2025 Theses Doctoral

Experimental Studies into Next-Generation Wireless Technologies: Full-Duplex and Millimeter-Wave

Kohli, Manav

Unending growth in Internet traffic has placed extreme demands on the capabilities of wireless networks, which often provide the last-mile delivery of data to the user. This demand has been exacerbated by modern applications, such as video streaming, and wireless networks will be further pushed by future applications such as massive-scale Internet-of-Things deployments and augmented/virtual reality.

Such applications may require certain performance guarantees including multi-gigabit data rates, sub-millisecond latency, as well as exceptional reliability. It is therefore important to develop technologies that will enable next-generation wireless networks capable of meeting these requirements. In this thesis, we use an experimental approach to developing and evaluating several key technologies to enable next-generation wireless networks, including full-duplex (FD) wireless and millimeter-wave (mmWave) network deployment.

This thesis is composed of three parts. The first covers FD wireless, where we use three generations of custom RF self-interference (SI) canceller hardware to build FD radios capable of sending and receiving signals at the same time and on the same frequency channel. We designed and deployed a first-of-its-kind open-access FD networking testbed within the city-scale COSMOS testbed, using RF SI cancellers based on the principle of frequency-domain equalization. We use the testbed to demonstrate median throughput gains of 1.1-1.9x in realistic low-power networks with an FD-capable base station (BS) and varying numbers of FD-capable users, closely matching analytical results.

We then use a wideband RF SI canceller based on the principle of time-domain equalization to evaluate an automatic configuration algorithm based on an orthogonal matching pursuit and suitable for mobile applications where swift reconfiguration of the RF SI canceller is necessary. We use a narrowband, phase-and-amplitude based RF SI canceller to evaluate a novel digital SI cancellation (SIC) algorithm based on a weighted least-squares finite impulse response filter that achieves up to 8 dB better performance over an unweighted least-squares method when the radio first switches on. Lastly, we use the same narrowband canceller to prototype an FD jammer-receiver, capable of intercepting an adversarial signal of interest while simultaneously jamming the intended recipient.

The second part covers mmWave channel modeling. As the wireless spectrum grows increasingly congested at lower frequencies (<6 GHz), use of higher frequencies is necessary. However, higher frequencies experience significant path loss and are more severely blocked by buildings and other structures, making network deployments challenging. To gain better insight into factors affecting mmWave signal propagation and inform network deployments in dense urban environments, we conduct three large-scale measurement campaigns to study the mmWave wireless channel at 28 GHz in outdoor-to-outdoor (O-O) and outdoor-to-indoor (O-I) scenarios. We use the measurement data to develop models of path loss, environmental angular spread, and temporal stability. We show, amongst other results, gigabit data rates achievable for users over 100 m away from the BS even in visually NLOS conditions, as well as a 20 dB additional loss caused by low-emissivity glass panels used in typical modern buildings.

Lastly, the third part of this thesis covers a set of measurement studies used to characterize wireless coverage of the outdoors COSMOS testbed and spectrum usage within the testbed area. We developed a custom measurement setup using a laptop to receive 802.11a data packets transmitted from various COSMOS nodes and record the received signal power. These results have been published online along with the corresponding raw data, providing a rich dataset for urban signal propagation at 2.4 GHz. We also used a mobile 28 GHz phased array antenna module (PAAM) to study the interference characteristics on a mmWave radiometer used to measure temperature, using the collected data to develop spectrum consumption models (SCMs) designed to protect such meteorologic equipment from unexpected interference.

In this thesis, we make a number of experimental contributions to the fields of FD wireless and mmWave channel modeling, as well as the further deployment of the COSMOS testbed. We believe these contributions to be important for meeting the increasingly stringent performance requirements of next-generation wireless networks.