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

Generating and measuring digital signal from capacitive pressure sensors in pressure analysis insole

Käesolev bakalaureusetöö kirjeldab koormusjaotuse mõõtmiseks inimese jalatallal erinevate füüsiliste tegevuste korral mõeldud sensortalla andmehõivemooduli ja sensorite elektroonika konstrueerimist. Vajadust alajäsemete koormuse mõõtmise süsteemi järele tunnevad paljud meditsiinierialad, näiteks spordimeditsiin, ortopeedia, taastusravi jms. Töö käigus valmis mõõtesüsteem, mis koosneb kahest sensortallast ja mis pikema ajaperioodi vältel võimaldab mõõta labajala koormusjaotust erinevates tingimustes, kasutajat oluliselt segamata. Kirjeldatud sensortallas on kasutatud 24 mahtuvuslikku sensorit, kusjuures mahtuvusele vastava sagedusega digitaalne signaal genereeritakse sensorite vahetus läheduses, vähendamaks mõõtmise müratundlikkust. Voolutarbe madalal hoidmiseks saavad sensorite signaaligeneraatorid toitepinge mikrokontrollerilt. Mõõtmisi sensoritelt tehakse diskreetimissagedusega 100 Hz. Mõõtetulemused on võimalik salvestada sensortallas paiknevas välkmälus või edastada kommunikatsioonimoodulile juhtmevaba ühendusega välisele seadmele edastamiseks. Mõõtetulemusi on võimalik salvestada kuni 190 minuti jooksul ja sensortalla tööaeg laetud akuga on vähemalt 3 h. Tööaeg varieerub sõltuvalt sellest, kas mõõtetulemused salvestatakse tallas või edastatakse välisele seadmele

Neural networks in the pursuit of invincible counterdrone systems

The growing range of possibilities provided by the proliferation of commercial unmanned aerial vehicles, or drones, raises alarming safety and security threats. The efficient mitigation of these threats depends on authorities having defense systems to counter both accidentally trespassing and maliciously operated drones. To effectively counter such vehicles, defense systems must be able to detect a new drone entering a restricted airspace; locate its position; identify its purpose; and, should the identification procedure mark it as a threat, neutralize it.acceptedVersionPeer reviewe

Estimating and Tracking Wireless Channels Under Carrier and Sampling Frequency Offsets

This article addresses the challenge of estimating and tracking wireless channels under carrier and sampling frequency offsets, which also incorporate phase noise and sampling time jitter. We propose a novel adaptive filter that explicitly estimates the channel impulse response, carrier frequency offset, and sampling frequency offset by minimizing the mean-square error (MSE) and, when the estimated parameters are time-varying, inherently performs tracking. The proposed filter does not have any requirements for the structure of the waveform, but the digital transmitted waveform must be known to the receiver in advance. To aid practical implementation, we derive upper bounds for the filter's step sizes. We also derive expressions for the filter's steady-state MSE performance, by extending the well-known energy conservation relation method to account for the self-induced nonstationarity and coupling of update equations that are inherent in the proposed filter. Theoretical findings are verified by comparison to simulated results. Proof-of-concept measurement results are also provided, which demonstrate that the proposed filter is able to estimate and track a practical wireless channel under carrier and sampling frequency offsets.publishedVersionPeer reviewe

Physical-Layer Reliability of Drones and Their Counter-Measures: Full vs. Half Duplex

In this article, we study the advantages and disadvantages that full-duplex (FD) radio technology brings to remote-controlled drone and counter-drone systems in comparison to classical half-duplex (HD) radio technology. We consider especially the physical-layer reliability perspective that has not yet been comprehensively studied. For establishing a solid analytical background, we first derive original closed-form expressions to evaluate demodulation and detection performance of frequency-hopped and frequency-shift keyed drone remote control signals under external or self-inflicted interference. The developed analytical tools are verified by comparison to simulated results and then used to study the impact that the operation mode has on the operable area of drones and effectiveness of counter-drone systems in different scenarios, linking the physical layer performance to practical safety. Analysis of the scenarios shows that FD operation compared to HD can improve the effectiveness of a counter-drone system and that in FD mode a drone can detect the attacks from the counter-drone system from a greater distance than in HD mode. However, two-way communication between the remote controller and drone in FD mode compared to HD significantly reduces the drone’s operable area when targeted by a smart counter-drone system.Peer reviewe

Known-Interference Cancellation in Cooperative Jamming : Experimental Evaluation and Benchmark Algorithm Performance

Physical layer security is a sought-after concept to complement the established upper layer security techniques in wireless communications. An appealing approach to achieve physical layer security is to use cooperative jamming with interference that is known to and suppressible by the legitimate receiver but unknown to, and hence not suppressible by, the eavesdropper. Suppressing known interference (KI), however, is challenging due to the numerous unknowns, including carrier and sampling frequency offsets, that impact its reception. This letter presents a measurement campaign that captures this challenge and then demonstrates the feasibility of solving that challenge by cancelling the KI using the frequency offsets least mean squares (FO-LMS) algorithm. Results show that KI suppression directly improves processing the signal-of-interest and that cooperative jamming effectively provides security at the physical layer.Peer reviewe

Analog Cancellation of Periodic Frequency-Modulated Jamming

Interference mitigation techniques often rely on suppressing the interference in the digital domain only. However, strong in-band interference from jamming can saturate a receiver’s front-end and, thus, limit the usefulness of plain digital methods. This is especially so in case of the self-interference (SI) encountered in enclosed full-duplex (FD) radios, but also in case of powerful interference in co-located radios. This work presents a digitally-assisted method and its implementation for the mitigation of narrowband periodic interference before quantization in co-located radios where, unlike in FD radios, the receiver does not have access to the transmitted interference waveform. Measurement results are presented that illustrate how the implementation affects GPS reception in the presence of such interference.publishedVersio

Analog Mitigation of Frequency-Modulated Interference for Improved GNSS Reception

Powerful in-band interference can saturate a receiver's front-end and limit the usefulness of digital interference suppression methods that are bounded by the receiver's limited dynamic range. This is especially true for the self-interference (SI) encountered in full-duplex (FD) radios, but also in the case of strong interference between co-located radios. However, unlike in FD radios, receivers co-located with interference sources do not typically have direct access to the transmitted interference. This work analyzes the performance of a digitally-assisted analog interference mitigation method and its implementation for the suppression of frequency-modulated (FM) interference before quantization in global navigation satellite system (GNSS) receivers that are co-located with interference sources. Over-the-air measurement results are presented that illustrate the effects of interference mitigation on GPS L1 and Galileo E1 reception in a commercial off-the-shelf GNSS receiver and a software-defined GNSS receiver. The analysis covers the effects of the interference mitigation on the radio frequency (RF) front-end, acquisition, tracking, and positioning stages.acceptedVersionPeer reviewe

Full-duplex transceivers for defense and security applications

The full-duplex (FD) radio technology that promises to improve the spectral efficiency of wireless communications was, however, initially used in continuous-wave (CW) radars by means of same-frequency simultaneous transmission and reception (SF-STAR). In this chapter, we explore how the recent advances in the FD technology, which have been mainly motivated by higher throughput in commercial networks, could in turn be used in defense and security applications, including CW radars and also electronic warfare (EW) systems. We suggest that, by integrating tactical communications with EW operations such as signals intelligence and jamming, multifunction military full-duplex radios (MFDRs) could provide a significant technical advantage to armed forces over an adversary that does not possess comparable technology. Similarly in the civilian domain, we examine the prospective benefits of SF-STAR concepts in security critical applications in the form of a radio shield.acceptedVersionPeer reviewe

Digitally Assisted Analog Mitigation of Narrowband Periodic Interference

Interference mitigation in radio-frequency (RF) receivers has been studied extensively in various contexts. And although most of the in-band interference mitigation techniques rely on suppressing the interference in the digital domain, strong in-band interference can saturate a receiver’s front-end and, thus, prevent it from receiving comparatively weak signals of interest. This is especially so in case of the self-interference (SI) encountered in enclosed full-duplex (FD) radios, but also in case of co- located jammers or radars and signals intelligence receivers. This work presents a digitally assisted method and its implementation for the mitigation of narrowband periodic interference before quantization in order to improve the sensitivity of receivers co- located with strong interference sources. Experimental results are provided and the potential for mitigating more complex waveforms, e.g., pseudorandom jamming, is discussed.acceptedVersionPeer reviewe