CN106664275B

CN106664275B - Physical layer frame format for WLAN

Info

Publication number: CN106664275B
Application number: CN201580010085.4A
Authority: CN
Inventors: 张鸿远; 徐明光; 孙亚崑
Original assignee: Marvell Asia Pte Ltd
Current assignee: Kaiwei International Co; Marvell International Ltd; Marvell Asia Pte Ltd
Priority date: 2014-01-07
Filing date: 2015-01-07
Publication date: 2020-08-18
Anticipated expiration: 2035-01-07
Also published as: EP3092759A1; WO2015105875A1; KR20160106123A; CN106664275A; KR102376949B1; JP6464494B2; JP2017510111A

Abstract

In a method for generating a physical layer (PHY) data unit for transmission via a communication channel, the PHY data unit conforming to a first communication protocol, a first communication device generating a PHY preamble for the PHY data unit, comprising: the method further includes generating a signal field, including the signal field and a copy of the signal field in the PHY preamble, and formatting the PHY preamble such that a first portion of the PHY preamble is decodable by a second communication device that conforms to the second communication protocol but does not conform to the first communication protocol to determine a duration of the PHY data unit based on the first portion of the PHY preamble. The first communication device generates a PHY data unit to include a PHY preamble and a PHY payload.

Description

Physical layer frame format for WLAN

Cross Reference to Related Applications

The present disclosure is a continuation-in-part application of united states patent application No. 14/523,678 entitled "Range Extension Mode for WiFi" filed 24/10 in 2014, which claims the benefits of united states provisional patent application No. 61/895,591 entitled "Range Extension PHY" filed 25/10 in 2013, 61/925,332 entitled "Range Extension PHY" filed 9/1 in 2014, united states provisional patent application No. 61/950,727 entitled "Range Extension PHY" filed 10/3 in 2014, and united states provisional patent application No. 61/987,778 entitled "Range Extension PHY" filed 2/5 in 2014, the entire disclosures of which are incorporated herein by reference in their entireties.

Further, the present disclosure claims U.S. provisional patent application No. 61/924,467 entitled "Physical Layer Frame Format WLAN" filed on 7.1.2014, U.S. provisional patent application No. 62/030,426 entitled "Physical Layer Frame Format WLAN" filed on 29.7.2014, U.S. provisional patent application No. 62/034,509 entitled "Physical Layer Frame Format WLAN" filed on 7.8.2014, the rights of U.S. provisional patent application No. 62/045,363 entitled "Physical Layer Frame Format WLAN" filed on 3.9.2014, U.S. provisional patent application No. 62/051,537 entitled "Physical Layer Frame Format WLAN" filed on 17.9.2014, and U.S. provisional patent application No. 62/089,032 entitled "Physical Layer Frame Format WLAN" filed on 8.12.2014, the entire disclosures of which are incorporated herein by reference in their entireties.

Technical Field

The present disclosure relates generally to wireless communication networks, and more particularly to physical layer (PHY) frame formats that facilitate coexistence with legacy (legacy) devices in wireless local area networks.

Background

When operating in an infrastructure mode, a Wireless Local Area Network (WLAN) typically includes an Access Point (AP) and one or more client stations. WLANs have evolved rapidly over the past decade. The development of WLAN standards, such as the Institute of Electrical and Electronics Engineers (IEEE)802.11a, 802.11b, 802.11g, and 802.11n standards, improves single-user peak data throughput. For example, the IEEE802.11 b standard specifies a single user peak throughput of 11 megabits per second (Mbps), the IEEE802.11a and 802.11g standards specify a single user peak throughput of 54Mbps, the IEEE802.11 n standard specifies a single user peak throughput of 600Mbps, and the IEEE802.11ac standard specifies a single user peak throughput in the gigabit per second (Gbps) range. Future standards promise to provide even greater throughput, such as throughput in the tens of Gbps range.

Disclosure of Invention

In an embodiment, a method is for generating a physical layer (PHY) data unit for transmission via a communication channel, the PHY data unit conforming to a first communication protocol. The method includes generating, at a first communication device, a PHY preamble for a PHY data unit, including: the method further includes generating a signal field, including the signal field and a copy of the signal field in the PHY preamble, and formatting the PHY preamble such that a first portion of the PHY preamble is decodable by a second communication device that conforms to the second communication protocol but does not conform to the first communication protocol to determine a duration of the PHY data unit based on the first portion of the PHY preamble. The method also includes generating, at the first communication device, the PHY data unit to include the PHY preamble and the PHY payload.

In various other embodiments, the method further comprises one or any suitable combination of two or more of the following features.

The signal field is a legacy signal field decodable by the second communication device; the legacy signal field is included in the first portion of the PHY preamble; and the legacy signal field contains information indicating a duration of the PHY data unit.

Generating the PHY preamble for the PHY data unit further comprises: generating a further signal field conforming to the second communication protocol and including the further signal field in the second portion of the PHY preamble.

The second portion of the PHY preamble is not decodable by the second communication device.

Generating the PHY preamble for the PHY data unit further comprises: a copy of the additional signal field is included in the second portion of the PHY preamble.

The signal field is a first signal field; and generating the PHY preamble for the PHY data unit further comprises: generating a second signal field decodable by a second communication device, wherein the second signal field includes information indicative of a duration of the PHY data unit, includes the second signal field in the first portion of the PHY preamble, and includes the first signal field in the second portion of the PHY preamble.

A PHY preamble for the PHY data unit is generated to include respective first guard intervals between Orthogonal Frequency Domain (OFDM) symbols in a first portion of the PHY preamble; and the method further includes generating, at the first communication device, the PHY payload to include respective second guard intervals between OFDM symbols of the PHY payload, wherein each second guard interval has a longer duration than each first guard interval.

The PHY preamble for the PHY data unit is generated to include a respective second guard interval between OFDM symbols in the second portion of the PHY preamble.

In another embodiment, the first communication device includes a network interface device having one or more integrated circuits configured to: generating a physical layer (PHY) preamble for a PHY data unit conforming to a first communication protocol, comprising: the method further includes generating a signal field, including the signal field and a copy of the signal field in the PHY preamble, and formatting the PHY preamble such that a first portion of the PHY preamble is decodable by a second communication device that conforms to the second communication protocol but does not conform to the first communication protocol to determine a duration of the PHY data unit based on the first portion of the PHY preamble. The one or more integrated circuits are further configured to: the PHY data unit is generated to contain the PHY preamble and the PHY payload.

In various other embodiments, the first communication device further comprises one or any suitable combination of two or more of the following features.

The signal field is a legacy signal field decodable by the second communication device; the one or more integrated circuits are configured to: including the legacy signal field in a first portion of the PHY preamble; and the legacy signal field contains information indicating a duration of the PHY data unit.

The one or more integrated circuits are configured to: generating a further signal field conforming to the second communication protocol and including the further signal field in the second portion of the PHY preamble.

The one or more integrated circuits are configured to: a copy of the additional signal field is included in the second portion of the PHY preamble.

The signal field is a first signal field; and the one or more integrated circuits are configured to: generating a second signal field decodable by a second communication device, wherein the second signal field contains information indicative of a duration of the PHY data unit, including the second signal field in a first portion of the PHY preamble, and including the first signal field in a second portion of the PHY preamble.

The one or more integrated circuits are configured to: generating a PHY preamble for a PHY data unit to include respective first guard intervals between Orthogonal Frequency Domain (OFDM) symbols in a first portion of the PHY preamble; and generating the PHY payload to include respective second guard intervals between OFDM symbols in the PHY payload, wherein each second guard interval has a longer duration than each first guard interval.

The one or more integrated circuits are configured to: the PHY preamble is generated to include a respective second guard interval between OFDM symbols in a second portion including the PHY preamble.

Drawings

Fig. 1 is a block diagram of an example Wireless Local Area Network (WLAN) according to an embodiment.

Fig. 2A and 2B are diagrams of a related art data unit format.

Fig. 3 is a diagram of another prior art data unit format.

Fig. 4 is a diagram of another prior art data unit format.

Fig. 5 is a diagram of another prior art data unit format.

Fig. 6A is a set of diagrams of modulation used to modulate symbols in a prior art data unit.

Fig. 6B is a set of diagrams of modulation used to modulate symbols in an example data unit, according to an embodiment.

Fig. 7A is a diagram of an Orthogonal Frequency Division Multiplexing (OFDM) data unit, according to an embodiment.

Fig. 7B is a set of diagrams of modulation used to modulate symbols in the data unit depicted in fig. 7A, according to an embodiment.

Fig. 8 is a block diagram of an OFDM symbol according to an embodiment.

Fig. 9A is a diagram illustrating an example data unit in which a conventional coding scheme is used for a preamble of the data unit, according to an embodiment.

Fig. 9B is a diagram illustrating an example data unit in which a conventional coding scheme is used for only a portion of a preamble of the data unit, according to an embodiment.

Fig. 10A is a diagram illustrating an example data unit in which pitch spacing adjustment is used in combination with block coding, according to an embodiment.

Fig. 10B is a diagram illustrating an example data unit in which pitch spacing adjustment is used in combination with block coding, according to another embodiment.

Fig. 11A is a diagram illustrating a regular pattern data unit, according to an embodiment.

FIG. 11B is a diagram illustrating a range expansion mode data unit, according to an embodiment.

12A-12B are diagrams illustrating two possible formats for a long training field, respectively, according to two example embodiments.

Fig. 13A is a diagram illustrating a non-legacy signal field of the regular mode data unit of fig. 11A, according to an embodiment.

Fig. 13B is a diagram illustrating a non-legacy signal field of the range extension mode data unit of fig. 11B, according to an embodiment.

Fig. 14A is a block diagram illustrating a range expansion mode data unit, according to an embodiment.

FIG. 14B is a diagram illustrating a legacy signal field of the range extension mode data unit of FIG. 14A, according to one embodiment.

Fig. 14C is a diagram illustrating a Fast Fourier Transform (FFT) window of the legacy signal field of fig. 14B at a legacy receiving device, according to an embodiment.

Fig. 15 is a block diagram illustrating a format of a non-legacy signal field according to an embodiment.

Fig. 16 is a block diagram illustrating an example PHY processing unit for generating a regular mode data unit using a regular coding scheme, according to an embodiment.

Fig. 17A is a block diagram of an example PHY processing unit for generating a range extension mode data unit using a range extension coding scheme, according to an embodiment.

Fig. 17B is a block diagram of an example PHY processing unit for generating a range expansion mode data unit, according to another embodiment.

Fig. 18A is a block diagram of an example PHY processing unit for generating a range extension mode data unit using a range extension coding scheme, according to another embodiment.

Fig. 18B is a block diagram of an example PHY processing unit for generating a range expansion mode data unit, according to another embodiment.

Fig. 19A is a block diagram of an example PHY processing unit for generating a range expansion mode data unit, according to another embodiment.

Fig. 19B is a block diagram of an example PHY processing unit for generating a range expansion mode data unit, according to another embodiment.

Fig. 20A is a diagram illustrating repetition of OFDM symbols in a preamble of a range extension mode data unit, according to an embodiment.

Fig. 20B is a diagram illustrating repetition of OFDM symbols in a preamble of a range extension mode data unit, according to an embodiment.

Fig. 20C is a diagram illustrating a time-domain repetition scheme for an OFDM symbol, according to one embodiment.

Fig. 20D is a diagram illustrating a repetition scheme for OFDM symbols, according to another embodiment.

Fig. 21 is a flow diagram of an example method for generating a data unit, according to an embodiment.

Fig. 22A is a diagram of a repeated 20MHz total bandwidth with a range extension data unit having 10MHz sub-bands, according to an embodiment.

Fig. 22B is a diagram of a 40MHz total bandwidth with repetition of range extension data units with 10MHz sub-bands, according to an embodiment.

Fig. 22C is a diagram of an example tone plan for the 32-FFT mode, according to an embodiment.

Fig. 23 is a diagram of an example data unit in which a range expansion pattern is used for a preamble of the data unit, according to an embodiment.

Fig. 24 is a block diagram of an example PHY processing unit for generating a range expansion mode data unit, according to another embodiment.

Fig. 25A is a diagram of an example 20MHz total bandwidth with an 1/2 tone spacing, according to an embodiment.

Fig. 25B is a diagram of an example 20MHz total bandwidth with an 1/2 tone spacing, according to an embodiment.

Fig. 26A is a diagram of non-legacy tone planning for a range expansion mode with FFT sizes of 64 and 1/2 tone spacings, according to an embodiment.

Fig. 26B is a diagram of non-legacy tone planning for a range expansion mode with

FFT size

128 and 1/2 tone spacing, according to an embodiment.

Fig. 26C is a diagram of non-legacy tone planning for a range expansion mode with FFT sizes of 256 and 1/2 tone spacings, according to an embodiment.

Fig. 27 is a flow diagram of an example method for generating a data unit, according to an embodiment.

FIG. 28 is a flow diagram of an example method for generating a data unit, according to another embodiment.

Fig. 29 is a diagram of a portion of an example PHY preamble conforming to a first communication protocol according to an embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 30 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 31 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 32 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 33 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 34 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 35 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 36 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment as compared to a portion of a preamble conforming to a legacy protocol.

Fig. 37 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 38A-D are diagrams illustrating examples of auto-detected symbols utilized with the example PHY preamble of fig. 37, in accordance with various embodiments.

Fig. 39 is a diagram of a portion of another example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion of a preamble conforming to a legacy protocol.

Fig. 40A is a diagram of a portion of another example PHY preamble conforming to a first communication protocol, according to another embodiment.

Fig. 40B is a diagram of a portion of another example PHY preamble conforming to a first communication protocol, according to another embodiment.

Fig. 41 is a diagram of a portion of another example PHY preamble conforming to a range expansion mode of a first communication protocol and a diagram of a portion of another example PHY preamble conforming to a normal mode of the first communication protocol compared to a portion of a preamble conforming to a legacy protocol, according to an embodiment.

Fig. 42 is a diagram of a portion of another example PHY preamble conforming to a range expansion mode of a first communication protocol and a portion of another example PHY preamble conforming to a normal mode of the first communication protocol compared to a portion of the preamble conforming to a legacy protocol, according to an embodiment.

Fig. 43 is a diagram of a portion of another example PHY preamble conforming to a range expansion mode of a first communication protocol and a portion of another example PHY preamble conforming to a normal mode of the first communication protocol compared to a portion of the preamble conforming to a legacy protocol, according to an embodiment.

Detailed Description

In the embodiments described below, a wireless network device, such as an Access Point (AP) of a Wireless Local Area Network (WLAN), transmits a data stream to one or more client stations. The AP is configured to operate with the client stations according to at least a first communication protocol. The first communication protocol is sometimes referred to herein as the "high efficiency Wi-Fi," "HEW" communication protocol, or the 802.11ax communication protocol. In some embodiments, different client stations in the vicinity of the AP are configured to operate according to one or more other communication protocols that define operation within the same frequency band as the HEW communication protocol, but at a generally lower data throughput. Lower data throughput communication protocols (e.g., IEEE802.11a, IEEE802.11 n, and/or IEEE802.11 ac) are collectively referred to herein as "legacy" communication protocols. In at least some embodiments, legacy communication protocols are generally deployed in indoor communication channels, and HEW communication protocols are deployed at least sometimes for outdoor communication, extended range communication, or communication in areas where the signal-to-noise ratio (SNR) of the transmitted signal is reduced.

According to an embodiment, the symbols transmitted by the AP are generated according to a range extension coding scheme that provides increased redundancy of the symbols or information bits encoded within the symbols. The redundancy increases the likelihood that the symbol will be successfully decoded by a device receiving the symbol from the AP, especially in areas of reduced SNR. The amount of redundancy needed to mitigate SNR degradation typically depends on the delay channel spread (e.g., for outdoor communication channels), other signals interfering with the symbols, and/or other factors. In an embodiment, the HEW communication protocol defines a normal mode and a range extension mode. In an embodiment, the normal mode is generally used with communication channels characterized by shorter channel delay spreads (e.g., indoor communication channels) or generally higher SNR values, while the range extension mode is generally used with communication channels characterized by relatively longer channel delay spreads (e.g., outdoor communication channels) or generally lower SNR values. In an embodiment, the regular coding scheme is used in the regular mode and the range extension coding scheme is used in the range extension mode.

In an embodiment, the data unit transmitted by the AP comprises a preamble and a data portion, wherein the preamble is used at least in part to signal various parameters for transmission of the data portion to the receiving device. In various embodiments, the preamble of the data unit is used to signal to the receiving device the particular coding scheme utilized in at least the data portion of the data unit. In some embodiments, the same preamble format is used in the normal mode as in the range extension mode. In one such embodiment, the preamble includes an indication set to indicate whether a regular coding scheme or a range extension coding scheme is used for at least the data portion of the data unit. In some embodiments, the indicated conventional coding scheme or range extension coding scheme is used for at least a portion of the preamble of the data unit in addition to the data portion of the data unit. In an embodiment, the receiving device determines the particular coding scheme to utilize based on the indication in the preamble of the data unit, and then decodes the appropriate remaining portion of the data unit (e.g., the data portion or a portion of the preamble and data portion) using the particular coding scheme.

In another embodiment, the preamble used in the range extension mode is formatted differently than the preamble used in the normal mode. For example, the preamble used in the range extension mode is formatted such that the receiving device can automatically (e.g., prior to decoding) detect that the data unit corresponds to the range extension mode. In an embodiment, when the receiving device detects that the data unit corresponds to the range expansion mode, the receiving device decodes the data portion of the data unit and, in at least some embodiments, at least a portion of the preamble and the data portion of the data unit using the range expansion coding scheme. On the other hand, in the embodiment, when the reception apparatus detects that the data unit does not correspond to the range expansion mode, the reception apparatus assumes that the data unit corresponds to the normal mode. The receiving device then decodes at least the data portion of the data unit using a conventional coding scheme.

Furthermore, in at least some embodiments, the preamble of a data unit in the regular mode and/or the range extension mode is formatted such that a client station operating according to a legacy protocol, rather than the HEW communication protocol, can determine that certain information about the data unit (such as the duration of the data unit) and/or that the data unit does not conform to the legacy protocol. Further, in an embodiment, the preamble of the data unit is formatted such that a client station operating according to the HEW protocol is able to determine that the data unit conforms to the HEW communication protocol and whether the data unit is formatted according to the normal mode or the range extension mode. Similarly, in an embodiment, a client station configured to operate according to the HEW communication protocol also transmits data units such as those described above.

In at least some embodiments, formatted data units such as those described above are useful, for example, for APs configured to operate with client stations according to a plurality of different communication protocols and/or for WLANs in which a plurality of client stations operate according to a plurality of different communication protocols. Continuing with the above example, a communication device configured to operate in accordance with both a HEW communication protocol (including a regular mode and a range extension mode) and a legacy communication protocol is able to determine that a given data unit is formatted in accordance with the HEW communication protocol and not the legacy communication protocol, and also determine that the data unit is formatted in accordance with the range extension mode and not the regular mode. Similarly, a communication device configured to operate according to a legacy communication protocol, rather than the HEW communication protocol, can determine that a data unit is not formatted according to the legacy communication protocol and/or determine a duration of the data unit.

Fig. 1 is a block diagram of an example Wireless Local Area Network (WLAN)10 according to an embodiment an AP 14 includes a host processor 15 coupled to a network interface 16. The network interface 16 includes a Media Access Control (MAC) processing unit 18 and a physical layer (PHY) processing unit 20. The PHY processing unit 20 includes a plurality of transceivers 21, and the transceivers 21 are coupled to a plurality of antennas 24. Although three transceivers 21 and three antennas 24 are illustrated in fig. 1, in other embodiments, the AP 14 includes other suitable numbers (e.g., 1, 2, 4,5, etc.) of transceivers 21 and antennas 24. In one embodiment, the MAC processing unit 18 and the PHY processing unit 20 are configured to operate in accordance with a first communication protocol (e.g., HEW communication protocol), including at least a first mode and a second mode of the first communication protocol. In some embodiments, the first mode corresponds to a range expansion mode that uses a range expansion coding scheme (e.g., block coding, bitwise replication, or symbol replication), a signal modulation scheme (e.g., phase shift keying or quadrature amplitude modulation), or both a range expansion coding scheme and a signal modulation scheme. The range extension mode is configured to increase the range and/or decrease a signal-to-noise ratio (SNR) as compared to a second mode (e.g., a conventional mode using a conventional coding scheme) at which successful decoding of PHY data units conforming to the range extension mode is performed. In various embodiments, the range extension mode reduces the transmission data rate compared to the conventional mode to enable successful decoding with increased range and/or reduced SNR ratio. In another embodiment, the MAC processing unit 18 and the PHY processing unit 20 are further configured to operate in accordance with a second communication protocol (e.g., the IEEE802.11ac standard). In yet another embodiment, the MAC processing unit 18 and the PHY processing unit 20 are additionally configured to operate in accordance with a second communication protocol, a third communication protocol, and/or a fourth communication protocol (e.g., IEEE802.11a standard and/or IEEE802.11 n standard).

The WLAN 10 includes a plurality of client stations 25. Although four client stations 25 are illustrated in fig. 1, in various scenarios and embodiments, the WLAN 10 includes other suitable numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25. At least one of the client stations 25 (e.g., client station 25-1) is configured to operate in accordance with at least a first communication protocol. In some embodiments, at least one of the client stations 25 is not configured to operate according to the first communication protocol, but is configured to operate according to at least one of the second communication protocol, the third communication protocol, and/or the fourth communication protocol (referred to herein as a "legacy client station").

The client station 25-1 includes a host processor 26 coupled to a network interface 27. The network interface 27 includes a MAC processing unit 28 and a PHY processing unit 29. The PHY processing unit 29 includes a plurality of transceivers 30, and the transceivers 30 are coupled to a plurality of antennas 34. Although three transceivers 30 and three antennas 34 are illustrated in fig. 1, in other embodiments, the client station 25-1 includes other suitable numbers (e.g., 1, 2, 4,5, etc.) of transceivers 30 and antennas 34.

According to an embodiment, the client station 25-4 is a legacy client station, i.e., the client station 25-4 does not support receiving and fully decoding data units transmitted by the AP 14 or another client station 25 according to the first communication protocol. Similarly, according to an embodiment, legacy client stations 25-4 do not support transmitting data units according to the first communication protocol. Legacy client stations 25-4, on the other hand, support receiving, fully decoding and transmitting data units according to the second communication protocol, the third communication protocol and/or the fourth communication protocol.

In an embodiment, one or both of the client stations 25-2 and 25-3 have the same or similar structure as the client station 25-1. In an embodiment, the client station 25-4 has a similar structure as the client station 25-1. In these embodiments, the same or similar structured client stations 25 as client station 25-1 have the same or different numbers of transceivers and antennas. For example, the client station 25-2 has only two transceivers and two antennas (not shown), according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 is configured to generate a data unit that conforms to the first communication protocol and has a format described herein. The transceiver(s) 21 are configured to transmit the generated data units via the antenna(s) 24. Similarly, the transceiver(s) 21 are configured to receive data units via the antenna(s) 24. According to various embodiments, the PHY processing unit 20 of the AP 14 is configured to process received data units that conform to the first communication protocol and have a format described below and determine that such data units conform to the first communication protocol.

In various embodiments, the PHY processing unit 29 of the client device 25-1 is configured to generate a data unit that conforms to the first communication protocol and has a format described herein. Transceiver(s) 30 are configured to transmit the generated data units via antenna(s) 34. Similarly, transceiver(s) 30 are configured to receive data units via antenna(s) 34. According to various embodiments, the PHY processing unit 29 of the client device 25-1 is configured to process received data units that conform to the first communication protocol and have a format described below and determine that such data units conform to the first communication protocol.

Fig. 2A is a diagram of a prior art frequency division multiplexing (OFDM) data unit 200 that the AP 14 is configured to transmit to legacy client stations 25-4 via OFDM modulation, according to an embodiment. In an embodiment, the legacy client station 25-4 is further configured to transmit the data unit 200 to the AP 14. The data unit 200 conforms to the IEEE802.11a standard and occupies a 20 megahertz (MHz) frequency band. The data unit 200 includes a preamble having a legacy short training field (L-STF)202, which is typically used for packet detection, initial synchronization, and automatic gain control, etc., and a legacy long training field (L-LTF)204, which is typically used for channel estimation and fine synchronization. The data unit 200 also includes a legacy signal field (L-SIG)206 for carrying certain physical layer (PHY) parameters about the data unit 200, such as, for example, the modulation type and coding rate used to transmit the data unit. Data unit 200 also includes a data portion 208. Fig. 2B is a diagram of an example data portion 208 (without low density parity check coding) that includes a service field, scrambled physical layer service data units (PSDUs), tail bits, and padding bits, if needed. The data unit 200 is designed for transmission over one spatial stream or space-time stream in a single-input single-output (SISO) channel configuration.

Fig. 3 is a diagram of a prior art OFDM data unit 300 that the AP 14 is configured to transmit to legacy client stations 25-4 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation, according to an embodiment. In an embodiment, the legacy client station 25-4 is also configured to transmit the data unit 300 to the AP 14. Data unit 300 conforms to the IEEE802.11 n standard, occupies a 20MHz frequency band, and is designed for a mixed mode case, i.e., when the WLAN includes one or more client stations that conform to the IEEE802.11a standard instead of the IEEE802.11 n standard. Data unit 300 includes a preamble having an L-STF 302, an L-LTF 304, an L-SIG 306, a high-throughput signal field (HT-SIG)308, a high-throughput short training field (HT-STF)310, and M data high-throughput long training fields (HT-LTFs) 312, where M is an integer generally determined by the number of spatial streams used to transmit data unit 300 in a multiple-input multiple-output (MIMO) channel configuration. In particular, according to the IEEE802.11 n standard, if the data unit 300 is transmitted using two spatial streams, the data unit 300 includes two HT-LTFs 312; if the data unit 300 is transmitted using three or four spatial streams, the data unit 300 includes four HT-LTFs 312. An indication of the particular number of spatial streams utilized is included in the HT-SIG field 308. The data unit 300 also includes a data portion 314.

Fig. 4 is a diagram of a prior art OFDM data unit 400 that the AP 14 is configured to transmit to legacy client stations 25-4 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation, according to an embodiment. In an embodiment, the legacy client station 25-4 is also configured to transmit the data unit 400 to the AP 14. Data unit 400 conforms to the IEEE802.11 n standard, occupies a 20MHz band, and is designed for the "greenfield mode" case, i.e., when the WLAN does not include any client stations that conform to the IEEE802.11a standard and only includes client stations that conform to the IEEE802.11 n standard. Data unit 400 includes a preamble having a high-throughput greenfield mode short training field (HT-GF-STF)402, a first high-throughput long training field (HT-LTF1)404, HT-SIG 406, and M data HT-LTFs 408, where M is an integer generally corresponding to the number of spatial streams used to transmit data unit 400 in a multiple-input multiple-output (MIMO) channel configuration. The data unit 400 also includes a data portion 410.

Fig. 5 is a diagram of a prior art OFDM data unit 500 that the AP 14 is configured to transmit to legacy client stations 25-4 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation, according to an embodiment. In an embodiment, the legacy client station 25-4 is further configured to transmit the data unit 500 to the AP 14. The data unit 500 conforms to the IEEE802.11ac standard and is designed for the "mixed field" case. The data unit 500 occupies a 20MHz bandwidth. In other embodiments or scenarios, data units similar to data unit 500 occupy different bandwidths, such as 40MHz, 80MHz, or 160MHz bandwidths. The data unit 500 includes a preamble having an L-STF 502, an L-LTF 504, an L-SIG 506, two first very high throughput signal fields (VHT-SIGA)508 including a first very high throughput signal field (VHT-SIGA1)508-1 and a second very high throughput signal field (VHT-SIGA2)508-2, a very high throughput short training field (VHT-LTF)510, M very high throughput long training fields 512 (where M is an integer), and a second very high throughput signal field (VHT-SIG-B) 514. The data unit 500 also includes a data portion 516.

Fig. 6A is a set of diagrams illustrating modulation of the L-SIG, HT-SIG1, and HT-SIG2 fields of the data unit 300 of fig. 3 as defined by the IEEE802.11 n standard. The L-SIG field is modulated according to Binary Phase Shift Keying (BPSK), while the HT-SIG1 and HT-SIG2 fields are modulated according to BPSK but on a quadrature axis (Q-BPSK). In other words, the modulation of the HT-SIG1 and HT-SIG2 fields are rotated by 90 degrees compared to the modulation of the L-SIG field.

FIG. 6B is a set of diagrams illustrating modulation of the L-SIG, VHT-SIGA1, and VHT-SIGA2 fields of the data unit 500 of FIG. 5 as defined by the IEEE802.11ac standard. Unlike the HT-SIG1 field in fig. 6A, the VHT-SIGA1 field is modulated according to BPSK, the same as the L-SIG field. On the other hand, the VHT-SIGA2 field is rotated by 90 degrees compared to the modulation of the L-SIG field.

Fig. 7A is a diagram of an OFDM data unit 700 that the AP 14 is configured to transmit to the client station 25-1 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation, according to an embodiment. In an embodiment, the client station 25-1 is further configured to transmit the data unit 700 to the AP 14. The data unit 700 conforms to the first communication protocol and occupies a 20MHz bandwidth. In other embodiments, data units conforming to the first communication protocol similar to data unit 700 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. The data unit 700 is suitable for a "mixed mode" situation, i.e., when the WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, data unit 700 is utilized in other situations as well.

In an embodiment, the data unit 700 includes a preamble 701 having an L-STF 702, an L-LTF704, an L-SIG706, two first HEW signal fields (HEW-SIGA) 708-1 including a first HEW signal field (HEW-SIGA1)708-1 and a second HEW signal field (HEW-SIGA2)708-2, a HEW short training field (HEW-STF)710, M HEW long training fields (HEW-LTF)712 (where M is an integer), and a third HEW signal field (HEW-SIGB) 714. Each of L-STF 702, L-LTF704, L-SIG706, HEW-SIGA 708, HEW-STF 710, M HEW-LTFs 712, and HEW-SIGB 714 includes an integer number of one or more OFDM symbols. For example, in an embodiment, the HEW-SIGA 708 includes two OFDM symbols, where the HEW-SIGA 708-1 field includes a first OFDM symbol and the HEW-SIGA2 includes a second OFDM symbol. In another embodiment, for example, the preamble 701 includes a third HEW signal field (HEW-SIGA3, not shown) and the HEW-SIGA 708 includes three OFDM symbols, where the HEW-SIGA 708-1 includes a first OFDM symbol, the HEW-SIGA2 includes a second OFDM symbol, and the HEW-SIGA3 includes a third OFDM symbol. In at least some examples, the HEW-SIGA 708 is collectively referred to as a single HEW signal field (HEW-SIGA) 708. In some embodiments, data unit 700 also includes a data portion 716. In other embodiments, data unit 700 omits data portion 716.

In the FIG. 7A embodiment, data unit 700 includes one of each of L-STF 702, L-LTF704, L-SIG706, HEW-SIGA 1708. In other embodiments where OFDM data units similar to data unit 700 occupy cumulative bandwidths other than 20MHz, in embodiments each of L-STF 702, L-LTF704, L-SIG706, HEW-SIGA 1708 is repeated over a corresponding number of 20MHz subbands of the total bandwidth of the data unit. For example, in an embodiment, the OFDM data units occupy 80MHz bandwidth, and thus in an embodiment include four of each of the L-STF 702, L-LTF704, L-SIG706, HEW-SIGA 1708. In some embodiments, the modulation of different 20MHz sub-band signals is rotated by different angles. For example, in one embodiment, the first sub-band is rotated by 0 degrees, the second sub-band is rotated by 90 degrees, the third sub-band is rotated by 180 degrees, and the fourth sub-band is rotated by 270 degrees. In other embodiments, different suitable rotations are utilized. In at least some embodiments, different phases of the 20MHz sub-band signals result in a reduced peak-to-average power ratio (PAPR) of the OFDM symbols in the data unit 700. In an embodiment, if the data unit conforming to the first communication protocol is an OFDM data unit occupying an accumulated bandwidth (such as 20MHz, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, etc.), the HEW-STF, HEW-LTF, HEW-SIGB, and HEW data portion occupy a corresponding total bandwidth of the data unit.

FIG. 7B is a set of diagrams illustrating modulation of the L-SIG706, HEW-SIGA 1708-1, and HEW-SIGA 2of FIG. 7A, according to an embodiment. In this embodiment, the L-SIG706, HEW-SIGA 1708-1, and HEW-SIGA 2708-2 fields have the same modulation as the modulation of the corresponding fields as defined by the IEEE802.11ac standard and depicted in FIG. 6B. Accordingly, the HEW-SIGA1 is modulated the same as the L-SIG field. On the other hand, the HEW-SIGA2 field is rotated by 90 degrees compared to the modulation of the L-SIG field. In some embodiments with the third HEW-SIGA3 field, the HEW-SIGA2 field is modulated identically to the L-SIG field and the HEW-SIGA1 field, while the HEW-SIGA3 field is rotated 90 degrees compared to the L-SIG field, the HEW-SIGA1 field, and the HEW-SIGA2 field.

In an embodiment, legacy client stations configured to operate according to the IEEE802.11a standard and/or the IEEE802.11 n standard will assume that, in at least some embodiments, the data unit 700 conforms to the IEEE802.11ac standard and will process the data unit 700 accordingly, because the modulation of the L-SIG706, HEW-SIGA 708-1, and HEW-SIGA 708-2 fields of the data unit 700 corresponds to the modulation of corresponding fields in a data unit conforming to the IEEE802.11ac standard (e.g., data unit 500 of fig. 5). For example, a client station that conforms to the IEEE802.11a standard will recognize the legacy IEEE802.11a standard portion of the preamble of the data unit 700 and will set the duration of the data unit (or data unit duration) according to the duration indicated in the L-SIG 706. For example, according to an embodiment, the legacy client station 25-4 will calculate a duration for the data unit based on the rate and length (e.g., in bytes) indicated in the L-SIG field 706. In an embodiment, the rate and length in the L-SIG field 706 are set such that a client station configured to operate according to a legacy communication protocol will calculate a packet duration (T) corresponding to, or at least approximating, the actual duration of the data unit 700 based on the rate and length. For example, in one embodiment, the rate is set to indicate the lowest rate defined by the IEEE802.11a standard (i.e., 6Mbps), and the length is set to the calculated value such that the packet duration calculated using the lowest rate at least approximates the actual duration of the data unit 700.

In an embodiment, when a legacy client station compliant with the IEEE802.11a standard receives a data unit 700, the duration for the data unit 700 will be calculated, for example, using the rate field and length field of the L-SIG field 706, and in an embodiment will wait until the end of the calculated packet duration before performing a Clear Channel Assessment (CCA). Thus, in this embodiment, the communication medium is prevented from being accessed by legacy client stations for at least the duration of the data unit 700. In an embodiment, legacy client stations will continue to decode data unit 700, but will fail an error check at the end of data unit 700 (e.g., using a Frame Check Sequence (FCS)).

Similarly, in an embodiment, when a legacy client station configured to operate according to the IEEE802.11 n standard receives a data unit 700, the packet duration (T) of the data unit 700 will be calculated based on the rate and length indicated in the L-SIG706 of the data unit 700. A legacy client station will detect the modulation (BPSK) of the first HEW signal field (HEW-SIGA1)708-1 and will assume that data unit 700 is a legacy data unit conforming to IEEE802.11 a. In an embodiment, legacy client stations will continue to decode data unit 700, but will fail an error check at the end of the data unit (e.g., using a Frame Check Sequence (FCS)). In any case, according to the IEEE802.11 n standard, in an embodiment, legacy client stations will wait until the end of the calculated packet duration (T) before performing a Clear Channel Assessment (CCA). Thus, in an embodiment, the duration for data unit 700 will prevent the communication medium from being accessed by legacy client stations.

In an embodiment, when a legacy client station configured to operate according to the IEEE802.11ac standard, but not the first communication protocol, receives the data unit 700, the packet duration (T) of the data unit 700 will be calculated based on the rate and length indicated in the L-SIG706 of the data unit 700. However, in an embodiment, legacy client stations will not be able to detect that data unit 700 does not conform to the IEEE802.11ac standard based on the modulation of data unit 700. In some embodiments, one or more HEW signal fields (e.g., HEW-SIGA1 and/or HEW-SIGA2) of the data unit 700 are formatted to purposely cause legacy client stations to detect errors in decoding the data unit 700 and thus stop decoding (or "drop") the data unit 700. For example, in an embodiment, the HEW-SIGA 708 of the data unit 700 is formatted to purposely cause an error when the SIGA field is decoded by a legacy device according to the IEEE802.11ac standard. Also, according to the IEEE802.11ac standard, in an embodiment, when an error is detected in decoding the VHT-SIGA field, the client station will discard the data unit 700 and wait until the end of the calculated packet duration (T), e.g., calculated based on the rate and length indicated in the L-SIG706 of the data unit 700, before performing a Clear Channel Assessment (CCA). Thus, in an embodiment, the duration for data unit 700 will prevent the communication medium from being accessed by legacy client stations.

Fig. 8 is a diagram of an OFDM symbol 800 according to an embodiment. In an embodiment, data unit 700 of fig. 7 includes an OFDM symbol, such as OFDM symbol 800. OFDM symbol 800 includes a Guard Interval (GI) portion 802 and an information portion 804. In an embodiment, the guard interval comprises a cyclic prefix that repeats an end portion of the OFDM symbol. In an embodiment, the guard interval portion 802 is used to ensure orthogonality of OFDM tones (tones) at a receiving device (e.g., client station 25-1) and minimize or eliminate inter-symbol interference due to multipath propagation in a communication channel via which OFDM symbols 800 are transmitted from a transmitting device (e.g., AP 14) to the receiving device. In an embodiment, the length of the guard interval portion 802 is selected based on an expected worst case channel delay spread in a communication channel between a transmitting device and a receiving device. For example, in an embodiment, a longer guard interval is selected for outdoor communication channels generally characterized by a longer channel delay spread as compared to a shorter guard interval selected for indoor communication channels generally characterized by a shorter channel delay spread. In an embodiment, the length of the guard interval portion 802 is selected based on the tone spacing (e.g., the spacing between the full width subcarrier frequencies of the data unit) with which the information portion 804 has been generated. For example, a longer guard interval is selected for a narrower tone spacing (e.g., 256 tones) as compared to a shorter guard spacing for a wider tone spacing (e.g., 64 tones).

According to an embodiment, the guard interval portion 802 corresponds to a short guard interval, a normal guard interval, or a long guard interval, depending on the transmission mode utilized. In an embodiment, a short or normal guard interval is used for indoor communication channels, communication channels with relatively short channel delay spreads, or communication channels with suitably high SNR ratios, and a long guard interval is used for outdoor communication channels, communication channels with relatively long delay spreads, or communication channels without suitably high SNR ratios. In an embodiment, a normal or short guard interval is used for some or all OFDM symbols of an HEW data unit (e.g., HEW data unit 700) when the HEW data unit is transmitted in the normal mode, and a long guard interval is used for at least some OFDM symbols of the HEW data unit when the HEW data unit is transmitted in the range extension mode.

In an embodiment, the Short Guard Interval (SGI) has a length of 0.4 μ s, the normal guard interval is 0.8 μ s, and the Long Guard Interval (LGI) has a length of 1.2 μ s or 1.8 μ s. In an embodiment, the information portion 804 has a length of 3.2 μ s. In other embodiments, the information portion 804 has an increased length corresponding to the pitch spacing with which the information portion 804 has been generated. For example, the information part 804 has a first length of 3.2 μ s for a conventional pattern using a first tone spacing of 64 tones and has a second length of 6.4 μ s for a second tone spacing of 128 tones, wherein both the second tone spacing and the second length are increased by an integer multiple of 2 compared to the first tone spacing and the first length. In an embodiment, the remaining length of information portion 804 is padded with copies of the received time domain signal (e.g., information portion 804 contains two copies of the received time domain signal). In other embodiments, other suitable lengths for the SGI, NGI, LGI and/or information portion 804 are utilized. In some embodiments, the SGI has a length that is 50% of the length of the NGI, and the NGI has a length that is 50% of the length of the LGI. In other embodiments, the SGI has a length that is 75% or less of the length of the NGI, and the NGI has a length that is 75% or less of the length of the LGI. In other embodiments, the SGI has a length that is 50% or less of the length of the NGI, and the NGI has a length that is 50% or less of the length of the LGI.

In other embodiments, OFDM modulation with reduced tone spacing is used in a range expansion mode using the same tone plan (e.g., a predetermined index sequence indicating which OFDM tones are assigned for data tones, pilot tones, and/or guard tones). For example, the conventional mode for a 20MHz bandwidth OFDM data unit uses a 64-point Discrete Fourier Transform (DFT) resulting in 64 OFDM tones (e.g., indices-32 to +31), and the range extension mode uses a 128-point DFT for the 20MHz OFDM data unit resulting in 128 OFDM tones (e.g., indices-64 to +63) within the same bandwidth. In this case, the tone spacing in the range extension mode OFDM symbol is reduced by a factor of 2 compared to the conventional mode OFDM symbol when the same tone plan is used (1/2). As another example, the normal mode for a 20MHz bandwidth OFDM data unit uses a 64-point Discrete Fourier Transform (DFT) resulting in 64 OFDM tones, and the range extension mode uses a 256-point DFT for the 20MHz OFDM data unit resulting in 256 OFDM tones. In this case, the tone spacing in the range extension mode OFDM symbol is reduced by a factor of 4 compared to the normal mode OFDM symbol (1/4). In such an embodiment, a long GI duration of, for example, 1.6 μ s is used. However, in an embodiment, the duration of the information portion of the range extension mode OFDM symbol increases (e.g., from 3.2 μ s to 6.4 μ s), and the GI portion duration remains the same as a percentage of the total OFDM symbol duration. Thus, in this case, in at least some embodiments, efficiency losses due to longer GI symbols are avoided. In various embodiments, the term "long guard interval" as used herein encompasses both an increased duration of the guard interval and a reduced OFDM tone spacing that effectively increases the duration of the guard interval.

Fig. 9A is a diagram illustrating an example data unit 900 in which a normal mode or a range expansion mode is used for a preamble of the data unit, according to an embodiment. The data cell 900 is substantially the same as the data cell 700 of fig. 7A and includes the same numbered elements as the data cell 700 of fig. 7A. The HEW-SIGA field 708 (e.g., HEW-SIGA 1708-1 or HEW-SIGA 2708-2) of the data unit 900 includes an encoding indication (CI)902 according to an embodiment, the CI indication 902 is set to indicate one of (i) a regular mode with a regular encoding scheme or (ii) a range extension mode with a range extension encoding scheme. In an embodiment, CI indication 902 includes one bit, where a first value of the bit indicates a normal mode and a second value of the bit indicates a range extension mode. In some embodiments, the CI indication is combined with a Modulation and Coding Scheme (MCS) indicator. In an embodiment, for example, the normal mode corresponds to MCS values determined to be valid by the legacy receiver device (e.g., following the IEEE802.11ac protocol), while the range extension mode corresponds to MSC values determined to be invalid (or not supported) by the legacy receiver device (e.g., not following the IEEE802.11ac protocol). In other embodiments, the CI indication 902 has a plurality of bits that indicate a plurality of normal mode MCS values and a plurality of range extension mode MCS values. As illustrated in fig. 9A, in the illustrated embodiment, a regular coding scheme is used for all OFDM symbols of the preamble of the data unit 700, and one of the regular coding scheme or the range extension coding scheme, as indicated by CI indication 902, is used for OFDM symbols of the data portion 716.

In embodiments such as OFDM symbols where a range extension coding scheme is used for the data portion 716, the range and/or SNR at which the PHY data unit is successfully decoded is generally improved (i.e., successfully decoded at longer range and/or lower SNR) as compared to conventional data units. In some embodiments, decoding of the preamble 701 generated using conventional coding schemes does not necessarily achieve improved range and/or SNR performance. In such an embodiment, transmission of at least a portion of the preamble at the transmission power boost increases the decoding range of the preamble 701 portion compared to the transmission power used to transmit the data portion 716. In some embodiments, the portion of the preamble 701 transmitted with transmission power boosting includes legacy fields (such as the L-STF 702, the L-LTF704, and the L-SIG 708) and/or non-legacy fields (such as the HEW-STF and the HEW-LTF). In various embodiments, the transmission power boost is 3dB, 6dB, or other suitable value. In some embodiments, the transmission power boost is determined such that the "boosted" preamble 701 is decodable with similar performance as compared to the "non-boosted" data portion 716 at the same location. In some embodiments, increased lengths of the L-STF 702, L-LTF704, and/or L-SIG706 are used in combination with transmission power boosting. In other embodiments, instead of transmit power boosting, L-STF 702, L-LTF704, and/or L-SIG706 of increased length are used.

Fig. 9B is a diagram illustrating an example data unit 950 in which a range extension coding scheme is used for a portion of a preamble of the data unit, according to an embodiment. The data unit 950 is substantially the same as the data unit 900 of fig. 9A except that the data unit 950 includes a preamble 751 in which the coding scheme indicated by the CI indication 902 is adapted to OFDM symbols of a portion of the preamble 751 and OFDM symbols of the data portion 716. In particular, in the illustrated embodiment, a normal coding scheme is used for the first portion 751-1 of the preamble 701 and one of either the normal coding scheme or the range extension coding scheme, as indicated by the CI indication 902, is used for the OFDM symbols of the second portion 751-2 of the preamble 751, except for the OFDM symbols of the data portion 716. Thus, in the illustrated embodiment, the coding scheme indicated by CI information 902 skips OFDM symbols corresponding to HEW-STF 710 and is applied starting with OFDM symbols corresponding to HEW-LTF 712-1. Skipping the HEW-STF 710 allows, in at least some embodiments, a device receiving the data unit 950 sufficient time to decode the CI indication 902 and appropriately set the receiver to begin decoding the OFDM symbol using the coding scheme indicated by the CI indication 902 prior to receiving such OFDM symbol.

Fig. 10A is a diagram illustrating an example data unit 1000 in which OFDM tone spacing adjustment is used in combination with bit and/or symbol repetition for a range expansion coding scheme, according to an embodiment. Data unit 1000 is substantially the same as data unit 900 of fig. 7A, except that in data unit 1000, when CI indication 902 indicates that a range extension coding scheme is being utilized, OFDM symbols of data portion 716 are generated using OFDM modulation having a reduced tone spacing compared to the tone spacing of the normal mode OFDM symbols used for data unit 1000.

Fig. 10B is a diagram illustrating an example data unit 1050 in which OFDM tone spacing adjustment is used in combination with bit and/or symbol repetition for a range expansion coding scheme, in accordance with another embodiment. Data unit 1050 is generally the same as data unit 950 of fig. 9B, except that in data unit 1050, when CI indication 902 indicates that a range extension coding scheme is utilized, OFDM symbols of second portion 751-2 and OFDM symbols of data portion 716 are generated using OFDM modulation with a reduced tone spacing compared to the tone spacing of the normal mode OFDM symbols used for data unit 1050. In the embodiment shown in fig. 10A, the total bandwidth of 20MHz is used with the normal tone spacing and guard interval in the first portion 751-1 and the 2 reduced tone spacing, long guard interval, and FFT size 64 repeated twice across the total bandwidth. In some embodiments, transmission power boosting is applied to the first portion 751-1. In other embodiments, other multiples, such as 4x, 8x, or other suitable values are used for one or more of the following: reduced tone spacing, increased guard interval, increased symbol duration, or increased repetition across the total bandwidth.

In some embodiments, a different preamble format is used for the range extension mode data unit than is used for the preamble of the regular mode data unit. In such an embodiment, the device receiving the data unit may automatically detect whether the data unit is a normal mode data unit or a range extension mode data unit based on the format of the preamble of the data unit. Fig. 11A is a diagram illustrating a regular pattern data unit 1100, according to an embodiment. The normal mode data unit 1100 includes a normal mode preamble 1101. The normal mode preamble 1101 is substantially the same as the preamble 701 of the data unit 700 of fig. 7A. In an embodiment, the preamble 1101 includes a HEW-SIGA field 1108 that includes a first HEW-SIGA1 field 1108-1 and a second first HEW-SIGA2 field 1108-1. In an embodiment, the HEW-SIGA field 1108 of the preamble 1101 (e.g., HEW-SIGA 11108-1 or HEW-SIGA 21108-2) includes the CI indication 1102. In an embodiment, the CI indication 1102 is set to indicate whether a range extension coding scheme or a regular coding scheme is used for the OFDM symbols of the data portion 716 of the data unit 1100. In an embodiment, the CI indication 1102 comprises one bit, wherein a first value of the bit indicates a regular coding scheme and a second value of the bit indicates a range extension coding scheme. As will be explained in more detail below, in an embodiment, the device receiving the data unit 1100 is able to detect that the preamble 1101 is a normal mode preamble instead of an extended mode preamble based on the format of the preamble 1101. In an embodiment, upon detecting that the preamble 1101 is a normal mode preamble, the receiving device determines, based on the CI indication 1102, whether a range extension coding scheme or a normal coding scheme is used for the OFDM symbols of the data portion 716 and decodes the data portion 716 accordingly. In some embodiments, when the CI indication 1102 indicates that the range extension coding scheme is to be utilized, OFDM symbols of a portion of the preamble 1101 (e.g., such as HEW-LTF and HEW-SIGB) and OFDM symbols of the data portion 716 are generated using OFDM modulation with a smaller tone spacing compared to the tone spacing of the normal mode OFDM symbols used for the data unit 1050.

Fig. 11B is a diagram illustrating a range expansion mode data unit 1150, according to an embodiment. The range extension mode data unit 1150 includes a range extension mode preamble 1151. The data unit 1150 is substantially similar to the data unit 1100 of fig. 11A, except that the preamble 1151 of the data unit 1150 is formatted differently than the preamble 1101 of the data unit 1100. In an embodiment, the preamble 1151 is formatted such that a receiving device operating in accordance with the HEW communication protocol is able to determine that the preamble 1151 is a range extension mode preamble rather than a regular mode preamble. In an embodiment, the range expansion mode preamble 1151 includes the L-STF 702, L-LTF704, and L-SIG706 and one or more first HEW signal fields (HEW-SIGA) 1152. In an embodiment, the preamble 1150 also includes one or more secondary L-SIG 1154 fields following the L-SIG field 706. In some embodiments, the secondary L-SIG(s) are followed by a second L-LTF field (L-LTF2) 1156. In other embodiments, the preamble 1151 omits the L-SIG(s) 1154 and/or the L-LTF 21156. In some embodiments, the preamble 1151 also includes a HEW-STF 1158, one or more HEW-LTF fields 1160, and a second HEW signal field (HEW-SIGB) 1162. In other embodiments, the preamble 1151 omits the HEW-STF 1158, the HEW-LTF(s) 1160, and/or the HEW-SIGB 1162. In an embodiment, the data unit 1150 further includes a data portion 716 (not shown in fig. 11B). In some embodiments, HEW signal field (HEW-SIGA)1152 is modulated using the same range extension coding scheme as data field 716.

In an embodiment, one or more symbols of HEW-SIGA1152 are modulated using, for example, QBPSK instead of BPSK, to allow automatic detection between a normal mode and a range extension mode of a receiving device operating according to the HEW communication protocol. In an embodiment, for example, where the normal mode preamble includes two BPSK symbols and one Q-BPSK symbol after the L-SIG706 field, the range extension mode preamble includes three BPSK symbols and one Q-BPSK symbol after the L-SIG706 field. In an embodiment, for example, when a 4x bitwise repetition of MCS0 with 48 data tones in each 64-FFT (20MHz) is used. In some embodiments, for example, where automatic detection distinguishes the normal mode from the range expansion mode, some bits are omitted from the HEW-SIGA1152, such as bits indicating the signal bandwidth, MCS value used, or other suitable bits.

In one embodiment, where the preamble 1151 includes one or more secondary L-SIGs 1154, the content of each of the L-SIGs 1154(s) is the same as the content of the L-SIG706 of the data unit 1150. In an embodiment, a receiving device receiving the data unit 1150 determines that the preamble 1151 corresponds to a range expansion mode preamble by detecting repetition(s) of the L-

SIG fields

706, 1154. Also, in an embodiment, both the rate subfield and the length subfield of the L-SIG706, as well as the rate subfield(s) and the length subfield(s) of the corresponding secondary L-SIG(s) 1154, are set to fixed (e.g., predetermined) values. In this case, in an embodiment, upon detecting the repetition(s) of the L-

SIG field

706, 1154, the receiving device uses the fixed value in the repeated L-SIG field as additional training information to improve the channel estimation. However, in some embodiments, at least the length sub-field of the L-SIG706 and the length sub-field of the corresponding at least secondary L-SIG(s) 1154 are not set to fixed values. For example, in an embodiment, the length field is instead set to a value determined based on the actual length of the data unit 1150. In one such embodiment, the receiving device first decodes the L-SIG706 and then detects the repetition(s) of the L-

SIG field

706, 1154 using the length subfield in the L-SIG 706. In another embodiment, the receiving device first detects the repetition(s) of the L-

SIG fields

706, 1154 and then combines the detected multiple L-

SIG fields

706, 1154 to improve the decoding reliability of the L-

SIG fields

706, 1154 and/or to improve channel estimation using redundant information in the multiple L-

SIG fields

706, 1154.

In embodiments where the preamble 1151 includes the L-LTF21156, the OFDM symbol(s) of the L-LTF21156 are generated using a range extension coding scheme. In another embodiment, where the preamble 1151 includes the L-LTF 211156, the OFDM symbol(s) of the L-LTF21156 are generated using a conventional coding scheme. If the Double Guard Interval (DGI) used in the L-LTF704 is long enough for the communication channel in which the data unit 1150 travels from the transmitting device to the receiving device, then the OFDM symbols for the L-LTF21156 are generated using a conventional coding scheme, or alternatively, in an embodiment, the preamble 1151 omits the L-LTF 21156.

In another embodiment, the preamble 1151 omits the secondary L-SIG(s) 1154 but includes the L-LTF 21156. In this embodiment, the receiving device detects that the preamble 1151 is a range expansion mode preamble by detecting the presence of the L-LTF 21156. 12A-12B are diagrams illustrating two possible formats of LTFs suitable for use as L-LTF21156, according to two example embodiments. Turning first to FIG. 12A, in a first exemplary embodiment, L-LTF 21200 is formatted in the same manner as L-LTF704, i.e., as defined by a legacy communication protocol (e.g., the IEEE802.11 a/n/ac standard). In particular, in the illustrated embodiment, L-LTF 212000 includes a Double Guard Interval (DGI)1202 followed by two

repetitions

1204, 1206 of a long training sequence. Turning now to FIG. 12B, in another example embodiment, L-LTF2 is formatted differently than L-LTF 704. In particular, in the illustrated embodiment, L-LTF 21208 includes a first normal guard interval 1210, a first repetition of a long training sequence 1212, a second normal guard interval 1214, and a second repetition of a long training sequence 1216.

Referring back to fig. 11B, in an embodiment, HEW-SIGA(s) 1152 are generated using a range expansion coding scheme. In an embodiment, the number of HEW-SIGAs 1152 is the same as the number of HEW-SIGA(s) 1108 of the regular pattern preamble 1101. Similarly, in an embodiment, the content of the HEW-SIGA1152 is the same as the content of the HEW-SIGA(s) 1108 of the regular-mode preamble 1101. In other embodiments, the number and/or content of HEW-SIGAs 1152 is different from the number and/or content of HEW-SIGA(s) 1108 of the regular-mode preamble 1101. In an embodiment, the device receiving the data unit 1150, based on detecting that the preamble 1151 corresponds to the range extension mode preamble, uses the range extension coding scheme to decode the HEW-SIGA(s) 1152 and properly interpret the HEW-SIGA(s) 1152 as defined for the range extension mode.

In embodiments where the preamble 1151 omits the L-SIG(s) 1154 and/or L-LTF21156, the receiving device determines whether the preamble corresponds to the range extension mode preamble 1151 or the normal mode preamble 1101 by detecting whether the HEW-SIGA field in the preamble was generated using the range extension coding scheme or the normal coding scheme based on an autocorrelation of the HEW-SIGA field using the range extension coding scheme and the normal coding scheme. Fig. 13A-13B are the HEW-SIGA1108 of the normal mode preamble 1101 and the HEW-SIGA1152 of the range extension mode preamble 1151, respectively, according to an embodiment. In the illustrated embodiment, the HEW-SIGA1108 of the regular-mode preamble 1101 includes a first NGI 1302, a first HEW-SIGA field 1304, a second NGI 1306, and a second HEW-SIGA field 1308. On the other hand, the HEW-SIGA1152 of the range extension mode preamble 1151 includes a first LGI 1310, a first HEW-SIGA field 1312, a second LGI 1314 and a second HEW-SIGA field 1312. In an embodiment, the receiving device performs a first autocorrelation of the HEW-SIGA field using a normal guard interval structure (such as the structure illustrated in fig. 13A), performs a second autocorrelation using a long guard interval structure (such as the structure illustrated in fig. 13B), and performs a comparison of the autocorrelation results. In an embodiment, if the autocorrelation of the HEW-SIGA field using the long guard interval produces a larger result compared to the result of the autocorrelation of the HEW-SIGA field using the normal guard interval, the receiving device determines that the preamble corresponds to the range expansion mode preamble 1151. On the other hand, in the embodiment, if the autocorrelation of the HEW-SIGA field using the normal guard interval produces a larger result compared to the result of the autocorrelation of the HEW-SIGA field using the long guard interval, the receiving apparatus determines that the preamble corresponds to the normal-mode preamble 1101.

Referring again to fig. 11B, in an embodiment, preamble 1151 is formatted such that legacy client stations can determine the duration of data unit 1150 and/or the data unit does not conform to a legacy communication protocol. Further, in an embodiment, preamble 1151 is formatted such that a client station operating according to the HEW protocol is able to determine that the data unit conforms to the HEW communication protocol. For example, at least two OFDM symbols of the L-SIG706 (such as the L-SIG(s) 1154 and/or the L-LTF21156 and/or the HEW-SIGA 1152) immediately following the preamble 1151 are modulated using BPSK modulation. In this case, in an embodiment, the legacy client station will treat the data unit 1150 as a legacy data unit, will determine the duration of the data unit based on the L-SIG706 and will refrain from accessing the medium for the determined duration. Also, in an embodiment, one or more other OFDM symbols of preamble 1151, such as one or more of HEW-SIG 1152(s), are modulated using Q-BPSK modulation, which allows client stations operating according to the HEW communication protocol to detect that data unit 1150 conforms to the HEW communication protocol.

In some embodiments, the HEW communication protocol allows for beamforming and/or multi-user MIMO (MU-MIMO) transmission in a range expansion mode. In other embodiments, the HEW communication protocol allows for only a single stream and/or only a single user transmission in the range extension mode. With continued reference to fig. 11B, in embodiments where the preamble 1151 includes a HEW-STF 1158 and HEW-LTF(s) 1160, the AP 14 applies beamforming and/or multi-user transmission starting with the HEW-STF 1158. In other words, in embodiments, the fields of the preamble 1151 preceding the HEW-STF 1158 are omni-directional and intended to be received by the intended recipient of the data unit 1150 in the multi-user mode, while the HEW-STF field 1158 and the preamble field following the HEW-STF field 1158 and the data portion following the preamble 1151 are beamformed and/or include different portions intended to be received by different intended recipients of the data unit 1150. In an embodiment, the HEW-SIGB field 1162 includes user-specific information for the intended recipient of the data unit 1150 in MU-MIMO mode. Depending on the embodiment, the HEW-SIGB field 1162 is generated using a conventional coding scheme or a range extension coding scheme. Similarly, HEW-STF 1158 is generated using a conventional coding scheme or a range extension coding scheme, depending on the embodiment. In an embodiment, the training sequence used on the HEW-STF 1158 is a sequence defined in a legacy communication protocol (such as in the IEEE802.11ac protocol).

On the other hand, in embodiments where the preamble 1151 omits the HEW-STF 1158 and HEW-LTF(s) 1160, beamforming and MUMIMO are not allowed in the extended guard interval mode. In this embodiment, only single-user single-stream transmission is allowed in extended guard interval mode. In an embodiment, the receiving device obtains a single stream channel estimate based on the L-LTF field 704 and demodulates the data portion of the data unit 1150 based on the channel estimate obtained based on the L-LTF field 704.

In some embodiments, the receiver device uses the HEW-STF field 1158 to restart the Automatic Gain Control (AGC) process for receiving the data portion 716. In an embodiment, the HEW-STF has the same duration as the VHT-STF (i.e., 4 microseconds). In other embodiments, the HEW-STF has a longer duration than the VHT-STF. In an embodiment, the HEW-STF has the same time domain periodicity as the VHT-STF, such that in the frequency domain, there is one non-zero tone every 4 tones and the same tone spacing as IEEE802.11ac is used. In other embodiments with 1/N tone spacing, the HEW-STF has one non-zero tone every 4 × N tones. In embodiments where the total bandwidth for the data units is greater than 20MHz (e.g., 40MHz, 80MHz, etc.), the HEW-STF uses the same wider bandwidth VHT-STF as IEEE802.11ac (i.e., a copy of the 20MHz VHT-STF for 40MHz, 80MHz, 160MHz, etc.).

Fig. 14A is a block diagram illustrating a range expansion mode data unit 1400, according to an embodiment. The data unit 1400 includes a range extension mode preamble 1401. The range extension mode preamble 1401 is substantially similar to the range extension mode preamble 1151 of fig. 11B, except that the L-SIG706 and the secondary L-SIG 1154 of the preamble 1151 are combined into a single L-SIG field 1406 in the preamble 1401. Fig. 14B is a diagram illustrating the L-SIG field 1406, according to one embodiment. In the embodiment of fig. 14B, the L-SIG field 1406 includes a double guard interval 1410, a first L-SIG field 1412 (which includes the contents of the L-SIG field 706 of the preamble 1151), and a second L-SIG field 1414 (which includes the contents of the secondary L-SIG2 field 1154 of the preamble 1151). In various embodiments, the L-SIG field 1406 includes a length subfield set to a fixed value or set to a variable value, as discussed above with respect to the L-

SIG fields

706, 1154 of fig. 11B. In various embodiments, redundant (repeated) bits in the L-SIG field 1406 are used for improved channel estimation, as discussed above with respect to the L-

SIG fields

706, 1154 of fig. 11B.

In an embodiment, legacy client stations receiving the data unit 1400 assume that the L-SIG field 1406 includes a normal guard interval. As illustrated in fig. 14C, in this embodiment, the FFT window assumed at legacy client stations for L-SGI information is shifted compared to the actual L-SIG field 1412. In an embodiment, to ensure that the constellation points within the FFT window correspond to BPSK modulation as expected by legacy client stations, and thus to allow legacy client stations to properly decode the L-SIG field 1412, the modulation of the L-SIG field 1412 is phase shifted relative to conventional BPSK modulation. For example, in a 20MHz OFDM symbol, if the normal guard interval is 0.8 μ s and the double guard interval is 1.6 μ s, then the modulation of OFDM tone k of L-SIG field 1412 is offset with respect to the corresponding OFDM tone k of the original L-SIG, as can be seen from:

thus, in an embodiment, the L-SIG field 1412 is modulated using inverted Q-BPSK instead of conventional BPSK. Thus, for example, in an embodiment, a bit of value 1 is modulated onto j and a bit of value 0 is modulated onto j, which results in a { j, -j } modulation rather than a conventional {1, -1} BPSK modulation. In an embodiment, legacy client stations may properly decode the L-SIG field 1412 due to the inverse Q-BPSK modulation of the L-SIG field 1412 and, in an embodiment, determine the duration of the data unit 1400 based on the L-SIG 1412 field. On the other hand, in an embodiment, a client station operating according to the HEW protocol may automatically detect that preamble 1401 is a range extension mode preamble by detecting repetition of L-SIG field 1412 or by detecting inverted Q-BPSK modulation of the L-SIG field within the FFT window of a legacy client station. Alternatively, in other embodiments, a client station operating according to the HEW protocol detects that preamble 1401 is a range extension mode preamble using other detection methods discussed above, such as based on the modulation or format of HEW-SIGA field(s) 1152.

Referring to fig. 11A-11B and 14A, in some embodiments, a long guard interval is used for the initial OFDM symbols of both the normal mode preamble (e.g., preamble 1101) and the range extension mode preamble (e.g., preamble 1151 or preamble 1401). For example, referring to FIGS. 11A-11B, in an embodiment, the L-STF field 702, the L-LTF field 704, and the L-

SIG fields

706, 1154 and the HEW-SIGA field 1152 are each generated using a long guard interval. Similarly, referring to FIG. 14A, in an embodiment, the L-STF field 702, L-LTF field 704, L-SIG field 1406, and HEW-SIGA(s) 1152 are generated using a long guard interval. In an embodiment, the receiving device may determine whether the preamble corresponds to a normal mode preamble or a range extension mode preamble based on the modulation of the HEW-SIGA field 1152 (e.g., Q-BPSK) or based on an indication contained in the HEW-SIGA field 1152 in various embodiments. Also, similar to the preamble 1151 of fig. 11B, the preamble 1401 of fig. 14A includes or omits a second L-LTF2 field 1156, depending on the embodiment and/or scenario.

Fig. 15 is a block diagram illustrating the format of the HEW-SIGA field 1500, according to an embodiment. In some embodiments, the HEW-SIGA field(s) of the data unit 1150 or the data unit 1400 are formatted as a HEW-SIGA field 1500. In some embodiments, the HEW-SIGA field(s) 1108 are formatted into the HEW-SIGA field 1500. The HEW-SIGA field 1500 includes a double guard interval 1502, a first repetition 1504 of the HEW-SIGA field, and a second repetition 1506 of the HEW-SIGA field. In an example embodiment, the DGI is 1.8 μ s, and each repetition of the HEW-SIGA is 3.2 μ s. In an embodiment, the repeated bits in the HEW-SIGA field 1500 are used to increase the reliability of the decoding of the HEW-SIGA field 1500. In an embodiment, the HEW-SIGA field 1500 format is used to automatically detect the range expansion mode preamble based on a comparison between the autocorrelation of the preamble HEW-SIGA field using the format of the HEW-SIGA field 1500 and the autocorrelation of the HEW-SIGA field using the preamble of a conventional HEW-SIGA field format used in the conventional mode (such as the format illustrated in fig. 13A). In some embodiments, the HEW-SIGA field 1500 is modulated with less redundancy than the data portion 716, as the additional time-domain repetition of the HEW-SIGA field 1500 provides sufficient improvement in decoding performance.

Fig. 16 is a block diagram illustrating an example PHY processing unit for generating a regular mode data unit using a regular coding scheme, according to an embodiment. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1600. In various embodiments and/or scenarios, the PHY processing unit 1600 generates a range extension data unit, such as, for example, one of the data units of fig. 9A, 9B, 10A, or 10B. The PHY processing unit 1600 includes a scrambler 1602 that generally scrambles the information bit stream to reduce the occurrence of long sequences of ones or zeros. The FEC encoder 1606 encodes the scrambled information bits to generate encoded data bits. In one embodiment, FEC encoder 1606 comprises a Binary Convolutional Code (BCC) encoder. In another embodiment, FEC encoder 1606 comprises a binary convolutional encoder followed by a punctured block. In yet another embodiment, the FEC encoder 1606 comprises a Low Density Parity Check (LDPC) encoder. Interleaver 1610 receives the encoded data bits and interleaves (i.e., changes the order of the bits) the bits to prevent long sequences of adjacent noise bits from entering a decoder at the receiver. The constellation mapper 1614 maps the interleaved sequence of bits to constellation points corresponding to different subcarriers of an OFDM symbol. More particularly, for each spatial stream, constellation mapper 1614 translates each bit sequence of length log2(M) into one of M constellation points.

The output of the constellation mapper 1614 continues to be operated on by an Inverse Discrete Fourier Transform (IDFT) unit 1618, which converts the constellation point blocks into time domain signals. In an embodiment or case where the PHY processing unit 1600 operates to generate data units for transmission via multiple spatial streams, the Cyclic Shift Diversity (CSD) unit 1622 inserts a cyclic shift into all but one of the spatial streams that prevents unintentional beamforming. The output of CSD unit 1622 is provided to a Guard Interval (GI) insertion and windowing unit 1626 which precedes the OFDM symbols by a circular extension of the OFDM symbols and smoothes the edges of each symbol pair to increase spectral attenuation. The output of the GI insertion and windowing unit 1626 is provided to an analog and Radio Frequency (RF) unit 1630 that converts the signal to an analog signal and upconverts the signal to an RF frequency for transmission.

In various embodiments, the range extension mode corresponds to the lowest data rate Modulation and Coding Scheme (MCS) of the regular mode and introduces redundancy or repetition of bits into the repetition of at least some fields or symbols of the data unit to further reduce the data rate. For example, in various embodiments and/or scenarios, the range extension mode introduces redundancy into the data portion of the range extension mode data unit and/or the repetition of non-legacy signal fields or symbols according to one or more range extension coding schemes described below. As an example, according to an embodiment, the regular mode data unit is generated according to a regular coding scheme. In various embodiments, the conventional coding scheme is an MCS selected from a set of Modulation and Coding Schemes (MCSs), such as MCS0 (binary phase shift keying (BPSK) modulation and a coding rate of 1/2) to MCS9 (coding rates of Quadrature Amplitude Modulation (QAM) and 5/6), and the higher order MCS corresponds to a higher data rate. In one such embodiment, the range extension mode data units are generated using a range extension coding scheme (such as modulation and coding as defined by MCS 0) and with increased bit repetition, block coding, or symbol repetition that further reduces the data rate.

Fig. 17A is a block diagram of an example PHY processing unit 1700 for generating a range extension mode data unit using a range extension coding scheme, according to an embodiment. In some embodiments, the PHY processing unit 1700 generates signal and/or data fields of a range expansion mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1700.

The PHY processing unit 1700 is similar to the PHY processing unit 1600 of fig. 16, except that the PHY processing unit 1700 includes a block encoder 1704 coupled to a scrambler 1702. In an embodiment, the block encoder 1704 reads the incoming (scrambled) information bits one block at a time, generates several copies of each block (or each bit in a block), interleaves the resulting bits according to a range expansion coding scheme, and outputs the interleaved bits for further encoding by an FEC encoder 1706 (e.g., a binary convolutional encoder). In general, according to an embodiment, each block contains a number of information bits that fill the data tones of a single OFDM symbol after having been encoded by block encoder 1704 and by FEC encoder 1706. As an example, in one embodiment, the block encoder 1704 generates two copies (2x repetition) of each block of 12 information bits to generate 24 bits to be included in an OFDM symbol. The 24 bits are then encoded by FEC encoder 1706 at an encoding rate of 1/2 to generate 48 bits that modulate the 48 data tones (e.g., using BPSK modulation) of the OFDM symbol. As another example, in another embodiment, block encoder 1704 generates four copies (4x repetitions) of each block of 6 information bits to generate 24 bits, which are then encoded by FEC encoder 1706 at an encoding rate of 1/2 to generate 48 bits of the 48 data tones of the modulated OFDM symbol. As yet another example, in another embodiment, block encoder 1704 generates two copies (2x repetition) of each block of 13 information bits to generate 26 bits, which are then encoded by FEC encoder 1706 at an encoding rate of 1/2 to modulate the generation of 52 bits of 52 data tones of an OFDM symbol. In other embodiments, the block encoder 1704 and FEC encoder 1706 are configured to generate 104, 208 or any suitable number of bits for modulation of the data tones of the OFDM symbol.

In some embodiments, the block encoder 1704 applies a 4x repetition scheme when generating the data (or signal) field as defined by MCS0 specified in the IEEE802.11 n standard for a 20MHz channel (i.e., having 52 data tones per OFDM symbol). In this case, according to an embodiment, the block encoder 1704 generates four copies of each block of 6 information bits to generate 24 bits and then adds two padding bits (i.e., two bits having predetermined values) to provide a specified number of bits (i.e., 26 bits for the 52 data tones) to the BCC encoder, which encodes the 26 bits using an encoding rate of 1/2 to generate 52 encoded bits for modulating the 52 data tones.

In one embodiment, the block encoder 1704 utilizes a "block-level" repetition scheme, in which each block of n bits is repeated m consecutive times. As an example, according to an embodiment, if m is equal to 4(4x repetition), the block encoder 1704 generates a sequence [ C, C ], where C is an n-bit block. In another embodiment, the block encoder 1704 utilizes a "bit-level" repetition scheme, in which each input bit is repeated m consecutive times. In this case, in an embodiment, if m is equal to 4(4x repetition), the block encoder 1704 generates a sequence [ b 1b 1b 1b 1b 2b 2b 2b 2b 3b 3b 3 b3. ], where b1 is the first bit in a block of bits, b2 is the second bit, and so on. In yet another embodiment, the block encoder 1704 generates copies of the m number of incoming bits and interleaves the resulting bit stream according to any suitable code. Alternatively, in yet another embodiment, the block encoder 1704 encodes the incoming bits or blocks of incoming bits using any suitable code, such as a Hamming block code having an encoding rate of 1/2, 1/4, etc., or any other block code having an encoding rate of 1/2, 1/4, etc. (e.g., (1, 2) or (1, 4) block codes, (12, 24) block codes or (6, 24) block codes, (13, 26) block codes, etc.).

According to an embodiment, the effective encoding rate corresponding to the combination of the encoding performed by block encoder 1704 and the encoding performed by FEC encoder 1706 is the product of the two encoding rates. For example, in an embodiment where block encoder 1704 utilizes 4x repetition (or coding rate of 1/4) and FEC encoder 1706 utilizes a coding rate of 1/2, the resulting effective coding rate is equal to 1/8. According to an embodiment, the data rate in the range extension mode is effectively reduced (e.g., by a factor of 2, 4, etc.) by a factor corresponding to the number of encoding rates applied by the block encoder 1704 as a result of the reduced encoding rate compared to the encoding rate used to generate a similar regular mode data unit.

According to some embodiments, the block encoder 1704 utilizes the same block encoding scheme used to generate the data portion of the control mode data unit for generating the signal field of the control mode data unit. For example, in an embodiment, the OFDM symbols of the signal field and the OFDM symbols of the data portion each include 48 data tones, and in this embodiment, for example, the block encoder 1704 applies a 2x repetition scheme to a 12-bit block for the signal field and the data portion. In another embodiment, the data portion and the signal field of the control mode data unit are generated using different block coding schemes. For example, in an embodiment, the long-range communication protocol specifies a different number of data tones per OFDM symbol than the number of data tones per OFDM symbol in the data portion. Thus, in this embodiment, the block encoder 1704 utilizes a different block size and, in some embodiments, a different encoding scheme than the block size and encoding scheme used to generate the data portion when operating on the signal field. For example, if the long-range communication protocol specifies 52 data tones per OFDM symbol of the signal field and 48 data tones per OFDM tone of the data portion, the block encoder 1704 applies a 2x repetition scheme to the 13-bit block of the signal field and a 2x repetition scheme to the 12-bit block of the data portion, according to one embodiment.

According to an embodiment, the FEC encoder 1706 encodes the block-encoded information bits. In an embodiment, BCC encoding is performed continuously over the entire field to be generated (e.g., the entire data field, the entire signal field, etc.). Thus, in this embodiment, the information bits corresponding to the fields to be generated are divided into blocks of a specified size (e.g., 6 bits, 12 bits, 13 bits, or any other suitable number of bits), each block is processed by a block encoder 1704, and the resulting data stream is then provided to an FEC encoder 1706 that successively encodes the incoming bits.

Similar to interleaver 1610 of fig. 16, in various embodiments interleaver 1710 changes the order of bits in order to provide diversity gain and reduce the chance that consecutive bits in the data stream will be corrupted in the transmission channel. However, in some embodiments, block encoder 1704 provides sufficient diversity gain and interleaver 1710 is omitted. In some embodiments, interleaver 1710 or FEC encoder 1706 provides the bits to constellation mapper 1614 for transmission, as described above.

For example, in some embodiments, the information bits in the data portion of the range extension mode data unit are padded (i.e., several bits of known value are added to the information bits) such that the data unit occupies an integer number of OFDM symbols. Referring to fig. 1, in some embodiments, padding is implemented in the

MAC processing units

18, 28 and/or the

PHY processing units

20, 29. In some such embodiments, the number of padding bits is determined according to a padding equation provided in a short-range communication protocol (e.g., the IEEE802.11a standard, the IEEE802.11 n standard, the IEEE802.11ac standard, etc.). In general, these padding equations involve calculating the number of padding bits based in part on the number of data bits per OFDM symbol (NDBPS) and/or the number of encoded data bits per symbol (NCBPS). According to an embodiment, in the range extension mode, the number of padding bits is determined based on the number of information bits (e.g., 6 bits, 12 bits, 13 bits, etc.) in the OFDM symbol before the information bits are block encoded by the block encoder 1704 and the BCC is encoded by the FEC encoder 1706. Therefore, the number of padding bits in the range extension mode data unit is substantially different from the number of padding bits in the corresponding normal-size data (or in the corresponding short-distance data unit). On the other hand, according to the embodiment, the number of coded bits per symbol is the same as the number of coded bits per symbol in the normal mode data unit (or in the corresponding short distance data unit), e.g., coded bits per OFDM24, 48, 52, etc.

Fig. 17B is a block diagram of an example PHY processing unit 1750 to generate a range expansion mode data unit according to another embodiment. In some embodiments, PHY processing unit 1750 generates the signal and/or data fields of a range expansion mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1750.

PHY processing unit 1750 is similar to PHY processing unit 1700 of fig. 17A, except that FEC encoder 1706 is replaced with LDPC encoder 1756 in PHY processing unit 1750. Thus, in this embodiment, the output of block encoder 1704 is provided for further block encoding by LDPC encoder 1756. In an embodiment, LDPC encoder 1756 utilizes block encoding corresponding to an encoding rate of 1/2 or block encoding corresponding to another suitable encoding rate. In the illustrated embodiment, PHY processing unit 1750 omits interleaver 1710 because adjacent bits in the information stream are typically spread out by the LDPC code itself and thus no further interleaving is needed. Further, in an embodiment, further frequency diversity is provided by LDPC tone remapping unit 1760. According to an embodiment, LDPC tone remapping unit 1760 reorders the encoded information bits or encoded block of information bits according to a tone remapping function. In general, a tone remapping function is defined such that consecutive encoded information bits or blocks of information bits are mapped onto non-consecutive tones in an OFDM symbol to facilitate data recovery at a receiver in situations where consecutive OFDM tones are adversely affected during transmission. In some embodiments, LDPC tone remapping unit 1760 is omitted. Referring again to fig. 7A, in various embodiments, a number of tail bits are typically added to each field of the data unit for proper operation of the FEC encoder 1706, e.g., to ensure that the BCC encoder is returned to a zero state after each field has been encoded. In one embodiment, for example, six tail bits are inserted at the end of the data portion before the data portion is provided to FEC encoder 1706 (e.g., after the bits are processed by block encoder 1704).

In some embodiments, the signal field of the range extension mode data unit has a different format compared to the signal field format of the regular mode data unit. In some such embodiments, the signal field of the range extension mode data unit is shorter than the signal field of the regular mode data unit. For example, according to an embodiment, only one modulation and coding scheme is used in the range extension mode, and thus less information (or no information) about the modulation and coding needs to be conveyed in the range extension mode signal field. Similarly, in an embodiment, the maximum length of the range extension mode data unit is shorter compared to the maximum length of the normal mode data unit, and in this case, fewer bits are required for the length subfield of the range extension mode signal field. By way of example, in one embodiment, the range extension mode signal field is formatted in accordance with the IEEE802.11 n standard, but omits certain subfields (e.g., a Low Density Parity Check (LDPC) subfield, a space-time block coding (STBC) subfield, etc.). Additionally or alternatively, in some embodiments, the range extension mode signal field includes a shorter Cyclic Redundancy Check (CRC) subfield (e.g., less than 8 bits) than a CRC subfield of the regular mode signal field. Generally, according to some embodiments, in the range extension mode, certain signal field subfields are omitted or modified and/or certain new information is added.

Fig. 18A is a block diagram of an example PHY processing unit 1800 for generating a range extension mode data unit using a range extension coding scheme, according to another embodiment. In some embodiments, the PHY processing unit 1800 generates signals and/or data fields of a range expansion mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1800.

The PHY processing unit 1800 is similar to the PHY processing unit 1700 of fig. 17A, except that the block encoder 1808 is positioned after the FEC encoder 1806 in the PHY processing unit 1800. Thus, in this embodiment, the information bits are first scrambled by scrambler 1802, encoded by FEC encoder 1806, and the FEC encoded bits are then replicated or otherwise block encoded by block encoder 1808. As in the example embodiment of the PHY processing unit 1700, in an embodiment, the processing of the FEC encoder 1806 is performed continuously for the entire field to be generated (e.g., the entire data portion, the entire signal field, etc.). Thus, in this embodiment, the information bits corresponding to the field to be generated are first encoded by FEC encoder 1806, and the BCC encoded bits are then divided into blocks of a specified size (e.g., 6 bits, 12 bits, 13 bits, or any other suitable number of bits). Each block is then processed by a block encoder 1808. As an example, in one embodiment, the FEC encoder 1806 encodes 12 information bits per OFDM symbol using an encoding rate of 1/2 to generate 24 BCC encoded bits and provides the BCC encoded bits to the block encoder 1808. In an embodiment, the block encoder 1808 generates two copies of each incoming block and interleaves the generated bits according to a range extension coding scheme to generate 48 bits to be included in an OFDM symbol. In one such embodiment, the 48 bits correspond to 48 data tones generated using a Fast Fourier Transform (FFT) of size 64 at IDFT processing unit 1818. As another example, in another embodiment, the FEC encoder 1806 encodes 6 information bits per OFDM symbol using an encoding rate of 1/2 to generate 12 BCC encoded bits and provides the BCC encoded bits to the block encoder 1808. In an embodiment, the block encoder 1808 generates two copies of each input block and interleaves the generated bits according to a range extension coding scheme to generate 24 bits to be included in an OFDM symbol. In one such embodiment, the 24 bits correspond to 24 data tones generated using an FFT of size 32 at IDFT processing unit 1818.

Similar to the block encoder 1704 of fig. 17A, the range extension encoding scheme used by the block encoder 1808 to generate the signal field of the range extension mode data unit is the same as or different from the range extension encoding scheme used by the block encoder 1808 to generate the data portion of the range extension mode data unit, depending on the embodiment. In various embodiments, the block encoder 1808 implements a "block-level" repetition scheme or a "bit-level" repetition scheme, as discussed above with respect to the block encoder 1704 of fig. 17A. Similarly, in another embodiment, the block encoder 1808 generates m number of copies of the incoming bits and interleaves or otherwise encodes the incoming bits or blocks of incoming bits according to a suitable code, such as a Hamming block code with an encoding rate of 1/2, 1/4, etc. or any other block code with an encoding rate of 1/2, 1/4, etc. (e.g., (1, 2) or (1, 4) block code, (12, 24) block code or (6, 24) block code, (13, 26) block code, etc.). According to an embodiment, the effective coding rate of the data unit generated by the PHY processing unit 1800 is the product of the coding rate used by the FEC encoder 1806 and the number of repetitions (or coding rate) used by the block encoder 1808.

In an embodiment, block encoder 1808 provides sufficient diversity gain such that no further interleaving of the coded bits is required, thus omitting interleaver 1810. One advantage of omitting interleaver 1810 is that in this case, an OFDM symbol having 52 data tones may be generated using a 4x or 6x repetition scheme even though the number of data bits per symbol is not an integer in some such cases. For example, in one such embodiment, the output of FEC encoder 1806 is divided into blocks of 13 bits, and each block is repeated four times (or block encoded at a rate of 1/4) to generate 52 bits to be included in an OFDM symbol. In this case, if FEC encoder 1806 utilizes an encoding rate of 1/2, the number of data bits per symbol is equal to 6.5. In an example embodiment with 6x repetition, FEC encoder 1806 encodes the information bits using an encoding rate of 1/2 and outputs a block divided into four bits. The block encoder 1808 repeats each four-bit block six times (or block encodes each block using an encoding rate of 1/6) and adds four padding bits to generate 52 bits to be included in the OFDM symbol.

As in the example of the PHY processing unit 1700 of fig. 17A discussed above, if padding is used by the PHY processing unit 1800, the Number of Data Bits Per Symbol (NDBPS) used for the padding bit calculation is the actual number of non-redundant data bits in the OFDM symbol (e.g., 6 bits, 12 bits, 13 bits, or any other suitable number of bits as in the above example). The number of bits per symbol (NCBPS) encoded using the pad bit calculation is equal to the number of bits actually contained in the OFDM symbol (e.g., 24 bits, 48 bits, 52 bits, or any other suitable number of bits contained in the OFDM symbol).

Also, as in the example of the PHY processing unit 1700 of fig. 17, several tail bits are typically inserted into each field of the data unit for proper operation of the FEC encoder 1806, e.g., to ensure that the BCC encoder is returned to a zero state after each field has been encoded. In one embodiment, for example, six tail bits are inserted at the end of the data portion before the data portion is provided to FEC encoder 1806 (i.e., after performing the processing of block encoder 1704). Similarly, in the case of a signal field, according to an embodiment, tail bits are inserted at the end of the signal field before it is provided to FEC encoder 1806. In an example embodiment where the block encoder 1808 utilizes a 4x repetition scheme (or another block code having an encoding rate of 1/4), the FEC encoder 1806 uses an encoding rate of 1/2 and the signal field includes 24 information bits (including tail bits), BCC encodes the 24 signal field bits to generate 48 BCC-encoded bits, which are then divided into four blocks of 12 bits each for further encoding by the block encoder 1808. Thus, in this embodiment, the signal field is transmitted over four OFDM symbols, each of which includes 6 information bits of the signal field.

In addition, in some embodiments, the PHY processing unit 1800 generates an OFDM symbol having 52 data tones in accordance with MCS0 specified in the IEEE802.11 n standard or the IEEE802.11ac standard, and the block encoder 1808 utilizes a 4x repetition scheme. In some such embodiments, extra padding is used to ensure that the resulting coded data stream to be included in an OFDM symbol comprises 52 bits. In one such embodiment, padding bits are added to the encoded information bits after the bits have been processed by block encoder 1808.

In the embodiment of fig. 18A, the PHY processing unit 1800 further includes a peak-to-average power ratio (PAPR) reduction unit 1809. In an embodiment, PAPR reduction unit 1809 flips bits in some or all of the repeated blocks to reduce or eliminate occurrences of the same bit sequence at different frequency locations in the OFDM symbol, thereby reducing the peak-to-average power ratio of the output signal. In general, bit flipping involves changing the value of a bit of zero to the value of a bit of one and changing the value of a bit of one to the value of a bit of zero. According to an embodiment, the PAPR reduction unit 1809 implements bit flipping using an XOR operation. For example, in embodiments utilizing 4x repetition of a block of coded bits, if the block of coded bits to be included in an OFDM symbol is denoted as C and if C ' ═ C XOR 1 (i.e., block C with flipped bits), then according to some embodiments, some possible bit sequences at the output of PAPR reduction unit 1809 are [ C C ' C ' ], [ C ' C ], [ C C ' C C ' ], [ C ' ] and so on. In general, any combination of blocks with flipped bits and blocks with non-flipped bits may be used. In some embodiments, PAPR unit 1809 is omitted.

Fig. 18B is a block diagram of an example PHY processing unit 1850 for generating a range expansion mode data unit, according to another embodiment. In some embodiments, the PHY processing unit 1850 generates the signal and/or data fields of the range expansion mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1850.

The PHY processing unit 1850 is similar to the PHY processing unit 1800 of fig. 18, except that the FEC encoder 1806 is replaced by an LDPC encoder 1856 in the PHY processing unit 1850. Thus, in this embodiment, the information bits are first encoded by LDPC encoder 1856, and the LDPC encoded bits are then replicated or otherwise block encoded by block encoder 1808. In an embodiment, LDPC encoder 1856 utilizes block encoding corresponding to an encoding rate of 1/2 or block encoding corresponding to another suitable encoding rate. In the illustrated embodiment, PHY processing unit 1850 omits interleaver 1810, as adjacent bits in the information stream are typically spread out by the LDPC code itself and thus no further interleaving is required according to embodiments. Further, in an embodiment, further frequency diversity is provided by LDPC tone remapping unit 1860. According to an embodiment, LDPC tone remapping unit 1860 reorders the encoded information bits or encoded blocks of information bits according to a tone remapping function. In general, a tone remapping function is defined such that consecutive encoded information bits or blocks of information bits are mapped onto non-consecutive tones in an OFDM symbol to facilitate data recovery at a receiver in situations where consecutive OFDM tones are adversely affected during transmission. In some embodiments, LDPC tone remapping unit 1860 is omitted.

Fig. 19A is a block diagram of an example PHY processing unit 1900 for generating a range expansion mode data unit according to another embodiment. In some embodiments, the PHY processing unit 1900 generates the signal and/or data fields of the range expansion mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1900.

The PHY processing unit 1900 is similar to the PHY processing unit 1800 of fig. 18A, except that the block encoder 1916 is positioned after the constellation mapper 1914 in the PHY processing unit 1900. Thus, in this embodiment, the BCC encoded information bits are mapped to constellation symbols after having been processed by the interleaver 1910 and the constellation symbols are then copied or otherwise block encoded by the block encoder 1916. According to an embodiment, the processing by FEC encoder 1906 is performed continuously over the entire field to be generated (e.g., the entire data field, the entire signal field, etc.). In this embodiment, the information bits corresponding to the generated field are first encoded by FEC encoder 1806 and the BCC encoded bits are then mapped to constellation symbols by constellation mapper 1914. The constellation symbols are then divided into blocks of a specified size (e.g., 6 symbols, 12 symbols, 13 symbols, or any other suitable number of symbols) and each block is then processed by a block encoder 1916. As an example, in embodiments utilizing 2x repetition, the constellation mapper 1914 generates 24 constellation symbols and the block encoder 1916 generates two copies of the 24 symbols to generate 48 symbols corresponding to 48 data tones of an OFDM symbol (e.g., as specified in the IEEE802.11a standard). As another example, in an embodiment with 4x repetition, the constellation mapper 1914 generates 12 constellation symbols and the block encoder 1916 generates four copies of the 12 constellation symbols to generate 48 symbols corresponding to the 48 data tones of the OFDM symbol (e.g., as specified in the IEEE802.11a standard). As yet another example, in an embodiment utilizing 2x repetition, the constellation mapper 1914 generates 26 constellation symbols and the block encoder 1916 repeats the 26 symbols (i.e., generates two copies of the 26 symbols) to generate 52 symbols corresponding to 52 data tones of an OFDM symbol (e.g., as specified in the IEEE802.11 n standard or the IEEE802.11ac standard). In general, in various embodiments and/or scenarios, the block encoder 1916 generates any suitable number of copies of a block of incoming constellation symbols and interleaves the generated symbols according to any suitable encoding scheme. Similar to the block encoder 1704 of fig. 17A and the block encoder 1808 of fig. 18A, the range extension encoding scheme used by the block encoder 1916 to generate the signal field(s) of the range extension mode data unit is the same as or different from the range extension encoding scheme used by the block encoder 1916 to generate the data portion of the range extension mode data unit, depending on the embodiment. According to an embodiment, the effective coding rate of the data unit generated by the PHY processing unit 1900 is the product of the coding rate used by the FEC encoder 1906 and the number of repetitions (or coding rate) used by the block encoder 1916.

According to an embodiment, because in this case redundancy is introduced after the information bits have been mapped to the constellation symbols, each OFDM symbol generated by the PHY processing unit 1900 includes fewer non-redundant data tones as compared to the OFDM data tones included in the regular mode data unit. Interleaver 1910 is thus designed to operate on fewer tones per OFDM symbol than an interleaver used in a conventional mode (such as interleaver 1610 of fig. 16) or an interleaver used in generating corresponding short-range data units. For example, in an embodiment with 12 non-redundant data tones per OFDM symbol, interleaver 1910 is designed with a column count of 6 (Ncol) and a row count of 2x bits per subcarrier (Nbpscs) (Nrow). In another example embodiment with 12 non-redundant data tones per OFDM symbol, interleaver 1910 is designed using a column number of 4 and Nrow of 3 x Nbpscs. In other embodiments, other interleaver parameters than those used in the normal mode are used for interleaver 1910. Alternatively, in an embodiment, block encoder 1916 provides sufficient diversity gain such that no further interleaving of the encoded bits is required, thus omitting interleaver 1910. In this case, as in the example embodiment utilizing the PHY processing unit 1800 of fig. 18A, an OFDM symbol having 52 data tones may be generated using a 4x or 6x repetition scheme, even though the number of data bits per symbol is not an integer in some such cases.

As in the example embodiments of the PHY processing unit of fig. 17A or the PHY processing unit 1800 of fig. 18A discussed above, if padding is used by the PHY processing unit 1900, the number used for padding bit calculation (NDBPS) is the actual number of non-redundant data bits in the OFDM symbol (e.g., 6 bits, 12 bits, 13 bits, or any other suitable number of bits as in the above examples). The Number of Coded Bits Per Symbol (NCBPS) used in the pad bit calculation is equal to the number of non-redundant bits contained in the OFDM symbol, which in this case corresponds to the number of bits (e.g., 12 bits, 24 bits, 26 bits, etc.) in the block of constellation symbols processed by the block encoder 1916.

In some embodiments, the PHY processing unit 1900 generates an OFDM symbol having 52 data tones according to MCS0 specified in the IEEE802.11 n standard or the IEEE802.11ac standard, and the block encoder 1916 utilizes a 4x repetition scheme. In some such embodiments, extra padding is used to ensure that the resulting coded data stream to be included in an OFDM symbol comprises 52 bits. In one such embodiment, padding bits are added to the encoded information bits after the bits have been processed by block encoder 1808.

In the embodiment of fig. 19, the PHY processing unit 1900 includes a peak-to-average power ratio (PAPR) reduction unit 1917. In an embodiment, peak to average power ratio unit 1917 will add phase offsets to some of the data tones modulated with the repeating constellation. For example, in one embodiment, the added phase offset is 180 degrees. The 180 degree phase shift corresponds to a sign inversion of the bits, which modulates the data tones implementing the phase shift. In another embodiment, the PAPR reduction unit 1917 adds a phase offset that is different from 180 degrees (e.g., a 90 degree phase offset or any other suitable phase offset). As an example, in an embodiment with 4x repetition, if a block of 12 constellation symbols to be included in an OFDM symbol is denoted C and if a single block repetition is performed, the resulting sequence is [ cc C ]. In some embodiments, PAPR reduction unit 1917 introduces a sign inversion (i.e., -C) or 90 degree phase shift (i.e., j × C) for some of the repeated blocks. In some such embodiments, the resulting sequence is, for example, [ C-C ], [ -C ], [ C-C C-C ], [ C-C ], [ Cj C, j C ] or any other combination of C, -C, j C and-j C. In general, in various embodiments and/or scenarios, any suitable phase offset may be introduced in any repeated block. In some embodiments, PAPR reduction unit 1809 is omitted.

In some embodiments, the PHY processing unit 1900 generates an OFDM symbol having 52 data tones according to MCS0 specified in the IEEE802.11 n standard or the IEEE802.11ac standard, and the block coding 1916 utilizes a 4x repetition scheme. In some such embodiments, additional pilot tones are inserted to ensure that the number of data tones and pilot tones in the resulting OFDM symbol is equal to 56, as specified in the short-range communication protocol. As an example, in an embodiment, six information bits are BCC encoded at an encoding rate of 1/2, and the resulting 12 bits are mapped to 12 constellation symbols (BPSK). The 12 constellation symbols modulate the 12 data tones, which are then repeated four times, generating 48 data tones. As specified in the IEEE802.11 n standard, four pilot tones are added, and 4 additional pilot tones are added to generate 56 data and pilot tones.

Fig. 19B is a block diagram of an example PHY processing unit 1950 for generating a range expansion mode data unit, according to another embodiment. In some embodiments, the PHY processing unit 1950 generates signal and/or data fields of a range expansion mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 1950.

The PHY processing unit 1950 is similar to the PHY processing unit 1900 of fig. 19, except that the FEC encoder 1906 is replaced by an LDPC encoder 1956 in the PHY processing unit 1950. Thus, in this embodiment, LDPC encoded information bits are mapped to constellation symbols by constellation mapper 1914 and the constellation symbols are then replicated or otherwise block encoded by block encoder 1916. In an embodiment, LDPC encoder 1956 utilizes block encoding corresponding to an encoding rate of 1/2 or corresponding to another suitable encoding rate. In the illustrated embodiment, the PHY processing unit 1950 omits the interleaver 1910, as adjacent bits in the information stream are typically scattered by the LDPC code itself and thus, according to embodiments, no further interleaving is needed. Furthermore, in an embodiment, further frequency diversity is provided by LDPC tone remapping unit 1960. According to an embodiment, the LDPC tone remapping unit 1960 reorders the encoded information bits or encoded blocks of information bits according to a tone remapping function. In general, a tone remapping function is defined such that consecutive encoded information bits or blocks of information bits are mapped onto non-consecutive tones in an OFDM symbol to facilitate data recovery at a receiver in situations where consecutive OFDM tones are adversely affected during transmission. In some embodiments, LDPC tone remapping unit 1960 is omitted.

In the embodiments described above with respect to fig. 17-19, the range expansion pattern introduces redundancy by repeating bits and/or constellation symbols in the frequency domain. Alternatively, in some embodiments, the range extension coding scheme comprises OFDM symbol repetition of the signal and/or data fields of the range extension mode data unit performed in the time domain. For example, fig. 20A is a 2x repetition of each OFDM symbol showing HT-SIG1 and HT-SIG2 fields in a preamble of a range extension mode data unit, according to an embodiment. Similarly, fig. 20B is a 2x repetition of each OFDM symbol showing the L-SIG field in the preamble of the range extension mode data unit, according to an embodiment. Fig. 20C is a diagram illustrating a time-domain repetition scheme for OFDM symbols in the data portion of the control pattern data unit, according to one embodiment. Fig. 20D is a diagram of a repetition scheme for OFDM symbols in a data portion, according to another embodiment. As shown, in the embodiment of fig. 20C, OFDM symbol repetition is continuously output, whereas in the embodiment of fig. 20D, OFDM symbol repetition is interleaved. In general, in various embodiments and/or scenarios, the interleaved OFDM symbol repetition is according to any suitable interleaving scheme.

Fig. 21 is a flowchart of an example method 2100 for generating a data unit, according to an embodiment. Referring to fig. 1, in an embodiment, the method 2100 is implemented by the network interface 16. For example, in one such embodiment, the PHY processing unit 20 is configured to implement the method 2100. According to another embodiment, the MAC processing 18 is also configured to implement at least a portion of the method 2100. With continued reference to fig. 1, in yet another embodiment, the method 2100 is implemented by the network interface 27 (e.g., the PHY processing unit 29 and/or the MAC processing unit 28). In other embodiments, method 2100 is implemented by other suitable network interfaces.

At block 2102, information bits to be included in the data unit are encoded according to a block code. For example, in one embodiment, the information bits are encoded using the block-level or bit-level repetition scheme described above with respect to block encoder 1704 of FIG. 17. At block 2104, the information bits are encoded using an FEC encoder, such as, for example, FEC encoder 1706 of fig. 17A or LDPC encoder 1756 of fig. 17B. At block 2106, information bits are mapped to constellation symbols. At block 2108, a plurality of OFDM symbols including constellation points is generated. At block 2110, a data unit including OFDM symbols is generated.

In one embodiment, as illustrated in fig. 21, the information bits are first encoded using a block encoder (block 2102) and the block encoded bits are then encoded using an FEC encoder (block 2104), such as described above, for example, with respect to fig. 17A. In another embodiment, the order of

blocks

2102 and 2104 is swapped. Thus, in this embodiment, the information bits are FEC encoded first, and the FEC encoded bits are encoded according to a block coding scheme, such as described above, for example, with respect to fig. 18A. In yet another embodiment, block 2102 is positioned after block 2106. In this embodiment, the information bits are FEC encoded at block 2104, the FEC encoded bits are mapped to constellation symbols at block 2106, and the constellation symbols are then encoded according to a block encoding or repetition scheme at block 2102, such as described above, for example, with respect to fig. 19A.

In various embodiments, the range extension coding scheme uses a reduced size Fast Fourier Transform (FFT) technique that outputs a reduced number of constellation symbols repeated over the total bandwidth to improve range and/or SNR performance. For example, in an embodiment, the constellation mapper maps a bit sequence to a plurality of constellation symbols corresponding to 32 subcarriers (e.g., 32-FFT mode) having 24 data tones. The 32 sub-carriers correspond to 10MHz sub-bands of the total 20MHz bandwidth. In this example, the constellation symbols are repeated across a total bandwidth of 20MHz to provide redundancy of the constellation symbols. In various embodiments, the reduced size FFT technique is used in combination with the bitwise replication and/or symbol replication techniques described above with respect to fig. 17-19.

In some embodiments where additional bandwidth is available (such as 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, etc.), 32 subcarriers are repeated across each 10MHz subband of the total bandwidth. For example, in another embodiment, the 32-FFT mode corresponds to a 5MHz sub-band of the total 20MHz bandwidth. In this embodiment, the plurality of constellations is repeated 4x across the total 20MHz bandwidth (i.e., in each 5MHz sub-band). Accordingly, the receiving device combines multiple constellations to improve the decoding reliability of the constellations. In some embodiments, the modulation of different 5MHz or 10MHz sub-band signals is rotated by different angles. For example, in one embodiment, the first sub-band is rotated by 0 degrees, the second sub-band is rotated by 90 degrees, the third sub-band is rotated by 180 degrees, and the fourth sub-band is rotated by 270 degrees. In other embodiments, different suitable rotations are utilized. In at least some embodiments, different phases of the 20MHz sub-band signals result in a reduced peak-to-average power ratio (PAPR) of the OFDM symbols in the data unit.

Fig. 22A is a diagram of a2 × repeating 20MHz total bandwidth of a range extension data unit having a 10MHz sub-band, according to an embodiment. As shown in fig. 22A, each sub-band of 10MHz is rotated by r1 and r2, respectively. Fig. 22B is a diagram of a 4 × repeated 40MHz total bandwidth of a range extension data unit having a 10MHz sub-band, according to an embodiment. As shown in fig. 22B, each sub-bandwidth of 10MHz is rotated by r1, r2, r3, and r4, respectively. Fig. 22C is a diagram of an example tone plan 2230 for a 32-FFT mode corresponding to a 10MHz sub-band, under an embodiment. The tone plan 2230 includes 32 total tones with 24 data tones, 2 pilot tones at indices +7 and-7, 1 direct current tone, and 5 guard tones, as shown in fig. 22. In embodiments where a reduced size FFT technique is used, the corresponding tone plan is used for the HEW-LTF field (when present). In other embodiments where a reduced size FFT technique is used but the HEW-LTF field is not present, the L-LTF field 704 is modified to include a respective index for additional ± 1 symbols of pilot tones to the modified tone plan. For example, in an embodiment, tones-29, -27, +27, and +29 are added to the tone plan for the L-LTF field. In another embodiment, 1 symbol is removed from the L-LTF tone plan in tones-2, -1, and 2 in the 20MHz bandwidth. Similar variations apply to the total bandwidth of 40MHz, 80MHz, 160MHz, etc.

Fig. 23 is a diagram of an example data unit 2300 in which a range expansion mode is used for a preamble 2301 of the data unit, according to an embodiment. In some embodiments, the preamble 2301 indicates both a normal mode and a range extension mode. In such embodiments, another method of distinguishing the normal mode from the range expansion mode is used, such as those described above with respect to fig. 9, 10 and 11.

Data unit 2301 is substantially similar to and includes like-numbered elements as data unit 1150 of fig. 11B, except that preamble 2301 of data unit 2300 is formatted differently than preamble 1151 of data unit 1101. In an embodiment, the preamble 2301 is formatted such that a receiving device operating in accordance with the HEW communication protocol is able to determine that the preamble 2301 is a range extension mode preamble rather than a normal mode preamble. In an embodiment, the preamble 2301 includes a modified long training field M-LTF 2304 and a modified signal field M-SIG2306 in place of the L-LTF704 and L-SIG706, respectively, as compared to the data unit 1151. In an embodiment, preamble 2301 includes L-STF 702, a double guard interval followed by two repetitions of a modified long training sequence as M-LTF 2304, a normal guard interval, and a modified signal field M-SIG. In some embodiments, the preamble 2301 also includes one or more first HEW signal fields (HEW-SIGA) 1152. In an embodiment, the preamble 2301 also includes one or more secondary M-SIG1154 fields following the L-SIG field 2306. In some embodiments, the secondary L-SIG(s) are followed by a second L-LTF field (L-LTF2) 1156. In other embodiments, the preamble 2301 omits the L-SIG(s) 1154 and/or the L-LTF 21156. In some embodiments, the preamble 2301 also includes a HEW-STF 1158, one or more HEW-LTF fields 1160, and a second HEW signal field (HEW-SIGB) 1162. In other embodiments, the preamble 2301 omits the HEW-STF 1158, the HEW-LTF(s) 1160, and/or the HEW-SIGB 1162. In an embodiment, data unit 2300 also includes data portion 716 (not shown in FIG. 23). In some embodiments, HEW signal field (HEW-SIGA)1152 is modulated using the same range extension coding scheme as data field 716.

In various embodiments, M-LTF 2304 corresponds to L-LTF704 multiplied by a predetermined sequence (e.g., a polar code). For example, using the index i, the ith constellation symbol of L-LTF704 is multiplied by the ith value of the predetermined sequence (e.g., + -1) to obtain M-LTF 2304, as shown in equation 1:

M-LTF_i＝C_i*L-LTF_i(equation 1)

Wherein C is a predetermined sequence. In some embodiments, the M-SIG2306 corresponds to the L-SIG706 multiplied by a predetermined sequence, as shown in equation 2:

M-SIG_i＝C_i*L-SIG_i(equation 2)

In some embodiments, the length of the predetermined sequence (i.e., the number of values) is equal to the sum of the number of data tones and the number of pilot tones per 20MHz band in the ieee802.11ac protocol, e.g., 52 values (i.e., for 48 data tones and 4 pilot tones).

In an embodiment, the predetermined sequence and the modified long training sequence each have a length greater than or equal to a sum of a number of data tones and a number of pilot tones. As described above with respect to the tone plan 2230 for the 32-FFT mode corresponding to the 10MHz sub-band, if the HEW-STF and/or HEW-LTF fields are not present in the range extension preamble, the receiver relies on the L-LTF field for subsequent field demodulation. In an embodiment, the tone plan mismatch between the 20MHz-LTF and 10MHz 32-FFT modes is corrected by inserting +1 or-1 symbols into the L-LTF for the missing tones (e.g., tones-29, -27, +27, and +29 for a total of 58 tones).

Fig. 24 is a block diagram of an example PHY processing unit 2400 for generating a range expansion mode data unit, according to another embodiment. In some embodiments, the PHY processing unit 2400 generates a signal and/or training field of a range extension mode data unit. Referring to fig. 1, in one embodiment, the AP 14 and the client station 25-1 each include a PHY processing unit, such as PHY processing unit 2400.

The PHY processing unit 2400 is similar to the PHY processing unit 1700 of fig. 17A, except that the tone multiplier 2404 is positioned after the constellation mapper 1614 in the PHY processing unit 2400. In some embodiments, tone multiplier 2404 generates i) a modified constellation symbol for the L-SIG field (i.e., M-SIG 2306) of the range expansion mode data unit and ii) a modified long training sequence for the L-LTF field (i.e., M-LTF 2304) of the range expansion mode data unit.

In some embodiments, the PHY processing unit 2400 is configured to generate the first long training sequence for the range expansion mode preamble at least by multiplying the predetermined sequence with a second long training sequence of the second communication protocol. In an embodiment, for example, pitch multiplier 2404 multiplies L-LTF704 by a predetermined sequence to obtain M-LTF 2304. In an embodiment, tone multiplier 2404 provides M-LTF 2304 to IDFT 1618 in place of L-LTF704 during the range expansion mode.

In an embodiment, the tone multiplier 2404 receives constellation symbols for data to be included in the L-SIG706 from the constellation mapper 1614 and constellation symbols for pilot tones from the pilot tone generator 2408. Thus, in an embodiment, the M-SIG2306 output from the tone multiplier 2404 includes modified constellation symbols for data tones and pilot tones to be converted to a time domain signal by the IDFT 1618.

In some embodiments, the receiver device decodes the M-SIG2306, e.g., using M-LTF 2304-based channel estimation. In this example, because the L-LTF704 and L-SIG706 have been multiplied by a predetermined sequence, the legacy receiver device effectively removes the multiplication as part of the channel estimation process or autocorrelation process. In an embodiment, the receiving device determines whether the preamble corresponds to the range extension mode preamble 2400 or the normal mode preamble 1101 by detecting whether the LTF field (e.g., either the M-LTF 2304 or the L-LTF704) in the preamble is generated with (e.g., multiplied by) the predetermined sequence or without the predetermined sequence based on the L-LTF field multiplied and not multiplied by the predetermined sequence for autocorrelation. In an embodiment, the receiving device performs a first autocorrelation of the LTF with L-LTF704, performs a second autocorrelation of the LTF with M-LTF 2304 and performs a comparison of the autocorrelation results. In an embodiment, if the autocorrelation with respect to M-LTF 2304 produces a larger result than the result of the autocorrelation with respect to L-LTF704, the receiving device determines that the preamble corresponds to range expansion mode preamble 2300. On the other hand, in an embodiment, if the autocorrelation of the LTF with the L-LTF704 produces a larger result than that of the autocorrelation with the M-LTF 2304, the receiving device determines that the preamble corresponds to the normal-mode preamble 1101. In some embodiments, the receiver device performs autocorrelation in the frequency domain according to equation 3:

wherein, y_iIs the last received and averaged L-LTF sequence, L_iIs the transmitted L-LTF sequence or modified long training sequence M-LTF belonging to IEEE802.11 a/n/ac. For example, L_iOr C for the range extension mode_i*L-LTF_iOr L-LTF for the conventional mode_i. In some scenarios, the cross-correlation of consecutive tones substantially removes channel effects, and frequency-domain matched filtering finds the most likely transmitted sequence. In some embodiments, the receiver device decodes additional fields (i.e., the HEW-SIG and/or data fields) of the data unit using the channel estimates from the M-LTFs. In some scenarios, the values of the predetermined sequence corresponding to the pilot tones are all ones, which allows phase tracking on the pilot tones.

In some embodiments, OFDM modulation with reduced tone spacing is used with the same size FFT to reduce the data rate in the range expansion mode. For example, a conventional pattern for a 20MHz bandwidth OFDM data unit uses a 64-point Fast Fourier Transform (FFT), producing 64 OFDM tones; the range extension mode uses a tone spacing reduced by this 2 to produce 128 OFDM tones within the same bandwidth. In this case, the tone spacing in the range extension mode OFDM symbol is reduced by a factor of 2 (1/2) compared to the frequency-scale OFDM symbol using the same 64-point FFT, 2x increased symbol duration, and 2x increased guard interval, wherein the symbols are then repeated in the remaining bandwidth. As another example, a conventional pattern for a 20MHz bandwidth OFDM data unit uses a 64-point Fast Fourier Transform (FFT), resulting in 64 OFDM tones; the range extension mode uses 1/4 reduced tone spacing for a 20MHz OFDM data unit, producing 256 MHz OFDM tones within the same bandwidth. In this case, the tone spacing in the range expansion mode OFDM symbol is reduced by a factor of 4 (1/4) compared to the normal OFDM symbol when using 4x increased symbol duration and 4x increased guard interval. In such an embodiment, a long GI duration of, for example, 1.6 μ s is used. However, in an embodiment, the duration of the information portion of the range extension mode OFDM symbol is increased (e.g., from 3.2 μ s to 6.4 μ s), and the GI portion duration remains the same as a percentage of the total OFDM symbol duration. Thus, in this case, in at least some embodiments, efficiency losses due to longer GI symbols are avoided. In various embodiments, the term "long guard interval" as used herein encompasses both an increased duration of the guard interval as well as an OFDM tone spacing that is effectively reduced by increasing the duration of the guard interval. In other embodiments, the tone spacing is decreased, the guard interval is increased and the symbol duration is increased by a factor of 6, 8 or other suitable value. In some embodiments, changes in tone spacing, guard interval, and symbol duration are used in combination with block-coded repetition symbol repetition, as described above.

In some embodiments, the total signal bandwidth of the data units for the range expansion mode is 20 MHz. For example, increased signal bandwidth is unlikely to further increase range or improve SNR performance. In some embodiments, the range expansion mode is configured to use an FFT size of up to 512 points. In such an embodiment, if the tone spacing is reduced by a factor of 4 for the range expansion mode, then the total bandwidth for the 512FFT is 40MHz, so the range expansion mode uses up to 40MHz signal bandwidth.

In other embodiments, the range expansion mode is configured for up to the maximum available signal bandwidth (e.g., 160 MHz). In various embodiments, for example, the 1/2 tone spacing corresponds to 64FFT for the 10MHz band, 128FFT for the 20MHz band, 256FFT for the 40MHz band, 512FFT for the 80MHz band, and 1024FFT for the 160MHz band. In some embodiments, the reduced tone spacing is used in combination with a smaller FFT size. In various embodiments, a shorter guard interval is used with a reduced tone spacing, e.g., a normal guard interval having a duration equal to 25% of the duration of an OFDM symbol and a short guard interval having a duration equal to 1/9 of the OFDM symbol.

In some embodiments, the range expansion mode uses smaller pitch spacing (i.e., 1/2, 1/4, etc.). In such an embodiment, the same FFT size represents a smaller bandwidth, e.g., the 1/2 tone spacing corresponds to 64FFT on the 10MHz band. In an embodiment, the tone plan of the same FFT size is the same for the range extension mode and the regular mode, e.g., the 64FFT in the range extension mode uses the same tone plan as in the 20MHz 64FFT in IEEE802.11 ac. Fig. 25A is a diagram of an example 20MHz total bandwidth with an 1/2 tone spacing, according to an embodiment. In this case, the index of the original DC tone for each 64FFT legacy tone plan is now in the middle of 10MHz rather than the middle of the total 20MHz bandwidth, and the index for the original guard tone is close to the true DC tone. In some embodiments where the frequency band for the range extension mode data unit is less than 20MHz, the non-legacy tone plan includes additional data or pilot tones at the index for the original DC tone, since the index will not overlap with the "true DC tone", since the minimum signal bandwidth is 20MHz for the range extension mode or the regular mode. In some embodiments, the non-legacy tone plan includes additional data tones in place of guard tones at edges of the legacy tone plan to maintain the same number of filler tones.

In other embodiments, as the tone spacing is reduced, the impact from the dc offset and Carrier Frequency Offset (CFO) becomes greater compared to the conventional mode. Fig. 25B is a diagram of an example 20MHz total bandwidth with an 1/2 tone spacing, according to an embodiment. In some embodiments, additional zero tones are defined for the dc tones near the frequency band of the non-legacy tone plan for the range extension mode as compared to the legacy tone plan of the same FFT size in the conventional mode. In various embodiments, the additional zero tones are defined only to exceed a predetermined FFT size and/or tone spacing, e.g., when the FFT size is greater than or equal to 128 with tone spacing reduction 1/2 or when the FFT size is greater than or equal to 256 with tone spacing reduction 1/4. In some embodiments, an increased number of guard tones is used for non-legacy tone planning for the range extension mode, e.g., to maintain an absolute guard space (e.g., absolute frequency space) at the same band edge as compared to the legacy tone planning for the normal mode. In this case, the total number of data tones and pilot tones in the non-legacy tone plan is less than the legacy tone plan. In some examples, the same absolute guard space facilitates filter design. In some embodiments, for example, where the total number of data tones planned for the non-legacy tones is not used for the same FFT size as for the regular mode, the PHY parameters for the FEC interleaver and/or LDPC tone mapper are redefined for the number of data tones planned for the non-legacy tones.

Fig. 26A is a diagram of a non-legacy tone plan 2600 for a range expansion mode with FFT sizes of 64 and 1/2 tone spacings, according to an embodiment. In the non-legacy tone plan 2600, additional guard tones (i.e., guard tones-28, -27, +28) are included as compared to the legacy tone plan for the normal mode. In some embodiments, the 64FFT fills the DC tones with either pilot tones or data tones. Fig. 26B is a diagram of a non-legacy tone plan 2601 for a range expansion mode with FFT sizes of 128 and 1/2 tone spacings, according to an embodiment. In the non-legacy tone plan 2601, additional guard tones (i.e., guard tones-58, -57, +58) and additional DC tones (i.e., DC tones-2, -1, 0, 1, 2) are included as compared to the legacy tone plan for the conventional mode. Fig. 26C is a diagram illustrating a non-legacy tone plan 2602 for a range expansion mode with FFT sizes of 256 and 1/2 tone spacings, according to an embodiment. In non-legacy tone plan 2602, additional guard tones (i.e., guard tones-122, -121, +122) and additional DC tones (i.e., DC tones-2, -1, 0, 1, 2) are included as compared to legacy tone plans for conventional modes. In other embodiments, additional guard tones and/or DC tones are added to the non-legacy tone plan for the range extension mode as compared to the conventional mode.

Fig. 27 is a flowchart of an example method 2700 for generating a data unit, according to an embodiment. Referring to fig. 1, in an embodiment, method 2700 is implemented by network interface 16. For example, in one such embodiment, the PHY processing unit 20 is configured to implement the method 2700. According to another embodiment, the MAC process 18 is also configured to implement at least a portion of the method 2700. With continued reference to fig. 1, in yet another embodiment, the method 2700 is implemented by the network interface 27 (e.g., the PHY processing unit 29 and/or the MAC processing unit 28). In other embodiments, method 2700 is implemented by other suitable network interfaces.

At block 2702, a first OFDM symbol for a data field is generated. In various embodiments, generating the OFDM symbol at block 2702 includes generating the OFDM symbol for the data portion according to one of a range extension coding scheme corresponding to the range extension mode or a regular coding scheme corresponding to the regular mode. In an embodiment, the range expansion coding scheme comprises the range expansion coding scheme described above with respect to fig. 10 (e.g., reduced pitch spacing). In another embodiment, the range extension coding scheme includes the range extension coding scheme described above with respect to fig. 17-20 (e.g., bitwise repetition or symbol repetition). In yet another embodiment, the range extension coding scheme includes the range extension coding scheme described above with respect to fig. 22 (e.g., data unit repetition). In yet another embodiment, the range extension coding scheme includes a suitable combination of the range extension coding schemes described above with respect to fig. 10, fig. 17-20, and fig. 22.

In an embodiment, generating OFDM symbols for the data portion of the PHY data unit according to the range extension coding scheme comprises: encoding the plurality of information bits using a Forward Error Correction (FEC) encoder (e.g.,

FEC encoder

1706, 1806, or 1906) to obtain a plurality of encoded bits; mapping the plurality of coded bits to a plurality of constellation symbols using, for example,

constellation mappers

1614 or 1914; an OFDM symbol containing a plurality of constellation symbols is generated using, for example,

IDFT

1618 or 1818. In an embodiment, generating the OFDM symbol further comprises performing one of: i) encode a plurality of information bits according to a block coding scheme (e.g., using block encoder 1704), ii) encode a plurality of encoded bits according to a block coding scheme (e.g., using block encoder 1808), or iii) encode a plurality of constellation symbols according to a block coding scheme (e.g., using block encoder 1916). In another embodiment, OFDM symbols for a data field are generated to include a plurality of constellation symbols in a first bandwidth portion of a channel bandwidth and a copy of the plurality of constellation symbols in a second bandwidth portion of the channel bandwidth, e.g., as described above with respect to fig. 22. In another embodiment, a plurality of copies of the constellation symbol are generated to include a predetermined phase offset.

At block 2704, a preamble of a data unit is generated. The preamble generated at block 2704 is generated to indicate whether at least a data portion of the data unit generated at block 2702 was generated using a range extension coding scheme or a regular coding scheme. In various embodiments and/or scenarios, at block 1604 one of the following is generated: the preamble 701 (fig. 9A, 10A), 751 (fig. 9B, 10B), 1101 (fig. 11A), 1151 (fig. 11B), or 1401 (fig. 14A). In other embodiments, other suitable preambles are generated at block 2704.

In an embodiment, the preamble is generated to have i) a first portion indicating a duration of the PHY data unit and ii) a second portion indicating whether to generate at least some OFDM symbols of the data portion according to a range extension coding scheme. In another embodiment, the first portion of the preamble is formatted such that the first portion of the preamble is decodable by a receiver device that conforms to the second communication protocol (e.g., a legacy communication protocol) but does not conform to the first communication protocol (e.g., a HEW communication protocol) to determine the duration of the PHY data unit based on the first portion of the preamble.

In an embodiment, the preamble generated at block 2704 includes a set of CI indications that indicate whether at least the data portion was generated using a range extension coding scheme or a normal coding scheme. In an embodiment, the CI indication includes one bit. In an embodiment, a portion of the preamble is generated using a coding scheme indicated by the CI indication in addition to the data portion. In another embodiment, the preamble generated at block 2704 is formatted such that the receiving device can automatically detect (e.g., without decoding) whether the preamble corresponds to a normal mode preamble or a range extension mode preamble. In an embodiment, the detection of the range extension mode preamble signals to the receiving device that at least the data portion was generated using a range extension coding scheme.

In an embodiment, generating the preamble includes generating a second portion of the preamble including a second OFDM symbol for i) the short training field according to the first communication protocol and ii) at least one copy of the short training field, and generating a third OFDM symbol for i) the long training field according to the first communication protocol and ii) at least one copy of the long training field. In another embodiment, the OFDM symbol for the data portion, the second OFDM symbol, and the third OFDM symbol have the same tone plan, which is different from the tone plan for the first portion of the preamble.

In another embodiment, block 2704 includes generating a first signal field for the PHY data unit according to a second communication protocol (e.g., a legacy communication protocol) and generating a second signal field as a copy of the first signal field to indicate that at least some OFDM symbols of the data field are generated according to a range extension mode. In another embodiment, the first signal field and the second signal field indicate that the duration of the PHY data unit is a predetermined duration and the second signal field is usable as a supplemental training field by a receiver device that conforms to the first communication protocol. In another embodiment, the first signal field and the second signal field are combinatorially decodable by a receiver device that conforms to the first communication protocol to increase a reliability of decoding of the first signal field and the second signal field.

In an embodiment, the first portion of the preamble includes i) a legacy short training field that conforms to the second communication protocol, ii) a non-legacy long training field, and iii) a legacy signal field that conforms to the second communication protocol, and the second portion of the preamble does not include any training fields. In this embodiment, a first plurality of constellation symbols is generated for a legacy short training field using legacy tone planning conforming to a second communication protocol, and a second plurality of constellation symbols is generated for a non-legacy long training field using non-legacy tone planning; and the OFDM symbols for the data field include a third plurality of constellation symbols generated using the non-legacy tone plan.

In an embodiment, the OFDM symbol is generated as a legacy preamble conforming to the second communication protocol using a first part of the preamble for which the normal guard interval is used, and the OFDM symbol is generated for a second part of the preamble using the long guard interval. In another embodiment, OFDM symbols for the non-legacy signal field and the non-legacy short training field of the second portion of the preamble are generated using a normal guard interval, and OFDM symbols for the second portion of the preamble are generated for the non-legacy long training field using a long guard interval. In another embodiment, the OFDM symbols are generated for legacy signal fields of a first portion of the preamble using a normal guard interval, and the OFDM symbols are generated for non-legacy signal fields of a second portion of the preamble using a long guard interval. In an embodiment, the second portion of the preamble is decodable by a receiver device compliant with the first communication protocol, and the long guard interval of the second preamble signals to the receiver device compliant with the first communication protocol that the PHY data unit is compliant with the range extension mode. In yet another embodiment, OFDM symbols are generated for a second portion of the preamble using a long guard interval for i) the non-legacy signal field and ii) a copy of the first OFDM symbol for the non-legacy signal field. In an embodiment, an OFDM symbol is generated for each of a plurality of fields of a second portion of a preamble comprising: i) a double guard interval, ii) a first OFDM symbol for a field, and iii) a second OFDM symbol for a field that is a duplicate of the first OFDM symbol.

At block 2706, a data unit is generated that contains the preamble generated at block 2704 and the data portion generated at block 2702. In an embodiment, the PHY data unit is generated according to the second communication protocol to include a double guard interval followed by a first portion of a signal field and a second portion of the signal field, with no guard interval between the first signal field and the second signal field.

In some embodiments, at least the first portion of the preamble is transmitted at a transmission power boost compared to the data field to increase a decoding range of the first portion of the preamble.

In another embodiment, OFDM symbols for the data field are generated using the first tone spacing and the long guard interval, and OFDM for the first portion of the preamble is generated using: i) a second tone spacing, which is different from the first tone spacing, and ii) a conventional guard interval. In another embodiment, the second tone spacing of the first portion of the preamble is an integer multiple of i) a legacy tone spacing conforming to the second communication protocol, and ii) the first tone spacing of the data field, and the regular guard interval is a legacy guard interval conforming to the second communication protocol. In another embodiment, OFDM symbols for a second portion of the preamble are generated, including i) at least a first OFDM symbol using a legacy tone spacing and a legacy guard interval and ii) at least a second OFDM symbol using the first tone spacing and a long guard interval. In yet another embodiment, OFDM symbols for the data field are generated using the first tone spacing to include a plurality of constellation symbols in a first bandwidth portion of the channel bandwidth and a copy of the plurality of constellation symbols in a second bandwidth portion of the channel bandwidth, and the first bandwidth portion and the second bandwidth portion have the same bandwidth. In another embodiment, generating the OFDM symbol for the data field includes generating a plurality of copies of the constellation symbol to contain the predetermined phase offset.

In an embodiment, generating the OFDM symbol for the data field includes generating the OFDM symbol for the data field using the first tone spacing, the long guard interval, and the long symbol duration. In another embodiment, generating the OFDM symbol for the first portion of the preamble includes generating the OFDM symbol for the first portion of the preamble using the second tone spacing, the normal guard interval, and the normal symbol duration. In another embodiment, the second tone spacing of the first portion of the preamble is an integer n times the i) legacy tone spacing and ii) the first tone spacing of the data field, the regular guard interval is the legacy guard interval, and the long symbol duration is an integer n times the regular symbol duration.

In another embodiment, generating OFDM symbols for a data field of the PHY data unit according to the range expansion mode comprises: generating an OFDM symbol for the data field using a non-legacy tone spacing and a non-legacy tone plan that do not conform to the second communication protocol; and generating the preamble includes generating OFDM symbols for a first portion of the preamble using a second tone spacing different from the non-legacy tone spacing and a legacy tone plan different from the non-legacy tone plan. In another embodiment, the non-legacy tone plan includes at least one guard tone in place of a corresponding data tone of the legacy tone plan that is close to the direct current tone. In an embodiment, the non-legacy tone plan includes at least one data tone in place of a corresponding guard tone of the legacy tone plan, such that the non-legacy tone plan and the legacy tone plan have the same number of data tones. In another embodiment, the non-legacy tone plan includes fewer data tones than the legacy tone plan and generating the OFDM symbol for the data field using the non-legacy tone spacing and the non-legacy tone plan includes encoding information bits for the OFDM symbol using an error correction code based on a number of data tones of the non-legacy tone plan. In an embodiment, the error correction code is a binary convolutional code. In another embodiment, the error correction code is a low density parity check code.

Fig. 28 is a flow diagram of an example method 2800 for generating a data unit, according to an embodiment. Referring to fig. 1, in an embodiment, the method 2800 is implemented by the network interface 16. For example, in one such embodiment, the PHY processing unit 20 is configured to implement the method 2800. According to another embodiment, the MAC processing 18 is also configured to implement at least a portion of the method 2800. With continued reference to fig. 1, in yet another embodiment, the method 2800 is implemented by the network interface 27 (e.g., the PHY processing unit 29 and/or the MAC processing unit 28). In other embodiments, method 2800 is implemented by other suitable network interfaces.

In an embodiment, at block 2802, a first plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols is generated for a first field of a preamble to be included in a PHY data unit. In some embodiments, each OFDM symbol of the first plurality of OFDM symbols corresponds to a first long training sequence of the first communication protocol obtained by at least multiplying a predetermined sequence by a second long training sequence of the second communication protocol. In an embodiment, at block 2804, a first plurality of information bits for a second field of a preamble is encoded to generate a first plurality of encoded bits.

In an embodiment, at block 2806, a first plurality of coded bits is mapped to a first plurality of constellation symbols. In an embodiment, at block 2808, a first plurality of modified constellation symbols is generated, which includes multiplying the first plurality of constellation symbols by a predetermined sequence. In an embodiment, at block 2810, a second plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols comprising the first plurality of modified constellation symbols is generated. In an embodiment, at block 2812, generating a preamble includes generating a preamble for a first plurality of OFDM symbols for a first field and a second plurality of OFDM symbols for a second field. At block 2814, a PHY data unit is generated to include at least a preamble.

In some embodiments, the first plurality of information bits comprises a first set of one or more information bits indicating a duration of the PHY data unit, the preamble being formatted such that the preamble is decodable by a receiver device that conforms to the second communication protocol but does not conform to the first communication protocol to determine the duration of the PHY data unit based on the preamble. In an embodiment, the ith value of the first long training sequence corresponds to the ith value corresponding to the second long training sequence multiplied by the ith value of the predetermined sequence, where i is an index.

In an embodiment, the length of the first long training sequence is greater than or equal to the sum of the number of data tones and the number of pilot tones in an OFDM symbol specified by the second communication protocol. In some embodiments, generating the first plurality of modified constellation symbols comprises multiplying the predetermined sequence by a plurality of pilot tone constellation symbols for the second communication protocol. In some embodiments, the value of the predetermined sequence corresponding to the plurality of pilot tone constellation symbols has a value of 1. In an embodiment, the predetermined sequence of values has a value of +1 or-1.

In some embodiments, generating the first plurality of OFDM symbols comprises generating the first plurality of OFDM symbols such that an autocorrelation output for a first field generated by a receiver compliant with the first communication protocol signals i) a first mode of the first communication protocol or ii) a second mode of the first communication protocol to enable automatic detection of the first mode or the second mode of the receiver device. In an embodiment, the first field includes a first long training sequence. In another embodiment, the first field includes a second long training sequence.

In an embodiment, method 2800 further comprises: encoding a second plurality of information bits for a data field of the PHY data unit to generate a second plurality of encoded bits; mapping the second plurality of coded bits to a second plurality of constellation symbols; generating the second plurality of modified constellation symbols comprises multiplying the predetermined sequence by the second plurality of constellation symbols; generating a third plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols comprising the second plurality of modified constellation symbols; and generating a data field comprising a third plurality of OFDM symbols, wherein generating the PHY data unit comprises generating the PHY data unit to contain at least the preamble and the data field.

Fig. 29 is a diagram of a portion 2900 of an example PHY preamble conforming to the HEW communication protocol according to an embodiment, as compared to a portion 2904 of the preamble conforming to the legacy protocol. In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit including the PHY preamble 2900 to the client station 25-1 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit containing the preamble 2900 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit containing the PHY preamble 2900 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit containing the preamble 2900 conforms to the first communication protocol using the techniques discussed below.

According to an embodiment, the data unit 2900 containing the PHY preamble conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and that contain preambles similar to preamble 2900 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 2900 is suitable for a "mixed mode" situation, i.e., when WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, preamble 2900 is utilized in other situations as well.

Leader 2900 includes L-LTF 204/304/504. In an embodiment, L-LTF 204/304/504 includes a dual guard interval 2908, a first L-LTF OFDM symbol 2912, and a second L-LTF OFDM symbol 2916. According to an embodiment, the preamble portion 2900 further includes an L-SIG206/306/506 that includes a guard interval 2920 and an L-SIG OFDM symbol 2924. According to an embodiment, L-LTF 204/304/504 and L-SIG206/306/506 are part of a first portion of preamble 2900 that matches a corresponding first portion of legacy preamble 2904 (e.g., a preamble compliant with the IEEE802.11a standard, the IEEE802.11 g standard, the IEEE802.11 n standard, and/or the IEEE802.11ac standard). The legacy device can decode the L-SIG206/306/506 and determine the length of the PHY data unit containing the PHY preamble 2900. For example, in an embodiment, the L-SIG206/306/506 includes a length field set to a value indicating the length of the PHY data unit containing the PHY preamble 2900.

The preamble 2900 includes a secondary L-SIG field 2928. In an embodiment, the L-SIG field 2928 is a copy of the L-SIG field 206/306/506. In an embodiment, a communication device configured to operate according to a first communication protocol is configured to detect repetition of the L-SIG field 206/306/506 in the preamble 2900 and, based on the detected reception of the L-SIG field 206/306/506, determine that the preamble 2900 conforms to the first communication protocol. In an embodiment, once a repetition of the L-SIG field 206/306/506, 2928 is detected, in an embodiment, the receiving device uses a duplicate in the repeated L-SIG field as additional training information to improve channel estimation. In some embodiments, the receiving device first decodes the L-SIG206/306/506 and then detects repetitions of the L-SIG fields 206/306/506, 2928 using the values of the length subfields in the L-SIG 206/306/506. In another embodiment, the receiving device first detects repetitions of the L-SIG fields 206/306/506, 2928 and then combines the detected multiple L-SIG fields 206/306/506, 2928 to improve the decoding reliability of the L-SIG fields 206/306/506, 2928 and/or uses redundant information in the multiple L-SIG fields 206/306/506, 2928 to improve channel estimation.

In an embodiment, the preamble 2900 also includes a HEW-SIG1 field 2932 that includes a DGI 2936 and a HEW-SIG1 field OFDM symbol 2940. The preamble 2900 also includes a secondary HEW-SIG1 field 2944. In an embodiment, the HEW-SIG1 field 2944 is a duplicate of the HEW-SIG1 field 2932. In an embodiment, a receiving device conforming to the first communication protocol uses the duplicate in the repeated HEW-

SIG1 fields

2932, 2944 as additional training information to improve channel estimation in an embodiment. In another embodiment, a receiving device conforming to the first communication protocol combines the detected multiple HEW-

SIG1 fields

2932, 2944 to improve the decoding reliability of the HEW-

SIG1 fields

2932, 2944 and/or uses redundant information in the multiple HEW-

SIG1 fields

2932, 2944 to improve channel estimation.

In an embodiment, the preamble portion 2900 is formatted to enable a receiving device configured according to a first communication protocol to determine that a data unit that includes the preamble 2900 conforms to the first communication protocol. For example, in an embodiment, LTF field 204/304/504 corresponds to modified LTF field 2304 of fig. 23, and in an embodiment, first legacy field 206/306/506 corresponds to modified legacy field 2306 of fig. 23. In this embodiment, a receiving device receiving a data unit containing preamble 2900 is able to detect that the data unit conforms to the first communication protocol by performing a first cross-correlation of LTFs 204/304/504 using a long training sequence of a legacy communication protocol and in embodiments performing a second cross-correlation of LTF field 204/304/504 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23.

In an embodiment, the preamble 3201 of the data unit 3200 is additionally formatted so that the legacy communication device can determine that the data unit 3200 does not conform to a legacy communication protocol. For example, in an embodiment, the first L-SIG field 3202, the second L-SIG field 3204, and the HEW-SIG1 field 3208 are each modulated such that the receiving device will detect BPSK modulation in an OFDM symbol at a corresponding location of the legacy data unit format 3220. For example, in an embodiment, upon detecting BPSK modulation in the OFDM symbol corresponding to the first L-SIG field 3202, the second L-SIG field 3204, and the HEW-SIG1 field 3206, the receiving device will stop processing the data unit 3200 and will refrain from accessing the medium for a duration determined based on the L-SIG field 3204.

Fig. 30 is a diagram of a portion 3000 of an example PHY preamble conforming to a first communication protocol according to another embodiment as compared to a portion 2904 of a preamble conforming to a legacy protocol. The preamble 3000 is similar to the preamble 2900 of fig. 29, and like-numbered elements are not discussed in detail for the sake of brevity. In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit including the PHY preamble 3000 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit containing the preamble 3000 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit including the PHY preamble 3000 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit containing the preamble 3000 conforms to the first communication protocol using the techniques discussed below.

According to an embodiment, the data unit including the PHY preamble 3000 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 3000 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 3000 is suitable for a "mixed mode" situation, i.e., when WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, preamble 3000 is utilized in other situations as well.

Unlike preamble 2900, preamble 3000 omits secondary L-SIG 2928. Furthermore, unlike preamble 2900, HEW-SIG13004 includes GI 3008 instead of DGI. The HEW-SIG13004 also includes HEW-SIG1 OFDM symbols 3012. In an embodiment, the HEW-SIG 13016 is a replica of the HEW-SIG 13004. Preamble 3000 also includes HEW-SIG 23020, which includes a DGI 3024 and HEW-SIG2OFDM symbol 3028.

According to an embodiment, L-LTF 204/304/504 and L-SIG206/306/506 are part of a first portion of preamble 3000 that matches a corresponding first portion of legacy preamble 2904 (e.g., a preamble compliant with the IEEE802.11a standard, the IEEE802.11 g standard, the IEEE802.11 n standard, and/or the IEEE802.11ac standard). The legacy device can decode the L-SIG206/306/506 and determine the length of the PHY data unit containing the PHY preamble 3000. For example, in an embodiment, the L-SIG206/306/506 includes a length field set to a value indicating the length of the PHY data unit containing the PHY preamble 3000.

In an embodiment, a communication device configured to operate according to the HEW protocol is configured to detect repetitions of the HEW-

SIG1 fields

3004, 3016 in the preamble 3000, and determine that the preamble 3000 conforms to the HEW communication protocol based on the detected repetitions of the HEW-

SIG1 fields

3004, 3016.

In an embodiment, a receiving device conforming to the HEW protocol uses repetitions in the repeated HEW-

SIG1 fields

3004, 3016 as additional training information to improve channel estimation in an embodiment. In another embodiment, a receiving device conforming to the HEW protocol combines the detected multiple 3004, 3016 to improve decoding reliability of the HEW-

SIG1 fields

3004, 3016 and/or uses redundant information in the multiple HEW-

SIG1 fields

3004, 3016 to improve channel estimation.

Fig. 31 is a diagram of a portion 3100 of an example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion 2904 of a preamble conforming to a legacy protocol. Preamble 3100 is similar to preamble 2900 of fig. 29 and preamble 3000 of fig. 30, and like-numbered elements are not discussed in detail for the sake of brevity.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit comprising the PHY preamble 3100 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 3100 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit comprising the PHY preamble 3100 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit comprising the preamble 3100 conforms to the first communication protocol using techniques discussed below.

According to an embodiment, the data unit comprising the PHY preamble 3100 conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 3100 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 3100 is suitable for a "mixed mode" scenario, i.e., when WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, the preamble 3100 is also utilized in other situations.

Unlike preamble 2900, HEW-SIG13004 includes a GI 3008 instead of a DGI. The HEW-SIG13004 also includes HEW-SIG1 OFDM symbols 3012. In an embodiment, the HEW-SIG 13016 is a replica of the HEW-SIG 13004. Preamble 3100 also includes HEW-SIG 23020, which includes DGI 3024 and HEW-SIG2OFDM symbol 3028.

Unlike preamble 3000, preamble 3100 includes a secondary L-SIG field 2928. In an embodiment, the L-SIG field 2928 is a copy of the L-SIG field 206/306/506.

In an embodiment, a communication device configured to operate according to the HEW protocol is configured to detect repetitions of the L-SIG field 206/306/506 in the preamble 2900, and determine that the preamble 2900 conforms to the HEW communication protocol based on the detected repetitions of the L-SIG field 206/306/506. In an embodiment, once the L-SIG fields 206/306/506, 2928 are detected, in an embodiment, the receiving device uses the duplicate in the repeated L-SIG field as additional training information to improve channel estimation. In some embodiments, the receiving device first decodes the L-SIG206/306/506 and then detects a repetition of the L-SIG field 206/306/506 using the value of the length subfield in the L-SIG 206/306/506. In another embodiment, the receiving device first detects repetitions of the L-SIG fields 206/306/506, 2928 and then combines the detected multiple L-SIG fields 206/306/506, 2928 to improve the decoding reliability of the L-SIG fields 206/306/506, 2928 and/or uses redundant information in the multiple L-SIG fields 206/306/506, 2928 to improve channel estimation.

SIG1 fields

3004, 3016.

SIG1 fields

3004, 3016 and/or uses redundant information in the multiple HEW-

SIG1 fields

3004, 3016 to improve channel estimation.

Fig. 32 is a diagram of a portion of a preamble 3200 of an OFDM data unit that the network interface device 16 of the AP 14 is configured to generate and transmit to the client station 25-1 via OFDM modulation, according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 3200 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to transmit a data unit comprising the preamble 3200 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit comprising the preamble 3200 conforms to the first communication protocol using the techniques discussed below.

The data unit containing preamble 3200 conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units conforming to the first communication protocol having preambles similar to preamble 3200 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. The data unit 700 is suitable for a "mixed mode" situation, i.e., when the WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, the data unit containing the preamble 3200 is also utilized in other cases.

The preamble 3200 includes a preamble 3210 having a first long guard interval 3202, a long training field 3204 having a first portion 3204-1 and a second portion 3204-2, a second long guard interval 3206, a first L-SIG field 3206-1, a second L-SIG field 3206-2, a third long guard interval 3202, a first HEW signal field HEW-SIG 13208, a fourth long guard interval 3202, and a second HEW signal field HEW-SIG 23210. In an embodiment, the first L-SIG field 3602-1 corresponds to the L-SIG field 706 of the data unit 700, and the second L-SIG field 3602-2 is a copy of the first L-SIG field 3062-1. In an embodiment, each long guard interval 3202 is a double guard interval that is twice as long as a conventional guard interval defined by legacy communication protocols. For example, in an embodiment, the normal guard interval defined by the legacy communication protocol is 0.8 μ s and the dual guard interval is 1.6 μ s. In another embodiment, each of the long guard intervals 3202 has another suitable value that is greater than a conventional guard interval defined by the legacy communication protocol. For example, in various embodiments, the regular guard interval defined by the legacy communication protocol is 0.8 μ s, and the long guard interval is 1.2 μ s, 2.4 μ s, 3.2 μ s, or another suitable value greater than 0.8 μ s.

With continued reference to FIG. 32, a legacy data unit format 3220 is illustrated for reference. A data unit conforming to format 3220 includes a dual protection interval 3222, a long training field 3224 having a first section 3224-1 and a second section 3224-2, a first conventional protection interval 3225, an L-SIG field 3226, an OFDM symbol 3228 corresponding to a signal field (e.g., an HT-SIG1 field or a VHT-SIG1 field) or an OFDM symbol depending on the data section of the particular legacy protocol to which format 3200 corresponds, a third conventional protection interval 3225, and an OFDM symbol 3230 corresponding to a signal field (e.g., an HT-SIG field or a VHT-SIG2 field) or an OFDM symbol depending on the data section of the particular legacy protocol to which format 3200 corresponds.

In an embodiment, the preamble 3201 of the data unit 3200 is formatted to enable a receiving device configured according to the first communication protocol to determine that the data unit 3200 corresponds to the first communication protocol. For example, in an embodiment, the L-LTF field 3204 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the first legacy signal field 3206 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device receiving data unit 3200 is able to detect that data unit 3200 conforms to the first communication protocol by performing a first cross-correlation of long training field 3202 using a long training sequence of a legacy communication protocol and, in embodiments, performing a second cross-correlation of L-LTF field 3202 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23. Additionally or alternatively, in embodiments, a receiving device receiving the data unit 3200 is able to detect that the data unit 3200 conforms to the first communication protocol by detecting the presence of the second L-SIG field 3205 in the preamble 3201.

In an embodiment, the preamble portion 3201 of the preamble 3200 is additionally formatted such that the legacy communication protocol is capable of determining that the data unit comprising the preamble 3200 does not comply with the legacy communication protocol. For example, in an embodiment, the first L-SIG field 3202, the second L-SIG field 3204, and the HEW-SIG1 field 3208 are each modulated such that the receiving device will detect BPSK modulation in the OFDM symbol at the corresponding location of the legacy data unit format 3220. For example, in an embodiment, upon detecting BPSK modulation in the OFDM symbol corresponding to the first L-SIG field 3202, the second L-SIG field 3204, and the HEW-SIG1 field 3206, the receiving device will stop processing the data unit 3200 and will refrain from accessing the medium for a duration determined based on the L-SIG field 3204. As illustrated in fig. 32, in an embodiment, the first L-SIG field 3204 in the time domain is not aligned with the corresponding OFDM symbol L-SIG 3224 in the legacy preamble 3220 due to the long guard interval preceding the L-SIG field 3210. On the other hand, the second L-SIG field 3212 is aligned with a corresponding OFDM symbol 3228 in the legacy preamble 3220. In the illustrated embodiment, similar to the first L-SIG field 3208, the HEW-SIG1 field is non-aligned in the time domain with the corresponding OFDM symbol 3230 in the legacy preamble.

In an embodiment, the constellation points of the first L-SIG field 3206-1 and the HEW-SIG1 field 3208 are pre-rotated such that the constellation points are treated as BPSK in an FFT window of an offset used by legacy communication devices having corresponding OFDM symbols in legacy format 3220. In an embodiment, the constellation points of the first L-SIG field 3206-1 and the HEW-SIG1 field 3208 are rotated by an amount determined by the length of the long guard interval caused by the duration of the long guard interval. For example, in embodiments where the long guard interval is as long as twice the conventional guard interval defined by legacy communication protocols, the constellation points of each of the first L-SIG field 3206-1 and the HEW-SIG1 field 3208 are rotated 90 degrees, as described above with respect to fig. 14B-14C. Thus, in this embodiment, the first L-SIG field 3206-1 and the HEW-SIG1 field 3208 are each modulated using an inverse QBPSK (R-QBPSK) modulation.

In an embodiment, the second L-SIG field 3206-2 is aligned with a corresponding OFDM symbol 3228 in the legacy format 3220 and, accordingly, the second L-SIG field 3206-2 is modulated using BPSK modulation. In this embodiment, the cyclic prefix of the second L-SIG field 3206-2 does not match the last portion of the first L-SIG field 3206-1 in an embodiment.

Fig. 33 is a diagram of a portion of a preamble 3300 of an OFDM data unit that the network interface device 16 of the AP 14 is configured to transmit to the client station 25-1 via OFDM modulation, according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 3300 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to transmit a data unit containing the preamble 3300 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit containing the preamble 3300 conforms to the first communication protocol using the techniques discussed below.

The data unit containing preamble 3300 conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and have preambles similar to preamble 3300 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths.

The preamble 3300 is similar to the preamble 3200 of fig. 2, except that the second long guard interval 3202-2 is replaced with a regular guard interval 3302 in the preamble 3301 of the preamble 3300 and the second L-SIG field 3206-2 is omitted from the data unit 3300. Further, the preamble 3301 includes a first HEW-SIG1 field 3208-1 and a second HEW-SIG1 field 3208-2, as compared to the single HEW-SIG1 field 3208 of the preamble 3200. In an embodiment, the second HEW-SIG1 field 3208-2 is a duplicate of the first HEW-SIG1 field 3208-1.

In an embodiment, the L-SIG field 3206 and the second HEW-SIG1 field 3208-2 are each aligned with their corresponding OFDM symbols in the legacy format 3220. On the other hand, the first HEW-SIG1 field 3208-1 is not aligned with its corresponding OFDM symbol of the legacy format 3220. In an embodiment, the constellation points of the first HEW-SIG field 3208-1 are pre-rotated (e.g., by 90 degrees) such that the receiving device will detect BPSK modulation in the FFT window corresponding to the offset of the OFDM symbol 3228. In an embodiment, the second HEW-SIG1 field 3208-2 is modulated using BPSK modulation such that the receiving device may detect BPSK modulation of the corresponding OFDM symbol 3330 in the legacy format 3200. In this case, however, in an embodiment, the modulation of the second HEW-SIG1 field 3208-2(BPSK) is different from the modulation of the first HEW-SIG1 field 3208-1 (e.g., R-QBPSK). Thus, the cyclic prefix of the second HEW-SIG1 field 3208-2 does not exactly match the corresponding last portion of the first HEW-SIG1 field 3208-1.

Alternatively, in another embodiment, the second HEW-SIG1 field 3208-2 is modulated with the same modulation (e.g., R-QBPSK) as the first HEW-SIG1 field 3208-1. In this embodiment, the cyclic prefix of the second signal field HEW-SIG1 field 3208-2 matches the last portion of the first signal field HEW-SIG1 field 3208-1, which enables the non-legacy device to more accurately detect that the data unit containing the preamble 3300 corresponds to the first communication protocol based on detecting a repetition of the HEW-SIG1 field in the data unit 3300. Also, in this embodiment, legacy devices will detect modulation (e.g., QPSK) of the offset in the corresponding OFDM symbol 3230, which may result in misdetection of data unit 3200 as a data unit conforming to the IEEE-802-11ac standard. However, the legacy device will interpret the second HEW-SIG1 field as the VHT-SIG2 field and will fail the CRC check of the VHT-SIG2 field. In an embodiment, in accordance with the IEEE802.11ac standard, the legacy device will then discard the data unit with preamble 3300 and in an embodiment will refrain from accessing the medium for the duration indicated in the L-SIG field 3206. Various methods for ensuring that legacy devices detect CRC errors based on decoding the second HEW-SIG1 field 3208-2 are described in us patent application No. 13/856,277 filed on 4/2013 (attorney docket No. MP 4709), which is incorporated herein by reference in its entirety.

Fig. 34 is a diagram of a portion of a preamble 3400 of an OFDM data unit that the network interface device 16 of the AP 14 is configured to transmit to a client station 25-1 via OFDM modulation, according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 3400 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to transmit a data unit including the preamble 3400 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 3400 conforms to the first communication protocol using the techniques discussed below.

The data unit including the preamble 3400 conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and have preambles similar to preamble 3400 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths.

In an embodiment, the preamble 3400 is similar to the preamble 3200 of fig. 32, except that the preamble 3401 of the preamble 3400 includes a long guard interval between OFDM symbols of the preamble 3401 and does not include a copy of the L-SIG field 3206. Further, in the illustrated embodiment, unlike in preamble 3200, the pre-rotation of constellation points in OFDM symbols of preamble 3400 is not aligned with corresponding OFDM symbols in legacy format 3220.

Fig. 35 is a diagram of a portion 3500 of a preamble of an OFDM data unit that the network interface device 16 of the AP 14 is configured to transmit to the client station 25-1 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation, according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 3500 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to transmit a data unit including the preamble 3500 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 3500 conforms to the first communication protocol using the techniques discussed below.

The data unit including preamble 3500 conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and have preambles similar to preamble 3500 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 3500 is identical to preamble 3400 of fig. 34, except that in preamble 3500, the second long guard interval 3302-2 is replaced with a conventional guard interval 3502. In this case, in an embodiment, the L-SIG field 3206 is aligned with its corresponding OFDM symbol (L-SIG field 3226) in legacy format 3220.

Fig. 36 is a diagram of a portion 3600 of an example PHY preamble compliant with a first communication protocol according to another embodiment compared to a portion 2904 of a preamble compliant with a legacy protocol. The preamble 3600 is similar to the preamble 2900 of fig. 29, and like-numbered elements are not discussed in detail for the sake of brevity.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit including the PHY preamble 3600 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 3600 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit containing the PHY preamble 3600 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit containing the preamble 3600 conforms to the first communication protocol using the techniques discussed below.

According to an embodiment, the data unit including the PHY preamble conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 3600 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 3600 is suitable for a "mixed mode" situation, i.e., when WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than a first communication protocol. In some embodiments, the preamble 3600 is utilized in other cases as well.

In an embodiment, the HEW-SIG field 3604 in the time domain is not aligned with the corresponding OFDM symbol (V) HT-SIG1 field 3608 in the legacy preamble 2904 due to the long guard interval 2936 preceding the HEW-SIG1 OFDM symbol 2940.

In an embodiment, the constellation points of the HEW-SIG1 OFDM symbol 2940 are rotated by an amount determined by the length of the long guard interval 2936 caused by the duration of the long guard interval 2936. For example, in an embodiment in which the long guard interval is as long as twice the conventional guard interval defined by the legacy communication protocol, the constellation points of the HEW-SIG1 OFDM symbol 2940 are rotated 90 degrees, as described above with respect to fig. 14B-14C. Thus, in an embodiment, the HEW-SIG1 field 3604 is modulated using an inverse QBPSK (R-QBPSK) modulation.

Fig. 37 is a diagram of a portion 3700 of a preamble of an OFDM data unit that the network interface device 16 of the AP 14 is configured to generate and transmit to the client station 25-1 via Orthogonal Frequency Domain Multiplexing (OFDM) modulation, according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 3700 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit including the preamble 3700 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 3700 conforms to the first communication protocol using the techniques discussed below.

The data unit including preamble 3700 conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 3700 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths.

The preamble 3700 is similar to the preamble 3300 of fig. 33, except that the preamble 3700 omits the second (duplicate) HEW-SIG1 field 3208-2 and includes the auto-detect OFDM symbol 3706. In an embodiment, the receiving device is capable of detecting that the data unit comprising the preamble 3700 conforms to the first communication protocol based on detecting the auto-detected OFDM symbol 3706 in the data unit 3700. In the illustrated embodiment, the automatic detection symbol 3706 immediately follows the L-SIG field 3206. In an embodiment, auto-detect symbol 3706 is aligned with its corresponding OFDM symbol in the legacy data unit and is modulated using BPSK modulation at least with respect to non-zero tones of the corresponding OFDM symbol in legacy format 3220. In an embodiment, the long guard interval 3710 is used with the HEW-SIG1 field 3208 of the preamble 3700. In an embodiment, the HEW-SIG1 field 3208 of the preamble 3700 is not aligned with the corresponding OFDM symbol in the legacy format 3220. In an embodiment, the constellation points of the HEW-SIG1 field 3208 are pre-rotated (e.g., by 90 degrees) so that legacy receiving devices will detect BPSK modulation using the FFT window of the corresponding OFDM symbol in legacy format 3220.

Fig. 38A-38D are diagrams illustrating auto-detecting OFDM symbols 3706 of a data cell 3700, according to several example embodiments. Turning first to fig. 38A, in an embodiment, auto-detect OFDM symbol 3706 includes five repetitions of an L-LTF sequence defined by a legacy communication protocol. In this embodiment, the non-legacy receiving device is able to detect that the data element 3700 conforms to the first communication protocol by reusing the start of the packet detection algorithm used to detect the start of the data element 3700 based on the L-STF field included in the start of the data element 3700. Turning now to fig. 38B, in an embodiment, auto-detect OFDM symbol 3706 includes two repetitions of a suitable predetermined sequence that is longer (corresponding to more OFDM tones) than the L-STF sequence defined by the legacy communication protocol. For example, in an embodiment, the predetermined sequence includes values corresponding to every other OFDM tone (e.g., an OFDM tone with indices in the set [ +/-2, +/4, +/-6, etc.) within each 20MHz frequency band of data unit 3700. Turning now to fig. 38C, in an embodiment, the auto-detect OFDM symbol 3706 includes five repetitions of the last portion (e.g., the last 0.8 μ β) of the L-SIG field 3206. Turning now to fig. 38C, in an embodiment, the auto-detect OFDM symbol 3706 includes two repetitions of a larger portion (e.g., 1.6 μ β) of the L-SIG field 3206 followed by a suffix portion of a subsection of the larger portion (e.g., 0.8 μ β) of the L-SIG field 3206.

In other embodiments, automatically detecting OFDM symbol 3706 includes any other suitable predetermined sequence that may be used at a receiving device to automatically detect that the data unit containing preamble 3700 conforms to the first communication protocol. For example, in various embodiments, the auto-detect OFDM symbol 3706 includes a predetermined Barker (Barker) code sequence, a predetermined Golay (Golay) sequence, or any other suitable predetermined sequence. In an embodiment, the receiving device detects that the data unit comprising the preamble 3700 conforms to the first communication protocol by detecting a high correlation of the auto-detected OFDM symbol 3706 with a predetermined sequence.

Fig. 39 is a diagram of a portion 3900 of an example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion 2904 of the preamble conforming to a legacy protocol. The preamble 3900 is similar to the preamble 2900 of fig. 29, and like-numbered elements are not discussed in detail for the sake of brevity.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit including the PHY preamble 3900 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 3900 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit including the PHY preamble 3900 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 3900 conforms to the first communication protocol using the techniques discussed below.

According to an embodiment, the data unit including the PHY preamble conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include a preamble similar to preamble 3900 can occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. The preamble 3900 is suitable for a "mixed mode" situation, i.e., when the WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, the preamble 3900 is also utilized in other situations.

According to an embodiment, the L-SIG 206/36/506, L-SIG 2928, and HEW-SIG 12932 are modulated using BPSK, but the HEW-SIG 12944 is modulated using rotated BPSK (e.g., Q-BPSK).

Fig. 40A is a diagram of a portion 4000 of another example PHY preamble conforming to a first communication protocol, according to another embodiment.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit comprising the PHY preamble 4000 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 4000 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit comprising the PHY preamble 4000 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 4000 conforms to the first communication protocol using the techniques discussed below.

According to an embodiment, the data unit including the PHY preamble conforms to a first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4000 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 4000 is suitable for a "mixed mode" situation, i.e., when WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, preamble 4000 is utilized in other situations as well.

The preamble 4000 includes a legacy portion 4004 having a first L-LTF OFDM symbol 4008, a second L-LTF OFDM symbol 4012, and an L-SIG OFDM symbol 4016. In an embodiment, a dual guard interval (not shown) is included before the L-LTF OFDM symbol 4008 and a guard interval is included between the L-LTF OFDM symbol 4012 and the L-SIG OFDM symbol 4016. According to an embodiment, the legacy device is able to decode the L-SIG 4016 and determine the length of the PHY data unit that includes the PHY preamble 4000. For example, in an embodiment, the L-SIG 4016 includes a length field set to a value indicating the length of a PHY data unit including the PHY preamble 4000.

In an embodiment, the L-LTF field 4012 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 4016 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device conforming to a first communication protocol is able to detect that a data unit including preamble 4000 conforms to the first communication protocol by performing a first cross-correlation of L-LTF 4008 using a long training sequence of a legacy communication protocol and in embodiments performing a second cross-correlation of L-LTF field 4012 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23.

The PHY preamble 4000 includes one or more HEW-STF OFDM symbols 4020, HEW-LTF1 OFDM symbols 4024, HEW-SIGA OFDM symbols 4028, one or more HEW-LTF OFDM symbols 4032, and HEW-SIGB OFDM symbols 4036. In an embodiment, DGI is included between L-SIG 4016 and HEW-STF 4020 a. In an embodiment, respective DGIs are included between HEW-STFOFDM symbol 4020b and HEW-LTF1 OFDM symbol 4024, between HEW-LTF1 OFDM symbol 4024 and HEW-sigaaofdm symbol 4028, between HEW-SIGA OFDM symbol 4028 and one or more HEW-LTF OFDM symbols 4032, and between one or more OFDM symbols 4032 and HEW-SIGB OFDM symbol 4036.

Fig. 40B is a diagram of a portion 4050 of another example PHY preamble conforming to a first communication protocol, according to another embodiment. Preamble 4050 is similar to preamble 4000 and like-numbered elements are not discussed in detail for the sake of brevity.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit data units comprising the PHY preamble 4050 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 4050 conforms to the first communication protocol using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit including the PHY preamble 4050 to the AP. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 4050 conforms to the first communication protocol using the techniques discussed below.

According to an embodiment, the data unit including the PHY preamble 4050 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4050 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. Preamble 4050 is suitable for a "mixed mode" situation, i.e., when WLAN 10 includes client stations (e.g., legacy client stations 25-4) that conform to a legacy communication protocol rather than the first communication protocol. In some embodiments, preamble 4050 is utilized in other situations as well.

According to an embodiment, the legacy device is able to decode the L-SIG 4016 and determine the length of the PHY data unit that includes the PHY preamble 4050. For example, in an embodiment, the L-SIG 4016 includes a length field set to a value indicating the length of a PHY data unit that includes the PHY preamble 4050.

The preamble 4050 also includes one or more secondary L-SIG 4054. In an embodiment, the one or more secondary L-SIG4054 are copies of the L-SIG 4016.

In an embodiment, the L-LTF field 4012 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 4016 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device conforming to a first communication protocol is able to detect that a data unit including a preamble 4050 conforms to the first communication protocol by performing a first cross-correlation of L-LTF 4008 using a long training sequence of a legacy communication protocol and, in an embodiment, performing a second cross-correlation of L-LTF field 4012 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23.

Additionally or alternatively, in an embodiment, a receiving device receiving a data unit including the preamble 4050 can detect that the data unit conforms to the first communication protocol by detecting the presence of the one or more secondary L-SIG fields 4054 in the preamble portion 4050.

In an embodiment, DGI is included between L-SIG4054 b and HEW-STF 4020 a. In an embodiment, respective DGIs are included between HEW-STF OFDM symbol 4020b and HEW-LTF1 OFDM symbol 4024, between HEW-LTF1 OFDM symbol 4024 and HEW-SIGA OFDM symbol 4028, between HEW-SIGA OFDM symbol 4028 and one or more HEW-LTF OFDM symbols 4032, and between one or more OFDM symbols 4032 and HEW-SIGB OFDM symbols 4036.

In some embodiments, techniques such as those described above may be used to detect data units that conform to a first communication protocol and to detect which of a plurality of modes (defined by the first communication protocol) the data units correspond. For example, fig. 41 is a diagram of a portion 4100 of an example PHY preamble conforming to a first communication protocol according to another embodiment as compared to a portion 2904 of the preamble conforming to a legacy protocol. Further, the PHY preamble 4100 also corresponds to a range expansion mode of the first communication protocol. Fig. 41 also includes an illustration of a portion 4104 of an example PHY preamble conforming to a first communication protocol according to another embodiment as compared to the portion 2904 of the preamble conforming to a legacy protocol. Further, the PHY preamble 4104 also corresponds to a normal mode of the first communication protocol.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit including the PHY preamble 4100 or the PHY preamble 4104 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 4100 or the preamble 4104 conforms to the first communication protocol using the techniques discussed below. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 4100 conforms to the range expansion mode and the data unit including the preamble 4104 conforms to the regular mode using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit including the PHY preamble 4100 or the PHY preamble 4104 to the AP 14. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the PHY preamble 4100 or the PHY preamble 4104 conforms to the first communication protocol using the techniques discussed below. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 4100 conforms to the range expansion mode and the data unit including the preamble 4104 conforms to the normal mode using the techniques discussed below.

According to an embodiment, the data unit including the PHY preamble 4100 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4100 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. According to an embodiment, the data unit comprising the PHY preamble 4101 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4104 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths.

The preamble 4100 is similar to the preamble 2900 of fig. 29, and like-numbered elements are not discussed in detail for the sake of brevity. The legacy device can decode the L-SIG206/306/506 and determine the length of the PHY data unit that includes the PHY preamble 4100. For example, in an embodiment, the L-SIG206/306/506 includes a length field set to a value indicating the length of the PHY data unit that includes the PHY preamble 4100.

In an embodiment, a communication device configured to operate according to the HEW protocol is configured to detect a repetition of the L-SIG field 206/306/506 in the preamble 4100 and determine that the preamble 4100 conforms to the first communication protocol based on the detected repetition of the L-SIG field 206/306/506. Further, the communication device configured to operate according to the first communication protocol is configured to determine that the preamble 4100 conforms to the range expansion mode of the first communication protocol based on the detected repetition of the L-SIG field 206/306/506.

The preamble 4104 includes DGI 4104, L-LTF 4108, L-LTF 4112, GI 4116, and L-SIG 4120. In an embodiment, the L-LTF field 4112 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 4120 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device conforming to the first communication protocol can detect that the data unit including the preamble 4104 conforms to the first communication protocol by performing a first cross-correlation of the L-LTF 4108 using a long training sequence of the legacy communication protocol and, in an embodiment, performing a second cross-correlation of the L-LTF field 4112 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23. In a similar manner, a receiving device conforming to the first communication protocol is able to detect that the data unit comprising the preamble 4104 conforms to the normal mode of the first communication protocol.

In another embodiment, the L-LTF field 2916 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 2924 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device that conforms to the HEW protocol is able to detect that the data unit including the preamble 4100 conforms to the HEW communication protocol by performing a first cross-correlation of the L-LTF 2912 using a long training sequence of the legacy communication protocol and, in embodiments, performing a second cross-correlation of the L-LTF field 2916 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23.

Fig. 42 is a diagram of a portion 4200 of an example PHY preamble compliant with a first communication protocol according to another embodiment compared to a portion 2904 of a preamble compliant with a legacy protocol. Further, the PHY preamble 4200 also corresponds to a range expansion mode of the first communication protocol. Fig. 42 also includes an illustration of a portion 4204 of an example PHY preamble compliant with a first communication protocol according to another embodiment compared to a portion 2904 of a preamble compliant with a legacy protocol. Further, the PHY preamble 4204 also corresponds to a regular mode of the first communication protocol.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit comprising the PHY preamble 4200 or the PHY preamble 4204 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 4200 or the preamble 4204 conforms to the first communication protocol using the techniques discussed below. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 4200 conforms to the range extension mode and the data unit comprising the preamble 4204 conforms to the normal mode using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit including the PHY preamble 4200 or the PHY preamble 4204 to the AP 14. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit comprising the PHY preamble 4200 or the PHY preamble 4204 conforms to the first communication protocol using techniques discussed below. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 4200 conforms to the range expansion mode and the data unit including the preamble 4204 conforms to the normal mode using techniques discussed below.

According to an embodiment, the data unit comprising the PHY preamble 4200 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4200 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. According to an embodiment, the data unit comprising the PHY preamble 4101 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4204 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths.

The preamble 4200 is similar to the preamble 3000 of fig. 30, and like-numbered elements are not discussed in detail for the sake of brevity. The legacy device can decode the L-SIG206/306/506 and determine the length of the PHY data unit that includes the PHY preamble 4200. For example, in an embodiment, the L-SIG206/306/506 includes a length field set to a value indicating the length of the PHY data unit that includes the PHY preamble 4200.

In an embodiment, a communication device configured to operate according to a first communication protocol is configured to detect a repetition of the HEW-

SIG1 field

3004, 3016 in the preamble 4200 and determine, based on the detected repetition of the HEW-

SIG1 field

3004, 3016, that the preamble 4200 conforms to the first communication protocol. Further, the communication device configured to operate according to the first communication protocol is configured to determine that the preamble 4200 conforms to the range expansion mode of the first communication protocol based on the detected repetition of the HEW-

SIG1 fields

3004, 3016.

The preamble 4204 is similar to the preamble 4104 of fig. 41, and like-numbered elements are not discussed in detail for the sake of brevity. In an embodiment, the L-LTF field 4112 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 4120 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device conforming to the first communication protocol can detect that the data unit including the preamble 4104 conforms to the first communication protocol by performing a first cross-correlation of the L-LTF 4108 using a long training sequence of the legacy communication protocol and, in an embodiment, performing a second cross-correlation of the L-LTF field 4112 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23. In a similar manner, a receiving device conforming to the first communication protocol is able to detect that the data unit comprising the preamble 4104 conforms to the normal mode of the first communication protocol.

In an embodiment, the L-LTF field 2916 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 2924 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device conforming to the first communication protocol is able to detect that the data unit including the preamble 4200 conforms to the first communication protocol by performing a first cross-correlation of the L-LTF 2912 using a long training sequence of a legacy communication protocol and, in embodiments, performing a second cross-correlation of the L-LTF field 2916 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23.

Fig. 43 is a diagram of a portion 4300 of an example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion 2904 of a preamble conforming to a legacy protocol. Further, the PHY preamble 4300 also corresponds to a range extension mode of the first communication protocol. Fig. 43 also includes an illustration of a portion 4304 of an example PHY preamble conforming to a first communication protocol according to another embodiment compared to a portion 2904 of a preamble conforming to a legacy protocol. Further, the PHY preamble 4304 also corresponds to a normal mode of the first communication protocol.

In an embodiment, the network interface device 16 of the AP 14 is configured to generate and transmit a data unit comprising the PHY preamble 4300 or the PHY preamble 4304 to the client station 25-1 via OFDM modulation according to an embodiment. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit comprising the preamble 4300 or the preamble 4304 conforms to the first communication protocol using techniques discussed below. In an embodiment, the network interface device 27 of the client station 25-1 is configured to determine that the data unit including the preamble 4300 conforms to the range extension mode and the data unit including the preamble 4304 conforms to the normal mode using the techniques discussed below.

In an embodiment, the network interface device 27 of the client station 25-1 is further configured to generate and transmit a data unit comprising the PHY preamble 4300 or the PHY preamble 4304 to the AP 14. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the PHY preamble 4300 or the PHY preamble 4304 conforms to the first communication protocol using techniques discussed below. In an embodiment, the network interface device 16 of the AP 14 is configured to determine that the data unit including the preamble 4300 conforms to the range extension mode and the data unit including the preamble 4304 conforms to the normal mode using techniques discussed below.

According to an embodiment, the data unit including the PHY preamble 4300 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4300 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths. According to an embodiment, the data unit comprising the PHY preamble 4101 conforms to the first communication protocol and occupies a 20MHz bandwidth. In various other embodiments, data units that conform to the first communication protocol and include preambles similar to preamble 4304 may occupy other suitable bandwidths, such as, for example, 40MHz, 80MHz, 160MHz, 320MHz, 640MHz, or other suitable bandwidths.

Preamble 4300 is similar to preamble 2900 of fig. 29, and like numbered elements are not discussed in detail for the sake of brevity. The legacy device can decode the L-SIG206/306/506 and determine the length of the PHY data unit that includes the PHY preamble 4300. For example, in an embodiment, the L-SIG206/306/506 includes a length field set to a value indicating the length of a PHY data unit that includes the PHY preamble 4300.

The data unit 4300 is similar to the data unit 2900 of fig. 29, except that the data unit 4300 omits the second (duplicate) L-SIG field 2928 and includes an auto-detected OFDM symbol 4308. In an embodiment, a receiving device compliant with the first communication protocol is capable of detecting that a data unit comprising the preamble 4300 is compliant with the first communication protocol based on detecting the automatically detected OFDM symbol 4308 in the preamble 4300. In the illustrated embodiment, the automatic detection symbol 4308 immediately follows the L-SIG field 206/306/506. In an embodiment, the auto-detected symbols 4308 are aligned with their corresponding OFDM symbols in legacy data unit format 2904 and modulated using BPSK modulation. In an embodiment, a receiving device compliant with the first communication protocol is able to detect that a data unit comprising the preamble 4300 is compliant with the first communication protocol based on detecting the automatically detected OFDM symbol 4308 in the preamble 4300, as discussed with respect to fig. 37.

The preamble 4304 is similar to the preamble 4104 of fig. 41, and like numbered elements are not discussed in detail for the sake of brevity. In an embodiment, the L-LTF field 4112 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 4120 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device conforming to a first communication protocol is able to detect that a data unit including preamble 4304 conforms to the first communication protocol by performing a first cross-correlation of L-LTF 4108 using a long training sequence of a legacy communication protocol and in embodiments performing a second cross-correlation of L-LTF field 4112 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23. In a similar manner, a receiving device conforming to the first communication protocol is able to detect that the data unit including the preamble 4304 conforms to the normal pattern of the first communication protocol.

In another embodiment, the L-LTF field 2916 corresponds to the modified LTF field 2304 of fig. 23, and in an embodiment, the L-SIG 2924 corresponds to the modified legacy signal field 2306 of fig. 23. In this embodiment, a receiving device that conforms to the HEW protocol is able to detect that the data unit including preamble 4300 conforms to the first communication protocol by performing a first cross-correlation of L-LTF 2912 using a long training sequence of the legacy communication protocol and, in embodiments, performing a second cross-correlation of L-LTF field 2916 using a modified long training sequence of the first communication protocol as described above with respect to fig. 23.

In various other embodiments, combining techniques such as those described above with respect to fig. 9A-28 with techniques such as those described above with respect to fig. 29-40B utilized enables a receiver conforming to a first communication protocol to determine which of a variety of different modes (e.g., range extension mode, normal mode, etc.) in which a data unit conforms to the first communication protocol.

In some embodiments where SIG fields (e.g., L-SIG, HEW-SIG1, etc.) are duplicated, time-varying tone mapping is utilized. For example, in an embodiment, a half-bandwidth cyclic shift tone mapper is used. In an embodiment, the tones on the first SIG OFDM symbol (time t1) correspond to:

SIGk(t₁)＝s_k(t1)＝s_k(equation 4)

Wherein, SIG_kIs the k-th tone of the SIG OFDM symbol, and s_kIs the kth BPSK symbol to be mapped to the SIG OFDM symbol. In an embodiment, the second (replicated) SIG OFDM symbol (time t)₂) The tones in (c) correspond to:

SIGk(t₂)＝s_k(t2)＝s_{(k+N/2)mod N}(equation 5)

Where N is the number of tones in the SIG OFDM symbol. Thus, in an embodiment, the BPSK symbols s are sequentially mapped to tones in the first SIG OFDM symbol, while the same BPSK symbols s are cyclically shifted on half of the tones in the second SIG OFDM symbol. In other embodiments, another suitable time-varying tone mapping is used to achieve time diversity across different SIG OFDM symbols.

In an embodiment, time diversity across different SIG OFDM symbols is achieved using different interleavers for the same coded bits on two OFDM symbols. In other embodiments, other suitable techniques for achieving time diversity across different SIG OFDM symbols are utilized.

In some embodiments, wherein the preamble conforms to the first communication protocol, the L-SIG field in the preamble conforming to the first communication protocol corresponds to L-SIG in a legacy preamble multiplied by the sequence ck:

L-SIG_k ^(HEW)＝c_k·L-SIG_k ^(HEW)(equation 6)

Where k is the tone index. In an embodiment, sequence c_kIs a sequence with a value of ± 1.

In some embodiments, one or more further L-SIG fields are included in a preamble that conforms to the first communication protocol.

In some embodiments, the HEW-SIG field includes data unit duration information, such as the number of bytes of the data unit, the number of OFDM symbols of the data unit, and so forth.

In some embodiments, configuring the HEW-SIG field to conform to the SIG field (e.g., SIGA) in the legacy preamble such that inclusion of a copy of the HEW-SIG field in the preamble will cause a legacy device (e.g., an IEEE 802.11ac receiver) to generate a SIGA CRC error with 100% probability. For example, in various embodiments, the bits in the HEW-SIG field are scrambled, including a 1-bit field set to ensure that the SIGA CRC will be in error, and so on. In another embodiment, the HEW-SIG field is designed to include bits corresponding to an invalid mode in legacy protocols.

In an embodiment, a method is for generating a physical layer (PHY) data unit for transmission via a communication channel, the PHY data unit conforming to a first communication protocol. The method includes generating, at a first communication device, a PHY preamble for a PHY data unit, including: the method further includes generating a signal field, including the signal field and a copy of the signal field in the PHY preamble, and formatting the PHY preamble such that a first portion of the PHY preamble is decodable by a second communication device that conforms to the second communication protocol but does not conform to the first communication protocol to determine a duration of the PHY data unit based on the first portion of the PHY preamble. The method also includes generating, at the first communication device, the PHY data unit to contain the PHY preamble and the PHY payload.

At least some of the various blocks, operations, and techniques described above may be implemented with hardware, a processor executing firmware instructions, and a processor executing software instructions, or any combination thereof. When implemented with a processor executing software or firmware instructions, the software or firmware instructions may be stored on any non-transitory tangible computer-readable medium or media such as a magnetic disk, optical disk, Random Access Memory (RAM), Read Only Memory (ROM), flash memory, magnetic tape, or the like. The software or firmware instructions may include machine-readable instructions that when executed by one or more processors cause the one or more processors to perform various acts.

When implemented in hardware, the hardware may include one or more of the following: discrete components, integrated circuits, Application Specific Integrated Circuits (ASICs), Programmable Logic Devices (PLDs), and the like.

While the present invention has been described with reference to specific examples, which are intended to be illustrative only and not to be limiting of the invention, changes, additions and/or deletions may be made to the disclosed embodiments without departing from the scope of the invention.

Claims

1. A method for generating a physical layer (PHY) data unit for transmission via a communication channel, the PHY data unit conforming to a first communication protocol, the method comprising:

generating, at a first communication device, a PHY preamble for the PHY data unit, comprising:

a signal field is generated and the signal field is generated,

including the signal field and a copy of the signal field in the PHY preamble, wherein the copy of the signal field occurs after the signal field in the PHY preamble, and wherein the presence of the copy of the signal field indicates to a third communication device that conforms to the first communication protocol that the PHY data unit conforms to the first communication protocol, an

Formatting the PHY preamble such that a first portion of the PHY preamble is decodable by a second communication device that conforms to a second communication protocol but does not conform to the first communication protocol to determine a duration of the PHY data unit based on the first portion of the PHY preamble; and

generating, at the first communication device, the PHY data unit to include the PHY preamble and a PHY payload.

2. The method of claim 1, wherein:

the signal field is a legacy signal field decodable by the second communication device;

the legacy signal field is contained in the first portion of the PHY preamble; and

the legacy signal field contains information indicating the duration of the PHY data unit.

3. The method of claim 2, wherein generating the PHY preamble for the PHY data unit further comprises:

generating a further signal field conforming to said first communication protocol, an

Including the additional signal field in a second portion of the PHY preamble.

4. The method of claim 3, wherein the second portion of the PHY preamble is not decodable by the second communication device.

5. The method of claim 3, wherein generating the PHY preamble for the PHY data unit further comprises:

including a copy of the additional signal field in the second portion of the PHY preamble.

6. The method of claim 1, wherein:

the signal field is a first signal field; and is

Generating the PHY preamble for the PHY data unit further comprises:

generating a second signal field decodable by the second communication device, wherein the second signal field includes information indicative of the duration of the PHY data unit,

including the second signal field in the first portion of the PHY preamble, an

Including the first signal field in a second portion of the PHY preamble.

7. The method of claim 6, wherein the second portion of the PHY preamble is not decodable by the second communication device.

8. The method of claim 1, wherein:

the PHY preamble for the PHY data unit is generated to include respective first guard intervals between orthogonal frequency domain OFDM symbols in the first portion of the PHY preamble; and

the method also includes generating, at the first communication device, the PHY payload to include respective second guard intervals between OFDM symbols of the PHY payload, wherein each second guard interval has a longer duration than each first guard interval.

9. A method according to claim 8, wherein the PHY preamble for the PHY data unit is generated to include a respective second guard interval between OFDM symbols in a second portion of the PHY preamble.

10. A first communications device, comprising:

a network interface device having one or more integrated circuits configured to:

generating a PHY preamble of a physical layer PHY data unit conforming to a first communication protocol, comprising:

a signal field is generated and the signal field is generated,

generating the PHY data unit to include the PHY preamble and a PHY payload.

11. The first communication device of claim 10, wherein:

the one or more integrated circuits are configured to: including the legacy signal field in the first portion of the PHY preamble; and is

12. The communication device of claim 11, wherein the one or more integrated circuits are configured to:

Including the additional signal field in a second portion of the PHY preamble.

13. The first communication device of claim 12, wherein the second portion of the PHY preamble is not decodable by the second communication device.

14. The communication device of claim 12, wherein the one or more integrated circuits are configured to:

15. The first communication device of claim 10, wherein:

the signal field is a first signal field; and is

The one or more integrated circuits are configured to:

including the second signal field in the first portion of the PHY preamble, an

Including the first signal field in a second portion of the PHY preamble.

16. The first communication device of claim 15, wherein the second portion of the PHY preamble is not decodable by the second communication device.

17. The communication device of claim 10, wherein the one or more integrated circuits are configured to:

generating the PHY preamble for the PHY data unit to include respective first guard intervals between orthogonal frequency domain OFDM symbols in the first portion of the PHY preamble; and

generating the PHY payload to include respective second guard intervals between OFDM symbols in the PHY payload, wherein each second guard interval has a longer duration than each first guard interval.

18. The first communication device of claim 17, wherein the one or more integrated circuits are configured to: generating the PHY preamble to include a respective second guard interval between OFDM symbols in a second portion of the PHY preamble.