Sphere decoding for OFDM systems over doubly selective channels

Orthogonal Frequency Division Multiplexing (OFDM) is a promising technology for high data rate transmission, that is widely used in modern wireless communication systems because of its suitability for frequency selective channels. However channel time variations destroy the orthogonality between sub-carriers resulting in Inter-Carrier Interference (ICI), that degrades performance in OFDM. Various techniques have been considered to mitigate the effects of ICI. In our work, we consider OFDM as a Multiple Input Multiple Output (MIMO) system in the frequency domain, and employ corresponding detection techniques that provide good performance despite the presence of ICI. As ICI is mainly contributed by a limited number of adjacent sub-carriers, the frequency domain channel matrix can be approximated as banded. This work introduces a reduced complexity Sphere Decoder (SD) for OFDM demodulation that is based on such banded matrix assumption. It is shown that the proposed algorithm provides performance and complexity advantages over competing detection techniques based on the Viterbi Algorithm (VA) operating in the frequency domain.