Subspace polynomials and limits to list decoding of Reed-Solomon codes

  • Authors:
  • Eli Ben-Sasson;Swastik Kopparty;Jaikumar Radhakrishnan

  • Affiliations:
  • Department of Computer Science, Technion-Israel Institute of Technology, Haifa, Israel;Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge;Tata Institute of Fundamental Research, Mumbai, India

  • Venue:
  • IEEE Transactions on Information Theory
  • Year:
  • 2010

Quantified Score

Hi-index 754.84

Visualization

Abstract

We show combinatorial limitations on efficient list decoding of Reed-Solomon codes beyond the Johnson-Guruswami-Sudan bounds. In particular,we showthat for arbitrarily large fields FN, |FN| = N, for any δ Ɛ, (0,1) and K = Nδ : • Existence: there exists a received word wN : FN → FN that agrees with a super-polynomial number of distinct degree K polynomials on ≈ N√δ points each; • Explicit: there exists a polynomial time constructible received word w1N : FN → FN that agrees with a superpolynomial number of distinct degree K polynomials, on ≈ 2√logN K points each. In both cases, our results improve upon the previous state of the art, which was ≈ Nδ/δ points of agreement for the existence case (proved by Justesen and Hoholdt), and ≈ 2Nδ points of agreement for the explicit case (proved by Guruswami and Rudra). Furthermore, for δ close to 1 our bound approaches the Guruswami-Sudan bound (which is √NK) and implies limitations on extending their efficient Reed-Solomon list decoding algorithm to larger decoding radius. Our proof is based on some remarkable properties of subspace polynomials. Using similar ideas, we then present a family of low rate codes that are efficiently list-decodable beyond the Johnson bound. This leads to an optimal list-decoding algorithm for the family of matrixcodes.