Method and device for transmitting acknowledgement in response to received frame

Abstract

To provide a method and a device for transmitting an acknowledgement in response to a data packet.SOLUTION: The receiver receives multiple data packets from multiple stations, and transmits an acknowledgement for that data packet to a source station by single transmission. The acknowledgement is transmitted using MU-MIMO. Alternatively, the acknowledgement is compacted and transmitted by single transmission. A short ACK frame is sent in response to the received frame. The short ACK frame includes an ACK sequence corresponding to an ID included in the received frame. The short ACK frame includes STF and ACK sequence. The short ACK frame is transmitted together with a short ACK indication. The short ACK frame is transmitted in response to an indication included in the received frame.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for transmitting an acknowledgement in response to a received frame. [Background technology]

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 61 / 646,040, filed May 11, 2012, U.S. Provisional Patent Application No. 61 / 669,390, filed July 9, 2012, U.S. Provisional Patent Application No. 61 / 699,531, filed September 11, 2012, and U.S. Provisional Patent Application No. 61 / 724,466, filed November 9, 2012, the contents of which are incorporated herein by reference.

[0003] A wireless local area network (WLAN) in infrastructure basic service set (BSS) mode has an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP typically has access or interface to a distribution system (DS) or another type of wired or wireless network that carries traffic within the BSS and from the BSS. Traffic to the STAs originating from outside the BSS arrives through the AP and is delivered to the STAs. Traffic originating from the STAs destined for destinations outside the BSS is sent to the AP and delivered to the respective destination. Traffic between STAs within the BSS also passes through the AP, with the source STA sending traffic to the AP, which delivers the traffic to the destination STA. Such traffic between STAs within the BSS is actually peer-to-peer traffic. Peer-to-peer traffic is sent directly between the source and destination STAs with a direct link setup (DLS) using IEEE 802.11e DLS or IEEE 802.11z tunneled DLS (TDLS). A WLAN in an Independent BSS (IBSS) has no AP and STAs communicate directly with each other.

[0004] In the current IEEE 802.11 infrastructure operating mode, an AP transmits beacons on a channel called the primary channel. The primary channel is 20 MHz wide and is the operating channel of the BSS. This channel is also used by STAs to establish connections with the AP. The channel access mechanism in 802.11 systems is carrier sense multiple access with collision avoidance (CSMA / CA). In this operating mode, every STA, including the AP, senses the primary channel, and if the channel is detected as busy, the STA and the AP back off. Thus, one STA (including the AP) can transmit on a given BSS at any given time.

[0005] In IEEE 802.11n, high-throughput (HT) STAs also use 40 MHz-wide channels for communication by combining a primary 20 MHz channel with another adjacent 20 MHz channel to form a 40 MHz-wide channel.

[0006] IEEE 802.11ac allows very high throughput (VHT) STAs to support 40 MHz, 80 MHz, and 160 MHz wide channels. 40 MHz and 80 MHz channels are formed by combining contiguous 20 MHz channels, just like IEEE 802.11n, while 160 MHz channels are formed by combining eight contiguous 20 MHz channels or two non-contiguous 80 MHz channels (80+80 configuration).

[0007] The channel operating bandwidth is reduced for the sub-1 GHz operating modes supported by IEEE 802.11af and IEEE 802.11ah. 802.11af supports 2 MHz, 4 MHz, and 8 MHz bandwidths for operation in TV White Space (TVWS). 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths for operation in non-TVWS. Some STAs in 802.11ah are considered sensors with limited capabilities and support a 1 MHz transmit mode. Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE INVENTION Accordingly, the present invention provides an improved method and apparatus for transmitting an acknowledgment in response to a received frame. [Means for solving the problem]

[0009] A method and apparatus are disclosed for transmitting acknowledgments in response to data packets in wireless communications. A receiver receives multiple data packets from multiple stations and transmits acknowledgments for the data packets to a source station in a single transmission. The acknowledgments are transmitted using multi-user multiple-input multiple-output (MU-MIMO). The acknowledgments are delayed in time after receiving the data packets. The acknowledgments may be transmitted based on an agreed-upon schedule, solicited by the station, or unsolicited after a predetermined number of data packets have been received.

[0010] Alternatively, the acknowledgements are aggregated and transmitted in a single transmission, such as in a Medium Access Control (MAC) Service Data Unit area, a MAC Protocol Data Unit area, or a Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) area.

[0011] A short acknowledgement (ACK) frame is sent in response to a received frame. The short ACK frame includes an ACK sequence corresponding to a sequence ID included in the received frame. The short ACK frame includes a short training field (STF) and an ACK sequence. The short ACK frame is transmitted with a short ACK indication. The short ACK frame is sent in response to an indication included in the received frame. [Brief explanation of the drawings]

[0012] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which: [Figure 1A] FIG. 1 is a system diagram of an exemplary communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] 1B is a system diagram of an example wireless transmit / receive unit (WTRU) used within the communication system shown in FIG. 1A. [Figure 1C] 1B is a system diagram of an example radio access network and an example core network used within the communication system shown in FIG. 1A. [Figure 2] FIG. 1 is a diagram of a conventional acknowledgement (ACK) frame. [Figure 3] FIG. 10 is a diagram of an example message exchange sequence for a data frame and a short ACK frame. [Figure 4] FIG. 1 is a diagram of an exemplary Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) data frame format. [Figure 5] FIG. 1 is a diagram of a normal PPDU and an exemplary Short ACK frame with a Short ACK indication. [Figure 6] 1 is a diagram of a normal PPDU and an exemplary short ACK frame with an extended short training field (STF). [Figure 7]1 is a diagram of a conventional Medium Access Control (MAC) frame format. [Figure 8] 1 is a diagram of an example of a PPDU frame structure for MU-MIMO Block ACK. [Figure 9] FIG. 10 is a diagram of an example message exchange sequence for delayed MU-MIMO Block ACK. [Figure 10] 1 is a diagram of a Block ACK Request (BAR) frame format. [Figure 11] FIG. 1 is a diagram of an example PPDU structure for an aggregated multi-user ACK (A-MU-ACK) frame. [Figure 12] 1 is a diagram of an example of ACK or Block ACK (BA) MAC Protocol Data Units (MPDUs) aggregated into a multi-user ACK frame coded with distinct adaptive modulation and coding schemes (MCSs). [Figure 13] 1 is a diagram of an example of ACK or Block ACK (BA) MAC Protocol Data Units (MPDUs) aggregated into a multi-user ACK frame coded with distinct adaptive modulation and coding schemes (MCSs). [Figure 14] FIG. 1 is a diagram of an example of aggregated multi-user ACK with a separate long training field (LTF) for each user to implement various MEMO schemes for the users. [Figure 15] FIG. 10 is a diagram of an example of a single-user piggyback ACK. [Figure 16] FIG. 10 is a diagram of an example of a single-user piggyback ACK aggregated at the MSDU level. [Figure 17] FIG. 10 is a diagram of an example of a piggyback ACK at the MPDU level. [Figure 18] FIG. 10 is a diagram of an example of piggyback ACK at the PPDU level. [Figure 19] FIG. 10 is a diagram of an example of a multi-user piggyback ACK. [Figure 20] FIG. 1 is a diagram of a conventional "ADDBA Request" frame action field format. [Figure 21]FIG. 1 is a diagram of a conventional "ADDBA Response" frame action field format. [Figure 22] FIG. 1 is a diagram of a conventional DELBA frame. [Figure 23] 10 is a diagram of an example of an ACK field in a delayed multi-user ACK frame for a pre-configured group of STAs. [Figure 24] 1 is a diagram of an example of an ACK field in a delayed multi-user ACK frame for an ad hoc group of STAs. [Figure 25] FIG. 1 is a diagram of a conventional short ACK frame format. [Figure 26] FIG. 10 is a diagram illustrating an example of a short ACK response. [Figure 27] FIG. 10 is a diagram of an example procedure for speed frame exchange for downlink data. [Figure 28] FIG. 10 is a diagram of an example procedure for speed frame exchange for uplink data. [Figure 29] FIG. 10 is a diagram of an example of a speed frame exchange using a short ACK frame (or a short BA frame) for downlink data. [Figure 30] FIG. 10 is a diagram of an example of a speed frame exchange using a short ACK (or short BA) frame for uplink data. [Figure 31] A diagram of an example of a speed frame exchange using a short PS-Poll frame and a short ACK (or short BA) frame. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1A is a diagram of an exemplary communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 is a multiple-access system that provides content, such as voice, data, video, messaging, and broadcast, to multiple wireless users. The communication system 100 enables the multiple wireless users to access such content through sharing of system resources, including wireless bandwidth. For example, the communication system 100 may use one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), etc.

[0014] 1A , communications system 100 includes wireless transmit / receive units (WTRUs) 102a, 102b, 102c, and 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, and 102d is any type of device configured to operate and / or communicate in a wireless environment. For example, WTRUs 102a, 102b, 102c, and 102d are configured to transmit and / or receive wireless signals and include user equipment (UE), mobile stations, fixed or mobile subscriber units, pagers, cellular phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, home appliances, etc.

[0015] The communications system 100 also includes a base station 114a and a base station 114b. Each of the base stations 114a, 114b is any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d and facilitate access to one or more communications networks, such as the core network 106, the Internet 110, and / or the network 112. For example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node B, an advanced Node B, a home Node B, a home advanced Node B, a site controller, an access point (AP), a wireless router, etc. Although the base stations 114a, 114b are each shown as a single element, it should be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0016] The base station 114a is part of the RAN 104, which also includes other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or base station 114b are configured to transmit and / or receive radio signals within a particular geographic area called a cell (not shown). The cells are further divided into cell sectors. For example, the cell associated with the base station 114a is divided into three sectors. Thus, in one embodiment, the base station 114a includes three transceivers, one for each sector of the cell. In other embodiments, the base station 114a uses multiple-input multiple-output (MIMO) technology and thus uses multiple transceivers for each sector of the cell.

[0017] The base stations 114a, 114b communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0018] More specifically, as noted above, the communication system 100 is a multiple-access system and uses one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a and the WTRUs 102a, 102b, 102c in the RAN 104 implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which establishes the air interface 116 using Wideband CDMA (WCDMA). WCDMA includes communication protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA includes High Speed ​​Downlink Packet Access (HSDPA) and / or High Speed ​​Uplink Packet Access (HSUPA).

[0019] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c implement a radio technology such as Enhanced UMTS Terrestrial Radio Access Network (E-UTRAN) that establishes the air interface 116 using Long Term Evolution (LTE) and / or Enhanced LTE (LTE-A).

[0020] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c implement a wireless technology such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), GSM EDGE (GERAN), or the like.

[0021] The base station 114b in FIG. 1A may be, for example, a wireless router, a Home NodeB, a Home Advanced NodeB, or an access point, and may use any suitable RAT to facilitate wireless connectivity in a local area, such as a business, home, vehicle, campus, etc. In one embodiment, the base station 114b and the WTRUs 102c, 102d implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d use a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b has a direct connection to the Internet 110. Therefore, the base station 114 b does not need to access the Internet 110 via the core network 106 .

[0022] The RAN 104 communicates with the core network 106, which is any type of network configured to provide voice, data, application, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A , it should be understood that the RAN 104 and / or core network 106 communicate directly or indirectly with other RANs that use the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104 using E-UTRA radio technology, the core network 106 also communicates with another RAN (not shown) that uses GSM radio technology.

[0023] The core network 106 also serves as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 includes a circuit-switched telephone network providing plain old telephone service (POTS). The Internet 110 includes a global system of interconnected computer networks and devices that use common communication protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Internet Protocol (IP) in the TCP / IP Internet protocol suite. The networks 112 include wired or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include another core network connected to one or more RANs that use the same RAT as the RAN 104 or a different RAT.

[0024] Some or all of the WTRUs 102a, 102b, 102c, and 102d in the communication system 100 include multi-mode capabilities. That is, the WTRUs 102a, 102b, 102c, and 102d include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A is configured to communicate with a base station 114a that uses a cellular-based wireless technology and a base station 114b that uses an IEEE 802 wireless technology.

[0025] 1B is a system diagram of an exemplary WTRU 102. As shown in FIG. 1B, the WTRU 102 includes a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It should be understood that the WTRU 102 may include any subcombination of the foregoing elements while remaining consistent with an embodiment.

[0026] The processor 118 may be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 118 performs signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 is coupled to the transceiver 120, which is coupled to the transmit / receive element 122. While FIG. 1B depicts the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0027] The transmit / receive element 122 is configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 is an antenna configured to transmit and / or receive RF signals. In another embodiment, the transmit / receive element 122 is an emitter / detector configured to transmit and / or receive, for example, IR signals, UV signals, or visible light signals. In other embodiments, the transmit / receive element 122 is configured to transmit and receive both RF signals and optical signals. It will be understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0028] 1B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may use MIMO technology. Thus, in one embodiment, the WTRU 102 includes two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0029] The transceiver 120 is configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As noted above, the WTRU 102 has multi-mode capabilities. Thus, the transceiver 120 includes multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11.

[0030] The processor 118 of the WTRU 102 is coupled to and receives user input data from the speaker / microphone 124, keypad 126, and / or display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 also outputs user data to the speaker / microphone 124, keypad 126, and / or display / touchpad 128. Furthermore, the processor 118 accesses information from and stores data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 includes random access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 includes a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, etc. In other embodiments, the processor 118 accesses information from and stores data in memory that is not physically located on the WTRU 102, such as on a server or on a home computer (not shown).

[0031] The processor 118 is configured to receive power from the power source 134 and distribute and / or control the power to other components within the WTRU 102. The power source 134 is any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0032] The processor 118 is also coupled to a GPS chipset 136 that is configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or instead of, information from the GPS chipset 136, the WTRU 102 receives location information from base stations (e.g., base stations 114a, 114b) over the air interface 116 and / or determines its location based on the timing of signals received from two or more nearby base stations. It will be understood that the WTRU 102 acquires location information by any suitable location determination method while remaining consistent with an embodiment.

[0033] Additionally, the processor 118 may be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, peripherals 138 may include an accelerometer, an electronic compass (e-compass), a satellite transceiver, a digital camera (for photos or videos), a Universal Serial Bus (USB) port, a vibration device, a television transceiver, a hands-free headset, a Bluetooth module, a frequency-changing (FM) radio unit, a digital music player, a media player, a video game player module, an internet browser, etc.

[0034] 1C is a system diagram of the RAN 104 and the core network 106 according to one embodiment. As noted above, the RAN 104 uses E-UTRA radio technology and communicates with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 also communicates with the core network 106.

[0035] The RAN 104 includes eNodeBs 140a, 140b, and 140c, although it should be understood that the RAN 104 may include any number of eNodeBs while remaining consistent with an embodiment. The eNodeBs 140a, 140b, and 140c each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the eNodeBs 140a, 140b, and 140c implement MIMO technology. Thus, the eNodeB 140a may use multiple antennas, for example, to transmit wireless signals to and receive wireless signals from the WTRU 102a.

[0036] Each of the eNodeBs 140a, 140b, 140c is associated with a particular cell (not shown) and is configured to handle radio resource management decisions, handover decisions, scheduling of users on the uplink and / or downlink, etc. As shown in Figure 1C, the eNodeBs 140a, 140b, 140c communicate with each other over an X2 interface.

[0037] 1C includes a mobile communications management device (MME), a serving gateway 144, and a packet data network (PDN) gateway 146. While each of the foregoing elements is shown as part of the core network 106, it should be understood that any one of these elements may be owned and / or operated by an entity other than the core network operator.

[0038] The MME 142 is connected to each of the eNodeBs 140a, 140b, 140c in the RAN 104 via an S1 interface and acts as a control node. For example, the MME 142 is responsible for authenticating users of the WTRUs 102a, 102b, 102c, activating / deactivating bearers, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 142 also provides a control plane function for switching between the RAN 104 and other RANs (not shown) that use other radio technologies, such as GSM or WCDMA.

[0039] The serving gateway 144 is connected to each of the eNode-Bs 140a, 140b, 140c in the RAN 104 via an S1 interface. The serving gateway 144 generally routes and forwards user data packets to / from the WTRUs 102a, 102b, 102c. The serving gateway 144 also performs other functions, such as anchoring the user plane during inter-eNode-B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, and managing and storing the context of the WTRUs 102a, 102b, 102c.

[0040] The serving gateway 144 is also connected to a PDN gateway 146, which provides the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0041] The core network 106 facilitates communication with other networks. For example, the core network 106 provides the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, and facilitates communication between the WTRUs 102a, 102b, 102c and traditional landline communication devices. For example, the core network 106 includes or communicates with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the core network 106 and the PSTN 108. Additionally, the core network 106 provides the WTRUs 102a, 102b, 102c with access to networks 112, including other wired or wireless networks owned and / or operated by other service providers.

[0042] The other network 112 is connected to an IEEE 802.11-based wireless local area network (WLAN) 160. The WLAN 160 includes an access router 165. The access router includes a gateway function. The access router 165 communicates with multiple access points (APs) 170a, 170b. Communication between the access router 165 and the APs 170a, 170b may be via wired Ethernet (IEEE 802.3 standard) or any type of wireless communication protocol. The AP 170a communicates wirelessly over the air interface with the WTRU 102d.

[0043] Hereinafter, the terms "short frame" and "null data packet" (NDP) will be used interchangeably. A short frame (such as a short ACK, short block ACK, short clear-to-send (CTS), or short probe request) is a Physical Layer Convergence Protocol (PLCP) protocol data unit (PPDU) that does not carry a data field. Hereinafter, the term "STA" (e.g., WTRU) includes a non-AP station or an AP station. The embodiments disclosed herein are implemented by a non-AP STA or an AP station (AP). Hereinafter, the disclosed embodiments apply to any 802.11 system and any wireless communication system.

[0044] Wireless transmissions can be erroneous, even if protection mechanisms such as channel coding and interleaving are used to protect the transmission. Therefore, mechanisms for acknowledging correct packet reception are introduced in WLAN systems. A STA / AP that successfully receives a data frame addressed to it sends an acknowledgment. If the STA / AP transmitting a frame does not receive an ACK within a predetermined amount of time, it assumes that the data frame was not received correctly and retransmits it. Not all data frames can be acknowledged in this way. The 802.11 standard also supports "no ACK", when the sender indicates that it does not explicitly expect an acknowledgment from the receiver of the data frame.

[0045] Block ACK was introduced in the 802.11e amendment. Block ACK improves system efficiency by allowing a receiver of multiple frames to send a single Block ACK to acknowledge a block of data frames. Block ACKs can be immediate or delayed.

[0046] 2 shows a conventional ACK frame 200. The conventional ACK frame 200 has a PLCP preamble including a short training field (STF) 202 and a long training field (LTF) 204, a signal (SIG) field 206, and an ACK body frame 208. The ACK body frame 208 has a 2-byte frame control field 210, a 2-byte duration field 212, a 6-byte receiver address (RA) field 214, and a 4-byte frame check sequence (FCS) 216. The information carried by the frame control field 210 indicates that this is an ACK frame. The RA field 214 indicates the originator of the data exchange session.

[0047] A Short ACK frame is used to acknowledge a data frame (or any other frame) from the originator. FIG. 3 illustrates an exemplary message exchange sequence for a data frame and a Short ACK frame. FIG. 3 also illustrates an exemplary PPDU frame structure for a Short ACK frame according to one embodiment. The originator transmits a data frame 310 to the receiver, which decodes the data frame 310 and transmits a Short ACK frame 320 to the originator to indicate successful or unsuccessful decoding of the data frame. In the data frame 310, the originator indicates that the expected ACK transmission will be a Short ACK. The originator explicitly or implicitly identifies an ACK sequence ID in the data frame 310. The receiver then includes the corresponding ACK sequence in the ACK sequence field 324 of the Short ACK frame 320.

[0048] The short ACK frame 320 includes an STF 322 and an ACK sequence field 324. The STF 322 is used for automatic gain control (AGC) and coarse time-frequency offset estimation. The short ACK frame 320 is distinguished from other frames by the STF 322.

[0049] An ACK sequence corresponding to the ACK sequence ID indicated by the data frame 310 indicates the corresponding data frame 310. The ACK sequence is modulated in the frequency domain or the time domain. For example, a set of predefined sequences with constant amplitude zero autocorrelation (CAZAC) properties is used as the ACK sequence. For example, Generalized Chirp Like (GCL) sequences are used. Zadoff-Chu (ZC) sequences are a special case of GCL sequences. Each sequence has a sequence ID. The sender implicitly or explicitly assigns this sequence ID in the transmitted data frame 310. The receiver includes the corresponding sequence in a short ACK frame 320. The short ACK frame 320 is used for simultaneous multi-user access because orthogonal sequences are chosen.

[0050] The sender demodulates the received short ACK frame by correlating it with the assigned ACK sequence in the frequency domain or the time domain. After the sender successfully demodulates the short ACK, the sender knows that it is an acknowledgment for a previously transmitted data packet. False positives are also possible. However, the probability of false positives is reduced by increasing the number of ACK sequences.

[0051] The unintended STAs set their Network Allocation Vector (NAV) when they demodulate the data packet 310 transmitted by the originator. The duration field carried by the data packet 310 is set with the understanding that the upcoming ACK will be a Short ACK. If the unintended STAs are unable to demodulate the data packet 310 but detect the Short ACK STF field, they identify this as a Short ACK frame and accordingly postpone accessing the medium.

[0052] The Extended Interframe Space (EIFS) is used to postpone when a frame is detected but not received correctly. In the current 802.11, EIFS = αSIFSTime + ACKTxTime + DIFS. If the system uses short ACK for all ACK transmissions, or if the STA knows that short ACK is being used, the STA uses the redefined EIFS or the newly defined EIFS_SACK to postpone. For example, EIFS_SACK = αSIFSTime + SACKTxTime + DIFS, where SACKTxTime is the time required to send an S-ACK frame at the lowest data rate.

[0053] The sender assigns an ACK Sequence ID for the short ACK frame in the data packet. The ACK Sequence ID may be implicit. For example, the ACK Sequence ID is determined as a function of one or any (full or partial) combination of the following parameters: scrambler seed (6 bits), FCS (4 bytes), CRC in the SIG field (4 bits), length field in the SIG field (9 to 21 bits), and / or basic service set identification (BSSID) (6 bytes).

[0054] Alternatively, the ACK Sequence ID may be explicitly indicated. For example, the ACK Sequence ID may be indicated by using a service field in the data frame. Figure 4 shows an exemplary PPDU data frame format. PPDU 400 includes a preamble 410, a SIG field 420, and a data field 430. The data field 430 includes a service field 432, an MPDU 434, and tail and padding bits 436. The service field 432 is a 16-bit field. The first 7 bits of the service field 432 are scrambler initialization bits, used to synchronize the descrambler, and are typically set to zero. The remaining 9 bits of the service field 432 are currently reserved. The reserved 9 bits of the service field 432 may be used to explicitly assign an ACK Sequence ID.

[0055] The sender indicates in its data packet that a Short ACK frame is expected in response to the data packet. This indication is provided by using the SIG field 420 (e.g., using a bit in the SIG field 420 to indicate that a Short ACK frame is expected or acceptable) or the Service field 432 (e.g., using a bit (e.g., bit 7) in the Service field 432 to indicate that a Short ACK frame is expected or acceptable).

[0056] In another embodiment, the receiver responds to the data frame with a Short ACK frame, and a Short ACK indication is explicitly or implicitly included in the Short ACK frame. The AP and STAs (intended and unintended) identify the frame as a Short ACK frame based on the Short ACK indication. The simple structure of the Short ACK frame allows the receiving STA to determine that it is a Short ACK frame before starting correlation detection of the ACK sequence.

[0057] The Short ACK indication may be included within the STF field. The STF contains several repetitions of the sequence. For example, most 802.11 systems contain 10 repetitions of the STF sequence, while the 802.11ah STF for 1 MHz has 20 repetitions. In one embodiment, the sign of one or more repetitions of the STF sequence is inverted to indicate that the frame is a Short ACK frame. Figure 5 shows a normal PPDU 510 and an exemplary Short ACK frame 520 with a Short ACK indication. In Figure 5, the signs of the last two STF sequences 522 are inverted to indicate that the frame is a Short ACK frame. This changes the autocorrelation behavior, so that the receiver detects that this is a Short ACK frame.

[0058] In other embodiments, an increased number of repetitions of the STF sequence are used to indicate a short ACK frame. Figure 6 shows an example short ACK frame 620 having a normal PPDU 610 and an extended STF 622. The receiver determines that the frame is a short ACK frame after detecting a longer than normal STF or autocorrelation platform.

[0059] The ACK frame is modulated and coded in the physical layer before transmission. The modulation and coding scheme (MCS) is the highest rate within the BSSBasicRateSet parameter that is less than or equal to the rate (MCS) of the previously received data frame. In this way, STAs in the BSS have the ability to detect the ACK frame.

[0060] To reduce the overhead from ACK, a higher MCS is more promising because it requires fewer OFDM symbols to transmit. In some 802.11 standards, an ACK indication field is defined in the SIG field and transmitted by the transmitter. The ACK indication is used to indicate information about the upcoming ACK frame. For example, in 802.11ah, the ACK indication has the following definition: 00: ACK; 01: BA; 10: No ACK; 11: Frame that is not ACK, BA, or CTS. With the ACK indication, non-intended STAs can figure out whether the upcoming frame is an ACK frame. Therefore, it is not necessary for STAs to understand the ACK frame body. In one embodiment, the requirement to select an MCS for an ACK frame in BSSBasicRateSet is relaxed when the ACK indication is used in the SIG field. In the absence of an ACK indication transmitted in the SIG field by the originator, non-intended STAs must decode the ACK frame and figure out that it is an ACK frame. Therefore, the ACK frame should use a basic MCS that all STAs can understand. The MCS should be the MCS defined in the BSSBasicRateSet. If there is an ACK indication in the SIG field from the originator, the unintended STAs detect the SIG field, realize that an ACK frame is coming, and defer for a certain duration. In this way, other STAs do not need to decode the ACK frame at all, and as a result, the ACK frame may use any MCS other than the one defined in the BSSBasicRateSet.

[0061] In other embodiments, the sender allocates an MCS and / or bandwidth for the ACK frame, and the receiver transmits the ACK frame with the pre-allocated MCS and / or bandwidth.

[0062] In 802.11ah, receivers should support both 1 MHz and 2 MHz reception, while transmitters are required to support 1 MHz. Thus, an AP can send a 2 MHz packet to a STA and explicitly or implicitly indicate in the data packet that the upcoming ACK will be sent at 1 MHz. Alternatively, the STA can send a 1 MHz packet to the AP, and the AP operating on a 2 MHz channel can choose to respond with either a 1 MHz or 2 MHz ACK. By sending the ACK at 2 MHz, the ACK overhead is reduced. In the above example, the STA indicates the bandwidth to be used by the AP for the ACK transmission.

[0063] In another example, a STA has two receive radio frequency (RF) chains but only one transmit RF chain. In the current standard, after the STA transmits one data stream packet to the AP, the AP transmits an ACK for one data stream. However, if the channel condition is very good, it is more efficient to allow the AP to transmit an ACK for two data streams. In one embodiment, the STA checks the channel condition when it receives the previous two data streams from the AP and determines whether the AP is suitable to transmit an ACK for two data streams.

[0064] When a sender sends a data packet to a receiver, if the sender has some knowledge of the channel from the receiver to the sender and is aware of asymmetric sending and receiving capabilities, the sender decides on a specific MCS and / or bandwidth for the ACK frame and indicates it in the data frame. Otherwise, the sender chooses an MCS equal to or less than the MCS used in the previous data packet and chooses a bandwidth according to the sender's and receiver's capabilities.

[0065] The selected MCS and bandwidth for the upcoming ACK frame are indicated in the MAC header of the data packet. Figure 7 shows a conventional MAC frame format. In the current 802.11 standard, an ACK policy subfield is defined in the QoS control field 710 of the MAC header. The ACK policy subfield is two bits in length and identifies the acknowledgement policy to be followed when delivering the MPDU. In one embodiment, the ACK policy subfield is extended for MCS and bandwidth indication. The number of bits required for MCS and bandwidth information varies depending on the standard. For example, in the case of 802.11ah, two bits are used to indicate the bandwidth, as shown in Table 1.

[0066] [Table 1]

[0067] Alternatively, the MCS and bandwidth for the ACK frame may be explicitly indicated in the SIG field, for example, several bits are added in the SIG field to represent the MCS and bandwidth for the ACK frame.

[0068] Alternatively, the MCS and bandwidth for the ACK frame may be implicitly indicated by setting the Duration field 720 in the MAC header. The Duration field 720 in the MAC header is set to the time value required to transmit the pending packet plus one ACK or Block ACK plus the short interframe space (SIFS) interval. The ACK or Block ACK duration value is calculated with the pre-assigned MCS and bandwidth.

[0069] When an ACK frame is transmitted with the pre-assigned MCS and bandwidth, the NAV setting is modified accordingly. The duration field 720 of a MAC frame transmitted by an originator holds a time value indicating the duration for which the originator expects the medium to be busy. Traditionally, an originator does not assign an MCS to an upcoming ACK frame. Therefore, the originator estimates the duration of the upcoming ACK transmission based on the lowest MCS supported by the system. With a pre-assigned MCS according to the embodiments disclosed herein, the originator estimates the upcoming ACK transmission with the assigned MCS and provides a more accurate time value in the duration field 720. In this way, unintended STAs set their NAV more accurately.

[0070] After the receiver correctly demodulates the data packet, it prepares an ACK packet accordingly. When explicit indication is used, the receiver transmits the ACK frame with the pre-assigned MCS and bandwidth. When implicit indication is used, the receiver transmits the ACK frame with the MCS and bandwidth that completes the ACK transmission within the specified duration. The MCS and bandwidth used by the receiver are not required to be the same as those chosen by the sender. However, the ACK PPDU duration must fit within the duration value set in the MAC frame format by the sender.

[0071] ACKs or BAs for multiple users (e.g., STAs) are transmitted via a single ACK or BA transmission. ACKs (or BAs) for multiple users may be aggregated in the spatial domain and transmitted using multi-user multiple-input multiple-output (MU-MIMO) or aggregated in the time domain and transmitted using aggregated multi-user ACKs.

[0072] In one embodiment, a delayed multi-user ACK or block ACK is transmitted using a MU-MIMO PPDU format. FIG. 8 shows an example of a PPDU frame structure for a MU-MIMO block ACK. The PPDU includes an omni portion 810 and an MU portion 820. The omni portion 810 is transmitted to all users, and the MU portion 820 is transmitted via each spatial stream of the MU-MIMO transmission. The omni portion 810 includes an STF, an LTS, and a SIG field (SIGA). The MU portion 820 includes an STF, an LTS, and an ACK body frame 822. The ACK body frame 822 shown in FIG. 8 is a BA frame 830. Alternatively, the ACK body frame 822 may be a normal ACK frame. The multi-user block ACK is applied to a delayed multi-user block ACK.

[0073] FIG. 9 shows an example message exchange sequence for delayed MU-MIMO Block ACK. STA1 acquires a channel and negotiates with the AP through several message exchanges 910 to set up a Block ACK session with the AP using a delayed Block ACK policy. The initiator (STA1 in this example) transmits data, followed by a Block ACK Request (BAR) 914. The BAR frame 914 requests an ACK frame 916 from the receiver (the AP in this example). FIG. 10 shows the BAR frame format. The BAR frame 914 includes a BAR control field 1002. If the BAR ACK policy field in the BAR control field 1002 is set to "1," the receiver immediately returns an ACK upon receiving the BAR frame 914. If the BAR ACK policy field in the BAR control field 1002 is set to "0," the receiver does not send an ACK upon receiving the BAR frame 914. In the example shown in FIG. 9, the AP sends an ACK 916 in response to the BAR frame 914. During each BA session, the unintended STAs (all STAs other than the originator (in this example, STA2 through STA4) and the recipient (in this example, the AP)) set their NAVs for the duration of the BA session. The AP holds the BA for STA1 and waits for a delayed transmission.

[0074] Next, STA2 acquires a channel, exchanges message 920 with the AP to set up a BA session, transmits data frame 922 and BAR frame 924 to the AP, and receives ACK frame 926 from the AP. Next, STA3 acquires a channel, exchanges message 930 with the AP to set up a BA session, transmits data frame 932 and BAR frame 934 to the AP, and receives ACK frame 936 from the AP. Next, STA4 acquires a channel, exchanges message 940 with the AP to set up a BA session, transmits data frame 942 and BAR frame 944 to the AP, and receives ACK frame 946 from the AP.

[0075] The AP groups several Block ACKs (in this example, BA1 to BA4) and transmits them using MU-MIMO transmission (i.e., delayed MU-MIMO BA). The AP groups multiple Block ACKs according to some grouping criteria (e.g., having similar Access Categories (ACs) or good spatial channel correlation) for MU-MIMO Block ACK transmission.

[0076] The AP modulates the BAs with different MU-MIMO weights and transmits them simultaneously. In the MU-MIMO BA frame, the BA ACK policy field in the BA control field indicates whether an ACK is required in response to the BA frame. The BA ACK policy field is set to "0" or "1" for all users. If the BA ACK policy field is set to "1", the BA frame 950 will not request an ACK response from the originator (STA1 to STA4 in this example). If the BA ACK policy field is set to "0", the BA frame 950 will request an ACK response 960 from the originator (STA1 to STA4 in this example), as shown in FIG. 9.

[0077] The ACK responses 960 from the STAs in response to the MU-MIMO BA 950 are transmitted by the STAs simultaneously using MU-MIMO, or the STAs transmit the ACKs sequentially, for example, according to a user position array defined in the group ID, which is included in the SIG field.

[0078] All APs / STAs included in the delayed MU-MIMO ACK sequence declare support for delayed Block ACK and MU-MIMO.

[0079] In another embodiment, rather than transmitting ACKs or BAs for multiple users in MU-MIMO, the ACKs or BAs are aggregated in the time domain and transmitted sequentially (i.e., aggregated multi-user ACK (A-MU-ACK)). A receiver (STA or AP) receives data packets, generates acknowledgment packets in response to the received data packets, aggregates the acknowledgment packets, and transmits the aggregated acknowledgment packet in a single transmission.

[0080] Figure 11 shows an example PPDU structure for an A-MU-ACK frame. In Figure 11, ACKs are aggregated at the MPDU level. The aggregated ACKs are either Block ACKs or regular ACKs. A PPDU 1100 for an A-MU-ACK includes a preamble 1110, a SIG field 1120, and a data field 1130. The data field 1130 contains an A-MU-ACK frame 1132. The A-MU-ACK frame 1132 contains ACK (or BA) MPDUs 1142 for one or more users (in this example, ACK1, ACK2, and ACK3) separated by ACK delimiters 1144. The ACK / BA MPDUs 1142 are aggregated at the MAC level, and the A-MU-ACK frame 1132 is passed to the physical layer as an aggregated MPDU packet. As a result, the A-MU-ACK frame 1132 is coded and modulated as a whole packet by the physical layer. The lowest MCS is used for the A-MU-ACK.

[0081] An ACK delimiter 1144 is inserted at the beginning of each ACK / BA MPDU 1142. The ACK delimiter 1144 is either 32 bits or 8 bits in length. A 32-bit ACK delimiter includes a length field, a CRC, and an 8-bit signature field. The length field is used to indicate the length of the upcoming ACK / BA MPDU. The signature field is used to detect the ACK delimiter when scanning for delimiters. An 8-bit ACK delimiter includes an 8-bit signature field that is used to detect the ACK delimiter when scanning for delimiters.

[0082] The aggregated multi-user ACK packet is broadcast or multicast to multiple users (e.g., STAs). Because different users have different wireless link qualities due to path loss, channel conditions, receiver sensitivity, etc., it is simple but inefficient to use the same MCS in the same aggregated multi-user ACK packet for all users. Furthermore, if a relatively low MCS is chosen, not all users will necessarily decode the aggregated multi-user ACK frame correctly.

[0083] ACK or BA MPDUs aggregated in a multi-user ACK frame may be coded with separate MCSs, as shown in Figures 12 and 13. In the example shown in Figures 12 and 13, the three ACK / BA MPDUs included in the aggregated multi-user ACK frame are coded separately with three MCSs (which may or may not be the same). The length and MCS for each MPDU are indicated in the SIG field. In Figure 12, the aggregated multi-user ACK frame includes a SIG field 1220 common to the three ACK MPDUs 1210a through 1210c. In Figure 13, separate SIG fields 1320a through 1320c are included for each ACK / BA MPDU 1310a through 1310c.

[0084] Multi-user aggregation is performed after constellation mapping and before the Inverse Discrete Fourier Transform (IDFT). Thus, one padding and tail bit field is added for all coded ACK frames except the last one. There is no need to insert more padding bits to round up to an integer number of OFDM symbols. For the last coded ACK frame, both tail and padding bits are inserted if necessary. The length field in the SIG field explicitly indicates the length of each ACK body frame in bytes according to this scheme.

[0085] Alternatively, multi-user aggregation may be performed after the IDFT (i.e., aggregation is in units of OFDM symbols). Each coded ACK frame occupies an integer number of OFDM symbols. Therefore, tail bits and OFDM symbol padding bits are added for each coded ACK frame. The length field in the SIG field indicates the length of each ACK body frame in units of bytes or OFDM symbols.

[0086] Figure 12 shows an example of an aggregated multi-user ACK with a common SIG field 1220. Figure 13 shows an example of an aggregated multi-user ACK with separate SIG fields 1320. In both Figures 12 and 13, each ACK / BA MPDU is coded with a separate MCS.

[0087] In the examples shown in Figures 12 and 13, all users use common preambles 1230, 1330 for channel estimation. Therefore, the use of MIMO schemes is limited. For example, if space-time block coding (STBC) is used, STBC is used for all users in a packet, and different MIMO schemes are not used for some of the users.

[0088] In other embodiments, various MIMO schemes are used when transmitting aggregated multi-user ACK frames, for example, using the PPDU structure shown in FIG. 14. FIG. 14 shows an example of an aggregated multi-user ACK with a separate LTF for each user to implement various MIMO schemes for the users. In FIG. 14, dedicated LTFs 1402 (in this example, LTF1, LTF2, and LTF3) are included for each user for AGC adjustment and channel estimation. The length of the dedicated LTF for each user depends on the number of data streams being transmitted and whether AGC is required. When there are separate LTFs, different MIMO schemes are used for different users (in this example, beamforming for users 1 and 3, and STBC for user 2).

[0089] In other embodiments, hierarchical modulation is used to simultaneously transmit ACKs for different users in different constellations of the same OFDM symbol(s). Hierarchical modulation can multiplex multiple data streams (e.g., for different users) into a single symbol stream where the base layer symbols and enhancement layer symbols are synchronously expanded before transmission.

[0090] Acknowledgments are piggybacked within data packets (i.e., piggyback ACKs). With piggyback ACKs, a data frame is overloaded with acknowledgments of previously received MAC Protocol Data Units (MPDUs) and / or polls for the STAs to which the frame is directed. Piggyback ACKs are used to reduce the overhead required for acknowledgment feedback.

[0091] The ACK and the data onto which it is piggybacked are sent toward a single user (i.e., a single-user piggyback ACK). Figure 15 shows a diagram of an example of a single-user piggyback ACK. The originator sends a data packet 1510 to the receiver. A piggyback ACK is used when the data is not time-sensitive. The originator indicates (e.g., in the data packet) that a piggyback ACK is possible. If the receiver has a data payload 1530 to send toward the originator, the receiver piggybacks the ACK 1520 with the data packet 1530. The piggyback ACK may be immediate or delayed. If the receiver does not have a data payload for the originator, the receiver may delay the ACK (i.e., piggyback the ACK with the data later).

[0092] Single-user piggyback ACK may be implemented at the MSDU level. Figure 16 shows an example of a single-user piggyback ACK aggregated at the MSDU level. An ACK (or BA) MSDU 1610 and a data MSDU 1620 are aggregated, and a modified MAC header 1630 is added to the aggregated ACK and data MSDU. The MAC header 1630 indicates that the frame's subtype is a data frame with a piggybacked ACK or BA. After the subtype field in the frame control field in the MAC header indicates that the frame is a data frame with a piggybacked ACK or BA, the sequence control field in the MAC header is extended to cover the sequence numbers of the data MSDU and ACK. If BA is used, the BA control field is included in the MAC header.

[0093] Single-user piggyback ACK may be implemented at the MPDU level. Figure 17 shows an example of piggyback ACK at the MPDU level. An ACK MPDU 1710 and a data MPDU 1720 are aggregated and passed to the physical layer. A common PLCP header and preamble are added to the aggregated packet to form a PPDU 1700. In this scheme, the ACK MPDU 1710 and the data MPDU 1720 are coded and modulated with the same MCS. The ACK and data are contained in separate MPDUs with separate MAC headers, and these MPDUs are separated by an MPDU delimiter.

[0094] Single-user piggyback ACK may be implemented at the PPDU level. Figure 18 shows an example of piggyback ACK at the PPDU level. The ACK and data are included in separate MPDUs, and these MPDUs are modulated and coded separately. Separate MCSs are used for these MPDUs. As shown in Figure 18, a common SIG field is used in which the MCSs for the ACK and data are defined. Alternatively, separate SIG fields may be included.

[0095] A single-user piggyback packet includes multiple data packets and / or multiple ACK / BA packets.

[0096] The ACK and data are sent to different users (i.e., a multi-user piggyback ACK). The piggyback ACK may be immediate or delayed. Figure 19 shows an example of a multi-user piggyback ACK. The originator sends a data packet 1910 to the receiver. If the data is not time-sensitive, the originator allows piggyback ACKs. In this case, the originator indicates (e.g., in the data packet) that piggyback ACKs are possible. The receiver may choose to piggyback the ACK 1920 with a data packet 1930 sent to a third STA.

[0097] Multi-user piggyback ACK may also be implemented at the MPDU level. In this case, the ACK and data MPDUs are aggregated and passed to the physical layer. The MAC header of each MPDU packet has its own receiver address (RA) information. A common PLCP header and preamble are added to the aggregated packet to form a PPDU. In this scheme, the ACK and data MPDUs are coded and modulated with the same MCS. Similar to single-user piggyback ACK, multi-user piggybacking within the MPDU region uses the frame format shown in Figure 17.

[0098] Multi-user piggyback ACK may be implemented in the PPDU domain, where the ACK and data are in separate MPDUs and are modulated and coded separately. A common SIG is used, where the MCS for the ACK and data is defined. Alternatively, separate SIGs may be used.

[0099] A multi-user piggyback ACK packet includes multiple data packets and / or multiple ACK or BA packets.

[0100] In the following, we describe an embodiment setup for delayed multi-user ACK (DMA), which is an efficient ACK mechanism that can effectively reduce the overhead for data packets by acknowledging packets from multiple users simultaneously.

[0101] A STA indicates to the AP during association or any other time that it is available to receive a delayed multi-user ACK. To facilitate delayed multi-user ACK, three new action frames are defined: a delayed multi-user ACK add request action frame (ADDDMA Request), a delayed multi-user ACK add response action frame (ADDDMA Response), and a delayed multi-user ACK delete frame (DELDMA).

[0102] The ADDMA frame is used to set up or modify a delayed multi-user ACK for a particular traffic class (TC) or traffic stream (TS). The "ADDMA Response" frame is sent in response to an "ADDMA Request" frame. The DELDMA frame is sent by the originator or receiver to terminate participation in a delayed multi-user ACK.

[0103] These three new action frames are implemented, for example, using the conventional Block ACK action frame. Exemplary Block ACK action field values ​​for the "ADDMA Request" frame, the "ADDMA Response" frame, and the DELDMA frame are shown in Table 2.

[0104] [Table 2]

[0105] The ADDMA request frame uses an ADDBA request frame. Figure 20 shows a conventional ADDBA request frame action field format. The Block ACK action field 2002 is set to "3," indicating this is an ADDMA request frame. The Block ACK policy bit in the Block ACK parameter set 2004 is interpreted as a regular delayed multi-user ACK for STAs not for a specific traffic class (TC) or traffic stream (TS) when set to "0," or as a delayed multi-user ACK for STAs for a specific TC or TS specified by the traffic identifier (TID) field in the Block ACK parameter set 2004 when set to "1." Several bits in the Block ACK timeout value field 2006 or other fields are used to indicate the delayed multi-user ACK option: scheduled delayed multi-user ACK, unsolicited delayed multi-user ACK, or solicited delayed multi-user ACK.

[0106] The ADDMA response frame uses an ADDBA response frame. Figure 21 shows the conventional ADDBA response frame action field format. The Block ACK action field 2102 is set to "4," indicating this is an ADDMA response frame. The Block ACK policy bit in the Block ACK parameter set 2104 is interpreted as a regular delayed multi-user ACK for STAs not for a specific TC or TS when set to "0," or as a delayed multi-user ACK for STAs for a specific TC or TS specified by the TID field in the Block ACK parameter set 2104 when set to "1." Several bits in the Block ACK timeout value field 2106 or other fields are used to indicate the delayed multi-user ACK option: scheduled delayed multi-user ACK, unsolicited delayed multi-user ACK, or solicited delayed multi-user ACK.

[0107] The DELBA frame is used as the format of the DELDMA frame. Figure 22 shows a conventional DELBA frame. The Block ACK Action field 2202 is set to "5", indicating that this is a DELDMA frame. One of the reserved bits in the DELBA parameter set field 2204 (bits 0 to 10) is interpreted as, when set to "0", to delete a delayed multi-user ACK for STAs not for a specific TC or TS, and when set to "1", to delete a delayed multi-user ACK for STAs for a specific TC or TS specified by the TID field in the DELBA parameter set 2204.

[0108] An STA indicates to the receiving STA or AP that it is capable of and willing to use the delayed multi-user ACK mechanism by sending an ADDMA Request frame to the receiving STA / AP. By sending an ADDMA Request frame, the STA indicates to the receiving STA / AP that it is initiating delayed multi-user ACK for only one TS or TC originating from itself, setting the Block ACK Policy bit to "1" and the TID field to the TID of the TS or TC.

[0109] The receiving STA / AP responds by sending an ADDMA Response frame. After receiving packets from that STA or other STAs with which it has set up a Delayed Multi-User ACK, the receiving STA / AP records the received packets. The receiving STA / AP later sends a Delayed Multi-User ACK frame at a preset time in the case of a Scheduled Delayed Multi-User ACK or an Unsolicited Delayed Multi-User ACK, or at the request of one of the other STAs in the case of a Solicited Delayed Multi-User ACK.

[0110] The transmitting STA or AP and the receiving STA or AP may eliminate the delayed multi-user ACK configuration by transmitting a DELDMA frame, which is immediately acknowledged by the other party in the delayed multi-user ACK.

[0111] After a STA transmits its packet, the packet is not immediately acknowledged by the receiving STA / AP because the receiving STA / AP accumulates packets from other STAs and then acknowledges them simultaneously using a delayed multi-user ACK frame.

[0112] Because STAs are battery-powered, it is desirable to have the STAs transmit their packets, transition to a doze state, and wake up at a predetermined time to receive a delayed multi-user ACK frame from the receiver (e.g., an AP). In the case of scheduled delayed multi-user ACK, an originator (e.g., a STA) that has already set up a DMA configuration with the receiver transitions to a doze state immediately after their own transmission and wakes up at the delayed multi-user ACK transmission interval following their own transmission to receive a delayed multi-user ACK frame from the receiver. The receiver indicates the delayed multi-user ACK transmission interval in a beacon, or short beacon, or other type of management, control, or action frame.

[0113] If the sender discovers by evaluating the delayed multi-user ACK frame that its packets have not been successfully received by the receiver, the sender may either immediately retransmit the unacknowledged packet or retransmit it at a later time.

[0114] In the case of unsolicited delayed multi-user ACK, the receiver (e.g., AP) determines that it has received enough packets from the sender (e.g., STA) that has already set up a DMA configuration with the receiver, and sends a delayed multi-user ACK frame to acknowledge all received packets.

[0115] For solicited delayed multi-user ACK, an originator (e.g., a transmitting STA) that has already set up a DMA configuration with a receiver sends a DMA request frame to the receiver at some predetermined or random interval. The receiver then sends a delayed multi-user ACK frame to acknowledge all packets received after receiving one or more DMA request frames that solicit the delayed multi-user ACK frame.

[0116] A DMA Request frame is implemented, for example, by using a Block ACK Action frame or any other management or control frame. When implemented as a Block ACK Action frame, the Block ACK Action field value is set to "6" to indicate this is a DMA Request frame. The DMA Request frame includes a DMA Request Options field to indicate whether the DMA request is for the entire group or an individual STA, and / or whether the DMA request is for regular ACKs only or for a Block ACK.

[0117] STAs may be pre-configured into groups autonomously or by the AP. For example, the AP announces STA group membership using a Group ID management frame or any other management or control frame. The receiver address in the MAC header of a Delayed Multi-User ACK frame for a group of STAs is a broadcast or multicast MAC address mutually agreed upon by the STAs and the AP.

[0118] A delayed multi-user ACK frame for a pre-configured group of STAs is implemented using a Block ACK action frame or any management or control frame. If implemented as a Block ACK action frame, the Block ACK action field value is set to '7' to indicate that this is a delayed multi-user ACK frame for a pre-configured group of STAs.

[0119] The delayed multi-user ACK frame for a pre-configured group of STAs includes an ACK option field to indicate that the DMA is for the pre-configured group and to indicate whether the ACK is a normal ACK or a Block ACK. The delayed multi-user ACK frame for a pre-configured group of STAs also includes a Block ACK option field to indicate whether the Block ACK for each member of the pre-configured group is Multi-TID, whether the Block ACK for each member of the pre-configured group is Multi-TID, and the number of TIDs per STA (K) that are acknowledged and / or the number of acknowledged frames per TID (N) per member of the pre-configured group.

[0120] A delayed multi-user ACK frame for a pre-configured group of STAs includes a field indicating the number of ACK fields. A delayed multi-user ACK frame for a pre-configured group of STAs includes an ACK field. Figure 23 shows an example of ACK fields in a delayed multi-user ACK frame for a pre-configured group of STAs. These ACK fields are arranged in the same order as the order of the STAs in the pre-configured group. Each ACK field includes K(TID+TID ACK) fields. The number K is specified by the number of TIDs per STA in the Block ACK option field. The TID ACK field includes a starting sequence number and a bitmap of N bits, each indicating an ACK for a frame for the associated TID.

[0121] A delayed multi-user ACK frame for an ad hoc group of STAs is implemented using a Block ACK frame or any management or control frame. A delayed multi-user ACK frame for an ad hoc group of STAs includes an Identification field that indicates this is a DMA frame. The Block ACK Action field value is set to 7 when implemented as a Block ACK Action frame.

[0122] A delayed multi-user ACK frame for an ad hoc group of STAs includes a DA field. The destination address in the MAC header in the DMA is a multicast or broadcast address mutually agreed upon by the STA and the AP. A delayed multi-user ACK frame for an ad hoc group of STAs includes an ACK option field. The ACK option field indicates that the DMA is for an ad hoc group and whether the ACK is a normal ACK or a block ACK.

[0123] The delayed multi-user ACK frame for an ad hoc group of STAs includes a Block ACK option to indicate whether the Block ACK for each member of the ad hoc group is multi-TID, the number of TIDs per STA (K) being acknowledged, and the number of ACKed frames per TID (N) per member of the ad hoc group.

[0124] A delayed multi-user ACK frame for an ad hoc group of STAs includes a field (Number of ACK fields) indicating the number of ACK fields included in the current DMA frame. A delayed multi-user ACK frame for an ad hoc group of STAs includes an ACK field. FIG. 24 shows an example of ACK fields in a delayed multi-user ACK frame for an ad hoc group of STAs. One ACK field is for each member of the ad hoc group. Each ACK field begins with an ID field containing the ID of the ad hoc group member. This ID may be a MAC address, an association ID (AID), or some other form of ID agreed upon by the STA and the AP. Each ACK field includes a K(TID+TID ACK) field. The number K is specified by the number of TIDs per STA in the Block ACK option field. The TID ACK field includes a starting sequence number and a bitmap of N bits, each of which indicates an ACK for a frame for the associated TID.

[0125] A short ACK frame is a shortened version of an ACK frame and does not have MAC layer fields. A short BA frame is a shortened version of a BA frame and does not have MAC layer fields. Figure 25 shows a conventional short ACK frame format. A conventional short ACK frame includes an STF field 2502, an LTF field 2504, and a SIG field 2506. The SIG field 2506 of a short ACK frame contains an indication that the frame is a short ACK frame and other indications and signaling, such as an ACK ID to indicate the intended receiver of the short ACK, a further data field, and a duration field for NAV setting. A short BA frame has the same structure as a short ACK frame. A short BA frame includes an STF field, an LTF field, and a SIG field. The SIG field of a short BA frame contains an indication that the frame is a short BA frame and other indications and signaling required for a short BA frame, such as a Block ACK ID to indicate the intended receiver of the BA, a start sequence control, and a block bitmap.

[0126] The 802.11ah standard provides a mechanism for early ACK indication. The SIG field contains ACK indication bits (2 bits) to indicate the type of acknowledgment expected in response to a frame to be acknowledged. These ACK indication bits are set to "00" for ACK, "01" for BA, and "10" for no ACK, with "11" currently reserved.

[0127] If a STA skips decoding the packet after the PHY preamble to save power or is unable to correctly decode the remainder of the packet, the STA obtains the "duration" value from the MAC header and is unable to update its NAV for medium access. In such cases, the STA postpones medium access for the duration of EIFS or EIFS-DIFS+AIFS[AC] after detecting that the medium is idle. DIFS is the DCF interframe space, and AIFS is the arbitration interframe space (used by the QoS function for a given access category). EIFS is defined as EIFS = SIFS + DIFS + ACK Time, where ACK Time is the time required to transmit an ACK frame at the lowest rate supported by the physical layer.

[0128] In one embodiment, the originator (STA or AP) requests or indicates that a short ACK or short BA (either a conventional format or the format shown in FIG. 2 according to one embodiment disclosed above) be sent by the receiver (AP or STA) in response to a frame instead of a regular ACK or BA. When a short ACK or short BA is used instead of a regular ACK or regular BA, respectively, the MAC protocol is enhanced and increases efficiency. FIG. 26 shows an example of a short ACK response. The originator sends a data frame 2602 to the receiver with a short ACK indication in the data frame 2602, and the receiver sends a short ACK 2604 in response. The short ACK indication is extended to a short BA indication. The originator sends a Block ACK Request (BAR) or an aggregated MPDU (AMPDU) with an immediate BAR with a short BA indication, and the receiver sends a short BA in response.

[0129] The originator conveys a short ACK indication or a short BA indication (hereinafter collectively referred to as a "short ACK indication") by using a "10" value for the ACK indication bit in the SIG field. The "10" ACK indication value is also used to convey a no-ACK response. These two indications are combined in the "10" value of the ACK indication as follows: A short EIFS is specified instead of an EIFS for these two cases. For these two cases, an unintended STA that does not have a duration value from the MAC header to update its NAV postpones medium access for the duration of the short EIFS after detecting that the medium is idle. The short EIFS is defined as Short EIFS = SIFS + DIFS + Short ACK Time, where Short ACK Time is the time required to transmit a short ACK frame. The Short ACK Time is defined as the sum of the time lengths of its fields (e.g., the STF, LTF, and SIG field lengths for 1 MHz or 2 MHz, and possibly higher bandwidth modes). Alternatively, the Short ACK Time is calculated as the time required to transmit the Short ACK frame contents at the lowest rate supported by the PHY. The Short EIFS is also defined as Short EIFS = SIFS + DIFS + Short BA Time, where Short BA Time is the time required to transmit the Short BA frame.

[0130] Alternatively, the originator of a frame may convey a short ACK indication within any portion of the physical layer portion of the frame (eg, within the preamble using one or more bits, or within a subfield within the SIG field).

[0131] Alternatively, the originator may convey the short ACK indication within the MAC portion of the frame (e.g., within the MAC header). For example, the short ACK indication may be indicated within a control field of the MAC header or by reusing any of the existing fields or bits in the MAC header.

[0132] A device (STA or AP) that receives a frame sent to it with an indication that a Short ACK or Short BA needs to be sent in response responds with a Short ACK frame or Short BA frame, respectively, which is sent SIFS after receiving the frame with the Short ACK or Short BA indication.

[0133] STAs and APs indicate their ability and preference to acknowledge packets using short ACK or short BA, for example, using existing or new IEs, fields, and subfields in association request and association response frames during the association process.

[0134] Alternatively, a short ACK or short BA is an acknowledgement that is enabled (ie, a short ACK or short BA is used instead of a normal ACK frame or a normal BA frame).

[0135] When a normal ACK or a normal BA is used, the value in the Duration field in the frame is generally estimated by the transmitter using the lowest MCS supported by the system. This tends to overestimate the duration and therefore leads to inefficient medium usage, since this Duration field is used by unintended STAs in the system to set their NAVs for medium access. When a short ACK or a short BA is to be used, the transmitter (STA or AP) more accurately sets the Duration value in the Duration field of the MAC header by using the time required to transmit the short ACK or short BA frame. This results in a more accurate duration value and therefore leads to more efficient medium usage, since this Duration field is used by receivers of unintended STAs in the system to set their NAVs for medium access.

[0136] The Short ACK or Short BA mechanism applies to aggregated transmissions. An AMPDU is an aggregated MAC PDU. A regular ACK frame or a regular BA frame is transmitted within an AMPDU. A Short ACK or Short BA does not have to be transmitted by a STA or AP as part of an AMPDU. A Short ACK or Short BA may be transmitted by a STA or AP as part of an aggregated PPDU in which several physical layer packets are aggregated in a reduced interframe space (RIFS) burst, in which multiple packets are transmitted consecutively with a RIFS interval between packets, to improve medium utilization efficiency. A RIFS is smaller than a SIFS.

[0137] A short CTS frame is a shortened version of a CTS frame that does not have MAC layer fields. A short CTS frame includes an STF field, an LTS field, and a SIG field. The SIG field of a short CTS frame includes an indication that the frame is a short CTS frame and other indications and signaling such as a CTS ID to indicate the intended receiver of the CTS frame, bandwidth, and duration for NAV settings.

[0138] The sender (STA or AP) (i.e., initiator) of a request-to-send (RTS) frame requests or indicates that a short CTS frame should be sent in response to the RTS frame by the intended receiver (AP or STA) (i.e., responder) of the RTS frame.

[0139] In one embodiment, such a short CTS indication is conveyed in the RTS frame by reusing the "10" value of the ACK indication bit in the SIG field. The "10" ACK indication bit is also used to convey a no-ACK response. These two indications or cases are combined in the "10" value of the ACK indication bit as follows: A short EIFS is specified instead of an EIFS for these two cases. For these two cases, an unintended STA that does not have a "duration" value from the MAC header to update its NAV will postpone medium access for the duration of the short EIFS after detecting that the medium is idle. The short EIFS is defined as Short EIFS = SIFS + DIFS + Short CTS Time. Short CTS Time is defined as the sum of the time lengths of its fields (i.e., the combined time lengths of the STF, LTF, and SIG fields for 1 MHz or 2 MHz and higher bandwidth modes). Alternatively, the short CTS time is calculated as the time required to transmit the short CTS frame contents at the lowest rate supported by the physical layer. The short ACK time may be the same as the short CTS time, or the short ACK time may be used instead of the short CTS time, because short ACK and short CTS frames have the same format and length, even though they carry different content.

[0140] Alternatively, the transmitter (i.e., initiator) of the RTS frame of a frame may signal it in any part of the physical layer portion of that frame (e.g., in the preamble using one or more bits, or in a subfield within the SIG field).

[0141] Alternatively, the transmitter (i.e., initiator) of the RTS frame may convey the short CTS indication within the MAC portion of the frame (e.g., within the MAC header). For example, the short CTS indication may be indicated within a control field of the MAC header or by reusing any of the existing fields or bits within the MAC header.

[0142] A device (STA or AP) that receives an RTS frame sent to it with an indication that a short CTS needs to be sent in response responds with a short CTS frame, which is sent SIFS after receiving the RTS frame with the short CTS indication.

[0143] STAs and APs may indicate their ability and / or preference to respond to RTS frames using short CTS frames, e.g., using any existing or new IEs, fields, or subfields in association request and association response frames during the association process.

[0144] Alternatively, a short CTS is a possible response to an RTS frame (i.e., a short CTS is used instead of a regular CTS frame).

[0145] When an RTS frame is sent by a device (AP or STA), that device sets the NAV for devices in its neighborhood. However, the response CTS is not received by the neighboring device. For example, the intended receiver (STA / AP) of the RTS frame fails to respond to the CTS frame or there is a failure to receive the CTS frame. According to the 802.11 standard, a STA that updates its last NAV based on the reception of an RTS frame resets its NAV after the CTS timeout interval if no reception is detected within the CTS timeout interval, which begins from the end of the reception of the RTS frame. The CTS timeout interval is calculated as (2 x SIFS) + (CTS Time) + Receiver Start Delay + (2 x Slot Time), where SIFS and Slot Time are system parameters. The CTS Time is calculated using the length of the CTS frame and the data rate at which the RTS frame was received.

[0146] In one embodiment, if a device (STA or AP) transmitting an RTS frame indicates that its response frame is a short CTS frame, or if a short CTS frame is an allowed response to an RTS frame, the short CTS timeout interval is used instead of the CTS timeout interval. For example, the short CTS timeout interval is obtained as (2 × SIFS) + (short CTS Time) + Receiver Start Delay + (2 × Slot Time), where SIFS and Slot Time are system parameters. The short CTS time is defined as the sum of the time lengths of its fields (e.g., the sum of the time lengths of the STF, LTF, and SIG fields). Alternatively, the short CTS time is calculated as the time required to transmit the short CTS frame contents at the lowest rate supported by the physical layer.

[0147] In one embodiment, the device (STA or AP) sending the RTS frame indicates that its response frame should be a short CTS frame, or if a short CTS frame is an allowed response to an RTS frame, the above-mentioned short CTS time is used in estimating the time to set in the duration / ID field of the RTS frame.

[0148] The 802.11ah standard introduced a speed frame exchange protocol made possible by the use of a More Data field and a Response Frame field. The More Data field is a 1-bit field that indicates whether there is more data to send. The More Data field allows the responding STA to set the Response Frame field appropriately. The Response Frame field (or ACK indication bit) is a 2-bit field that indicates the type of frame that is coming up. The Response Frame field is set to "00" for ACK, "01" for BA, "10" for no ACK, or "11" for a frame that is neither ACK, CTS, nor BA (i.e., indicating that the response frame is a data frame).

[0149] 27 and 28 show exemplary procedures for speed frame exchange for the downlink and uplink, respectively. In FIG. 27, a STA sends a PS-Poll frame 2702 to an AP to retrieve data. The AP responds with an ACK 2704 with the "more data" field set to "1" and the response frame field set to "11." The AP then sends a data frame 2706 with the more data field set to "0" and the response frame field set to "00." The STA receives the data frame 2706 and sends an ACK frame 2708 with the more data field set to "0" and the response frame field set to "10."

[0150] In Figure 28, a STA sends a data frame 2802 to an AP with the more data field set to "1" and the response frame field set to "00". The AP then sends an ACK frame 2804 with the more data field set to "0" and the response frame field set to "11". The STA then sends another data frame 2806 with the more data field set to "0" and the response frame field set to "00". The AP then sends an ACK frame 2808 with the more data field set to "0" and the response frame field set to "10".

[0151] In one embodiment, short ACK frames and short BA frames are used in a speed frame exchange. Short ACK frames are used in response to PS-Poll frames or data frames. Short BA frames are used in response to AMPDUs. The SIG field of the short ACK and short BA frames includes a response frame field (or ACK indication field) and / or further data fields. The response frame field (or ACK indication field) is used in conjunction with further data fields of the short ACK or short BA frame to perform a speed frame exchange.

[0152] Figure 29 shows an example of a speed frame exchange using a Short ACK frame (or Short BA frame) for downlink data. A STA sends a PS-Poll frame 2902 to retrieve data from the AP. The AP responds with a Short ACK frame 2904 with the more data field set to "1" and the response frame field set to "11." The AP sends a data frame 2906 with the more data field set to "0" and the response frame field set to either Short ACK for a non-aggregated data frame or Short BA for an aggregated data frame. The STA then responds with a Short ACK (or Short BA) 2908 depending on the data type received, with the more data field set to "0" and the response frame field set to "10."

[0153] 30 shows an example of a speed frame exchange using a Short ACK (or Short BA) frame for uplink data. A STA sends a data frame 3002 (or AMPDU) to an AP with the more data field set to "1" and the response frame field set to either Short ACK or Short BA, depending on the data type. The AP then sends a Short ACK frame 3004 (or Short BA) with the more data field set to "0" and the response frame field set to "11." The STA then sends another data frame 3006 (or AMPDU) with the more data field set to "0" and the response frame field set to Short ACK or Short BA. The AP then sends a Short ACK frame 3008 (or Short BA) with the more data field set to "0" and the response frame field set to "10."

[0154] As an example, the response frame field (or ACK indication field) value may be set to "00" to indicate a short ACK, "01" to indicate a short BA, or "10" to indicate a short ACK and a short BA.

[0155] In another embodiment, a short PS-Poll frame is used in the speed frame exchange. The SIG field of the short PS-Poll frame contains either a response frame field (or ACK indication field) or a more data field, or both. The short PS-Poll from the STA indicates that the response is a short ACK frame and that there is more data to send.

[0156] Figure 31 shows an example of a speed frame exchange using short PS-Poll frames and short ACK (or short BA) frames. A STA sends a short PS-Poll frame 3102 with the more data field set to "1" and the response frame field set to Short ACK to retrieve data from the AP. The AP responds with a short ACK frame 3104 with the more data field set to "0" and the response frame field set to "11." The STA sends a data frame 3106 (or AMPDU) with the "more data" field set to "0" and the response frame field set to Short ACK for a non-aggregated data frame or Short BA for an aggregated data frame. The AP then responds with a short ACK 3108 (or short BA) depending on the data type received, with the more data field set to "0" and the response frame field set to "10."

[0157] The More Data field is set based on whether the STA has uplink data. If a Short PS-Poll frame is sent by a STA on an unscheduled wake-up event, the Response Frame field is set to indicate Short ACK, since the AP will most likely send an acknowledgment rather than data.

[0158] In a regular MAC frame, the duration field in the MAC header is used to set the NAV for unintended receivers of the frame, but short frames (e.g., short ACK, short BA, short CTS) do not have a duration field and do not carry duration information.

[0159] When a STA wakes up from a sleep state and monitors the medium to receive a frame sequence and set its NAV, the STA continues to perform clear channel assessment (CCA) until a regular frame (not a short frame) with a duration field is detected, a short frame with duration information is detected, or a period of time equals ProbeDelay, which is specified as a system parameter. If a short frame is received and it contains a duration field or information in the SIG field, the STA uses it to set its NAV. If a short frame is received and it does not contain a duration field or information, the STA ignores the frame for NAV setting.

[0160] If an unintended STA receives a short frame that does not include a duration field or information, the unintended STA does not update its NAV and retains its existing NAV setting, which was triggered by the duration setting in an earlier frame of the frame exchange sequence (e.g., the sounding sequence in the case of a short beamforming report (BR) poll, or the data and ACK frame sequence in the case of a short BA).

[0161] If the short frame has a duration field or information, the unintended STA updates its NAV based on the duration field or information if the new NAV value is greater than the current / existing NAV value.

[0162] When an unintended STA receives a short PS-Poll frame, the unintended STA updates its NAV setting using the duration required to transmit a response frame (e.g., data, ACK, short ACK) plus one SIFS interval if the new NAV value is greater than the current NAV value. Alternatively, the unintended STA updates its NAV setting using a default response frame or a system-specified response frame duration if no response frame is indicated in the short PS-Poll frame. Alternatively, the unintended STA updates its NAV using the duration required to transmit a response frame (e.g., data, ACK, short ACK) indicated in the short PS-Poll frame plus one SIFS interval if the new NAV value is greater than the current NAV value. The unintended STA includes any required overhead or additional response frames (e.g., ACK frames) for the response frame indicated in the short PS-Poll frame and associated SIFS intervals in its duration calculation.

[0163] In one embodiment, short frames (e.g., short BA, short BR-Poll, and short Probe Request) include a duration field or information in the SIG field for NAV setting. The size of the SIG field is increased, for example, by using a higher MCS.

[0164] When a STA initiates communication with an AP using an initiation or trigger frame (e.g., a PS-Poll frame or a data frame), the STA establishes its transmit opportunity (TXOP) duration by setting the duration field of that frame, thereby setting the NAV of unintended receivers / STAs. In a speed frame exchange where there is downlink data transmitted by the AP and the STA is the TXOP holder or TXOP initiator, the STA first estimates the duration for the entire TXOP (the entire sequence of frames) and uses it to set the duration field in the frame it transmits to set its NAV. For example, the estimate is based on one or more of any data to transmit, the expected data to be received, the expected MCS to be used, and the inter-frame spacing (e.g., SIFS). The STA truncates any excess unused TXOP duration with a CF-End frame.

[0165] Alternatively, the STA estimates the duration for its initiation or trigger frame, any required response frame(s), and interframe space(s) (e.g., SIFS), and sets the duration field in its initiation / trigger frame based on that estimate. The STA then extends the TXOP duration each time the AP indicates that it has more data ("More Data" field = 1). The STA does not extend the TXOP duration beyond the specified TXOP duration limit for a given QoS transmission (e.g., specified by EDCA rules).

[0166] A STA uses a CF-End frame to truncate the medium reservation or TXOP duration for a speed frame exchange when it has no data to send or receive.

[0167] The AP sets the duration value in the frame it transmits based on the duration value in the frame it receives from the STA.

[0168] When an unintended STA receives a PS-Poll frame, the unintended STA updates its NAV setting using the duration required to transmit a response frame (e.g., data, ACK, short ACK) plus one SIFS interval if the new NAV value is greater than the current NAV value. Alternatively, the unintended STA sets its NAV setting using a default response frame or a system-specified response frame duration if no response frame is indicated in the PS-Poll frame. Alternatively, the unintended STA sets its NAV setting using the duration required to transmit a response frame (e.g., data, ACK, short ACK) indicated in the PS-Poll frame plus one SIFS interval if the new NAV value is greater than the current NAV value. The unintended STA includes any required overhead or additional response frames (e.g., ACK frames) for the response frame indicated in the PS-Poll frame and associated SIFS intervals in its duration calculation.

[0169] A station sends a probe request frame when it needs to obtain information from another station. A short probe request frame is used instead of a regular probe request frame. The short probe request frame includes an STF field, an LTF field, and a SIG field. The SIG field of the short probe request frame includes, among other indications, an indication that the frame is a short probe request frame and required signaling such as access network options, a partial SSID, and an indication of whether a probe response or a short beacon is expected in response to the short probe request frame.

[0170] When a STA receives a short beacon with a change sequence that differs from the change sequence stored by the STA, the STA needs to update its system information by using a probe request frame that carries the change sequence and triggering the AP to send an optimized probe response frame that includes the change sequence and the system information elements that need to be updated by the STA.

[0171] Due to its smaller size, using an NDP probe request frame is more efficient than using a regular probe request frame, which would occupy more medium time, especially when there are many STAs that want to update their system information. Also, power consumption at the STAs is reduced by using an NDP probe request frame. This is especially useful when full beacons are not transmitted frequently or short beacons are used in the BSS.

[0172] In one embodiment, the NDP probe request frame includes a modification sequence stored in the STA, for example, by using a small size modification sequence (e.g., a 4-bit sequence instead of an 8-bit sequence) that can be accommodated within the limited bits available in the SIG field.

[0173] The NDP probe request frame indicates which system information elements are required by the STA (e.g., a bitmap representing a subset of system information elements). The NDP probe request frame indicates that the change sequence in the last received short beacon is different from the change sequence stored in the STA.

[0174] The NDP probe request frame indicates which set of predefined system information elements is required by the STA. These sets of predefined system information elements are indexed, and the index representing the set of system information is signaled in the NDP probe request frame. For example, the predefined set of system information elements can be a set of system information elements or fields containing required information such as timestamp, beacon interval, and capabilities, a set of system information elements or fields containing other information such as EDCA parameters, quiet elements, BSS load, channel switch announcement, HT operation elements, and VHT operation elements, or a set of system information elements or fields containing any combination of required information and other information. For example, the above signaling can be implemented by using one or more reserved bits in the SIG field of the NDP probe request frame.

[0175] When a STA sends an NDP probe request frame containing a change sequence stored in the STA, the AP sends an optimized probe response frame containing the change sequence and the system information elements that need to be updated by the STA. The AP can do this by storing previous change sequences and the IDs of the corresponding changed system information elements. The AP finds the updated information to send by comparing the received change sequence from the STA with its stored previous change sequences.

[0176] When the STA sends an NDP probe request frame indicating which system information elements are required, the AP sends an optimized probe response frame containing the system information elements and change sequence that need to be updated by the STA.

[0177] When a STA sends an NDP probe request frame indicating which set of predefined system information elements is required, the AP sends an optimized probe response frame containing the indicated set of predefined system information elements and the modified sequence.

[0178] When a STA sends an NDP probe request frame indicating that the change sequence in the last received short beacon is different from the change sequence stored in the STA, the AP sends an optimized probe response frame that includes a predefined or basic set of system information elements that need to be updated by the STA and the change sequence.

[0179] In any of the above embodiments, the response to the probe request frame is a short probe response frame that includes the information requested or indicated in the NDP probe request frame.

[0180] The NDP PS-Poll frame is used for active polling. The NDP PS-Poll frame includes an STF field, an LTF field, and a SIG field. The SIG field of the short PS-Poll frame contains an indication that the frame is a short PS-Poll frame, as well as other indications or signaling required for the short PS-Poll frame, such as the AID or partial AID of the sending STA, the BSSID or partial BSSID of the BSS with which the STA is associated, and the preferred MCS for the STA to receive data from the AP.

[0181] The NDP PS-Poll frame contains signaling to request a BSS change sequence and / or a current timestamp. This signaling is contained within the SIG field of the NDP PS-Poll frame. One or more bits of the SIG field are used to indicate a change sequence request and / or a current timestamp request from the AP. One or more bits of the SIG field are used to indicate whether one or more of the following fields are included: preferred MCS, change sequence request, and / or current timestamp request.

[0182] When a STA sends an NDP PS-Poll frame containing a request for a BSS change sequence, the AP either sends the BSS change sequence immediately in the response frame or indicates in the response frame to the STA that it should check for a beacon. When a STA sends an NDP PS-Poll frame containing a request for a current timestamp, the AP either sends the current timestamp immediately in the response frame or indicates in the response frame to the STA that it should check for a beacon.

[0183] Either the frame from the AP sent in response to the PS-Poll frame, such as ACK or data, carries the requested information from the AP. Alternatively, a new response frame from the AP may be defined for the PS-Poll frame and carry the requested information from the AP. This frame may be of any type, such as management, control, or data.

[0184] Although embodiments are described herein with reference to the IEEE 802.11 protocol, it should be understood that these embodiments are applicable to any wireless communication system. Although SIFS is used as the inter-frame spacing in various embodiments, other inter-frame spacings, such as RIFS or other agreed-upon time intervals, may also be used.

[0185] Embodiment

[0186] 1. A method for use in a station transmitting an acknowledgment in response to a data packet in wireless communications.

[0187] 2. The method of embodiment 1, comprising receiving data packets from a plurality of stations.

[0188] 3. The method of embodiment 2, including generating an acknowledgement for the data packet.

[0189] 4. The method of embodiment 3, including obtaining a transmission opportunity.

[0190] 5. The method of embodiment 4, including transmitting the acknowledgments for the data packets to the multiple stations in a single transmission.

[0191] 6. The method of embodiment 5, wherein the acknowledgement is transmitted using MU-MIMO.

[0192] 7. The method of any one of embodiments 5 to 6, wherein the acknowledgement is sent a predetermined time after receiving the data packet.

[0193] 8. A method according to any one of embodiments 5 to 7, wherein the acknowledgement is sent based on an agreed schedule or a request by one of the stations, or on the condition that a predetermined number of data packets have been received.

[0194] 9. The method of embodiment 4, wherein generating an acknowledgement for the data packet comprises generating an acknowledgement packet for the data packet and aggregating the acknowledgement packet.

[0195] 10. The method of embodiment 9, wherein transmitting the acknowledgment includes transmitting the aggregated acknowledgment packets in the single transmission.

[0196] 11. The method of embodiment 10, wherein the acknowledgement packets are aggregated within a MAC service data unit, a MAC protocol data unit, or a PPDU.

[0197] 12. A method for use in a station transmitting an acknowledgment in wireless communications.

[0198] 13. The method of embodiment 12, comprising receiving a frame indicating a sequence ID.

[0199] 14. The method of embodiment 13, comprising transmitting a short ACK frame in response to the received frame, the short ACK frame including an ACK sequence corresponding to the sequence ID.

[0200] 15. The method of embodiment 14, wherein the short ACK frame includes an STF and an ACK sequence.

[0201] 16. The method of any one of embodiments 14-15, wherein the Short ACK frame is transmitted with a Short ACK indication.

[0202] 17. The method of any one of embodiments 14-16, wherein the short ACK frame is transmitted in response to an indication included within the frame.

[0203] 18. A WTRU for transmitting an acknowledgement in response to a data packet in wireless communication.

[0204] 19. The WTRU of embodiment 18, comprising a processor configured to receive data packets from a plurality of stations.

[0205] 20. The WTRU of embodiment 19, wherein the processor is configured to generate an acknowledgement for the data packet.

[0206] 21. The WTRU of embodiment 19, wherein the processor is configured to send the acknowledgment for the data packet to the station in a single transmission.

[0207] 22. The WTRU of embodiment 21, wherein the processor is configured to transmit the acknowledgement using Multi-Multiple Input / Output Multiple Input (MU-MIMO).

[0208] 23. The WTRU of any one of embodiments 21-22, wherein the processor is configured to send the acknowledgment a predetermined time after receiving the data packet.

[0209] 24. The WTRU of any one of embodiments 21 to 23, wherein the processor is configured to send the acknowledgment based on an agreed-upon schedule or upon request by one of the plurality of stations, or upon condition that a predetermined number of data packets have been received.

[0210] 25. The WTRU of embodiment 21, wherein the processor is configured to generate acknowledgment packets for the data packets and aggregate the acknowledgment packets, and the aggregated acknowledgment packets are transmitted in the single transmission.

[0211] 26. The WTRU of embodiment 25, wherein the processor is configured to aggregate the acknowledgement packets within a MAC service data unit, a MAC protocol data unit, or a PPDU.

[0212] 27. A WTRU for transmitting an acknowledgement in wireless communication.

[0213] 28. The WTRU of embodiment 27, comprising a processor configured to receive a frame.

[0214] 29. The WTRU of embodiment 28, wherein the processor is configured to transmit a short ACK frame in response to the received frame.

[0215] 30. The WTRU of embodiment 29, wherein the received frame indicates a sequence ID, and the short ACK frame includes an ACK sequence corresponding to the sequence ID.

[0216] 31. The WTRU of any one of embodiments 29-30, wherein the short ACK frame includes an STF and an ACK sequence.

[0217] 32. The WTRU of any one of embodiments 29-31, wherein the short ACK frame is sent with a short ACK indication.

[0218] 33. The WTRU of any one of embodiments 29-32, wherein the short ACK frame is sent in response to an indication included in the frame.

[0219] Although features and elements are described above in particular combinations, those skilled in the art will understand that each feature or element can be used alone or in any combination with the other features and elements. Furthermore, the methods described herein may be implemented in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable storage media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs). A processor associated with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

[Claim 1] 1. A method performed by a first station (first STA), comprising: receiving one or more data frames from a second STA; receiving, from the second STA, a multi-user acknowledgment request frame configured to solicit a block acknowledgment frame associated with the one or more data frames, the multi-user acknowledgment request frame configured to indicate that the solicited response is a block acknowledgment frame, the multi-user acknowledgment request frame configured for multiple STAs; transmitting the block acknowledgement frame in response to determining that the multi-user acknowledgement request frame is intended for the first STA, the block acknowledgement frame configured to acknowledge receipt of the one or more data frames received by the first STA; A method for providing

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