Abstract:
A method that comprises receiving, by an access point (AP), an interval value from a station (STA). The interval value corresponds to a frequency with which the STA listens to the AP. The method also comprises commanding, by the AP, the STA to refrain from transmitting data to the AP until a period expires. The commanding comprises the AP setting a duration of the period to correspond to the interval value. The method further comprises transferring, by the AP, data to the STA after the period expires.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 61/160,518, filed on Mar. 16, 2009 (Attorney Docket No. TI-67817PS), which is hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Various wireless devices (e.g., access points and stations) may communicate with each other by way of a network, such as a wireless local area network (WLAN) that adopts any suitable protocol (e.g., 802.11x). At least some of these wireless devices may be battery-operated, meaning that their power resources are finite and should be conserved to the extent possible. 
       SUMMARY 
       [0003]    The problems noted above are solved in large part by a technique that enables various devices in a wireless network to remain in a power-conservation mode for extended periods of time, thereby conserving power. In some embodiments, the technique comprises a method that includes receiving, by an access point (AP), an interval value from a station (STA). The interval value corresponds to a frequency with which the STA listens to the AP. The method also comprises commanding, by the AP, the STA to refrain from transmitting data to the AP until a period expires. The commanding comprises the AP setting a duration of the period to correspond to the interval value. The method further comprises transferring, by the AP, data to the STA after the period expires. 
         [0004]    In some embodiments, the technique comprises a method that includes a station (STA) transmitting an interval value to an access point (AP). The interval value corresponds to a frequency with which the STA listens to the AP. The interval value is less than additional interval values of other STAs with which the AP communicates. As a result of receiving a command from the AP, the STA refrains from transmitting data to the AP until a period expires and the STA powers down at least some data transmission circuitry during the period. A duration of the period corresponds to the interval value. The method also comprises receiving, by the STA, data from the AP after the period expires. 
         [0005]    In some embodiments, the technique is implemented in a system that comprises a transceiver and a processor coupled to the transceiver that receives an interval value from a station (STA). The interval value corresponds to a timing with which the STA listens to the transceiver. The processor commands the STA to cease data transmissions to the transceiver until a period expires. A duration of the period associates with the interval value. The transceiver does not transmit data to the STA during the period. After the period expires, the transceiver is reactivated and transmits data to the STA. 
         [0006]    In some embodiments, the technique is implemented in a system that comprises a transceiver and a processor coupled to the transceiver. The transceiver transmits an interval value to an access point (AP). The interval value corresponds to a timing with which the processor listens for signals from the AP. The processor does not transmit data to the AP until a period expires and the transceiver is powered down during the period. The period has a duration that corresponds to the interval value. The transceiver reactivates and sends a signal to the AP after the period expires. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which: 
           [0008]      FIG. 1  shows a block diagram of an illustrative system implementing the techniques disclosed herein in accordance with embodiments; 
           [0009]      FIGS. 2   a - 2   b  show additional block diagrams of a device of the system of  FIG. 1  implementing the techniques disclosed herein in accordance with embodiments; 
           [0010]      FIG. 3  shows a timing diagram that illustrates Contention-Free Periods (CFPs) and Contention Periods (CPs); 
           [0011]      FIG. 4  shows another timing diagram, in accordance with embodiments; and 
           [0012]      FIGS. 5-6  show flow diagrams of methods that may be implemented in accordance with embodiments. 
       
    
    
     NOTATION AND NOMENCLATURE 
       [0013]    Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. In some embodiments, to “power down” means to partially or completely deactivate. In some embodiments, to “power down” means to reduce power supply. In some embodiments, to “power up” means to partially or completely activate. In some embodiments, to “power up” means to increase power supply. 
       DETAILED DESCRIPTION 
       [0014]    The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment. 
         [0015]    Disclosed herein is a technique that enables various devices in a wireless network to remain in a power-conservation mode for extended periods of time, thereby conserving power. The technique comprises a set of interactions between a wireless access point (AP) and wireless stations (STAs). Generally, the technique comprises the AP instructing the STAs to remain in a “quiet mode” (i.e., to refrain from transmitting data on the network and to power down any circuit logic that does not need to be active when the STA is refraining from transmitting data on the network) for as long as possible. During this quiet mode, the AP also refrains from transmitting data on the network and powers down any circuit logic that does not need to be active when the AP is refraining from transmitting data on the network. The quiet mode is interrupted at predetermined intervals to ensure that the STAs have an opportunity to transmit and receive data from the AP. In some embodiments, these predetermined intervals correspond to the frequency at which the STAs check the network for signals from the AP, as explained below. In some embodiments, the technique is implemented using any of a variety of 802.11 or other protocols. 
         [0016]      FIG. 1  shows an illustrative block diagram of a system network  100  implementing the technique in accordance with embodiments. The network  100  includes, for instance, a wireless local area network (WLAN) that enables devices to communicate using any of a variety of suitable protocols (e.g., an 802.11 protocol; all 802.11 protocols are incorporated herein by reference). These network  100  devices include an access point (AP)  102  comprising an antenna  104 , a first station (STA)  106  comprising an antenna  112 , a second STA  108  comprising an antenna  114 , and a third STA  110  comprising an antenna  116 . Suitable replacements may be used in lieu of the antennas shown in  FIG. 1 . The AP  102  and STAs  106 ,  108 ,  110  may comprise the same or different types of devices and may comprise, among other things, desktop, laptop, notebook and netbook computers; mobile communication devices including mobile phones and personal digital assistants; and other suitable, battery-operated, wireless communication devices. 
         [0017]      FIG. 2   a  shows an illustrative block diagram of a device  200  of the network  100  of  FIG. 1 . The device  200  is a general representation of any or all of the AP  102  and the STAs  106 ,  108 ,  110 . The AP  102  and the STAs  106 ,  108 ,  110  may be more complex than the general representation of the device  200  shown in  FIG. 2   a . The device  200  comprises a processor  202  that couples with a transceiver  204 , an antenna  206 , and storage  208 . The storage  208  comprises software  210 . When executed by the processor  202 , the software  210  causes the processor  202  to perform some or all of the actions that are described herein and that are attributed to that particular device  200 . For instance, as a consequence of executing the software  210 , the processor  202 —embedded in the AP  102 —performs some or all of the actions attributed herein to the AP  102 . The device  200  may include additional circuit logic, as desired. 
         [0018]    Referring again to  FIG. 1 , in some embodiments, the AP  102  and the STAs  106 ,  108 ,  110  function in a master-slave relationship. Stated another way, the AP  102  dictates at least some of the functions of the STAs  106 ,  108 ,  110 , and particularly how those STAs interact with other devices on the network  100 . Accordingly, the AP  102  periodically broadcasts a beacon signal to the STAs  106 ,  108 ,  110 . The beacon signal comprises various information that synchronizes the network  100  and ensures that the STAs  106 ,  108 ,  110  and the AP  102  are “on the same page.” 
         [0019]    In some embodiments, the AP  102  may broadcast a beacon to the STAs  106 ,  108 ,  110  that instruct the STAs  106 ,  108 ,  110  to enter a mode known in 802.11 protocol as the Point Coordination Function (PCF). The PCF is a mode that enables the AP  102  to act as master to the slave STAs  106 ,  108 ,  110 . The PCF, in turn, contains two sub-modes. When the network  100  operates in the first of these sub-modes, known as the Contention Free Period (CFP), the AP  102  coordinates network traffic among the STAs  106 ,  108 ,  110 , giving each STA an opportunity to transmit data to and receive data from the AP  102  without interruption from the other STAs (contention arises due to the limited amount of traffic that the network  100  can support). When the network  100  operates in the second of these sub-modes, known as the Contention Period (CP), each of the STAs  106 ,  108 ,  110  attempts to send data to and receive data from the AP  102  amid contention with other STAs (i.e., without direction or network resource allocation from the AP  102 ). The AP  102  causes the network  100  to enter the CFP sub-mode using a beacon signal that it broadcasts to the STAs  106 ,  108 ,  110 . The AP  102  causes the network  100  to exit the CFP sub-mode and enter the CP sub-mode using an appropriate command signal that is broadcast to the STAs  106 ,  108 ,  110 , such as the Contention Free end (CF_end) command. Once in the CP sub-mode, the AP  102  may again cause the network  100  to enter the CFP sub-mode using a beacon signal that is broadcast to the STAs  106 ,  108 ,  110 . 
         [0020]      FIG. 3  shows a timing diagram  300  that illustrates these sub-modes. Specifically, the diagram  300  includes beacons  312 ,  314 ,  316 ,  318  and  320 , each of which is broadcast by the AP  102  to the STAs  106 ,  108 ,  110 . The timing diagram  300  also comprises CFP and CP sub-modes  302 ,  304 ,  306 ,  308  and  310 . In particular, the AP  102  causes the network  100  to enter the CFP sub-mode using beacon  312 . As explained, when the network  100  is in the CFP sub-mode, the AP  102  dictates which STAs  106 ,  108 ,  110  may transmit or receive data and when they may do so. Subsequently, the AP  102  causes the network  100  to enter the CP sub-mode by broadcasting a CF_end signal or other appropriate signal (i.e., at points  322  and  324 ). As explained, when the network  100  is in the CP sub-mode, the STAs  106 ,  108 ,  110  attempt to send and receive data without direction from the AP  102 . Thus, still referring to  FIG. 3 , the beacon  312  initiates the CFP  302 ; the CF_end  322  initiates the CP  304 ; the beacon  316  initiates the CFP  306 ; the CF_end  324  initiates the CP  308 ; and the beacon  320  initiates the CFP  310 . 
         [0021]      FIG. 4  shows another timing diagram  400  in accordance with embodiments. The diagram  400  includes beacons  412 ,  414 ,  416 ,  418  and  420 . Each of these beacons is broadcast by the AP  102  to the STAs  106 ,  108 ,  110 . The timing diagram  400  also comprises CFP and CP sub-modes  402 ,  404 ,  406 ,  408  and  410 . In contrast to the CFPs and CPs of the timing diagram  300  and in accordance with embodiments, however, the AP  102  adjusts the time durations of the CFPs and CPs of the timing diagram  400  in accordance with parameters obtained from the STAs  106 ,  108 ,  110 . In some embodiments, these parameters include “listen intervals.” An STA&#39;s listen interval is an indication of how frequently the STA will “listen,” or monitor/check the network  100 , for a signal from the AP  102 , such as a beacon signal or other instruction. Listen intervals may be programmed as desired or the STAs may determine their own listen intervals. In the example shown in  FIG. 4 , the STA  106  has a listen interval  422 , while STA  108  has a listen interval  424  and the STA  110  has a listen interval  426 . In accordance with embodiments, the STAs  106 ,  108 ,  110  transmit their respective listen intervals to the AP  102 . The STA  106 ,  108 ,  110  listen intervals may be pre-programmed or may be self-determined by the STAs upon association with the network  100 . In turn, the AP  102  compares the listen intervals received from the various STAs and adjusts the length of the CFPs (e.g., CFP  402 ,  406 ,  410 ) to match the shortest listen interval received from among the STAs. In the example shown, the STA  106  has the shortest listen interval (i.e., listen interval  422 ), so the AP  102  adjusts the durations of the CFPs to match the duration of listen interval  422 . Points  428 ,  430  and  432  signify the endpoints of the listen intervals  422 ,  424  and  426 , respectively. Stated another way, the points  428 ,  430  and  432  are those at which the STAs  106 ,  108 , and  110  exit power conservation mode (or “sleep” mode) and notify the AP  102  (e.g., using a Power Save Poll (PSPoll) signal or some other suitable signal) that it is once again ready to exchange data with the AP  102 . 
         [0022]    Justifying such an adjustment is the fact that any information that the AP  102  transmits before the STAs  106 ,  108 ,  110  listen to the AP  102  will be of no use because none of the STAs will hear that information. Because no transmissions are sent from the AP  102  to an STA  106 ,  108 ,  110  or from an STA  106 ,  108 ,  110  to the AP  102  prior to expiry of the STA  106 &#39;s listen interval  422 , radio circuitry housed within the AP  102  and the STAs  106 ,  108 ,  110  preferably are deactivated to conserve power and extend battery life. Thus, during the CFP  402  and subsequent CFPs, the AP  102  refrains from communicating with the STAs  106 ,  108 ,  110  and powers down some or all of its radio circuit logic (e.g., transceiver  204 ). Similarly, during the CFP  402  and subsequent CFPs, each of the STAs  106 ,  108 ,  110  refrains from communicating with the AP  102  and powers down some or all of its radio circuit logic (e.g., transceiver  204 ). As a result, the battery lives of the AP  102  and the STAs  106 ,  108 ,  110  are extended. 
         [0023]      FIG. 2   b  illustrates how the processor  202  powers up and powers down various components during CFPs. In some embodiments, the processor  202 , upon the start of a CFP mode, will power down some or all of radio frequency (RF) circuit logic  212 . Such circuit logic  212  includes the transceiver  204  and may include any other suitable circuit logic used to communicate with other devices in the network  100 . In some embodiments, the processor  202  powers up and powers down the RF circuit logic  212  using activation circuit logic  214 . The activation circuit logic  214  may include, for instance, various switches and other suitable circuitry that enables the processor  202  to activate and deactivate some or all of the RF circuit logic  212 . 
         [0024]    Referring to  FIGS. 3 and 4 , the CFP  402  is longer in duration than is the CFP  302 . As explained, this is true because the AP  102  extends the CFP  402 &#39;s duration to match or otherwise correspond to the duration of the shortest listen interval among the listen intervals  422 ,  424 ,  426  (in the present case, listen interval  422 ). Thus, both the CFP  402  and the listen interval  422  terminate at point  428 . Although a beacon  414  is shown in  FIG. 4  to explain how beacon signals are timed, in at least some embodiments, the AP  102  sends no beacon signals during the CFP  402  or any other CFP. Nevertheless, in such embodiments, the CFP  402  may still be said to comprise at least one beacon interval because—although the AP  102  does not actually transmit the beacon  414 —the scheduled beacon interval (i.e., the Target Beacon Transmit Time, or TBTT) still falls at the time indicated by beacon  414  in  FIG. 4 . In some embodiments, the AP  102  may send beacon signals in one or more CFPs so that new STAs joining the network  100  may be able to synchronize with other devices in the network  100 . In some such embodiments, the STAs  106 ,  108 ,  110  do not receive the AP  102 &#39;s beacon signals because the STAs  106 ,  108 ,  110  are asleep (i.e., in a power-conservation mode). 
         [0025]    Because of the information it has received from the STAs  106 ,  108 ,  110 , the AP  102  is cognizant of the fact that at point  428 , the STA  106  will listen to the network  100  for signals from the AP  102 . Thus, at point  428 , the AP  102  broadcasts a CF_end signal (or other appropriate signal) that tells all listening STAs that the CFP  402  has ended. At point  428 , the STA  106  is listening and, thus, the STA  106  transmits a signal (e.g., a PSPoll) to the AP  102  indicating that it is ready to exchange data with the AP  102 . Because the STAs  108 ,  110  are not yet awake, the STA  106  generally will be able to communicate with the AP  102  unhindered. At point  430 , however, the STA  108  wakes up because its listen interval  424  has expired. Upon exiting power conservation mode, the STA  108  transmits a signal to the AP  102  (e.g., a PSPoll signal) notifying the AP  102  that the STA  108  is ready to exchange data with the AP  102 . Similarly, at point  432 , the STA  110  arises and notifies the AP  102  that it is ready to receive data from and/or transmit data to the AP  102 . 
         [0026]    In some embodiments, the AP  102  may prematurely terminate a CFP by broadcasting a CF_end signal if it so desires. In some embodiments, the AP  102  may choose to transmit data downstream to an STA  106 ,  108 ,  110  during the CFP sub-mode, despite the fact that the AP  102  and the STAs  106 ,  108 ,  110  preferably remain in a “sleep” mode during CFPs. The AP  102  may accomplish this by broadcasting a beacon  412  that instructs only some STAs to go to sleep. The STA(s) to which the AP  102  expects to transmit during the CFP may remain outside the sleep mode. 
         [0027]      FIG. 5  shows a flow diagram of an illustrative method  500  in accordance with embodiments. The method  500  begins with the AP determining the STAs&#39; listening intervals (block  502 ). As explained, the AP is able to determine the STAs&#39; listening intervals because the STAs transmit this information to the AP. The method  500  also comprises the AP beginning the CFP period; the AP ordering the STAs to enter sleep mode; and the AP itself going to sleep (block  504 ). The method  500  further comprises the AP determining whether the minimum listening intervals among all listening intervals of the STAs has passed (block  506 ). If so, the method  500  continues with the AP terminating the CFP and receiving a request from any awake STA(s) and sending data to such STA(s) if data exists for those STA(s) and is ready for transmission (block  508 ). The method  500  further comprises the AP continuing to receive requests from STAs as they awaken and responding with data if such data exists and is ready for transmission (block  510 ). The method  500  still further comprises the AP terminate the CP period (block  512 ). Control of the method  500  is then returned to block  504 . The steps of the method  500  may be altered as desired (e.g. the steps may be rearranged or deleted or additional steps may be added to the method  500 ). 
         [0028]      FIG. 6  shows a flow diagram of an illustrative method  600  in accordance with embodiments. The method  600  comprises an STA informing the AP of its listening interval (block  602 ). The method  600  also comprises the STA sleeping (i.e., entering a power-conservation mode) in response to a command received from the AP (block  604 ). The method  600  further comprises the STA, upon expiration of its listening interval, waking up (i.e., exiting power-conservation mode), listening to the beacon, and transmitting a data request to the AP (block  606 ). The method  600  still further comprises the STA receiving data from the AP if the AP has such data for the STA and if the data is ready for transmission and the STA transmitting data to the AP if the STA has such data and the data is ready for transmission (block  608 ). The steps of the method  600  may be altered as desired (e.g., the steps may be rearranged or deleted or additional steps may be added to the method  500 ). 
         [0029]    The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.