Pilot Sequence Design for mmWave Cellular Systems With Relay Stations in the Presence of Blockage

Due to short wavelength and weak diffraction ability, millimeter-wave (mmWave) signals are highly susceptible to blockage, which results in significant degradation in received signal power. As a possible solution for overcoming the blockage problem in millimeter-wave communication systems, the deployment of a relay station (RS) has been considered in recent years. In this paper, we discuss the problems to be considered in a relay-assisted mmWave cellular system based on orthogonal frequency division multiplexing. We describe a frame structure and a pilot-based training method to achieve efficient RS selection during blockage. In addition, a method designed to overcome the inter-symbol interference problem caused by different symbol time offsets of pilot signals received from adjacent RSs in the relay-assisted mmWave cellular system is discussed. Then, we propose two different types of pilot sequences that allow a mobile station to distinguish among the pilot sources in multi-cell multi-relay environments: pilot signals based on the Zadoff-Chu sequence (PS1) and pilot signals based on the m-sequence (PS2). The correlation property of PS2 is derived and compared with that of PS1 and another sequence (Gold sequence). Simulations are performed using a blockage model to verify the properties, constraints, and advantages and disadvantages of the proposed pilot sequences in RS-assisted mmWave cellular systems.