Orthogonal frequency division multiplexing (OFDM) symbol formats for a wireless local area network (WLAN)

In a method of generating an orthogonal frequency division multiplexing (OFDM) symbol, a plurality of information bits is encoded to generate a plurality of coded bits. The plurality of information bits corresponds to a first bandwidth, while the OFDM symbol includes a number of data tones corresponding to a second bandwidth. The coded bits are mapped to a plurality constellation symbols. The constellation symbols are mapped to a first plurality of data subcarriers corresponding to a first portion of the OFDM symbol and to a second plurality of data subcarriers corresponding to a second portion of the OFDM symbol. A subset of data subcarriers in the first plurality of data subcarriers and in the second plurality of data subcarriers are set to one or more predetermined values. The OFDM symbol is then generated to include at least the first plurality of data subcarriers and the second plurality of data subcarriers.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and, more particularly, to communicating device capabilities between devices in a wireless network.

BACKGROUND

Development of wireless local area network (WLAN) standards such as the Institute for Electrical and Electronics Engineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards, has improved single-user peak data throughput. For example, the IEEE 802.11b Standard specifies a single-user peak throughput of 11 megabits per second (Mbps), the IEEE 802.11a and 802.11g Standards specify a single-user peak throughput of 54 Mbps, and the IEEE 802.11n Standard specifies a single-user peak throughput of 600 Mbps. Work has begun on a new standard, IEEE 802.11ac, that promises to provide even greater throughput.

SUMMARY

According to a first embodiment, a method of generating an orthogonal frequency division multiplexing (OFDM) symbol of a data unit to be transmitted via a communication channel includes encoding a plurality of information bits to generate a plurality of coded bits to be included in the OFDM symbol, wherein the plurality of information bits corresponds to a first bandwidth, and wherein the OFDM symbol includes a number of data tones corresponding to a second bandwidth, the second bandwidth larger than the first bandwidth. The method also includes mapping the plurality of coded bits to a plurality constellation symbols and mapping the plurality of constellation symbols to a first plurality of data subcarriers corresponding to a first portion of the OFDM symbol. The method further includes setting a subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values. The method further still includes mapping the plurality of constellation symbols to a second plurality of data subcarriers corresponding to a second portion of the OFDM symbol, and setting a subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values. The method additionally includes generating the OFDM symbol to include at least the first plurality of data subcarriers and the second plurality of data subcarriers.

In another embodiment, an apparatus comprises a network interface configured to encode a plurality of information bits to generate a plurality of coded bits to be included in an OFDM symbol, wherein the plurality of information bits corresponds to a first bandwidth, and wherein the OFDM symbol includes a number of data tones corresponding to a second bandwidth, the second bandwidth larger than the first bandwidth. The network interface is also configured to map the plurality of coded bits to a plurality constellation symbols, and map the plurality of constellation symbols to a first plurality of data subcarriers corresponding to a first portion of the OFDM symbol. The network interface is also configured to set a subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values. The network interface is further still configured to map the plurality of constellation symbols to a second plurality of data subcarriers corresponding to a second portion of the OFDM symbol, and set a subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values. The network interface is additionally configured to generate the OFDM symbol to include at least the data subcarriers corresponding to the first potion and the data subcarriers corresponding to the second portion.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as an access point (AP) of a wireless local area network (WLAN) transmits data streams to one or more client stations. In an embodiment, the AP is configured to operate with client stations according to a first communication protocol (e.g., the IEEE 802.11ac Standard). Additionally, a different client station in the vicinity of the AP is configured to operate according to a second communication protocol (e.g., the IEEE 802.11n Standard, the IEEE 802.11a Standard, the IEEE 802.11g Standard, etc.), in an embodiment. The first communication protocol and the second communication protocol define operation in a frequency ranges above 1 GHz, and are generally used for applications requiring relatively short range wireless communication with relatively low data rates. The first communication protocol is referred to herein as a very high throughput (VHT) protocol, and the second communication protocol is referred to herein as a legacy protocol. In some embodiments, the AP is additionally or alternatively configured to operate with client stations according to a third communication protocol. The third communication protocol defines operation in a sub 1 GHz frequency ranges and is typically used for applications requiring relatively long range wireless communication with relatively low data rates. The first communication protocol and the second communication protocol are collectively referred to herein as “short range” communication protocols, and the third communication protocol is referred herein as a “long range” communication protocol.

In an embodiment, each one of communication protocols (e.g., short range protocols, long range protocols) defines multiple transmission channel bandwidths. In some embodiments, a data unit transmitted or received by the AP includes a preamble comprising a legacy portion corresponding to a bandwidth defined in a legacy protocol (e.g., 20 MHz bandwidth defined in the 802.11a protocol) and a VHT portion corresponding to the same or a different channel bandwidth defined in the VHT protocol (e.g., 80 MHz bandwidth defined in the VHT protocol). According to an embodiment, the preamble of a data unit includes a plurality of signal fields that carry information required at the receiver to properly identify and decode the data unit. In some embodiments, for example, two signal fields are included in the preamble, a first signal field included in a legacy portion of the preamble and modulated in a manner similar to the legacy portion of the data unit, and a second signal field included in a VHT portion of the preamble and modulated in a manner similar to the VHT data portion of the data unit. In one such embodiment, the second signal field is modulated similar to the VHT data portion of the data unit but using a lower coding rate and a smaller constellation size than the VHT data portion. Further, in some embodiments, bit allocation for the second signal field is the same regardless of the specific channel bandwidth that the data unit occupies. For example, in an embodiment, bit allocation is specified for the smallest possible bandwidth defined by the VHT protocol (e.g., 20 MHz bandwidth, 40 MHz, etc.) and bit insertion and/or duplication is utilized to transmit the second signal field in a higher VHT bandwidth. Further, in an embodiment, a VHT data portion of a data unit includes multiple spatial data streams directed to a single user (SU) or multiple users (MU), while the second signal field is limited to a single data stream. In these embodiments, the single stream of the second signal field is mapped in some manner to the multiple space streams and/or multiple users corresponding to the data portion of the data unit.

FIG. 1is a block diagram of an example embodiment of a wireless local area network (WLAN)10that utilizes various signal field modulation and mapping techniques described herein. An AP14includes a host processor15coupled to a network interface16. The network interface16includes a medium access control (MAC) processing unit18and a physical layer (PHY) processing unit20. The PHY processing unit20includes a plurality of transceivers21, and the transceivers are coupled to a plurality of antennas24. Although three transceivers21and three antennas24are illustrated inFIG. 1, the AP14can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers21and antennas24in other embodiments. In one embodiment, the MAC processing unit18and the PHY processing unit20are configured to operate according to a first communication protocol (e.g., the IEEE 802.11ac Standard, now in the process of being standardized). The first communication protocol is also referred to herein as a very high throughput (VHT) protocol. In another embodiment, the MAC processing unit18and the PHY processing unit20are also configured to operate according to at least a second communication protocol (e.g., the IEEE 802.11n Standard, the IEEE 802.11a Standard, etc.). In yet another embodiment, the MAC processing unit18and the PHY processing unit20are additionally or alternatively configured to operate according to a long range communication protocol (e.g., the IEEE 802.11ah Standard, the IEEE 802.11af Standard, etc.).

The WLAN10includes a plurality of client stations25. Although four client stations25are illustrated inFIG. 1, the WLAN10can include different numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations25in various scenarios and embodiments. At least one of the client stations25(e.g., client station25-1) is configured to operate at least according to the first communication protocol.

The client station25-1includes a host processor26coupled to a network interface27. The network interface27includes a MAC processing unit28and a PHY processing unit29. The PHY processing unit29includes a plurality of transceivers30, and the transceivers30are coupled to a plurality of antennas34. Although three transceivers30and three antennas34are illustrated inFIG. 1, the client station25-1can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30and antennas34in other embodiments.

In an embodiment, one or all of the client stations25-2,25-3and25-4, have a structure the same as or similar to the client station25-1. In these embodiments, the client stations25structured the same as or similar to the client station25-1have the same or a different number of transceivers and antennas. For example, the client station25-2has only two transceivers and two antennas, according to an embodiment.

In various embodiments, the PHY processing unit20of the AP14is configured to generate data units conforming to the first communication protocol. The transceiver(s)21is/are configured to transmit the generated data units via the antenna(s)24. Similarly, the transceiver(s)24is/are configured to receive the data units via the antenna(s)24. The PHY processing unit20of the AP14is configured to process received data units conforming to the first communication protocol, according to an embodiment.

In various embodiments, the PHY processing unit29of the client device25-1is configured to generate data units conforming to the first communication protocol. The transceiver(s)30is/are configured to transmit the generated data units via the antenna(s)34. Similarly, the transceiver(s)30is/are configured to receive data units via the antenna(s)34. The PHY processing unit29of the client device25-1is configured to process received data units conforming to the first communication protocol, according to an embodiment.

FIG. 2is a diagram of a data unit250that the AP14is configured to transmit to the client station25-1, according to an embodiment. In an embodiment, the client station25-1is also configured to transmit the data unit250to the AP14. The data unit250conforms to the VHT protocol and occupies an 80 MHz band. In other embodiments, data units similar to the data unit250occupy different bandwidths such as 20 MHz, 40 MHz, 120 MHz, 160 MHz, or any suitable bandwidth. Additionally, the band need not be contiguous in frequency, but may include two or more smaller bands separated in frequency. For example, according to an embodiment, the data unit250occupies a 160 MHz band composed of two non-contiguous 80 MHz bands separated in frequency by some suitable minimum bandwidth, in some scenarios such as when conditions and devices support a 160 MHz channel. The data unit250includes a preamble having four legacy short training fields (L-STFs)252, four legacy long training fields (L-LTFs)254, four legacy signal fields (L-SIGs)256, four first very high throughput signal fields (VHT-SIGAs)258a very high throughput short training field (VHT-STF)262, N very high throughput long training fields (VHT-LTFs)264, where N is an integer, and a second very high throughput signal field (VHT-SIGB)268. The data unit250also includes a data portion272. The L-STFs252, the L-LTFs254, and the L-SIGs256form a legacy portion. The VHT-STF262, the VHT-SIGAs258, the VHT-LTFs264, the VHT-SIGB268, and the data portion266form a very high throughput (VHT) portion.

In the embodiment ofFIG. 2, each of the L-STFs252, each of the L-LTFs254, each of the L-SIGs256, and each of the VHT-SIGAs258, occupy a 20 MHz band. In the present disclosure, several example data units, including the data unit250, having an 80 MHz contiguous bandwidth are described for the purposes of illustrating embodiments of frame formats, but these frame format embodiments and other embodiments are applicable to other suitable bandwidths (including noncontiguous bandwidths). For instance, although the preamble ofFIG. 2includes four of each of the L-STFs252, the L-LTFs254, the L-SIGs256, and the VHT-SIGAs258, in other embodiments in which the orthogonal frequency division multiplex (OFDM) data unit occupies a cumulative bandwidth other than 80 MHz, such as 20 MHz, 40 MHz, 120 MHz, 160 MHz, etc., a different suitable number of the L-STFs252, the L-LTFs254, the L-SIGs256, and the VHT-SIGAs258is utilized accordingly (e.g., one of each of the L-STFs252, the L-LTFs254, the L-SIGs256, and the VHT-SIGAs258, for an OFDM data unit occupying 20 MHz, two of each of the fields for a 40 MHz bandwidth OFDM data unit, six of each of the fields for a 120 MHz bandwidth OFDM data unit, and eight of each of the fields for a 160 MHz bandwidth OFDM data unit). Also in a 160 MHz bandwidth OFDM data unit, for example, the band is not contiguous in frequency, in some embodiments and situations. Thus, for example, the L-STFs252, the L-LTFs254, the L-SIGs256, and the VHT-SIGAs258occupy two or more bands that are separated from each other in frequency, and adjacent bands are separated in frequency by at least one MHz, at least five MHz, at least 10 MHz, at least 20 MHz, for example, in some embodiments. In the embodiment ofFIG. 2, each of the VHT-STF262, the VHT-LTFs264, the VHT-SIGB268, and the data portion266occupy an 80 MHz band. If the data unit conforming to the first communication protocol is an OFDM data unit that occupies a cumulative bandwidth such as 20 MHz, 40 MHz, 120 MHz, or 160 MHz OFDM, the VHT-STF, VHT-LTFs, VHT-SIGB and VHT data portion occupy the corresponding whole bandwidth of the data unit, according to an embodiment.

Further, according to the embodiment ofFIG. 2in which the device generating the data unit250includes multiple antennas and is capable of transmit beamforming or beamsteering, the VHT-SIGA258is included within an unsteered (or “omnidirectional” or “pseudo-omnidirectional”; the terms “unsteered” and “omnidirectional” as used herein are intended to also encompass the term “pseudo-omnidirectional”) portion of the data unit250and contains PHY information that is common to each of the client stations25inFIG. 1. On the other hand, the VHT-SIGB268is contained in a “steered” portion. In an embodiment in which the data unit250is a multi-user transmission (e.g., the data unit250includes independent data streams for corresponding different receive devices), the steered portion includes different data for different clients25that are simultaneously transmitted, via the antennas24inFIG. 1, over different spatial channels to carry different (or “user-specific”) content to each of the client stations25. Accordingly, in these embodiments the VHT-SIGAs258carry information common to all users, while the VHT-SIGB268includes user-specific information. On the other hand, in an embodiment in which the data unit250is a single-user transmission, the steered portion includes data for a particular client25that are transmitted and beamsteered, via the antennas24, to the client station25.

According to an embodiment, each the VHT-SIGAs258comprises two OFDM symbols that are modulated in a manner similar to the legacy L-SIG fields256. On the other hand, the VHT-SIGB field268comprises a single OFDM symbol that is modulated in a manner similar to the VHT data portion272, according to some embodiments and/or scenarios described below.

FIG. 3is a block diagram of an example PHY processing unit300configured to generate an OFDM symbol, according to an embodiment. For example, in an embodiment and/or scenario, the PHY processing unit300generates an OFDM symbol corresponding to the VHT-SIGB268of the data unit250(FIG. 2). In another embodiment and/or scenario, the PHY processing unit300generates an OFDM symbol corresponding to the data portion272of the data unit250. In other embodiments and/or scenarios, the PHY processing unit300generates an OFDM symbol corresponding to another portion of the data unit250, or an OFDM symbol to be included in another suitable data unit, in other embodiments and/or scenarios. Referring toFIG. 1, the AP14and the client station25-1, in one embodiment, each include a PHY processing unit such as the PHY processing unit300.

According to an embodiment, the PHY unit300includes a forward error correction (FEC) encoder302that generally encodes an input data stream to generate a corresponding encoded stream. In one embodiment, the FEC encoder utilizes binary convolutional coding (BCC) with the coding rate of 1/2. In other embodiments, the FEC encoder utilizes other suitable coding types and/or other suitable coding rates. The FEC encoder302is coupled to a frequency interleaver304that interleaves bits of an encoded stream (i.e., changes the order of the bits) to prevent long sequences of adjacent noisy bits from entering a decoder at the receiver.

A constellation mapper306maps an interleaved sequence of bits to constellation points corresponding to different subcarriers of an OFDM symbol. More specifically, the constellation mapper306translates every log2(M) into one of M constellation points. In one embodiment, the constellation mapper306operates according to a binary phase shift keying (BPSK) modulation scheme. In other embodiments, other suitable modulation schemes are utilized. The constellation mapper306is coupled to a tone duplication and insertion unit308that implements various duplication and insertion techniques described below in various embodiments and/or scenarios.

The output of the tone duplication and insertion unit308is presented to a stream mapper unit312, according to an embodiment. In an embodiment, the stream mapper312spreads the constellation points to a greater number of space-time streams. A pilot generator unit310generates pilot tones to be used, for example, for frequency offset estimation at the receiver, and insets the pilot tones into the symbol OFDM tones at the space-time outputs of the stream mapper312. A plurality of cyclic shift diversity (CSD) units314insert cyclic shifts into all but one of the space-time streams to prevent unintentional beamforming.

A spatial mapping unit316maps the space-time streams to transmit chains corresponding to one or more available transmit antennas. In various embodiments, spatial mapping includes one or more of: 1) direct mapping, in which constellation points from each space-time stream are mapped directly onto transmit chains (i.e., one-to-one mapping); 2) spatial expansion, in which vectors of constellation point from all space-time streams are expanded via matrix multiplication to produce inputs to the transmit chains; and 3) beamforming, in which each vector of constellation points from all of the space-time streams is multiplied by a matrix of steering vectors to produce inputs to the transmit chains.

In one embodiment, the spatial mapping unit316applies a steering matrix Q (e.g., multiplies an NSTS×1 signal vector s by Q, i.e., Qs), where Q has a size of (NTX×NSTS), where NTXis the number of transmit chains and NSTSis the number of space-time streams. When beamforming is utilized, the matrix Q is generated based on the multiple input multiple output (MIMO) channel between the transmitter and the receiver. In one embodiment, NTXhas a maximum value of 8. In another embodiment, NTXhas a maximum value of 16. In other embodiments, NTXhas a different maximum value such as 4, 32, 64, etc.

Each output of the spatial mapping unit316corresponds to a transmit chain, and each output of the spatial mapping unit316is operated on by an inverse discrete Fourier transform (IDFT) unit318that converts a block of constellation points to a time-domain signal. In an embodiment, the IDFT unit318is configured to implement an inverse fast Fourier transform (IFFT) algorithm. Each time-domain signal is provided to a transmit antenna for transmission.

The number of sub-carriers (or tones) in an OFDM symbol generally depends on the bandwidth (BW) of the channel being utilized, according to an embodiment. For example, an OFDM symbol for a 20 MHz channel corresponds to a size 64 IDFT and includes 64 tones, whereas an OFDM symbol for a 40 MHz channel corresponds to a size 128 IDFT and includes 128 tones, according to an embodiment. In an embodiment, the tones in an OFDM symbol include guard tones for filter ramp up and ramp down, DC tones for mitigating radio frequency interference, and pilot tones for frequency offset estimation. The remaining tones can be used to transmit data or information bits (“data tones”), according to an embodiment. General transmitter flow of an example PHY processing unit configured to generate data units conforming to the first communication protocol as well as various example transmission channels and tone mappings that are utilized in the data units corresponding to some embodiments of the present disclosure are described in U.S. patent application Ser. No. 12/846,681, entitled “Methods and Apparatus for WLAN Transmission”, filed on Jul. 29, 2010, which is hereby incorporated by reference herein in its entirety.

In an embodiment, tone and/or bit allocation for an OFDM symbol in a data unit is the same regardless of the channel bandwidth occupied by the data unit. For example, OFDM symbols are generated according to a format defined for a “base” bandwidth, such as the smallest channel bandwidth defined by the communication protocol, and tone duplications and insertion techniques described herein are used to generate OFDM symbols corresponding to wider channel bandwidths. For example, a 20 MHz channel bandwidth is used as the base bandwidth, in an embodiment. In this embodiment, OFDM symbols are generated according to tone and/or bit allocation defined for a 20 MHz channel bandwidth, and tone duplication and insertions techniques described herein are utilized to generate OFDM symbols corresponding to higher bandwidth channels, such as a 40 MHz channel, an 80 MHz channel, etc. In another embodiments, a 40 MHZ bandwidth is used as the base bandwidth, and higher bandwidth OFDM symbols are generated using tone duplication and insertion techniques described herein. In other embodiments, other suitable base bandwidths are utilized.

Generally speaking, any suitable bandwidth corresponding to an IDFT of size N can be utilized as a base bandwidth, and tone duplication and insertion techniques described herein can be used to generate an OFDM symbol corresponding to an IDFT of larger size, such as a kN-point IDFT, based on tone and/or bit allocation defined for the N-point IDFT, where N and k are integers, in various embodiments and/or scenarios. It should be noted that while tone duplication and insertion techniques are described below as generally performed to generate a wider bandwidth signal field based on tone and/or bit allocation defined for a lower bandwidth signal field, such techniques are not limited to OFDM symbols corresponding to signal fields and are applied to OFDM symbols corresponding to other field (e.g., training fields, data field) of an OFDM data unit, in other embodiments.

As an example, referring again toFIG. 2, the bit allocation for the VHT-SIGB field268of the data unit250is the same regardless of the channel bandwidth occupied by the particular data unit being generated, according to an embodiment. Also, in some embodiments, the same number of guard tones, DC tones, and pilot tones are used in an OFDM symbol generated for the VHT-SIGB268as in a symbol generated for the data portion of the data unit250. In one such embodiment, the guard tones, the DC tones, and the pilot tones are the same frequency tones within an OFDM symbol generated for the VHT-SIGB field268as in an OFDM symbol generated for the data portion272.

In an embodiment, VHT-SIGB field268bit allocation corresponds to a 20 MHz OFDM symbol with the corresponding number of data tones, and the same bit allocation is utilized for data units corresponding to larger bandwidths (e.g., 40 MHz, 80 MHz, etc.). In one such embodiment, 26 bits are allocated for the VHT-SIGB field, with 20 bits allocated for information bits and 6 bits allocated for tail bits, for example. In an embodiment in which VHT-SIGB field268is encoded with a BCC encoder at ½ coding rate, the 26 bits are encoded into 52 data bits corresponding to the 52 data tones available for a 20 MHz channel. In other embodiments, other suitable bit allocations and other suitable coding and modulation schemes are used for the VHT-SIGB field268. In various embodiments and/or scenarios in which the same number of bits is allocated for larger bandwidth channels with a corresponding larger number of data tones, tone duplication and insertion techniques described herein are utilized to fill the remaining available data tones.

FIG. 4is a diagram of an OFDM symbol400generated for a VHT-SIGB field (such as VHT-SIGB field268ofFIG. 2) of a data unit for a 40 MHz channel, according to an embodiment. The OFDM symbol400corresponds to a size 128 IDFT and includes 128 tones. The 128 tone slots are indexed from −64 to +63, in an embodiment. The 128 tones include guard tones, a direct current (DC) tones, data tones, and pilot tones. The six lowest frequency tones and the five highest frequency tones are guard tones. The three tones indexed from −1 to +1 are DC tones. The OFDM symbol400also includes 6 pilot tones and 108 data tones, according to an embodiment. As illustrated inFIG. 4, the 108 data tones include 52 tones corresponding to the VHT-SIGB bits with 2 inserted tones, and the resulting 54 tones are duplicated once in order to fill the remaining tones of the OFDM symbol. In the OFDM symbol400, the two inserted tones occupy the lowest data/pilot frequency tone slots in the lower channel sideband and the two lowest data/pilot frequency tone slots in the upper channel sideband.

FIG. 5is a diagram of another example OFDM symbol500generated for a VHT-SIGB field (such as VHT-SIGB field268ofFIG. 2) of a data unit for a 40 MHz channel, according to another embodiment. The OFDM symbol500is similar to the OFDM symbol400except that the insertion tones in the OFDM symbol500occupy the two lowest data/pilot frequency tone slots in the lower channel sideband and the two highest data/pilot frequency tone slots in the upper channel sideband.

In other embodiments, the two insertion tones occupy any other suitable data/pilot frequency tone slots in the OFDM symbol400or the OFDM symbol500.

FIG. 6is a diagram of an OFDM symbol600generated for a VHT-SIGB field (such as VHT-SIGB field268ofFIG. 2) of a data unit for an 80 MHz channel, according to an embodiment. The OFDM symbol600corresponds to a size 256 IDFT and includes 256 tones. The 256 tone slots are indexed from −128 to +127, in an embodiment. The 256 tones include guard tones, DC tones, data tones, and pilot tones. The six lowest frequency tones and the five highest frequency tones are guard tones. The three tones indexed from −1 to +1 are DC tones. The OFDM symbol350also includes 8 pilot tones and 234 data tones. The 234 data tones include 52 tones corresponding to the VHT-SIGB information bits, 52 tones that are duplicates of the VHT-SIGB information bits and 13 inserted tones, and the resulting 117 tones duplicated once. In the OFDM symbol600, the thirteen inserted tones occupy the lowest frequency pilot/data tone slots in the lower channel sideband and the lowest frequency pilot/data tone slots in the upper channel sideband.

FIG. 7is a diagram of another OFDM symbol700(such as VHT-SIGB field268ofFIG. 2) generated for a VHT-SIGB field of a data unit for an 80 MHz channel, according to another embodiment. The OFDM symbol700is similar to the OFDM symbol600except that the insertion tones in the OFDM symbol700occupy the thirteen lowest frequency data/pilot tone slots in the lower channel sideband and the highest frequency data/pilot tone slots in the upper channel sideband.

In other embodiments, the thirteen insertion tones occupy other suitable data/pilot tone slots in the OFDM symbol600or the OFDM symbol700.

According to an embodiment or a situation, the insertion tones in symbol400, the insertion tones in the symbol500, the insertion tones in the symbol600, and/or the insertion tones in the symbol700carry values of some of the VHT-SIGB information bits and/or VHT-SIGA information bits. Similarly, in some other embodiments and/or situations, the insertion tones in symbol400, the insertion tones in the symbol500, the insertion tones in the symbol600, and/or the insertion tones in the symbol700carry values of some of the LSIG information bits. Alternatively, in other embodiments and/or situations, the insertion tones in symbol400, the insertion tones in the symbol500, the insertion tones in the symbol600, and/or the insertion tones in the symbol700are null (0) tones. These embodiments have an advantage of using no extra transmit power for transmitting the insertion tones (i.e., all of the transmit power is used for the VHT-SIGB information and tail bits). In other embodiment and/or scenarios, the insertion tones in symbol400, the insertion tones in the symbol500, the insertion tones in the symbol600, the insertion tones in the symbol700tones are modulated with any other suitable values.

In other embodiments and/or scenarios, the insertion tones in symbol400, the insertion tones in the symbol500, the insertion tones in the symbol600, and/or the insertion tones in the symbol700are modulated with any other suitable values.

In an embodiment, the client station25-1inFIG. 1discards the inserted tones in a VHT-SIGB field of a received data unit during the decoding and demodulation process. Alternatively, if the inserted tones are of values corresponding to some information bits of a signal field (e.g., VHT-SIGA, VHT-SIGB, L-SIG), the receiver utilizes the extra diversity provided thereby during the decoding and demodulating process rather than simply discarding the inserted tones, according to an embodiment.

In some embodiments, an 80 MHz signal field is generated using tone and/or bit allocation for a 40 MHz bandwidth as the base bandwidth. For example, an 80 MHz VHT-SIGB field is generated using tone and/or bit allocation defined for a 40 MHz VHT-SIGB field, using tone duplication and insertion techniques described herein to fill the remaining data tones in the 80 MHz VHT-SIGB field, in an embodiment. Similarly, a 160 MHZ signal field is generated using tone and/or bit allocation for an 80 MHz signal field, using tone duplication and insertion techniques described herein to fill the remaining data tones of the 160 MHz field, in an embodiment. In another embodiment, a 160 MHz MHz field is generated using tone and/or bit allocation for a 40 MHz bandwidth signal field, using tone insertion and duplication techniques described herein. Generally speaking, a base bandwidths B is utilized to generate an OFDM symbol for a mB bandwidth communication channel, where m is an integer, in various embodiments and/or scenarios.

In an embodiment, a field corresponding to a 20 MHz or another suitable bandwidth is utilized to generate a larger base bandwidth, such as a 40 MHz base bandwidth. For example, one or more uncoded bits are inserted into a bit stream corresponding to a 20 MHz bandwidth channel or another suitable bandwidth channel such that, after encoding, the encoded bit stream corresponds to a larger bandwidth, such as a 40 MHz bandwidth. Then, tone duplication and insertion techniques are applied to the base bandwidth to generate OFDM symbols for higher bandwidth channels. For example, referring toFIG. 3, duplication of uncoded information bits is utilized and, if needed, one or more additional bits are added to the uncoded information bit stream (e.g., before duplication of the bits or after duplication of the bits occurs) prior to providing the bit stream to the encoder302, such that, after being encoded by the encoder302, the resulting bit stream (coded bits) corresponds to a wider base bandwidth, such as a 40 MHz base bandwidth. In this embodiment, the coded bits are then provided to the constellation mapping unit306, which maps the coded bits to constellation points corresponding to OFDM tones of the base bandwidth, such as a 40 MHz bandwidth. Then, tone duplication and insertion unit308duplicates the resulting OFDM tones and/or inserts additional OFDM tones to generate a wider bandwidth OFDM symbol, such as an 80 MHz OFDM symbol or a 160 MHz OFDM symbol, for example, in an embodiment.

As discussed above, in some embodiments, the AP14 is configured to communicate with one or more client stations according to a long range communication protocol which generally defines operation in sub 1 GHz frequency ranges. In some such embodiments, the long range communication protocol defines one or more physical layer data unit formats the same as or similar to physical layer data unit format defined by one or more of the short range communication protocols. In one embodiment, to support communication over a longer range, and also to accommodate typically smaller bandwidth channels available at lower (sub 1-GHz) frequencies, the long range communication protocol defines data units having a format that is substantially the same as a physical layer data unit format defined by a long range communication protocol, but generated using a lower clock rate. In an embodiment, the AP operates at a clock rate suitable for short range (and high throughput) operation, and down-clocking is used to generate a new clock signal to be used for the sub 1 GHz operation. As a result, in this embodiment, a data unit that conforms to the long rage communication protocol (“long range data unit”) maintains a physical layer format of a data unit that generally conforms to a short range communication protocol (“short range data unit”), but is transmitted over a longer period of time. As an example, data units that conform to the IEEE 802.11ah Standard are generated according to a format defined in the IEEE 802-11n Standard or IEEE 802-11ac Standard, but generated using a clock signal down-clocked by a ratio of ten. In this embodiment, short range data units generally correspond to channel bandwidths described above (e.g., 20 MHz, 40 MHz, 80 MHz, 160 MHz), and long range data units have corresponding bandwidths down-clocked with the down-clocking ratio of 10 (e.g., 2 MHz, 4 MHz, 8 MHz, 16 MHz).

In other embodiments, other suitable down-clocking ratios are utilized. For example, data units according to the IEEE 802.11 of are down-clocked versions of the IEEE 802.11n or IEEE 802.11ac data units with the down-clocking ration of 7.5, in an embodiment. Additionally, in some embodiments, the long range communication protocol defines one or more additional bandwidth channels, such as a 1 MHz bandwidth channel, intended for operations requiring higher signal to noise ration performance, such as extended range or control mode operations, for example. Various examples of long range data units generated by down-clocking as well as example PHY formats of long range data units utilized in some embodiments are described in U.S. patent application Ser. No. 13/359,336, filed Jan. 26, 2012, which is hereby incorporated by reference herein in its entirety.

In some such embodiments, a lowest down-clocked channel bandwidth is utilized as the base bandwidth, and tone duplication and insertion techniques described herein are used to generate OFDM symbols corresponding to higher channel bandwidths. For example, tone and/or bit allocation defined for OFDM symbols corresponding to a 1 MHz base bandwidth or a 2 MHz base bandwidth is utilized to generate OFDM symbols corresponding to higher bandwidths, and tone duplication and insertion techniques described herein are utilized to generate OFDM symbols for higher bandwidth channels (e.g., 2 MHz, 4 MHz, 8 MHz, 16 MHz). As an example, referring toFIGS. 4 and 5, the depicted OFDM symbols400and500correspond to a 4 MHz bandwidth of the long range communication protocol generated using tone allocation defined for a 2 MHz bandwidth channel, according to various embodiments. As another example, referring toFIGS. 6 and 7, the depicted OFDM symbols600and700correspond to an 8 MHz bandwidth of the long range communication protocol generated using tone allocation defined for a 2 MHz bandwidth channel, in various embodiments. In another embodiment, tone and/or bit allocation for another suitable base bandwidth, such as 4 MHz bandwidth, is utilized, and tone duplication and insertion techniques described herein are used to generate OFDM symbols corresponding to a higher bandwidth channel, such as an 8 MHz channel or a 16 MHz channel. Generally speaking, a base bandwidths B is utilized to generate an OFDM symbol for a mB bandwidth communication channel, where m is an integer, in various embodiments and/or scenarios.

Referring again toFIG. 2, in embodiments in which the data portion272includes multiple spatial streams, the VHT-SIGB field268is mapped to the multiple streams accordingly. In some such embodiments, the VHT-STF fields264that contain training sequences corresponding to the multiple spatial streams are mapped to multiple spatial streams via a matrix P. In some embodiments and/or scenarios, the same matrix P is used to map a single data stream in the VHT-SIGB field268to multiple data streams corresponding to multiple spatial streams in the VHT-data portion272. More specifically, in an embodiment, the VHT-LTF training fields264are mapped to the corresponding spatial streams according to:
VHTLTF(k)=[L1,L2, . . . LNLTF]=Q(k)D(k)[P*1,P*2, . . . P*NLTF]s(k)Equation 1
where Q(k)corresponds to spatial mapping of the kthtone of a VHT-LTF training field, D(k)corresponds to a CSD phase shift for the kthtone, P*1, . . . , P*NLTFare columns of the mapping matrix P, and S(k)is the kthtone of a VHT-LTF training symbol.

Referring still toFIG. 2, according to an embodiment, the VHT-SIGB field268is mapped to multiple spatial streams of the data unit250using one of the columns P*1, . . . , P*NLTFof Equation 1. For example, in an embodiment, the first column of the P matrix is used to map the VHT-SIGB field268:
VHTSIGB(k)=Q(k)D(k)P*1sVHTSIGB(k)Equation 2
where SVHTSIGB—U1(k)is the kthtone of the VHT-SIGB symbol. In other embodiments and/or scenarios, a different column of the P matrix is used to map the VHT-SIGB field268.

In some embodiments, the data unit250is a multiuser (MU) data unit, i.e., the data unit250includes user-specific information for more than one user (e.g., more than one of the client stations25inFIG. 1). For example, the data unit250includes use-specific information for two users (i.e., the data unit250is a “two-user” data unit), according to an embodiment. The data unit250includes data for different numbers of users (e.g., 3 users, 4 users, 5 users, etc.) in other embodiments and/or scenarios. In some such embodiments, the number of VHT-LTF fields264is directly related to the sum of spatial streams for all intended recipients of the data unit (users), and a single “giant” mapping matrix P is used to jointly map the training information tones for all users and all spatial streams. For example, if the data unit250is a two-user data unit, the VHT-LTF fields268are mapped, in an embodiment, according to:

With continued reference toFIG. 2, according to an embodiment in which the data unit250is a two-user data unit, the VHT-SIGB field268is, therefore, steered to the two users (assuming that each user does not see interference from the other user). In this case, the single stream of the VHT-SIGB filed268is mapped to multiple spatial streams and the multiple users using any column P(U1)—*1, . . . , P(U1)—*NLTFor P(U2)—*1, . . . , P(U2)—*NLTFof Equation 3. For example, in an embodiment, the first column of the joint P matrix is used to map the VHT-SIGB field268for user1according to:
VHTSIGBU1(k)=QU1(k)DU1(k)P(U1)—*1sVHTSIGB—U1(k)Equation 4
where SVHTSIGB—U1(k)is the VHT-SIGB symbol kthtone for user1. In other embodiments, other columns of the joint P matrix are used to steer the VHT-SIGB field268to the intended user via the multiple data streams.

FIG. 8is a flow diagram of an example method800for generating and transmitting a PHY data unit having a signal field, such as a VHT-SIGB or another suitable field, according to an embodiment. The method800is implemented at least partially by a PHY processing unit such as the PHY processing unit20(FIG. 1), the PHY processing unit29(FIG. 1), and/or the PHY processing unit300(FIG. 3), andFIG. 8will be described with reference toFIG. 3for ease of explanation. In other embodiments, however, another suitable PHY processing unit and/or network interface implements the method800.

At block804, a signal field of a preamble of a PHY data unit is generated. In an embodiment, the VHT-SIGB field is generated. In another embodiment, another suitable signal field is generated.

At block808, the signal field generated at block804is mapped to a first plurality of data subcarriers corresponding to a first frequency portion of an OFDM symbol. For example, the BPSK constellation mapping block306maps the signal field to a first plurality of data subcarriers corresponding to a first frequency portion of an OFDM symbol. In another embodiment, another suitable processing block of a network interface implements block808.

At block812, a set of data subcarriers in the first plurality of data subcarriers are set to predetermined values. For example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “+1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “−1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to a null value. In an embodiment, the block812is implemented by the tone duplications and insertions block308inFIG. 3. In another embodiment, another suitable processing block of a network interface implements block812.

At block816, the signal field generated at block804is mapped to a second plurality of data subcarriers corresponding to a second frequency portion of the OFDM symbol. For example, the tone duplications and insertions block308inFIG. 3maps the signal field to a second plurality of data subcarriers corresponding to the second frequency portion of the OFDM symbol. In another embodiment, another suitable processing block of a network interface implements block816.

At block820, a set of data subcarriers in the second plurality of data subcarriers are set to predetermined values. For example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “+1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “−1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to a null value. In an embodiment, the block820is implemented by the tone duplications and insertions block308inFIG. 3. In another embodiment, another suitable processing block of a network interface implements block820.

At block824, guard tones, DC tones, and/or pilot tones in the first frequency portion and the second frequency portion are set. In an embodiment, the block824is implemented at least partially by the VHT pilots generation block310. In another embodiment, another suitable processing block of a network interface implements block824.

At block828, the PHY data unit is transmitted. For example, in an embodiment, a PHY processing unit that implements the method800at least partially causes the PHY data unit to be transmitted.

FIG. 9is a flow diagram of another example method900for generating and transmitting a PHY data unit having a signal field, such as a VHT-SIGB or another suitable field, according to an embodiment. The method900is implemented at least partially by a PHY processing unit such as the PHY processing unit20(FIG. 1), the PHY processing unit29(FIG. 1), and/or the PHY processing unit300(FIG. 3), andFIG. 9will be described with reference toFIG. 3for ease of explanation. In other embodiments, however, another suitable PHY processing unit and/or network interface implements the method900.

At block904, a plurality of training fields are generated. For example, in an embodiment, a plurality of VHT-LTF fields are generated, in an embodiment. At block908, the training fields are mapped to signal streams using a mapping matrix. In an embodiment, the mapping matrix comprises the matrix P discussed above. In other embodiments, other suitable mapping matrices are utilized. In an embodiment, the block908is implemented by the mapping block312. In other embodiments, however, another suitable block of a PHY processing unit and/or a network interface implements block908.

At block912, a signal field of a preamble of a PHY data unit is generated. In an embodiment, the VHT-SIGB field is generated. In another embodiment, another suitable signal field is generated. At block916, the signal field is mapped to a plurality of signal streams using a column of the mapping matrix utilized at block908. In an embodiment, a column of the matrix P discussed above is utilized. In other embodiments, a column of another suitable mapping matrix is utilized. In an embodiment, the first column of the matrix P is utilized. In other embodiments, a column other than the first column of the matrix P is utilized.

At block920, the signal streams are mapped to spatial streams. In an embodiment, the signal streams are mapped to spatial streams using the matrix Q discussed above. In other embodiments, other suitable matrices are utilized. In an embodiment, the block920is implemented by the spatial mapping block316. In other embodiments, however, another suitable block of a PHY processing unit and/or a network interface implements block920.

At block924, the PHY data unit is transmitted. For example, in an embodiment, a PHY processing unit that implements the method900at least partially causes the PHY data unit to be transmitted. Block924includes transmitting (or causing to be transmitted) at least i) the plurality of training fields, and ii) the signal field, via the plurality of spatial streams.

FIG. 10is a flow diagram of another example method950for generating and transmitting a multi-user PHY data unit having a signal field, such as a VHT-SIGB or another suitable field, according to an embodiment. The method950is implemented at least partially by a PHY processing unit such as the PHY processing unit20(FIG. 1), the PHY processing unit29(FIG. 1), and/or the PHY processing unit300(FIG. 3), andFIG. 10will be described with reference toFIG. 3for ease of explanation. In other embodiments, however, another suitable PHY processing unit and/or network interface implements the method950.

At block954, a plurality of training fields are generated for a multi-user PHY data unit. For example, in an embodiment, a plurality of VHT-LTF fields are generated. At block958, the training fields are mapped to signal streams using a mapping matrix. In an embodiment, the mapping matrix comprises the giant matrix P discussed above. In other embodiments, other suitable mapping matrices are utilized. In an embodiment, the block958is implemented by the mapping block312. In other embodiments, however, another suitable block of a PHY processing unit and/or a network interface implements block958.

At block962, a first signal field of a preamble of the multi-user PHY data unit is generated, wherein the first signal field corresponds to a first client device. In an embodiment, the VHT-SIGB field is generated. In another embodiment, another suitable signal field is generated. At block966, the first signal field is mapped to a plurality of signal streams using a portion of a column of the mapping matrix utilized at block958, wherein the portion corresponds to the first client device. In an embodiment, a portion of a column of the giant matrix P discussed above is utilized, wherein the portion corresponds to the first client device. In other embodiments, a portion of a column of another suitable mapping matrix is utilized. In an embodiment, a portion of the first column of the giant matrix P is utilized. In other embodiments, a portion of a column other than the first column of the giant matrix P is utilized.

At block970, a second signal field of a preamble of the multi-user PHY data unit is generated, wherein the second signal field corresponds to a second client device. In an embodiment, the VHT-SIGB field is generated. In another embodiment, another suitable signal field is generated. At block974, the second signal field is mapped to a plurality of signal streams using a portion of the column of the mapping matrix utilized at block958, wherein the portion corresponds to the second client device. In an embodiment, a portion of a column of the giant matrix P discussed above is utilized, wherein the portion corresponds to the second client device. In other embodiments, a portion of a column of another suitable mapping matrix is utilized. In an embodiment, a portion of the first column of the giant matrix P is utilized. In other embodiments, a portion of a column other than the first column of the giant matrix P is utilized. In an embodiment, the same column is utilized in blocks966and974.

At block978, the signal streams are mapped to spatial streams. In an embodiment, the signal streams are mapped to spatial streams using a matrix Q as discussed above. In other embodiments, other suitable matrices are utilized. In an embodiment, the block978is implemented by the spatial mapping block316. In other embodiments, however, another suitable block of a PHY processing unit and/or a network interface implements block978.

At block982, the multi-user PHY data unit is transmitted. For example, in an embodiment, a PHY processing unit that implements the method950at least partially causes the PHY data unit to be transmitted. Block982includes transmitting (or causing to be transmitted) at least i) the plurality of training fields, ii) the first signal field, and iii) the second signal field via the plurality of spatial streams.

FIG. 11is a flow diagram of an example method1000for generating an OFDM symbol of a PHY data unit, according to an embodiment. The method1000is implemented at least partially by a PHY processing unit such as the PHY processing unit20(FIG. 1), the PHY processing unit29(FIG. 1), and/or the PHY processing unit300(FIG. 3), in some embodiments. In other embodiments, other suitable PHY processing units and/or other suitable network interfaces implement the method1000.

At block1002, a plurality of information bits is encoded to generate a plurality of coded information bits to be included in an OFDM symbol. The plurality of information bits corresponds to a first bandwidth, and the OFDM symbol includes a number of data subcarriers corresponding to a second bandwidth, the second bandwidth being larger than the first bandwidth. For example, the plurality of information bits corresponds to a base channel bandwidth B, such as a 1 MHz bandwidth, a 2 MHz bandwith, a 4 MHz bandwidth, a 20 MHz bandwidth, a 40 MHz bandwidth, or another suitable base channel bandwidth, and the OFDM symbol includes a number of data tones corresponding to a channel bandwidth that is larger than the base bandwidth, for example an mB bandwidth channel, where m is a suitable integer greater than one, in various embodiments and/or scenarios.

At block1004, the plurality of coded bits is mapped to a plurality of constellation symbols. At block1006, the plurality of constellation symbols is mapped to a first plurality of data subcarriers corresponding to a first frequency portion of an OFDM symbol.

At block1008, a set of one or more data subcarriers in the first plurality of data subcarriers are set to predetermined values. For example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “+1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “−1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to a null value. In an embodiment, the block1006is implemented by the tone duplications and insertions block308inFIG. 3. In another embodiment, another suitable processing block of a network interface implements block1006.

At block1010, the plurality of constellation symbols is mapped to a second plurality of data subcarriers corresponding to a second frequency portion of the OFDM symbol. For example, the tone duplications and insertions block308inFIG. 3maps the signal field to a second plurality of data subcarriers corresponding to the second frequency portion of the OFDM symbol. In another embodiment, another suitable processing block of a network interface implements block1010.

At block1012, a set of one or more data subcarriers in the second plurality of data subcarriers are set to predetermined values. For example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “+1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to “−1” value or some other suitable value. As another example, in an embodiment, at least some of the subcarriers in the set of subcarriers are set to a null value. In an embodiment, the block1012is implemented by the tone duplications and insertions block308inFIG. 3. In another embodiment, another suitable processing block of a network interface implements block1012.

At block1014, the OFDM symbol is generated to include at least the first plurality of data subcarrers and the second plurality of data subcarriers. In an embodiment, the OFDM symbol is generated to further include one or more of (i) guard tones, (ii) DC tones, and (iii) pilot tones. In an embodiment, the OFDM symbol conforms to a format defined by a short range communication protocol, such as the IEEE 802.11n Standard or the IEEE 802.11ac Standard, for example. In another embodiment, the OFDM symbol conforms to a communication protocol, such as the IEEE 802.11ah Standard or the IEEE 802.11af Standard, and is a down-clocked version (e.g., with same tone and/or bit allocation) of an OFDM symbol that conforms to a short range communication protocol. In other embodiments, the OFDM symbol conforms to one or more other suitable communication protocols.

In an embodiment, the OFDM symbol is to be included in a preamble of a data unit. For example, the OFDM symbol corresponds to a signal field or a training field to be included in the preamble, in some embodiments and/or scenarios. In other embodiments and/or scenarios, the OFDM symbol is to be included in a data portion of a data unit.

At least some of the various blocks, operations, and techniques described above may be implemented utilizing hardware, a processor executing firmware instructions, a processor executing software instructions, or any combination thereof. When implemented utilizing a processor executing software or firmware instructions, the software or firmware instructions may be stored in any tangible, non-transitory, computer readable storage medium or media such as a magnetic disk, an optical disk, a RAM, a ROM, a flash memory, hard disk drive, optical disk drive, tape drive, etc. 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.

According to a first embodiment, a method of generating an orthogonal frequency division multiplexing (OFDM) symbol of a data unit to be transmitted via a communication channel includes encoding a plurality of information bits to generate a plurality of coded bits to be included in the OFDM symbol, wherein the plurality of information bits corresponds to a first bandwidth, and wherein the OFDM symbol includes a number of data tones corresponding to a second bandwidth, the second bandwidth larger than the first bandwidth. The method also includes mapping the plurality of coded bits to a plurality constellation symbols and mapping the plurality of constellation symbols to a first plurality of data subcarriers corresponding to a first portion of the OFDM symbol. The method further includes setting a subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values. The method further still includes mapping the plurality of constellation symbols to a second plurality of data subcarriers corresponding to a second portion of the OFDM symbol, and setting a subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values. The method additionally includes generating the OFDM symbol to include at least the first plurality of data subcarriers and the second plurality of data subcarriers.

In other embodiments, the method includes any combination of one or more of the following features.

Setting the subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the first plurality of data subcarriers to a null value.

Setting the subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the second plurality of data subcarriers to the null value.

Setting the subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the first plurality of data subcarriers to a non-zero value.

Setting the subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the second plurality of data subcarriers to the non-zero value.

The method further comprises mapping the plurality of constellation symbols to a third plurality of data subcarriers corresponding to a third portion of the OFDM symbol, setting a subset of data subcarriers in the third plurality of data subcarriers to one or more predetermined values.

Generating the OFDM symbol further comprises including the third plurality of data subcarriers in the OFDM symbol.

The method further comprises generating a preamble of a physical layer (PHY) data unit, wherein the preamble includes the OFDM symbol.

The method further comprises generating a data portion of a physical layer (PHY) data unit, wherein the data portion includes the OFDM symbol.

The method further comprises (i) inserting one or more additional bits into the plurality of information bits and (ii) duplicating the plurality of information bits and the additional bits, prior to encoding the information bits, to generate a plurality of duplicated bits, wherein encoding the information bits comprises encoding the plurality of duplicated bits.

The first bandwidth corresponds to a bandwidth B and the second bandwidth corresponds to a bandwidth mB, wherein m is an integer.

In another embodiment, an apparatus comprises a network interface configured to encode a plurality of information bits to generate a plurality of coded bits to be included in an OFDM symbol, wherein the plurality of information bits corresponds to a first bandwidth, and wherein the OFDM symbol includes a number of data tones corresponding to a second bandwidth, the second bandwidth larger than the first bandwidth. The network interface is also configured to map the plurality of coded bits to a plurality constellation symbols, and map the plurality of constellation symbols to a first plurality of data subcarriers corresponding to a first portion of the OFDM symbol. The network interface is also configured to set a subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values. The network interface is further still configured to map the plurality of constellation symbols to a second plurality of data subcarriers corresponding to a second portion of the OFDM symbol, and set a subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values. The network interface is additionally configured to generate the OFDM symbol to include at least the data subcarriers corresponding to the first potion and the data subcarriers corresponding to the second portion.

In other embodiment, the apparatus includes any combination of one or more of the following features.

The network interface is further configured to include, in the OFDM symbol, one or more of (i) guard tones, (ii) direct current (DC) tones and (iii) pilot tones.

Setting the subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the first plurality of data subcarriers to a null value.

Setting the subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the second plurality of data subcarriers to the null value.

Setting the subset of data subcarriers in the first plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the first plurality of data subcarriers to a non-zero value.

Setting the subset of data subcarriers in the second plurality of data subcarriers to one or more predetermined values comprises setting at least one data subcarrier in the subset of data subcarriers in the second plurality of data subcarriers to the non-zero value.

The network interface is further configured to map the plurality of constellation symbols to a third plurality of data subcarriers corresponding to a third portion of the OFDM symbol, map a subset of data subcarriers in the third plurality of data subcarriers to one or more predetermined values; and generate the OFDM symbol to further include the third plurality of data subcarriers.

The network interface is further configured to generate a preamble of a physical layer (PHY) data unit, wherein the preamble includes the OFDM symbol.

The network interface is further configured to generate a data portion of a physical layer (PHY) data unit, wherein the data portion includes the OFDM symbol.

The network interface is further configured to insert one or more additional bits into the plurality of information bits; and duplicate the plurality of information bits and the additional bits, prior to encoding the information bits, to generate a plurality of duplicated bits, wherein encoding the information bits comprises encoding the plurality of duplicated bits.

The first bandwidth corresponds to a bandwidth B and the second bandwidth corresponds to a bandwidth mB, wherein m is an integer.