Patent Publication Number: US-2023163884-A1

Title: Wifi multi-band communication

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 17/214,430 (now U.S. Pat. No. 11,563,525), entitled “WIFI MULTI-BAND COMMUNICATION,” filed Mar. 26, 2021, which is a continuation of U.S. patent application Ser. No. 16/399,517 (now U.S. Pat. No. 10,966,227), entitled “WIFI MULTI-BAND COMMUNICATION,” filed Apr. 30, 2019, which claims the benefit of U.S. Provisional Patent Application No. 62/791,519, entitled “FREQUENCY DIVISION DUPLEX (FDD) OVER CHANNEL AGGREGATION” filed on Jan. 11, 2019. All of the applications identified above are hereby incorporated herein by reference in their entireties. 
     This application is also related to U.S. patent application Ser. No. 16/162,113 (now U.S. Pat. No. 10,805,051), entitled “WiFi Channel Aggregation,” filed on Oct. 16, 2018, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF TECHNOLOGY 
     The present disclosure relates generally to wireless communication systems, and more particularly to data transmission and reception over multiple communication channels. 
     BACKGROUND 
     Wireless local area networks (WLANs) have evolved rapidly over the past two decades, and development of WLAN standards such as the Institute for Electrical and Electronics Engineers (IEEE) 802.11 Standard family 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, the IEEE 802.11n Standard specifies a single-user peak throughput of 600 Mbps, and the IEEE 802.11ac Standard specifies a single-user peak throughput in the gigabits per second (Gbps) range. The IEEE 802.11ax Standard now under development significantly improves throughput over the IEEE 802.11ac Standard. 
     SUMMARY 
     In an embodiment, a method for duplex communication in a wireless local area network (WLAN) includes: generating, at a first communication device, a first packet; transmitting, by the first communication device, the first packet via a first WLAN communication channel having a first radio frequency (RF) bandwidth; generating, at the first communication device, a second packet; after transmitting the first packet, transmitting, by the first communication device, the second packet via the first WLAN communication channel; and receiving, at the first communication device, a transmission from one or more second communication devices that overlaps in time with transmission of the second packet, the transmission from the one or more second communication devices being received via a second WLAN communication channel having a second RF bandwidth. 
     In another embodiment, a first communication device configured to operate in a WLAN comprises: a wireless network interface device that includes one or more integrated circuit (IC) devices, a first RF radio implemented at least partially on the one or more IC devices, and a second RF radio implemented at least partially on the one or more IC devices. The one or more IC devices are configured to: generate a first packet; control the first RF radio to transmit the first packet via a first WLAN communication channel having a first RF bandwidth; generate a second packet; after transmitting the first packet, control the first RF radio to transmit the second packet via the first WLAN communication channel; and receive, via the second RF radio, a transmission from one or more second communication devices that overlaps in time with transmission of the second packet, the transmission from the one or more second communication devices being received via a second WLAN communication channel having a second RF bandwidth. 
     In yet another embodiment, a method for duplex communication in a WLAN includes: receiving, at a first communication device, a first packet via a first WLAN communication channel having a first RF bandwidth; after receiving the first packet, receiving, at the first communication device, a second packet via the first WLAN communication channel; generating, at the first communication device, a third packet; and transmitting, by the first communication device, the third packet via a second WLAN communication channel having a second RF bandwidth, wherein transmission of the third packet overlaps in time with reception of the second packet. 
     In still another embodiment, a first communication device configured to operate in a WLAN comprises: a wireless network interface device that includes one or more IC devices, a first RF radio implemented at least partially on the one or more IC devices, and a second RF radio implemented at least partially on the one or more IC devices. The one or more IC devices are configured to: receive, via the first RF radio, a first packet via a first WLAN communication channel having a first RF bandwidth; after receiving the first packet, receive, via the first RF radio, a second packet via the first WLAN communication channel; generate a third packet; and control the second RF radio to transmit the third packet via a second WLAN communication channel having a second RF bandwidth, wherein transmission of the third packet overlaps in time with reception of the second packet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an example wireless local area network (WLAN), according to an embodiment. 
         FIG.  2 A  is a block diagram of an example physical layer (PHY) data unit, according to an embodiment. 
         FIG.  2 B  is a block diagram of an example preamble of a PHY data unit, according to an embodiment. 
         FIG.  3    is a block diagram of an example system architecture configured for multi-channel communication, according to an embodiment. 
         FIG.  4 A  is a diagram of an example system architecture corresponding to a communication device configured for multi-channel operation, according to an embodiment. 
         FIG.  4 B  is a diagram of another example system architecture corresponding to a communication device configured for multi-channel operation, according to another embodiment. 
         FIG.  5    is a diagram of an example signal transmission sequence over aggregated communication channels, according to an embodiment. 
         FIG.  6    is a diagram of an example signal transmission sequence over aggregated communication channels using frequency division duplexing, according to an embodiment. 
         FIG.  7    is a diagram of another example signal transmission over aggregated communication channels using frequency division duplexing, according to another embodiment. 
         FIG.  8 A  is a diagram of an example channelization scheme corresponding to multiple channels, according to an embodiment. 
         FIG.  8 B  is a diagram of another example channelization scheme corresponding to multiple channels, according to another embodiment. 
         FIG.  9    is a diagram of another example system architecture corresponding to a communication device configured for multi-channel operation, according to another embodiment. 
         FIG.  10    is a flow diagram of an example method for wireless local area network (WLAN) communication, according to an embodiment. 
         FIG.  11    is a flow diagram of another example method for WLAN communication, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The Federal Communication Commission (FCC) now permits wireless local area networks (WLANs) to operate in multiple radio frequency (RF) bands, e.g., the 2.4 GHz band (approximately 2.4 to 2.5 GHz), and the 5 GHz band (approximately 5.170 to 5.835 GHz). Recently, the FCC proposed that WLANs can also operate in the 6 GHz band (5.925 to 7.125 GHz). Current IEEE 802.11 Standard protocols only permit a WLAN to operate in one RF band at a time. For example, the IEEE 802.11n Standard protocol is defined only for operation in the 2.4 GHz band, whereas the IEEE 802.11ac Standard protocol is defined only for operation in the 5 GHz band. The IEEE 802.11ax Standard protocol, now under development, will permit a WLAN to operate in the 2.4 GHz band or the 5 GHz band, but not both the 2.4 GHz band and the 5 GHz band at the same time. 
     A future WLAN protocol, now under development, may permit multi-band operation in which a WLAN can use spectrum in multiple RF bands at the same time. For example, the future WLAN protocol may permit aggregation of spectrum in a first RF band with spectrum in a second RF band to form a composite communication channel that can be used to transmit packets that span the composite communication channel. As another example, the future WLAN protocol may employ frequency division duplex (FDD) techniques in which a first communication channel in a first RF band is used for one type of communications (e.g., downlink data transmissions, or data communications) and a second communication channel in a second RF band is used for another type of communications (e.g., uplink data transmissions, or acknowledgments of the data communications). In some scenarios, FDD techniques provide duplexing gain by allowing traffic in two directions simultaneously, for example, downlink and uplink traffic, or forward and reverse traffic. 
     Multi-channel communication techniques described below are discussed in the context of wireless local area networks (WLANs) that utilize protocols the same as or similar to protocols defined by the 802.11 Standard from the Institute of Electrical and Electronics Engineers (IEEE) merely for explanatory purposes. In other embodiments, however, multi-channel communication techniques are utilized in other types of wireless communication systems such as personal area networks (PANs), mobile communication networks such as cellular networks, metropolitan area networks (MANs), satellite communication networks, etc. 
       FIG.  1    is a block diagram of an example wireless local area network (WLAN)  110 , according to an embodiment. The WLAN  110  includes an access point (AP)  114  that comprises a host processor  118  coupled to a network interface device  122 . The network interface device  122  includes one or more medium access control (MAC) processors  126  (sometimes referred to herein as “the MAC processor  126 ” for brevity) and one or more physical layer (PHY) processors  130  (sometimes referred to herein as “the PHY processor  130 ” for brevity). The PHY processor  130  includes a plurality of transceivers  134 , and the transceivers  134  are coupled to a plurality of antennas  138 . Although three transceivers  134  and three antennas  138  are illustrated in  FIG.  1   , the AP  114  includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) of transceivers  134  and antennas  138  in other embodiments. In some embodiments, the AP  114  includes a higher number of antennas  138  than transceivers  134 , and antenna switching techniques are utilized. 
     In an embodiment, the network interface device  122  includes multiple PHY processors  130  to facilitate multi-band communication, where respective PHY processors  130  correspond to respective RF bands. In another embodiment, the network interface device  122  includes a single PHY processor  130 , where each transceiver  134  includes respective RF radios corresponding to respective RF bands to facilitate multi-band communication. 
     The network interface device  122  is implemented using one or more integrated circuits (ICs) configured to operate as discussed below. For example, the MAC processor  126  may be implemented, at least partially, on a first IC, and the PHY processor  130  may be implemented, at least partially, on a second IC. As another example, at least a portion of the MAC processor  126  and at least a portion of the PHY processor  130  may be implemented on a single IC. For instance, the network interface device  122  may be implemented using a system on a chip (SoC), where the SoC includes at least a portion of the MAC processor  126  and at least a portion of the PHY processor  130 . 
     In an embodiment, the host processor  118  includes a processor configured to execute machine readable instructions stored in a memory device (not shown) such as a random access memory (RAM), a read-only memory (ROM), a flash memory, etc. In an embodiment, the host processor  118  may be implemented, at least partially, on a first IC, and the network device  122  may be implemented, at least partially, on a second IC. As another example, the host processor  118  and at least a portion of the network interface device  122  may be implemented on a single IC. 
     In various embodiments, the MAC processor  126  and/or the PHY processor  130  of the AP  114  are configured to generate data units, and process received data units, that conform to a WLAN communication protocol such as a communication protocol conforming to the IEEE 802.11 Standard or another suitable wireless communication protocol. For example, the MAC processor  126  may be configured to implement MAC layer functions, including MAC layer functions of the WLAN communication protocol, and the PHY processor  130  may be configured to implement PHY functions, including PHY functions of the WLAN communication protocol. For instance, the MAC processor  126  may be configured to generate MAC layer data units such as MAC service data units (MSDUs), MAC protocol data units (MPDUs), etc., and provide the MAC layer data units to the PHY processor  130 . The PHY processor  130  may be configured to receive MAC layer data units from the MAC processor  126  and encapsulate the MAC layer data units to generate PHY data units such as PHY protocol data units (PPDUs) for transmission via the antennas  138 . Similarly, the PHY processor  130  may be configured to receive PHY data units that were received via the antennas  138 , and extract MAC layer data units encapsulated within the PHY data units. The PHY processor  130  may provide the extracted MAC layer data units to the MAC processor  126 , which processes the MAC layer data units. 
     PHY data units are sometimes referred to herein as “packets”, and MAC layer data units are sometimes referred to herein as “frames”. 
     In connection with generating one or more radio frequency (RF) signals for transmission, the PHY processor  130  is configured to process (which may include modulating, filtering, etc.) data corresponding to a PPDU to generate one or more digital baseband signals, and convert the digital baseband signal(s) to one or more analog baseband signals, according to an embodiment. Additionally, the PHY processor  130  is configured to upconvert the one or more analog baseband signals to one or more RF signals for transmission via the one or more antennas  138 . 
     In connection with receiving one or more signals RF signals, the PHY processor  130  is configured to downconvert the one or more RF signals to one or more analog baseband signals, and to convert the one or more analog baseband signals to one or more digital baseband signals. The PHY processor  130  is further configured to process (which may include demodulating, filtering, etc.) the one or more digital baseband signals to generate a PPDU. 
     The PHY processor  130  includes amplifiers (e.g., a low noise amplifier (LNA), a power amplifier, etc.), a radio frequency (RF) downconverter, an RF upconverter, a plurality of filters, one or more analog-to-digital converters (ADCs), one or more digital-to-analog converters (DACs), one or more discrete Fourier transform (DFT) calculators (e.g., a fast Fourier transform (FFT) calculator), one or more inverse discrete Fourier transform (IDFT) calculators (e.g., an inverse fast Fourier transform (IFFT) calculator), one or more modulators, one or more demodulators, etc. 
     The PHY processor  130  is configured to generate one or more RF signals that are provided to the one or more antennas  138 . The PHY processor  130  is also configured to receive one or more RF signals from the one or more antennas  138 . 
     The MAC processor  126  is configured to control the PHY processor  130  to generate one or more RF signals by, for example, providing one or more MAC layer data units (e.g., MPDUs) to the PHY processor  130 , and optionally providing one or more control signals to the PHY processor  130 , according to some embodiments. In an embodiment, the MAC processor  126  includes a processor configured to execute machine readable instructions stored in a memory device (not shown) such as a RAM, a read ROM, a flash memory, etc. In another embodiment, the MAC processor  126  includes a hardware state machine. 
     The WLAN  110  includes a plurality of client stations  154 . Although three client stations  154  are illustrated in  FIG.  1   , the WLAN  110  includes other suitable numbers (e.g., 1, 2, 4, 5, 6, etc.) of client stations  154  in various embodiments. The client station  154 - 1  includes a host processor  158  coupled to a network interface device  162 . The network interface device  162  includes one or more MAC processors  166  (sometimes referred to herein as “the MAC processor  166 ” for brevity) and one or more PHY processors  170  (sometimes referred to herein as “the PHY processor  170 ” for brevity). The PHY processor  170  includes a plurality of transceivers  174 , and the transceivers  174  are coupled to a plurality of antennas  178 . Although three transceivers  174  and three antennas  178  are illustrated in  FIG.  1   , the client station  154 - 1  includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) of transceivers  174  and antennas  178  in other embodiments. In some embodiments, the client station  154 - 1  includes a higher number of antennas  178  than transceivers  174 , and antenna switching techniques are utilized. 
     The network interface device  162  is implemented using one or more ICs configured to operate as discussed below. For example, the MAC processor  166  may be implemented on at least a first IC, and the PHY processor  170  may be implemented on at least a second IC. As another example, at least a portion of the MAC processor  166  and at least a portion of the PHY processor  170  may be implemented on a single IC. For instance, the network interface device  162  may be implemented using an SoC, where the SoC includes at least a portion of the MAC processor  166  and at least a portion of the PHY processor  170 . 
     In an embodiment, the host processor  158  includes a processor configured to execute machine readable instructions stored in a memory device (not shown) such as a RAM, a ROM, a flash memory, etc. In an embodiment, the host processor  158  may be implemented, at least partially, on a first IC, and the network device  162  may be implemented, at least partially, on a second IC. As another example, the host processor  158  and at least a portion of the network interface device  162  may be implemented on a single IC. 
     In various embodiments, the MAC processor  166  and the PHY processor  170  of the client device  154 - 1  are configured to generate data units, and process received data units, that conform to the WLAN communication protocol or another suitable communication protocol. For example, the MAC processor  166  may be configured to implement MAC layer functions, including MAC layer functions of the WLAN communication protocol, and the PHY processor  170  may be configured to implement PHY functions, including PHY functions of the WLAN communication protocol. The MAC processor  166  may be configured to generate MAC layer data units such as MSDUs, MPDUs, etc., and provide the MAC layer data units to the PHY processor  170 . The PHY processor  170  may be configured to receive MAC layer data units from the MAC processor  166  and encapsulate the MAC layer data units to generate PHY data units such as PPDUs for transmission via the antennas  178 . Similarly, the PHY processor  170  may be configured to receive PHY data units that were received via the antennas  178 , and extract MAC layer data units encapsulated within the PHY data units. The PHY processor  170  may provide the extracted MAC layer data units to the MAC processor  166 , which processes the MAC layer data units. 
     The PHY processor  170  is configured to downconvert one or more RF signals received via the one or more antennas  178  to one or more baseband analog signals, and convert the analog baseband signal(s) to one or more digital baseband signals, according to an embodiment. The PHY processor  170  is further configured to process the one or more digital baseband signals to demodulate the one or more digital baseband signals and to generate a PPDU. The PHY processor  170  includes amplifiers (e.g., an LNA, a power amplifier, etc.), an RF downconverter, an RF upconverter, a plurality of filters, one or more ADCs, one or more DACs, one or more DFT calculators (e.g., an FFT calculator), one or more IDFT calculators (e.g., an IFFT calculator), one or more modulators, one or more demodulators, etc. 
     The PHY processor  170  is configured to generate one or more RF signals that are provided to the one or more antennas  178 . The PHY processor  170  is also configured to receive one or more RF signals from the one or more antennas  178 . 
     The MAC processor  166  is configured to control the PHY processor  170  to generate one or more RF signals by, for example, providing one or more MAC layer data units (e.g., MPDUs) to the PHY processor  170 , and optionally providing one or more control signals to the PHY processor  170 , according to some embodiments. In an embodiment, the MAC processor  166  includes a processor configured to execute machine readable instructions stored in a memory device (not shown) such as a RAM, a ROM, a flash memory, etc. In an embodiment, the MAC processor  166  includes a hardware state machine. 
     In an embodiment, each of the client stations  154 - 2  and  154 - 3  has a structure that is the same as or similar to the client station  154 - 1 . Each of the client stations  154 - 2  and  154 - 3  has the same or a different number of transceivers and antennas. For example, the client station  154 - 2  and/or the client station  154 - 3  each have only two transceivers and two antennas (not shown), according to an embodiment. 
     In various embodiments, the AP  114  is configured to generate an MPDU  180  and transmit the MPDU  180  to the client station  154 - 1  in a first WLAN communication channel (e.g., channel  608 ,  FIG.  6   ), and further configured to receive an acknowledgment  181  from the client station  154 - 1  in a second WLAN communication channel (e.g., channel  616 ,  FIG.  6   ). In an embodiment, the first WLAN communication channel has a first RF bandwidth and the second WLAN communication channel has a second RF bandwidth that does not overlap the first RF bandwidth. In a further embodiment, the first RF bandwidth and the second RF bandwidth are separated by a gap in frequency and are non-contiguous. In at least some scenarios, communication in the WLAN  110  is improved by receiving the acknowledgment  181  in a different communication channel, which provides improved timing efficiency (“duplex gain”). For instance, using the second communication channel frees up the first communication channel for subsequent transmissions thereon without requiring a wait period (e.g., short interframe space) between an end of the MPDU  180  and a beginning of the acknowledgment  181 . 
       FIG.  2 A  is a diagram of an example PPDU  200  that the network interface device  122  ( FIG.  1   ) is configured to generate and transmit to one or more client stations  154  (e.g., the client station  154 - 1 ), according to an embodiment. The network interface device  162  ( FIG.  1   ) may also be configured to transmit data units the same as or similar to the PPDU  200  to the AP  114 . The PPDU occupies a 20 MHz bandwidth or another suitable bandwidth, in an embodiment. Data units similar to the PPDU  200  occupy other suitable bandwidth such as 40 MHz, 60 MHz, 80 MHz, 100 MHz, 120 MHz, 140 MHz, 160 MHz, 180 MHz, 200 MHz, etc., for example, in other embodiments. 
     The PPDU  200  includes a PHY preamble  204  and a PHY data portion  208 . The PHY preamble  204  includes at least one of a legacy portion  212  and a non-legacy portion  216 , in at least some embodiments. In an embodiment, the legacy portion  212  is configured to be processed by legacy communication devices in the WLAN  110  (i.e., communication devices that operate according to a legacy communication protocol), enabling the legacy communication devices to detect the PPDU  200  and to obtain PHY information corresponding to the PPDU  200 , such as a duration of the PPDU  200 . 
       FIG.  2 B  is a diagram of an example PHY preamble  220 . In an embodiment, the PHY preamble  220  corresponds to the PHY preamble  204 . In an embodiment, the PHY preamble  220  is included in the legacy portion  212 . In another embodiment, the PHY preamble  220  is included in the non-legacy portion  216 . The PHY preamble  220  includes one or more short training fields (STFs)  224 , one or more long training field (LTFs)  228 , and one or more signal fields (SIGs)  232 . In an embodiment, the STFs  224  and the LTFs  228  are used for packet detection, automatic gain control (AGC), frequency offset estimation, channel estimation, etc. In an embodiment, the number of LTFs in the LTFs  228  correspond to a number of spatial/space-time streams used for transmission of the PPDU  200 . In an embodiment, the SIGs  232  are used to signal PHY communication parameters (e.g., a modulation and coding scheme (MCS), a number of spatial streams, a frequency bandwidth, etc.) corresponding to the PPDU  200 . 
     In some embodiments, the PHY preamble  220  omits one or more of the fields  224 - 232 . In some embodiments, the PHY preamble  220  includes one or more additional fields not illustrated in  FIG.  2 B . In some embodiments, the order of the fields  224 - 232  is different than illustrated in  FIG.  2 B . In an embodiment, the PPDU  200  is generated and transmitted as a sequence of orthogonal frequency division multiplexing (OFDM) symbols. In an embodiment, each of the STF  224 , the LTF  228 , the SIG  232 , and the data portion  208  comprises one or more OFDM symbols. 
     In an embodiment, the PPDU  200  is a multi-user (MU) orthogonal frequency division multiple access (OFDMA) data unit in which independent data streams are transmitted to multiple client stations  154  using respective sets of OFDM tones allocated to the client stations  154 . For example, in an embodiment, available OFDM tones (e.g., OFDM tones that are not used as DC tone and/or guard tones) are segmented into multiple resource units (RUs), and each of the multiple RUs is allocated to data to one or more client stations  154 . In an embodiment, the independent data streams in respective allocated RUs are further transmitted using respective spatial streams, allocated to the client stations  154 , using multiple-input multiple-output (MIMO) techniques. In an embodiment, the PPDU  200  is a MU-MIMO PHY data unit in which independent data streams are transmitted to multiple client stations  154  using respective spatial streams allocated to the client stations  154 . 
     In an embodiment, an operating frequency band of a communication device in the WLAN  110  is divided into a plurality of smaller component channels. In an embodiment, the operating frequency band is divided into component channels, each corresponding to a width of 20 MHz, or another suitable frequency bandwidth. Multiple component channels may be concatenated to form a wider channel. For instance, a 40 MHz channel may be formed by combining two 20 MHz component channels, an 80 MHz channel may be formed by combining two 40 MHz channels, a 160 MHz channel may be formed by combining two 80 MHz channels. In an embodiment, the operating frequency band is divided into component channels of a width different than 20 MHz. 
     In an embodiment, the PPDU  200  has a 20 MHz frequency bandwidth and is transmitted in a 20 MHz channel. In other embodiments, the PPDU  200  may have a frequency bandwidth of 40 MHz, 80 MHz, 100 MHz, 120 MHz, etc., and is correspondingly transmitted over a 40 MHz, 80 MHz, 100 MHz, 120 MHz, etc., channel, respectively. In some such embodiments, at least a portion of the PPDU  200  (e.g., at least a legacy portion of the PHY preamble  204 , or the entirety of the PHY preamble  204 ) is generated by generating a field corresponding to a 20 MHz component channel bandwidth and repeating the field over a number of 20 MHz component channels corresponding to the transmission channel, in an embodiment. For example, in an embodiment in which the PPDU 200 occupies an 80 MHz channel, at least the legacy portion 212 corresponding to the 20 MHz component channel bandwidth is replicated in each of four 20 MHz component channels that comprise the 80 MHz channel. 
     In an embodiment, one or more communication devices in the WLAN  110  (e.g., the AP  114 , the client station  154 , etc.) are configured for various multi-channel operations. In an embodiment, multi-channel operation includes multi-band communication, i.e., operating according to a communication protocol that permits concurrent operation of a single wireless network across multiple RF bands and includes hardware that is configured to provide concurrent communications over multiple RF bands. Such communication devices are referred to herein as “multi-band communication devices” or frequency division duplexing (FDD) communication devices. In an embodiment, at least one client station  154  (e.g., the client station  154 - 3 ) may include hardware or may operate according to a communication protocol (e.g., a legacy communication protocol) that is not configured for multi-band communications (i.e., the protocol only permits a wireless network to operate in a single RF band at a given time), and may operate only in one of the multiple RF bands (at a given time) being used by multi-band devices. Such communication devices are referred to herein as “single-band communication devices”. 
     In an embodiment, one or more communication devices in the WLAN  110  (e.g., the AP  114 , the client station  154 , etc.) are configured for various multi-channel operations. In an embodiment, multi-channel operation corresponds asynchronous dual-band concurrent (DBC) operation over two or more communication channels. For instance, in an embodiment, the AP  114  is configured to transmit a first signal in a first communication channel, and simultaneously transmit a second signal over a second communication channel. In an embodiment, the AP  114  is configured to transmit a first signal in a first communication channel, and simultaneously receive a second signal over a second communication channel. In an embodiment, the AP  114  is configured to receive a first signal in a first communication channel, and simultaneously receive a second signal over a second communication channel. In any of the above cases corresponding to DBC operation, the transmission/reception of the first signal and the second signal may be asynchronous. For instance, in an embodiment, one or both of corresponding start times and end times of the first signal and the second signal may be different. 
     In various embodiments, multiple different frequency bands within the RF spectrum are employed for signal transmissions within the WLAN  110 . In an embodiment, different communication devices (i.e., the AP  114  and the client stations  154 ) may be configured for operation in different frequency bands (e.g., radio frequency bandwidths). In an embodiment, at least some communication devices (e.g., the AP  114  and the client station  154 ) in the WLAN  110  may be configured for operation over multiple different frequency bands. In an embodiment, the first communication channel is separated in frequency from the second communication channel, i.e., there is a gap in frequency between the first communication channel and the second communication channel (in other words, the first communication channel is not contiguous with the second communication channel). In an embodiment, the first communication channel and the second communication channel do not overlap each other. 
     Exemplary frequency bands include, a first frequency band corresponding to a frequency range of approximately 2.4 GHz-2.5 GHz (“2 GHz band”), and a second frequency band corresponding to a frequency range of approximately 5 GHz-5.9 GHz (“5 GHz band”) of the RF spectrum. In an embodiment, one or more communication devices within the WLAN may also be configured for operation in a third frequency band in the 6 GHz-7 GHz range (“6 GHz band”). Each of the frequency bands comprise multiple component channels which may be combined within the respective frequency bands to generate channels of wider bandwidths, as described above. In an embodiment corresponding to multi-channel operation over a first communication channel and a second communication channel, the first communication channel and the second communication channel may be in separate frequency bands, or within a same frequency band. 
     In an embodiment, the first communication channel and the second communication channel have different frequency bandwidths (e.g., 80 MHz and 20 MHz, 80 MHz and 40 MHz, 160 MHz and 20 MHz, or other suitable bandwidths). In an embodiment, the first communication channel and the second communication channel consist of respective different numbers of component channels. 
       FIG.  3    is a diagram of a system architecture corresponding to a communication device  300  configured for DBC operation (e.g., a multi-band communication device). In an embodiment, the communication device  300  corresponds to the AP  114 . In another embodiment, the communication device  300  corresponds to the client station  154 - 1 . In an embodiment, the communication device  300  is configured for operation over two or more RF bands. For example, in an embodiment, the communication device  300  is configured to communicate via a first WLAN communication channel having a first RF bandwidth and via a second WLAN communication channel having a second RF bandwidth that does not overlap the first RF bandwidth. In some embodiments, the communication device  300  includes a packet forwarding processor  304  configured to forward packets among the two RF bands and another network connection (e.g., a wired connection or wide area network connection, not shown). The communication device  300  also includes a first MAC processor  308  (MAC-1), a second MAC processor  312  (MAC-2), a first PHY processor  316 , and a second PHY processor  320 . The first MAC processor  308  is coupled to the first PHY processor  316 , and the second MAC processor  312  is coupled to the second PHY processor  320 . The first MAC processor  308  exchanges frames with the first PHY processor  316 , and the second MAC processor  312  exchanges frames with the second PHY processor  320 . 
     In an embodiment, the first MAC processor  308  and the second MAC processor  312  correspond to the MAC processor  126  of  FIG.  1   . In another embodiment, the first MAC processor  308  and the second MAC processor  312  correspond to the MAC processor  166  of  FIG.  1   . In an embodiment, the first PHY processor  316  and the second PHY processor  320  correspond to the PHY processor  130  of  FIG.  1   . In another embodiment, the first PHY processor  316  and the second PHY processor  320  correspond to the PHY processor  170  of  FIG.  1   . 
     The first PHY processor  316  includes a first baseband signal processor  324  (Baseband-1) coupled to a first RF radio  328  (Radio-1). The second PHY processor  320  includes a second baseband signal processor  332  (Baseband-2) coupled to a second RF radio  336  (Radio-2). In an embodiment, the RF radio  328  and the RF radio  336  correspond to the transceivers  134  of  FIG.  1   . In another embodiment, the RF radio  328  and the RF radio  336  correspond to the transceivers  174  of  FIG.  1   . In some embodiments, the RF radio  328  is configured to operate on a first RF band, and the RF radio  336  is configured to operate on a second RF band. In an embodiment, the first RF band is different from the second RF band, for example, the first RF band does not overlap the second RF band. In a further embodiment, the first RF band is separated from the second RF band by a frequency gap of, for example, 10 MHz, 20 MHz, 500 MHz, or another suitable frequency gap. In an embodiment, the frequency gap includes one or more communication channels that are not used by the communication device  300 , but are used by other communication devices, for example, other WLAN access points, WLAN client stations, or other wireless communication devices (not shown). In another embodiment, the RF radio  328  and the RF radio  336  are both configured to operate on the same RF band. 
     The MAC-1  308  is configured to generate frames and to provide the frames to the Baseband-1  324 . The Baseband-1  324  is configured to receive frames from the MAC-1  308 , generate a baseband signal corresponding to PPDUs. The Radio-1  328  upconverts the baseband signal and generates RF signals corresponding to the PPDUs for transmission over the first communication channel via one or more antennas (not shown). Similarly, the Radio-1  328  is configured to receive RF signals corresponding to PPDUs received over the first communication channel via the one or more antennas and generate a baseband signal corresponding to the received PPDUs. The Baseband-1  324  decodes and de-encapsulates the PPDUs to generate frames and provides the frames to the MAC-1  308 . The MAC-1  308  processes the frames. 
     Operations of the MAC-2  312 , the Baseband-2  332 , and the Radio-2  336  correspond to operations of the MAC-1  308 , the Baseband-1  324 , and the Radio-1  328  as described above, except that the MAC-2  312 , the Baseband-2  332 , and the Radio-2  336  operate in the second communication channel. For instance, MAC-2  312 , the Baseband-2  332 , and the Radio-2  336  generate/transmit PPDUs and receive/process PPDUs transmitted/received over the second communication channel. 
     In an embodiment corresponding to DBC operation, the MAC-1  308 , the Baseband-1  324 , the MAC-2  312 , and the Baseband-2  332  are configured for asynchronous operation in the first communication channel and the second communication channel. For instance, transmissions/receptions in the first communication channel are not synchronized or coordinated with transmissions/receptions in the second communication channel, according to an embodiment. For instance, the MAC-1  308  and the MAC-2  312  do not coordinate media access control functions, and the Baseband-1  324  and the Baseband-2  332  do not coordinate transmission timing, according to an embodiment. 
     In an embodiment, the forwarding processor  304  is omitted and the MAC-   1     308  and the MAC-2  312  are coupled to another suitable processor (e.g., the host processor  118  ( FIG.  1   )) that performs one or more higher level operations corresponding to data transmission and reception over the multiple communication channels. For instance, in an embodiment, the processor performs one or more operations corresponding to Layer 3 and above, as characterized in the Open Systems Interconnection (OSI) model. 
     Although only two MAC processors and two PHY processors are shown in  FIG.  3   , the communication device  300  has three, four, or more MAC processors and PHY processors that are configured to communicate on three, four, or more respective communication channels, in various embodiments. In an embodiment, for example, the communication device  300  includes i) the MAC processor  308  and PHY processor  316  configured to operate in the 2.4 GHz band, ii) the MAC processor  312  and PHY processor  320  configured to operate in the 5 GHz band, and iii) a MAC processor (not shown) and PHY processor (not shown) configured to operate in the 6 GHz band (or another suitable band). 
       FIG.  4 A  is a diagram of an example system architecture corresponding to a communication device  400  configured for multi-channel operation (e.g., a multi-band communication device), according to an embodiment. For instance, in an embodiment, the communication device  400  is configured for synchronous or asynchronous transmission/reception over aggregated communication channels. In an embodiment, the communication device  400  corresponds to the AP  114 . In another embodiment, the communication device  400  corresponds to the client station  154 - 1 . 
     In an embodiment, the communication device  400  is configured for operation over two or more communication channels and includes a forwarding processor  404 . The communication device  400  also includes a single MAC processor  408 , a first PHY processor  416 , and a second PHY processor  420 . The single MAC processor  408  is coupled to the first PHY processor  416  and the second PHY processor  420 . The single MAC processor  408  exchanges frames with the first PHY processor  416  and the second PHY processor  420 . 
     In an embodiment, the single MAC processor  408  corresponds to the MAC processor  126  of  FIG.  1   . In another embodiment, the single MAC processor  408  corresponds to the MAC processor  166  of  FIG.  1   . In an embodiment, the first PHY processor  416  and the second PHY processor  420  correspond to the PHY processor  130  of  FIG.  1   . In another embodiment, the first PHY processor  416  and the second PHY processor  420  correspond to the PHY processor  170  of  FIG.  1   . 
     The first PHY processor  416  includes a first baseband signal processor  424  (Baseband-1) coupled to a first RF radio  428  (Radio-1). The second PHY processor  420  includes a second baseband signal processor  432  (Baseband-2) coupled to a second RF radio  436  (Radio-2). In an embodiment, the RF radio  428  and the RF radio  436  correspond to the transceivers  134  of  FIG.  1   . In an embodiment, the RF radio  428  is configured to operate on a first RF band, and the RF radio  436  is configured to operate on a second RF band. In another embodiment, the RF radio  428  and the RF radio  436  are both configured to operate on the same RF band. 
     Although only two PHY processors  416  and  420  are shown in the embodiment of  FIG.  4 A , in another embodiment, the communication device  400  includes one or more additional PHY processors (not shown), for instance, a third PHY processor (not shown) configured to operate on yet another RF band that is different from the first and second RF bands. In an embodiment, for example, the first, second, and third PHY processors are configured to operate on the 2.4 GHz, 5 GHz, and 6 GHz bands, respectively. In other embodiments, other suitable bands are utilized (e.g., 60 GHz, “sub-1 GHz” or 900 MHz, 3.6 GHz, 4.9 GHz, etc.). 
     In an embodiment, the MAC processor  408  generates and parses data corresponding to MAC layer data units (e.g., frames) into a plurality of data streams corresponding to respective communication channels. The MAC processor  408  provides the parsed data streams to the Baseband-1  424  and the Baseband-2  432 . The Baseband-1  424  and the Baseband-2  432  are configured to receive the respective data streams from the MAC processor  408 , and encapsulate and encode the respective data streams to generate respective baseband signals corresponding to PPDUs. In an embodiment, the respective baseband signals have different bandwidths. The Baseband-1  424  and the Baseband-2  432  provide the respective baseband signals to the Radio-1  428  and the Radio-2  436 . The Radio-1  428  and Radio-2  436  upconvert the respective baseband signals to generate respective RF signals for transmission via the first communication channel and the second communication channel, respectively. The Radio-1  428  transmits a first RF signal via the first communication channel and the Radio-2  436  transmits a second RF signal via a second communication channel. 
     The communication device  400  also includes synchronization control circuitry  440 , in some embodiments. The synchronization control circuitry  440  is configured to ensure that respective transmitted signals over the first communication channel and the second communication channel are synchronized. The synchronization control circuitry  440  is coupled to the Baseband-1  424  and the Baseband-2  432  to ensure that the respective baseband signals are synchronized in time. In some embodiments, the synchronization control circuitry  440  ensures that some transmitted signals are synchronized, while other transmitted signals are not synchronized. 
     The Radio-1  428  and the Radio-2  436  are also configured to receive respective RF signals via the first communication channel and the second communication channel, respectively. The Radio-1  428  and the Radio-2  436  generate respective baseband signals corresponding to the respective received signals. In an embodiment, the generated respective baseband signals have different bandwidths. The generated respective baseband signals are provided to the respective baseband signal processors Baseband-1  424  and Baseband-2  432 . The Baseband-1  424  and the Baseband-2  432  generate respective data streams that are provided to the MAC processor  408 . The MAC processor  408  processes the respective data streams. In an embodiment, the MAC processor  408  de-parses the data streams received from the Baseband-1  424  and the Baseband-2  432  into a single information bit stream. 
     In an embodiment, the forwarding processor  404  is omitted and the MAC processor  408  is coupled to another suitable processor (e.g., the host processor  118  ( FIG.  1   )) that performs one or more higher level operations corresponding to data transmission and reception. For instance, in an embodiment, the other processor performs one or more operations corresponding to Layer 3 and above as characterized in the OSI model. 
       FIG.  4 B  is a diagram of an example system architecture corresponding to a communication device  450  configured for multi-channel operation (e.g., a multi-band communication device), according to another embodiment. For instance, in an embodiment, the communication device  450  is configured for synchronous or asynchronous transmission/reception over aggregated communication channels. In an embodiment, the communication device  450  corresponds to the AP  114 . In another embodiment, the communication device  450  corresponds to the client station  154 - 1 . The communication device  450  is similar to the communication device  400  of  FIG.  4 A , and like-numbered elements are not discussed in detail for purposes of brevity. 
     The communication device  450  includes a single MAC processor  458  coupled to a PHY processor  466 . The single MAC processor  408  exchanges frames with the PHY processor  466 . In an embodiment, the single MAC processor  458  corresponds to the MAC processor  126  of  FIG.  1   . In another embodiment, the single MAC processor  458  corresponds to the MAC processor  166  of  FIG.  1   . In an embodiment, the PHY processor  466  corresponds to the PHY processor  130  of  FIG.  1   . In another embodiment, the PHY processor  466  corresponds to the PHY processor  170  of  FIG.  1   . The PHY processor  466  includes a single baseband signal processor  474 . The single baseband signal processor  474  is coupled to the Radio-1  428  and the Radio-2  436 . 
     In an embodiment, the MAC processor  458  generates data corresponding to MAC layer data units (e.g., frames) and provides the frames to the baseband signal processor  474 . The baseband signal processor  474  is configured to receive frames from the MAC processor  458 , and parse data corresponding to the frames into a plurality of bit streams. The baseband signal processor  474  is also configured to encapsulate and encode the respective bit streams to generate respective baseband signals corresponding to PPDUs. In an embodiment, the respective baseband signals have different bandwidths. The baseband signal processor  474  provides the respective baseband signals to the Radio-1  428  and the Radio-2  436 . The Radio-1  428  and Radio-2  436  upconvert the respective baseband signals to generate respective RF signals for transmission via the first communication channel and the second communication channel, respectively. The Radio-1  428  transmits a first RF signal via the first communication channel and the Radio-2  436  transmits a second RF signal via a second communication channel. 
     The baseband signal processor  474  is configured to ensure that respective transmitted signals over the first communication channel and the second communication channel are synchronized, in some embodiments. For example, the baseband signal processor  474  is configured to generate the respective baseband signals such that the respective baseband signals are synchronized in time. 
     The Radio-1  428  and the Radio-2  436  are also configured to receive respective RF signals via the first communication channel and the second communication channel, respectively. The Radio-1  428  and the Radio-2  436  generate respective baseband signals corresponding to the respective received signals. In an embodiment, the generated respective baseband signals have different bandwidths. The generated respective baseband signals are provided to the baseband signal processor  474 . The baseband signal processor  474  generates respective bit streams, and de-parses the bit streams into a data stream corresponding to frames. The baseband signal processor  474  provides the frames to the MAC processor  458 . The MAC processor  458  processes the frames. 
     Although only two RF radios  428  and  436  are shown in the embodiment of  FIG.  4 B , in another embodiment, the communication device  400  includes one or more additional RF radios (not shown), for instance, a third RF radio (not shown) configured to operate on yet another RF band that is different from the first and second RF bands. In an embodiment, for example, the first, second, and third RF radios are configured to operate on the 2.4 GHz, 5 GHz, and 6 GHz bands, respectively. In other embodiments, other suitable bands are utilized (e.g., 60 GHz, “sub-1 GHz” or 900 MHz, 3.6 GHz, 4.9 GHz, etc.). 
       FIG.  5    is a diagram of an example synchronized transmission sequence  500  over aggregated communication channels, according to an embodiment. In an embodiment, the transmission sequence  500  is generated and transmitted by the network interface device  122  ( FIG.  1   ) to one or more client stations  154  (e.g., the client station  154 - 1 ). In an embodiment, the network interface device  122  generating the transmission sequence  500  has a structure of the communication device  400  ( FIG.  4 A ). In another embodiment, the network interface device  122  generating the transmission sequence  500  has a structure of the communication device  450  ( FIG.  4 B ). In another embodiment, the transmission sequence  500  is generated and transmitted by the network interface device  162  ( FIG.  1   ) to the AP  114 . In an embodiment, the network interface device  162  generating the transmission sequence  500  has a structure of the communication device  400  ( FIG.  4 A ). In another embodiment, the network interface device  162  generating the transmission sequence  500  has a structure of the communication device  450  ( FIG.  4 B ). 
     In an embodiment, the transmission sequence  500  corresponds to a single user (SU) transmission that is generated and transmitted to a single communication device. In an embodiment, the transmission sequence  500  corresponds to a multi-user (MU) transmission that includes data for multiple communication devices (e.g., the client stations  154 ). For example, in an embodiment, the MU transmission sequence  500  is an OFDMA transmission. In another embodiment, the MU transmission sequence  500  is a MU-MIMO transmission. 
     In the embodiment shown in  FIG.  5   , the transmission sequence  500  includes a downlink transmission  502  and an uplink transmission  503 . In another embodiment, the directions of the transmissions  502  and  503  are reversed so that the transmission  502  is an uplink transmission and the transmission  503  is a downlink transmission. The downlink transmission  502  includes a first RF signal  504  in a first communication channel  508  and a second RF signal  512  in a second communication channel  516 . The first RF signal  504  comprises a PHY preamble  420  and a PHY data portion  424 . The second RF signal  512  comprises of a PHY preamble  528 , a data portion  532 , and optional padding  536 . The uplink transmission  503  includes a third RF signal  506  in the first communication channel  508  and a fourth RF signal  514  in the second communication channel  516 . The third RF signal  506  comprises a PHY preamble  540  and a PHY data portion  544 . The second RF signal  512  comprises a PHY preamble  548  and a data portion  552 . In an embodiment, the first and second RF signals  504  and  512  include correspond to downlink MPDUs transmitted to a client station  154 , while the third and fourth RF signals  506  and  514  correspond to acknowledgments of the downlink MPDUs (e.g., the respective PHY data portions include ACK frames, block ACK frames, or other suitable acknowledgments) transmitted by the client station  154 . In an embodiment, the client station  154  transmits the third and fourth RF signals  506  and  514  after a short interframe space (SIFS), for example, to allow a suitable time for the client station  154  to process and generate the third and fourth RF signals  506  and  514 . 
     In an embodiment, transmission of the first RF signal  504  and the second RF signal  512  are synchronized such that they start at a same time instance t 1  and end at a same time instance t 3 . In an embodiment, the transmission sequence  500  is further synchronized such that the PHY preamble  520  and the PHY preamble  528  are of a same duration. In an embodiment in which the PHY data portion  532  has a shorter duration than the PHY data portion  524 , the PHY data portion  532  is appended with the padding  536  so that transmission of the signal  512  ends at t 3 . 
     In an embodiment, the PHY preamble  520  and the PHY preamble  528  are formatted in a manner similar to the PHY preamble  204  of  FIG.  2   . In an embodiment, at least a portion of the PHY preamble  520  and at least a portion of the PHY preamble  528  have the same structure and/or include the same information. In an embodiment, at least a portion of the PHY preamble  520  and at least a portion of the PHY preamble  528  are identical. 
     In various embodiments, the first communication channel  508  and the second communication channel  516  are in different RF bands or are co-located in a same RF band. In an embodiment, the RF band(s) correspond to the 2 GHz band, the 5 GHz band, the 6 GHz band, or another suitable band, as described above. The first communication channel  508  and the second communication channel  516  may each be comprised of one or more component channels. In an embodiment, a frequency bandwidth of the first communication channel  508  (i.e., a frequency bandwidth of the first RF signal  504  and third RF signal  506 ) is different than a frequency bandwidth of the second communication channel  516  (i.e., a frequency bandwidth of the second RF signal  512  and the fourth RF signal  514 ). In various embodiments, for example, respective RF bandwidths of the first communication channel  508  and the second communication channel  516  are 80 MHz and 20 MHz, 160 MHz and 20 MHz, 320 MHz and 40 MHz, or other suitable bandwidths. In another embodiment, the RF bandwidth of the first communication channel  508  is the same as the RF bandwidth of the second communication channel  516 . 
     In an embodiment, the first communication channel  508  and the second communication channel  516  do not overlap. In a further embodiment, the first communication channel  508  and the second communication channel  516  are separated in frequency, e.g., the channels are non-contiguous. For example, a gap Δf in frequency exists between the first communication channel  508  and the second communication channel  516 . In various embodiments, the gap Δf is at least 500 kHz, at least 1 MHz, at least 5 MHz, at least 20 MHz, etc. In some embodiments, the gap Δf is 320 MHz, 500 MHz, 1 GHz, or more, for example, where the first communication channel  508  is within the 2.4 GHz band and the second communication channel  516  is within the 5 GHz band. 
     In some embodiments, the first RF signal  504  is transmitted via a first number of spatial or space-time streams (hereinafter referred to as “spatial streams” for brevity), and the second RF signal  512  is transmitted via a second number of spatial streams that is different than the first number of spatial streams. In one such embodiment, the PHY preamble  520  and the PHY preamble  528  comprise a same number of LTFs even when the first RF signal  504  is transmitted via a first number of spatial streams and the second RF signal  512  is transmitted via a second number of spatial streams that is different than the first number of spatial streams. In an embodiment, the same number of LTFs correspond to one of the first signal  404  and the second signal  412  with the larger number of spatial streams. In other embodiments, the first RF signal  504  and the second RF signal  512  are transmitted via a same number of spatial streams. 
     In an embodiment, at least the PHY data portion  524  and at least the PHY data portion  532  employ different encoding schemes and/or modulation schemes. As an example, in an embodiment, the PHY data portion  524  is generated using a first MCS and the PHY data portion  432  is generated using a second, different MCS. In other embodiments, the PHY data portion  524  and the PHY data portion  532  are generated using a same MCS. 
     In an embodiment, the transmission sequence  500  corresponds to a single PPDU, where a first frequency portion of the single PPDU is transmitted via the first channel  508  and a second frequency portion of the single PPDU is transmitted via the second channel  516 . In another embodiment, the first RF signal  504  corresponds to a first PPDU and the second RF signal  512  corresponds to a second PPDU. In an embodiment, each of the PHY preambles  520  and  528 , and the PHY data portions  524  and  532 , are comprised of one or more OFDM symbols. 
     In various embodiments, the communication device  400  ( FIG.  4 A ) is configured to generate at least a portion of the transmission sequence  500  and to receive at least a portion of the transmission sequence  500 . In an embodiment, for example, the communication device  400  synchronously transmits the RF signals  504  and  512  and receives the RF signals  506  and  514 . In another embodiment, the communication device  400  receives the RF signals  504  and  512  and synchronously transmits the RF signals  506  and  514 . 
     In another embodiment, the communication device  450  ( FIG.  4 B ) is configured to generate at least a portion of the transmission sequence  500  and to receive at least a portion of the transmission sequence  500 . In an embodiment, for example, the communication device  450  synchronously transmits the RF signals  504  and  512  and receives the RF signals  506  and  514 . In another embodiment, the communication device  450  receives the RF signals  504  and  512  and synchronously transmits the RF signals  506  and  514 . 
       FIG.  6    is a diagram of an example signal transmission sequence  600  over aggregated communication channels using frequency division duplexing, according to an embodiment. In the embodiment shown in  FIG.  6   , the transmission sequence  600  includes transmissions  602 ,  603 , and  604 , where the transmissions  602  and  604  are downlink transmissions (e.g., from the AP  114  to one or more client stations  154 ) in a first communication channel  608  and the transmission  603  is an uplink transmission (e.g., from the client stations  154  to the AP  114 ) in a second communication channel  616 . In other words, the first communication channel  608  of the aggregated communication channels is designated for downlink traffic and the second communication channel  616  of the aggregated communication channels is designated for uplink traffic. The communication channels  608  and  616  are similar to the communication channels  508  and  516  described above with respect to  FIG.  5   . Accordingly, the communication channels  608  and  616  are in different RF bands (e.g., 2 GHz, 5 GHz, 6 GHz, etc.), in various embodiments. 
     In another embodiment, the transmissions  602  and  604  are uplink transmissions and the transmission  603  is a downlink transmission. In other words, the first communication channel  608  is designated for uplink traffic and the second communication channel  616  is designated for downlink traffic. In yet another embodiment, the first communication channel  608  is designated for forward traffic and the second communication channel  616  is designated for reverse traffic (e.g., acknowledgments to the forward traffic). In other words, management frames and data frames are transmitted on the first communication channel  608  regardless of whether they are transmitted by the AP  114  or by the client station  154 , while acknowledgment frames are similarly transmitted on the second communication channel  616 . In some embodiments, the AP  114  transmits a trigger frame (e.g., trigger frame  742 ,  FIG.  7   ) to one or more client stations  154  to trigger an uplink transmission (e.g., uplink transmission  603 ). 
     In the embodiment shown in  FIG.  6   , the downlink transmission  602  includes a first RF signal  620  having a PHY preamble  622  and PHY data portion  624 , the downlink transmission  604  includes a second RF signal  660  having a PHY preamble  662  and a PHY data portion  664 , and the uplink transmission  603  includes a third RF signal  640  having a PHY preamble  642  and PHY data portion  644 . The PHY preambles  622  and  662  are similar to the PHY preamble  520 , while the PHY data portions  624  and  664  are similar to the PHY data portion  524 . 
     The PHY preamble  642  is similar to the PHY preamble  540  and the PHY data portion  644  is similar to the PHY data portion  544 . However, in the embodiment shown in  FIG.  6   , the client station transmits the third RF signal  660  (i.e., the acknowledgment of the first RF signal  620 ) in the second communication channel  616 , instead of the first communication channel  608 . In some scenarios, the AP  114  and client stations  154  designate the first communication channel  608  for forward traffic or downlink traffic and designate the second communication channel  616  for uplink traffic or reverse traffic when the first communication channel  608  has a larger RF bandwidth (e.g., higher data transmission capacity) than the second communication channel  616 . In some such scenarios, the overall throughput of the WLAN  110  is improved because the higher capacity channel (the first communication channel  608 ) is not monopolized by the second RF signal  640  and the SIFS period that precedes the second RF signal  640  before the third RF signal  660  can be transmitted. In some scenarios, by utilizing frequency division duplexing with the first communication channel  608  and the second communication channel  616  with separate RF radios (i.e., RF radios  428  and  436 ) in non-overlapping RF bandwidths, the AP  114  and client stations  154  have improved MAC protocol efficiency because traffic in both directions (uplink and downlink, forward and reverse, etc.), such as the RF signals  640  and  660 , can be transmitted and received simultaneously. 
     In various embodiments, the communication device  400  ( FIG.  4 A ) is configured to generate at least a portion of the transmission sequence  600  and to receive at least a portion of the transmission sequence  600 . In an embodiment, for example, the communication device  400  transmits the RF signals  620  and  660  and receives RF signal  640 . In another embodiment, the communication device  400  receives the RF signals  620  and  660  and transmits the RF signal  640 . 
     In some embodiments, the communication device  450  ( FIG.  4 B ) is configured to generate at least a portion of the transmission sequence  600  and to receive at least a portion of the transmission sequence  600 . In an embodiment, for example, the communication device  450  transmits the RF signals  620  and  660  and receives RF signal  640 . In another embodiment, the communication device  450  receives the RF signals  620  and  660  and transmits the RF signal  640 . 
     In an embodiment, the communication device  400  or the communication device  450  is configured to select the bands of the first and second communication channels  608  and  616  so that interference between the communication channels is reduced. In an embodiment, for example, when the 2.4 GHz band, the 5 GHz band, and 6 GHz band are available, the communication device  400  selects the 6 MHz band and the 2.4 GHz band for the first and second communication channels  608  and  616 , respectively, so that interference between the communication channels is reduced. 
     In an embodiment, the communication device  400  or  450  is configured to select RF bandwidths for the first and second communication channels  608  and  616  so that interference between the communication channels is reduced (e.g., interference caused by the simultaneous reception of the third RF signal  603 . In an embodiment, for example, the communication device  400  selects a 320 MHz bandwidth in an upper frequency range of the 6 GHz band (e.g., 6530-6850 MHz) for the first communication channel  608  and selects a 40 MHz bandwidth in a lower frequency range of the 5 GHz band (e.g., 5150 MHz to 5190 MHz) for the second communication channel  616 . In another embodiment, for example, the communication device  400  selects an 80 MHz bandwidth in an upper frequency range of the 5 GHz band (e.g., 5735-5815 MHz) for the first communication channel  608  and selects a 20 MHz bandwidth in a lower frequency range of the 5 GHz band (e.g., 5190 MHz to 5210 MHz) for the second communication channel  616 . 
       FIG.  7    is a diagram of an example MU transmission sequence  700  over an aggregated communication channel using frequency division duplexing, according to an embodiment. In the embodiment shown in  FIG.  7   , the transmission sequence  700  includes transmissions  702 ,  703 , and  704 , where the transmissions  702  and  704  are downlink transmissions (e.g., from the AP  114  to one or more client stations  154  referred to as STA1, STA2, and STA3) and the transmission  703  is an uplink transmission (e.g., from the client stations  154  to the AP  114 ). In this embodiment, the first communication channel  708  of the aggregated communication channels is designated for downlink traffic and the second communication channel  716  of the aggregated communication channels is designated for uplink traffic and optionally, triggers for the uplink traffic. The communication channels  708  and  716  are similar to the communication channels  508  and  516  described above with respect to  FIG.  5   . Accordingly, the communication channels  708  and  716  are in different RF bands (e.g., 2 GHz, 5 GHz, 6 GHz, etc.), in various embodiments. 
     In an embodiment, the transmission sequence  700  is generated and transmitted by the network interface device  122  ( FIG.  1   ) to a plurality of client stations  154 . In another embodiment, the transmission sequence  700  is generated and transmitted by the network interface device  162  ( FIG.  1   ) to a plurality of other client stations  154  and optionally the AP  114 . 
     In the embodiment shown in  FIG.  7   , the downlink transmission  702  includes a first RF signal  720  having a PHY preamble  722  and PHY data portion  724  in a first communication channel  708 , the downlink transmission  704  includes a second RF signal  740  having a PHY preamble  742  and PHY data portion  744  in a second communication channel  716 , and the uplink transmission  703  includes a third RF signal  760  having a PHY preamble  762  and PHY data portion  764  in the second communication channel  716 . In an embodiment, the PHY data portion  724  corresponds to a downlink MPDU and the PHY data portion  764  corresponds to an acknowledgment of the downlink MPDU, while the PHY data portion  744  corresponds to a trigger frame that triggers the acknowledgment. 
     In various embodiments, the first communication channel  708  and the second communication channel  716  are similar to the first communication channels  508  and  608  and the second communication channels  516  and  616 , respectively, as described above with reference to  FIG.  5    and  FIG.  6   . In an embodiment, for example, the first communication channel  708  is designated for downlink traffic and the second communication channel  716  is designated for uplink traffic. In another embodiment, the first communication channel  708  is designated for forward traffic and the second communication channel  716  is designated for reverse traffic. 
     The PHY preambles  722 ,  742 , and  762  are similar to the PHY preamble  520 . In an embodiment in which the first communication channel  708  comprises multiple component channels, at least a portion of the PHY preamble  722  (e.g., a legacy portion) is generated by generating a field corresponding to one component channel and duplicating the field over one or more other component channels corresponding to the first communication channel  708 . In an embodiment in which the second communication channel  716  comprises multiple component channels, at least a portion of the PHY preamble  742  or  762  (e.g., a legacy portion) is generated by generating a field corresponding to one component channel and duplicating the field over one or more other component channels corresponding to the second communication channel  716 . 
     In various embodiments, the first communication channel  708  and the second communication channel  716  are in different RF bands or are co-located in a same RF band. In an embodiment, the RF band(s) correspond to the 2 GHz band, the 5 GHz band, and the 6 GHz bands, as described above. The first communication channel  708  and the second communication channel  716  may each be comprised of one or more of component channels. In an embodiment, a frequency bandwidth of the first communication channel  708  (i.e., a frequency bandwidth of the first RF signal  720 ) is different than a frequency bandwidth of the second communication channel  716  (i.e., a frequency bandwidth of the second RF signal  740  and third RF signal  760 ). In another embodiment, the frequency bandwidth of the first communication channel  708  is the same as the frequency bandwidth of the second communication channel  716 . 
     In an embodiment, the first communication channel  708  and the second communication channel  716  are separated in frequency. For example, a gap Δf in frequency exists between the first communication channel  708  and the second communication channel  716 . In various embodiments, the gap Δf is at least 500 kHz, at least 1 MHz, at least 5 MHz, at least 20 MHz, etc. 
     In some embodiments, the transmission sequence  700  utilizes MU-MIMO, for example, the first RF signal  720  is transmitted via a first number of spatial streams, and the second RF signal  740  and third RF signal  760  are transmitted via a second number of spatial streams that is different than the first number of spatial streams. In one such embodiment, the PHY preamble  722  and the PHY preambles  742  and  762  comprise a same number of LTFs even when the first RF signal  720  is transmitted via a first number of spatial streams and the second and third RF signals  740  and  760  are transmitted via a second number of spatial streams that is different than the first number of spatial streams. In an embodiment, the same number of LTFs correspond to one of the first RF signal  720  and the second and third RF signals  740  and  760  with the larger number of spatial streams. In other embodiments, the first RF signal  720  and the second and third RF signals  740  and  760  are transmitted via a same number of spatial streams. In an embodiment, at least a PHY payload portion  724  and at least a PHY data payload  764  employ different encoding schemes and/or modulation schemes. 
     In some embodiments, the transmission sequence  700  utilizes OFDMA, for example, the PHY payload portion  724  includes respective frequency multiplexed data for respective client stations  154 . Individual data within the data portion  724  are transmitted to corresponding client stations  154  in corresponding allocated RUs  724 - 1 ,  724 - 2 , and  724 - 3 . Individual data within the data portion  764  are transmitted from the corresponding client stations  154  in corresponding allocated RUs  764 - 1 ,  764 - 2 , and  764 - 3 . In various embodiments, some or all of RUs  724 / 764  use different encoding schemes and/or modulation schemes. As an example, the RU  764 - 1  and the RU  724 - 2  are generated using different MCSs and/or different numbers of spatial/space-time streams, etc. 
     In various embodiments, the communication device  400  ( FIG.  4 A ) is configured to generate at least a portion of the transmission sequence  700  and to receive at least a portion of the transmission sequence  700 . In an embodiment, for example, the communication device  400  transmits the RF signals  720  and  740  and receives RF signal  760 . In another embodiment, the communication device  400  receives the RF signals  720  and  740  and transmits the RF signal  760 . 
     In some embodiments, the communication device  450  ( FIG.  4 A ) is configured to generate at least a portion of the transmission sequence  700  and to receive at least a portion of the transmission sequence  700 . In an embodiment, for example, the communication device  450  transmits the RF signals  720  and  740  and receives RF signal  760 . In another embodiment, the communication device  450  receives the RF signals  720  and  740  and transmits the RF signal  760 . 
     The multiple communication channels that correspond to the multiple radios are sometimes referred to herein as “the radio channels” for ease of explanation. In some embodiments, one of the component channels across the multiple radio channels is designated as a primary channel. The one radio channel that includes the designated primary channel is sometimes referred to herein as “the primary radio channel”. Other component channels across the multiple radio channels that are not a primary channel are sometimes referred to herein as “secondary channels”. 
       FIG.  8 A  is a diagram of an example channelization scheme  800  corresponding to multi-channel operation, according to an embodiment. In an embodiment, the channelization scheme  800  is employed for signal transmissions such as described above in reference to  FIGS.  5 - 7   , and/or for other transmissions across multiple radio channels. 
     The channelization scheme  800  illustrates a first communication channel  804  (also referred to herein as “the first radio channel  804 ”) aggregated with a second communication channel  808  (also referred to herein as “the second radio channel  808 ”). In various embodiments, the radio channels  804  and  808  correspond to communication channels  508  and  516 , communication channels  608  and  616 , or communication channels  708  and  716 , as described above in reference to  FIG.  5   ,  FIG.  6   , and  FIG.  7   , respectively. In other embodiments, the radio channels  804  and  808  correspond to other suitable radio channels. 
     The first radio channel  804  comprises one or more component channels, and the second radio channel  808  comprises one or more component channels. In the channelization scheme  800 , a single component channel  812  in the radio channel  804  is designated as the primary channel (e.g., for management frames and control frames). The remaining one or more component channels  816  (if any) in the first radio channel  804  are designated as secondary channels  816 . Similarly, the one or more component channels  820  in the second radio channel  808  are designated as secondary channels. In an embodiment, the first radio channel  804  and the second radio channel  808  are separated in frequency as described above. 
     In an embodiment in which the first radio channel  804  and the second radio channel  808  correspond to different RF bands, and in which one or more client stations  154  are only capable of operating in only one of the RF bands, the AP  114  designates the primary channel to be in the one radio channel  804 / 808  that corresponds to the one RF band in which the one or more client stations  154  are only capable of operating. In an embodiment where the first radio channel  804  is in the 5 GHz band and the second radio channel  808  is in the 6 GHz band, the AP  114  designates the primary channel to be in the 5 GHz band when a legacy WLAN communication device (i.e., a single band station such as an 802.11ac client station or another device that does not support the 6 GHz band). In an embodiment in which the radio channel  804  and the radio channel  808  correspond to different RF bands, and in which one or more client stations  154  are only capable of operating in only one of the RF bands, the AP  114  is not permitted to designate the primary channel to be in a radio channel  804 / 808  that does not correspond to the one RF band in which the one or more client stations  154  are only capable of operating. 
     In some embodiments, the WLAN  110  includes i) an AP  114  that is a multi-band communication device and communicates over the first radio channel  804  and second radio channel  808 , ii) a first client station  154  that is multi-band communication device and communicates over the first radio channel  804  and the second radio channel  808 , and iii) a second client station  154  that is a single-band communication device (i.e., a legacy WLAN communication device) and communicates only over the first radio channel  804 . In an embodiment, the AP  114  designates i) the first radio channel  804  as a downlink channel and the second radio channel  808  as an uplink channel for the first multi-band communication device, and ii) the first radio channel  804  as a downlink and uplink channel for the single-band communication device. In another embodiment, the AP  114  designates i) the first radio channel  804  as a forward channel and the second radio channel  808  as a reverse channel for the first multi-band communication device, and ii) the first radio channel  804  as a forward and reverse channel for the single-band communication device. 
       FIG.  8 B  is a diagram of another example channelization scheme  850  corresponding to multi-channel operation, according to another embodiment. In an embodiment, the channelization scheme  850  is employed for signal transmissions as described above in reference to  FIGS.  5 - 7   . The channelization scheme  850  includes a first communication channel  854  (also referred to herein as “the first radio channel  854 ”) aggregated with a second communication channel  858  (also referred to herein as “the second radio channel  858 ”). In various embodiments, the radio channels  854  and  858  correspond to communication channels  508  and  516 , communication channels  608  and  616 , or communication channels  708  and  716 , as described above in reference to  FIG.  5   ,  FIG.  6   , and  FIG.  7   , respectively. In other embodiments, the radio channels  854  and  858  correspond to other suitable radio channels. 
     The first radio channel  854  comprises one or more component channels, and the second radio channel  858  comprises one or more component channels. For the channelization scheme  850 , the AP  114  designates respective primary channels for both radio channels  854  and  858 . For example, a channel  862  in the first radio channel  854  is designated as a primary channel corresponding to the first radio channel  854  (sometimes referred to herein as “the first primary channel  862 ”), and a component channel  866  in the second radio channel  858  is designated as a primary channel corresponding to second radio channel  858  (sometimes referred to herein as “the second primary channel  866 ”). The remaining one or more component channels  870  (if any) in the first radio channel  854  are designated as secondary channels. Similarly, the one or more component channels  874  in the second radio channel  858  are designated as secondary channels. In an embodiment, the first radio channel  854  and the second radio channel  858  are separated in frequency as described above. 
     In an embodiment, the AP  114  operating according to the channelization scheme  850  transmits beacon frames in both of the primary channels  862  and  866 . In an embodiment, the beacon frames transmitted in both of the primary channels  862  and  866  are the same beacon frame. 
     In some embodiments, at least some communication devices (e.g., client stations  154 ) may operate according to a legacy communication protocol that does not define more than one primary channel for transmission over aggregated channels. In at least some such embodiments, the legacy communication devices may be allocated for operation in only a single communication channel (e.g., one of the communication channels  854  and  858 ). Alternatively, the legacy communication devices may be configured for independent and asynchronous operation in both communication channels  854  and  858 , such as DBC operation described above. 
     In some embodiments, the WLAN  110  includes i) an AP  114  that is a multi-band communication device and communicates over the first radio channel  854  and second radio channel  858 , ii) a first client station  154  that is multi-band communication device and communicates over the first radio channel  854  and the second radio channel  858 , iii) a second client station  154  that is a single-band communication device (i.e., a legacy WLAN communication device) and communicates only over the first radio channel  854 , and iv) a third client station  154  that is a single-band communication device and communicates only over the second radio channel  858 . In an embodiment, the AP  114  designates i) the first radio channel  854  as a downlink channel and the second radio channel  858  as an uplink channel for the first, multi-band client station, and ii) the first radio channel  854  as a downlink and uplink channel for the second, single-band communication device, and iii) the second radio channel  858  as a downlink and uplink channel for the third, single-band communication device. In another embodiment, the AP  114  designates i) the first radio channel  854  as a forward channel and the second radio channel  858  as a reverse channel for the first multi-band communication device, ii) the first radio channel  854  as a forward and reverse channel for the second, single-band communication device, and iii) the second radio channel  858  as a forward and reverse channel for the third, single-band communication device. 
       FIG.  9    is a diagram of an example system architecture corresponding to a communication device  900  configured for different modes multi-channel operating modes. In other words, the communication device  900  provides a network interface device configured to implement i) a DBC mode as described above with respect to  FIG.  3   , ii) a synchronous multi-channel mode as described above with respect to  FIG.  4 A , and/or iii) an asynchronous multi-channel mode as described above with respect to  FIG.  5   ,  FIG.  6   ,  FIG.  7   ,  FIG.  8 A , and  FIG.  8 B . In an embodiment, the communication device  900  is utilized in the AP  114  or the client station  154 . In an embodiment, the communication device  900  is configured to selectively transmit and/or receive signals described above with reference to  FIGS.  5 - 7   . In an embodiment, the communication device  900  is further configured for selective DBC operation as described above with reference to  FIG.  3   . 
     The communication device  900  is similar to the communication device  400  as described above with respect to  FIG.  4 A , and like-numbered elements not described in detail for purpose of brevity. The communication device  900  includes a packet forwarding processor  904  configured to forward packets among the two communication channels and a WAN connection (not shown). The communication device  900  also includes a master MAC processor  908  (MAC-M), a second MAC processor  912  (MAC-2), a first PHY processor  916 , and a second PHY processor  920 . The master MAC processor  908  is coupled to both the first PHY processor  916  and the second PHY processor  920 . The second MAC processor  912  is coupled to the second PHY processor  920 . The master MAC processor  908  exchanges frame data with the first PHY processor  916 , and the second MAC processor  912  exchanges frame data with the second PHY processor  920 . In the multi-channel modes, the master MAC processor  908  also exchanges frame data with the first PHY processor  916  while the second MAC processor  912  is idle. 
     In an embodiment, master MAC processor  908  and the second MAC processor  912  correspond to the MAC processor  126  of  FIG.  1   . In another embodiment, the master MAC processor  908  and the second MAC processor  912  correspond to the MAC processor  166  of  FIG.  1   . In an embodiment, the first PHY processor  916  and the second PHY processor  920  correspond to the PHY processor  130  of  FIG.  1   . In another embodiment, the first PHY processor  916  and the second PHY processor  920  correspond to the PHY processor  170  of  FIG.  1   . 
     The communication device  900  also includes synchronization control circuitry  932 . 
     In the multi-channel modes, the forwarding processor  904  exchanges data only with the master MAC processor  908 ; and the master MAC processor  908 , the first PHY processor  916 , the second PHY processor  920 , and the synchronization control circuitry  932  operate in a manner similar to communication device  400  of  FIG.  4 A . Also in the multi-channel modes, the second PHY processor  920  exchanges frame data with the master MAC processor  908  while the second MAC processor  912  is idle. 
     On the other hand, in the DBC mode, the forwarding processor  904  exchanges data with both the master MAC processor  908  and the second MAC processor  912 ; and the master MAC processor  908 , the second MAC processor  912 , the first PHY processor  916 , and the second PHY processor  920 , operate in a manner similar to communication device  300  of  FIG.  3   . Also in the DBC mode, the synchronization control circuitry  932  is idle. 
     The communication device  900  is configured to selectively switch between the multi-channel modes and the DBC mode. In an embodiment, the choice of a particular mode of operation is determined based on the volume of traffic and/or a number of client station  154  being serviced by the AP  114 . In an embodiment, if a large number of client stations  154  that can operate on both the first communication channel and the second communication channel are present in the WLAN  110 , DBC operation is preferred. In an embodiment, if a large number of client stations  154  are present on a single communication channel, multi-channel operation is preferred. In an embodiment, the AP  114  may prefer multi-channel operation when the AP  114  is servicing a small number of client station  154  with a high throughput. 
       FIG.  10    is a flow diagram of an example method  1000  for wireless local area network (WLAN) communication by a first WLAN communication device, according to an embodiment. In some embodiments, the AP  114  of  FIG.  1    is configured to implement the method  1000  (in other words, the AP  114  is the first WLAN communication device). In an embodiment, the method  1000  is implemented by the AP  114  by utilizing the communication device  400 , the communication device  450 , or the communication device  900  as described above with reference to  FIGS.  4 A-B  and  9 . The method  1000  is described, however, in the context of the AP  114  merely for explanatory purposes and, in other embodiments, the method  1000  is implemented by another suitable device such as the client station  154 . In various embodiments, the method  1000  is utilized to generate signals corresponding to those described above in reference to  FIGS.  5 - 7   . In various embodiments, the method  1000  is utilized with channelizations such as described above in reference to  FIGS.  8 A-B . 
     At block  1004 , the AP  114  generates a first media access control (MAC) data unit. In an embodiment, the MAC data unit is an MPDU, A-MPDU, MMPDU, or other suitable MAC data unit. In an embodiment, the first MAC data unit corresponds to the PHY data portion  624  ( FIG.  6   ) and includes, for example, an MPDU intended for a client station  154 . In another embodiment, the first MAC data unit corresponds to the PHY data portion  724 - 1 ,  724 - 2 , or  724 - 3  ( FIG.  7   ). 
     At block  1008 , the AP  114  transmits the first MAC data unit to a second WLAN communication device via a first WLAN communication channel having a first radio frequency (RF) bandwidth. In an embodiment, the second WLAN communication is the client station  154  to which the first MAC data unit is transmitted. In an embodiment, the first WLAN communication channel corresponds to the communication channel  608 . In another embodiment, the communication channel corresponds to the communication channel  708 . In an embodiment, the first RF bandwidth is a bandwidth within the 5 GHz band, the 6 GHz band, or another suitable band. 
     At block  1012 , the AP  114  receives a second MAC data unit from the second WLAN communication device via a second WLAN communication channel having a second RF bandwidth that does not overlap the first RF bandwidth, where the second MAC data unit corresponds to an acknowledgment of the first MAC data unit from the second WLAN communication device. In an embodiment, for example, the AP  114  receives the acknowledgment  644  via the second communication channel  616  ( FIG.  6   ). In another embodiment, the AP  114  receives the acknowledgment  764 - 1 ,  764 - 2 , or  764 - 3  via the second communication channel  716 . 
     In an embodiment, generating the first MAC data unit includes providing, by a single MAC layer processor implemented on one or more integrated circuit (IC) devices of the first WLAN communication device, the first MAC data unit to one or more baseband signal processors of the first WLAN communication device, wherein the one or more baseband signal processors are implemented on the one or more IC devices, and generating, at the one or more baseband signal processors, a first baseband signal that corresponds to the first MAC data unit. In an embodiment, for example, the single MAC layer processor corresponds to the MAC processor  408  ( FIG.  4 A ), MAC processor  458  ( FIG.  4 B ), or MAC processor  908  ( FIG.  9   ) and the first baseband signal processor corresponds to the baseband processor  424  or  432  ( FIG.  4 A ), the baseband processor  474  ( FIG.  4 B ), or the baseband processor  924  or  928  ( FIG.  9   ). 
     In an embodiment, transmitting the first MAC data unit comprises transmitting, by a first RF radio of a plurality of RF radios of the first WLAN communication device and to the second WLAN communication device via the first WLAN communication channel, a first RF signal that corresponds to the first baseband signal and occupies the first RF bandwidth. In an embodiment, for example, the RF radio  428  transmits the first RF signal  620  ( FIG.  6   ) or the first RF signal  720  ( FIG.  7   ). 
     In some embodiments, receiving the second MAC data unit includes receiving, at a second RF radio of the plurality of RF radios and from the second WLAN communication device via the second WLAN communication channel, a second RF signal that corresponds to the second MAC data unit and occupies the second RF bandwidth. In some such embodiments, the method  1000  further includes generating, by the one or more baseband signal processors, a second baseband signal that corresponds to the second MAC data unit, and generating, by the one or more baseband signal processors, the second MAC data unit using the second baseband signal. In an embodiment, for example, the AP  114  receives the RF signal  640  at the RF radio  436 . 
     In an embodiment, the method  1000  further includes: providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; and transmitting, by the first RF radio and to the second WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal. In an embodiment, the first RF radio transmits at least a portion of the third RF signal simultaneously with reception by the second RF radio of at least a portion of the second RF signal. In an embodiment, the third MAC data unit corresponds to the PHY data portion  664  and the third RF signal corresponds to the RF signal  660 . 
     In an embodiment, the first WLAN communication channel includes a primary channel and the method  1000  further includes: providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; transmitting, by the first RF radio and to a legacy WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; receiving, at the first RF radio and from the legacy WLAN communication device via the first WLAN communication channel, a fourth RF signal that corresponds to an acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth baseband signal that corresponds to the acknowledgment of the third MAC data unit; and generating, by the one or more baseband signal processors, a fourth MAC data unit that corresponds to the acknowledgment of the third MAC data unit. In an embodiment, for example, the primary channel corresponds to the primary channel  812  and the AP  114  generates and transmits a MAC data unit to a legacy WLAN communication device, as described above with respect to  FIG.  8 A . 
     In some embodiments, the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include forward traffic, and the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include reverse traffic that acknowledges the forward traffic. In an embodiment, the forward traffic includes multi-user, multiple input multiple output (MU-MIMO) forward traffic transmitted to a plurality of WLAN communication device that includes the second WLAN communication devices, and the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. In an embodiment, the forward traffic includes orthogonal frequency division multiple access (OFDMA) forward traffic to a plurality of WLAN communication devices that includes the second WLAN communication device, and the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     In some embodiments, the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include downlink traffic transmitted from the first WLAN communication device, wherein the first WLAN communication device is a WLAN access point, and the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include uplink traffic transmitted to the WLAN access point. In one such embodiment, the downlink traffic includes MU-MIMO traffic to a plurality of WLAN communication devices that includes the second WLAN communication device, and the uplink traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. In another such embodiment, the downlink traffic includes OFDMA data units transmitted to a plurality of WLAN communication devices that includes the second WLAN communication device, and the uplink traffic includes OFDMA data units that are transmitted by the plurality of WLAN communication devices and triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     In an embodiment, the first and second RF bandwidths have different respective bandwidths and one of the first and second RF bandwidths is larger than another of the first and second RF bandwidths. In an embodiment, for example, the respective first and second RF bandwidths are 80 MHz and 20 MHz, 160 MHz and 20 MHz, 320 MHz and 40 MHz, or other suitable bandwidths, as described above with respect to  FIG.  5    and  FIG.  6   . 
     In an embodiment, the first RF bandwidth and the second RF bandwidth are separated by at least 160 MHz. 
       FIG.  11    is a flow diagram of an example method  1100  for wireless local area network (WLAN) communication by a first WLAN communication device, according to an embodiment. In some embodiments, the client station  154  of  FIG.  1    is configured to implement the method  1100 . In an embodiment, the method  1100  is implemented by the client station  154  by utilizing the communication device  400 , the communication device  450 , or the communication device  900  as described above with reference to  FIGS.  4 A-B  and  9 . The method  1100  is described, however, in the context of the client station  154  merely for explanatory purposes and, in other embodiments, the method  1100  is implemented by another suitable device such as the AP  114 . In various embodiments, the method  1100  is utilized to receive and process signals corresponding to those described above in reference to  FIGS.  5 - 7   . In various embodiments, the method  1100  is utilized with channelizations such as described above in reference to  FIGS.  8 A-B . 
     At block  1104 , the client station  154  (as a first WLAN communication device) receives a first MAC data unit from a second WLAN communication device via a first WLAN communication channel having a first radio frequency (RF) bandwidth. In an embodiment, the MAC data unit is an MPDU, A-MPDU, MMPDU, or other suitable MAC data unit. In an embodiment, the first MAC data unit corresponds to the PHY data portion  624  ( FIG.  6   ) and includes, for example, an MPDU intended for the client station  154 . In another embodiment, the first MAC data unit corresponds to the PHY data portion  724 - 1 ,  724 - 2 , or  724 - 3  ( FIG.  7   ). 
     At block  1108 , the client station  154  generates a second MAC data unit configured to acknowledge the first MAC data unit. In an embodiment, for example, the client station generates the acknowledgment  644 . In another embodiment, the client station  154  generates the acknowledgment  764 - 1 ,  764 - 2 , or  764 - 3 . 
     At block  1112 , the client station  154  transmits the second MAC data unit to the second WLAN communication device via a second WLAN communication channel having a second RF bandwidth that does not overlap the first RF bandwidth. In an embodiment, for example, the client station  154  transmits the acknowledgment  644  as the RF signal  640 . 
     In an embodiment, receiving the first MAC data unit includes receiving, at a first RF radio of a plurality of RF radios of the first WLAN communication device and from the second WLAN communication device via the first WLAN communication channel, a first RF signal that corresponds to the first MAC data unit and occupies the first RF bandwidth, generating, by one or more baseband signal processors implemented on one or more integrated circuit (IC) devices of the first WLAN communication device, a first baseband signal that corresponds to the first MAC data unit, and generating, by the one or more baseband signal processors, the first MAC data unit using the first baseband signal. In an embodiment, the first RF radio corresponds to the RF radio  428  and receives the RF signal  620  from the AP  114 . 
     In an embodiment, generating the second MAC data unit includes providing, by a single MAC layer processor implemented on the one or more IC devices, the second MAC data unit to the one or more baseband signal processors, and generating, at the one or more baseband signal processors, a second baseband signal that corresponds to the second MAC data unit. In an embodiment, for example, the MAC layer processor is the MAC processor  408  or  474  and the baseband signal processor is the baseband processor  424  or  432  ( FIG.  4 A or  4 B ). 
     In an embodiment, transmitting the second MAC data unit includes transmitting, by a second RF radio of the plurality of RF radios and to the second WLAN communication device via the second WLAN communication channel, a second RF signal that corresponds to the second baseband signal and occupies the second RF bandwidth. In an embodiment, the second RF radio is the RF radio  436  that transmits the RF signal  640 . 
     In an embodiment, the method  1100  further includes providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; and transmitting, by the second RF radio and to the second WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; wherein the second RF radio transmits at least a portion of the third RF signal simultaneously with reception by the first RF radio of at least a portion of the first RF signal. In an embodiment, for example, the client station  154  receives the RF signal  660  and simultaneously transmits the RF signal  640 . 
     In an embodiment, the first WLAN communication channel includes a primary channel, the method  1100  further including: providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; transmitting, by the first RF radio and to a legacy WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; receiving, at the first RF radio and from the legacy WLAN communication device via the first WLAN communication channel, a fourth RF signal that corresponds to an acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth baseband signal that corresponds to the acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth MAC data unit that corresponds to the acknowledgment of the third MAC data unit. 
     In an embodiment, the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include forward traffic, and the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include reverse traffic that acknowledges the forward traffic. 
     In an embodiment, the forward traffic includes multi-user, multiple input multiple output (MU-MIMO) forward traffic transmitted to a plurality of WLAN communication device that includes the second WLAN communication devices, the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     In an embodiment, the forward traffic includes orthogonal frequency division multiple access (OFDMA) forward traffic to a plurality of WLAN communication devices that includes the second WLAN communication device, and the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     In an embodiment, the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include downlink traffic transmitted to the first WLAN communication device, wherein the first WLAN communication device is a WLAN client station. In an embodiment, the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include uplink traffic transmitted from the WLAN client station. 
     In an embodiment, the downlink traffic includes MU-MIMO traffic to a plurality of WLAN communication devices that includes the first WLAN communication device, and the uplink traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     In an embodiment, the downlink traffic includes OFDMA data units transmitted to a plurality of WLAN communication devices that includes the first WLAN communication device, and the uplink traffic includes OFDMA data units that are transmitted by the plurality of WLAN communication devices and triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     In an embodiment, the first and second RF bandwidths have different respective bandwidths and one of the first and second RF bandwidths is larger than another of the first and second RF bandwidths. 
     In an embodiment, the first RF bandwidth and the second RF bandwidth are separated by at least 160 MHz. 
     Embodiment 1: A method for wireless local area network (WLAN) communication by a first WLAN communication device, the method comprising: generating, at the first WLAN communication device, a first media access control (MAC) data unit; transmitting, from the first WLAN communication device, the first MAC data unit to a second WLAN communication device via a first WLAN communication channel having a first radio frequency (RF) bandwidth; receiving, at the first WLAN communication device, a second MAC data unit from the second WLAN communication device via a second WLAN communication channel having a second RF bandwidth that does not overlap the first RF bandwidth, wherein the second MAC data unit corresponds to an acknowledgment of the first MAC data unit from the second WLAN communication device. 
     Embodiment 2: The method of embodiment 1, wherein: generating the first MAC data unit comprises providing, by a single MAC layer processor implemented on one or more integrated circuit (IC) devices of the first WLAN communication device, the first MAC data unit to one or more baseband signal processors of the first WLAN communication device, wherein the one or more baseband signal processors are implemented on the one or more IC devices, and generating, at the one or more baseband signal processors, a first baseband signal that corresponds to the first MAC data unit; transmitting the first MAC data unit comprises transmitting, by a first RF radio of a plurality of RF radios of the first WLAN communication device, to the second WLAN communication device via the first WLAN communication channel, a first RF signal that corresponds to the first baseband signal and occupies the first RF bandwidth; receiving the second MAC data unit comprises receiving, at a second RF radio of the plurality of RF radios and from the second WLAN communication device via the second WLAN communication channel, a second RF signal that corresponds to the second MAC data unit and occupies the second RF bandwidth, generating, by the one or more baseband signal processors, a second baseband signal that corresponds to the second MAC data unit, and generating, by the one or more baseband signal processors, the second MAC data unit using the second baseband signal. 
     Embodiment 3. The method of embodiment 2, further comprising: providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; transmitting, by the first RF radio and to the second WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; wherein the first RF radio transmits at least a portion of the third RF signal simultaneously with reception by the second RF radio of at least a portion of the second RF signal. 
     Embodiment 4. The method of embodiment 2, wherein the first WLAN communication channel includes a primary channel, the method further including: 
     providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; transmitting, by the first RF radio and to a legacy WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; receiving, at the first RF radio and from the legacy WLAN communication device via the first WLAN communication channel, a fourth RF signal that corresponds to an acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth baseband signal that corresponds to the acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth MAC data unit that corresponds to the acknowledgment of the third MAC data unit. 
     Embodiment 5. The method of embodiment 1, wherein: the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include forward traffic; the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include reverse traffic that acknowledges the forward traffic. 
     Embodiment 6. The method of embodiment 5, wherein: the forward traffic includes multi-user, multiple input multiple output (MU-MIMO) forward traffic transmitted to a plurality of WLAN communication device that includes the second WLAN communication devices; and the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 7. The method of embodiment 5, wherein: the forward traffic includes orthogonal frequency division multiple access (OFDMA) forward traffic to a plurality of WLAN communication devices that includes the second WLAN communication device; and 
     the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 8. The method of embodiment 1, wherein: the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include downlink traffic transmitted from the first WLAN communication device, wherein the first WLAN communication device is a WLAN access point; the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include uplink traffic transmitted to the WLAN access point. 
     Embodiment 9. The method of embodiment 8, wherein: the downlink traffic includes MU-MIMO traffic to a plurality of WLAN communication devices that includes the second WLAN communication device; and the uplink traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 10. The method of embodiment 8, wherein: the downlink traffic includes OFDMA data units transmitted to a plurality of WLAN communication devices that includes the second WLAN communication device; and the uplink traffic includes OFDMA data units that are transmitted by the plurality of WLAN communication devices and triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 11. The method of embodiment 1, wherein the first and second RF bandwidths have different respective bandwidths and one of the first and second RF bandwidths is larger than another of the first and second RF bandwidths. 
     Embodiment 12. The method of embodiment 1, wherein the first RF bandwidth and the second RF bandwidth are separated by at least 160 MHz. 
     Embodiment 13. A method for wireless local area network (WLAN) communication by a first WLAN communication device, the method comprising: receiving, at the first WLAN communication device, a first media access control (MAC) data unit from a second WLAN communication device via a first WLAN communication channel having a first radio frequency (RF) bandwidth; generating, at the first WLAN communication device, a second MAC data unit configured to acknowledge the first MAC data unit; transmitting, by the first WLAN communication device, the second MAC data unit to the second WLAN communication device via a second WLAN communication channel having a second RF bandwidth that does not overlap the first RF bandwidth. 
     Embodiment 14. The method of embodiment 13, wherein: receiving the first MAC data unit comprises receiving, at a first RF radio of a plurality of RF radios of the first WLAN communication device and from the second WLAN communication device via the first WLAN communication channel, a first RF signal that corresponds to the first MAC data unit and occupies the first RF bandwidth, generating, by one or more baseband signal processors implemented on one or more integrated circuit (IC) devices of the first WLAN communication device, a first baseband signal that corresponds to the first MAC data unit, and generating, by the one or more baseband signal processors, the first MAC data unit using the first baseband signal; generating the second MAC data unit comprises providing, by a single MAC layer processor implemented on the one or more IC devices, the second MAC data unit to the one or more baseband signal processors, and generating, at the one or more baseband signal processors, a second baseband signal that corresponds to the second MAC data unit; transmitting the second MAC data unit comprises transmitting, by a second RF radio of the plurality of RF radios and to the second WLAN communication device via the second WLAN communication channel, a second RF signal that corresponds to the second baseband signal and occupies the second RF bandwidth. 
     Embodiment 15. The method of embodiment 14, further comprising: providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; transmitting, by the second RF radio and to the second WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; wherein the second RF radio transmits at least a portion of the third RF signal simultaneously with reception by the first RF radio of at least a portion of the first RF signal. 
     Embodiment 16. The method of embodiment 14, wherein the first WLAN communication channel includes a primary channel, the method further including: 
     providing, by the single MAC layer processor, a third MAC data unit to the one or more baseband signal processors; generating, at the one or more baseband signal processors, a third baseband signal that corresponds to the third MAC data unit; transmitting, by the first RF radio and to a legacy WLAN communication device via the first WLAN communication channel, a third RF signal that corresponds to the third baseband signal; receiving, at the first RF radio and from the legacy WLAN communication device via the first WLAN communication channel, a fourth RF signal that corresponds to an acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth baseband signal that corresponds to the acknowledgment of the third MAC data unit; generating, by the one or more baseband signal processors, a fourth MAC data unit that corresponds to the acknowledgment of the third MAC data unit. 
     Embodiment 17. The method of embodiment 13, wherein: the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include forward traffic; the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include reverse traffic that acknowledges the forward traffic. 
     Embodiment 18. The method of embodiment 17, wherein: the forward traffic includes multi-user, multiple input multiple output (MU-MIMO) forward traffic transmitted to a plurality of WLAN communication device that includes the second WLAN communication devices; and the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 19. The method of embodiment 17, wherein: the forward traffic includes orthogonal frequency division multiple access (OFDMA) forward traffic to a plurality of WLAN communication devices that includes the second WLAN communication device; and 
     the reverse traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 20. The method of embodiment 14, wherein: the first RF bandwidth and first WLAN communication channel are designated for MAC data units that include downlink traffic transmitted to the first WLAN communication device, wherein the first WLAN communication device is a WLAN client station; the second RF bandwidth and the second WLAN communication channel are designated for MAC data units that include uplink traffic transmitted from the WLAN client station. 
     Embodiment 21. The method of embodiment 20, wherein: the downlink traffic includes MU-MIMO traffic to a plurality of WLAN communication devices that includes the first WLAN communication device; and the uplink traffic is triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 22. The method of embodiment 20, wherein: the downlink traffic includes OFDMA data units transmitted to a plurality of WLAN communication devices that includes the first WLAN communication device; and the uplink traffic includes OFDMA data units that are transmitted by the plurality of WLAN communication devices and triggered by a trigger MAC data unit transmitted via the second WLAN communication channel to the plurality of WLAN communication devices. 
     Embodiment 23. The method of embodiment 13, wherein the first and second RF bandwidths have different respective bandwidths and one of the first and second RF bandwidths is larger than another of the first and second RF bandwidths. 
     Embodiment 24. The method of embodiment 13, wherein the first RF bandwidth and the second RF bandwidth are separated by at least 160 MHz. 
     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 computer readable memory such as on a magnetic disk, an optical disk, or other storage medium, in a RAM or ROM or flash memory, processor, 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. 
     When implemented in hardware, the hardware may comprise one or more of discrete components, an integrated circuit, an application-specific integrated circuit (ASIC), a programmable logic device (PLD), etc. 
     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.