Non-Orthogonal Multiple Access Scheme Using Directional THz Antennas Under Positioning Errors

In this work, the implementation of a Non-Orthogonal Multiple Access (NOMA) scheme over directional Terahertz (THz) links is studied. It is well known that for directional THz antennas, precise alignment between antennas is a major requirement. However, for dynamic systems with mobile nodes, positioning and antenna alignment are continuous processes that cannot be perfectly achieved in practical conditions. To this end, we investigate the performance of the NOMA system in the presence of tracking and antenna misalignment errors and show that even antenna misalignment errors of less than one degree can affect the performance of the considered NOMA system based on directional THz antennas. In this paper, by considering real channel parameters, such as real 3D array antenna patterns and positioning estimation errors, a comprehensive modeling of the considered NOMA system is provided, which is used to obtain the closed-form expressions of the probability distribution function of the channel gain, the bit error rate, and the channel capacity. Moreover, a set of simulation and analytical results is explored and discussed to investigate the performance of the considered NOMA system and the impact of different parameters.