WO2009057080A2

WO2009057080A2 - Wireless communication system featuring enhanced unscheduled automatic power save delivery

Info

Publication number: WO2009057080A2
Application number: PCT/IB2008/054547
Authority: WO
Inventors: Naveen Kakani
Original assignee: Nokia Corporation; Nokia, Inc.
Priority date: 2007-11-01
Filing date: 2008-10-31
Publication date: 2009-05-07
Also published as: WO2009057080A3

Abstract

Disclosed herein are apparatus, method, and computer program product whereby an access point receives a trigger frame from a station. The access point sends a new frame to the station, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station. The access point transmits the data to the station when the period of time elapses.

Description

WIRELESS COMMUNICATION SYSTEM FEATURING ENHANCED UNSCHEDULED AUTOMATIC POWER SAVE DELIVERY

TECHNICAL FIELD:

The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer program products and, more specifically, relate to techniques to conserve power in a wireless local area network.

BACKGROUND:

Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:

AC access category

ACs access categories

AP access point

BSS basic service set

DL downlink (in a direction from an AP to a STA) EDCA enhanced distributed channel access

MAC medium access control

MMPDU medium access control management protocol data unit

MSDU medium access control service data unit

OFDM orthogonal frequency division multiplex PHY physical

PSMP power save multi-poll

QoS quality of service

RD reverse direction

RIFS recovery inter- frame space SP service period

STA station

TXOP transmit opportunity

U-APSD unscheduled automatic power-save delivery

UL uplink (in a direction from a STA to an AP) VoIP voice over internet protocol

WLAN wireless local area network

In the foregoing definitions, the PSMP is considered herein to be a mechanism that provides a time schedule that is used by an AP and its STAs to access the wireless medium. The mechanism is controlled using a PSMP action frame.

In the foregoing definitions, the BSS is considered herein to be a set of STAs that have successfully synchronized using JOIN service primitives, and one STA that has used a START primitive. Membership in a BSS does not imply that wireless communication with all other members of the BSS is possible.

It can be noted that there may exist some embodiments where an AP per se is not present in the BSS, such as in certain types of ad hoc wireless local area networks.

A document of general interest to this invention is: "Wireless LAN medium access control (MAC) and physical layer (PHY) specifications: Medium access control (MAC) quality of service (QoS) enhancements," IEEE Std. 802.1 Ie -2005, Nov. 2005. Section 11.2 "Power Management".

Another document of interest is US 2006/0285517 Al , "Scheduling Data Transmissions to Improve Power Efficiency in a Wireless Network", Naveen K. Kakani. In paragraph [0024] of this US Patent Application Publication it is stated that after a station is associated with an AP, the two nodes may establish a data transmission schedule, indicating a service period, for example, by exchanging one or more frames or messages indicating a schedule start time for the service period. A variety of different mechanisms may be used to exchange or agree on a time for a service period. For example, the IEEE 802.11 e draft specification allows for power management through automatic power-save delivery (APSD). APSD provides two delivery mechanisms: scheduled APSD and unscheduled AP SD . Stations may use unscheduled AP SD (U-AP SD) to have all or some of their frames delivered to them from the AP during unscheduled service periods. An unscheduled service period may begin when the AP receives a trigger message from the station. According to scheduled APSD (S-APSD), a station may receive a data transmission schedule from an AP indicating a service start time and service interval when the station may receive and transmit frames during scheduled service periods. For example, by using APSD, a station may conserve power and extend battery life by remaining in a lower power state, and then waking during a scheduled or unscheduled service period to receive and transmit data.

hi the current WLAN standard the time from when a trigger frame is sent to the time when data is present on the medium is variable. With the use of devices capable of more than just voice service, the current WLAN standard does not permit a STA to allow data of a multiple AC in a power efficient manner.

hi conventional practice a STA configures an AC to be Delivery Enabled or Trigger Enabled, or both. The STA transmits a trigger frame (QoS Data or QoS NULL) to initiate U-APSD SP. The trigger frame can belong to the AC(s) that are configured to be trigger enabled. During the U-APSD SP data of a different AC can be transmitted. Also, during a U-APSD SP a STA cannot initiate a second U-APSD SP by transmitting a second trigger frame.

A SP starts at the time the AP receives a trigger frame and it ends after the AP has attempted to transmit at least one MSDU or MMPDU associated with a delivery-enabled AC and destined for the non-AP STA, but no more than the number indicated in a Max SP Length field if the field (QoS capability field in Association and re-association request frame) has a nonzero value.

Figure 1 shows a power save mechanism in accordance with the current standard, and illustrates the operations that occur at the AP and at the STA (station x), and the signaling between them.

The use of this conventional approach has several problems associated therewith. For example, the time between a STA transmitting the trigger frame and receiving data from the AP can vary from few hundreds of microseconds to a millisecond or more. The amount of delay depends generally on the architecture of the AP between the radio link and a host (where data may be queued), on the load of the system, and on the AC of the data to be transmitted, hi a scenario where the AP has data of different ACs queued for a given STA, the AP needs to initiate channel access for each AC. This implies that the STA needs to be awake for a longer period of time (and thus consuming battery power) based on the load at the AP.

SUMMARY:

A first embodiment of the invention is a method comprising: receiving a trigger frame from a station at an access point; sending a new frame to the station, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station; and transmitting the data to the station when the period of time elapses.

Another embodiment of the invention is a method comprising: transmitting a trigger frame from the station to an access point; receiving a new frame from the access point, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station; and determining whether to enter a power saving mode, or perform some other action, during the period of time before the access point transmits data to the station.

A further embodiment of the invention is a computer readable medium encoded with a computer program executable by a processor to perform actions comprising: receiving a trigger frame from a station at an access point; sending a new frame to the station, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station; and transmitting the data to the station when the period of time elapses.

A still further embodiment of the invention is a computer readable medium encoded with a computer program executable by a processor to perform actions comprising: transmitting a trigger frame from the station to an access point; receiving a new frame from the access point, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station; and determining whether to enter a power saving mode, or perform some other action, during the period of time before the access point transmits data to the station.

Another further embodiment of the invention is an apparatus, comprising: a receiver configured to receive a trigger frame from a station; a controller configured to compose a new frame to the station, the new frame comprising information for informing the station of an amount of time that will elapse before the station receives data; and a transmitter configured to send the new frame and to send the data to the station when the period of time elapses.

Another further embodiment of the invention is an apparatus, comprising a transmitter configured to transmit a trigger frame to an access point; a receiver configured to receive a new frame from the access point, the new frame comprising information for indicating an amount of time that will elapse before receiving data from the access point; and a controller configured to determine whether to enter a power saving mode, or perform some other action, during the period of time before receiving the data from the access point.

Another further embodiment of the invention is an apparatus, comprising means for receiving a trigger from a station; means for composing a frame, the frame comprising information for informing the station of an amount of time that will elapse before transmitting data to the station; and means for transmitting the frame to the station and for transmitting the data to the station when the period of time elapses.

Another further embodiment of the invention is an apparatus comprising: means for transmitting a trigger frame to an access point; means for receiving a frame from the access point, the frame comprising information for indicating an amount of time that will elapse before receiving data from the access point; and means for determining at least whether to enter a power saving mode during the period of time before receiving the data from the access point. BRIEF DESCRIPTION OF THE DRAWINGS

In the attached Drawing Figures:

Figure 1 shows a power save mechanism in accordance with a current IEEE 802.1 Ie standard.

Figure 2 shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.

Figure 3 illustrates conventional reception by an AP of triggers from two STAs (STAl, STA2), ACKs sent in response, and the subsequent transmission of data for ACx and ACy to STAl and STA2.

Figure 4 illustrates the use of a novel new frame to indicate to the respective STAs when to be awake to receive their AC data.

Figure 5 is a logic flow diagram that illustrates a method, and the result of execution of computer program instructions, at the AP in accordance with exemplary embodiments of this invention.

Figure 6 is a logic flow diagram that illustrates a method, and the result of execution of computer program instructions, at the STA in accordance with exemplary embodiments of this invention.

DETAILED DESCRIPTION

It is desirable for the AP to send data to a STA as soon as possible in order to conserve battery power. The inventor has recognized that certain traffic characteristics allow the wireless medium to be used effectively for, as non-limiting examples: data retrieval; the scheduling of the data of multiple STAs of the same AC to be transmitted to most effectively use the wireless medium (effective use of TXOP), thereby reducing the number of channel accesses by the AP; and the scheduling of data of different ACs for the same or a different STA, thereby reducing the number of channel accesses that are required.

Described herein is a novel new frame (which may be a management frame or a control frame), and how the novel new frame can be used with various scheduling algorithms. The use of the new frame allows for a STA to know when data scheduling can occur, which enables the STA to make a decision to either sleep (e.g., to enter a low power mode of operation) or to perform some other task, such as transmitting UL data.

Reference is first made to Figure 2 for illustrating a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention, hi Figure 2 a wireless system 1 is adapted for communication with at least one STA 10 via an AP 12. The system 1 , in general, may be compatible with IEEE 802- 11 or similar protocols, hi a typical implementation there will a plurality of STAs 10 that are served by the AP 12. Figure 2 shows an exemplary number (3) of STAs 10, referred to individually as STAl, STA2, STA3, which may be considered to form a BSS. The system 1 may include a connection with at least one host 14 that may buffer data going to, and coming from, the STA 10. An external network 16, such as the Internet, maybe coupled to the system 1 via the host 14 or directly through the AP 12, depending on the specifics of the system implementation. The STA 10 includes a controller such as data processor (DP) 1OA, a memory (MEM) 1OB that stores a program (PROG) 1OC, and a suitable radio frequency (RF) transceiver 1 OD for bidirectional wireless communications with the AP 12 via a wireless link 11. Note that in some implementations there may be one or more relay elements or nodes (not shown) through which the wireless link 11 passes. The AP 12 also includes a controller such as DP 12A, a MEM 12B that stores a PROG 12C, and a suitable RF transceiver 12D. The AP 12 may be coupled via a data path 13 to the host 14. The PROGs 1OC and 12C are assumed to include program instructions that, when executed by the associated DP, enable the electronic device to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail. For the purposes of describing the exemplary embodiments of this invention it may be assumed that both the STA 10 and the AP 12 include a MAC layer or function 1 OE, 12E, respectively, and that associated with the MAC layers 1 OE, 12E are power management (PWR MNGT) units or functions 1 OF, 12F, respectively, that operate in accordance with the exemplary embodiments of this invention. The STA 10 may include a data source/sink such as, but not limited to, a codec 1 OF, such as an AMR codec suitable for use in conducting a VoIP communication connection. The functionality associated with a PHY layer is assumed to be handled at least in part by the transceivers 10D, 12D, and associated Layer 1 circuitry and components.

Figure 2 also shows a data queue 12G at the AP 12 that is organized in accordance with the exemplary embodiments of this invention, as described below.

In general, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 1 OA of the STA 10 and by the DP 12 A of the AP 12, or by hardware, or by a combination of software and hardware.

In general, the various embodiments of the STA 10 can include, but are not limited to, radio telephones (such as cellular phones), personal digital assistants (PDAs) having wireless communication capabilities, portable or fixed computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.

The MEMs 1OB and 12B maybe of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 1 OA and 12A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

The exemplary embodiments of this invention are now described in further detail.

It is assumed that STA 10 can at any given point of time have traffic associated with different ACs, and that optimizations related exclusively to a VoIP usage scenarios may not be an optimal solution for all usage cases.

It is assumed that various usage scenarios can include, but are not limited to, simultaneous VoIP and video streaming, and simultaneous VoIP and e-mail download.

There are various traffic characteristics that can be used for better throughput and power savings. As non-limiting examples of access categories (ACs):

AC3 : Delay sensitive, there is a need to transmit data as soon as possible;

AC2 : Delay sensitive, but also requires high reliability; and

ACl and ACO : Require good reliability, and can tolerate some amount of delay (latency).

In accordance with the exemplary embodiments of this invention, upon receiving a trigger frame the AP 12 transmits a response an acknowledgement to the trigger frame and it is followed by the transmission of a "new frame" indicating when the STA 10 can expect to receive data, hi another embodiment the STA 10 can also acknowledge (ACK) the reception of the new frame to the AP 12.

Note that in the case of a legacy (conventional) power saving approach it was possible for the AP 12 to know if there is any queued data for the STA 10. An enhancement to this legacy capability is to provide knowledge of what AC(s) data is present for the STA 10.

The new frame transmitted by the AP 12 signals to the STA 10 that the STA 10 can expect to receive data in Z time units. The time units maybe measured in microseconds. The time units may be measured in multiples of, e.g., 2 or 4 microseconds (RIFS spacing or OFDM symbol length). As such, subsequent references herein to "Z microseconds" should be construed broadly to encompass any number of suitable time units.

Z may be defined (in general) as Z= w + x +y. where x is the timed needed for fetching the data, y is the channel access time, and w is the time needed to complete data of the current AC, and any other AC, before the channel access of data transmission of a next AC to the STA 10. For some AC, for example the first AC, w is equal to 0, and for some other AC (e.g., later AC) x may be equal to 0. In general then, the new frame as employed herein conveys Z for any AC.

The conditions of selecting a value of Z may include:

Condition 1 : Z microseconds > w microseconds + x microseconds + y microseconds; assuming

Complete the data of any AC before the AC associated with this Z in approximately w microseconds (note that this is not a fixed parameter) Fetch the data in approximately x microseconds (note that this is not a fixed parameter)

Based on the load in the system, if the channel access time is approximately y microseconds (note that this is not a fixed parameter). Condition 2: Z microseconds < the delay that the AC traffic can tolerate.

Since the AP 12 can receive multiple trigger frames from STAs 10 in the BSS, and the fetch operation for a particular STA's data can be performed in parallel when the AP 12 is performing channel access to transmit other STA's data, the choice of parameter Z may in practice be determined by Condition 2

If a STA 10 has data of multiple ACs to transmit, the STA 10 may choose to transmit data of another AC during the period Z microseconds (assuming that the STA 10 has/can access to the medium). If the AP 12 has data of multiple ACs to transmit to the STA 10 then one of a plurality of embodiments of transmission procedures, also referred to herein without a loss of generality as "mechanisms", can be used.

Mechanism 1 : The AP 12 transmits data of an AC first, and at the end of transmitting the data of the AC, signals the STA 10 when it can expect data of another AC (determined by parameter y or w + y microseconds). The AP 12 can choose to start transmission of data to a STA 10 with the highest priority AC data that is queued for the STA 10. Also, an obtained TXOP can be used to transmit data of the same AC to other STAs 10 in the BSS (if they are requested to be awake at that time).

It can be noted that the foregoing paragraph refers to the parameter y orw +y, as opposed to the parameter Z. A reason for this is that when the AP 12 receives a trigger frame, it performs a fetch operation based on the STA 10. If the data of all ACs is available to the AP 12 in one fetch operation, it obtains the data of all ACs together. Otherwise the AP 12 may not know that there is data for another AC. However, note that it may be possible to generalize this concept to include the case where the AP 12 obtains the data of different ACs one after the other.

If a STA 10 has data of multiple ACs then the AP 12 can start transmitting data in any AC order. In one embodiment the AP 12 begins transmitting data to the STA 10 with the AC that is the highest priority AC of the queued data. This can be advantageous in a situation such as the STA 10 having data of VoIP (AC3) and Video (AC2), where VoIP is scheduled every 20 msec and Video is scheduled every 100 msec (as non-limiting examples). If the STA 10 has sent a trigger frame at a time when the AP 12 has just finished transmitting VoIP data to other STAs 10 in the network, and immediately thereafter there is Video scheduled to be transmitted, then the AP 12 may transmit the Video first and delay the VoIP transmission for that STA 10 until the next scheduling period (as it is still within the delay requirements of the VoIP traffic).

A benefit of the use of mechanism 1 is that data can be transmitted to multiple STAs 10. Note, however, that a TXOP is obtained by an EDCA mechanism, and hence a STA 10 that has data associated with multiple ACs should be awake at multiple times, or the STA 10 needs to stay awake for a longer time. Note further that if there are multiple STAs 10 that have data of the same AC, they can be scheduled to be awake at the same time (start of TXOP synchronized by Z microseconds) so that the TXOP can be used effectively.

Note that a RD mechanism with AC constraint may be used by the AP 12 to carry out data exchange with the STAs 10 in the BSS. hi a RD mechanism the AP 12 gains access to the medium either by AC constraint or by non- AC constraint, and at any given time the AP controls the usage of the obtained TXOP to either transmit data to a STA 10 or to receive data from a STA 10 in the BSS without any further channel access. If the medium was obtained with AC constraint the STA 10 that is signaled to use the medium can use the medium to transmit data only of the AC for which the TXOP was granted. The AP can use the obtained TXOP to carry out data exchange with one or more STAs 10 (sequentially) in the B S S .

hi mechanism 1 the new frame that was described above is used to signal to the recipient

STA 10 when to expect data of the next AC. The data transfer then occurs in the following manner:

Step 1 : The AP 12 gains access to the medium and transfers the data of ACx;

Step 2: After transmitting the data of ACx, and if there is data of another AC queued at the AP 12 for the STA 10, the AP 12 uses the new frame (as described above) to inform the STA 10 when to expect data of another AC. It can be noted here that the AP 12 may transmit the data of the same AC to other STAs 10, as the TXOP is obtained on an AC basis.

Steps 1 and 2 are repeated until the AP 12 does not have data of any AC queued for the

STA 10.

Mechanism 2 : hi this embodiment the AP 12 can obtain a TXOP without AC constraint, and can use a RD mechanism to complete the data transmission of all ACs to a single STA 10. Note that in this embodiment the AP 10 uses the new frame to inform the STA 10 of when to wake up to receive the data

A benefit of the use of this approach is that it allows completion of data transfer for all (one or more) ACs for a single STA 10.

Mechanism 3 : This embodiment uses a PSMP frame at the time when the STAs 10 are awake, and completes all DL transmissions to the STAs 10 in the BSS. Note that in this embodiment the AP 10 also uses the new frame to inform the STA 10 of when to wake up to receive the data. A PSMP frame communicates a schedule of STAs 10 in the BSS, and indicates when they can expect to receive data from the AP 12 and when they are allowed to transmit data on the medium. The data exchange following the schedule indicated in PSMP frame is referred to as a PSMP sequence. Data transmission in a PSMP sequence happens without any AC constraint (allocated time from AP to STAx (or) STAx to AP can be used to transmit data of any AC). In a PSMP sequence each STA 10 is allocated a transmission opportunity only once.

It can be noted with regard to the distinction between the functionality of the new frame and the PSMP frame that the new frame informs the STA 10 when to be awake, and when the STA 10 is awake the first frame that will be received is the PSMP frame which indicates, from the time of reception of the PSMP frame ,when the STA 10 may receive and transmit data on the medium, hi general, the PSMP frame is intended to inform one or more STAs 10 in the system when to expect to TX and RX data.

A benefit of the use of the exemplary embodiments of this invention is that it also allows completion of data transfer for all (one or more) ACs for a single STA 10. Note, however, that the AP 12 preferably groups (and orders) the STAs 10 so that QoS constraints are met.

It should be noted further that one or more of the above mechanisms can be used without a need for any signaling or protocol changes. That is, if a STA 10 has transmitted a trigger frame it does not need to know if it will receive data using RD, or PSMP, or by

Unicast transmissions. Once the STA 10 is awake at the specified time it may receive data by any one of the mechanisms deemed appropriate by the AP 12. For example, a STA 10 may be a PSMP-capable STA (i.e., it can understand the PSMP frame and can read the contents of the PSMP frame), but if the AP 12 has received a trigger from only one or two STAs 10, the AP 12 can choose not to use a PSMP frame even though all the of STAs 10 that have sent the trigger frame are PSMP capable (cost of overhead of PSMP frame). Note that there can be some signaling, such as STA 10 signaling to the AP 12 that the STA 10 is PSMP capable, or RD capable, etc., but this occurs only once (at the time of association).

To gain a further understanding of the exemplary embodiments of this invention, it is useful to contrast Figure 3 (which shows a conventional reception of triggers from two STAs 10 (STAl , ST A2), the ACKs sent in response, and the subsequent transmission of data for ACx and ACy to STAl and STA2), with Figure 4 (which shows the use of the new frame to indicate to the respective STAs 10 when to be awake to receive their AC data). Note that this procedure enables the STAs 10 to enter the sleep mode, if they elect to do so, while waiting to receive their respective AC data.

Note that in Figure 4 vertical bold arrows show the schedule that the AP 12 can maintain for ACx. As an example, for voice traffic the AP 12 can accumulate all of the data for 20 milliseconds, and then begin transmission (ACx data for STAs in the BSS) at the end of the 20 millisecond period. Note that the STAs 10 referred to in the preceding sentence are those that have sent a trigger frame, and that are signaled to be awake at that time (or) STAs 10 that are already scheduled to be awake (e.g., S-APSD STAs 10) at that time (or) STAs 10 that are not in a Power Save mode (those STAs 10 that are always awake).

In Figure 4 data for STAl arrives at the vertical bold arrow, but once the data for STAl of ACx is complete, the new frame is sent to STAl indicating when to expect data for ACy. Thus, the first time when the new frame is sent after the ACK frame it conveys the information for only ACx, and not both ACx and ACy (e.g., the AP 12 may not at this time have knowledge of how much traffic there is for ACx). This is explained in further detail below in reference to mechanism 1 : transmit data an AC first (possibly the highest AC), and at the end of transmission signal the STA 10 when it can expect to receive data from the medium for other AC (determined by parameter Z microseconds.)

As was indicated above, the STA 10 may ACK the receipt of the new frame to the AP 12.

hi an exemplary implementation of the invention the AP 12, as opposed to simply maintaining information as to whether it has any queued data for a certain STA 10, also maintains in the data queue 12G the AC(s) of the queued data, and a value for the parameter Z for each AC associated with the BSS. In this way, and in response to a receipt of a trigger from any STA 10 in the BSS, the AP 12 is aware of for which AC(s) there is queued data, and the AP 12 can respond to the trigger (using the new frame) and signal the STA 10 of the awake time of Z microseconds that meets the delay constraint for the AC, and that also enables the AP 12 to schedule data for that particular AC for all of the STAs 10 in the BSS.

The exemplary embodiments of this invention provide for the new frame to be transmitted to the STA 10 in response to the trigger frame. The content of the new frame may comprise:

the expected data schedule time: awake time (Z microseconds); and

the AC or ACs for which a STA 10 has queued data at the AP 12. Note that if a certain STA 10 has data of a specific AC queued at the AP 12, then information concerning this queued data at the AP 12 enables the STA 10 to determine if it will wait until the DL transmission of data of the indicated AC before it performs an UL transmission, or instead if it prefers to transmit its queued UL data (possibly because of a delay constraint).

The content of the new frame may also comprise an indication of an amount of data queued for each AC.

It should be appreciated that the use of the exemplary embodiments of this invention provides a number of advantages. For example, for mechanism 1 the exemplary embodiments allow for power savings at a STA 10 from the time of sending the trigger frame until the data is actually received from the AP 12. The use of mechanism 1 also allows the STA 10 to transmit data in the UL (e.g., the TXOP owner is the AP 12, and it can allow the STA 10 to use the TXOP to transmit any queued data). The use of mechanism 1 is also beneficial when the STA 10 has data of multiple ACs, and if there is data of a higher priority AC queued at the AP 12 for other STAs 10 in the BSS, a power save STA 10, after receiving data for the higher priority AC, can go back to the power save mode until receipt of data from a lower priority AC.

The mechanism 2 described above provides all of the advantages of mechanism 1, and furthermore can allow the STA 10 to receive data of all of the queued ACs together.

The mechanism 3 described above provides all of the advantages of mechanisms 1 and 2, and furthermore can allow the STA 10 to have knowledge of a precise schedule in which to expect to receive data in the DL, as well as a schedule of when to transmit data in the UL.

Based on the foregoing it should be apparent that the exemplary embodiments of this invention provide a method, apparatus and computer program product(s) to enhance U-APSD (unscheduled automatic power-save delivery) functionality in a wireless communication system.

(A) Referring to Figure 5, in accordance with a method, and the operation of a computer program at the AP 12, at Block 5 A the AP receives a trigger frame from a STA; at Block 5B the AP sends a new frame to the STA, the new frame comprising information for informing the STA of an amount of time that will elapse before the AP transmits data to the STA; and at Block 5C the AP transmits the data to the STA when the period of time elapses.

(B) The method of the preceding paragraph, where the amount of time Z is expressed in, for example, microseconds, and is given by Z = w + x + y, where x is the timed needed for fetching the data, y is the channel access time, and w is the time needed to complete data of the current AC, and any other AC, before the channel access of data transmission of a next AC to the STA 10. hi a first condition:

Z microseconds > w microseconds + x microseconds + y microseconds; assuming

Complete the data of any AC before the AC associated with this Z in approximately w microseconds; Fetch the data in approximately x microseconds; and

Based on the load in the system, the channel access time is approximately y microseconds; and in a second condition: Z microseconds < the delay that traffic of an associated access category can tolerate.

(C) The method of paragraph (A), where the AP transmits data of a higher priority access category first, and at the end of transmitting the higher priority data, signals the STA when it can expect data of another access category.

(D) The method of the preceding paragraph, where an obtained TXOP is used to transmit data of the same AC to another STA in a BSS.

(E) The method of paragraph (A), where the AP obtains a TXOP without access category constraint, and uses a reverse direction mechanism to complete the data transmission of all queued ACs to the STA, where the AP sends the new frame to the STA to inform the STA of when to wake up to receive the data.

(F) The method of paragraph (A), where the AP uses a power save multi-poll frame at a time when all STAs of a BSS are awake, and completes all DL transmissions to the STAs in the BSS, where the AP sends the new frame to the STAs to inform the STAs of when to wakeup to receive the PSMP frame so that they can receive data.

(G) The method of the preceding paragraphs, further comprising the AP maintaining a data queue that comprises indications of access categories of queued data, and a value for the parameter Z for each access category associated with the BSS, whereby in response to a receipt of the trigger frame from any STA in the BSS, the AP has knowledge of which AC(s) have queued data, and responds to the trigger frame to signal the STA of an awake time of Z microseconds that meets a delay constraint for the AC.

(H) The method of the preceding paragraph, where the AP is further enabled to schedule data for a particular access category for a plurality of STAs in the BSS.

(I) The method of paragraph (A), where the new frame comprises, in addition to an indication of the amount of time that will elapse before the AP transmits data to the STA, an identification of an access category or access categories for which the STA has queued data at the AP.

(J) The method of paragraph (I), where the new frame further comprises an indication of an amount of data queued for each access category.

It should be further appreciated that the exemplary embodiments of this invention pertain to apparatus at AP 12, which may be embodied as a means for receiving a trigger from a station, means for composing a frame, the frame comprising information for informing the station of an amount of time that will elapse before transmitting data to the station, and means for transmitting the frame to the station and for transmitting the data to the station when the period of time elapses.

Referring to Figure 6, in accordance with a method, and the operation of a computer program at the STA 10, at Block 6 A the STA transmits a trigger frame to an AP; at Block 6B the STA receives a new frame from the AP, the new frame comprising information for informing the STA of an amount of time that will elapse before the AP transmits data to the STA; and at Block 6C the STA determines whether to enter a power saving mode, or perform some other action, during the period of time before the AP transmits data to the STA.

The method of the preceding paragraph, where the other action comprises transmitting data to the AP. It should be further appreciated that the exemplary embodiments of this invention pertain to apparatus at the STA 10, which may be embodied as a means for transmitting a trigger frame to an access point, means for receiving a frame from the access point, the frame comprising information for indicating an amount of time that will elapse before receiving data from the access point, and means for determining at least whether to enter a power saving mode during the period of time before receiving the data from the access point.

The various blocks shown in Figures 5 and 6 may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s).

In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention.

For example, while the exemplary embodiments have been described above in the context of a WLAN, such as an IEEE802.i l -type system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system, and that they may be used to advantage in other types of wireless communication systems.

It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples.

Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

CLAIMS What is claimed is:

1. A method, comprising:

receiving a trigger frame from a station at an access point;

sending a new frame to the station, the new frame comprising information for informing the station of an amount cf time that will elapse before the access point transmits data to the station; and

transmitting the data to the station when the period of time elapses.

2. The method as in claim 1 , where the period of time, Z, is defined as the sum of w, x, and y, where x is the time needed for fetching the data, y is a channel access time, and w is the time needed to complete data of a current access category, and any other access category, before the channel access of data transmission of a next access category to the station.

3. The method as in claim 2, where Z is greater than or equal to the sum of w, x, and y, assuming completing the data of any access category before the access category associated with Z in w microseconds, fetching the data in x microseconds, and based on the load, the channel access time in y microseconds, where x, y, and z are variable.

4. The method as in claim 2, Z is less than or equal to a delay that traffic of an associated access category can tolerate.

5. The method as in one of claims 1-4, where the access point transmits data of a higher priority access category first, and at the end of transmitting the higher priority data, signals the station when it can expect data of another access category.

6. The method as in one of claims 2-5, where an obtained transmission opportunity is used to transmit data of the same access category to another station in a basic service set.

7. The method as in one of claims 2-4, where the access point obtains a transmission opportunity without access category constraint, and uses a reverse direction mechanism to complete the data transmission of all queued access categories to the station, where the access point sends the new frame to the station to inform the station of when to wake up to receive the data.

8. The method as in one of claims 2-4, where the access point uses a power save multi-poll frame at a time when all stations associated with a basic service set are awake, and completes all downlink transmissions to the stations in the basic service set, where the access point sends the new frame to the stations to inform the stations of when to wake up to receive the power save multi-poll frame.

9. The method as in one of claims 2-7 further comprising the access point maintaining a data queue that comprises indications of access categories of queued data, and a value for the time Z for each access category associated with a basic service set, where in response to a receipt of the trigger frame from any station in the basic service set, the access point responds to the trigger frame to signal the station of an awake time of Z that meets a delay constraint for the access category.

10. The method as in one of claims 1 -9, where the access point is further enabled to schedule data for a particular access category for a plurality of stations in a basic service set.

11. The method as in any of claims 1-7 or 9-10 , where the new frame further comprises, in addition to an indication of the amount of time that will elapse before the access point transmits data to the station, an identification of an access category or access categories for which the station has queued data at the access point.

12. The method as in claim 11 , where the new frame further comprises an indication of an amount of data queued for each access category.

13. A method, comprising:

transmitting a trigger frame from a station to an access point;

receiving a new frame from the access point, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station; and

determining at least whether to enter a power saving mode, or perform some other action, during the period of time before the access point transmits data to the station.

14. The method as in claim 13 where the other action comprises transmitting data to the access point.

15. A computer readable medium encoded with a computer program executable by a processor to perform actions comprising:

receiving a trigger frame from a station at an access point;

sending a new frame to the station, the new frame comprising information for informing the station of an amount of time that will elapse before the access point transmits data to the station; and

transmitting the data to the station when the period of time elapses.

6. The computer readable medium encoded with a computer program of claim 15, where the period of time, Z, is defined as the sum of w, x, and y, where x is the time needed for fetching the data, y is a channel access time, and w is the time needed to complete data of a current access category, and any other access category, before the channel access of data transmission of a next access category to the station.

17. The computer readable medium encoded with a computer program of claim 16, where Z is greater than or equal to the sum of w, x, anάy, assuming completing the data of any access category before the access category associated with Zϊn w microseconds, fetching the data in x microseconds, and based on the load, the channel access time in y microseconds, where x, y, and z are variable.

18. The computer readable medium encoded with a computer program of claim 16, where Z is less than or equal to a delay that traffic of an associated access category can tolerate.

19. A computer readable medium encoded with a computer program executable by a processor to perform actions comprising:

transmitting a trigger frame from a station to an access point;

20. An apparatus comprising: a receiver configured to receive a trigger frame from a station;

a controller configured to compose a new frame to the station, the new frame comprising information for informing the station of an amount of time that will elapse before the station receives data; and

a transmitter configured to send the new frame and to send the data to the station when the period of time elapses.

21. The apparatus as in claim 20, where the period of time, Z, is defined as the sum of w, x, and y, where x is the time needed for fetching the data, y is a channel access time, and w is the time needed to complete data of a current access category, and any other access category, before the channel access of data transmission of a next access category to the station.

22. The apparatus as in claim 21 , where Z is greater than or equal to the sum of w, x, and y, assuming completing the data of any access category before the access category associated with Z in w microseconds, fetching the data in x microseconds, and based on the load, the channel access time in y microseconds, where x, y, and z are variable.

23. The apparatus as in claim 21 , where Z is less than or equal to a delay that traffic of an associated access category can tolerate.

24. The apparatus as in one of claims 20-23, where the controller is configured to transmit data of a higher priority access category first, and at the end of transmitting the higher priority data, is configured to signal the station when it can expect data of another access category.

25. The apparatus as in one of claims 21-24, where the controller is further configured to transmit data of the same access category to another station in a basic service set based on an obtained transmission opportunity.

26. The apparatus as in one of claims 21-23, where the apparatus obtains a transmission opportunity without access category constraint, and uses a reverse direction mechanism to complete the data transmission of all queued access categories to the station, where the controller is configured to send the new frame to the station to inform the station of when to wake up to receive the data.

27. The apparatus as in one of claims 21-23, where the apparatus uses a power save multi-poll frame at a time when all stations associated with a basic service set are awake, and completes all downlink transmissions to the stations in the basic service set, where the controller is configured to send the new frame to the stations to inform the stations of when to wake up to receive the power save multi-poll frame.

28. The apparatus as in one of claims 21-26, further comprising the controller maintaining a data queue that comprises indications of access categories of queued data, and a value for the time Z for each access category associated with a basic service set, where in response to a receipt of the trigger frame from any station in the basic service set, the controller is configured to respond to the trigger frame to signal the station of an awake time of Z microseconds that meets a delay constraint for the access category.

29. The apparatus as in one of claims 20-28, where the controller is further configured to schedule data for a particular access category for a plurality of stations in a basic service set.

30. The apparatus as in any of claims 20-26 or 28-29, where the new frame further comprises, in addition to an indication of the amount of time that will elapse before the station receives data, an identification of an access category or access categories for which the station has queued data at the apparatus.

31. The apparatus as in one of claims 30, where the new frame further comprises an indication of an amount of data queued for each access category.

32. An apparatus comprising:

a transmitter configured to transmit a trigger frame to an access point;

a receiver configured to receive a new frame from the access point, the new frame comprising information for indicating an amount of time that will elapse before receiving data from the access point; and

a controller configured to determine whether to enter a power saving mode, or perform some other action, during the period of time before receiving the data from the access point.

33. The apparatus as in claim 32 where the other action comprises transmitting data to the access point.

34. An apparatus comprising:

means for receiving a trigger from a station;

means for composing a frame, the frame comprising information for informing the station of an amount of time that will elapse before transmitting data to the station; and

means for transmitting the frame to the station and for transmitting the data to the station when the period of time elapses.

35. An apparatus comprising:

means for transmitting a trigger frame to an access point; means for receiving a frame from the access point, the frame comprising information for indicating an amount of time that will elapse before receiving data from the access point; and

means for determining at least whether to enter a power saving mode during the period of time before receiving the data from the access point.