Initial Access Optimization for Millimeter Wave Wireless Networks

Abstract : The initial access in 5G New Radio (NR) standalone millimeter wave (mmWave) uses the techniques of beam sweeping to Figure out appropriate directions of transmission and reception. Beam sweeping refers to the transmission of cell specific signals by the base station (BS) while switching beam direction in a sequential manner in order to cover the whole cell. The conventional beam sweeping consists of transmitting sequentially and periodically the beams, according to a fixed pattern, which results in an initial access latency. The aim of this paper is to minimize the overall number of timeslots needed to connect all users to the BS by allowing using multiple beams in some slots and then activating the beams in a prioritized and controlled manner rather than sequentially and periodically as in the conventional scheme. The problem is formulated as a combinatorial optimization problem, for which a Semidefinite Relaxation-based (SDR-based) solving approach is proposed. Numerical results demonstrate that our scheme outperforms significantly the conventional beam sweeping.