Direct link digital radio signal transmission between mobile unit e.g. car telephone and base station - attributing pseudo-random code to each mobile of multiple access system, transmitting messages on carrier frequency modulated by code, with carrier frequency continuously variable

摘要

The transmitter has a two state phase changer acting on a carrier frequency then modulated by a fixed frequency response to produce a digitised response. The received signal passes through an antenna (31) and receiver module (32) contg. a down-converter. The signal obtained is applied to a demodulator (38), with a VCO (39) having a matching response to the transmitted signal, and set to the carrier signal transmitted (40) with an offset. The resulting carrier response is applied to a phase lock loop (43) and a demodulator (41) for reproducing the phase information and recovering the digital response. ADVANTAGE - Large number of transmissions can be present at same time without interfering with each other, and being confidential to the sender and receiver. Uses data spreading technique.