A scalable LDPC decoder ASIC architecture with bit-serial message exchange

We present a scalable bit-serial architecture for ASIC realizations of low-density parity check (LDPC) decoders. Supporting the architecture's potential, we describe a decoder implementation for a (256,128) regular-(3,6) LDPC code that has a decoded information throughput of 250 Mbps, a core area of 6.96 mm(2) in 180-nm 6-metal CMOS, and an energy efficiency of 7.56 nJ per uncoded bit at low signal-to-noise ratios. The decoder is fully block-parallel, with all bits of each 256-bit codeword being processed by 256 variable nodes and 128 parity check nodes that together form an 8-stage iteration pipeline. Extrinsic messages are exchanged bit-serially between the variable and parity check nodes to significantly reduce the interleaver wiring. Parity check node processing is also bit-serial. The silicon implementation performs 32 iterations of the min-sum decoding algorithm on two staggered codewords in the same pipeline. The results of a supplementary layout study show that the reduced wiring congestion makes the decoder readily scaleable up to the longer kilobit-size LDPC codewords that appear in important emerging communication standards. (C) 2007 Elsevier B.V. All rights reserved.