Pilot reuse and interference-aided MMSE detection for D2D underlay massive MIMO

In uplink device-to-device (D2D) underlay cellular systems, massive multiple-input multiple-output (MIMO) seems promising as the large antenna array at the base station (BS) can nearly null the D2D-to-cellular interference. However, the channel-state information (CSI) from all users is required to obtain this advantage. For the orthogonal training scheme, the pilot overhead increases with the number of D2D users, leading to a loss of the achievable spectral efficiency. In this paper, we propose a pilot scheduling scheme for D2D underlay massive MIMO systems, which allows D2D users to reuse the pilots of cellular users so that the pilot overhead can be reduced. Moreover, a novel interference-aided minimum mean square error (MMSE) detector is proposed to suppress the D2D-to-cellular interference, utilizing the estimated CSI from not only cellular users but D2D users as well. Furthermore, we derive the large-scale approximations of the signal-to-interference-plus-noise ratios (SINRs), which are asymptotically tight and accurate, even for a small number of BS antennas. Based on these SINR approximations, performance analyses are given to provide more insights. Simulation results show that the proposed pilot reuse scheme and detector significantly increase the achievable sum spectral efficiency, as compared with the conventional massive MIMO and other baseline schemes.