Parallel concatenated Gallager codes and their applications in CDMA wireless networks

A new class of parallel concatenated codes built from the parallel concatenation of Low-Density Parity-Check (LDPC) codes, called Parallel Concatenated Gallager Codes (PCGCs) is presented. The motivation is to use the good LDPC codes in the well known turbo code structure to break the fairly complex decoding of a long code into steps, while maintaining the information loss between the component decoders and minimizing any information loss between the decoding steps. In this scheme, component LDPC codes interact in parallel concatenation directly without interleavers.; We intend to show that short-frame PCGCs have good error correcting capabilities in both Additive White Gaussian Noise (AWGN) and Rayleigh fading channels.; Analysis of the proposed coding scheme using both iterative and Maximum Likelihood (ML) decoding are presented. Techniques based on Gaussian approximation of the extrinsic information and trajectories projection are used to design the codes and analyze their performance. We derive an upper bound on the number of codewords of a certain weight and combine it with available bounding techniques on the frame and bit error rates to study the codes' asymptotic performance. Simulation results of a digital communication system employing PCGCs both in AWGN and Rayleigh fading channels are presented to exhibit the good performance of the codes in more realistic environments.; The good performance of PCGCs increases the capacity of Code Division Multiple Access (CDMA) systems while the low encoding and decoding complexity of such codes keep the signal processing delays within a reasonable limit. Applications of PCGCs in future wireless networks becomes feasible under the recent advancements in the VLSI implementations of the reduced complexity sum-product decoding algorithm.