Limits to List Decoding Random Codes

  • Authors:
  • Atri Rudra

  • Affiliations:
  • Department of Computer Science and Engineering, University at Buffalo, SUNY, Buffalo, 14620

  • Venue:
  • COCOON '09 Proceedings of the 15th Annual International Conference on Computing and Combinatorics
  • Year:
  • 2009

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Abstract

It has been known since [Zyablov and Pinsker 1982] that a random q -ary code of rate 1 *** H q (ρ ) *** *** (where 0 ρ q , *** 0 and H q (·) is the q -ary entropy function) with high probability is a (ρ ,1/*** )-list decodable code. (That is, every Hamming ball of radius at most ρn has at most 1/*** codewords in it.) In this paper we prove the "converse" result. In particular, we prove that for every 0 ρ q , a random code of rate 1 *** H q (ρ ) *** *** , with high probability, is not a (ρ ,L )-list decodable code for any , where c is a constant that depends only on ρ and q . We also prove a similar lower bound for random linear codes.