Patent Publication Number: US-9414311-B2

Title: Systems and methods for power savings in wireless communications

Description:
FIELD OF THE PRESENT INVENTION 
     The present disclosure generally relates to wireless communications and more particularly relates to systems and methods for coordinating power saving modes between networks nodes. 
     BACKGROUND OF THE INVENTION 
     Wireless networks are increasingly employed to provide various communication functions including voice, video, packet data, messaging and the like, such as through use of wireless local area networks (WLANs) conforming to 802.11 standards established by The Institute of Electrical and Electronics Engineers. WLANs are often configured in an infrastructure network topology in which an access point (AP) coordinates communications for a number of associated stations (STAs) as well as providing management and control functions. However, another important network topology involves two or more STAs, or peers, that directly exchange information without the use of an AP as an intermediary. Such ad hoc networks rely on a peer to peer relationship between the stations. While peer to peer communications systems may provide greater convenience by avoiding the need for an AP, accommodations may be required to provide functionality that would otherwise be performed by a centralized control device. 
     Since many devices used in wireless communications systems are mobile, enhanced power management techniques are desirable to extend battery life. To this end, considerably effort has been expended in infrastructure networks to develop power saving techniques, many of which involve increasing the amount of time the STAs and AP may spend in low power modes of operation, known as sleep or doze modes. As with other network functions, a STA may coordinate entry and exit from a power save mode with its AP. In one power management strategy, a STA may asynchronously signal that it is entering a power save mode through the use of a power management message contained in a packet sent to the AP. Upon receipt of a power management message indicating the STA is in power save mode, the AP may buffer packets to be sent to the STA. The AP periodically transmits beacons with a traffic indication message (TIM) that may be used to indicate that data is ready to be transmitted to the STA. The period of time between beacon transmissions may be termed the beacon interval. The STA generally utilizes a period of time called the listen interval, corresponding to a plurality of beacon intervals, to coordinate its power save with the AP. The AP buffers data for the STA during the listen interval and the STA may awaken from power save mode to receive the beacon at the end of each listen interval. If the beacon indicates data is pending, the STA will initiate transfer of that data. Conversely, if no data is ready to be transmitted, the STA may return to power save mode. 
     In contrast, a peer to peer network lacks an AP for coordination of power management and may be unable to utilize the same strategies. For example, the high speed extensions in the BLUETOOTH® (Bluetooth) 3.0 specification enable two devices having WLAN radios communicating over a Bluetooth link to establish a Bluetooth Alternate MAC/PHY (AMP) link by using the WLAN radios in a peer to peer relationship. Implementation of the Bluetooth AMP link involves operation of the WLAN radios of both devices in an AP-like mode, including the continuous, periodic transmission of beacon frames while the AMP link is active. As a consequence, conventional power saving mechanisms for WLAN devices involving a device entering a power save mode for a period of time, such as the use of a power management message as described above, may not be employed while maintaining the AMP link. Further, since the beacon transmissions occur regardless of data transfer, this requirement may represent inefficient power consumption. For example, when network conditions result in periods when traffic is not being exchanged, such as when there is a delay in streaming from the backhaul and no data is being transferred over the AMP link, this power expenditure provides no benefit. 
     Other peer to peer communications systems, such as the WiFi Direct™ (WiFi Direct) protocol, may exhibit similar inefficiencies when the need to periodically transmit beacons interferes with the ability of a device to utilize power management strategies. Further, within the context of this disclosure, other network topologies may be considered to have analogous aspects to these peer to peer examples and similarly benefit from enhanced coordination of power save modes between network nodes. For example, a device may be configured to operate in a software-enabled access point mode to provide access point-like functionality. Such implementations are known as “softAPs.” 
     Accordingly, there is a need for coordinating power management between peers in a wireless communication system. The techniques of this disclosure satisfy this and other needs. 
     SUMMARY OF THE INVENTION 
     This disclosure is directed to systems and methods for coordinating power saving modes between networks nodes. In one aspect, the systems include a device for wireless communication with a wireless local area network (WLAN) module configured to implement a WLAN communications link, wherein maintaining the communications link includes periodically transmitting a beacon frame containing a power save information element with the WLAN module and a peer power save module configured to include in the power save information element of the beacon frame information indicating the WLAN module will enter a power save mode. The peer power save module may be further configured to include the information indicating the WLAN module will enter a power save mode in the power save information element after the communications link has been inactive for a predefined period of time. Further, the power save information element may include a count value such that the peer power save module is further configured to decrement the count value from an initial value with each beacon transmission after the communications link has been inactive for the predefined period of time. In such embodiments, the peer power save module may be configured to transition the WLAN module to a power save mode when the count value reaches zero. Additionally, the power save information element may include a duration value such that the WLAN module is configured to remain in the power save mode for a period of time corresponding to the duration value. 
     As desired, the peer power save module may also be configured to track a number of times the WLAN module has entered the power save mode while the communications link has been inactive and to disable the communications link when the number exceeds a threshold. In addition, the device may be further configured to maintain an alternate communications link to allow the disabled communications link to be re-enabled. 
     In some embodiments, the communications link is a Bluetooth Alternate MAC/PHY (AMP) link. In another embodiment, the device may be configured to function as a softAP. 
     In another aspect, the systems may include a device for wireless communication having a wireless local area network (WLAN) module configured to implement a WLAN communications link, wherein maintaining the communications link includes periodically receiving a beacon frame sent by a peer device containing a power save information element with the WLAN module and a peer power save module configured to transition the WLAN module to a power save mode after receiving a beacon frame wherein the power save information element includes information the peer device will enter a power save mode. The power save information element may also include a count value such that the peer power save module may be configured to transition the WLAN module to a power save mode when the count value is zero and the power save information element includes information the peer device will enter a power save mode. Further, the power save information element may also include a duration value such that the WLAN module is configured to remain in the power save mode for a period of time corresponding to the duration value. 
     In yet another aspect, the methods of the disclosure may include the steps of implementing a wireless local area network (WLAN) communications link with a WLAN module, periodically transmitting a beacon frame containing a power save information element including information indicating the WLAN module is in active mode, and transmitting a beacon frame containing a power save information element including information indicating the WLAN module will enter a power save mode. Further, transmitting the beacon frame containing the power save information element including information indicating the WLAN module will enter a power save mode may occur after the communications link has been inactive for a predefined period of time. As desired, the methods may also include transmitting a series of beacon frames having a power save information element with a count value that decrements from an initial value with each transmission after the communications link has been inactive for the predefined period of time. In addition, the WLAN module may be placed in a power save mode when the count value reaches zero. In some embodiments, the power save information element may also include a duration value, such that the methods may include maintaining the WLAN module in the power save mode for a period of time corresponding to the duration value. 
     The noted methods may further include the steps of tracking a number of times the WLAN module has entered the power save mode while the communications link has been inactive and disabling the communications link when the number exceeds a threshold. Further, the methods may include maintaining an alternate communications link to allow the disabled communications link to be re-enabled. 
     In another aspect, the methods of the disclosure may include the steps of implementing a wireless local area network (WLAN) communications link with a WLAN module, receiving a beacon frame sent by a peer device containing a power save information element including information indicating the peer device will enter a power save mode, and placing the WLAN module in a power save mode after receiving the beacon frame. Further, the power save information element may also include a count value, such that the methods may include placing the WLAN module in a power save mode when the count value is zero and the power save information element includes information the peer device will enter a power save mode. As desired, the methods may also include sending a message to other associated devices indicating a transition to the power save mode. Still further, the power save information element may also include a duration value, such that the methods include the step of maintaining the WLAN module in the power save mode for a period of time corresponding to the duration value. 
     A further aspect of the disclosure is directed to a non-transitory processor-readable storage medium for coordinating a power save mode of a wireless local area network (WLAN) module implementing a WLAN communications link; the processor readable storage medium having instructions thereon, the instructions including code for causing periodic transmission of a beacon frame containing a power save information element including information indicating the WLAN module is in active mode and code for causing transmission of a beacon frame containing a power save information element including information indicating the WLAN module will enter a power save mode. 
     In addition, the storage medium may also include code for causing transmission of the beacon frame containing the power save information element including information indicating the WLAN module will enter a power save mode after the communications link has been inactive for a predefined period of time. 
     As desired, the storage medium may include code for causing the transmission of a series of beacon frames having a power save information element with a count value which decrements from an initial value with each transmission after the communications link has been inactive for the predefined period of time. Further, the storage medium may include code for causing the WLAN module to enter a power save mode when the count value reaches zero. When the power save information element also includes a duration value, the storage medium may include code for maintaining the WLAN module in the power save mode for a period of time corresponding to the duration value. 
     Further, the storage medium may include code for tracking a number of times the WLAN module has entered the power save mode while the communications link has been inactive and code for disabling the communications link when the number exceeds a threshold. In addition, the storage medium may also include code for maintaining an alternate communications link to allow the disabled communications link to be re-enabled. 
     An additional aspect of the disclosure is directed to a non-transitory processor-readable storage medium for coordinating a power save mode of a wireless local area network (WLAN) module implementing a WLAN communications link; the processor readable storage medium having instructions thereon, the instructions including code for causing reception of a beacon frame containing a power save information element including information indicating the WLAN module is in active mode and code for causing the WLAN module to enter a power save mode after receiving the beacon frame. Additionally, the power save information element may also include a count value, such that the storage medium may also include code for placing the WLAN module in a power save mode when the count value is zero and the power save information element includes information the peer device will enter a power save mode. As desired, the storage medium may also include code for sending a message to other associated devices indicating a transition to the power save mode. Further, when the power save information element includes a duration value, the storage medium may also include code for maintaining the WLAN module in the power save mode for a period of time corresponding to the duration value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages will become apparent from the following and more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawing, and in which like referenced characters generally refer to the same parts or elements throughout the views, and in which: 
         FIG. 1  depicts a peer to peer wireless communication system, according to an embodiment of the invention; 
         FIG. 2  is a schematic representation of the format of a beacon frame that may be used to coordinate a power save mode between peers, according to an embodiment of the invention; 
         FIG. 3  depicts a flowchart showing a routine for sending beacon frames to coordinate a power save mode between peers, according to an embodiment of the invention; 
         FIG. 4  depicts a flowchart showing a routine for receiving beacon frames to coordinate a power save mode between peers, according to an embodiment of the invention; 
         FIG. 5  schematically depicts functional blocks of a peer communications device, according to an embodiment of the invention; 
         FIG. 6  represents portions of a Bluetooth stack incorporating an AMP link; and 
         FIG. 7  depicts a sequence diagram showing the use of beacon frames to coordinate a power save mode between peers, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At the outset, it is to be understood that this disclosure is not limited to particularly exemplified materials, architectures, routines, methods or structures as such may, of course, vary. Thus, although a number of such options, similar or equivalent to those described herein, can be used in the practice or embodiments of this disclosure, the preferred materials and methods are described herein. 
     It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of this disclosure only and is not intended to be limiting. 
     Some portions of the detailed descriptions which follow are presented in terms of procedures, logic blocks, processing and other symbolic representations of operations on data bits within a computer or processor memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present application, discussions utilizing the terms such as “accessing,” “receiving,” “sending,” “using,” “selecting,” “determining,” “normalizing,” “multiplying,” “averaging,” “monitoring,” “comparing,” “applying,” “updating,” “measuring,” “deriving” or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     Embodiments described herein may be discussed in the general context of processor-executable instructions residing on some form of processor-readable medium, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or distributed as desired in various embodiments. 
     In the figures, a single block may be described as performing a function or functions; however, in actual practice, the function or functions performed by that block may be performed in a single component or across multiple components, and/or may be performed using hardware, using software, or using a combination of hardware and software. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. Also, the exemplary wireless communications devices may include components other than those shown, including well-known components such as a processor, memory and the like. 
     The techniques described herein may be implemented in hardware, software, firmware, or any combination thereof, unless specifically described as being implemented in a specific manner. Any features described as modules or components may also be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. If implemented in software, the techniques may be realized at least in part by a non-transitory processor-readable storage medium comprising instructions that, when executed, performs one or more of the methods described above. The non-transitory processor-readable data storage medium may form part of a computer program product, which may include packaging materials. 
     The non-transitory processor-readable storage medium may comprise random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, other known storage media, and the like. The techniques additionally, or alternatively, may be realized at least in part by a processor-readable communication medium that carries or communicates code in the form of instructions or data structures and that can be accessed, read, and/or executed by a computer or other processor. 
     The various illustrative logical blocks, modules, circuits and instructions described in connection with the embodiments disclosed herein may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), application specific instruction set processors (ASIPs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. The term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured as described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     For purposes of convenience and clarity only, directional terms, such as top, bottom, left, right, up, down, over, above, below, beneath, rear, back, and front, may be used with respect to the accompanying drawings or particular embodiments. These and similar directional terms should not be construed to limit the scope of the invention in any manner and may change depending upon context. Further, sequential terms such as first and second may be used to distinguish similar elements, but may be used in other orders or may change also depending upon context. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the disclosure pertains. 
     Further, all publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety. 
     Finally, as used in this specification and the appended claims, the singular forms “a, “an” and “the” include plural referents unless the content clearly dictates otherwise. 
     As will be discussed in detail below, this disclosure is directed to systems and methods for implementing power save modes of operation while maintaining a WLAN communications link. The techniques of the invention involve coordinating power save mode periods between the participating devices through the use of a Peer Power Save Information Element (PPS IE) included in the beacon frame transmitted by one of the devices. The PPS IE may include an Enable bit, a PPS Count value and a PPS Duration. The PPS Count may be decremented from an initial value after each beacon transmission until the count reaches zero, at which point the device may be configured to enter power save mode for the period indicated by the PPS Duration. Upon entry to the power save mode, portions of the WLAN system may operate in a low power mode, such as a sleep or doze state. The device may track the duration of time spent in the power save mode and awaken after the corresponding period of time to begin transmitting and receiving beacons again. 
     These systems and methods are described in reference to an exemplary wireless communication system  100  as shown in  FIG. 1 , which fundamentally includes at least two nodes, peer  102  and peer  104 . In this embodiment, peer  102  and peer  104  each have Bluetooth (BT) modules  106  and  108 , respectively, and WLAN modules  110  and  112 , respectively. The Bluetooth specification allows for the creation of a personal area network (PAN) between a master and up to seven slaves and is often used to connect and exchange information between mobile phones, computers, digital cameras, wireless headsets, speakers, keyboards, mice or other input peripherals, and similar devices. Conventional Bluetooth communications employ a dedicated physical layer as indicated by Bluetooth modules  106  and  108  using a frequency-hopping spread spectrum technique. The data transfer rate of a Bluetooth 2.0 system employing an enhanced data rate (EDR) is up to 3 Mbps. To achieve higher throughput, a peer to peer AMP link as defined by Bluetooth 3.0 may employ the physical layer of collocated WLAN modules  110  and  112  to achieve a rate of up to 24 Mbps. In other embodiments, WLAN module  110  of peer  102  and WLAN module  112  of peer  104  may communicate using another suitable peer to peer protocol, such as WiFi Direct. For example, peer  102  may function in the role of a WiFi Direct Peer to Peer (P2P) Group Owner (GO) and peer  104  may function in the role of a WiFi Direct P2P Client. 
     Operation of peer  102  in the network connection with peer  104  includes the periodic transmission of a management frame known as a beacon. Although discussed in the context of peer  102 , it will be appreciated that peer  104  may also transmit a beacon frame, such as when the peer to peer connection is an AMP link or in other network topologies. As such, these techniques may also be extended to peer  104  as applicable. Further, these techniques may also be applied to other network architectures having analogous aspects. In one example, a device configured to function as a softAP may be considered to operate in a manner similar to the other peer to peer architectures disclosed herein, since this configuration involves direct communication between the softAP and an associated device. As such, peer  102  may also be a device acting in a softAP role while peer  104  may be a station associated with the softAP. To the extent that IEEE 802.11 protocols may dictate certain operational characteristics for a device acting in a softAP role that conflict with aspects of this disclosure, such as a requirement for the continuous transmission of periodic beacons, a softAP functioning as peer  102  may constitute a proprietary solution. 
     The beacon frame is used to communicate parameters regarding operation of the peer to peer communication, including identification information, supported rates, timing information and the like. The time interval between the start of two consecutive beacons is called a beacon interval and may be used to establish a target beacon transmit time (TBTT). The beacon interval may be fixed or variable and may be set to a suitable duration, e.g., 100 msec. 
     An example of a generalized beacon frame  200  having a format corresponding to IEEE 802.11 standards is depicted in  FIG. 2 . As shown, frame  200  includes a MAC header  202 , containing the frame control  204 , duration/ID, address and sequence control fields, a variable length frame body  206  that may include required fields as well as optional vendor-oriented information elements, and cyclic redundancy check (CRC) field  208  that provides a frame check sequence (FCS) function. The frame control  204  segment of MAC header  202  includes fields providing various types of control information, including an identification of the 802.11 protocol of the frame, the type and subtype of the frame, distribution system information, information regarding additional information to be transmitted, security and order information.  FIG. 2  also shows that frame body  206  preferably contains Peer Power Save (PPS) information element (IE)  210 . As will be described below, the fields of PSS IE  210  may be used by peer  102  to communicate information to peer  104  to coordinate entry and exit from a power save mode. As will be appreciated, frame body  206  may include a plurality of proprietary information elements that may be vendor-defined, any of which may be employed as PPS IE  210 . Alternatively, a new PPS IE  210  may be defined and incorporated into the relevant 802.11 protocol. 
     In one aspect, the PPS IE may include information in the form of an “Enabled” field of one bit to indicate whether peer  102  will enter a power save mode. Accordingly, the PPS IE Enabled field may have a value of ‘0’ to indicate that peer  102  is in active mode and may have a value of ‘1’ to indicate that peer  102  will enter a power save mode. In another aspect, the PPS IE may include a “Count” field having an integer variable. As will be described below, the Count field is a counter that decrements from a given initial number with each beacon transmission, such that peer  102  may enter a power save mode after the Count field reaches 0. The Count field may have any suitable initial value configured to provide the appropriate performance in delaying entry of peer  102  to a power save mode. In one example, the initial value of the Count field may be 5. In yet another aspect, the PPS IE may also include a “Duration” field to communicate the duration for which peer  102  will be in a power save mode. In some embodiments, the Duration field may be an integer representing a given number of beacon intervals. Setting the Duration field to 0 may be used to prevent peer  102  from entering a power save mode, regardless of the other parameters. 
     To provide proper coordination of power save modes between peers, it is desirable for all devices participating in the network to be configured to process the information associated with the PPS IE. The capabilities of each device may be confirmed by parsing any beacon frames sent by other devices that are received by peer  102 , such as those sent by peer  104 , to determine the presence of PPS IE  210 . Provided that all beacons sent by participating devices contain a PPS IE, peer  102  may enter and exit a power save mode as indicated by the PPS IE  210  in its beacon transmissions without disrupting operation of the network as the other devices will have proper notification of the change in state. On the other hand, if any participating device transmits a beacon frame without a PPS IE, this may be taken as an indication that the device lacks the functionality and peer  102  may operate in a compatibility mode in which peer  102  does not enter a power save mode. 
     A suitable routine for sending a beacon with a PPS IE to coordinate entry and exit from a power save mode that may be used in the systems and methods of this disclosure is depicted in the flowchart shown in  FIG. 3 . The routine starts with the establishment of a communications link between the physical layers of the respective WLAN modules, such as an AMP link between WLAN module  110  of peer  102  and WLAN module  112  of peer  104  as indicated by step  302 . Next, peer  102  transmits a default beacon with PPS IE  210  having the Enable field set to ‘0’ to indicate peer  102  is operating in active mode in step  304 . The PPS Count field also may be set to the initial value. As will be appreciated, peer  102  may initiate a transition to a power save state when the communications link with peer  104  exhibits a threshold level of inactivity, such as over a predefined period of time. As represented by step  306 , peer  102  may determine whether a period without activity over the communications link exceeds a predefined inactive time, t 1 , which may be set to any suitable value that provides a desired balance between performance and power efficiency. If activity has occurred, peer  102  may transmit another default beacon as indicated by the return of the routine to step  304 . On the other hand, if the threshold time has elapsed, peer  102  may then decrement the PPS IE Count field by one in step  308 . Next, peer  102  may set the PPS IE Enable field to ‘1’ and send a beacon frame in step  310 . Then, peer  102  may confirm whether the communications link is still inactive as indicated by step  312 . If the link has experienced activity, the routine returns to step  304  to reset the PPS IE Count field and set the Enable bit to ‘0.’ If the link is still inactive, the routine continues to step  314  and peer  102  checks the Count field of the PPS IE to determine if the counter has elapsed. If the value is greater than or equal to one, the routine returns to step  308  to send another beacon frame. If the value equals zero, however, peer  102  may enter a power save mode as indicated by step  316 , wherein WLAN module  110  may operate in a low power or inactive mode, which includes a cessation of beacon transmission. Finally, peer  102  may remain in power save mode until a period of time corresponding to the Duration field of PPS IE has elapsed. As indicated by step  318 , the routine returns to step  316  until the Duration has elapsed, at which point peer  102  reactivates and returns to step  304  to reset the PPS IE Count field and set the Enable bit to ‘0’. 
     It may be desirable to employ a Count value that corresponds to the operating context of peer  102 . For example, if Bluetooth module  106  of peer  102  is acting in the role of a master with respect to a plurality of associated slave devices, it may be desirable to set the initial Count value to a number sufficient to allow indication of the upcoming transition to a power save mode to be communicated to all the associated devices, such as the exemplary value of 5 as given above. In other contexts, the Count value may be set to a lower number if peer  102  is in communication with only one or a few other devices. 
     Similarly, a suitable routine for receiving a beacon with a PPS IE to coordinate entry and exit from a power save mode that may be used in the systems and methods of this disclosure is depicted in the flowchart shown in  FIG. 4 . The routine starts with the establishment of a WLAN communications link between peer  102  and  104  as indicated by step  402 . Next, peer  104  receives a beacon with a PPS IE  210  transmitted by peer  102  as indicated by step  404 . Peer  104  checks the values of the Enable and Count fields of PPS IE in step  406 . If the Enable bit is not set to ‘1’ or the Count value is not set to ‘0,’ peer  104  may operate normally and return to step  404  to await reception of another beacon. However, if both the Enable bit is set to ‘1’ and the Count value is set to ‘0,’ peer  104  may determine that peer  102  will be entering a power save mode for the time period advertised by the Duration value. Correspondingly, peer  104  may also enter a power save mode as indicated by step  408 , wherein WLAN module  112  operates in a low power state. Peer  104  may remain in power save mode until a period of time corresponding to the Duration field of PPS IE has elapsed. As indicated by step  410 , the routine returns to step  408  until the Duration has elapsed, at which point peer  104  may return to active mode and the routine may return to step  404  to await reception of another beacon or other transmission from peer  102 . 
     Under some situations, peer  104  may be associated with other devices, such as by employing Bluetooth module  108  to form Bluetooth communications link by acting in the role of a Bluetooth master with respect to additional Bluetooth slave devices. In such embodiments, peer  104  may be configured to send messages to the associated devices indicating the transition to the power save mode. For example, peer  104  may send a PPS IE to these other associated devices. By employing these techniques, peer  104  as well as peer  102  may obtain the power savings benefits. 
     In some embodiments, it may be desirable for the device initiating the power save coordination, such as peer  102 , to track the number of times the power save mode is entered without experiencing activity over the communications link. A threshold number of iterations may be established such that when exceeded, peer  102  may be configured to disable the communications link. Peer  102  may be further configured to maintain an alternate communications link with peer  104  when the communications link is disabled, such as a Bluetooth link between respective Bluetooth modules  106  and  108 . By maintaining the alternate communications link, the disabled communications link may be easily reestablished when conditions warrant, such as when sufficient data has been buffered for transmission at peer  102  or peer  104  that may be sent using a higher rate provided by the restored communications link. 
     As discussed above, embodiments of this disclosure are suitable for use in a Bluetooth communication system featuring AMP link capability. Accordingly,  FIG. 5  is a high level schematic diagram of the principle functional blocks of peer  102 . Generally, peer  102  may employ an architecture in which the lower levels of the respective protocol stacks of Bluetooth module  106  and WLAN module  110  are implemented in firmware and hardware modules, including Bluetooth module  106  and WLAN module  110 . Bluetooth module  106  includes Link Manager Protocol (LMP)  502  for managing the Bluetooth radio frequency link between peer  102  and peer  104  by performing advertisement, scanning, connection and security functions. Bluetooth module  106  also includes Link Controller (LC)  504  for performing the hardware-specific transmission and reception of electronic signals. Likewise, WLAN module  110  includes media access controller (MAC)  506  that performs functions related to the handling and processing of frames of data including verification, acknowledgment, routing, formatting and the like. Incoming and outgoing frames are exchanged between MAC  506  and physical layer (PHY)  508 , which as shown here includes the functions of modulating the frames according to the relevant 802.11 protocol as well as providing the analog processing and RF conversion necessary to provide transmission and reception of wireless signals. In embodiments implementing a Bluetooth AMP link, information from upper layers of the Bluetooth protocol stack are directly exchanged with MAC  506  and PHY  508  of WLAN module  110 . 
     As shown, Bluetooth module  106  and WLAN module  110  each have an associated antenna, antennas  510  and  512 , respectively. As desired, one or more antennas may be shared between the modules using switching techniques known in the art. In some embodiments, Bluetooth module  106  and WLAN module  110  may be collocated on a common system, e.g., on the same circuit board or on distinct circuit boards within the same system, or may be embedded on the same integrated circuit as in a system on a chip (SoC) implementation. 
     Peer  102  also includes host CPU  516  configured to perform the various computations and operations involved with the functioning of peer  102 . Host CPU  516  is coupled to Bluetooth module  106  and WLAN module  110  through bus  518 , which may be implemented as a peripheral component interconnect express (PCIe) bus, a universal serial bus (USB), a universal asynchronous receiver/transmitter (UART) serial bus, a suitable advanced microcontroller bus architecture (AMBA) interface, a serial digital input output (SDIO) bus, or other equivalent interface. Upper layers of the protocol stacks of the Bluetooth and WLAN systems are generally implemented in software as Drivers  520  stored in memory  522  that may be accessed by host CPU  516  over bus  518 . Details regarding the Bluetooth protocol stack are discussed below in reference to  FIG. 6 . 
     As shown, WLAN module  110  also includes Peer Power Save (PPS) module  524  that may be implemented as processor readable instructions stored in firmware and operable by WLAN module  110  as shown. PPS module  524  may be configured to perform steps associated with the routines depicted in  FIGS. 3 and 4 , for example. In other embodiments, PPS module  524  may be implemented in software or hardware at any suitable location within peer  104 . 
     Turning now to  FIG. 6 , a more detailed representation of Bluetooth protocol stack  600  is shown, particularly with regard to the logical division of the upper Bluetooth protocol layers implemented as software processes operating in host CPU  516  and the use of WLAN lower protocol layers in an AMP link. As shown, Bluetooth protocol stack  600  generally features a host stack operating in host CPU  516  having an application and profile layer  602  and a Bluetooth core  604 . Bluetooth core  604  includes a logical link control and adaptation protocol (L2CAP) layer  606  that provides multiplexing of data from the upper protocol layers and the formatting of packets. The packaged data is exchanged over host controller interface (HCI)  606  with the lower layer protocols, LMP  502  and LC  504  discussed above. Bluetooth core  604  also includes AMP controller  610  for creating and maintaining an AMP link using WLAN module  110 . In particular, AMP controller  610  exchanges packets with protocol adaptation layer (PAL)  612  which in turn provides communication with MAC  506  and PHY  508  of WLAN module  110 . Accordingly, after AMP controller  610  establishes an AMP link between peer  102  and peer  104 , data may be received and sent from the upper layers of Bluetooth stack  600  directly to the lower layers of WLAN module  110 . 
     An example of power save mode coordination in the context of an AMP link involving peer  102  and peer  104  is depicted in  FIG. 7  as a sequence diagram. As shown, creation of the AMP link involves interoperation of WLAN module  110 , in particular MAC  506  and PHY  508 , and PAL  612  on peer  102  and WLAN module  112  and corresponding PAL  702  on peer  104 . Creation of the AMP link involves a request  704  generated by peer  102  and sent by WLAN module  110  that is received by peer  104  at WLAN module  112 . WLAN module  112  returns a response  706  resulting in the formation of AMP link  708 . As described above, peer  102  and peer  104  each periodically transmit beacon frames while the AMP link is active. Beacon group  710  sent by peer  102  includes PPS IE  210  having the Enable bit set to ‘0’ as the inactivity interval represented by t 1  has not elapsed. However, in beacon group  712 , the inactivity interval t 1  has elapsed, so that each beacon frame has a PPS IE  210  with the Enable bit set to ‘1’ and with a Count value that decrements by one. In this example, the initial Count value is 5 so that beacon frame  714  following beacon group  712  has a PPS IE with the Enable bit set to ‘1’ and a Count value of ‘0.’ Conversely, peer  104  may simply transmit the same beacon frame for each beacon in group  716 . Since peer  104  is not coordinating the power save mode in this example, each frame may include a PPS IE with the Enable bit set to ‘0’ to indicate peer  104  is configured to interpret and process the information associated with a PSS IE and may coordinate a power save mode as signaled by peer  102 . 
     Following transmission of beacon frame  714 , WLAN module  110  may enter a power save mode and sends signal  718  to PAL  612  to begin clocking the Duration advertised in the PPS IE, represented by t D . Similarly, upon reception of beacon frame  714  at WLAN module  112 , peer  104  sends signal  720  to PAL  702  to begin clocking the t D  and WLAN module  112  also enters a power save mode. Upon completion of t D , PAL  612  sends signal  722  to WLAN module  110  and PAL  702  sends signal  724  to WLAN module  112  to return the respective WLAN modules to active state. Peer  102  and peer  104  may then resume sending beacon frames as indicated by beacon groups  726  and  728 . 
     Described herein are presently preferred embodiments. However, one skilled in the art that pertains to the present invention will understand that the principles of this disclosure can be extended easily with appropriate modifications to other applications.