Experimental Analysis of Receiver Design for Near-Field Coordinated Beamforming

Abstract

Next-generation wireless networks are envisioned to operate in sub-THz bands to enable increased data rates and sensing resolution. In such bands, Coordinated Beamforming (CoBF) will be a critical technique to mitigate performance degradation that can occur when highly directional links are occluded by mobile environmental obstructions. Moreover, due to decreased wavelength, sub-THz networks can increasingly operate in the near field, which yields non-planar wavefronts at receivers. In this paper, we present the first experimental study of receiver (RX) beamforming for sub-THz CoBF operating in the near field. Specifically, we introduce a suite of RX beamforming policies that span Channel State Information at the Receiver (CSIR) requirements as well as RX beamforming capabilities. At one extreme, we define a baseline RX beamforming policy that uses an electromagnetic wave model to compute CSIR, accounting for transmitter location, beam type, and near-field propagation characteristics; the RX then compensates for the computed phase profile over each RX array element to maximize coherent combining. At the other extreme, we consider strategies that, despite operating in the near field, employ far-field beam steering via a linear phase gradient at the receiver. Such policies are not only simple in CSIR requirements (not requiring phase information for each antenna element) but also simplify receiver configuration, requiring only a single parameter to characterize a linear phase gradient. We first experimentally study an unobstructed CoBF link and quantify the benefits of compensating for the nonlinear incident phase as compared to conventional far-field oriented methods. We then experimentally study obstructed links and measure the performance of the policies under partial blockage, as well as RX power improvement from real-time adaptation to blockage.