Trunked radio monitoring system
First Claim
1. A method of monitoring communications in a trunked communication system in which digital messages incorporating a talk group identification code identifying a talk group, and a channel assignment code identifying a working channel frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that may change between communications, the method comprising:
- with a frequency tunable receiver, monitoring and storing digital information transmitted on a control channel;
testing portions of the stored information for a pattern of bits identifying a message including a channel assignment code and a talk group identification code, to identify a message;
upon finding a message, extracting from the message the channel assignment code and the talk group identification code;
comparing the talk group identification code extracted from the message to a plurality of talk group identification codes of interest and, if the talk group identification code extracted from the message is one of the talk group identification codes of interest, tuning the receiver to the working channel corresponding to the channel assignment code extracted from the message; and
monitoring voice transmissions on the working channel without participating in the voice communications.
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Accused Products
Abstract
A method and apparatus for passively monitoring communications in a trunked communication system. Digital messages transmitted over a control channel at a particular frequency are monitored with a receiver. Transmitted communication signals are demodulated and stored. The stored signals are tested to identify messages and to extract talk group and channel assignment codes. If the talk group is a talk group of interest, the receiver is tuned to the frequency corresponding to the channel assignment code so that voice communications are monitored. The receiver is tuned to the control channel after each voice communication so that a communication including multiple transmissions on different frequencies is coherently monitored by retuning the receiver in accordance with the received channel assignment codes. In an alternative embodiment, separate receivers are provided for the control channel and for voice communications. The voice receiver is continually tuned to different working channels in response to talk group and channel assignment codes extracted from stored information received by the control channel receiver.
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Citations
41 Claims
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1. A method of monitoring communications in a trunked communication system in which digital messages incorporating a talk group identification code identifying a talk group, and a channel assignment code identifying a working channel frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that may change between communications, the method comprising:
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with a frequency tunable receiver, monitoring and storing digital information transmitted on a control channel;
testing portions of the stored information for a pattern of bits identifying a message including a channel assignment code and a talk group identification code, to identify a message;
upon finding a message, extracting from the message the channel assignment code and the talk group identification code;
comparing the talk group identification code extracted from the message to a plurality of talk group identification codes of interest and, if the talk group identification code extracted from the message is one of the talk group identification codes of interest, tuning the receiver to the working channel corresponding to the channel assignment code extracted from the message; and
monitoring voice transmissions on the working channel without participating in the voice communications. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for monitoring communications in a trunked communication system in which digital messages incorporating a talk group identification code identifying a talk group, and a channel assignment code identifying a working channel frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that may change between communications, the apparatus comprising:
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a receiver tunable in frequency for monitoring digital information transmitted on a control channel and voice communications on a plurality of working channels;
a demodulator for demodulating the digital information received by the receiver on the control channel and producing demodulated information;
a first memory storing demodulated information received on the control channel;
testing means for testing portions of the demodulated information stored in the first memory for a pattern of bits identifying a message including a channel assignment code and a talk group identification code, to identify a message;
analyzing means for extracting the channel assignment code and the talk group identification code from a message stored in the first memory;
a second memory storing a plurality of talk group identification codes of interest without participating in the voice communications;
comparing means for comparing the talk group identification code extracted from the message to the plurality of talk group identification codes of interest stored in the second memory and for generating an indication if the talk group identification code extracted from the message matches one of the plurality of talk group identification codes of interest; and
tuning means for tuning the receiver to a working channel corresponding to the channel assignment code extracted from the message when the comparing means indicates that the talk group identification code extracted from the message is a talk group identification code of interest. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. An apparatus for monitoring communications in a trunked communication system in which digital messages incorporating a talk group identification code identifying a talk group, and a channel assignment code identifying a working channel frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that may change between communications, the apparatus comprising:
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a control channel receiver tunable in frequency for monitoring digital information transmitted on a control channel without participating in the voice communications;
a voice channel receiver tunable in frequency for monitoring voice communications on working channels;
a demodulator for demodulating the digital information received by the control channel receiver on the control channel and producing demodulated information;
a first memory storing demodulated information;
testing means for testing portions of the demodulated information stored in the first memory for a pattern of bits identifying a message including a channel assignment code and a talk group identification code, to identify a message;
analyzing means for extracting the channel assignment code and the talk group identification code from a message stored in the first memory;
a second memory storing talk group identification codes of interest;
comparing means for comparing the talk group identification code extracted from the message to the plurality of talk group identification codes of interest stored in the second memory and for generating an indication if the talk group identification code extracted from the message matches one of the plurality of talk group identification codes of interest; and
first tuning means for tuning the voice channel receiver to a working channel corresponding to the channel assignment code extracted from the message when the comparing means indicates that the talk group identification code extracted from the message is a talk group identification code of interest. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. In a trunked communication system in which digital messages incorporating a talk group identification code identifying a talk group, and a channel assignment code identifying a working channel frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that may change between communications, a method of producing a frequency map of channel assignment codes and working channel frequencies comprising:
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monitoring a working channel frequency until a message including a talk group identification code is received on the working channel;
extracting a talk group identification code from the message received on the working channel;
upon extracting the talk group identification code, monitoring the control channel for messages and extracting the talk group identification code and channel number of the working channel from each message received on the control channel; and
comparing the talk group identification code from the message received on the working channel with the talk group identification code of a message received on the control channel and, when the talk group identification codes match, entering the working channel frequency and corresponding channel number in a frequency map. - View Dependent Claims (36)
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37. A method of monitoring communications in a trunked communication system in which digital messages incorporating a talk group identification code identifying a talk group, and a channel assignment code identifying a working channel frequency on which a voice communication within the talk group takes place, are transmitted over a control channel and voice communications are transmitted over working channels that may change between communications, the method comprising:
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with a frequency tunable receiver, monitoring digital information transmitted on a control channel;
testing the digital information for a pattern of bits indicating presence of a message within the digital information;
upon identifying the presence of a message, locating the message, and, if present in the message, extracting from the message a channel assignment code and a talk group identification code;
comparing the talk group identification code extracted from the message to a plurality of talk group identification codes of interest and, if the talk group identification code extracted from the message is one of the plurality of talk group identification codes of interest, tuning the receiver to the working channel corresponding to the channel assignment code extracted from the message; and
monitoring voice transmissions on the working channel without participation in the voice communications. - View Dependent Claims (38, 39, 40, 41)
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Specification