Doppler-tolerant sequence design for positioning high-speed vehicles in millimeter-wave cellular systems

Future fifth-generation (5G) New Radio (NR) services consider positioning an integral part of a system that provides high precision using millimeter-wave (mmWave) cellular networks. While the 5G standard for positioning is not fully defined yet, the positioning reference signal (PRS) used in long-term evolution (LTE) system is being considered. Since the conventional LTE PRS is designed for LTE systems below 6 GHz, it is more sensitive and inefficient for high-speed vehicle (HSV) experiencing a high Doppler effect in mmWave cellular systems. In this paper, a new sequence, called an oscillatory pulse sequence (OPS), is proposed for the positioning of HSVs in mmWave cellular systems. The ambiguity function (AF) and cross-ambiguity function of OPS are analyzed to examine its autocorrelation and cross-correlation properties in the existence of Doppler shift. The performance of the proposed OPS is compared with the performance of LTE PRS, Zadoff-Chu, and linear-frequency modulated waveforms with respect to correlation, time ambiguity, and Doppler tolerance. The analytic and simulation results show that the OPS provides an accurate timing (distance) estimation in the existence of a high Doppler shift, which is the ideal characteristic of the AF for positioning. The OPS is especially suitable for orthogonal frequency division multiplexing (OFDM) systems because it can be easily multiplexed with other signals in the frequency domain.