An Improved Multiple-Symbol Differential Sphere Decoding for Differential Unitary Space-Time Modulation

Multiple-symbol differential sphere decoding (MSDSD) is an attractive solution for transmission over multiple-input multiple-output (MIMO) Rayleigh-fading channels, which jointly processes blocks of N received symbols. However, for the application of a sphere decoding algorithm using the Schnorr-Euchner enumeration strategy, the explicit ordering of the ML metric for candidate symbols is still computational demanding, especially for large constellation size. In this paper, we show that for a specific construction of constellations, there exists an efficient method to calculate and enumerate the ML metric in ascending order, and only a few candidates (much fewer than the constellation size) for one component of the N received symbols need to be check during the search, which lead to significant complexity reduction in calculation. This conclusion helps to strike the best trade-offs among performance and complexity