Inner Distance Measure Bounds on the Minimal Euclidean Distance for Symmetric PSK Block Codes

The minimum Euclidean distance is a fundamental quantity for block-coded PSK. In this paper improvements are made of bounds for this quantity that are explicit functions of the alphabet size q, block length n and code size |C|. Earlier work, where the restriction q=8 was used, is continued by a generalisation allowing any q. The bound generalizes Elias critical sphere argument, which localizes the optimization problem to one neighbourhood, by use of so called inner distance measure for defining the shape of a sphere. Remark that codes which fulfill the bound with equality exist, and are best possible in terms of minimum Euclidean distance, for given parameters q, n and |C|.