Abstract:
A method and circuit for indicating signal faults in wireless transmissions, particularly, a carrier leak, includes an input to receive a wireless signal, a bias detector that detects a bias in a portion of the signal and outputs a bias value indicative of the bias, an evaluator configured to compare the bias value to at least one allowable transmission signal value, and output a signal when the bias value is outside the allowable transmission signal value, and an output, responsive to the evaluator, to indicate a carrier leakage in the wireless signal. A buffer may be provided between the input and the evaluator. The sensitivity of the circuit may be adjusted and a protocol determination may be made.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to provisional U.S. Patent Application No. 60/658,334, filed on Mar. 3, 2005, the disclosure of which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed generally to a method and apparatus that detects wireless transmission problems and, more particularly, to detecting carrier leakage. Moreover, the invention is directed to a method and device to receive and/or recover a transmission frame in the presence of carrier leakage. 
     2. Related Art 
     In order to transmit data in a transmission frame in a wireless system from a transmitter to a receiver, including a wireless network, the transmitter must first turn on or power up a power amplifier and/or other related components. Normally the power up process takes about two to three micro-seconds for a power amplifier, and its associated circuitry, to fully power up in order to transmit a transmission frame. During the period of time that the power amplifier is powering up, no transmission of a transmission frame with data takes place. This is done in order to minimize any signal distortion caused by powering up the amplifier. However, the wireless system transmitter may transmit during the power up time period an unmodulated radio frequency carrier prior to the transmission of the transmission frame. The power of this unmodulated radio frequency carrier or carrier leakage in the transmission frame is typically about 20 to 30 dB below the actual signal power of the remaining part of the transmission frame. Moreover, the carrier leakage may have an almost near DC characteristic in that the signal is mostly ones or zeros. 
       FIG. 1  shows an exemplary transmission frame  100  having carrier leakage  110  in the front portion of the transmission frame  100 . In particular, the desired portion of the transmission frame  100  that is to be received in a receiver is the preamble  120 , header/signal field  140 , and data  160  (payload). It is not desired for a receiver to receive any carrier leakage  110 . In this regard, the undesired reception of the carrier leakage  110  is generally minimal when there is a large distance between the transmitter and the receiver. Accordingly, desired signal strength can be still be above the receiver sensitivity level whereas the carrier leakage  110  is then buried in thermal noise and the carrier leakage  110  has little or no effect. Moreover, the reduced power of the carrier leakage  110  (specified at about 20-30 dB below the actual signal power) allows the receiver to be able to avoid receiving this undesired signal in the background. 
     Carrier leakage is more problematic when the transmitter and receiver are relatively close, such as in current Wireless Local Area Networks (WLAN) systems, for example those compliant with IEEE 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(n), 802.16, and 802.20, which are being used with increasing frequency in relatively close quarters in homes, businesses, and commercial applications. When the transmitter and the receiver are relatively close, the receiver has a tendency to falsely start receiver processing in response to the carrier leakage  110 . In particular, the nearer the receiver to the transmitter and the shorter duration of the energy at an antenna can potentially or falsely start receiver processing, gain control, signal detection, and/or synchronization mechanisms and the like. For example, in some WLAN systems, such as IEEE 802.11(a), the initial symbol timing synchronization relies on certain periodicity of a short preamble. Since the unmodulated radio frequency carrier, including the carrier leakage  110 , is near DC at a base band, this fulfills the periodicity requirement and subsequently causes the receiver to faultily trigger and start detection of the transmission frame  100  together with the carrier leakage  110 . Since the carrier leakage  110  is much lower in power compared to the actual transmission frame  100  parts including the preamble  120  of the signal, the header/signal field  140 , and data  160 , when the gain control locks on to the carrier leakage  110 , the remaining part of the transmission frame  100  including parts  120 ,  140 ,  160  may be saturated in the transmitter and lost once received in receiver. This would subsequently cause a significant degradation in the throughput performance that has been both observed in real operation and environments in the lab, as well as in simulations. 
     SUMMARY OF THE INVENTION 
     The invention provides a method and apparatus that detects carrier leakage and subsequently mitigates any problems associated with the carrier leakage in a receiver device and that furthermore includes other advantages apparent from the discussion herein. 
     The invention may be implemented in a number of ways. According to one aspect of the invention a circuit includes an input to receive a wireless signal, a bias detector that detects a bias in a portion of the signal and outputs a bias value indicative of the bias, an evaluator configured to compare the bias value to at least one allowable transmission signal value, and output a signal when the bias value is outside the allowable transmission signal value, and an output, responsive to the evaluator, to indicate a carrier leakage in the wireless signal. One of a receiver and a transceiver may include the above-noted circuit. A wireless transmission system may include at least one of a transmitter and a transceiver to emit a wireless signal and at least one of a receiver and a transceiver may include the above-noted circuit. 
     The circuit may include a buffer that stores a portion of the wireless signal and outputs the portion of the signal to the bias detector. The buffer may be configured to output an in-phase channel and a quadrature-phase channel to the bias detector. 
     The bias may include logical states in the portion of the signal and the bias detector may include a counter to count a number of different logical states in the portion of the signal and output a total number of one of the logical states counted as the bias value. The logical states may be ones and zeros and the counter may be configured to count the number of ones or zeros and output a total number of ones or zeros. The evaluator may be configured to compare the total number to at least one allowable transmission signal value, and output the signal when the total number may be outside the allowable transmission signal value. The at least one allowable transmission signal value may include a first threshold value and a second threshold value, and the evaluator may output the signal when the number of one of the logical states is greater than the first threshold value or less than the second threshold value. 
     The input may include a first input and second input, the bias detector may include a first bias detector and second bias detector, the evaluator may include a first evaluator and second evaluator, and each evaluator may output a comparison signal as the signal. 
     The output may include control logic and a sensitivity circuit, responsive to a control input, to select a logical combination of the comparison signals of the evaluators. The sensitivity circuit may include a selector responsive to the control input to select the logical combination. The evaluators may include comparators and the selector may include a multiplexer. 
     The circuit further may include a first buffer and a second buffer that store a portion of the wireless signal from the first input and the second input, respectively, and output the portion of the signal via an in-phase channel and a quadrature-phase channel, and a size of the portion of the wireless signal may be responsive to a window size signal. The bias may be the number of ones and zeros, and the first and second bias detectors may be counters configured to count the number of ones or zeros received from the in-phase channel and the quadrature-phase channel portion of the wireless signal and separately output a total number of ones or zeros for each of the in-phase channel and the quadrature-phase channel. 
     The circuit may include a protocol determination circuit, responsive to a type of wireless signal received and the carrier leakage, to indicate a signal protocol and an absence of a carrier leakage. 
     Alternatively, the bias detector may include a timer that determines the amount of time a logical state is resident in the portion of the signal and outputs the time as the bias value. The evaluator then may be configured to compare the time to at least one allowable transmission signal value, and output the signal when the time is outside the allowable transmission signal value. In a further alternative, the bias may be transitions between logical states in the portion of the signal and the bias detector may include a counter to count the number of transitions between logical states in the portion of the signal and output a total number of transitions. The evaluator may be configured to compare the number of transitions to at least one allowable transmission signal value, and output the signal when the number of transitions is outside the allowable transmission signal value. 
     According to another aspect of the invention a method of detecting wireless signals includes the steps of receiving a wireless signal, detecting a bias in a portion of the signal and outputting a bias value indicative of the bias, comparing the bias value to at least one allowable transmission signal value, and outputting a signal when the value is outside the allowable transmission signal value, and outputting, responsive to the signal, a signal indicating a carrier leakage in the wireless signal. One of a receiver and a transceiver may use the method noted-above. A wireless transmission system may include at least one of a transmitter and a transceiver to emit a wireless signal and at least one of a receiver and a transceiver may use the above-noted method. The method further may include storing a portion of the wireless signal and outputting the portion of the signal before the detecting step. The step of outputting a portion of the signal before the detecting step further may include outputting an in-phase channel and a quadrature-phase channel. The bias detecting step may include detecting and counting first and second logical states in the portion of the signal and outputting a total number of the first or second logical states counted as the bias value. The logical states may be ones and zeros and the step of counting further may include counting the number of ones or zeros and separately outputting a total number of ones or zeros. The step of counting further may include counting the number of ones or zeros received from an in-phase channel and a quadrature-phase channel. 
     The step of evaluating may include a comparing the total number to at least one allowable transmission signal value, and outputting the carrier leakage signal when the total number may be outside the allowable transmission signal value. The at least one allowable transmission signal value may include a first threshold value and a second threshold value, and the step of comparing may include outputting a comparison signal when the total number of logical states is greater than the first threshold value or less than the second threshold value. The step of receiving a wireless signal may include receiving a first wireless signal and a second wireless signal, the step of detecting a bias may include detecting a bias in the first wireless signal and the second wireless signal, and the step of comparing the bias value may include comparing each of the bias values in the first wireless signal and the second wireless signal to at least one allowable transmission signal and outputting first and second comparison signals. 
     The method may include a step of changing a sensitivity, responsive to a control input, to select a logical combination of the first and second comparison signals. The method further may include the step of determining a protocol, responsive to a type of wireless signal received and the wireless signal fault, to indicate a signal protocol and an absence of a wireless signal fault. 
     Alternatively, the bias detecting step may include determining an amount of time a logical state is resident in the portion of the signal and outputting the time as the bias value. The step of comparing then may include comparing the time to at least one allowable transmission signal value, and outputting the carrier leakage signal when the time is outside the allowable transmission signal value. In a further alternative, the bias may be transitions between logical states in the portion of the signal and the step of detecting may include counting the number of transitions and separately outputting a total number of transitions. The step of comparing may include comparing the total number of transitions to at least one allowable transmission signal value, and outputting the carrier leakage signal when the total number of transitions is outside the allowable transmission signal value. 
     In yet another aspect of the invention a circuit includes means for receiving a wireless signal, means for detecting a bias in a portion of the signal and outputting a bias value indicative of the bias, means for comparing the bias value to at least one allowable transmission signal value and for outputting a signal when the value is outside the allowable transmission signal value, and means for outputting, responsive to the evaluating means, a signal indicative of a carrier leakage. One of a receiver and a transceiver may include the circuit noted-above. A wireless transmission system may include at least one of a transmitter and a transceiver to emit a wireless signal and at least one of a receiver and a transceiver may include the above-noted circuit. The circuit further may include means for storing a portion of the wireless signal and for outputting the portion of the signal. The storing means may be configured to output an in-phase channel and a quadrature-phase channel. The bias detecting means may include means for counting first and second logical states in the portion of the signal, and outputting a total number of the first or second logical states counted as the bias value. The logical states may be ones and zeros and counter means may count the number of ones or zeros and output a total number of ones or zeros. The comparing means may compare the total number to at least one allowable transmission signal value, and output the signal when the total number is outside the allowable transmission signal value. The at least one allowable transmission signal value may include a first threshold value and a second threshold value, and the comparing means may output a comparison signal when the number ones or zeros is greater than the first threshold value or is less than the second threshold value. 
     The input means may include first and second input means, the counter means may include first and second counter means, and the comparing means may include first and second comparing means, with each comparing means outputting a comparison signal. 
     The outputting means may include means for logically combining and means, responsive to a control input, for adjusting the sensitivity of the circuit to carrier leakage. The sensitivity means may include means for selecting a logical combination of the comparison signals of the comparing means. 
     The circuit further may include first and second means for storing a portion of the wireless signal and outputting the portion of the signal via an in-phase channel and a quadrature-phase channel. The first and second counter means may count the number of different logical states received from the in-phase channel and the quadrature-phase channel portion of the wireless signal and separately output a total number of different logical states for each of the in-phase channel and the quadrature-phase channel. The circuit may include means, responsive to a type of wireless signal and the carrier leakage, for indicating a signal protocol and an absence of a carrier leakage in the wireless signal. 
     Alternatively, the bias detecting means may determine the amount of time a logical state is resident in the portion of the signal and output the time as the bias value. The comparing means may compare the time to at least one allowable transmission signal value, and output the signal when the time is outside the allowable transmission signal value. In a further alternative, the bias may include transitions between logical states in the portion of the signal and the bias detecting means may count the number of transitions between logical states in the portion of the signal and output a total number of transitions. The comparing means may compare the total number to at least one allowable transmission signal value, and output the signal when the total number is outside the allowable transmission signal value. 
     According to a further aspect of the invention a computer includes executable code for detecting wireless signals and the computer executes the steps of receiving a wireless signal, detecting a bias in a portion of the signal and outputting a bias value indicative of the bias, comparing the bias value to at least one allowable transmission signal value, and outputting a signal when the value is outside the allowable transmission signal value, and outputting, responsive to the signal, a signal indicating a carrier leakage in the wireless signal. One of a receiver and a transceiver may use the computer and executable code noted-above. A wireless transmission system may include at least one of a transmitter and a transceiver to emit a wireless signal and at least one of a receiver and a transceiver may use the above-noted computer and executable code. The computer and executable code further may include storing a portion of the wireless signal and outputting the portion of the signal before the detecting step. The step of outputting a portion of the signal before the detecting step further may include outputting an in-phase channel and a quadrature-phase channel. The bias detecting step may include detecting and counting first and second logical states in the portion of the signal and outputting a total number of the first or second logical states counted as the bias value. The logical states may be ones and zeros and the step of counting further may include counting the number of ones or zeros and separately outputting a total number of ones or zeros. The step of counting further may include counting the number of ones or zeros received from an in-phase channel and a quadrature-phase channel. The step of evaluating may include a comparing the total number to at least one allowable transmission signal value, and outputting the carrier leakage signal when the total number may be outside the allowable transmission signal value. The at least one allowable transmission signal value may include a first threshold value and a second threshold value, and the step of comparing may include outputting a comparison signal when the total number of logical states is greater than the first threshold value or less than the second threshold value. 
     The step of receiving a wireless signal may include receiving a first wireless signal and a second wireless signal, the step of detecting a bias may include detecting a bias in the first wireless signal and the second wireless signal, and the step of comparing the bias value may include comparing each of the bias values in the first wireless signal and the second wireless signal to at least one allowable transmission signal and outputting first and second comparison signals. The computer and executable code may include a step of changing a sensitivity, responsive to a control input, to select a logical combination of the first and second comparison signals. The computer and executable code further may include the step of determining a protocol, responsive to a type of wireless signal received and the wireless signal fault, to indicate a signal protocol and an absence of a wireless signal fault. 
     Alternatively, the bias detecting step may include determining an amount of time a logical state is resident in the portion of the signal and outputting the time as the bias value. The step of comparing then may include comparing the time to at least one allowable transmission signal value, and outputting the carrier leakage signal when the time is outside the allowable transmission signal value. In a further alternative, the bias may include transitions between logical states in the portion of the signal and the step of detecting further may include counting the number of transitions and separately outputting a total number of transitions. The step of comparing may include comparing the total number of transitions to at least one allowable transmission signal value, and outputting the carrier leakage signal when the total number of transitions is outside the allowable transmission signal value. 
     Additional features, advantages, and embodiments of the invention may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the detailed description serve to explain the principles of the invention. No attempt is made to show structural details of the invention in more detail than may be necessary for a fundamental understanding of the invention and the various ways in which it may be practiced. In the drawings: 
         FIG. 1  shows a typical transmission frame with a transmission having carrier leakage; 
         FIG. 2  shows a single input single output (SISO) receiver and transmitter system that may use the carrier leakage detection circuits of the invention; 
         FIG. 3  shows a circuit for detecting carrier leakage in a SISO transceiver constructed according to the principles of the invention; 
         FIG. 4  shows a more detailed embodiment of the circuit for detecting carrier leakage shown in  FIG. 3 ; 
         FIG. 5  shows a multiple input multiple output (MIMO) receiver and transmitter system that may use the carrier leakage detection circuits of the invention; 
         FIG. 6  shows a circuit for detecting carrier leakage in a MIMO transceiver constructed according to the principles of the invention; 
         FIG. 7  shows a more detailed embodiment of the circuit for detecting carrier leakage shown in  FIG. 6 , including a sensitivity selector; 
         FIG. 8  shows a circuit for detecting carrier leakage similar to  FIG. 7 , but without a sensitivity selector; 
         FIG. 9  shows a circuit that may be used with the carrier leakage detection circuits of the invention for operating with a plurality of transmission protocols; 
         FIG. 10  shows a flow chart of a process for detecting carrier leakage that may be implemented in the circuits of the invention; and 
         FIGS. 11 ,  12 ,  13 ,  14 , and  15  show various exemplary implementations of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the invention may be practiced and to further enable those of skill in the art to practice the embodiments of the invention. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the invention, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings. 
       FIG. 2  schematically shows how the invention may be implemented in a wireless single input single output (SISO) receiver and transmitter system  600 . In particular, the wireless system  600  includes a transmitter  610  that transmits a transmission frame  100  to a receiver  620 . Of course, it should be apparent that the transmitter  610  can also include a receiver (transceiver) and the receiver  620  can include a transmitter (transceiver). The receiver  620  shown in  FIG. 2  further includes a carrier leak detector circuit of the invention. Accordingly, the receiver  620  is able to detect carrier leakage  110 , control reception based thereon, and operate with greater throughput. 
       FIG. 3  shows a circuit for detecting carrier leakage in a SISO transceiver such as a SISO system  600 . In particular, the received transmission frame  100  is received initially in a receiver and a characteristic of the signal, such as the logical states thereof, is stored in the buffer  510 . The logical states contemplated for use in the invention may be any logical states known in the art, including polarity, logical ones and zeros, and similar states. For ease of explanation, the detailed description will reference ones and zeros as the exemplary logical states, but any such known logical state may be employed in the invention. As described herein, in order to determine whether the characteristic of the signal stored in the buffer has a particular bias in favor of a logical state, the circuits of the invention either count the number of a particular logical state, such ones or zeros, in the stored signal, the number of the transitions between logical state in the stored signal, or the time period in which a particular logical state is resident in the signal. Once the logical state is counted or timed in a bias detector of the invention, a bias evaluator determines whether the signal has a particular bias in favor of one of the logical states by comparing the values to one or more predetermined thresholds. The invention uses this bias information to detect a carrier leakage, which carrier leakage  110  does not typically have an equal number of logical states. On the contrary, carrier leakage typically has a predominant number of one state. Accordingly, detecting a bias for a window or portion of a signal allows detection of the carrier leakage. 
     The buffer  510  holds the characteristics of the received signal within a window of time. The size of window may be controlled based on a window size input  550 . The window size input  550  may be set by various features such as the transmission protocol type or may be adaptive to the various other transmission factors in order to increase throughput. The values stored in the buffer  510  are output as an in-phase and quadrature-phase signal that is input to a bias detector  520  that detects a bias in the signal output from the buffer  510  from the in-phase and quadrature-phase outputs. The bias detector may employ a counter, such as described in the  FIG. 4  embodiment, to determine the quantity of a signal polarity, or logical states, such as ones or zeros, present in a signal with the amount of any of these signal components indicating a bias. Alternatively, a timer may be employed to measure in a time window the length of time a signal polarity, or logical state, such as ones or zeros, are resident (present) in a signal. In another embodiment, the bias may be detected based on the number of transitions from one state to another state. Detecting the number of transitions from one state to another allows the detection of a bias. The amount of bias is then output by bias detector  520  to bias evaluators  530  and  540 , which may be comparator circuits, such as described in the  FIG. 4  embodiment. 
     The output of the bias evaluator circuits  530  and  540  determine whether or not the bias has met a minimum threshold or failed to meet a maximum threshold (i.e., has allowable transmission signal values). In particular, if the bias exceeds a maximum threshold or is less than minimum threshold, a signal indicating carrier leakage is set and output from the bias evaluator  530  and/or  540 . The outputs of the bias evaluators  530  and  540  are input to a control circuit  501  that outputs a leakage detection signal based on at least a logical combination of the output of bias evaluators  530  and  540 . The signal subsequently is used at least in part to disable the receiver to avoid a reception error and reduced throughput. 
       FIG. 4  shows a more detailed embodiment of the  FIG. 3  circuit for the detection of carrier leakage  110  in a SISO type receiver. In particular, the received transmission frame  100  is received initially in a receiver and the signal characteristics, such as the polarities, are stored in a buffer  510 , such as a short sync buffer, as ones (or alternatively zeros) based on input  599 . The window time may be responsive to a window time signal  550 . The buffer  510  holds the polarities of the received signal within the window of time. The values stored in the buffer  510  are output as an in-phase and quadrature-phase signal that is input to a counter  520  that counts the number of ones that are output from the buffer  510  from the in-phase and quadrature-phase outputs within a given time period. The counter value provides an indication of whether the samples that are currently being received are part of WLAN short preamble or near-DC leakage. If it is a short preamble, the number of ones and zeros would be roughly the same since the signal fluctuates about DC. However, if it is a strong near-DC leakage, buffered sign bits would be mostly ones or mostly zeros depending on the polarity. Once the number of ones has been counted in counter  520 , the counter  520  outputs the number of ones to comparator circuits  530  and  540 , respectively. 
     In a specific embodiment shown in  FIG. 4 , the buffer  510  holds the polarities of the received signal within a 1.6 microsecond window that is associated with a particular sampling rate of 40 MHz. Accordingly there are 64 such stored polarities within the 1.6 microsecond window. 
     As noted herein, carrier leakage  100  does not typically have an equal number of ones and zeros. On the contrary, a carrier leakage typically has a predominant number of zeros or a predominant number of ones. Accordingly, counting the number of ones for a window or portion of a signal allows detection of the carrier leakage. The comparator circuits  530  and  540  determine whether or not the number of ones and/or the number of zeros has met a minimum threshold or failed to meet a maximum threshold. Thus, the output of comparator circuits  530  and  540  is based on whether or not the number of ones (or the number of zeros) has met a minimum threshold or failed to meet a maximum threshold (i.e., has allowable transmission signal values). In particular, when the number of ones exceeds a maximum threshold (SS_leak_TH) or is less than window size minus the maximum threshold (for example 64 minus the maximum threshold SS_leak_TH (minimum threshold)), a carrier leakage signal is set and output from the comparator circuit  530  and/or comparator circuit  540 . The outputs of the comparator circuit  530  and the comparator circuit  540  are input to an OR gate  550  in control circuit  501 . 
     The OR gate  550  outputs the carrier leakage detection signal when the carrier leakage detection signal is received from either the comparator circuit  530  or the comparator circuit  540 . Thereafter the OR gate  550  inputs the carrier leakage detection signal to an AND gate  580 . The AND gate  580  ANDs the carrier leakage detection signal together with a signal detection signal (!sigDet). The signal detection signal goes high when the receiver has received a valid Clear Channel Assessment (CCA) signal. So when the carrier leakage signal is high and the valid CCA received signal is high, the AND gate  580  outputs a leakage detection signal. The signal subsequently disables the receiver to avoid a transmission error and reduced throughput. 
       FIG. 5  schematically shows how the invention may be implemented in a wireless Multiple Input Multiple Output (MIMO) receiver and transmitter system  800 . In particular, the wireless system  800  includes at least a transmitter  610  that transmits a transmission frame  100  to a receiver  620 , and a transmitter  610   n  that transmits a transmission frame  100   n  to a receiver  620   n . Of course, it should be apparent that the transmitters  610 ,  610   n  can also include receivers (transceivers) and the receivers  620 ,  620   n  may include also transmitters (transceivers). In addition, there may be more than two transmitters and/or more than two receivers. The receivers  620 ,  620   n  shown in  FIG. 5  further include a carrier leak detector circuit of the invention. Accordingly, the receivers  620 ,  620   n  are able to detect carrier leakage  110 , control reception based thereon, and operate with greater throughput. 
       FIG. 6  shows a circuit for the detection of carrier leakage  110  in a MIMO transceiver, such as MIMO system  800 . The characteristics of an input  299  of the transmission frame  100  are stored in a buffer  210  as logical states in the same manner as described above in connection with the SISO embodiments. The buffer  210  holds the logical states of the received transmission frame  100  within a limited time window that is associated with a particular sampling rate, with the window of time being adjustable responsive to an input  250 . The values stored in the buffer  210  are output as an in-phase (I) signal and a quadrature-phase (Q) signal that are input to bias detector  220 . The bias detector  220  detects the bias in the in-phase and quadrature-phase inputs within a given time-period in a manner similar to that described in connection with the  FIG. 3  bias detector  520 . Once the bias is detected, the bias is output to bias evaluators  230  and  240 , which may be comparator circuits as described in the  FIGS. 7 and 8  embodiments. 
     The I and Q phases are 90 degrees offset from one another. The 90-degree separation allows for two distinct windows in which the bias is detected. However, it is contemplated that a single-phase system could be used, however it may not be as robust as the I and Q phases but may require less circuit or chip area. 
     The bias evaluators  230  and  240  determine whether or not a bias has met a minimum threshold or failed to meet a maximum threshold in a manner similar to that described in connection with the  FIG. 3  bias evaluators  530 ,  540 . The outputs of bias evaluators  230  and  240  are input to a control  201 . 
     A second parallel system for use in the MIMO transceiver is also shown in  FIG. 6 . In particular, a buffer  215  holds the characteristics of another received signal within a window based on input  298 , with the window size of buffer  215  being adjustable in response to a signal  251 . The values stored in the buffer  215  are again output as an in-phase and quadrature-phase signal that are input to a bias detector  225  that detects a bias as noted above. Once the bias has been detected, the bias value is output to the bias evaluators  235  and  245 . 
     The bias evaluators  235  and  245  again determine whether or not the bias has met a minimum threshold or failed to meet a maximum threshold or is within allowable transmission signal values as noted above with bias evaluators  530 ,  540  of  FIG. 3 . The outputs of bias evaluators  235  and  245  are also input to the control  201 . 
     The control  201  thus receives the carrier leakage detection signal from circuits  230 ,  235 ,  240 ,  245  together with a signal detection signal (!sigDet) and optionally a sensitivity level signal (LEAK_DET_ANT_AND), such as shown in  FIG. 7  described below. The signal detection signal (!sigDet) goes high when the receiver has received a CCA signal. So when the carrier leakage signal is high and there is a valid CCA signal received such that the carrier leakage signal (!sigDet) is high, the control  201  will combine these signals logically and output a leakage detection signal (leakDetEff) accordingly based on the sensitivity level signal LEAK_DET_ANT_AND (if employed). 
       FIG. 7  shows a more detailed embodiment of the circuit for detecting carrier leakage shown in  FIG. 6 , including a sensitivity selector. The logical states such as the polarities of an input  299  of the transmission frame  100  are stored in a buffer  210 , such as a short sync buffer, as ones (or alternatively zeros). The buffer  210  holds the polarities of the received transmission frame  100  within a limited time window that is associated with a particular sampling rate. The length of the window being based on input  250 . The values stored in the buffer  210  are output as an in-phase (I) signal and a quadrature-phase (Q) signal that are input to a counter  220 . The counter  220  counts the number of ones that are input from the buffer  210  from the in-phase and quadrature-phase inputs within a given time-period. Once the number of ones has been counted in counter  220 , the counter  220  outputs the number of ones respectively to comparator circuits  230  and  240 . Additionally, it is contemplated that multiple counters can be used to count the number of ones that are input from the buffer  210  from the in-phase and quadrature-phase inputs. 
     The I and Q phases are 90 degrees offset from one another. The 90-degree separation allows for two distinct windows in which to count ones or zeros. However, it is contemplated that a single-phase system could be used, however it may not be as robust as the I and Q phases but may require less circuit or chip area. 
     In a specific embodiment shown in  FIG. 7 , the buffer  210  may hold the polarities of the received signal within a 1.6 microsecond window. This is associated with a 40 MHz sampling rate. Accordingly, there are 64 such stored polarities within the 1.6 microsecond window. 
     In one particular embodiment, if the number of ones exceeds the maximum threshold (SS_leak_TH) or is less than window-size minus the maximum threshold (for example, less than 64 minus the maximum threshold SS_leak_TH (minimum threshold)), a signal indicating carrier leakage is output from comparator circuit  230  or circuit  240 . In other words, the basis for comparison is whether the number of ones is within allowable transmission signal values indicative of a data transmission. The outputs of comparator circuit  230  and comparator circuit  240  are input to an OR gate  250  in control circuit  201 . The OR gate  250  outputs the carrier leakage detection signal (leakDet_ 1 ) when the carrier leakage detection signal is received from either the comparator circuit  230  or the comparator circuit  240 . Thereafter the OR gate  250  inputs the carrier leakage detection signal (leakDet_ 1 ) to both an AND gate  260  and an OR gate  265 . 
     A second parallel system for use in the MIMO transceiver is also shown in  FIG. 7 . In particular, a buffer  215 , such as a short sync buffer, holds the polarities of another received signal within a window based on input  298 . The values stored in the buffer  215  are again output as an in-phase and quadrature-phase signal that are input to a counter  225  that counts the number of ones that are input from the buffer  215  from the in-phase and quadrature-phase inputs within a given time-period window based on input  251 . Once the number of ones has been counted in the counter  225 , this counter outputs the number of ones respectively to comparator circuits  235  and  245 . 
     The comparator circuits  235  and  245  determine whether or not the number of ones has met a minimum threshold or failed to meet a maximum threshold or are within allowable transmission signal values. In particular, if the number of ones exceeds the maximum threshold (SS_leak_TH) or is less than a window size minus the maximum threshold (for example, 64 minus the maximum threshold SS_leak_TH (minimum threshold)), a signal indicating carrier leakage is set and output from comparator circuit  235  and/or circuit  245 . The outputs of comparator circuit  235  and comparator circuit  245  are input to an OR gate  255  in control circuit  201 . The OR gate  255  outputs the carrier leakage detection signal (leakDet — 2) when the carrier leakage detection signal is received from either the comparator circuit  235  or the comparator circuit  245 . Thereafter, the OR gate  255  also outputs the carrier leakage detection signal (leakDet_ 2 ) to both the AND gate  260  and the OR gate  265  that form a logical combination of the signals (leakDet_ 1 , leakDet_ 2 ). 
     The output of both the AND gate  260  and the OR gate  265  is input to a multiplexer  270 . The choice of whether the carrier leakage detection signal from the AND gate  260  or the carrier leakage detection signal from the OR gate  265  is selected is based on the selection signal (LEAK_DET_ANT_AND) the multiplexer  270  receives to select either the AND gate  260  or the OR gate  265  outputs. The choice of the AND gate  260  or the OR gate  265  input is a matter of sensitivity preference. More specifically, the sensitivity of determining whether the carrier leakage  110  is detected is higher with the OR gate  265  than the AND gate  260 . In other words, the AND gate  260  requires at least one leak detection signal from each input  298 ,  299 , whereas the OR gate  265  requires only one. 
     When the multiplexer  270  receives the carrier leakage detection signal on a channel that has been selected by the selection signal, the multiplexer  270  outputs the carrier leakage detection signal when carrier leakage has been detected by that channel. This output is input to an AND gate  280 . The AND gate  280  ANDs the carrier leakage detection signal together with a signal detection signal (!sigDet). The signal detection signal goes high when the receiver has received a valid clear channel assessment (CCA) signal. So when the carrier leakage signal is high and there is a valid CCA signal received such that the carrier leakage signal (!sigDet) is high, the AND gate  280  outputs a leakage detection signal (leakDetEff). 
       FIG. 8  shows a circuit for the detection of carrier leakage similar to the  FIG. 7  circuit, but without a sensitivity selector in the control circuit  401 . The logical states, such as polarities of an input  499 , are stored in a buffer  410 , such as a short sync buffer, as ones (or alternatively zeros). The buffer  410  holds the polarities of the received signal within a limited time window that is associated with a particular sampling rate or based on an input  450 . The values stored in the buffer  410  are output as an in-phase and quadrature-phase signal that is input to a counter  420 . The counter  420  counts the number of ones or zeros that are input from the buffer  410  from the in-phase and quadrature-phase inputs within a given time-period. Once the number of ones has been counted in counter  420 , the counter  420  outputs the number (ctr I, dr Q) of ones to comparator circuits  430  and  440 , respectively. 
     In a specific embodiment shown in  FIG. 8 , the buffer  410  may hold the polarities of the received signal within a 1.6 microsecond window. This is associated with a 40 MHz sampling rate. Accordingly there are 64 such stored polarities within the 1.6 microsecond window. 
     The comparator circuits  430  and  440  determine whether or not the number of ones and the number of zeros has met a minimum threshold or failed to meet a maximum threshold (i.e. is within allowable values of good transmission). In one particular embodiment, if the number of ones exceeds the maximum threshold (SS_leak_TH) or is less than window size minus the maximum threshold (for example, 64 minus the maximum threshold SS_leak_TH (minimum threshold)), a carrier leakage signal is set and output from comparator circuit  430  and/or circuit  440 . The outputs of comparator circuit  430  and comparator circuit  440  are input to an OR gate  450  in control  401 . The OR gate  450  outputs the carrier leakage detection signal (leakDet_ 1 ) when the carrier leakage detection signal is received from either the comparator circuit  430  or the comparator circuit  440 . Thereafter the OR gate  450  inputs the carrier leakage detection signal (leakDet_ 1 ) to an AND gate  460 . 
     A second parallel system for use in the MIMO transceiver is also shown in  FIG. 8 . In particular, a buffer  415 , such as a short sync buffer, holds the polarities of another received signal  498  within a window of time based on input  451 . The values stored in the buffer  415  are again output as an in-phase and quadrature-phase signal that are input to a counter  425  that counts the number of ones that are input from the buffer  415  from the in-phase and quadrature-phase outputs. Once the number of ones has been counted in counter  425 , this counter outputs the number ones (ctrOnel, ctrOneQ) respectively to comparator circuits  435  and  445 . 
     The comparator circuits  435  and  445  again determine whether or not the number of ones and the number of zeros has met a threshold or is within allowable transmission values. In one particular embodiment, when the number of ones exceeds the maximum threshold (SS_leak_TH) or is less than a window size minus the maximum threshold (SS_leak_TH (minimum threshold)), a carrier leakage signal is set and output from comparator circuit  435  and/or comparator circuit  445  in control  401 . The outputs of comparator circuit  435  and comparator circuit  445  are input to an OR gate  455 . The OR gate  455  outputs the carrier leakage detection signal (leakDet_ 2 ) when the carrier leakage detection signal is received from either the comparator circuit  435  or the comparator circuit  445 . 
     The output of the both the OR gate  450  (leakDet_ 1 ) and the OR gate  455  (leakDet_ 2 ) inputs to an AND gate  460 . The output of AND gate  460  inputs to an AND gate  480  that ANDs the carrier leakage detection signal together with a signal detection signal (!sigDet). The signal detection signal (!sigDet) goes high when the receiver has received a valid CCA signal. So when the carrier leakage signal is high and the valid CCA signal is high (!sigDet), the AND gate  480  outputs a leakage detection signal (leakDetEff). This output may then be used in conjunction with the  FIG. 9  circuit or alternatively without the  FIG. 9  circuit described below to avoid receiving transmission errors. Additionally, an OR gate may be substituted for the AND gate  460  for increased sensitivity. 
       FIG. 9  shows a circuit for use with any of the leakage detection signal circuits of the invention that is responsive to a protocol type signal to output a protocol signal when there is no carrier leakage or disable a protocol signal when there is carrier leakage. In particular, circuit  300  shown in  FIG. 9  receives, from AND gate  280  or control  501  for example, the leakage detection signal (leakDetEff) in both an AND gate  310  and an AND gate  320 . Also being input to the AND gate  310  is a cs11b signal, which is indicative of a CCA signal from the receiver indicating reception of a particular WLAN transmission protocol type, such as for example one that is compliant with IEEE 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(n), 802.16, or 802.20. Similarly, the AND gate  320  receives the leakage detection signal together with a CCA signal, such as a cs11ng signal indicating reception of a different particular WLAN transmission protocol type, for example one that is compliant with IEEE 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(n), 802.16, or 802.20. Accordingly, an absence of an output from the AND gate  310  of a cs11b′ signal disables the erroneous reception of the carrier leakage  110  for that transmission type; and the absence of an output from the AND gate  320  of a ca11ng′ signal disables the erroneous reception of the carrier leakage  110  for that transmission type. Moreover, it is contemplated that the leakage detection signal also may reset the gain acquisition control circuitry, other similar circuitry, or system state in a transmitter to ensure transmission reception. 
       FIG. 10  shows an exemplary logic flow chart of a process for detecting carrier leakage according the principles of the invention, which may be implemented in the circuits of the invention. As shown in step S 1000 , a wireless signal, such as a WLAN transmission frame  100 , is received in a receiver. Next in step S 1002 , bias in a characteristic of the received wireless signal such as logical state is detected in accordance with the principles of the invention discussed above. The bias value of the signal that is detected is output in step S 1004 . 
     As further shown in step S 1006  of  FIG. 10 , it is determined whether or not the bias is outside allowable transmission values. In particular, when the bias is outside the allowable transmission values, then there is most likely some carrier leakage in the wireless signal. More specifically, the bias is outside the allowable transmission values when the bias has failed to meet a minimum threshold and/or exceeded a maximum threshold. When it is determined that the bias value is outside an allowable transmission value the logic will flow to step S 1008  along the Yes branch of the flow chart of  FIG. 10 . In step S 1008 , a signal indicating carrier leakage is output. The signal indicating carrier leakage subsequently may be logically combined with other receiver signals to disable the receiver to avoid a reception error and reduced throughput caused by carrier leakage. On the other hand, should the bias value be inside an allowable transmission value, the logic will flow to the No branch. Accordingly, the process of detecting carrier leakage may be repeated for further received wireless signals. 
     It should be noted that although the counters are described in the above-noted embodiments as counting ones it is contemplated that the counters could also count zeros, changes in states or transitions, or any other logical states known in the art. 
     In accordance with various embodiments of the invention, the methods described herein are intended for operation with dedicated hardware implementations including, but not limited to, semiconductors, application specific integrated circuits, programmable logic arrays, and other hardware devices constructed to implement the methods and modules described herein. Moreover, various embodiments of the invention described herein are intended for operation as software programs running on a computer processor. Furthermore, alternative software implementations including, but not limited to, distributed processing, component/object distributed processing, parallel processing, virtual machine processing, any future enhancements, or any future protocol can also be used to implement the methods described herein. 
     It should also be noted that the software implementations of the invention as described herein are optionally stored on a tangible storage medium, such as: a magnetic medium such as a disk or tape; a magneto-optical or optical medium such as a disk; or a solid state medium such as a memory card or other package that houses one or more read-only (non-volatile) memories, random access memories, or other re-writable (volatile) memories. A digital file attachment to email or other self-contained information archive or set of archives is considered a distribution medium equivalent to a tangible storage medium. Accordingly, the invention is considered to include a tangible storage medium or distribution medium, as listed herein and including art-recognized equivalents and successor media, in which the software implementations herein are stored. 
     The invention can be implemented in a variety of devices, some of which are described in more detail below. Referring now to  FIG. 11 , the invention can be implemented in a set top box  1180 . The invention may implement either or both signal processing and/or control circuits, which are generally identified in  FIG. 11  at  1184 , a WLAN interface and/or mass data storage of the set top box  1180 . The set top box  1180  receives signals from a source such as a broadband source and outputs standard and/or high definition audio/video signals suitable for a display  1188  such as a television and/or monitor and/or other video and/or audio output devices. The signal processing and/or control circuits  1184  and/or other circuits (not shown) of the set top box  1180  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other set top box function. 
     The set top box  1180  may communicate with mass data storage  1190  that stores data in a nonvolatile manner. The mass data storage  1190  may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The set top box  1180  may be connected to memory  1194  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The set top box  1180  also may support connections with a WLAN via a WLAN network interface  1196  constructed according the principles of the invention. 
     Referring now to  FIG. 12 , the invention can be implemented in a high definition television (HDTV)  1220 . The invention may implement either or both signal processing and/or control circuits, which are generally identified in  FIG. 12  at  1222 , a WLAN interface and/or mass data storage of the HDTV  1220 . The HDTV  1220  receives HDTV input signals in either a wired or wireless format and generates HDTV output signals for a display  1226 . In some implementations, signal processing circuit and/or control circuit  1222  and/or other circuits (not shown) of the HDTV  1220  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other type of HDTV processing that may be required. 
     The HDTV  1220  may communicate with mass data storage  1227  that stores data in a nonvolatile manner such as optical and/or magnetic storage devices. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The HDTV  1220  may be connected to memory  1228  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The HDTV  1220  also may support connections with a WLAN via a WLAN network interface  1229  constructed according the principles of the invention. 
     Referring now to  FIG. 13 , the invention can be implemented in a control system of a vehicle  1330 , a WLAN interface and/or mass data storage of the vehicle control system. In some implementations, the invention can be implemented a powertrain control system  1332  that receives inputs from one or more sensors such as temperature sensors, pressure sensors, rotational sensors, airflow sensors and/or any other suitable sensors and/or that generates one or more output control signals such as engine operating parameters, transmission operating parameters, and/or other control signals. 
     The invention may also be implemented in other control systems  1340  of the vehicle  1330 . The control system  1340  may likewise receive signals from input sensors  1342  and/or output control signals to one or more output devices  1344 . In some implementations, the control system  1340  may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated. 
     The powertrain control system  1332  may communicate with mass data storage  1346  that stores data in a nonvolatile manner. The mass data storage  1346  may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The powertrain control system  1332  may be connected to memory  1347  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The powertrain control system  1332  also may support connections with a WLAN via a WLAN network interface  1348  constructed according the principles of the invention. The control system  1340  may also include mass data storage, memory and/or a WLAN interface (all not shown). 
     Referring now to  FIG. 14 , the invention can be implemented in a cellular phone  1450  that may include a cellular antenna  1451 . The invention may implement either or both signal processing and/or control circuits, which are generally identified in  FIG. 14  at  1452 , a WLAN interface and/or mass data storage of the cellular phone  1450 . In some implementations, the cellular phone  1450  includes a microphone  1456 , an audio output  1458  such as a speaker and/or audio output jack, a display  1460  and/or an input device  1462  such as a keypad, pointing device, voice actuation and/or other input device. The signal processing and/or control circuits  1452  and/or other circuits (not shown) in the cellular phone  1450  may process data, perform coding and/or encryption, perform calculations, format data and/or perform other cellular phone functions. 
     The cellular phone  1450  may communicate with mass data storage  1464  that stores data in a nonvolatile manner such as optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The cellular phone  1450  may be connected to memory  1466  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The cellular phone  1450  also may support connections with a WLAN via a WLAN network interface  1468  constructed according the principles of the invention. 
     Referring now to  FIG. 15 , the invention can be implemented in a media player  1500 . The invention may implement either or both signal processing and/or control circuits, which are generally identified in  FIG. 15  at  1504 , a WLAN interface and/or mass data storage of the media player  1500 . In some implementations, the media player  1500  includes a display  1507  and/or a user input  1508  such as a keypad, touchpad and the like. In some implementations, the media player  1500  may employ a graphical user interface (GUI) that typically employs menus, drop down menus, icons and/or a point-and-click interface via the display  1507  and/or user input  1508 . The media player  1500  further includes an audio output  1509  such as a speaker and/or audio output jack. The signal processing and/or control circuits  1504  and/or other circuits (not shown) of the media player  1500  may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other media player function. 
     The media player  1500  may communicate with mass data storage  1510  that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. The mass data storage may include optical and/or magnetic storage devices for example hard disk drives HDD and/or DVDs. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8″. The media player  1500  may be connected to memory  1514  such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The media player  1500  also may support connections with a WLAN via a WLAN network interface  1516  constructed according the principles of the invention. Still other implementations in addition to those described above are contemplated. 
     While the invention has been described in terms of exemplary embodiments, those skilled in the art will recognize that the invention can be practiced with modifications in the spirit and scope of the appended claims. These examples given above are merely illustrative and are not meant to be an exhaustive list of all possible designs, embodiments, applications or modifications of the invention.