An FM multiplex broadcasting system for traffic information services

A new data broadcasting system for a traffic information service using an FM subcarrier has been developed. This system uses a new digital modulation method called LMSK (level-controlled minimum shift keying) which is multipath proof, and a powerful error correction code which is a product code of the shortened difference set cyclic codes. This system has a large transmission capacity of 16 kb/s. The FM multiplex broadcasting can provide characters, graphics and traffic data by multiplexing digital signals with existing FM radio broadcasting signals. The characteristics of FM multiplex broadcasting paths are described, an outline of LMSK and the error correction method is given, the transmission quality measured in a driving car in the service area of the NHK Tokyo FM station is reported, and its applications to traffic information services is shown.