Comparison Between Serial and Parallel Concatenated Channel Coding Schemes Using Continuous Phase Modulation over AWGN and Fading Channels

A generic M-ary continuous phase modulation (CPM) scheme, with a modulation index of h = M 1 , can be decomposed into a continuous-phase encoder (CPE) followed by a memoryless modulator (MM), where the CPE is linear over the ring of integers modulo M (M being the code radix). Thus, for a binary CPM scheme, M = 2 while for a quaternary scheme, M = 4. By designing a channel encoder (CE), which is a convolutional encoder, to operate over the same ring of integers modulo M, the CE and the CPE can be combined to create another M-ary convolutional encoder called an extended CE. In this paper, we use a code radix of 4 i.e. M = 4. Here, a 1⁄2 rate CE over the ring of integers modulo 4 is combined with the CPE of a 4-ary CPM scheme whose modulation index is h = 1⁄4 to create a quaternary extended CE. Using this trellis coded modulation design, the paper compares the performance of a serial and a parallel-concatenated channel-coding scheme over AWGN and Rayleigh slow flat fading channels. In both schemes, the inner encoder is the quaternary extended CE and the outer encoder is another quaternary convolutional encoder. Due to its lower code rate, the parallel scheme has a better BER performance than the serial scheme. The coding gain is, however, modest. For the parallel scheme, a BER of 2.8 X 10 was attainable at 4 dB Eb/N0 in the AWGN channel.