HK1220851B - Methods and apparatus for multiple user uplink - Google Patents

Description

Method and apparatus for multi-user uplink

Technical Field

Certain aspects of the present disclosure relate generally to wireless communications and, more particularly, to methods and apparatus for multi-user uplink communications in wireless networks.

Background Art

In many telecommunications systems, a communication network is used to exchange messages between several spatially separated interacting devices. Networks can be categorized by geographic scope, which can be, for example, a metropolitan area, a local area, or a personal area. Such networks may be designated as wide area networks (WANs), metropolitan area networks (MANs), local area networks (LANs), or personal area networks (PANs), respectively. Networks also differ based on the switching/routing technology used to interconnect the various network nodes and devices (e.g., circuit switching versus packet switching), the type of physical medium used for transmission (e.g., wired versus wireless), and the set of communication protocols used (e.g., Internet Protocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when network elements are mobile and therefore have dynamic connectivity requirements, or when the network architecture is formed in an ad hoc rather than fixed topology. Wireless networks utilize an invisible physical medium using electromagnetic waves in radio, microwave, infrared, optical, and other frequency bands in an unguided propagation mode. Compared to fixed wired networks, wireless networks advantageously facilitate user mobility and rapid field deployment.

To address the ever-increasing bandwidth requirements of wireless communication systems, various approaches are being developed to allow multiple user terminals to communicate with a single access point (AP) by sharing channel resources while achieving high data throughput. Given limited communication resources, it is desirable to reduce the amount of traffic transferred between the AP and multiple terminals. For example, when multiple terminals send uplink communications to an AP, it is desirable to minimize the amount of uplink traffic required to complete all transmissions. Consequently, there is a need for improved protocols for uplink transmissions from multiple terminals.

Summary of the Invention

Various implementations of systems, methods, and devices within the scope of the appended claims each have several aspects, no single aspect of which is solely responsible for the desirable attributes described herein. Some prominent features are described herein, but they do not limit the scope of the appended claims.

Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. Note that the relative dimensions of the following figures may not be drawn to scale.

One aspect of the present disclosure provides a method for wireless communication. The method includes transmitting a clear-to-transmit (CTX) message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request for the two or more stations to concurrently transmit uplink data at a specific time. The method also includes receiving a plurality of uplink data transmissions from at least two stations at the specific time.

Another aspect of the present disclosure provides an apparatus for wireless communication. The apparatus includes a transmitter configured to transmit a clear-to-transmit (CTX) message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request for the two or more stations to concurrently transmit uplink data at a specific time. The apparatus also includes a receiver configured to receive multiple uplink data transmissions from at least two stations at the specific time.

Another aspect of the present disclosure provides an apparatus for wireless communication. The apparatus includes means for transmitting a clear-to-transmit (CTX) message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request for the two or more stations to concurrently transmit uplink data at a specific time. The apparatus further includes means for receiving multiple uplink data transmissions from at least two stations at the specific time.

Another aspect of the present disclosure provides a non-transitory computer-readable medium. The medium includes instructions that, when executed, cause a processor to perform a method for transmitting a clear-to-transmit (CTX) message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request for the two or more stations to concurrently transmit uplink data at a specific time. The medium further includes instructions that, when executed, cause the processor to perform a method for receiving multiple uplink data transmissions from at least two stations at the specific time.

BRIEF DESCRIPTION OF THE DRAWINGS

1 illustrates a multiple-access multiple-input multiple-output (MIMO) system with access points and user terminals.

2 illustrates a block diagram of access point 110 and two user terminals 120m and 120x in a MIMO system.

3 illustrates various components that may be utilized in a wireless device that may be employed within a wireless communication system.

4A illustrates a timing diagram of an example frame exchange including uplink (UL) MU-MIMO communications.

4B illustrates a timing diagram of an example frame exchange including uplink (UL) MU-MIMO communications.

FIG5 shows a timing diagram of another example frame exchange for UL-MU-MIMO communication.

FIG6 shows a timing diagram of another example frame exchange for UL-MU-MIMO communication.

FIG7 shows a timing diagram of another example frame exchange for UL-MU-MIMO communication.

FIG8 is a message sequence diagram of one embodiment of multi-user uplink communication.

FIG9 illustrates a diagram of one embodiment of a request to transmit (RTX) frame.

FIG10 illustrates a diagram of one embodiment of a clear-to-transmit (CTX) frame.

FIG11 is a diagram showing another embodiment of a CTX frame.

FIG12 is a diagram showing another embodiment of a CTX frame.

FIG13 is a diagram showing another embodiment of a CTX frame.

14 illustrates a flow chart of an aspect of an example methodology for providing wireless communication.

DETAILED DESCRIPTION

The various aspects of the novel system, device and method are described more fully below with reference to the accompanying drawings. However, the present teachings can be implemented in many different forms and should not be interpreted as being limited to any specific structure or function given throughout the disclosure. Specifically, these aspects are provided to make the disclosure thorough and complete, and they will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein, those skilled in the art will appreciate that the scope of the disclosure is intended to cover any aspect of the novel systems, devices and methods disclosed herein, whether implemented independently or in combination with any other aspect of the present invention. For example, any number of aspects set forth herein can be used to implement a device or practice method. In addition, the scope of the present invention is intended to cover devices or methods practiced using other structures, functionality, or structures and functionality that are supplementary to or different from the various aspects of the present invention set forth herein. It should be understood that any aspect disclosed herein can be implemented by one or more elements of the claims.

Although specific aspects are described herein, numerous variations and permutations of these aspects fall within the scope of this disclosure. Although some benefits and advantages of preferred aspects are mentioned, the scope of this disclosure is not intended to be limited to specific benefits, uses, or objectives. On the contrary, various aspects of this disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the accompanying drawings and the following description of preferred aspects. The detailed description and drawings merely illustrate the disclosure and do not limit it, the scope of which is defined by the appended claims and their equivalents.

Wireless network technology may include various types of wireless local area networks (WLANs). WLANs can be used to interconnect nearby devices using widely used networking protocols. Various aspects described herein may be applied to any communication standard, such as Wi-Fi, or more generally any member of the IEEE 802.11 wireless protocol family.

In some aspects, wireless signals may be transmitted according to the high-efficiency 802.11 protocol using orthogonal frequency division multiplexing (OFDM), direct sequence spread spectrum (DSSS) communication, a combination of OFDM and DSSS communication, or other schemes. Implementations of the high-efficiency 802.11 protocol may be used for Internet access, sensors, metering, smart grids, or other wireless applications. Advantageously, aspects of certain devices that implement this particular wireless protocol may consume less power than devices that implement other wireless protocols, may be used to transmit wireless signals over short distances, and/or may be able to transmit signals that are less likely to be blocked by objects (such as people).

In some implementations, a WLAN includes various devices that serve as components for accessing the wireless network. For example, there can be two types of devices: access points ("APs") and clients (also known as stations, or "STAs"). Generally speaking, an AP serves as the hub or base station of a WLAN, while a STA serves as a user of the WLAN. For example, a STA can be a laptop computer, a personal digital assistant (PDA), a mobile phone, etc. In one example, a STA connects to an AP via a wireless link compliant with Wi-Fi (e.g., IEEE 802.11 protocols such as 802.11ah) to obtain general connectivity to the Internet or other wide area networks. In some implementations, a STA can also be used as an AP.

The techniques described herein can be used in various broadband wireless communication systems, including communication systems based on orthogonal multiplexing schemes. Examples of such communication systems include spatial division multiple access (SDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and the like. SDMA systems can utilize sufficiently different directions to simultaneously transmit data belonging to multiple user terminals. TDMA systems can allow multiple user terminals to share the same frequency channel by dividing the transmission signal into different time slots, each time slot being assigned to a different user terminal. TDMA systems can implement GSM or some other standard known in the art. OFDMA systems utilize orthogonal frequency division multiplexing (OFDM), a modulation technique that divides the entire system bandwidth into multiple orthogonal subcarriers. These subcarriers may also be referred to as frequency tones, frequency bins, etc. In OFDM, each subcarrier can be independently modulated with data. OFDM systems can implement IEEE 802.11 or some other standard known in the art. SC-FDMA systems can transmit on subcarriers distributed across the system bandwidth using interleaved FDMA (IFDMA), on blocks of adjacent subcarriers using localized FDMA (LFDMA), or on multiple blocks of adjacent subcarriers using enhanced FDMA (EFDMA). Generally speaking, modulation symbols are sent in the frequency domain with OFDM, while they are sent in the time domain with SC-FDMA. SC-FDMA systems can implement 3GPP-LTE (3rd Generation Partnership Project Long Term Evolution) or other standards.

The teachings herein may be incorporated into (eg, implemented within or performed by) various wired or wireless devices (eg, nodes). In some aspects, a wireless node implemented in accordance with the teachings herein may comprise an access point or an access terminal.

An access point ("AP") may include, be implemented as, or be referred to as, a Node B, a radio network controller ("RNC"), an evolved Node B, a base station controller ("BSC"), a base transceiver station ("BTS"), a base station ("BS"), a transceiver function ("TF"), a radio router, a radio transceiver, a basic service set ("BSS"), an extended service set ("ESS"), a radio base station ("RBS"), or some other terminology.

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

FIG1 is a diagram illustrating a multiple-access, multiple-input, multiple-output (MIMO) system 100 having access points and user terminals. For simplicity, only one access point 110 is shown in FIG1 . An access point is generally a fixed station that communicates with each user terminal and may also be referred to as a base station or some other terminology. A user terminal, or STA, may be fixed or mobile and may also be referred to as a mobile station or wireless device or some other terminology. An access point 110 may communicate with one or more user terminals 120 on a downlink and an uplink at any given moment. The downlink (i.e., forward link) is the communication link from the access point to the user terminal, while the uplink (i.e., reverse link) is the communication link from the user terminal to the access point. A user terminal may also communicate peer-to-peer with another user terminal. A system controller 130 couples to each access point and provides coordination and control for these access points.

Although portions of the following disclosure will describe user terminals 120 capable of communicating via spatial division multiple access (SDMA), for certain aspects, the user terminals 120 may also include some user terminals that do not support SDMA. Thus, for such aspects, the AP 110 may be configured to communicate with both SDMA user terminals and non-SDMA user terminals. This approach may facilitate allowing older versions of user terminals that do not support SDMA ("legacy" stations) to remain deployed in an enterprise to extend their useful life, while allowing newer SDMA user terminals to be introduced where deemed appropriate.

System 100 employs multiple transmit and receive antennas for data transmission on the downlink and uplink. Access point 110 is equipped with _Nap antennas and represents multiple-input (MI) for downlink transmissions and multiple-output (MO) for uplink transmissions. The set of K selected user terminals 120 collectively represents multiple-output for downlink transmissions and multiple-input for uplink transmissions. For pure SDMA, if the data symbol streams for the K user terminals are not multiplexed in code, frequency, or time by some means, then _Nap ≤ K ≤ 1 is required. K can be greater than _Nap if the data symbol streams can be multiplexed using TDMA techniques, using different code channels in CDMA, using disjoint sets of subbands in OFDM, etc. Each selected user terminal can transmit and/or receive user-specific data to and from the access point. In general, each selected user terminal can be equipped with one or more antennas (i.e., _Nut ≥ 1). The K selected user terminals may have the same number of antennas, or one or more user terminals may have a different number of antennas.

The SDMA system 100 can be a time division duplex (TDD) system or a frequency division duplex (FDD) system. In a TDD system, the downlink and uplink share the same frequency band. In an FDD system, the downlink and uplink use different frequency bands. The MIMO system 100 can also utilize a single carrier or multiple carriers for transmission. Each user terminal can be equipped with a single antenna (e.g., to reduce costs) or multiple antennas (e.g., where the additional cost can be supported). If each user terminal 120 shares the same frequency channel by dividing transmission/reception into different time slots, each of which can be assigned to a different user terminal 120, the system 100 can also be a TDMA system.

FIG2 illustrates a block diagram of access point 110 and two user terminals 120 m and 120 x in MIMO system 100. Access point 110 is equipped with N _t antennas 224 a through 224 ap. User terminal 120 m is equipped with N _{ut, m} antennas 252 ma through 252 mu, while user terminal 120 x is equipped with N _{ut, x} antennas 252 xa through 252 xu. Access point 110 is a transmitting entity for the downlink and a receiving entity for the uplink. User terminal 120 is a transmitting entity for the uplink and a receiving entity for the downlink. As used herein, a “transmitting entity” is an independently operated device or apparatus capable of transmitting data via a wireless channel, while a “receiving entity” is an independently operated device or apparatus capable of receiving data via a wireless channel. In the following description, the subscript "dn" denotes downlink, the subscript "up" denotes uplink, N _up user terminals are selected for simultaneous transmission on the uplink, and N _dn user terminals are selected for simultaneous transmission on the downlink. _{N up} may or may not be equal to N _dn , and N _up and N _dn may be static values or may change for each scheduling interval. Beam steering or some other spatial processing technique may be used at access point 110 and/or user terminal 120.

On the uplink, at each user terminal 120 selected for uplink transmission, a transmit (TX) data processor 288 receives traffic data from a data source 286 and control data from a controller 280. The TX data processor 288 processes (e.g., encodes, interleaves, and modulates) the traffic data for that user terminal based on the coding and modulation scheme associated with the rate selected for that user terminal and provides a data symbol stream. A TX spatial processor 290 performs spatial processing on the data symbol stream and provides N _ut,m transmit symbol streams for the N _ut,m antennas. Each transmitter unit (TMTR) 254 receives and processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) a corresponding transmit symbol stream to generate an uplink signal. _{The N ut,m} transmitter units 254 provide N _ut,m uplink signals for transmission from the N _ut,m antennas 252, e.g., for transmission to the access point 110.

N _up user terminals may be scheduled for simultaneous transmission on the uplink. Each of these user terminals may perform spatial processing on its own respective data symbol stream and transmit its respective set of transmit symbol streams on the uplink to access point 110.

At access point 110, N _up antennas 224a through 224ap receive uplink signals from all N _up user terminals transmitting on the uplink. Each antenna 224 provides a received signal to a respective receiver unit (RCVR) 222. Each receiver unit 222 performs processing complementary to that performed by transmitter unit 254 and provides a received symbol stream. An RX (receive) spatial processor 240 performs receiver spatial processing on the N _up received symbol streams from N _up receiver units 222 and provides N _up recovered uplink data symbol streams. Receiver spatial processing may be performed based on channel correlation matrix inversion (CCMI), minimum mean square error (MMSE), soft interference cancellation (SIC), or some other technique. Each recovered uplink data symbol stream is an estimate of the data symbol stream transmitted by the respective user terminal. An RX data processor 242 processes (e.g., demodulates, deinterleaves, and decodes) each recovered uplink data symbol stream based on the rate used for that stream to obtain decoded data. The decoded data for each user terminal may be provided to a data sink 244 for storage and/or to a controller 230 for further processing.

On the downlink, at access point 110, TX data processor 210 receives traffic data for N _dn user terminals scheduled for downlink transmission from data source 208, control data from controller 230, and possibly other data from scheduler 234. The various types of data may be sent on different transmission channels. TX data processor 210 processes (e.g., encodes, interleaves, and modulates) the traffic data for each user terminal based on a rate selected for that user terminal. TX data processor 210 provides N _dn downlink data symbol streams for the N _dn user terminals. TX spatial processor 220 performs spatial processing (such as precoding or beamforming) on the N _dn downlink data symbol streams and provides N _up transmit symbol streams for N _up antennas. Each transmitter unit 222 receives and processes a corresponding transmit symbol stream to generate a downlink signal. N _up transmitter units 222 provide N _up downlink signals for transmission from, for example, N _up antennas 224 to user terminal 120.

At each user terminal 120, N _ut,m antennas 252 receive N _up downlink signals from access point 110. Each receiver unit 254 processes the received signal from its associated antenna 252 and provides a received symbol stream. An RX spatial processor 260 performs receiver spatial processing on the N _ut,m received symbol streams from the N _ut,m receiver units 254 and provides a recovered downlink data symbol stream for the user terminal 120. The receiver spatial processing may be performed in accordance with CCMI, MMSE, or some other technique. An RX data processor 270 processes (e.g., demodulates, deinterleaves, and decodes) the recovered downlink data symbol stream to obtain decoded data for the user terminal.

At each user terminal 120, a channel estimator 278 estimates the downlink channel response and provides a downlink channel estimate, which may include a channel gain estimate, an SNR estimate, a noise variance, etc. Similarly, a channel estimator 228 estimates the uplink channel response and provides an uplink channel estimate. A controller 280 at each user terminal typically derives a spatial filter matrix for that user terminal based on the downlink channel response matrix H _dn,m for that user terminal. A controller 230 derives the spatial filter matrix for the access point based on the effective uplink channel response matrix H _up,eff . The controller 280 at each user terminal may send feedback information (e.g., downlink and/or uplink eigenvectors, eigenvalues, SNR estimates, etc.) to the access point 110. Controllers 230 and 280 may also control the operation of various processing units at the access point 110 and user terminal 120, respectively.

3 illustrates various components that may be used in a wireless device 302 that may be employed within the wireless communication system 100. The wireless device 302 is an example of a device that may be configured to implement the various methods described herein. The wireless device 302 may implement an access point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 that controls the operation of the wireless device 302. The processor 304 may also be referred to as a central processing unit (CPU). Memory 306, which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor 304. A portion of the memory 306 may also include non-volatile random access memory (NVRAM). The processor 304 typically performs logical and arithmetic operations based on program instructions stored in the memory 306. The instructions in the memory 306 may be executable to implement the methods described herein.

Processor 304 may include or be a component of a processing system implemented with one or more processors. The one or more processors may be implemented with any combination of general-purpose microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), controllers, state machines, gating logic, discrete hardware components, dedicated hardware finite state machines, or any other suitable entity capable of performing calculations or other manipulations on information.

The processing system may also include a machine-readable medium for storing software. Software should be broadly interpreted to mean any type of instructions, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable code format). These instructions, when executed by the one or more processors, cause the processing system to perform the various functions described herein.

The wireless device 302 may also include a housing 308 that may contain a transmitter 310 and a receiver 312 to allow transmission and reception of data between the wireless device 302 and a remote location. The transmitter 310 and the receiver 312 may be combined into a transceiver 314. A single or multiple transceiver antennas 316 may be attached to the housing 308 and electrically coupled to the transceiver 314. The wireless device 302 may also include (not shown) multiple transmitters, multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that may be used to attempt to detect and quantify the level of a signal received by the transceiver 314. The signal detector 318 may detect signals such as total energy, energy per subcarrier per symbol, power spectral density, and other signals. The wireless device 302 may also include a digital signal processor (DSP) 320 for processing signals.

The various components of the wireless device 302 may be coupled together by a bus system 322 , which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus.

Certain aspects of the present disclosure support the transmission of uplink (UL) signals from multiple STAs to an AP. In some embodiments, the UL signal may be transmitted in a multi-user MIMO (MU-MIMO) system. Alternatively, the UL signal may be transmitted in a multi-user FDMA (MU-FDMA) or similar FDMA system. Specifically, Figures 4-8 and 10 illustrate UL-MU-MIMO transmissions 410A, 410B, 1050A, and 1050B, which are equally applicable to UL-FDMA transmissions. In these embodiments, UL-MU-MIMO or UL-FDMA transmissions may be sent from multiple STAs to an AP simultaneously and may create efficiencies in wireless communications.

The increasing number of wireless and mobile devices is placing increasing pressure on the bandwidth requirements of wireless communication systems. Given limited communication resources, it is desirable to reduce the amount of traffic transferred between an AP and multiple STAs. For example, when multiple terminals are sending uplink communications to an access point, it is desirable to minimize the uplink traffic required to complete all transmissions. Thus, the embodiments described herein support utilizing communication switching, scheduling, and specialized frames to increase the throughput of uplink transmissions to the AP.

FIG4A is a timing diagram illustrating an example of a UL-MU-MIMO protocol 400 that can be used for UL communication. As shown in FIG4A and in conjunction with FIG1 , AP 110 can transmit a clear-to-transmit (CTX) message 402 to user terminal 120 to indicate which STAs can participate in the UL-MU-MIMO scheme, so that specific STAs know to start UL-MU-MIMO. In some embodiments, the CTX message can be transmitted in the payload portion of a physical layer convergence protocol (PLCP) protocol data unit (PPDU). An example of a CTX frame structure is described more fully below with reference to FIG12-14 .

Once the user terminal 120 receives a CTX message 402 from the AP 110 listing the user terminal, the user terminal may transmit an UL-MU-MIMO transmission 410. In FIG4A, STA 120A and STA 120B transmit UL-MU-MIMO transmissions 410A and 410B containing physical layer convergence protocol (PLCP) protocol data units (PPDUs). Upon receiving the UL-MU-MIMO transmission 410, the AP 110 may transmit a block acknowledgment (BA) 470 to the user terminal 120.

FIG4B is a timing diagram illustrating an example of a UL-MU-MIMO protocol that may be used for UL communications. In FIG4B , CTX frames are aggregated in an A-MPDU message 407. Aggregated A-MPDU message 407 may provide user terminal 120 with time to process prior to transmitting an UL signal, or may allow AP 110 to send data to user terminal 120 prior to receiving uplink data.

Not all APs or user terminals 120 may support UL-MU-MIMO or UL-FDMA operations. The capability indication from the user terminal 120 may be indicated in a High Efficiency Radio (HEW) capability element included in an association request or a probe request and may include bits indicating the capability, the maximum number of spatial streams that the user terminal 120 can use in UL-MU-MIMO transmissions, the frequencies that the user terminal 120 can use in UL-FDMA transmissions, the minimum and maximum power and power backoff granularity, and the minimum and maximum time adjustments that the user terminal 120 can perform.

The capability indication from the AP may be indicated in a HEW capability element included in an association response, beacon, or probe response and may include bits indicating the capability, the maximum number of spatial streams that a single user terminal 120 can use in UL-MU-MIMO transmission, the frequencies that a single user terminal 120 can use in UL-FDMA transmission, the required power control granularity, and the required minimum and maximum time adjustments that the user terminal 120 should be able to perform.

In one embodiment, a capable user terminal 120 may request to become part of the UL-MU-MIMO (or UL-FDMA) protocol from a capable AP by sending a management frame to the AP indicating a request to enable use of the UL-MU-MIMO feature. In one aspect, the AP 110 may respond by either granting or denying use of the UL-MU-MIMO feature. Once use of UL-MU-MIMO is granted, the user terminal 120 may expect CTX messages 402 at various times. Additionally, once the user terminal 120 is enabled to operate the UL-MU-MIMO feature, the user terminal 120 may follow a specific operating mode. If multiple operating modes are possible, the AP may indicate to the user terminal 120 which mode to use in an HEW capability element, management frame, or operating element. In one aspect, the user terminal 120 may dynamically change operating modes and parameters during operation by sending different operating elements to the AP 110. In another aspect, the AP 110 may dynamically switch operating modes during operation by sending updated operating elements or management frames to the user terminal 120 or in beacons. In another aspect, the operating mode may be indicated in a setup phase and may be set up per user terminal 120 or for a group of user terminals 120. In another aspect, the operating mode may be specified per traffic identifier (TID).

FIG5 is a timing diagram illustrating an example of an operational mode of UL-MU-MIMO transmission in conjunction with FIG1 . In this embodiment, user terminal 120 receives a CTX message 402 from AP 110 and sends an immediate response to AP 110. The response may be in the form of a Clear to Send (CTS) 408 or another similar signal. In one aspect, the requirement to send a CTS may be indicated in CTX message 402 or may be indicated during the setup phase of communication. As shown in FIG5 , STA 120A and STA 120B may transmit CTS 1 408A and CTS 2 408B messages in response to receiving CTX message 402. The modulation and coding scheme (MCS) of CTS 1 408A and CTS 2 408B may be based on the MCS of CTX message 402. In this embodiment, CTS 1 408A and CTS 2 408B contain the same bits and the same scrambling sequence so that they can be transmitted to AP 110 at the same time. The duration field of the CTS 408 signal may be based on the duration field in the CTX signal, removing the time for the CTX PPDU. UL-MU-MIMO transmissions 410A and 410B are then transmitted by the STAs 120A and 120B listed in the CTX 402 signal. The AP 110 may then send an acknowledgment (ACK) signal to the STAs 120A and 120B. In some aspects, the ACK signal may be a serial ACK signal or a BA to each station. In some aspects, the ACK may be polled. This embodiment creates efficiency by transmitting the CTS 408 signal from multiple STAs to the AP 110 simultaneously (rather than sequentially), which saves time and reduces the possibility of interference.

FIG6 is a timing diagram illustrating another example of an operational mode for UL-MU-MIMO transmission in conjunction with FIG1 . In this embodiment, user terminals 120A and 120B receive a CTX message 402 from AP 110 and are permitted to begin UL-MU-MIMO transmission after a time (T) 406 has elapsed after the PPDU carrying the CTX message 402 ends. T 406 may be a short interframe space (SIFS), a point interframe space (PIFS), or another time potentially adjusted with an additional offset as indicated by AP 110 in CTX message 402 or via a management frame. The SIFS and PIFS times may be fixed in the standard or may be indicated by AP 110 in CTX message 402 or in a management frame. T 406 may improve synchronization or allow user terminals 120A and 120B time to process CTX message 402 or other messages before transmitting.

4-6 in conjunction with FIG1 , UL-MU-MIMO transmissions 410 may have a common duration. The duration of the UL-MU-MIMO transmission 410 for a user terminal utilizing the UL-MU-MIMO feature may be indicated in the CTX message 402 or during the setup phase. To generate a PPDU with the required duration, the user terminal 120 may construct a PLCP service data unit (PSDU) such that the length of the PPDU matches the length indicated in the CTX message 402. Alternatively, the user terminal 120 may adjust the data aggregation level in the media access control (MAC) protocol data unit (A-MPDU) or the data aggregation level in the MAC service data unit (A-MSDU) to approach a target length. Alternatively, the user terminal 120 may add an end-of-file (EOF) padding delimiter to achieve the target length. In another approach, padding or an EOF padding field is added at the beginning of the A-MPDU. One benefit of having all UL-MU-MIMO transmissions have the same length is that the power level of the transmission remains constant.

In some embodiments, user terminal 120 may have data to upload to the AP, but user terminal 120 has not yet received a CTX message 402 or other signal indicating that user terminal 120 may begin UL-MU-MIMO transmission.

In one mode of operation, user terminals 120 may not transmit outside of a UL-MU-MIMO transmission opportunity (TXOP) (e.g., following a CTX message 402). In another mode of operation, user terminals 120 may transmit a frame for initializing UL-MU-MIMO transmission and may subsequently transmit during the UL-MU-MIMO TXOP if, for example, they were instructed to transmit during the UL-MU-MIMO TXOP in the CTX message 402. In one embodiment, the frame used to initialize UL-MU-MIMO transmission may be a request to transmit (RTX), a frame specifically designed for this purpose (an example of an RTX frame structure is described more fully below with reference to Figures 8 and 9). The RTX frame may be the only frame that the user terminal 120 is allowed to use to initiate a UL MU MIMO TXOP. In one embodiment, the user terminal may not transmit outside of a UL-MU-MIMO TXOP except for sending an RTX. In another embodiment, the frame used to initialize UL MU MIMO transmission may be any frame that indicates to the AP 110 that the user terminal 120 has data to transmit. These frames may be pre-negotiated to indicate a UL MU MIMO TXOP request. For example, the following may be used to indicate that the user terminal 120 has data to send and is requesting a UL MU MIMO TXOP: an RTS, a data frame, or a QoS null frame (where bits 8-15 of the QoS control frame are set to indicate more data), or a PS-Poll. In one embodiment, the user terminal may not transmit outside of the TXOP except for sending a frame to trigger the UL MU MIMO TXOP, where the frame may be an RTS, PS-Poll, or QoS null frame. In another embodiment, the user terminal may send single-user uplink data as usual and may indicate a request for a UL MU MIMO TXOP by setting a bit in the QoS control frame of its data packet. FIG7 is a timing diagram illustrating an example in which the frame used to initialize UL-MU-MIMO is an RTX 701, in conjunction with FIG1 . In this embodiment, the user terminal 120 sends an RTX 701 including information about the UL-MU-MIMO transmission to the AP 110. As shown in FIG7 , AP 110 may respond to RTX 701 with a CTX message 402, thereby granting the UL-MU-MIMO TXOP immediately following the CTX message 402 for transmitting the UL-MU-MIMO transmission 410. Alternatively, AP 110 may respond with a CTS message granting a single-user (SU) UL TXOP. Alternatively, AP 110 may respond with a frame (e.g., an ACK or CTX with a special indication) that acknowledges receipt of RTX 701 but does not grant an immediate UL-MU-MIMO TXOP. Alternatively, AP 110 may respond with a frame that acknowledges receipt of RTX 701, does not grant an immediate UL-MU-MIMO TXOP, but grants a delayed UL-MU-MIMO TXOP, and may identify the time at which the TXOP is granted. In this embodiment, AP 110 may send a CTX message 402 to start UL-MU-MIMO at the granted time.

On the other hand, AP 110 may respond to RTX 701 with an ACK or other response signal that does not grant UE 120 UL-MU-MIMO transmission, but instead indicates that UE 120 should wait for a time (T) before attempting another transmission (e.g., sending another RTX). In this regard, the time (T) may be indicated by AP 110 during the setup phase or in the response signal. On the other hand, AP 110 and UE 120 may agree on a time at which UE 120 may transmit RTX 701, RTS, PS-Poll, or any other request for UL-MU-MIMO TXOP.

In another mode of operation, the user terminal 120 may transmit a request for UL-MU-MIMO transmission 410 according to a conventional contention protocol. In another aspect, the contention parameter of the user terminal 120 using UL-MU-MIMO is set to a different value than other user terminals not using the UL-MU-MIMO feature. In this embodiment, the AP 110 may indicate the value of the contention parameter in a beacon, association response, or through a management frame. In another aspect, the AP 110 may provide a delay timer that prevents the user terminal 120 from transmitting for a certain amount of time after each successful UL-MU-MIMO TXOP or after each RTX, RTS, PS-Poll, or QoS Null frame. The timer may be restarted after each successful UL-MU-MIMO TXOP. In one aspect, the AP 110 may indicate the delay timer to the user terminal 120 during the setup phase, or the delay timer may be different for each user terminal 120. In another aspect, AP 110 may indicate a delay timer in CTX message 402, or the delay timer may depend on the order of user terminals 120 in CTX message 402 and may be different for each terminal.

In another mode of operation, AP 110 may indicate a time interval during which user terminals 120 are permitted to transmit UL-MU-MIMO transmissions. In one aspect, AP 110 indicates to user terminals 120 the time interval during which these user terminals are permitted to send RTX or RTS or other requests to AP 110 for UL-MU-MIMO transmissions. In this regard, user terminals 120 may utilize conventional contention protocols. In another aspect, user terminals may not initiate UL-MU-MIMO transmissions during this time interval, but AP 110 may send CTX or other messages to the user terminals to initiate UL-MU-MIMO transmissions.

In certain embodiments, a user terminal 120 enabled for UL-MU-MIMO may indicate to the AP 110 that it is requesting a UL-MU-MIMO TXOP because it has data waiting for the UL. In one aspect, the user terminal 120 may send an RTS or PS-Poll to request a UL-MU-MIMO TXOP. In another embodiment, the user terminal 120 may send any data frame, including a Quality of Service (QoS) null data frame, where bits 8-15 of the QoS control field indicate a non-empty queue. In this embodiment, the user terminal 120 may determine during the setup phase which data frames (e.g., RTS, PS-Poll, QoS null frames, etc.) will trigger UL-MU-MIMO transmission when bits 8-15 of the QoS control field indicate a non-empty queue. In one embodiment, the RTS, PS-Poll, or QoS null frame may include a 1-bit indication that allows or does not allow the AP 110 to respond with a CTX message 402. In another embodiment, the QoS null frame may include TX power information and per-TID queue information. The TX power information and the per-TID queue information may be inserted into two bytes of the sequence control and QoS control fields in a QoS null frame, and the modified QoS null frame may be sent to the AP 110 to request a UL-MU-MIMO TXOP. In another embodiment, referring to Figures 1 and 7, the user terminal 120 may send RTX 701 to request a UL-MU-MIMO TXOP.

In response to receiving an RTS, RTX, PS-Poll, or QoS null frame, or other triggering frame as described above, AP 110 may transmit a CTX message 402. In one embodiment, referring to FIG. 7 , after transmitting the CTX message 402 and completing the UL-MU-MIMO transmissions 410A and 410B, the TXOP is returned to STAs 120A and 120B, which may decide how to use the remaining TXOP. In another embodiment, referring to FIG. 7 , after transmitting the CTX message 402 and completing the UL-MU-MIMO transmissions 410A and 410B, the TXOP remains with AP 110, and AP 110 may use the remaining TXOP for additional UL-MU-MIMO transmissions by transmitting another CTX message 402 to STAs 120A and 120B or to other STAs.

FIG8 is a message sequence diagram for one embodiment of multi-user uplink communication. Message exchange 800 illustrates the communication of wireless messages between AP 110 and three stations 120a-c. Message exchange 800 indicates that each of STAs 120a-c transmits a request-to-transmit (RTX) message 802a-c to AP 110. Each of RTX messages 802a-c indicates that the transmitting station 120a-c has data available for transmission to AP 110.

After receiving each of the RTX messages 802a-c, AP 110 may respond with a message indicating that AP 110 has received the RTX. As shown in FIG8 , AP 110 transmits an ACK message 803a-c in response to each of the RTX messages 802a-c. In some embodiments, AP 110 may transmit a message (e.g., a CTX message) indicating that each of the RTX messages 802a-c has been received, but that AP 110 has not yet granted a transmission opportunity for uplink data to the stations 120a-c. In FIG8 , after sending ACK message 803c, AP 110 transmits a CTX message 804. In some aspects, CTX message 804 is transmitted to at least stations 120a-c. In some aspects, CTX message 804 is broadcast. In some aspects, CTX message 804 indicates which stations have been granted permission to transmit data to AP 110 during the transmission opportunity. In some aspects, the start time of the transmission opportunity and its duration may be indicated in CTX message 804. For example, the CTX message 804 may indicate that the stations STA 120a - c should set their network allocation vectors to be consistent with the NAV 812 .

At the time indicated by the CTX message 804, the three stations 120a-c transmit data 806a-c to the AP 110. The data 806a-c are transmitted at least partially concurrently during the transmission opportunity. The transmission of the data 806a-c may utilize uplink multi-user multiple input multiple output transmission (UL-MU-MIMO) or uplink frequency division multiple access (UL-FDMA).

In some aspects, stations STAa-c may transmit filler data so that the transmissions of each station transmitting during a transmission opportunity have approximately equal durations. Message exchange 800 shows STA 120a transmitting filler data 808a while STA 120c transmits filler data 808c. The transmission of filler data ensures that the transmissions from each of STAs 120a-c complete at approximately the same time. This may allow for more balanced transmit power throughout the transmission duration, thereby optimizing AP 110 receiver efficiency.

After AP 110 receives data transmissions 806a-c, AP 110 transmits an acknowledgment 810a-c to each of stations 120a-c. In some aspects, acknowledgments 810a-c may be transmitted at least partially concurrently using DL-MU-MIMO or DL-FDMA.

FIG9 illustrates one embodiment of an RTX frame 900. The RTX frame 900 includes a frame control (FC) field 910, a duration field 915 (optional), a transmitter address (TA)/allocation identifier (AID) field 920, a receiver address (RA)/basic service set identifier (BSSID) field 925, a TID field 930, an estimated transmission (TX) time field 950, and a TX power field 970. The FC field 910 indicates a control subtype or an extended subtype. The duration field 915 instructs any receiver of the RTX frame 900 to set a network allocation vector (NAV). In one aspect, the RTX frame 900 may not include the duration field 915. The TA/AID field 920 indicates the source address, which may be an AID or a full MAC address. The RA/BSSID field 925 indicates the RA or BSSID used by STAs to concurrently transmit uplink data. In one aspect, the RTX frame may not include the RA/BSSID field 925. The TID field 930 indicates the access category (AC) for which the user has data. The estimated TX time field 950 indicates the time requested for the UL-TXOP and may be the time required for the user terminal 120 to transmit all the data in its buffer at the currently scheduled MCS. The TX power field 970 indicates the power at which the frame is transmitted and may be used by the AP to estimate link quality and adapt the power backoff indication in the CTX frame.

In some embodiments, before UL-MU-MIMO communication can occur, AP 110 can collect information from user terminals 120 that can participate in UL-MU-MIMO communication. AP 110 can optimize the collection of information from user terminals 120 by scheduling transmissions from user terminals 120.

As discussed above, the CTX message 402 can be used in various communications. FIG10 illustrates an example of the structure of a CTX frame 1000. In this embodiment, the CTX frame 1000 is a control frame that includes a frame control (FC) field 1005, a duration field 1010, a transmitter address (TA) field 1015, a control (CTRL) field 1020, a PPDU duration field 1025, a STA information (info) field 1030, and a frame check sequence (FCS) field 1080. The FC field 1005 indicates a control subtype or an extended subtype. The duration field 1010 instructs any receiver of the CTX frame 1000 to set a network allocation vector (NAV). The TA field 1015 indicates a transmitter address or BSSID. The CTRL field 1020 is a general field that may include information regarding the format of the rest of the frame (e.g., the number of STA information fields and the presence or absence of any subfields within the STA information field), an indication of rate adaptation for the user terminal 100, an indication of allowed TIDs, and an indication that a CTS must be sent immediately following the CTX frame 1000. The indication of rate adaptation may include data rate information, such as a number indicating how much the STA should reduce its MCS compared to the MCS it has been using for single-user transmissions. The CTRL field 1020 may also indicate whether the CTX frame 1000 is being used for UL MU MIMO, UL FDMA, or both, thereby indicating whether the Nss or Tone Allocation field is present in the STA Information field 1030.

Alternatively, the indication of whether CTX is for UL MU MIMO or UL FDMA may be based on the value of the subtype. Note that UL MU MIMO and UL FDMA operation can be performed jointly by specifying to the STA both the spatial streams to use and the channels to use, in which case both fields are present in CTX; in this case, the Nss indication is referred to as a specific tone allocation. The PPDU Duration 1025 field indicates the duration of the subsequent UL-MU-MIMO PPDU that the user terminal 120 is allowed to transmit. The STA Information 1030 field contains information about a specific STA and may include a per-STA (per user terminal 120) information set (see STA Information 1 1030 and STA Information N 1075). The STA information 1030 field may include an AID or MAC address field 1032 identifying the STA, a number of spatial streams field (Nss) 1034 indicating the number of spatial streams that the STA can use (in a UL-MU-MIMO system), a time adjustment 1036 field indicating the time the STA should adjust its transmission compared to the reception of a trigger frame (in this case, CTX), a power adjustment 1038 field indicating the power backoff the STA should perform from the declared transmit power, a frequency tone allocation 1040 field indicating the frequency tone or frequency that the STA can use (in a UL-FDMA system), an allowed TID 1042 field indicating the allowable TIDs, an allowed TX mode 1044 field indicating the allowed TX mode, an MCS 1046 field indicating the MCS that the STA should use, and a TX start time field 1048 indicating the start time when the STA transmits uplink data. In some embodiments, the allowed TX modes may include short/long guard interval (GI) or cyclic prefix mode, binary convolutional code (BCC)/low density parity check (LDPC) mode (typically a coding mode), or space-time block coding (STBC) mode.

In some embodiments, the STA information fields 1030-1075 can be excluded from the CTX frame 1000. In these embodiments, the CTX frame 1000 with the missing STA information field can indicate to the user terminal 120 receiving the CTX frame 1000 that a request message for uplink data (e.g., RTS, RTX, or QoS Null) has been received, but a transmission opportunity has not yet been granted. In some embodiments, the control field 1020 can include information about the requested uplink. For example, the control field 1020 can include a wait time before sending data or another request, a reason code as to why the request was not granted, or other parameters for controlling medium access from the user terminal 120. The CTX frame with the missing STA information field can also be applied to the CTX frames 1100, 1200, and 1300 described below.

In some embodiments, a user terminal 120 receiving a CTX frame with an indication of an allowed TID 1042 may be allowed to transmit data for only that TID, data for the same or higher TID, data for the same or lower TID, any data, or first transmit data for only that TID and then transmit data for other TIDs if no data is available. The FCS 1080 field indicates the FCS value used for error detection in the CTX frame 1000.

FIG11 illustrates another example of a CTX frame 1100 structure. In this embodiment, and in conjunction with FIG10 , the STA Information 1030 field does not include an AID or MAC Address 1032 field. Instead, the CTX frame 1000 includes a Group Identifier (GID) 1026 field, which identifies STAs concurrently transmitting uplink data by group identifier (rather than individual identifiers). FIG12 illustrates another example of a CTX frame 1200 structure. In this embodiment, and in conjunction with FIG11 , the GID 1026 field is replaced by the RA 1014 field, which identifies the STA group by a multicast MAC address.

13 is a diagram illustrating an example of the structure of a CTX frame 1300. In this embodiment, the CTX frame 1300 is a management frame that includes a management MAC header 1305 field, a body 1310 field, and an FCS 1380 field. The body 1310 field includes an IE ID 1315 field identifying an information element (IE), a LEN 1320 field indicating the length of the CTX frame 1300, a CTRL 1325 field including the same information as the CTRL 1020 field, a PPDU Duration 1330 field indicating the duration of the subsequent UL-MU-MIMO PPDU that the user terminal 120 is allowed to transmit, a STA Information 1 1335 field, and an MCS 1375 field that may indicate the MCS to be used by all STAs in subsequent UL-MU-MIMO transmissions or an MCS backoff to be used by all STAs in subsequent UL-MU-MIMO transmissions. The STA Information 1 1335 (together with the STA Information N 1370) field represents per-STA fields, which include an AID 1340 field identifying the STA, a Number of Spatial Streams field (Nss) 1342 field indicating the number of spatial streams the STA can use (in a UL-MU-MIMO system), a Time Adjustment 1344 field indicating when the STA should adjust its transmission time compared to the reception of a trigger frame (CTX in this case), a Power Adjustment 1348 field indicating when the STA should power back off from the declared transmit power, a Tone Assignment 1348 field indicating the tones or frequencies the STA can use (in a UL-FDMA system), an Allowed TIDs 1350 field indicating the allowable TIDs, and a TX Start Time field 1048 indicating the start time when the STA transmits uplink data.

In one embodiment, CTX frames 1000 or 1300 may be aggregated into an A-MPDU to provide user terminal 120 with time to process before transmitting an UL signal. In this embodiment, padding or data may be added after the CTX to allow user terminal 120 additional time to process the incoming packet. One benefit of padding the CTX frame, compared to increasing the interframe space (IFS) as described above, may be to avoid potential contention issues with UL signals from other user terminals 120. In one aspect, if the CTX is a management frame, an additional padding information element (IE) may be sent. In one aspect, if the CTX is aggregated into an A-MPDU, an additional A-MPDU padding delimiter may be included. The padding delimiter may be an EoF delimiter (4 bytes) or other padding delimiter. In another aspect, padding may be implemented by adding data, control, or management MPDUs, as long as these MPDUs do not need to be processed within the IFS response time. The MPDU may include an indication to the receiver that an immediate response is not required and that any subsequent MPDUs will not require an immediate response. In another aspect, user terminal 120 may request a minimum duration of the CTX frame or padding from AP 110. In another embodiment, padding may be implemented by adding PHY OFDMA symbols that may include undefined bits that carry no information or may include sequences of bits that carry information as long as they do not need to be processed within the IFS time.

In some embodiments, AP 110 may initiate a CTX transmission. In one embodiment, AP 110 may send CTX message 402 according to a conventional Enhanced Distributed Channel Access (EDCA) contention protocol. In another embodiment, AP 110 may send CTX message 402 at a scheduled time. In this embodiment, AP 110 may indicate the scheduled time to user terminals 120 using a restricted access window (RAW) indication in the beacon that indicates a time reserved for a group of user terminals 120 to access the medium, a target wake time (TWT) agreement with each user terminal 120 that instructs multiple user terminals 120 to wake up at the same time to participate in UL-MU-MIMO transmissions, or information in other fields. Outside of the RAW and TWT, user terminals 120 may be allowed to transmit any frames, or only a subset of frames (e.g., non-data frames). User terminals 120 may also be prohibited from transmitting certain frames (e.g., they may be prohibited from transmitting data frames). User terminals 120 may also indicate that they are in a dormant state. One advantage of scheduled CTX is that multiple user terminals 120 may be instructed the same TWT or RAW time and may receive transmissions from the AP 110 .

14 is a flow diagram of an exemplary wireless communication method 1400 in accordance with certain embodiments described herein. One of ordinary skill in the art will recognize that the method 1400 may be implemented by any suitable device and system.

In operation block 1405, the method 1400 includes transmitting a clear-to-transmit (CTX) message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message also including a request for the two or more stations to concurrently transmit uplink data at a specific time. In operation block 1410, the method 1400 also includes receiving a plurality of uplink data from at least two stations at the specific time.

In some embodiments, an apparatus for wireless communication may perform some of the functions of method 1400. The apparatus includes means for transmitting a clear-to-transmit (CTX) message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message also including a request for the two or more stations to concurrently transmit uplink data at a specific time. The apparatus may also include means for receiving a plurality of uplink data transmissions from at least two stations at the specific time.

Those skilled in the art will understand that information and signals may be represented using any of a variety of different techniques and technologies. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Various modifications to the implementations described in this disclosure may be apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, this disclosure is not intended to be limited to the implementations shown herein, but rather to be accorded the broadest scope consistent with the claims, the principles disclosed herein, and the novel features. The word "exemplary" is used specifically herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as superior or preferred over other implementations.

Certain features described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable subcombination. Furthermore, while features may be described above as functioning in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be omitted from that combination, and a claimed combination may be directed to a subcombination, or variations of a subcombination.

The various operations of the methods described above may be performed by any suitable means capable of performing these operations, such as various hardware and/or software components, circuits, and/or modules. Generally speaking, any operation illustrated in the figures may be performed by corresponding functional means capable of performing these operations.

The various illustrative logical blocks, modules, and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

In one or more aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted via a computer-readable medium as one or more instructions or code. Computer-readable media include both computer storage media and communication media, including any medium that facilitates the transfer of a computer program from one location to another. A storage medium may be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Any connection is also properly referred to as a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwaves, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves are included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wherein disk often reproduces data magnetically while disc reproduces data optically with laser. Thus, in some aspects, computer-readable media may include non-transitory computer-readable media (e.g., tangible media). Additionally, in some aspects, computer-readable media may include transient computer-readable media (e.g., signals). The above combinations should also be included within the scope of computer-readable media.

The methods disclosed herein include one or more steps or actions for implementing the described methods. These method steps and/or actions may be interchangeable with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of the specific steps and/or actions may be modified without departing from the scope of the claims.

In addition, it should be appreciated that the modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by the user terminal and/or base station where applicable. For example, such a device can be coupled to a server to facilitate the transfer of the means for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage device (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.) so that once the storage device is coupled to or provided to the user terminal and/or base station, the device can obtain the various methods. In addition, any other suitable technology suitable for providing the methods and techniques described herein to a device may be utilized.

While the foregoing is directed to various aspects of the present disclosure, other and further aspects of the disclosure may be devised without departing from the basic scope thereof, the scope of which is determined by the claims that follow.

Claims (29)

1. An apparatus for wireless communication, comprising: A transmitter configured to send a Clear Transmission CTX message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request from the two or more stations to concurrently transmit uplink data at a specific time, wherein the CTX message includes a duration field of Physical Layer Convergence Protocol (PLCP) Protocol Data Units (PPDUs) indicating the duration of multiple uplink data transmissions permitted for transmission by the two or more stations; and A receiver configured to receive the plurality of uplink data transmissions from at least two of the two or more stations at the specified time. 2. The apparatus of claim 1, wherein the uplink transmission opportunity has a common duration for each of the plurality of uplink data transmissions. 3. The apparatus as claimed in claim 1, wherein the specific time is the short inter-frame interval (SIFS) or point inter-frame interval (PIFS) time after the end of the transmission of the message. 4. The apparatus of claim 1, wherein the receiver is further configured to receive a plurality of clear transmission CTS messages having a common scrambling sequence after the transmission of the CTX message has ended and before the plurality of uplink data has been received. 5. The apparatus of claim 1, wherein the CTX message includes one or more station STA information fields for a specific station. 6. The apparatus of claim 5, wherein the one or more station STA information fields include an indication of the allowed transmission modes. 7. The apparatus of claim 6, wherein the indication of the permitted transmission mode includes one or more of the following: short/long guard interval (GI) or cyclic prefix mode, binary convolutional code (BCC)/low-density parity check (LDPC) mode, and space-time block coding (STBC) mode. 8. The apparatus of claim 5, wherein the one or more station (STA) information fields include a frequency modulation (FM) allocation field, the FM allocation field indicating the frequency modulation and/or frequency used for transmitting uplink data using a frequency division multiple access (FDMA) system and/or an orthogonal FDMA system. 9. The apparatus of claim 5, wherein the one or more STA information fields include a transmission start time field indicating the start time of uplink data transmission. 10. The apparatus of claim 5, wherein the one or more STA information fields include one or more of the following: address identifier field, number and index of spatial streams, time adjustment field, power adjustment field, allowed traffic identifier field, and modulation and coding scheme field. 11. The apparatus of claim 1, wherein the CTX message includes a group identifier (GID) field indicating two or more stations as a group of stations concurrently transmitting uplink data at the specified time. 12. The apparatus of claim 1, wherein the CTX message includes a receiver address RA field indicating the unicast or multicast addresses of the two or more stations concurrently transmitting uplink data at the specified time. 13. The apparatus of claim 1, wherein the CTX message includes a field indicating data rate information about the two or more stations that are concurrently transmitting uplink data at the specified time. 14. The apparatus of claim 1, wherein the CTX message includes one or more of a frame control field, a transmitter address field, a duration field, and a Basic Service Set Identifier (BSSID) field. 15. The apparatus of claim 1, wherein the CTX message comprises a management frame or a control frame. 16. The apparatus of claim 1, wherein the receiver is further configured to receive a request to transmit uplink data from the two or more stations. 17. The apparatus of claim 16, wherein the request to transmit uplink data includes a request to send an RTS message, a request to transmit an RTX message, a power saving PS polling message, or a quality of service (QoS) null message. 18. The apparatus of claim 16, wherein the transmitter is further configured to transmit a second CTX message in response to the request to transmit uplink data, the second CTX message indicating that the request to transmit uplink data has been received, but excluding the uplink transmission opportunity. 19. The apparatus of claim 1, wherein the transmitter is further configured to transmit the CTX message aggregated with the second message. 20. A method for wireless communication, comprising: A Clear Transmission CTX message is sent to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request from the two or more stations to concurrently transmit uplink data at a specific time, wherein the CTX message includes a duration field of Physical Layer Convergence Protocol (PLCP) Protocol Data Units (PPDUs) indicating the duration of multiple uplink data transmissions permitted for the two or more stations to send; and The plurality of uplink data transmissions are received from at least two of the two or more stations at the specified time. 21. The method of claim 20, wherein the CTX message includes a receiver address RA field indicating the unicast or multicast addresses of the two or more stations concurrently transmitting uplink data at the specific time, wherein the CTX message further includes one or more station STA information fields. 22. The method as described in claim 20, wherein the one or more STA information fields include one or more of the following: address identifier field, spatial stream quantity field, time adjustment field, power adjustment field, allowed traffic identifier field, and modulation and coding scheme field. 23. The method of claim 20, further comprising transmitting the CTX message aggregated with the second message. 24. A device for wireless communication, comprising: Means for transmitting a clear transmission CTX message to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request from the two or more stations to concurrently transmit uplink data at a specific time, wherein the CTX message includes a duration field of a Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) indicating the duration of multiple uplink data transmissions permitted for transmission by the two or more stations; and A means for receiving the plurality of uplink data transmissions from at least two of the two or more stations at the specified time. 25. The device of claim 24, wherein the CTX message further includes a receiver address RA field indicating the unicast or multicast addresses of the two or more stations concurrently transmitting uplink data at the specific time. 26. The device as claimed in claim 24, wherein the CTX message includes one or more STA information fields, the STA information fields including one or more of the following: address identifier field, spatial stream quantity field, time adjustment field, power adjustment field, allowed traffic identifier field, modulation and coding scheme field, indication of allowed transmission mode, and frequency modulation allocation field. 27. A non-transitory computer-readable medium including instructions that, when executed, cause a processor to perform a method comprising: A Clear Transmission CTX message is sent to two or more stations, the CTX message indicating an uplink transmission opportunity, the CTX message further including a request from the two or more stations to concurrently transmit uplink data at a specific time, wherein the CTX message includes a duration field of Physical Layer Convergence Protocol (PLCP) Protocol Data Units (PPDUs) indicating the duration of multiple uplink data transmissions permitted for the two or more stations to send; and The plurality of uplink data transmissions are received from at least two of the two or more stations at the specified time. 28. The medium of claim 27, wherein the method further comprises receiving a plurality of clear transmission CTS messages having a common scrambling sequence at a time after the transmission of the CTX message has ended and before the plurality of uplink data have been received. 29. The medium of claim 27, wherein transmitting the CTX message includes transmitting the CTX message in response to a request to transmit uplink data.