Systems and methods for access point triggered transmissions after traffic indication map paging

Systems, methods, and devices for reducing collisions in a wireless communications network are described herein. In one aspect an apparatus for wireless communication is provided. The apparatus includes a transmitter configured to transmit a first message over a communication medium to a plurality of nodes configured to be selectively at least partially powered down during time periods in which the first message is not expected to be transmitted. The first message indicates a subset of the plurality of nodes for which data is available for transmission. The apparatus further includes a controller configured to initiate a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted.

BACKGROUND

The present application relates generally to wireless communications, and more specifically to systems, methods, and devices for performing uplink transmissions for nodes operating in a power saving mode.

The devices in a wireless network may transmit/receive information between each other. Further, devices that are not actively transmitting/receiving information in the wireless network may enter a doze state to conserve power, where the devices do not actively transmit/receive information in the doze state. These devices may further utilize paging messages to determine when to wake up from a doze state and enter an awake state in order to transmit/receive data. Thus, improved systems, methods, and devices for managing uplink transmissions after a paging message are desired.

SUMMARY

The systems, methods, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this invention provide advantages that include improved paging for devices in a wireless network.

One aspect of this disclosure provides an apparatus for wireless communication, the apparatus comprising a transmitter configured to transmit a first message over a communication medium to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and a controller configured to initiate a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted.

In one aspect, a method for wireless communication is disclosed, the method comprising transmitting a first message over a communication medium to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and initiating a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted.

In one aspect, an apparatus for wireless communication is disclosed, the apparatus comprising means for transmitting a first message over a communication medium to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and means for initiating a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted.

In one aspect, a computer program product is disclosed, comprising computer readable medium comprising code for transmitting a first message over a communication medium to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and code for initiating a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted.

In one aspect, an apparatus for wireless communication is disclosed, the apparatus comprising a receiver configured to receive a first message over a communication medium, the first message being transmitted to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and receive data according to a process for transmitting the data available to the subset of the plurality of nodes, the process being initiated by a node transmitting the first message after transmitting the first message.

In one aspect, a method for wireless communication is disclosed, the method comprising receiving a first message over a communication medium, the first message being transmitted to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and receiving data according to a process for transmitting the data available to the subset of the plurality of nodes, the process being initiated by a node transmitting the first message after transmitting the first message.

In one aspect, an apparatus for wireless communication is disclosed, the apparatus comprising means for receiving a first message over a communication medium, the first message being transmitted to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and means for receiving data according to a process for transmitting the data available to the subset of the plurality of nodes, the process being initiated by a node transmitting the first message after transmitting the first message.

In one aspect, a computer program product is disclosed, comprising computer readable medium comprising code for receiving a first message over a communication medium, the first message being transmitted to a plurality of nodes, wherein the first message indicates a subset of the plurality of nodes for which data is available for transmission, the first message further indicating a time at which data will be transmitted to nodes of the subset of the plurality of nodes; and code for receiving data according to a process for transmitting the data available to the subset of the plurality of nodes, the process being initiated by a node transmitting the first message after transmitting the first message.

DETAILED DESCRIPTION

Popular wireless network technologies may include various types of wireless local area networks (WLANs). A WLAN may be used to interconnect nearby devices together, employing widely used networking protocols. The various aspects described herein may apply to any communication standard, such as a wireless protocol.

In some aspects, wireless signals in a sub-gigahertz band may be transmitted according to the 802.11ah protocol using orthogonal frequency-division multiplexing (OFDM), direct-sequence spread spectrum (DSSS) communications, a combination of OFDM and DSSS communications, or other schemes. Implementations of the 802.11ah protocol may be used for sensors, metering, and smart grid networks. Advantageously, aspects of certain devices implementing the 802.11ah protocol may consume less power than devices implementing other wireless protocols, and/or may be used to transmit wireless signals across a relatively long range, for example about one kilometer or longer.

In some implementations, a WLAN includes various devices which are the components that access the wireless network. For example, there may be two types of devices: access points (“APs”) and clients (also referred to as stations, or “STAB”). In general, an AP may serve as a hub or base station for the WLAN and an STA serves as a user of the WLAN. For example, an STA may be a laptop computer, a personal digital assistant (PDA), a mobile phone, etc. In an example, an STA connects to an AP via a WiFi (e.g., IEEE 802.11 protocol such as 802.11ah) compliant wireless link to obtain general connectivity to the Internet or to other wide area networks. In some implementations an STA may also be used as an AP. A STA or an AP may be referred to as a node in a wireless communications network.

An access point (“AP”) may also comprise, be implemented as, or known as a NodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller (“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, or some other terminology.

A station “STA” may also comprise, be implemented as, or known as an access terminal (“AT”), a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, user equipment, or some other terminology. In some implementations an access terminal may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, a headset, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a gaming device or system, a global positioning system device, or any other suitable device that is configured to communicate via a wireless medium.

As discussed above, certain of the devices described herein may implement the 802.11ah standard, for example. Such devices, whether used as an STA or AP or other device, may be used for smart metering or in a smart grid network. Such devices may provide sensor applications or be used in home automation. The devices may instead or in addition be used in a healthcare context, for example for personal healthcare. They may also be used for surveillance, to enable extended-range Internet connectivity (e.g., for use with hotspots), or to implement machine-to-machine communications.

FIG. 1shows an exemplary wireless communication system100in which aspects of the present disclosure may be employed. The wireless communication system100may operate pursuant to a wireless standard, for example the 802.11ah standard. The wireless communication system100may include an AP104, which communicates with STAs106.

A variety of processes and methods may be used for transmissions in the wireless communication system100between the AP104and the STAs106. For example, signals may be sent and received between the AP104and the STAs106in accordance with OFDM/OFDMA techniques. If this is the case, the wireless communication system100may be referred to as an OFDM/OFDMA system. Alternatively, signals may be sent and received between the AP104and the STAs106in accordance with CDMA techniques. If this is the case, the wireless communication system100may be referred to as a CDMA system.

A communication link that facilitates transmission from the AP104to one or more of the STAs106may be referred to as a downlink (DL)108, and a communication link that facilitates transmission from one or more of the STAs106to the AP104may be referred to as an uplink (UL)110. Alternatively, a downlink108may be referred to as a forward link or a forward channel, and an uplink110may be referred to as a reverse link or a reverse channel.

The AP104may act as a base station and provide wireless communication coverage in a basic service area (BSA)102. The AP104along with the STAs106associated with the AP104and that use the AP104for communication may be referred to as a basic service set (BSS). It should be noted that the wireless communication system100may not have a central AP104, but rather may function as a peer-to-peer network between the STAs106. Accordingly, the functions of the AP104described herein may alternatively be performed by one or more of the STAs106.

The AP104may transmit a beacon signal (or simply a “beacon”), via a communication link such as the downlink108, to other nodes STAs106of the system100, which may help the other nodes STAs106to synchronize their timing with the AP104, or which may provide other information or functionality. Such beacons may be transmitted periodically. In one aspect, the period between successive transmissions may be referred to as a superframe. Transmission of a beacon may be divided into a number of groups or intervals. In one aspect, the beacon may include, but is not limited to, such information as timestamp information to set a common clock, a peer-to-peer network identifier, a device identifier, capability information, a superframe duration, transmission direction information, reception direction information, a neighbor list, and/or an extended neighbor list, some of which are described in additional detail below. Thus, a beacon may include information both common (e.g., shared) amongst several devices, and information specific to a given device.

In some aspects, a STA106may be required to associate with the AP104in order to send communications to and/or receive communications from the AP104. In one aspect, information for associating is included in a beacon broadcast by the AP104. To receive such a beacon, the STA106may, for example, perform a broad coverage search over a coverage region. A search may also be performed by the STA106by sweeping a coverage region in a lighthouse fashion, for example. After receiving the information for associating, the STA106may transmit a reference signal, such as an association probe or request, to the AP104. In some aspects, the AP104may use backhaul services, for example, to communicate with a larger network, such as the Internet or a public switched telephone network (PSTN).

FIG. 2shows an exemplary functional block diagram of a wireless device202that may be employed within the wireless communication system100ofFIG. 1. The wireless device202is an example of a device that may be configured to implement the various methods described herein. For example, the wireless device202may comprise the AP104or one of the STAs106.

The wireless device202may also include a housing208that may include a transmitter210and/or a receiver212to allow transmission and reception of data between the wireless device202and a remote location. The transmitter210and receiver212may be combined into a transceiver214. An antenna216may be attached to the housing208and electrically coupled to the transceiver214. The wireless device202may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas.

The wireless device200may be configured to operate in a low power or “doze” state where the wireless device200does not actively transmit/receive information. For example a portion or all of the transceiver214may be at least partially powered down.

The transmitter210may be configured to wirelessly transmit messages, which may be referred to as “paging messages” that are configured to indicate to other wireless devices whether or not the wireless devices need to wake up from a doze state and enter an awake state as discussed below. For example, the transmitter210may be configured to transmit paging messages generated by the processor204, discussed above. When the wireless device202is implemented or used as a STA106, the processor204may be configured to process paging messages. When the wireless device202is implemented or used as an AP104, the processor204may also be configured to generate paging messages.

The receiver212may be configured to wirelessly receive paging messages.

The wireless device202may also include a signal detector218that may be used in an effort to detect and quantify the level of signals received by the transceiver214. The signal detector218may detect such signals as total energy, energy per subcarrier per symbol, power spectral density and other signals. The wireless device202may also include a digital signal processor (DSP)220for use in processing signals. The DSP220may be configured to generate a packet for transmission. In some aspects, the packet may comprise a physical layer data unit (PPDU).

The wireless device202may further comprise a user interface222in some aspects. The user interface222may comprise a keypad, a microphone, a speaker, and/or a display. The user interface222may include any element or component that conveys information to a user of the wireless device202and/or receives input from the user.

The various components of the wireless device202may be coupled together by a bus system226. The bus system226may include a data bus, for example, as well as a power bus, a control signal bus, and a status signal bus in addition to the data bus. Those of skill in the art will appreciate the components of the wireless device202may be coupled together or accept or provide inputs to each other using some other mechanism.

Although a number of separate components are illustrated inFIG. 2, those of skill in the art will recognize that one or more of the components may be combined or commonly implemented. For example, the processor204may be used to implement not only the functionality described above with respect to the processor204, but also to implement the functionality described above with respect to the signal detector218and/or the DSP220. Further, each of the components illustrated inFIG. 2may be implemented using a plurality of separate elements.

The wireless device202may comprise an AP104or an STA106, and may be used to transmit and/or receive communications including paging messages. That is, either AP104or STA106may serve as transmitter or receiver devices of paging messages. Certain aspects contemplate signal detector218being used by software running on memory206and processor204to detect the presence of a transmitter or receiver.

The STA106may have a plurality of operational modes. For example, the STA106may have a first operational mode referred to as an active mode. In the active mode, the STA106may always be in an “awake” state and actively transmit/receive data with the AP104. Further, the STA106may have a second operational mode referred to as a power save mode. In the power save mode, the STA106may be in the “awake” state or a “doze” or “sleep” state where the STA106does not actively transmit/receive data with the AP104. For example, the receiver212and possibly DSP220and signal detector218of the STA106may operate using reduced power consumption in the doze state. The STA106may at least partially power down a portion of a transceiver in the doze state. Further, in the power save mode, the STA106may occasionally enter the awake state to listen to messages from the AP104(e.g., paging messages) that indicate to the STA106whether or not the STA106needs to “wake up” (e.g., enter the awake state) at a certain time so as to be able to transmit/receive data with the AP104.

Accordingly, in certain wireless communication systems100, the AP104may transmit paging messages to a plurality of STAs106in a power save mode in the same network as the AP104, indicating whether or not there is data buffered at the AP104for the STAs106. The STAs106may also use this information to determine whether they need to be in an awake state or a doze state. For example, if an STA106determines it is not being paged, it may enter a doze state. Alternatively, if the STA106determines it may be paged, the STA106may enter an awake state for a certain period of time to receive the page and further determine when to be in an awake state based on the page. Further, the STA106may stay in the awake state for a certain period of time after receiving the page. In another example, the STA106may be configured to function in other ways when being paged or not being paged that are consistent with this disclosure.

In some aspects, paging messages may comprise a bitmap (not shown in this figure), such as a traffic identification map (TIM). In certain such aspects, the bitmap may comprise a number of bits. These paging messages may be sent from the AP104to STAs106in a beacon or a TIM frame. Each bit in the bitmap may correspond to a particular STA106of a plurality of STAs106, and the value of each bit (e.g., 0 or 1) may indicate the state the corresponding STA106should be in (e.g., doze state or awake state). Accordingly, the size of the bitmap may be directly proportional to the number of STAs106in the wireless communications system100. Therefore, a large number of STAs106in the wireless communications system100may result in a large bitmap.

FIG. 3illustrates a plurality of partitioned paging messages302transmitted by the AP104to STAs106in the wireless communication system100ofFIG. 1. As shown, time increases horizontally across the page over the time axis304. As shown, the AP104is configured to transmit a plurality of paging messages302. The paging messages302may be sent in a TIM frame, a beacon, or using some other appropriate signaling. The STAs106may be configured to listen to one or more of the paging messages302. Following the one or more paging messages302, the STAs106may be configured to transmit requests to the AP104and receive a response from the AP104.

The paging process may result in a high number of STAs106receiving the one or more paging messages302. For example, a high number of STAs106in the same TIM may receive the one or more paging messages302, which may lead to one or more STAs106contending to transmit requests to the AP104on the medium after the TIM. Accordingly, collisions resulting in corrupted data received by the AP104may occur in situations in which at least two STAs106attempt to transmit requests to the AP104at or nearly at a same time.

FIG. 4illustrates a polling request mechanism400. The polling request mechanism400shown may be used by the AP104and the STAs106in the wireless communication system100ofFIG. 1. As shown, time increases horizontally across the page from slot time424to slot time440. The implementation shown byFIG. 4shows a contention based system, where different STAs may contend to gain access to the medium. In contrast,FIGS. 5-8as will be further described below show alternative implementations which may have improvements in various aspects over the implementation ofFIG. 4as will be further described below.

In general, after the transmission of a paging message, such as TIM410, a time interval may be reserved for the paged STAs106. The reservation may be achieved by transmitting a message (e.g., paging message, additional message) to cause non-paged STAs to defer access to the medium for the duration of the reserved period. In some implementations, the deferred access can be achieved by setting a duration field value of a reserving frame so that non-paged STAs can set their network allocation vector (NAV). In other implementations, the deferred access can be achieved by sending an additional frame preceding or following the paging frame, where the additional frame indicates the duration of the reserved period.

During the reserved time interval, the paged STAs106can send requests to the AP104(e.g., Power Saving polls (PS-POLL) requests412,416, and420) and receive a response from the AP104(e.g., response414,418, and422). Multiple paged STAs106can contend during the reserved time interval in accordance with various methods, as described herein. In some embodiments, STAs106that have not been paged cannot contend during the reserved time interval. Once the reserved time interval is over, STAs106can start contending to send the requests to the AP104. In an embodiment, the AP104may determine the duration of the reserved time interval. The reserved time interval should be sufficient for all the paged STAs106to send requests to the AP104and receive a response from the AP104. By way of example, and not limitation, the duration of the reserved time interval may be a function of the number of paged STAs106.

The polling request mechanism400illustrates an embodiment in which STAs402,404, and406can transmit requests, like PS-POLLs412,416, and420, to AP408in such a way so as to avoid collisions. STAs402,404, and406may be similar to STAs106as described herein. In some embodiments, the STAs402,404, and406may transmit requests to the AP408in a certain order. AP408may be similar to AP104as described herein. The paging message, such as TIM410, may implicitly or explicitly define an ordering for the STAs402,404, and406. For example if the TIM410bitmap indicates that both STA402and STA404are paged, then the TIM410bitmap also implicitly or explicitly indicates whether STA402is before or after STA404. In an example, the order could be determined by the order in which the paged STAs appear in the bitmap representation. Consider a bitmap {0, 1, 0, 0, 1, 1}, where the STA associated with the bit in position2is assumed to be before the STA associated with the bit in position5. In some implementations, the compressed bitmap may be expressed as list of STA identifiers. In this case the sequence in which the STA identifiers appear in the list may determine the order. Consider the list {13, 25, 5, 22}, where the STA associated with identifier “13” is assumed to come before STA identified by “5.” In another aspect, the order may be derived from the value of the STA identifier irrespective of the message representation.

In some implementations, the position of the STA402,404, or406within the TIM410bitmap sequence may be a function of the position of the STA402,404, or406as described above. The order may further be dependent on other indications, the indications being either included in the paging message or assumed to be known at the STAs402,404, and/or406. For example, the indication may include the Timing Synchronization Function (TSF) within the paging message (e.g., TIM410). In such an implementation, the first STA may be the one whose identifier is set to “1” and has a position within the TIM410bitmap sequence which is first in the order after the position associated with the 12 least significant bits (LSBs) of the TSF. Many other functions incorporating various indications can be included to achieve a similar result as that based on the TSF. One beneficial result of including the TSF in the computation of the order is that the order may be changed at each transmission, provided that the portion of the used TSF is different at each transmission.

In some implementations, the sender of the paging message may determine the order of the paged STAs according to any criteria including the usage of the ordering information. For example the sender, AP408, may order the STAs402,404, and406based on their QoS requirements, power saving requirements, or other performance parameters. It may be desirable in some implementation for the sender of the paging message to include in the message an explicit indication of the order. This explicit indication of the order may not be based on the TIM410bitmap, but rather on other factors as described herein.

For illustrative purposes only, and not meant to be limiting,FIG. 4depicts an order of STA402, STA404, and then STA406. While STA402may be the first STA to transmit a request to the AP408, the STA402may not do so immediately after the TIM410. Each of STAs402,404, and406may be configured to use a carrier sense multiple access with collision avoidance (CSMA/CA) based medium access procedure, such as the distributed coordination function (DCF) or the enhanced distributed channel access (EDCA) as defined in the IEEE 802.11 standard. In such a medium access mechanism, a STA402,404, or406that wants to access the medium for the transmission of a frame initializes a back-off counter. The back-off counter may be initialized with a random number chosen in an appropriate interval. For example, an appropriate interval may be a value between 0 and a duration of a contention window (CW). The back-off counter may be decremented while the transmission medium (e.g., channel) is idle—in other words, no activity is detected on the transmission medium. The transmission medium may be considered to be idle if no activity is detected for a distributed inter-frame space (DIFS) or an arbitration inter-frame space (AIFS) interval. After the medium has been idle for a DIFS or AIFS interval of time, the back-off counter may be decremented by one unit per each additional consecutive idle interval of a duration equal to a slot time. When activity is detected on the medium, the back-off countdown may be frozen and restarted when the medium becomes idle again, as described herein. The STAs402,404, and406may transmit a packet on the medium when the back-off counter reaches zero or any other integer that represents a lowest value of the counter. The DIFS interval may be defined as
DIFS=SIFS+(2*slot time)  (1)
where SIFS is a short inter-frame space. The AIFS interval may be defined as
AIFS=SIFS+(n*slot time)  (2)
where n is greater than or equal to 2.

Each of STAs402,404, and406may be configured to use a deterministic back-off value to initialize a back-off counter, where an initial value of the back-off counter may be based on the order of the paged STAs402,404, and406. For example, an initial value of the back-off counter for STA402may be 1, an initial value of the back-off counter for STA404may be 2, and an initial value of the back-off counter for STA406may be 3. In this way, an initial value of the back-off counter may be different for each STA402,404, and406so as to allow each STA402,404, and406to access the medium in different time instants.

In some implementations, the back-off counter for each STA402,404, and406may decrement the back-off value when the channel over which the STAs402,404, and406communicate with the AP408is idle for the duration of a slot time424,426,428,430,432,434,436,438, and440. As an example, a regular slot time may be a slot time defined in the IEEE 802.11 standard or a similar CSMA/CA protocol. The STAs402,404, and/or406may be configured to transmit a PS-POLL request412,416, and/or420when their respective back-off value reaches zero or any other integer that represents a lowest value of the counter.

In the implementation described inFIG. 4, each STA402,404, and406is configured to send polling messages to the AP408in order to request the data that is buffered for the STA402,404, and406. In some instances, this may create extra overhead and have other undesirable effects. It may be desirable to have an improved way for multiple STAs to be able to access the medium in a reliable way after receiving a paging message such as a TIM frame. For example, it may be important to reduce power consumption, reduce medium occupancy, and minimize the time each paged STA402,404, and406is an awake state. In addition, an implementation for providing access to a medium may also need to take into account a hidden node. A hidden node may be a node that is in communication with an AP408, but which is hidden from other STAs (i.e., the other STAs are not aware of the existence of the hidden node). In this case, problems may arise for collision avoidance techniques that depend on a STAs ability to sense the medium. In this case it is desirable for a mechanism to reduce/eliminate collisions while also minimizing access delay to the channel. Furthermore, an access scheme after a TIM page may also be robust to handle, for example, adjacent overlapping basic service set (OBSS) transmissions. An OBSS transmission516may occur if a STA, such as STA404, identifies with two or more basic service sets, where each basic service set include an AP and associated STAs. The OBSS transmission may originate from an AP other than AP408.

As such, according to one implementation, an AP408may initiate a process for transmitting the data available to paged STAs402,404, and406after a paging message is received. For example, an AP408may reserve a communication medium exclusively for pages STAs after a TIM page410for a certain time interval that may be known or indicated in the TIM page410frame. The AP408may be configured to estimate the duration for the exclusive time interval based on the number of buffered units (and their associated length) it has planned to sent to the various paged STAs during the time interval. All STAs for which the AP408has no data buffered as indicated in received the TIM page410may set their NAV for the specified duration. STAs402,404, and406that are paged (i.e., the TIM page indicates that the AP408has data buffered for sending to the STAs402,404, and406) may enter an “awake” mode and be configured to listen for control messages from the AP408. As will be described in further detail below, the AP408may send a first control message indicating that it is planning to send data to a particular paged STA402. For example, the control message may function similarly to a request to send (RTS) message indicating the particular paged STA402to which it plans to transmit buffered data. The paged STA402may respond with a second control message indicating that it is ready to receive the buffered data. For example, the second control message may function similarly to a clear to send (CTS) message indicating that it is ready to receive the buffered data. Other paged STAs404and406may sleep for a time period indicated in the first control message. This process may repeat for all paged STAs. Paged STAs that do not receive their intended first control message (e.g., they were somehow still asleep or receiving some other conflicting message such as an OBSSS transmission) may thereafter solicit the AP408by sending a polling message such as a PS-POLL frame during a reserved or a non-reserved time period. This may happen after the time period after the AP408has indicated that it will send data transmissions to each of the STAs.

FIG. 5illustrates an exemplary implementation for AP508initiated transmissions after a TIM page510. The TIM page510may be referred to as a first message. The AP508may be configured to send a TIM page510to all STAs (i.e., nodes) within a wireless communication network. For example the TIM page510may be sent to all STAs as defined by a basic service set. The transmission of a TIM page510may happen periodically during a scheduled time interval. In some embodiments, the STAs within the network may be configured to enter a doze state when they do not expect to receive data. These STAs within the network may be configured to awaken from a doze state during the scheduled time interval to receive the TIM page510, and otherwise return to the doze state unless the TIM page510indicates that data is buffered for that STA. After the TIM page510is transmitted, the AP508may be configured to initiate a process to communicate data available to each of the paged STAs. For example, the AP508may be configured to reserve a period of duration526for transmission of buffered data units to paged STAs502,504, and506. This period of time526may be known or specified in the TIM page510. This period of time may be based, at least in part, upon the number of paged STAs or the Other non-paged STAs (not shown) for which no data is buffered may be configured to enter a doze state for at least this period of time526. In addition or alternatively, each non-paged STA (not shown) may set the network allocation vector (NAV) for the reserved period of time indicated.

After the TIM page510is transmitted by the AP508, the AP508may poll each paged STA502,504, and506for which it has buffered data (e.g., buffered units) by sending a first control message to each paged STA502,504, and506. Each first control message may indicate a particular paged STA502,504, and506for which data is planned to be sent. The order of when the AP508sends each first control message may be based on the paged STAs order/position in the TIM bitmap or other parameters (e.g., QoS, etc.). As an example, in one exemplary implementation, the AP508may send a first control message512athat indicates that it plans to send buffered data to STA1502. All paged STAs502,504, and506may be awake to receive the first control message512a. The first control message512amay indicate an amount of time for which data is planned to be sent to STA502. STAs504and506, not indicated in the first control message512a, may sleep and/or set their NAV based on a time period indicated in the first control message512a. The first control message512amay be configured as or function similarly to a request to send (RTS) message.

STA1502, if awake, may respond to the first control message512awith a second control message514aafter some frame spacing amount. The second control message514amay indicate that the STA1502is ready or is planning on receiving the data transmission from the AP508. In some implementations, the second control message514amay be configured as or function similarly to a clear to send (CTS) message. In response to receiving the second control message514a, the AP508may send data516athat is intended for STA1502. Thereafter, the STA1502may send, and the AP508may receive, an acknowledgment message518a. After the time period specified in the first control message512ahas ended, the AP508may send a subsequent first control message512bindicating that it is planning on transmitting buffered data to STA2504. The subsequent first control message512bmay also indicate a period of time for which it plans to send data to STA2504. STAs502and506may enter into a sleep mode for the period of time indicated in the first control message512b. In this case, STA2504may for some reason fail to receive the first control message512bor be unable to respond with a second control message. For example, STA2504may be in a sleep mode for some reason (e.g., for the time period522) and not receive the first control message512b. In another case STA2504may be receiving an OBSSS transmission as described above, or be unable to respond. In this case, if the AP508does not receive a second control message from STA2504, then the AP508may not send any data. However, the AP508may not send any other first control messages until the time period indicated in the first control message512bhas elapsed as shown by the time period528, as other STAs502and506may be configured to sleep during this time.

After the time period528, the AP508may send a subsequent first control message512cindicating that the AP508is planning/requesting to send buffered data to STA3506. The first control message512cmay indicate a time period for transmission of data to STA3506. In this case, STAs502and504may be awake to receive the first control message512cand set their NAV in response and/or sleep for the duration of the time period indicated in the first control message512c. In other implementations, once a paged STA has received its buffered data from the AP508, it may sleep for the remainder of the duration526and set its NAV accordingly. After receiving the first control message512c, STA3506may respond with a second control message514cas described above indicating that it is ready to receive the buffered data. Thereafter, the AP508may send data516cto STA3506. The AP508may thereafter receive an acknowledgement message518cfrom STA3506if the data was received successfully. In some cases, if an acknowledgment message518cis not received, the AP508may be configured to resend a first control message (not shown) in an attempt to resend the data. This process may be repeated for all STAs for which the AP508has buffered data to send.

In some cases, STA2504may awaken in time period524, or be configured to otherwise communicate with AP508(e.g., a collision) after missing or being unable to respond to the first control message512b. In this case, the STA2504may be configured to send a polling message520to the AP508requesting the data that is buffered for STA2504. For example, STA2504may send a PS-POLL to the AP508soliciting for transmission of buffered units. In response, the AP508may send the data516bto STA2504and receive an acknowledgment518b.

In some cases, one of the paged STAs502,504, or506may be a hidden node. For example, STA3506may be hidden with respect to STAs502and504but all may see transmissions from AP508. In this case, as each STA502,504, and506is waiting for an AP508response, waiting for the response is sufficient to protect the STAs502,504, and506access to the medium.

In some implementations, the paging message, such as a TIM page, may implicitly or explicitly define an ordering of the STAs. For example, the order of when the AP508sends each first control message may be based on the paged STAs order/position in the TIM bitmap. In some implementations, the STAs may be configured to selectively at least partially power down during times at which they do not expected data to be transmitted to them. The STAs may be configured to selectively at least partially power down in response to their order/position in the TIM bitmap. For example, the AP508may send a TIM bitmap to STA1502, STA2504and to STA3506which may indicate that each STA has data buffered for it. Each STA may be configured to determine the order in which it was identified in the TIM bitmap, and to use this information, at least in part, to determine how long it may at least partially power down or sleep. For example, STA3506may be the third STA in the TIM bitmap. STA3506may use this information to sleep for a time period equivalent to how long it may take to transmit data to STA1502and STA2504.

In some implementations, data may be sent for a delivery to a single STA individually. For example, the AP508may send data516athat is intended for STA1502. This data may be intended only for STA1502, and thus may be send for delivery to STA1502. This type of system may be referred to as a unicast system, and may comprise a one-to-one connection between a STA, such as STA1502, and the AP508. In some implementations, the data may be multicast data intended for a plurality of STAs. For example, data may be intended for STA1502, STA2504and STA3506. Multicast data may be intended for each STA, or may be intended for a subset of STAs. It may be desirable to send data to each STA individually, or it may be desirable to send data to a plurality of STAs at the same time. For example, the AP508may be configured to multicast data to a plurality of STAs at the same time. It may be advantageous in such an implementation to not have STAs send control messages to the AP508, as this may result in a larger number of control messages if data is intended to be multicast to a large number of STAs.

FIG. 6illustrates another exemplary implementation for access point initiated transmissions after a traffic map indicator page. This implementation may function similarly to that shown inFIG. 5, however, as shown inFIG. 6, an AP608may send a first control message to a next STA if the current STA did not reply with a second control message after only waiting for the duration of the second control message along with some additional small time period. For example, the additional small time period may be correspond to a distributed inter-frame space (DIFS) duration as defined above.

As shown, an AP608may transmit a TIM page610that may reserve a time period626for transmission of buffered data to paged STAs602,604, and606. As similarly shown inFIG. 5, the AP608may thereafter send a first control message612aindicating that it is requesting to send data to STA1602. Thereafter, STA1602may send a second control message614athat indicates that it is ready to receive the data from the AP608. The AP608may thereafter send data616ato STA1602and receive an acknowledgment618a. Thereafter, AP608may transmit a subsequent first control message612bindicating that it is requesting to send data to STA2608. However, as described above, for various reasons (e.g., collision or in a sleep mode), STA2608may not respond with a second control message. In this case, rather than waiting for a planned duration, if the AP608does not receive the second control message from STA2604, the AP608may send another first control message612cafter waiting for the time period in which it may receive a second control message along with some additional defined amount of time such as DIFS shown in part by the time period628. The first control message612cwould indicate the AP608is intending to transmit buffered data for STA3606. In this case, the first control messages612a,612b, and612cmay not indicate any time period for which data will be sent in the event that no corresponding second control message is received. All paged STAs602,604, and606may be configured to remain in an awake mode for the duration626in case a first control message is sent. However, in some implementations, once a paged STA has received its buffered data, it may enter a sleep mode for the duration626after sending an acknowledgment message.

After the first control message612cis sent, STA3606may send a second control message614bindicating that it is ready to receive the buffered data. The AP608may thereafter send the data616cand receive an acknowledgement message618c.

In addition, while STA2604did not respond to its corresponding first control message612b, STA2604may be configured to be able to thereafter receive buffered data from the AP608at some point. As such there may be a reserved or non-reserved time period in which STA2604may send a polling message620(e.g., a PS-POLL) to the AP608requesting data transmissions. In response, the AP608may send the corresponding data616band receive an acknowledgement message618b.

The implementation described above with reference toFIG. 6may increase the time in which paged STAs may be configured to be in a awake state, however, less of a reserved transmission may be wasted if one of the paged STAs does not respond. As such, this implementation may in some aspects improve medium utilization and reduces access delay for all STAs when at least some of the STAs are not active during TIM paging.

FIG. 7illustrates another implementation for access point initiated transmissions after a traffic map indicator page. In this case, the AP708may also reserve a duration726for sending buffered data to paged STAs702,704, and706after a TIM page710is transmitted by an AP708. The duration726may be indicated in the TIM page710allowing non-paged STAs to go into sleep mode. Thereafter, the AP708may be configured to send the buffered data to the paged STAs702,704, and706without waiting for any responses (e.g., second control messages) from corresponding paged STAs702,704, and706. For example, after sending a TIM page710, the AP708may send a fourth control message712athat indicates that the AP708is planning to send data to STA1712a. Thereafter, the AP708may send data716abuffered to the STA1702without waiting for any response and may thereafter receive an acknowledgment message718afrom STA1702if STA1702received the data716a. This may be repeated for STAs704and706where the AP708may send fourth control signals712band712cand thereafter send data716band716bbuffered to the STAs704and706as shown. In this case, the AP708may only receive an acknowledgment message718cfrom STA3706if STA3706received the data716c. The AP708may also send a fourth control message and any buffered data to any other paged STAs. A further time period within the duration726may also be used for paged STAs that did not receive their respective transmissions. In that case, a paged STA2704may send a polling message720(e.g., a PS-POLL) to the AP708requesting its buffered data. In response the AP708may send data716bto STA2704and in response may receive an acknowledgment message718b. The AP708may further receive polling messages from other pages STAs. Based on the fourth control message, if a paged STA determines that it is not the recipient of data about to be sent, it can enter a doze state for a NAV duration based on information in the fourth control message. In other implementations, each paged STA may stay awake and watch for its buffered data to be sent which may be further indicated by the fourth control signal. In some implementations, once its data has been received, the paged STA may go into a doze state for the remaining duration726. In some implementations, the fourth control message may be configured as or function similarly to a clear-to-send to self (CTS-To-Self) message.

FIG. 8illustrates another exemplary implementation for access point initiated transmissions after a traffic map indicator page. As shown inFIG. 8, as compared toFIG. 7, the fourth control message may not be sent. In this case no control messages are sent indicating that data will be sent to a paged STA. In this case, the AP808may send buffered data during a reserved period within the duration826to all paged STAs802,804, and806. Each packet of buffered data may be intended for a single STA, in a unicast system as shown inFIG. 8, or for a plurality of STAs, in a multicast system. In this case each paged STA802,804, and806may stay in an awake state until it sees data intended for that paged STA802,804, and806. In some implementations, after receiving the data, and if there is no more buffered data for the STA, it may enter into a doze state for a remainder of the reserved duration826. If data was sent to a paged STA2804, but the paged STA2804was either asleep or there was a collision, STA2804may thereafter sending a polling message820to request paged data during a reserved (e.g., guard) or non-reserved time interval. The AP808may then resend the data816band may receive an acknowledgment message818b.

It should be appreciated that each device may operate according to several modes that may correspond to each of the implementations or combinations thereof described inFIGS. 5-8. As such, depending on the mode, the AP and STAs may be configured to operate differently, where the mode be selected based on various operating conditions and parameters.

FIG. 9is a flowchart of an exemplary method for access point initiated transmissions after a traffic map indicator page. At block902, the method may include transmitting a first message over a communication medium to a plurality of nodes configured to be selectively at least partially powered down during time periods in which the first message is not expected to be transmitted. The first message indicates a subset of the plurality of nodes for which data is available for transmission. The first message may correspond to a TIM page. In block904, the method includes initiating a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted. The process may correspond to any implementation described above with reference toFIGS. 5-8or any combination thereof. The method900may be implemented in an access point.

FIG. 10is a functional block diagram of an exemplary wireless device1000that may be employed within the wireless communication system100. The device1000includes means1002for transmitting a first message over a communication medium to a plurality of nodes configured to be selectively at least partially powered down during time periods in which the first message is not expected to be transmitted. The first message indicates a subset of the plurality of nodes for which data is available for transmission. The first message may correspond to a TIM page message. In one implementation, the means for transmitting a first message may be configured to perform one or more of the functions discussed above with reference to block902. The device1000may further includes means1004for initiating a process for transmitting the data available to the subset of the plurality of nodes after the first message is transmitted. The means for initiating a process1004may be configured to perform one or more of the functions discussed above with reference to block902. The means1002may include a transmitter. The means1004may include a controller.

FIG. 11is a flowchart of an exemplary method for receiving access point initiated transmissions after a traffic map indicator page. In block1102, the method may include receiving a first message over a communication medium. The first message is transmitted to a plurality of nodes configured to be selectively at least partially powered down during time periods in which the first message is not expected to be transmitted. The first message indicates a subset of the plurality of nodes for which data is available for transmission. In block1104, the method further includes receiving data according to a process for transmitting the data available to the subset of the plurality of nodes. The process is initiated by a node transmitting the first message after transmitting the first message.

FIG. 12is a functional block diagram of an exemplary wireless device1200that may be employed within the wireless communication system100. The device1200includes means1202for receiving a first message over a communication medium. The first message is transmitted to a plurality of nodes configured to be selectively at least partially powered down during time periods in which the first message is not expected to be transmitted. The first message indicates a subset of the plurality of nodes for which data is available for transmission. In an embodiment, means1202for receiving the first message may be configured to perform one or more of the functions discussed above with respect to block1102. The device1200further includes means1204for receiving data according to a process for transmitting the data available to the subset of the plurality of nodes, the process being initiated by a node transmitting the first message after transmitting the first message. The first message may correspond to a TIM page message. In an embodiment, means1204for receiving data may be configured to perform one or more of the functions discussed above with respect to block1104. The means1202and1204may include a receiver.

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. Further, a “channel width” as used herein may encompass or may also be referred to as a bandwidth in certain aspects.