The present invention relates to network communications, and, in particular embodiments, to a system and method for WLAN OFDMA design of uplink and downlink transmissions.
Wireless Local Area Networks (WLANs) commonly operate in unlicensed spectrum bands. Rules for operation in these bands force competing devices to share the available resources and defer their intended transmissions when the medium is sensed busy. The medium refers to the transmission channel or bandwidth shared by multiple components of the WLAN to transmit uplink and downlink signals. The bandwidth (or frequency range) is shared for uplink and downlink transmissions. Typically, a WLAN uses an Orthogonal Frequency-Division Multiplexing (OFDM) transmission format in which all transmission resources are assigned to a single device. Random assignment is commonly achieved using carrier sense multiple access with collision avoidance (CSMA/CA). With CSMA/CA a device wins access to the medium, transmits its data up to a pre-defined period of time, and then gives up the medium for other devices to compete for transmission. In contrast, Orthogonal Frequency Division Multiple Access (OFDMA) is a transmission and access mechanism that accommodates multiple-user transmissions simultaneously. OFDMA is commonly implemented in wireless infrastructures operating in the licensed bands in order to meet timing information in terms of frame structure and the scheduling of resources among a subset of users. There is a need for efficient schemes for implementing OFDMA in WLANs.
In accordance with an embodiment, a method by an access point (AP) for Orthogonal Frequency Division Multiple Access (OFDMA) downlink transmission in a Wireless Local Area Network (WLAN) includes sending a signaling requesting protection of a transmission channel for downlink transmissions from access by stations (STAs) associated with the AP. The method further includes sending an OFDMA physical layer Protocol Data Unit (PPDU) to the STAs, and sending a Block Acknowledgement Request (BAR) to the STAs. In return, a Block Acknowledgement (BA) is received from each one of the STAs.
In accordance with another embodiment, a method by an STA for OFDMA downlink transmission in a WLAN includes detecting a signaling from an AP. The signaling indicates the AP requesting protection of a transmission channel from access by a plurality of STAs associated with the AP including the STA. The method further includes receiving, from the AP an OFDMA PPDU, and receiving, from the AP, a BAR. The BAR is sent to all participating STAs. In return, the STA sends a BA to the AP.
In accordance with another embodiment, a method by a STA for OFDMA uplink transmissions in a WLAN includes sending a signaling requesting protection of a transmission channel from access by an AP of the STA. The method further includes sending, to the AP, a frame indicating start of OFDMA transmission by the STA, and receiving, from the AP, an OFDMA Begin Receive (OBR) frame. The OBR frame is sent by the AP to a plurality of STAs associated with the AP including the STA. The STA then sends, to the AP, an OFDMA PPDU and a BAR after the OFDMA PPDU. In return, the STA receives a BA from the AP.
In accordance with another embodiment, a method by an AP for OFDMA uplink transmission in a WLAN includes detecting a signaling from a STA. The signaling indicates the STA requesting protection of a transmission channel from access by the AP. The method further includes receiving, from the STA, a frame indicating start of OFDMA transmission by the STA, and sending, to a plurality of STAs associated with the AP including the STA, an OBR frame. The AP then receives, from the STA, an OFDMA PPDU followed by a BA, and sends to the STA with a BA.
In accordance with another embodiment, an AP supporting OFDMA transmission in a WLAN comprises a processor and a computer readable storage medium storing programming for execution by the processor. The programming includes instructions to send a signaling requesting protection of a transmission channel from access by STAs associated with the AP, and send an OFDMA PPDU to the STAs. The programming includes further instructions to send a BAR to the STAs, and receive a BA from each one of the STAs.
In accordance with yet another embodiment, a user station supporting OFDMA transmission in a WLAN comprises a processor and a computer readable storage medium storing programming for execution by the processor. The programming includes instructions to send a signaling requesting protection of a transmission channel from access by an AP of the user station, and send, to the AP, a frame indicating start of OFDMA transmission by the STA. The programming includes further instructions to receive, from the AP, an OBR frame which is sent by the AP to a plurality of STAs associated with the AP, and send, to the AP, an OFDMA PPDU. The programming further configure the user station to send a BAR to the AP, and receive a BA from the AP.
The foregoing has outlined rather broadly the features of an embodiment of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
Disclosed herein are system and method embodiments for WLAN OFDMA operations in uplink and downlink transmissions.
The STAs and the AP compete for access to a shared medium, e.g., shared wireless channel bandwidth, symbols, or subcarriers. Access to the medium may be based on random access mechanisms such as carrier sense multiple access with collision avoidance (CSMA/CA) or using a scheduling mechanism that allows the STAs and AP access to the medium at specified or predetermined times. Irrespective of how access to the medium is obtained, a downlink (DL) OFDMA transmission opportunity (TXOP) is obtained when the AP has the right to access the medium and communicates with multiple STAs in a single OFDMA transmission. An uplink (UL) OFDMA TXOP is obtained when a STA gains access to the medium and is ready to start an UL OFDMA TXOP by inviting other STAs to share the available transmission resources, e.g. the subcarriers.
In general, an OFDMA system consists of an integer Nsc of subcarriers defined in a channel of certain bandwidth, W Megahertz (MHz). For example in WLAN, the bandwidth W is usually set to 20 MHz. The subcarrier separation Δf is given by Δf=W/Nsc. The OFDMA symbol duration Ts is given by 1/Δf. The quantity Nsc is set at 64 in WLAN OFDM implementation. With the introduction of OFDMA to WLAN, Nsc may be set to a higher value, such as 256 or 512 to achieve finer granularity. During each OFDMA transmission (uplink or downlink), a number of subcarriers are allocated to each of the users participating in the transmission.
Alternatively, the AP can protect the medium by sending a request-to-send (RTS) message to one of its associated STAs. The STA then responds with a CTS message back to the AP. The RTS and CTS messages are sent using non-HT format. The AP then generates an OFDMA physical layer (PHY) Protocol Data Unit (PPDU) that includes frames destined to a number of STAs. For instance, the recipient STAs can be identified by a group ID (GrpID) in the OFDMA SIG field. The OFDMA resource allocation portion in the SIG field may be determined by any previous suitable packet transmission from the AP to the STAs, instead of using any separate channel sounding for the channel response information per each STA. For example, packets that were used for the contention to access the medium by each STA can also be used to get the channel response of each STA and to determine OFDMA resource allocation portion in the SIG field.
When the transmission of the OFDMA PPDU is finished, the AP requests acknowledgements from those STAs participating in the OFDMA transmission. Specifically, the AP sends Block Acknowledgement Request (BAR) frames using OFDMA, one frame for each of the participating STAs. Each STA responds with a Block ACK (BA) frame according to one of the following scenarios. If UL OFDMA is supported, then the participating STAs use OFDMA to send their BAs in the uplink direction. In this case, timing information for synchronizing the uplink transmissions needs to be propagated from the AP to the STAs. The timing information may be included in the BAR frame by extending the BAR information field.
Alternatively, if UL OFDMA is not supported, then the participating STAs need to send their BA frames in sequence. One way to determine the sequence for sending the BA frames is for the AP to transmit the BAR frames one after the other using non-HT format (e.g., without using OFDMA format). However, this approach produces some overhead. Instead, the AP can send an explicit sequence using some of the reserved bits in the BAR control field in the BAR frame.
The STA then sends an OFDMA Begin Transmission (OBX) frame to the AP. The reception of the OBX frame by the AP is an indication that the STA wishes to start an UL OFDMA TXOP by sharing the medium with other STAs. The AP selects other STAs to participate in the UL OFDMA, e.g., STAx and STAy in
The CPU 910 may comprise any type of electronic data processor. The memory 920 may comprise any type of system memory such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), a combination thereof, or the like. In an embodiment, the memory 920 may include ROM for use at boot-up, and DRAM for program and data storage for use while executing programs. In embodiments, the memory 920 is non-transitory. The mass storage device 930 may comprise any type of storage device configured to store data, programs, and other information and to make the data, programs, and other information accessible via the bus. The mass storage device 930 may comprise, for example, one or more of a solid state drive, hard disk drive, a magnetic disk drive, an optical disk drive, or the like.
The video adapter 940 and the I/O interface 960 provide interfaces to couple external input and output devices to the processing unit. As illustrated, examples of input and output devices include a display 990 coupled to the video adapter 940 and any combination of mouse/keyboard/printer 970 coupled to the I/O interface 960. Other devices may be coupled to the processing unit 901, and additional or fewer interface cards may be utilized. For example, a serial interface card (not shown) may be used to provide a serial interface for a printer.
The processing unit 901 also includes one or more network interfaces 950, which may comprise wired links, such as an Ethernet cable or the like, and/or wireless links to access nodes or one or more networks 980. The network interface 950 allows the processing unit 901 to communicate with remote units via the networks 980. For example, the network interface 950 may provide wireless communication via one or more transmitters/transmit antennas and one or more receivers/receive antennas. In an embodiment, the processing unit 901 is coupled to a local-area network or a wide-area network for data processing and communications with remote devices, such as other processing units, the Internet, remote storage facilities, or the like.
While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.
Number | Date | Country | |
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61917791 | Dec 2013 | US |