Interference-Tolerant Wireless Distributed Beamforming Receiver Array With Low-Latency Frequency Synchronization

Abstract

We present a novel, scalable, distributed beamforming receiver array architecture capable of self-synchronization using an analog phase-locked loop (PLL). Wireless frequency synchronization of distributed nodes is achieved at the receiver front-end and at carrier frequency level with extremely low latency, while direct data demodulation is performed at the same time. Compared to existing techniques, frequency synchronization is accomplished without using back-and-forth feedback between the radio nodes within the distributed network. In this work, we demonstrate the wireless beamforming operation through phase alignment of synchronized signals at the output of PLLs. The local oscillator (LO) signal at each receiver is automatically synchronized with the received signal, and the receiver directly down-converts and demodulates the data. Therefore, the need for phase alignment at the carrier frequency translates to the delay adjustment of the demodulated data at an intermediate frequency (IF) for beamforming. A custom-designed receiver at the millimeter-wave frequency band fabricated in Global-Foundry’s SiGe BiCMOS technology was used for this study. We provide a comprehensive study of distributed beamforming arrays (DBAs) in the presence of interference signals. The emergence of spurious intermodulation (IM) components in the output spectrum of the PLL due to interference signal was observed. We experimentally demonstrate that the coherent combination of signals from different receiving nodes can significantly suppress the interference in distributed arrays once accurate phase alignment of carrier signals is achieved. Additionally, the effects of interference on the phase noise were experimentally studied. A 130-Mb/s data link was established between the transmitter and distributed receiver array by introducing appropriate time delays during the post-processing stages.