## Abstract

This work studies the deviations of the error exponent of the constant composition code ensemble around its expectation, known as the error exponent of the typical random code (TRC). In particular, it is shown that the probability of randomly drawing a codebook whose error exponent is smaller than the TRC exponent is exponentially small; upper and lower bounds for this exponent are given, which coincide in some cases. In addition, the probability of randomly drawing a codebook whose error exponent is larger than the TRC exponent is shown to be double-exponentially small; upper and lower bounds to the double-exponential exponent are given. The results suggest that codebooks whose error exponent is larger than the error exponent of the TRC are extremely rare. The key ingredient in the proofs is a new large deviations result of type class enumerators with dependent variables.

Original language | English |
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Article number | 9095265 |

Pages (from-to) | 6635-6659 |

Number of pages | 25 |

Journal | IEEE Transactions on Information Theory |

Volume | 66 |

Issue number | 11 |

DOIs | |

State | Published - Nov 2020 |

## Keywords

- Error exponent
- expurgated exponent
- large deviations
- typical random code

## All Science Journal Classification (ASJC) codes

- Information Systems
- Computer Science Applications
- Library and Information Sciences