Pilot reuse for device-to-device underlay massive MIMO systems

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. But the channel state information from all the users including D2D users to the BS is required to obtain the advantage. For the orthogonal channel training scheme, the pilot overhead becomes large with the number of users increasing, and constitutes a bottleneck for improvement of the system sum-throughput. In this paper, we propose pilot reuse (PR) for D2D underlay massive MIMO systems to reduce the pilot overhead and increase the system sum-throughput. Further, we develop a pilot scheduling algorithm under the criterion of minimizing the sum of mean square errors of channel estimation. Numerical results show that the proposed PR scheme can greatly increase the system sum-throughput at the price of slight degradation of cellular performance, compared to the conventional massive MIMO system.