Hybrid True-Time-Delay Array-Based Subband Beam Design for Multi-User Data Communication

In this paper we consider a wideband millimeterwave and terahertz (THz) beamforming to support simultaneous data communication with multiple spatially separated users. The beamforming objective is to orthogonalize users across subbands by deploying frequency-dependent beams with a subband-specific spatial response. Analog True-Time-Delay (TTD) antenna arrays are a promising architecture for generating subband beams using a single radio frequency RF chain. An analog TTD array can realize subband beams however the beams cannot achieve flat gain response in each subband and uniform gain distribution across subbands, limiting their utility in practical deployments. Hybrid TTD arrays offer additional degrees of freedom to improve the beamforming design. This work proposes the optimization of the Hybrid TTD codebooks to achieve the desired sub-band beams. We propose an alternating minimization algorithm and a low-complexity heuristic solution for subband beam design. Simulation results show beamforming performance improvement as a function of RF chains, and demonstrate that scaling RF chains proportional to half of the number of users is sufficient to achieve near-digital beamforming performance.