Trellis-coded M-ary orthogonal modulation

Abstract

We have introduced the trellis-coded M-ary (M=32) 4-dimensional (4-D) orthogonal modulation scheme. Here, a rate 4/5 convolutional encoder generates one of 32 possible symbols every T seconds. Then the signal mapping for 32 symbols is performed by a M-ary 4-D orthogonal modulator. The M-ary 4-D modulator employs the vectors which is derived by the optimization technique of signal waveforms in a 4-D sphere. The technique is used in maximizing the minimum Euclidean distance between a set of signal points on a multidimensional sphere. After combining coding with M-ary 4-D modulation, we have obtained a considerable improvement in the free minimum distance of the system. The new system achieves asymptotic coding gains up to 6.4 dB over the uncoded two-independent QPSK scheme and 3.4 dB over the two-independent 2-D TCM scheme.