Other Research Projects – ND Wireless Institute
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Fast Mobile Network Characterization (FMNC)

The proliferation of smart devices has placed considerable pressure on the data capacity of the cellular network. WiFi has emerged as the de-facto technology for selectively augmenting capacity for the short term. Critically, though, while WiFi generally tends to a positive for the user experience, user performance on WiFi is not always an improvement. In particular, automated roaming to WiFi has a strong potential to reflect poorly on the network carrier, institution, or place of business. Roaming and dead spots in WiFi coverage coupled with the “hard” handoff necessary to roam back to cellular further compound challenges.

The primary challenge is how to effectively gauge the capacity and quality of the wireless link for a given mobile device at a given location. Traditional techniques for speed testing tend to be exceptionally heavyweight (ex. SpeedTest.net) moving potentially tens of megabits of traffic and taking on the order of seconds to complete. Lighter weight variants fare better with regards to cost but tend to suffer under packet aggregation optimizations introduced in more recent WiFi and cellular variants. For decisions such as roaming or more importantly, upstream decisions with regards to data routing, such information may only be of limited value by the time it is finally resolved. The focus of this work is to radically overhaul in-band characterization of network performance by delivering reasonable network characterization requiring two magnitudes less of data (< 100 KB) and doing so on the order of less than a quarter of a second (< 250 ms).

The FMNC project started in 2015 and is sponsored by InterDigital and Nokia via the BWAC I/UCRC, an NSF program. Aaron Striegel is the PI for this project.

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

DroneSounder: Measuring Cellular Signals

There is a largely anticipated market for drones and applications of drones across many verticals. With thousands of drones roaming the skies, in many cases semi- or fully autonomously, there is an urgent need for robust, high bandwidth, and standardized technologies to enable drone-ground and drone-drone wireless communication. The purpose of the Drone Sounder project is to build a test platform for signal measurements and waveform prototyping over such links.

Each Drone Sounder will be comprised of a COTS drone, 1-2 mobile phones, a software-defined radio (SDR), and one or more radio antennas. Drone Sounder will enable the following signal measurements, in several frequency bands of interest:

  • Commercial or emulated cellular base stations on the ground to a drone
  • Drone to emulated cellular base stations on the ground
  • Drone interference to emulated mobile devices on the ground
  • Drone to drone communications

Detailed study of the measurement data will enable the project team to provide recommendations on the frequency bands to utilize for various aspects of drone communication (command and control, detect-and-avoid, navigation, and payload) for both drone-ground and drone-drone communication.

The Drone Sounder project started in January 2016 and is sponsored by InterDigital via the BWAC I/UCRC, an NSF program. Aaron Striegel, J. Nicholas Laneman, and Hai Lin are the PIs for this project.

802.11ax: AN Uplink MU-MIMO SDR Testbed

The proliferation of smartphones and growth of user-generated content has led to substantial increase in uplink traffic in use by mobile devices. Multi-input multi-output (MIMO) technology has been successfully adopted in past 802.11 standards, leading to high throughput and robust performance. Downlink MU-MIMO (DL MU-MIMO) was introduced in 802.11ac, where an access point (AP) with multiple transmit antennas is able to transmit multiple data streams to multiple spatially distributed stations (STAs) at the same time. To address the challenge of burgeoning uplink traffic is one of the primary objectives of the new IEEE 802.11ax. Uplink multi-user MIMO (UL MU-MIMO) can improve uplink capacity by enabling multiple spatially separated clients to access the channel at the same time and is especially useful in scenarios where the STAs have limited number of antennas (e.g. typical smartphones). The focus of this project is to build a software-defined radio (SDR) testbed for prototyping UL MU-MIMO and studying related design trade-offs. The project uses the Wireless Institute’s Software Defined Radio (SDR) Lab, namely the National Instruments (NI) USRP RIOs, the LabVIEW Communications System Design Suite, and NI’s 802.11 Application Framework.

The project is anticipated to have several phases. As the first step, we have already implemented two algorithms for UL MU-MIMO: Carrier Frequency Offset (CFO) correction at STAs, and multiuser detection (MUD) of users at the AP. The prototyping setup includes two NI USRP RIOs associated with their host computers, where the AP is implemented in one USRP and two stations are implemented in the second USRP. In comparison with the SISO system, we are able to get doubled system throughput. In the next step, we plan to add transmit power control functionality to the current framework to study the UL performance for the situations in which distances of stations to the AP are not similar. In addition, we will study the effect of asynchronous UL MU transmissions on the system performance. 

The 802.11ax project was started in 2015 and is sponsored by InterDigital and National Instruments via the BWAC I/UCRC, an NSF program. J. Nicholas Laneman is the PI for this project.