|Title of Invention||
METHOD AND APPARATUS FOR FAST CLOSED-LOOP RATE ADAPTATION IN A HIGH RATE PACKET DATA TRANSMISSION
|Abstract||In a high data rate communication system capable of variable rate transmission, an open loop rate control can be adjusted with a closed loop rate control to maximize throughput. An access point generates interleaved multi-slot packets that allow an access terminal to transmit indicator messages to the access point in accordance with recently received data carried within slots of the multi-slot packets.|
METHOD AND AFPAEATUS FOR TAST CLOSED-LOOP RATE ADAPTATION IN A HIGH RAATE PACKET DATA TRANSMISSION
B ACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to data communication. More particularly, the present invention relates to a novel and improved method and apparatus for performing tast closed-loop rate adaptation in a high rate packet data
11. Description of the Related Art
Mobile computing and data access is sleadily becoming available to an increasing number if users.. The development and introduction of new data services and ted-mologies th.at will provide continuous data connectvity and full access 1:0 inionnation is presently occnrring. Users can now use a variety of electronic devices to retrieve voice or data information stored on other electronic devices; or data netword. Some or these electronic devices can connect to data resources through wires and some can connect to data resources through vvirelens solutions. As used herein an access termunal is a device provuding data connectivity to a user- An acct:ss terinirhal may be coupled to a computing device such as a desktop computer, a laptop computer, or a personal data assistant (PDA), or it may be physically incorporated into any such devices. An access point is equipment that provides data connectivity between a packet switrlied data netword and access terminals.
-An example of an access terminal that can be used to provide wireless connectivity is a mobile telephone that is part of a communication system capable of supporting a variety of applications. One such communication system is a code division multiple access (CDMA) system which conforms to
A significant difference between voice rervices and data services is the fact thai the former imposes stringent and fixed delay requirements. Typically. the overall one-way delay of speech frames must be less than 100 msec. In contrast, the data delay can become a variable parameter used to optimize the effcienry of the data commnnlcation system. Specifically, more efficient error correcting coding techniques which require significantly larger delays th^n
those that can be tolerated by voice services can be utilized. An exemplary efficient coding scheme for data is disclosed in U.S. Patent Application Serial No. 08/743,6SS, entitled 'SOFT DECISION OUTPUT DECODER FOR DECODING CONVOLUTIONALLY ENCODED CODEWORDS", filed November 6, 1996, assigned to the assignee of the present invention and incorporated by reference herein.
messure of the efficiency of the data transmission capability of the communicatin system.
It is well known that in cellular systems, the signal-to-interference-and" noise ratio (SINR) of at\y given user- is a function of the location of the user within the coverage area. In order to maintam a given level of service, time division multiple access (TDMA) and frequency division multiple access (IDXIA) systems resort to frequency reuse techniques, i.e. not all frequency channels and/or time slots are used in each base station. In a CDMA system, the same frequency allocaion is reused in every cell of the system, thereby improving the overall efficiency. The SINR measured at any given vtser's mobile station determines the information rate that can he supported iot ttiis
ACCURATELY PREDICTING SIGNAL TO INTERFERENCE AND NOISE RATIO TO nvlPROVE COMMUNICATIONS SYSTEM PERFORMANCE/' assigned to the assignee of the present invention and incorporated herein by reference. The predicted SINR determines the maximum data rate that can be
The present invention is directed to a novel and improved improved method and apparatus for modifying an open-loop rate adaptation algorithum to produce a hybrid open loop/closed loop rate adaptation scheme. An access point
advantageously generates a time interleaved structure for slots in data packets, allowing an access terminal to transmit indicator messages to the access point during periods associated with gaps inserted into the interleaved structure.
In one aspect of the invention, the periods associated with the interleaved gaps are of sufficient duration to allow the access terminal to decode the data carried in the slots and to send an indicator message based on the decoded data. In an alternative aspect of the Invention, the indicator messages are based on an estimated signal-to-mterference-and-noise level.
In another aspect of the invention,, the indicator messages are one bit long, which is interpreted by the access point in accordance with the timing of the arrival of the bit.
If there is data to he transmitted to the access terminal the data is sent by a central controlier to all access points in the active set and stored in a queue at
each access point. A paging message is then sen.t by one or more access points to the access tenninal on the respective control, channels. The access point may transmit all such paging messages at the same time across several access points in order to ensure reception even when time access terminal is switching
at which to transmit the data to the selected access terminal based on the most recent value of the DRC message received from the access terminal. Additionally, the access point uniquely identifies a transmission to a particular access terminal by appending an identifying preamble to a data packet directed
slot corresponds to a period of 1.666m5, or equivalently, 204S chips transmitted at the chip rate 1,2288 Mcps.
In an HDR system, code symbols that are transmitted ina packeet at data rates of 307.2 kbps and below are repeats of the code symbols that are transmitted in a packet at 614.4 kbps[t1] In general, most of the code sytnbols transmitted in a given slot are .-shifted repartitions of the code symbols transmitted in the first slot of the packet. The lower data rates require a lower SINR for a given low probability of packet error, "Hence if the access terminal determines that channel conditions are not favorable, the access terminal will transmit a DRC message requesting a data rate below 614.4 kbps. The access point will then transmit multi-slot packets in accordance with thc sttucture described in FIG. T However, if the actual channel conditiozis improve so thiat
the access terminal needs fewer repeated code symbols than origmally specified by the open-loop rate adaptation algorithm, the structure described in FIG 1 will allow the access terrminal to transmit an indicator message, such as a STOP
requesting the retransmission of the data carried in a specified slot. The structure of FIG. 1 allows the access point to retransmit the data on the very next slot, referred to herein as an extended data slot following the decoding of the EXTENT) indicator message. FIG. 3 is an illustration of this use for an EXTEND indicator message. Data packet 300 is constructed in accordance with the structure of FIG. 1/ so that altematingg slots are designated gap slots. A DKC
In one exemplary embodiment the access terminal may be allowed to send up to NEXT(i) EXTEND indicator messages per packet where i=l, 2,.,., 11 corresponds to one of the Data Rates illustrated in Table 1.
The procedure described above for a closed loop rate adaptation is exemplary in transmissions where the data packet comprises one or two slots. It should be noted that the extended data slot carries code symbols tliat are repetitions of previously transmitted code symbols, and therefore, the code symbols the extended data slots may be advantageously soft-corabined with the pre.viously received code symbols prior to the decoding step in order to improve reliability. The identification of which code symbols are to be reansmitted in an extended data slot is an implementation detail and does not effect the scope of this invention.
access point can also interpret the FCL bit as an EXTEND indicator message if a previous EXTEND indicator message caused the retransmissioin of a slot of a specified packet exactly in slot n-1 and less thiin NEXT EXTEND indicator messages have been processed for this packet. If none of these situations are applicable, then the bit can be discarded as a false alarm.
in every N' slot. Jv-1 slots are gap slots, wherein the access tertrunai may use the delay associated with the gap slots to attempt decoding the data received in. the previous data slot. As is well known in the art, blocks of data bits may be transmitted with coding to enable the recipient of the data to determine the existence of any errors in the data transmissin. An example of such a coding technique is the generation of cyclic redundancy check (CRC) symbols. In one aspect of this embodiment, the delay caused by the uniform insertion of gaps enables the access terminal to decode CRC bits and to determine if the data slot was successfully decoded. Rather than sendin.g indicator messages based on
n+1 However, the access point will interpret the FCL bit as an EXTEND indicator message if a packet scheduledto this access terminal, according to a requested data rate, ended exactly in slot n-p-1, wherein p is the period of the assigned data slots to an access terminal. Alternatively, the access point can also interpret the FCL bit as an EXTEND indicator message if a previous EXTEND indicator message caused the retransmission of a slot of a specified packet exactly in slot n-p^l, and le;>s than N^-j, EXTEND indicator messages have been processed for this packet. If none of tl^ese situations are applicable,
begun at n, then the current slot n+3 data would have been transmitted at slot n+2, which would have overlapped the data slot pattern scheduled with DRC message 510.
.In a maimer similar to the transmission of indicator messages for the one-slot gap pattern embodiment, STOP indicator messages and EXTEND indicator messages can be used in the non-uniform N-slot gap pattern. In addition^ the formulation of the indicator messages can be accomplished using only one bit, if the system discriminates the context of the bit upon usage. For
may be more desirable to implement a non-uniform slot gap pattern. For exampie, during high, speed data transmissions, only one slot of data is transmitted with large amounts of code symbols. In such cases, the access terminal would require a relatively long duration to decode the received code symbols. Hence, the implementation of a uniform slot pattern would require correspondingly large periods with large amounts of gap slots, which would not be efficient. Under this circumtstance, a non-uniform gap .slot pattern may be preferable.
Access point 700 transnuts a data packet to access terminal 701. While receiving the data packet the access terminal 701 may feed the results from the SINR estimation element 722 to the closed loop rate control element 725 or alternatively, the access terminal 701 may feed the results from the decoder 720 to the closed loop rate control element 725- Buffer 721 may be inserted to aid in the ordered deliveryof decoded information from the decoder 720 to the tipper layer protocols, which will not be described herein. The dosed loop rate control element 725 can use results from either the decoder 720 or the SIKTR estimation element 722 to detennme whether to generate an indication
The FCL rate adaptation method also improves the throughput rate by allowing the open loop rate control scheme to be aggressive in requesting one-slot packets at higher rates, since the FCL rate adaptation method allows for the transmission of an extended slot of data if a high rate packet cannot be decoded successfully. Throughput is also improved when the FCL rate adaptation method stops a multi-slot packet earlier than expected by the open loop rate control algorithm.
other embodiments without the use of the invenive factity. Thus the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principlas and novel features disclosed herein,
1. A method for increasing the data throughput rate of a communication
network, comprising the steps of;
generating a phurality of data slots and a plurality of gap slots at an
access pointy wherein the plurality of data slots are Interleaved with the
plurality of gap slots to form a plurality of packets;
transmitting the plurality of packets to an access terminal; and detecting the plurality of packets at the access terminal, wherein the
access terminal transmits at least one indicator message to the access point
indicating a reception status.
2. The method of Claim 1, wherein the plurality' of data slots are interleaved with the plurality' ot gap slots in an alternating pattern,
3. Tl\e method of Claim i, wherein the plurality of data slots aj-e interleaved with thr plurality of gap slots such that every Nth slot is a gap slot.
4. The method of Claim 1, wherein the pluralityy of data slots ar^-* interleaved with the plurality of gap slots m accordance with an aperiodic structure-
5. A method tor increasing the data throughput rate for transmissions from an access point to an access terminal comprising the steps of;
generating a plnrality of data packets at the access point for transmission to the access terminal, wherein each of the plurality of data packets comprises at least one slot, and the access point designates each slot in each of the plurality of data packets as a data slot or a gap slot;
transmitting the plurality of data packets to the access terminal at an initiatdata rate;
determining a set of estimated chennal parameters at the access termman;
transmitting a data request message to the access point based on the set of estimated channel parameters, wherein the step of transmitting the plurality of data packets to the access ternmal is performed in accordance with the data request message;
determining a set of actual channel parameters at the access terminal;
transmitting an indicator message to the access pomt if the set of actual channel parameters passes a predetermined quality amount, wherem the step of transmitting Is performed during a time period associated with at least one gap slot; and
modifying a subsequent data packet for transmission to the access terminal in accordance with the indicator message received at the access point.
deciding the bit is a request tor retransmission if a previous indicator bit caused a retransmission of an already transmitted packet in slot n-2 and fewer than a predetermined number of retransmissions have been already processed for the plurality of data packets; and
deciding the bit is a false alaim. if no conditions are satisfied.
deciding the bit is a request for retransmission if a previous indicator but caused a retransmission of an already transmitted packet in slot n-N(i), and fewer than a predeternuned number of retransmissions have been already processed for the plurality of data packets; and
deciding the bit is a false alarm if no conditions are satisfied.
11. The method of Claim 5/ wherein the set of actual channel paxanieter.
comprises a signal^to-interference and noise ratio.
12, The method of Claim 5, wherein the step of determining a set of actual
channel parameters comprises the step of decoding the plurality of data packets
at the access terminal to deterntine a packet error evertt, wherein the packet
error event indicates a good data packet reception or a bad data packet
13. The method at Claim 12, wherein the step of decoding the pluality of
data packets at the access terminal comprises the steps of:
decoding a plurality of cyclic redundancy' check (CRC) bits; and comparing the decoded plurality of CRC bits with an estimated quality
metric, wherein the estimated qua]ity metric is computed from the set of
estimated chennel parameters-
14. The method of Claim 5, wherein the step of transmitting the mdicator
message to the access point comprises the steps of:
processing code symbols to deternnine a probability value for transmission errors; and
transmitting an extend indicator message if the probability' value tor transmission errors is greater than a predetermined amount.
15, The method of Claim 12, wherein the indicator message comprises a bit
received during a slot n, and the access point designates each slot in the:
plurality- of data packets in accordance vvith an alternating pattern, wherein the step of modifying the subsequent data packet for transmission to tlie access tenninal comprises the steps of:
deciding the bit is a request for a termination ol traasmissioii it a repetition of one of the plurality of data packets is already scheduled for slot
17. The method 0/ Claim 12,, wherein the indicator message comprises a bit-received during a slot n, wherein the step of modifying the subsequent data packet for transmission to the access terminal comprises the steps of:
deciding the bit is a request for a termination of transmission if a repetition of one of the plurality of data packets is already scheduled for s\o
21. The apparatus of Claim 19, wherein the quality value is detenxuned by a
packet error value based on the decoded plurality of data slots.
22. All apparatus for adjusting an open loop rate control process,
a scheduler at an access point for Scheduling a plurality' of interleaved data slots and gap slots wherein the schedule is compled to at least one buffer
that stores data to be transmitted on a forward linl *
a data rate request message decoder coupled to the scheduler for decoding a plurality of data request messages received on a reverse link channel, and for inputting data rate request information to th.e scheduler; and
an indicator message decode: coupled to the scheduler for decoding th.e plurality of indicator messages received on the reverse link channel and for inputting decoded indicator messages to the schediuler.
24. A method for increasing the data throughput rate substantially as herein described with reference to the accompanying drawings.
|Indian Patent Application Number||IN/PCT/2002/1843/CHE|
|PG Journal Number||07/2008|
|Date of Filing||11-Nov-2002|
|Name of Patentee||M/S. QUALCOMM INCORPORATED|
|Applicant Address||5775 Morehouse Drive, San Diego, CALIFORNIA 92121|
|PCT International Classification Number||H04L 12/56|
|PCT International Application Number||PCT/US2001/015381|
|PCT International Filing date||2001-05-11|