Non-Asymptotic Bounds for Optimal Fixed-to-Variable Lossless Compression without Prefix Constraints

Bounds on optimal guessing moments serve to improve non-asymptotic bounds on the cumulant generating function of the codeword lengths for fixed-to-variable optimal lossless source coding without prefix constraints. Non-asymptotic bounds on the reliability function of discrete memoryless sources are presented as well. Lower bounds on the cumulant generating function of the codeword lengths are given, by means of the smooth Rényi entropy, for source codes that allow decoding errors.