The proliferation of transmissions in the RF spectrum demands robust and responsive signal analysis techniques to detect and label malicious activity. Traditional methods struggle to balance sensitivity and accuracy in real-time. This paper introduces Nomad, a modular system that combines global spectral pattern recognition with localized energy detection and classic signal processing methods for efficient and accurate RF analysis. Nomad's innovative architecture facilitates rapid development and deployment, while its intuitive visualizations provide actionable insights into even weak signals within complex RF environments.

Modern mmWave systems have limited scalability due to inflexibility in performing frequency multiplexing. All the frequency components in the signal are beamformed to one direction via pencil beams and cannot be streamed to other user directions. We present a new flexible mmWave system called mmFlexible that enables flexible directional frequency multiplexing, where different frequency components of the mmWave signal are beamformed in multiple arbitrary directions with the same pencil beam. Our system makes two key contributions: (1) We propose a novel mmWave front-end architecture called a delay-phased array that uses a variable delay and variable phase element to create the desired frequency-direction response. (2) We propose a novel algorithm called FSDA (Frequency-space to delay-antenna) to estimate delay and phase values for the real-time operation of the delay-phased array. Through evaluations with mmWave channel traces, we show that mmFlexible provides a 60-150% reduction in worst-case latency compared to baselines1.

Millimeter-wave (mmWave) communications are crucial for unlocking the potential of future communication systems. Phased arrays play a vital role in generating directional beams, mitigating the high path-loss associated with these frequencies. Consequently, implementing beamforming within the radio is necessary to serve users in various directions. Applications such as AR/VR and vehicular communications demand rapid beam direction changes, typically within microseconds, to maintain stable connections when the user is mobile. In this demonstration, we showcase a mmWave setup capable of switching beams at microsecond intervals, along with a compact and portable user equipment setup for conducting experiments with high user mobility.

Spectrum sensing systems provide real-time feedback essential for spectrum sharing. However, the growth of spectrum sharing is limited by the capabilities of these spectrum sensors. Sharing a new frequency band is only possible if sensors can detect activity in that band with sufficient time granularity and signal fidelity to meet spectrum sharing policy requirements. In this work, we introduce Crescendo, a system design that shows we can achieve wideband, real-time, high-fidelity spectrum sensing using sweeping spectrum sensors. We first provide an analysis that demonstrates there are operating points of sweeping sensors that can sense multiple popular protocols. Then we demonstrate these sensors can be built in practice with an adaptive gain super-heterodyne RF frontend with high-fidelity LO generation, and evaluate a prototype built with COTS components. In our benchmarks, Crescendo outperforms prior wideband spectrum sensors, achieving a 30 dB increase in dynamic range and 10 dB increase in SNR.

With its ability to communicate long distances, LoRa promises city-scale IoT deployments for smart city applications. This long-range, however, also increases contention as many thousands of devices are connected. Recently, CSMA has been proposed as a viable MAC for resolving contention in LoRa networks. In this paper, supported by measurements, we demonstrate that CSMA is ineffective in urban deployments. While gateways stationed at rooftops enjoy a long communication range, 70% of the devices placed at street level fail to sense each others' transmissions and remain hidden, owing to obstructions by tall structures. We present Busy Signal Multiple Access (BSMA), where the LoRa gateway transmits a downlink busy signal while receiving an uplink transmission. The IoT devices defer uplink transmissions while a busy signal is present. Practically viable BSMA requires a full-duplex LoRa gateway - i.e., a gateway that can simultaneously receive and transmit in the same channel. We develop the first full Duplex LoRa gateway in the 915 MHz ISM band, overcoming challenges that arise from a 9× greater delay spread and the need for 1000× greater self-interference cancellation. Our implementation works with COTS LoRa devices and improves network capacity by 100% compared to CSMA in bursty loads while being fair to all IoT devices near and far.

Software Defined Radios (SDRs) combine a universal radio frontend with flexible processing. The radio frontend can be tuned to capture various wireless signals, while software processing allows quick and scalable deployment for diverse applications. SDRs seem like a good fit for the ever-evolving needs of today's spectrum usage: SDRs can be deployed today, then managed and upgraded with software to support the needs of tomorrow. However, the prevailing architecture of SDRs prevent real-time observation of wideband RF signals due to backhaul and processing resource constraints.

Millimeter-wave communication with high throughput and high reliability is poised to be a gamechanger for V2X and VR applications. However, mmWave links are notorious for low reliability since they suffer from frequent outages due to blockage and user mobility. We build mmReliable, a reliable mmWave system that implements multi-beamforming and user tracking to handle environmental vulnerabilities. It creates constructive multi-beam patterns and optimizes their angle, phase, and amplitude to maximize the signal strength at the receiver. Multi-beam links are reliable since they are resilient to occasional blockages of few constituent beams compared to a single-beam system. We implement mmReliable on a 28 GHz testbed with 400 MHz bandwidth, and a 64 element phased array supporting 5G NR waveforms. Rigorous indoor and outdoor experiments demonstrate that mmReliable achieves close to 100\% reliability providing 2.3x improvement in the throughput-reliability product than single-beam systems.