TRANSMISSION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional

Application No. 62/188,080 filed on July 2, 2015, the contents of which are hereby incorporated by reference herein.

BACKGROUND

[0002] A wireless local area network (WLAN) in Infrastructure Basic

Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP typically may have access or interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic in and out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to the respective destinations.

[0003] Traffic between STAs within the BSS may also be sent through the AP where the source STA sends traffic to the AP and the AP delivers the traffic to the destination STA. Such traffic between STAs within a BSS may be peer-to-peer traffic. Such peer-to-peer traffic may also be sent directly between the source and destination STAs with a direct link setup (DLS) using an IEEE 802. l ie DLS or an 802. l lz tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may have no AP, and all STAs may communicate directly with each other. This mode of communication may be referred to as an "ad-hoc" mode of communication.

SUMMARY

[0004] The following description includes methods, systems, and apparatuses for using orthogonal frequency-division multiple access (OFDMA) to send a transmission frame to multiple stations (STAs) over a channel in a wireless local access network (WLAN). [0005] Embodiments may include: partitioning, by a scheduler, a channel into multiple sub-channels for transmitting data packets to the multiple STAs, wherein the number of sub-channels corresponds to the number of STAs; partitioning, by the scheduler , a long data packet destined for a first STA of the plurality of STAs into multiple sub-packets, wherein the long data packet does not fit into a determined transmission time; and transmitting a first portion of the multiple sub-packets on a first sub-channel assigned to the first STA and a remaining portion of the multiple sub-packets on available resources in the rest of the multiple sub -channels in the determined transmission time.

[0006] Embodiments may also include: partitioning, by a scheduler, the channel into multiple sub-channels for transmitting data packets to the multiple STAs, wherein the number of sub-channels is less than the number of STAs such that a first STA is not assigned a sub-channel; allocating, by the scheduler, a sub-channel assigned to a second STA for transmission of a first data packet destined for the first STA; and transmitting, by the AP, the first data packet in available resources of the sub-channel assigned to the second STA.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

[0008] FIG. 1A is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented;

[0009] FIG. IB is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A;

[0010] FIG. 1C is a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in FIG. 1A; [0011] FIG. 2 is an illustration showing the operation of an enhanced distributed channel access (EDCA) in IEEE 802.11η;

[0012] FIG. 3 is an example of a simple, but low spectral usage, resource allocation method;

[0013] FIG. 4 is an example of resource allocation with higher spectral utilization;

[0014] FIG. 5 is a graph of power spectrum density of a partially loaded

OFDM signal with RF in-phase/quadrature (I/Q) imbalance;

[0015] FIG. 6 is an example of interference problem due to in-I/Q imbalance in an OBSS scenario;

[0016] FIG. 7 is a chart of bit error rate (BER) performance of an interfered signal;

[0017] FIG. 8 is an illustration of sub-channelization for the 20MHz channel bandwidth;

[0018] FIGS. 9A-9B are examples of proposed dynamic frame structure using a station ID field (IDF);

[0019] FIGS. 10A-10B are examples of a proposed dynamic frame structure with sequential transmission of short data packets;

[0020] FIGS. 11A-11B are examples of a proposed dynamic frame structure using time slots;

[0021] FIGS. 12A-12B are examples of a proposed dynamic frame structure using IDF SIG and IDF delimiters;

[0022] FIGS. 13A-13B are examples of a proposed dynamic frame structure using IDF SIG and IDF delimiters with sequential transmission of short data packets;

[0023] FIGS. 14A-14B are examples of a proposed dynamic frame structure using IDF SIG and IDF delimiters with time slots;

[0024] FIG. 15 is an exemplary design of an IDF signature (SIG) field;

[0025] FIG. 16 is another exemplary design of the IDF SIG field;

[0026] FIG. 17 is a dynamic frame structure using medium access control (MAC) headers;

[0027] FIG. 18 is a high efficiency (HE) operational information element; [0028] FIG. 19 is an illustration showing how each block acknowledgment (BA) Information field may be addressed to different packet fragments sent over different sub-channels;

[0029] FIG. 20 is a first exemplary embodiment of a sequential channel based multi-packet-fragment block acknowledgement (MPFBA)/BA for a dynamic framing scheme (DFS);

[0030] FIG. 21 is a second exemplary embodiment of a sequential channel based MPFBA/BA for a DFS;

[0031] FIG. 22 is a third exemplary embodiment of a sequential channel based BA for a DFS;

[0032] FIG. 23 is a first exemplary embodiment of a simultaneous subchannel based MPFBA/BA for a DFS;

[0033] FIG. 24 is a second exemplary embodiment of a simultaneous sub-channel based BA for a DFS;

[0034] FIG. 25 is a third exemplary embodiment of a simultaneous subchannel based BA for a DFS; and

[0035] FIG. 26 is a fourth exemplary embodiment of a simultaneous subchannel based data/BA for a DFS; and

[0036] FIG. 27 is an illustration wherein the spectral resources are allocated to users in a symmetrical way.

DETAILED DESCRIPTION

[0037] FIG. 1A is a diagram of an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ 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), and the like.

[0038] As shown in FIG. 1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 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, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like.

[0039] The communications systems 100 may also include a base station

114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the core network 106, the Internet 110, and/or the other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

[0040] The base station 114a may be part of the RAN 104, which may also include 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 the base station 114b may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station 114a may employ multiple -input multiple-output (MIMO) technology and, therefore, may utihze multiple transceivers for each sector of the cell.

[0041] The base stations 114a, 114b may 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).

[0042] More specifically, as noted above, the communications system

100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High- Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

[0043] In another embodiment, the base station 114a and the WTRUs

102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

[0044] In other embodiments, the base station 114a and the WTRUs

102a, 102b, 102c may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-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), and the like.

[0045] The base station 114b in FIG. 1A may be a wireless router, Home

Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may 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 may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize 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 may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the core network 106.

[0046] The RAN 104 may be in communication with the core network

106, which may be any type of network configured to provide voice, data, applications, 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, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high- level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 and/or the core network 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may be utilizing an E-UTRA radio technology, the core network 106 may also be in communication with another RAN (not shown) employing a GSM radio technology.

[0047] The core network 106 may also serve 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 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks 112 may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks 112 may include another core network connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0048] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular -based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0049] FIG. IB is a system diagram of an example WTRU 102. As shown in FIG. IB, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display /touchp ad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0050] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform 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 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. While FIG. IB depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0051] The transmit/receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

[0052] In addition, although the transmit/receive element 122 is depicted in FIG. IB as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0053] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit/receive element 122 and to demodulate the signals that are received by the transmit/receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example. [0054] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display /touchp ad 128 (e.g., a liquid crystal display (LCD) display unit or organic hght-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display /touchp ad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 130 and/or the removable memory 132. The nonremovable memory 130 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0055] The processor 118 may receive power from the power source 134, and may be configured to distribute and/or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0056] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment. [0057] The processor 118 may further 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, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

[0058] FIG. 1C is a system diagram of the RAN 104 and the core network 106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0059] The RAN 104 may include eNode-Bs 140a, 140b, 140c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 140a, 140b, 140c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 140a, 140b, 140c may implement MIMO technology. Thus, the eNode-B 140a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0060] Each of the eNode-Bs 140a, 140b, 140c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in FIG. 1C, the eNode-Bs 140a, 140b, 140c may communicate with one another over an X2 interface.

[0061] The core network 106 shown in FIG. 1C may include a mobility management entity gateway (MME) 142, a serving gateway 144, and a packet data network (PDN) gateway 146. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0062] The MME 142 may be connected to each of the eNode-Bs 140a,

140b, 140c in the RAN 104 via an Si interface and may serve as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 142 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0063] The serving gateway 144 may be connected to each of the eNode

Bs 140a, 140b, 140c in the RAN 104 via the Si interface. The serving gateway 144 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0064] The serving gateway 144 may also be connected to the PDN gateway 146, which may provide 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.

[0065] The core network 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the core network 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0066] Other network 112 may further be connected to an IEEE 802.11 based wireless local area network (WLAN) 160. The WLAN 160 may include an access router 165. The access router may contain gateway functionality. The access router 165 may be in communication with a plurality of access points (APs) 170a, 170b. The communication between access router 165 and APs 170a, 170b may be via wired Ethernet (IEEE 802.3 standards), or any type of wireless communication protocol. AP 170a is in wireless communication over an air interface with WTRU 102 d.

[0067] Using the IEEE 802.1 lac infrastructure mode of operation, an access point (AP) of a wireless local access network (WLAN) may transmit a beacon on a fixed channel, usually the primary channel. This channel may be 20 MHz wide, and may be the operating channel of an Infrastructure Basic Service Set (BSS). This channel may also be used by one or more stations (STAs) to establish a connection with the AP. The fundamental channel access mechanism in an IEEE 802.11 system may be Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). In this mode of operation, every STA, including the AP, may sense the primary channel. If the channel is detected to be busy, the STA may back off. Accordingly, only one STA may transmit at any given time in a given BSS.

[0068] In IEEE 802.11η, High Throughput (HT) STAs may also use a 40

MHz wide channel for communication. This is achieved by combining the primary 20 MHz channel, with an adjacent 20 MHz channel to form a 40 MHz wide contiguous channel.

[0069] In IEEE 802.1 lac, Very High Throughput (VHT) STAs may support 20MHz, 40 MHz, 80 MHz, and 160 MHz wide channels. The 40 MHz and 80 MHz channels may be formed by combining contiguous 20 MHz channels similar to IEEE 802.11η described above. A 160 MHz channel may be formed either by combining 8 contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels (i.e., an 80+80 configuration). For the 80+80 configuration, the data, after channel encoding, may be passed through a segment parser that divides it into two streams. Inverse Fast Fourier Transform (IFFT) and time domain processing may be done on each stream separately. The streams may then be mapped on to the two channels and the data may be transmitted. At the receiver, this mechanism may be reversed, and the combined data may be sent to the MAC.

[0070] Sub 1 GHz modes of operation may be supported by IEEE

802.11af and IEEE 802.11ah. For these specifications, the channel operating bandwidths and carriers may be reduced relative to those used in IEEE 802.11η and IEEE 802.11ac. The IEEE 802.11 af specification may support 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum. The IEEE 802.11ah specification may support 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using the non-TVWS spectrum. A possible use case for IEEE 802.11ah may be support for Meter Type Control/Machine-Type Communications (MTC) devices in a macro coverage area. MTC devices may have limited capabilities including only support for limited bandwidths, but may also include a requirement for a very long battery life.

[0071] WLAN systems that support multiple channels and channel bandwidths (e.g., IEEE 802.11η, IEEE 802.1 lac, IEEE 802.11af, and IEEE 802.11ah) may include a channel which is designated as the primary channel. The primary channel may, but not necessarily, have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may therefore be limited by the STA operating in a BSS that supports the smallest bandwidth operating mode. In the example of IEEE 802.11ah, the primary channel may be 1 MHz wide if there are STAs (e.g., MTC type devices) that only support a 1 MHz mode, even if the AP and other STAs in the BSS may support a 2 MHz, 4 MHz, 8 MHz, 16 MHz, or other channel bandwidth operating modes. Carrier sensing, and NAV setting, may depend on the status of the primary channel. If the primary channel is busy, for example due to a STA supporting only a 1 MHz operating mode that is transmitting to the AP, then the entire available frequency bands may be considered busy even though majority of them stay idle and are available.

[0072] In the United States, the available frequency bands which may be used by IEEE 802.11ah are from 902 MHz to 928 MHz. In Korea it is from 917.5 MHz to 923.5 MHz. In Japan it is from 916.5 MHz to 927.5 MHz. The total bandwidth available for IEEE 802.11ah may be 6 MHz to 26 MHz depending on the country code.

[0073] Referring now to FIG. 2, the operation of an enhanced distributed channel access (EDCA) in 802.11η is shown. EDCA is an extension of the basic distributed coordination function (DCF) introduced in the 802.11 to support prioritized QoS. It may support contention based access of the medium.

[0074] A Point Coordination Function (PCF) on the other hand, uses contention free channel access to support time-bounded services with polling by the AP to each STA in the BSS. The AP may send a polhng message after waiting for PCF Interframe Space (PIFS), and if a client has nothing to transmit, it may return a null data frame. It may be deterministic, which may be fair and efficient for both low duty-cycle and heavy/burst traffic. Hybrid Coordination Function (HCF) Controlled Channel Access (HCCA) is an enhancement of PCF in which the AP can poll a STA during both contention period (CP) and contention-free period (CFP). It may transmit multiple frames under one poll.

[0075] Recently, the IEEE 802.11 High Efficiency WLAN (HEW) Study

Group (SG) was created to explore the scope and purpose of a possible future amendment to enhance the quality of service all users experience for a broad spectrum of wireless users in many usage scenarios, including high-density scenarios in the 2.4 GHz and 5 GHz band. New use cases which support dense deployments of APs, STAs, and associated Radio Resource Management (RRM) technologies are being considered by the HEW SG.

[0076] Potential applications for HEW include emerging usage scenarios such as data delivery for stadium events, high user density scenarios such as train stations or enterprise/retail environments, increased dependence on video delivery, and wireless services for medical applications. The IEEE Standard board approved the IEEE 802.1 lax Task Group (TG) to solve problems including interference mitigation for sticky client as well as peer-to- peer transmission within infrastructure networks.

[0077] Transmission procedures in current IEEE 802.11 implementations (802.11a/g/n/ac/ah) may assume the use of the entire allocated bandwidth for transmission and reception. As mentioned above, IEEE 802.1 lax is a task group with the agenda to enhance the performance of 802.11 to address spectral efficiency, area throughput, and robustness to collisions and interference. Orthogonal Frequency-Division Multiple Access (OFDMA) is a method which has been used in LTE and WiMax to address inefficiencies caused by resource scheduling.

[0078] The OFDMA method may allocate the entire channel to a single user as is in IEEE 802.1 lac. However, a direct application of OFDMA to WiFi may introduce backward compatibility issues. Coordinated Orthogonal Block- based Resource Allocation (COBRA) introduced OFDMA methods to resolve WiFi backward compatibility issues and the implicit inefficiencies that are caused by channel based resource scheduling. For example, COBRA may enable transmissions over multiple smaller frequency-time resource units. Thus, multiple users may be allocated to non-overlapping frequency-time resource units, and may be enabled to transmit and receive simultaneously. A sub-channel may be defined as a basic frequency resource unit that an AP may allocate to a STA. For example, keeping the requirement of backward compatibility with IEEE 802.11n/ac in mind, a sub-channel may be defined as a 20 MHz channel. Note that these sub-channels may have bandwidths less than 20 MHz or they may be limited to bandwidths of 20 MHz.

[0079] Technologies in COBRA may include multicarrier modulation, filtering, time, frequency, space, and polarization domains as the basis for the transmission and coding scheme. A COBRA scheme may be implemented using, for example, OFDMA Sub-channelization, SC-FDMA Sub- channelization, and filter-Bank Multicarrier Sub-channelization.

[0080] In order to enable COBRA transmissions, the following features, among others, have been introduced: methods for coverage range extension, methods of grouping users, methods for channel access, preamble designs for low overhead, methods for beamforming and sounding, methods for frequency and timing synchronization, and methods for link adaptation. Timing and frequency synchronization algorithms for COBRA have been introduced; however, issues remain for their practical implementation in future WLAN systems.

[0081] Multi-user and single user multiple parallel (MU-PCA) channel access schemes have also been introduced. MU-PCA addresses several additional methods to those introduced with COBRA. For example, one method may be multi-user/single-user parallel channel access using transmit/receive with symmetrical bandwidth. This may include down-link parallel channel access for multiple/single users, up-link parallel channel access for multiple/single users, combined down-link and up-link parallel channel access for multiple/single users, design to support unequal MCS and unequal transmit power for SU-PCA and COBRA, physical layer (PHY) designs and procedures to support multi-user/single-user parallel channel access using transmit/receive with symmetrical bandwidth, and mixed MAC/PHY multi-user parallel channel access.

[0082] Another method may be multi-user/single-user parallel channel access transmit/receive with asymmetrical bandwidth. This may include MAC designs and procedures for downlink, uplink, and combined uplink and downlink for multi-user/single-user parallel channel access using transmit/receive with asymmetrical bandwidth. It may also include PHY designs and procedures to support multi-user/single-user parallel channel access using transmit/receive with asymmetrical bandwidth.

[0083] Additional techniques such as scalable channel utilization in which STAs may scale their transmission bandwidths based on channel or traffic availability have also been proposed.

[0084] The use of OFDMA in IEEE 802.11 may potentially improve the system special efficiency and special utilization over the legacy multiple access schemes. However, the improvements may not be achievable if there is lack of a mechanism that supports flexible resource allocation. In particular, there may be specific problems that may arise when OFDMA is used.

[0085] One problem may be low spectral usage when packet sizes of different users are very different. In a typical OFDMA system, the channel may be partitioned into multiple sub-channels (i.e., resource blocks/units). A scheduler may allocate those sub-channels for different STAs based on channel conditions of radio links and some other criteria (e.g., service type). Since, in WLAN, a channel may only be used in the TDM fashion (i.e., one direction, DL or UL, at a time), and the packet size for one STA to transmit or receive could be very different from the others, achieving maximum spectral usage and minimum signaling overhead may be a challenge.

[0086] Referring now to FIG. 3, an example of a simple, but low spectral usage, resource allocation method is shown. FIG. 3 shows one example of resource allocation, in which the total channel bandwidth is partitioned into four equal fragments 302-308, one for each sub-channel. Four data packets 310-316, with different sizes, may be allocated to those sub-channels. The subchannel allocation information may be included in the signaling (SIG) field 318. Due to significant difference in packet sizes, the sub-channels that carry shorter packet will be underutilized. Padding 320, which may include a useless signal to fill up those sub-channels after the transmission of useful signals, may be needed to keep the channel occupied. This may also lead to the issue of low energy efficiency.

[0087] Referring now to FIG. 4, an example of resource allocation with higher spectral utilization is shown. FIG. 4 shows another example of resource allocation method, by which the channel is partitioned into a set of unequal size of sub-channels 402-408 based on the channel condition and the size of the data packets 410-416. The packet with more data 410 may take the subchannel with wider bandwidth. This method does help improve spectral utilization, but since the channel may need to be partitioned into sub-channels with higher granularity, the signaling for allocating the frequency resource for different STAs could be very complicated, which may lead to higher control overhead. [0088] Another problem may be acknowledgment (ACK) design for the dynamic frame scheme. When dynamic framing scheme is used, multiple packet fragments for a STA may be coded independently so in case of an error, not all packet fragments may need to be retransmitted. In order to acknowledge whether the whole packet is successfully received, more than one ACK/block acknowledgment (BA) may be needed for the STA assuming one ACK/BA is used for each packet fragment. This may result in large overhead and delay. Also considering that a dynamic frame supports multi-STA data transmissions simultaneously, it is may be desirable to design an efficient ACK frame and associated procedures that effectively support the dynamic frame scheme.

[0089] Another problem may be interference due to radio frequency (RF) in-phase/quadrature (I/Q) imbalance in OFDMA. In OFDMA, frequency resources presented in the form of sub-channels may be assigned to different radio links which may all be in either uplink or downlink directions. When a signal is transmitted over a sub-channel allocated on one side of the channel relative to the central frequency, it may create interference on the other side of the channel (e.g., as the image of the original signal) due to RF I/Q amplitude and phase imbalances.

[0090] Referring now to FIG. 5, a graph of power spectrum density of a partially loaded OFDM signal with RF I/Q imbalance is shown. FIG. 5 shows a snapshot of a scenario in which, among 256 subcarriers in 20 MHz channel, a sub-channel (SC) with subcarriers from 199 to 224, shown as SC A 502, is loaded with data. Due to RF I/Q imbalance, about 23dBr interference is generated in the image of the sub-channel with subcarriers from -119 to -224, shown as SC B 504.

[0091] In a single BSS scenario, such as OFDMA DL, this interference may not be significant since the transmit powers on all sub-channels are the same and so are the Rx powers of those sub-channels at each STA. However, in OFDMA UL, where there may be no power control or the power control may not accurate, the interference at the image sub-channel (SC B 504) may be significant, especially when the STA using SC B 504 is farther from the AP than the STA using SC A 502.

[0092] Referring now to FIG. 6, an example of interference problem due to I/Q imbalance in an OBSS scenario is shown. In OBSS scenarios in which some BSSs share the same channel, the interference problem may be more significant in both UL OFDMA and DL OFDMA since there may be no coordinated power control between the transmitters in neighboring BSSs. FIG. 6 depicts an OBSS DL scenario in which access point 1 (API) 602 may use SC A 604 to transmit data to station 1 (STAl) 606 and access point 2 (AP2) 608 may use SC B 610 to transmit data to station 2 (STA2) 612. STA2 612 may be located closer to API 602 than to AP2 608. Due to I/Q imbalance at API's 602 transmission, it may create interference to STA2 612 on SC B 610 with power that may be comparable to the power of the desired signal from AP2 608.

[0093] Referring now to FIG. 7, a chart of bit error rate (BER) performance of a signal undergoing interference is shown. FIG. 7 shows the BER performance of the signal transmitted on SC B 610 that may suffer from interference due to transmission on SC A 604 with I/Q imbalance. The value dP may represent the power difference between SC A 604 and SC B 610. Power difference being greater than 0 (dP > 0) may indicate signal power on SC B 610 is lower than that on SC A 604. As shown in this figure, if power is not well controlled, there may be significant performance loss.

[0094] Another problem may be low spectral utilization due to use of guard subcarriers between sub-channels. When introducing OFDMA to IEEE 802.11, with consideration of reusing the hardware and software of earlier standards (e.g., IEEE 802.11 a/b/g/n/ac/ah), the method of sub-channelization may leave some subcarriers empty.

[0095] Referring now to FIG. 8, an illustration of sub-channelization for the 20MHz channel bandwidth is shown. One method of sub-channelization may be to partition 256 subcarriers into 9 resource blocks 802 with 26 subcarriers per resource block. In addition to three direct current (DC) subcarriers and channel guard bands (11 subcarriers total), one subcarrier 904 between resource blocks may be left unused (or nulled). The nulled subcarriers may be needed for UL transmission to prevent adjacent sub-channel leakage due to power difference and frequency offset between different STAs. However, for DL transmission, they may be wasted. A manner by which to utilize the subcarriers between the resource blocks may need to be specified.

[0096] In an embodiment, a dynamic framing scheme (DFS) using an

STA identification (ID) Field may be used to address the low spectral usage when packet sizes of different users are very different. The longer data PHY packets may be broken into multiple fragments (or sub-packets) so that, after the shorter packet is transmitted on a sub-channel, a fragment of a longer packet can be allocated to that sub-channel and be transmitted. A STA ID field (IDF) may be attached at the beginning of each long data packet fragment so that each STA receiver can detect if data being transmitted in the following OFDM symbols. The IDF may not only include STA ID information, but also the data fragment length and some training sequence. This may be implemented in DL-OFDMA since each of all STAs in the group may need to perform OFDM demodulation via Fast Fourier Transform (FFT) operations over the full bandwidth of the channel. Accordingly, the STAs may be easily able to detect the existence and value of the ID for data field by correlation or coding, for example.

[0097] Referring now to FIGS. 9A-9B, an example of proposed dynamic frame structure using IDF is shown. In step 950, channel conditions and other system information (e.g., interference level) may be determined, and subchannels may allocated to different STAs, for example, four STAs, for DL data transmissions. In step 952, a channel 902 may be partitioned into four subchannels, labeled as SCI 904, SC2 906, SC3 908, and SC4 910, which may have the same or different bandwidths. In an embodiment, this may be done by a scheduler. The scheduler may be located with the AP. In this example, it may be assumed that the channel condition over SCi is favorable for STAi (for i = 1, 2, 3, 4). In step 954, a long data packet destined for a single STA may be partitioned into multiple sub-packets. In an embodiment, the long data packet may not fit in the determined transmission frame. As shown in FIG. 9A, since the packet length for STAI, Datal, is the longest among all packets, it may be partitioned into three fragments, i.e., Datal = {Datal l 916, Datal2 918, Datal3 920}. The number and the length of these fragments may depend on the lengths of other packets and channel/interference conditions for STAl over those SCs. The decision how to partition the data may be done by the scheduler. In step 956, a training sequence may be sent to all the STAs. In step 958, the allocation of the sub-channels may be signaled in a signaling (SIG) field 912 or in the IDFs 914, which are shown as "optional" in the figure. The SIG field 912 may be a single signaling field, or multiple ones, such as SiG-A and Sig-B in IEEE 802.1 lac and IEEE 802.1 lax.

[0098] In this example, it is assumed that SCI 904, SC2 906, and SC3

908 are good enough for STAl receiving Datal. If this is not the case, the transmitter may choose different sub-channels using different modulation types or modulation and coding schemes (MCS), which may be indicated in the IDF 914. Furthermore, each packet fragment may use different modulation and coding rates, based on, for example, a MCS table, which can also be indicated in the IDF 914. In this case, a packet fragment (PF) may be considered as a sub-packet which can be demodulated and decoded independently from the other sub-packets. One advantage of this may be if one of the sub-packets is not received, it may only be necessary to retransmit that sub-packet, rather the whole packet. The decoded packet may be generated by concatenating the sub-packets. If sub-packets are not coded separately, the concatenation of the sub-packets with soft symbols may need to be done first before demodulation and decoding the whole packet.

[0099] In step 960, the data packets and a portion of the fragmented sub-packets for all the STAs may be transmitted simultaneously on their corresponding SCs, including Datal l 916 for STAl. In step 962, once a short data packet is transmitted, a fragmented sub-packet of long data packet destined for a STA assigned another SC may be sent on the resource which was used to transmit the short data packet. As shown in FIG. 9A, after transmission of Data3 922 for STA3 is completed, the AP may send an IDF 914 to indicate that the following data field is for STAl. Then, Datal2 918 may be sent. Similarly, after transmission of Data2 924 for STA2 is completed, the AP may send an IDF 914 to indicate that the following data field is for STA1.

[0100] Referring now to FIGS. 10A-10B, an example of a proposed dynamic frame structure with sequential transmission of short data packets is shown. As shown in FIG. 10A, attaching an IDF 1002 at the beginning of the data packet or the segment of the data packet also enables transmitting short packets sequentially on a sub-channel while a long packet is transmitted on another sub-channel. In this embodiment, the IDF 1002 may not indicate a fragmentation of a packet, but of information regarding a sequential short data packet for another STA.

[0101] In step 1050, channel conditions and other system information

(e.g., interference level) may be determined, and sub-channels may allocated to different STAs, for example, four STAs (not shown), for DL data transmissions. In step 1052, a channel 1020 may be partitioned into three subchannels, labeled as SCI 1004, SC2 1006, and SC3 1008, which may have the same or different bandwidths. In an embodiment, this may be done by a scheduler. The scheduler may be located with the AP. In step 1054, data packets for the STAs may be allocated to different SCs. The decision of which data packets are transmitted on which channels may be made by the scheduler and may be based on a number of factors, such as channel conditions, bandwidth, and interference.

[0102] In step 1056, a training sequence 1016 may be sent to all the

STAs. In step 1058, the allocation of the sub-channels may be signaled in a SIG field 1018 or in the IDFs 1002, which are shown as "optional" in the figure. The SIG field 1018 may be a single signaling field, or multiple ones, such as SIG-A and SIG-B in IEEE 802.1 lac and IEEE 802.1 lax. In step 1060, data packets for a portion of the STAs may be sent simultaneously on the SCs. This can be seen in FIG. 10A by the transmission of Datal 1014 on SCI 1004, the transmission of Data3 1010 on SC2 1006, and the transmission of Data4 1022 on SC3 1008. In step 1062, once a short data packet is transmitted, another data packet for a STA that did not receive an initial SC assignment may be transmitted on a SC assigned to another STA. In other words, data packets for the remaining STAs without assignments may be transmitted in empty resources on previously assigned SCs. This can be seen in FIG. 10A by the transmission of Data2 1012 after the transmission of Data3 1010 on SC2 1006 while Datal 1014 is transmitted on SCI 1004. Data packets destined for the different STAs may be identified by an IDF field 1002 transmitted prior to the data packet.

[0103] Referring now to FIGS. 11A-11B, an example of a proposed dynamic frame structure using time slots 1102 is shown. To further reduce the overhead, the transmission frame may be partitioned into time slots 1102, each of which may include several OFDM symbols. In this case, an IDF 1104 may be a whole time slot or a part of a time slot. In addition, since a data packet or a fragment of a data packet may not fill up an integer number of time slots, padding 1106 may be needed for those partially filled time slots. Optionally, the padding bytes may be added so that each data fragment is a multiple of four bytes in length to assist subframe delineation at the receiver side.

[0104] In step 1150, channel conditions and other system information

(e.g., interference level) may be determined, and sub-channels may allocated to different STAs, for example, four STAs, for DL data transmissions. In step 1152, a channel 1116 may be partitioned into four sub-channels, labeled as SC I 1108, SC2 1110, SC3 1112, and SC4 1114, which may have the same or different bandwidths. In an embodiment, this may be done by a scheduler. The scheduler may be located with the AP. It should be noted that more or less sub-channels may be used. In this example, it may be assumed that the channel condition over SCi is favorable for STAi (for i = 1, 2, 3, 4). In step 1154, a long data packet destined for a single STA may be partitioned into multiple sub-packets. In an embodiment, the long data packet may not fit in the determined transmission frame. As shown in FIG. 11A, since the packet length for STAl, Datal, is the longest among all packets, it may be partitioned into three fragments, i.e., Datal = {Datal 1 1122, Datal2 1124, Datal3 1126}. The number and the length of these fragments may depend on the lengths of other packets and channel/interference conditions for STAl over those SCs. The decision how to partition the data may be done by the scheduler. In step 1156, a training sequence 1118 may be sent to all the STAs. In step 1158, the allocation of the sub-channels may be signaled in a SIG field 1120 or in the IDFs 1104, which are shown as "optional" in the figure. The SIG field 1120 may be a single signaling field, or multiple ones, such as SiG-A and Sig-B in IEEE 802.1 lac and IEEE 802.1 lax.

[0105] In step 1160, the data packets and sub-packets for all the STAs may be transmitted simultaneously on their corresponding SCs, including Datal l 1122 for STAl 1108. In step 1162, once a short data packet is transmitted, a fragmented sub-packet of long data packet destined for a STA assigned another SC may be sent on the resource which was used to transmit the short data packet. Padding 1106 may be included in order to completely fill a time slot 1102. As shown in FIG. 11A, after transmission of Data3 1128 for STA3 is completed, the AP may send an IDF 1104 to indicate that the following data field is for STAl. Then, Datal2 1124 may be sent. Similarly, after transmission of Data2 1130 for STA2 is completed, the AP may send an IDF 1104 to indicate that the following data field is for STAl. In addition, since a data packet or a fragment of a data packet may not fill up an integer number of time slots 1102, padding 1106 may be sent after a data packet is finished.

[0106] It should be noted that the ideas above may be extended to multiple user multiple -input and multiple-output (MU MIMO), in which OFDMA may be achieved in each spatial space (e.g., eigen-space) and the subchannels may be allocated at a per spatial space basis. As a result, the packet partition method and corresponding signals in the IDF may also be given at per spatial space basis.

[0107] The IDF may be designed with many factors in mind. The IDF may include information, such as, for example, STA ID, length, packet fragment size, modulation and coding scheme, number of packet fragments, and packet fragment index.

[0108] The STA ID may be used for each STA in the OFDMA group to determine if the upcoming fragment is allocated to it. The STA ID in the IDF field may be combined with other IDs defined in the signaling (SIG) field to identify a STA. The design of STA ID may depend on the design of others IDs in SIG field. The other IDs may include, for example, the mac address of the BSS (BSSID) in the SIG field and the association ID (AID) in the IDF field, the mac address of the BSS (BSSID) in the SIG field, and a compressed version of the AID in the IDF field, the BSS color and group ID in the SIG field and AID in the IDF field, and the BSS color and group ID in the SIG field and a compressed version of the AID in the IDF field.

[0109] The length may be the packet size in the unit of Bytes. This field may be optional when A-MPDU is carried in the fragment. The packet fragment size may be presented in terms of OFDM symbols. The unintended STAs may use it to stop the ID detection till transmission of the upcoming fragment is completed, which may help to reduce the power consumption. The MCS index may include different MCS levels depending on channel and other conditions. The number of packet fragments information may be needed for a receiver to know how many packet fragments will need to be concatenated. This information may be signaled in the signaling field of the OFDMA packet. The packet fragment index may help the receiver know how to concatenate the fragments of a packet that may be broken into multiple fragments and transmitted over different sub-channels before decoding. If the IDF is coded, a cyclic redundancy check (CRC) may be needed.

[0110] Optionally, a 1 bit LastSCFragment may be introduced to indicate the last fragment across multiple sub-channels to be concatenated for a long packet. For example, a 1 may denote the last fragment of the packet. In FIG. 9, this bit for Datall 916, Datal2 918, Datal3 920, Data 2 924, Data 3 922, and Data 4 926 may be set to 0, 0, 1, 1 and 1 respectively. Once the receiver detects the LastSCFragment is equal to 1, it may not search for more fragments over other sub-channels, and may start to concatenate all received fragments together to do demodulate and decode.

[0111] In an embodiment, the IDF may have a fixed length. The fixed length may be agreed in the standard, or set up by the AP. If the fixed length is set up by the AP, the AP may broadcast this information in a beacon frame, such that all the IDFs transmitted in the beacon interval may use the same length. In another embodiment, the IDFs within one frame may have the same length. However, the length may be changed from frame to frame. The IDF length may be signaled in the SIG field. In another embodiment, the IDFs within one frame may have different lengths. The transmitter may signal the lengths of the IDFs explicitly in the SIG field. In an alternative method, the transmitter may not signal the length of the IDFs, and the receiver may perform hypothesis testing.

[0112] In an embodiment, the IDF may have an IDF delimiter training field perpended to it. This field may contain a known sequence which may allow the receiver to detect the beginning of a new fragment frame or sub- frame. This field may be used as extra training field for channel estimation, especially in the case where the number of training fields in a preamble part is not enough to support the assigned data streams in the fragment frame. For example, the training field in the preamble part may be good for single data stream transmission and the fragment frame may be assigned to carry two data streams. In this case, the IDF delimiter training field may have one or two extra training fields for spatial domain channel estimation. This field may also be used when the transmitter knows that the receiver of the fragment frame may experience a channel with mobility.

[0113] Whether the IDF delimiter training field is present may be signaled in the SIG field. This field may be optional when one or a combination of the follow conditions are meet: the fragment frame may start from the first OFDM data symbol (right after the preamble part), and the training field in preamble part is enough for the fragment frame to perform channel estimation.

[0114] The SIG field may be designed to include, for example, the following information: a length field, spatial transmission schemes, a precoding field, the total number of frame fragments, and IDF delimiter indicator, and an ID. The length field may be used to indicate the length of the entire OFDMA frame. The length field may be in the unit of OFDM symbols, slots, subframes, TTIs, or bytes. The spatial transmission schemes field may be used to indicate the maximum number of spatial streams and the maximum number of spatial-time streams. Depending on the number in this field, extra training fields may be inserted right after the SIG field but before the IDFs and data parts.

[0115] The precoding field may be used to indicate whether the frame is precoded. When this field is set, all the frame fragments on the same subchannel may use the same set of precoding weights. It should be noted that the term sub-channel may refer to a frequency sub-channel. For example, there are four sub-channels SCI 1108, SC2 1110, SC3 1112, and SC4 1114 shown in FIG. 11A. The total number of frame fragments field may be used to indicate the total number of frame fragments to all the users. The IDF dehmiter indicator field may be used to indicate whether a dehmiter may be presented before the IDF. This may be a single value for all of the fragment frames, or a bitmap where each bit may indicate the presence of IDF dehmiter on one fragment frame. The ID field may be used to signal the group ID or the transmitter ID. A STA may combine this field and STA ID fields in IDF to identify whether it is a potential receiver of this frame.

[0116] In another embodiment, a combined IDF signaling (IDF SIG) field may be transmitted right after the common SIG field, but before the fragment frames. The IDF SIG field may contain information about all the fragmented packets and may combine the information that is presented in the individual IDF fields described above into one transmission prior to the sending of the data packets and fragmented packets.

[0117] Referring now to FIGS. 12A-14B, exemplary designs of a common

IDF SIG field are shown. FIGS. 12A-12B show an example of a proposed dynamic frame structure similar the embodiment described above with reference to FIGS. 9A-9B, but additionally including an IDF SIG field 1202 and IDF delimiters 1204.

[0118] In step 1250, channel conditions and other system information

(e.g., interference level) may be determined, and sub-channels may allocated to different STAs, for example, four STAs, for DL data transmissions. In step 1252, a channel 1206 may be partitioned into four sub-channels, labeled as SC I 1208, SC2 1210, SC3 1212, and SC4 1214, which may have the same or different bandwidths. In an embodiment, this may be done by a scheduler. The scheduler may be located with the AP. In this example, it may be assumed that the channel condition over SCi is favorable for STAi (for i = 1, 2, 3, 4). In step 1254, a long data packet destined for a single STA may be partitioned into multiple sub-packets. In an embodiment, the long data packet may not fit in the determined transmission frame. As shown in FIG. 12A, since the packet length for STAl, Datal, is the longest among all packets, it may be partitioned into three fragments, i.e., Datal = {Datal 1 1220, Datal2 1222, Datal3 1224}. The number and the length of these fragments may depend on the lengths of other packets and channel/interference conditions for STAl over those SCs. The decision how to partition the data may be done by the scheduler.

[0119] In step 1256, a training sequence 1216 may be sent to all the

STAs. In step 1258, the allocation of the sub-channels may be signaled in a SIG field 1218 or in a combined IDF field 1202 in step 1260. The SIG field 1218 may be a single signaling field, or multiple ones, such as SIG-A and SIG- B in IEEE 802.1 lac and IEEE 802.1 lax. In an embodiment, IDF delimiters 1204, which are shown as "optional" in the figure, may be sent.

[0120] In this example, it is assumed that SCI 1208, SC2 1210, and SC3

1212 are good enough for STAl receiving Datal. If this is not the case, the transmitter may choose different sub-channels using different modulation types or modulation and coding schemes (MCS), which may be indicated in the common IDF SIG field 1204. Furthermore, each packet fragment may use different modulation and coding rates, based on, for example, a MCS table, which can also be indicated in the common IDF SIG field 1204. In this case, a packet fragment (PF) may be considered as a sub-packet which can be demodulated and decoded independently from the other sub-packets. One advantage of this may be if one of the sub-packets is not received, it may only be necessary to retransmit that sub-packet, rather the whole packet. The decoded packet may be generated by concatenating the sub-packets. If sub- packets are not coded separately, the concatenation of the sub-packets with soft symbols may need to be done first before demodulation and decoding the whole acket.

[0121] In step 1262, the data packets and sub-packets for all the STAs may be transmitted simultaneously on their corresponding SCs, including Datal l 1220 for STAl. In step 1264, once a short data packet is transmitted, a fragmented sub-packet of long data packet destined for a STA assigned another SC may be sent on the resource which was used to transmit the short data packet. As shown in FIG. 12A, after transmission of Data3 1226 for STA3 is completed, the AP may send an IDF delimiter 1204 to indicate that the following data field is no longer for STA3. Then, Data 12 1222 may be sent. Similarly, after transmission of Data2 1228 for STA2 is completed, the AP may send an IDF delimiter 1204 to indicate that the data field is no longer for STA2.

[0122] FIGS. 13A-13B show an example of a proposed dynamic frame structure similar to the embodiments described above with reference to FIGS. 10A-10B, but additionally including an IDF SIG field 1302 and IDF delimiters 1304. The IDF SIG field 1302 may be a single field or multiple fields.

[0123] In step 1350, channel conditions and other system information

(e.g., interference level) may be determined, and sub-channels may allocated to different STAs, for example, four STAs (not shown), for DL data transmissions. In step 1352, a channel 1306 may be partitioned into three subchannels, labeled as SCI 1308, SC2 1310, and SC3 1312, which may have the same or different bandwidths. In an embodiment, this may be done by a scheduler. The scheduler may be located with the AP. In step 1354, data packets for the STAs may be allocated to different SCs. The decision of which data packets are transmitted on which channels may be made by the scheduler and may be based on a number of factors, such as channel conditions, bandwidth, and interference.

[0124] In step 1356, a training sequence 1314 may be sent to all the

STAs. In step 1358, the allocation of the sub-channels may be signaled in a SIG field 1316 or in a combined IDF field 1302 in step 1360. The SIG field 1316 may be a single signaling field, or multiple fields, such as SIG-A and SIG-B in IEEE 802.1 lac and IEEE 802.1 lax. In an embodiment, IDF delimiters 1304, which are shown as "optional" in the figure, may be sent. In step 1362, data packets for a portion of the STAs may be sent simultaneously on the SCs. This can be seen in FIG. 13A by the transmission of Datal 1318 on SCI 1308, the transmission of Data3 1322 on SC2 1310, and the transmission of Data4 1324 on SC3 1312. In step 1364, once a short data packet is transmitted, another data packet for a STA that did not receive an initial SC assignment may be transmitted on a SC assigned to another STA. In other words, data packets for the remaining STAs without assignments may be transmitted in empty resources on previously assigned SCs. This can be seen in FIG. 13A by the transmission of Data2 1320 after the transmission of Data3 1322 on SC2 11310 while Datal 1318 is transmitted on SCI 1308. Data packets destined for the different STAs may be separated by the IDF delimiters 1304 transmitted after a data packet.

[0125] FIGS. 14A-14B show an example of a proposed dynamic frame structure similar to those as described above with reference to FIGS. 11A-11B but additionally including an IDF SIG field 1402 and IDF delimiters 1404 within time slots 1406. In step 1450, channel conditions and other system information (e.g., interference level) may be determined, and sub-channels may allocated to different STAs, for example, four STAs, for DL data transmissions. In step 1452, a channel 1408 may be partitioned into four subchannels, labeled as SC I 1410, SC2 1412, SC3 1414, and SC4 1416, which may have the same or different bandwidths. In an embodiment, this may be done by a scheduler. The scheduler may be located with the AP. It should be noted that more or less sub-channels may be used. In this example, it may be assumed that the channel condition over SCi is favorable for STAi (for i = 1, 2, 3, 4). In step 1454, a long data packet destined for a single STA may be partitioned into multiple sub-packets. In an embodiment, the long data packet may not fit in the determined transmission frame. As shown in FIG. 14A, since the packet length for STAI, Datal, is the longest among all packets, it may be partitioned into three fragments, i.e., Datal = {Datal 1 1422, Datal2 1424, Datal3 1426}. The number and the length of these fragments may depend on the lengths of other packets and channel/interference conditions for STAl over those SCs. The decision how to partition the data may be done by the scheduler.

[0126] In step 1456, a training sequence 1418 may be sent to all the

STAs. In step 1458, the allocation of the sub-channels may be signaled in a SIG field 1420 or in a combined IDF field 1402 in step 1458. The SIG field 1420 may be a single signaling field, or multiple ones, such as SIG-A and SIG- B in IEEE 802.1 lac and IEEE 802.1 lax. In step 1462, the data packets and sub-packets for all the STAs may be transmitted simultaneously on their corresponding SCs, including Datal l 1422 for STAl. In step 1464, once a short data packet is transmitted, a fragmented sub-packet of long data packet destined for a STA assigned another SC may be sent on the resource which was used to transmit the short data packet. Padding 1432 may be included in order to completely fill a time slot 1102. As shown in FIG. 14A, after transmission of Data3 1428 for STA3 is completed, the AP may send an IDF delimiter 1404 to indicate that the following data field is for STAl. Then, Data 12 1424 may be sent. Similarly, after transmission of Data2 1430 for STA2 is completed, the AP may send an IDF delimiter 1404 to indicate that the following data field is for STAl. In addition, since a data packet or a fragment of a data packet may not fill up an integer number of time slots 1402, padding 1432 may be sent after a data packet is finished.

[0127] Referring now to FIG. 15, an exemplary design of an IDF SIG field 1502 is shown. It should be noted that with this design, the number of fragment frames assigned for each STA may be signaled in the SIG field (not shown). The IDF SIG field 1502 may contain a CRC field 1524 and a STA info field 1504, which may include a STA ID field 1506 and one or more fragment info fields 1508. The one or more fragment info fields 1508 may contain, for example, SC allocation information 1510, an OFDM signal start 1512, fragment size 1514, MCS 1516, Nss 1518, length 1520, and an IDF delimiter field 1522.

[0128] The STA Info field 1504 may contain information of each receiving STA. The number of STA Info fields 1504 may be signaled in the SIG field. The STA ID 1506 may be utilized to identify the receiving STA. The STA ID 1506 may be an AID, a compressed version AID, or other type of ID. The receiver may combine the information carried in SIG field and STA ID field 1506 to determine whether it is the potential receiver.

[0129] The one or more fragment info fields 1508 may contain information of fragment frames assigned to this STA. The number of fragment frames assigned to each STA may be signaled in the SIG field. The subchannel allocation information field may indicate which sub-channel the fragment is assigned. The SC allocation field 1510 may be a bitmap, where each set bit may represent a sub-channel assigned to this fragment frame. The OFDM signal start field 1512 may be used to indicate the starting OFDM symbol assigned to this fragment frame. The fragment size field 1514 may be used to indicate how long the fragment frame may be. The field may be signaled in the unit of OFDM symbols. By combining the OFDM symbol start field 1512 and the fragment size field 1514, a STA may be able to know the starting and ending point of this fragment frame. The MCS field 1516 may be the MCS level utilized on this fragment frame. The Nss field 1518 may be the number of spatial streams carried on this fragment frame. The length field 1520 may be the number of bytes transmitted over the fragment frame. The IDF delimiter field 1522, when set, may instruct an IDF delimiter to be prepended to the fragment frame.

[0130] Referring now to FIG. 16, another exemplary design of an IDF

SIG field 1602 is shown. With this design, the total number of fragment frames (i.e., sub-packets) of this transmission may be signaled in the SIG field (not shown). The IDF SIG field 1602 may contain one or more fragment info fields 1604 that contain information about each fragment frame. The number of fragment frames assigned to each STA may be signaled in the SIG field. Each fragment info field may contain, for example, a STA ID 1606, a fragment index 1608, sub-channel allocation information 1610, an OFDM symbol start 1612, fragment size 1614, MCS 1616, Nss, length 1618, and an IDF delimiter field 1622. [0131] The STA ID 1606 may be utilized to identify the receiving STA.

The STA ID 1606 may be an AID, a compressed version AID, or other type of ID. The receiver may combine the information carried in SIG field and STA ID field 1606 to determine whether it is the potential receiver. The fragment index 1608 is for the specified STA. For example, this STA may be assigned three fragment frames. The fragment index 1608 may indicate which fragment frame this is. The sub-channel allocation information field 1610 may indicate which sub-channel the fragment is assigned. The SC allocation field 1610 may be a bitmap, where each set bit may represent a sub-channel assigned to this fragment frame. The OFDM symbol start field 1612 may be used to indicate the starting OFDM symbol assigned to this fragment frame. The fragment size field 1614 may be used to indicate how long the fragment frame may be. The field may be signaled in the unit of OFDM symbols. By combining the OFDM symbol start field 1612 and the fragment size field 1614, a STA may be able to know the starting and ending point of this fragment frame. The Nss field 1618 may be the number of spatial streams carried on this fragment frame. The length field 1620 may be the number of bytes transmitted over the fragment frame. The IDF delimiter field 1622, when set, may instruct an IDF delimiter to be prepended to the fragment frame.

[0132] In an embodiment, a control wrapper frame may be designed. In

IEEE 802.1 lac an aggregate medium access control (MAC) Protocol Data Unit (A-MPDU) format was introduced. In IEEE 802.1 lac, even a single MPDU may be transmitted as an A-MPDU. By using this approach, IEEE 802.1 lac moved to an all aggregate transmission scheme. In other words, the IEEE 802.1 lac MAC may take over the function of the framing decisions from the PHY. The PHY may only transmit the total frame length without concern for determining the MPDU length. This approach may relieve the PHY of carrying a potentially large number of bits to represent the MPDU length. It should be noted that a single frame in IEEE 802.1 lac may carry as much as four and a half megabytes of data. The length indication of the frame may be provided in the MPDU delimiters as a part of the high data rate payload instead of the PLCP header, which uses the lowest possible transmission rate. [0133] In an embodiment, the IDFs described above may be replaced by a MAC header that may be decoded by the MAC rather than the PHY. With this approach, the PHY may only need to know the maximum MPDU data length of the four MPDUs that may be transmitted simultaneously. The length for each MPDU in the transmission frame may be controlled by a field in the MAC header called a sub-channel A-MPDU length exponent. The subchannel A-MPDU length exponent may be determined by the following formulae

2 ^{13 +£} P° ^nent [n] Equation (1) where the superscript Exponent may be an integer from 0 to 7, and n may be a sub-channel index from 1 to the maximum number of sub-channels, which may be 4.

[0134] Referring now to FIG. 17, a dynamic frame structure using MAC headers 1702 is shown. It should be noted that more than one A-MPDU length exponent may comprise one transmission frame as shown in FIG. 17. In an embodiment, the sub-channel A-MPDU length exponent may be combined with the IDFs described above. For example the IDF may be used for IEEE 802.1 lax STAs in a group, while at the same time the sub-channel A-MPDU length exponent may be used for the IEEE 802.1 lax frame in a sector.

[0135] In an embodiment, the dynamic framing schemes described above may be a modified with a very high throughput (VHT) Capabilities Information Element (IE), and/or a new high efficiency (HE) Capabilities Information Element. These IEs may be described below. A VHT capabilities IE defined for the IEEE 802.1 lac system may be the main information element used in management frames to set up operation of a WLAN network. The VHT capabihties IE may be included in IEEE 802.1 lac probe request and probe response frames to enable a STA to match its capabilities with those of the network and vice versa.

[0136] The PHY may have an IE that describes its operational capabilities including, for example, MCS support, rate support, and a number of spatial streams. With the introduction of OFDMA and UL MU-MIMO there may be new operational capabilities that the PHY will be required to support. [0137] Referring now to FIG. 18, a HE operational IE 1800 is shown.

The HE operational IE may include sub-channel information for up to N channels. In FIG. 18, sub-channel 1802, sub-channel 2 1804, and sub-channel 4 1806 are shown. For each sub-channel, the channel information, MCS, spatial stream supported by the APs, and connected STAs which are HE compatible may be defined. In addition, as in IEEE 802.1 lac, a basic channel width 1808, channel center frequency 0 field 1810, and channel center frequency 1 field 1812 may be indicated in the IE.

[0138] The basic channel width field 1808 may be 1 byte. For either 20

MHz or 40 MHz operation, the basic channel width field 1808 may be set to 0. In 80 MHz operation, the basic channel width field 1808 may be set to 1. Because it may be necessary to distinguish the 160 MHz channel width (a value of 2) from the 80+80 MHz channel structure (a value of 3), they may receive separate values in the base channel width field 1808. The base channel width field 1808 may specify the maximum number of sub-channels that may be supported by HE operation. An indication for a channel width less than 20MHz may also be supported. For example, any or all of the channel widths 2.5 MHz, 5MHz, 10 MHz, and 15 MHz may be supported. It should be noted that other values of channel width field 1808 may be reserved.

[0139] The channel center frequency 0 field 1810 may be 1 byte. In

IEEE 802.1 lac, the channel center frequency 0 field 1810 may only be used with 80 and 160 MHz operation to transmit the center channel frequency of the BSS. In 80+80 MHz IEEE 802.1 lac operation, it may be the center channel frequency of the lower frequency segment. For HE operation, the channel center frequency 0 field 1810 may be extended to support 20 MHz and 40 MHz operation. In this case, the channel width IE may be used to determine how to interpret this IE.

[0140] The channel center frequency 1 field 1812 may be 1 byte. This field may be used only with 80+80 MHz operation to transmit the center channel frequency of a second segment.

[0141] In an embodiment, a multi -packet-fragment block ACK (MPFBA) may be designed for the dynamic frame scheme. In an example, a multi-traffic identifier (multi-TID) BA frame format may be reused for MPFBA transmissions wherein modifications are introduced. An indication that the frame is a MPFBA may be added by one or any combination of the following methods. In a first embodiment, the MPFBA may be signaled using new type, and/or subtype in a frame control field. For example, a new type=l l may be defined and the corresponding type description may be MPFBA. In another example, a new subtype may be defined subtype=any of [0000, 0011] under the existing control type (01). In another embodiment, the MPFBA may be signaled using the combination of multi-TID, compressed bitmap, and groupcast with retries (GCR) subfields in a block ACK request (BAR) control field. For example, [Multi-TID, Compressed Bitmap, GCR]=[1, 1, 1] may be used to indicate a MPFBA frame.

[0142] Referring now to FIG. 19, an illustration showing how each BA

Information field may be addressed to different packet fragments is shown. The different packet fragments may be sent over different sub-channels. Bits B0-B 10 of a Per TID info field 1902 may carry a packet fragment ID, which may identify the intended packet fragment of a BA information field 1904. In the BA information field 1904, and if bit Bl l in the Per TID info field 1902 is set, then a BlockAck bitmap 1906 and a Block Act Starting Sequence Control subfield 1908 may not be present. In this case, the BA information field 1904 may indicate an ACK for the STA with AID indicated in the Per TID info field 1902.

[0143] The number of BA information fields 1904, indicating the number of intended packet fragments of the MPFBA frame, contained in the frame may need to be signaled. This may be done by one of the following examples. In an example, the number of BA information fields 1904 may be signaled using a TID_Info subfield 1910 in a BA control field 1912. This subfield may be reinterpreted as the number of BA information fields 1904. In another example, the number of BA information fields 1904 may be signaled using reserved bits 1914 in the BA control field 1912.

[0144] In another embodiment, a 64x16 bit uncompressed Block ACK bitmap 1906 may be reused by reinterpreting the 16 bits that were used for the fragment of MSDU as an indication of packet fragments for one STA with the dynamic framing scheme. This embodiment may support up to 64 MPDUs and up to 16 packet fragments for one STA. It should be noted that this may not allow for the fragmenting of MAC service data units (MSDUs). The 16 bits may present any of the following: the index of sub-channel where each packet fragment is sent with multi -packet-fragment BAs aggregation, and the index of packet fragments to SU MPFBA to support multiple packet fragment aggregation.

[0145] To make sure the STA understands it is the MPFBA rather than

SU version of the un-compressed BA, it may be indicated in a frame control field 1916. This may be done by defining a new type, a new subtype, or a new type and subtype. For example, a new type=l l may be defined and the corresponding type description may be MPFBA. In another example, a new subtype may be defined subtype=any of [0000, 0011] under the existing control type (01).

[0146] In another embodiment, the ACK/BA may be individually fed back on a per packet fragment basis in the UL. Due to the packet fragments, more than one ACK/BA may need to be fed back from the STA to the AP. The one or more ACK/BA may be sent sequentially in time domain, or simultaneously in code domain, frequency domain and/or spatial domain, or any combination of them as described above.

[0147] In another embodiment, MU packets (or packet fragments) may be aggregated over one sub-channel. This may be done using any one of the following procedures: poll BAs over this sub-channel or whole channel, transmit sequential BAs without polling, simultaneously transmit in either CDMA or SDMA over the sub-channel or the whole channel, or piggyback ACK/BA with data on the corresponding sub-channel in UL.

[0148] In an embodiment, the ACK procedure and frame structures for dynamic framing scheme may be implemented by one or any combination of sequential ACK and/or simultaneous ACK design as described above. For ACK procedures and frame structures described below, any of the dynamic framing designs described above may be used. [0149] Referring now to FIG. 20, a first exemplary embodiment of a sequential channel based MPFBA/BA for a DFS is shown. It should be noted that the sequential nature of the MPFBA/BA may allow for an AP to reorder the feedback, such that shorter packets may be fed back first, thereby reducing latency time. In an embodiment, an AP (not shown) may be in communication with STAl, STA2, STA3, and STA4. A short interframe space (SIFS) time after the termination of the downlink simultaneous transmission by the dynamic frame, STAl may send a MPFBA or BA frame to the AP depending on whether the packet of STAl was fragmented or not. If more than one packet fragments were sent to STAl from AP, MPFBA 2002 may be used; otherwise the BA may be used. Then SIFS time upon the reception of STAl's MPFBA 2002 or BA, the AP may send block ACK request (BAR) or MPFBA, shown in FIG. 20 as BAR 2004, BAR 2006, and BAR 2008 to the rest of the STAs one by one. The requested STA may feedback the BA or MPFBA accordingly, shown in FIG. 20 as BA 2010, BA 2012, and BA 2014, depending on whether the packet of STAl was fragmented or not. In this example, STAl has 3 packet fragments, shown as Data 11 2016, Data 12 2018, and Data 2020. The rest of the STAs in the dynamic frame transmission (i.e., STA2, ST A3, and STA4) are not fragmented, so MPFBA is feedback from STAl and BAR/BA for STA2, ST A3 and STA4 is sequentially used.

[0150] Referring now to FIG. 21, a second exemplary embodiment of a sequential channel based MPFBA/BA for a DFS is shown. It should be noted that the sequential nature of the MPFBA/BA may allow for an AP to reorder the feedback, such that shorter packets may be fed back first, thereby reducing latency time. This embodiment may reduce the signaling overhead due to the MPFBAR or BAR used to request acknowledgement for each individual STA after the first STA. This embodiment may introduce a new control frame 2102 to schedule or request the group of sequential MPFBAs and/or BAs. The control frame 2102 may be sent in an interval of time equal to SIFS after or before DL dynamic frame data transmission. The control frame 2102 may include one or more of the following information: how many STAs are scheduled to sequentially feedback the acknowledgement, the order of STAs that are scheduled to feed back the acknowledgement; the time separation between the adjacent ACK/BA/MPFBA, and the ACK policy.

[0151] Referring now to FIG. 22, a third exemplary embodiment of a sequential channel based BA for a DFS is shown. It should be noted that the sequential nature of the MPFBA/BA may allow for an AP to reorder the feedback, such that shorter packets may be fed back first, thereby reducing latency time. Instead of using the combined MPFBA for the STA with more than one packet fragments, as described above, normal ACK or BA for each packet fragment may be individually acknowledged to the AP. These may be separated by SIFS and indicated as BA for packet fragment 11, 12 and 13 of STA1, shown as BA STAll 2202, BA STA 12 2204, and BA STA13 2206 in this example. Accordingly, the control frame 2208 may include one or more of the following information: how many packet fragments are scheduled to sequentially feedback the acknowledgement, the order of STAs and/or packet fragments are scheduled to feed back the acknowledgement, the time separation between the adjacent ACK/BA, and the ACK policy.

[0152] In order to further reduce signal overhead, simultaneous ACK design may be used for a dynamic framing scheme.

[0153] Referring now to FIG. 23, a first exemplary embodiment of a simultaneous sub-channel based MPFBA/BA for a DFS is shown. A SIFS time after the termination of the downlink simultaneous transmission by the dynamic frame, all STAs may simultaneously send a MPFBA or BA frame to the AP depending on whether the packet of each STA was fragmented or not. If more than one packet fragments were sent to the STA from AP, MPFBA may be used; otherwise the BA may be used. In this example, STAl may send MPFBA 2302, STA2 may send BA 2304, STA3 may send 2306, and STA4 may send BA 2308. MPFBA or BA may be simultaneously sent on the same subchannel as the first packet fragment of the corresponding STA.

[0154] Referring now to FIG. 24, a second exemplary embodiment of a simultaneous sub-channel based BA for a DFS is shown. A SIFS time after the termination of the downlink simultaneous transmission by the dynamic frame, all STAs may simultaneously send one or more ACK/BA frames to the AP depending on whether the packet of each STA was fragmented or not. If more than one packet fragments were sent to the STA from the AP, more than one ACKs/BAs may be simultaneously as a group on the same sub-channel in a CDMA or SDMA fashion. In FIG. 24, STA may send a BA for Data 11 2404, Data 12 2406, and Data 13 2408 as a group 2402. STA 2 may send a BA 2410, STA 3 may send a BA 2412, and STA 4 may send a BA 2414 on individual subchannels. The sub-channel to carry ACK/BA may be the same sub-channel as the first packet fragment of the corresponding STA was sent.

[0155] Referring now to FIG. 25, a third exemplary embodiment of a simultaneous sub-channel based BA for a DFS is shown. A SIFS time after the termination of the downlink simultaneous transmission by the dynamic frame, all STAs may simultaneously send one or more ACK/BA frames to the AP depending on whether the packet of each STA was fragmented or not. If more than one packet fragments were sent to the STA from AP, more than one ACKs/BAs may need to be fed back for this STA to the AP. If more than one STA packet fragments were sent on the same sub-channel, then more than one ACK/BA may need to be fed back on the same sub-channel by CDMA or SDMA, otherwise one BA may be sent on one sub-channel. In FIG. 25, Data 2 2502 and Data 13 2504 may be sent on the same sub-channel, SC2. Accordingly, BA STA2 2506 and BA STA 13 2508 may be sent on that same sub-channel, SC2. Similarly, Data 3 2510 and Data 12 2512 may be sent on the same sub-channel, SC3, and BA STA3 2514 and BA STA 12 2516 may be sent on that same sub-channel. The AP may determine if the retransmission is needed based on each BA for each packet fragment.

[0156] Referring now to FIG. 26, a fourth exemplary embodiment of a simultaneous sub-channel based data/BA for a DFS is shown. A SIFS time after the termination of the downlink simultaneous transmission by the dynamic frame, all STAs may simultaneously send one ACK/BA for each packet fragment to the AP. In FIG. 26, this is shown as BA STAll 2602, BA STA12 2604, BA STA3 2606, and BA STA4 2608. If any ACKs/BAs are still left to be fed back to the AP, then another sub-channel based ACK/BA frame may be simultaneously filled with the rest of the BAs and UL data if the sub- channel is not fully filled by the ACK/BAs. This is shown by UL Data STAl 2610, BA STA 13 2612, BA STA12 2614, and UL Data STA4 2616.

[0157] In an embodiment, a new ACK policy may be defined for the dynamic frame schemes described above. The ACK policy may be defined as any or all of the following: per packet fragment; per STA (or user), which may include one or more packet fragments during one dynamic frame transmission; per sub-channel, which may include one or multiple STAs (or users) packets or packet fragments; and per dynamic frame/burst transmission.

[0158] The same or different ACK policy may be used for multi-STAs within the multi-STA BA and multi-STA BAR frame for dynamic framing scheme. For example, some users may require an immediate BA, and others may require a delayed BA. An alternative example may be that all the STAs within a multi-STA BA frame may require either an immediate or a delayed BA.

[0159] The same or different ACK policy may be used for multiple packet fragments of one user within the multi-packet-fragment BA (MPFBA) and multi-packet-fragment BAR (MPFBAR) frame. For example, some packet fragments may require an immediate BA, and others may require a delayed BA. An alternative example may be that all packet fragments for one STA may require either an immediate or a delayed BA within the current MPFBA or MPFBAR frame.

[0160] An additional embodiment may be that the same ACK policy, such as either an immediate or a delayed BA, may be used for all STAs that are addressed, and their fragments may be addressed within a dynamic frame.

[0161] An embodiment may include a resource allocation method and signaling method to avoid the interference from the image sub-channels due to I/Q imbalance.

[0162] Referring to FIG. 27, an illustration wherein the spectral resources are allocated to users in a symmetrical way is shown. In an embodiment, resources for a single STA may be allocated to be symmetric about a center channel frequency. Although the interference due to I/Q imbalance may still exist, it may only impact on signals for the same user. The interference may be managed as the powers of the signals on the image resource blocks may always, or can be made to be, close to each other. The symmetric resource allocation may be signaled explicitly in the SIG field. When this resource allocation pattern is applied, the resource allocation signaling may be simplified by scheduling RUs to STAs on half size of the bandwidth.

[0163] In an embodiment, nulled subcarriers may be used in DL transmission. The nulled subcarriers described above may be needed for UL transmission, especially when there may be spectral leakage from one subchannel to an adjacent one due synchronization errors. However, for DL transmission, those nulled subcarriers may not be necessary since signals transmitted over the sub-channels may be perfectly synchronized. Those subcarriers may be configured to carry additional training/pilot sequences for channel estimation, synchronization, or beam tracking/search. The subcarriers may be configured to carry additional signaling/controls, such as, power control and user specific or system transmission modes.

[0164] Although the embodiments described herein consider 802.11 specific protocols, it is understood that the solutions described herein are not restricted to this scenario and are applicable to other wireless systems as well.

[0165] Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer- readable medium for execution by a computer or processor. Examples of computer-readable 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, a read only memory (ROM), a random access memory (RAM), a register, 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 in association 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.

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