Pilot tones in distributed resource unit (dRU) transmission

Abstract

The present disclosure provides methods, devices, and systems for increasing the transmission power of a wireless communication device operating on a power spectral density (PSD) limited wireless channel. Some implementations relate more specifically to a pilot tone design supporting distributed transmission. A transmitting device may modulate a Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) on a number (M) of tones representing a logical RU associated with a legacy tone plan, and may further map the M tones to M non-contiguous subcarrier indexes associated with the wireless channel. The transmitting device may transmit a PPDU over the wireless channel using a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indexes. In some implementations, the relative positions of the N pilot tones may be different from the relative positions of the number (K) of pilot tones associated with the logical RU.

Description

[Technical field]

[0001] REFERENCE TO RELATED APPLICATIONS This patent application claims priority to commonly assigned U.S. patent application Ser. No. 17 / 390,828, entitled "PILOT TONES IN DISTRIBUTED RESOURCE UNIT (DRU) TRANSMISSION," filed July 30, 2021. The disclosures of all prior applications are considered part of this patent application and are incorporated by reference into this patent application.

[0002] FIELD OF THE DISCLOSURE The present disclosure relates generally to wireless communications, and more specifically, to pilot tone transmission in distributed resource units (dRUs, or simply "dRU"). [Background technology]

[0003] A wireless local area network (WLAN) may be formed by one or more access points (APs) that provide a shared wireless communication medium for use by several client devices, also called stations (STAs). The basic building block of a WLAN that conforms to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 family of standards is the Basic Service Set (BSS) managed by the AP. Each BSS is identified by a Basic Service Set Identifier (BSSID) advertised by the AP. The AP periodically broadcasts beacon frames to enable any STA within wireless range of the AP to establish or maintain a communication link with the WLAN.

[0004] In some instances, APs and STAs may be subject to power spectral density (PSD) limitations. For example, some APs and STAs operating in the 6 gigahertz (GHz) frequency band may be required to comply with a low power indoor (LPI) power class that limits the transmit power of APs and STAs (in the 6 GHz band) to 5 decibel-milliwatts per megahertz (dBm / MHz) and -1 dBm / MHz, respectively. In other words, transmit power in the 6 GHz band is PSD limited per MHz. Such PSD limitations may undesirably reduce the range of wireless communications and may reduce the packet detection and channel estimation capabilities of APs and STAs. Summary of the Invention

[0005] The systems, methods, and devices of the present disclosure each have several innovative aspects, no single aspect of which is solely responsible for the desirable properties disclosed herein.

[0006] One innovative aspect of the subject matter described in this disclosure may be implemented as a method of wireless communication that may be performed by a wireless communication device and may include modulating a physical layer convergence protocol (PLCP) protocol data unit (PPDU) on a number (M) of tones representing logical resource units (RUs) associated with a number (K) of pilot tones, each having a respective position relative to the M tones, mapping the M tones to M non-contiguous subcarrier indices of a plurality of subcarrier indices across a wireless channel, where the M tones mapped to the M non-contiguous subcarrier indices represent a distributed resource unit (dRU), and transmitting, via the wireless channel, a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices, where a relative position of the N pilot tones is different from a relative position of the K pilot tones.

[0007] In some aspects, N may be different from K. In some other aspects, N may be equal to K. In some implementations, the N pilot tones may carry the same value as the K pilot tones. In some implementations, M=26, and the relative positions of the K pilot tones can be changed by mapping the M tones to M non-contiguous subcarrier indices, and the N pilot tones represent the K pilot tones as a result of the mapping. In some implementations, the relative positions of the K pilot tones can be shifted by −3 or +3 by mapping the M tones to M non-contiguous subcarrier indices.

[0008] In some aspects, the relative positions of the N pilot tones may be associated with N subcarrier indexes of the plurality of subcarrier indexes. In some implementations, the N subcarrier indexes may be symmetrically arranged around a center frequency associated with the wireless channel. In some other implementations, the N subcarrier indexes may be asymmetrically arranged around a center frequency associated with the wireless channel. In some implementations, the N subcarrier indexes may include N / 2 equidistant subcarrier indexes that are positioned above a carrier frequency associated with the wireless channel and may include N / 2 equidistant subcarrier indexes that are positioned below the carrier frequency.

[0009] In some implementations, each of the N subcarrier indices can represent a respective pilot tone position associated with a 26-tone dRU. In some other implementations, at least one of the N subcarrier indices can represent a pilot tone position unique to an M-tone dRU. In some implementations, each of the N subcarrier indices can be located at a respective distance from a starting subcarrier index of the M non-contiguous subcarrier indices based on the position of the starting subcarrier index relative to the wireless channel and the dRU index associated with the dRU.

[0010] Another innovative aspect of the subject matter described in this disclosure may be implemented in a wireless communication device. In some implementations, the wireless communication device may include at least one processor and at least one memory communicatively coupled to the at least one processor and storing processor-readable code. In some implementations, execution of the processor-readable code by the at least one processor causes the wireless communication device to perform operations including modulating a PPDU on a number (M) of tones representing logical RUs associated with a number (K) of pilot tones, each having a respective position relative to the M tones, mapping the M tones to M non-contiguous subcarrier indexes of a plurality of subcarrier indexes across a wireless channel, where the M tones mapped to the M non-contiguous subcarrier indexes represent a dRU, and transmitting a PPDU including a number (N) of pilot tones over the wireless channel, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indexes, where the relative positions of the N pilot tones are different from the relative positions of the K pilot tones.

[0011] Another innovative aspect of the subject matter described in this disclosure may be implemented as a method of wireless communication that may be performed by a wireless communication device and may include receiving a PPDU over a wireless channel, the PPDU being carried on a number (M) of tones mapped to M non-contiguous subcarrier indices of a plurality of subcarrier indices across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indices representing a dRU, recovering from the received PPDU a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices, and demapping the M tones from the M non-contiguous subcarrier indices, the demapped M tones representing a logical RU associated with a number (K) of pilot tones, each having a respective position relative to the demapped M tones, and a relative position of the K pilot tones different from a relative position of the N pilot tones.

[0012] In some aspects, N may be different from K. In some other aspects, N may be equal to K. In some implementations, the N pilot tones may carry the same value as the K pilot tones. In some implementations, M=26, and the relative positions of the N pilot tones can be changed by demapping the M tones to M non-contiguous subcarrier indices, with the K pilot tones representing the N pilot tones as a result of the mapping. In some implementations, the relative positions of the N pilot tones can be shifted by −3 or +3 by demapping the M tones to M non-contiguous subcarrier indices.

[0013] In some aspects, the relative positions of the N pilot tones may be associated with N subcarrier indexes of the plurality of subcarrier indexes. In some implementations, the N subcarrier indexes may be symmetrically arranged around a center frequency associated with the wireless channel. In some other implementations, the N subcarrier indexes may be asymmetrically arranged around a center frequency associated with the wireless channel. In some implementations, the N subcarrier indexes may include N / 2 equidistant subcarrier indexes that are positioned above a carrier frequency associated with the wireless channel and may include N / 2 equidistant subcarrier indexes that are positioned below the carrier frequency.

[0014] In some implementations, each of the N subcarrier indices can represent a respective pilot tone position associated with a 26-tone dRU. In some other implementations, at least one of the N subcarrier indices can represent a pilot tone position unique to an M-tone dRU. In some implementations, each of the N subcarrier indices can be located at a respective distance from a starting subcarrier index of the M non-contiguous subcarrier indices based on the position of the starting subcarrier index relative to the wireless channel and the dRU index associated with the dRU.

[0015] Another innovative aspect of the subject matter described in this disclosure may be implemented in a wireless communication device. In some implementations, the wireless communication device may include at least one processor and at least one memory communicatively coupled to the at least one processor and storing processor-readable code. In some implementations, execution of the processor-readable code by at least one processor causes the wireless communication device to perform operations including receiving a PPDU over a wireless channel, the PPDU being carried on a number (M) of tones mapped to M non-contiguous subcarrier indices of a plurality of subcarrier indices across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indices representing a dRU; recovering from the received PPDU a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices; and demapping the M tones from the M non-contiguous subcarrier indices, the demapped M tones representing a logical RU associated with a number (K) of pilot tones, each having a respective position relative to the demapped M tones, the relative positions of the K pilot tones being different from the relative positions of the N pilot tones. [Brief description of the drawings]

[0016] The details of one or more implementations of the subject matter described in this disclosure 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. It should be noted that the relative dimensions of the following figures may not be drawn to scale. [Figure 1] 1 is a pictorial diagram of an exemplary wireless communication network. [Figure 2A] 1 illustrates an example protocol data unit (PDU) that may be used for communication between an access point (AP) and one or more wireless stations (STAs). [Figure 2B]FIG. 2B illustrates example fields in the PDU of FIG. 2A. [Diagram 3] 1 illustrates an example Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) that can be used for communication between an AP and one or more STAs. [Figure 4] 1 is a block diagram of an example wireless communication device. [Figure 5A] FIG. 2 is a block diagram of an example AP. [Figure 5B] 1 is a block diagram of an exemplary STA. [Figure 6] 1 shows a frequency diagram illustrating an example distributed tone mapping according to some implementations. [Figure 7] FIG. 1 illustrates a frequency diagram illustrating an example mapping of logical resource units (RUs) to distributed RUs (dRUs) over a shared radio channel, according to some implementations. [Figure 8] FIG. 1 illustrates a frequency diagram showing an example mapping of logical RUs to dRUs according to some implementations. [Figure 9A] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel according to a legacy tone plan. [Figure 9B] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel according to a distributed tone plan. [Figure 10] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 11] 1 shows a frequency diagram illustrating an example model for allocating pilot tones in a dRU, according to some implementations. [Figure 12] 1 illustrates a frequency diagram showing example pilot tone candidates for a 26-tone dRU, according to some implementations. [Figure 13A] 1 shows a frequency diagram illustrating an example pilot tone allocation for a 26-tone dRU, according to some implementations. [Figure 13B]13 shows another frequency diagram illustrating an example pilot tone allocation for a 26-tone dRU, according to some implementations. [Figure 14] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 15] 1 illustrates a frequency diagram showing example pilot tone candidates for a 242-tone dRU, according to some implementations. [Figure 16A] 1 shows a frequency diagram illustrating an example pilot tone allocation for a 242-tone dRU, according to some implementations. [Figure 16B] 13 shows another frequency diagram illustrating an example pilot tone allocation for a 242-tone dRU, according to some implementations. [Figure 17] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 18A] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 18B] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 18C] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 18D] 1 shows a frequency diagram illustrating an example distribution of pilot tones across a wireless channel, according to some implementations. [Figure 19] 1 shows a flowchart illustrating an example process for wireless communication supporting pilot tones in dRU transmissions, according to some implementations. [Figure 20] 1 shows a flowchart illustrating an example process for wireless communication supporting pilot tones in dRU transmissions, according to some implementations. [Figure 21] 1 shows a block diagram of an exemplary wireless communication device according to some implementations. [Figure 22] 1 shows a block diagram of an exemplary wireless communication device according to some implementations.

[0017] Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The following description is directed to several implementations for the purpose of describing the innovative aspects of the present disclosure. However, those skilled in the art will readily recognize that the teachings herein can be applied in many different ways. The described implementations can be implemented in any device, system, or network capable of transmitting and receiving radio frequency (RF) signals according to one or more of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, the IEEE 802.15 standard, the Bluetooth standard defined by the Bluetooth Special Interest Group (SIG), or the Long Term Evolution (LTE), 3G, 4G, or 5G (New Radio (NR)) standards promulgated by the 3rd Generation Partnership Project (3GPP), among others. The described implementations may be implemented in any device, system, or network capable of transmitting and receiving RF signals according to one or more of the following technologies or techniques: Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Single User (SU) Multiple Input Multiple Output (MIMO), and Multi-User (MU) MIMO. The described implementations may also be implemented using other wireless communication protocols or RF signals suitable for use in one or more of a wireless personal area network (WPAN), wireless local area network (WLAN), wireless wide area network (WWAN), or internet of things (IOT) network.

[0019] Various aspects relate generally to distributed transmission, and more specifically, to pilot tone design supporting distributed transmission in a power spectral density (PSD) limited wireless channel. As used herein, the term "distributed transmission" refers to a Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) transmission on non-contiguous tones (or subcarriers) of a wireless channel (e.g., according to a "distributed tone plan"). In contrast, the term "continuous transmission" refers to a PPDU transmission on one or more sets of contiguous tones representing one or more resource units (RUs) respectively, as defined by existing versions of the IEEE 802.11 standard (also referred to as a "legacy tone plan"). For example, for distributed transmission, a transmitting device may modulate a PPDU on a number (M) of tones representing logical RUs associated with a legacy tone plan, and may further map the M tones to M non-contiguous subcarrier indexes associated with the wireless channel. In some aspects, a transmitting device may transmit a PPDU over a wireless channel using a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indexes. In some implementations, the relative positions of the N pilot tones may be different than the relative positions of some (K) pilot tones associated with a logical RU (defined by the legacy tone plan). For example, K=2 pilot tones may be assigned to the 6th and 20th tones of M tones representing a logical RU (defined by the legacy tone plan), and N=2 pilot tones may be assigned to the 2nd and 15th tones of M tones mapped to M non-contiguous subcarrier indices.

[0020] Particular implementations of the subject matter described in this disclosure may be implemented to achieve one or more of the following potential advantages: Distributed transmission provides greater flexibility in medium utilization for PSD-limited wireless channels. In some implementations, a distributed tone plan may map pilot tone locations associated with logical RUs to localized regions of the wireless channel. The pilot tones are used for phase alignment and parameter tracking. However, when pilot tones are pushed into localized regions of the wireless channel, interference in such localized regions may effectively eliminate pilot tones in the dRU. For example, a receiving device may fail to receive any pilot tones if it experiences a deep fade in any of these localized regions. However, by changing the relative positions of pilot tones between logical RUs (as defined by the legacy tone plan) and dRUs, aspects of the present disclosure may ensure that pilot tones associated with a dRU are uniformly distributed across the wireless channel, or are otherwise distributed in a manner that is more robust to interference on the wireless channel. For example, uniformly distributing pilot tones across the wireless channel increases the likelihood that a receiving device will receive at least some of the pilot tones even if it experiences a deep fade in one or more localized regions of the wireless channel.

[0021] FIG. 1 illustrates a block diagram of an exemplary wireless communication network 100. According to some aspects, the wireless communication network 100 may be an example of a wireless local area network (WLAN), such as a Wi-Fi network (and hereinafter referred to as WLAN 100). For example, the WLAN 100 may be a network that implements at least one of the IEEE 802.11 family of wireless communication protocol standards (such as those defined by the IEEE 802.11-2020 specification or amendments thereof, including but not limited to 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az, 802.11ba, and 802.11be). The WLAN 100 may include multiple wireless communication devices, such as an access point (AP) 102 and multiple stations (STAs) 104. Although only one AP 102 is shown, the WLAN network 100 may also include multiple APs 102.

[0022] Each of the STAs 104 may also be referred to as a mobile station (MS), mobile device, mobile handset, wireless handset, access terminal (AT), user equipment (UE), subscriber station (SS), or subscriber unit, among other possible examples. The STAs 104 may represent a variety of devices, such as a mobile phone, a personal digital assistant (PDA), other handheld device, a netbook, a notebook computer, a tablet computer, a laptop, a display device (e.g., a TV, a computer monitor, a navigation system, among others), a music or other audio or stereo device, a remote control device ("remote"), a printer, a kitchen appliance or other household appliance, a key fob (e.g., for a passive keyless entry and start (PKES) system), among other possible examples.

[0023] A single AP 102 and the associated set of STAs 104 may be referred to as a Basic Service Set (BSS) managed by the respective AP 102. FIG. 1 additionally illustrates an example coverage area 108 of the AP 102, which may represent a Basic Service Area (BSA) of the WLAN 100. The BSS may be identified to users by a Service Set Identifier (SSID) and to other devices by a Basic Service Set Identifier (BSSID), which may be a Medium Access Control (MAC) address of the AP 102. The AP 102 periodically broadcasts a beacon frame ("beacon") containing the BSSID to enable any STAs 104 within radio range of the AP 102 to "associate" or reassociate with the AP 102 to establish or maintain a respective communication link 106 with the AP 102 (hereinafter also referred to as a "Wi-Fi link"). For example, the beacon may include an identification of the primary channel used by each AP 102, as well as timing synchronization functionality for establishing or maintaining timing synchronization with the AP 102. The APs 102 may provide access to external networks to various STAs 104 in the WLAN via their respective communication links 106.

[0024] To establish a communication link 106 with an AP 102, each of the STAs 104 is configured to perform passive or active scanning operations ("scans") on frequency channels in one or more frequency bands (e.g., the 2.4 GHz, 5 GHz, 6 GHz, or 60 GHz bands). To perform passive scanning, the STAs 104 listen for beacons, which are transmitted by the respective APs 102 at regular time intervals called target beacon transmission times (TBTTs) (measured in time units (TUs), where one TU may equal 1024 microseconds (μs)). To perform active scanning, the STAs 104 generate probe requests and transmit them continuously on each channel to be scanned, and listen for probe responses from the APs 102. Each STA 104 may be configured to perform authentication and association operations to identify or select an AP 102 to associate with and establish a communication link 106 with the selected AP 102 based on scanning information obtained through passive or active scanning. The AP 102 assigns an association identifier (AID) to the STA 104 at the height of the association operation, and the AP 102 uses the AID to track the STA 104 .

[0025] As a result of the increasing ubiquity of wireless networks, a STA 104 may have the opportunity to select one of many BSSs within range of the STA or to select among multiple APs 102 that together form an extended service set (ESS) including multiple connected BSSs. The extended network stations associated with the WLAN 100 may be connected to a wired or wireless distribution system that may allow multiple APs 102 to be connected in such an ESS. Thus, a STA 104 may be covered by more than one AP 102 and may associate with different APs 102 at different times for different transmissions. Additionally, after association with an AP 102, the STA 104 may also be configured to periodically scan its surroundings to find a more suitable AP 102 to associate with. For example, a STA 104 moving with respect to its associated AP 102 may perform a "roaming" scan to find another AP 102 with more desirable network characteristics, such as a greater received signal strength indicator (RSSI) or a lower traffic load.

[0026] In some cases, the STAs 104 may form a network without involving the AP 102 or other devices other than the STAs 104 themselves. One example of such a network is an ad-hoc network (or wireless ad-hoc network). An ad-hoc network may alternatively be referred to as a mesh network or a peer-to-peer (P2P) network. In some cases, the ad-hoc network may be implemented within a larger wireless network, such as the WLAN 100. In such an implementation, the STAs 104 may be able to communicate with each other via the AP 102 using the communication link 106, but the STAs 104 may also communicate with each other directly via a direct wireless link 110. In addition, two STAs 104 may communicate via the direct communication link 110 regardless of whether both STAs 104 are associated with and served by the same AP 102. In such an ad-hoc system, one or more of the STAs 104 may assume the role filled by the AP 102 in the BSS. Such STAs 104 may be referred to as group owners (GOs) and may coordinate transmissions within the ad-hoc network. Examples of direct wireless links 110 include Wi-Fi direct connections, connections established by using Wi-Fi Tunneled Direct Link Setup (TDLS) links, and other P2P group connections.

[0027] The AP 102 and the STAs 104 can function and communicate (via their respective communication links 106) according to the IEEE 802.11 family of wireless communication protocol standards (such as those defined by the IEEE 802.11-2016 specification or amendments thereof, including, but not limited to, 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az, 802.11ba, and 802.11be). These standards define WLAN radio and baseband protocols for the PHY layer and the medium access control (MAC) layer. The AP 102 and the STAs 104 transmit and receive wireless communications (hereinafter also referred to as "Wi-Fi communications") between each other in the form of Physical Layer Convergence Protocol (PLCP) Protocol Data Units (PPDUs). The AP 102 and the STAs 104 in the WLAN 100 may transmit PPDUs over an unlicensed spectrum, which may be a portion of a spectrum that includes frequency bands traditionally used by Wi-Fi technology, such as the 2.4 GHz band, the 5 GHz band, the 60 GHz band, the 3.6 GHz band, and the 700 MHz band. Some implementations of the AP 102 and the STAs 104 described herein may also communicate in other frequency bands, such as the 6 GHz band, which may support both licensed and unlicensed communications. The AP 102 and the STAs 104 may also be configured to communicate over other frequency bands, such as shared licensed frequency bands, in which multiple operators may have licenses to operate in the same or one or more overlapping frequency bands.

[0028] Each of the frequency bands may include multiple sub-bands or frequency channels. For example, PPDUs conforming to IEEE 802.11n, 802.11ac, 802.11ax, and 802.11be standard amendments may be transmitted over 2.4, 5 GHz, or 6 GHz bands, each of which is divided into multiple 20 MHz channels. Thus, these PPDUs are transmitted over physical channels with a minimum bandwidth of 20 MHz, although larger channels may be formed through channel bonding. For example, PPDUs may be transmitted over physical channels with bandwidths of 40 MHz, 80 MHz, 160 MHz, or 320 MHz by bonding together multiple 20 MHz channels.

[0029] Each PPDU is a composite structure that includes a PHY preamble and a payload in the form of a PHY service data unit (PSDU). Information provided in the preamble may be used by a receiving device to decode subsequent data in the PSDU. In instances where a PPDU is transmitted over bonded channels, the preamble field may be replicated and transmitted in each of the multiple component channels. The PHY preamble may include both a legacy portion (or "legacy preamble") and a non-legacy portion (or "non-legacy preamble"). The legacy preamble may be used for packet detection, automatic gain control, and channel estimation, among other applications. The legacy preamble may also generally be used to maintain compatibility with legacy devices. The format, coding, and information provided therein of the non-legacy portion of the preamble are based on the particular IEEE 802.11 protocol to be used to transmit the payload.

[0030] 2A illustrates an exemplary protocol data unit (PDU) 200 usable for wireless communication between an AP 102 and one or more STAs 104. For example, the PDU 200 may be configured as a PPDU. As shown, the PDU 200 includes a PHY preamble 202 and a PHY payload 204. For example, the preamble 202 may include a legacy portion that itself includes a legacy short training field (L-STF) 206, which may consist of two BPSK symbols, a legacy long training field (L-LTF) 208, which may consist of two BPSK symbols, and a legacy signal field (L-SIG) 210, which may consist of two BPSK symbols. The legacy portion of the preamble 202 may be configured in accordance with the IEEE 802.11a wireless communication protocol standard. The preamble 202 may also include a non-legacy portion that includes one or more non-legacy fields 212 that conform to an IEEE wireless communication protocol, such as, for example, an IEEE 802.11ac, 802.11ax, 802.11be, or later wireless communication protocol standard.

[0031] The L-STF 206 generally enables the receiving device to perform automatic gain control (AGC) and coarse timing and frequency estimation. The L-LTF 208 generally enables the receiving device to perform fine timing and frequency estimation, and also enables the receiving device to perform an initial estimation of the wireless channel. The L-SIG 210 generally enables the receiving device to determine the duration of a PDU and use the determined duration to avoid transmitting over the PDU. For example, the L-STF 206, the L-LTF 208, and the L-SIG 210 may be modulated according to a binary phase shift keying (BPSK) modulation scheme. The payload 204 may be modulated according to a BPSK modulation scheme, a quadrature BPSK (Q-BPSK) modulation scheme, a quadrature amplitude modulation (QAM) modulation scheme, or another suitable modulation scheme. The payload 204 may include a PSDU that includes a data field (DATA) 214, which may carry higher layer data, for example in the form of a Medium Access Control (MAC) Protocol Data Unit (MPDU) or an Aggregated MPDU (A-MPDU).

[0032] 2B illustrates an example L-SIG 210 in the PDU 200 of FIG. 2A. The L-SIG 210 includes a data rate field 222, a reserved bit 224, a length field 226, a parity bit 228, and a tail field 230. The data rate field 222 indicates a data rate (note that the data rate indicated in the data rate field 212 may not be the actual data rate of the data carried in the payload 204). The length field 226 indicates the length of the packet, e.g., in units of symbols or bytes. The parity bit 228 may be used to detect bit errors. The tail field 230 includes tail bits that may be used by a receiving device to terminate the operation of a decoder (e.g., a Viterbi decoder). The receiving device may use the data rate and length indicated in the data rate field 222 and the length field 226 to determine the time length of the packet, e.g., in units of microseconds (μs) or other time units.

[0033] 3 illustrates an exemplary PPDU 300 that may be used for communication between an AP 102 and one or more STAs 104. As described above, each PPDU 300 includes a PHY preamble 302 and a PSDU 304. Each PSDU 304 may represent (or "carry") one or more MAC Protocol Data Units (MPDUs) 316. For example, each PSDU 304 may carry an aggregate MPDU (A-MPDU) 306 that includes an aggregation of multiple A-MPDU subframes 308. Each A-MPDU frame 306 may include an MPDU frame 310 that includes a MAC delimiter 312 and a MAC header 314 prior to an associated MPDU 316 that comprises a data portion ("payload" or "frame body") of the MPDU frame 310. Each MPDU frame 310 may also include a frame check sequence (FCS) field 318 for error detection (e.g., the FCS field may include a cyclic redundancy check (CRC)) and padding bits 320. The MPDU 316 may carry one or more MAC service data units (MSDUs) 326. For example, the MPDU 316 may carry an aggregate MSDU (A-MSDU) 322 that includes multiple A-MSDU subframes 324. Each A-MSDU subframe 324 includes a corresponding MSDU 330 preceded by a subframe header 328 and possibly followed by padding bits 332.

[0034] Referring again to the MPDU frame 310, the MAC delimiter 312 serves as a marker of the start of the associated MPDU 316 and may indicate the length of the associated MPDU 316. The MAC header 314 may include multiple fields that contain information that defines or indicates characteristics or attributes of the data encapsulated within the frame body 316. The MAC header 314 includes a duration field that indicates a duration that lasts from the end of the PPDU to at least the end of an acknowledgement (ACK) or block ACK (BA) of the PPDU to be transmitted by the receiving wireless communication device. The use of the duration field helps to reserve the wireless medium for the indicated duration, allowing the receiving device to establish its network allocation vector (NAV). The MAC header 314 also includes one or more fields that indicate the address of the data encapsulated within the frame body 316. For example, the MAC header 314 may include a combination of a source address, a transmitter address, a receiver address, or a destination address. The MAC header 314 may further include a frame control field that includes control information. The frame control field may specify a frame type, for example, a data frame, a control frame, or a management frame.

[0035] Figure 4 shows a block diagram of an example wireless communication device 400. In some implementations, the wireless communication device 400 may be an example of a device for use in a STA, such as one of the STAs 104 described with reference to Figure 1. In some implementations, the wireless communication device 400 may be an example of a device for use in an AP, such as the AP 102 described with reference to Figure 1. The wireless communication device 400 is capable of transmitting (or outputting for transmission) and receiving wireless communications (e.g., in the form of wireless packets). For example, a wireless communication device may be configured to transmit and receive packets in the form of physical layer convergence protocol (PLCP) protocol data units (PPDUs) and medium access control (MAC) protocol data units (MPDUs) that conform to IEEE 802.11 wireless communication protocol standards, such as those defined by the IEEE 802.11-2016 specification or amendments thereof, including, but not limited to, 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az, 802.11ba, and 802.11be.

[0036] The wireless communication device 400 may be or include a chip, system on chip (SoC), chipset, package, or device including one or more modems 402, such as a Wi-Fi (IEEE 802.11 compliant) modem. In some implementations, the one or more modems 402 (collectively "modems 402") additionally include a WWAN modem (e.g., a 3GPP 4G LTE or 5G compliant modem). In some implementations, the wireless communication device 400 also includes one or more radios 404 (collectively "radios 404"). In some implementations, the wireless communication device 406 further includes one or more processors, processing blocks, or processing elements 406 (collectively "processors 406") and one or more memory blocks or elements 408 (collectively "memory 408").

[0037] The modem 402 may include an intelligent hardware block or device, such as, for example, an application-specific integrated circuit (ASIC), among other possible examples. The modem 402 is generally configured to implement a PHY layer. For example, the modem 402 is configured to modulate packets and output the modulated packets to the radio 404 for transmission over a wireless medium. The modem 402 is also configured to obtain modulated packets received by the radio 404 and demodulate the packets to provide demodulated packets. In addition to the modulator and demodulator, the modem 402 may further include digital signal processing (DSP) circuitry, an automatic gain control (AGC), a coder, a decoder, a multiplexer, and a demultiplexer. For example, while in a transmit mode, data obtained from the processor 406 is provided to a coder, which encodes the data to provide coded bits. The coded bits are then mapped to points in a modulation constellation (using a selected MCS) to provide modulated symbols. The modulated symbols are then N SS number of spatial streams or N STS The modulated symbols in each spatial or space-time stream may then be multiplexed and converted via an Inverse Fast Fourier Transform (IFFT) block, followed by being provided to a DSP circuit for Tx windowing and filtering. The digital signal may then be provided to a digital-to-analog converter (DAC). The resulting analog signal may then be provided to a frequency up-converter and ultimately to the radio 404. In an implementation involving beamforming, the modulated symbols in each spatial stream are precoded via a steering matrix prior to their provision to the IFFT block.

[0038] While in the receive mode, the digital signal received from the radio 404 is provided to the DSP circuitry, which is configured to acquire the received signal, for example, by detecting the presence of a signal and estimating an initial timing and frequency offset. The DSP circuitry is further configured to digitally condition the digital signal, for example, using channel (narrowband) filtering, analog impairment adjustment (such as to correct I / Q imbalance), and finally applying a digital gain to obtain a narrowband signal. The output of the DSP circuitry may then be provided to an AGC, which is configured to use information extracted from the digital signal in one or more received training fields, for example, to determine an appropriate gain. The output of the DSP circuitry is also coupled to a demodulator, which is configured to extract modulated symbols from the signal and calculate, for example, logarithm likelihood ratios (LLRs) for each bit position of each subcarrier in each spatial stream. The demodulator is coupled to a decoder, which may be configured to process the LLRs to provide decoded bits. The decoded bits from all of the spatial streams are then provided to a demultiplexer for demultiplexing, which may then be descrambled and provided to the MAC layer (processor 406) for processing, evaluation, or interpretation.

[0039] The radio 404 generally includes at least one radio frequency (RF) transmitter (or “transmitter chain”) and at least one RF receiver (or “receiver chain”), which may be combined into one or more transceivers. For example, the RF transmitter and RF receiver may each include various DSP circuitry including at least one power amplifier (PA) and at least one low noise amplifier (LNA). The RF transmitter and RF receiver may then be coupled to one or more antennas. For example, in some implementations, the wireless communication device 400 may include or be coupled to multiple transmit antennas (each with a corresponding transmit chain) and multiple receive antennas (each with a corresponding receive chain). Symbols output from the modem 402 are provided to the radio 404, which then transmits the symbols via the coupled antenna. Similarly, symbols received via the antennas are obtained by the radio 404, which then provides the symbols to the modem 402.

[0040] The processor 406 may include an intelligent hardware block or device, such as, for example, a processing core, a processing block, a central processing unit (CPU), a microprocessor, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD) such as a field programmable gate array (FPGA), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The processor 406 processes information received via the radio 404 and modem 402, and processes information output via the modem 402 and radio 404 for transmission over a wireless medium. For example, the processor 406 may implement a control plane and a MAC layer configured to perform various operations related to the generation and transmission of MPDUs, frames, or packets. The MAC layer is configured to perform or facilitate frame coding and decoding, spatial multiplexing, space-time block coding (STBC), beamforming, and OFDMA resource allocation, among other operations or techniques. In some implementations, the processor 406 may generally control the modem 402 to cause the modem to perform the various operations described above.

[0041] The memory 408 may include a tangible storage medium, such as a random-access memory (RAM) or a read-only memory (ROM) or a combination thereof. The memory 408 may also store non-transitory processor or computer executable software (SW) code, including instructions that, when executed by the processor 406, cause the processor to perform various operations described herein for wireless communication, including generating, transmitting, receiving, and interpreting MPDUs, frames, or packets. For example, various functions of the components disclosed herein, or various blocks or steps of the methods, operations, processes, or algorithms disclosed herein, may be implemented as one or more modules of one or more computer programs.

[0042] FIG. 5A illustrates a block diagram of an exemplary AP 502. For example, the AP 502 may be an exemplary implementation of the AP 102 described with reference to FIG. 1. The AP 502 includes a wireless communication device (WCD) 510 (although the AP 502 itself may also be generally referred to as a wireless communication device as used herein). For example, the wireless communication device 510 may be an exemplary implementation of the wireless communication device 400 described with reference to FIG. 4. The AP 502 also includes multiple antennas 520 coupled to the wireless communication device 510 for transmitting and receiving wireless communications. In some implementations, the AP 502 additionally includes an application processor 530 coupled to the wireless communication device 510 and a memory 540 coupled to the application processor 530. The AP 502 further includes at least one external network interface 550 that enables the AP 502 to communicate with a core network or a backhaul network to provide access to an external network, including the Internet. For example, the external network interface 550 may include one or both of a wired (e.g., Ethernet) network interface and a wireless network interface (such as a WWAN interface). Some of the above-mentioned components may communicate directly or indirectly with some of the other components via at least one bus. The AP 502 further includes a housing that contains the wireless communication device 510, the application processor 530, the memory 540, and at least a portion of the antenna 520 and the external network interface 550.

[0043] FIG. 5B illustrates a block diagram of an exemplary STA 504. For example, the STA 504 may be an exemplary implementation of the STA 104 described with reference to FIG. 1. The STA 504 includes a wireless communication device 515 (although the STA 504 itself may also be generally referred to as a wireless communication device as used herein). For example, the wireless communication device 515 may be an exemplary implementation of the wireless communication device 400 described with reference to FIG. 4. The STA 504 also includes one or more antennas 525 coupled with the wireless communication device 515 for transmitting and receiving wireless communications. The STA 504 additionally includes an application processor 535 coupled with the wireless communication device 515, and a memory 545 coupled with the application processor 535. In some implementations, the STA 504 further includes a user interface (UI) 555 (such as a touch screen or keypad) and a display 565, and the display 565 may be integrated with the UI 555 to form a touch screen display. In some implementations, the STA 504 may further include one or more sensors 575, such as, for example, one or more inertial sensors, accelerometers, temperature sensors, pressure sensors, or altitude sensors. Some of the above-mentioned components may communicate directly or indirectly with other components via at least one bus. The STA 504 further includes a housing that contains the wireless communication device 515, the application processor 535, the memory 545, and at least a portion of the antenna 525, the UI 555, and the display 565.

[0044] As mentioned above, some APs and STAs may be subject to power spectral density (PSD) limitations. For example, some APs and STAs operating in the 6 GHz frequency band may be required to comply with a low power indoor (LPI) power class that limits the transmit power of the APs and STAs (in the 6 GHz band) to 5 dBm / MHz and -1 dBm / MHz, respectively. In other words, the transmit power in the 6 GHz band is PSD limited per MHz. Such PSD limitations may undesirably reduce the range of wireless communications and may reduce the packet detection and channel estimation capabilities of the APs and STAs.

[0045] Various aspects relate generally to distributed transmission, and more specifically, to pilot tone design supporting distributed transmission in PSD-limited wireless channels. As used herein, the term "distributed transmission" refers to PPDU transmission on non-contiguous tones (or subcarriers) of a wireless channel (e.g., according to a "distributed tone plan"). In contrast, the term "continuous transmission" refers to PPDU transmission on one or more sets of contiguous tones representing one or more RUs each, as defined by existing versions of the IEEE 802.11 standard (also referred to as "legacy tone plan"). For example, for distributed transmission, a transmitting device may modulate a PPDU on a number (M) of tones representing logical RUs associated with a legacy tone plan, and may further map the M tones to M non-contiguous subcarrier indexes associated with a wireless channel, where the M tones mapped to the M non-contiguous subcarrier indexes represent dRUs associated with the distributed tone plan. In some aspects, a transmitting device may transmit a PPDU over a wireless channel using a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indexes. In some implementations, the relative positions of the N pilot tones may be different than the relative positions of some (K) pilot tones associated with a logical RU (defined by the legacy tone plan). For example, K=2 pilot tones may be assigned to the 6th and 20th tones of M tones representing a logical RU (defined by the legacy tone plan), and N=2 pilot tones may be assigned to the 2nd and 15th tones of M tones mapped to M non-contiguous subcarrier indices.

[0046] Particular implementations of the subject matter described in this disclosure may be implemented to achieve one or more of the following potential advantages: Distributed transmission provides greater flexibility in medium utilization for PSD-limited wireless channels. In some implementations, a distributed tone plan may map pilot tone locations associated with logical RUs to localized regions of the wireless channel. The pilot tones are used for phase alignment and parameter tracking. However, when pilot tones are pushed into localized regions of the wireless channel, interference in such localized regions may effectively eliminate pilot tones in the dRU. For example, a receiving device may fail to receive any pilot tones if it experiences a deep fade in any of these localized regions. However, by changing the relative positions of pilot tones between logical RUs (as defined by the legacy tone plan) and dRUs, aspects of the present disclosure may ensure that pilot tones associated with a dRU are uniformly distributed across the wireless channel, or are otherwise distributed in a manner that is more robust to interference on the wireless channel. For example, uniformly distributing pilot tones across the wireless channel increases the likelihood that a receiving device will receive at least some of the pilot tones even if it experiences a deep fade in one or more localized regions of the wireless channel.

[0047] FIG. 6 illustrates a frequency diagram 600 showing an example distributed tone mapping according to some implementations. More specifically, FIG. 6 illustrates an example mapping of a payload 601 of a PPDU 602 to a set of tones or subcarriers for transmission over a wireless channel. In some implementations, the payload 601 may be modulated on a regular RU (rRU) corresponding to a logical RU 604 associated with a legacy tone plan and further mapped to a distributed RU (dRU) 606 according to the distributed tone plan. The logical RU 604 represents the number of tones or subcarriers allocated for transmission of the PPDU 602. In contrast, the dRU 606 represents the physical resource (identified by a subcarrier index) that is modulated to transmit the PPDU 602. As used herein, the term "distributed RU" (or dRU) refers to any logical RU distributed across a set of non-contiguous subcarrier indexes, and the term "distributed tone plan" refers to a set of non-contiguous subcarrier indexes associated with a dRU.

[0048] Existing versions of the IEEE 802.11 standard define a number of RUs and multiple RUs (MRUs) of various sizes that map to consecutive tones or subcarriers across a frequency bandwidth (or radio channel). For example, a 242-tone RU maps to 242 consecutive subcarrier indices across a 20 MHz bandwidth. Similarly, a 484+242-tone MRU maps to 484 consecutive subcarrier indices across a 40 MHz bandwidth and 242 consecutive subcarrier indices across a 20 MHz bandwidth. As used herein, the term "regular RU" (or rRU) refers to any RU or MRU configuration supported by existing versions of the IEEE 802.11 standard (including the IEEE 802.11be amendment of the IEEE 802.11 standard), and the term "legacy tone plan" refers to any tone plan defined by existing versions of the IEEE 802.11 standard.

[0049] In some implementations, the logical RU 604 may represent an rRU defined by an existing version of the IEEE 802.11 standard. In other words, the logical RU 604 maps directly to a respective rRU according to the legacy tone plan. In the example of FIG. 6, the logical RU 604 includes 26 tones. Thus, under the legacy tone plan, the logical RU 604 would map directly to 26 contiguous or consecutive subcarrier indexes across a 2 MHz subchannel. However, when mapped to an rRU, the transmit power of the logical RU 604 may be severely limited based on the PSD of the wireless channel. For example, the LPI power class limits the transmit power of the AP and STA to 5 dBm / MHz and −1 dBm / MHz, respectively, in the 6 GHz band. Thus, the transmit power per tone of the logical RU 604 is limited by the number of tones that are mapped to each 1 MHz subchannel of the wireless channel. Thus, each 1 MHz subchannel of a PSD-limited channel may be referred to herein as a “PSD-limited subchannel.”

[0050] Aspects of the present disclosure recognize that by distributing the tones across a wider bandwidth, the transmit power per tone of the logical RU 604 can be increased. By increasing the transmit power per tone, the overall transmit power of the logical RU 604 can also be increased. Thus, in some implementations, the logical RU 604 can be mapped to a set of non-contiguous subcarrier indices across a wider bandwidth channel. For example, with reference to FIG. 6, the logical RU 604 is mapped to the dRU 606 according to a distributed tone plan. More specifically, the logical RU 604 is mapped to 26 non-contiguous subcarrier indices spread across a 40 MHz radio channel (also referred to herein as the "dRU spread bandwidth"). Compared to the tone mapping described above with respect to the legacy tone plan, the distributed tone mapping shown in FIG. 6 effectively reduces the number of tones (of the logical RU 604) for each 1 MHz subchannel. For example, each of the 26 tones can be mapped to a different 1 MHz subchannel of the 40 MHz channel. As a result, each AP or STA implementing the distributed tone mapping of FIG. 6 can maximize its per-tone transmit power (and thereby maximize the overall transmit power of the logical RU 604).

[0051] In some implementations, the transmitting device (such as a STA or AP) may include a distributed tone mapper that maps the logical RU 604 to the dRU 606 in the frequency domain (such as described with reference to FIG. 6). The dRU 606 is then converted (such as by an inverse fast Fourier transform (IFFT)) to a time domain signal for transmission over a wireless channel. The receiving device (such as an AP or STA) receives the time domain signal over the wireless channel and converts (such as by a fast Fourier transform (FFT)) the time domain signal back to the dRU 606. In some implementations, the receiving device may include a distributed tone demapper that demaps the dRU 606 to the logical RU 604. In other words, the distributed tone demapper reverses the mapping performed by the distributed tone mapper in the transmitting device. The receiving device may then recover the information carried (or modulated) on the logical RU 604 as a result of the demapping.

[0052] In the example of Figure 6, the logical RUs 604 are uniformly distributed across the 40 MHz radio channel. However, in an actual implementation, the logical RUs 604 may be mapped to any suitable pattern of non-contiguous subcarrier indexes. For example, in some aspects, the distance between any pair of modulated tones may be smaller or larger than the distance shown in Figure 6. Still further, in some aspects, multiple logical RUs may be mapped to interleaved subcarrier indexes of a shared radio channel.

[0053] Figure 7 shows a frequency diagram illustrating an example mapping of logical RUs to dRUs on a shared radio channel according to some implementations. More specifically, Figure 7 shows an example mapping of logical RUs 712 and 714 to dRUs 716 and 718, respectively. In some implementations, each of the logical RUs 712 and 714 can carry user data for a respective STA (not shown for simplicity).

[0054] In the example of FIG. 7, each of the logical RUs 712 and 714 includes 26 tones. In some implementations, the logical RUs 712 and 714 are mapped to the dRUs 716 and 718, respectively, according to a distributed tone plan. More specifically, each of the logical RUs 712 and 714 is mapped to a respective set of 26 non-contiguous subcarrier indexes spread across a 40 MHz radio channel. Thus, as shown in FIG. 7, the dRU 716 is interleaved with the dRU 718 across the shared 40 MHz radio channel. Aspects of the present disclosure recognize that by interleaving the dRUs 716 and 718, the transmit power per tone of each dRU can be significantly increased without sacrificing spectral efficiency.

[0055] To support distributed transmission, new packet design and signaling are required to indicate whether a PPDU should be transmitted on tones across rRUs (following the legacy tone plan) or on tones across dRUs (following the distributed tone plan). For example, existing versions of the IEEE 802.11 standard define a trigger frame format that can be used to request transmission of a TB PPDU from one or more STAs. The trigger frame allocates resources to the STAs for transmission of the TB PPDU and indicates how the TB PPDU should be configured for transmission. For example, the trigger frame can indicate the logical RUs (or MRUs) that are allocated for transmission in the TB PDDU. In some implementations, the trigger frame can be further configured to carry tone distribution information that indicates whether the logical RUs (or MRUs) map to the rRUs or the dRUs.

[0056] FIG. 8 illustrates a frequency diagram showing an example mapping of logical RUs 804 to dRUs 806 according to some implementations. In the example of FIG. 8, the logical RU 804 includes 52 tones and the dRU spreading bandwidth is equal to 40 MHz. In some implementations, the 52 tones associated with the logical RU 804 may be mapped to 52 non-contiguous subcarrier indexes associated with a 40 MHz channel according to a distributed tone plan that maps the first 26 tones of the logical RU 804 to every 18th subcarrier index starting with subcarrier index 1, and maps the remaining 26 tones of the logical RU 804 to every 18th subcarrier index starting with subcarrier index 10. In other words, the 52-tone logical RU 804 is treated as two 26-tone RUs offset by 9 subcarrier indexes for purposes of distributed tone mapping.

[0057] In the example of FIG. 8, the first tone (tone_idx=1) of logical RU 804 is mapped to subcarrier index 1, and the second tone (tone_idx=2) of logical RU 804 is mapped to subcarrier index 19. This process continues until the 26th tone (tone_idx=26) of logical RU 804 is mapped to subcarrier index 451. After the first 26 tones of logical RU 804 are mapped to dRU 806, the process is repeated for the next 26 tones of logical RU 804 starting at a subcarrier offset of 9. In other words, the 27th tone (tone_idx=27) of logical RU 804 is mapped to subcarrier index 10, and the 28th tone (tone_idx=28) of logical RU 804 is mapped to subcarrier index 28. This process continues until the 52nd tone (tone_idx=52) of logical RU 804 is mapped to subcarrier index 460. Thus, as shown in FIG. 8, the distributed tone plan effectively interleaves two 26-tone RUs across the dRU spreading bandwidth.

[0058] Aspects of the present disclosure recognize that such interleaving of RUs can change the distribution of pilot tones across the radio channel. For example, FIG. 9A illustrates a frequency diagram 900 illustrating an example distribution of pilot tones across the radio channel according to a legacy tone plan. More specifically, FIG. 9A illustrates pilot tone positions associated with a 26-tone rRU distributed across a 40 MHz channel. As shown in FIG. 9A, the pilot tones are uniformly distributed across the entire 40 MHz channel. In contrast, FIG. 9B illustrates a frequency diagram 910 illustrating an example distribution of pilot tones across the radio channel according to a distributed tone plan. More specifically, FIG. 9B illustrates pilot tone positions when an existing 26-tone logical RU is mapped to a 40 MHz channel according to the distributed tone plan described above with reference to FIG. 8, with the pilot tones mapped according to their relative positions within the corresponding rRU. As shown in FIG. 9B, the pilot tones are pushed into two localized regions of the 40 MHz channel.

[0059] The pilot tones are used for phase alignment and parameter tracking. Aspects of the present disclosure recognize that when pilot tones are pushed into a localized region of a wireless channel (such as shown in FIG. 9B), interference in such a localized region can effectively eliminate the pilot tones in the dRU. For example, if a receiving device experiences a deep fade, narrowband interference, or spur in the localized region shown in FIG. 9B, it may not receive any of the pilot tones. In some aspects, the relative position of the pilot tones associated with a dRU (also referred to as "scattered pilots") may be different from the relative position of the pilot tones associated with the associated rRU (also referred to as "legacy pilots"). For example, a change in the relative pilot tone position from the rRU to the dRU can ensure a more uniform or robust distribution of the scattered pilots across the dRU spreading bandwidth.

[0060] For example, referring to FIG. 9A, each 26-tone rRU includes a pair of pilot tones (one on either side of the carrier frequency on which the rRU is transmitted). The legacy tone plan defines two sets of relative pilot tone positions that can be assigned to the pilot tone pairs of any 26-tone rRU, namely [6,20] and [7,21]. In other words, the pilot tones are assigned to the pilot tone pairs of some 26-tone rRUs (rRU26 i ) can be assigned to the 6th and 20th tone positions of some other 26 tones rRU (rRU26 j ) can be assigned to the 7th and 21st tone positions of rRU26 i Relative pilot tone position in rRU26 j Since there is negligible difference between the relative pilot tone positions within the rRU 26, when multiple 26-tone logical RUs are mapped to the dRU spreading bandwidth in an interleaved manner (such as described with reference to FIG. 8), the pilot tone positions are pushed into two localized regions shown in FIG. 9B. i It will be appreciated that greater diversity between the relative pilot tone positions in the rRU 26j and the relative pilot tone positions in the rRU 26j can help to improve the distribution of pilot tones across the dRU spreading bandwidth.

[0061] In some implementations, the distributed tone plan may change the pilot tone positions associated with a logical RU so that the pilot tone positions are spread across a larger portion of the wireless channel when mapped to the dRU. For example, the 26 tones of each logical RU may be spread across a larger portion of the wireless channel when mapped to the dRU. i The relative pilot tone position associated with rRU may be shifted three tones to the left (resulting in a new relative pilot tone position [3,17]), jThe relative pilot tone positions associated with may be shifted three tones to the right (resulting in a new relative pilot tone position [10,24]). As a result, when multiple 26-tone logical RUs are mapped to a dRU spreading bandwidth in an interleaved manner, the pilot tones will be distributed over a wider range of subcarrier indices in the resulting dRU. For example, FIG. 10 shows a frequency diagram 1000 illustrating an example distribution of pilot tones as a result of changing the relative pilot tone positions associated with the 26-tone logical RUs. Compared to the pilot tone distribution shown in FIG. 9B, the new relative pilot tone positions associated with FIG. 10 significantly improve the spreading of the pilot tones mapped to each dRU.

[0062] Aspects of the present disclosure recognize that larger RU sizes are associated with a larger number of pilot tones and therefore naturally more robust to narrowband interference. Thus, in some implementations, the relative pilot tone positions associated with RU sizes greater than 26 may remain unchanged. Tables 1-3 provide an overview of how the new relative pilot tone positions affect the mapping of pilot tones to various dRUs distributed across dRU spreading bandwidths of 20 MHz, 40 MHz, and 80 MHz, respectively. In Tables 1-3, a -3 tone shift is applied to relative pilot tone position [6,20] and a +3 tone shift is applied to relative pilot tone position [7,21]. However, various other tone shifts may be applied to any of the 26 tone RUs. For example, in some implementations, a +3 tone shift may be applied to relative pilot tone position [6,20] and a -3 tone shift may be applied to relative pilot tone position [7,21]. In some other implementations, a shift of -3 tones may be applied to the relative pilot tone positions associated with RU26-1 through RU26-9 (inclusive, [6,20] and [7,21]), and a shift of +3 tones may be applied to the relative pilot tone positions associated with RU26-10 through RU26-18 (inclusive, [6,20] and [7,21]).

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] Aspects of the present disclosure recognize that the robustness of the pilot tones to narrowband interference can be further improved by distributing the pilot tones more uniformly across the bandwidth of the wireless channel. For example, the bandwidth of the wireless channel can be subdivided into several (N) equal-sized portions such that a respective pilot tone can be assigned to each bandwidth portion for a given dRU. In some implementations, the distributed tone plan can assign N scattered pilots to each of the N bandwidth portions after mapping the tones of the logical RU to the non-contiguous subcarrier indexes associated with the dRU. In such implementations, the relative location of the scattered pilots within the dRU may not depend on the relative location of the legacy pilots within the logical RU to which the tones of the dRU are mapped. Thus, the scattered pilots can be more optimally distributed across the dRU spreading bandwidth.

[0067] FIG. 11 shows a frequency diagram 1100 illustrating an example model for allocating pilot tones in a dRU, according to some implementations. More specifically, frequency diagram 1100 shows an M-tone dRU 1106 having a number (N) of allocated pilot tones. The number of pilot tones, N, can be associated with a distributed tone plan that is used to map the M tones to M non-contiguous subcarrier indices associated with the dRU 1106. For simplicity, the M tones are identified by their relative tone indexes 1 through M in FIG. 11 (rather than their physical subcarrier indexes).

[0068] In some aspects, a distributed tone plan may allocate a fixed number of distributed pilots N for a given dRU spreading bandwidth. In other words, the number of distributed pilots N may remain the same for a different number of tones M mapped to the same dRU spreading bandwidth. Thus, the number of distributed pilots N may be different (e.g., larger or smaller) than the number of legacy pilots (K) associated with the logical RU to which the M tones are mapped (N≠K). For example, four distributed pilots (N=4) may be allocated to a dRU spreading bandwidth of 80 MHz, regardless of whether a 26-tone logical RU (K=2) or a 242-tone logical RU (K=8) is mapped to the 80 MHz bandwidth. Aspects of the present disclosure recognize that when N>K, the additional pilot tones should not come at the expense of one or more data tones in the dRU. Thus, in some implementations, one or more of the N distributed pilots may be transmitted on a "common" subcarrier index that is different from the M non-contiguous subcarrier indexes to which the M tones are mapped.

[0069] In some other aspects, the distributed tone plan may allocate as many scattered pilots N to the dRU 1106 as the number K of legacy pilots associated with the logical RU to which the M tones are mapped (N=K). For example, when a 26-tone logical RU (K=2) is mapped to a 26-tone dRU, the distributed tone plan may allocate two scattered pilots (N=2) to the resulting dRU. Since N=K, the N scattered pilots may be transmitted on the subset of M non-contiguous subcarrier indexes to which the M tones are mapped. In some implementations, the N scattered pilots may carry the same pilot sequence (or may be modulated with the same pilot value) as the K legacy pilots associated with the logical RU to which the M tones are mapped. In some implementations, the N scattered pilots may also be transmitted in a long training field (LTF) of a PPDU used to estimate a channel associated with the dRU 1106. In such implementations, the pilot sequence carried by the N scattered pilots may depend on the LTF sequence (such as defined by existing versions of the IEEE 802.11 standard).

[0070] In some aspects, the distributed tone plan may distribute the N pilot tones evenly across the bandwidth associated with the dRU 1106. Aspects of the present disclosure recognize that the tones closest to the carrier frequency (DC) and the tones closest to the edge of the wireless channel are most likely to be corrupted and therefore may be unreliable for use in pilot tone transmission. Thus, in some implementations, the "usable" bandwidth (BW) of the wireless channel may exclude one or more of the tones closest to or adjacent to the edge of the wireless channel and may also exclude one or more of the tones closest to or adjacent to the DC. As used herein, the term "usable bandwidth" refers to any portion of a wireless channel to which scattered pilots may be assigned.

[0071] As shown in FIG. 11, the available bandwidth is subdivided into N pilot regions of equal size (each spanning 1 / N of the total available bandwidth). In some implementations, half of the N pilot tones can be assigned to N / 2 subcarrier indices located below DC (also referred to as the "lower bandwidth portion"), and the other half of the N pilot tones can be assigned to N / 2 subcarrier indices located above DC (also referred to as the "upper bandwidth portion"). More specifically, each of the N pilot tones can be assigned to a subcarrier index located in a respective one of the N pilot regions. For example, a first pilot tone of the N pilot tones can be assigned to a subcarrier index located in the Pilot 1 region, and an Nth pilot tone of the N pilot tones can be assigned to a subcarrier index located in the Pilot N region.

[0072] In some implementations, the N / 2 pilot tones assigned to the lower bandwidth portion may be transmitted on N / 2 approximately equally spaced subcarrier indices located in the lower bandwidth portion, and the N / 2 pilot tones assigned to the upper bandwidth portion may be transmitted on N / 2 approximately equally spaced subcarrier indices located in the upper bandwidth portion. Thus, the N / 2 pilot tones in the lower bandwidth portion may have the same relative tone positions in each of the first N / 2 pilot regions, and the N / 2 pilot tones in the upper bandwidth portion may have the same relative tone positions in each of the remaining N / 2 pilot regions. Table 4 provides a summary of example suitable pilot tone spacings for various sizes of dRUs and various dRU spreading bandwidths.

[0073] [Table 4]

[0074] In some implementations, the N pilot tones may be arranged symmetrically around DC. In other words, the N / 2 subcarrier indices in the lower bandwidth portion may be arranged at the same distance from DC as the N / 2 subcarrier indices in the upper bandwidth portion. For example, if the first pilot tone is transmitted on the lowest subcarrier index located in the Pilot 1 region, the Nth pilot tone is transmitted on the highest subcarrier index located in the Pilot N region. By allocating the N pilot tones symmetrically around DC, only half of the pilot tone positions need to be stored in memory.

[0075] In some other implementations, the N pilot tones may be positioned asymmetrically around DC. More specifically, each of the N subcarrier indices may be positioned the same distance from the lowest subcarrier index in each of the N pilot regions. For example, if the first pilot tone is transmitted on the lowest subcarrier index located in the Pilot 1 region, then the Nth pilot tone is transmitted on the lowest subcarrier index located in the Pilot N region. Aspects of the present disclosure recognize that such pilot tone allocation may result in a reduced peak-to-average power ratio (PAPR).

[0076] As described with reference to Figures 9A and 9B, the lack of diversity between the relative pilot tone positions in different RUs may cause the scattered pilots to be pushed into localized regions of the dRU spreading bandwidth as a result of the interleaved tone mapping (such as described with reference to Figure 8). Thus, in some implementations, the distributed tone plan may assign different relative pilot tone positions to different dRUs. Furthermore, the physical pilot tone position in a given dRU may depend on both the starting subcarrier index at which the dRU is transmitted and the dRU index (i) associated with the dRU (for i = 1:n, where n is the number of dRUs that can transmit simultaneously on the shared radio channel). For example, if only two M-tone dRUs can transmit simultaneously on the shared radio channel and the 1st pilot tone of the first dRU is transmitted on the lowest subcarrier index located in the pilot 1 region of the first dRU, the 1st pilot tone of the second dRU may not be transmitted on the lowest subcarrier index located in the pilot 1 region of the second dRU.

[0077] FIG. 12 illustrates a frequency diagram 1200 showing example pilot tone candidates for a 26-tone dRU 1206 according to some implementations. As shown in FIG. 12, the 26 tones of the dRU 1206 are mapped to 26 non-contiguous subcarrier indices associated with a wireless channel. For simplicity, the 26 tones are identified in FIG. 12 by their relative tone indexes 1-26, rather than their physical subcarrier indexes. In some implementations, the dRU 1206 may be an example of the M-tone dRU 1106 of FIG. 11, where M=26 and N=2. Thus, two scattered pilots may be assigned to the dRU 1206.

[0078] In the example of FIG. 12, tones 1, 13, 14, and 26 (located closest to the edges of the DC and dRU spreading bandwidths) are excluded as potential pilot tone candidates. The remaining available bandwidth is subdivided into two pilot regions (each spanning ½ of the bandwidth) that match the placement of the two pilot tones. For example, the pilot 1 region encompasses tones 2-12, which are located in the lower bandwidth portion of the dRU 1206, and the pilot 2 region encompasses tones 15-25, which are located in the upper bandwidth portion of the dRU 1206. As discussed above with reference to FIG. 11, the distributed tone plan can assign scattered pilots to relative tone positions in each of the two pilot regions based on the starting subcarrier index at which the dRU 1206 is transmitted and the dRU index associated with the dRU 1206.

[0079] According to the existing legacy tone plan, a larger rRU is constructed from multiple smaller rRUs. For example, a 52-tone rRU inherits its tone positions from two adjacent 26-tone rRUs that span the same bandwidth as the 52-tone rRU. In some aspects, a larger dRU can inherit their pilot tone positions from multiple smaller dRUs according to a hierarchical structure. In other words, the pilot tone positions for all dRUs of various sizes can be inherited from the pilot tone positions (P26) associated with one or more 26-tone dRUs. For example, a 52-tone dRU can inherit its pilot tone positions (P52) from two 26-tone dRUs (P52=2). * P26), the 106-tone dRU can inherit its pilot tone positions (P106) from two 52-tone dRUs, downsampled by a factor of 2 (P106=1 / 2(2 * P52), the 242-tone dRU can inherit its pilot tone position (P242) from the two 106-tone dRUs (P242=2 * P106), a 484-tone dRU can inherit its pilot tone position (P484) from two 242-tone dRUs (P282=2* In some implementations, a distributed tone plan can ensure fair distribution of pilot tones for dRUs of various sizes and for multiple dRUs that are mapped to a shared radio channel.

[0080] FIG. 13A shows a frequency diagram 1300 illustrating example pilot tone allocations for a 26-tone dRU, according to some implementations. In some implementations, each 26-tone dRU in FIG. 13A may be an example of a 26-tone dRU 1206 in FIG. 12. More specifically, FIG. 13A shows eighteen 26-tone dRUs (dRU261 to dRU266) that can be mapped to a 40 MHz radio channel. 18 Exemplary relative pilot tone allocations (dP261 to dP26 18 In some implementations, pilot tone allocations dP261 to dP26 18 can be optimized for a 26-tone dRU to result in a substantially fair distribution of pilot tones across all dRU sizes and dRU spreading bandwidths.

[0081] In the example of FIG. 13A, the pilot tones are asymmetrically arranged around DC. Furthermore, tones 1, 12, 13, 14, 25, and 26 (located closest to DC and the edge of the dRU spreading bandwidth) are excluded as potential pilot tone candidates. As a result, only 10 unique relative pilot tone positions can be assigned to the 18 dRUs. In other words, at least some of the dRUs must have the same relative pilot tone position. In some implementations, the same relative pilot tone position can be assigned to multiple dRUs that are located a sufficient distance apart according to a distributed tone plan. In such implementations, the spacing of the pilot tones may depend on the spacing of the starting subcarrier index to which the dRUs are mapped.

[0082] As shown in FIG. 13A, the relative pilot tone position (2,15) corresponds to dRU261 and dRU26 11 and the relative pilot position (3,16) is assigned to dRU266 and dRU26 16 and the relative pilot tone position (4,17) is assigned to dRU263 and dRU26 13 and the relative pilot tone position (5,18) is assigned to dRU268 and dRU26 18 and the relative pilot tone position (6,19) is assigned to dRU26 14 , relative pilot tone position (7,20) is assigned to dRU 265, and relative pilot tone position (8,21) is assigned to dRU 262 and dRU 266. 10 and the relative pilot tone position (9,22) is assigned to dRU267 and dRU26 15 and the relative pilot tone position (10, 23) is assigned to dRU264 and dRU26 12 and the relative pilot tone position (11,24) is assigned to dRU269 and dRU26 17 is assigned to.

[0083] FIG. 13B illustrates another frequency diagram 1310 showing example pilot tone allocations for a 26-tone dRU, according to some implementations. In some implementations, each 26-tone dRU in FIG. 13B may be an example of a 26-tone dRU 1206 in FIG. 12. More specifically, FIG. 13B illustrates eighteen 26-tone dRUs (dRU261 through dRU266) that can be mapped to a 40 MHz radio channel. 18 Exemplary relative pilot tone allocations (dP261 to dP26 18 In some implementations, pilot tone allocations dP261 to dP26 18 can be optimized for a 26-tone dRU to result in a substantially fair distribution of pilot tones across all dRU sizes.

[0084] In the example of FIG. 13B, the pilot tones are symmetrically arranged around DC. Furthermore, tones 1, 12, 13, 14, 15, and 26 (located closest to DC and the edge of the dRU spreading bandwidth) are excluded as potential pilot tone candidates. As a result, only 10 unique relative pilot tone positions can be assigned to the 18 dRUs. In other words, at least some of the dRUs must have the same relative pilot tone position. In some implementations, the same relative pilot tone position can be assigned to multiple dRUs that are located a sufficient distance apart according to a distributed tone plan. In such implementations, the spacing of the pilot tones may depend on the spacing of the starting subcarrier index to which the dRUs are mapped.

[0085] As shown in FIG. 13B, the relative pilot tone position (2,25) is symmetrical with respect to DC, with RU261 and dRU26 11 and the relative pilot position (3,24) is assigned to dRU266 and dRU26 16 and the relative pilot tone position (4,23) is assigned to dRU263 and dRU26 13 and the relative pilot tone position (5,22) is assigned to dRU268 and dRU26 18 and the relative pilot tone position (6,21) is assigned to dRU26 14 , relative pilot tone position (7,20) is assigned to dRU 265, and relative pilot tone position (8,19) is assigned to dRU 262 and dRU 266. 10 and the relative pilot tone position (9,18) is assigned to dRU267 and dRU26 15 and the relative pilot tone position (10,17) is assigned to dRU264 and dRU26 12 and the relative pilot tone position (11,16) is assigned to dRU269 and dRU26 17 is assigned to.

[0086] Tables 5-7 provide an overview of example pilot tone allocations associated with various dRU sizes mapped to dRU spreading bandwidths of 20 MHz, 40 MHz, and 80 MHz, respectively, according to the hierarchical structure described with reference to Figures 12-13B.

[0087] [Table 5]

[0088] [Table 6]

[0089] [Table 7]

[0090] FIG. 14 illustrates a frequency diagram 1400 showing an example distribution of pilot tones across a radio channel according to some implementations. More specifically, FIG. 14 illustrates pilot tone locations assigned to a 242-tone dRU mapped to an 80 MHz radio channel according to the hierarchical structure described above with reference to FIGS. 12-13B and Tables 5-7. The pilot tones are distributed across a relatively wide range of frequencies, but some parts of the radio channel contain a greater density of pilot tones than other parts. In other words, by ensuring a fairly fair distribution of pilot tones across all dRU sizes, the dRU26-based hierarchical structure may not provide an optimal pilot tone allocation for any particular dRU size. In some aspects, the distributed tone plan can assign pilot tones to each dRU in a manner that is optimized for a given dRU size, for example, by maintaining equidistant spacing between pilot tones in each dRU.

[0091] FIG. 15 illustrates a frequency diagram 1500 showing example pilot tone candidates for a 242-tone dRU 1506 according to some implementations. As shown in FIG. 15, the 242 tones of the dRU 1506 are mapped to 242 non-contiguous subcarrier indices associated with a wireless channel. For simplicity, the 242 tones are identified in FIG. 15 by their relative tone indexes 1-242, rather than their physical subcarrier indexes. In some implementations, the dRU 1506 may be an example of the M-tone dRU 1106 of FIG. 11, where M=242 and N=8. Thus, eight scattered pilots may be assigned to the dRU 1506.

[0092] In the example of Figure 15, tones 1, 2, 119, 120, 121, 122, 123, 124, 241, and 242 (located closest to the edges of the DC and dRU spreading bandwidths) are eliminated as potential pilot tone candidates. The remaining available bandwidth is subdivided into eight pilot regions (each spanning 1 / 8 of the bandwidth) consistent with the placement of the eight pilot tones. In the lower bandwidth portion of the dRU 1506, the pilot 1 region encompasses tones 3-31, the pilot 2 region encompasses tones 32-60, the pilot 3 region encompasses tones 61-89, and the pilot 4 region encompasses tones 90-118. In the upper bandwidth portion of the dRU 1506, the pilot 5 region covers tones 125 to 153, the pilot 6 region covers tones 154 to 182, the pilot 7 region covers tones 183 to 211, and the pilot 8 region covers tones 212 to 240. As discussed above with reference to FIG. 11 , the distributed tone plan may assign scattered pilots to relative tone positions in each of the eight pilot regions based on the starting subcarrier index at which the dRU 1506 is transmitted and the dRU index associated with the dRU 1506.

[0093] In some implementations, the distributed tone plan may ensure that the four pilot tones in the lower bandwidth portion of the dRU 1506 are equidistant from each other and the four pilot tones in the upper bandwidth portion of the dRU 1506 are equidistant from each other. In such implementations, the eight distributed pilots may be optimally allocated to a particular dRU 1506 (rather than being hierarchically allocated based on pilot tone positions in one or more 26-tone dRUs). Thus, one or more of the pilot tone positions allocated to the dRU 1506 may be unique to the 242-tone dRU and thus may not overlap with pilot tone positions allocated to any 26-tone dRU that may be mapped to the same dRU spreading bandwidth as the dRU 1506. Although described in the context of a 242-tone dRU, the pilot tone optimization per dRU may be applicable to dRUs of any size. For example, one or more pilot tone positions assigned to one or more pilot tone positions assigned to a 52-tone dRU may be specific to the 52-tone dRU, one or more pilot tone positions assigned to a 106-tone dRU may be specific to the 106-tone dRU, and one or more pilot tone positions assigned to a 484-tone dRU may be specific to the 484-tone dRU.

[0094] FIG. 16A shows a frequency diagram 1600 illustrating an example pilot tone allocation for a 242-tone dRU according to some implementations. In some implementations, each 242-tone dRU in FIG. 16A may be an example of a 242-tone dRU 1506 in FIG. 15. More specifically, FIG. 16A shows example relative pilot tone candidates associated with four 242-tone dRUs that may be mapped to an 80 MHz radio channel. In some implementations, the candidate pilot tone positions may be optimized for the 242-tone dRU to result in equidistant placement of pilot tones among all 242-tone dRUs that may be mapped to a shared radio channel.

[0095] In the example of Figure 16A, the pilot tones are symmetrically positioned around DC. Furthermore, tones 1, 2, 119, 120, 121, 122, 123, 124, 241, and 242 (located closest to DC and the edge of the dRU spreading bandwidth) are excluded as potential pilot tone candidates. As a result, 30 unique relative pilot tone positions can be assigned to the four dRUs. Because the number of unique relative pilot tone positions is greater than the number of 242-tone dRUs that can be mapped to an 80 MHz channel, each dRU can have a different pilot tone offset. In other words, the relative pilot tone position assigned to the first 242-tone dRU (dRU2421) may be different from the relative pilot tone position assigned to any of the remaining 242-tone dRUs (dRU2422 to dRU2424), the relative pilot tone position assigned to dRU2422 may be different from the relative pilot tone position assigned to any of dRU2421, dRU2423, or dRU2424, the relative pilot tone position assigned to dRU2423 may be different from the relative pilot tone position assigned to any of dRU2421, dRU2422, or dRU2424, and the relative pilot tone position assigned to dRU2424 may be different from the relative pilot tone position assigned to any of dRU2421 to dRU2424.

[0096] As shown in FIG. 16A, relative pilot tone positions (7, 36, 65, 94, 149, 178, 207, 236) are assigned to dRU 2421, relative pilot tone positions (14, 43, 72, 101, 142, 171, 200, 229) are assigned to dRU 2422, relative pilot tone positions (21, 50, 79, 108, 135, 164, 193, 222) are assigned to dRU 2423, and relative pilot tone positions (28, 57, 86, 115, 128, 157, 186, 215) are assigned to dRU 2424. Thus, the four scattered pilots assigned to the lower bandwidth portion of each 242-tone dRU are equally spaced (30 tones apart), and the four scattered pilots assigned to the upper bandwidth portion of each 242-tone dRU are equally spaced (30 tones apart).

[0097] FIG. 16B illustrates another frequency diagram 1610 showing example pilot tone allocations for a 242-tone dRU according to some implementations. In some implementations, each 242-tone dRU in FIG. 16B may be an example of a 242-tone dRU 1506 in FIG. 15. More specifically, FIG. 16B illustrates example relative pilot tone candidates associated with four 242-tone dRUs that may be mapped to an 80 MHz radio channel. In some implementations, the candidate pilot tone positions may be optimized for the 242-tone dRU to result in equidistant placement of pilot tones among all 242-tone dRUs that may be mapped to a shared radio channel.

[0098] In the example of Figure 16B, the pilot tones are asymmetrically positioned around DC. Furthermore, tones 1, 2, 119, 120, 121, 122, 123, 124, 241, and 242 (located closest to DC and the edge of the dRU spreading bandwidth) are excluded as potential pilot tone candidates. As a result, 30 unique relative pilot tone positions can be assigned to the four dRUs. Because the number of unique relative pilot tone positions is greater than the number of 242-tone dRUs that can be mapped to an 80 MHz channel, each dRU can have a different pilot tone offset. In other words, the relative pilot tone position assigned to the first 242-tone dRU (dRU2421) may be different from the relative pilot tone position assigned to any of the remaining 242-tone dRUs (dRU2422 to dRU2424), the relative pilot tone position assigned to dRU2422 may be different from the relative pilot tone position assigned to any of dRU2421, dRU2423, or dRU2424, the relative pilot tone position assigned to dRU2423 may be different from the relative pilot tone position assigned to any of dRU2421, dRU2422, or dRU2424, and the relative pilot tone position assigned to dRU2424 may be different from the relative pilot tone position assigned to any of dRU2421 to dRU2424.

[0099] As shown in FIG. 16B, relative pilot tone positions (7, 36, 65, 94, 129, 158, 187, 216) are assigned to dRU 2421, relative pilot tone positions (14, 43, 72, 101, 136, 165, 194, 223) are assigned to dRU 2422, relative pilot tone positions (21, 50, 79, 108, 143, 172, 201, 230) are assigned to dRU 2423, and relative pilot tone positions (28, 57, 86, 115, 150, 179, 208, 237) are assigned to dRU 2424. Thus, the four scattered pilots assigned to the lower bandwidth portion of each 242-tone dRU are equally spaced (30 tones apart), and the four scattered pilots assigned to the upper bandwidth portion of each 242-tone dRU are equally spaced (30 tones apart).

[0100] Tables 8-11 provide an overview of example pilot tone allocations associated with various dRU sizes mapped to dRU spreading bandwidths of 20 MHz, 40 MHz, and 80 MHz, respectively, in accordance with the per-dRU pilot tone optimization described with reference to Figures 15-16B.

[0101] [Table 8]

[0102] [Table 9]

[0103] [Table 10]

[0104] [Table 11]

[0105] FIG. 17 shows a frequency diagram 1700 illustrating an example distribution of pilot tones across a wireless channel according to some implementations. More specifically, FIG. 17 shows pilot tone positions assigned to a 242-tone dRU mapped to an 80 MHz wireless channel according to the per-dRU pilot tone optimization described above with reference to FIGS. 15-16B and Tables 8-11. Compared to the pilot tone distribution shown in FIG. 14, the per-dRU pilot tone optimization results in a more uniform distribution of pilot tones across the bandwidth of the wireless channel. Thus, the pilot tone allocation shown in FIG. 17 may be even more robust to narrowband interference than the pilot tone allocation shown in FIG. 14.

[0106] Tables 12-14 provide a summary of example pilot tone indexes associated with the relative pilot tone positions shown by Tables 8-11, respectively. Figures 18A-18D show frequency diagrams 1800-1830, respectively, illustrating example distributions of pilot tones across a wireless channel, according to some implementations. More specifically, Figures 18A-18D show pilot tone positions assigned to a 26-tone dRU, a 52-tone dRU, a 106-tone dRU, and a 242-tone dRU, respectively, mapped to a 40 MHz wireless channel according to the per-dRU pilot tone optimization described above with reference to Figures 15-16B and Tables 8-14.

[0107] [Table 12]

[0108] [Table 13]

[0109] [Table 14]

[0110] 19 shows a flowchart illustrating an example process 1900 for wireless communication supporting pilot tones in dRU transmissions according to some implementations. In some implementations, the process 1900 may be performed by a wireless communication device operating as or within an AP, such as one of the APs 102 or 502 described above with reference to FIG. 1 and FIG. 5A, respectively. In some other implementations, the process 1900 may be performed by a wireless communication device operating as or within a network node, such as one of the STAs 104 or 504 described above with reference to FIG. 1 and FIG. 5B, respectively.

[0111] In some implementations, process 1900 begins at block 1902 with modulating a PPDU on a number (M) of tones representing a logical RU associated with a number (K) of pilot tones, each having a respective position relative to the M tones. At block 1904, process 1900 proceeds to mapping the M tones to M non-contiguous subcarrier indices of a plurality of subcarrier indices across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indices representing a dRU. At block 1906, process 1900 proceeds to transmit a PPDU including a number (N) of pilot tones over the wireless channel, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices, the relative positions of the N pilot tones being different than the relative positions of the K pilot tones.

[0112] In some aspects, N may be different from K. In some other aspects, N may be equal to K. In some implementations, the N pilot tones may carry the same value as the K pilot tones. In some implementations, M=26, and the relative positions of the K pilot tones can be changed by mapping the M tones to M non-contiguous subcarrier indices, and the N pilot tones represent the K pilot tones as a result of the mapping. In some implementations, the relative positions of the K pilot tones can be shifted by −3 or +3 by mapping the M tones to M non-contiguous subcarrier indices.

[0113] In some aspects, the relative positions of the N pilot tones may be associated with N subcarrier indexes of the plurality of subcarrier indexes. In some implementations, the N subcarrier indexes may be symmetrically arranged around a center frequency associated with the wireless channel. In some other implementations, the N subcarrier indexes may be asymmetrically arranged around a center frequency associated with the wireless channel. In some implementations, the N subcarrier indexes may include N / 2 equidistant subcarrier indexes that are positioned above a carrier frequency associated with the wireless channel and may include N / 2 equidistant subcarrier indexes that are positioned below the carrier frequency.

[0114] In some implementations, each of the N subcarrier indices can represent a respective pilot tone position associated with a 26-tone dRU. In some other implementations, at least one of the N subcarrier indices can represent a pilot tone position unique to an M-tone dRU. In some implementations, each of the N subcarrier indices can be located at a respective distance from a starting subcarrier index of the M non-contiguous subcarrier indices based on the position of the starting subcarrier index relative to the wireless channel and the dRU index associated with the dRU.

[0115] 20 shows a flowchart illustrating an example process 2000 for wireless communication supporting pilot tones in dRU transmissions, according to some implementations. In some implementations, the process 2000 can be performed by a wireless communication device operating as or within an AP, such as one of the APs 102 or 502 described above with reference to FIG. 1 and FIG. 5A, respectively. In some other implementations, the process 2000 can be performed by a wireless communication device operating as or within a network node, such as one of the STAs 104 or 504 described above with reference to FIG. 1 and FIG. 5B, respectively.

[0116] In some implementations, process 2000 begins at block 2002 with receiving a PPDU over a wireless channel, the PPDU being carried on a number (M) of tones mapped to M non-contiguous subcarrier indexes of a plurality of subcarrier indexes across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indexes representing a dRU. At block 2004, process 2000 proceeds to recover a number (N) of pilot tones from the received PPDU, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indexes. At block 2006, process 2000 proceeds to demap the M tones from the M non-contiguous subcarrier indexes, the demapped M tones representing a logical RU associated with a number (K) of pilot tones, each having a respective position relative to the demapped M tones, the relative positions of the K pilot tones being different than the relative positions of the N pilot tones.

[0117] In some aspects, N may be different from K. In some other aspects, N may be equal to K. In some implementations, the N pilot tones may carry the same value as the K pilot tones. In some implementations, M=26, and the relative positions of the N pilot tones can be changed by demapping the M tones to M non-contiguous subcarrier indices, with the K pilot tones representing the N pilot tones as a result of the mapping. In some implementations, the relative positions of the N pilot tones can be shifted by −3 or +3 by demapping the M tones to M non-contiguous subcarrier indices.

[0118] In some aspects, the relative positions of the N pilot tones may be associated with N subcarrier indexes of the plurality of subcarrier indexes. In some implementations, the N subcarrier indexes may be symmetrically arranged around a center frequency associated with the wireless channel. In some other implementations, the N subcarrier indexes may be asymmetrically arranged around a center frequency associated with the wireless channel. In some implementations, the N subcarrier indexes may include N / 2 equidistant subcarrier indexes that are positioned above a carrier frequency associated with the wireless channel and may include N / 2 equidistant subcarrier indexes that are positioned below the carrier frequency.

[0119] In some implementations, each of the N subcarrier indices can represent a respective pilot tone position associated with a 26-tone dRU. In some other implementations, at least one of the N subcarrier indices can represent a pilot tone position unique to an M-tone dRU. In some implementations, each of the N subcarrier indices can be located at a respective distance from a starting subcarrier index of the M non-contiguous subcarrier indices based on the position of the starting subcarrier index relative to the wireless channel and the dRU index associated with the dRU.

[0120] Figure 21 shows a block diagram of an example wireless communication device 2100 according to some implementations. In some implementations, the wireless communication device 2100 is configured to perform the process 1900 described above with reference to Figure 19. The wireless communication device 2100 may be an example implementation of the wireless communication device 400 described above with reference to Figure 4. For example, the wireless communication device 2100 may be a chip, SoC, chipset, package, or device including at least one processor and at least one modem (e.g., a Wi-Fi (IEEE 802.11) modem or a cellular modem).

[0121] The wireless communication device 2100 includes a receiving component 2110, a communications manager 2120, and a transmitting component 2130. The communications manager 2120 further includes a modulating component 2122 and a mapping component 2124. One or more portions of the components 2122 and 2124 may be implemented at least in part in hardware or firmware. In some implementations, at least some of the components 2122 or 2124 are implemented at least in part as software stored in a memory (such as the memory 408). For example, one or more portions of the components 2122 and 2124 may be implemented as non-transitory instructions (or "code") executable by a processor (such as the processor 406) to perform the functions or operations of the respective components.

[0122] The receiving component 2110 is configured to receive RX signals from one or more other wireless communication devices over a wireless channel. The communication manager 2120 is configured to control or manage communications with one or more other wireless communication devices. In some implementations, the modulation component 2122 can modulate a PPDU on a number (M) of tones representing a logical RU associated with a number (K) of pilot tones, each having a respective position relative to the M tones, and the mapping component 2124 can map the M tones to M non-contiguous subcarrier indexes of a plurality of subcarrier indexes across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indexes representing a dRU. The transmitting component 2130 is configured to transmit TX signals to one or more other wireless communication devices over a wireless channel. In some implementations, the transmitting component 2130 can transmit over a wireless channel a PPDU including a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices, where the relative positions of the N pilot tones are different from the relative positions of the K pilot tones.

[0123] Figure 22 shows a block diagram of an example wireless communication device 2200 according to some implementations. In some implementations, the wireless communication device 2200 is configured to perform the process 2000 described above with reference to Figure 20. The wireless communication device 2200 may be an example implementation of the wireless communication device 400 described above with reference to Figure 4. For example, the wireless communication device 2200 may be a chip, SoC, chipset, package, or device including at least one processor and at least one modem (e.g., a Wi-Fi (IEEE 802.11) modem or a cellular modem).

[0124] The wireless communication device 2200 includes a receiving component 2210, a communications manager 2220, and a transmitting component 2230. The communications manager 2220 further includes a pilot tone recovery component 2222 and a demapping component 2224. One or more portions of the components 2222 and 2224 may be implemented at least in part in hardware or firmware. In some implementations, at least some of the components 2222 or 2224 are implemented at least in part as software stored in a memory (such as the memory 408). For example, one or more portions of the components 2222 and 2224 may be implemented as non-transitory instructions (or "code") executable by a processor (such as the processor 406) to perform the functions or operations of the respective components.

[0125] The receiving component 2210 is configured to receive an RX signal from one or more other wireless communication devices over a wireless channel. In some implementations, the receiving component 2210 can receive a PPDU over the wireless channel, where the PPDU is carried on a number (M) of tones mapped to M non-contiguous subcarrier indexes of a plurality of subcarrier indexes across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indexes representing a dRU. The communications manager 2220 is configured to control or manage communications with one or more other wireless communication devices. In some implementations, the pilot tone recovery component 2222 can recover a number (N) of pilot tones from the received PPDU, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices, and the demapping component 2224 can demap the M tones from the M non-contiguous subcarrier indices, where the demapped M tones represent logical RUs associated with a number (K) of pilot tones, each having a respective position relative to the remapped M tones, and where the relative positions of the K pilot tones are different from the relative positions of the N pilot tones. The transmitting component 2230 is configured to transmit the TX signal to one or more other wireless communication devices over a wireless channel.

[0126] The following numbered clauses describe example implementations. 1. A method of wireless communication by a wireless communication device, comprising: modulating a Physical Layer Convergence Protocol (PLCP) Protocol Data Unit (PPDU) on a number (M) of tones representing a logical resource unit (RU) associated with a number (K) of pilot tones, each RU having a respective position relative to the M tones; Mapping the M tones to M non-contiguous subcarrier indices of a plurality of subcarrier indices across a wireless channel, the M tones mapped to the M non-contiguous subcarrier indices representing a distributed resource unit (dRU); transmitting, over a wireless channel, a PPDU including a number (N) of pilot tones, each having a respective position relative to the M tones mapped to the M non-contiguous subcarrier indices, the relative positions of the N pilot tones being different from the relative positions of the K pilot tones; A method comprising: 2. The method of clause 1, wherein N is equal to K. 3. The method of clause 1 or 2, wherein N pilot tones carry the same value as K pilot tones. 4. The method of any one of clauses 1 to 3, wherein M=26, and mapping M tones to M non-consecutive subcarrier indices changes the relative positions of K pilot tones, and N pilot tones represent the K pilot tones as a result of the mapping. 5. The method of any one of clauses 1 to 4, wherein mapping M tones to M non-contiguous subcarrier indices shifts the relative positions of the K pilot tones by -3 or +3. 6. The method of claim 1, wherein N is different from K. 7. The method of any one of clauses 1 to 6, wherein the relative positions of the N pilot tones are associated with N subcarrier indices of a plurality of subcarrier indices. 8. The method of any one of clauses 1 to 7, wherein the N subcarrier indices are arranged symmetrically around a center frequency associated with the wireless channel. 9. The method of any one of clauses 1 to 7, wherein the N subcarrier indices are arranged asymmetrically around a center frequency associated with the wireless channel. 10. The method of any one of clauses 1 to 9, wherein the N subcarrier indices include N / 2 equidistant subcarrier indices positioned above a carrier frequency associated with the wireless channel and N / 2 equidistant subcarrier indices positioned below the carrier frequency. 11. The method of any one of clauses 1 to 10, wherein each of the N subcarrier indices represents a respective pilot tone position associated with a 26-tone dRU. 12. The method of any one of clauses 1 to 10, wherein at least one of the N subcarrier indices represents a pilot tone position specific to a dRU of the M tones. 13. A method according to any one of clauses 1 to 12, wherein each of the N subcarrier indexes is located at a respective distance from a starting subcarrier index of the M non-consecutive subcarrier indexes based on the position of the starting subcarrier index relative to the wireless channel and the dRU index associated with the dRU. 14. A wireless communication device, comprising: At least one processor; at least one memory communicatively coupled to the at least one processor and storing processor-readable code; wherein the processor-readable code is configured, when executed by at least one processor, to perform any one or more of the methods of clauses 1 to 13. Wireless communication devices. 15. A method of wireless communication performed by a wireless communication device, comprising: receiving a physical layer (PHY) convergence protocol (PLCP) protocol data unit (PPDU) over a wireless channel, the PPDU being carried on a number (M) of tones mapped to M non-contiguous subcarrier indexes of a plurality of subcarrier indexes across the wireless channel, the M tones mapped to the M non-contiguous subcarrier indexes representing a distributed resource unit (dRU); Recovering from the received PPDU a number (N) of pilot tones, each having a respective position for the M tones mapped to the M non-contiguous subcarrier indices; Demapping M tones from M non-contiguous subcarrier indexes, where the demapped M tones represent logical resource units (RUs) associated with a number (K) of pilot tones, each RU having a respective position relative to the demapped M tones, and where the relative positions of the K pilot tones are different from the relative positions of the N pilot tones; A method comprising: 16. The method of claim 15, wherein N is equal to K. 17. The method of claim 15 or 16, wherein N pilot tones carry the same value as K pilot tones. 18. The method of any one of clauses 15 to 17, wherein M=26, and demapping M tones from M non-consecutive subcarrier indexes changes relative positions of N pilot tones, and K pilot tones represent the N pilot tones as a result of the demapping. 19. The method of any one of clauses 15 to 18, wherein demapping the M tones from the M non-consecutive subcarrier indices shifts the relative positions of the N pilot tones by -3 or +3. 20. The method of claim 15, wherein N is different from K. 21. The method of any one of clauses 15 to 20, wherein the relative positions of the N pilot tones are associated with N subcarrier indices of a plurality of subcarrier indices. 22. The method of any one of clauses 15 to 21, wherein the N subcarrier indices are arranged symmetrically around a center frequency associated with the wireless channel. 23. The method of any one of clauses 15 to 21, wherein the N subcarrier indices are arranged asymmetrically around a center frequency associated with the wireless channel. 24. The method of any one of clauses 15 to 23, wherein the N subcarrier indices include N / 2 equidistant subcarrier indices positioned above a carrier frequency associated with the wireless channel and N / 2 equidistant subcarrier indices positioned below the carrier frequency. 25. The method of any one of clauses 15 to 24, wherein each of the N subcarrier indices represents a respective pilot tone position associated with a 26-tone dRU. 26. The method of any one of clauses 15 to 24, wherein at least one of the N subcarrier indices represents a pilot tone position specific to a dRU of the M tones. 27. A method according to any one of clauses 15 to 26, wherein each of the N subcarrier indices is located at a respective distance from the starting subcarrier index of the M non-contiguous subcarriers based on the position of the starting subcarrier index relative to the wireless channel and the dRU index associated with the dRU. 28. A wireless communication device, comprising: At least one processor; at least one memory communicatively coupled to the at least one processor and storing processor-readable code; and the processor-readable code, when executed by at least one processor, is configured to perform any one or more of the methods of clauses 15 to 27. Wireless communication devices.

[0127] As used herein, phrases referring to "at least one of" or "one or more of" a list of items refer to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to encompass the possibilities of a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a, b, and c.

[0128] The various example components, logic, logic blocks, modules, circuits, operations, and algorithmic processes described with respect to implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware, or software, including the structures disclosed herein and structural equivalents thereof. The interchangeability of hardware, firmware, and software has been described generally in terms of functionality and illustrated in the various example components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented in hardware, firmware, or software depends on the particular application and design constraints imposed on the overall system.

[0129] Various modifications of the implementations described in this disclosure may be readily 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 the present disclosure. Thus, the claims are not intended to be limited to the implementations shown herein, but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

[0130] Moreover, various features that are described herein in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable subcombination. Thus, although features may be described above as working in a particular combination, and may even initially be claimed as such, in some cases one or more features from the claimed combination may be deleted from that combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination.

[0131] Similarly, although operations are shown in the figures in a particular order, this should not be understood as requiring such operations to be performed in the particular order or sequential order shown, or that all of the operations shown be performed, to achieve a desired result. Furthermore, the figures may generally illustrate one or more exemplary processes in the form of a flowchart or flow diagram. However, other operations not shown may be incorporated into the generally illustrated exemplary process. For example, one or more additional operations may be performed before, after, simultaneously with, or between any of the illustrated operations. In some situations, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the program components and systems described may generally be integrated together in a single software product or packaged into multiple software products. [Explanation of symbols]

[0132] 400 Wireless communication devices 402 Modem 406 Wireless communication devices 406 Processing Elements 406 Processor 408 Memory 510 Wireless communication devices 515 Wireless communication devices 520 Antenna 525 Antenna 530 Application Processor 535 Application Processor 540 Memory 545 Memory 550 External Network Interface 565 Display 575 Sensor 2100 Wireless communication devices 2110 Receiving Component 2120 Communications Manager 2122 Modulation Components 2124 Mapping Components 2130 Transmission Component 2200 Wireless Communication Devices 2210 Receiving Component 2220 Communications Manager 2222 Pilot Tone Restoration Component 2224 Demapping Component 2230 Transmission Component

Claims

1. A method of wireless communication performed by a wireless communication device, comprising: modulating a physical layer convergence protocol (PLCP) protocol data unit (PPDU) on some (M) of the tones representing logical resource units (RUs) associated with some (K) pilot tones, each having a respective position for each of the M tones; mapping the M tones to M discontinuous subcarrier indices out of a plurality of subcarrier indices across a wireless channel, wherein the M tones mapped to the M discontinuous subcarrier indices represent a distributed resource unit (dRU); transmitting the PPDU via the wireless channel, including transmitting some (N) pilot tones, each having a respective position for each of the M tones mapped to the M discontinuous subcarrier indices, wherein the relative positions of the N pilot tones are different from the relative positions of the K pilot tones; comprising: wherein the relative positions of the N pilot tones are associated with N subcarrier indices out of the plurality of subcarrier indices, and each of the N subcarrier indices represents a respective pilot tone position associated with a 26-tone dRU.

2. wherein N is equal to K; the N pilot tones carry the same values as the K pilot tones; M = 26, and mapping the M tones to the M discontinuous subcarrier indices changes the relative positions of the K pilot tones, and as a result of the mapping, the N pilot tones represent the K pilot tones; the method according to claim 1, wherein mapping the M tones to the M discontinuous subcarrier indices shifts the relative positions of the K pilot tones by -3 or +3.

3. The method according to claim 1, wherein N is different from K.

4. wherein the N subcarrier indices are arranged symmetrically around a center frequency associated with the wireless channel, or The method according to claim 1, wherein the N sub-carrier indices are asymmetrically arranged around a center frequency associated with the radio channel.

5. including N / 2 equally spaced sub-carrier indices arranged above a carrier frequency associated with the radio channel and N / 2 equally spaced sub-carrier indices arranged below the carrier frequency, or at least one of the N sub-carrier indices represents a pilot tone position specific to a dRU of M tones, or each of the N sub-carrier indices is arranged at a distance from a start sub-carrier index of the M discontinuous sub-carrier indices based on a position of a start sub-carrier index for the radio channel and a dRU index associated with the dRU. The method according to claim 1.

6. A wireless communication device, at least one processor; at least one memory communicatively coupled to the at least one processor and storing processor-readable code; wherein when the processor-readable code is executed by the at least one processor, modulates a physical layer convergence protocol (PLCP) protocol data unit (PPDU) on some (M) of the tones representing logical resource units (RUs) associated with some (K) pilot tones, each having a respective position for each of the M tones; maps the M tones to M discontinuous sub-carrier indices among a plurality of sub-carrier indices across a radio channel, and the M tones mapped to the M discontinuous sub-carrier indices represent a distributed RU (dRU); transmits some (N) pilot tones, each having a respective position for each of the M tones, via the radio channel, the relative positions of the N pilot tones being different from the relative positions of the K pilot tones, including some (N) pilot tones; configured as such. The relative positions of the N pilot tones are associated with N sub-carrier indices among the plurality of sub-carrier indices, and each of the N sub-carrier indices represents a respective pilot tone position associated with a 26-tone dRU. Wireless communication device. Claim 7 The relative positions of the N pilot tones include N / 2 equally-spaced sub-carrier indices arranged above the carrier frequency associated with the wireless channel and N / 2 equally-spaced sub-carrier indices arranged below the carrier frequency, and are associated with N sub-carrier indices among the plurality of sub-carrier indices. Each of the N sub-carrier indices is arranged at a respective distance from the start sub-carrier index of the M discontinuous sub-carriers based on the position of the start sub-carrier index with respect to the wireless channel and the dRU index associated with the dRU. The wireless communication device according to claim 6. Claim 8 A method of wireless communication performed by a wireless communication device, Receiving a Physical Layer (PHY) Convergence Protocol (PLCP) Protocol Data Unit (PPDU) via a wireless channel, where the PPDU is carried on several (M) tones mapped to M discontinuous sub-carrier indices among the plurality of sub-carrier indices across the wireless channel, and the M tones mapped to the M discontinuous sub-carrier indices represent a Distributed Resource Unit (dRU); receiving, Restoring several (N) pilot tones, each having a respective position for the M tones mapped to the M discontinuous sub-carrier indices, from the received PPDU. Demapping the M tones from the M discontinuous sub-carrier indices, wherein the demapped M tones represent logical resource units (RUs) each having a respective position with respect to the demapped M tones and associated with some (K) pilot tones, and wherein the relative positions of the K pilot tones are different from the relative positions of the N pilot tones; comprising; wherein the relative positions of the N pilot tones are associated with N sub-carrier indices among the plurality of sub-carrier indices, and each of the N sub-carrier indices represents a respective pilot tone position associated with a 26-tone dRU, a method. **Claim 9** N is equal to K, preferably, the N pilot tones carry the same values as the K pilot tones, preferably, M = 26, and demapping the M tones from the M discontinuous sub-carrier indices changes the relative positions of the N pilot tones, and the K pilot tones represent the N pilot tones as a result of the demapping, preferably, The method according to claim 8, wherein demapping the M tones from the M discontinuous sub-carrier indices shifts the relative positions of the N pilot tones by -3 or +3. **Claim 10** The method according to claim 8, wherein N is different from K. **Claim 11** the N sub-carrier indices are arranged symmetrically around the center frequency associated with the radio channel, or, the N sub-carrier indices are arranged asymmetrically around the center frequency associated with the radio channel, the method according to claim 8. **Claim 12** The method according to claim 8, wherein the N sub-carrier indices include N / 2 equally spaced sub-carrier indices arranged above the carrier frequency associated with the radio channel and N / 2 equally spaced sub-carrier indices arranged below the carrier frequency. **Claim 13** at least one of the N sub-carrier indices represents a pilot tone position specific to the dRU of the M tones, or, The method according to claim 8, wherein each of the N sub-carrier indices is arranged at a respective distance from the start sub-carrier index for the radio channel based on the position of the start sub-carrier index for the radio channel and the dRU index associated with the dRU.

14. A wireless communication device, comprising at least one processor, and at least one memory communicatively coupled to the at least one processor and storing processor-readable code, wherein when the processor-readable code is executed by the at least one processor, a physical layer convergence protocol (PLCP) protocol data unit (PPDU) is received via a radio channel, the PPDU being carried on some (M) tones mapped to M discontinuous sub-carrier indices out of a plurality of sub-carrier indices across the radio channel, the M tones mapped to the M discontinuous sub-carrier indices representing a distributed resource unit (dRU), restoring some (N) pilot tones each having a respective position for the M tones mapped to the M discontinuous sub-carrier indices from the received PPDU, demapping the M tones from the M discontinuous sub-carrier indices, the demapped M tones representing a logical RU associated with some (K) pilot tones each having a respective position for the demapped M tones, the relative positions of the K pilot tones being different from the relative positions of the N pilot tones, is configured to wherein the relative positions of the N pilot tones are associated with N sub-carrier indices out of the plurality of sub-carrier indices, and each of the N sub-carrier indices represents a respective pilot tone position associated with a 26-tone dRU. A wireless communication device.

15. The relative positions of the N pilot tones include N / 2 equidistant sub-carrier indices arranged above the carrier frequency associated with the radio channel and N / 2 equidistant sub-carrier indices arranged below the carrier frequency, and are associated with N sub-carrier indices among the plurality of sub-carrier indices. Each of the N sub-carrier indices is arranged at a distance from the start sub-carrier index of the M discontinuous sub-carriers based on the position of the start sub-carrier index with respect to the radio channel and the dRU index associated with the dRU. The wireless communication device according to claim 14.

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