Iterative demodulation and decoding for a mobile packet system with parallel concatenated trellis-coded modulation

We describe a mobile packet radio waveform. that employs parallel concatenated trellis-coded modulation, or turbo trellis-coded modulation, in conjunction with continuous-phase modulation. The code symbols are interleaved before they are modulated to provide protection from partial-band interference, frequency-selective fading, and other types of channel degradation. The received signal is iteratively demodulated (noncoherently) and decoded. The receiver obtains channel quality estimates to aid in the decoding process. Simulation and prototype results from a JTRS 2A radio at VHF are presented to show the performance of the system for AWGN and partial-band interference channels. Relative to the conventional SINCGARS VHF packet waveform, a greater than threefold improvement in spectral efficiency is realized without loss of range or increase in spectral occupancy. Future plans to accelerate demodulator and decoder speeds and to improve performance in partial-band interference channels are presented. While applied initially to FH spread spectrum, the turbo trellis-coded technology is also applicable to direct-sequence systems.