Title of Invention

SYSTEM AND METHOD FOR POWER SAVING IN DISTRIBUTED WIRELESS PERSONAL AREA NETWORKS

Abstract

This invention explains a system and method for power saving in distributed wireless personal area networks where the said system comprising: PS-Anchor which has a constant power supply and is elected using a connection distributed election procedure; and means to disseminate the information about the devices that are in hibernate mode and the information of after how many superframes each hibernating device will wake up.

Full Text

FIELD OF TECHNOLOGY This invention relates to the field of wireless mobile ad-hoc networks. Further, this invention relates to medium access control for wireless personal area networks that are based on wireless mobile ad-hoc networks. Particularly this invention relates to distributed medium access control for wireless personal area networks which does not have any central coordinator. Devices communicating in a wireless personal area networks are typically mobile and use power from a secondary source like battery that is included in the device. This invention particularly relates power saving techniques that can be implemented in decentralized and distributed wireless personal area networks. DESCRIPTION OF RELATED ART The wireless personal area networks are defined to operate in the personal operating space, i.e. in a range of approximately 10 meters. The IEEE (http://www.ieee.org) is involved in defining standards for such wireless personal area networks. The Ultra Wide Band (UWB) technology can provide data rates exceeding several hundreds of Mbps in this personal operating space. In wireless personal area networks, the medium is shared between all the devices for communication with each other. The devices go to power save state, to save battery power, whenever possible. This necessitates 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, how to detect and resolve beacon collisions, how to use power optimally, etc. Medium access control for wireless personal area networks can be designed 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 medium access operations for all the devices. All other devices seek help of the centralized coordinator for medium access operations like joining the network, reserving channel time, etc. In the distributed approach, the medium access operations are distributed evenly across all devices in the network and all the devices share the load of managing medium access operations for each other. While the IEEE standards currently employ a centralized medium access control mechanisms, some distributed medium access control mechanisms are under discussions for WPANs as they offer flexibility, e.g. in terms of mobility of devices. Figure 1 show the wireless personal area network, which is based on distributed approach and which does not have any centralized coordinator It involves a decentralized WPAN, in which each of the devices is a light coordinator and there is no dedicated coordinator present. All devices cooperate and share information with each other to perform the medium 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, Power save etc. This is a Distributed WPAN system which is formed in an ad-hoc fashion. Each device periodically broadcasts the information about its neighbors and allocated channel time to its neighbors. The Distributed medium access control approach relies on a timing concept called the Superframe. Superframe has a fixed length in time and is divided into a number of time windows which are called time slots. Time slots are also referred to as Medium Access Slots in the literature. Some of the time slots are used by the devices to send their beacons and the others are used by the devices to send the data. The slots in which beacons are sent may be referred as beacon slots and the slots in which data is sent may be referred as data slots. The length of a beacon slot may be less than the length of a data slot. The beacon slots may be distributed across the slots in the superframe or may appear together at the start of the superframe. In addition, the number of beacon slots may be fixed or variable leading to different configurations of Distributed Medium Access Control mechanisms. Figure 2 illustrates the superframe structure, specified by the Multiband OFDM Alliance (MBOA, http://www.multibandofdm.orq) draft vO.5. It consists of several Medium Access Slots (As an example, the number is shown as 256). Some Medium Access Slots (MAS) constitute beacon period (comprising of beacon slots corresponding to multiple devices) and remaining MASs constitute data period (comprising of data slots that may be used by different devices in the network to transmit data to other devices in the network), employs a superframe duration of 65,536 micro-second with 256 MASs. and each MAS is of 256 microsecond duration. Information about superframe is being broadcasted by each device in its broadcasted beacons, so 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). Devices that belong to the same beacon period shall utilize the same BPST for the superframe. However, some of the devices may define a different time as their BPST. In such case, two or more beacon groups may coexist for the device. MASs are numbered relative to this starting time. The devices shall transform the numbering of MASs of other beaconing periods into the time reference of their main beaconing period. A device can be part of several beaconing periods but has to select one beaconing period as its main beaconing period. Devices include the occupancy status of the beacon slots in the Beacon Period in all beacons, using Information Elements (IE), e.g. BPOIE. The BPOIE shall only include beacon information of devices that belong to the same beaconing group. Upon reception of a beacon frame, a device saves the DEVID of the sender and the slot number where the beacon is received. This information is included in the BPOIE sent in the following superframe. Only the information of beacons received during a superframe is included in the BPOIE sent in the following superframe. If the DEVID of the device is missing in the BPOIE from a neighboring beacon during a predefined number of successive superframes, this means that the corresponding device will change the corresponding beacon slot to an idle slot during the next superframe.. Data reservations can be maintained, and don't need to be re-negotiated if the beacon slot is changed. MBOA-MAC in its present form has defined two modes of operation, active mode and hibernating mode. In active mode the device can either be in awake state or in sleep state. In awake state the device's transmitter and receivers are fully powered using more power even if they are not currently transmitting or receiving (idle condition). In the sleep state the device has powered down its transmitter and receiver circuitry and is using minimum power. In the active mode, devices switch between awake and sleep state depending on the data reservations already announced during the beacon period. The second power saving mechanism is where devices announce that they want to go to Hibernating (HB) mode. Devices that are going into hibernate mode announce in their beacon that they will be in hibernation for a certain number of superframes, during which they will be in deep sleep mode; they will not send or receive beacons or any other traffic; or will not try to listen any other traffic. Other devices in its BG will note this announcement and continue to include those devices in their BPOIE until the mentioned wakeup interval. Also, devices in the BG will maintain information in their local database about devices that are hibernating and will defer communication to them until they power on and start sending beacons. V The present state of art in this field, as discussed in MBOA MAC vO.5, has certain limitations, namely, if a device does not hear the beacon in which a device announces its intention to go to hibernation, then the device might not know as to when the hibernating device will again come to active mode. If such devices want to communicate with hibernating devices, they have to be awake for long periods of time to see in which superframe the hibernating device will wake up. Currently the power save mechanism, as defined in the current art, suffers from the following limitations: 1. If a new device joins the BG, it does not have the information about, when each of the devices in hibernation mode would wakeup. The active devices which have this information keep it in their local database only. 1 2. When a hibernating device wakes up and changes to active mode, it will not know the other devices that went to sleep during its hibernating period. So, the device may have to continue to stay in active mode for undetermined amount of time in order to communicate with such devices. Hence, such long waits will deplete the power of devices quickly. 3. In the case of high mobility, the BG of a device can change frequently. In such scenarios the device will not be able to decide the reason for not hearing other devices' beacon even though its neighbors are reflecting some devices in their BPOIE. A beacon may not be heard due to several reasons like, the sending device is out of range or it is in hibernating mode etc. SUMMARY OF THE INVENTION The primary object of this invention is therefore to provide a system and method for distributing power save information of devices in the wireless personal area networks, in a decentralized ad-hoc network topology where all devices undertake the role of a light coordinator and there is no dedicated central coordinator. Using this information, the devices can make decisions about when to switch to long power save mode and when to schedule their wakeup to active mode. This kind of scheduled sleep and wakeup will result in saving the battery power of the device as well as increasing the lifetime of the ad-hoc network. It is another object of the invention to provide a mechanism, where new devices can determine the power save status and their related wakeup interval of other devices in its BG. The present invention relates to a system that allows an improved medium access control in the Wireless Personal Area Networks based on mobile ad-hoc networks in decentralized and distributed manner. The invention relates to system and method which enables all devices to make decisions on when to switch to power save mode and when they should wake up to communicate with intended receivers. The system for the invention comprises of electing Power Save Anchor (PS-Anchor) devices in a decentralized manner that will help in announcing to the network the power save status of the various devices in their BG and a method for withdrawing of devices from the role of being an Anchor. The present invention comprises of system and method which would solve the problems associated with current art, in the following manner: 1. Due to the lack of centralized entity in systems employing distributed medium access control, distribution/dissemination of information required by devices for reasons like power save is not available to all devices. Here we propose the election of Power Save Anchors (PS-Anchor) using a distributed election algorithm. The proposed PS-Anchor device is a device that has constant power supply connection or is a resource-rich device (i.e., high in battery power). 2. Present invention includes the method for electing and withdrawing devices as Power Save Anchors (PS-Anchor). This election/withdrawal procedure does not require any additional control messages to be exchanged between its neighbors and only uses the beacon and existing Information Element (e.g., BPOIE) information exchanged in the beacons. 3. Present invention includes mechanisms to disseminate the information about the devices that are in hibernate mode and also the information of after how many superframes each hibernating device will wake up. For this, it is proposed to include an Information Element (IE) called Power Save Anchor Information Element (PS Anchor IE) in the beacon of PS-Anchors. 4. The information in the PS Anchor IE can be used by devices to schedule their sleep and wakeup intervals. Current art does not provide any direction towards how a device should decide when to go to sleep and how to set the duration of its sleep interval. Accordingly, the invention provides a method for a device to be elected as a PS-Anchor and to know the other devices that are in hibernating mode in its BG along with the superframe in which a hibernating device will change to active mode. Accordingly, the invention provides mechanism for devices to schedule their sleep and wakeup intervals according to the information provided in the PS Anchor IE sent by PS-Anchors. This will result in power save for all participating devices. Accordingly, the present invention explains a system for power saving in distributed wireless personal area networks where the said system comprises: (a) PS-Anchor which has a constant power supply and is elected using a distributed election procedure; and (b) means to disseminate the information about the devices that are in hibernate mode and the information of after how many superframes each hibernating device will wake up. For disseminating the information an Information Element (IE) which is the Power Save Anchor Information Element (PS Anchor IE) is included in the beacon of PS-Anchors. The information in the PS Anchor IE is used by devices to schedule their sleep and wakeup intervals. A device in the WPAN performs the function of PS-Anchor device if the said device has constant power supply connection or is a resource-rich device. A device in the WPAN performs the function of PS-Anchor device if the said device has sufficient secondary memory to maintain status of devices that are in hibernating mode in its BG. A device in the WPAN also perform the function of PS-Anchor device if the device has sufficient spare bytes in its beacon to send information about hibernating devices.A device in the WPAN also perform the function of PS-Anchor device if the device is willing to perform the role of a PS-Anchor where until the time a device is functioning as a PS-Anchor it should not go into power save mode. The PS Anchor IE contains the information of which devices are in hibernate mode and the information of after how many superframes each hibernating device will wake up, where the length field is variable and depends on the number of devices in the BG of the PS-Anchor that are in hibernate mode. The DEVID of the hibernating device is a field of length 2 bytes. The Wakeup countdown field is the wakeup time of the hibernating device in number of superframes from current superframe. Accordingly, the present invention further explains a method for power saving in distributed wireless personal area networks where the said method comprises the steps of: (a) selecting the PS-Anchor; (b) withdrawal of a device from being a PS-Anchor; (c) switching a device from active mode to Hibernate mode; and (d) communication of a device with another device in hibernate mode. For selecting the PS-Anchor two selection criteria are involved, where in the first criteria is that there are no PS-Anchors in the device's BG, the device checks if it is able to provide power save information for a non-zero number of neighbors in its BG. The device finds out if there are some devices in its BG which are also in the BG of its neighbors; this condition is deduced using the BPOIE information that is received from each of the device neighbors. For each device in the device BG, the number of devices both in the range of the device and in the range of that neighbor is found and from this said number, the device and its neighbor is excluded by subtracting 2. The cumulative sum of the number of devices for all the neighbors of the device is found and if the sum is greater than zero then the device has some neighbor pairs for which it can provide power save information and it can elect itself as a PS-Anchor. In the second criteria if there are some PS-Anchors already present in the device's BG, then the device evaluate if all of its neighbors are serviced by those Anchors. The device saves the BPOIE information of all the devices in its BG from the beacon sent by those neighbor devices where the beacon of a device gives the information about whether a device is a PS-Anchor or not. For the device to become a PS-Anchor in the existing BG it is deduced using the BPOIE of neighbor devices and the BPOIE of the PS-Anchor found in the device's BG where if every pair of devices in the device's BG is able to receive the power save information from existing PS- Anchors, then there is no requirement for the device to become a PS-Anchor and it is deduced by pairing the neighbors in the device's BPOIE and checking if they are in the BPOIE of some other PS-Anchor in the device's BG. If the network topology is such that there are some device pairs which are not in the range of existing PS-Anchors then this device can become a PS-Anchor. For withdrawal of a device from being a PS-Anchor a device which is functioning as a PS-Anchor periodically check to see the need for it to function as a PS-Anchor continues to exist using the two selection criteria's and if one of the above criteria evaluates to be false it withdraws from being a PS-Anchor. Switching a device from active mode to Hibernate mode involves the device going into hibernate mode announcing the same where the said information is noted by all the PS-Anchor devices and later included in the proposed PS Anchor IE. The Hibernate mode device does not send or listen to beacon for the number of superframes that it has announced in its beacon and after wakeup, the device listens to all the beacons and the whole superframe to get a snapshot of the network and DRP reservations. The other objects, features and advantages of the present invention will be more apparent from ensuing detailed description of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 illustrates the WPAN as a decentralized and distributed ad-hoc network. The WPAN includes many devices that are indicated as points. Circles drawn around the respective devices indicate ranges in which beacons of the corresponding devices are received, respectively. Additionally, the devices included in a circle form a beacon group. Figure 2 illustrates the superframe structure in current art, which indicates MAS , beacon periods and data period; The superframe structure as illustrated in FIG. 2 is based on what is defined by the Multiband OFDM (Orthogonal Frequency Division Modulation) Alliance. A superframe is composed of two types of MASs (Medium Access Slots). One type is a beacon slot MAS and the other type is data slot. A beacon period is composed of beacon slot MASs according to the number of devices connected in the same beacon group. The remaining part of MASs, other than the beacon period constitute a data period, composed of medium access slots that can be used by devices in the network in order to transfer data to other devices in the network. Figure 3 illustrates the presence of PS-Anchor devices in a WPAN. Nodes represented with a square are the PS-Anchor devices. Figure 4 illustrates the structure of the proposed Power Save Anchor Information Element (PS Anchor IE); The power save Anchor information element includes fields of DEVID of hibernating device, wakeup countdown, length and an element ID. The power save Anchor information element includes information about the hibernating devices and information about how many superframes should pass in order for the respective hibernating device to be awake from current superframe. The length of the fields is variable, and number of elements depends on the number of hibernating devices in the beacon group of the corresponding PS anchor. Figure 5 illustrates the criteria used in deciding whether a device should elect itself as a PS Anchor or not. If PS anchors exist in the beacon group of the device P, it should be checked if all neighboring devices of the device P are served by the PS anchors. Two certain devices in the beacon group of the device P may attempt to communicate with each other, and one of them may be a hibernating device. Accordingly, such two devices should simultaneously be informed by one of the operating PS anchors. Otherwise, the two devices cannot receive each other's power saving state. The device P judges such situations using the beacon period occupancy information of the neighboring devices and the beacon period occupancy information of the PS anchors found in the beacon group of the device P. The devices connected by the line segment are not informed by the other existing PS Anchors, hence P can decide to elect itself as a PS Anchor. DETAILED DESCRIPTION OF THE INVENTION A preferred embodiment of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiment is 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. The present invention relates to a system that allows an improved medium access control in the decentralized Wireless Personal Area Networks based on mobile ad-hoc networks. The invention relates to system and method, which allows device to make decisions on when to switch to power save mode, and when it should wake up to communicate with intended receivers. The system for the invention comprises of a method for electing and withdrawing PS-Anchor devices in a decentralized manner that will help in announcing to the network the power save status of the various devices in their BG using a new beacon information element which is sent in the PS-Anchor device's beacon. Accordingly, the invention provides a method for a device to be elected as a PS-Anchor and also for a PS-Anchor device to withdraw from the role of the PS-Anchor. Accordingly, the invention also provides a method for a device, including new device also to know the other devices that are in hibernating mode in its BG and for a device to know the superframe in which a hibernating device will change to active mode. Accordingly, the invention provides mechanism for devices to schedule their sleep and wakeup intervals according to the information provided in the PS Anchor IE sent by PS-Anchors. This will result in power save for all participating devices. The subsequent subsections describe the invented individual entities to effect the invention. 1, Figure 3 illustrates a WPAN and how some of the devices in them can perform the function of PS-Anchor devices. A device can elect itself as a PS-Anchor if it has the following characteristics: 1) The device has constant power supply connection or is a resource-rich device (i.e., high battery power). 2) The device has sufficient memory to maintain status of devices that are in hibernating mode in its BG. 3) The device has sufficient spare bytes in its beacon to send information about hibernating devices. 4) The device is willing to perform the role of a PS-Anchor. Also, it is mandatory that until the time a device is functioning as a PS-Anchor it should not go into power save mode. 2. Figure 4 illustrate structure of proposed Power Save Anchor Information Element (PS Anchor IE). PS Anchor IE contains the information of which devices are in hibernate mode and the information of after how many superframes each hibernating device will wake up from current superframe. The length field is variable and depends on the number of devices in the BG of the PS-Anchor that are in hibernate mode. The subsequent subsections describe the operation of the invention: 1. PS-Anchor selection procedure A device, P which has the characteristics mentioned above should use the following two selection criteria to elect itself as a PS-Anchor. In case there are no PS-Anchors in P's BG, P has to check if it will be able to provide power save information for a non-zero number of neighbors in its BG. P has to find out if there are some devices in its BG which are also in the BG of its neighbors. Only if such a topology exist then it will be useful for the network to have P as a PS-Anchor. This condition can be deduced using the BPOIE information that is received from each of P's neighbors. For each device in P's BG, the number of devices both in the range of P and in the range of that neighbor is found. From this number, exclude P and its neighbor by subtracting 2. The cumulative sum of the above value for all the neighbors of P is found. If this sum is greater than zero then P has some neighbor pairs for which it can provide power save information and so it should elect itself as a PS-Anchor. The above operation that needs to be done by P on the BPOIE information received from the neighbor nodes can be represented mathematically as follows. Let S,- be the set which gives the neighbors of device i. # represents the cardinality (i.e. the number of elements in the set) of Si. A measure for the usefulness of P to be elected as PS-Anchor can be derived from the following equation. #Sp U = Z (#(Sp n Si) - 2) / #Si Here X indicates summation operation, while D indicates the intersection operation, which returns the common elements in a given pair of sets. #(Sp PI S\) gives the number of common nodes in the BPOIE of P and in the BPOIE of device i. The summation of ail such values for every neighbor of P is returned in U. If U has a value greater than 0 then it indicates that P can provide power save information for a non-zero set of devices in its BG. ii. If there are some PS-Anchors already present in P's BG, then P has to evaluate if all of its neighbors are serviced by those Anchors. P saves the BPOIE information of all the devices in its BG from the beacon sent by those neighbor devices. The beacon of a device also gives the information about whether a device is a PS-Anchor or not. The requirement for P to become a PS-Anchor in the existing BG can be deduced using the BPOIE of neighbor devices and the BPOIE of the PS-Anchor found in P's BG. If every pair of devices in P's BG is able to receive the power save information from existing PS-Anchors, then there is no requirement for P to become a PS-Anchor. This is deduced by pairing the neighbors in P's BPOIE and checking if they are also in the BPOIE of some other PS-Anchor in the P's BG. If the network topology is such that there are some device pairs which are not in the range of existing PS-Anchors then there is a requirement for P to become a PS-Anchor. Below we give a description of the same in the form of an algorithm which can be implemented easily and its execution is bounded by the number of devices in P's BG. If the above algorithm evaluates the value for requirement index to be greater than 0, then there is a requirement for P to become a PS-Anchor, else it may refrain from becoming a PS-Anchor. Refer Figure 5, which illustrates that there is a requirement for the device P in center of the figure to become a PS-Anchor. The above algorithm can be run by a prospective PS-Anchor after listening to the beacons of its BP for a few superframes, so that it has sufficient information about other PS-Anchors in its BG. The decision to become a PS- Anchor is made with this information and announced in the next beacon in the form of PS Anchor IE. A field in the beacon that reflects the features of a device can also be used to indicate that this device is a PS-Anchor. 2. Withdrawal of a device from being a PS-Anchor A device which is functioning as a PS-Anchor should periodically check to see if the need for it to function as a PS-Anchor continues to exist. It can be verified using the two selection criteria given in the above section. If a PS-Anchor device sees that one of the above criteria evaluates to be false it can withdraw from being a PS-Anchor. 3. A device switching from active mode to Hibernate mode The operations to be done by a device going into hibernate mode are same as detailed in the current art. A device going into hibernate mode shall announce the same in its beacon. This information is noted by all the PS-Anchor devices and later include this information in the proposed PS Anchor IE. The Hibernate mode device need not send or listen to beacons for the plural numbers of superframes that it has announced in its beacon. After wakeup, the device has to listen to all the beacons and also the whole superframe to get a snapshot of the network and DRP reservations. 4. A device needs to communicate with another device in hibernate mode. As an example, let us assume that device Y wants to communicate with device H which is in hibernate mode. Device P is the PS-Anchor device in the BG of H and Y. There can be two situations for device Y: i. Y was present in the network when device H announced to go in hibernate mode. In which case Y has the information about when H will wake up. ii. Device Y has moved into the BG of H and hears about it's hibernate status by listening to the PS Anchor IE of PS-Anchor P. From that information, it knows for how many more superframes H will be in hibernating mode. Y has to defer from sending any frames until H wakes up. After H wakes up, Y will have to listen to the beacon of H and then decide if it is still in its BG and then send any frames to H. By using the above invention all the devices in a given WPAN will be able to schedule their active and hibernate modes according to the hibernate intervals of the destination devices with which they want to communicate. This effectively reduces the need for devices to be awake and idle, waiting for the destination devices to come out of hibernate mode. This results in an effective savings of power for all the devices in network. The above-presented description is of the best mode contemplated for carrying out the present invention. The manner and process of making and using it is in such a full, clear, and concise and exact terms as to enable to any person skilled in the art to which it pertains to make and use this invention. New embodiments in particular, which also lie within the scope of the invention can be created, in which different details of the different examples can in a purposeful way be combined with one another. This invention is however, susceptible to modifications and alternate constructions from that disclosed above which are fully equivalent. Consequently, it is not the intention to limit this invention to the particular embodiment disclosed. On the contrary, the intention is to cover all modifications and alternate constructions coming within the spirit and scope of the invention as generally expressed by the following claims which particularly point out and distinctly claim the subject matter of the invention. GLOSSARY OF TERMS AND DEFINITONS THEREOF BG: Beacon Group BPOIE: Beacon Period Occupancy Information Element BPST: Beacon Period Start Time DEVID: Device ID DRP: Distributed Reservation Protocol HB: Hibernate IE: Information Element IEEE: Institute of Electrical and Electronics Engineers MAC: Medium Access Control MBOA: Multi Band OFDM Alliance MAS: Medium Access Slot PS: Power Save PS-Anchor: Power Save Anchor PS Anchor IE: Power Save Anchor Information Element UWB: Ultra Wide Band WPAN: Wireless Personal Area Network WE CLAIM: 1. A system for power saving in distributed wireless personal area networks where the said system comprising: (a) PS-Anchor which has a constant power supply and is elected using a distributed election procedure; and (b) means to disseminate the information about the devices that are in hibernate mode and the information of after how many superframes each hibernating device will wake up. 2. A system as claimed in claim 1 wherein for disseminating the information through an Information Element (IE) which is the Power Save Anchor Information Element (PS Anchor IE), is included in the beacon of PS-Anchors. 3. A system as claimed in claim 1 wherein the information in the received PS Anchor IE is used by devices to schedule their sleep and wakeup intervals. 4. A system as claimed in claim 1 wherein a device in the WPAN perform the function of PS-Anchor devices if the said device has constant power supply connection or is a resource-rich device. 5. A system as claimed in claim 1 wherein a device in the WPAN perform the function of PS-Anchor devices if the said device has sufficient memory to maintain status of devices that are in hibernating mode in its BG. 6. A system as claimed in claim 1 wherein a device in the WPAN perform the function of PS-Anchor devices if the device has sufficient spare bytes in its beacon to send information about hibernating devices. 7. A system as claimed in claim 1 wherein a device in the WPAN perform the function of PS-Anchor devices if the device is willing to perform the role of a PS-Anchor where until the time a device is functioning as a PS-Anchor it should not go into power save mode. 8. A system as claimed in claim 1 wherein PS Anchor IE contains the information of which devices are in hibernate mode and the information of after how many superframes each hibernating device will wake up from current superframe, where the length field is variable and depends on the number of devices in the BG of the PS-Anchor that are in hibernate mode. 9. A system as claimed in claim 1 wherein the DEVID of the hibernating device is a field is generally of length 2 bytes and at least of 1 bit. 10. A system as claimed in claim 1 wherein the Wakeup countdown in the wakeup time of the hibernating device in number of superframes from current superframe. 11. A method for power saving in distributed wireless personal area networks where the said method comprising the steps of: (a) selecting the PS-Anchor; (b) withdrawal of a device from being a PS-Anchor; (c) switching a device from active mode to Hibernate mode; and (d) communication of a device with another device in hibernate mode. 12. A method as claimed in claim 11 wherein for selecting the PS-Anchor two selection criteria are involved, where in the first criteria is that, there are no PS-Anchors in the device's BG, the device checks if it is able to provide power save information for a non-zero number of neighbors in its BG. 13. A method as claimed in claim 12 wherein the device finds out if there are some devices in its BG which are also in the BG of its neighbors then the condition is deduced using the BPOIE information that is received from each of the device neighbors. 14. A method as claimed in claim 12 wherein for each device in the device BG, the number of devices both in the range of the device and in the range of that neighbor is found and from this said number, the device and its neighbor is excluded by subtracting 2. 15. A method as claimed in claim 12 wherein the cumulative sum of the number of devices for all the neighbors of the device is found and if the sum is greater than zero then the device has some neighbor pairs for which it can provide power save information and it can elect itself as a PS-Anchor. 16. A method as claimed in claim 12 wherein in the second criteria if there are some PS-Anchors already present in the device's BG, then the device evaluate if all of its neighbors are serviced by those Anchors. 17.A method as claimed in claim 16 wherein the device saves the BPOIE information of all the devices in its BG from the beacon sent by those neighbor devices where the beacon of a device gives the information about whether a device is a PS-Anchor or not. 18. A method as claimed in claim 16 wherein for the device to become a PS-Anchor in the existing BG it is deduced using the BPOIE of neighbor devices and the BPOIE of the PS-Anchor found in the device's BG where if every pair of devices in the device's BG is able to receive the power save information from existing PS-Anchors, then there is no requirement for the device to become a PS-Anchor and it is deduced by pairing the neighbors in the device's BPOIE and checking if they are in the BPOIE of some other PS-Anchor in the device's BG. 19. A method as claimed in claim 16 wherein if the network topology is such that there are some device pairs which are not in the range of existing PS-Anchors then the device should become a PS-Anchor. 20. A method as claimed in claim 11 wherein for withdrawal of a device from being a PS-Anchor a device which is functioning as a PS-Anchor periodically check to see the need for it to function as a PS-Anchor continues to exist using the two selection criteria's and if one of the above criteria evaluates to be false it may withdraw from being a PS-Anchor. 21. A method as claimed in claim 11 wherein switching a device from active mode to Hibernate mode involves the device going into hibernate mode announcing the same where the said information is noted by all the PS-Anchor devices and later included in the proposed PS Anchor IE. 22. A system for power saving in distributed wireless personal area networks as herein described particularly with reference to the drawings. 23. A method for power saving in distributed wireless personal area networks as herein described particularly with reference to the drawings. Dated this 14*^ day of June 2005

Documents:

0555-che-2004 description (provisional)-duplicate.pdf

0555-che-2004 drawings-duplicate.pdf

555-che-2004 abstract.pdf

555-che-2004 claims duplicate.pdf

555-che-2004 claims granted.pdf

555-che-2004 description (complete) granted.pdf

555-che-2004 power of attorney.pdf

555-che-2004-abstract.pdf

555-che-2004-claims.pdf

555-che-2004-correspondnece-others.pdf

555-che-2004-correspondnece-po.pdf

555-che-2004-description(complete).pdf

555-che-2004-description(provisional).pdf

555-che-2004-drawings.pdf

555-che-2004-form 1.pdf

555-che-2004-form 5.pdf

555-che-2004-form 9.pdf