Abstract:
Enhancements are provided to lower power consumption in a wireless communication device. A traffic indicator message is designated to be positioned at or near a first burst to be transmitted to a subscriber station. Further, a clock signal provided to a decoder in the subscriber station has a variable frequency, the frequency being chosen based on the nature of the data to be decoded. Data needing immediate decoding is processed with a high speed clock. Other data are processed with a lower speed clock to reduce power consumption. Also, control information that is demodulated when the subscriber station is in sleep mode is batch processed when the subscriber station becomes active again.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/642,817, now U.S. Pat. No. 8,660,617, filed on Dec. 19, 2006, which claims the benefit of U.S. Provisional Application No. 60/771,629, filed Feb. 9, 2006. The disclosures of the applications identified above are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates generally to wireless communication devices and methods. More particularly, this method relates to an enhanced sleep mode operation for a broadband wireless communication system. 
     Wireless communication systems are being developed to permit high speed, wireless communication of data from point to point in a network. For such a system, an air interface standard defines transmission formats and timing to permit reliable communication between transmitters and receivers. Other features and capabilities may be added by the air interface as well. The transmitters and receivers may be stand-alone devices such as mobile telephones or may be incorporated with other devices such as computers or routers. 
     One example of such a system is known as Worldwide Interoperability for Microwave Access, or WiMAX. WiMAX is defined according to standards published by the Institute of Electrical and Electronics Engineers (IEEE) which are generally referred to as IEEE 802.16. One version of the standard, generally referred to as 802.16e, sets forth requirements with respect to access by both fixed and mobile devices. In a WiMAX system, a subscriber station can communicate by radio with one or more base stations (BS). Each BS provides communication services to subscriber stations in a service area near the BS. In a WiMAX system, communication can be point to point or point to multipoint, and a subscriber station can have multiple active or inactive connections to other radios in the system. 
     A key feature required for use by a mobile device is a low power sleep mode. Mobile devices are powered by rechargeable batteries, and minimization of power consumption is a key design feature. When a mobile device is not transmitting or receiving data in an active mode, the mobile device is able to enter the low power sleep mode to conserve battery power. When the device receives a trigger, it discontinues the sleep mode and resumes normal operation in the active mode. 
     For entry into sleep mode, a WiMAX mobile device negotiates sleep mode per connection. In the negotiation, the mobile device exchanges sleep duration, awaken duration and sleep start duration with the network. If all connections are in sleep mode, the subscriber station can start low power mode operation. The subscriber station exits the low power operation if it receives any one of (1) a wake up message, or mobile traffic indication message, which indicates the system has data to transmit to the subscriber station; (2) data traffic on the connection identifier (CID) which is in sleep mode; or (3) data traffic from a host interface which uses the subscriber station to communicate with the WiMAX network. 
     While sleep mode operation has been successful in reducing battery power consumption and extending the operating life of mobile devices, it would be desirable to provide for an improved method and apparatus for controlling sleep mode operation in a wireless communication system such as a WiMAX network. 
     SUMMARY OF THE DISCLOSURE 
     By way of introduction, embodiments described below provide a method and system for reduced power consumption in a subscriber station of a wireless communication system. In one preferred embodiment, a traffic indicator message is designated to be positioned at or near a first burst to be transmitted to the subscriber station. The subscriber station may then decode and process only the first portion of the transmission to determine if it should return to sleep mode based on whether or not the traffic indicator message is present. In another preferred embodiment, a clock signal provided to a decoder in the v station has a variable frequency, the frequency being adjusted based on the nature of the data to be decoded. Data needing immediate decoding is processed with a high speed clock. Other data are processed with a lower speed clock to reduce power consumption. In still another preferred embodiment, control information that is demodulated when the subscriber station is inactive in the sleep mode is batch processed when the subscriber station becomes active again. Other preferred embodiments are provided, and each of the preferred embodiments described herein can be used alone or in combination with one another. 
     Various embodiments will now be described with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is block diagram of a radio communication system; 
         FIG. 2  illustrates communication format in the radio communication system of  FIG. 1 ; 
         FIGS. 3-5  are flow diagrams illustrating operation of the radio communication system of  FIG. 1 ; 
         FIG. 6A  is a functional block diagram of a high definition television; 
         FIG. 6B  is a functional block diagram of a vehicle control system; 
         FIG. 6C  is a functional block diagram of a cellular phone; 
         FIG. 6D  is a functional block diagram of a set top box; and 
         FIG. 6E  is a functional block diagram of a media player. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawing,  FIG. 1  is a block diagram of a radio communication system  100 . The system  100  includes at least one base station (BS)  102  and at least one subscriber station  104 . In  FIG. 1 , the system  100  is shown with a single BS  102  and a single subscriber station  104  so as to not unduly complicate the drawing figure. However, it is to be understood that the system  100  may be operated with any suitable number of base stations and any suitable number of subscriber stations. The subscriber stations may be fixed or mobile. 
     Radio communication in the system  100  is accomplished using an air interface standard. The air interface standard defines message format, content and timing to permit reliable communication among components of the system  100 , such as BS  102  and subscriber station  104 . In the illustrated example, the air interface standard is IEEE Std. 802.16e, published by the Institute of Electrical and Electronics Engineers, Inc. referred to as 802.16. The techniques and principles described herein may of course be extended to other air interface standards, including standards developed for voice and data communication or combinations of the two, for connection oriented and connectionless communication links. 
     The BS  102  provides radio communication to subscriber stations such as subscriber station  104  in the area surrounding BS  102 . The BS  102  is equipped with one or more antennas for radio communication at the appropriate frequency and using the proper modulation. A downlink, from the BS  102  to the subscriber station  104 , operates on a point to multipoint (PMP) basis. The IEEE Std. 802.16e wireless link operates with a central BS such as BS  102  and is capable of handling multiple independent communications simultaneously. Within a given frequency channel and antenna sector, all stations receive the same transmission, or parts thereof. The BS  102  is the only transmitter operating in this direction, so it transmits without having to coordinate with other stations, except for the overall time division duplexing (TDD) that may divide time into uplink and downlink transmission periods. The downlink is generally broadcast. Subscriber stations such as subscriber station  104  share the uplink to the BS  102  on a demand basis. Depending on the class of service utilized, the subscriber station  104  may be issued rights to transmit in every frame by the BS  102 , or the right to transmit may be granted by the BS  102  after receipt of a request from the user. The BS  102  may also provide communication for the subscriber station  104  to other subscriber stations or to other equipment outside the system  100  (not shown in  FIG. 1 ). 
     The subscriber station  104  in the illustrated embodiment includes a radio section  108  and a host  110 . The radio section  108  provides radio communication with remote radios such as BS  102 . The host  110  provides any other data processing or other electronic functions. Examples of the host  110  include a personal computer (PC), a personal digital assistant (PDA), other radio device such as a cell phone, etc. In general, the host  110  uses and benefits from the radio communication provided by the radio section  108 . 
     The radio section  108  includes an antenna  112 , a receiver  114 , a transmitter  116 , a medium access control (MAC) layer  118 , a baseband modem  120 , a processor  122 , memory  124 , a host interface  126 , a clock circuit  128 , a CPU clock circuit  130 , a power control circuit  132  and a battery  134 . In other embodiments, the radio section  108  may include other or alternative components, and some of the illustrated components may be combined. For example, the receiver  112  and transmitter  114  may be combined as a transceiver. 
     The antenna  112  is suitable for radio communication at the frequencies and modulation of interest. For radio reception, the antenna  112  converts detected electromagnetic energy into electrical signals and provides the electrical signals to the receiver  114 . For a radio transmission, the antenna  112  is provided with electrical signals from the transmitter  116  and converts the electrical signals to electromagnetic energy. 
     The receiver  114  receives the electrical signals from the antenna  112  and converts them from radio frequency to baseband frequency. The receiver  114  filters the received radio frequency signal and converts these signals to baseband signals or intermediate frequency (IF) signals. The baseband modem  120  then demodulates the received IF or baseband frequency signals and provides the demodulated data to the MAC  118 . The MAC  118  decodes the data. The decode is typically done partly in hardware and partly in software. 
     The transmitter  116  receives baseband signals from the processor  122 . The transmitter  116  modulates the baseband signals and shifts them up to radio frequency for transmission by the antenna  112 . 
     The modem  120  is coupled to the receiver  114  to receive the baseband or IF signals. The modem  120  is further coupled with the processor  122  to receive control signals and provide decoded information received from the BS  102  and other transmitters. The modem  120  may be any suitable arrangement, such as custom logic, a gate array or logic array, designed to receive and decode baseband signals. In one implementation, the hardware decoder  120  is designed for decoding information on the downlink, such as the WiMAX downlink map (DLMAP). If the DLMAP changes, the structure or operation of the modem  120  may have to change. In the preferred arrangement, a portion of the DLMAP processing is done with hardware and a portion is done with software. After demodulating baseband information, the modem  120  conveys the result to the MAC for decoding and subsequent storage in the memory  124 . Alternatively, the decoded data may be provided directly to the processor  122 . 
     The processor  122  controls operation of the radio section  108  of the subscriber station  104 . The processor  122  may be any suitable microprocessor, digital signal processor or other central processing unit (CPU). The processor  122  operates in conjunction with data and instructions stored in the memory  124  to control the operation of the radio section  108 . The memory  124  may include any combination of read/write memory, read only memory, flash memory, and any other storage device. The memory  124  may be a single device or may be distributed. For example, a portion of the memory  124  may be integrated with the processor  122 . At least a portion of the memory  124  corresponds to the memory space of the processor  122 . 
     The host interface  126  controls exchange of data with the host  110 . The host interface  126  is further coupled with the processor  122  to permit exchange of data between the host  110  and the processor  122 . In one exemplary embodiment, in which the host  110  engages the radio section  108  for radio communication with a remote source through the BS  102 , the host interface  126  receives information from the host  110  for transmission to the remote source and, in turn, receives from the processor  122  information from the remote source. The host interface  126  may operate to encode, decode or otherwise reformat the information for proper usage by the radio section  108  and the host  110 . 
     The clock circuit  128  produces clocking signals to control timing of the components of the radio section  108 . Connections to other components are not shown in  FIG. 1  so as not to unduly complicate the drawing figure. The CPU clock circuit  130  provides clocking signals to the processor  122 . The CPU clock circuit  130  controls the frequency of the processor clock signal. The processor&#39;s operating speed is generally related to the frequency of the clock signal provided by the CPU clock circuit  130 . When the clock signal has a relatively higher frequency, the processor  122  runs faster, processing data faster. In contrast, when the clock signal has a relatively lower frequency, the processor  122  runs slower. The frequency of the CPU clock circuit  130  is related to the power consumption of the processor  122  and other circuits controlled by the processor  122 . When the frequency is higher, the power consumption is higher. Therefore, when possible, it is desirable in a device such as the subscriber station  104  to reduce the clock frequency and the operating frequency of the processor  122  as much as possible. 
     The power control circuit  132  controls entry into and exit from a low power sleep mode by components of the subscriber station  104 . The power control circuit  132  operates to manage depletion of the battery  134 , which provides operating power for the subscriber station  104 . The power control circuit  132  responds to information about the status of the radio section  108  to place the radio section  108  in a low power sleep mode or to return the radio section  108  from the low power sleep mode to an active mode. For example, if all connections between the subscriber station  104  and other transmitters in the system  100  are in sleep mode, the power control circuit  132  places the subscriber station  104  in the low power sleep mode. In another embodiment, the power control circuit  132  could also control the voltage rails of the different units along with the frequency. Not all connections between the power control circuit  132  and the battery  134  are shown in  FIG. 1 . 
       FIG. 2  illustrates communication format in a wireless communication system such as the system of  FIG. 1 .  FIG. 2  shows the format of a down link frame  202  for a time division duplex (TDD) communication system. The down link frame  202  includes a preamble  204 , broadcast control section  206 , and time division multiple access (TDM) subframes  208 ,  210 ,  212 . 
     The preamble  204  is used by the subscriber station  104  to derive time synchronization and phase coherency and filter adaptation. The preamble  204  may include predefined data that may be used by the receiver  114  to adjust to the current channel parameters between the BS  102  and the subscriber station  104 . 
     The broadcast control section  206  includes a frame control header (FCH)  214 , a downlink map (DLMAP)  216  and an uplink map (ULMAP)  218 . In a point to multipoint transmission system such as WiMAX, the BS  102  is broadcasting to all subscriber stations  104  in the area served by the BS  102 . All subscriber stations  104  receive the transmission/broadcast. Information in the DLMAP  206  informs the subscriber stations as to which subscriber station the communication is intended for. Information in the ULMAP informs the subscriber stations about resources assigned on an uplink for responding to the BS  102 . The DLMAP  206  and ULMAP  208  form a frame control section of the down link frame  202 . The broadcast control section  206  may also include a down link channel descriptor (DCD) message (not shown). A DCD message is transmitted by a BS  102  at a periodic interval to define the characteristics of a downlink physical channel. 
     After the broadcast control section  206 , the following TDM portion carries the data, organized into bursts or subframes  208 ,  210 ,  212  with different burst profiles. Each subscriber station  104  receives and decodes the control information of the DLMAP  206  and looks for headers indicating data for that subscriber station  104  in the remainder of the downlink subframes. 
       FIG. 3  is a flow diagram illustrating operation of the radio communication system of  FIG. 1 . The flow diagram of  FIG. 3  illustrates an improved technique by which the subscriber station  104  may enter sleep mode Thereby reducing power and conserving battery. 
     The IEEE 802.16 air interface standard defines sleep mode per connection. The subscriber station  104  negotiates sleep mode per connection. That is, the subscriber station  104 , under control of the processor  122  ( FIG. 1 ), determines that sleep mode is an option, for example because there is no current communication traffic. The subscriber station  104  communicates with the BS  102  and exchanges information defining sleep duration, awaken duration and sleep start time. This process is in accordance with the IEEE 802.16 air interface standard. 
     Once the subscriber station  104  is in sleep mode, it awakens or returns to active mode when it is required to process traffic. This occurs, for example, if the subscriber station  104  receives a mobile traffic indication message from the BSS  102 . A mobile traffic indication message indicates that the BS  102  has information to convey to the subscriber station  104 , and the information is not control or other overhead information, but rather traffic for processing. In the example of a WiMAX system, a mobile traffic indication message is referred to as a MOB-TRF_IND message. Further, the subscriber station  104  awakens if it receives data traffic on a connection which is in sleep mode. Finally, the subscriber station  104  returns to active mode if it receives traffic on a host interface, such as the host interface  126  of the subscriber station  104  of  FIG. 1 . 
     Since many wireless communication systems utilize frame-based protocols, such as IEEE 802.16, these awaken indications are typically sent at any time in a down link frame. As a result, a particular subscriber station  104  must demodulate and decode the entire down link frame to find an indication intended for the particular subscriber station  104 . Demodulation is performed by the receiver  114  and associated circuitry to convert the received signals to baseband. Decoding is done by the modem  120  and MAC  118  or the processor  122 . A down link frame can be up to 5 ms in duration. Performing these functions during that entire duration can consume substantial battery power and deplete the battery  134 . 
     In accordance with one embodiment, the mobile traffic indication message is sent by the BS  102  to the subscriber station  104  only as part of the first downlink burst. For example, in a WiMAX system, the MOB-TRF_IND message, if present, is sent after the ULMAP or a DCD message. 
     This situation is illustrated in the flow diagram of  FIG. 3 . At block  302 , the subscriber station  104  enters the sleep mode. In the sleep mode, whatever circuitry that can be powered down has been powered down under control of for example, the power control circuit  132 . The receiver  114  may remain active to receive transmitted control information and convert the received information to baseband and store the information without decoding. The decoding components, such as the modem  120 , the MAC  118  and the processor  122 , are preferably powered down. 
     At block  304 , the base station BS  102  begins a transmission for the subscriber station  104 . The BS  102  formats a communication, for example, in the format illustrated in  FIG. 2 . The communication will include several bursts, for example, as illustrated in  FIG. 2 . Only formation of a first burst is illustrated in  FIG. 3 . 
     The BS  102  sends a FCH  204 . The FCH  204  is used by the receiver  114  to synchronize and equalize the received signals. 
     At block  306 , the BS  102  sends the DLMAP. At block  308 , the BS  102  sends the ULMAP or DCD message, in accordance with the IEEE 802.16 protocol. At block  310 , the BS  102  transmits a MOB-TRF_IND message, the receipt of which causes the subscriber station  104  to exit the low power sleep mode and return to active mode. 
     After sending the mobile traffic indication message or MOB-TRF_IND message as part of the first burst, the BS  102  continues transmitting the rest of its communication. This includes sending data packets for the MSs  104  in the first burst, at block  312 , after the MOB-TRF_IND message. The BS  102  then sends the remaining bursts with information for other subscriber stations in the system, at block  314 . 
     At the subscriber station  104 , the information sent by the BS  102  is detected and processed as appropriate. The FCH is used to equalize the receiver  114  and obtain synchronization. At block  316 , the DLMAP and either the ULMAP or DCD messages are received and decoded. Based on the information in these messages, the subscriber station is able to identify the down link channel and the uplink channel. 
     At block  318 , the subscriber station  104  detects the MOB-TRF_IND message sent by the BS  102  at block  310 . This message is decoded at block  320 , using the MAC  118  or the processor  122 . In response to detecting and decoding the MOB-TRF_IND message, at block  322  the subscriber station  104  exits the low power sleep mode or wakes up. The subscriber station  104  is now in a position to process the data traffic being sent to it by the BS  102 , including receiving and decoding the data packets, at block  324 , sent by the BS  102 . At block  326 , the subscriber station  104  receives and processes the information contained in the data packets. When conditions permit, the subscriber station  104  returns to the sleep mode, at block  328 , in the conventional fashion. 
     If there is no traffic for the subscriber station  104  at block  310 , the BS  102  does not transmit the MOB-TRF_IND message. Accordingly, at blocks  318 ,  320 , there is no MOB-TRF_IND message to receive and detect. If no MOB-TRF_IND message is detected, the subscriber station  104  remains in the low power sleep mode, thereby conserving maximum battery power. By positioning the MOB-TRF_IND message at or near the beginning of a transmission from the BSS  102  to a subscriber station  104 , the subscriber station  104  can remain in the low power sleep mode for the maximum duration. 
     In a WiMAX system, each down link frame can be 5 ms in duration. In accordance with this embodiment, the subscriber station  104  remains in sleep mode rather than having to exit the sleep mode to decode the entire first down link frame. In such a case, assuming a frame with four bursts of equal duration, this embodiment provides a saving of more than 200% in sleep mode power conservation. Other wireless systems employing this technique may benefit as much or more. 
       FIG. 4  is a flow diagram illustrating another aspect of operation of the radio communication system of  FIG. 1 . The illustrated operation can further reduce sleep mode power consumption by properly controlling the CPU clock signal based on the frame processing requirement of the received frame. In this example, the WiMAX downlink map (DLMAP) requires a higher CPU clock frequency as the DLMAP message is decoded before the baseband buffer overflows. In the context of  FIG. 1 , the baseband buffer is a portion of memory  124  storing information which has been received at the subscriber station  104  and converted to baseband signals, but not yet decoded. In conventional systems, the CPU clock is either fixed at the speed required to decode the DLMAP in the required amount of time, or the CPU clock may toggle between on and off, where the on frequency is the speed required to decode the DLMAP in the required amount of time. This on-off toggling provides some power savings by turning off the CPU clock when not needed. However, there is room for further improvement. 
     In accordance with this embodiment, a low power implementation involves first, increasing the CPU clock to a higher frequency to process the DLMAP, and second, reducing the CPU clock to a lower frequency after the DLMAP has been processed. The CPU clock is active at all times. That is, the CPU clock is not turned off altogether. However, the frequency or operational speed of the CPU clock is adjusted according to the content of the frame so that frame portions requiring rapid processing are processed with a high speed clock signal and frame portions permitting slower processing are processed with a low speed clock signal. Since power dissipation from the battery is generally proportional to the clock frequency, this embodiment further reduces power consumption and extends battery life. 
     This process is illustrated in  FIG. 4 .  FIG. 4  is a modification of a portion of the flow illustrated in  FIG. 3 . At block  402 , the BS  102  transmits a DLMAP, analogous to block  306  of  FIG. 3 . Subsequently, as indicated by block  404 , the BS  102  proceeds with its remaining transmission activity in accordance with the air interface standard. 
     At the MS  104 , at block  406 , the DLMAP is received. The frame portion including the DLMAP is detected by the receiver  114 , converted to baseband and stored in memory for processing. The processor  122  becomes aware that the DLMAP is available, either based on information provided by the receiver  114  or because system timing corresponds to a time when the DLMAP should be present, and begins processing the DLMAP. 
     At block  408 , the processor clock is increased. In the embodiment of  FIG. 1 , this may be done by use of the CPU clock circuit  130 . The CPU clock circuit  130  provides clocking signals to the processor  122 . The CPU clock circuit  130  controls the frequency of the processor clock signal based on the frequency of the clock signal received from the clock circuit  128 . When a frame portion requiring high speed processing is encountered, the CPU clock circuit  130  increases the clock signal provided to the processor  122 , thereby increasing the processing speed of the processor  122 . 
     At block  410 , the DLMAP is decoded by the processor  122  operating at the relatively higher clock frequency. In a WiMAX system, the DLMAP may be large in size and contains substantial information. Because the DLMAP defines the features and format of the downlink, the subscriber station  104  must decode the DLMAP substantially in real time or as the DLMAP is received. Operating the processor  122  at a clock frequency sufficient for decoding the received data in the time required ensures that the DLMAP is decoded accurately. At block  412 , once the DLMAP is processed, the clock speed or clock frequency is reduced to a slow, non-zero rate so that some data processing can continue at block  414 . However, due to the reduced clock frequency, the power consumption of the subscriber station  104  during this time is substantially reduced relative to power consumption during times when the processor clock speed is relatively high. 
     This technique can, of course, be extended beyond a WiMAX system. Other systems using a known data format may employ this technique as well. Any time some of the received data must be processed at a relatively high clock frequency, or may be processed at a relatively low clock frequency, the clock frequency used to process the data may be adjusted accordingly to minimize power drain in the system. This technique may be extended even farther, to a case in which the location of high-decode-speed data or low-decode-speed data is contained in the frame itself. The receiving system may read control information contained in the frame, locate the data to be processed in the frame and adjust clock speed accordingly. The adjusted clock speed may be a processor clock, as illustrated in  FIG. 1 , or may be a hardware decoding clock, or any other type of timing signal. 
       FIG. 5  is a flow diagram illustrating another aspect of operation of the radio communication system of  FIG. 1 . The illustrated operation can further reduce sleep mode power consumption by batch processing control messages sent on the downlink from the BS  102  to the subscriber station  104 . 
     In a WiMAX system, during normal operation, received bursts are de-concatenated into MAC Protocol Data Unit (MPDU). A MPDU is the data unit exchanged between peer entities of the same protocol layer. On the downlink, the MPDU is the data unit generated for the next lower layer. The subscriber station  104  checks the connection identifier (CID) for each MPDU and compares the CID with a list of CIDs it maintains for CID filtering. Only if the CID matches the CID filter is the frame processed and system clocks enabled. 
     During sleep mode, the subscriber station  104  needs to process the ULMAP. This is done, for example, to determine whether the subscriber station  104  needs to send a bandwidth request in the next frame. The subscriber station  104  must also process the uplink channel descriptor (UCD) message and the downlink channel descriptor (DCD) message. The UCD message defines the characteristics of an uplink channel from the subscriber station  104  to the BS  102 . The DCD message defines the characteristics of a downlink channel to the subscriber station  104  from the BS  102 . There are other broadcast messages sent by the BS  102  which the subscriber station  104  must process since they contain important control information. In a conventional implementation, this control information (contained in the MPDUs) is processed as soon as it is received to ensure low latency. Processing in this context involves decoding the received control information and acting on instructions and data decoded therefrom. 
     In accordance with this embodiment, these control messages may be processed in a batch at the end of a frame. The only message that requires quick processing is the DLMAP. The DLMAP should be processed sufficiently early to allow programming an uplink channel descriptor for the next burst. 
     For enhanced low power consumption in sleep mode, the subscriber station  104  receives MPDUs sent by the BS  102  and creates a batch of MPDUs to be processed by the processor. These messages are processed by the processor  122  either before or after the DLMAP is processed. 
     This process is illustrated in  FIG. 5 . At block  502 , the base station BS  102  sends MPDUs to the subscriber station  104 . The MPDUs may include any control message that does not require urgent or near-real-time processing, but whose processing may be deferred for a time. At block  504 , the MPDUs sent from the BS  102  are received at the subscriber station  104 . During this time, the subscriber station  104  is in the low power sleep mode. For example, the receiver is active and functioning to demodulate received messages such as the MPDUs. However, other portions of the subscriber station  104  such as the modem  118  and the processor  122  are in a low power condition and unable to decode the received MPDUs. 
     At block  506 , the subscriber station  104  stores the received MPDUs for subsequent processing. The MPDU data may be stored in any convenient memory location of the subscriber station  104 . At block  508 , the subscriber station  104  exits the low power sleep mode and, at block  510 , processes the MPDUs. The received MPDUs are processed as a batch. That is, all MPDUs received during the sleep mode are processed only when the subscriber station  104  exits the sleep mode to process information which must be processed rapidly, such as the ULMAP, at block  512 . In one embodiment, processing involves increasing the CPU clock signal frequency, decoding the received control messages as a group, then reducing the CPU clock signal frequency. The MPDUs may be processed before the ULMAP, as shown in  FIG. 5 , or they may be processed after the ULMAP. This enhancement ensures that the CPU clock signal is changed only once when the ULMAP is to be processed. 
     Referring now to  FIGS. 6A-6E , various exemplary implementations of embodiments of the present invention are shown. As shown in  FIG. 6A , embodiments of the present invention can be implemented in a high definition television (HDTV)  620 . The HDTV  620  includes a wireless local area network (WLAN) circuit  629  which may be configured in accordance with the subscriber station  104  of  FIG. 1 . Embodiments of the present invention may be implemented in either or both signal processing and/or control circuits, which are generally identified in  FIG. 6A  at  622  or a WLAN interface  629 . The HDTV  620  receives HDTV input signals in either a wired or wireless format and generates HDTV output signals for a display  626 . In some implementations, signal processing circuit and/or control circuit  622  and/or other circuits (not shown) of the HDTV  620  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other type of HDTV processing that may be required. 
     The HDTV  620  may communicate with mass data storage  627  that stores data in a nonvolatile manner such as optical and/or magnetic storage devices. The HDTV  620  may be connected to memory  628  such as random access memory (RAM), read only memory (ROM), low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The HDTV  620  also may support connections with a WLAN via a WLAN network interface  629 . 
     Referring now to  FIG. 6B , embodiments of the present invention may be implemented in a WLAN interface  648  of a vehicle  630 . The vehicle  630  includes a wireless local area network circuit  648  which may be configured in accordance with the subscriber station  104  of  FIG. 1 . In some implementations, embodiments of the present invention may be implemented as part of a power train control system  632  that receives inputs from one or more sensors  646  such as temperature sensors, pressure sensors, rotational sensors, airflow sensors and/or any other suitable sensors; the power train control system  630  also generates one or more output control signals  638 , such as engine operating parameters, transmission operating parameters, or other control signals. 
     Embodiments of the present invention may also be implemented in another control system  640  of the vehicle  630 . The control system  440  may likewise receive signals from input sensors  642  and output control signals  644 . In some implementations, the control system  640  may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated. 
     The powertrain control system  632  may communicate with mass data storage  646  that stores data in a nonvolatile manner. The mass data storage  646  may include optical and/or magnetic storage devices including, for example, hard disk drives (HDDs) and/or digital video disks (DVDs). The powertrain control system  632  may be connected to memory  647 , such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The control system  640  may also include mass data storage, memory and/or a WLAN interface (all not shown). 
     Referring now to  FIG. 6C , embodiments of the present invention can be implemented in a cellular phone  650  that may include a cellular antenna  651 . The cellular phone  650  includes a wireless local area network circuit  668  which may be configured in accordance with the subscriber station  104  of  FIG. 1 . In some implementations, the cellular phone  650  includes a microphone  656 , an audio output  658  such as a speaker and/or audio output jack, a display  660  and/or an input device  662  such as a keypad, pointing device, voice actuation and/or other input device. The signal processing and/or control circuits  652  and/or other circuits (not shown) in the cellular phone  650  may process data, perform coding and/or encryption, perform calculations, format data and/or perform other cellular phone functions. 
     The cellular phone  650  may communicate with mass data storage  664  that stores data in a nonvolatile manner such as optical and/or magnetic storage devices including, for example hard disk drives (HDDs) and/or DVDs. The cellular phone  650  may be connected to memory  666  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. 
     Referring now to  FIG. 6D , embodiments of the present invention can be implemented in a set top box  680 . The set top box  680  includes a wireless local area network circuit  696  which may be configured in accordance with the subscriber station  104  of  FIG. 1 . The set top box  680  receives signals from a source  692  such as a broadband source and outputs standard and/or high definition audio/video signals suitable for a display  688  such as a television, monitor or other video and/or audio output devices. The signal processing and/or control circuits  684  and/or other circuits (not shown) of the set top box  680  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other set top box functions. 
     The set top box  680  may communicate with mass data storage  690  that stores data in a nonvolatile manner. The mass data storage  690  may include optical and/or magnetic storage devices for example hard disk drives (HDDs) and/or DVDs. The set top box  680  may be connected to memory  694  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. 
     Referring now to  FIG. 6E , embodiments of the present invention can be implemented in a media player  600 . The media player  600  includes a wireless local area network circuit  616  which may be configured in accordance with the subscriber station  104  of  FIG. 1 . In some implementations, the media player  600  may include a display  607  and/or a user input  608  such as a keypad, touchpad and the like. In some implementations, the media player  600  may employ a graphical user interface (GUI) that typically employs menus, drop down menus, icons and/or a point-and-click interface via the display  607  and/or user input  608 . The media player  600  may further include an audio output  609  such as a speaker and/or audio output jack. The signal processing and/or control circuits  604  and/or other circuits (not shown) of the media player  600  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other media player functions. 
     The media player  600  may communicate with mass data storage  610  that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. The mass data storage may include optical and/or magnetic storage devices for example hard disk drives (HDDs) and/or DVDs. The media player  600  may be connected to memory  614  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. Still other implementations in addition to those described above are contemplated. 
     It is intended that the foregoing detailed description be understood as an illustration of selected forms that the invention can take and not as a definition of the invention. It is only the following claims, including all equivalents, that are intended to define the scope of this invention.