Apparatus and method for monitoring a trunked radio communications system

Abstract

The present invention provides a method and apparatus for monitoring a trunked radio communications system by using some type of radio scanning receiver that is not designed for that purpose. In addition, the invention provides a method for automatically determining the polarity of the received control channel data. Further, the invention provides a method for automatically determining the type of trunked radio communications system. In addition the invention provides a method for automatically determining the channels in a trunked radio system and a method for automatically determining the bit rate of transmitted digital signals over a control channel of a trunked radio communications system.

1 . A method of monitoring communications in a trunked communication system comprising the steps of: setting both an appropriate data and sampling rate, wherein the sampling rate is set substantially higher than the data rate; receiving a plurality of digital data messages on a control channel transmitted from at least one trunking radio system wherein each digital data message includes a preamble and a coded information frame; identifying the polarity of the incoming digital data messages; sampling the received digital message at the sample rate; identifying type and data rate of the trunking system, wherein the type and date rate are identified by comparing incoming samples to pre-calculated set of preamble patterns; selecting an appropriate set of parameters and values based upon the system type identified; reconstructing the stream of digital messages by selecting samples from the sample data stream to produce an output data stream.  
   
   
       2 . The method as recited in  claim 1 , wherein if the polarity of the data stream of an incoming digital data message is negative, inverting the polarity of that data stream to be positive.  
   
   
       3 . The method as recited in  claim 1 , includes the step of searching a selected frequency band to discover a logical channel to frequency associations.  
   
   
       4 . The method as recited in  claim 1 , wherein the selected sample rate must be high enough so as to generate a bit phase compensator table can be built to encompass all required incoming bits.  
   
   
       5 . The method as recited in  claim 1 , wherein calculating the plurality of parameters and values are used by the monitoring system to select an optimally aligned bit pattern and to synchronize the decoding element of the monitoring system further includes the steps of; calculating the required values and parameters of the bit phase compensation table: generating a subset of the message preamble, wherein the subset of the preamble message is used by a correlator array to detect the presence of the radio system to be selected; calculating the preamble test value wherein the preamble test value is used be the correlator array to establish the type of radio system and speed at which the radio system is transmitting its digital message; computing the inverse preamble test value used for the data messages of those radio systems that are found inverted radio system wherein the inverse test value is calculated by inverting the bits of the preamble test value; generating a plurality of correlator mask values wherein a mask value is calculated for each test value that the correlator array uses to select the data bits in the preamble to compared; and determining an appropriate preamble alignment interval.  
   
   
       6 . The method as recited in  claim 5 , wherein the plurality of parameters and values are stored in at least one lookup table.  
   
   
       7 . The method as recited in  claim 1 , wherein the codes that specify the talk group and channel assignment are extracted from the reconstructed coded information frame.  
   
   
       8 . The method as recited in  claim 6 , wherein the talk group and channel assignment codes are compared to an array of stored, predefined codes.  
   
   
       9 . The method as recited in  claim 7 , wherein if the codes match tuning the frequency tuned radio receiver of the monitoring system to the appropriate working voice channel and monitoring the resultant radio communications traffic.  
   
   
       10 . A computer program product including a computer useable medium having computer readable code embodied therein for monitoring analog voice communications traffic in a trucked radio communications system where the computer program product comprising a computer readable program code devices of the monitoring system configured to set both an appropriate data and sampling rate, wherein the sampling rate is set substantially higher than the data rate; a computer readable program code devices of the monitoring system configured to receive a plurality of digital data messages on a control channel transmitted from at least one trunking radio system wherein each digital data message includes a preamble and a coded information frame; a computer readable program code devices of the monitoring system configured to identify the polarity of the incoming digital data messages; a computer readable program code devices of the monitoring system configured to sample the received digital message at the sample rate; a computer readable program code devices of the monitoring system configured to identify type and data rate of the trunking system, wherein the type and date rate are identified by comparing incoming samples to pre-calculated set of preamble patterns; a computer readable program code devices of the monitoring system configured to select an appropriate set of parameters and values based upon the system type identified; a computer readable program code devices of the monitoring system configured to reconstruct the stream of digital messages by selecting samples from the sample data stream to produce an output data stream.  
   
   
       11 . The computer program product as recited in  claim 10 , wherein if the polarity of the data stream of an incoming digital data message is negative, inverting the polarity of that data stream to be positive.  
   
   
       12 . The computer program product as recited in  claim 10 , includes the step of searching a selected frequency band to discover a logical channel to frequency associations.  
   
   
       13 . The computer program product as recited in  claim 10 , wherein the computer readable program code devices of the monitoring system is configured to select a sample rate high enough so as to generate a bit phase compensator table built to encompass all required incoming bits.  
   
   
       14 . The computer program product as recited in  claim 10 , wherein the computer readable program code devices of the monitoring system is configured to calculate the plurality of parameters and values used by the monitoring system to select an optimally aligned bit pattern and to synchronize the decoding element includes the steps of, a computer readable program code devices of the monitoring system configured to calculate the required values and parameters of the bit phase compensation table; a computer readable program code devices of the monitoring system configured to generate a subset of the message preamble, wherein the subset of the preamble message is used by a correlator array to detect the presence of the radio system to be selected; a computer readable program code devices of the monitoring system configured to calculate the preamble test value wherein the preamble test value is used be the correlator array to establish the type of radio system and speed at which the radio system is transmitting its digital message; a computer readable program code devices of the monitoring system configured to compute the inverse preamble test value used for the data messages of those radio systems that are found inverted radio system wherein the inverse test value is calculated by inverting the bits of the preamble test value; a computer readable program code devices of the monitoring system configured to generate a plurality of correlator mask values wherein a mask value is calculated for each test value that the correlator array uses to select the data bits in the preamble to compared; and a computer readable program code devices of the monitoring system configured to determine an appropriate preamble alignment interval.  
   
   
       15 . The computer program product as recited in  claim 14 , wherein the computer readable program code devices of the monitoring system is configured to store the plurality of parameters and values in at least one lookup table.  
   
   
       16 . The computer program product as recited in  claim 10 , wherein the computer readable program code devices of the monitoring system is configured to extract the codes that specify the talk group and channel assignment from the reconstructed coded information frame.  
   
   
       17 . The computer program product as recited in  claim 16 , wherein the computer readable program code devices of the monitoring system is configured to compare the talk group and channel assignment codes to an array of stored, predefined codes.  
   
   
       18 . The computer program product as recited in  claim 16 , wherein the computer readable program code devices of the monitoring system is configured to tune the frequency tuned radio receiver of the monitoring system to the appropriate working voice channel and monitoring the resultant radio communications traffic, if the codes match.  
   
   
       19 . A system for monitoring communications in a trunked communication system comprising of: circuitry for setting both an appropriate data and sampling rate, wherein the sampling rate is set substantially higher than the data rate; circuitry for receiving a plurality of digital data messages on a control channel transmitted from at least one trunking radio system wherein each digital data message includes a preamble and a coded information frame; circuitry for identifying the polarity of the incoming digital data messages; circuitry for sampling the received digital message at the sample rate; circuitry for identifying type and data rate of the trunking system, wherein the type and date rate are identified by comparing incoming samples to pre-calculated set of preamble patterns: circuitry for selecting an appropriate set of parameters and values based upon the system type identified; and circuitry for reconstructing the stream of digital messages by selecting samples from the sample data stream to produce an output data stream.  
   
   
       20 . The apparatus as recited in  claim 19 , wherein if the polarity of the data stream of an incoming digital data message is negative, inverting the polarity of that data stream to be positive.  
   
   
       21 - 28 . (canceled)