Design Considerations for Spatially Coupled LDPC Codes under Decoding Latency Constraints

In this paper, we begin by reviewing the design of spatially coupled low-density parity-check (SC-LDPC) codes with belief- propagation based sliding window decoding (SWD) from the point of view of protograph constructions. We then discuss the potential for an SC-LDPC code to achieve better performance than the iterative decoding threshold of its underlying LDPC block code (LDPC-BC), subject to a constraint on decoding latency. In particular, we examine the problem of decoder error propagation that can occur under tight latency constraints and performance requirements and can severely degrade the decoded error rate. The existing literature on how to deal with this problem is then reviewed and the advantages and disadvantages of some proposed solutions are summarized, with emphasis on the code doping technique. Finally, various design tradeoffs and open research problems related to the ultimate goal of designing SC-LDPC codes with SWD to operate near capacity with moderate values of decoding latency, memory, and computational complexity are discussed, focusing on both the waterfall and error floor regions of the decoded error rate performance curve.