Performance of passive UHF RFID in cascaded correlated generalized Rician fading

Ultra high frequency radio frequency identification (UHF RFID) systems can use passive tags to reflect the signal from the reader’s transmitting antenna back to the reader’s receiving antenna for information delivery. This gives a cascaded channel that is a product of two fading components. In this work, the probability of detection, defined as the probability that the received power is above the receiver sensitivity, is derived when the two fading components suffer from correlated generalized Rician fading. This includes the Rayleigh, Rician and Nakagamim channels in the literature as special cases. Numerical results are presented to show the effects of link distances, receiver sensitivities and channel parameters on the detection probability

On the Effect of Correlation on the Capacity of Backscatter Communication Systems

We analyse the effect of correlation between the forward and backward links on the capacity of backscatter communication systems. To that aim, we obtain an analytical expression for the average capacity under a correlated Rayleigh product fading channel, as well as closed-form asymptotic expressions for the high and low signal-to-noise ratio (SNR) regimes. Our results show that correlation is indeed detrimental for a fixed target SNR; contrarily to the common belief, we also see that correlation can be actually beneficial in some instances when a fixed power budget is considered.Comment: This work has been submitted for publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

RIScatter: unifying backscatter communication and reconfigurable intelligent surface

Backscatter Communication (BackCom) nodes harvest energy from and modulate information over an external electromagnetic wave. Reconfigurable Intelligent Surface (RIS) adapts its phase shift response to enhance or attenuate channel strength in specific directions. In this paper, we show how those two seemingly different technologies (and their derivatives) can be unified to leverage their benefits simultaneously into a single architecture called RIScatter. RIScatter consists of multiple dispersed or co-located scatter nodes, whose reflection states can be adapted to partially engineer the wireless channel of the existing link and partially modulate their own information onto the scattered wave. This contrasts with BackCom (resp. RIS) where the reflection pattern is exclusively a function of the information symbol (resp. Channel State Information (CSI)). The key principle in RIScatter is to render the probability distribution of reflection states (i.e., backscatter channel input) as a joint function of the information source, CSI, and Quality of Service (QoS) of the coexisting active primary and passive backscatter links. This enables RIScatter to softly bridge, generalize, and outperform BackCom and RIS; boil down to either under specific input distribution; or evolve in a mixed form for heterogeneous traffic control and universal hardware design. For a single-user multi-node RIScatter network, we characterize the achievable primary-(total-)backscatter rate region by optimizing the input distribution at the nodes, the active beamforming at the Access Point (AP), and the backscatter detection regions at the user. Simulation results demonstrate RIScatter nodes can exploit the additional propagation paths to smoothly transition between backscatter modulation and passive beamforming

Second Order Statistics of -Fisher-Snedecor Distribution and Their Application to Burst Error Rate Analysis of Multi-Hop Communications

An advantage of using the composite fading models (CFMs) is their ability to concurrently address the impact of multi-path and shadowing phenomena on the system performance in wireless communications. A Fisher-Snedecor (FS) F CFM has been recently proposed as an experimentally verified and tractable fading model that can be efficiently applied for 5G and beyond 5G wireless communication systems. This paper provides second-order (s-order) performance analysis of the product of N independent but not identically distributed (i.n.i.d) FS F random variables (RVs). In particular, accurate and closedform approximations for level crossing rate (LCR) and average fade duration (AFD) of the product of N i.n.i.d FS F(N-FS F) RVs are successfully derived by exploiting a general property of a Laplace approximation method for evaluation of the N -folded integral-form LCR expression. Based on the obtained s-order statistical results, the burst error rate and maximum symbol rate of the N -FS F distribution are addressed and thoroughly examined. The numerical results of the considered performance measures are discussed in relation to the N-FS F multi-path and shadowing severity parameters. Moreover, the impact of the number of hops (N) of the N -FS F CFM on the s-order metrics, the burst error rate and maximum symbol rate are numerically evaluated and investigated. The derived s-order statistical results can be used to address the cooperative relay-assisted (RA) communications for vehicular systems. Monte-Carlo (M - C) simulations for the addressed statistical measures are developed in order to confirm the provided theoretical results.This work was supported in part by UC3M and the European Union's Horizon 2020 Programme under the Marie Sklodowska-Curie Grant through the CONEX-Plus Project under Agreement 801538; in part by the IRENE-EARTH Project under Grant PID2020-115323RB-C33/AEI/10.13039/501100011033; in part by ERDF and the Spanish Government Projects under Grant PID2019-106808RA-I00 AEI/FEDER, UE; in part by CDTI Cervera Project INTEGRA under Grant CER-20211031; in part by the Secretaria d'Universitats i Recerca de la Generalitat de Catalunya under Project 2017-SGR-00376 and Project Fem IoT under Grant 001-P-001662; in part by the European Commission Project CPSoSaware; and in part by the Cost Actions under Grant CA19111, Grant CA20120, and Grant CA16220.Publicad

Wireless networks physical layer security : modeling and performance characterization

Intrigued by the rapid growth and expand of wireless devices, data security is increasingly playing a significant role in our daily transactions and interactions with different entities. Possible examples, including e-healthcare information and online shopping, are becoming vulnerable due to the intrinsic nature of wireless transmission medium and the widespread open access of wireless links. Traditionally, the communication security is mainly regarded as the tasks at the upper layers of layered protocol stack, security techniques, including personal access control, password protection, and end-to-end encryption, have been widely studied in the open literature. More recently, plenty of research interests have been drawn to the physical layer forms of secrecy. As a new but appealing paradigm at physical layer, physical layer security is based on two pioneering works: (i) Shannon’s information-theoretic formulation and (ii) Wyner’s wiretap formulation. On account of the fundamental of physical layer security and the different nature of various wireless network, this dissertation is supposed to further fill the lacking of the existing research outcomes. To be specific, the contributions of this dissertation can be summarized as three-fold:(i) exploration of secrecy metrics to more general fading channels; (ii) characterization a new fading channel model and its reliability and security analysis in digital communication systems; and (iii) investigation of physical layer security over the random multiple-input multiple-output (MIMO) α −μ fading channels. Taking into account the classic Alice-Bob-Eve wiretap model, the first contribution can be divided into four aspects: (i) we have investigated the secrecy performance over single-input single-output (SISO) α −μ fading channels. The probability of non-zero (PNZ) secrecy capacity and the lower bound of secrecy outage probability (SOP) are derived for the special case when the main channel and wiretap channel undergo the same non-linearity fading parameter, i.e., α. Later on, for the purpose of filling the gap of lacking closed-form expression of SOP in the open literature and extending the obtained results in chapter 2 to the single-input multiple-output (SIMO) α − μ wiretap fading channels, utilizing the fact that the received signal-tonoise ratios (SNRs) at the legitimate receiver and eavesdropper can be approximated as new α −μ distributed random variables (RVs), the SOP metric is therefore derived, and given in terms of the bivariate Fox’s H-function; (ii) the secrecy performance over the Fisher-Snedecor F wiretap fading channels is initially considered. The SOP, PNZ, and ASC are finalized in terms of Meijer’s G-function; (iii) in order to generalize the obtained results over α −μ and Fisher-Snedecor F wiretap fading channels, a more flexible and general fading channel, i.e., Fox’s H-function fading model, are taken into consideration. Both the exact and asymptotic analysis of SOP, PNZ, and average secrecy capacity (ASC), are developed with closed-form expressions; and (iv) finally, motivated by the fact that the mixture gamma (MG) distribution is an appealing tool, which can be used to model the received instantaneous SNRs over wireless fading channels, the secrecy metrics over wiretap fading channels are derived based on the MG approach. Due to the limited transmission power and communication range, cooperative relays or multi-hop wireless networks are usually regarded as two promising means to address these concerns. Inspired by the obtained results in Chapters 2 and 3, the second main contribution is to propose a novel but simple fading channel model, namely, the cascaded α −μ. This new distribution is advantageous since it encompasses the existing cascaded Rayleigh, cascaded Nakagami-m, and cascaded Weibull with ease. Based on this, both the reliability and secrecy performance of a digital system over cascaded α −μ fading channels are further evaluated. Closed-form expressions of reliability metrics (including amount of fading (AF), outage probability, average channel capacity, and average symbol error probability (ABEP).) and secrecy metrics (including SOP, PNZ, and ASC) are respectively provided. Besides, their asymptotic behaviors are also performed and compared with the exact results. Considering the impacts of users’ densities, spatial distribution, and the path-loss exponent on secrecy issue, the third aspect of this thesis is detailed in Chapter 8 as the secrecy investigation of stochastic MIMO system over α −μ wiretap fading channels. Both the stochastic geometry and conventional space-time transmission (STT) scheme are used in the system configuration. The secrecy issue is mathematically evaluated by three metrics, i.e., connection outage, the probability of non-zero secrecy capacity and the ergodic secrecy capacity. Those three metrics are later on derived regarding two ordering scheme, and further compared with Monte-Carlo simulations

Realistic chipless RFID: identification and localization

Für die weitere Massenverbreitung von RFID Systemen ist ein günstiges und genaues Verfahren zur Objektlokalisierung und –verfolgung zwingend erforderlich. Chiplose RFID Systeme erlauben im Gegensatz zu herkömmlichen chipbehafteten RFID Systemen den Einsatz von einfachen, druckbaren RFID Tags, eine Möglichkeit zum Einstieg in die Ära von extrem billigen RFID Tags. Diese Dissertation konzentriert sich auf die Lösung von drei Herausforderungen bei der Erkennung von chiplosen RFID Tags innerhalb geschlossener Räume. Der erste in der vorliegenden Arbeit diskutierte Aspekt beschäftigt sich mit Methoden zum Eliminieren des Störechos der Umgebung (clutter removal techniques). Im chiplosen RFID System ist das Umgebungsstörecho definiert durch das von der Umgebung reflektierte Signal, das nicht mit dem RFID Tag interagiert. Die Stärke dieses Signals ist in jedem Fall größer als die des vom RFID Tag zurückgestrahlten (backscattered) Signals, was die Signaturerkennung des RFID Tags unmöglich macht. Zur Lösung dieses Problems schlage ich zwei Algorithmen vor. Der erste ist die Leerraum-Kalibrierung (empty room calibration). Bei diesem Algorithmus werden die Messungen mit RFID Tag von denen ohne RFID Tags abgezogen. Der zweite Algorithmus basiert auf dem Rake-Receiver unter Nutzung einer Zufallsfolge (PN sequence), er erfordert keine zusätzliche Kalibrierung. Der zweite Aspekt betrifft die Notch Erkennung und Identifikation, ein sehr wichtiger Bereich des chiplosen RFID Systems. Er ist dafür verantwortlich, die Notchs in Bits umzuwandeln. Für eine effektive Detektion werden Windowing (Fenster) Verfahren vorgeschlagen, wobei jedes Fenster einen oder auch keinen Notch beinhalten kann. Insgesamt drei neue Verfahren zur Notch Erkennung wurden implementiert. Als erstes ein Matched Filter (MF), in dem der einkommende Notch mit einem Referenz Notch verglichen wird. Das zweite Verfahren basiert auf einer gefensterten Singulärwertzerlegung, damit kann sowohl der Notch erkannt werden, als auch seine Bandbreite bestimmt werden. Als drittes Verfahren wird das dynamische Frequency Warping vorgestellt. Diese Technik nutzt nichtlineare um die Notche unddie Frequenzverschiebungen, die an den Notches auftreten, zu erkennen. Als dritter Aspekt wird die Lokalisierung der RFID Tags in dieser Dissertation diskutiert. Dazu werden zwei Algorithmen erklärt und implementiert. Der erste Algorithmus beruht auf der Triangulation durch drei getrennte RFID Lesegeräte, während sich der zweite die Position des RFID Tags aus der Signalstärke und dem Winkel des vom RFID Tag kommenden Signals berechnet. Alle genannten Algorithmen und Verfahren wurden in einer realen Innenraum Testumgebung mit RFID Tags und einer Software Defined Radio (SDR) Plattform vermessen, um die Zuverlässigkeit der Algorithmen unter normalen Bedingungen zu überprüfen.For mass deployment of RFID systems, cheap and accurate item level identification and tracking are profoundly needed. Fortunately, unlike conventional chip-based RFID, chipless RFID systems offers low-cost printable tags holding a better chance to enter the era of penny-cost tags. This dissertation concentrated on solving three challenges in the detection of the chipless tag inside an indoor environment. The first aspect discussed in the thesis are the chipless RFID clutter removal techniques. In chipless RFID the environmental clutter response is defined as the signal reflected from the environment, that does not interact with the tag. This signal has higher power than the backscattered signal from the tag, rendering the tag signature undetectable. Two algorithms to overcome this problem was used, the first is empty room calibration. The first algorithm is based on subtracting the measurement with the tag from the one without. The second algorithm is Rake receiver using PN sequence; this algorithm requires no pre-measurement calibration. The second aspect is notch detection and identification which is a critical part of the chipless system. This part is responsible for converting the notches into bits. For effective detection, a windowing operation is proposed, where each window may contain a notch or not. Three novel techniques are implemented to detect the notch. The first is matched filter were a reference notch is compared with the incoming signal. The second is window based singular value decomposition, where a constellation is created to detect not only the existence of a notch but also the bandwidth of the notch. The third notch detection technique is dynamic frequency warping. This technique utilizes non-linear warping to detect the notch and the frequency shifts that occurs on the notch. The third aspect discussed in the thesis is tag localization. In this aspect, two algorithms are implemented and explained. The first is trilateration which requires three different readers. The second localization algorithm exploits received signal strength and angle of arrival to detect the location of the tag accurately. All the algorithms were tested using a real testbed to validate the reliability of the techniques. The measurements were done using fabricated tags in an indoor environment using Software Defines Radio (SDR)

Advanced Trends in Wireless Communications

Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics

Design of indoor communication infrastructure for ultra-high capacity next generation wireless services

The proliferation of data hungry wireless devices, such as smart phones and intelligent sensing networks, is pushing modern wireless networks to their limits. A significant shortfall in the ability of networks to meet demand for data is imminent. This thesis addresses this problem through examining the design of distributed antenna systems (DAS) to support next generation high speed wireless services that require high densities of access points and must support multiple-input multiple-output (MIMO) protocols. First, it is shown that fibre links in DAS can be replaced with low-cost, broadband free-space optical links, termed radio over free-space optics (RoFSO) links. RoFSO links enable the implementation of very high density DAS without the need for prohibitively expensive cabling infrastructure. A 16m RoFSO link requiring only manual alignment is experimentally demonstrated to provide a spurious-free dynamic range (SFDR) of > 100dB/Hz^2/3 over a frequency range from 300MHz- 3.1GHz. The link is measured to have an 802.11g EVM dynamic range of 36dB. This is the first such demonstration of a low-cost broadband RoFSO system. Following this, the linearity performance of RoFSO links is examined. Because of the high loss nature of RoFSO links, the directly-modulated semiconductor lasers they use are susceptible to high-order nonlinear behaviour, which abruptly limits performance at high powers. Existing measures of dynamic range, such as SFDR, assume only third-order nonlinearity and so become inaccurate in the presence of dominant high-order effects. An alternative measure of dynamic range called dynamic-distortion-free dynamic range (DDFDR) is then proposed. For two different wireless services it is observed experimentally that on average the DDFDR upper limit predicts the EVM knee point to within 1dB, while the third-order SFDR predicts it to within 6dB. This is the first detailed analysis of high-order distortion effects in lossy analogue optical links and DDFDR is the first metric able to usefully quantify such behaviour. Next, the combination of emerging MIMO wireless protocols with existing DAS is examined. It is demonstrated for the first time that for small numbers of MIMO streams (up to ~4), the capacity benefits of MIMO can be attained in existing DAS installations simply by sending the different MIMO spatial streams to spatially separated remote antenna units (RAU). This is in contrast to the prevailing paradigm of replicating each MIMO spatial stream at each RAU. Experimental results for two representative DAS layouts show that replicating spatial streams provides an increase of only ~1% in the median channel capacity over merely distributing them. This compares to a 3-4% increase of both strategies over traditional non-DAS MIMO. This result is shown to hold in the multiple user case with 20 users accessing 3 base stations. It is concluded that existing DAS installations offer negligible capacity penalty for MIMO services for small numbers of spatial streams, including in multi-user MIMO scenarios. Finally, the design of DAS to support emerging wireless protocols, such as 802.11ac, that have large numbers of MIMO streams (4-8) is considered. In such cases, capacity is best enhanced by sending multiple MIMO streams to single remote locations. This is achieved using a novel holographic mode division multiplexing (MDM) system, which sends each separate MIMO stream via a different propagation mode in a multimode fibre. Combined channel measurements over 2km of mode-multiplexed MMF and a typical indoor radio environment show in principle a 2x2 MIMO link providing capacities of 10bit/s/Hz over a bandwidth of 6GHz. Using a second experimental set-up it is shown that the system could feasibly support at least up to a 4x4 MIMO system over 2km of MMF with a condition number >15dB over a bandwidth of 3GHz, indicating a high degree of separability of the channels. Finally, it is shown experimentally that when a fibre contains sharp bends (radius between 20mm and 7.2mm) the first 6 mode-groups used for multiplexing exhibit no additional power loss or cross-coupling compared with unbent fibre, although mode-groups 7, 8 and 9 are more severely affected. This indicates that at least 6x6 multiplexing is possible in standard installations with tight fibre bends.For their financial support, I would like to thank the Rutherford Foundation of the Royal Society of New Zealand, the Cambridge Commonwealth Trust and the EPSRC