Design and Optimization of Combined Constellation Shaping and Bit LDPC Coded Modulation Using EXIT Chart

Abstract:
The demand for reliable transmission with higher data rates in modern communication systems is growing rapidly. To meet this demand, multilevel modulation schemes have to be considered in combination with powerful forward error correction (FEC) codes. However, the use of uniform signal constellations can not achieve the capacity limit and a so-called shaping gain is still available. This gain can be obtained by employing non-equiprobable signal constellations. In this paper, we combine the shaping technique with low-density parity-check (LDPC) coded modulation schemes to approach the channel capacity. Furthermore, the concatenation of LDPC codes, constellation shaping techniques and mapping schemes is designed and optimized by using extrinsic information transfer (EXIT) charts. Simulation results show that the optimized systems can achieve a shaping gain up to 0.6 dB even for 64-QAM systems.