Fully transparent phase/Doppler invariant trellis-coded modulation

The paper considers the problem of digital transmission over a channel with phase ambiguity generated either by a constant phase shift or a Doppler frequency shift. It is well known that differential encoding/decoding techniques can be used to remove the constant phase and Doppler frequency shift of the received sequence in an uncoded communication system. The same techniques can be used for a coded system, provided that the transmitted sequence is transparent to the phase rotations of the signal space caused by constant phase and Doppler frequency shift ambiguities. Necessary and sufficient conditions are derived for a trellis-coded modulation scheme to be fully transparent rotationally invariant and new procedures are proposed for the design of fully transparent phase-invariant trellis codes, Doppler-invariant trellis codes, and phase/Doppler-invariant trellis codes.<>