A Study on Coding-Spreading Trade-Off in LDPC-Coded IDMA System

A capacity-achieving low-density parity-check(LDPC) code is applied to interleave-division multiple-access(IDMA) system,and the associated codingspreading tradeoff problem is investigated.The required minimum SNR for reliable data and voice transmission based on the bit error rate(BER) of 106 and 10-3 over AWGN channel at different code rates are sought to explore the coding-spreading tradeoff.Simulation results show that the optimal LDPC code rates in LDPC-coded IDMA system are between 0.4 and 0.5 for reliable communication services over AWGN channel.The performance advantage of the proposed system is significant,compared with the traditional convolutioncoded IDMA system at 0.5 code-rate.