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

Abstract

Initial access in millimeter-wave (mmW) wireless is critical toward successful realization of the fifth-generation (5G) wireless networks and beyond. Limited bandwidth in existing standards and use of phase-shifters in analog/hybrid phasedantenna arrays (PAA) are not suited for these emerging standards demanding low-latency direction finding. This work proposes a reconfigurable true-time-delay (TTD) based spatial signal processor (SSP) with frequency-division beam training methodology and wideband beam-squint less data communications. Discrete-time delay compensated clocking technique is used to support 800 MHz bandwidth with a large unity-gain bandwidth ring-amplifier (RAMP)-based signal combiner. To extensively characterize the proposed SSP across different SSP modes and frequency-angle pairs, an automated testbed is developed using computer-vision techniques that significantly speeds up the testing progress and minimize possible human errors. Using seven levels of time-interleaving for each of the 4 antenna elements, the TTD SSP has a delay range of 3.8 ns over 800 MHz and achieves unique frequency-to-angle mapping in the beamtraining mode with nearly 12 dB frequency-independent gain in the beamforming mode. The SSP is prototyped in 65nm CMOS with an area of 1.98mm 2 consuming only 29 mW excluding buffers. Further, an error vector magnitude (EVM) of 9.8% is realized for 16-QAM modulation at a speed of 122.8 Mb/s.

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

“…Note that frequency-dependent beams can be realized by using leaky-wave antennas. However, these antennas are bulky and inefficient, especially at mmWave bands [20]. Hence, we focus the discussion of frequency-dependent beams using JPTA.…”

“…The conclusion of these works focuses on the beam training overhead reduction, where a single OFDM symbol is enough to accurately estimate the AoD regardless of the number of antennas in arrays. Another important outcome out of all these works is the feasibility of JPTA beamforming in practice and that it can be realized through the current state-of-the-art technology as demonstrated in [20].…”

“…Other related interesting works include [31], where mapping frequencies and spatial directions in TTD systems is discussed, [21] where the authors proposed using fixed delay units instead of adjustable ones to reduce the energy consumption. Another interesting work is [20], where the authors showed that JPTA could be realized using CMOS technology as an alternative to bulky Rotman lenses.…”