Walsh function synthesis of the combined multiple shift-keyed modulated signals

Introduction of redundancy in modulation of shift-keyed signals by combining phase, frequency and/or amplitude information elements, can increase their detection probability. To make receiving side measurements for evaluation of detection probability and spectral occupancy penalty it is necessary to build a flexible, but simple for realization, modulator by which all combinations of the shift-keyed signals can be easily synthesized. The paper introduces the Walsh function based generator for synthesis of the combined multiple shift-keyed signals: M/sub P/-PSK/M/sub F/-FSK, M/sub P/-PSK/M/sub P/-ASK, PSK/M/sub A/-ASK, and M/sub F/-PSK/M/sub A/-FSK/M/sub A/-ASK. The proposed generation technique is chosen because the generator can be realized digitally in the small ROM-less PLD with a small number of components outside of the chip. The core of the generator is synthesis of the sine-wave carrier by Walsh functions. This synthesized carrier is modulated by a digital signal, producing single or combined shift-keyed modulated signals. Frequency modulation is achieved by a change of input clock frequency, discrete phase shifts are synthesized within a generator by the special shift-functions set, and discrete amplitude elements are obtained from the attached gain control amplifier. The generator is realized digitally in low complexity PLD, with a D/A conversion weighted resistor network and gain control amplifier outside of the chip. The paper presents oscillograms and power spectrum for the two combined multiple shift-keyed modulated signals.