The heart of the RadioHound System is a low-cost, pervasive, persistent spectrum sensor that leverages low-cost SDRs suitable for deployment in mobile environments. RadioHound maps the entire spectrum from 25 MHz to 6 GHz, and will have the capability to support mmWave bands. RadioHound enables spectrum mapping in real time, providing a reliable indicator of spectrum utilization. It’s beacon capabilities provide a mechanism for measuring radio signal propagation between devices. Because of its portability and low cost, widespread deployment can give a good understanding of device-to-device and device-to-infrastructure connectivity, especially in crowded or dense environments.

The widespread deployment of RadioHound enables understanding of Wireless network architectures in new frequency bands, spectrum sharing possibilities and algorithm testing, and spectral efficiency and utilization measurements across large geographic areas. The overall cost of the RadioHound Node and the low-cost SDR (a commercial DVB-T receiver), but without the three antennas for the sub-GHz range or the mmWave front-end MMIC, is around $70. The eventual target is a sensor costing less than $10.

RadioHound System

The RadioHound System comprises three components: the RadioHound Sensor (Hardware), the RadioHound Cloud and the RadioHound App (Software). The hardware sensor includes a tri-band RF front end (including a tunable wideband receiver, tunable narrow-band beacon transmitters, and transverses for specialized frequency bands) and three antennas for the different bands: 25-100 MHz, 0.1-0.4 GHz, and 0.4-6 GHz respectively. The external operating environment of RadioHound requires a host to communicate with and allow data collection, management, and transmission to the RadioHound Cloud. The host provides geo-location capability, storage, and transmission to the central database, and can have different form factors, with the Raspberry Pi being the simplest and most nomadic. The RadioHound sensor derives its power from the host. The power consumption in the current Phase 1 (proof of concept) is 3W, with an envisioned target of 0.5W in future phases.

The RadioHound Cloud involves the scalable partitioning of functions into the following separate server instances: data warehouse for storage and retrieval of records, check in server for authorization of nodes, and allows for future provisions for security. The RadioHound app provides two functions: send commands to the RadioHound sensors and enhanced visualization of the data stored in the Cloud through a GUI web app. The system software also includes a master controller that sends jobs to nodes and a state machine for data flow control amongst other functions.

Sponsors and Collaborators

The RadioHound project was started in July 2015 with sponsorship from InterDigital and Nokia (previously Alcatel Lucent) via the BWAC I/UCRC, an NSF program. Subsequent funding from and collaboration with the US Army Research Laboratory helped to mature the platform toward an initial proof of concept and field deployment. Future phases will focus on reducing the cost and power needs of the sensors, developing a cost-scalable Millimeter Wave MMIC, and the evolution of the software.

RadioHound is a Wireless Institute multi-PI project, with the hardware components developed by Jonathan Chisum and Bertrand Hochwald (Lead PI), and the software components by J. Nicholas Laneman and Aaron Striegel.

Electrical Engineering graduate students currently working on the project are Abbas Termos and Xiangbo Meng. Former graduate students involved in the project include Nik Kleber (Raytheon Technologies), Arash Ebadi Shahrivar (Qualcomm), and Lihua Wan.

Related Publications

“RadioHound: A pervasive sensing network for sub-6 GHz dynamic spectrum monitoring,” https://arxiv.org/abs/1610.06212.

Related Publications

Overview

One of the key challenges of millimeter wave systems is the increased path loss at high frequencies compared with current sub-6 GHz wireless networks. A proposed solution is to employ high-gain antenna arrays which compensate for the path loss but have a corresponding narrow beamwidth. In order to maintain a wireless link with a mobile device, beam-steering is employed. Traditional beam-steering uses active phased arrays which incur a high cost and power dissipation. An alternative to active phased array beam steering antennas is the passive Luneberg lens which boasts zero power dissipation, low-loss, and high gain. However, the Luneberg lens is a bulky 3D (spherical) gradient index (GRIN) lens traditionally requiring elaborate machining of concentric shells of dielectric. Due to the difficulties of fabrication this lens has traditionally only been realized in bands below 20 GHz.

Lens antennas

With recent advances in additive manufacturing of high-performance and low-loss RF materials, such GRIN lenses can be realized with a low-profile while maintaining their wideband performance. However, the reduction in volume results in unavoidable degradation in beam-scanning performance, reducing the field-of-view and limiting its use in modern mobile wireless networks. To address this Professor Chisum and his team have proposed several novel architectures including compound and hybrid lens architectures comprising collections of several lenses or combinations of sparse phased-arrays and lenses, respectively. Professor Chisum is sponsored by the Office of Naval Research and has collaborations with leading 3D-printing companies in industry in order to prove the methods are viable in the current and future bands for 5G and 6G wireless networks. 

In order to realize GRIN lenses we have developed a suite of manufacturing processes for gradient index media targeting the millimeter wave bands from 8-100+ GHz. One method, based upon a perforated dielectric, mixes air and dielectric in varying ratios throughout the volume of the lens in order to sculpt the electromagnetic fields as they propagate through the lens. This method is highly reliable, extremely wideband, and very low loss. It can currently be realized by drilling standard high-frequency PCB substrates or through 3D printing. A lower-cost alternative is based upon a metallo-dielectric mixture in which small metal inclusions provide strong localized polarization. These methods are amenable to standard PCB printing and are thus very low-cost. While their frequency response is traditionally narrowband due to material resonances, we have been exploring methods to push the material resonances out of the bands of interest. This method currently supports operation up to 40 GHz.

One of the advantages of a GRIN lens is the many degrees of freedom available for design. This permits a designer to simultaneously pursue multiple design objectives such as bandwidth, efficiency, wide field-of-view, and even low sidelobe levels. However, such a multi-objective optimization requires a rapid and accurate numerical solver. Current state-of-the-art electromagnetic solvers using high-performance computing (HPC) clusters still require hours to solve a single iteration of the lens optimization. Therefore we have developed in-house codes which combine curved-ray geometrical optics with diffraction theory in order to solve the radiation pattern of a lens candidate in less than one minute, and with ~0.1dB accuracy compared to the full-wave electromagnetic solvers.

A new networking paradigm

The hardware is now mature and capable of offering high-performance millimeter-wave beam-scanning antennas for mobile wireless base-stations, or for tracking of low-earth-orbit (LEO) satellite communications. The next phase of this research is to collaborate with other WI researchers in order to demonstrate network-level properties including beam identification and tracking, search and track, make-before-break capabilities, and even the ability to operate with a deployed 5G NR waveform.

Sponsors and Collaborators

The GRIN lens antenna project is currently funded by the Office of Naval Research (ONR) and the Department of Homeland Security (DHS) with past support ship from the Satcom industry. We are collaborating with industry-leading additive manufacturing companies including Fortify and NanoDimension, as well as MIT Lincoln Laboratory.

Publications

N. Garcia, J. Chisum, “Compound GRIN Fanbeam Lens Antenna with Wideband Wide-angle Beamscanning“ IEEE Transactions on Antennas and Propagation, Jun. 2022

N. Garcia, W. Wang, J. Chisum, “Feed Corrective Lenslets for Enhanced Beamscan in Lens Antenna Systems“ Optica Express, Apr. 2022

W. Wang, N. Garcia, and J. Chisum, “The Systematic Design of Non-commensurate Impedance Matching Tapers for Ultra Wideband Gradient Index (GRIN) Lens Antennas“ IEEE Transactions on Antennas and Propagation, Jul. 2021

N. Garcia, J. Chisum, “Reduced dimensionality optimizer for efficient design of wideband millimeter‐wave 3D metamaterial GRIN lenses“ Microwave and Optical Technology Letters, May 2021

N. Garcia, J. Chisum, “High-Efficiency, Wideband GRIN Lenses With Intrinsically Matched Unit Cells“ IEEE Transactions on Antennas and Propagation, Apr. 2020

W. Wang, J. Chisum, “Hybrid Geometrical Optics and Uniform Asymptotic Physical Optics for Rapid and Accurate Practical GRIN Lens Design“ 2022 IEEE/MTT-S International Microwave Symposium, Jun. 2022

Efficient use of spectrum is key to allowing government and commercial wireless technologies to flourish in the future. The RF spectrum below 6 GHz, in particular, has become extremely valuable as wireless communications technologies supplant wired solutions. As everyone looks for “1000x” improvements over the existing generation of wireless communications, one of the main challenges has become how to better utilize frequencies at 6 GHz and below.

Notre Dame’s Wireless Institute is actively engaged in researching and developing system models, sensing algorithms, and signaling schemes for utilizing spectrum more efficiently. The vision is to create localized spectrum efficiency maps, possibly in coordination with national geo-location databases, to enable wireless devices to dynamically find under-utilized spectrum, while minimizing interference.

To accomplish this, the RadioHound project has been initiated to develop a new spectrum efficiency monitoring platform – a system with a network of high-resolution, low-cost distributed overlay and compare local, real-time spectrum usage and efficiency to the FCC/NTIA radio spectrum sensors, a central data store, and an interface for analytics and visualization that could frequency allocation chart. The spectrum monitors would also be sufficiently sensitive, portable, programmable and low cost to provide an invaluable resource for mapping out spectrum efficiency across the United States. A complete understanding of the space-time efficiency utilization of spectrum is the key to improving it and will enable the regulated sharing of any inefficiently utilized spectrum resources.