Structured OFDM Design for Massive MIMO Systems with Dual-Wideband Effects

Massive multiple-input multiple-output (mMIMO) channels in wideband systems may exhibit the severe delay spread, due to its spatial- and frequency-wideband (dual-wideband) effects. The typical orthogonal frequency division multiplexing (OFDM) technology have to insert a larger number of cyclic prefix (CP) to overcome the inter-symbol interference (ISI) induced by delay spread. The additional CP overhead will counteract the improvement of spectral efficiency by the large antenna array. To address the issue, this paper proposes a structure OFDM modulation approach to reduce the CP overhead for wideband mMIMO systems with dual-wideband effects. Specifically, we propose a joint spatial precoding and frequency domain equalization scheme to maximize the system spectrum efficiency, where the closed-form solutions of precoding vectors and equalization matrices are derived by exploiting the unique characteristic of composite channel matrix. Numerical simulations indicate that the proposed scheme can effectively deal with the dual-wideband effects and significantly improve the spectral efficiency with low CP overhead.