Title of Invention

SYSTEM AND METHOD FOR POWER SAVING IN WIRELESS PERSONAL AREA NETWORKS

Abstract

The invention explains a system and method for power saving in wireless personal area networks comprising: means for power saving involving a new parameter Global Wake Frequency (GWF), which periodically awake all the devices in a common global superframe as Global Wake Superframes (GWS); means for power saving involving a new parameter maintained locally by all the devices as Local Wake Frequency (LWF); means for a device to periodically wake up in superframe referred as Local Wake Superframes (LWS); means for devices to find the earliest common superframe in which they can communicate with a hibernating device; and means for the devices to independently vary their sleeping periods, based on the network activity, and communicate it to all other hibernating devices.

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. More particularly, this invention relates to system and method for Synchronized Power Save in wireless personal area networks based on ultra wide band (UWB) systems. 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. Power Save mechanism 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 devices. Figure 1 shows 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 mechanism 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 other are used by the devices to send the data. The slots in which beacon is sent may be referred as beacon slots and the slots in which data is sent may be referred as called 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.org) 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 MAS slots 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 beacon slots, and each MAS slot 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). Beacon Group (BG) of a device is referred to as the set of devices, whose beacons are received by the device in a beacon period in which, the device beacons. Devices that belong to the same beacon group shall utilize the same BPST for the superframe. However, some of the devices may define a different time as their BPST. In such case, 2 or more beacon groups may coexist. MASs are numbered relative to this starting time. The devices shall transform the numbering of MASs of other beaconing groups into the time reference of their main beaconing group. A device can be part of several beaconing groups but has to select one beaconing group as its main beaconing group. The Power saving mechanisms in the current art defines two states for the device - Active and Sleep. Sleep is the state in which the device saves power by switching off its receivers, transmitters or other modules for short periods of time (a few MAS slots) within the superframe. The device may sleep for an extended duration which is usually a multiple number of superframes. Devices mode of being in sleep state is called hibernation. Before going to hibernation, device advertises/announces this to other neighboring devices. Devices can hibernate and sleep independent of other devices in network. Currently the power saving mechanisms, as defined in MBOA MAC vO.5 system, suffers from the following limitations: 1. Current art specifies that whenever a device goes to hibernation, it transmits the information in its beacon about its hibernation state and the superframe when it would be awake again. Wake up time of the hibernating device is known to the active devices only. Other hibernating devices and new devices, which did not receive the beacon from the device which was going in hibernation, cannot know about the hibernating device. 2. A hibernating device has no way to know if some other device has requirement for communication with it. In addition, there is no provision for other devices to notify this requirement to the hibernating device. 3. There is no hibernating/power saving mechanism that allows all devices in the network to simultaneously and periodically awake in a particular superframe and perform the time synchronization. 4. Current art does not specify how devices can vary their sleeping periods dynamically. For example a device would like to sleep for lesser time if there is high activity in the network and vice-versa. SUMMARY OF THE INVENTION The primary object of the invention is to provide a system and method for power saving for the UWB wireless personal area networks, which are based on wireless ad-hoc networks, in a distributed (decentralized) network topology where each of the devices undertakes the role of a light coordinator and there is no dedicated central coordinator. It is an object of the invention to provide the mechanism for all the devices to wakeup globally, simultaneously and periodically in the same particular superframe. It is another object of the invention to provide the mechanism for all the devices to wakeup locally, individually and periodically in a particular superframe. It is another object of the invention to provide a mechanism for hibernating and new devices to know about the sleeping times of the other neighboring devices that are currently in power save (hibernating) mode. It is another object of the invention to provide a mechanism where devices can vary their sleeping periods based on the network activity and communicate it effectively to other hibernating devices. It is another object of the invention to provide a facility for all the devices to perform global time synchronization efficiently, get updates about all the DRP reservations and perform device discovery. The present invention relates to a system that allows an improved power saving mechanism for the Wireless Personal Area Networks based on mobile ad-hoc networks in decentralized and distributed manner. The invention relates to system and method which allows all the devices to wakeup globally, simultaneously and periodically in a particular superframe, referred to as "global wake superframe" in the present invention for the sake of explanation. The invention relates to system and method which allows all the devices to wakeup individually and periodically in a particular superframe, referred to as "local wake superframe" in the present invention for the sake of explanation. The invention relates to system and method which allows the devices to independently vary their sleeping times (i.e. number of superframes) in the hibernating mode, based on the network activity and communicate it effectively to the other hibernating devices. The present invention comprises of system and method which would solve the problems associated with current art, in the following manner: 1. Invention provides method by which all devices (hibernating or not) are awake simultaneously during a particular superframe. This superframe is referred to as "global wake superframe" in the present invention. 2. Invention provides method by which a device in hibernating mode is individually and periodically woken up. The specific superframe when a device is periodically awake is referred to as "local wake superframe" in the present invention. 3. In the global wake up superframe, since all devices are awake, all devices (that may be hibernating) discover other devices (which may also be hibernating devices). They also come to know each others local (individual) sleep periods from the beacons. 4. New devices come to know about hibernating devices and their local sleep periods on hearing a global wake up superframe. 5. Upon listening to the global wake superframe, each device (new, hibernating or active) gets the full update of all the DRP reservations periodically. 6. Upon listening to the global wake superframe all the devices get time synchronized simultaneously. 7. A device advertises its changed local sleep interval in the beacon of the global wake up superframe. Thus all the devices easily come to know of the changed (if any) sleep interval of all the hibernating devices in the global wake up superframe. Accordingly the invention provides the system and method for power saving in a synchronized manner. Accordingly the invention provides a mechanism for all the devices to wakeup globally, simultaneously and periodically in a same particular superframe. Accordingly the invention also provides the mechanism for all the devices to wakeup locally, individually and periodically in a particular superframe. Accordingly, the invention provides a method for all the devices to get time synchronized periodically in the global wakeup superframe. Accordingly, the invention provides a method for all the devices to get updates about all the DRP reservations periodically in the global wakeup superframe. Accordingly, the invention provides a method for all the devices to discover all the other neighboring devices periodically in the global wakeup superframe. Accordingly, the invention provides a method for all the devices to know about the sleep periods of the hibernating devices by periodic advertisements in the beacons in the global wakeup superframe. Accordingly, the present invention explains a system for power saving in wireless personal area networks comprising: (a) means for power saving involving a new parameter Global Wake Frequency (GWF), which periodically awake all the devices in a common global superframe as Global Wake Superframes (GWS); (b) means for power saving involving a new parameter maintained locally by all the devices as Local Wake Frequency (LWF); (c) means for a device to periodically wake up in superframe referred as Local Wake Superframes (LWS); and (d) means for the devices to independently vary their sleeping periods, based on the network activity, and communicate it to all other hibernating devices. GWF defines the frequency of occurrence of GWS where GWF is the global parameter for the network which is known to all the devices of the network. After every GWF number of superframes, a GWS will occur when all devices are awake. Global Wake Superframe is defined as, when {(Clock) mod GWF} == 0, where (Clock) is the device clock, which is time synchronized to the network and GWF is computed in the time. LWF defines the frequency of occurrence of LWS where LWF is the parameter which is locally decided by the devices based on the amount of network activity around itself. After every LWF number of superframes, a hibernating device will wake up, irrespective of whether other devices are active or hibernating. Local Wake Superframe is defined as, when {(Clock) mod LWF} == 0 where (Clock) is the device clock, which is time synchronized to the network and LWF is computed in the time.The GWF is larger than LWF indicating that GWS occurs less frequently than LWS. Accordingly, the present invention further explains a method for power saving in wireless personal area networks comprising the steps of: (a) constituting the superframe when all the devices of the network are awake during the superframe by the GWS; (b) hearing beacons; and (c) explicit DRP requesting and DRP responding, wherein during GWS all the devices get globally time synchronized, update DRP allocations in the superframe and do device discovery. The next GWS following the existing GWS is based on the GWF parameter where the devices which hear a GWS have knowledge of the position of next GWS based on the GWF parameter. LWS constitutes the superframes when the devices choose to periodically wake up continuously in that particular superframe where a device is awake in its LWS. All devices irrespective of their LWF is awake in the GWS superframes. Devices vary their sleeping periods based on their magnitude of network activity, by changing their LWF parameter. Each device advertises its LWF parameter to all the other neighboring devices by including it in its beacon and in GWS, the (changed) LWF value is available to all other devices where all devices maintain the latest LWF of other devices in their BG.As each device knows the LWF the devices which want to talk to the hibernating device starts its communication in the next LWS of the destination device. The other objects, features and advantages of the present invention will be apparent from the accompanying drawings and the detailed description as follows. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 illustrates the WPAN as a decentralized and distributed ad-hoc network system and range of all devices; Figure 2 illustrates the superframe structure in current art, which includes MAS and beacon periods; Figure 3 illustrates the operation of the invention, using an example, showing time axis with the occurrence of GWSs for the GWF=5 and LWSs for the LWF as 2, 3 chosen by the hibernating devices 1 and 2 respectively. DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 illustrates the WPAN as a decentralized and distnbuted ad-hoc network system and range of all devices. The black dots represent devices and the circles are the effective ranges of the respective devices. Note the absence of any centralized infrastructure. In such an ad hoc network, each device cooperates to provide various networking and management functions like device discovery, routing, channel reservation, etc. These devices are generally small and battery powered with limited amount of power available for performing different kind of operations including communication with other devices. Figure 2 illustrates the superframe structure in current art. Beaconing slots are present at the start of the superframe and are reserved for sending beacon by various devices. Except for the beaconing slots, the rest of the slots called MASs can be used by devices for their communication. Devices which are not communicating during particular MAS can sleep. Figure 3 illustrates the operation of the invention. Device 1 has chosen a LWF of 2, hence is guaranteed to be awake in every {(Clock) mod 2} == 0 superframes i.e. N, N+2, N+4 .... Device 2 has chosen a LWF of 3, hence is guaranteed to be awake in every {(Clock) mod 3} == 0 superframes i.e. N, N+2, N+4 .... In addition, the GWF value for the network is 5 which implies that all devices need to be awake in every {(Clock) mod 5} == 0 superframe i.e. N, N+5, N+10, ... The figure also shows that devices need to be awake in the GWF irrespective of whether it is their LWF or not. It is evident from the figure that Device 1 and Device 2 can hear each other in at least GWF superframes N, N+5, N+10 and can initiate communication. 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 power saving mechanism in the decentralized Wireless Personal Area Networks based on mobile ad-hoc networks. The system for the invention comprises of a new power saving mechanism involving a new parameter known globally by all the devices called as Global Wake Frequency (GWF), a method to periodically awake all the devices in a common global superframe referred as Global Wake Superframes (GWS), a new parameter maintained locally by all the devices called as Local Wake Frequency (LWF), mechanism for a device to periodically wake up in superframe referred as Local Wake Superframes (LWS) and mechanism for the devices to independently vary their sleeping periods, i.e. LWF based on the network activity, and communicate it to all other hibernating devices. Accordingly the invention provides system and method which allows the devices, willing to save power, by letting them periodically sleep until the next LWS or GWS. Accordingly the invention allows devices to wake up during their LWSs while mandating the wake up only in the Global Wake Super frame (GWS). Accordingly, the invention provides mechanism for each device to independently choose the number of superframes that it wants to sleep, i.e. LWF, depending on the amount of network activity around it. Accordingly, the invention provides a facility for all the devices to get time synchronized periodically in the GWS. Accordingly, the invention provides a facility for all the devices to get updates about all the DRP reservations periodically in the GWS. Accordingly, the invention provides a facility for all the devices to discover all the other neighboring devices periodically in the GWS. Accordingly, the invention provides a method for all the devices to know about the sleep period of the hibernating devices by respective advertisements (containing LWF) in the beacons periodically in the GWS. The subsequent subsections describe the individual entities to effect the invention. 1. GWF defines the frequency of occurrence of GWS. That is, after every GWF number of superframes, a GWS will occur when all devices are awake. GWF can be the global parameter for the network or subset of the network. It is known to all the devices of the network or subset of the network. Global Wake Superframe is defined as, when {(Clock) mod GWF} == 0, where (Clock) is the device clock, which is time synchronized to the network and GWF is computed in the time. It is possible that Clock parameter is provided by a single device to a set of devices. 2. LWF defines the frequency of occurrence of LWS. That is, after every LWF number of superframes, a hibernating device will wake up, irrespective of whether other devices are active or hibernating. LWF is the parameter which is locally (independently) decided by the devices based on the amount of network activity around itself. Local Wake Superframe is defined as, when {(Clock) mod LWF} == 0 where (Clock) is the device clock, which is time synchronized to the network and LWF is computed in the time. It is possible that Clock parameter is provided by a single device to a set of devices. 3. For a meaningful and efficient power save mechanism, the GWF is larger than LWF. Thus GWS occurs less frequently than LWS. 4. Figure 3 describes the above mentioned GWF, GWSs, LWF and LWSs to effect the invention: 1. In Figure 3, GWF is considered to be as 5. Thus if superframe N is GWS then all the devices have to wake up for the next GWS in N+5*^ superframe. 2. in Figure 3, hibernating device 1 is considered to have chosen its LWF as 2. Thus it has to wake up in N, N+2, N+4, N+5(GWS), N+7, N+9, N+10(GWF) etcsuperframes. 3, In Figure 3, hibernating device 2 is considered to have chosen its LWF as 3. Thus it has to wake up in N, N+3, N+5(GWS), N+8, N+10(GWF) etc superframes. 4. The numbers for GWF and LWF are only for illustrative purpose. The choice for any other numbers for GWF and LWF does not affect the operation of the invention, i.e. the operation of the invention is independent of specific choice of LWF and GWF. The subsequent subsections describe the operation of the invention: 1. GWS constitutes the superframe when all the devices of the network are awake during the superframe, hear beacons, send explicit DRP requests and DRP responses. Thus, during GWS all the devices get globally time synchronized, update DRP allocations in the superframe and perform device discovery. 2. The next GWS following the existing GWS is based on the GWF parameter. Devices which hear a GWS thus have knowledge of the position of next GWS based on the GWF parameter. 3. LWS constitutes the superframes when the devices choose to periodically wake up continuously in that particular superframe. A device has to be awake in its LWS. 4. All devices irrespective of their LWF have to be awake in the GWS superframes. In other superframes, the device may go to sleep or be awake. 5. Devices can vary their sleeping periods based on their magnitude of network activity, by changing their LWF parameter. Each device advertises its LWF parameter to all the other neighboring devices by including it in its beacon. In GWS, the (changed) LWF value is available to all other devices. All devices maintain the latest LWF of other devices in their BG. 6. LWS is with reference to the GWS. Since each device knows the LWF thus the devices which want to talk to the hibernating device starts its communication in the next LWS of the destination device. LWF and GWF can be advertised in other form also. LWF can be changed by the device depending on different parameters. GWF can be changed by the device depending on local or global parameters. 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, 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 BPST: Beacon Period Start Time DRP: Distributed Reservation Protocol GWF: Global Wake Frequency GWS: Global Wake Superframe IEEE: Institute of Electrical and Electronics Engineers LWF: Local Wake Frequency LWS: Local Wake Superframe MAC: Medium Access Control MAS: Medium Access Slot MBOA: Multi Band OFDM Alliance OFDM: Orthogonal Frequency Division Multiplexing UWB: Ultra Wide Band WPAN: Wireless Personal Area Network WE CLAIM 1. A system for power saving in wireless personal area networks comprising: (a) means for power saving involving a new parameter Global Wake Frequency (GWF), which periodically awake all the devices in a common global superframe as Global Wake Superframes (GWS); (b) means for power saving involving a new parameter maintained locally by all the devices as Local Wake Frequency (LWF); (c) means for a device to periodically wake up in superframe referred as Local Wake Superframes (LWS); and (d) means for the devices to independently vary their sleeping periods, based on the network activity, and communicate it to all other hibernating devices. 2. A system as claimed in claim 1 wherein GWF defines the frequency of occurrence of GWS where GWF is the global parameter for the network which is known to all the devices of the network. 3. A system as claimed in claim 1 wherein GWF can be derived by a device or can be derived from network information or can be statically assigned. 4. A system as claimed in claim 1 wherein after every GWF number of superframes, a GWS will occur when all devices are awake. 5. A system as claimed in claim 1 wherein parameters of the network may be used by the devices to calculate Global Wake Superframe in an ad hoc manner. One such a method is defined as, when {(Clock) mod GWF} == 0, where (Clock) is the device clock, which is time synchronized to the network and GWF is computed in the time and the system is capable of Clock parameter provided by a single device to a set of devices. 6. A system as claimed in claim 1 wherein LWF defines the frequency of occurrence of LWS where LWF is the parameter which is locally decided by the devices based on the amount of network activity around itself. 7. A system as claimed in claim 1 wherein after every LWF number of superframes, a hibernating device will wake up, irrespective of whether other devices are active or hibernating. 8. A system as claimed in claim 1 wherein parameters of the network may be used by the devices to calculate Local Wake Superframe in an ad hoc manner. One such a method is defined as, when {(Clock) mod LWF} == 0 where (Clock) is the device clock, which is time synchronized to the network and LWF is computed in the time. 9. A system as claimed in claim 1 wherein the GWF is larger than LWF indicating that GWS occurs less frequently than LWS. 10. A system as claimed in claim 1 wherein the sleeping and hibernation patterns of the constituent devices can be dynamically varied based by varying GWF and LWF parameters on network conditions and other variables to achieve maximum synchronized power saving by local or global decisions of parameters. 11. A method for power saving in wireless personal area networks comprising the steps of: (a) constituting the superframe when all the devices of the network are awake during the superframe by the GWS; (b) recording the LWF value of all the neighbors with whom the device wants to communicate either in present or future; (c) determining the earliest superframe in which a device is guaranteed to be awake; and (d) providing the additional ability for all devices in the network to get globally time synchronized, update DRP allocations in the superframe and do device discovery .periodically during GWS, thereby achieving vital network management functionality in addition to maximizing power saving for all the devices by limiting such operations to the minimum. 12. A method as claimed in claim 11 wherein the next GWS following the existing GWS is based on the GWF parameter where the devices which hear a GWS have knowledge of the position of next GWS based on the GWF parameter. 13. A method as claimed in claim 11 wherein LWS constitutes the superframes when the devices choose to periodically wake up continuously in that particular superframe where a device is awake in its LWS. 14. A method as claimed in claim 11 wherein all devices irrespective of their LWF is awake in the GWS superframes. 15. A method as claimed in claim 11 wherein devices vary their sleeping periods based on their magnitude of network activity, by changing their LWF parameter. 16. A method as claimed in claim 11 wherein each device advertises its LWF parameter to all the other neighboring devices by including it in its beacon and in GWS, the (changed) LWF value is available to all other devices where ail devices maintain the latest LWF of other devices in their BG. 17. A method as claimed in claim 11 wherein as each device knows the LWF the devices which want to talk to the hibernating device starts its communication in the next LWS of the destination device. 18. A system for power saving in wireless personal area networks substantially as herein described particularly with reference to the drawings. 19. A method for power saving in wireless personal area networks substantially as herein described particularly with reference to the drawings. Dated this 14*^ day of June 2005

Documents:

0553-che-2004 claims duplicate.pdf

0553-che-2004 description(complete) duplicate.pdf

0553-che-2004 drawings duplicate.pdf

553-che-2004 claims granted.pdf

553-che-2004 form 1.pdf

553-che-2004 form 2.pdf

553-che-2004-abstract.pdf

553-che-2004-claims.pdf

553-che-2004-correspondnece-others.pdf

553-che-2004-correspondnece-po.pdf

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

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

553-che-2004-drawings.pdf

553-che-2004-form 1.pdf

553-che-2004-form 5.pdf

553-che-2004-form 9.pdf