We implement and experimentally demonstrate a distributed, phase-coherent, mesh relay network that executes spatiotemporal beamforming on a communications signal. Each single-antenna node of this mesh network amplifies, predistorts, and forwards its reception to a receiver. In this configuration, an incoherent network of N nodes enhances the received power of a signal of interest by a factor of N compared to a single-input single-output communications link. By synchronizing these distributed nodes and constructing a spatiotemporal beamformer, we increase this factor to a maximum of N ² and enable significant interference rejection capabilities. To achieve phase-coherence across the network elements, we execute a distributed synchronization algorithm using training data from the source node. We construct spatiotemporal beamformers by solving an MMSE optimization, which we continually reoptimize using new observations of training sequences and updated channel estimates. We present results from two over-the-air experimental demonstrations, one without and one with an external interferer. In the former, we demonstrate a 17.4 dB signal-to-noise ratio (SNR) improvement compared to the 18.1 dB theoretical bound for an eight-element network. In the latter, we demonstrate an 11.3 dB SNR improvement and a 14.6 dB interference reduction.

Editor’s notes: Spectrum sensing systems enable efficient use of the electromagnetic spectrum for communication. This article presents key challenges, requirements, design choices, and emerging trends for next-generation spectrum sensing applications. —Swarup Bhunia, University of Florida, USA

Validating RF applications is traditionally time consuming, even for relatively simple systems. We developed the WISCA Software-Defined Radio Network (WISCANet) to accelerate the implementation and validation of radio applications over-the-air (OTA). WISCANet is a hardwareagnostic control software that automatically configures and controls a software-defined radio (SDR) network. By abstracting the hardware controls away from the user, WISCANet allows a non-expert user to deploy an OTA application by simply defining a baseband processing chain in a high level language. This technology reduces transition time between system design and OTA deployment, accelerates debugging and validation processes, and makes OTA experimentation more accessible to users that are not radio hardware experts. WISCANet emulates real-time RF operations, enabling users to perform real-time experiments without the typical restrictions on processing speed and hardware capabilities. WISCANet also supports multiple RF front-ends (RFFEs) per compute node, allowing sub-6 and mmWave systems to coexist on the same node. This coexistence enables simultaneous baseband processing that simplifies and enhances advanced algorithms and beyond-5G applications. In this study, we highlight the capabilities of WISCANet in several sub-6 and mmWave over-the-air demonstrations. The open source release of this software may be found on the WISCA GitHub page.