Abstract:
A system includes a storing module configured to receive records. The records include dynamic frequency selection (DFS) information. A data extraction module is configured to extract the DFS information from a first plurality of the records. A control module is configured to determine whether the DFS information in each of the first plurality of records is a radar signal and generate a radar detected signal when at least a first predetermined number of the first plurality of records are a first type of radar signal. A polling module is configured to selectively poll the storing module for additional records received after the first plurality of records when at least a second predetermined number and less than the first predetermined number of the first plurality records are the first type of radar signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/821,719, filed Jun. 25, 2007, which claims the benefit of U.S. Provisional Application No. 60/817,325 filed Jun. 29, 2006. The disclosures of the above applications are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to wireless networks, and more particularly to systems and methods for detecting radar signals in wireless network devices. 
     BACKGROUND 
     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. 
     The I.E.E.E. has defined various standards for configuring wireless networks and devices. For example, 802.11, 802.11(a), 802.11(b), 802.11(g), 802.11(h), 802.11(n), 802.16, and 802.20. According to these standards, wireless network devices may be operated in either an infrastructure mode or an ad-hoc mode. In the infrastructure mode, the wireless network devices or client stations communicate with each other through an access point. In the ad-hoc mode, the wireless network devices communicate directly with each other and do not employ an access point. 
     Referring now to  FIG. 1 , a first wireless network  10  is illustrated in an infrastructure mode. The first wireless network  10  includes one or more client stations  12  and one or more access points (AP)  14 . The client station  12  and the AP  14  transmit and receive wireless signals  16 . The AP  14  is a node in a network  18 . The network  18  may be a local area network (LAN), a wide area network (WAN), or another network configuration. The network  18  may include other nodes such as a server  20  and may be connected to a distributed communications system  22  such as the Internet. 
     Referring now to  FIG. 2 , a second wireless network  24  operates in an ad-hoc mode. The second wireless network  24  includes multiple client stations  26 - 1 ,  26 - 2 , and  26 - 3  that transmit and receive wireless signals  28 . The client stations  26 - 1 ,  26 - 2 , and  26 - 3  collectively form a LAN and communicate directly with each other. The client stations  26 - 1 ,  26 - 2 , and  26 - 3  are not necessarily connected to another network. 
     To minimize radio frequency (RF) interference, some wireless networks may operate in a 5 GHz band. However, regulatory requirements governing the use of the 5 GHz band vary from country to country. For example, some countries utilize the 5 GHz band for military radar communications. Therefore, wireless networks operating in the 5 GHz band generally employ dynamic frequency selection (DFS) to avoid interference with radar communications. Specifically, wireless network devices generally employ DFS to switch to a different channel of the 5 GHz band to avoid interfering with radar communications. 
     In infrastructure mode, the AP  14  transmits beacons to inform the client stations  12  that the AP uses DFS. When the client stations  12  detect radar on a channel, the client stations  12  notify the AP  14 . Based on this information, the AP  14  uses DFS to select the best channel for network communications that will not interfere with radar. 
     In ad-hoc mode, one client station may be designated as a DFS owner. The DFS owner is responsible for collecting information from other client stations. If any client station in the ad-hoc network detects radar, the DFS owner uses DFS to select the best channel for network communications that does not interfere with radar. For example, if station  26 - 1  is the DFS owner, it is responsible for collecting information from stations  26 - 2  and  26 - 3 . If any of the stations  26 - 1 ,  26 - 2 , and  26 - 3  detects radar, station  26 - 1  uses DFS to select the best channel and notify stations  26 - 2  and  26 - 3  to switch to that channel. 
     Referring now to  FIGS. 3A-3C , radar signals generally comprise bursts of pulses that have predetermined pulse widths and pulse repetition rates.  FIG. 3A  shows a burst of radar. Radar signals can be tone or chirp type. Frequency of tone type radar pulses is generally fixed, whereas frequency of chirp type radar pulses may vary linearly. Based on characteristics such as pulse width (PW), pulse repetition rate (PRI), etc., radar signals may be classified into different types. For example, a table in  FIG. 3B  shows types of radar signals and respective standards specified by the federal communications commission (FCC). Similarly, a table in  FIG. 3C  shows types of radar signals and respective standards specified by the European telecommunications standards institute (ETSI). 
     SUMMARY 
     A system comprises a first-in first-out (FIFO) module, a polling module, a data extraction module, and a control module. The FIFO module receives records having dynamic frequency selection (DFS) information generated based on pulses received and generates a control signal for every N of the records received, where N is an integer greater than or equal to 1. The polling module selectively polls the FIFO module and reads M of the records received by the FIFO module, where M is an integer greater than or equal to 1 and less than N. The data extraction module extracts the DFS information from the N of the records when the control signal is received and selectively extracts the DFS information from the M of the records. The control module determines whether the pulses are a type of radar based on the DFS information extracted from at least N of the (N+M) of the records. 
     In another feature, the DFS information comprises pulse widths and pulse repetition rates of the pulses, signal strength of radio frequency (RF) signals in the pulses, and whether the pulses are one of a tone type and a chirp type radar pulses. 
     In another feature, the polling module polls the FIFO module when the DFS information extracted from a predetermined number of records out of the N of the records indicates that the pulses are not radar pulses. 
     In another feature, the system further comprises a buffer module that stores the DFS information extracted by the data extraction module. 
     In another feature, The pulses are received from at least one burst of radar. 
     In another feature, the control module determines that the pulses are a type of tone radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a tone radar pulse, an average of pulse widths in the DFS information extracted from each of the at least N of the (N+M) of the records approximately matches a pulse width of a predetermined type of tone radar, a difference between a maximum and a minimum of the pulse widths is less than a predetermined threshold, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match a pulse repetition interval of the predetermined type of tone radar. 
     In another feature, the control module determines that the pulses are a type of chirp radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a chirp radar pulse, pulse widths in the DFS information extracted from the at least N of the (N+M) of the records approximately match pulse widths of a predetermined type of chirp radar, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match pulse repetition intervals of the predetermined type of chirp radar. 
     In another feature, the control module determines whether the pulses are a type of one of a tone radar and a chirp radar based on pulse widths in the DFS information extracted from at least N of the records when the pulses are received from at least one burst of radar and when the pulses are separated by at least one data packet. 
     In another feature, the control module determines that the pulses are a type of tone radar when the pulse widths match a pulse width of a predetermined type of tone radar and wherein the control module determines that the pulses are a type of chirp radar when the pulse widths match pulse widths of a predetermined type of chirp radar. 
     In another feature, the pulses comprise radio frequency (RF) signals and the DFS information includes a number of zero-crossings of the RF signals per bin for a plurality of bins, where the bin is a time period greater than or equal to a smallest of pulse widths of predetermined types of radar pulses. 
     In another feature, the control module determines that the pulses are tone type radar pulses when a difference between maximum and minimum values of the number of zero-crossings is less than a predetermined threshold. 
     In another feature, the control module determines that the pulses are chirp type radar pulses when differences between the number of zero-crossings in adjacent bins are greater than a first predetermined threshold and a rate of change of the number of zero-crossings in successive bins is less than a second predetermined threshold. 
     In another feature, a medium access controller (MAC) comprises the system and further comprises a physical layer module (PHY) that communicates the records to the MAC. 
     In another feature, a wireless network device comprises the MAC and further comprises at least one antenna that receives the pulses and that communicates the pulses to the PHY. 
     In another feature, a radar detection device comprises the system. 
     In still other features, a method comprises receiving records having dynamic frequency selection (DFS) information generated based on pulses received in a first-in first-out (FIFO) module and generating a control signal for every N of the records received, where N is an integer greater than or equal to 1. The method further comprises selectively polling the FIFO module and reading M of the records received by the FIFO module, where M is an integer greater than or equal to 1 and less than N. The method further comprises extracting the DFS information from the N of the records when the control signal is received, selectively extracting the DFS information from the M of the records, and determining whether the pulses are a type of radar based on the DFS information extracted from at least N of the (N+M) of the records. 
     In another feature, the method further comprises receiving the records having the DFS information that includes pulse widths and pulse repetition rates of the pulses, signal strength of radio frequency (RF) signals in the pulses, and whether the pulses are one of a tone type and a chirp type radar pulses. 
     In another feature, the method further comprises polling the FIFO module when the DFS information extracted from a predetermined number of records out of the N of the records indicates that the pulses are not radar pulses. 
     In another feature, the method further comprises storing the DFS information extracted by the data extraction module. 
     In another feature, the method further comprises receiving the pulses from at least one burst of radar. 
     In another feature, the method further comprises determining that the pulses are a type of tone radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a tone radar pulse, an average of pulse widths in the DFS information extracted from each of the at least N of the (N+M) of the records approximately matches a pulse width of a predetermined type of tone radar, a difference between a maximum and a minimum of the pulse widths is less than a predetermined threshold, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match a pulse repetition interval of the predetermined type of tone radar. 
     In another feature, the method further comprises determining that the pulses are a type of chirp radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a chirp radar pulse, pulse widths in the DFS information extracted from the at least N of the (N+M) of the records approximately match pulse widths of a predetermined type of chirp radar, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match pulse repetition intervals of the predetermined type of chirp radar. 
     In another feature, the method further comprises determining whether the pulses are a type of one of a tone radar and a chirp radar based on pulse widths in the DFS information extracted from at least N of the records when the pulses are received from at least one burst of radar and when the pulses are separated by at least one data packet. 
     In another feature, the method further comprises determining that the pulses are a type of tone radar when the pulse widths match a pulse width of a predetermined type of tone radar and determining that the pulses are a type of chirp radar when the pulse widths match pulse widths of a predetermined type of chirp radar. 
     In another feature, the method further comprises receiving the records when the pulses include radio frequency (RF) signals and wherein the DFS information includes a number of zero-crossings of the RF signals per bin for a plurality of bins, where the bin is a time period greater than or equal to a smallest of pulse widths of predetermined types of radar pulses. 
     In another feature, the method further comprises determining that the pulses are tone type radar pulses when a difference between maximum and minimum values of the number of zero-crossings is less than a predetermined threshold. 
     In another feature, the method further comprises determining that the pulses are chirp type radar pulses when differences between the number of zero-crossings in adjacent bins are greater than a first predetermined threshold, and a rate of change of the number of zero-crossings in successive bins is less than a second predetermined threshold. 
     In another feature, the method further comprises communicating between a physical layer module (PHY) and a medium access controller (MAC) and communicating the records to the MAC. 
     In another feature, the method further comprises receiving the pulses via at least one antenna in a wireless network device and communicating the pulses to the PHY. 
     In another feature, the method further comprises determining whether the pulses include radar when the pulses are received by a radar detection device. 
     In still other features, a system comprises first-in first-out (FIFO) means for receiving records having dynamic frequency selection (DFS) information generated based on pulses received and generating a control signal for every N of the records received, where N is an integer greater than or equal to 1. The system further comprises polling means for selectively polling the FIFO means and reading M of the records received by the FIFO means, where M is an integer greater than or equal to 1 and less than N. The system further comprises data extraction means for extracting the DFS information from the N of the records when the control signal is received and selectively extracting the DFS information from the M of the records, and control means for determining whether the pulses are a type of radar based on the DFS information extracted from at least N of the (N+M) of the records. 
     In another feature, the DFS information comprises pulse widths and pulse repetition rates of the pulses, signal strength of radio frequency (RF) signals in the pulses, and whether the pulses are one of a tone type and a chirp type radar pulses. 
     In another feature, the polling means polls the FIFO means when the DFS information extracted from a predetermined number of records out of the N of the records indicates that the pulses are not radar pulses. 
     In another feature, the system further comprises buffer means for storing the DFS information extracted by the data extraction means. 
     In another feature, the pulses are received from at least one burst of radar. 
     In another feature, the control means determines that the pulses are a type of tone radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a tone radar pulse, an average of pulse widths in the DFS information extracted from each of the at least N of the (N+M) of the records approximately matches a pulse width of a predetermined type of tone radar, a difference between a maximum and a minimum of the pulse widths is less than a predetermined threshold, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match a pulse repetition interval of the predetermined type of tone radar. 
     In another feature, the control means determines that the pulses are a type of chirp radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a chirp radar pulse, pulse widths in the DFS information extracted from the at least N of the (N+M) of the records approximately match pulse widths of a predetermined type of chirp radar, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match pulse repetition intervals of the predetermined type of chirp radar. 
     In another feature, the control means determines whether the pulses are a type of one of a tone radar and a chirp radar based on pulse widths in the DFS information extracted from at least N of the records when the pulses are received from at least one burst of radar and when the pulses are separated by at least one data packet. 
     In another feature, the control means determines that the pulses are a type of tone radar when the pulse widths match a pulse width of a predetermined type of tone radar and wherein the control means determines that the pulses are a type of chirp radar when the pulse widths match pulse widths of a predetermined type of chirp radar. 
     In another feature, the pulses comprise radio frequency (RF) signals and the DFS information includes a number of zero-crossings of the RF signals per bin for a plurality of bins, where the bin is a time period greater than or equal to a smallest of pulse widths of predetermined types of radar pulses. 
     In another feature, the control means determines that the pulses are tone type radar pulses when a difference between maximum and minimum values of the number of zero-crossings is less than a predetermined threshold. 
     In another feature, the control means determines that the pulses are chirp type radar pulses when differences between the number of zero-crossings in adjacent bins are greater than a first predetermined threshold, and a rate of change of the number of zero-crossings in successive bins is less than a second predetermined threshold. 
     In another feature, a medium access controller (MAC) comprises the system and further comprises physical layer means (PHY) for communicating the records to the MAC. 
     In another feature, a wireless network device comprises the MAC and further comprises at least one antenna means for receiving the pulses and communicating the pulses to the PHY means. 
     In another feature, a radar detection device comprises the system. 
     In still other features, a computer program executed by a processor comprises receiving records having dynamic frequency selection (DFS) information generated based on pulses received in a first-in first-out (FIFO) module and generating a control signal for every N of the records received, where N is an integer greater than or equal to 1. The computer program further comprises selectively polling the FIFO module and reading M of the records received by the FIFO module, where M is an integer greater than or equal to 1 and less than N. The computer program further comprises extracting the DFS information from the N of the records when the control signal is received, selectively extracting the DFS information from the M of the records, and determining whether the pulses are a type of radar based on the DFS information extracted from at least N of the (N+M) of the records. 
     In another feature, the computer program further comprises receiving the records having the DFS information that includes pulse widths and pulse repetition rates of the pulses, signal strength of radio frequency (RF) signals in the pulses, and whether the pulses are one of a tone type and a chirp type radar pulses. 
     In another feature, the computer program further comprises polling the FIFO module when the DFS information extracted from a predetermined number of records out of the N of the records indicates that the pulses are not radar pulses. 
     In another feature, the computer program further comprises storing the DFS information extracted by the data extraction module. 
     In another feature, the computer program further comprises receiving the pulses from at least one burst of radar. 
     In another feature, the computer program further comprises determining that the pulses are a type of tone radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a tone radar pulse, an average of pulse widths in the DFS information extracted from each of the at least N of the (N+M) of the records approximately matches a pulse width of a predetermined type of tone radar, a difference between a maximum and a minimum of the pulse widths is less than a predetermined threshold, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match a pulse repetition interval of the predetermined type of tone radar. 
     In another feature, the computer program further comprises determining that the pulses are a type of chirp radar when the DFS information extracted from each of the at least N of the (N+M) of the records includes information that a corresponding one of the pulses is a chirp radar pulse, pulse widths in the DFS information extracted from the at least N of the (N+M) of the records approximately match pulse widths of a predetermined type of chirp radar, and pulse repetition intervals in the DFS information extracted from a predetermined number of the at least N of the (N+M) of the records approximately match pulse repetition intervals of the predetermined type of chirp radar. 
     In another feature, the computer program further comprises determining whether the pulses are a type of one of a tone radar and a chirp radar based on pulse widths in the DFS information extracted from at least N of the records when the pulses are received from at least one burst of radar and when the pulses are separated by at least one data packet. 
     In another feature, the computer program further comprises determining that the pulses are a type of tone radar when the pulse widths match a pulse width of a predetermined type of tone radar and determining that the pulses are a type of chirp radar when the pulse widths match pulse widths of a predetermined type of chirp radar. 
     In another feature, the computer program further comprises receiving the records when the pulses include radio frequency (RF) signals and wherein the DFS information includes a number of zero-crossings of the RF signals per bin for a plurality of bins, where the bin is a time period greater than or equal to a smallest of pulse widths of predetermined types of radar pulses. 
     In another feature, the computer program further comprises determining that the pulses are tone type radar pulses when a difference between maximum and minimum values of the number of zero-crossings is less than a predetermined threshold. 
     In another feature, the computer program further comprises determining that the pulses are chirp type radar pulses when differences between the number of zero-crossings in adjacent bins are greater than a first predetermined threshold, and a rate of change of the number of zero-crossings in successive bins is less than a second predetermined threshold. 
     In another feature, the computer program further comprises communicating between a physical layer module (PHY) and a medium access controller (MAC) and communicating the records to the MAC. 
     In another feature, the computer program further comprises receiving the pulses via at least one antenna in a wireless network device and communicating the pulses to the PHY. 
     In another feature, the computer program further comprises determining whether the pulses include radar when the pulses are received by a radar detection device. 
     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. 
     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 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is functional block diagram of a wireless network operating in an infrastructure mode according to the prior art; 
         FIG. 2  is a function block diagram of a wireless network operating in an ad-hoc mode according to the prior art; 
         FIG. 3A  shows a burst of pulses in a radar signal; 
         FIG. 3B  is a table listing parameters of different types of radar signals in the United States; 
         FIG. 3C  is a table listing parameters of different types of radar signals in Europe; 
         FIG. 4A  is a functional block diagram of an exemplary system for detecting radar in a wireless network device according to the present disclosure; 
         FIG. 4B  depicts a sliding-window scheme used by the system of  FIG. 4A  to detect radar according to the present disclosure; 
         FIG. 4C  shows radar pulses in a burst of radar; 
         FIG. 4D  shows radar pulses in two bursts of radar; 
         FIG. 4E  shows radar pulses in multiple bursts of radar separated by data packets; 
         FIG. 5A  shows zero-crossings of a radio frequency signal in a bin; 
         FIG. 5B  is a graph of number of zero-crossings per bin as a function of number of bins for a tone type radar; 
         FIG. 5C  is a graph of number of zero-crossings per bin relative as a function of number of bins for a chirp type radar; 
         FIG. 6A  shows a first portion of a flowchart of an exemplary method for detecting radar in a wireless network device according to the present disclosure; 
         FIG. 6B  shows a second portion of the flowchart of the exemplary method for detecting radar in a wireless network device according to the present disclosure; 
         FIG. 7A  is a functional block diagram of a high definition television; 
         FIG. 7B  is a functional block diagram of a vehicle control system; 
         FIG. 7C  is a functional block diagram of a cellular phone; 
         FIG. 7D  is a functional block diagram of a set top box; and 
         FIG. 7E  is a functional block diagram of a mobile device. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Systems and methods for detecting radar in wireless networks are disclosed in U.S. patent application Ser. No. 11/493,473 filed on Jul. 26, 2006, which is incorporated herein by reference in its entirety. The systems and methods may be implemented in at least one of a baseband processor (BBP) and a medium access controller (MAC) of a wireless network device. The systems and methods detect radar by analyzing isolated pulses. Consequently, the systems and methods may mis-detect radar when the pulses are generated by noise or interference. Radar may be correctly detected by analyzing a series of pulses in a burst or bursts of radar. 
     Referring now to  FIGS. 4A-4E , a system  100  for detecting radar comprises a MAC FIFO module  102  and a radar detection module  104 . The radar detection module  104  comprises a data extraction module  106 , a buffer module  108 , a control module  110 , and a polling module  112 . When a wireless network device (not shown) receives pulses that are radar pulses or may be radar pulses, the wireless network device may perform dynamic frequency selection (DFS) and may communicate on a channel other than the current channel. 
     When the pulses received by the wireless network device are radar pulses or may be radar pulses, a BBP in the wireless network device may generate a 64-byte DFS record for each pulse. The DFS record may include 8 bytes of DFS information, such as radar type (tone or chirp), pulse width (PW), pulse repetition rate (PRI), etc., and 56 bytes of frequency information. 
     A MAC FIFO module  102  in the wireless network device receives the DFS records from the BBP. The memory size of the MAC FIFO module  102 , however, is generally limited. Thus, the number of DFS records that may be queued in the MAC FIFO module  102  may be limited and may be determined by a queue size. The queue size may be programmable and may be set to 10, for example. 
     When the MAC FIFO module  102  receives a predetermined number of DFS records called a window size (W), which is less than the queue size, the MAC FIFO module  102  generates an interrupt or a control signal. Upon receiving the interrupt, the radar detection module  104  analyzes the DFS records and determines the type of radar received by the BBP. W is programmable and may typically be set to half the queue size. Thus, W may be five if the queue size is 10, and the MAC FIFO module  102  may generate the interrupt after receiving five DFS records. A maximum value of W is less than or equal to a DFS interrupt threshold. 
     Upon receiving the control signal, the data extraction module  106  extracts the DFS information from the five DFS records and outputs the DFS information to the buffer module  108 . The memory size of the buffer module  108  is generally greater than the memory size of the MAC FIFO module  102 . The buffer module  108  stores the DFS information in locations starting at a location determined by a write pointer as shown in  FIG. 4B . Additionally, when the BBP is unable to validate frequency information, the buffer module  108  may store the frequency information of the DFS records for subsequent validation. 
     A read pointer in the buffer module  108  determines a location from where the control module  110  begins reading DFS information as shown in  FIG. 4B . The control module  110  reads DFS information stored in (read pointer+W) locations in the buffer module  108  and processes the DFS information to determine the type of radar pulses received by the wireless network device. The control module  110  increments the read pointer after processing the DFS information. Effectively, the window comprising W locations moves or slides to next W locations in the buffer module  108  during each processing cycle. Thus, the window may be called a moving or a sliding window of size W. 
     The system  100  can correctly detect the type of radar if the buffer module  108  receives at least five records indicating that the pulses are radar pulses. Occasionally, however, due to noise or interference (e.g., spikes generated by microwave devices), some of the DFS records may be corrupted. For example, when W=5, DFS record numbers  2  and  3  may be corrupted. In that case, the DFS information in the corrupted records may indicate that the received pulses are not radar pulses. 
     The control module  110  analyzes the DFS information in the W records. If the control module  110  determines that a majority of the DFS records indicate that the received pulses are radar pulses, the polling module  112  performs interrupt driven polling. The polling module  112  retrieves additional records from the MAC FIFO module  102  before the MAC FIFO module  102  generates the next interrupt. 
     Specifically, the control module  110  checks the DFS information in (read pointer+W) locations in the buffer module  108 . If the DFS information in a majority of the W locations (e.g., three out of five) indicates that the received pulses are of a known type of radar, the control module  110  outputs a polling signal to the polling module  112 . The polling module  112  initiates a timer or a counter (not shown) that is set to count a predetermined time equal to T*X μS, where X=16 μS if the wireless network device is FCC-compliant and X=32 μS if the wireless network device is ETSI-compliant. T is selected such that the predetermined time is at least equal to the duration of a longest radar burst. 
     While the timer is counting, the polling module  112  polls the MAC FIFO module  102  and checks if any additional DFS records are received subsequent to the last interrupt. The polling module  112  retrieves any additional DFS records received by the MAC FIFO module  102  and outputs the additional DFS records to the data extraction module  106 . The data extraction module  106  extracts the DFS information (and optionally, the frequency information) from the additional DFS records. The buffer module  108  stores the DFS information from the additional DFS records in locations starting at the current location of the write pointer. 
     When the timer expires, the control module  110  checks the location of the write pointer to determine if the buffer module  108  received any additional DFS information. If the buffer module  108  received additional DFS information and has valid DFS information in a total of at least W locations, the control module  110  analyses the DFS information in the W locations as follows. 
     The control module  110  compares the PW and PRI data in the DFS information in W locations to the PW and PRI data of known types of radar, which is tabulated in  FIGS. 3B-3C . The control module  110  may store the PW and PRI data of the known types of radar in the form of a look-up table in memory. Typically, the look-up table may include radar patterns having predetermined PW-PRI relationships, which are tabulated in  FIGS. 3B-3C . Comparing the PW and PRI data in W locations with radar patterns in the look-up table may be faster than individually comparing the PW and PRI data with each PW and PRI of each type of radar. 
     Alternately, the look-up table may include acceptable PRI values corresponding different PW values of known types of radar. In that case, the control module  110  may only determine whether the PW data in the DFS information matches PW of a known type of radar. Subsequently, the control module  110  may find corresponding acceptable PRI (and the type of radar) by comparing the PW data to the PW values in the look-up table instead of actually determining PRI and then comparing the PRI to the PRI data of all known types of radar. 
     The control module  110  uses different comparison criteria to determine the type of radar since DFS records may be generated in different ways. For example, the five DFS records may be generated by five consecutive radar pulses in the same burst having identical PW and PRI as shown in  FIG. 4C  or by a total five pulses from two consecutive bursts having identical PW but unequal PRI as shown in  FIG. 4D . In either case, the control module  110  determines which type of tone or chirp radar may be present in the pulses received by the BBP as follows. 
     If the DFS information in all five records indicates that the radar pulses are tone type, then the control module  110  compares the PW and PRI data in each record with the PW and PRI data of known types of radar. Specifically, the control module  110  determines whether the difference between a maximum pulse width and a minimum pulse width of the five pulse widths in the five records is less than or equal to a threshold pulse width, which may be equal to 2 μS. 
     Additionally, the control module  110  determines whether the average of the maximum and minimum pulse widths matches a valid pulse width (i.e., a pulse width of a known type of radar). The value of the valid pulse width may differ depending on whether the radar pulses are FCC-compliant or ETSI-compliant. Finally, since the radar pulses may be from two consecutive bursts, the control module  110  determines whether the PRI data in a majority of the five records (e.g., three of five records) matches the PRI of a known type of tone radar having the valid PW. 
     If, however, the DFS information in all five records indicates that the radar pulses are chirp type, then the control module  110  compares the PW and PRI data in each record with the PW and PRI data of known types of radar. Since PW and PRI are variable in chirp radar, the control module  110  determines whether the pulse widths in the five records approximately match one of the known chirp radar patterns shown in  FIG. 3B  or  3 C. Additionally, the control module  110  determines whether the PRI data in a majority of the five records (e.g., three of five records) approximately matches the PRI of a known type of chirp radar. 
     Occasionally, the BBP may simultaneously receive radar and packets of wireless data (or interference) as shown in  FIG. 4E . In that case, the BBP may receive radar pulses from different bursts as shown. Additionally, pulse widths of received radar pulses may be identical in case of tone radar or variable in case of chirp radar. Thus, the PW (or pulse widths in case of a chirp radar) in the five records may match PW (or pulse widths) of a known type of tone (or chirp) radar. In either case, however, the PRI of the received pulses may vary due to the presence of packets of wireless data (or interference) between the radar pulses. Thus, the control module  110  cannot accurately determine the type of radar by comparing PRI in any of the five records to the PRI of known types tone and/or chirp radar. 
     Since PRI cannot be used to accurately determine the type of radar, the control module  110  increases the window size and compares PW data in the increased number of records to confirm the type of radar. For example, the window size may be increased from five to eight and read DFS information stored in locations (read pointer−3) to (read pointer+4) in the buffer module  108 . In that case, the control module  110  may compare PW data from all eight records to the PW (or pulse widths in case of chirp radar) of known types of tone (or chirp) radar. Alternatively, the window size may be increased from five to ten, and PW from a majority of records (e.g., seven or eight of the ten records) may be compared to the PW (or pulse widths in case of chirp radar) of known types of radar. 
     Occasionally, due to noise or interference, the BBP may be unable to correctly validate frequency information of the radar pulses. In that case, the control module  110  processes the frequency information in the 56 bytes of the W records to determine whether the pulses that generated the W records are of tone or chirp type. 
     Referring now to  FIGS. 5A-5C , a radio frequency (RF) signal in a radar pulse transitions multiple times between high and low states as shown in  FIG. 5A . During each transition, the RF signal crosses a point in time, called a zero-crossing point, where the amplitude of the RF signal is approximately zero as shown. A bin or bin size is a predetermined time period within which the RF signal crosses points of zero-amplitude a predetermined number of times. That is, the RF signal has a predetermined number of zero-crossings within a predetermined bin size. The number of zero-crossings within a bin and the bin size for a particular type of radar are determined based on the FCC or ETSI standards. Typically, the bin size is at least equal to a minimum pulse width of all radar signals. For example, the bin size may be at least 2 μS. 
     The frequency information in each of the five records includes number of zero-crossings. The number of zero-crossings for tone radar is approximately the same in different bins as shown in  FIG. 5B . The control module  110  determines whether a difference between maximum and minimum number of zero-crossings in all bins is less than or equal to a predetermined threshold, called a tone zero-crossing threshold (Threshold tone ) If true, the control module  110  determines that the radar pulses are tone type. 
     On the other hand, the frequency of the RF signal varies linearly in chirp radar. Consequently, the number of zero-crossings in each bin may vary from bin to bin as shown in  FIG. 5C . Zero-crossings less than a predetermined threshold are disregarded in determining whether the radar is chirp radar. If the difference d i  between the number of zero-crossings in adjacent bins for all i bins is greater than Threshold tone , the control module  110  determines that the radar is not a tone radar. That is, if d 1  denotes the number of zero-crossings in bin 1 , d 2  denotes the number of zero-crossings in bin 2 , etc., then the radar is not a tone radar if (d i −d i+1 )&gt;Threshold tone  for all i. 
     For a linear chirp radar, the rate of change of zero-crossings (denoted by the slope of the plots in  FIG. 5C ) between adjacent bins is approximately the same. The control module  110  determines whether the absolute value of the differences in number of zero-crossings between adjacent bins (i.e., |(d i −d i+1 )|) for all i bins is less than a predetermined threshold called a chirp zero-crossing threshold (Threshold chirp ). If true, the control module  110  determines that the radar is chirp type. 
     Referring now to  FIGS. 6A-6B , a method  200  for detecting radar in a wireless network device begins at step  202 . A media access controller (MAC) determines in step  204  if the wireless network device is performing dynamic frequency selection (DFS). If true, a baseband processor (BBP) outputs records comprising DFS information to a MAC FIFO module  102  in step  206 . 
     The MAC FIFO module  102  checks in step  208  if the number of records queued is greater than or equal to a window size (e.g., five). If true, the MAC FIFO module  102  generates an interrupt or a control signal in step  210 . Upon receiving the interrupt, a data extraction module  106  receives the five records from the MAC FIFO module  102  and extracts DFS information from each of the five records in step  212 . The DFS information is stored in a buffer module  108  in step  214 . 
     A control module  110  checks in step  216  if the DFS information in all five records indicates that the received pulses are radar pulses. If false, the control module  110  determines in step  218  if the DFS information in a majority of the five records (e.g., three of five) indicates that the received pulses are radar pulses. If false, steps  204  through  218  are repeated. 
     If the result of step  218  is true, a polling module  112  starts a timer in step  220 . The timer counts a predetermined period of time in step  222 . The MAC FIFO module  102  determines in step  224  if five more records are received in the queue to generate next interrupt. If true, the control module  110  resets the timer in step  226 , and steps starting from step  212  are repeated. 
     If the result of step  224  is false, the control module  110  checks in step  228  if the timer finished counting time. If false, steps starting at step  222  are repeated. If the timer finished counting time and the MAC FIFO module  102  did not generate another interrupt, the polling module  112  checks in step  230  if the MAC FIFO module  102  received any more records. If false, steps starting at  220  are repeated. If true, the polling module  112  receives additional records from the MAC FIFO module  102  in step  232 , and steps starting step  212  are repeated. 
     If the result of step  216  is true, the control module  110  determines in step  234  if the DFS information in all five records indicates that the received pulses are of tone type radar. If false, the control module  110  determines in step  236  if the DFS information in all five records indicates that the received pulses are of chirp type radar. 
     If the results of steps  234  and  236  are true, the control module  110  determines in step  238  if pulse width information in the five records matches with the pulse width information of a known tone or chirp radar. If false, the control module  110  determines in step  240  that the pulses received are not radar pulses, and steps starting at step  204  are repeated. If true, however, the control module  110  determines in step  242  if PRI information in a majority of the five records matches the PRI information of a known tone or chirp radar. If true, the control module  110  generates a control signal in step  244  identifying the type of detected radar. 
     If the results of steps  236  and  244  are false, then in step  246 , the control module  110  increases the window size (e.g., from five to eight), reads additional records stored in the buffer module  108 , and steps starting at step  234  are repeated. 
     Referring now to  FIGS. 7A-7E , various exemplary implementations incorporating the teachings of the present disclosure are shown. 
     Referring now to  FIG. 7A , the teachings of the disclosure can be implemented in a network interface  343  of a high definition television (HDTV)  337 . The HDTV  337  includes a HDTV control module  338 , a display  339 , a power supply  340 , memory  341 , a storage device  342 , the network interface  343 , and an external interface  345 . 
     The HDTV  337  can receive input signals from the network interface  343  and/or the external interface  345 , which can send and receive information via cable, broadband Internet, and/or satellite. The HDTV control module  338  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  339 , memory  341 , the storage device  342 , the network interface  343 , and the external interface  345 . 
     Memory  341  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  342  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The HDTV control module  338  communicates externally via the network interface  343  and/or the external interface  345 . The power supply  340  provides power to the components of the HDTV  337 . 
     Referring now to  FIG. 7B , the teachings of the disclosure may be implemented in a network interface  352  of a vehicle  346 . The vehicle  346  may include a vehicle control system  347 , a power supply  348 , memory  349 , a storage device  350 , and the network interface  352 . The vehicle control system  347  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. 
     The vehicle control system  347  may communicate with one or more sensors  354  and generate one or more output signals  356 . The sensors  354  may include temperature sensors, acceleration sensors, pressure sensors, rotational sensors, airflow sensors, etc. The output signals  356  may control engine operating parameters, transmission operating parameters, suspension parameters, etc. 
     The power supply  348  provides power to the components of the vehicle  346 . The vehicle control system  347  may store data in memory  349  and/or the storage device  350 . Memory  349  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  350  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The vehicle control system  347  may communicate externally using the network interface  352 . 
     Referring now to  FIG. 7C , the teachings of the disclosure can be implemented in a network interface  368  of a cellular phone  358 . The cellular phone  358  includes a phone control module  360 , a power supply  362 , memory  364 , a storage device  366 , and a cellular network interface  367 . The cellular phone  358  may include the network interface  368 , a microphone  370 , an audio output  372  such as a speaker and/or output jack, a display  374 , and a user input device  376  such as a keypad and/or pointing device. 
     The phone control module  360  may receive input signals from the cellular network interface  367 , the network interface  368 , the microphone  370 , and/or the user input device  376 . The phone control module  360  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  364 , the storage device  366 , the cellular network interface  367 , the network interface  368 , and the audio output  372 . 
     Memory  364  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  366  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). The power supply  362  provides power to the components of the cellular phone  358 . 
     Referring now to  FIG. 7D , the teachings of the disclosure can be implemented in a network interface  385  of a set top box  378 . The set top box  378  includes a set top control module  380 , a display  381 , a power supply  382 , memory  383 , a storage device  384 , and the network interface  385 . 
     The set top control module  380  may receive input signals from the network interface  385  and an external interface  387 , which can send and receive information via cable, broadband Internet, and/or satellite. The set top control module  380  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  385  and/or to the display  381 . The display  381  may include a television, a projector, and/or a monitor. 
     The power supply  382  provides power to the components of the set top box  378 . Memory  383  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  384  may include an optical storage drive, such as a DVD drive, and/or a hard disk drive (HDD). 
     Referring now to  FIG. 7E , the teachings of the disclosure can be implemented in a network interface  394  of a mobile device  389 . The mobile device  389  may include a mobile device control module  390 , a power supply  391 , memory  392 , a storage device  393 , the network interface  394 , and an external interface  399 . 
     The mobile device control module  390  may receive input signals from the network interface  394  and/or the external interface  399 . The external interface  399  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  390  may receive input from a user input  396  such as a keypad, touchpad, or individual buttons. The mobile device control module  390  may process input signals, including encoding, decoding, filtering, and/or formatting, and generate output signals. 
     The mobile device control module  390  may output audio signals to an audio output  397  and video signals to a display  398 . The audio output  397  may include a speaker and/or an output jack. The display  398  may present a graphical user interface, which may include menus, icons, etc. The power supply  391  provides power to the components of the mobile device  389 . Memory  392  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  393  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. 
     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.