Optimization of Low-Density Parity Check decoder performance for OpenCL designs synthesized to FPGAs

Open Computing Language (OpenCL) is a high-level language that allows developers to produce portable software for heterogeneous parallel computing platforms. OpenCL is available for a variety of hardware platforms, with compiler support being recently expanded to include Field-Programmable Gate Arrays (FPGAs). This article investigates flexible OpenCL designs for the iterative min-sum decoding algorithm for (3,6)-regular Low-Density Parity Check (LDPC) codes over a range of codeword lengths. The target FPGA hardware is the Altera Stratix V GX A7 based Nallatech 385n board. The computationally demanding LDPC decoding algorithm offers several forms of parallelism that could be exploited by the Altera Offline Compiler (AOC version 15.1) for OpenCL. Our best decoder design produced a corrected codeword throughput of 68.22 Mbps at the compiler-selected FPGA clock frequency of 163.88 MHz for a length-2048 (3,6)-regular LDPC code. For a length-1024 (3,6)-regular LDPC code, our best design produced a throughput of 54.8 Mbps (32 decoding iterations) which significantly improves on the throughput of around 7 Mbps (30 decoding iterations) produced by an OpenCL based decoder design reported by Falcao et al. for the same size of LDPC code.