Analysis and simulation of a hybrid modulation scheme for embedding data in amplitude-modulated signals

Zero synchronous modulation (ZSM) is a novel hybrid modulation scheme which employs angle modulation to transmit a data signal in addition to analogue envelope modulation. The bandwidth of a ZSM signal is restricted to that of conventional DSB-AM by synchronising data with the occurrence of complex zeros of the analogue input. The theoretical basis of ZSM is discussed and a new algorithm is given for locating complex zeros in real time. Analysis of ZSM is extended to implementation errors at the transmitter due to inaccurate zero location and finite truncation of angle modulating functions. The special case of sinusoidal envelope modulation is discussed. Simulation results illustrate the performance of ZSM under practical operating conditions with sinusoidal, random and voiced speech analogue input. Power spectra are computed which indicate that average data rates of about half the bandwidth of the analogue envelope modulating signal can be sustained without a significant increase in bandwidth over conventional DSB-AM.<>