WO2015094363A1

WO2015094363A1 - Smart beacon processing

Info

Publication number: WO2015094363A1
Application number: PCT/US2013/077178
Authority: WO
Inventors: Ayelet Alon; Rafi Ben-Tal; Oren Kaidar
Original assignee: Intel IP Corporation
Priority date: 2013-12-20
Filing date: 2013-12-20
Publication date: 2015-06-25

Abstract

Described are methods to reduce the duration spent by a WLAN station device in an active receive mode for the purpose of beacon processing, which may be referred to as smart beacon processing. Such mart beacon processing may be compromised of any or all of the following techniques: optimized preamble processing, early beacon processing, and smart FIFO (first-in-first-out) buffering by the physical layer.

Description

SMART BEACON PROCESSING Technical Field

[0001] Embodiments described herein relate generally to wireless networks and communications systems.

Background

[0002] Beacon processing is a basic task of an 802.11 WLAN (wireless local area network), or WiFi, device as part of connection maintenance. Beacons are management frames sent by the Access Point (AP) every defined interval, referred to as the Beacon Interval. Beacon frames include fields and information elements (IEs) that contain information about the network. Beacon processing refers to the reception and processing of beacon management frames by the associated WiFi station. The processing of beacon frames allows the WiFi station to be updated with the characteristics of the networks it is connected to, and trigger the required changes in the device operation when applicable.

Beacon frames also include indications as to whether directed (unicast) or non- directed (broadcast or multicast) are pending for transmission or about to be transmitted.

[0003] Beacon processing has a major impact on device power consumption. WiFi stations, as part of connection maintenance, must remain active when a beacon frame is expected in order to be able to receive and process the frame. The impact of the duration spent by the station in waiting for, receiving, and processing the beacon frame every beacon interval is extremely significant when the WiFi device is otherwise idle. Due to the limited battery power supply of a mobile device, it would be desirable to minimize the power consumed by the device solely for this activity. Previous methods, in which the WiFi device remains active during the entire interval for beacon frame reception and processing, are not sufficient enough to meet desired power consumption targets. Brief Description of the Drawings

[0004] Fig. 1 illustrates a basic service set that includes a station device associated with an access point.

[0005] Fig. 2 is a diagram illustrating the reduction in a WLAN device's active time when waking up to receive a process beacon frames.

[0006] Fig. 3 illustrates the medium access control layer and physical layer subsystems of a WLAN station device.

[0007] Fig. 4 illustrates an example of procedure performed by an idle station device using early beacon processing.

Detailed Description

[0008] In an 802.1 1 local area network (LAN), the entities that wirelessly communicate are referred to as stations. A basic service set (BSS) refers to a plurality of stations that remain within a certain coverage area and form some sort of association. In one form of association, the stations communicate directly with one another in an ad-hoc network. More typically, however, the stations associate with a central station dedicated to managing the BSS and referred to as an access point (AP). Fig. 1 illustrates a BSS that includes a station device 100 associated with an access point (AP) 110, where the AP 100 may be associated with a number of other stations 120. The device 100 may be any type of device with functionality for connecting to a WiFi network such as a computer, smart phone, or a UE (user equipment) with WLAN access capability, the latter referring to terminals in a LTE (Long Term Evolution) network. The device 100 includes an RF (radio frequency transceiver) 102 and processing circuitry 101. The processing circuitry includes the functionalities for WiFi network access via the RF transceiver as well as functionalities for beacon processing as described herein. The RF transceivers of the station device 100 and access point 110 may each incorporate one or more antennas. The RF transceiver 100 with multiple antennas and processing circuitry 101 may implement one or more MIMO (multi-input multi-output) techniques such as spatial multiplexing, transmit/receive diversity, and beam forming. [0009] In an 802.1 1 WLAN, the stations communicate via a layered protocol where peer layers in each station pass protocol data units (PDUs) between each other that are encapsulated service data units (SDUs) of the next higher layer. The IEEE 802.11 standard defines multiple physical layers (PHYs) and a common medium access control (MAC) layer for wireless local area networking. The MAC layer is a set of rules that determine how to access the medium in order to send and receive data. The MAC layer provides, among other things, addressing and channel access control that makes it possible for multiple stations on a network to communicate. The details of transmission and reception are left to the PHY layer. The PHY layer may be regarded as further split into two parts: the Physical Layer Convergence Procedure (PLCP), to map MAC frames onto the medium, and a Physical Medium Dependent (PMD) system to actually transmit the frames.

[0010] The MAC and PHY layers as implemented by the processing circuitry of a station may be regarded as separate MAC and PHY subsystems. In certain of the embodiments described below, one or both of the MAC and PHY subsystems may be operated in either an active or sleep state, the latter being a power saving idle state. In one embodiment, the MAC subsystem includes a power management module for transitioning both the radio transceiver and the PHY subsystem between active and sleep states. In another embodiment, the PHY subsystem includes a power management module for transitioning the MAC subsystem between active and sleep states.

[0011] Transmissions in an 802.11 network are in the form of frames of which there are three main types: data frames, control frames, and management frames. Data frames carry data from station to station. Control frames are used in conjunction with data frames deliver data reliably from station to station. Management frames are used by the AP to perform supervisory functions. One type of management frame is the beacon frame. Beacon frames are transmitted periodically by the AP at defined beacon intervals. Beacon frames contain information about the network and also indicate whether the AP has buffered data which is addressed to a particular station or stations, indicated by a traffic indication map (TIM). Certain beacon frames may also contain a delivery traffic indication map (DTIM) which indicates that group addressed traffic will be delivered in a subsequent frame. Stations that are associated with an AP and are otherwise idle must thus be in an active state to receive and process the beacon frames at the defined beacon intervals.

[0012] Described herein are methods to reduce the duration spent by a station device in an active receive (RX) mode for the purpose of beacon processing, which may be referred to as smart beacon processing. Such mart beacon processing may be compromised of any or all of the following techniques:

optimized PLCP preamble processing, early beacon processing, and smart FIFO (first-in- first-out) buffering by the PHY layer. Optimized PLCP preamble processing is applicable when the WLAN operates in 802.11(b) mode where frames are transmitted with a long PLCP preamble for synchronization purposes. The optimized PLCP preamble processing allows the physical layer to be synchronized with a short synchronization time that starts after the beginning of the PLCP preamble, thus allowing the WiFi device to start reception of beacons later. Early beacon processing refers to allowing the MAC layer to process the beacon fields and IEs during its arrival without waiting for the transmission of the beacon frame to successfully complete. This technique allows the MAC layer to decide whether beacon frame reception can be aborted so that the receiver (i.e, PHY subsystem and RF transceiver) can be turned off after a partial processing of the frame without waiting for frame completion. The partial processing of the beacon includes the beacon's fields and IEs up to the Traffic indication map (TIM) field to insure delivery of directed or non-directed frames. Smart FIFO buffering between the PHY and MAC subsystems refers to allowing the MAC subsystem to remain idle, while the PHY subsystem receives the beacon, until a partial frame is available for processing. Each technique may be used alone, or a combination of some or all of the techniques may be utilized in conjunction with each other.

[0013] Fig. 2 is a diagram that shows how smart beacon processing may reduce a WLAN device's active time when waking up to receive a process beacon frames. An example beacon frame 210 is shown as beginning with a PLCP preamble/header 21 1 (shown in figure as lasting 192 μ$ΰθ) and followed by a MAC header 212, a beacon frame body 213 that includes a TIM 214, and frame check sequence (FCS) 215 at the end of the frame. The idle device must awaken from a sleep state to an active state in order to process the beacon frame. As shown in the figure, during normal processing, the PHY subsystem remains active for the entire duration of beacon frame, and the MAC subsystem is active slightly longer in order to process the received frame. Using smart beacon processing, the durations of active states of the PHY and/or MAC subsystems necessary for beacon reception and processing may be shortened. Optimized PLCP preamble processing allows the PHY subsystem to activate after the beginning of the PLCP preamble (e.g., 100 μ$ΰθ as shown in the figure). Smart FIFO buffering between the PHY and MAC subsystems allows the MAC subsystem to remain idle until the TIM region of the beacon frame is nearly reached. Early beacon processing allows the MAC subsystem to abort the processing early after the TIM in the frame is reached. Smart beacon processing allows the window in which the WiFi device is active to be reduced for beacon reception. This significantly reduces the power consumption when a WLAN station device is in an idle/associated state while maintaining the ability to receive traffic. Previous operating procedures are based on the whole beacon frame being received successfully by the device before initiating beacon processing.

[0014] In one embodiment, the MAC and PHY subsystems may be as illustrated in Fig. 3. The MAC subsystem 310 includes a power manager 31 1, responsible for the decision of when to power down the device and when to wake it up, for example, prior to and after the reception of beacon frames. The MAC subsystem 310 further includes a receive manager 312, responsible for deciding when to receive transmitted frames by, for example, initiating the delivery of pending frames from the AP according to a TIM indication. The

MAC subsystem 310 further includes a connection manager 311, responsible for the connection maintenance, such as for triggering changes in device operation as a result of changes in the network as advertised in the beacon frames. The MAC subsystem also includes a frame analyzer module 314, responsible for the parsing and processing of received frames, and for propagating the applicable information to the relevant modules of the MAC subsystem. The frame analyzer includes a beacon parser 315, responsible for parsing the beacon fields and IEs. The PHY subsystem 320 includes modem 321, responsible for PPDU (PLCP PDU) processing and a PHY system consists of Rx FIFO 322, used for buffering received data before it is propagated to the MAC system.

[0015] Optimized PLCP preamble processing allows the device to save some of the length of PLCP preamble. The length of long PLCP preamble and header when the WLAN is operating in 802.1 lb mode is 192 microseconds. By using less bits to for synchronization, as in a short PLCP preamble, the device may reduce the synchronization time to about 96 microseconds to save more than half of the initial time. For optimized PLCP preamble processing, the power manager module schedules the device to wake up from sleep in the middle of the expected PLCP preamble, instead of the start of beacon targeted time. Upon wakeup for the targeted time, the device enters the receive operation and the modem synchronizes with the signal as it is being received over the air. The late wakeup may be initiated only when the connection manager module indicates that the network is sending beacons with a long preamble (192usec), otherwise the modem may not have enough time to synchronize on the signal.

[0016] Early beacon processing allows the device to save some of the beacon reception time. The duration of a beacon frame depends on the number of fields and IEs included in it. As AP's implementations progress with the 802.1 1 specifications, more and more IEs are added to the transmitted beacon, increasing its duration. The duration of a typical beacon frame transmitted in the 2.4Ghz band is usually around 2 milliseconds, while typical beacon frame durations transmitted in the 5.2Ghz band are usually around 400 microseconds. Early beacon processing allows skipping most of the beacon reception time, after the MAC header and a few of the beacon fields and IEs are received. This may reduce the actual beacon reception time to 900 microseconds and 150 microseconds, respectively, saving more than half of the initial time. For early beacon processing, the beacon parser in the frame analyzer module processes the beacon frames fields and IEs as it arrives over the air. Once TIM field arrives, the beacon parser may check for an indication that either directed or non- directed frames are pending for transmission. According to this indication, the receive manager module may initiate delivery of a pending directed frame once beacon transmission has ended according to the 802.11 protocol. In addition, according to this indication, the device may remain active after a DTIM beacon transmission has ended for delivery of broadcast and multicast traffic according to the 802.11 protocol. If there is no indication of pending frames, the power manager module may cause that PHY subsystem and RF subsystem to abort reception immediately and initiate a sleep sequence to cause the device to enter a sleep state.

[0017] Fig. 4 illustrates an example of procedure performed by an idle station device using early beacon processing. At stage SI, a frame arrives when a beacon is expected, i.e., at the frame interval. At stage S2, the MAC header is processed. If the received frame is not a beacon frame, the device returns to stage S 1 to wait for a beacon frame. If the received frame is a beacon frame, the beacon fields/IEs are processed at stage S3 until the TIM is reached. Next, if the TIM is a groupcast (Gcast) indication, the device sets a groupcast expected indicator at stage S4. If the TIM is a unicast (Ucast) indication, the device sets a unicast expected indicator at stage S5. If neither a unicast or a groupcast is expected, the device aborts reception at stage S6 and enters a sleep state at stage S10. Otherwise, the next beacon fields/IEs are processed at stage S3 until an end-of-file (EoF) marker is reached. If all of the beacon fields/IEs have been processed and pass the CRC (cyclic redundancy check), the device either initiates delivery of the unicast at stage S8 or waits for the groupcast at stage S9, depending upon whether a groupcast or unicast indicator was set previously. After either completion or timeout of the groupcast or unicast, the device enters the sleep state at stage 10. The device would then sleep until the next beacon interval.

[0018] Smart FIFO between the PHY and MAC layers allows the device to save power by keeping the MAC layer in a sleep state and only waking it for few microseconds instead of the whole beacon reception time. MAC processing of a beacon takes a few microseconds, while beacon reception takes 2 milliseconds (or 400 microseconds if early beacon processing is performed as in the example of Fig. 2). Using a smart FIFO buffer between the PHY and MAC layers, received beacon bytes are stored until a watermark in the beacon frame before being released for MAC subsystem processing. The watermark may be set just short of including all beacon fields that precede the TIM fields: MAC header, timestamp, beacon interval, capability information, SSID (service set identifier), supported rate, and DS (direct sequence) parameter set. As some of those fields may have variable length, the watermark can either be estimated according to a common beacon example or set according to the last received beacon frame from the associated AP. When the device waits for a beacon while in an

idle/associated state, the MAC subsystem may be turned off (i.e., put in a sleep state) as long as the watermark is not reached. The PHY and RF subsystems may remain active to allow reception. Once the beacon is transmitted over the air, the received bytes are stored in the Rx FIFO until the watermark in crossed. Then, the MAC subsystem wakes up for the processing of the received data.

Additional Notes and Examples

[0019] In Example 1 , a method for operating a wireless station device having physical layer (PHY) and medium access control layer (MAC) subsystems, comprises: associating with a wireless access point (AP) and receive beacon frames therefrom at specified beacon intervals; partially processing a received beacon frame in the MAC subsystem up to a traffic indication map (TIM) contained in the beacon frame; and if the TIM does not indicate that there are frames pending for delivery, transitioning the radio transceiver and PHY subsystem to a sleep state until the next beacon interval.

[0020] In Example 2, the subject matter of Example 1 may optionally include: in the PHY subsystem, storing MAC protocol data units (PDUs) extracted from the beacon frame in a buffer before passing the MAC PDUs to the MAC subsystem; continuing to store the MAC PDUs in the buffer until a designated watermark is reached in the beacon frame; and, when the watermark is reached, transitioning the MAC subsystem from a sleep state to an active state and pass the buffered MAC PDUs to the MAC subsystem for processing.

[0021] In Example 3, the subject matter of Example 2 may optionally include: wherein the watermark is set just short of including all beacon fields that precede TIM fields including MAC header, timestamp, beacon interval, capability information, and supported rate fields.

[0022] In Example 4, the subject matter of Example 2 may optionally include: wherein the watermark is set according to common beacon patterns. [0023] In Example 5, the subject matter of Example 2 may optionally include: wherein the watermark is set according to one or more previous beacon frames received from the AP.

[0024] In Example 6, the subject matter of any of Examples 1 through 5 may optionally include: operating in an 802.1 lb mode; and, if the AP is sending beacons with a long PLCP (packet layer convergence protocol) preamble, maintaining the PHY subsystem and radio transceiver in a sleep state until after a beacon frame is expected to arrive so as to process only a shorter part of the PLCP preamble of the beacon frame.

[0025] In Example 7, a method for operating a wireless station device having physical layer (PHY) and medium access control layer (MAC) subsystems, comprises: associating with a wireless access point (AP) and receive beacon frames therefrom at specified beacon intervals; in the PHY subsystem, storing MAC protocol data units (PDUs) extracted from the beacon frame in a buffer before passing the MAC PDUs to the MAC subsystem; continuing to store the MAC PDUs in the buffer until a designated watermark is reached in the beacon frame; and, when the watermark is reached, transitioning the MAC subsystem from a sleep state to an active state and pass the buffered MAC PDUs to the MAC subsystem for processing.

[0026] In Example 8, the subject matter of Example 7 may optionally include: wherein the watermark is set just short of including all beacon fields that precede TIM fields including MAC header, timestamp, beacon interval, capability information, and supported rate fields.

[0027] In Example 9, the subject matter of Example 7 may optionally include: wherein the watermark is set according to common beacon patterns.

[0028] In Example 10, the subject matter of Example 7 may optionally include: wherein the watermark is set according to one or more previous beacon frames received from the AP.

[0029] In Example 1 1 , a wireless station device, comprises: a radio transceiver and processing circuitry that includes physical layer (PHY) and medium access control layer (MAC) subsystems and wherein the MAC subsystem includes a power management module for transitioning the radio transceiver and PHY subsystems between active and sleep states; and wherein the processing circuitry is to associate with a wireless access point (AP) and receive beacon frames therefrom at specified beacon intervals and to perform any of the methods as set forth in Examples 1 through 10.

[0030] In Example 12, a computer-readable medium contains instructions for performing any of the methods as set forth in Examples 1 through 10.

[0031] The above detailed description includes references to the

accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments that may be practiced. These embodiments are also referred to herein as "examples." Such examples may include elements in addition to those shown or described.

However, also contemplated are examples that include the elements shown or described. Moreover, also contemplate are examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

[0032] Publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) are supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

[0033] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In the appended claims, the terms "including" and "in which" are used as the plain- English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to suggest a numerical order for their objects.

[0034] The embodiments as described above may be implemented in various hardware configurations that may include a processor for executing instructions that perform the techniques described. Such instructions may be contained in a machine-readable medium such as a suitable storage medium or a memory or other processor-executable medium.

[0035] The embodiments as described herein may be implemented in a number of environments such as part of a wireless local area network (WLAN), 3rd Generation Partnership Project (3GPP) Universal Terrestrial Radio Access Network (UTRAN), or Long-Term-Evolution (LTE) or a Long-Term-Evolution (LTE) communication system, although the scope of the invention is not limited in this respect. An example LTE system includes a number of mobile stations, defined by the LTE specification as User Equipment (UE), communicating with a base station, defined by the LTE specifications as an eNodeB.

[0036] Antennas referred to herein may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some embodiments, instead of two or more antennas, a single antenna with multiple apertures may be used. In these embodiments, each aperture may be considered a separate antenna. In some multiple-input multiple-output (MIMO) embodiments, antennas may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result between each of antennas and the antennas of a transmitting station. In some MIMO embodiments, antennas may be separated by up to 1/10 of a wavelength or more.

[0037] In some embodiments, a receiver as described herein may be configured to receive signals in accordance with specific communication standards, such as the Institute of Electrical and Electronics Engineers (IEEE) standards including IEEE 802.1 1-2007 and/or 802.1 l(n) standards and/or proposed specifications for WLANs, although the scope of the invention is not limited in this respect as they may also be suitable to transmit and/or receive communications in accordance with other techniques and standards. In some embodiments, the receiver may be configured to receive signals in accordance with the IEEE 802.16-2004, the IEEE 802.16(e) and/or IEEE 802.16(m) standards for wireless metropolitan area networks (WMANs) including variations and evolutions thereof, although the scope of the invention is not limited in this respect as they may also be suitable to transmit and/or receive communications in accordance with other techniques and standards. In some embodiments, the receiver may be configured to receive signals in accordance with the Universal Terrestrial Radio Access Network (UTRAN) LTE communication standards. For more information with respect to the IEEE 802.11 and IEEE 802.16 standards, please refer to "IEEE Standards for Information Technology— Telecommunications and Information Exchange between Systems" - Local Area Networks - Specific Requirements - Part 1 1 "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY), ISO/IEC 8802-1 1 : 1999", and Metropolitan Area Networks - Specific Requirements - Part 16: "Air Interface for Fixed Broadband Wireless Access Systems," May 2005 and related amendments/versions. For more information with respect to UTRAN LTE standards, see the 3rd Generation Partnership Project (3GPP) standards for UTRAN-LTE, release 8, March 2008, including variations and evolutions thereof.

[0038] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with others. Other embodiments may be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is to allow the reader to quickly ascertain the nature of the technical disclosure, for example, to comply with 37 C.F.R. § 1.72(b) in the United States of America. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. However, the claims may not set forth every feature disclosed herein as embodiments may feature a subset of said features. Further, embodiments may include fewer features than those disclosed in a particular example. Thus, the following claims are hereby incorporated into the Detailed Description, with a claim standing on its own as a separate embodiment. The scope of the embodiments disclosed herein is to be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. A method for operating a wireless station device having physical layer (PHY) and medium access control layer (MAC) subsystems, comprising:

associating with a wireless access point (AP) and receiving beacon frames therefrom at specified beacon intervals;

partially processing a received beacon frame in the MAC subsystem up to a traffic indication map (TIM) contained in the beacon frame; and

if the TIM does not indicate that there are frames pending for delivery, transitioning the radio transceiver and PHY subsystem to a sleep state until the next beacon interval.

2. The method of claim 1 further comprising:

in the PHY subsystem, storing MAC protocol data units (PDUs) extracted from the beacon frame in a buffer before passing the MAC PDUs to the MAC subsystem;

continuing to store the MAC PDUs in the buffer until a designated watermark is reached in the beacon frame; and,

when the watermark is reached, transitioning the MAC subsystem from a sleep state to an active state and pass the buffered MAC PDUs to the MAC subsystem for processing.

3. The method of claim 2 wherein the watermark is set just short of including all beacon fields that precede TIM fields including MAC header, timestamp, beacon interval, capability information, and supported rate fields.

4. The method of claim 2 wherein the watermark is set according to common beacon patterns.

5. The method of claim 2 wherein the watermark is set according to one or more previous beacon frames received from the AP.

6. The method of claim 1 further comprising:

operating in an 802.1 lb mode; and,

if the AP is sending beacons with a long PLCP (packet layer convergence protocol) preamble, maintaining the PHY subsystem and radio transceiver in a sleep state until after a beacon frame is expected to arrive so as to process only a shorter part of the PLCP preamble of the beacon frame.

7. A computer-readable medium containing instructions for operating a wireless station device having physical layer (PHY) and medium access control layer (MAC) subsystems by:

associating with a wireless access point (AP) and receive beacon frames therefrom at specified beacon intervals;

8. The medium of claim 7 wherein the watermark is set just short of including all beacon fields that precede TIM fields including MAC header, timestamp, beacon interval, capability information, and supported rate fields.

9. The medium of claim 7 wherein the watermark is set according to common beacon patterns.

10. The medium of claim 7 wherein the watermark is set according to one or more previous beacon frames received from the AP.

1 1. A wireless station device, comprising:

a radio transceiver and processing circuitry that includes physical layer (PHY) and medium access control layer (MAC) subsystems and wherein the MAC subsystem includes a power management module for transitioning the radio transceiver and PHY subsystems between active and sleep states;

wherein the processing circuitry is to:

associate with a wireless access point (AP) and receive beacon frames therefrom at specified beacon intervals;

partially process a received beacon frame in the MAC subsystem up to a traffic indication map (TIM) contained in the beacon frame; and

if the TIM does not indicate that there are frames pending for delivery, transition the radio transceiver and PHY subsystem to a sleep state until the next beacon interval.

12. The device of claim 1 1 wherein the PHY subsystem includes a power management module for transitioning the MAC subsystem between active and sleep states and processing circuitry is to:

in the PHY subsystem, store MAC protocol data units (PDUs) extracted from the beacon frame in a buffer before passing the MAC PDUs to the MAC subsystem;

continue to store the MAC PDUs in the buffer until a designated watermark is reached in the beacon frame; and,

when the watermark is reached, transition the MAC subsystem from a sleep state to an active state and pass the buffered MAC PDUs to the MAC subsystem for processing.

13. The device of claim 12 wherein the watermark is set just short of including all beacon fields that precede TIM fields including MAC header, timestamp, beacon interval, capability information, and supported rate fields.

14. The device of claim 12 wherein the watermark is set according to common beacon patterns.

15. The device of claim 12 wherein the watermark is set according to one or more previous beacon frames received from the AP.

16. The device of claim 1 1 wherein the processing circuitry is to:

operate in an 802.1 lb mode; and,

if the AP is sending beacons with a long PLCP (packet layer convergence protocol) preamble, maintain the PHY subsystem and radio transceiver in a sleep state until after a beacon frame is expected to arrive so as to process only a shorter part of the PLCP preamble of the beacon frame.

17. A wireless station device, comprising:

wherein the processing circuitry is to:

18. The device of claim 17 wherein the watermark is set just short of including all beacon fields that precede TIM fields including MAC header, timestamp, beacon interval, capability information, and supported rate fields.

19. The device of claim 17 wherein the watermark is set according to one or more previous beacon frames received from the AP.

20. The device of claim 17 wherein the radio transceiver incorporates one or more antennas.