Abstract:
A method of coordinating devices in a wireless network is provided. First capability data associated with a first type of power source and a first state of the power source of a first device is received at a second device. Second capability data is transmitted to the first device from the second device. The second capability data is associated with a second type of power source and a second state of the power source of the second device. The first capability data is compared with the second capability data at the second device. If the comparison indicates the first capability data is less desirable than the second capability data, the second capability data is transmitted again to the first device from the second device. If the comparison indicates the first capability data is more desirable than the second capability data, the first capability data is received again from the first device at the second device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/704,744 that was filed Nov. 12, 2003, the disclosure of which is incorporated by reference in its entirety; which is a continuation-in-part of U.S. patent application Ser. No. 10/662,364 that was filed Sep. 16, 2003, now U.S. Pat. No. 7,245,947, the disclosure of which is incorporated by reference. 
    
    
     BACKGROUND 
     The present invention relates to wireless communications. More particularly, the present invention relates to techniques for controlling selection of a coordinating device in a wireless ad hoc network. 
     Short range wireless systems typically involve devices that have a communications range of one hundred meters or less. To provide communications over long distances, these short range systems often interface with other networks. For example, short range networks may interface with cellular networks, wireline telecommunications networks, and the Internet. 
     Wireless piconets, also referred to as personal area networks (PANs) typically operate in unlicensed portions of the radio spectrum, usually either in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band or the 5 GHz Unlicensed-National Information Infrastructure (U-NII) band. Examples of wireless piconet technology include the Bluetooth standard and the IEEE 802.15.3 standard. 
     Bluetooth defines a short-range radio network, originally intended as a cable replacement. It can be used to create ad hoc networks of up to eight devices, where one device is referred to as a master device. The other devices are referred to as slave devices. The slave devices can communicate with the master device and with each other via the master device. The Bluetooth Special Interest Group, Specification Of The Bluetooth System, Volumes 1 and 2, Core and Profiles: Version 1.1, Feb. 22, 2001, describes the principles of Bluetooth device operation and communication protocols. Bluetooth devices operate in the 2.4 GHz radio band reserved for general use by Industrial, Scientific, and Medical (ISM) applications. These devices are designed to find other Bluetooth devices within their communications range and to discover what services they offer. 
     IEEE 802.15.3 defines a framework for devices to communicate at high data rates (e.g., 55 Mbps) at short ranges across ad hoc networks. Currently, an IEEE 802.15.3 piconet may support a large number of devices, such as 250. These devices share frequency channels by employing time division multiple access (TDMA) transmission and Carrier Sensing Multiple Access (CSMA) techniques. IEEE 802.15.3 piconets include a device known as a piconet controller or coordinator (PNC) and one or more other devices (referred to as DEVs). 
     The PNC is a device that controls piconet resources. In particular, the PNC performs functions, such as controlling the basic timing for the piconet, and regulating the admission of devices into the piconet. In addition, the PNC manages quality of service (QoS) and security aspects of the piconet. To perform these functions, the PNC typically cannot enter an “idle” or “sleep” mode. Thus, the PNC consumes more power than the other devices in the piconet. Therefore, it is desirable to assign the PNC role to devices having a good battery condition, or even a fixed power supply. 
     Multiple devices may join and leave the piconet during its existence. Likewise, different devices may assume the PNC role at various times. The process in which the PNC role is transferred between a first device and a second device is referred to herein as PNC handover. IEEE 802.15.3 provides for PNC handover through the use of a PNC handover command, which is issued for various reasons. 
     However, these reasons do not currently include the status of a battery, but only information on the availability of a fixed power supply. In an ad hoc network, none of the devices may have a fixed power supply. The knowledge of battery levels in such a network could be used for balancing power consumption. The inability to determine the battery level in such a network may also cause a device with low battery power (that otherwise appears as a good PNC candidate) to be unable to reject the PNC role because of its low battery power, and run out of power after the PNC role is transferred to it. Accordingly, techniques are needed for taking available power source capacity of devices into consideration during PNC handover processes. 
     In addition to the short-range networking techniques described above, ultra wideband (UWB) techniques have become an attractive solution for short-range wireless communications because they allow for devices to exchange information at relatively high data rates. Current FCC regulations permit UWB transmissions for communications purposes in the frequency band between 3.1 and 10.6 GHz. However, for such transmissions, the spectral density has to be under −41.3 dBm/MHz and the utilized bandwidth has to be higher than 500 MHz. 
     There are many UWB transmission techniques that can fulfill these requirements. A common and practical UWB technique is called impulse radio (IR). In IR, data is transmitted by employing short baseband pulses that are separated in time by gaps. Thus, IR does not use a carrier signal. These gaps make IR much more immune to multipath propagation problems than conventional continuous wave radios. RF gating is a particular type of IR in which the impulse is a gated RF pulse. This gated pulse is a sine wave masked in the time domain with a certain pulse shape. 
     IR transmission facilitates a relatively simple transmitter design, which basically requires a pulse generator and an antenna. This design does not necessarily require a power amplifier, because transmission power requirements are low. In addition, this design does not generally require modulation components such as voltage controlled oscillators (VCOs) and mixers, because the impulses are baseband signals. 
     In general, IR receiver designs are more complex than their corresponding transmitter designs. However, these designs are much simpler than conventional receiver designs because they typically do not employ intermediate frequency (IF) signals or filters. However, to fulfill spectral requirements, IR impulses have to be very short in duration (e.g., a couple of nanoseconds). This requirement places stringent timing demands on receiver timing accuracy. The fulfillment of these demands can also provide IR receivers with accurate time resolution and positioning capabilities. 
     SUMMARY 
     In an exemplary embodiment, a method of coordinating devices in a wireless network is provided. First capability data associated with a first type of power source and a first state of the power source of a first device is received at a second device. Second capability data is transmitted to the first device from the second device. The second capability data is associated with a second type of power source and a second state of the power source of the second device. The first capability data is compared with the second capability data at the second device. If the comparison indicates the first capability data is less desirable than the second capability data, the second capability data is transmitted again to the first device from the second device. If the comparison indicates the first capability data is more desirable than the second capability data, the first capability data is received again from the first device at the second device. 
     In another exemplary embodiment, a memory is provided that includes computer-readable instructions that, upon execution by a processor, cause a computing device to implement the operations of the method of coordinating devices in a wireless network. 
     In another exemplary embodiment, a device is provided that includes, but is not limited to, an antenna configured to send and receive data in a wireless network, a processor, and a memory including computer-readable instructions that, upon execution by the processor, cause the device to implement the operations of the method of coordinating devices in a wireless network. 
     Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number. The present invention will be described with reference to the accompanying drawings, wherein: 
         FIG. 1  is a diagram of an exemplary operational network environment; 
         FIG. 2  is a block diagram of an exemplary communications device. architecture; 
         FIG. 3  is a block diagram of an exemplary communications device implementation; 
         FIG. 4  is a block diagram of an exemplary device architecture in accordance with an embodiment. 
         FIG. 5  is an exemplary IEEE 802.15.3 High Rate (HR) frame format in accordance with an embodiment; 
         FIG. 6  is an exemplary IEEE 802.15.3 High Rate (HR) capability field format in accordance with an embodiment; 
         FIG. 7  is an exemplary IEEE 802.15.3 High Rate (HR) priority list in accordance with an embodiment; 
         FIG. 8  is an exemplary IEEE 802.15.3 High Rate (HR) priority list with power source status indication (PSSI) support in accordance with an embodiment; and 
         FIGS. 9 and 10  are flowcharts of exemplary coordinator selection processes. 
         FIG. 11  is a flowchart of a technique in which a device transmits energy information; 
         FIG. 12  is a flowchart of a technique In which PNC handover commands are used to convey energy information; 
         FIG. 13  is a diagram showing an exchange of information between two network devices; 
         FIG. 14  is a diagram of an operational environment including a handover information database; and 
         FIG. 15  is a flowchart of an operational sequence of a device. 
     
    
    
     DETAILED DESCRIPTION 
     I. Operational Environment 
     Before describing the invention in detail, it is helpful to describe an environment in which the invention may be used. Accordingly,  FIG. 1  is a diagram of an operational environment  100  that includes a parent piconet US 2005/0075084 Al  106  and a child piconet  110 . In embodiments, piconets  106  and  110  may operate according to various standards, such as IEEE 802.15.3 and Bluetooth. 
     Piconet  106  includes a coordinator device  102  and a plurality of devices  104 . Coordinator device  102  controls the resources of piconet  106 . For example, coordinator  102  controls the basic timing of piconet  106  and regulates the admission of devices into piconet  106 . In addition, coordinator  102  may manage various quality of service (QoS) and security aspects of the piconet. In embodiments employing IEEE 802.15.3, coordinator device  102  may be a piconet coordinator (PNC), while devices  104  are referred to as DEVs. In embodiments employing Bluetooth, coordinator device  102  may be a master device. 
     The devices of piconet  106  exchange information through the transmission of wireless signals. These signals may be, for example, carrier-based or ultra wideband (UWB) signals. Various multiple access techniques may be employed so that the devices of piconet  106  may share allocated portions of a wireless communications media (e.g., a frequency range In the RF communications spectrum). Exemplary multiple access techniques include time division multiple access (TDMA), time division duplex (TDD), frequency division multiple access (FDMA), and code division multiple access (CDMA). 
     For instance, in embodiments involving IEEE 802.15.3, the devices of piconet  106  communicate according o a TDMA frame structure that includes a beacon period, a contention access period, and a channel time allocation period (CTAP) (also referred to as a contention free period). Embodiments employing Bluetooth employ a TDD frame format. This TDD format includes alternating slots in which master and slave devices communicate according to a polling scheme. 
     Child piconet  110  may operate with a portion of bandwidth allocated from parent piconet  106 , such as a TDMA time slot of the parent piconet  106 . As shown in  FIG. 1 , child piconet  110  includes a coordinator device  108 , which performs functions similar to the functions performed by coordinator device  102 . 
       FIG. 1  illustrates a configuration of piconets  106  and  110  at a given point in time. However, the characteristics of these networks may change over time. For instance, during operation, the membership of piconet  106  may change through the departure and arrival of different devices. In addition, the coordinator role may be transferred from device  102  to another device in piconet  106  according to a coordinator handover operation. Such coordinator handovers may be performed in accordance with power-based techniques of the present invention. 
     For example, in one aspect of the method and system herein, the devices exchange device parameters. This information may be exchanged during initial formation of the wireless network or after establishment thereof. The device parameters may include a power source status indicator of a device indicating the available power source capacity for the device. The initial coordinator or subsequent coordinators to which control is handed off may be determined according to the power source status indicator of one or more devices in the wireless network. 
     II. Wireless Communications Device 
       FIG. 2  is a block diagram showing a wireless communications device architecture, which may be used for devices  102 ,  104  and  108 . Although this architecture is described in the context of Bluetooth and UWB communications, it may be employed with other wireless communications technologies. 
     The device architecture of  FIG. 2  includes a host  202 , which is coupled to a Bluetooth segment  210 , and a UWB segment  220 . Host  202  is responsible for functions involving user applications and higher protocol layers, while Bluetooth segment  210  and UWB segment  220  are responsible for lower layer protocols. More particularly, Bluetooth segment  210  is responsible for Bluetooth specific communications with other devices, and UWB segment  220  is responsible for UWB specific communications with other devices. 
     As shown in  FIG. 2 , Bluetooth segment  210  includes a host controller interface (HCl)  212 , a Bluetooth module  214  with a link manager and a link controller, a Bluetooth transceiver  216 , and an antenna  218 . 
     The link manager performs functions related to Bluetooth link set-up, security and control. These functions involve discovering corresponding link managers at remote devices and communicating with them according to a link manager protocol (LMP). To perform these functions, LMP defines a set of messages, which are also referred to as protocol data units (PDUs). The Link manager exchanges these PDUs with link managers at remote devices. 
     The link manager exchanges information with host  202  across HCl  212 . This information may include commands received from host  202 , and information transmitted to host  202 . HCl  212  defines a set of messages, which provide for this exchange of information. 
     The link controller operates as an intermediary between the link manager and Bluetooth transceiver  216 . The link controller also performs baseband processing for Bluetooth transmission, such as error correction encoding and decoding. In addition, the link controller exchanges data between corresponding link controllers at remote devices according to physical layer protocols. Examples of such physical layer protocols include retransmission protocols such as the automatic repeat request (ARQ) protocol. 
       FIG. 2  shows that Bluetooth transceiver  216  is coupled to an antenna  218 . Transceiver  216  includes electronics that allow the device of  FIG. 2  (in conjunction with antenna  218 ) to exchange wireless Bluetooth signals with devices, such as a remote device  104 . Such electronics include modulators and demodulators, amplifiers, and filters. 
     When the device of  FIG. 2  engages in UWB communications, it employs the services of UWB segment  220 . As shown in  FIG. 2 , UWB segment  220  includes an interface  222 , a UWB module  224 , a UWB transceiver  226 , and an antenna  228 . Interface  222  provides for communications between host  202  and UWB module  224 . 
     UWB module  224  provides for the exchange of information across UWB links according to one or more protocol layers. For example, UWB module may provide session management functionality to manage various UWB sessions. In addition, UWB module  224  may perform base US 2005/0075084 Al band processing, such as error correction encoding and decoding. In addition, UWB module  224  performs various link level protocols with remote devices according to physical layer protocols. Examples of such protocols include retransmission protocols such as the automatic repeat request (ARQ) protocol. 
     In an aspect of the method and system herein, UWB module  224  may implement the IEEE 802.15.3 Righ Rate (RR) framework to perform communications in an ad hoc wireless communications network environment. Amore detailed discussion of an exemplary implementation employing the IEEE 802.15.3 framework is provided below with reference to  FIGS. 4 through 8 . 
     UWB transceiver  226  is coupled to antenna  228 . UWB transceiver  226  includes electronics, which allow the device of  FIG. 2  (in conjunction with antenna  228 ) to exchange wireless UWB signals with devices, such as remote devices  104  and  108 . For the transmission of UWB signals, such electronics may include a pulse generator. For the reception of UWB signals, such electronics may include timing circuitry and filters. 
     The architecture of  FIG. 2  may be implemented in hardware, software, firmware, or any combination thereof. One such implementation is shown in  FIG. 3 . This implementation includes a processor  310 , a memory  320 , and an interface  340  such as an interface to other devices or a user. In addition, the implementation of  FIG. 3  includes transceivers  350  and antennas  352 . Transceivers  350  may include a Bluetooth transceiver (e.g.,  216 ) and UWB transceiver (e.g.,  226 ) such as described above with reference to  FIG. 2  or other suitable types of transceivers which support ad hoc wireless networking. 
     As shown in  FIG. 3 , processor  310  is coupled to transceivers  350 . Processor  310  controls device operation. Processor  310  may be implemented with one or more microprocessors that are each capable of executing software instructions stored in memory  320 . 
     Memory  320  includes random access memory (RAM), read only memory (ROM), and/or flash memory, and stores information in the form of data and software components (also referred to herein as modules). These software components include instructions that can be executed by processor  310 . Various types of software components may be stored in memory  320 . For instance, memory  320  may store software components that control the operations of transceivers  350 . Also, memory  320  may store software components that provide for the functionality of host  202 , interface  212 , BT module  214  (e.g., link manager, link controller, etc.), interface  22 , UWB Module (e.g., Media Access Control (MAC), PRY, etc.). 
     In addition, memory  320  may store software components that control the exchange of information through interface  340 . As shown in  FIG. 3 , user interface  340  is also coupled to processor  310 . Interface  340  facilitates the exchange of information with a user or other device or component.  FIG. 3  shows that interface  340  includes an input portion  342  and an output portion  344 . Input portion  342  may include one or more devices that allow a user or other devices to input information. Examples of such devices include keypads, touch screens and microphones, and data communications interfaces such as serial port, parallel port, 1394 interface, USB interface, and so forth. Output portion  344  allows a user or other device to receive information from the wireless communications device. Thus, output portion  344  may include various devices, such as a display, and one or more audio speakers, and data communications interfaces such as serial port, parallel port, 1394 interface, USB interface, and so forth. Exemplary displays include liquid crystal displays (LCDs), and video displays. 
     The elements shown in  FIG. 3  may be coupled according to various techniques. One such technique involves coupling transceivers  350 , processor  310 , memory  320 , and interface  340  through one or more bus interfaces. 
     In addition, each of these components is coupled to a power source facility  330  which includes a power manager  332 , fixed power source interface  334  such as an AC/DC interface for connecting to a fixed power supply, and a battery  336  such as a removable and rechargeable battery pack. Power manager  332  or the like may be employed to manage power usage in the wireless communications device. Such management may include detection and maintenance of information on power source availability or power source status for the device, and selective control of power source for device functions and components. Power manager  332  may be configured as part of the device&#39;s operating system or a separate module or so forth, as desired. 
     III. Exemplary IEEE 802.15.3 Piconet Implementation 
       FIG. 4  is a diagram of an exemplary device architecture  400 . This architecture allows devices to employ various wireless communications frameworks (such as IEEE 802.15.3) according to embodiments of the present invention. Device architecture  400  provides for communications with other devices according to a multi-layered protocol stack. As shown in  FIG. 4 , this protocol stack includes a physical layer  410 , a data link layer  420 , and a convergence layer  430 . The elements of  FIG. 4  may be implemented in hardware, software, firmware, or any combination thereof. 
     Physical layer  410  includes a physical (PRY) sublayer  412 . PRY sub-layer  412  is responsible for transmitting and receiving signals with a wireless medium. These signals may be RF signals (carrier-based and/or UWB) as well as optical signals. In addition, PRY sub-layer  412  receives data for transmission from data link layer  420  and sends it to data link layer  420  as symbols (e.g., bit streams) corresponding to wireless signals received from the wireless medium. 
     Data link layer  420  includes a media access control (MAC) sub-layer  422 . MAC sub-layer  422  performs functions Involving formatting of data for transmission, synchronization of transmissions, flow control, and error detection/correction. As shown in  FIG. 4 , MAC sub-layer  422  communicates with PRY sublayer  412  via a PRY service access point (SAP) interface. 
     A convergence layer  430  includes one or more convergence sub-layers  432 . Sub-layers  432  provide for higher layer functions, such as applications. Such applications include (but are not limited to) audio, video, high speed data access, voice (e.g., telephony), IP, USB, 1394 and so forth. 
       FIG. 4  shows that MAC sub-layer exchanges information with a MAC layer management entity (MLME)  424  and PHY sub-layer  412  exchanges information with a PHY layer management entity (PLME)  414 . 
     MLME  424  and PLME  414  provide for basic signaling functions to be performed between piconet devices so that connections may be set-up, managed, and released. In addition, these signaling functions may exchange information that facilitate the coordinator handover techniques of the present invention. Such information includes various device status information, as well as commands or messages for directing a coordinator handover according to the techniques of the present invention. 
     As shown in  FIG. 4 , MLME  424  and PLME  414  are coupled to a device management entity (DME)  440  by corresponding service access point (SAP) interfaces. DME  440  directs various fuctions of MLME  424  and PLME  414  involving, for example, resource allocation decisions. 
       FIG. 5  is a diagram of an exemplary IEEE 802.15.3 TDMA frame format. This frame format includes a repeating pattern of superframes. This frame format may be employed in networks employing the techniques of the present invention. 
     As shown in  FIG. 5 , each superframe includes a beacon period, a contention access period, and a contention free period. The beacon period is used to convey control information from the coordinator to the entire piconet. Examples of such control information involve, for example, synchronization, transmit power level constraints, and the allocation of time slots to devices in the piconet. The contention access period is used for devices to transmit information to the piconet coordinator. Such information includes authentication requests and channel time requests. Transmissions during the contention access period may employ a protocol, such as slotted Aloha, which has been proposed for the enhanced 802.15.3 MAC for UWB. The channel time allocation period (CTAP) (contention free period) includes management channel time allocation (MCTA) slots and channel time allocation (CTA) slots, which are used for isochronous streams and asynchronous data connections. 
       FIG. 6  is an exemplary capability field format  600  identifying various capability attributes or characteristics of a device for implementing the IEEE 802.15.3 framework. Format  600  may include a PNC Capable field identifying whether the device is capable of being a coordinator; a Supported Data Rates field identifying the data rates supportable by a device; an Asynchronous Data Support field identifying whether the device supports asynchronous data communications; and a Neighbor PNC field identifying the neighboring PNC such as by its piconet address (PNID) or other identifier. Format  600  may further include Power Save Mode field (PSAVE) identifying whether the device supports power saving modes; a Power Source (PSRC) field identifying the type of Power Source (e.g., Fixed or Battery) employed by the device; a Security (SEC) field identifying whether the device supports security features such as encryption; and PNC Designated Mode (Des Mode) identifying the device&#39;s desirability to operate in PNC designated mode. 
     In accordance with an aspect of the method and system herein, format  600  may further include a Power Source Status Indicator (PSSI) for indicating available power source or power source status of the device. The power source statuses may include, for example, a fixed power supply, a full or almost full battery, half battery and nearly depleted battery. These may be reflected in the following priority:
         1—Fixed Power Supply Condition   2—Full Battery Condition (and/or Almost Full Battery Condition)   3—Half Battery Condition   4—Empty Battery Condition (and/or Almost Empty Battery Condition).       

     The above is simply an example of power source conditions and status information. Other conditions, either even more specific (e.g., percentage level, etc.) or general (e.g., Good Power Source Condition and Bad Power Source Condition), may be maintained and transmitted to other devices to facilitate determination of an initial or subsequent coordinator(s) of the wireless network. It may, however, be desirable to reduce the categories of conditions and employ general or broad categor(ies) of condition definitions since devices may have different power capacities and power consumption is difficult to forecast exactly. 
     Another way of introducing the condition of power source is to enhance the PSRC bit with one or more bits. For instance, modifying the PRSC to have two more bits allows for enable the determination of power source condition, such as with the PSSI as described above, and would eliminate the need for a separate field(s) such as the PSSI. An example of the represented conditions using two bits may be as follows:
         1(11)—Fixed Power Supply Condition   2(10)—Full Battery Condition (and/or Almost Full Battery Condition)   3(01)—Half Battery Condition   4(00)—Empty Battery Condition (and/or Almost Empty Battery Condition).       

     The power source capacity level could be determined in PHY/MAC layer or set by higher layers depending on implementation. 
     Format  600  may also include one or more Reserved fields for maintaining and identifying other device capabilities to facilitate network communications. 
       FIG. 6  is simply one example of a capability field format. The various field orders, field types and field lengths (e.g., bites)) may be configured to facilitate communications and the method and system herein. For example, the capability field format may include more or less field types and the field lengths may be increased and decreased. Although the power source status indicator may be maintained, as part of device capability information, such information may be maintained or provided in other formats or with other information to implement the method and system herein. The coordinator may request, maintain and update the capability information of all devices. 
       FIG. 7  is an exemplary IEEE 802.15.3 priority list which may be employed in the determination of a coordinator according to various device attributes or characteristics. As shown in  FIG. 7 , various device characteristics have been prioritized to assist when comparing devices to determine or select which device should be the coordinator. 
     In this example, eight device attributes may be examined in the following priority order (from highest to lowest): (1) PNC Designated Mode (Des Mode), (2) Security (SEC), (3) Power Source (PSRC), (4) Power Save Modes (PSAVE), (5) Maximum Number of Available Guaranteed Time Slots (GTS), (6) Transmitter Power Level, (7) Maximum PHY Rate and (8) Device Address (e.g., Piconet Address). 
     PNC Des Mode identifies whether the device&#39;s current designated mode is PNC. APNC Des Mode bit equal to one (which reflects a desire to be a PNC) is preferred. 
     SEC identifies whether the device supports security features, such as encryption. A SEC bit equal to one (which acknowledges support for security) is preferred. 
     PSRC identifies the type of power source such as a fixed or battery power source. A PRSC bit equal to one (which identifies a fixed power source) is preferred. 
     PSAVE identifies whether the device supports power saving modes. A PSAVE bit equal to one (which acknowledges support for power saving modes) is preferred. 
     The transmitter power level, Maximum PHY Rate and Device address are self explanatory. Higher values for these attributes are preferred. 
     The priority list or the like may be employed by a PNC or DEVs to determine the desirability of a device as a candidate for coordinator. The coordinator selection processes may take place during formation of a piconet to ascertain which device should take on the role of coordinator, or may take place after formation of a piconet when the PNC desires to handover its role as a coordinator, or when another DEV challenges the PNC for the coordinator role, or upon other events or factors. 
       FIG. 8  is an exemplary IEEE 802.15.3 priority list with power source status indicator (PSSI) support. The priority list of  FIG. 8  is substantially the same as  FIG. 7  discussed above, except for the addition of a power source status indicator (PSSI) device attribute with a priority level of four. The PSSI identifies available power or power source status of a device. The preferred PSSI is one reflecting higher power capacity such as fixed power supply source or full battery condition, as discussed above with reference to  FIG. 6 . 
     It may be desirable to have the PSSI at a relatively high priority level on the priority list, particularly from the prospective of battery operated devices. In this way, an approach is provided to address the possibility of handing over or giving the coordinator role to a device with low battery. Although  FIG. 8  shows PSSI attribute with a priority level of four, the PSSI or the like may be assigned a higher or lower priority level on the priority list depending on various factors such as the application environment (e.g., game playing, transferring files, etc.), etc. 
     Although the above discusses an example of a priority list implementation, other approaches and formats may be employed to determine or select a coordinator according to power source status of at least one of the devices of the wireless network. Instead of a priority list, coordinator selection may be based on a weighted average of the attributes of a device as compared to other devices or a threshold, and so forth. Each priority level may also have one or more corresponding device parameters (e.g., priority level “x” is associated with PSSI below two and PSAVE equal one, etc.). 
     Although  FIGS. 4 through 8  discuss a UWB implementation using the IEEE 802.15.3 framework, other frameworks such as Bluetooth or a carrier-based implementation using the IEEE 802.15.3 framework may be employed in the method and system herein. 
     IV. Device Interactions 
       FIG. 9  is a flowchart of an exemplary coordinator selection process  900  which may take place during the formation of a wireless network, such as shown in  FIG. 1 , including a plurality of devices (e.g.,  102  and  104 ) with one device being designated as the coordinator (e.g.,  102 ). The network may be a Bluetooth piconet, or a UWB piconet implementing the IEEE 802.15.3 framework. 
     At step  902 , wireless communication devices (DEVs) begin negotiations to form a wireless network, such as an ad hoc wireless network. This may be initiated by one device discovering the presence of another device. The devices exchange messages to set up communications therebetween. These messages may include device parameters, such as the device attributes discussed above with reference to  FIGS. 7 and 8 . 
     At steps  904  and  906 , a coordinator selection procedure may be initiated and device parameters are evaluated for at least one of the devices, respectively. The device parameters include at least a power source status indicator indicating available power or power source status of a device. At step  908 , a device is determined or selected as a suitable candidate for coordinator based on at least the power source status indicator of at least one of the devices. 
     The steps  906  and  908  may be performed, for example, employing priority lists described above with reference to  FIGS. 7 and 8 . These priorities of device parameters may be stored, retrieved or accessed, as desired. One or more or all of the devices may be assigned a priority depending on the device(s)&#39; parameters, such as a device&#39;s parameter(s) matching an appropriate priority category on the priority list. A coordinator candidate device may then be selected from the one or more devices having the highest assigned priority. 
     In one example, the evaluation and determination steps may involve the devices transmitting or broadcasting their parameters or priorities. The devices compare their own parameters or priority versus the parameters or priority of the other devices. As comparisons are made, those devices with less desirable parameters or priority stop transmitting or broadcasting. The remaining transmitting or broadcasting device is determined to be a suitable coordinator candidate or winner. 
     At step  910 , wireless network operations are established with the determined device as the coordinator, and communications may then proceed between the devices. The coordinator may act as a conduit to route communications between devices and/or facilitate establishment of peer-to-peer communications directly between devices. 
       FIG. 10  is a flowchart of an exemplary coordinator selection process  1000  which may take place after formation of a wireless network, such as shown in  FIG. 1 , including a plurality of devices (e.g.,  102  and  104 ) with one device being designated as the coordinator (e.g.,  102 ). The network may be a Bluetooth piconet, or a UWB piconet implementing the IEEE 802.15.3 framework. 
     At step  1002 , the coordinator initiates a coordinator selection procedure. This procedure may be initiated based on various events or factors, which may include the following:
         (1) A new device seeks entry or is added to the wireless network (e.g., such as a new device with improved power source status);   (2) A device or the coordinator seeks to leave or leaves the wireless network (e.g., the available power of the coordinator is less than a predetermined threshold or the coordinator is moving out of range);   (3) The device parameters of one or more of the devices in the wireless network changes (e.g., a device becomes coupled to a fixed power supply);   (4) A triggering event occurs at the coordinator (e.g., user defined thresholds, such as power thresholds or other factors or circumstances, are met);   (5) Another device challenges the coordinator for the coordinator position; and   (6) User of the coordinator device initiates the procedure.       

     The above are simply a few examples of events or factors which may cause the initiation of the coordinator selection procedure. Other events and factors may also initiate the procedure, as desired. 
     At step  1004 , the coordinator evaluates the device parameters for at least one of the devices. The device parameters include at least a power source status indicator indicating available power or power source status of a device. At step  1006 , the coordinator determines or selects a device as a suitable candidate for the coordinator position based on at least the power source status indicator of at least one of the devices. 
     The steps  1004  and  1006  may be performed, for example, employing the priority lists described above with reference to  FIGS. 7 and 8 . These priorities of device parameters may be stored, retrieved or accessed, as desired. One or more or all of the devices may be assigned a priority depending on the device(s)&#39; parameters, such as a device&#39;s parameter(s) matching an appropriate priority category on the priority list. A coordinator candidate device may then be selected from the one or more devices having the highest assigned priority. 
     At step  1008 , the coordinator hands over the coordinator position to the determined device or candidate. This may involve exchanging messages between the two devices. For example, the coordinator may direct the candidate to coordinate wireless communications between the devices, with a request to hand over coordinator position from the coordinator and the candidate may respond by accepting such a request. The coordinator may also send to the candidate information of the devices in the wireless network and/or other information necessary to implement the coordinator duties. Other devices are also informed of the change in responsibilities. 
     Thereafter, the coordinator relinquishes its duties as the coordinator, and the candidate obtains control as the new coordinator. 
     V. Residual Energy Encoding 
     As described above, the present invention includes techniques in which an available energy condition may be encoded, for example, as a PSSI indicator. As an example, four conditions are described above: fixed power supply, full battery, half battery, and empty (or almost empty) battery. 
     Table 1 provides an exemplary encoding scheme of such conditions. According to this scheme, a class value is assigned to each of these conditions. In the rightmost column, Table 1 shows interpretation information for each of these class values. This interpretation information shows how devices of these classes may be considered as PNC candidates during PNC handover procedures. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Residual energy level coding. 
               
             
          
           
               
                 Class 
                 Status 
                 Interpretation 
               
               
                   
               
               
                 3 
                 fixed power supply 
                 PNC role always possible 
               
               
                 2 
                 battery almost full 
                 PNC role now possible 
               
               
                 1 
                 battery half 
                 PNC role not desirable 
               
               
                 0 
                 battery almost empty 
                 PNC role not possible 
               
               
                   
               
             
          
         
       
     
     According to the classes and interpretations of Table 1, a device announces that it can always perform the coordinator (e.g., PNC) role when it is connected to a fixed power supply; that it can currently perform the coordinator role when the residual energy almost full; that it still may perform the coordinator role when its residual energy is at half battery (but it is preferable to avoid such a role); and that the coordinator role cannot be covered when the residual energy is at battery almost empty. 
     The association of the classes in Table 1 with actual energy reference values may be performed by a device according to a mapping, such as the one provided below in Table 2. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Mapping of actual energy level values to level classes. 
               
             
          
           
               
                 Class 
                 Status 
                 Residual Energy 
               
               
                   
               
               
                 3 
                 fixed power supply 
                 — 
               
               
                 2 
                 battery almost full 
                 &gt;66% 
               
               
                 1 
                 battery half 
                 &lt;66%, and 33% 
               
               
                 0 
                 battery almost empty 
                 &lt;33% 
               
               
                   
               
             
          
         
       
     
     The actual values in Table 2 are provided as an example. Other mappings are within the scope of the present invention. For Instance, class 2 could be mapped to &gt;61%, class 1 could be mapped to 21%-60%, and class 0 could be mapped to 0%-20% (“battery empty”). A lower top percentage associated with class 0 would delay a situation in which no device desires to assume the coordinator role. In further embodiments, reference values may be changed according to factors such as the specific capacity of a device&#39;s battery and/or the expected energy consumption of the device. 
     Moreover, a greater number of class values may be used. In embodiments, this may be implemented through the allocation of a greater number of bits to communicate class values. By increasing the number of class values, a greater degree of energy level uniformity among devices in a network may be achieved. 
     VI. Notification of Residual Energy 
     According to the present invention, a device (DEV) may transmit its residual energy level (encoded, for example, in the manner of Tables 1 and 2) to other devices in the network. Such transmissions may occur, for example, when the device&#39;s residual energy level changes classes, either downwards or upwards.  FIG. 11  is a flowchart of a technique in which a device transmits energy information. This technique may be performed in various network environments, such as the environment of  FIG. 1 . Accordingly, in IEEE 802.15.3 environments, this device may be a DEV. In Bluetooth environments, this device may be a slave device. 
     As shown in  FIG. 11 , in a step  1102 , the device detects a change in its residual energy status. This change may be a change of the device&#39;s energy condition in either an upward direction (i.e., more residual energy) or a downward direction (i.e., less residual energy). However, in embodiments of the present invention, this change may include a downward change in the device&#39;s energy condition and not an upward change. Such energy conditions may be in the form of energy classes, as described above with reference to Table 1. Next, in step  1104 , the device transmits its residual energy level to its coordinator (e.g., its PNC). 
     Various techniques may be employed by devices to communicate residual energy information. In implementations involving IEEE 802.15.3 piconets, PNC and DEV capabilities provided by the current standard may be employed. For example, residual energy information may be communicated using capabilities information elements (IEs) currently provided by IEEE 802.15.3. For example, the PNC Des-mode and PSRC bits currently provided by IEEE 802.15.3 may be employed to convey residual energy information. 
     According to the current IEEE 802.15.3 standard, the PSRC bit is set to one if the DEV is receiving power from an alternating current source. Otherwise, the PSRC bit is set to zero. The PNC Des-Mode bit is set to one when the device desires to be the PNC. Otherwise, the PNC DesMode bit is set to zero. 
     According to embodiments of the present invention, an exemplary modification to the usage of the PSRC and PNC Des-Mode bits is provided below in Table 3. In this modification, classes 1 and 2 are merged into a single class, thus providing a reduced resolution. These classes may be associated with interpretations, as shown in Table 1. In this case, the merged class is interpreted as class 2 in Table 1. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Energy levels coded using existing 
               
               
                 bits in PNC and DEV Capabilities. 
               
             
          
           
               
                 Class 
                 Status 
                 PSRC 
                 PNC-DES 
               
               
                   
               
               
                 3 
                 fixed power supply 
                 1 
                 1 
               
               
                 2 
                 battery almost full 
                 0 
                 1 
               
               
                 1 
                 battery half 
                 0 
                 1 
               
               
                 0 
                 battery almost empty 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     Currently, IEEE 802.15.3 provides for exchange of PNC and DEV capabilities when devices associate. For moments throughout device association periods, the present invention provides further techniques for exchanging residual energy information between devices. This advantageously allows for changes in battery energy levels to be communicated. 
     One such technique involves PNC information requests. IEEE 802.15.3 currently provides for PNC information requests, which are transmitted by a PNC. PNC information requests may be sent to a specific DEV (setting DEVID) or to all DEVs (setting BcstID). PNC information requests may be transmitted in response to requests or unsolicited. According to the present invention, PNCs may transmit residual energy level information (e.g., the class codes of Table 1) in PNC information requests. These PNC information requests may be unsolicited. 
     A further technique involves PNC probe requests. IEEE 802.15.3 provides for PNC probe requests, which may be sent to a specific DEV. Moreover, PNC probe requests may also be sent from DEV to DEV. According to the present invention, PNC probe requests may be used to transmit residual energy level information (e.g., the class codes of Table 1). 
     An additional technique for exchanging residual energy information (e.g., the class codes of Table 1) involves PNC handover commands. In embodiments of the present invention, such residual energy information may be included by enhanced devices in response to a PNC handover command. 
     IEEE 802.15.3 currently provides for a PNC to transmit a PNC handover command to an elected DEV. As a response to this command, the elected DEV may refuse by responding with a result code. The present invention provides for residual energy-based PNC handover operations to be performed in networks having both devices that operate according to the current IEEE 802.15.3 standard, and devices that provide for enhanced energy-based processing capabilities, as described herein. Alternatively, these energy-based operations may be performed in networks having only devices that provide for enhanced energy-based processing capabilities. An example of such an operation is shown in  FIG. 12 . 
       FIG. 12  is a flowchart of a technique in which PNC handover commands are used to convey energy information. This technique may be performed in various network environments, such as the environment of  FIG. 1 . As shown in  FIG. 12 , this technique includes a step  1201 . In this step, one or more triggering events occur. These triggering event(s) may include the energy condition of the current network coordinator changing downward. For example, the PNC&#39;s energy class, as described above with reference to Table 1, may change to a class denoting a lower residual energy level. Such a triggering event allows for fair battery consumption among devices in the network. 
     In embodiments of the present invention, such triggering events may based on various events or factors, which may include the following:
         (1) A new device seeks entry or is added to the wireless network (e.g., such as a new device with improved power source status);   (2) A device or the coordinator seeks to leave or leaves the wireless network (e.g., the available power of the coordinator is less than a predetermined threshold or the coordinator is moving out of range);   (3) The device parameters of one or more of the devices in the wireless network changes (e.g., a device becomes coupled to a fixed power supply);   (4) A triggering event occurs at the coordinator (e.g., user defined thresholds, such as power thresholds or other factors or circumstances, are met);   (5) Another device challenges the coordinator for the coordinator position; and   (6) User of the coordinator device initiates the procedure.       

     A step  1202  follows step  1201 . In this step, initial PNC handover commands (referred to herein as pseudo PNC handover commands) are issued to all DEVs that are eligible to take on the PNC role. These pseudo PNC handover commands are transmitted one after the other, for example, in order of the priority table defined by IEEE 802.15.3. 
     In a step  1204 , DEVs which do not possess enhanced energy-based processing capabilities respond according to the current version of IEEE 802.15.3. 
     In a step  1206 , all DEVs operated by a fixed power supply (e.g., AC power) respond according to the current standard. That is, these DEVs may respond to the pseudo handover command by accepting the role of PNC. 
     In a step  1208 , all battery operated DEVs having enhanced energy-based processing capabilities refuse the pseudo PNC handover command. This comprises sending an enhanced response to the PNC. The enhanced response includes a special result code, in which the residual energy status information (e.g., a class code of Table 1) is embedded. These “enhanced” responses are chosen so that no erroneous behavior is induced in “plain standard” DEVs. 
     In a step  1209 , the PNC determines whether the PNC role has been accepted. If there has been no acceptance, then all DEVs in the network have refused the pseudo PNC handover command. When there has been no acceptance of the PNC role, operation proceeds to a step  1210 . In this step, the “enhanced responses” are collected and ranked by the current PNC, which has enhanced energy-based processing capabilities. 
     In a step  1212  an elected PNC is determined. This determination is based on the ranking performed in step  1210 . Accordingly, this ranking and determination may employ a priority list, such as the priority lists of  FIGS. 7 and 8 . In the case of  FIG. 8 , the power source status indicator (PSSI) information is provided by the responses received in step  1208 . 
     In a step  1214 , in which the current PNC issues a PNC handover command (referred to herein as a true PNC handover command to the elected DEV, which has enhanced energy-based processing capabilities. 
     In a step  1216 , after receiving the true PNC handover command, the elected DEV accepts the PNC role. A step  1218  follows step  1216 . In this step, the PNC relinquishes control of the network to the elected coordinator. 
     In order for pseudo and true PNC handover commands to be distinguished, the present invention provides a time duration referred to herein as the minimum PNC handover cycle (MinPNCHOCycle) time. This time duration may be established at the PNC and DEVs during device association. Accordingly, a PNC does not issue a pseudo PNC handover command procedure before MinPNCHOCycle is elapsed after the previous pseudo PNC handover command. Accordingly, a true PNC handover command follows a pseudo PNC handover command within a duration less than MinPNCHOCycle. This feature prevents a DEV from mistaking a pseudo PNC handover command for a true PNC handover command. 
       FIG. 13  is a diagram showing an exchange of information between a PNC  1310  and a DEV  1312 , according to the approach of  FIG. 12 . This exchange is shown to occur in a chronological sequence according to a time axis  1301 . This exchange of  FIG. 13  may be performed in various network environments, such as the environment of  FIG. 1 . 
     As shown in  FIG. 13 , PNC  1310  transmits a pseudo PNC handover command  1302 , which is received by DEV  1312 . Next, DEV  1312  sends a refusal  1304  to PNC  1310 . This refusal includes energy level information, such as a residual energy class code from Table 1. 
     Next, PNC  1310  transmits a true PNC handover command  1306 . DEV  1312  receives this command and transmits an acceptance  1308  to PNC  1310 . At this point, DEV  1312  may assume the role of PNC. 
     The techniques described above with reference to  FIGS. 11-13  may be employed in various communications frameworks. These environments include UWB and/or carrier-based implementations of the IEEE 802.15.3 framework, a Bluetooth framework, as well as other communications frameworks. 
     VII. Database 
     According to the techniques described herein, a device may transmit its residual energy level information (encoded, for example, in the manner of Tables 1 and 2) to other devices in the network. For instances, devices may transmit such information to the network coordinator (e.g., PNC or master). Based on this information (as well as other information), coordinator handover operations may be performed. As described above, such handover operations may employ a priority list to determine a future coordinator. 
     Accordingly, a network may maintain a database that stores information, such as residual energy level information for each network device and a priority list that drives coordinator handover decisions. In addition, other information, such as device information specified by the priority list may be stored by the database. 
     This database may be dynamically maintained. For instance, as device related information changes (for example, as residual energy level information changes), the database contents are updated to reflect these changes. Such changes may be made in response to updated information transmitted by network devices, for example, as described above with reference to  FIG. 11 . 
     In embodiments, the database is maintained only at the coordinator. However, in further embodiments, the database is maintained as a “common knowledge” by all of the devices in the network. This may be implemented as a distributed database maintained by each device, or a server device. When the database is maintained only at the coordinator, the coordinator passes (e.g., transfers) the information to the new coordinator upon completion of a coordinator handover. 
       FIG. 14  is a diagram illustrating the environment of  FIG. 1  in which coordinator  102  includes a handover information database  1402 . Database  1402  includes information described above, such as such as residual energy level information, a priority list, and device information specified by the priority list. 
     Accordingly, such database implementations may be employed in the techniques described herein with reference to  FIGS. 9-12 , and  15 . 
     Upon selection of a new coordinator device, database  1402  (or its contents) is transferred to the newly selected coordinator device. As an example,  FIG. 14  illustrates a transfer operation  1404  in which database  1402  is passed to a particular device  104 . 
     Accordingly, a coordinator may perform various steps, which are shown in  FIG. 15 . In a step  1502 , the coordinator may maintain a handover information database that stores at least residual energy status information (e.g., class codes) for each device in the network. This database may also store other device parameters, as well as a priority list. In a step  1504 , the coordinator may receive updated residual energy status information from the devices in the network. Based on this received information, the database is dynamically updated in step  1506 . 
     Moreover, in a step  1508 , the coordinator may select one of the remote devices as a best candidate for coordinating future communications in the network. This selection may be based on at least the residual energy status information stored in the database. In embodiments, this selection may include the techniques described above with reference to  FIG. 12 . Upon selection, the coordinator may transfer the database to the selected device in a step  1510 . 
     VIII. Conclusion 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not in limitation. For instance, although examples have been described involving Bluetooth and UWB and WPAN technologies, other short-range and longer range communications technologies and wireless networks, such as Wireless Local Area Network (WLAN), are within the scope of the present invention. 
     Accordingly, it will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.