| 摘要 |
A pragmatic trellis-code modulated digital communications system (20) is provided, in which a demodulator (24) is configured to demodulate a quadrature input signal (62) into an estimation (64) of digital data (54) conveyed thereby. The demodulator (24) includes a branch-metrics generator (74) incorporating a soft-decision generator (82), a delay circuit (86), and a likelihood generator (88); a convolutional encoding circuit; and a hard-decision estimator (78) incorporating a hard-decision generator (98), a selection circuit (104), and an encoding circuit (106). The soft-decision generator (82) generates encoded-bit estimates (ŝ0, ŝ1) from the input signal (62). The delay circuit (86) delays one estimate (ŝ1) relative to the other (ŝ0). The likelihood generator (88) generates likelihoods ({circumflex over (m)}00, {circumflex over (m)}01, {circumflex over (m)}10, {circumflex over (m)}11) thereof. The convolutional decoding circuit (76) generates a first data-estimation portion (92) therefrom. The hard-decision generator (98) generates uncoded-bit estimate groups (ê00, ê01, ê10, ê11) from the input signal (62). The selection circuit (104) selects one of the groups (ê00, ê01, ê10, ê11) to be a second data estimation portion (94). The convolutional encoding circuit (106) encodes the first data-estimation portion (92) to produce selection-bit estimates (ĉ0, ĉ1) with which to control the selection circuit (104).
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