Frequency-Dependent Precoding for Wideband Terahertz Communication Systems

Terahertz (THz) multiple-input multiple-output (MIMO) beamforming is a key technology to support immersive mobile services in 6G communication systems. In the beamforming vector generation, the analog phase shifter which generates the phase invariant to the signal frequency have been widely used. However, since the spatial directions of the subcarrier channels are functions of the subcarrier frequency in the wideband THz systems, the beamforming techniques based on the analog phase shifters suffer from a severe beamforming gain loss. In this paper, we propose a novel beamforming technique that exploits the true time delay (TTD)-based phase shifters to generate multiple frequency-dependent beamforming vectors for the wideband THz systems. Intriguing feature of the proposed scheme is to exploit a deliberately designed TTD-based signal propagation network called calibrator to bridge the gap between the desired beamforming vectors and the frequency-dependent beamforming vectors. In doing so, the signal power is concentrated onto the mainlobe so that the generated beamforming vectors can achieve the maximum beamforming gain. From the numerical results, we demonstrate that the proposed scheme achieves more than 80% data rate gain over the conventional beamforming schemes.