Abstract:
A system including a physical layer module and a control module. The physical layer module is configured to generate a first clear channel assessment for a first sub-channel of a communication channel and generate a second clear channel assessment for a second sub-channel of the communication channel. The first clear channel assessment indicates whether the first sub-channel is free or busy. The second clear channel assessment indicates whether the second sub-channel is free or busy. The control module is configured to, in response to the second sub-channel being busy, extend a duration of the second clear channel assessment by a predetermined period of time, and transmit data via (i) only the first sub-channel or (ii) both the first sub-channel and the second sub-channel based on (a) the first clear channel assessment, (b) the second clear channel assessment, and (c) the extended duration of the first clear channel assessment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 13/279,520, filed on Oct. 24, 2011, which is a continuation of U.S. patent application Ser. No. 11/866,754 (now U.S. Pat. No. 8,050,200), filed on Oct. 3, 2007, which claims the benefit of U.S. Provisional Application No. 60/828,140, filed on Oct. 4, 2006. The entire disclosures of the above application are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to communication systems, and more particularly to selecting transmission channels in wireless transmitters. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    I.E.E.E. sections 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(h), and 802.11(n) (collectively sections 802.11), which are incorporated herein by reference in their entirety, define ways for configuring wireless networks and devices. According to these standards, wireless network devices may operate in either an ad-hoc mode or an infrastructure mode. 
         [0005]    Referring now to  FIGS. 1 and 2 , in the ad-hoc mode, each client station  10 - 1 ,  10 - 2 , . . . , and  10 -N (collectively client stations  10 ) communicates directly with other client stations  10  without requiring an access point (AP). In  FIG. 2 , in the infrastructure mode, each client station  20 - 1 ,  20 - 2 , . . . , and  20 -M (collectively client stations  20 ) communicates with other client stations  20  through an AP  24 . The AP  24  may provide a connection to a network  26 , a server  28 , and/or for the Internet  30 . 
         [0006]    Referring generally to  FIGS. 3A-3B , a wireless network device (hereinafter device)  50  is shown. The device  50  may be the AP  24  or one of the client stations  10 ,  20 . In  FIG. 3A , the device  50  may comprise at least one antenna  52 , a physical layer (PHY) module  54 , and a medium access controller (MAC) module  56 . Additionally, the device  50  may include a processor  58  and other components. The PHY module  54  may communicate with the medium (i.e., air) via the antenna  52 . The PHY module  54  may comprise a radio frequency (RF) transceiver module  55  that transmits and receives data to and from the medium via the antenna  52 . The MAC module  56  may communicate with the PHY module  54  and the processor  58 . 
         [0007]    In  FIG. 3B , the RF transceiver module  55  may comprise a transmitter module  70  that transmits data and a receiver module  72  that receives data in the form of modulated RF carriers via the antenna  52 . The transmitter module  70  may comprise an encoder module, a modulator module, an analog-to-digital converter (ADC) module, etc. (all not shown). The receiver module  72  may comprise an automatic gain control (AGC) module, a filter module, an ADC converter module, a demodulator module, a decoder module, etc. (all not shown). 
         [0008]    802.11 provides that data may be simultaneously transmitted via multiple channels in a predetermined frequency-band. For example, devices that comply with section 802.11(a) may transmit data at 20 MHz via eight 20 MHz channels in a 5 GHz frequency-band; devices that comply with section 802.11(b) may transmit data at 20 MHz via fourteen 20 MHz channels in a 2.4 GHz frequency-band, etc. 
         [0009]    Devices that comply with section 802.11(n) may transmit data at 20 MHz or 40 MHz via a 40 MHz channel. The 40 MHz channel may comprise two 20 MHz channels. A first 20 MHz channel is called a primary channel or a control channel. A second 20 MHz channel is called a secondary channel or an extension channel. The 802.11(n)-compliant devices may transmit data at 40 MHz via the 40 MHz channel when communicating with other 802.11(n)-compliant devices. Additionally, 802.11(n)-compliant devices may transmit data at 20 MHz via the control channel when communicating with the devices that comply with 802.11 sections other than 802.11(n). 
         [0010]    A wireless network (hereinafter network) may include devices that comply with different 802.11 sections. For example, the network may comprise the AP  24  and a first set of client stations  20  that complies with section 802.11(n). Additionally, the network may include a second set of client stations  20  that comply with 802.11 sections other than section 802.11(n) (e.g., 802.11(a), 802.11(b), 802.11(g), etc.). The AP  24  may transmit and receive data at 40 MHz via the 40 MHz channel when communicating with the first set of client stations  20  and may transmit and receive data via the 20 MHz control channel when communicating with the second set of client stations  20 . 
         [0011]    Occasionally, the AP  24  may transmit data at 40 MHz when data transmitted by devices in other networks may be present in the extension channel. For example, other networks may include devices that comply with 802.11 sections other than section 802.11(n) and that transmit data at 20 MHz in a channel that may overlap with the MHz extension channel of the AP  24 . Consequently, collisions may occur when the AP  24  transmits data at 40 MHz. 
         [0012]    Additionally, collisions may occur when the AP  24  transmits data at 40 MHz while other devices that comply with 802.11 sections other than section 802.11(n) communicate in the network at 20 MHz via the extension channel. Collisions may also occur when multiple devices that comply with the section 802.11(n) simultaneously transmit data in the network. 
         [0013]    When collisions occur, data may get corrupted. Corrupted data may be discarded when received. When data received is corrupted, the data may have to be retransmitted. Thus, collisions may decrease throughput and quality of service (QoS) of the network. 
         [0014]    To minimize collisions, devices in wireless networks utilize a carrier sense multiple access (CSMA) protocol to determine when a channel is free to transmit data. Ideally, only one device may transmit data via the channel at a given time. Typically, the devices “listen” for activity (i.e., the devices sense presence or absence of RF carriers) in the channel before transmitting data via that channel. Listening for activity is generally referred to as carrier sensing (CS). Since multiple devices perform CS by simultaneously accessing the medium (i.e., air), the protocol is called carrier sense multiple access protocol. Activity in the channel may also be sensed by performing energy detection (ED), wherein presence or absence of RF energy in the channel is detected. 
         [0015]    Specifically, the PHY module  54  may generate clear channel assessments (CCAs) for the control and extension channels based on whether radio frequency (RF) activity is present or absent in the channel. The CCAs may indicate whether the channels are busy or free. Typically, the CCA for the channel is asserted (i.e., when CCA=1) when a channel is busy, and the CCA for the channel is cleared when the channel is free (i.e., when CCA=0). The terms clear, free, and idle are used interchangeably and synonymously throughout this disclosure. 
         [0016]    The PHY module  54  may communicate the CCAs to the MAC module  56 . Based on the CCAs, the MAC module  56  may decide whether to transmit data via the channel. For example, the MAC module  56  may decide that data may be transmitted via a channel when the channel is free (i.e., when CCA=0). Additionally, the MAC module  56  may decide to “back off” (i.e., to not transmit data) when the channel is busy (i.e., when CCA=1). 
       SUMMARY 
       [0017]    A system comprises a signal processing module and a control module. The signal processing module receives a first clear channel assessment (CCA) signal for a first sub-channel of a communication channel, increases a pulse width of the first CCA signal by a predetermined period of time, and generates a second CCA signal. The control module receives the second CCA signal and a third CCA signal for a second sub-channel of the communication channel. The control module transmits data via one of the second sub-channel and the communication channel based on the second and third CCA signals. 
         [0018]    In another feature, the first and second sub-channels include extension and control channels of the communication channel, respectively. The bandwidth of each of the first and second sub-channels is 20 MHz. The bandwidth of the communication channel is 40 MHz. 
         [0019]    In another feature, the control module generates a value for the predetermined period of time based on an amount of radio frequency (RF) activity in the first sub-channel. 
         [0020]    In another feature, the control module transmits data via the second sub-channel at a transmission rate of the second sub-channel when the third CCA signal indicates that the second sub-channel is clear and when the second CCA signal indicates that the first sub-channel is busy. 
         [0021]    In another feature, the control module transmits data via the communication channel at a transmission rate of the communication channel when the second and third CCA signals indicate that the first and second sub-channels are clear, respectively. 
         [0022]    In another feature, the control module does not transmit data when the third CCA signal indicates that the second sub-channel is busy. 
         [0023]    In another feature, the control module transmits data via the second sub-channel at a transmission rate of the communication channel when the third CCA signal indicates that the second sub-channel is clear. 
         [0024]    In another feature, the control module does not transmit data via the communication channel and via the second sub-channel when one of the second and third CCA signals indicates that one of the first and second sub-channels is busy, respectively. 
         [0025]    In another feature, the system further comprises a rate control module that receives feedback from the control module when data is transmitted via one of the second sub-channel and the communication channel and that determines modulation and coding scheme (MCS) rates based on the feedback. 
         [0026]    In another feature, a medium access controller (MAC) comprises the system that communicates with a physical layer (PHY) module and that receives the first and third CCA signals from the PHY module, wherein the PHY module complies with I.E.E.E. section 802.11(n). 
         [0027]    In another feature, the system further comprises the PHY module, wherein the PHY module comprises a carrier sensing module that senses radio frequency (RF) carriers in at least one of the first and second sub-channels and that generates the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0028]    In another feature, the system further comprises the PHY module, wherein the PHY module comprises an energy sensing module that senses radio frequency (RF) energy in at least one of the first and second sub-channels and that generates the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0029]    In another feature, the system further comprises the PHY module, wherein the PHY module comprises a signal strength sensing module that senses strengths of RF signals detected in the first and second sub-channels. The signal strength sensing module compares the strengths to first and second predetermined thresholds, respectively. The signal strength sensing module generates first and second relative signal strength index (RSSI) signals that indicate whether the strengths are greater than or equal to the first and second predetermined thresholds, respectively. 
         [0030]    In another feature, the PHY module generates the first and third CCA signals based on the first and second RSSI signals. 
         [0031]    In another feature, the control module determines whether the communication channel is one of clear and busy based on the first and second RSSI signals. 
         [0032]    In another feature, the MAC comprises a counter module that generates a plurality of counts based on at least one of states of the first, second, and third CCA signals and activity in the first and second sub-channels. 
         [0033]    In another feature, the system further comprises a mode control module that communicates with the MAC, that receives the counts from the counter module, and that determines a transmit mode of the MAC based on the counts, wherein the transmit mode is one of first and second transmit modes. 
         [0034]    In another feature, the MAC transmits data via the second sub-channel at a rate of the second sub-channel when the MAC is in the first transmit mode. The MAC transmits data via the communication channel at a rate of the communication channel when the MAC is in the second transmit mode. 
         [0035]    In still other features, a method comprises receiving a first clear channel assessment (CCA) signal for a first sub-channel of a communication channel and generating a second CCA signal by increasing a pulse width of the first CCA signal by a predetermined period of time. The method further comprises receiving the second CCA signal and a third CCA signal for a second sub-channel of the communication channel. The method further comprises transmitting data via one of the second sub-channel and the communication channel based on the second and third CCA signals. 
         [0036]    In another feature, the first and second sub-channels include extension and control channels of the communication channel, respectively. The bandwidth of each of the first and second sub-channels is 20 MHz. The bandwidth of the communication channel is 40 MHz. 
         [0037]    In another feature, the method further comprises generating a value for the predetermined period of time based on an amount of radio frequency (RF) activity in the first sub-channel. 
         [0038]    In another feature, the method further comprises transmitting data via the second sub-channel at a transmission rate of the second sub-channel when the third CCA signal indicates that the second sub-channel is clear and when the second CCA signal indicates that the first sub-channel is busy. 
         [0039]    In another feature, the method further comprises transmitting data via the communication channel at a transmission rate of the communication channel when the second and third CCA signals indicate that the first and second sub-channels are clear, respectively. 
         [0040]    In another feature, the method further comprises not transmitting data when the third CCA signal indicates that the second sub-channel is busy. 
         [0041]    In another feature, the method further comprises transmitting data via the second sub-channel at a transmission rate of the communication channel when the third CCA signal indicates that the second sub-channel is clear. 
         [0042]    In another feature, the method further comprises not transmitting data via the communication channel and via the second sub-channel when one of the second and third CCA signals indicates that one of the first and second sub-channels is busy, respectively. 
         [0043]    In another feature, the method further comprises receiving feedback after transmitting data via one of the second sub-channel and the communication channel and determining modulation and coding scheme (MCS) rates based on the feedback. 
         [0044]    In another feature, the method further comprises communicating with a physical layer (PHY) module and receiving the first and third CCA signals from the PHY module, wherein the PHY module complies with I.E.E.E. section 802.11(n). 
         [0045]    In another feature, the method further comprises sensing radio frequency (RF) carriers in at least one of the first and second sub-channels and generating the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0046]    In another feature, the method further comprises sensing radio frequency (RF) energy in at least one of the first and second sub-channels and generating the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0047]    In another feature, the method further comprises sensing strengths of RF signals detected in the first and second sub-channels and comparing the strengths to first and second predetermined thresholds, respectively. The method further comprises generating first and second relative signal strength index (RSSI) signals that indicate whether the strengths are greater than or equal to the first and second predetermined thresholds, respectively. 
         [0048]    In another feature, the method further comprises generating the first and third CCA signals based on the first and second RSSI signals. 
         [0049]    In another feature, the method further comprises determining whether the communication channel is one of clear and busy based on the first and second RSSI signals. 
         [0050]    In another feature, the method further comprises generating a plurality of counts based on at least one of states of the first, second, and third CCA signals and activity in the first and second sub-channels. 
         [0051]    In another feature, the method further comprises determining a transmit mode based on the counts, wherein the transmit mode is one of first and second transmit modes. 
         [0052]    In another feature, the method further comprises transmitting data via the second sub-channel at a rate of the second sub-channel in the first transmit mode. 
         [0053]    In another feature, the method further comprises transmitting data via the communication channel at a rate of the communication channel in the second transmit mode. 
         [0054]    In still other features, a system comprises signal processing means for processing signals that receives a first clear channel assessment (CCA) signal for a first sub-channel of a communication channel, that increases a pulse width of the first CCA signal by a predetermined period of time, and that generates a second CCA signal. The system further comprises control means for controlling data transmission that receives the second CCA signal and a third CCA signal for a second sub-channel of the communication channel. The control means transmits data via one of the second sub-channel and the communication channel based on the second and third CCA signals. 
         [0055]    In another feature, the first and second sub-channels include extension and control channels of the communication channel, respectively. The bandwidth of each of the first and second sub-channels is 20 MHz. The bandwidth of the communication channel is 40 MHz. 
         [0056]    In another feature, the control means generates a value for the predetermined period of time based on an amount of radio frequency (RF) activity in the first sub-channel. 
         [0057]    In another feature, the control means transmits data via the second sub-channel at a transmission rate of the second sub-channel when the third CCA signal indicates that the second sub-channel is clear and when the second CCA signal indicates that the first sub-channel is busy. 
         [0058]    In another feature, the control means transmits data via the communication channel at a transmission rate of the communication channel when the second and third CCA signals indicate that the first and second sub-channels are clear, respectively. 
         [0059]    In another feature, the control means does not transmit data when the third CCA signal indicates that the second sub-channel is busy. 
         [0060]    In another feature, the control means transmits data via the second sub-channel at a transmission rate of the communication channel when the third CCA signal indicates that the second sub-channel is clear. 
         [0061]    In another feature, the control means does not transmit data via the communication channel and via the second sub-channel when one of the second and third CCA signals indicates that one of the first and second sub-channels is busy, respectively. 
         [0062]    In another feature, the system further comprises rate control means for controlling modulation and coding scheme (MCS) rates that receives feedback from the control means when data is transmitted via one of the second sub-channel and the communication channel, and that determines the MCS rates based on the feedback. 
         [0063]    In another feature, a medium access controller (MAC) comprises the system, wherein the MAC communicates with a physical layer (PHY) module and receives the first and third CCA signals from the PHY module, wherein the PHY module complies with I.E.E.E. section 802.11(n). 
         [0064]    In another feature, the system further comprises the PHY module, wherein the PHY module comprises carrier sensing means for sensing radio frequency (RF) carriers in at least one of the first and second sub-channels and for generating the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0065]    In another feature, the system further comprises the PHY module, wherein the PHY module comprises energy sensing means for sensing radio frequency (RF) energy in at least one of the first and second sub-channels and for generating the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0066]    In another feature, the system further comprises the PHY module, wherein the PHY module comprises signal strength sensing means for sensing signal strength that senses strengths of RF signals detected in the first and second sub-channels. The signal strength sensing means compares the strengths to first and second predetermined thresholds, respectively. The signal strength sensing means generates first and second relative signal strength index (RSSI) signals that indicate whether the strengths are greater than or equal to the first and second predetermined thresholds, respectively. 
         [0067]    In another feature, the PHY module generates the first and third CCA signals based on the first and second RSSI signals. 
         [0068]    In another feature, the control means determines whether the communication channel is one of clear and busy based on the first and second RSSI signals. 
         [0069]    In another feature, the MAC comprises counting means for generating a plurality of counts based on at least one of states of the first, second, and third CCA signals and activity in the first and second sub-channels. 
         [0070]    In another feature, the system further comprises mode control means for controlling transmit modes, wherein the mode control means communicates with the MAC, receives the counts from the counting means, and determines a transmit mode of the MAC based on the counts, wherein the transmit mode is one of first and second transmit modes. 
         [0071]    In another feature, the MAC transmits data via the second sub-channel at a rate of the second sub-channel when the MAC is in the first transmit mode. The MAC transmits data via the communication channel at a rate of the communication channel when the MAC is in the second transmit mode. 
         [0072]    In still other features, a computer program executed by a processor comprises receiving a first clear channel assessment (CCA) signal for a first sub-channel of a communication channel and generating a second CCA signal by increasing a pulse width of the first CCA signal by a predetermined period of time. The computer program further comprises receiving the second CCA signal and a third CCA signal for a second sub-channel of the communication channel. The computer program further comprises transmitting data via one of the second sub-channel and the communication channel based on the second and third CCA signals. 
         [0073]    In another feature, the first and second sub-channels include extension and control channels of the communication channel, respectively. The bandwidth of each of the first and second sub-channels is 20 MHz. The bandwidth of the communication channel is 40 MHz. 
         [0074]    In another feature, the computer program further comprises generating a value for the predetermined period of time based on an amount of radio frequency (RF) activity in the first sub-channel. 
         [0075]    In another feature, the computer program further comprises transmitting data via the second sub-channel at a transmission rate of the second sub-channel when the third CCA signal indicates that the second sub-channel is clear and when the second CCA signal indicates that the first sub-channel is busy. 
         [0076]    In another feature, the computer program further comprises transmitting data via the communication channel at a transmission rate of the communication channel when the second and third CCA signals indicate that the first and second sub-channels are clear, respectively. 
         [0077]    In another feature, the computer program further comprises not transmitting data when the third CCA signal indicates that the second sub-channel is busy. 
         [0078]    In another feature, the computer program further comprises transmitting data via the second sub-channel at a transmission rate of the communication channel when the third CCA signal indicates that the second sub-channel is clear. 
         [0079]    In another feature, the computer program further comprises not transmitting data via the communication channel and via the second sub-channel when one of the second and third CCA signals indicates that one of the first and second sub-channels is busy, respectively. 
         [0080]    In another feature, the computer program further comprises receiving feedback after transmitting data via one of the second sub-channel and the communication channel and determining modulation and coding scheme (MCS) rates based on the feedback. 
         [0081]    In another feature, the computer program further comprises communicating with a physical layer (PHY) module and receiving the first and third CCA signals from the PHY module, wherein the PHY module complies with I.E.E.E. section 802.11(n). 
         [0082]    In another feature, the computer program further comprises sensing radio frequency (RF) carriers in at least one of the first and second sub-channels and generating the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0083]    In another feature, the computer program further comprises sensing radio frequency (RF) energy in at least one of the first and second sub-channels and generating the first and third CCA signals indicating whether the at least one of the first and second sub-channels is one of clear and busy. 
         [0084]    In another feature, the computer program further comprises sensing strengths of RF signals detected in the first and second sub-channels and comparing the strengths to first and second predetermined thresholds, respectively. The computer program further comprises generating first and second relative signal strength index (RSSI) signals that indicate whether the strengths are greater than or equal to the first and second predetermined thresholds, respectively. 
         [0085]    In another feature, the computer program further comprises generating the first and third CCA signals based on the first and second RSSI signals. 
         [0086]    In another feature, the computer program further comprises determining whether the communication channel is one of clear and busy based on the first and second RSSI signals. 
         [0087]    In another feature, the computer program further comprises generating a plurality of counts based on at least one of states of the first, second, and third CCA signals and activity in the first and second sub-channels. 
         [0088]    In another feature, the computer program further comprises determining a transmit mode based on the counts, wherein the transmit mode is one of first and second transmit modes. 
         [0089]    In another feature, the computer program further comprises transmitting data via the second sub-channel at a rate of the second sub-channel in the first transmit mode. 
         [0090]    In another feature, the computer program further comprises transmitting data via the communication channel at a rate of the communication channel in the second transmit mode. 
         [0091]    In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a computer readable medium such as but not limited to memory, non-volatile data storage and/or other suitable tangible storage mediums. 
         [0092]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0093]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0094]      FIG. 1  is a functional block diagram of an exemplary wireless network operating in ad-hoc mode according to the prior art; 
           [0095]      FIG. 2  is a functional block diagram of an exemplary wireless network operating in infrastructure mode according to the prior art; 
           [0096]      FIG. 3A  is a functional block diagram of an exemplary wireless network device according to the prior art; 
           [0097]      FIG. 3B  is a functional block diagram of a transceiver in a wireless network device according to the prior art; 
           [0098]      FIG. 4A  is a functional block diagram of an exemplary wireless network device; 
           [0099]      FIG. 4B  is a functional block diagram of an exemplary receiver in the wireless network device of  FIG. 4A ; 
           [0100]      FIG. 4C  depicts clear channel assessment (CCA) signals generated by the receiver of  FIG. 4B ; 
           [0101]      FIG. 5A  is a functional block diagram of an exemplary wireless network device that may transmit data in an opportunistic mode according to the present disclosure; 
           [0102]      FIG. 5B  depicts CCA signals generated according to the present disclosure; 
           [0103]      FIG. 6A  is a functional block diagram of an exemplary wireless network device according to the present disclosure; 
           [0104]      FIG. 6B  depicts a table comprising various counts generates by a medium access controller (MAC) module according to the present disclosure; 
           [0105]      FIGS. 7A and 7B  depict flowcharts of a method for transmitting data in an opportunistic mode according to the present disclosure; 
           [0106]      FIG. 8A  is a functional block diagram of a high definition television; 
           [0107]      FIG. 8B  is a functional block diagram of a vehicle control system; 
           [0108]      FIG. 8C  is a functional block diagram of a cellular phone; 
           [0109]      FIG. 8D  is a functional block diagram of a set top box; and 
           [0110]      FIG. 8E  is a functional block diagram of a mobile device. 
       
    
    
     DETAILED DESCRIPTION 
       [0111]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module, circuit and/or device refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0112]    In wireless network devices that comply with I.E.E.E. section 802.11(n), physical layer (PHY) modules provide medium access controller (MAC) modules clear channel assessments (CCAs) for control and extension channels. Based on the CCAs (i.e., based on whether the control and/or the extension channel is free), MAC modules determine whether to transmit data via the control channel portion of a 40 MHz channel, via the entire 40 MHz channel, or not at all. Typically, the MAC modules may operate in two modes. In a first mode, which may be called an aggressive mode, the MAC modules may ignore the CCAs for the extension channel and transmit data at 40 MHz when the control channel is free. In a second mode, which may be called a conservative mode, the MAC modules may not transmit data at all unless both control and extension channels are free. 
         [0113]    Referring now to  FIGS. 4A-4C , a wireless network device (hereinafter device)  50 - 1  that generates various clear channel assessment (CCA) signals is shown. The device  50 - 1  may comply with I.E.E.E. section 802.11(n) and may communicate via a 40 MHz channel that includes a 20 MHz control channel and a 20 MHz extension channel. 
         [0114]    In  FIG. 4A , the device  50 - 1  is shown to include the antenna  52 , a physical layer (PHY) module  54 - 1 , and a medium access controller (MAC) module  56 - 1 . The antenna  52  may communicate received signals to the PHY module  54 - 1 . The PHY module  54 - 1  may generate a CCA signal for the control channel (CCA_c) and a CCA signal for the extension channel (CCA_e). 
         [0115]    Additionally, the PHY module  54 - 1  may generate signals that indicate a relative signal strength index (RSSI) of radio frequency (RF) signals sensed in the control and extension channels. The signals may be called RSSI_c and RSSI_e, respectively. The PHY module  54 - 1  may communicate the CCA_c, CCA_e, RSSI_c, and RSSI_e signals to the MAC module  56 - 1 . The MAC module  56 - 1  may determine the CCA for the 40 MHz channel (hereinafter the CCA) based on CCA_c and/or CCA_e. 
         [0116]    Based on the CCA, CCA_c, and/or CCA_e, the MAC module  56 - 1  may determine whether to transmit data at 20 MHz via the control channel, at 40 MHz via the 40 MHz channel, or not at all. For example, the MAC module  56 - 1  may determine that data may be transmitted at 40 MHz via the 40 MHz channel when CCA=0 or not to transmit data at all when CCA=1. 
         [0117]    In  FIG. 4B , the PHY module  54 - 1  may comprise a receiver module  100 . The receiver module  100  may generate the CCA_c, CCA_e, RSSI_c, and RSSI_e signals as follows. The receiver module  100  may comprise a channel sensing module  102  and a signal strength sensing module  104 . The channel sensing module  102  may comprise a carrier sensing module  106  and an energy sensing module  108 . The carrier sensing module  106  may sense presence or absence of RF carriers in the control and/or extension channels. The energy sensing module  108  may detect RF energy in the control and/or extension channels. 
         [0118]    The signal strength sensing module  104  may determine the RSSI of RF signals that may be sensed in the control and/or extension channels. The signal strength sensing module  104  may generate a high RSSI_c and/or RSSI_e signal (i.e., RSSI_c=1 and/or RSSI_e=1) when the RSSI of RF signals sensed in the control and/or extension channels is greater than or equal to a predetermined threshold. The predetermined threshold for the control channel may be different than the predetermined threshold for the extensions channel. 
         [0119]    In  FIG. 4C , when the carrier sensing module  106  and/or the energy detection module  108  detects RF activity  120  in the control channel, the receiver module  100  may generate a high CCA_c signal  122  (i.e., CCA_c=1). CCA_c=1 may indicate that the control channel is busy. When the carrier sensing module  106  and/or the energy detection module  108  detects RF activity  124  in the extension channel, the receiver module  100  may generate a high CCA_e signal  126  (i.e., CCA_e=1). CCA_e=1 may indicate that the extension channel is busy. 
         [0120]    When the carrier sensing module  106  and/or the energy detection module  108  detects RF activity  128  in the control and extension channels, the receiver module  100  may generate a high CCA_c signal  130  (i.e., CCA_c=1) and a high CCA_e signal  132  (i.e., CCA_e=1). CCA_c=1 and CCA_e=1 may indicate that the control and extension channels are busy. Additionally, when the RF signals sensed in the control or extension channel are very strong, the receiver module  100  may set CCA_c=1 and CCA_e=1. 
         [0121]    The PHY module  54 - 1  may communicate CCA_c and CCA_e signals to the MAC module  56 - 1 . Based on the state of CCA_c and/or CCA_e signals, the MAC module  56 - 1  may determine the CCA for the 40 MHz channel. Based on the CCA, CCA_c, and/or CCA_e, the MAC module  56 - 1  may determine whether to transmit data at 20 MHz via the control channel, at 40 MHz via the 40 MHz channel, or not at all. Generally, when CCA_c=1 (i.e., when the control channel is busy), the MAC module  56 - 1  may decide to wait or backoff for a period of time before deciding whether to transmit data. Thereafter, the MAC module  56 - 1  may check CCA_c again to determine whether to transmit data. 
         [0122]    Specifically, the MAC module  56 - 1  may determine the CCA aggressively or conservatively. Accordingly, the MAC module  56 - 1  may operate in the aggressive mode or the conservative mode, respectively. In the aggressive mode, the MAC module  56 - 1  may disregard the extension channel (i.e., CCA_e) and may determine CCA for the 40 MHz channel based on CCA_c (i.e., CCA=CCA_c). Specifically, the MAC module  56 - 1  may determine that data may be transmitted at 40 MHz when the control channel is free (i.e., when CCA=CCA_c=0). Accordingly, the MAC module  56 - 1  may determine that data may be transmitted at 40 MHz when the control channel is free although the extension channel may be busy. Collisions may occur, however, if data is transmitted at 40 MHz when the control channel is free but the extension channel is busy. 
         [0123]    Alternatively, in the conservative mode, the MAC module  56 - 1  may determine the CCA based on a logical OR of CCA_c and CCA_e (i.e., CCA=(CCA_c OR CCA_e)). Thus, CCA=1 when CCA_c=1 or CCA_e=1, and CCA=0 only when CCA_c=0 and CCA_e=0. Specifically, the MAC module  56 - 1  may determine that data may be transmitted only when both control and extension channels are free. Additionally, the MAC module  56 - 1  may determine that data may not be transmitted at all when the control channel or the extension channel is busy. Accordingly, the MAC module  56 - 1  may determine that data may not be transmitted at all when the extension channel is busy although the control channel may be free to transmit data at 20 MHz. Consequently, the throughput of the 40 MHz channel may decrease. 
         [0124]    The present disclosure discloses an opportunistic mode that minimizes collisions and maximizes throughput. In the opportunistic mode, a MAC module may increase a pulse width of the CCA_e signal by a programmable duration and may generate a signal called CCA_e_stretched. The MAC module may backoff and determine the CCA for the 40 MHz channel based on the CCA-c signal. When the MAC module is ready to transmit based on the CCA, the MAC module may determine whether to transmit data at 20 MHz or 40 MHz based on whether the CCA_e_stretched signal is asserted or clear, respectively. 
         [0125]    Referring now to  FIGS. 5A and 5B , a device  200  is shown to comprise the antenna  52 , the PHY module  54 - 1 , and a MAC module  150 . The MAC module  150  may determine whether to transmit data at 20 MHz via the control channel or at 40 MHz via the control and extension channels in the opportunistic mode as follows. In  FIG. 5A , the MAC module  150  may comprise a signal processing module  152  and a control module  154 . The MAC module  150  may receive the CCA_c, CCA_e, RSSI_c, and RSSI_e signals from the PHY module  54 - 1 . The signal processing module  152  may increase the pulse width of the CCA_e signal by a programmable duration T and may generate a CCA_e_stretched signal  160  as shown in  FIG. 5B . 
         [0126]    The MAC module  150  may determine the CCA based on the CCA_c signal (i.e., CCA=CCA_c) and may be ready to transmit data when CCA=0 (i.e., when the control channel is free). When CCA=0, the control module  154  may determine in real time whether to transmit data at 20 MHz via the control channel or at 40 MHz via both control and extension channels based on a state of the CCA_e_stretched signal. 
         [0127]    Specifically, when CCA=0, if the CCA_e_stretched signal is asserted (i.e., if CCA_e_stretched=1), the control module  154  may determine that the extension channel is busy and that the data may be transmitted at 20 MHz via the control channel. 
         [0128]    On the other hand, when CCA=0, if the CCA_e_stretched signal is not asserted (i.e., if CCA_e_stretched=0), the control module  154  may determine that the extension channel is free and that the data may be transmitted at 40 MHz via both control and extension channels. 
         [0129]    Thus, the MAC module  150  may operate in one of the following three modes. In the aggressive mode, the control module  154  may determine CCA based on CCA_c (i.e., CCA=CCA_c). The control module  154  may ignore CCA_e and may determine that data may be transmitted in 40 MHz when CCA_c=0. In the conservative mode, the control module  154  may determine CCA based on a logical OR of CCA_c and CCA_e (i.e., CCA=(CCA_c OR CCA_e)). The control module  154  may determine that data may be transmitted at 40 MHz only when CCA_c=0 and CCA_e=0. Data may not be transmitted at all if CCA_c=1 or CCA_e=1. In the opportunistic mode, the control module  154  may determine CCA based on CCA_c (i.e., CCA=CCA_c). The control module  154  may determine that data may be transmitted at 20 MHz if CCA_c=0 and CCA_e_stretched=1. Data may be transmitted at 40 MHz if CCA_c=0 and CCA_e_stretched=0. 
         [0130]    The following examples illustrate some of the advantages of the opportunistic mode over the aggressive and conservative modes. In Example 1, the extension channel may be busy 100% of the time. Data may be transmitted at 40 MHz 100% of the time in the aggressive mode. Data transmitted at 40 MHz may, however, collide 100% of the time with the data in the extension channel in the aggressive mode. This is because in aggressive mode, data is transmitted at 40 MHz irrespective of traffic in the extension channel so long as the control channel is free. Alternatively, in the conservative mode, data may not be transmitted at all when the extension channel is busy 100% of the time. On the other hand, in the opportunistic mode, data may be successfully transmitted (i.e., without collisions) at 20 MHz via the control channel 100% of the time. 
         [0131]    In Example 2, the extension channel may be free 100% of the time. Data may be successfully transmitted at 40 MHz 100% of the time in the aggressive mode, at 40 MHz 100% of time in the conservative mode, and at 40 MHz 100% of the time in the opportunistic mode. 
         [0132]    In Example 3, the extension channel may be busy 25% of the time. In aggressive mode, data may be transmitted at 40 MHz 100% of the time. Data transmission at 40 MHz may, however, succeed only 75% of the time and may fail 25% of the time due to collisions with the data in the extension channel. Alternatively, in the conservative mode, data may be transmitted at 40 MHz 75% of the time. In the opportunistic mode, on the other hand, data may be transmitted at 40 MHz 75% of the time and at 20 MHz during the remaining 25% of the time. Thus, the opportunistic mode can increase the throughput of the 40 MHz channel and achieve maximum throughput under most conditions of the extension channel. 
         [0133]    The control module  154  may determine a value of T that may give other devices that communicate only at 20 MHz (20 MHz devices) a fair opportunity to communicate via the extension channel when the extension channel becomes free. Specifically, the control module  154  may set the value of T that may give the 20 MHz devices sufficient time (equal to T) after the falling edge of the CCA_e signal (i.e., after the extension channel becomes free) to grab the extension channel. Additionally, properly setting the value of T allows for completion of any data exchange that may be ongoing in the extension channel. In other words, increasing the pulse width of the CCA_e signal by time T is equivalent to performing a backoff based on CCA_e. 
         [0134]    The control module  154  may control the fairness to the 20 MHz devices by properly tuning the value of T. The control module  154  may tune the value of T based on the amount of activity sensed in the extension channel and the fairness to be given to the 20 MHz devices. For example, the control module  154  may increase T to increase fairness to the 20 MHz devices when the amount of activity sensed in the extension channel is high. 
         [0135]    Collisions in the 40 MHz channel may decrease in the opportunistic mode since the control module  154  may utilize the extension channel to transmit data at 40 MHz via the control and extension channels only when no other 20 MHz device grabs the extension channel (i.e., only when CCA_e_stretched=0). Additionally, the throughput of the 40 MHz channel may increase in the opportunistic mode since the control module  154  may utilize the control channel to transmit data at 20 MHz instead of not transmitting data at all when another 20 MHz device grabs the extension channel (i.e., when CCA_e_stretched=1). 
         [0136]    Referring now to  FIGS. 6A-6B , a device  200 - 1  is shown to comprise the antenna  52 , the PHY module  54 - 1 , a MAC module  150 - 1 , a rate control module  182 , and a mode control module  184 . In  FIG. 6A , the MAC module  150 - 1  may comprise the signal processing module  152 , the control module  154 , and a counter module  180 . The rate control module  182  may communicate with the control module  154  and may determine modulation and coding scheme (MCS) rates. The mode control module  184  may communicate with the counter module  180 , may receive data shown in the table in  FIG. 6B  from the counter module  180 , and may determine whether the device  200 - 1  should operate in a pure 20 MHz mode or a pure 40 MHz mode. 
         [0137]    Typically, the rate control module  182  may adapt MCS rates based on the quality of the channel. The rate control module  182  may optimally determine the MCS rates when the rate at which data was last transmitted can be known. In the opportunistic mode, however, since the control module  154  may determine whether to transmit data at 20 MHz or 40 MHz in real time, the rate control module  182  may not know the rate at which data was in fact transmitted. Accordingly, the control module  154  may provide feedback to the rate control module  182  regarding the rate at which data was last transmitted in the opportunistic mode. 
         [0138]    For a given link, the MCS rates for 20 MHz and 40 MHz modes of transmission may be different, and the rate control module  182  may be able to specify different MCS rates for 20 MHz and 40 MHz modes. For example, a MCS rate R for 20 MHz mode may be supplied with each packet of data to be transmitted. A programmable offset may be used when the packet is transmitted at 40 MHz instead. Specifically, if the offset is −1, a MCS rate (R−1) may be used in the 40 MHz mode unless the MCS rate is 0 or 8. If the offset is +1, a MCS rate (R+1) may be used in the 40 MHz mode unless the MCS rate is 7 or 15. The MCS rate R may be used in the 40 MHz mode if the offset is 0. 
         [0139]    Additionally, the counter module  180  may provide the mode control module  184  data shown in the table in  FIG. 6B . Specifically, the counter module  180  may comprise a plurality of counters that count cumulative durations for which the conditions shown in the table occur. Based on the data, the mode control module  184  may determine whether the device  200 - 1  should operate purely in 20 MHz mode, 40 MHz mode, etc. 
         [0140]    For example, when the CCA_extension Strong Count is greater than or equal to a predetermined threshold count, the mode control module  184  may determine that activity in the extension channel is strong and that the device  200 - 1  may operate purely in the 20 MHz mode. Alternatively, when the CCA_extension Weak Count is greater than or equal to a predetermined threshold count, the mode control module  184  may determine that activity in the extension channel is weak and that the device  200 - 1  may operate purely in the opportunistic 40 MHz mode. Additionally, when the activity in the extension channel is very low, the mode control module  184  may determine that the device  200 - 1  may operate purely in the 40 MHz mode, etc. 
         [0141]    Referring now to  FIGS. 7A and 7B , a method  250  for transmitting data in the opportunistic mode is shown. The method  250  comprises steps executed in parallel by the signal processing module  152  and the control module  154 . Accordingly, steps executed by the signal processing module  152  are shown in  FIG. 7A  as method  250 - 1 , and the steps executed by the control module  154  are shown in  FIG. 7B  as method  250 - 2 . The method  250  comprises the methods  250 - 1  and  250 - 2 . Although ascending numbers are used for the steps of the methods  250 - 1  and  250 - 2 , the methods  250 - 1  and  250 - 2  are performed in parallel and not sequentially. 
         [0142]    In  FIG. 7A , the method  250 - 1  begins at step  252 . The signal processing module  152  receives the CCA_e signal in step  254 . The signal processing module  152  increases the pulse width of the CCA_e signal by the programmable duration T and generates the CCA_e_stretched signal in step  255 . The method  250 - 1  ends in step  256 . 
         [0143]    In  FIG. 7B , the method  250 - 2  begins in step  257 . The control module  154  determines in step  258  whether CCA_c=1 or CCA_c=0. When CCA_c=1, the MAC module  150 - 1  backs off in step  260 , and the method  250 - 2  returns to step  257 . When CCA_c=0, the control module  154  determines in step  262  whether CCA_e_stretched=1 or CCA_e_stretched=0. When CCA_e_stretched=1, the control module  154  determines in step  264  that data may be transmitted at 20 MHz via the control channel. When CCA_e_stretched=0, the control module  154  determines in step  266  that data may be transmitted at 40 MHz via the control and extension channels. The control module  154  provides feedback to the rate control module  182  in step  268  regarding whether data was transmitted at 20 MHz or 40 MHz. The method  250 - 2  ends in step  270 . 
         [0144]    Referring now to  FIGS. 8A-8E , various exemplary implementations incorporating the teachings of the present disclosure are shown. Referring now to  FIG. 8A , the teachings of the disclosure can be implemented in a network interface  443  of a high definition television (HDTV)  437 . The HDTV  437  includes a HDTV control module  438 , a display  439 , a power supply  440 , memory  441 , a storage device  442 , the network interface  443 , and an external interface  445 . If the network interface  443  includes a wireless local area network interface, an antenna (not shown) may be included. 
         [0145]    The HDTV  437  can receive input signals from the network interface  443  and/or the external interface  445 , which can send and receive data via cable, broadband Internet, and/or satellite. The HDTV control module  438  may process the input signals, including encoding, decoding, filtering, and/or formatting, and generate output signals. The output signals may be communicated to one or more of the display  439 , memory  441 , the storage device  442 , the network interface  443 , and the external interface  445 . 
         [0146]    Memory  441  may include random access memory (RAM) and/or nonvolatile memory such as flash memory, phase change memory, or multi-state memory, in which each memory cell has more than two states. The storage device  442  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The HDTV control module  438  communicates externally via the network interface  443  and/or the external interface  445 . The power supply  440  provides power to the components of the HDTV  437 . 
         [0147]    Referring now to  FIG. 8B , the teachings of the disclosure may be implemented in a network interface  452  of a vehicle  446 . The vehicle  446  may include a vehicle control system  447 , a power supply  448 , memory  449 , a storage device  450 , and the network interface  452 . If the network interface  452  includes a wireless local area network interface, an antenna (not shown) may be included. The vehicle control system  447  may be a powertrain control system, a body control system, an entertainment control system, an anti-lock braking system (ABS), a navigation system, a telematics system, a lane departure system, an adaptive cruise control system, etc. 
         [0148]    The vehicle control system  447  may communicate with one or more sensors  454  and generate one or more output signals  456 . The sensors  454  may include temperature sensors, acceleration sensors, pressure sensors, rotational sensors, airflow sensors, etc. The output signals  456  may control engine operating parameters, transmission operating parameters, suspension parameters, etc. 
         [0149]    The power supply  448  provides power to the components of the vehicle  446 . The vehicle control system  447  may store data in memory  449  and/or the storage device  450 . Memory  449  may include random access memory (RAM) and/or nonvolatile memory such as flash memory, phase change memory, or multi-state memory, in which each memory cell has more than two states. The storage device  450  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The vehicle control system  447  may communicate externally using the network interface  452 . 
         [0150]    Referring now to  FIG. 8C , the teachings of the disclosure can be implemented in a network interface  468  of a cellular phone  458 . The cellular phone  458  includes a phone control module  460 , a power supply  462 , memory  464 , a storage device  466 , and a cellular network interface  467 . The cellular phone  458  may include the network interface  468 , a microphone  470 , an audio output  472  such as a speaker and/or output jack, a display  474 , and a user input device  476  such as a keypad and/or pointing device. If the network interface  468  includes a wireless local area network interface, an antenna (not shown) may be included. 
         [0151]    The phone control module  460  may receive input signals from the cellular network interface  467 , the network interface  468 , the microphone  470 , and/or the user input device  476 . The phone control module  460  may process signals, including encoding, decoding, filtering, and/or formatting, and generate output signals. The output signals may be communicated to one or more of memory  464 , the storage device  466 , the cellular network interface  467 , the network interface  468 , and the audio output  472 . 
         [0152]    Memory  464  may include random access memory (RAM) and/or nonvolatile memory such as flash memory, phase change memory, or multi-state memory, in which each memory cell has more than two states. The storage device  466  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The power supply  462  provides power to the components of the cellular phone  458 . 
         [0153]    Referring now to  FIG. 8D , the teachings of the disclosure can be implemented in a network interface  485  of a set top box  478 . The set top box  478  includes a set top control module  480 , a display  481 , a power supply  482 , memory  483 , a storage device  484 , and the network interface  485 . If the network interface  485  includes a wireless local area network interface, an antenna (not shown) may be included. 
         [0154]    The set top control module  480  may receive input signals from the network interface  485  and an external interface  487 , which can send and receive data via cable, broadband Internet, and/or satellite. The set top control module  480  may process signals, including encoding, decoding, filtering, and/or formatting, and generate output signals. The output signals may include audio and/or video signals in standard and/or high definition formats. The output signals may be communicated to the network interface  485  and/or to the display  481 . The display  481  may include a television, a projector, and/or a monitor. 
         [0155]    The power supply  482  provides power to the components of the set top box  478 . Memory  483  may include random access memory (RAM) and/or nonvolatile memory such as flash memory, phase change memory, or multi-state memory, in which each memory cell has more than two states. The storage device  484  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). 
         [0156]    Referring now to  FIG. 8E , the teachings of the disclosure can be implemented in a network interface  494  of a mobile device  489 . The mobile device  489  may include a mobile device control module  490 , a power supply  491 , memory  492 , a storage device  493 , the network interface  494 , and an external interface  499 . If the network interface  494  includes a wireless local area network interface, an antenna (not shown) may be included. 
         [0157]    The mobile device control module  490  may receive input signals from the network interface  494  and/or the external interface  499 . The external interface  499  may include USB, infrared, and/or Ethernet. The input signals may include compressed audio and/or video, and may be compliant with the MP3 format. Additionally, the mobile device control module  490  may receive input from a user input  496  such as a keypad, touchpad, or individual buttons. The mobile device control module  490  may process input signals, including encoding, decoding, filtering, and/or formatting, and generate output signals. 
         [0158]    The mobile device control module  490  may output audio signals to an audio output  497  and video signals to a display  498 . The audio output  497  may include a speaker and/or an output jack. The display  498  may present a graphical user interface, which may include menus, icons, etc. The power supply  491  provides power to the components of the mobile device  489 . Memory  492  may include random access memory (RAM) and/or nonvolatile memory such as flash memory, phase change memory, or multi-state memory, in which each memory cell has more than two states. The storage device  493  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The mobile device may include a personal digital assistant, a media player, a laptop computer, a gaming console, or other mobile computing device. 
         [0159]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.