Communication scheme using non-coherent frequency detection of

Abstract

A reduced cost digital data modulation and demodulation scheme for very small aperture terminal (VSAT) satellite communication systems combines non-coherent frequency detection with trellis-coded, multi-frequency modulation. The technique is robust to phase noise and frequency uncertainty and is capable of achieving the performance of rate one-half phase shift keyed modulation. The code width of data to be transmitted bears a prescribed relationship to the size of a multiple frequency set and the selection of a given combination of frequencies within that set for transmission during a respective baud. One portion the data is convolutionally encoded and provides a pointer to one of plural groups of orthogonal signal sets associated with frequencies into which the multiple frequency set has been partitioned. Another portion of the data identifies the frequency combination within the group pointed to by the one portion. The combined portions encode a multi-frequency waveform transmitted to the receiver site. At the receiver site, the sequence of multi-frequency tones produced by the transmitter encoder is detected by non-coherent frequency detection. For each baud, the outputs of matched filters are examined to determine the most likely set of frequencies to have been transmitted during that baud. Most likely frequency combination determinations provide soft decision inputs to a Viterbi decoder.