Group-Based Noncoherent Space-Frequency Codes and Efficient Decoding

In this paper, we focus on noncoherent space-frequency (SF) coded multiple-input-multiple-output orthogonal-frequency-division-multiplexing (MIMO-OFDM) systems. Based on OFDM subcarrier grouping, a group-based unitary space- frequency code is proposed and the effect of grouping on system performance is studied. Comparing to the coding scheme without grouping, which implements SF coding among all the OFDM tones, the proposed group-based coding scheme can greatly reduce the decoding complexity, making the noncoherent SF codes more applicable to practical use. By relating the noncoherent SF codes with packings in Grassmann manifold, we propose an efficient decoding method by restricting the implementation of decoding within a subset of the codebook. Numerical results are presented to demonstrate and verify our proposals.