A novel trellis coded modulation system without signal point expansion

In conventional trellis coded modulation (TCM), the number of signal points in the constellation is doubled by additional redundant bits. This paper proposes a novel TCM system without signal point expansion which employs 2/sup m/ kinds of trellis paths depending upon m encoder input bits, instead of 2/sup m+1/ kinds of paths of conventional TCM. The number of cosets assigned to trellis paths and total number of signal points can be reduced to half of those in conventional TCM. Therefore, it is possible to implement a coded modulation systems without signal point expansion by additional redundant bits, and the effective bit rate becomes unity. This scheme achieves a considerable coding gain in comparison to the traditional uncoded systems, and to the conventional TCM system. Furthermore, as the proposed scheme needs only half the signal points of conventional TCM, the average power is lower and it is less sensitive to the carrier phase offset.