Patent Description:
Next generation Wireless Local Area Networks (WLANs) will be deployed in high-density environments that include multiple access points providing wireless access to large numbers of mobile stations in the same geographical area. Next-generation WLANs will also need to simultaneously support various traffic types having diverse quality of service (QoS) requirements, as mobile devices are increasingly used to access streaming video, mobile gaming, and other services. Institute of Electrical and Electronics Engineers (IEEE) <NUM>. 11ax is being developed to address these challenges, and is expected to provide up to four times the throughput of IEEE <NUM>. 11ac networks.

Due to high proficiency with high bandwidth efficiency, orthogonal frequency division multiplexing (OFDM) has been selected for WLAN communication systems. Nevertheless, OFDM suffers from Carrier Frequency Offset (CFO). CFO has been recognized as a major disadvantage of OFDM. CFO can lead to the frequency mismatch in transmitter and receiver oscillator. Lack of the synchronization, of the local oscillator signal for down conversion in the receiver, with the carrier signal contained in the received signal, can cause the performance of OFDM to degrade. In other words, the orthogonality of the OFDM relies on the condition that the transmitter and receiver operate with exactly the same frequency reference. If this is not the case, the perfect orthogonality of the subcarrier will be lost, which can result in CFO. One solution to CFO has been proposed by<NPL>. The authors propose joint estimation of multiple CFOs and Subcarrier Frequency Offsets in the uplink of OFDM/SDMA (space division multiple access) systems. In Häring's paper traffic from different users is spatially multiplexed on the same frequency resources. Pilot symbols are proposed for estimation of residual CFO, but on subcarriers which are time-division multiplexed with data, and shared with other stations transmitting over the same frequencies. Methods are desired which enable more accurate and frequent pilot symbol phase estimation and work within the framework of Orthogonal Frequency Division Multiple Access (OFDMA).

Technical advantages are generally achieved, by embodiments of this disclosure which describe an apparatus and a method for OFDMA tone allocation in the next generation Wi-Fi networks.

The making and using of 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. OFDMA tone allocations are discussed in <CIT>.

IEEE <NUM>. 11ax networks will utilize OFDMA for uplink transmissions such that different resource units (RUs) of a single OFDMA frame are communicated by different mobile devices. Notably, RUs transmitted by different mobile devices may not be completely aligned in the frequency domain, which may result in loss of orthogonality among subcarriers. Aspects of this disclosure include pilot symbols in resource units (RUs) of uplink OFDMA frames in order to allow access points (APs) to perform residual carrier frequency offset compensation upon reception. Access points perform residual frequency offset compensation by tracking a phase of symbols in the RUs based on pilots carried in the respective RUs. In some embodiments, a single pilot is carried in each RU. In other embodiments, multiple pilots are carried in each RU. In one example, the uplink OFDMA frame carries a fourteen tone RU consisting of <NUM> data tones and <NUM> pilot tones. In another example, the uplink OFDMA frame carries a sixteen tone RU consisting of <NUM> data tones and <NUM> pilot tones. In yet another embodiment, the uplink OFDMA frame carries a twenty-eight tone RU consisting of <NUM> data tones and <NUM> pilot tones.

Aspects of this disclosure provide embodiment OFDMA frame tone allocations for IEEE <NUM>. 11ax networks. In one embodiment, an OFDMA frame includes a <NUM>-tone payload consisting of <NUM> data and pilot tones and <NUM> null tones. The <NUM> null tones consist of guard tones and at least one direct current (DC) tone. In one example, the <NUM>-tone payload consists of <NUM> data tones, <NUM> common pilot tones, and <NUM> null tones. In another example, the <NUM>-tone payload consists of <NUM> data tones, <NUM> common pilot tones, and <NUM> null tones. In yet another example, the <NUM>-tone payload may consist of <NUM> data tones, <NUM> common pilot tones, and <NUM> null tones. The OFDMA frame may be a downlink OFDMA frame or an uplink OFDMA frame.

In another embodiment, an OFDMA frame includes a <NUM>-tone payload consisting of <NUM> data and pilot tones and <NUM> null tones. In one example, the <NUM>-tone payload consists of <NUM> data tones, <NUM> common pilot tones, and <NUM> null tones. In another example, the <NUM>-tone payload consists of <NUM> data tones, <NUM> common pilot tones, and <NUM> null tones. In yet another example, the <NUM>-tone payload consists of <NUM> data tones, <NUM> common pilot tones, and <NUM> null tones. The OFDMA frame is a downlink OFDMA frame or an uplink OFDMA frame. These and other aspects are described in greater detail below.

<FIG> illustrates a wireless network <NUM> for communicating data. The wireless network <NUM> includes an access point (AP) <NUM> having a coverage area <NUM>, a plurality of mobile devices <NUM>, and a backhaul network <NUM>. The AP <NUM> may comprise any component capable of providing wireless access by, among other things, establishing uplink (dashed line) and/or downlink (dotted line) connections with the mobile devices <NUM>, such as a base station, an enhanced base station (eNB), a femtocell, and other wirelessly enabled devices. The mobile devices <NUM> may comprise any component capable of establishing a wireless connection with the AP <NUM>, such as a mobile station (STA), or other wirelessly enabled devices. The backhaul network <NUM> may be any component or collection of components that allow data to be exchanged between the AP <NUM> and a remote end. In some embodiments, there may be multiple such networks, and/or the network may comprise various other wireless devices, such as relays, low power nodes, etc..

Aspects of this disclosure include separate pilot signals in RUs carried in uplink orthogonal frequency division multiple access (OFDMA) frames. <FIG> illustrates an uplink OFDMA frame <NUM> carrying a plurality of RUs <NUM>, <NUM>, <NUM> each of which includes one or more separate pilot tones <NUM>, <NUM>, <NUM>, respectively. At least some of the RUs <NUM>, <NUM>, <NUM> are transmitted by different mobile stations. It should be appreciated that the number of RUs carried in an OFDMA frame may depend on characteristics (e.g., sizes) of the OFDMA frame and/or the RUs. The separate pilot tones <NUM>, <NUM>, <NUM> are dedicated to the corresponding RU <NUM>, <NUM>, <NUM>. In some embodiments, each of the RUs <NUM>, <NUM>, <NUM> carry a single pilot tone. In other embodiments, at least one of the RUs <NUM>, <NUM>, <NUM> carry multiple pilot tones. In some implementations, different RUs <NUM>, <NUM>, <NUM> carry different numbers of pilot tones. The access point (AP) receiving the uplink OFDMA frame <NUM> will perform residual carrier frequency offset estimation on the uplink OFDMA frame <NUM> in accordance with the separate pilot tone(s) <NUM>, <NUM>, <NUM> carried by the respective RUs <NUM>, <NUM>, <NUM>.

<FIG> illustrates a diagram of an embodiment tone allocation scheme for a <NUM>-tone payload <NUM> of an OFDMA frame to be communicated over a <NUM> frequency channel. The OFDMA frame is a downlink OFDMA frame or an uplink OFDMA frame. As shown, the <NUM>-tone payload <NUM> includes data and pilot tones <NUM>, as well as null tones <NUM>. The null tones <NUM> consist of guard tones and at least one direct current (DC) tone. The guard tones may prevent overlapping of OFDMA symbols and reduce intersymbol interference. The guard tone(s) may be located on the first and/or last subcarrier(s) and DC tones may be located around or near a center subcarrier of the OFDMA frame. The data and pilot tones <NUM> are partitioned into a plurality of resource units (RUs) <NUM>.

In an embodiment, the <NUM>-tone payload <NUM> consists of <NUM> data and pilot tones <NUM> and <NUM> null tones <NUM>. In one example, the <NUM> data and pilot tones <NUM> consists of <NUM> data tones and <NUM> common pilot tones. In another example, the <NUM> data and pilot tones <NUM> consists of <NUM> data tones and <NUM> common pilot tones. In yet another example, the <NUM> data and pilot tones <NUM> consists of <NUM> data tones and <NUM> common pilot tones.

In another embodiment, the <NUM>-tone payload <NUM> consists of <NUM> data and pilot tones <NUM> and <NUM> null tones <NUM>. In one example, the <NUM> data and pilot tones <NUM> consists of <NUM> data tones and <NUM> common pilot tones. In another example, the <NUM> data and pilot tones <NUM> consists of <NUM> data tones and <NUM> common pilot tones. In yet another example, the <NUM> data and pilot tones <NUM> consists of <NUM> data tones and <NUM> common pilot tones.

At least some of the data and pilot tones <NUM> are partitioned into one or more resource units (RUs) <NUM>, which are distributed over the OFDMA frame <NUM>. <FIG> illustrates a diagram of an embodiment tone allocation scheme for an OFDMA resource unit (RU) <NUM>. As shown, the OFDMA RU <NUM> comprises data tones <NUM> and pilot tones <NUM>. In one embodiment, the OFDMA RU <NUM> is a fourteen tone RU consisting of <NUM> data tones <NUM> and <NUM> pilot tones <NUM>. In yet another embodiment, the OFDMA RU <NUM> is a twenty-eight tone RU consisting of <NUM> data tones <NUM> and <NUM> pilot tones <NUM>.

<FIG> illustrates a flowchart of an embodiment method <NUM> for receiving uplink OFDMA frames, as is performed by an access point (AP). As shown, the method <NUM> begins at step <NUM>, where the AP receives an OFDMA frame carrying RUs communicated by different mobile stations. Each of the RUs carries a separate pilot signal. Next, the method <NUM> proceeds to step <NUM>, where the AP performs residual carrier frequency offset estimation on the uplink OFDMA frame in accordance with the pilot signals carried by each of the RUs. Residual frequency offset compensation includes estimating a carrier frequency offset based on dedicated pilots carried in OFDMA transmissions. For uplink (UL) OFDMA transmissions, residual carrier frequency offset compensation allows the access point to track a phase of each symbol based on pilots carried in resource units (RUs).

Notably, residual carrier frequency offset compensation may also be performed on downlink (DL) OFDMA transmissions based on pilots carried in OFDM symbols. Residual carrier frequency offset compensation may be represented by the following formula: Yn,k = HkPn,kej<NUM>πnε, where Y is the received signal, n is the symbol index, k is the subcarrier index where pilots are located, H is the channel, P is the pilot, and ε is the residual carrier frequency offset. In an embodiment, residual carrier frequency offset compensation may be performed according to the following formula: <MAT>, where <MAT>.

As <NUM> in TGax adopts OFDMA as the new spectrum utilization method, techniques for setting the granularity on the minimum resource units (RUs) in the frequency domain are needed. Initial tone allocations for the various possible combinations of granularity were proposed in <CIT>. Aspects of this disclosure provide additional tone allocation design/patterns.

Embodiments of this disclosure set the tone allocation of an OFDM symbol with <NUM> FFT per <NUM>. The proposal in <CIT> set the number of guard tones at twenty-seven and the DC null at one for <NUM> FFT per <NUM>, thereby providing <NUM> available tones for data and pilot signals. In some implementations, <NUM> tones may not have been enough tones to support the number of pilots in an OFDMA symbol or a RU. Aspects of this disclosure provide an alternative tone allocation.

In DL OFDMA, there may be four, six, or eight pilots. For UL OFDMA, there are one or more pilots (e.g., one pilot, two pilots, etc.) for each RU. Aspects of this disclosure provide <NUM> tones available for data and pilots, with thirty-two tones being reserved for guard tones and DC null tones. If <NUM> data and pilot tones are provided for DL OFDMA, then it is possible to support four, six, or eight pilots in a <NUM> OFDMA symbol, with <NUM>, <NUM>, or <NUM> tones being available for carrying data. In some embodiments, the input and output bits at the channel encoder are integer multiples for some or all MCS cases.

As for the UL OFDMA, pilots are provided for every RU. When there are sixteen RUs per <NUM> OFDMA symbol, then fourteen tones( e.g., twelve data tones and two pilot tones) may be provided for each RU. When there are fourteen RUs per <NUM> OFDMA symbol, then sixteen tones (e.g., fourteen data tones and two pilot tones) may be provided for each RU. When there are eight RUs per <NUM> OFDMA symbol, then twenty-eight tones (e.g., twenty-six data tones and two pilot tones) may be provided for each RU. Other combinations are also possible.

<FIG> illustrates an input/output configuration of an IFFT module. The input/output configuration of the inverse FFT (IFFT) module may be updated based on the proposed tone assignments described above. Embodiments of this disclosure provide an input/output configuration of the IFFT module for <NUM> FFT per <NUM> under the <NUM>. 11ac TX spectral mask for the tone allocation proposed by this disclosure.

<FIG> illustrates a block diagram of an embodiment processing system <NUM> for performing methods described herein, which may be installed in a host device. As shown, the processing system <NUM> includes a processor <NUM>, a memory <NUM>, and interfaces <NUM>-<NUM>, which may (or may not) be arranged as shown in <FIG>. The processor <NUM> may be any component or collection of components adapted to perform computations and/or other processing related tasks, and the memory <NUM> may be any component or collection of components adapted to store programming and/or instructions for execution by the processor <NUM>. In an embodiment, the memory <NUM> includes a non-transitory computer readable medium. The interfaces <NUM>, <NUM>, <NUM> may be any component or collection of components that allow the processing system <NUM> to communicate with other devices/components and/or a user. For example, one or more of the interfaces <NUM>, <NUM>, <NUM> may be adapted to communicate data, control, or management messages from the processor <NUM> to applications installed on the host device and/or a remote device. As another example, one or more of the interfaces <NUM>, <NUM>, <NUM> may be adapted to allow a user or user device (e.g., personal computer (PC), etc.) to interact/communicate with the processing system <NUM>. The processing system <NUM> may include additional components not depicted in <FIG>, such as long term storage (e.g., non-volatile memory, etc.).

In some embodiments, the processing system <NUM> is included in a network device that is accessing, or part otherwise of, a telecommunications network. In one example, the processing system <NUM> is in a network-side device in a wireless or wireline telecommunications network, such as a base station, a relay station, a scheduler, a controller, a gateway, a router, an applications server, or any other device in the telecommunications network. In other embodiments, the processing system <NUM> is in a user-side device accessing a wireless or wireline telecommunications network, such as a mobile station, a user equipment (UE), a personal computer (PC), a tablet, a wearable communications device (e.g., a smartwatch, etc.), or any other device adapted to access a telecommunications network.

In some embodiments, one or more of the interfaces <NUM>, <NUM>, <NUM> connects the processing system <NUM> to a transceiver adapted to transmit and receive signaling over the telecommunications network. <FIG> illustrates a block diagram of a transceiver <NUM> adapted to transmit and receive signaling over a telecommunications network. The transceiver <NUM> may be installed in a host device. As shown, the transceiver <NUM> comprises a network-side interface <NUM>, a coupler <NUM>, a transmitter <NUM>, a receiver <NUM>, a signal processor <NUM>, and a device-side interface <NUM>. The network-side interface <NUM> may include any component or collection of components adapted to transmit or receive signaling over a wireless or wireline telecommunications network. The coupler <NUM> may include any component or collection of components adapted to facilitate bi-directional communication over the network-side interface <NUM>. The transmitter <NUM> may include any component or collection of components (e.g., up-converter, power amplifier, etc.) adapted to convert a baseband signal into a modulated carrier signal suitable for transmission over the network-side interface <NUM>. The receiver <NUM> may include any component or collection of components (e.g., down-converter, low noise amplifier, etc.) adapted to convert a carrier signal received over the network-side interface <NUM> into a baseband signal. The signal processor <NUM> may include any component or collection of components adapted to convert a baseband signal into a data signal suitable for communication over the device-side interface(s) <NUM>, or vice-versa. The device-side interface(s) <NUM> may include any component or collection of components adapted to communicate data-signals between the signal processor <NUM> and components within the host device (e.g., the processing system <NUM>, local area network (LAN) ports, etc.).

Claim 1:
A method for receiving an uplink frame(<NUM>) in a wireless communication system, the method comprising:
Receiving (<NUM>), by an access point, AP(<NUM>), an uplink orthogonal frequency division multiple access, OFDMA, frame(<NUM>), wherein the uplink OFDMA frame comprises a payload(<NUM>), the payload comprising one or more OFDMA symbols,
each of the one or more OFDMA symbols comprising <NUM> tones per <NUM> of channel bandwidth including data tones and dedicated pilot tones(<NUM>), the data tones and dedicated pilot tones(<NUM>) being partitioned into a plurality of resource units, RUs(<NUM>), the resource units(<NUM>) communicated by at least two different mobile stations(<NUM>),
wherein each of the RUs(<NUM>, <NUM>, <NUM>) in each OFDMA symbol carries at least two dedicated pilot tones(<NUM>, <NUM>, <NUM>); and
performing (<NUM>) residual carrier frequency offset compensation by tracking a phase of pilot symbols in each RU of each payload OFDMA symbol based on the at least two dedicated pilot tones carried in each respective RU, wherein the residual carrier frequency offset compensation includes estimating a residual carrier frequency offset based on the at least two dedicated pilot tones carried in each respective RU.