Trellis coded modulation using partially overlapped signal sets of non-equiprobable signaling

In conventional trellis coded modulation (TCM), a higher-ary modulation scheme combining with a convolutional code is employed not to expand the transmitted bandwidth. This forces the system to be attended by signal constellation expansion and increasing the average signal power. As solutions to avoid signal constellation expansion, TCM systems using totally overlapped signal sets (TO-TCM and RU-TCM) were proposed. These schemes can realize a coded modulation system with no signal constellation expansion and achieve more coding gain than conventional TCM. However, a problem that the systems with totally overlapped signal sets might be catastrophic has been remained. The authors propose a novel TCM system using partially overlapped signal sets of nonequiprobable signaling (PO-TCM-NE). This scheme employs the partially overlapped signal constellation to control increasing signal points, and to avoid catastrophic error propagation. The nonequiprobable signaling is employed to reduce average signal power. Coding gain of proposed PO-TCM-NE is considerably improved; in consequence the average signal power is reduced much lower than other TCM systems with equiprobable signaling.