Method and apparatus for detecting the movement of a device that receives a signal broadcast from a relative fixed position

Abstract

A system for detecting the movement of a device that receives a signal broadcast from a relative fixed position, such as a set-top terminal in a Direct Broadcast Satellite (DBS) system, is disclosed, using the phase shift of the broadcast signal, as received by the device. A set-top terminal or similar mechanism restricts access to the transmitted multimedia information using stored decryption keys. If a set-top terminal is moved, the distance between the set-top terminal and the satellite will change, thereby causing a measurable phase shift in the signal received by the set-top terminal. The set-top terminal periodically or intermittently records a sequence of bits received from the satellite and provides the recorded bits to the service provider server for analysis. If the set-top terminal has been moved, the recorded bits will shift. The sequence of bits may be recorded at random intervals, triggered by an external event, shown, for example, by an accurate internal clock, a request sent by a terrestrial paging network, or a request sent by a low-earth-orbit (LEO) satellite messaging system. The service provider detects relative movements of the set-top terminals by instructing a group of set-top terminals in geographical proximity to start recording at the same time, and comparing the sequence of bits recorded by each set-top terminal.