Precoding Design of Beam Squint Compensation for Massive MIMO-OFDM in Non-Terrestrial Networks

Broadband Massive Multiple Input Multiple Output (Massive MIMO) systems are considered the core technology for Non-Terrestrial Networks (NTNs), enabling wide-area coverage and high-speed data transmission. However, these systems are limited by the beam squint effect, which causes frequency-dependent shifts in the beam direction, resulting in a degradation of array gain and increase of inter-beam interference. To mitigate the impact of beam squint, traditional methods adjust the pattern of the antenna array using precoding techniques, which is unsuitable for NTN scenarios for its high hardware costs and energy consumption. In this work, we first analyze the beam squint effect using the steering vector of the antenna array, and provide the solution for the beam pointing deviation angle. We then generalize the solution about the deviation angle to a general antenna array. Next, we construct a compensation matrix based on the correlation between the deviation angle and carrier frequency, covering the angular adjustment information for all subcarriers. Finally, we design a hybrid precoding method using the compensation matrix to adjust for the pointing deviations of different subcarriers. Simulation results demonstrate that the proposed method requires fewer pilot resources. Under limited pilots, our method achieves higher spectrum efficiency. Therefore, the proposed beam squint compensation hybrid precoding method is more suitable for NTN scenarios.