Beam Detection Analysis for 5G mmWave Initial Acquisition

In conventional initial acquisition (IA) process, a base-station (BS) periodically transmits synchronization signals called pilot signals on downlink (DL) channels to assist a user-equipment (UE) to connect to the cellular system. This paper introduces a new approach where the IA is done on an uplink (IL) channel where multiple base station's receivers detect the pilot beams. A primary contribution of the paper is the development of an analytical technique that can compare various mmWave IA schemes including detection of directional pilot beams transmitted by multiple transmitters (as in conventional downlink IA process) and the newly proposed UL scheme. The analysis derives the non-centrality parameter for the directional beam detection problem that quantifies the detection performance with respect to the pilot signal's duration and bandwidth, the number of sweeping beams, total transmitted power per beam, and the antenna size at the receiver(s). The above selection of design parameters for IA processes allows us to investigate the overall impact of the various IA schemes on power consumption, latency, or hardware implementation complexity. The analysis and simulation results show that the proposed UL scheme does not compromise on the detection performance compared to the conventional DL schemes. Furthermore, we show via simulation that pilot signal's bandwidth and sweeping beam's directional offset can attribute to large variations in detection performances. From these results we conclude that an UL scheme can provide a low latency and a flexible cell search process catered to each mmWave transmission channel between a BS and a UE.