Design of Rate 3/4, 16-States, 16-PSK, Trellis-Coded Modulation Code for AWGN Channel

摘要

Generally, 'encoding and decoding' and 'modulation and demodulation' are considered as two independent isolated activities, while designing any digital communication system. Implementation of 'encoding and decoding' such as block coding, TCM, turbo coding ensures that the errors introduced by the channel are mitigated, and the implementation of 'modulation and demodulation' such as BPSK, 8-PSK, 64-QAM at the baseband level enables the optimum data transfer depending on the channel conditions. In order to improve the BER, error correction schemes are implemented in the digital communication system under design, wherein data is encoded prior transmission; however, in this process bandwidth gets expanded. This bandwidth expansion, however, can be mitigated by suitability changing the modulation schemes, e.g. if the normal modulation scheme used is BPSK but if data is encoded at the rate 1/2, then changing modulation scheme to QPSK will preserve the bandwidth. Integration of convolutional code with the modulation type is known as trellis-coded modulation (TCM). The concept of TCM was though invented in 1970s; it is presently being utilised in many contemporary systems engaged in the field of data communication. A new TCM scheme having rate 3/4, 16-state, 16-PSK, in respect of additive white Gaussian noise (AWGN) channel has been proposed in this paper. Results have been quite encouraging and have indicated the coding gain of approximately 2 dB when compared to uncoded 8-PSK.