Time Modulated Arrays Beamforming for Non-Terrestrial Network User Terminal

Abstract

Though beamforming is the fundamental element of satellite communication, it incurs costs, complexity, and power consumption. In this paper, we study a Time-Modulated Array (TMA) beamforming design on the Non-Terrestrial Network (NTN) User Terminal (UT) to receive a signal from a Low Earth Orbit (LEO) satellite downlink. Despite its simplicity and cost-effectiveness, conventional TMA has intrinsic gain, flexibility, and interference limitations. We compared TMA beamforming with the conventional phased array and studied a tri-state switching method to address the TMA limitations. Based on the 3GPP beam pattern, we studied the beamforming cost and complexity to achieve a viable Signal-To-Noise Plus Interference Ratio (SINR). To facilitate low-cost TMA beamforming, we first derive the Direction of Arrival (DoA) to the TMA switching parameters mapping. Subsequently, we formulate a constrained nonlinear multi-variable problem and solve it using iterative optimization based on perfect DoA. Additionally, we use an analytical approach to suppress sidelobes and unused harmonics using alternating switching. Furthermore, we develop an Alternating Direction Method of Multipliers (ADMM) and Adaptive Switching Parameters Control (ASPC) methods to design TMA beamforming based on a beacon signal. We compare TMA and phased array beamforming techniques, confirming the promising performance of TMA with reduced cost, complexity, and power consumption.