] Although various embodiments have been shown and described in detail, the claims are not limited to any particular embodiment. None of the above description should be read as implying that any particular element, step, range, or function is essential such that it must be included in the claims scope. The scope of patented subject matter is defined only by the claims. The extent of legal protection is defined by the words recited in the allowed claims and their equivalents. No claim is intended to invoke paragraph 6 of 35 USC §112 unless the words "means for" are used. WO 2006/075951 PCT/SE2006/000032 12 CLAIMS 1. A method for managing an overload or congestion condition between nodes in a radio access network (RAN) (14) transporting data received from one or more mobile terminals (20), characterized by: monitoring for congestion in the RAN associated with transporting uplink information from one or more mobile terminals through the RAN; detecting congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN; and reducing the detected congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. 2. The method in claim 1, wherein the mobile terminals transmit information to the RAN using high speed uplink packet access (HSUPA) or using one or more enhanced uplink dedicated channels (E-DCHs). 3. The method in claim 1, wherein the RAN includes a radio network controller (16) coupled to a radio base station (18), and wherein the radio network controller detects uplink congestion over an interface between the radio network controller and the radio base station. 4. The method in claim 3, wherein the RAN includes the first radio network controller coupled to a second radio network controller, and wherein one of the radio network controllers detects uplink congestion over an interface between the first and second radio network controllers. 5. The method in claim 3, wherein the reducing includes talcing an action to reduce a parameter associated with a bit rate at which uplink mobile terminal information is transported through the RAN. WO 20(16/075951 PCT/SE2006/000032 13 6. The method in claim 5, wherein the uplink mobile terminal information is communicated using uplink data flows, and wherein the bit rate parameter is reduced by reducing a bit rate of one or more uplink data flows. 7. The method in claim 5, wherein the bit rate parameter is reduced based on an absolute bit rate parameter value or on a relative bit rate parameter value. 8. The method in claim 7, wherein the absolute bit rate parameter value corresponds to a maximum bit rate or transmission power and the relative bit rate parameter value corresponds to a percentage or fraction of a current bit rate or transmission power. 9. The method in claim 5, wherein the bit rate parameter is reduced by sending control information in a control plane or in a user data plane. 10. The method in claim 5, wherein the bit rate parameter is reduced using scheduling grants or credits for uplink mobile terminal communications. 11. The method in claim 5, wherein the bit rate parameter is reduced by dropping one or more frames of one or more uplink mobile terminal communications. 12. The method in claim 5, wherein the bit rate parameter is reduced by releasing one or more diversity handover radio links. 13. The method in claim 5, wherein the bit rate parameter is reduced using negative acknowledgement messages. 14. The method in claim 3, wherein first amount of bandwidth allocated to uplink dedicated channels and a second amount of bandwidth is allocated to enhanced uplink dedicated channels, and wherein the radio network controller sends a message to the radio base station to reduce the second amount of bandwidth when uplink congestion is detected in the RAN. WO 2006/075951 PCT/SE2006/000032 14 15. Apparatus for use in managing an overload or congestion condition between nodes in a radio access network (RAN) (14) transporting data received from one or more mobile terminals (20), characterized by: a congestion detector (30) for monitoring and detecting congestion in the RAN associated with transporting information uplink from one or more mobile terminals through the RAN, and a congestion controller (32) for reducing the detected congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. 16. The apparatus in claim 15, wherein the RAN is configured to receive mobile terminal information using high speed uplink packet access (HSUPA) or using one or more enhanced uplink dedicated channels (E-DCHs). 17. The apparatus in claim 15, wherein the RAN includes a radio network controller (16) coupled to a radio base station (16), and wherein the apparatus is implemented in the radio network controller. 18. The apparatus in claim 17, wherein the RAN includes the first radio network controller coupled to a second radio network controller, and wherein one of the radio network controllers is configured to detect uplink congestion over an interface between the first and second radio network controllers. 19. The apparatus in claim 17, wherein the congestion controller is configured to reduce a parameter associated with a bit rate at which mobile terminal information is transported through the RAN. 20. The apparatus in claim 19, wherein the uplink mobile terminal information is communicated using uplink data flows, and wherein the congestion controller is configured to send a signal to the radio base station to reduce a bit rate of one or more uplink data flows. WO 2006/075951 PCT/SE2006/000032 15 21. The apparatus in claim 19, wherein the congestion controller is configured to send an absolute bit rate parameter value or a relative bit rate parameter value for use by the radio base station to reduce a bit rate or power of one or more uplink mobile terminal transmissions. 22. The apparatus in claim 19, wherein the congestion controller is configured to reduce the bit rate parameter by sending control information in a control plane or in a user data plane to the radio base station. 23. The apparatus in claim 19, wherein the congestion controller is configured to send a signal to the radio base station to restrict scheduling of one or more uplink transmission grants or credits. 24. The apparatus in claim 15, wherein the congestion controller is configured to release one or more diversity handover radio links to reduce the detected congestion. 25. The apparatus in claim 15, wherein a first amount of bandwidth allocated to uplink dedicated channels and a second amount of bandwidth is allocated to enhanced uplink dedicated channels, and wherein the radio network controller is configured to send a message to the radio base station to reduce the second amount of bandwidth when uplink congestion is detected in the RAN. 26. Apparatus for use in managing an overload or congestion condition in a radio access network (RAN) (14) associated with transporting information uplink from one or more mobile terminals (20) through the RAN, characterized by: a scheduler (44) for scheduling uplink transmissions from one or more mobile terminals, and a congestion controller (40), coupled to the scheduler, for reducing congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN. WO 2006/075951 PCT/SE2006/000032 16 27. The apparatus in claim 26, wherein the congestion controller is configured to receive one or more messages from a radio network controller in the RAN including information associated with reducing congestion in the RAN associated with transporting information uplink from mobile terminals through the RAN.0 28. The apparatus in claim 27, wherein the congestion controller is configured to instruct the scheduler to restrict uplink transmission grants or credits provided to the one or more mobile terminals. 29. The apparatus in claim 27, wherein the congestion controller is configured to drop one or more frames associated with one or more uplink mobile terminal communications. 30. The apparatus in claim 27, wherein the congestion controller is configured to reduce a bit rate or power associated with one or more uplink mobile terminal communications using negative acknowledgement messages. Congestion in a radio access network (RAN) associated with transporting uplink information originating from one or more mobile terminals is detected. That detected RAN congestion is reduced using any suitable technique (several examples are described) and may be implemented in one or more nodes in the RAN. One advantageous (but non-limiting) application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs).

Full Text

TECHNICAL FIELD
The technical field relates to mobile data communications, and more particularly, to
regulating uplink communications from mobile radio terminals in a radio access network.
BACKGROUND
There is an ever increasing demand for wireless communication devices to perform a
variety of applications. Some of those applications require substantial bandwidth. For
example, next generation wireless communication systems may offer high speed downlink
packet access (HSDPA) and high speed uplink packet access (HSUPA) to provide enhanced
data rates over the radio interface to support Internet access and multimedia type applications.
The enhanced uplink concept currently being considered in the 3rd Generation Project
Partnership (3 GPP) intends to introduce substantially higher peak data rates over the radio
interface in the uplink direction. Enhanced uplink data communications will likely employ
fast scheduling and fast hybrid automatic repeat request (HARQ) with soft combining in the
radio base station. Fast scheduling allows the radio base station to control when a wireless
terminal is transmitting in the uplink direction and at what data transmission rate. Data
transmission rate and transmission power are closely related, and scheduling can thus also be
seen as a mechanism to vary the transmission power used by the mobile terminal for
transmitting over an enhanced uplink channel. Because neither the amount of uplink data to
be transmitted nor the transmission power available in the mobile terminal at the time of
transmission is known to the radio base station. As a result, the final selection of data rate
will likely be performed in the mobile terminal. But the radio base station can set an upper
limit on the data rate and/or transmission power that the mobile terminal may use to transmit
over an enhanced uplink data channel.
Although the primary focus of enhanced uplink is on the radio interface performance
and efficiency, the "bottleneck" may well occur further upstream from the radio interface in
the transport of the uplink information between nodes in the radio access network (RAN).
For example, the available uplink bit rate over the interface between a radio base station node
in the RAN and a radio network controller node in the RAN (referred to as the Iub interface)
may be a fraction of the available uplink bit rate over the radio interface. In this situation,
high speed uplink packet access may overload the Iub interface between the radio base station
and the radio network controller during peak bit rates. Figure 1 illustrates that even though
the downlink HSDPA bit rate over the radio interface is higher than the uplink HSUPA bit
2

rate, the available bandwidth for high speed packet access data between the radio network
controller and the radio base station is even less than the uplink HSUPA bit rate. The dashed
line representing Iub High Speed Packet Access (HSPA) bandwidth limit is lower that the
HSDPA and HSUPA bandwidths.
Consider the following simple example. A radio base station (sometimes referred to
as a "Node B" using 3GPP terminology) controls three cells that have an enhanced uplink
data transmission capability. Assume that the radio base station is connected to a radio
network controller using one 4 Mbps link to support the enhanced uplink data transmitted
from the radio base station and the radio network controller. Assume that the enhanced
uplink capability may be up to 4 Mbps per cell. In this situation, enhanced uplink
communication data from three cells at or near capacity cannot be transported from the radio
base station to the radio network controller over the single 4 Mbps link. The result is a
congested or overload situation. This congestion could result in long delays and loss of data,
which reduces quality of service.
One possible solution to avoid this kind of overload situation would be to "over
provision" the bandwidth resources in the radio access network for communications between
radio network controllers and radio base stations. But this is inefficient, costly, and in some
existing mobile communications networks, not practical. For high speed downlink, an
HSDPA flow control algorithm could be employed by the radio base station to reduce the
available downlink HSDPA bit rate to a level that suits the Iub interface bandwidth. But this
control methodology cannot be employed in the opposite uplink direction because, as
explained above, the amount of uplink data to be transmitted from mobile terminals is not
known to the radio base station. Should the uplink enhanced bit rate over the radio interface
significantly exceed the Iub uplink bandwidth, congestion will likely occur with long delays
and possibly lost or otherwise corrupted data frames. What is needed, therefore, is a way to
detect and then control an overload or other congested situation in the radio access network
as a result of uplink mobile terminal communications being transported between nodes in the
radio access network.
SUMMARY
The technology described herein meets this need as well as other needs. Congestion
associated with transporting in the RAN uplink information originating from one or more
mobile terminals is detected. That detected congestion is then reduced using any suitable
technique(s) and may be implemented in one or more nodes in the RAN. One advantageous
3

(but non-limiting) application is to a RAN that supports high speed uplink packet access
(HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs). Uplink
congestion may be detected over an interface between a radio network controller and a radio
base station (the Iub interface) and/or an interface between radio network controllers (the Iur
interface).
Although congestion reduction may be performed in any suitable fashion, one
example approach is to reduce a parameter associated with a bit rate at which uplink mobile
terminal information is transported through the RAN. For example, where the uplink mobile
terminal information is communicated using uplink data flows, the bit rate parameter may be
reduced by reducing a bit rate of one or more uplink data flows. It may be appropriate to limit
the bit rate of the one or more uplink data flows actually causing the congestion in the RAN;
alternatively, the bit rate of one or more lower priority uplink data flows may be reduced.
There are a number of different ways that the bit rate parameter may be reduced. For
example, a bit rate parameter value may correspond to an absolute bit rate parameter value or
a relative bit rate parameter value sent to one or more mobile terminals, e.g., a maximum bit
rate or transmission power or a percentage or fraction of a current bit rate or transmission
power. Another approach is to reduce the bit rate parameter using a capacity limitation
message. If the RNC detects a congested condition in the RAN, it can send a capacity
limitation to a radio base station, which then schedules uplink transmissions from mobile
terminals to effect that capacity limitation, e.g., by using scheduling grants or credits.
In some situations, more drastic measures may be necessary to reduce the bit rate
parameter such as dropping one or more frames of one or more uplink mobile terminal
communications. In soft/softer handover situations, one or more of the diversity handover
links may be released to reduce the bit rate parameter. Another technique employs sending
negative acknowledgment messages for received packets back to the mobile terminal causing
the mobile terminal to retransmit those negatively acknowledged packets. This effectively
reduces the uplink bit rate through the RAN.
The congestion control may be implemented by sending control information either
over a separate control signaling channel or in a user data plane where the control signaling is
sent along with the data over a data channel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a graph illustrating the high speed packet access bandwidth for both the
uplink and downlink directions as compared to the RAN bandwidth;
4

Figure 2 is a block diagram of a mobile communications system including an example
radio access network (RAN);
Figure 3 is a diagram illustrating various uplink chancels used by mobile terminals for
communicating over the radio/air interface with the RAN;
Figure 4 is a function block diagram illustrating various interfaces between multiple
nodes in a radio access network;
Figure 5 is a flow chart diagram illustrating example steps for uplink RAN congestion
detection and control;
Figure 6 is a function block diagram illustrating one example implementation for
uplink RAN congestion detection and control;
Figure 7 illustrates a capacity limitation message being sent from the RNC to the
radio base station to reduce detected congestion or load in the RAN; and
Figure 8 is a diagram illustrating a mobile terminal in soft handover in which a
weaker soft handover leg is dropped in order to reduce uplink RAN congestions.
DETAILED DESCRIPTION
In the following description, for purposes of explanation and non-limitation, specific
details are set forth, such as particular nodes, functional entities, techniques, protocols,
standards, etc. in order to provide an understanding of the described technology. For
example, one advantageous applications is to enhanced uplink communications in accordance
with 3GPP specifications. But other applications and other standards may be employed. It
will apparent to one skilled in the art that other embodiments may be practiced apart from the
specific details disclosed below. In other instances, detailed descriptions of well-known
methods, devices, techniques, etc. are omitted so as not to obscure the description with
unnecessary detail. Individual function blocks are shown in the figures. Those skilled in the
art will appreciate that the functions of those blocks may be implemented using individual
hardware circuits, using software programs and data in conjunction with a suitably
programmed microprocessor or general purpose computer, using applications specific
integrated circuitry (ASIC), and/or using one or more digital signal processors (DSPs).
Referring to Figure 2, an example network 10 that supports wireless communications
is illustrated. Network 10 may accommodate one or more standard architectures including a
universal mobile telecommunications system (UMTS) and other systems based on code
division multiple access (CDMA), GPRS/EDGE and other systems based on time division
multiple access (TDMA) systems, etc. In CDMA, different wireless channels are
5

distinguished using different channelization codes or sequences, (these distinct codes are used
to encode different information streams), which may then be modulated at one or more
different carrier frequencies for simultaneous transmission. A receiver may recover a
particular stream or flow for the receive signal using the appropriate code or sequence to
decode the received signal. In TDMA, the radio spectrum is divided into time slots. Each
time slot allows only one user to transmit and/or receive. TDMA requires precise timing
between the transmitter and the receiver so that each user may transmit its information during
its allocated time slot.
The network 10 includes a radio access network (RAN) 14 and one or more core
network(s) 12. One example radio access network is the UMTS terrestrial access network
(UTRAN) used in third generation cellular systems. Core network 14 typically supports
circuit-based communications as well as packet-based communications. The RAN 14
includes one or more radio network controllers (RNCs) 16. Each RNC is coupled to one or
more radio base stations (RBSs) 18 sometimes referred to as Node B's. The communications
interface between Node Bs and RNCs is referred to as the Iub interface, and the
communications interface between RNCs is referred to as the Iur interface. Transport of
information over the Iub and Iur interfaces is typically based on asynchronous transfer mode
(ATM) or Internet Protocol (IP). Wireless terminals 20 (referred to hereafter as mobile
terminals) communicate over an air or radio interface with the RAN 14. The radio interface
is referred to as the Uu interface. The two center mobile terminals are shown communicating
with both RBSs 18.
Although attention has recently been paid to high speed downlink packet access
(HSDPA), there is increasing interest in high speed uplink packet access (HSUPA), also
referred to as "enhanced uplink" and as enhanced uplink dedicated channel (E-DCH).
Enhanced uplink employs several uplink channels from each mobile terminal with an active
uplink connection as illustrated in Figure 3. The enhanced dedicated physical data channel
(E-DPDCH) carries enhanced uplink data (at higher bit rates), in addition to the normal
dedicated physical data channels (DPDCHs) used for regular uplink data communication.
The dedicated physical control channel (DPCCH) carries pilot symbols and out-of-band
control signaling. Out-of-band control signaling related to enhanced uplink, e.g., uplink
scheduling requests, may be carried on the enhanced dedicated physical control channel (E-
DPCCH).
6

As explained above, there is the possibility, particularly with enhanced uplink data
communications, that the enhanced uplink bit rate over the air interface exceeds the uplink
bandwidth limits for communications between nodes in the radio access network. This point
was illustrated in Figure 1. These kinds of bandwidth restrictions between nodes in a radio
access network may only become more significant as radio access networks expand or
become more complicated. Consider, for example, the radio access network shown in Figure
4 in which multiple RNCs (RNC1, RNC2, ..., RNCn) are coupled to multiple radio base
stations (RBS1, RBS2, ..., RBSn) by way of one or more aggregation nodes 22. The
aggregation nodes 22 may be, for example, ATM switches, IP routers, etc. and are optional.
Each aggregation node (1) aggregates data traffic from the RBSs to the RNCs and (2) splits
the data traffic from the RNCs to the individual RBSs. In this more sophisticated radio
access network, there are multiple Iur and Iub interfaces which may have limited bandwidth
capability. Some type of congestion control should be in place to avoid congestion, delay,
and overload situations caused by receiving uplink data over the radio interface at a rate
greater than what can be currently transported over any one of these RAN interfaces.
Reference is now made to the flowchart in Figure 5 which illustrates an uplink RAN
congestion control routine. Congestion is monitored in the RAN that is associated with
transporting uplink information through the RAN (step S2). An overload or congestion
condition is detected between nodes in the RAN related to uplink information for example by
detecting frame (or other data unit) losses (step S4). Frame losses may be detected using a
frame sequence number (FSN). Each transport bearer between an RNC and a radio base
station has its own sequence number. It is assumed that when a frame sequence number is
detected as missing, that the corresponding frame is lost due to congestion.
Alternatively, or in addition, delay build-up can be monitored to detect a congestion
condition. In transport networks that include large buffers, congestion may not normally
result in frame losses, but rather in a build-up of delay time in the buffer before packets are
transmitted. Rather than relying on detected frame losses, which may result in severe delays,
each user plane frame transmitted from a base station uplink to an RNC includes a field for a
real-time stamp, e.g., a control frame number (CFN) plus a subframe number. If the RNC
detects a time stamp "drift," meaning that the delay is increasing, the RNC can then
determine there is congestion. For example, if uplink frames are delayed more than 30 msec
in addition to the delay that is prevailing in non-congested circumstances, this is a good
indicator of uplink congestion in the RAN.
7

Returning to Figure 5, once an overload or congestion condition is detected, one or
more actions is taken to reduce the detected uplink congestion in the RAN (step S6). There
are various techniques and implementations for reducing that detected uplink congestion in
the RAN. Some non-limiting examples are described below.
Consider the example implementation shown in Figure 6 in which both the radio
network controller 16 and the radio base station 18 perform certain tasks in reducing uplink
RAN congestion. The RNC 16 includes an uplink RAN congestion detector 30 and uplink
RAN congestion controller 32, and a handover controller 34. The RNC 16 includes other
functional entities which are not pertinent to this description and therefore are not shown.
The radio base station 18 includes an uplink RAN congestion controller 40, an automatic
repeat request (ARQ) controller 42, (which in a preferred implementation is a hybrid ARQ
(HARQ) controller), a mobile terminal uplink scheduler 44, and radio circuitry 46. The radio
base station 18 has other entities and circuitry for performing the functions not pertinent to
the description and therefore are not shown.
The uplink RAN congestion detector 30 monitors and detects uplink RAN congestion
using, for example, frame loss detection or delay build-up detection as described above.
Other techniques may be employed. The uplink RAN congestion controller 32 processes
congestion detection information provided by detector 30, and based on certain
characteristics of one or more congested uplink flows, the uplink RAN congestion controller
32 may decide to limit the uplink load in the RAN using any suitable methodology. For
example, the congestion controller 32 may limit a maximum data rate/transmission power
grant that the mobile terminal uplink scheduler 44 is allowed to assign to a particular mobile
terminal or to a mobile terminal uplink data flow. The mobile terminal subjected to this
maximum data rate/power restriction can be the same mobile terminal or data flow which is
experiencing the congestion on one or more flows, or it may be a different mobile terminal or
data flow, perhaps with a lower priority.
Alternatively, the uplink RAN congestion controller 32 may limit the maximum data
rate/transmission power that the uplink scheduler 44 is allowed to assign to a group of mobile
terminals. The uplink RAN congestion controller 32 may communicate the maximum data
rate/transmission power to the radio base station 18 using a CAPACITY LIMITATION
message, as illustrated in Figure 7. The CAPACITY LIMITATION notification message
includes the maximum bit rate/power that the uplink scheduler 44 may assign to one or more
mobile terminal uplink flows. The CAPACITY LIMITATION message may also include a
8

time interval over which the maximum bit rate/power restriction applies. On the other hand,
the limits may remain in effect until a new capacity limitation message is received. The
uplink CAPACITY LIMITATION notification may be sent either in the RAN "user plane"
using a control frame embedded with the data or in the RAN "control plane" using control
signaling over an explicit control channel. Example control signaling protocols includes
Node B Application Part (NBAP) /RNS Application Part/RNSAP).
The maximum bit rate/power may be expressed, for example, as an absolute limit,
such as 200 Kbps, or as a prohibition from using a transport format indicator (TFI) exceeding
a particular value, such as TFI 12. An example in terms of an absolute transmission power
might be a maximum allowed transmission power offset, and an example of a relative limit
might be a percentage by which to reduce the current bit rate/power, e.g., 50%. Again, the
load may be reduced with respect to the affected mobile terminal, an affected uplink flow, an
aggregated load of multiple mobile terminals, or different mobile terminals or different flows
that are less prioritized than the affected one(s).
Alternatively, when the uplink RAN congestion controller 40 in the radio base station
18 receives a capacity limitation notification on the uplink RAN congestion controller 32, the
congestion controller 40 may limit the scheduling grants assigned to a particular mobile
terminal or group of mobile terminals. In a RAN supporting soft-handover, a mobile terminal
can be connected to multiple cells controlled by one or several radio base stations. Of the
cells in this "active set," the strongest (in terms of a pilot signal) is typically chosen as the
"serving cell" responsible for the primary control of the mobile terminal. Via this serving
cell, the radio base station can assign absolute grants limiting the maximum bit-rate/power of
the mobile terminal. In order to control the, inter-cell interference, the radio base stations can
also send relative grants via non-serving cells. Relative grants indicate if one or a group of
mobile terminals should increase, hold, or decrease their current bit-rate/power. Any of these
grants can be based on scheduling requests sent in the uplink from the mobile terminal to the
radio base-stations. Such scheduling requests typically include, e.g., the desired bit-rate or
the present buffer fill-levels in the mobile terminal.
In the situation where the radio base station controls the serving cell of the mobile
terminal, the uplink RAN congestion controller 40 limits the absolute grant of that mobile
terminal; alternatively, the uplink RAN congestion controller 40 assigns relative grants
(up/hold/down) so that the RNC capacity limitation is fulfilled. The uplink scheduler 44 can
provide scheduling information to the mobile terminal to control the upper limit of the mobile
9

terminal transmission data rate/transmission power. The "absolute grant channel" may carry
an absolute scheduling grant on a shared channel which includes (a) the identity of the mobile
terminal (or a group of mobile terminals) for which the grant is valid and (b) the maximum
resources that this mobile terminal (or group of mobile terminals) may use. A "relative grant
channel" carries a relative scheduling grant on a dedicated channel and includes at least one
bit that registers an incremental up/hold/down. The absolute grant channel is read from the
serving cell. The relative grant channel may be read from additional cells, e.g., in the case of
soft handover, from all cells in the active set. If a mobile terminal is assigned to read the
relative grant channel from a set of cells, the mobile terminal must not increase its data rate or
power offset if any cell in the active set signals a hold. Similarly, if any of the cells relative
grants is set to down, the mobile terminal must decrease the rate or power offset with some
predefined step size. When the radio base station does not control the mobile terminal
serving cell, the uplink RAN congestion controller 40 assigns relative grant indications
(up/hold/down) to fulfill the RNC capacity limitation.
As another alternative already explained above, the uplink RAN congestion controller 40
may discard RAN data frames so that the RAN capacity limitation assigned by the RNC is
fulfilled without affecting scheduling grants. Rather than discarding frames, the uplink RAN
congestion controller 40 may instruct the H/ARQ controller 42 to send a NACK message for
each received and discarded data unit back to the mobile terminal. NACKing the discarded
data frames from a non-serving cell triggers re-transmission of those discarded data frames,
unless some other link has received those data frames correctly. The effect is reduced
pressure on the RAN transport.
It is possible that the sending of capacity limitation control frames to inform the
uplink RAN congestion controller 40 to lower the bit rate/transmission power relative to the
normal bit rate/transmission power per HSUPA flow will result in the following behavior. If
the uplink scheduler 44, which controls the HSUPA flow bit rates, lowers the flow bit rate
from one of the mobile terminals by modifying its scheduling grants, it is likely that the
uplink scheduler 44 will schedule another mobile terminals to transmit in its place.
Moreover, it is likely that the mobile terminal associated with RAN congestion has excellent
uplink radio/air interface performance. Therefore, scheduling another mobile instead of the
congested mobile to transmit in the uplink should reduce the congestion of the uplink RAN
congested flows.
10

After recovery from a congestion condition, as detected by the uplink RAN
congestion detector 30, the uplink RAN congestion controller 32 may restore the original data
rate or transmission power by sending notification to the radio base station. Alternatively,
and as explained above, a configurable or predefined period of time may be set after which
the temporary restriction on the uplink scheduler 44 is released. This latter approach may be
preferred because explicit signaling from the RNC is not required.
Consider a situation in which the mobile terminal 20 that is subject to RAN
congestion is in soft handover, as illustrated in Figure 8. In this example, mobile terminal 20
has three soft handover links LI, L2, and L3 to three base stations RBS1, RBS2, and RBS3,
respectively. Assume that the congested radio link L3 is not the "serving" handover link.
Typically, the serving link is the strongest one of the handover links based on detected signal
strength measurements. The uplink RAN congestion controller 32 may decide to release the
weaker handover radio link L3, which is subject to congestion in the RAN, and leave links LI
and L2. This congestion reduction approach has the benefit of not affecting the bit rate over
the radio interface. Any capacity loss associated with loss of macro-diversity over the air
interface is less impacting than the RAN congestion associated with link L3.
The RAN Iub and Iur interfaces each likely have a maximum total uplink bandwidth.
A certain, relatively small amount of each maximum bandwidth is allocated for control
signaling. The rest of the remaining bandwidth may be divided as desired between uplink
dedicated data channels (X) and enhanced uplink dedicated data channels (Y), where the
remaining bandwidth = (X + Y). When the RNC detects uplink congestion over one of the
interfaces, it sends a message to the RBS to reduce the enhanced uplink dedicated data
channels bandwidth by a certain percentage selected to reduce the congestion without
impacting the enhanced uplink services too much. When the congestion condition is
alleviated or after a predetermined time period, the enhanced uplink dedicated data channels
bandwidth may be restored to Y.
The above technology solves the problem of uplink RAN congestion without having
to over-provision the RAN transport network. The RAN congestion is reduced by adapting
the uplink mobile transmissions load to the current uplink RAN resource situation. In other
words, the data frame bit rate in the RAN can be adapted to present RAN bandwidth
restrictions. As a result, the data frame delays and losses can be minimized even where the
uplink radio interface could provide higher bit rates than what the RAN transport network can
offer.
11

Although various embodiments have been shown and described in detail, the claims
are not limited to any particular embodiment. None of the above description should be read
as implying that any particular element, step, range, or function is essential such that it must
be included in the claims scope. The scope of patented subject matter is defined only by the
claims. The extent of legal protection is defined by the words recited in the allowed claims
and their equivalents. No claim is intended to invoke paragraph 6 of 35 USC §112 unless the
words "means for" are used.
12

WE CLAIM:
1. A method for managing an overload or congestion condition between nodes in a radio
access network (RAN) (14) transporting data received from one or more mobile
terminals (20), characterized by:
monitoring for congestion in the RAN associated with transporting uplink information
from one or more mobile terminals through the RAN;
detecting congestion in the RAN associated with transporting information uplink from
mobile terminals through the RAN; and
reducing the detected congestion in the RAN associated with transporting information
uplink from mobile terminals through the RAN.
2. The method in claim 1, wherein the mobile terminals transmit information to the RAN
using high speed uplink packet access (HSUPA) or using one or more enhanced
uplink dedicated channels (E-DCHs).
3. The method in claim 1, wherein the RAN includes a radio network controller (16)
coupled to a radio base station (18), and wherein the radio network controller detects
uplink congestion over an interface between the radio network controller and the radio
base station.
4. The method in claim 3, wherein the RAN includes the first radio network controller
coupled to a second radio network controller, and wherein one of the radio network
controllers detects uplink congestion over an interface between the first and second
radio network controllers.
5. The method in claim 3, wherein the reducing includes taking an action to reduce a
parameter associated with a bit rate at which uplink mobile terminal information is
transported through the RAN.
6. The method in claim 5, wherein the uplink mobile terminal information is
communicated using uplink data flows, and wherein the bit rate parameter is reduced
by reducing a bit rate of one or more uplink data flows.
13

7. The method in claim 5, wherein the bit rate parameter is reduced based on an absolute
bit rate parameter value or on a relative bit rate parameter value.
8. The method in claim 7, wherein the absolute bit rate parameter value corresponds to a
maximum bit rate or transmission power and the relative bit rate parameter value
corresponds to a percentage or fraction of a current bit rate or transmission power.
9. The method in claim 5, wherein the bit rate parameter is reduced by sending control
information in a control plane or in a user data plane.
10. The method in claim 5, wherein the bit rate parameter is reduced using scheduling
grants or credits for uplink mobile terminal communications.
11. The method in claim 5, wherein the bit rate parameter is reduced by dropping one or
more frames of one or more uplink mobile terminal communications.
12. The method in claim 5, wherein the bit rate parameter is reduced by releasing one or
more diversity handover radio links.
13. The method in claim 5, wherein the bit rate parameter is reduced using negative
acknowledgement messages.
14. The method in claim 3, wherein first amount of bandwidth allocated to uplink
dedicated channels and a second amount of bandwidth is allocated to enhanced uplink
dedicated channels, and wherein the radio network controller sends a message to the
radio base station to reduce the second amount of bandwidth when uplink congestion
is detected in the RAN.
15. Apparatus for use in managing an overload or congestion condition between nodes in
a radio access network (RAN) (14) transporting data received from one or more
mobile terminals (20), characterized by:
14

a congestion detector (30) for monitoring and detecting congestion in the RAN
associated with transporting information uplink from one or more mobile terminals
through the RAN, and
a congestion controller (32) for reducing the detected congestion in the RAN
associated with transporting information uplink from mobile terminals through the
RAN.
16. The apparatus in claim 15, wherein the RAN is configured to receive mobile terminal
information using high speed uplink packet access (HSUPA) or using one or more
enhanced uplink dedicated channels (E-DCHs).
17. The apparatus in claim 15, wherein the RAN includes a radio network controller (16)
coupled to a radio base station (16), and wherein the apparatus is implemented in the
radio network controller.
18. The apparatus in claim 17, wherein the RAN includes the first radio network
controller coupled to a second radio network controller, and wherein one of the radio
network controllers is configured to detect uplink congestion over an interface
between the first and second radio network controllers.
19. The apparatus in claim 17, wherein the congestion controller is configured to reduce a
parameter associated with a bit rate at which mobile terminal information is
transported through the RAN.
20. The apparatus in claim 19, wherein the uplink mobile terminal information is
communicated using uplink data flows, and wherein the congestion controller is
configured to send a signal to the radio base station to reduce a bit rate of one or more
uplink data flows.
21. The apparatus in claim 19, wherein the congestion controller is configured to send an
absolute bit rate parameter value or a relative bit rate parameter value for use by the
radio base station to reduce a bit ratp or power of one or more uplink mobile terminal
transmissions.
15

22. The apparatus in claim 19, wherein the congestion controller is configured to reduce
the bit rate parameter by sending control information in a control plane or in a user
data plane to the radio base station.
23. The apparatus in claim 19, wherein the congestion controller is configured to send a
signal to the radio base station to restrict scheduling of one or more uplink
transmission grants or credits.
24. The apparatus in claim 15, wherein the congestion controller is configured to release
one or more diversity handover radio links to reduce the detected congestion.
25. The apparatus in claim 15, wherein a first amount of bandwidth allocated to uplink
dedicated channels and a second amount of bandwidth is allocated to enhanced uplink
dedicated channels, and wherein the radio network controller is configured to send a
message to the radio base station to reduce the second amount of bandwidth when
uplink congestion is detected in the RAN.
26. Apparatus for use in managing an overload or congestion condition in a radio access
network (RAN) (14) associated with transporting information uplink from one or
more mobile terminals (20) through the RAN, characterized by:
a scheduler (44) for scheduling uplink transmissions from one or more mobile
terminals, and
a congestion controller (40), coupled to the scheduler, for reducing congestion in the
RAN associated with transporting information uplink from mobile terminals through
the RAN.
27. The apparatus in claim 26, wherein the congestion controller is configured to receive
one or more messages from a radio network controller in the RAN including
information associated with reducing congestion in the RAN associated with
transporting information uplink from mobile terminals through the RAN.
16

28. The apparatus in claim 27, wherein the congestion controller is configured to instruct
the scheduler to restrict uplink transmission grants or credits provided to the one or
more mobile terminals.
29. The apparatus in claim 27, wherein the congestion controller is configured to drop one
or more frames associated with one or more uplink mobile terminal communications.
30. The apparatus in claim 27, wherein the congestion controller is configured to reduce a
bit rate or power associated with one or more uplink mobile terminal communications
using negative acknowledgement messages.

Dated this 9th day of August 2007
WO 2006/075951 PCT/SE2006/000032
1
UPLINK CONGESTION DETECTION AND CONTROL BETWEEN NODES IN A RADIO
ACCESS NETWORK
TECHNICAL FIELD
[0001] The technical field relates to mobile data communications, and more
particularly, to regulating uplink communications from mobile radio terminals in a radio access
network.
BACKGROUND
[0002] There is an ever increasing demand for wireless communication devices to
perform a variety of applications. Some of those applications require substantial bandwidth.
For example, next generation wireless communication systems may offer high speed downlink
packet access (HSDPA) and high speed uplink packet access (HSUPA) to provide enhanced
data rates over the radio interface to support Internet access and multimedia type applications.
[0003] The enhanced uplink concept currently being considered in the 3rd Generation
Project Partnership (3GPP) intends to introduce substantially higher peak data rates over the
radio interface in the uplink direction. Enhanced uplink data communications will likely
employ fast scheduling and fast hybrid automatic repeat request (HARQ) with soft combining
in the radio base station. Fast scheduling allows the radio base station to control when a
wireless terminal is transmitting in the uplink direction and at what data transmission rate.
Data transmission rate and transmission power are closely related, and scheduling can thus also
be seen as a mechanism to vary the transmission power used by the mobile terminal for
transmitting over an enhanced uplink channel. Because neither the amount of uplink data to be
transmitted nor the transmission power available in the mobile terminal at the time of
transmission is known to the radio base station. As a result, the final selection of data rate will
likely be performed in the mobile terminal. But the radio base station can set an upper limit on
the data rate and/or transmission power that the mobile terminal may use to transmit over an
enhanced uplink data channel.
[0004] Although the primary focus of enhanced uplink is on the radio interface
performance and efficiency, the "bottleneck" may well occur further upstream from the radio
interface in the transport of the uplink information between nodes in the radio access network
(RAN). For example, the available uplink bit rate over the interface between a radio base
station node in the RAN and a radio network controller node in the RAN (referred to as the Iub

WO 2006/075951 PCT/SE2006/000032
2
interface) may be a fraction of the available uplink bit rate over the radio interface. In this
situation, high speed uplink packet access may overload the Iub interface between the radio
base station and the radio network controller during peak bit rates. Figure 1 illustrates that
even though the downlink HSDPA bit rate over the radio interface is higher than the uplink
HSUPA bit rate, the available bandwidth for high speed packet access data between the radio
network controller and the radio base station is even less than the uplink HSUPA bit rate. The
dashed line representing Iub High Speed Packet Access (HSPA) bandwidth limit is lower that
the HSDPA and HSUPA bandwidths.
[0005] Consider the following simple example. A radio base station (sometimes
referred to as a "Node B" using 3GPP terminology) controls three cells that have an enhanced
uplink data transmission capability. Assume that the radio base station is connected to a radio
network controller using one 4 Mbps link to support the enhanced uplink data transmitted from
the radio base station and the radio network controller. Assume that the enhanced uplink
capability may be up to 4 Mbps per cell. In this situation, enhanced uplink communication
data from three cells at or near capacity cannot be transported from the radio base station to the
radio network controller over the single 4 Mbps link. The result is a congested or overload
situation. This congestion could result in long delays and loss of data, which reduces quality of
service.
[0006] One possible solution to avoid this kind of overload situation would be to "over
provision" the bandwidth resources in the radio access network for communications between
radio network controllers and radio base stations. But this is inefficient, costly, and in some
existing mobile communications networks, not practical. For high speed downlink, an HSDPA
flow control algorithm could be employed by the radio base station to reduce the available
downlink HSDPA bit rate to a level that suits the Iub interface bandwidth. But this control
methodology cannot be employed in the opposite uplink direction because, as explained above,
the amount of uplink data to be transmitted from mobile terminals is not known to the radio
base station. Should the uplink enhanced bit rate over the radio interface significantly exceed
the Iub uplink bandwidth, congestion will likely occur with long delays and possibly lost or
otherwise corrupted data frames. What is needed, therefore, is a way to detect and then
control an overload or other congested situation in the radio access network as a result of
uplink mobile terminal communications being transported between nodes in the radio access
network.

WO 2006/075951 PCT/SE2006/000032
3
SUMMARY
[0007] The technology described herein meets this need as well as other needs.
Congestion associated with transporting in the RAN uplink information originating from one
or more mobile terminals is detected. That detected congestion is then reduced using any
suitable technique(s) and may be implemented in one or more nodes in the RAN. One
advantageous (but non-limiting) application is to a RAN that supports high speed uplink packet
access (HSUPA) and/or one or more enhanced uplink dedicated channels (E-DCHs). Uplink
congestion may be detected over an interface between a radio network controller and a radio
base station (the Iub interface) and/or an interface between radio network controllers (the Iur
interface).
[0008] Although congestion reduction may be performed in any suitable fashion, one
example approach is to reduce a parameter associated with a bit rate at which uplink mobile
terminal information is transported through the RAN. For example, where the uplink mobile
terminal information is communicated using uplink data flows, the bit rate parameter may be
reduced by reducing a bit rate of one or more uplink data flows. It may be appropriate to limit
the bit rate of the one or more uplink data flows actually causing the congestion in the RAN;
alternatively, the bit rate of one or more lower priority uplink data flows may be reduced.
[0009] There are a number of different ways that the bit rate parameter may be
reduced. For example, a bit rate parameter value may correspond to an absolute bit rate
parameter value or a relative bit rate parameter value sent to one or more mobile terminals,
e.g., a maximum bit rate or transmission power or a percentage or fraction of a current bit rate
or transmission power. Another approach is to reduce the bit rate parameter using a capacity
limitation message. If the RNC detects a congested condition in the RAN, it can send a
capacity limitation to a radio base station, which then schedules uplink transmissions from
mobile terminals to effect that capacity limitation, e.g., by using scheduling grants or credits.
[0010] In some situations, more drastic measures may be necessary to reduce the bit
rate parameter such as dropping one or more frames of one or more uplink mobile terminal
communications. In soft/softer handover situations, one or more of the diversity handover
links may be released to reduce the bit rate parameter. Another technique employs sending
negative acknowledgment messages for received packets back to the mobile terminal causing
the mobile terminal to retransmit those negatively acknowledged packets. This effectively
reduces the uplink bit rate through the RAN.

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[0011] The congestion control may be implemented by sending control information
either over a separate control signaling channel or in a user data plane where the control
signaling is sent along with the data over a data channel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGURE 1 is a graph illustrating the high speed packet access bandwidth for
both the uplink and downlink directions as compared to the RAN bandwidth;
[0013] Figure 2 is a block diagram of a mobile communications system including an
example radio access network (RAN);
[0014] Figure 3 is a diagram illustrating various uplink chancels used by mobile
terminals for communicating over the radio/air interface with the RAN;
[0015] Figure 4 is a function block diagram illustrating various interfaces between
multiple nodes in a radio access network;
[0016] Figure 5 is a flow chart diagram illustrating example steps for uplink RAN
congestion detection and control;
[0017] Figure 6 is a function block diagram illustrating one example implementation
for uplink RAN congestion detection and control;
[0018] Figure 7 illustrates a capacity limitation message being sent from the RNC to
the radio base station to reduce detected congestion or load in the RAN; and
[0019] Figure 8 is a diagram illustrating a mobile terminal in soft handover in which a
weaker soft handover leg is dropped in order to reduce uplink RAN congestions.
DETAILED DESCRIPTION
[0020] In the following description, for purposes of explanation and non-limitation,
specific details are set forth, such as particular nodes, functional entities, techniques, protocols,
standards, etc. in order to provide an understanding of the described technology. For example,
one advantageous applications is to enhanced uplink communications in accordance with
3GPP specifications. But other applications and other standards may be employed. It will
apparent to one skilled in the art that other embodiments may be practiced apart from the
specific details disclosed below. In other instances, detailed descriptions of well-known
methods, devices, techniques, etc. are omitted so as not to obscure the description with
unnecessary detail. Individual function blocks are shown in the figures. Those skilled in the
art will appreciate that the functions of those blocks may be implemented using individual

WO 2006/075951 PCT/SE2006/000032
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hardware circuits, using software programs and data in conjunction with a suitably
programmed microprocessor or general purpose computer, using applications specific
integrated circuitry (ASIC), and/or using one or more digital signal processors (DSPs).
[0021] Referring to Figure 2, an example network 10 that supports wireless
communications is illustrated. Network 10 may accommodate one or more standard
architectures including a universal mobile telecommunications system (UMTS) and other
systems based on code division multiple access (CDMA), GPRS/EDGE and other systems
based on time division multiple access (TDMA) systems, etc. In CDMA, different wireless
channels are distinguished using different channelization codes or sequences, (these distinct
codes are used to encode different information streams), which may then be modulated at one
or more different carrier frequencies for simultaneous transmission. A receiver may recover a
particular stream or flow for the receive signal using the appropriate code or sequence to
decode the received signal. In TDMA, the radio spectrum is divided into time slots. Each time
slot allows only one user to transmit and/or receive. TDMA requires precise timing between
the transmitter and the receiver so that each user may transmit its information during its
allocated time slot.
[0022] The network 10 includes a radio access network (RAN) 14 and one or more
core network(s) 12. One example radio access network is the UMTS terrestrial access network
(UTRAN) used in third generation cellular systems. Core network 14 typically supports
circuit-based communications as well as packet-based communications. The RAN 14 includes
one or more radio network controllers (RNCs) 16. Each RNC is coupled to one or more radio
base stations (RBSs) 18 sometimes referred to as Node B's. The communications interface
between Node Bs and RNCs is referred to as the lub interface, and the communications
interface between RNCs is referred to as the Iur interface. Transport of information over the
lub and Iur interfaces is typically based on asynchronous transfer mode (ATM) or Internet
Protocol (IP). Wireless terminals 20 (referred to hereafter as mobile terminals) communicate
over an air or radio interface with the RAN 14. The radio interface is referred to as the Uu
interface. The two center mobile terminals are shown communicating with both RBSs 18.
[0023] Although attention has recently been paid to high speed downlink packet access
(HSDPA), there is increasing interest in high speed uplink packet access (HSUPA), also
referred to as "enhanced uplink" and as enhanced uplink dedicated channel (E-DCH).
Enhanced uplink employs several uplink channels from each mobile terminal with an active
uplink connection as illustrated in Figure 3. The enhanced dedicated physical data channel (E-

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DPDCH) carries enhanced uplink data (at higher bit rates), in addition to the normal dedicated
physical data channels (DPDCHs) used for regular uplink data communication. The dedicated
physical control channel (DPCCH) carries pilot symbols and out-of-band control signaling.
Out-of-band control signaling related to enhanced uplink, e.g., uplink scheduling requests, may
be carried on the enhanced dedicated physical control channel (E-DPCCH).
[0024] As explained above, there is the possibility, particularly with enhanced uplink
data communications, that the enhanced uplink bit rate over the air interface exceeds the uplink
bandwidth limits for communications between nodes in the radio access network. This point
was illustrated in Figure 1. These lands of bandwidth restrictions between nodes in a radio
access network may only become more significant as radio access networks expand or become
more complicated. Consider, for example, the radio access network shown in Figure 4 in
which multiple RNCs (RNC1, RNC2, ..., RNCn) are coupled to multiple radio base stations
(RBS1, RBS2, ..., RBSn) by way of one or more aggregation nodes 22. The aggregation
nodes 22 may be, for example, ATM switches, IP routers, etc. and are optional. Each
aggregation node (1) aggregates data traffic from the RBSs to the RNCs and (2) splits the data
traffic from the RNCs to the individual RBSs. In this more sophisticated radio access network,
there are multiple Iur and Iub interfaces which may have limited bandwidth capability. Some
type of congestion control should be in place to avoid congestion, delay, and overload
situations caused by receiving uplink data over the radio interface at a rate greater than what
can be currently transported over any one of these RAN interfaces.
[0025] Reference is now made to the flowchart in Figure 5 which illustrates an uplink
RAN congestion control routine. Congestion is monitored in the RAN that is associated with
transporting uplink information through the RAN (step S2). An overload or congestion
condition is detected between nodes in the RAN related to uplink information for example by
detecting frame (or other data unit) losses (step S4). Frame losses may be detected using a
frame sequence number (FSN). Each transport bearer between an RNC and a radio base
station has its own sequence number. It is assumed that when a frame sequence number is
detected as missing, that the corresponding frame is lost due to congestion.
[0026] Alternatively, or in addition, delay build-up can be monitored to detect a
congestion condition. In transport networks that include large buffers, congestion may not
normally result in frame losses, but rather in a build-up of delay time in the buffer before
packets are transmitted. Rather than relying on detected frame losses, which may result in
severe delays, each user plane frame transmitted from a base station uplink to an RNC includes

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a field for a real-time stamp, e.g., a control frame number (CFN) plus a subframe number. If
the RNC detects a time stamp "drift," meaning that the delay is increasing, the RNC can then
determine there is congestion. For example, if uplink frames are delayed more than 30 msec in
addition to the delay that is prevailing in non-congested circumstances, this is a good indicator
of uplink congestion in the RAN.
[0027] Returning to Figure 5, once an overload or congestion condition is detected, one
or more actions is taken to reduce the detected uplink congestion in the RAN (step S6). There
are various techniques and implementations for reducing that detected uplink congestion in the
RAN. Some non-limiting examples are described below.
[0028] Consider the example implementation shown in Figure 6 in which both the
radio network controller 16 and the radio base station 18 perform certain tasks in reducing
uplink RAN congestion. The RNC 16 includes an uplink RAN congestion detector 30 and
uplink RAN congestion controller 32, and a handover controller 34. The RNC 16 includes
other functional entities which are not pertinent to this description and therefore are not shown.
The radio base station 18 includes an uplink RAN congestion controller 40, an automatic
repeat request (ARQ) controller 42, (which in a preferred implementation is a hybrid ARQ
(HARQ) controller), a mobile terminal uplink scheduler 44, and radio circuitry 46. The radio
base station 18 has other entities and circuitry for performing the functions not pertinent to the
description and therefore are not shown.
[0029] The uplink RAN congestion detector 30 monitors and detects uplink RAN
congestion using, for example, frame loss detection or delay build-up detection as described
above. Other techniques may be employed. The uplink RAN congestion controller 32
processes congestion detection information provided by detector 30, and based on certain
characteristics of one or more congested uplink flows, the uplink RAN congestion controller
32 may decide to limit the uplink load in the RAN using any suitable methodology. For
example, the congestion controller 32 may limit a maximum data rate/transmission power
grant that the mobile terminal uplink scheduler 44 is allowed to assign to a particular mobile
terminal or to a mobile terminal uplink data flow. The mobile terminal subjected to this
maximum data rate/power restriction can be the same mobile terminal or data flow which is
experiencing the congestion on one or more flows, or it may be a different mobile terminal or
data flow, perhaps with a lower priority.
[0030] Alternatively, the uplink RAN congestion controller 32 may limit the maximum
data rate/transmission power that the uplink scheduler 44 is allowed to assign to a group of

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mobile terminals. The uplink RAN congestion controller 32 may communicate the maximum
data rate/transmission power to the radio base station 18 using a CAPACITY LIMITATION
message, as illustrated in Figure 7. The CAPACITY LIMITATION notification message
includes the maximum bit rate/power that the uplink scheduler 44 may assign to one or more
mobile terminal uplink flows. The CAPACITY LIMITATION message may also include a
time interval over which the maximum bit rate/power restriction applies. On the other hand,
the limits may remain in effect until a new capacity limitation message is received. The uplink
CAPACITY LIMITATION notification may be sent either in the RAN "user plane" using a
control frame embedded with the data or in the RAN "control plane" using control signaling
over an explicit control channel. Example control signaling protocols includes Node B
Application Part (NBAP) /RNS Application Part/RNSAP).
[0031] The maximum bit rate/power may be expressed, for example, as an absolute
limit, such as 200 Kbps, or as a prohibition from using a transport format indicator (TFI)
exceeding a particular value, such as TFI 12. An example in terms of an absolute transmission
power might be a maximum allowed transmission power offset, and an example of a relative
limit might be a percentage by which to reduce the current bit rate/power, e.g., 50%. Again,
the load may be reduced with respect to the affected mobile terminal, an affected uplink flow,
an aggregated load of multiple mobile terminals, or different mobile terminals or different
flows that are less prioritized than the affected one(s).
[0032] Alternatively, when the uplink RAN congestion controller 40 in the radio base
station 18 receives a capacity limitation notification on the uplink RAN congestion controller
32, the congestion controller 40 may limit the scheduling grants assigned to a particular mobile
terminal or group of mobile terminals. In a RAN supporting soft-handover, a mobile terminal
can be connected to multiple cells controlled by one or several radio base stations. Of the cells
in this "active set," the strongest (in terms of a pilot signal) is typically chosen as the "serving
cell" responsible for the primary control of the mobile terminal. Via this serving cell, the radio
base station can assign absolute grants limiting the maximum bit-rate/power of the mobile
terminal. In order to control the inter-cell interference, the radio base stations can also send
relative grants via non-serving cells. Relative grants indicate if one or a group of mobile
terminals should increase, hold, or decrease their current bit-rate/power. Any of these grants
can be based on scheduling requests sent in the uplink from the mobile terminal to the radio
base-stations. Such scheduling requests typically include, e.g., the desired bit-rate or the
present buffer fill-levels in the mobile terminal.

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[0033] In the situation where the radio base station controls the serving cell of the
mobile terminal, the uplink RAN congestion controller 40 limits the absolute grant of that
mobile terminal; alternatively, the uplink RAN congestion controller 40 assigns relative grants
(up/hold/down) so that the RNC capacity limitation is fulfilled. The uplink scheduler 44 can
provide scheduling information to the mobile terminal to control the upper limit of the mobile
terminal transmission data rate/transmission power. The "absolute grant channel" may carry
an absolute scheduling grant on a shared channel which includes (a) the identity of the mobile
terminal (or a group of mobile terminals) for which the grant is valid and (b) the maximum
resources that this mobile terminal (or group of mobile terminals) may use. A "relative grant
channel" carries a relative scheduling grant on a dedicated channel and includes at least one bit
that registers an incremental up/hold/down. The absolute grant channel is read from the
serving cell. The relative grant channel may be read from additional cells, e.g., in the case of
soft handover, from all cells in the active set. If a mobile terminal is assigned to read the
relative grant channel from a set of cells, the mobile terminal must not increase its data rate or
power offset if any cell in the active set signals a hold. Similarly, if any of the cells relative
grants is set to down, the mobile terminal must decrease the rate or power offset with some
predefined step size. When the radio base station does not control the mobile terminal serving
cell, the uplink RAN congestion controller 40 assigns relative grant indications (up/hold/down)
to fulfill the RNC capacity limitation.
[0034] As another alternative already explained above, the uplink RAN congestion
controller 40 may discard RAN data frames so that the RAN capacity limitation assigned by
the RNC is fulfilled without affecting scheduling grants. Rather than discarding frames, the
uplink RAN congestion controller 40 may instruct the H/ARQ controller 42 to send a NACK
message for each received and discarded data unit back to the mobile terminal. NACKing the
discarded data frames from a non-serving cell triggers re-transmission of those discarded data
frames, unless some other link has received those data frames correctly. The effect is reduced
pressure on the RAN transport.
[0035] It is possible that the sending of capacity limitation control frames to inform the
uplink RAN congestion controller 40 to lower the bit rate/transmission power relative to the
normal bit rate/transmission power per HSUPA flow will result in the following behavior. If
the uplink scheduler 44, which controls the HSUPA flow bit rates, lowers the flow bit rate
from one of the mobile terminals by modifying its scheduling grants, it is likely that the uplink
scheduler 44 will schedule another mobile terminals to transmit in its place. Moreover, it is

WO 2006/075951 PCT/SE2006/000032
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likely that the mobile terminal associated with RAN congestion has excellent uplink radio/air
interface performance. Therefore, scheduling another mobile instead of the congested mobile
to transmit in the uplink should reduce the congestion of the uplink RAN congested flows.
[0036] After recovery from a congestion condition, as detected by the uplink RAN
congestion detector 30, the uplink RAN congestion controller 32 may restore the original data
rate or transmission power by sending notification to the radio base station. Alternatively, and
as explained above, a configurable or predefined period of time may be set after which the
temporary restriction on the uplink scheduler 44 is released. This latter approach may be
preferred because explicit signaling from the RNC is not required.
[0037] Consider a situation in which the mobile terminal 20 that is subject to RAN
congestion is in soft handover, as illustrated in Figure 8. In this example, mobile terminal 20
has three soft handover links LI, L2, and L3 to three base stations RBS1, RBS2, and RBS3,
respectively. Assume that the congested radio link L3 is not the "serving" handover link.
Typically, the serving link is the strongest one of the handover links based on detected signal
strength measurements. The uplink RAN congestion controller 32 may decide to release the
weaker handover radio link L3, which is subject to congestion in the RAN, and leave links LI
and L2. This congestion reduction approach has the benefit of not affecting the bit rate over
the radio interface. Any capacity loss associated with loss of macro-diversity over the air
interface is less impacting than the RAN congestion associated with link L3.
[0038] The RAN Iub and Iur interfaces each likely have a maximum total uplink
bandwidth. A certain, relatively small amount of each maximum bandwidth is allocated for
control signaling. The rest of the remaining bandwidth may be divided as desired between
uplink dedicated data channels (X) and enhanced uplink dedicated data channels (Y), where
the remaining bandwidth = (X + Y). When the RNC detects uplink congestion over one of the
interfaces, it sends a message to the RBS to reduce the enhanced uplink dedicated data
channels bandwidth by a certain percentage selected to reduce the congestion without
impacting the enhanced uplink services too much. When the congestion condition is alleviated
or after a predetermined time period, the enhanced uplink dedicated data channels bandwidth
may be restored to Y.
[0039] The above technology solves the problem of uplink RAN congestion without
having to over-provision the RAN transport network. The RAN congestion is reduced by
adapting the uplink mobile transmissions load to the current uplink RAN resource situation. In
other words, the data frame bit rate in the RAN can be adapted to present RAN bandwidth

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restrictions. As a result, the data frame delays and losses can be minimized even where the
uplink radio interface could provide higher bit rates than what the RAN transport network can
offer.
[0040] Although various embodiments have been shown and described in detail, the
claims are not limited to any particular embodiment. None of the above description should be
read as implying that any particular element, step, range, or function is essential such that it
must be included in the claims scope. The scope of patented subject matter is defined only by
the claims. The extent of legal protection is defined by the words recited in the allowed claims
and their equivalents. No claim is intended to invoke paragraph 6 of 35 USC §112 unless the
words "means for" are used.

WO 2006/075951 PCT/SE2006/000032
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CLAIMS
1. A method for managing an overload or congestion condition between nodes in a
radio access network (RAN) (14) transporting data received from one or more mobile
terminals (20), characterized by:
monitoring for congestion in the RAN associated with transporting uplink information
from one or more mobile terminals through the RAN;
detecting congestion in the RAN associated with transporting information uplink from
mobile terminals through the RAN; and
reducing the detected congestion in the RAN associated with transporting information
uplink from mobile terminals through the RAN.
2. The method in claim 1, wherein the mobile terminals transmit information to
the RAN using high speed uplink packet access (HSUPA) or using one or more enhanced
uplink dedicated channels (E-DCHs).
3. The method in claim 1, wherein the RAN includes a radio network
controller (16) coupled to a radio base station (18), and wherein the radio network controller
detects uplink congestion over an interface between the radio network controller and the radio
base station.
4. The method in claim 3, wherein the RAN includes the first radio network
controller coupled to a second radio network controller, and wherein one of the radio network
controllers detects uplink congestion over an interface between the first and second radio
network controllers.
5. The method in claim 3, wherein the reducing includes talcing an action to reduce
a parameter associated with a bit rate at which uplink mobile terminal information is
transported through the RAN.

WO 20(16/075951 PCT/SE2006/000032
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6. The method in claim 5, wherein the uplink mobile terminal information is
communicated using uplink data flows, and wherein the bit rate parameter is reduced by
reducing a bit rate of one or more uplink data flows.
7. The method in claim 5, wherein the bit rate parameter is reduced based on an
absolute bit rate parameter value or on a relative bit rate parameter value.
8. The method in claim 7, wherein the absolute bit rate parameter value
corresponds to a maximum bit rate or transmission power and the relative bit rate parameter
value corresponds to a percentage or fraction of a current bit rate or transmission power.
9. The method in claim 5, wherein the bit rate parameter is reduced by sending
control information in a control plane or in a user data plane.
10. The method in claim 5, wherein the bit rate parameter is reduced using
scheduling grants or credits for uplink mobile terminal communications.
11. The method in claim 5, wherein the bit rate parameter is reduced by dropping
one or more frames of one or more uplink mobile terminal communications.
12. The method in claim 5, wherein the bit rate parameter is reduced by releasing
one or more diversity handover radio links.
13. The method in claim 5, wherein the bit rate parameter is reduced using negative
acknowledgement messages.
14. The method in claim 3, wherein first amount of bandwidth allocated to uplink
dedicated channels and a second amount of bandwidth is allocated to enhanced uplink
dedicated channels, and wherein the radio network controller sends a message to the radio base
station to reduce the second amount of bandwidth when uplink congestion is detected in the
RAN.

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14
15. Apparatus for use in managing an overload or congestion condition between
nodes in a radio access network (RAN) (14) transporting data received from one or more
mobile terminals (20), characterized by:
a congestion detector (30) for monitoring and detecting congestion in the RAN
associated with transporting information uplink from one or more mobile terminals through the
RAN, and
a congestion controller (32) for reducing the detected congestion in the RAN associated
with transporting information uplink from mobile terminals through the RAN.
16. The apparatus in claim 15, wherein the RAN is configured to receive mobile
terminal information using high speed uplink packet access (HSUPA) or using one or more
enhanced uplink dedicated channels (E-DCHs).
17. The apparatus in claim 15, wherein the RAN includes a radio network
controller (16) coupled to a radio base station (16), and wherein the apparatus is implemented
in the radio network controller.
18. The apparatus in claim 17, wherein the RAN includes the first radio network
controller coupled to a second radio network controller, and wherein one of the radio network
controllers is configured to detect uplink congestion over an interface between the first and
second radio network controllers.
19. The apparatus in claim 17, wherein the congestion controller is configured to
reduce a parameter associated with a bit rate at which mobile terminal information is
transported through the RAN.
20. The apparatus in claim 19, wherein the uplink mobile terminal information is
communicated using uplink data flows, and wherein the congestion controller is configured to
send a signal to the radio base station to reduce a bit rate of one or more uplink data flows.

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21. The apparatus in claim 19, wherein the congestion controller is configured to
send an absolute bit rate parameter value or a relative bit rate parameter value for use by the
radio base station to reduce a bit rate or power of one or more uplink mobile terminal
transmissions.
22. The apparatus in claim 19, wherein the congestion controller is configured to
reduce the bit rate parameter by sending control information in a control plane or in a user data
plane to the radio base station.
23. The apparatus in claim 19, wherein the congestion controller is configured to
send a signal to the radio base station to restrict scheduling of one or more uplink transmission
grants or credits.
24. The apparatus in claim 15, wherein the congestion controller is configured to
release one or more diversity handover radio links to reduce the detected congestion.
25. The apparatus in claim 15, wherein a first amount of bandwidth allocated to
uplink dedicated channels and a second amount of bandwidth is allocated to enhanced uplink
dedicated channels, and wherein the radio network controller is configured to send a message
to the radio base station to reduce the second amount of bandwidth when uplink congestion is
detected in the RAN.
26. Apparatus for use in managing an overload or congestion condition in a radio
access network (RAN) (14) associated with transporting information uplink from one or more
mobile terminals (20) through the RAN, characterized by:
a scheduler (44) for scheduling uplink transmissions from one or more mobile
terminals, and
a congestion controller (40), coupled to the scheduler, for reducing congestion in the
RAN associated with transporting information uplink from mobile terminals through the RAN.

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27. The apparatus in claim 26, wherein the congestion controller is configured to
receive one or more messages from a radio network controller in the RAN including
information associated with reducing congestion in the RAN associated with transporting
information uplink from mobile terminals through the RAN.0
28. The apparatus in claim 27, wherein the congestion controller is configured to
instruct the scheduler to restrict uplink transmission grants or credits provided to the one or
more mobile terminals.
29. The apparatus in claim 27, wherein the congestion controller is configured to
drop one or more frames associated with one or more uplink mobile terminal communications.
30. The apparatus in claim 27, wherein the congestion controller is configured to
reduce a bit rate or power associated with one or more uplink mobile terminal communications
using negative acknowledgement messages.

Congestion in a radio access network (RAN) associated with transporting uplink
information originating from one or more mobile terminals is detected. That detected RAN
congestion is reduced using any suitable technique (several examples are described) and may
be implemented in one or more nodes in the RAN. One advantageous (but non-limiting)
application is to a RAN that supports high speed uplink packet access (HSUPA) and/or one
or more enhanced uplink dedicated channels (E-DCHs).

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=w6GRgC5WQET6HNMzt4dKMg==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

278249

Indian Patent Application Number

2919/KOLNP/2007

PG Journal Number

53/2016

Publication Date

23-Dec-2016

Grant Date

19-Dec-2016

Date of Filing

09-Aug-2007

Name of Patentee

TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Applicant Address

SE-164 83 STOCKHOLM

Inventors:

#	Inventor's Name	Inventor's Address
1	LUNDH, PETER	EKSÄTRAVÄGEN 218, SE-127 61 SKÄRHOLMEN
2	SÅGFORS, MATS	JUNGFRUSVÄNGEN 33 G 12, FI-02400 KYRKSLÄTT

PCT International Classification Number

H04L12/26

PCT International Application Number

PCT/SE2006/000032

PCT International Filing date

2006-01-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/035,021	2005-01-14	U.S.A.