A Guard Interval Control Scheme Using Theoretical System Capacity for UAV MU-MIMO-OFDM THP Systems

Abstract

This paper proposes a guard interval (GI) control scheme using the theoretical system capacity for unmanned aerial vehicle (UAV) multi-user multiple-input and multiple-output orthogonal frequency-division multiplexing (MU-MIMO-OFDM) Tomlinson-Harashima precoding (THP) systems. Considering the need for coverage extension assumed in sixth-generation mobile communication systems (6G), we consider UAVs as users as well. Therefore, variation in delay spread between users is assumed to increase due to differences in the communication distance and flight height. In such scenarios, GI length is typically determined from the longest delay among all mobile stations (MSs) to eliminate inter-symbol interference (ISI). However, this leads to significant degradation in transmission efficiency. The proposed scheme adopts a GI length that maximizes the theoretical system capacity derived from the correlation calculation while allowing some ISI, which reduces transmission overhead. Moreover, considering the assumed spatial correlation, particularly in UAV communications, THP is adopted as the MU-MIMO precoding method. The effectiveness of the proposed scheme is demonstrated via computer simulations in comparison with the traditional scheme adjusted to the largest multipath delay.