Low-Latency Beam-Multiplexing Scheme for Efficient Cell Search in Massive MIMO Systems

In massive multiple-input multiple-output (MIMO) systems, highly directional transmissions are widely applied to mitigate the severe path loss during cell search. However, as the number of base station (BS) antennas increases, the large number of directional beams required for the highly directional connections will significantly increase the latency of the cell search. In this paper, we focus on the transmitting and the receiving of the primary synchronization signal (PSS), which is a crucial first step in cell search. To reduce cell search latency, we propose a PSS beam-multiplexing scheme that significantly reduces the time required for the BS to transmit all available beams by transmitting multiple PSS beams simultaneously. Meanwhile, to maximize the benefits of the proposed scheme, we also introduce an optimal beam estimation approach and a PSS detection approach. Simulation results indicate that our beam-multiplexing scheme outperforms the existing beam sweeping scheme in terms of PSS reception and significantly reduces cell search latency, particularly in fast-varying channels.