A new modulation scheme for multitransmitter simulcast digital mobile radio communication

Many mobile radio communication systems require digital siganling simultaneously from multiple transmitters from the viewpoints of efficient frequency utilization and simplified receiver construction. This paper describes a new modulation scheme in order to realize a simulcast digital transmission. In this method modulation signal is made by superimposing a sinusoidal wave on an ordinary rectangular digital wave. When Manchester-coded type signal is used, the frequency of the sinusoidal wave is twice as much as that of the original bit-rate and the relative phase difference between the two waves is different at each base station. In order to clarify the feasibility of this technique, experimental simulation tests are performed on 900-MHz band in two transmitter construction. It is proved that this modulation scheme does not only give the same amount of the improvement effect on the digital signaling on an overlapped area, but also makes the allowable carrier frequency drift several times lager than that of the carrier frequency offset strategy.