Effects of Varying Message Precision in Digit-Online LDPC Decoders

Abstract

Increasing the pipeline depth of bit-parallel message-passing low-density parity-check (LDPC) decoders can be done by increasing the number of simultaneously decoded frames, or by decreasing the amount of parallelism in the decoder. In digit-serial decoders, the pipeline depth can also be increased by increasing message precision. Digit-online decoders are a class of digit-serial decoders that use redundant notation to allow for most-significant-digit-first processing of LLR messages. This paper examines the effect of changing the precision of LLRs on the throughput, area and energy efficiency of digit-online decoders for the irregular WiMAX rate 3/4A length 1056 block code. Both single-frame and frame-interlaced decoding are considered. Digit-online decoders have a throughput that is largely independent of message precision. Frame-interlaced decoding has a higher throughput than single-frame, but has an increased energy/bit cost.