Wideband Millimeter-Wave Beam Training with True-Time-Delay Array Architecture

Abstract

Millimeter-wave communications rely on beamforming gain from both transmitters and receivers to compensate for severe propagation loss. To achieve adequate gain, beam training is required to identify propagation directions. The main challenge in beam training arises from maintaining low overhead with increased array size. This paper presents a novel one-shot beam training technique that utilizes the emerging architecture of true-time-delay (TTD) arrays. We first show that TTD arrays facilitate frequency dependent beam steering. The proposed training procedure with TTD arrays then exploits this fact by using a single radio-frequency-chain to multiplex different subcarriers into different sounding directions. We derive conditions on the parameters of TTD array configuration and physical layer to achieve scanning of the entire angular domain with a single orthogonal frequency-division multiplexing (OFDM) training symbol. The estimation of propagation directions with high resolution is achieved via low-complexity digital signal processing of spatially coded subcarriers. Simulation results show that this TTD array based approach requires an order-ofmagnitude fewer training symbols than those of phased arrays.

Multi-Mode Spatial Signal Processor with Rainbow-like Fast Beam Training and Wideband Communications using True-Time-Delay Arrays

“…To alleviate the above problems, the authors introduce architectures that can synthesize rainbow-like beams to detect the entire angular range in a single OFDM symbol [2], [9]. The key idea is to place different signal delays in different antenna branches to exacerbate beam squint intentionally among subcarriers.…”

“…1(b) shows the frequency-division based beam scanning approach that obtains the CSI by observing different array frequency responses within a single orthogonal frequency-division multiplexing (OFDM) symbol saving criti-cal time needed for beam scanning. Nevertheless, the need for a constant group delay in the frequency-division based beam training limits its realization when using phase shifters [2]. The phase shift approximation of the inter-element time delay holds true over a small fractional bandwidth only leading to large errors at the band edges and degraded signal-to-noise ratio as the channel bandwidth scales up as shown in Fig.…”

“…The authors' recent works have shown a reconfigurable TTD-based SSP with large delay-bandwidth product that creates unique frequency-to-angle map for fast beamtraining and reduces the scan time of analog PAAs from several symbols to a single OFDM symbol [2], [8], [9]. In [10], the authors demonstrated a reconfigurable TTD SSP hardware for the first time that can be easily reconfigured for both beamtraining and beamforming over 800 MHz modulated bandwidth.…”

“…Comparison with state-of-the-art TTD SSP. 3V biases input buffers only;2 Baseband delay circuit, mixers, and LO;3 Excluding I/O buffers for testing; 4 Estimated from Fig.15(d) …”

Wideband Beamforming with Rainbow Beam Training using Reconfigurable True-Time-Delay Arrays for Millimeter-Wave Wireless

“…Instead of suppressing the beam squint effect evident in mmW arrays, we will exploit this effect to our advantage by introducing intentionally large time delays in each antenna branch to realize frequency-dependent probing beams which can be exploited to accelerate the channel probing capability. These frequency-dependent beams will be fully controlled by adjusting the delay introduced in TTD circuits [60].…”