Analysis and optimization design of P-LDPC coded hybrid FSO/RF systems

In this paper, we study a hybrid free-space optical/radio-frequency (FSO/RF) communication system deploying protograph-based low-density parity-check (P-LDPC) codes. We use the protograph-based extrinsic information transfer (PEXIT) algorithm to accurately evaluate the system performance and employ the hybrid FSO/RF symbol mapping technique and the generalized variable degree matched mapping (G-VDMM) interleaver to enhance the performance. To make the optimization feasible and simpler for high-level modulation, we propose a much simpler but efficient design method: select a conventional Gray-labeled mapping scheme and then optimize the G-VDMM interleaver. Both numerical analyses and simulations verify that the performance of a hybrid FSO/RF system can be greatly improved by optimizing the symbol mapping and bit interleaving.