Signal Detection for HF Skywave Massive MIMO-OFDM with Slepian Transform

In this paper, we investigate signal detection for high frequency (HF) skywave massive multiple-input multiple-output (MIMO) systems with orthogonal frequency division multiplexing (OFDM) modulation. We first reveal the relationship of sparse supports between the beam domain channel and the Fourier spectrum of the space domain channel for HF skywave massive MIMO-OFDM channels. We then propose a separate Slepian transform (SST) based detector, where a set of modulated Slepian sequences are designed separately for user terminals (UTs). Before the MMSE detection, the Slepian transform is performed to reduce the dimension for each UT, thus avoiding high dimensional matrices multiplications and inversions. To further reduce the computational complexity, we propose a joint Slepian transform (JST) based detector, where a fixed set of modulated Slepian sequences are designed, and Slepian transforms of the observation vector can be efficiently implemented based on low-dimensional fast Fourier transform (FFT). Simulation results demonstrate the attractive performance and excellent complexity advantage of proposed detectors.