Enhancing User Detection via SS Burst Repetition in 5G Millimeter Wave Systems

Fifth-generation millimeter wave (mmWave) systems deploy spatial beam search using synchronization signal (SS) blocks for initial access (IA). Technique based on narrow beam sweeping procedure completed in a single SS burst is optimum for idle users that have arrived before IA. With a maximum IA duration of 5ms specified by 3GPP Release 15, the probability of user arrival during IA is non-trivial. For these users, existing search procedures will result in significant discovery delays and low detection probability. This work considers an alternative scenario wherein the user arrives after the commencement of IA. In such cases, a single SS burst may not suffice and one must consider repeating the SS burst to enhance user detection probability and reduce IA delay. Repetition of SS burst brings the trade-off between half-power beamwidth (HPBW) and the number of SS blocks per burst i.e., large HPBW supports a smaller number of SS blocks per burst and vice-versa. To achieve high accuracy of angular position with SS burst repetition, a grating-based search has been proposed which utilizes antenna element spacing greater than half-wavelength. This paper presents an IA delay, location error and detection analysis for both scenarios; with and without SS burst repetition. Simulation results demonstrate the enhanced performance of the proposed grating search technique with SS burst repetition in terms of user detection, reduced IA delay, and low angular position error.