How GPUs Can Outperform ASICs for Fast LDPC Decoding

Journal:

Proceedings of the 2009 ACM SIGARCH International Conference on Supercomputing

Abstract(summary):

Due to huge computational requirements, powerful Low-Density Parity-Check (LDPC) error correcting codes, discovered in the early 1960s, have only recently been adopted by emerging communication standards. LDPC decoders are supported by VLSI technology, which delivers good parallel computational power with excellent throughputs, but at the expense of significant costs. In this work, we propose an alternative flexible LDPC decoder that exploits data-parallelism for simultaneous multi-codeword decoding, supported by multithreading on CUDA-based graphics processing units (GPUs). The ratio of arithmetic operations per memory access is low for the efficient min-sum LDPC decoding algorithm proposed, which causes a bottleneck due to memory latency and data collisions. We propose runtime data realignment to allow coalesced parallel memory accesses to be performed by distinct threads inside the same warp. The memory access patterns of LDPC codes are random, which does not admit the simultaneous use of coalescence in both read and write operations of the decoding process. To overcome this problem we have developed a data mapping transformation which allows new addresses to be contiguously accessed for one of the mentioned memory access types. Our implementation shows throughputs above 100 Mbps and BER curves that compare well with ASIC solutions.

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