WO2006091809A2

WO2006091809A2 - Scheduling of acknowledgement in systems supporting frame aggregation

Info

Publication number: WO2006091809A2
Application number: PCT/US2006/006589
Authority: WO
Inventors: Yousuf Saifullah; Naveen Kakani; Jari Jokela
Original assignee: Nokia Corporation
Priority date: 2005-02-23
Filing date: 2006-02-23
Publication date: 2006-08-31
Also published as: WO2006091809A3

Abstract

Methods, devices and computer program products for scheduling of acknowledgement by a communication station that is configured to operate in a communications system that supports frame aggregation. Communication stations can determine when to schedule acknowledgements based on aggregated frame information.

Description

SCHEDULING OF ACKNOWLEDGMENT IN SYSTEMS SUPPORTING FRAME AGGREGATION

FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of wireless communication technologies such as Wireless Local Area Network (WLAN) technology. More particularly, this invention relates to scheduling Acknowledgements (ACK) sent in response to different MAC Protocol Data Unites (MPDUs) present in an aggregated frame.

BACKGROUND INFORMATION

[0002] This section is intended to provide a background or context to the invention that is receited in the claims. The description herein may include concepts that could be pursued, buar are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated therein, what is described in this section is not admitted to be prior art by inclusion in this section. [0003] Wireless local area networks (WLANs) are becoming increasingly popular for both business and residential applications. For instance, many companies are deploying WLANs in place of, or as an enhancement to, the corporate local area network. Additionally, many service industry businesses, e.g., restaurants and hotels, have deployed WLANs to provide customers with access to the Internet and/or other data networks. As WLANs have become increasingly more widespread, the number of applications designed for execution on WLAN-compliant stations has increased as well. For example, typical WLAN-compliant stations feature text messaging application, Internet browsers, and streaming content palyers among other application. A user may concurrently run any number of applications on a WLAN-compliant station. [0004] It is particularly desirable to minimize signaling and control consumption of wireless resources in a shared resource wireless network as wireless system resources are finite and limited by the system bandwidth. Vast amounts of labor and capital have been expended to identify techniques that provide increased throughput in a shared resource system. In an IEEE 802.11 compliant network, for example, proposals have been made to improve medium access control (MAC) layer throughput by the use of single receiver station frame aggregation (SRA) or multiple receiver station frame aggregation (MRA). When MRA is employed, an aggregated frame contains one or more frames respectively directed to one or more of several stations.

[0005] In a WLAN, a responder station is often required to acknowledge the receipt of data received from an initiator station. An acknowledgement (ACK) signal sent from a responder station to the initiator station provides a confirmation to the initiator station that the responder station correctly received transmitted data. In WLAN- compliant devices, ACKs are generated at the medium access control (MAC) layer. Such an acknowledgement mechanism consumes valuable system bandwidth. [0006] If traditional ACK sending rules are used, in a frame aggregation system, ACKs may contend with each other and backoff because there is no proper coordination in the sending of these ACKs. This resulted can result in increased delay in sending ACKs and thus decreased throughput. Thus, there is a need to enhance the ACK function in frame aggregated systems in order to avoid ACK contention and backoff.

SUMMARY OF THE INVENTION

[0007] Embodiments of the invention relates to methods, computer program products and communication stations for scheduling acknowledgements, wherein the communications station is configured to operate in a wireless communication system comprising one or more communications stations. Each station in the communications network can be configured to place an acknowledgement indication in an aggregated frame control header. Scheduling can involve receiving a transmission at the communication station, determining whether the communication station should send acknowledgement information based on the received transmission, and if it is determined that acknowledgement information should be sent, determining a time at which the communication station is to schedule transmission of acknowledgement information.

[0008] The determining the time can include determining a duration for the acknowledgement information for all communications stations in the wireless communication system, determining which of the communication stations in the wireless communication system are scheduled to transmit acknowledgement information, and determining which of the communication stations in the wireless communication system do not have acknowledgement information to send. Determining the time can also be based on an implicit knowledge of an intended acknowledgement type by the communication station [0009] Determining which of the communications stations in the wireless communication system are scheduled to transmit acknowledgement information and which do not have acknowledgement information to send can be based on acknowledgement indication information included in the aggregated control frame header.

[0010] The acknowledgement indication can be placed in the aggregated frame control header in a MAC layer and can include an acknowledgement message, a block acknowledgement message and/or an indication of no acknowledgement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a simplified block diagram of an exemplary network environment.

[0012] FIG. 2 is a block diagram of an exemplary station of FIG. 1.

[0013] FIG. 3 A is a diagram of an embodiment of an aggregation frame having multi-rate aggregation control information included in PHY layer preamble and headers.

[0014] FIG. 3B is a diagram of an embodiment of rate control field set that show multiple instances of a station control field set of the aggregation frame shown in FIG.

3A. [0015] FIG. 3C is a diagram of an embodiment of frame subfields of a particular dat rate included in a frame field of the aggregation frame shown in FIG. 3 A. [0016] FIG. 4 is a diagram of an embodiment of an aggregate frame having multi- rate aggregation control information included in the MAC layer. [0017] FIG. 5 is a simplified diagram of a legacy frame structure implemented according to the prior art.

[0018] FIG. 6 is a simplified diagram of an aggregate frame structure configured for enhanced power efficiency that may incorporate information described in FIGs. 3A-4. [0019] FIG. 7 is a diagram of an embodiment of a aggregate frame having ACK information included in the MAC layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting.

[0021] Referring to FIG. 1, a simplified block diagram of an exemplary network 100 environment is illustrated. The network 100 is one example of a shared resource network. For example, the network 100 may be implemented as a wireless local area network (WLAN) conforming to the IEEE 802.11 standards. [0022] In this example, the network 100 comprises two basic service sets (BSSs) 1 and 2 although any number of BSSs may be included in the network 100. BSSs 1 and 2 can provide respective coverage areas 10 and 11 in which WLAN stations (STAs) 20-23 may communicate via a wireless medium with one another or with other communication or computational devices in other external networks that interface with the network 100. BSSs 1 and 2 can be communicatively interconnected by a distribution system (DS) 30. DS 30 enables mobile device support by providing requisite logical services for handling address to destination. mapping and integration of multiple BSSs. Each BSS indluces an access point (AP) that provides access to DS 30. In the example shown in FIG. 1, BSSs 1 and 2 have respective APs 40 and 41. DS 30 provided by APs 40 and 41 and BSSs 1 and 2 facilitate creation of a wireless network of arbitrary size and complexity, and the collection of DS 30 and BSSs 1 and 2 is commonly referred to as an extended service set (ESS) network. Logical integration between the network 100 and non-IEEE 802.11 LANs, e.g. LAN 50, can be provided by portal 60. Various other configuration of network 100 are possible. For example, coverage areas 10 and 11 may partially overlap or may be collocated. Moreover, embodiments of the invention may be deployed in a WLAN comprising a single independent BSS.

[0023] Each of the STAs 20-23 may be implemented as a respective data processing system adapted for communication in a wireless network such as a wireless laptop computer, a personal digital assistant, a cellular telephone, or other device capable of data communications. A STA may comprise a processing unit, such as a general purpose microprocessor and/or an application specific integrated circuit, a memory device, such as a random access memory, a read-only memory, or another storage device for holding machine-readable data, a communication interface, such as a wireless communication card, and various other components and peripheral devices. [0024] FIG. 2 illustrates one station in the form of a mobile computer 112 within which the present invention may be implemented. It should be understood, however, that the present invention is not intended to be limited to one particular type of mobile computer 112 or other electronic device. Instead, the present invention can be incorporated into virtually any type of electronic device, including but not limited to laptop and desktop computers, personal digital assistants, dictating machines, integrated messaging devices, printers, scanners, fax machines and other devices. [0025] The mobile computer 112 of FIG. 2 includes a housing 130, a display 132 in the form of a liquid crystal display, a keypad 134, a battery 140, an infrared port 142, an antenna 144, radio interface circuitry 152, codec circuitry 154, a controller 156 and a memory 158.

[0026] FIG. 3 A is a diagram of an embodiment of an aggregated frame 400 having multi-rate aggregation control information included in the Physical (PHY) layer preamble and headers such as those described in various IEEE 802.11 standards. In this embodiment, a station may be adapted to recognize whether any MAC frame in aggregate frame 400 is addressed to the station by reading only the physical layer header. An explicit indication of the position of payload data addressed to the station allows the station to enter a sleep mode rather than reading all MAC headers to determine which frames are addressed to the station.

[0027] In the example of FIG. 3 A, aggregate frame 400 includes a physical layer preamble 402, a physical layer header 404, and a payload or frame field 406. Physical layer header 404 includes various multi-rate aggregation control fields. The aggregation control information added at the PHY layer may comprise one or more of the following files: a rate (RATE) field 420, 425, a rate offset field 421, 426, a station count field 422, 427, a station ID field 423, 428, a station offset field 424, 429, a tail field 430, and a pad bit field 431.

[0028] A rate control field set can comprise aggregation control information of a single data rate for one or more stations. Fields in a rate control field set are mutually associated. Any number of rate control field sets may be included in aggregate frame 400 dependent on the number of data rates represented by aggregate frame 400 and system constraints on the available length of aggregate frame 400. In the example illustrated in FIG. 3 A, two rate control field sets 445 and 446 are shown. Rate control field set 445 includes control information of a data rate (RATE#1), and rate control field set 446 includes control information of another data rate (RATE#2). [0029] The rate field indicates a particular data rate value at which one or more STAs have MAC frames encoded in aggregate frame 400. In the present example, two rate fiels 420 and 425 are included in aggregate frame 400, and thus aggregate frame 400 includes payload data of two data rates (RATE#,1 and RATE#2). Rate offset field 421 and 426 respectively include an identification of an offset length for a mid-amble or payload data. A mid-amble is preferably frame 400 and thereby provides a delimiter between aggregate data of different data rates. A rate offset value specifies a length from a reference point, such as the beginning of frame field 406, the beginning of physical header 404, or the like, to the beginning of data encoded at the data rate associated with the rate offset value (or alternatively, to a mid-amble preceding data encoded at the data rate associated with the rate offset value). In the examples provided herein, assume rate offset values provide offsets measured from the beginning of frame field 406. For a first rate offset field 421, the rate offset value specified thereby indicates an offset length to the beginning of payload data encoded at the first data rate stored in frame field 406. For subsequent rate offset field 426 associated with data rate RATE#2, the rate offset value specified thereby indicates an offset length to a mid-amble that precedes a first data payload encoded at the associated data rate. For example rate offset field 426 specifies an offset from the beginning of frame field 406 to the beginning of data encoded at data rate RATE#2. The offset length identified in a rate offset field may, for example, define an offset length in terms of OFDM symbols, time duration in micro-seconds, length in bytes, or the like. An offset length in bytes may indicate the length of MPDUs for an associated station.

[0030] A station count field indicates a number of stations that have aggregated data for a data rate associated with the station count field. Aggregate frame 400 includes two station count fields 422 and 427 that each respectively identify the number of stations having data in aggregate frame 400 that is encoded at the data rate associated with station count fields 422 and 427. For example station count field 422 has a value that specifies a number, M, of stations that have data encoded at the data rate (RATE#1) identified in associated rate field 420. Likewise, station count field 427 has a value that specifies a number, N, of stations that have data encoded at the data rate (RATE#2) identified in associated rate field 425.

[0031] Control information uniquely associated with a single station may be organized or otherwise configured in sets of associated control information. As referred to herein, a station control field set comprises control information of a single station. In the present example, a station control field set 450A-450M, 451 includes one or more station ID fields 423, 428 and a station offset field 424, 429 although other control information related to a single station may be included in a station control field set. A station ID field indicates a destination STA address or other identifier. A station offset field may indicate an offset in terms of OFDM symbols, time in micro-seconds, length in bytes, or the like for a STA identified in an associated STA ID field. Particularly, a station offset field specifies an offset length of station payload data encoded at a particular rate measured from the beginning of aggregate data encoded at the data rate. Thus, a rate offset value and a station offset value collectively identify the position within aggregate data at which data addressed to a particular station is located. A STA determines its payload offset in the aggregated data based on the station offset field in conjunction with an associated rate offset field. In this manner, a station may enter an idle period and thereafter wake up or reactivate to receive only the MAC frame data addressed thereto. A length in bytes identified in a station offset field may indicate the length of individual MPDU frame lengths for each station. The station offset may comprise a single value (or alternatively, a set of values) for each MPDU frame addressed to a STA. [0032] The illustrative example shows a single instance of station control field set 450A-450M and 451 respectively located within rate control field set 445 and 446 to simplify the illustration. However, multiple instances of station control fiel set 450A- 450M and 451 may respectively be included in rate control field set 445 and 446. For example, FIG. 3B is a diagram of an embodiment of rate control field set 445 that shows M instances of station control field set 450A-450M. Each of station control field sets 450A-450M includes a respective station ID field 423A-423M and a corresponding station offset field 424A-424M. Each station control field set 450A- 450M is uniquely associated with a single station by way of the station ID respectively included in station ID field 423A-423M. In a similar manner, rate control field set 446 may include N instances of station control field set 451 with each instance of the station control field set including a respective station ID field and a corresponding station offset field.

[0033] Other rate control field sets may below rate control field set 446. After a final rate control field set of physical layer header 404, a tail field 430 and a pad bit field 431 may be appended to physical layer header 404. Tail field 430 indicates the end of physical layer header 404. Unused bits of a symbol may be used in pad bit field 431 or reserved bits to consume the remainder of physical layer header 404. [0034] Frame field 406 follows physical layer header 404 and may include aggregate multi-rate payload data in one or more data subfields. Frame subfields may be configured in one or more data sequences each having payload data of a common data rate. For example, a RATE#1 data sequence 490 includes payload data encoded at the data rate RATE#1 and RATE#2 data sequence 491 includes payload data encoded at the data rate RATE#2. in the present example, data sequences 490 and 491 each respectively include one or more instances of frame subfϊelds 470 and 471. Each instance of frame subfield 470 includes payload data encoded at the data rate RATE#1, and each instance of frame subfield 470 is addressed to one of the M stations specified in station ID field 423A-423M. In a similar manner, each instance of frame subfield 471 includes payload data encoded at the data rate RATE#2, and each instance of frame subfield 471 is addressed to one of the N stations specified in an instance of station ID field 428. Data of different data rates are preferably separated by a mid-amble 480 or other delimiter.

[0035] In the illustrative example, a single instance of frame subfield 470 is shown in RATE#1 data sequence 490, and a single instance of frame subfield 471 is shown in RATE#2 data sequence 491 to simplify the illustration. However, one or more instances of frame subfield 470 and 471 may respectively be included in data sequence 490 and 491. The particular number of frame subfϊelds included in a data sequence is dependent on the number of stations having payload data at the corresponding data rate. For example, FIG. 3C is a diagram of an embodiment of frame subfields having payload data encoded at the data rate RATE#1. Frame subfϊelds are sequentially ordered in RATE#1 data sequence 490; Mid-ambles 480A- 480L may be inserted between payload data addressed to different stations. For example, mid-amble 480A is inserted between frame subfields 470A and 470B. Mid- amble 480 is inserted after a final frame subfield 470M and separates frames of different data rates.

[0036] Each of frame subfields 470A-470M contain payload data addressed to a station identified in rate control field set 445 assocaited with the data rate RATE#1 of data sequence 490. Particularly, frame subfields 470A-470M contain payload data addressed to a respective station identified in station ID field 423 A-423M of station control field set 450A-450M shown in FIG. 3B. In a similar manner, N instances of frame subfield 471 having data encoded at the data rate RATE#2 are included in frame field 406, and each instance of frame subfield 471 contains payload data addressed to one of the ISf stations specified in respective instances of station ID field 428.

[0037] FIG. 4 is a diagram of an embodiment of an aggregate frame 500 having multi-rate aggregation control information included in the MAC layer Aggregate frame 500 may includes a physical layer preabme 502, a physical layer header 504, and a frame field 506 in the MAC layer of aggregate frame 500. Aggregation control information included in data grame 506 provides enhanced power efficiency and multi-rate aggregation. Aggregation control information may be included in the MAC layer by way of a MAC frame 510 included in frame field 506. MAC frame 510 may include a frame control field 511 and a duration/ID field 512. Frame control field 511 may include, for example, various subfields that define a protocol version, a frame type and frame subtype that define the function of the frame, whether the frame is destined for a DS or exiting a DS, and other control information. Duration/ID field 512 may define the duration of aggregate frame 500. For example the duration of aggregate frame 500 specified in duration/ID field 512 may be represented by the number of symbols, bits, bytes, the duration in micro-seconds, or the like. [0038] Aggregation control information included in MAC frame 510 comprises one of more instances of a rate count field 513 and a "more rate" field 518, 524. A rate count field indicates a number of different data rates present in aggregate frame 500. The rate count field allows a STA decoder to determine an end of the aggregation control information. A "more rate" field may be implemented as a signle bit field that indicates whether a station has to wake up at a subsequent mid-amble to obtain data at an additional rate. That is, a "more rate" field is used to indicate to a station that the station has data of multiple rates addressed thereto in aggregate frame 500. For example, it is possible that a station has data at multiple rates addressed thereto in a multicast scenario. In this instance, data addressed to the station as part of the multicast traffic may be transmitted at one rate, while data uniquely transmitted to the station as unicast traffic may be transmitted at another data rate. [0039] Additionally, aggregation control information included in MAC frame 510 may comprise one o more instances of the following fields: a rate field 514, 520, a rate offset field 515, 521, a station count field 516, 522, a station ID field 517, 523, and a station offset field 519, 525 all of which may be configured and contain similar control information as described above with reference to FIGs. 3A-3C. [0040] In the illustrative example, aggregation control information includes a rate count field 513 that identifies the number of data rates present in aggregate frame 500. A first rate field 514 may include an identification of a first data rate of frames that are included in aggregate frame 500. A subsequent rate offset field 515 includes an offset length that specifies an offset to the beginning of frames encoded at the data rate identified in rate field 514. A subsequent station count field 516 includes a numerical identifier of the number, M, of stations having frames at the data rate identified in rate field 514. One or more station control field sets 550 including station ID field 517, "more rate" field 518, and station offset field 519 follow station count field 516. Station control field set 550 comprises aggregation control information of a single station. A single station control field set 550 is shown to simplify the illustration. However, a number, M, of one or more instances of station control field set 550 are included in a rate control field set 545. Each instance of station control field set 550 is uniquely associated with a single station by way of the station ID included in station ID field 517 of a given station control field set. Other rate control field sets, such as rate control field set 546, that specify control information of frames encoded at other rates may be included in MAC header 510 subsequent to a final station offset field 519 of rate control field set 545. In the present example, rate control field set 546 specifies aggregation control information for stations having frames encoded at a data rate RATE#2 in aggregate frame 500. Particularly, rate control field set 546 specifies control information for a number, N, of stations that have frames encoded at data rate RATE#2 in aggregate frame 500. Thus, N instances of station control field set 551 are included in rate control field set 546. A cyclic redundancy check (CRC) 526 may be appended to MAC frame 510 after the final rate control field set.

[0041] Payload data of one or more data rates carried in frame field 506 subsequent MAC frame 510 is included in various frame subfields. In' the present example, a single instance of frame subfield 570 having frames of data rate RATE#1 and a single instance of frame subfield 571 having frames of data rate RATE#2 are shown included in frame field 506 to simplify the illustration. However, M instances of frame subfield 570 are included in RATE#1 data sequence 590, and N instances of frame subfield 571 are included in RATE#2 data sequence 591. A final instance of frame subfield 570 and a first instance of frame subfield 571 are separated by a mid- amble 580 to delimit the data rates RATE#1 and RATE#2. Payload offsets are determined by receiving stations in a manner similar to that described above with reference to FIGS. 3A-3C.

[0042] As described above, aggregation control information in an aggregate frame that facilitates enhanced power efficiency may be disposed at various locations in the aggregate frame. FIG. 5 is a simplified diagram of a legacy frame structure 600. Legacy frame structure 600 includes a legacy PHY preamble 602, a legacy PHY header 604, and remaining frame data 606, such as encapsulated MAC frames and the like. FIG. 6 is a simplified diagram of an aggregate frame structure 700 configured for enhanced power efficiency that may incorporate the aggregation control information features described above with reference to FIG. 4. Aggregate frame structure 700 is configured to support multiple PHY rates. Particularly, aggregate frame 700 includes a legacy PHY preamble 702, a legacy PHY header 704, a secondary PHY preamble 706, a secondary PHY header 708, and remaining frame data 710. In one implementation, aggregation control information at the PHY layer may be included in secondary PHY header 708. In this configuration, the aggregation control information is added to secondary PHY header 708 or subsequent the secondary PHY header in remaining frame data 710. In another implementation, the aggregation control may be implemented in the MAC layer and thus disposed in remaining frame data 710. Still another configuration provides for the aggregation control to be located in the MAC layer between legacy PHY header 704 and secondary PHY preamble 706. This option provides the advantage of backward compatibility such that a legacy terminal or STA may evaluate a duration/ID field of the aggregation control information and utilize the duration/ID data to remain dormant.

[0043] As discussed above, because an aggregated frame may contain MPDUs destined to different stations, legacy ACK sending rules may cause ACKs to contend with each other and back off, resulting in increased delay in sending ACKs and decreased throughput. In one aspect of the invention, an indication regarding ACKs can be placed in the aggregated frame header. One embodiment of Aggregated Frame Control (AFC) at the MAC layer is described with respect to FIG 4. In another aspect a STA can send one aggregated ACK in response to an aggregated frame. In yet another aspect, the invention describes particular STAs scheduling their ACKs. [0044] In an exemplary embodiment of this invention, shown in FIG. 7, an ACK indication can be placed in the aggregated frame control header in the MAC layer for each of the receiving STAs. The ACK indication can be placed using two bits, such that 00 indicates "No ACK", 01 indicates "ACK", and 10 indicates "Block ACK" (For Immediate Block ACK only, as the delayed block ACK doesn't need to be sent right away).

[0045] In this embodiment, the aggregated frame 800 includes a physical layer preamble 802, a physical layer header 804, and a frame field 806 in the MAC layer of aggregated frame 800. Aggregated ACK information may be included in the MAC layer by way of a MAC frame 810 included in frame field 806. MAC frame 810 may include a frame control field 811 and a duration/ID field 512. ACK information included in MAC frame 810 may comprise one or more instances of STA ID field 813 and ACK indication field 814. The STA ID field 813 and ACK indication field 814 can be repeated in the MAC frame 810 once for each receiving STA. In this manner, an ACK indication can be placed in the aggregated frame to eliminate ACK contention.

[0046] In another embodiment, no explicit ACK indication, as above, is included the aggregation frame control header, and the receiving STAs determine their ACK schedules based on an implicit ACK type, i.e. ACK or Block ACK. It still another aspect, AFC, with or without ACK indication, may be distributed across all the aggregated frames instead of being placed at one location at the beginning of the frame.

[0047] The AFC has information for each of the receiving STAs. Usually AFC is placed in front of all the aggregated MPDUs. It can be read by each of the receiving STA. AFC contains information such as data rate, destination address, etc. for each receiving STA. A receiving STA determines the number of ACKs and Block ACKs, based on the information received in the AFC.

[0048] In another aspect of the invention, the STAs determine the scheduling of their ACK and Block ACK. It is also possible that an aggregation uses only one particular type of ACK, e.g. Block ACK. In this case, no indication regarding ACKs is received by the STAs in the aggregated frame header. The instant invention can also be applicable in such cases and the receiving STAs would determine the schedule for transmission based on an implicit knowledge of the intended ACK type. [0049] In one exemplary embodiment, an STA can determine its time for sending an ACK wherein the data rate for ACK and Block ACK for all the STAs are not constant or the same. An STA calculates its ACKDuration, which is the time taken to send a packet acknowledging one packet, and BlockACKDuration, which is the time taken to send a packet acknowledging multiple packets, by observing the data rate for the other STAs in the AFC. If a STA has multiple data rates, then a pre-defined rule may be used for the ACK/Block ACK Data Rate, e.g. the lowest data rate for the STA in the aggregated frame. This exemplary embodiment is illustrated below: [0050] Let the number of STA's in the aggregate be 'N', and they are denoted as STA(I), ... STA(N). Let the ACK_dur(i) denote the time required by STA(i) to send its ACK on the wireless medium (transmission time).

• If STA(i) has ACK indication bits set to 00, then ACK_dur(i) = 0

• If STA(i) has ACK indication bits set to 01, then ACK_dur(i) = time taken to send a single packet acknowledging a single packet (depends on the rate of transmission, and the size of the packet)

• If ST A(i) has ACK indication bits set to 10, then ACK_dur(i) = time taken to send a packet acknowledging multiple packets (depends on the rate of transmission, and the size of the packet)

[0051] In the set of STA's indexed from 1 to k, the number of STA's that do not have any ACK to sent may be denoted by No_ACK(l,k). In other words, No_ACK(l,k) number of STA's have ACK indication bits set to "00" in the set of

[0052] Let Sched_ACK(i) denote the time when STA(i) can send its ACK from the end of the downlink or received transmission. This can be determined from the following:

⁽-1

Sched __ ACK(I) = ∑ ACK_ dur(j) + {SIFS * (i - No _ ACK(I, O))

J=I

i-1

[0053] Here, ^] ACK _ dur(j) denotes the time taken to send the ACK packets on

7=1 the wireless medium, and SJFS * (i - No __ ACK(I, /)) denotes the idle time of the wireless medium (time for which there was no data on the wireless medium). [0054] Note that SIFS is a regular time for which the STA waits for the medium to be free before it sends any data on the medium. It is also possible that any other value or no value, instead of SIFS, may used by a STA.

[0055] In another exemplary embodiment, where the data rate of ACK and Block ACK transmission for all the STAs is constant, then the channel occupancy time, denoted by ACKSendingTime, can be determined from the following:

ACKSendingTime = NumACKs*ACKDuration + NumBlockACKs*BlockACKDuration + SIFS*(NumACKS + NumBlockACKs)

[0056] Here, ACKDuration is the time taken to send a packet acknowledging one packet and BlockACKDuration is the time taken to send a packet acknowledging multiple packets, NumACKS denote the number of STA' s in the aggregate with ACK indication bits set to 01, and NumBlockACKs denote the number of STA' s in the aggregate with ACK indication bits set to 10.

[0057] Some of the advantages provided by the instant invention are that it improves data throughput by removing contention from the ACKs sent in response to an aggregated frame and it works with both multi-rate and single rate-aggregation. [0058] While several embodiments of the invention have been described, it is to be understood that modification and changes will occur to those skilled in the art to which the invention pertains. The invention is not limited to a particular embodiment, but extends to various modifications, combinations, and permutations that nevertheless fall within the scope and spirit of the appended claims.

Claims

WHAT IS CLAIMED IS:

L A method in a communication station for scheduling acknowledgements, wherein the communications station is configured to operate in a wireless communication system comprising one or more communications stations, the method comprising: receiving a transmission at the communication station; determining whether the communication station should send acknowledgement information based on the received transmission; and if it is determined that acknowledgement information should be sent, determining a time at which the communication station is to schedule transmission of acknowledgement information.

2. The apparatus of claim 1, wherein each station in the communications network places an acknowledgement indication in an aggregated frame control header.

3. The method of claim 2, wherein determining the time further comprises; determining a duration for the acknowledgement information for all communications stations in the wireless communication system; determining which of the communication stations in the wireless communication system are scheduled to transmit acknowledgement information; and determining which of the communication stations in the wireless communication system do not have acknowledgement information to send.

4. The method of claim 3, wherein determining which of the communications stations in the wireless communication system are scheduled to transmit acknowledgement information is based on acknowledgement indication information included in the aggregated control frame header.

5. The method of claim 3, wherein determining which of the communication stations in the wireless communication system do not have acknowledgement information to send is based on acknowledgement indication information included in the aggregated control frame header.

6. The method of claim 2, wherein acknowledgement indication is placed in the aggregated frame control header in a MAC layer..

7. The method of claim 2, wherein the acknowledgment indication includes an acknowledgement message.

8. The method of claim 2, wherein the acknowledgement indication includes a block acknowledgement message.

9. The method of claim 2, wherein the acknowledgement indication includes an indication of no acknowledgement.

10. The method of claim 1, wherein determining the time is based on an implicit knowledge of an intended acknowledgement type by the communication station.

11. A computer program product embedded on a computer readable medium for scheduling acknowledgements by a communication station, wherein the communications station is configured to operate in a wireless communication system comprising one or more communications stations, the program product, comprising: computer code configure for: receiving a transmission at the communication station; determining whether the communication station should send acknowledgement information based on the received transmission; and if it is determined that acknowledgement information should be sent, determining a time at which the communication station is to schedule transmission of acknowledgement information.

12. The program product of claim 11 , wherein each station in the communications network places an acknowledgement indication in an aggregated frame control header.

13. The program product of claim 12, wherein the computer code for determining the time further comprises; computer code for determining a duration for the acknowledgement information for all communications stations in the wireless communication system; computer code for determining which of the communication stations in the wireless communication system are scheduled to transmit acknowledgement information; and computer code for determining which of the communication stations in the wireless communication system do not have acknowledgement information to send.

14. The program product of claim 13, wherein the computer code for determining which of the communications stations in the wireless communication system are scheduled to transmit acknowledgement information is configured to read acknowledgement indication information included in the aggregated control frame header.

15. The program product of claim 13, wherein the computer code for determining which of the communication stations in the wireless communication system do not have acknowledgement information to send is configured to read acknowledgement indication information included in the aggregated control frame header.

16. The program product of claim 12, wherein acknowledgement indication is placed in the aggregated frame control header in a MAC layer..

17. The program product of claim 12, wherein the acknowledgment indication includes an acknowledgement message.

18. The program product of claim 12, wherein the acknowledgement indication includes a block acknowledgement message.

19. The program product of claim 12, wherein the acknowledgement indication includes an indication of no acknowledgement.

20. The program product of claim 11 , wherein the computer code for determining the time relies on an implicit knowledge of an intended acknowledgement type by the communication station.

21. A communications station configured to operating in a wireless communication system comprising one or more communication stations, the communication station comprising: a receiver configured to receive frame aggregation information; and a processor configured to process the frame aggregation information to determine a time for scheduling transmission of an acknowledgement by the communication station based on the frame aggregation information.

22. The communication station of claim 21 , wherein each station in the communications network is configured to place an acknowledgement indication in an aggregated frame control header.

23. The communication station of claim 22, wherein the processor determines the time for scheduling transmission of an acknowledgement by determining a duration for the acknowledgement information for all communications stations in the wireless communication system, determining which of the communication stations in the wireless communication system are scheduled to transmit acknowledgement information, and determining which of the communication stations in the wireless communication system do not have acknowledgement information to send.

24. The communication station of claim 23, wherein the processor determines which of the communications stations in the wireless communication system are scheduled to transmit acknowledgement information is based on acknowledgement indication information included in the aggregated control frame header.

25. The communication station of claim 23, wherein the processor determines which of the communication stations in the wireless communication system do not have acknowledgement information to send is based on acknowledgement indication information included in the aggregated control frame header.

26. The communication station of claim 22, wherein the acknowledgement indication is placed in the aggregated frame control header in a MAC layer..

27. The communication station of claim 22, wherein the acknowledgment indication includes an acknowledgement message.

28. The communication station of claim 22, wherein the acknowledgement indication includes a block acknowledgement message.

29. The communication station of claim 22, wherein the acknowledgement indication includes an indication of no acknowledgement.

30. The communication station of claim 21 , wherein the processor determines the time is based on an implicit knowledge of an intended acknowledgement type by the communication station.