WO2025059051A1 - Phase rotation of pilot signals in wireless communication systems - Google Patents

Abstract

A method performed by a device operating in an orthogonal frequency-division multiple access (OFDMA) wireless local area network (WLAN) system includes: generating a physical protocol data unit (PPDU) comprising (i) a preamble and (ii) a data field, where a plurality of resource units (RUs) are allocated for the data field and assigned to a plurality of users, with each user assigned at least one RU comprising at least one pilot subcarrier, applying phase rotations to the at least one pilot subcarrier in the at least one RU of each user, where values of the phase rotations are different for pilot subcarriers in RUs of different users, and transmitting the PPDU to a receiver.

Description

PHASE ROTATION OF PILOT SIGNALS IN WIRELESS COMMUNICATION

SYSTEMS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to U.S. Provisional Application Serial No. 63/537,699, filed on September 11, 2023, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

[0002] The present disclosure generally relates to a wireless communication system.

BACKGROUND

[0003] IEEE 802.11 is a set of standards for wireless LANs, commonly known as Wi-Fi. Several amendments to the IEEE 802.11 standard have introduced Orthogonal Frequency Division Multiplexing (OFDM) as the modulation scheme. OFDM is a multi-carrier modulation technique used in Wi-Fi to transmit data simultaneously on multiple subcarriers.

SUMMARY

[0004] The present disclosure is directed to systems and techniques that apply phase rotations to pilot signals in a wireless communication system that implements Orthogonal Frequency Division Multiple Access (OFDMA) which is based on OFDM. In some implementations, the phase rotations are configured to apply phase rotations to pilot signals of different users. Such features can have various technical benefits, such as reducing a Peak-to-Average Power Ratio (PAPR) of pilot transmissions in a downlink (DL) scenario.

[0005] According to one aspect, a method performed by a device operating in an orthogonal frequency-division multiple access (OFDMA) wireless local area network (WLAN) system, can include generating a physical protocol data unit (PPDU) including (i) a preamble and (ii) a data field, where a plurality of resource units (RUs) are allocated for the data field and assigned to a plurality of users, with each user assigned at least one RU comprising at least one pilot subcarrier, applying phase rotations to the at least one pilot subcarrier in the at least one RU of each user, where values of the phase rotations for pilot subcarriers in RUs are different for at least two of the users, and transmitting the PPDU to a receiver.

[0006] Implementations according to this aspect can include one or more of the following features. For example, the at least one pilot subcarrier can be generated based on the following equation,

where: p_n is a polarity in OFDMA symbol n which is the same for every pilot subcarrier in one OFDMA symbol,

Pn is the pilot subcarrier in OFDMA symbol n on tone k, and

R% is phase rotation applied to the pilot subcarrier in OFDMA symbol n for user u.

[0007] In some implementations, applying the phase rotations can include applying phase rotations to the at least one pilot subcarrier and data subcarriers in the at least one RU of each user, and values of the phase rotations for pilot subcarriers and data subcarriers in RUs are different for at least two of the users. In some implementations, the preamble can include a long training field adjacent to the data field in the PPDU, applying the plurality of phase rotation values can include applying the phase rotations to the at least one pilot subcarrier in the at least one RU and a corresponding long training field of each user, and values of the phase rotations for long training fields and pilot subcarriers in RUs are different for at least two of the users. In some examples, a value of the phase rotation is selected from among a set of real numbers and/or complex numbers. [0008] In some implementations, the at least one pilot subcarrier is generated based on the following equation,

where: p_n is a polarity in OFDMA symbol n which is the same for every pilot subcarrier across alternatesymbol basis,

Pn is the pilot subcarrier in OFDMA symbol n on tone k, and

Rn is phase rotation applied to the pilot subcarrier in OFDMA symbol n for user u.

[0009] According to another aspect, a method performed by a device operating in an orthogonal frequency-division multiple access (OFDMA) a wireless local area network (WLAN) system can include generating a physical protocol data unit (PPDU) including (i) a preamble and (ii) a data field, where a plurality of resource units (RUs) are allocated for the data field and assigned to a plurality of users, with each user assigned at least one RU comprising at least one pilot subcarrier, applying phase rotations to the at least one at least one pilot subcarrier in the at least one RU per 20 MHz band, where values of the phase rotations for pilot subcarriers in RUs are different for at least two 20 MHz bands, and transmitting the PPDU.

[0010] Implementations according to this aspect can include one or more of the following features. For example, applying the phase rotations can include applying the phase rotations to data subcarriers and the at least one pilot subcarrier per 20 MHz band, and values of the phase rotations for data subcarriers and pilot subcarriers in RUs are different for at least two 20 MHz bands.

[0011] In some examples, a value of the phase rotation is selected from among a set of real numbers and/or complex numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a diagram illustrating an example of network environment.

[0013] FIG. 2A is a diagram illustrating an example of a PPDU implemented in an IEEE 802.11 -based system.

[0014] FIG. 2B is a diagram illustrating another example of a PPDU implemented in an IEEE 802.11 -based system.

[0015] FIG. 3 A is a diagram illustrating an example of portions of a PPDU to which different phase rotations are applied, according to an implementation of the present disclosure.

[0016] FIG. 3B is a diagram illustrating an example of portions of a PPDU to which different phase rotations are applied, according to another implementation of the present disclosure.

[0017] FIG. 4 is a flowchart showing an example transmission procedure.

DETAILED DESCRIPTION

[0018] Implementations described in the present disclosure may be applied to various wireless communication systems. For example, implementations of the present disclosure may be applied to a wireless local area network (WLAN) system. In some implementations, the WLAN implements technologies that are consistent with one or more IEEE 802.11 standards, such as the IEEE 802.1 la/g/n/ac standard, the IEEE 802.1 lax standard, and/or the IEEE 802.11be standard. In general, implementations of the present disclosure may be applied to other types of wireless communication systems and are not limited to a particular technical standard. [0019] FIG. 1 is a diagram illustrating an example of wireless network environment 100. The wireless network environment 100 can include a first device 110 and a second device 120.

[0020] The devices 110 and 120 can implement various types of devices in the wireless network 100. For example, one or more of devices 110 and 120 can implement a mobile device, which can also be referred to as a mobile terminal, a station (ST A), a wireless transmit/ receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit, a user, or the like. In addition, one or more of devices 110 and 120 can implement other types of devices, such as a network, an access point (AP), a base station (BS), a node-B, a repeater, a router, a relay, or the like. The devices 110 and 120 can also be referred to with other terminology such as a receiving apparatus, a transmitting apparatus, a receiving STA, a transmitting STA, a transmitting AP, a receiving AP, a receiving device, a transmitting device, or the like.

[0021] In some implementations, the devices 110 and 120 can serve as an AP or a non-AP. For example, the devices 110 and 120 can serve as the AP and/or the non-AP.

[0022] In some scenarios, the devices 110 and 120 can support various communication standards in addition to the IEEE 802.11 standard. For example, a communication standard (e.g., LTE, LTE-A, 5G NR standard) or the like based on the 3GPP family of standards may be supported. In addition, the devices 110 and 120 can be implemented as various types of devices such as a mobile phone, a vehicle, a personal computer, or the like. In addition, the devices 110 and 120 can support communication for various communication services such as voice calls, video calls, data communication, and self-driving (autonomous-driving), or the like.

[0023] The devices 110 and 120 can be configured to communicate with each other via one or more communications networks wirelessly or wired. The communication network can include, but not limited to, any one of a combination of different types of suitable communications networks such as, for example, broadcasting networks, cable networks, public networks (e.g., the Internet), private networks, wireless networks, cellular networks, or any other suitable private and/or public networks. Further, the communications networks can have any suitable communication range associated therewith and may include, for example, global networks (e.g., the Internet), metropolitan area networks (MANs), wide area networks (WANs), local area networks (LANs), or personal area networks (PANs). In addition, the communications networks can include any type of medium over which network traffic may be carried including, but not limited to, coaxial cable, twisted-pair wire, optical fiber, a hybrid fiber coaxial (HFC) medium, microwave terrestrial transceivers, radio frequency communication mediums, white space communication mediums, ultra-high frequency communication mediums, satellite communication mediums, or any combination thereof.

[0024] The devices 110 and 120 can include one or more communications antennas. The one or more communications antennas can be any suitable type of antennas corresponding to the communications protocols used by the devices 110 and 120. Some non-limiting examples of suitable communications antennas include Wi-Fi antennas, IEEE 802.11 family of standards compatible antennas, directional antennas, non-directional antennas, dipole antennas, folded dipole antennas, patch antennas, multiple-input multiple-output (MIMO) antennas, omnidirectional antennas, quasi-omnidirectional antennas, or the like. The one or more communications antennas may be communicatively coupled to a radio component to transmit and/or receive signals, such as communications signals to and/or from the devices 110 and 120.

[0025] The devices 110 and 120 can be configured to perform directional transmission and/or directional reception in conjunction with wirelessly communicating in a wireless network. The devices 110 and 120 can be configured to perform such directional transmission and/or reception using a set of multiple antenna arrays (e.g., DMG antenna arrays or the like). Each of the multiple antenna arrays can be used for transmission and/or reception in a particular respective direction or range of directions. The devices 110 and 120 can be configured to perform any given directional transmission towards one or more defined transmit sectors. The devices 110 and 120 can be configured to perform any given directional reception from one or more defined receive sectors.

[0026] In some implementations, MIMO beamforming in a wireless network can be accomplished using RF beamforming and/or digital beamforming. In performing a given MIMO transmission, the devices 110 and 120 can be configured to use all or a subset of its one or more communications antennas to perfomi MIMO beamforming.

[0027] The devices 110 and 120 can include a medium access control (MAC) conforming to the IEEE 802.11 standard and a physical layer interface for a radio medium.

[0028] The first device 110 may include a processor 111, a memory 112, and a transceiver 113. The processor 111, memory 112, and transceiver 113 can be implemented individually as separate chips, or at least two blocks/functions can be implemented through a single chip. [0029] The transceiver 113 of the first device 110 can perform a signal transmission/reception operation. For example, an IEEE 802.11 packet (e.g., IEEE 802.1 la/b/g/n/ac/ax/be, etc.) can be transmitted/received.

[0030] The transceiver 113 can refer to any suitable radio and/or transceiver for transmitting and/or receiving radio frequency (RF) signals in the bandwidth and/or channels corresponding to the communications protocols utilized by the first device 110 to communicate with the second device 120. The radio components may include hardware and/or software to modulate and/or demodulate communications signals according to pre-established transmission protocols. The radio components may further have hardware and/or software instructions to communicate via one or more Wi-Fi and/or Wi-Fi direct protocols, as standardized by the IEEE 802.11 standards. For example, the radio component, in cooperation with the communications antennas, may be configured to communicate in one or more frequency bands, such as the 2.4 GHz, 5 GHz, 6 GHz, or 60 GHz bands. The radio component can include any known receiver and baseband suitable for communicating via the communications protocols. The radio component may further include other components, such as one or more of a low noise amplifier (LNA), additional signal amplifiers, an analog-to-digital (A/D) converter, one or more buffers, and digital baseband.

[0031] In some implementations, the first device 110 can implement an access point (AP) operating in a WLAN system. For example, the processor 111 of the AP may receive a signal through the transceiver 113, process a reception (RX) signal, generate a transmission (TX) signal, and provide control for signal transmission. The memory 1 12 of the AP can store a signal (e.g., RX signal) received through the transceiver 113, and can store a signal (e.g., TX signal) to be transmitted through the transceiver 113.

[0032] In some implementations, the second device 120 can implement a non-AP device, such as a station (STA). For example, the transceiver 123 of a non-AP can perform a signal transmission/reception operation. For example, an IEEE 802.11 packet (e.g., IEEE 802.1 la/b/g/n/ac/ax/be packet, etc.) can be transmitted/received.

[0033] In some implementations, a processor 121 of the non-AP device can receive a signal through the transceiver 123, process an RX signal, generate a TX signal, and provide control for signal transmission. A memory 122 of the non-AP device can store a signal (e.g., RX signal) received through the transceiver 123, and can store a signal (e.g., TX signal) to be transmitted through the transceiver. [0034] In some implementations, the operations of the device 1 10 (120) can be controlled by the processing chip 114 (124) of the device 110 (120). For example, software code 115 (125) related to the operations of the device 110 (120) can be stored in the memory 112 (122) of the device 110 (120) and the software code can be executed by the processor 111 (121) to control the operations of the device 110 (120).

[0035] In scenarios where the network 100 implements an IEEE 802.11 -based standard, the devices 110 and 120 can communicate via physical layer (PHY) protocol data units (PPDUs). The frame format of each PPDU includes a preamble that is prepended to data. The preamble includes various fields and sub-fields which can be used for various purposes (e.g., automatic gain control, timing synchronization, etc.) and provides information to the receiver to correctly receive the data in the PPDU. An example of fields that can be implemented in a PPDU, including preamble fields and a data field, is shown below:

[0036] The above fields are just examples of fields that can be included in the PPDU. In general, the PPDU can include only some of these fields and can also include other fields (and sub-fields). Furthermore, the particular names of the fields shown above are merely examples, and the particular names of the fields is not limited thereto. For example, in some implementations, the EHT-LTF can alternatively be referred to by other names, such as ultra- high-throughput (UHT)-LTF. [0037] An example of an operation for generating the TX/RX signal or performing the data processing and computation in advance can include: determining/obtaining/configuring/computing/decoding/encoding bit information of a field included in a PPDU, determining/configuring/obtaining a time resource or frequency resource (e.g., a subcarrier resource) or the like used for the field included the PPDU, determining/configuring/obtaining a specific sequence (e.g., a pilot sequence, an STF/LTF sequence, an extra sequence applied to SIG) or the like used for the field included in the PPDU, a power control operation and/or power saving operation applied for the device, and determining/obtaining/configuring/decoding/encoding or the like of an ACK signal.

[0038] In some implementations, a variety of information used by various devices for determining/obtaining/configuring/computing/decoding/decoding a TX/RX signal (e.g., information related to a field/subfield/control field/parameter/power or the like) can be stored in the memories 112 and 122.

[0039] In some implementations, processing chips 114 and 124 can include the processors 111 and 121 and the memories 112 and 122. In some implementations, the processing chips 114 and 124 can perform operations for a mobile terminal, a wireless device, a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile subscriber unit, a user, a user ST A, a network, a base station, a Node-B, an access point (AP), a repeater, a router, a relay, a receiving unit, a transmitting unit, a receiving STA, a transmitting STA, a receiving device, a transmitting device, a receiving apparatus, and/or a transmitting apparatus. For example, technical features of the devices 110 and 120 discussed herein can be performed by the processing chips 114 and 124.

[0040] In some implementations, the software codes 115 and 125 can be included in the memories 112 and 122. The software codes 115 and 126 can include instructions for controlling an operation of the processors 111 and 121. The software codes 115 and 125 can be included as various programming languages.

[0041] The processors 111 and 121 or processing chips 114 and 124 can include an application-specific integrated circuit (ASIC), other chipsets, a logic circuit and/or a data processing device. The processor can be an application processor (AP). For example, the processors 111 and 121 or processing chips 114 and 124 can include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), and a modulator and demodulator (modem).

[0042] An uplink refers to a directional link for communication from a non-AP (e.g., STA) to an AP. An uplink PPDU/packet/signal or the like may be transmitted through the uplink. In addition, a downlink refers to a directional link for communication from an AP to the non-AP (e.g., STA). A downlink PPDU/packet/signal or the like may be transmitted through the downlink.

[0043] FIGS. 2A and 2B are diagrams illustrating examples of a PPDU in an IEEE 802.11- based standard. The particular PPDU format and fields shown in FIGS. 2A and 2B are merely examples, and it should be appreciated that the PPDU can be implemented without one or more of the fields shown in these figures, and/or implement other fields not shown in these figures.

[0044] The example of FIG. 2A shows a PPDU that includes various fields, such as a legacy short training field (L-STF), legacy long training field (L-LTF), legacy signal field (L-SIG), repeated legacy signal field (RL-SIG), universal signal field (U-SIG), EHT signal field (EHT- SIG), EHT short training field (EHT-STF), and EHT long training field (EHT-LTF). These fields form the preamble of the PPDU. In addition, the PPDU includes a data field immediately after the EHT-LTF in the example of FIG. 2 A.

[0045] The PPDU depicted in FIG. 2A can be sent to a single user or to multiple users. The related EHT-SIG field, along with the U-SIG, can provide RU/MRU allocations and other information the devices need to understand the packet. In some implementations, when the PPDU is sent to multiple users, the transmission can be OFDMA or MU-MIMO. In some implementations, a RU including 242 tones or more in an OFDMA transmission can employ MU- MIMO technology to deliver the RU to as many as eight users simultaneously.

[0046] The example of FIG. 2B shows a PPDU that includes various fields, such as L-STF, L- LTF, L-SIG, RL-SIG, U-SIG, EHT-STF, and EHT-LTF. These fields form the preamble of the PPDU. In addition, the PPDU includes a data field immediately after the EHT-LTF in FIG. 2B.

[0047] The PPDU frame format in FIG. 2B is similar to the PPDU frame format in FIG. 2A, with the exception that the FIG. 2B format excludes the EHT-SIG field. Furthermore, the EHT- STF field may be extended to twice its length compared to the EHT-STF field in FIG. 2A, to improve performance and reliability for uplink transmissions. In some implementations, the PPDU of FIG. 2B can be transmitted by devices in response to receiving a control frame (e.g., a “trigger frame”) from the AP, where the control frame allocates resources and request responses from one or more devices. As such, the devices can use the PPDU depicted in FIG. 2B to reply to the trigger sent by the AP.

[0048] As discussed above, the PPDU can include a long training field (LTF, e.g., EHT-LTF or UHT-LTF) which is a component of the physical layer structure used in an IEEE 802.11 -based communication systems, particularly in the OFDM modulation scheme. The LTF can be a sequence of known symbols that are transmitted before the actual data symbols in each OFDM symbol. The LTF can help channel estimation and synchronization at the receiver’s end to receive the data in the data field of the PPDU.

[0049] For example, as the transmitted signal traverses the wireless channel, the signal is affected by various factors like multipath fading and interference. These effects may cause the received signal to deviate from the original transmitted signal. By comparing the received LTF symbols with the known transmitted LTF symbols, the receiver can estimate how the channel has distorted the signal. This information can be used to adjust and equalize the received data symbols accurately.

[0050] By way of further example, the LTF symbol can serve the purpose of symbol and time synchronization. The receiver can use the known LTF symbols to align its receiver with the incoming signal, ensuring that it correctly identifies the start of each symbol and the boundaries between symbols.

[0051] In some implementations, the LTF sequence may be longer than the regular data symbols, which provides more robust channel estimation.

[0052] A PPDU can refer to a complete packet or frame of data ready for transmission and include not only the OFDM symbols but also control information, headers, and potentially other elements required for the data to be transmitted, received, and processed correctly. For example, the PPDU can encompass the entire packet structure, which can include multiple OFDM symbols and may also include additional elements like preamble and MAC layer headers. The PPDU can be generated and processed at higher layers of the communication protocol stack, including the data link and network layers.

[0053] An OFDM symbol can be a fundamental unit of data transmission in OFDM-based systems and includes multiple subcarriers in the frequency domain, with each subcarrier carrying a portion of the transmitted information. For example, the OFDM symbol includes, in the frequency domain, data subcarriers and may also include pilot subcarriers for channel estimation and synchronization. The OFDM symbol can be generated by modulating the data onto these subcarriers and is typically used for a short duration in the transmission process.

[0054] In some implementations, an OFDM symbol can include one or more resource units (RUs), where each of the one or more resource units include subcarriers (frequency resources) and a duration of time (time resources) allocated for communication. A resource unit (RU) can include data subcarriers and pilot sub carriers. A plurality of RUs can be allocated from a data field of a PPDU and assigned to a plurality of users, with each user assigned at least one RU including at least one pilot subcarrier.

[0055] Thus, an OFDM symbol is a building block of the data transmission process within a wireless communication system that employs OFDM modulation and represents a small chunk of data transmission, typically covering a short time duration. In some implementations, multiple OFDM symbols can be combined within a PPDU, which represents a complete packet or frame of data with additional control and framing information. The PPDU can encompass the entire data transmission process, from data encapsulation to physical layer modulation and transmission, and can be handled at higher layers of the communication stack.

[0056] In some implementations, an OFDM symbol can include one or more pilot tones, which is a specific subcarrier that carries known information. A tone can refer to a subcarrier. The pilot tones can help in estimating the characteristics of the communication channel. For example, since the transmitted pilot symbols are known at the receiver, any deviations or distortions in the received pilot values can be attributed to the channel’s effects. By comparing the known pilot values with the received pilot values, the receiver can estimate the frequency response or channel gain and phase at each subcarrier. This information can be helpful for equalizing and correcting the data subcarriers.

[0057] In some implementations, the pilot tones can help with symbol and timing synchronization. For example, the receiver can use the known pilot locations and values to align itself with the incoming signal, ensuring that it correctly identifies the start of each symbol and the boundaries between symbols.

[0058] In some implementations, pilot tones enable coherent detection, where the receiver can use phase information to accurately demodulate data symbols. This can help in systems using Quadrature Amplitude Modulation (QAM) or other phase-sensitive modulation schemes. [0059] In some implementations, in between the pilot tones, data subcarriers can be located. The channel estimates obtained from the pilot tones can be interpolated to estimate the channel response at the data subcarriers. This interpolation can help in equalizing and correcting the data more accurately.

[0060] In some implementations, the channel quality information derived from pilot tones can be used to adapt the modulation and coding schemes. For example, if the channel conditions are good, higher-order modulation and coding can be employed to transmit data at higher rates. In contrast, in poor channel conditions, lower-order modulation and coding may be used to ensure more reliable communication.

[0061] Thus, the pilot tones can be inserted into an OFDM symbol to carry known reference information and can help in channel estimation, synchronization, coherent detection, and adaptive modulation and coding, ultimately enhancing the reliability and performance of data transmission in OFDM-based communication systems.

[0062] FIG. 3A is a diagram illustrating an example of a portion of the PPDU frame format. In this example, only a portion of the PPDU is shown, including a long training field (e.g., EHT- LTF or UHT-LTF) and a data field. Different resource areas of the data field can be allocated to different users. For example, this can be done in an OFDMA system in which an AP transmits the PPDU to multiple users on the downlink. Each user can be allocated one or more RUs within the data field of the PPDU.

[0063] In the example of FIG. 3A, four users are allocated across the whole frequency bandwidth. As shown in this example, each user is allocated a number of pilot subcarriers (e.g., user 1 is allocated pilot subcarriers 303a and 303b) in the user’s RU.

[0064] Described next is one approach for generating pilot subcarriers, and a problem with such an approach. In this approach, each pilot subcarrier is generated using the equation below: Pn * Pn where: p_n is the polarity in OFDMA symbol n which is the same for every pilot subcarrier in one OFDMA symbol, and

Pn is the pilot subcarrier in symbol n on subcarrier k. [0065] In this approach, because the polarity p_n is the same for all pilot subcarriers in a given symbol, the aggregate of the pilot subcarriers across all users can potentially generate peaks in the time domain, resulting in large Peak-to-Average Power Ratio (PAPR).

[0066] The PAPR refers to the ratio between the peak power and the average power of the transmitted signal. PAPR quantifies how much the amplitude of the signal varies from its average value. A high PAPR indicates that the signal’s peak power is significantly higher than its average power. High PAPR can be problematic in practical systems. For example, high PAPR can degrade the efficiency of power amplifiers in the transmitter, and also increase the error vector magnitude (EVM), degrade the receiver performance, increase adjacent channel leakage ratio, and also degrade performance of users in adjacent channels.

[0067] For example, for a pilot design of a 26-tone Resource Unit (RU) in a single OFDM symbol, the pilot sequences remain consistent across different 26-tone RUs. If an Access Point (AP) schedules multiple 26-tone RUs for multiple Stations (STAs), then this result in several repeated templates of pilot sequences. In a scenario where the AP schedules 36 STAs, each allocated a 26-tone RU within one symbol, the pilot subcarriers for all 36 STAs can add up to result in a large PAPR. In such cases, the repetition of pilots in the frequency domain can manifest as peaks in the time domain, resulting in a high PAPR.

[0068] PHASE ROTATIONS OF PILOT TONES

[0069] Problems such as high-PAPR discussed above can be addressed by using implementations of the present disclosure. According to implementations of the present disclosure, phase rotations are applied to pilot subcarriers of different users within a PPDU. For example, the phase rotations can be randomly generated for each user, or the phase rotations can be applied to each user based on a predetermined phase rotation rule. This can help ensure that the pilot subcarrier(s) of different users is assigned different phase rotations, and can help avoid scenarios where many same-phase pilot subcarriers aggregate to result in a large PAPR.

[0070] In one implementation (implementation #1), the phase rotations can be applied to pilot tones in both the data field and in the long training field (e.g., EHT-LTF or UHT-LTF). In another implementation (implementation #2), the phase rotation is only applied to pilot tones in the data field. Both implementations are described in detail below.

[0071] Implementation #! [0072] In the example of FIG. 3A, phase rotations are applied to pilot subcarriers in the data field and also to a corresponding EHT-LTF sequence of the preamble for each user, where the EHT-LTF sequence and the pilot subcarriers have the identical tone indices.

[0073] For example, for user 1 in FIG. 3A, a first phase rotation value can be applied to the pilot subcarriers 303a and 303b and to the corresponding EHT-LTF sequence 301. In some implementations, a first phase rotation value “1” can be applied to the pilot subcarriers 303a and 303b and the corresponding EHT-LTF sequence 301, where a phase rotation value of “1” refers to zero phase rotation (i.e. , a full 360-degree rotation in the complex plane, representing a complete cycle around the unit circle in the complex plane).

[0074] For user 2, a second phase rotation value can be applied to the pilot subcarriers 313a and 313b and the corresponding EHT-LTF sequence 311. In some implementations, a second phase rotation value “-1” can be applied to the pilot subcarriers 313a and 313b and the corresponding EHT-LTF sequence 311, where a phase rotation value of “-1” refers to a 180- degree phase rotation in which the phase of the signal is inverted or flipped by half of a cycle. In the complex plane, this corresponds to moving from one side of the origin to the opposite side while staying on the unit circle.

[0075] For user 3, a third phase rotation value can be applied to the pilot subcarriers 323a and 323b and the corresponding EHT-LTF sequence 321. In some implementations, a third phase rotation value “j” can be applied to the pilot subcarriers 323a and 323b and the corresponding EHT-LTF sequence 321 , where a phase rotation value of “j” refers to a 90-degree counterclockwise rotation in the complex plane in which the phase of the complex number is shifted by one-quarter of a cycle.

[0076] For user 4, a fourth phase rotation value can be applied to the pilot subcarriers 333a and 333b and the corresponding EHT-LTF sequence 331. In some implementations, a fourth phase rotation value “-j” can be applied to the pilot subcarriers 333a and 333b and the corresponding EHT-LTF sequence 331, where a phase rotation value of “-j” refers to a 90-degree clockwise rotation in the complex plane in which the phase of the complex number is shifted by one-quarter of a cycle in the opposite direction of a counterclockwise rotation.

[0077] The specific values of phase rotations discussed above are merely examples, and other values of phase rotations can be applied to the users, while ensuring that the phase rotations are distinct for each user. By ensuring different phases for pilot tones of different users, this can help the transmitter can exploit the distinct phase rotations of the pilot tones to reduce the transmitter’s overall PAPR when simultaneously transmitting the multiple pilot tones.

[0078] Furthermore, in this implementation #1 of FIG. 3A, since both the EHT-LTF sequence and the pilot subcarriers are rotated with the same phase rotation value, the receiver perceives this rotation transparently. In particular, the same phase rotation is applied to both the preamble and data, thus allowing the receiver to seamlessly utilize the channel estimation obtained from the preamble for data reception.

[0079] However, in some scenarios, the techniques of implementation #1 discussed above can have has a drawback of potentially increasing the PAPR of the long training field in the preamble (e.g., the EHT-LTF or UHT-LTF of the preamble). For example, if the sequence of the EHT-LTF is modified (by the phase rotations discussed above), then this can result in an increase of PAPR in the EHT-LTF in scenario where the EHT-LTF sequence itself has already been configured/optimized for low PAPR without the phase rotation at individual tones. For example, in some scenarios, the EHT-LTF sequence itself is already configured with phase rotations designed to reduce PAPR of the preamble. In such scenarios, applying additional phase rotations to the EHT-LTF according to implementation #1 could result in an increase of the overall PAPR for the EHT-LTF portion of the PPDU.

[0080] Implementation #2

[0081 ] FIG. 3B shows an alternative implementation in which phase rotations are only applied to the data field of the PPDU, without changing the existing preamble (e.g., without changing the EHT-LTF). This can be useful in scenarios where the existing preamble already implements a form of phase rotation (e.g., existing phase rotations in the EHT-LTF of the preamble). In such scenarios, the existing EHT-LTF may already be configured to achieve low PAPR. As such, implementation #2 of FIG. 3B would only apply the additional phase rotations to the data field, without changing any existing phase rotations that may be applied to the EHT-LTF in the preamble. This approach can have an advantage of achieving low PAPR in the data field, while also maintaining low PAPR in the preamble (e.g., without disturbing the existing EHT-LTF which may already be configured to achieve low PAPR).

[0082] The phase rotations applied to the pilot tones in the data field can be configured in various ways. Some examples are described below. These examples can be used in either implementation described above. [0083] Alt 1: phase rotations are applied only to pilot tones (not data tones) in the data field of the PPDU, on a per-user basis. For example, phase rotations (e.g., randomly generated phase rotations or phase rotations generated based on a predetermined rule) can be assigned to pilot tones of each user in the data field, on a per-user basis so that pilot subcarriers of different users have phase rotations that are generated differently from pilot tones of other users.

[0084] For example, the pilot subcarriers can be generated using the equation below:

Pn * P * , where: p_n is the polarity in OFDMA symbol n which is the same for every pilot subcarrier in one OFDMA symbol,

Pn is the pilot subcarrier in symbol n on subcarrier k, and

/?“ is phase rotation applied to the pilot subcarrier in OFDMA symbol n for user u.

[0085] For example, in FIG. 3B, the above equation can be applied to generate the pilot subcarriers 303a and 303b for user 1 using a first phase rotation value ?„, generate the pilot subcarriers 313a and 313b for user 2 using a second phase rotation value R^. generate the pilot subcarriers 323a and 323b of user 3 using a third phase rotation value R^, and generate the pilot subcarriers 333a and 333b for user 4 using a fourth phase rotation value R^.

[0086] It should be noted that the above equation potentially generates different phase rotations for each symbol n, but other configurations are possible. For example, in some scenarios, phase rotations can be generated for groups of symbols (e.g., to groups of m symbols), instead of for every symbol, as long as the phase rotations applied for different users are generated differently for any given symbol. Also, it should be noted that, depending on the algorithm or mapping that generates the phase rotation values R^, the actual phase rotation value applied to any given pilot tone for a user may be identical to a phase rotation value applied to another pilot tone for another user. In particular, this can happen if the number of users exceeds the number of possible phase rotation values. However, even in such scenarios, the techniques described above can still help reduce overall PAPR by helping to distribute (e.g., randomize) the phase rotations of different pilot tones for different users as compared to scenarios where the pilot tones of all the users share the same phase value.

[0087] Alt 2: phase rotations are applied only to pilot tones (not data tones) in the data field, on a per-bandwidth basis. For example, phase rotations can be generated for pilot tones within fixed ranges of frequencies (e.g., within each 20 MHz channel), irrespective of how the pilot tones are allocated to different users. For example, a phase rotation is generated for pilot tones within data segments for each 20 MHz channel, where these data segments are allocated across the frequency bandwidth. As such, depending on the size of the bandwidth portion to which the phase rotations are applied, the phase rotations can be applied to a greater number or fewer number of pilot tones.

[0088] Alt 3: phase rotations are applied to both pilot tones and data tones in the data field, on a per-user basis. This is similar to Alt 1, above, except that the phase rotations are applied to both pilot tones and data tone (not just pilot tones) in the data field. For example, phase rotations (e.g., randomly generated phase rotations or phase rotations generated using a predetermined rule) can be applied to both pilot tones and data tones of each user in the data field, on a per-user basis so that both pilot and data tones of different users have phase rotations that are generated differently from pilot and data tones of other users. As such, the phase rotations are directly applied to the entire RU/MRU of each user (including both data tones and pilot tones).

[0089] Alt 4: phase rotations are applied to both pilot tones and data tones in the data field, on a per-bandwidth basis. This is similar to Alt 2, above, except that the phase rotations are applied to both pilot tones and data tone (not just pilot tones) in the data field. For example, phase rotations can be generated for pilot tones and data tones within fixed ranges of frequencies (e.g., within each 20 MHz channel), irrespective of how the pilot tones and data tones are allocated to different users. For example, a phase rotation is generated for pilot tones and data tones within data segments for each 20 MHz channel, where these data segments are allocated across the frequency bandwidth. As such, depending on the size of the bandwidth portion to which the phase rotations are applied, the phase rotations can be applied to a greater number or fewer number of pilot tones and data tones.

[0090] The technique of implementation #2 can therefore help maintain a low PAPR in both the preamble and also in the data field. However, implementation #2 can have the potential drawback of requiring the receiver to account for the differing phase rotations between the preamble and data during the demodulation process. For example, if the phase rotations applied to the data field are different from any phase rotations applied to the EHT-LTF, then the receiver should be aware of the change in phase when the receiver uses the channel estimate obtained from the EHT-LTF to demodulate the data field. Thus, in some implementations, a protocol or rule can be implemented that enables a receiver to know the phase rotation that has been applied to the data field. For example, an implicit rule, such as a mapping of phase rotations to RUs or to users, can be employed so that the receiver knows the phase rotation of pilot tones in the data field. In some implementations, explicit signaling can also be used to inform the receiver of phase rotations of pilot tones in the data field.

[0091] For any of the examples and implementations discussed above, a value of phase rotation can be selected from any number of possible values of phase rotations. As an example, a phase rotation can be selected (e.g., randomly or according to a predetermined rule such as a mapping of phase rotation values to RUs or users) from among phase rotation values including [1 , -1] or among phase rotation values including [1, -1, j, -j], or other values. In general, the phase rotation values can be selected from a set that encompasses a wide range of real numbers and/or complex numbers, offering flexibility in the selection of phase values to suit various applications. [0092] In addition, the phase rotation techniques described above can be applied for downlink and/or uplink transmission.

[0093] FIG. 4 is a flowchart showing an example of transmission procedure 400 performed by a first device (e.g., a first device 110). In some implementations, this procedure can be performed by an AP transmitting a PPDU on a downlink to a non-AP device (e.g., a STA).

[0094] In step 401, a first device can generate a physical protocol data unit (PPDU). The PPDU can include (i) a preamble (e.g., a preamble that includes EHT-LTF 301, 311, 321, and 331) and (ii) a data field. A plurality of resource units (RUs) can be allocated for the data field and assigned to a plurality of users, with each user assigned at least one RU including at least one pilot subcarrier.

[0095] In step 402, the first device can apply phase rotations to the at least one pilot subcarrier in the at least one RU of each user, where values of the phase rotations are different for pilot subcarriers in RUs for at least two of the users.

[0096] The phase rotations can be generated according to any of implementation #1 or implementation #2 described above, and any of Alt-1, Alt-2, Alt-3, or Alt-4 described above. For example, in some implementations, the first device can generate the at least one pilot subcarrier based on the following equation,

Pn * Pn * Rn, where: p_n is the polarity in OFDMA symbol n which is the same for every pilot subcarrier in one OFDMA symbol, is the pilot subcarrier in OFDMA symbol n on subcarrier k, and

/?“ is phase rotation applied to the pilot subcarrier in OFDMA symbol n for user u.

[0097] In step 403, the first device can transmit the PPDU to which the phase rotations are applied in step 402 to a second device (e.g., a second device 120).

[0098] The features described can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device, for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0099] While this disclosure contains many specific implementation details, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular implementations of particular inventions. Certain features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0100] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Claims

CLAIMS What is claimed is:

1. A method performed by a device operating in an orthogonal frequency-division multiple access (OFDMA) wireless local area network (WLAN) system, the method comprising: generating a physical protocol data unit (PPDU) comprising (i) a preamble and (ii) a data field, wherein a plurality of resource units (RUs) are allocated for the data field and assigned to a plurality of users, with each user assigned at least one RU comprising at least one pilot subcarrier; applying phase rotations to the at least one pilot subcarrier in the at least one RU of each user, wherein values of the phase rotations are different for at least two of the users; and transmitting the PPDU to a receiver.

2. The method of claim 1, wherein the at least one pilot subcarrier is generated based on the following equation,

Pn * Pn * Pn, where: p_n is a polarity in OFDMA symbol n which is the same for every pilot subcarrier in one OFDMA symbol,

Pn is the pilot subcarrier in OFDMA symbol n on subcarrier k, and

Rn is phase rotation applied to the pilot subcarrier in OFDMA symbol n for user u.

3. The method of claim 1 , wherein applying the phase rotations comprises applying phase rotations to the at least one pilot subcarrier and to data subcarriers in the at least one RU of each user, and wherein values of the phase rotations are different for at least two of the users.

4. The method of claim 1, wherein the preamble includes a long training field allocated next to the data field and to which one or more subcarriers are allocated, wherein applying the plurality of phase rotation values comprises applying the phase rotations to the at least one pilot subcarrier in the at least one RU and to a corresponding subcarrier of the long training field of each user, and wherein values of the phase rotations are different for at least two of the users.

5. The method of claim 1, wherein a value of the phase rotation is selected from among a set of real numbers and/or complex numbers.

6. The method of claim 1, wherein the at least one pilot subcarrier is generated based on the following equation,

Pn * Pn * n, where: p_n is a polarity in OFDMA symbol n which is the same for every pilot subcarrier across alternate-symbol basis,

P is the pilot subcarrier in OFDMA symbol n on subcarrier k, and n is phase rotation applied to the pilot subcarrier in OFDMA symbol n for user u.

7. A method performed by a device operating in an orthogonal frequency-division multiple access (OFDMA) a wireless local area network (WLAN) system, the method comprising: generating a physical protocol data unit (PPDU) comprising (i) a preamble and (ii) a data field, wherein a plurality of resource units (RUs) are allocated for the data field and assigned to a plurality of users, with each user assigned at least one RU comprising at least one pilot subcarrier; applying phase rotations to the at least one pilot subcarrier in the at least one RU per 20 MHz band, wherein values of the phase rotations are different for at least two of the 20 MHz bands; and transmitting the PPDU.

8. The method of claim 7, wherein applying the phase rotations comprises applying the phase rotations to data subcarriers and to the at least one pilot subcarrier per 20 MHz band, wherein values of the phase rotations are different for data subcarriers and pilot subcarriers in RUs per 20 MHz band.

9. The method of claim 7, wherein a value of the phase rotation is selected from among a set of real numbers and/or complex numbers.