Design of RF Self-interference Cancellation Circuit for 100-W Full-Duplex Radio at 225-400 MHz

The full-duplex (FD) technology enables future military radios to simultaneously transmit and receive (STAR) on the same and adjacent frequencies. This enhances spectral efficiency and makes simultaneous integrated tactical communications and electronic warfare operations possible as opposed to the current time- or frequency-division radios used in military applications. The main challenge in implementing full-duplex radios is the strong self-interference (SI) between the transmitter and the receiver requiring solutions how to cancel the coupling, which has been largely resolved at higher ultra high frequency (UHF) bands for low power transmission. This paper presents a radio-frequency SI cancellation circuit suitable especially for very high-power military applications at military-relevant lower UHF band (225-400 MHz). The circuit couples power from the transmitter and tunes the phase and amplitude of the signal to destructively combine with the received SI, and thus isolates the receiver and transmitter. The paper introduces a concept consisting of a 90° vector modulator and switchable delay lines for a low-loss and high-power-handling cancellation circuit that enables operation with very-high transmit powers of even up to 1 kW.acceptedVersionPeer reviewe

Multifunction Radios and Interference Suppression for Enhanced Reliability and Security of Wireless Systems

Wireless connectivity, with its relative ease of over-the-air information sharing, is a key technological enabler that facilitates many of the essential applications, such as satellite navigation, cellular communication, and media broadcasting, that are nowadays taken for granted. However, that relative ease of over-the-air communications has significant drawbacks too. On one hand, the broadcast nature of wireless communications means that one receiver can receive the superposition of multiple transmitted signals. But on the other hand, it means that multiple receivers can receive the same transmitted signal. The former leads to congestion and concerns about reliability because of the limited nature of the electromagnetic spectrum and the vulnerability to interference. The latter means that wirelessly transmitted information is inherently insecure. This thesis aims to provide insights and means for improving physical layer reliability and security of wireless communications by, in a sense, combining the two aspects above through simultaneous and same frequency transmit and receive operation. This is so as to ultimately increase the safety of environments where wireless devices function or where malicious wirelessly operated devices (e.g., remote-controlled drones) potentially raise safety concerns. Specifically, two closely related research directions are pursued. Firstly, taking advantage of in-band full-duplex (IBFD) radio technology to benefit the reliability and security of wireless communications in the form of multifunction IBFD radios. Secondly, extending the self-interference cancellation (SIC) capabilities of IBFD radios to multiradio platforms to take advantage of these same concepts on a wider scale. Within the first research direction, a theoretical analysis framework is developed and then used to comprehensively study the benefits and drawbacks of simultaneously combining signals detection and jamming on the same frequency within a single platform. Also, a practical prototype capable of such operation is implemented and its performance analyzed based on actual measurements. The theoretical and experimental analysis altogether give a concrete understanding of the quantitative benefits of simultaneous same-frequency operations over carrying out the operations in an alternating manner. Simultaneously detecting and jamming signals specifically is shown to somewhat increase the effective range of a smart jammer compared to intermittent detection and jamming, increasing its reliability. Within the second research direction, two interference mitigation methods are proposed that extend the SIC capabilities from single platform IBFD radios to those not physically connected. Such separation brings additional challenges in modeling the interference compared to the SIC problem, which the proposed methods address. These methods then allow multiple radios to intentionally generate and use interference for controlling access to the electromagnetic spectrum. Practical measurement results demonstrate that this effectively allows the use of cooperative jamming to prevent unauthorized nodes from processing any signals of interest, while authorized nodes can use interference mitigation to still access the same signals. This in turn provides security at the physical layer of wireless communications

Networking for next generation NBWF radios

This work studies the networking scheme of NATO's next generation narrow band waveform (NBWF) radios. The key techniques that effectively enable the multihop capabilities for the NBWF radios are described first. Then a network emulator is developed to evaluate two critical algorithms, the link metrics mapping algorithm and the relay node selection algorithm, employing realistic network scenario parameters. Performance results are illustrated and the options for dynamic algorithm adaptation are elaborated