Abstract:

Coded Overlapped Code Division Multiplexing System with Turbo Product structure (TPC--OVCDM) is introduced, and Trellis coded modulation (TCM) code is employed as error correcting code for uncoded OVCDM system. In such a scheme, row code and column code are TCM and OVCDM spreading code respectively. Data bits are only encoded directly by TCM and transform them into a matrix, each column of this matrix is then permuted by symbol interleaver before being encoded by OVCDM spreading code. During iterative decoding process in the receiver, two constituent decoders use symbol by symbol BCJR algorithm in the log domain. Decoding order of two sub codes can not be exchanged in arbitrary order and depend on the encoding order. Proportion between TCM coding and OVCDM coding is an important factor to affect system performance. For fixed coding structure and symbol interleaver, performance of TPC-OVCDM systems with different proportion on additive white Gaussian noise (AWGN) channel have been simulated. Simulation results show that TPC-OVCDM system with reasonable proportion can achieve significant coding gain compared with uncoded OVCDM system under the condition of same spectral efficiency at bit error rate level of 10-5.

Key words:

overlapped code division multiplexing, trellis coded modulation,TPC-OVCDM, iterative decoding.