Efficient Low-density Parity-check Codes for Cooperative Communication

Download or read book Efficient Low-density Parity-check Codes for Cooperative Communication written by Osso Vahabzadeh and published by . This book was released on 2014 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, we address code design problem for cooperative communication over different channel models with emphasis on low complexity designs and structured codes that are attractive for practical implementation. We start with the problem of designing efficient codes for the relay node in Gaussian relay channels. For a class of capacity approaching codes for this channel model, called bilayer lengthened LDPC (BL-LDPC) codes, we calculate a measure of decoding complexity as a function of the number of decoding iterations and propose a technique to design complexity-optimized BL-LDPC codes by minimizing the complexity measure of these codes. This is made possible by generalizing the EXIT charts to the case of BL-LDPC codes. Motivated by the fact that there are usually stricter hardware restrictions at the relay node, our technique targets minimizing the decoding complexity of the relay code. Furthermore, excessive delay due to decoding high rate codes at the relay results in additional delay at the destination. Using our technique, we design bilayer codes with noticeable reduction in decoding complexity and delay compared to the rate-optimized codes reported in the literature. Next, we study the achievable rates for the decode-and-forward (DF) relaying strategy for the Rayleigh fading relay channel where the links have independent normalized Rayleigh fading coefficients and the channel side information is perfectly known at the corresponding receivers but not at the transmitters. We design BL-LDPC codes for this scenario for the case when the source-relay link is much stronger than the source-destination link as well as for the case when these two links have comparable SNRs. We also propose a novel two-user cooperation scheme for the block fading channel model that employs protograph-based LDPC codes. The proposed scenario is based on time division where each user transmits its message to the base station (BS) in two successive frames. Cooperation is performed by employing the Alamouti scheme Whenever it is possible. Additionally, the users encode their information over protograph-based LDPC codes that allow flexible selection of rates and code lengths. Finally, we introduce rate-compatible protograph-based root LDPC (RCPB-R-LDPC) codes for cooperative communication over block fading channels and propose two methods to construct these codes. The proposed techniques are based on the extension technique and offer broad design rates resulting in high flexibility. Furthermore, they are based on protograph constructions with minimum distance growing linearly with the block length, a property that improves the error floor performance of the designed codes. The outage probability limit under BPSK modulation is obtained for the cooperative scheme employed in this work and was used to evaluate the WER performance of the designed codes.