List Decoding of Insertion and Deletion Codes
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Insertion and deletion (Insdel for short) errors are synchronization errors in communication systems caused by the loss of positional information of the message. Since the work by Guruswami and Wang [12] that studied list decoding of binary codes with deletion errors only, there have been some further investigations on the list decoding of insertion codes, deletion codes and insdel codes. However, unlike classical Hamming metric or even rank-metric, there are still many unsolved problems on list decoding of insdel codes. The purpose of the current paper is to move toward complete or partial solutions for some of these problems. Our contributions mainly consist of three parts. Firstly, we provide an upper bound on the list decoding radius of an insdel code in terms of its rate. This bound provides some improvements when degenerated to insertions only and deletions only compared to the previous results in [17]. Secondly, we analyse the list decodability of random insdel codes. It shows that although there is a gap between the list decoding radius of random insdel codes and our upper bound on list decoding radius, when the alphabet size is sufficiently large, this gap no longer exists. In addition, we show that list decoding of random insdel codes surpasses the Singleton bound when there are more insertion errors than deletion errors and the alphabet size is sufficiently large. We also find that our results improve some previous findings in [17] and [12]. Furthermore, our results reveal the existence of an insdel code that can be list decoded against insdel errors beyond its minimum insdel distance while still having polynomial list size. Lastly, we construct a family of explicit insdel codes with efficient list decoding algorithm. As a result, we obtain a Zyablov-type bound for insdel errors.
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