Full-Duplex Multifunction Transceivers: Combining Radar, Communication and Security

A full-duplex (FD) capable transceiver is a device that can transmit and receive simultaneously over the same frequency resources. The traditional issue of such setups has originated from the strong self-interference between the transmission and reception sides. Recent research in the field has shown that the cancelation of the self-interference down to the receiver noise floor is technologically feasible. Consequently, it is time to start investigating potential applications for full-duplex devices. The original application in the majority of the existing research has been to improve wireless communication performance through the increase of spectrum efficiency on the heavily contested frequency resources. However, there exists other possible applications.

One such application is the combining of several functions, namely communication, radar sensing and physical layer security, into a single system. The first of the functionalities considered herein is communication, which refers to the inclusion of information bits into a wireless waveform through the modulation of its properties, such as amplitude and phase. The second is radar sensing, where a received waveform reflected by a target entity is inspected to infer the target’s properties, such as range and radial velocity. Last is physical layer security, which can be further separated into jamming and spectral monitoring. Jamming refers to transmitting a strong waveform over a target signal with the goal of preventing an unauthorized receiver from benefiting from it. Meanwhile, spectral monitoring refers to receiving a certain portion of the radio spectrum with the goal of detecting and possibly demodulating any signals present. Herein, this combining of functions is referred to as multifunctionality, effectively causing a radio frequency convergence.

Multifunctionality is a research direction that has rapidly gained interest in the recent years. With multifunctionality, several different functions typical for wireless systems are combined in a way that allows for increased spectral efficiency and possible performance benefits from, for instance, increased channel state information. Through multifunctionality, several of the aforementioned functions can be combined in innovative ways, some of which are joint radar and communication (JRC) and cooperative jamming. The existing systems in literature have been shown to function with half-duplex devices, however full-duplex has the potential to reduce the interference between the functions.

This Thesis presents two FD-capable transceiver structures. The first of these is a novel continuous-wave transceiver (CW-TRX) based on frequency-modulated continuous-wave (FMCW)-radars. The second is an example of a traditional FD direct- conversion transceiver (DC-TRX). These FD capable transceiver structures are tested in various combinations of multifunctionality tasks with simulations and experimental measurements. Finally, a novel multifunction combination of joint radar, communication and security (JRCS) is presented; and the performance of the two transceivers in this task is investigated. The simulated and measured results demonstrate that the CW-TRX provides an effective way to remove self-interference in the analog domain when the transmit signal is a continuous-wave frequency sweeping tone, making the transceiver effective in several multifunctionality tasks. Meanwhile, the DC-TRX seems very promising in the JRCS task, with simulated results showing that the system is capable of enforcing a fixed jamming-to-signal power ratio (JSR) at any eavesdropper while its own radar sensing and two-way data transfer performances are minimally affected.