Pragmatic trellis-coded digital communication with multi-stage branch metrics

Abstract

A pragmatic trellis-code modulated digital communications system (,) is provided, in which a demodulator (,) is configured to demodulate a quadrature input signal (,) into an estimation (,) of digital data (,) conveyed thereby. The demodulator (,) includes a branch-metrics generator (,) incorporating a soft-decision generator (,), a delay circuit (,), and a likelihood generator (,); a convolutional encoding circuit; and a hard-decision estimator (,) incorporating a hard-decision generator (,), a selection circuit (,), and an encoding circuit (,). The soft-decision generator (,) generates encoded-bit estimates (ŝ,, ŝ,) from the input signal (,). The delay circuit (,) delays one estimate (ŝ,) relative to the other (ŝ,). The likelihood generator (,) generates likelihoods ({circumflex over (m)},, {circumflex over (m)},, {circumflex over (m)},, {circumflex over (m)},) thereof. The convolutional decoding circuit (,) generates a first data-estimation portion (,) therefrom. The hard-decision generator (,) generates uncoded-bit estimate groups (ê,, ê,, ê,, ê,) from the input signal (,). The selection circuit (,) selects one of the groups (ê,, ê,, ê,, ê,) to be a second data estimation portion (,). The convolutional encoding circuit (,) encodes the first data-estimation portion (,) to produce selection-bit estimates (ĉ,, ĉ,) with which to control the selection circuit (,).