Pilot Allocation Algorithm Based on User Grouping in Massive MIMO Systems

In order to improve the accuracy of the pilot-aided channel estimation in massive multiple-input multiple-output (MIMO) systems, a user grouping based pilot allocation algorithm (UGPA) is proposed according to the large-scale fading coefficient. The users are divided into the cell-edge and the cell-center groups, whereby the edge users apply for the orthogonal pilot that cannot reused in all cells. On the contrast, the center users apply for the pilot which can be reused by other cell user. Alternatively, the cell-center users are sorted in ascending order by the polar angles, and the pilot sequences are sequentially allocated. That ensures a large spacing between the central users who select the same pilot. Furthermore, in order to decrease the pilot overhead, an improved user grouping based pilot allocation algorithm (IUGPA) is proposed based on the UGPA, which joints the user location information. To begin with, the user grouping is performed according to the user’s uplink channel large-scale fading. Then, the cell-edge users are selected a second division based on the space distance between the user and base station, and the same pilot allocation strategy as the UGPA is adopted. The simulation results demonstrated that the IUGPA algorithm significantly reduce the pilot overhead compared with the soft pilot reuse (SPR) algorithm. Moreover, the uplink sum achievable rate is boosted with the UGPA algorithm and the IUGPA algorithm at different degrees.