Trellis Coded Multi-Level Gaussian FSK

A reduced complexity coherent receiver for trellis-coded (TCM) M-GFSK is described, using a simplified Laurent detector followed by a Viterbi algorithm that jointly provides maximum likelihood (ML) sequence detection and decoding of the TCM. This increases the size of M over that which is currently feasible. The spectral efficiency achieved with an example scheme with M = 32 is 6 bits/s/Hz, equivalent to 64-QAM. The performance in noise is worse than 64-QAM, however M-GFSK is constant-envelope allowing transmitter amplifiers to operate at saturation without spectral re-growth which more than compensates the degradation in cases where power is limited, such as with satellite links or radio links for battery operated user terminals.