Title of Invention	A METHOD FOR SPATIAL REUSE WITH LINKS USING TRANSMIT POWER CONTROL IN A WIRELESS PERSONAL AREA NETWORK
Abstract	The invention pertains to a system and method for channel time reservation in the medium access control functionality of wireless personal area networks, based on ultra wide band (UWB) systems for spatial reuse with links using transmit power control wherein a device in the network can provide information about the time slots in which other devices can reuse the same slots, which are already in use for communication. According to the invention the transmit power used to transmit all type of frames in the master link is less than the maximum power used to transmit beacon frames. In the system the devices of the slave link listen to the medium at the beginning of the reservation for a pre-defined duration to determine whether the slave device is within the interference range of the master link and the slave devices negotiate with each other for an adequate transmit power while reusing the data slots so as to ensure that the slave link does not interfere with the communication going on in the master link.

Title of Invention

A METHOD FOR SPATIAL REUSE WITH LINKS USING TRANSMIT POWER CONTROL IN A WIRELESS PERSONAL AREA NETWORK

Abstract

The invention pertains to a system and method for channel time reservation in the medium access control functionality of wireless personal area networks, based on ultra wide band (UWB) systems for spatial reuse with links using transmit power control wherein a device in the network can provide information about the time slots in which other devices can reuse the same slots, which are already in use for communication. According to the invention the transmit power used to transmit all type of frames in the master link is less than the maximum power used to transmit beacon frames. In the system the devices of the slave link listen to the medium at the beginning of the reservation for a pre-defined duration to determine whether the slave device is within the interference range of the master link and the slave devices negotiate with each other for an adequate transmit power while reusing the data slots so as to ensure that the slave link does not interfere with the communication going on in the master link.

Full Text	FIELD OF THE INVENTION This invention relates, in general, to the field of wireless mobile ad-hoc networks and in particular to medium access control for wireless personal area networks that are based on wireless mobile ad-hoc networks. Specifically the invention relates to mechanisms, for channel time reservations in the wireless personal area networks, which allows the devices to communicate data with other devices in the network. More accurately this invention encompasses a method for spatial reuse with links using transmit power control. DESCRIPTION OF RELATED ART Wireless personal area networks, which are defined to function in the personal operating space, i.e. in a range of approximately 10 meters can be implemented using MAC protocols like IEEE-802.15.3 or MBOA MAC standard. Ultra Wide Band (UWB) technology can provide data rates exceeding several hundreds of Mbps in such personal operating space. In wireless personal area networks, the medium is shared between all the devices in order to facilitate communication with each other. This calls for a medium access control mechanism for the devices to manage medium access, broadly including how it may join the network, how it can transfer data at the required rate to another device, how the medium is best used etc. The medium access control for wireless personal area networks can be conceived in two approaches - centralized and distributed. In the centralized approach, one of the device acts on behalf of the whole network to coordinate in managing the media access operations for all the devices. All other devices seek help of the centralized coordinator for media access operations like joining the network, reserving channel time, etc. On the other hand, in the Distributed approach, the media access operations are distributed evenly across all devices in the network and the entire devices share the load of managing media access operations for each other. Figure 1 shows the wireless personal area network, which is based on IEEE-802.15,3, and illustrates the centralized media access control approach. It involves a network referred as piconet, in which a device may act as the coordinator (referred as piconet coordinator or PNC in literature). The PNC performs the functions of allowing a device (referred as DEV) to join, allocating it a channel (time slot) to transmit to another device, synchronization mechanisms etc. This can be viewed as a centralized WPAN system, which is formed on an ad-hoc basis. Figure 2 shows the wireless personal area network, which does not have any centralized coordinator. In other words, it illustrates the distributed media access control approach. In this method, all devices cooperate and share information with each other to perform the media access control tasks such as allowing a new device to join, allocation of channel time to a device to transmit data to another device, synchronization mechanisms etc. This is a Distributed WPAN system, which again is formed in an ad-hoc fashion. The Distributed media access control approach relies on a timing concept called the superframe. The superframe has a fixed length in time and is divided into a number of time windows, which are called time slots. The devices use some of the time slots for sending their beacons, meanwhile reserving some others for transferring data. The slots in which beacon is sent are called beacon slots and the slots in which data is sent are called data slots. The beacon slots typically appear together at the start of the superframe and are lesser in length than a data slot. In addition, the number of beacon slots may be fixed or variable, leading to different configurations of Distributed Medium Access Control mechanisms. Figure 3 illustrates the superframe structure, as specified by the Multiband OFDM Alliance (MBOA) draft 0.98. It is evident from the figure that it consists of several Medium Access Slots (as an example, the number is shown as 256), which include the beacon period - comprising of the beacon slots used by multiple devices to send the beacon frame - and data period, which may be used by different devices in the network to transmit data to other devices in the network. Typically, superframe duration is 64 millisecond, and each MAS is of 256 microsecond duration. Information about the device’s characteristics and its usage of the superframe is being broadcasted by each device in its beacon frame, sent during the beacon period, so that the neighbors of that device can use that information for further processing. The start time of the superframe is determined by the beginning of the beacon period and defined as the beacon period start time (BPST). It is important to note here that the channel time allocation schemes should be independent of the actual values of these parameters. It is also important to note that channel time allocation scheme is independent of number of beacon period and data period in superframe. Further, the channel time negotiation is a scheme of negotiation of channel time, which is a time slot, lying anywhere in the superframe regardless of the beacon period or data period. It follows that devices, in order to communicate, need to find a free slot from the beacon slots to send its beacon. A device, which is sending its beacon regularly, is considered to be a part of the network. Once a beacon slot is reserved, the device can use it as long as it remains as a part of the network. Further, devices need free data slot to communicate with each other. But, in order to reserve such a data slot, it is necessary to know that both the transmitter and receiver are free in that particular data slot at a given time. The data slots are freed by the device as and when the communication with the other device is over. Once freed, these data slots get added to the free data slot pool and are subsequently reserved by other devices for further use. In order to avoid interference and hidden node and exposed node problems, it has been set that no device can reserve a slot already reserved by another device in its two hop neighborhood. The reservation of data slots usually takes place in a completely distributed manner, with the devices sharing information and helping each other to reserve slots. Here it is important to note that, unlike in the centralized WPAN, no device acts as a central coordinator for the various medium access operations. The present state of art in this field has certain limitations as explained herein below. It is a common knowledge that during the period when data communication is in progress in a certain set of data slots, no other device pair in the two-hop neighborhood of the first pair of devices can start a communication in the same set of data slots. This kind of a very rigid data slot reservation mechanism actually reduces the throughput of the wireless network. For a given network, there could arise several scenarios in which multiple simultaneous communications between different pair of devices is possible. The MBOA MAC protocol does not allow for such reuse of communication channel. For increasing the throughput of the wireless networks, the simultaneous use of the communicating channel by multiple pair of devices is essential. But, most MAC protocols in wireless networks do not define methods that facilitate spatial reuse. Listed below are the limitations specific to MBOA MAC version 0.98 with respect to reserving data slots that facilitate spatial reuse. In the data slot reservation protocol of MBOA MAC version 0.98, after a DRP reservation is made, all the neighbors in the two hop neighborhood of the communicating devices are silenced for the whole duration of the communication. It implies that many devices in the hidden node region and in the exposed node region would not be able to use the same slots when the communication is in progress. This is illustrated in the Figure 5, wherein the circle around S denotes the exposed node region and the circle around D denotes the hidden node region. The system as such is having a number of disadvantages. The MBOA MAC version 0.98 does not describe any mechanism by which non-interfering communications can reserve and use the same data slots. In the MBOA MAC protocol and in wireless MAC protocols in general, there is no method by which a sending/receiving device can announce that it is willing to facilitate spatial reuse in the slots used for its communication. A device that wants to reuse the channel cannot know as to when it should scan to find out if interference is possible in an already existing data communication. There is no method by which devices can ensure that communication between a pair of devices does not interfere with the communication in another pair of devices in its transmission range. In the MBOA MAC version 0.98 protocol, there is no method by which a device can propagate the information of spatial reuse data slots to its two hop neighbors. Also, in the MAC protocol, there is no mechanism by which devices communicating can use transmit power control to achieve spatial reuse and power savings. Also it is found in one of the prior art literature that a method for simultaneous transmission of a plurality of signals from a plurality of the fixed stations on a single selected frequency is possible. Each of the transmissions is directed to a selected one of the mobile cellular phone devices. Such simultaneous transmission is attained by adjusting power levels in the transmission frequency in a given cellular area such that the transmission by the fixed station within the area does not interfere with the reception of the signals by another mobile unit in another cellular area. Even though, the method of achieving simultaneous transmissions appears to be similar to the one envisaged by the invention, the prior art literature is different since it talks about the method in the context of mobile cellular networks and is no way connected to use of UWB. From the foregoing, it is quite evident that the state of the art literature is silent with regard to addressing medium access controls for wireless personal area networks based on wireless mobile ad-hoc networks. Having concerned about the scenario, the inventors proposes a system and method to resolve the above, by which it is possible to manage channel time reservation in the medium access control functionality for wireless personal area networks based on ultra wide band (UWB) systems. SUMMARY OF THE INVENTION The primary object of the invention is, therefore, to provide a system and method that increases the throughput achieved by the wireless network. It is another object of the invention to provide a method where a device in the network can provide information about the time slots in which other devices can reuse the same slots, which are already in use for communication. It is yet another object of the invention to provide a system by which a device in the network can listen for specific time period in order to identify if there is any interference in its transmission or reception range due to other communicating devices. It is also an object of the invention to use the application characteristics to easily and efficiently allow spatial reuse in the channel time used for its data communication. Accordingly, the present invention provides a method for channel time reservation in the medium access control functionality of wireless personal area networks, based on ultra wide band (UWB) systems for spatial reuse with links using transmit power control wherein a device in the network can provide information about the time slots in which other devices can reuse the same slots, which are already in use for communication. The invention also provides a system for spatial reuse with links using transmit power control, wherein all the devices in the network listen for specific time period in order to identify if there is any interference in its transmission or reception range due to other communicating devices. These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS Figure 1 illustrates the centralized media access control approach in a wireless personal area network, which is based on the IEEE-802.15.3 protocol. Figure 2 illustrates the distributed media access control approach in wireless personal area network, which does not have any centralized coordinator. Figure 3 illustrates the skeleton of beacon slots and data slots within the superframe. Figure 4 illustrates the relation between the transmit power and range. Figure 5 illustrates the typical reservation mechanism where all the other devices in the whole range of the sender and receiver side are silenced. Figure 6 illustrates how more than one pair of devices can communicate during the same data slots when both the communicating pair of devices are using appropriate transmit power control. Figure 7 illustrates the exchange of frames in the Master Link and the Slave Link with respect to Figure 6. Figure 8 describes the fields in the Link Spatial Reuse Information Element. The source and destination device ID are the DevID of the source and destination devices as mentioned in the beacon of the respective devices. Figure 9 illustrates the structure of a new information element called the Spatial Reuse Availability IE, SPRJWailabilityJE. Figure 10 is a MSC used to explain one of the scenarios in which the source of the slave link is outside of the beacon group of the Master Link devices and the 8 destination of the slave link is in the beacon group of the Master Link devices. DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. Before starting the detailed description, some of the basic features associated with the invention are described herein. Throughput can be defined as the total number of bits successfully transmitted and received in the network. The system and method described here specifies an enhancement to the existing method for channel reservation in a completely distributed wireless personal area networks. The network under consideration is a wireless ad-hoc network with varying network topology. The mechanisms specified in the invention can be applied for channel time reservation in other distributed networks where the channel time is slotted and distributed reservation is deemed necessary for reserving the channel time. It is assumed that, in the media access layer protocol under consideration that there exists a system and method for agreeing upon the transmit power to be used in a specific communication. A secondary benefit of using this data reservation protocol is the reduction in the battery power used by all the communicating devices. Hence, devices use the network for longer periods before a recharge is required for their batteries. The proposed method defines a channel access mechanism that is an extension to the existing method in the MBOA MAC protocol. The method provides an easy way for identifying the slots that are available for spatial reuse and reserving such slots for communication. Multiple communications existing during the same time slots result in increased throughput for the network. The silencing of devices in the two-hop neighborhood because of the hidden node and exposed node problem reduces the achievable throughput of the network. But, by using the method of this invention, many links that fall in the region of the hidden node or exposed node can still initiate communication, thereby effectively increasing the throughput of the network. There is no requirement of additional channel negotiation procedure apart from the DRP Request and Response for using the spatial reuse slots. As transmit power control is used, the reception and interference range of a communication is far reduced. The technique still maintains the distributed method of medium access. The mobility among the nodes that are using spatial reuse can easily be tracked using the initial RTS and CTS frame exchange sent by the devices in the Master Link. The communications established using the reservation mechanism listed in this invention could continue to proceed without disruption even if the Master Link terminates its reservation. The commercial advantage of implementing the system and method specified in this invention is that wireless network can achieve a throughput much higher than the actual maximum possible by the physical interface. The devices that are participating in the spatial reuse communications can all achieve power savings as all uses only less power to transmit than the maximum in all their reservations. Hence, in network scenarios where frequent recharge of batteries is not possible, this method eventually results in increased network lifetime and lifetime of individual device. Now the invention is explained in detail below with reference to the drawings. Figure 1 illustrates the centralized media access control approach in a wireless 10 personal area network, which is based on the IEEE-802.15.3 protocol. The piconet range, different piconet elements like DEV and PNC, frames being transferred in piconet like beacon and data transfer between DEV to DEV, PNC to DEV and DEV to PNC are shown. This figure is included to show the difference between a centralized and distributed wireless personal area network. Figure 2 illustrates the distributed media access control approach in wireless personal area network, which does not have any centralized coordinator. The various devices (DEV) are shown as dark circles (bullets), with their ranges in circles. The devices cooperate and share information with each other to perform the media access control operations. Figure 3 illustrates the skeleton of beacon slots and data slots within the superframe. The numbers in the figure, such as superframe duration, number of beacon slots and number of data slots are indicative. A change in these numbers does not affect the operation of the present invention. The control information is transmitted by devices in beacon frames in chosen beacon slots. The data slots are used for communication and are reserved using the distributed reservation protocol. Figure 4 illustrates the relation between the transmit power and range. The bigger bold circle around S and D represent the range when the maximum transmit power (Pmax) is used. Power Pmax has to be used to send beacon frames so that all the devices in the wireless network can gain information about the network topology. For data frames the communicating devices can choose to use Pmax or some power P Figure 5 illustrates the typical reservation mechanism where all the other devices in the whole range of the sender and receiver side are silenced. When devices S and D are communicating, devices S1 and D1 cannot use the same data slots in order to avoid the interference that they may cause to the existing communication. 11 Figure 6 illustrates how more than one pair of devices can communicate during the same data slots when both the communicating pair of devices are using appropriate transmit power control. S and D use power P and devices S1 and D1 use power P1, where P1 Figure 7 illustrates the exchange of frames in the Master Link and the Slave Link with respect to Figure 6. The beacon frames are transmitted with maximum power P1, the RTS, CTS, DATA and ACK frames exchanged between the Master Link devices use power P2 and the DATA, ACK frames exchanged between the slave devices use power P3, where power levels follow the relation P3 Figure 8 describes the fields in the Link Spatial Reuse Information Element. The source and destination device ID are the DevID of the source and destination devices as mentioned in the beacon of the respective devices. Stream ID is the stream identification of the Master Link as given in the DRP IE. Transmit power field identifies the power that will be used to transmit frames between the source and destination device. The flag field is used to inform to the neighbors whether the reservation of one link or all the channel reservations between the source and destination identified in this information element are available for spatial reuse. Figure 9 illustrates the structure of a new information element called the Spatial Reuse Availability IE, SPR_Availability_IE. The SPR_AvailabilityJE is maintained internally by each device and is updated when the device receives a DRP-IE for an established DRP, along with the LINK_SPR_IE for that reservation broadcast in the beacon by the owner and/or target of the reservation. The SPR_AvailabilityJE provides the required information that is to be known for every spatial reuse reservation. One value is the Allocation field, which defines the data slots as in the DRP-IE, and the second is the power level as in the LINK_SPRJE for that link. The first field of the SPR_AvailabilityJE gives the number of such (Allocation field, power level) pair values that are present in the information element. The SPR_Availability_IE is added to the beacon when a reservation target device of a 12 slave link wants to re-negotiate the slots that are suggested in the corresponding DRP Request. Figure 10 is a MSC used to explain one of the scenarios in which the source of the slave link is outside of the beacon group of the Master Link devices and the destination of the slave link is in the beacon group of the Master Link devices. The source device does not hear the LINK_SPRJE sent by the devices of the Master Link. Hence, for the reservation request sent by the source the destination device sends a response with the Reason Code set to Pending. The destination then uses the SPR_Availability_IE stored in its internal database to identify all the spatial reuse slots along with the power levels using which it can reach the source. The updated SPR_Availability_IE is included in the beacon frame for certain number of superframes or until a DRP reservation is in progress. This facilitates the source to identify and change its reservation slots to use the spatial reuse slots mentioned in the SPR_Availability_IE. The source then sends the changed DRP Request again to the destination, which is then accepted by the destination, thus enabling spatial reuse. The proposed invention speaks about a system and method which allows certain devices to re-use channel time currently being used by other pair of devices. This decision to use the same slots reserved by another pair of devices is taken in a completely distributed manner without the need for a centralized coordinator. The system for the invention comprises of a distributed medium access control mechanism involving a superframe structure made up of timing slots where all inter device communication takes place within the time slots. The slots may be reserved by devices for their communication needs. Slots are reserved in a completely distributed manner without the need for any centralized coordinator. The beacons transmitted by every device in every superframe are transmitted at a maximum power say, Pmax, which is defined in the MBOA MAC-PHY interface. This is required so that the range of MBOA MAC devices is kept a constant, which is a sphere of 10 m radius. 13 The system of invention assumes that devices use the implicit-DRP mechanism to reserve the slots in which data communication will take place. The reservation mechanism as listed in the MBOA MAC version 0.98 is assumed. In implicit-DRP mechanism, after channel negotiation, both the sender and the receiver will include an information element called DRP-IE in every beacon, until the data slots are used. The DRP IE in the beacon announces that there is an ongoing communication between the two devices in certain slots. This invention assumes that Transmit Power Control (TPC) negotiation is possible between the communicating devices and that a simple and efficient method is known to MAC by which devices can agree on the power that is sufficient for them to communicate. The MBOA MAC specifies the different power levels for transmissions and the maximum number of power levels is set to a predefined value, NumTxPowerLevels. A table in the MBOA MAC-PHY interface specification lists the power values for the different interfaces. Figure 4 explains how the range of the devices vary according to the transmit power used. In this invention, a link that is established first using free data slots and where the devices send the LINK_SPRJE is referred to as the Master Link, Other links that reuse some or all of the data slots reserved by the Master Link for communication are referred to as Slave Links. The invention makes sure that the communication in the Slave Links will not interfere with the communication in the Master Links. Multiple Slave links can exists for one Master Link, thereby giving significant throughput increase for the wireless network. Refer Figure 6. The Master Link devices should not include the LINK_SPRJE if the transmit power used is the maximum transmit power Pmax If Pmax is used then using the invention described in this document no spatial reuse is possible. The Slave link devices should not include LINK_SPRJE as the existence and communication of the slave link is dependent on the power level of the Master Link. The system and method of the invention introduces a new information element 14 called LINK_SPRJE (Link Spatial Reuse Information Element). The fields in this IE are defined in Figure 8. This IE is included in the beacon of devices that have already negotiated a DRP using free slots and agreed to use transmit power, say P, which is less than Pmax. Inclusion of LINK_SPRJE in the beacon indicates the willingness of the Master Link to co-operate with other communication links to enable spatial reuse. The interference range of a transmission is directly proportional to the transmission power. Hence, links using less transmission power will have a smaller reception and interference range. The parameters sent along with LINK_SPRJE are the identification of source device, identification of destination device, identification of Master link(i.e, stream_id), transmit power to be used, and a flag field. The pair of devices source and destination identify each of their communication link with a unique streamjd. If the communicating devices want to allow spatial reuse only for the link identified by stream_id, then the flag field is set to 0. However, if the communicating devices want to facilitate spatial reuse in all the links between the source and destination devices mentioned in the LINK_SPRJE, then this information can be indicated by setting the flag field to 1. Further, the invention introduces a new information element called the Spatial Reuse Availability IE, SPR_AvailabilityJE. The structure of the SPR_AvailabilityJE is given in Figure 9. The SPR_AvailabilityJE is maintained internally by each device and is updated when the device receives an established DRP-IE along with the LINKJ3PRJE for that reservation being broadcast by the owner and/or target of the reservation. As in Figure 6, when S2, S1, S3 and D2, D3, D4 see the DRP-IE sent by S or D along with the LINK_SPR_IE, they will add/update the DRP Allocation and Power Level for this link. Subsequently, when the neighbors of S and D have to initiate or accept a DRP request they can try to use the slots mentioned in the SPR_AvailabilityJE, subject to the power level constraints. The following are the mandatory steps to be followed by the devices of the Master Link: 15 1. The transmit power used to transmit all type of frames in the Master Link, should be less than the maximum power used to transmit beacon frames. 2. The LINK_SPRJE is included in every beacon frame sent by each of the devices in the Master Link. 3. In a given superframe, the device should not use transmit power greater than the value indicated in the LINK_SPR_IE. However, the device can renegotiate the transmit power value and indicate it in its LINK_SPR_IE in the following superframes and then switch to that transmit power. 4. The source device needs to transmit a RTS frame at the beginning of the DRP reservation and the destination should respond with a CTS frame. The RTS/CTS communication is done using the transmit power mentioned in the LINK_SPRJE. Even if the device does not have any communication to be done in the current superframe, the RTS/CTS transmissions have to be sent in the first slot of the reservation. The following are the steps to be followed by the devices of the Slave Link: 1. Both the devices of the Slave Link need to listen to the medium at the beginning of the reservation for RTS+CTS+2SIFS duration. If the device hears any one or both of the messages RTS/CTS or any interference, then the slave device is within the interference range of the Master Link. The slave devices will not initiate DRP with the same slots. Slave Links by listening to the RTS/CTS transfer confirm that they are not in the current transmission range of the Master Link. Devices that hear the RTS/CTS frames will not include the information about that reservation in the SPR_AvailabilityJE. If the device does not hear the RTS/CTS or any interference then the device updates its SPR_AvailabilityJE with the DRP_Allocation value and power level of the Master Link. 2. Slave Links while using the data slots of the Master Link should negotiate a transmit power between the two devices which is less than what is advertised in LINK_SPRJE as Tx_pwr. Slave Links can initiate DRP negotiation for some or all of the MAS slots identified in the SPR_AvailabilityJE, by following the same rules as in MBOA MAC version 0.98, except that it will assume the slots listed in its SPR_Availability_IE are free or available. 16 3. The devices of the slave link should use transmit power less than what is identified in their SPR_AvailabiltyJE. This is to make sure that the slave link does not interfere with the communication going on in the Master Link. 4. After establishing the slave link with spatial reuse slots, the slave devices have to listen at the beginning of the channel reserved by the Master Link for a duration of RTS+CTS+2SIFS. If RTS/CTS or any interference is heard then atleast one of the slave devices or one of the master devices have moved into the range of each other. In this instance, for this current superframe the slave device will not initiate any communication. If the same situation exists for more than a certain number of superframes then the slave devices will have to initiate DRP modify and move to other free slots. This is a situation that can occur where the devices are highly mobile. 5. The Slave devices can also use PCA communication between them. The clear channel sensing done before the start of the PCA communication will identify if there are any other slave links in its neighborhood. The Master Link can choose to close the DRP connection according to the applications requirement When the slave links see that the Master Link is terminated, the slave devices can choose to facilitate spatial reuse and announce the LINK_SPRJE and Spatial Reuse flag in their DRP-IE or choose to be normal DRP Links that block other simultaneous communication in their two hop neighborhood. The method specified in this invention facilitates multiple slave links to exist in the two hop range of a Master Link as long as the DRP reservation or PCA access follow the rules as specified in the MBOA MAC Specification. The invention allows spatial reuse to be exploited in reservations that are of type HARD and SOFT. In soft reservations, the owner of the reservation device can initiate communication with different target devices according to the rules of PCA. Irrespective of the type of reservation, if the target device announces in the LINKJ5PRJE that a certain transmit power is going to be used, then during that 17 superframe the transmit power should neither be increased or decreased. This is to ensure that there in no interference between the other communication links that are using the same data slots. The method of using UDA, UDR for hard DRP reservations can also be used by devices that are part of the Master Link. However, any other device that wants to use the released channel should check for other DRP reservations that are announced in the beacon for the same slots, as mentioned in the MBOA MAC Specification. The method of the invention is described below with the help of examples. Consider the scenario depicted in Figure 6. Devices S, D, S1 and D1 are in the network sending beacons in their respective beacon slots at power Pmax. Devices S and D establish a DRP (Hard or Soft) according to the requirement of their application using segmented/contiguous slots say N1 to N2, following the DRP reservation rules specified in MBOA MAC specification. Slots N1 to N2 should be free for communication both at S and D as can be inferred from their Availability IE information. From the application characteristics running in S, if it is known to MAC that the current communication will exist for a long period of time then S and D can try to facilitate spatial reuse. By other mechanisms out of the scope of this invention and within the features provided in the MBOA MAC protocol, devices S and D agree that a certain power say P is sufficient for two way communication between the devices. Thus, the inner dotted circle around S and D actually indicate the transmission range of the Master Link. After negotiating the power P, devices S and D include a LINK_SPRJE in every beacon with the parameters as defined in Figure 8. With the above steps, devices S and D have announced to the network that the slots N1 to N2 are available for reuse by other devices that can do transmit power control. Next, if device S1 wants to start a communication with D1, S1 will check the availability of slots at both S1 and D1. In order to use spatial reuse, S1 will first check its SPR_AvailabilityJE and find that slots N1 to N2 are available for 18 communication. The slots N1 to N2 in the Availability IE of S1 will be marked as used, but to use spatial reuse the information in SPR_Availability_IE is supersedes the information in Availability IE. Next, S1 checks the Availability IE and SPR_AvailabilityJE of D1 to verify if the same set of slots are free at D1, after which device S1 will try to negotiate a transmit power less than P, say P1 for two way communication with D1. If a communication link with transmit power P1 is feasible between devices S1 and D1, then device S1 will initiate a DRP request to D1 for a reservation in the slots N1 to N2. The DRP negotiation will follow the request response procedure. However, if the communication link with power P1 is not possible then S1 will avoid the spatial reuse slots and use some other slots that are available at both S1 and D1. Similarly, in Figure 6, a second pair of devices S2 and D2 can try to initiate a communication after S and D have reserved the slots N1 to N2 and announced the spatial reuse information element. Now, S2 has the Availability IE of D2 and can decide to request reservation for slots say, X1 to X2. S2 will frame its DRP Request and send it to D2. However, since D2 is in the Beacon group of device S and D, D2 has the spatial reuse information that slots N1 to N2 can also be used instead of X1 to X2. So, D2 will send a DRP response with the reservation as “Pending”. In the same beacon, D2 will include a SPR_Availability_IE as given in Figure 9. The SPR_Availability_IE will indicate all the slots that can be reused at device D2 (slots N1 to N2 will also be included in this), and the power level at which the Master Link of each reservation is communicating. The SPR_Availability_IE can be included in the beacon of D2 for a certain fixed number of superframes, so that S2 will receive that information and be able to change its DRP requests accordingly. Next, S2 will try to verify if it can have a two way communication with D2 with transmit power less than P, say P2. If such a reduced transmit power is identified between S2 and D2, then S2 can decide to change its allocation to any one of the allocations mentioned in the SPR_Availability_IE and issue a changed DRP request for say, slots N1 to N2. Now, D2 can decide to accept the reservation and issue a DRP Response. In this manner, both the Master Links and Slave Link can operate without interference in the same data slots. However, if S2 and D2 cannot identify a transmit power less 19 than what is used by the Master Link, then spatial reuse is not possible. S2 and D2 will try to use free slots in which they do not have any transmit power restrictions. In Figure 6, devices S3 and D4 may try to exploit the spatial reuse enabled by devices S and D, but during the mandatory listen period at the beginning of the channel reservation period of the Master Link, the devices will hear RTS and CTS, hence they will not try to initiate DRP reservation in the slots reserved by the Master Link. The SPR_Availability_IE is added to the beacon frame whenever a device sends the DRP Response with the Reason code as “Pending” in order to try reuse of slots mentioned in the SPR_AvailabiltyJE. However, a device can also choose to periodically send the SPR_Availability_IE to advertise the slots that enable spatial reuse. This will facilitate the two-hop neighbors to consider the spatial reuse slots first when they try to choose slots for a communication. The framing and sending of the Availability IE as defined in the MAC MBOA version 0.98 does not change while adopting the changes defined in this invention for channel reservation using spatial reuse. The described method for spatial reuse can be used only for devices that have unicast traffic between two devices. Using spatial reuse slots for multicast traffic will not be feasible since, it is difficult to negotiate a given transmit power for a large number of destination devices. Broadcast communication can never be tried on slots already used by a communication. The system and method specified in this invention is an enhancement to the existing channel reservation protocol and is completely backward compatible with devices that implement the MBOA MAC version 0.98. If a device does not want to use the spatial reuse slots it can choose to use the free slots in the Availability IE for channel reservation. 20 it will also be obvious to those skilled in the art that other control methods and apparatuses can be derived from the combinations of the various methods and apparatuses of the present invention as taught by the description and the accompanying drawings and these shall also be considered within the scope of the present invention. Further, description of such combinations and variations is therefore omitted above. It should also be noted that the host for storing the applications include but not limited to a microchip, microprocessor, handheld communication device, computer, rendering device or a multi function device. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom. 21 GLOSSARY OF TERMS AND DEFINITIONS THEREOF BP: Beacon Period BPST: Beacon Period Start Time Beacon Group: Devices that can hear each others Beacon are said to be in the same Beacon Group CTS: Clear To Send DEV: Device DEVID: Device Identifier DP: Data Period DRP: Distributed Reservation Protocol PCA: Prioritized Contention Access ID: Identifier IE: Information Element IEEE: Institute of Electrical and Electronics Engineers Link: The communication channel established between two devices MAC: Medium Access Control MAS: Medium Access Slot MBOA: Multi Band OFDM Alliance MSC: Message Sequence Chart OFDM: Orthogonal Frequency Division Multiplexing PHY: Physical Layer PNC: Piconet Coordinator QoS: Quality of Service IFS: Short Inter Frame Space RTS: Request To Send SIFS: Short Inter Frame Space TDMA: Time Division Multiple Access UDA: Unused DRP reservation announcement UDR: Unused DRP reservation response UWB: Ultra Wide Band WPAN: Wireless Personal Area Network

Full Text

FIELD OF THE INVENTION
This invention relates, in general, to the field of wireless mobile ad-hoc networks and in particular to medium access control for wireless personal area networks that are based on wireless mobile ad-hoc networks. Specifically the invention relates to mechanisms, for channel time reservations in the wireless personal area networks, which allows the devices to communicate data with other devices in the network. More accurately this invention encompasses a method for spatial reuse with links using transmit power control.
DESCRIPTION OF RELATED ART
Wireless personal area networks, which are defined to function in the personal operating space, i.e. in a range of approximately 10 meters can be implemented using MAC protocols like IEEE-802.15.3 or MBOA MAC standard. Ultra Wide Band (UWB) technology can provide data rates exceeding several hundreds of Mbps in such personal operating space. In wireless personal area networks, the medium is shared between all the devices in order to facilitate communication with each other. This calls for a medium access control mechanism for the devices to manage medium access, broadly including how it may join the network, how it can transfer data at the required rate to another device, how the medium is best used etc.
The medium access control for wireless personal area networks can be conceived in two approaches - centralized and distributed. In the centralized approach, one of the device acts on behalf of the whole network to coordinate in managing the media access operations for all the devices. All other devices seek help of the centralized coordinator for media access operations like joining the network, reserving channel time, etc. On the other hand, in the Distributed approach, the media access operations are distributed evenly across all devices in the network and the entire devices share the load of managing media access operations for each other. Figure 1 shows the wireless personal area network, which is based on IEEE-802.15,3, and

illustrates the centralized media access control approach. It involves a network referred as piconet, in which a device may act as the coordinator (referred as piconet coordinator or PNC in literature). The PNC performs the functions of allowing a device (referred as DEV) to join, allocating it a channel (time slot) to transmit to another device, synchronization mechanisms etc. This can be viewed as a centralized WPAN system, which is formed on an ad-hoc basis.
Figure 2 shows the wireless personal area network, which does not have any centralized coordinator. In other words, it illustrates the distributed media access control approach. In this method, all devices cooperate and share information with each other to perform the media access control tasks such as allowing a new device to join, allocation of channel time to a device to transmit data to another device, synchronization mechanisms etc. This is a Distributed WPAN system, which again is formed in an ad-hoc fashion.
The Distributed media access control approach relies on a timing concept called the superframe. The superframe has a fixed length in time and is divided into a number of time windows, which are called time slots. The devices use some of the time slots for sending their beacons, meanwhile reserving some others for transferring data. The slots in which beacon is sent are called beacon slots and the slots in which data is sent are called data slots. The beacon slots typically appear together at the start of the superframe and are lesser in length than a data slot. In addition, the number of beacon slots may be fixed or variable, leading to different configurations of Distributed Medium Access Control mechanisms.
Figure 3 illustrates the superframe structure, as specified by the Multiband OFDM Alliance (MBOA) draft 0.98. It is evident from the figure that it consists of several Medium Access Slots (as an example, the number is shown as 256), which include the beacon period - comprising of the beacon slots used by multiple devices to send the beacon frame - and data period, which may be used by different devices in the network to transmit data to other devices in the network. Typically, superframe duration is 64 millisecond, and each MAS is of 256 microsecond duration.

Information about the device’s characteristics and its usage of the superframe is being broadcasted by each device in its beacon frame, sent during the beacon period, so that the neighbors of that device can use that information for further processing. The start time of the superframe is determined by the beginning of the beacon period and defined as the beacon period start time (BPST). It is important to note here that the channel time allocation schemes should be independent of the actual values of these parameters. It is also important to note that channel time allocation scheme is independent of number of beacon period and data period in superframe. Further, the channel time negotiation is a scheme of negotiation of channel time, which is a time slot, lying anywhere in the superframe regardless of the beacon period or data period.
It follows that devices, in order to communicate, need to find a free slot from the beacon slots to send its beacon. A device, which is sending its beacon regularly, is considered to be a part of the network. Once a beacon slot is reserved, the device can use it as long as it remains as a part of the network. Further, devices need free data slot to communicate with each other. But, in order to reserve such a data slot, it is necessary to know that both the transmitter and receiver are free in that particular data slot at a given time. The data slots are freed by the device as and when the communication with the other device is over. Once freed, these data slots get added to the free data slot pool and are subsequently reserved by other devices for further use. In order to avoid interference and hidden node and exposed node problems, it has been set that no device can reserve a slot already reserved by another device in its two hop neighborhood.
The reservation of data slots usually takes place in a completely distributed manner, with the devices sharing information and helping each other to reserve slots. Here it is important to note that, unlike in the centralized WPAN, no device acts as a central coordinator for the various medium access operations.

The present state of art in this field has certain limitations as explained herein below. It is a common knowledge that during the period when data communication is in progress in a certain set of data slots, no other device pair in the two-hop neighborhood of the first pair of devices can start a communication in the same set of data slots. This kind of a very rigid data slot reservation mechanism actually reduces the throughput of the wireless network. For a given network, there could arise several scenarios in which multiple simultaneous communications between different pair of devices is possible. The MBOA MAC protocol does not allow for such reuse of communication channel.
For increasing the throughput of the wireless networks, the simultaneous use of the communicating channel by multiple pair of devices is essential. But, most MAC protocols in wireless networks do not define methods that facilitate spatial reuse. Listed below are the limitations specific to MBOA MAC version 0.98 with respect to reserving data slots that facilitate spatial reuse.
In the data slot reservation protocol of MBOA MAC version 0.98, after a DRP reservation is made, all the neighbors in the two hop neighborhood of the communicating devices are silenced for the whole duration of the communication. It implies that many devices in the hidden node region and in the exposed node region would not be able to use the same slots when the communication is in progress. This is illustrated in the Figure 5, wherein the circle around S denotes the exposed node region and the circle around D denotes the hidden node region.
The system as such is having a number of disadvantages. The MBOA MAC version 0.98 does not describe any mechanism by which non-interfering communications can reserve and use the same data slots. In the MBOA MAC protocol and in wireless MAC protocols in general, there is no method by which a sending/receiving device can announce that it is willing to facilitate spatial reuse in the slots used for its communication. A device that wants to reuse the channel cannot know as to when it should scan to find out if interference is possible in an already existing data communication. There is no method by which devices can ensure that

communication between a pair of devices does not interfere with the communication in another pair of devices in its transmission range. In the MBOA MAC version 0.98 protocol, there is no method by which a device can propagate the information of spatial reuse data slots to its two hop neighbors. Also, in the MAC protocol, there is no mechanism by which devices communicating can use transmit power control to achieve spatial reuse and power savings.
Also it is found in one of the prior art literature that a method for simultaneous transmission of a plurality of signals from a plurality of the fixed stations on a single selected frequency is possible. Each of the transmissions is directed to a selected one of the mobile cellular phone devices. Such simultaneous transmission is attained by adjusting power levels in the transmission frequency in a given cellular area such that the transmission by the fixed station within the area does not interfere with the reception of the signals by another mobile unit in another cellular area.
Even though, the method of achieving simultaneous transmissions appears to be similar to the one envisaged by the invention, the prior art literature is different since it talks about the method in the context of mobile cellular networks and is no way connected to use of UWB.
From the foregoing, it is quite evident that the state of the art literature is silent with regard to addressing medium access controls for wireless personal area networks based on wireless mobile ad-hoc networks. Having concerned about the scenario, the inventors proposes a system and method to resolve the above, by which it is possible to manage channel time reservation in the medium access control functionality for wireless personal area networks based on ultra wide band (UWB) systems.
SUMMARY OF THE INVENTION
The primary object of the invention is, therefore, to provide a system and method

that increases the throughput achieved by the wireless network.
It is another object of the invention to provide a method where a device in the network can provide information about the time slots in which other devices can reuse the same slots, which are already in use for communication.
It is yet another object of the invention to provide a system by which a device in the network can listen for specific time period in order to identify if there is any interference in its transmission or reception range due to other communicating devices.
It is also an object of the invention to use the application characteristics to easily and efficiently allow spatial reuse in the channel time used for its data communication.
Accordingly, the present invention provides a method for channel time reservation in the medium access control functionality of wireless personal area networks, based on ultra wide band (UWB) systems for spatial reuse with links using transmit power control wherein a device in the network can provide information about the time slots in which other devices can reuse the same slots, which are already in use for communication.
The invention also provides a system for spatial reuse with links using transmit power control, wherein all the devices in the network listen for specific time period in order to identify if there is any interference in its transmission or reception range due to other communicating devices.
These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Figure 1 illustrates the centralized media access control approach in a wireless personal area network, which is based on the IEEE-802.15.3 protocol.
Figure 2 illustrates the distributed media access control approach in wireless personal area network, which does not have any centralized coordinator.
Figure 3 illustrates the skeleton of beacon slots and data slots within the
superframe.
Figure 4 illustrates the relation between the transmit power and range.
Figure 5 illustrates the typical reservation mechanism where all the other devices in the whole range of the sender and receiver side are silenced.
Figure 6 illustrates how more than one pair of devices can communicate during the same data slots when both the communicating pair of devices are using appropriate transmit power control.
Figure 7 illustrates the exchange of frames in the Master Link and the Slave Link with respect to Figure 6.
Figure 8 describes the fields in the Link Spatial Reuse Information Element. The source and destination device ID are the DevID of the source and destination devices as mentioned in the beacon of the respective devices.
Figure 9 illustrates the structure of a new information element called the Spatial Reuse Availability IE, SPRJWailabilityJE.
Figure 10 is a MSC used to explain one of the scenarios in which the source of the slave link is outside of the beacon group of the Master Link devices and the
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destination of the slave link is in the beacon group of the Master Link devices.
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail.
Before starting the detailed description, some of the basic features associated with the invention are described herein. Throughput can be defined as the total number of bits successfully transmitted and received in the network. The system and method described here specifies an enhancement to the existing method for channel reservation in a completely distributed wireless personal area networks. The network under consideration is a wireless ad-hoc network with varying network topology. The mechanisms specified in the invention can be applied for channel time reservation in other distributed networks where the channel time is slotted and distributed reservation is deemed necessary for reserving the channel time. It is assumed that, in the media access layer protocol under consideration that there exists a system and method for agreeing upon the transmit power to be used in a specific communication.
A secondary benefit of using this data reservation protocol is the reduction in the battery power used by all the communicating devices. Hence, devices use the network for longer periods before a recharge is required for their batteries.

The proposed method defines a channel access mechanism that is an extension to the existing method in the MBOA MAC protocol. The method provides an easy way for identifying the slots that are available for spatial reuse and reserving such slots for communication. Multiple communications existing during the same time slots result in increased throughput for the network. The silencing of devices in the two-hop neighborhood because of the hidden node and exposed node problem reduces the achievable throughput of the network. But, by using the method of this invention, many links that fall in the region of the hidden node or exposed node can still initiate communication, thereby effectively increasing the throughput of the network. There is no requirement of additional channel negotiation procedure apart from the DRP Request and Response for using the spatial reuse slots. As transmit power control is used, the reception and interference range of a communication is far reduced. The technique still maintains the distributed method of medium access.
The mobility among the nodes that are using spatial reuse can easily be tracked using the initial RTS and CTS frame exchange sent by the devices in the Master Link. The communications established using the reservation mechanism listed in this invention could continue to proceed without disruption even if the Master Link terminates its reservation.
The commercial advantage of implementing the system and method specified in this invention is that wireless network can achieve a throughput much higher than the actual maximum possible by the physical interface. The devices that are participating in the spatial reuse communications can all achieve power savings as all uses only less power to transmit than the maximum in all their reservations. Hence, in network scenarios where frequent recharge of batteries is not possible, this method eventually results in increased network lifetime and lifetime of individual device.
Now the invention is explained in detail below with reference to the drawings. Figure 1 illustrates the centralized media access control approach in a wireless
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personal area network, which is based on the IEEE-802.15.3 protocol. The piconet range, different piconet elements like DEV and PNC, frames being transferred in piconet like beacon and data transfer between DEV to DEV, PNC to DEV and DEV to PNC are shown. This figure is included to show the difference between a centralized and distributed wireless personal area network.
Figure 2 illustrates the distributed media access control approach in wireless personal area network, which does not have any centralized coordinator. The various devices (DEV) are shown as dark circles (bullets), with their ranges in circles. The devices cooperate and share information with each other to perform the media access control operations.
Figure 3 illustrates the skeleton of beacon slots and data slots within the superframe. The numbers in the figure, such as superframe duration, number of beacon slots and number of data slots are indicative. A change in these numbers does not affect the operation of the present invention. The control information is transmitted by devices in beacon frames in chosen beacon slots. The data slots are used for communication and are reserved using the distributed reservation protocol.
Figure 4 illustrates the relation between the transmit power and range. The bigger bold circle around S and D represent the range when the maximum transmit power (Pmax) is used. Power Pmax has to be used to send beacon frames so that all the devices in the wireless network can gain information about the network topology. For data frames the communicating devices can choose to use Pmax or some power P Figure 5 illustrates the typical reservation mechanism where all the other devices in the whole range of the sender and receiver side are silenced. When devices S and D are communicating, devices S1 and D1 cannot use the same data slots in order to avoid the interference that they may cause to the existing communication.
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Figure 6 illustrates how more than one pair of devices can communicate during the same data slots when both the communicating pair of devices are using appropriate transmit power control. S and D use power P and devices S1 and D1 use power P1, where P1 Figure 7 illustrates the exchange of frames in the Master Link and the Slave Link with respect to Figure 6. The beacon frames are transmitted with maximum power P1, the RTS, CTS, DATA and ACK frames exchanged between the Master Link devices use power P2 and the DATA, ACK frames exchanged between the slave devices use power P3, where power levels follow the relation P3 Figure 8 describes the fields in the Link Spatial Reuse Information Element. The source and destination device ID are the DevID of the source and destination devices as mentioned in the beacon of the respective devices. Stream ID is the stream identification of the Master Link as given in the DRP IE. Transmit power field identifies the power that will be used to transmit frames between the source and destination device. The flag field is used to inform to the neighbors whether the reservation of one link or all the channel reservations between the source and destination identified in this information element are available for spatial reuse.
Figure 9 illustrates the structure of a new information element called the Spatial Reuse Availability IE, SPR_Availability_IE. The SPR_AvailabilityJE is maintained internally by each device and is updated when the device receives a DRP-IE for an established DRP, along with the LINK_SPR_IE for that reservation broadcast in the beacon by the owner and/or target of the reservation. The SPR_AvailabilityJE provides the required information that is to be known for every spatial reuse reservation. One value is the Allocation field, which defines the data slots as in the DRP-IE, and the second is the power level as in the LINK_SPRJE for that link. The first field of the SPR_AvailabilityJE gives the number of such (Allocation field, power level) pair values that are present in the information element. The SPR_Availability_IE is added to the beacon when a reservation target device of a
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slave link wants to re-negotiate the slots that are suggested in the corresponding DRP Request.
Figure 10 is a MSC used to explain one of the scenarios in which the source of the slave link is outside of the beacon group of the Master Link devices and the destination of the slave link is in the beacon group of the Master Link devices. The source device does not hear the LINK_SPRJE sent by the devices of the Master Link. Hence, for the reservation request sent by the source the destination device sends a response with the Reason Code set to Pending. The destination then uses the SPR_Availability_IE stored in its internal database to identify all the spatial reuse slots along with the power levels using which it can reach the source. The updated SPR_Availability_IE is included in the beacon frame for certain number of superframes or until a DRP reservation is in progress. This facilitates the source to identify and change its reservation slots to use the spatial reuse slots mentioned in the SPR_Availability_IE. The source then sends the changed DRP Request again to the destination, which is then accepted by the destination, thus enabling spatial reuse.
The proposed invention speaks about a system and method which allows certain devices to re-use channel time currently being used by other pair of devices. This decision to use the same slots reserved by another pair of devices is taken in a completely distributed manner without the need for a centralized coordinator.
The system for the invention comprises of a distributed medium access control mechanism involving a superframe structure made up of timing slots where all inter device communication takes place within the time slots. The slots may be reserved by devices for their communication needs. Slots are reserved in a completely distributed manner without the need for any centralized coordinator. The beacons transmitted by every device in every superframe are transmitted at a maximum power say, Pmax, which is defined in the MBOA MAC-PHY interface. This is required so that the range of MBOA MAC devices is kept a constant, which is a sphere of 10 m radius.
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The system of invention assumes that devices use the implicit-DRP mechanism to reserve the slots in which data communication will take place. The reservation mechanism as listed in the MBOA MAC version 0.98 is assumed. In implicit-DRP mechanism, after channel negotiation, both the sender and the receiver will include an information element called DRP-IE in every beacon, until the data slots are used. The DRP IE in the beacon announces that there is an ongoing communication between the two devices in certain slots.
This invention assumes that Transmit Power Control (TPC) negotiation is possible between the communicating devices and that a simple and efficient method is known to MAC by which devices can agree on the power that is sufficient for them to communicate. The MBOA MAC specifies the different power levels for transmissions and the maximum number of power levels is set to a predefined value, NumTxPowerLevels. A table in the MBOA MAC-PHY interface specification lists the power values for the different interfaces. Figure 4 explains how the range of the devices vary according to the transmit power used.
In this invention, a link that is established first using free data slots and where the devices send the LINK_SPRJE is referred to as the Master Link, Other links that reuse some or all of the data slots reserved by the Master Link for communication are referred to as Slave Links. The invention makes sure that the communication in the Slave Links will not interfere with the communication in the Master Links. Multiple Slave links can exists for one Master Link, thereby giving significant throughput increase for the wireless network. Refer Figure 6. The Master Link devices should not include the LINK_SPRJE if the transmit power used is the maximum transmit power Pmax If Pmax is used then using the invention described in this document no spatial reuse is possible. The Slave link devices should not include LINK_SPRJE as the existence and communication of the slave link is dependent on the power level of the Master Link.
The system and method of the invention introduces a new information element
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called LINK_SPRJE (Link Spatial Reuse Information Element). The fields in this IE are defined in Figure 8. This IE is included in the beacon of devices that have already negotiated a DRP using free slots and agreed to use transmit power, say P, which is less than Pmax. Inclusion of LINK_SPRJE in the beacon indicates the willingness of the Master Link to co-operate with other communication links to enable spatial reuse. The interference range of a transmission is directly proportional to the transmission power. Hence, links using less transmission power will have a smaller reception and interference range.
The parameters sent along with LINK_SPRJE are the identification of source device, identification of destination device, identification of Master link(i.e, stream_id), transmit power to be used, and a flag field. The pair of devices source and destination identify each of their communication link with a unique streamjd. If the communicating devices want to allow spatial reuse only for the link identified by stream_id, then the flag field is set to 0. However, if the communicating devices want to facilitate spatial reuse in all the links between the source and destination devices mentioned in the LINK_SPRJE, then this information can be indicated by setting the flag field to 1.
Further, the invention introduces a new information element called the Spatial Reuse Availability IE, SPR_AvailabilityJE. The structure of the SPR_AvailabilityJE is given in Figure 9. The SPR_AvailabilityJE is maintained internally by each device and is updated when the device receives an established DRP-IE along with the LINKJ3PRJE for that reservation being broadcast by the owner and/or target of the reservation. As in Figure 6, when S2, S1, S3 and D2, D3, D4 see the DRP-IE sent by S or D along with the LINK_SPR_IE, they will add/update the DRP Allocation and Power Level for this link. Subsequently, when the neighbors of S and D have to initiate or accept a DRP request they can try to use the slots mentioned in the SPR_AvailabilityJE, subject to the power level constraints.
The following are the mandatory steps to be followed by the devices of the Master Link:
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1. The transmit power used to transmit all type of frames in the Master Link, should be less than the maximum power used to transmit beacon frames.
2. The LINK_SPRJE is included in every beacon frame sent by each of the devices in the Master Link.
3. In a given superframe, the device should not use transmit power greater than the value indicated in the LINK_SPR_IE. However, the device can renegotiate the transmit power value and indicate it in its LINK_SPR_IE in the following superframes and then switch to that transmit power.
4. The source device needs to transmit a RTS frame at the beginning of the DRP reservation and the destination should respond with a CTS frame. The RTS/CTS communication is done using the transmit power mentioned in the LINK_SPRJE. Even if the device does not have any communication to be done in the current superframe, the RTS/CTS transmissions have to be sent in the first slot of the reservation.
The following are the steps to be followed by the devices of the Slave Link:
1. Both the devices of the Slave Link need to listen to the medium at the beginning of the reservation for RTS+CTS+2SIFS duration. If the device hears any one or both of the messages RTS/CTS or any interference, then the slave device is within the interference range of the Master Link. The slave devices will not initiate DRP with the same slots. Slave Links by listening to the RTS/CTS transfer confirm that they are not in the current transmission range of the Master Link. Devices that hear the RTS/CTS frames will not include the information about that reservation in the SPR_AvailabilityJE. If the device does not hear the RTS/CTS or any interference then the device updates its SPR_AvailabilityJE with the DRP_Allocation value and power level of the Master Link.
2. Slave Links while using the data slots of the Master Link should negotiate a transmit power between the two devices which is less than what is advertised in LINK_SPRJE as Tx_pwr. Slave Links can initiate DRP negotiation for some or all of the MAS slots identified in the SPR_AvailabilityJE, by following the same rules as in MBOA MAC version 0.98, except that it will assume the slots listed in its SPR_Availability_IE are free or available.
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3. The devices of the slave link should use transmit power less than what is identified in their SPR_AvailabiltyJE. This is to make sure that the slave link does not interfere with the communication going on in the Master Link.
4. After establishing the slave link with spatial reuse slots, the slave devices have to listen at the beginning of the channel reserved by the Master Link for a duration of RTS+CTS+2SIFS. If RTS/CTS or any interference is heard then atleast one of the slave devices or one of the master devices have moved into the range of each other. In this instance, for this current superframe the slave device will not initiate any communication. If the same situation exists for more than a certain number of superframes then the slave devices will have to initiate DRP modify and move to other free slots. This is a situation that can occur where the devices are highly mobile.
5. The Slave devices can also use PCA communication between them. The clear channel sensing done before the start of the PCA communication will identify if there are any other slave links in its neighborhood.
The Master Link can choose to close the DRP connection according to the applications requirement When the slave links see that the Master Link is terminated, the slave devices can choose to facilitate spatial reuse and announce the LINK_SPRJE and Spatial Reuse flag in their DRP-IE or choose to be normal DRP Links that block other simultaneous communication in their two hop neighborhood.
The method specified in this invention facilitates multiple slave links to exist in the two hop range of a Master Link as long as the DRP reservation or PCA access follow the rules as specified in the MBOA MAC Specification.
The invention allows spatial reuse to be exploited in reservations that are of type HARD and SOFT. In soft reservations, the owner of the reservation device can initiate communication with different target devices according to the rules of PCA. Irrespective of the type of reservation, if the target device announces in the LINKJ5PRJE that a certain transmit power is going to be used, then during that
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superframe the transmit power should neither be increased or decreased. This is to ensure that there in no interference between the other communication links that are using the same data slots.
The method of using UDA, UDR for hard DRP reservations can also be used by devices that are part of the Master Link. However, any other device that wants to use the released channel should check for other DRP reservations that are announced in the beacon for the same slots, as mentioned in the MBOA MAC Specification.
The method of the invention is described below with the help of examples. Consider the scenario depicted in Figure 6. Devices S, D, S1 and D1 are in the network sending beacons in their respective beacon slots at power Pmax. Devices S and D establish a DRP (Hard or Soft) according to the requirement of their application using segmented/contiguous slots say N1 to N2, following the DRP reservation rules specified in MBOA MAC specification. Slots N1 to N2 should be free for communication both at S and D as can be inferred from their Availability IE information. From the application characteristics running in S, if it is known to MAC that the current communication will exist for a long period of time then S and D can try to facilitate spatial reuse. By other mechanisms out of the scope of this invention and within the features provided in the MBOA MAC protocol, devices S and D agree that a certain power say P is sufficient for two way communication between the devices. Thus, the inner dotted circle around S and D actually indicate the transmission range of the Master Link. After negotiating the power P, devices S and D include a LINK_SPRJE in every beacon with the parameters as defined in Figure 8. With the above steps, devices S and D have announced to the network that the slots N1 to N2 are available for reuse by other devices that can do transmit power control.
Next, if device S1 wants to start a communication with D1, S1 will check the availability of slots at both S1 and D1. In order to use spatial reuse, S1 will first check its SPR_AvailabilityJE and find that slots N1 to N2 are available for
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communication. The slots N1 to N2 in the Availability IE of S1 will be marked as used, but to use spatial reuse the information in SPR_Availability_IE is supersedes the information in Availability IE. Next, S1 checks the Availability IE and SPR_AvailabilityJE of D1 to verify if the same set of slots are free at D1, after which device S1 will try to negotiate a transmit power less than P, say P1 for two way communication with D1. If a communication link with transmit power P1 is feasible between devices S1 and D1, then device S1 will initiate a DRP request to D1 for a reservation in the slots N1 to N2. The DRP negotiation will follow the request response procedure. However, if the communication link with power P1 is not possible then S1 will avoid the spatial reuse slots and use some other slots that are available at both S1 and D1.
Similarly, in Figure 6, a second pair of devices S2 and D2 can try to initiate a communication after S and D have reserved the slots N1 to N2 and announced the spatial reuse information element. Now, S2 has the Availability IE of D2 and can decide to request reservation for slots say, X1 to X2. S2 will frame its DRP Request and send it to D2. However, since D2 is in the Beacon group of device S and D, D2 has the spatial reuse information that slots N1 to N2 can also be used instead of X1 to X2. So, D2 will send a DRP response with the reservation as “Pending”. In the same beacon, D2 will include a SPR_Availability_IE as given in Figure 9. The SPR_Availability_IE will indicate all the slots that can be reused at device D2 (slots N1 to N2 will also be included in this), and the power level at which the Master Link of each reservation is communicating. The SPR_Availability_IE can be included in the beacon of D2 for a certain fixed number of superframes, so that S2 will receive that information and be able to change its DRP requests accordingly. Next, S2 will try to verify if it can have a two way communication with D2 with transmit power less than P, say P2. If such a reduced transmit power is identified between S2 and D2, then S2 can decide to change its allocation to any one of the allocations mentioned in the SPR_Availability_IE and issue a changed DRP request for say, slots N1 to N2. Now, D2 can decide to accept the reservation and issue a DRP Response. In this manner, both the Master Links and Slave Link can operate without interference in the same data slots. However, if S2 and D2 cannot identify a transmit power less
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than what is used by the Master Link, then spatial reuse is not possible. S2 and D2 will try to use free slots in which they do not have any transmit power restrictions.
In Figure 6, devices S3 and D4 may try to exploit the spatial reuse enabled by devices S and D, but during the mandatory listen period at the beginning of the channel reservation period of the Master Link, the devices will hear RTS and CTS, hence they will not try to initiate DRP reservation in the slots reserved by the Master Link.
The SPR_Availability_IE is added to the beacon frame whenever a device sends the DRP Response with the Reason code as “Pending” in order to try reuse of slots mentioned in the SPR_AvailabiltyJE. However, a device can also choose to periodically send the SPR_Availability_IE to advertise the slots that enable spatial reuse. This will facilitate the two-hop neighbors to consider the spatial reuse slots first when they try to choose slots for a communication. The framing and sending of the Availability IE as defined in the MAC MBOA version 0.98 does not change while adopting the changes defined in this invention for channel reservation using spatial reuse.
The described method for spatial reuse can be used only for devices that have unicast traffic between two devices. Using spatial reuse slots for multicast traffic will not be feasible since, it is difficult to negotiate a given transmit power for a large number of destination devices. Broadcast communication can never be tried on slots already used by a communication.
The system and method specified in this invention is an enhancement to the existing channel reservation protocol and is completely backward compatible with devices that implement the MBOA MAC version 0.98. If a device does not want to use the spatial reuse slots it can choose to use the free slots in the Availability IE for channel reservation.
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it will also be obvious to those skilled in the art that other control methods and apparatuses can be derived from the combinations of the various methods and apparatuses of the present invention as taught by the description and the accompanying drawings and these shall also be considered within the scope of the present invention. Further, description of such combinations and variations is therefore omitted above. It should also be noted that the host for storing the applications include but not limited to a microchip, microprocessor, handheld communication device, computer, rendering device or a multi function device.
Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.
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GLOSSARY OF TERMS AND DEFINITIONS THEREOF
BP: Beacon Period
BPST: Beacon Period Start Time
Beacon Group: Devices that can hear each others Beacon are said to be in the
same Beacon Group
CTS: Clear To Send
DEV: Device
DEVID: Device Identifier
DP: Data Period
DRP: Distributed Reservation Protocol
PCA: Prioritized Contention Access
ID: Identifier
IE: Information Element
IEEE: Institute of Electrical and Electronics Engineers
Link: The communication channel established between two devices
MAC: Medium Access Control
MAS: Medium Access Slot
MBOA: Multi Band OFDM Alliance
MSC: Message Sequence Chart
OFDM: Orthogonal Frequency Division Multiplexing
PHY: Physical Layer
PNC: Piconet Coordinator
QoS: Quality of Service
IFS: Short Inter Frame Space
RTS: Request To Send
SIFS: Short Inter Frame Space
TDMA: Time Division Multiple Access
UDA: Unused DRP reservation announcement
UDR: Unused DRP reservation response
UWB: Ultra Wide Band
WPAN: Wireless Personal Area Network

Documents:

320-CHE-2006 EXAMINATION REPORT REPLY RECEIVED 04-01-2013.pdf

320-CHE-2006 AMENDED CLAIMS 04-01-2013.pdf

320-CHE-2006 AMENDED PAGES OF SPECIFICATION 04-01-2013.pdf

320-CHE-2006 FORM-1 04-01-2013.pdf

320-CHE-2006 FORM-13 04-01-2013.pdf

320-CHE-2006 OTHER PATENT DOCUMENT 04-01-2013.pdf

320-CHE-2006 POWER OF ATTORNEY 04-01-2013.pdf

320-CHE-2006 CORRESPONDENCE OTHERS.pdf

320-CHE-2006 FORM 1.pdf

320-che-2006-abstract.pdf

320-che-2006-claims.pdf

320-che-2006-correspondence-others.pdf

320-che-2006-description(complete).pdf

320-che-2006-drawings.pdf

320-che-2006-form 1.pdf

320-che-2006-form 26.pdf

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Patent Number

255283

Indian Patent Application Number

320/CHE/2006

PG Journal Number

07/2013

Publication Date

15-Feb-2013

Grant Date

08-Feb-2013

Date of Filing

24-Feb-2006

Name of Patentee

SAMSUNG INDIA SOFTWARE OPERATIONS PRIVATE LIMITED

Applicant Address

BAGMANE LAKEVIEW, BLOCK 'B', NO. 66/1 BAGMANE TECH PARK, CV RAMAN NAGAR, BYRASANDRA BANGALORE-560093, KARNATAKA, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	THENMOZHI ARUNAN	EMPLOYED AT SAMSUNG INDIA SOFTWARE OPERATIONS PVT. LTD., HAVING ITS OFFICE AT, BAGMANE LAKEVIEW, BLOCK 'B', NO. 66/1 BAGMANE TECH PARK, CV RAMAN NAGAR, BYRASANDRA BANGALORE-560093, KARNATAKA, INDIA

PCT International Classification Number

H04L 12/24

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA