Book Description

Bit-interleaved coded modulation with iterative decoding (BICM-ID) is considered for hybrid wireless channels that consist of parallel free space optical (FSO) and radio frequency (RF) links. Novel symbol mappers are proposed. In contrast to conventional symbol mappers that operate separately over the two links, the proposed mappers jointly optimize error performance over both the FSO and RF links. A greedy hybrid symbol assignment algorithm is presented to obtain mappings that are found to provide significantly better performance over conventional mapping. A technique to analyze the asymptotic bit error performance of the proposed hybrid symbol mapping is developed. Numerical results demonstrate the benefits of the hybrid symbol mappers over the conventional symbol mappers. Hybrid FSO/RF symbols that require multiple uses of the FSO channel for each use of the RF link to exploit the much higher bandwidth available with the FSO link are designed. An orthogonal evolutionary (OE) algorithm to obtain optimal symbol mappings is investigated. New cost functions to be used in the OE algorithm are proposed for different signal-to-noise ratio (SNR) regimes. Numerical results show that the proposed symbol mappings provide significant gain in term of SNR over the conventional mappings. In case of hybrid symbols that consist of 2 RF bits and 1 FSO bit, with a fixed FSO SNR of 3 dB, more than 6 dB gain in RF SNR is obtained over the conventional mappings. Similarly, for a fixed RF SNR of 2 dB, more than 8 dB gain in FSO SNR is obtained. The use of the proposed hybrid symbols in a relay network is investigated. Toward this goal, first an adaptive decode and forward (DF) cooperative diversity scheme based on BICM-ID for RF channels is investigated. Optimized constellation mappings for the source and the relay are designed. A genetic algorithm to find the optimized mapping is investigated. New error performance analysis for adaptive DF scheme using BICM-ID is proposed. Next, a quantize and encode forwarding (QEF) technique is developed where the soft information received at the relay is quantized and relayed to the destination. The relay-to-destination (RD) link can be a high bandwidth FSO link or a hybrid FSO/RF link. The use of the proposed symbol mappers in the RD link is studied for both FSO and hybrid FSO/RF links. Numerical results show that the use of a 3-bit quantizer at the relay provides a bit error rate (BER) performance close to a genie-aided maximal ratio combiner that directly combines information available at the relay and the destination. The use of BICM-ID with the proposed symbol mappers is also studied for quadrature amplitude modulation (QAM) symbols, and a significant performance gain over conventional symbol mappings is observed.