Detection and prevention of channel grabbing in a wireless

Abstract

A method and system for detecting a voice channel grab by a pirate in a cellular telephone network. Initially, RF signals transmitted to and from an authorized cellular telephone over the control and voice channels are monitored to track call processing activities and obtain various data that are used to detect potential voice channel grabbing attempts. The data may include such things as RSSI, change power output messages and responses, and hook-flash signal. From the data, the system looks for two events. A first event is an unexpected change or an absence of an expected change in the voice channel RF signal indicating that the pirate may be transmitting on the voice channel. The first event may be any one or more of the following: (1) a sudden upward shift in the voice channel RSSI; (2) an unexpected phase shift of either the RF signal or the SAT signal contained in the RF signal; and (3) an absence of an expected shift in the RSSI that corresponds to the change power level message from the network. The second event is receipt of a message indicative of a request to establish a new telephone connection such as a hook-flash message initiating a call conference. When the unexpected change in the RF signal and the message indicative of the request to establish the new telephone connection are detected, the system determines that the voice channel assigned to the authorized cellular telephone has been grabbed by the pirate. When the system determines that the channel grab has occurred, it prevents the pirate from establishing the new telephone connection by preventing receipt of dialed digits or terminating the connection on the voice channel.