Other Research Projects – ND Wireless Institute
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Millimeter Wave Wireless

To realize the vision of millimeter waves for commercial wireless we are examining cross-disciplinary approaches to meet the beam-agile, wideband requirements while maintaining sufficiently low power and cost to be deployable in small cells and mobile devices. This problem requires a “full-stack” solution from the network layer to the physical layer so we approach the problem through a collaboration of systems analysis, circuit design, and integration of emerging materials and devices. In the Advanced Millimeter-Wave Lab, we are able to design, fabricate, and measure novel transceiver architectures and RF front-ends (including beam steering) for millimeter-wave wireless communications as well as evaluate new materials and devices offering unique capabilities at millimeter waves.

Low Complexity, Low Cost, Low Power RF

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 3D (spherical) gradient index 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.

Recently, the method of transformation optics has been presented as a means of physically distorting an electromagnetic structure and maintaining its functionality by spatially varying the permittivity throughout the structure. This has enabled the design of flat lenses but they require so-called gradient index optics. Over the past year, we have developed a process for manufacturing gradient index optics targeting the millimeter wave bands from 30-150 GHz. The approach is known as perforated media.

Crowded Spectrum: Dynamic Sensing and Sharing

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.

Distributed Spectrum Sensing