초록 ▼

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. When a first bit pattern is detected in a digital message, subsequently transmitted data is s

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. When a first bit pattern is detected in a digital message, subsequently transmitted data is stored. Information is extracted from the stored data to obtain a channel assignment code indicating a frequency over which communications take place and a talk group identification code identifying a talk group in the trunked communication system participating in a communication. 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 successfully 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 received by the control channel receiver.

대표청구항 ▼

[ We 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 frequency on which a voice communication within the talk group ta

[ We 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 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 change between communications, the method comprising:with a frequency tunable receiver, monitoring digital messages on a control channel to detect a first bit pattern in the digital messages;upon detection of the first bit pattern in a digital message, storing data subsequently transmitted on the control channel;extracting information from the stored data and analyzing the extracted information to obtain a channel assignment code and a talk group identification code;comparing the talk group identification code obtained from the stored data to talk group identification codes of interest and, if the talk group identification code obtained from the stored data is a talk group identification code of interest, tuning the receiver to a working channel corresponding to the channel assignment code obtained from the stored data; andmonitoring voice transmissions on the working channel.