Performance analysis of hybrid ARQ schemes in optical communications

The channel in the intensity modulation-direct detection (IMDD) system, which is one of the typical optical communication systems, can be modeled as a Z-channel, where only “1-to-0” errors are produced. Consequently, by applying the all-unidirectional error-detecting code, error-free communication can be realized by using an ARQ (Automatic Repeat Request) scheme in which the codeword containing errors is retransmitted. From such a viewpoint, this paper discusses the application of a hybrid ARQ scheme to optical communications. First, the throughput is used as the evaluation measure. It is shown that the hybrid ARQ scheme (hybrid SR+GBN ARQ scheme), which combines a single-error correction/all-unidirectional error detection code (SEC/AUED code) with the selective Go-Back-N method is the ARQ scheme most suited to the optical communication from a practical viewpoint, including the fact that it can be realized using a receiver buffer with finite length. We propose an SEC/AUED code that allows coding/decoding with practicable computational complexity, even if the code length is great. The performance is evaluated for the hybrid SR+GBN ARQ scheme. It is shown that a throughput exceeding 99.8% can be realized if the error rate of the channel is less than 10−6. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(3): 73–82, 1997