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

Abstract

The decadal research in integrated true-time-delay arrays have seen organic growth enabling realization of wideband beamformers for large arrays with wide aperture widths. This article introduces highly reconfigurable delay elements implementable at analog or digital baseband that enables multiple Spatial Signal Processing (SSP) functions including wideband beamforming, wideband interference cancellation, and fast beam training. Details of the beam-training algorithm, system design considerations, system architecture and circuits with large delay range-to-resolution ratios are presented leveraging integrated delay compensation techniques. The article lays out the framework for true-time-delay based arrays in next-generation network infrastructure supporting 3D beam training in planar arrays, low latency massive multiple access, and emerging wireless communications standards.

Extending Uplink Coverage of mmWave and Terahertz Systems Through Joint Phase-Time Arrays

“…JPTA can be used to reduce the overheads in beam training [17], [22], [24]- [28], [41] which can be realized by a pure TTD network [24], [29], [30], JPTA [25]- [28], or hybrid (multiple RF-chains) JPTA [17]. All of these works assume a uniform delay model, where the delay difference between any two consecutive antennas (∆t) is uniform, and it is sufficient to set ∆t proportional to the inverse of the bandwidth to achieve the near-optimal gain across the whole 180 • angular region under the narrow-band assumption.…”

“…In [22], using JPTA to mitigate beam squinting in the data communications phase and to create rainbow beams in the initial access phase. In our work, we look at the potential of using JPTA with rainbow beams in the data communications phase since the algorithm we use takes care of the beam squint effect while designing the delays [16].…”

“…Recent advances improved the scalability and enabled the large delay range-to-resolution ratios [18]- [21], which have made the implementation of JPTA feasible. Prior work has explored specific architecture and usage of JPTA, referring it as TD [22] or delay-phase precoding (DPP) [23]. In [16], we explored the full potential of JPTA by showing that JPTA can realize several beneficial frequency-dependent beamforming behaviors, which cannot be efficiently realized with PAAs.…”

“…The main use cases of JPTA in the prior work are to combat beam squint and/or to achieve fast beam training [17], [22]- [36] as we explain in detail in Section II. Briefly, at highfrequency bands, the ratio between the bandwidth and the center frequency is relatively high, which causes beams at different frequencies to point to different physical directions, which results in losing some of the array gain [37].…”

“…Briefly, at highfrequency bands, the ratio between the bandwidth and the center frequency is relatively high, which causes beams at different frequencies to point to different physical directions, which results in losing some of the array gain [37]. By using frequency-dependent beamforming, the delays in the delay units can be set to mitigate this effect and restore a uniform array gain across the different frequencies [22], [23], [32]- [35].…”