Bit-interleaved coded modulation with iterative decoding (BICM-ID) using signal space diversity (SSD) over non-orthogonal amplify-and-forward (NAF) relay channels.

摘要

Diversity is a powerful technique to improve the reliability of digital communications systems over wireless channels. In this thesis, the error performance and precoder design of a bandwidth-efficient bit-interleaved coded modulation with iterative decoding (BICM-ID) system over a non-orthogonal amplify-and-forward (NAF) half-duplex single-relay channel is investigated to effectively combine cooperative, time and modulation diversities.;Attention is then paid to the NAF-BICM-ID system using a 2 x 2 precoder, where a closed-form expression of the bound is obtained. Based on this expression, the optimal class of 2 x 2 precoders is developed. Different from the optimal precoders designed for uncoded systems, the derived precoder indicates that the source terminal only needs to send the superposition of the first symbol and the rotated version of the second one in the first time slot, while being silent in the remaining slot to achieve the best asymptotic performance. For a good convergence property, it is further shown that a rotation angle that maximizes the minimum Euclidean distance of the superposition constellation should be used. Optimal rotation angles are then analytically determined for various modulation schemes. The usefulness of the proposed precoder is verified by both the error bound and simulation results.;Finally, based on extrinsic information transfer (EXIT) charts, both the convergence property and the asymptotic performance of the system using optimal precoders are analyzed when different code rates are used. Analytical and simulation results show that the proposed precoders not only exploit full cooperative diversity but also offer significant coding gains for a wide range of code rates over the optimal precoders for uncoded NAF systems.;At first, a tight union bound on the asymptotic bit error probability (BEP) of the NAF-BICM- ID system employing signal space diversity (SSD) via a precoder is derived for an arbitrary cooperative block length of 2N. This bound provides a useful tool to predict the error performance without the need of time-consuming simulations. A design criterion that characterizes the effect of the precoder to the performance is then developed, which gives an insight on how to obtain a good precoder to fully exploit diversity.