Better Lower Bounds for Locally Decodable Codes

  • Authors:
  • Amit Deshpande;Rahul Jain;T. Kavitha;Jaikumar Radhakrishnan;Satyanarayana V. Lokam

  • Affiliations:
  • -;-;-;-;-

  • Venue:
  • CCC '02 Proceedings of the 17th IEEE Annual Conference on Computational Complexity
  • Year:
  • 2002

Quantified Score

Hi-index 0.00

Visualization

Abstract

An error-correcting code is said to be {\em locally decodable} if a randomized algorithm can recover any single bit of a message by reading only a small number of symbols of a possibly corrupted encoding of the message.Katz and Trevisan \cite{KT} showed that any such code C:\{0,1\} \rightarrow \Sigma^m with a decoding algorithm that makes at most q probes must satisfy m= \Omega((n/ \log|\Sigma|)^{q/(q-1)}). They assumed that the decoding algorithm is non-adaptive, and left open the question of proving similar bounds for adaptive decoders.We improve the results of \cite{KT} in two ways. First, we give a more direct proof of their result. Second, and this is our main result, we prove that m=\Omega({(n/\log |\Sigma|)}^{q/(q-1)}) even if the decoding algorithm is adaptive. An important ingredient of our proof is a randomized method for {\em smoothening} an adaptive decoding algorithm. The main technical tool we employ is the {\em Second Moment Method}.