Cooperative relaying techniques have recently received significant interests from both academia and industry due to their ability to provide spatial diversity to address the ever increasing demand for extended network coverage, higher data rates without sacrificing extra power resources, greater mobility and enhanced reliability. This thesis mainly considers two themes. Firstly, in the context of self-powered multiple-input-multiple-output (MIMO) full-duplex (FD) relaying, our research focuses on design and performance analysis of MIMO FD relaying systems in the presence of practical transmission impairments. Namely, the impact of spatial fading correlation, imperfect channel state information (CSI), loopback self-interference (LI), and co-channel interference (CCI) on the system performance are investigated. Secondly, in the context of wirelessly-powered MIMO HD relaying, our research focuses on energy beamforming which is used to maximize the overall harvested energy so as to enable longer-distance wireless power transfer when compared to the single antenna nodes. Namely, in the presence of MIMO relaying systems, hop-by-hop information and energy beamforming is proposed where the transmitted signal is steered along the strongest eigenmode of each hop. The wirelessly powered relay scavenge energy from the source information radio-frequency (RF) signal through energy beamforming, where both the time-switching receiver (TSR) and power-splitting receiver (PSR) are considered, then uses the harvested energy to forward the source message to the destination. Our research focuses on developing a comprehensive analytical framework for deriving new closed-form expressions for the outage probability and ergodic capacity for amplify-and-forward (AF) relaying systems, including simpler tight bounds and asymptotic high signal-to-noise (SNR) ratio analysis. First, the optimization problem for the design of source, relay, and destination precoding and/or decoding weight vectors which maximizes the overall signal-to-interference-plus-noise ratio (SINR) is formulated. Then, in order to get closed-form precoding and decoding weight vectors, a sub-optimal solution based on null space projection designed to completely suppress the LI and/or CCI is proposed, through which a closed-form overall SINR is presented. Simulation results show the exactness and tightness of the proposed exact and bound analytical expressions, respectively.

abstract: Full-duplex communication has attracted significant attention as it promises to increase the spectral efficiency compared to half-duplex. Multi-hop full-duplex networks add new dimensions and capabilities to cooperative networks by facilitating simultaneous transmission and reception and improving data rates. When a relay in a multi-hop full-duplex system amplifies and forwards its received signals, due to the presence of self-interference, the input-output relationship is determined by recursive equations. This thesis introduces a signal flow graph approach to solve the problem of finding the input-output relationship of a multi-hop amplify-and-forward full-duplex relaying system using Mason's gain formula. Even when all links have flat fading channels, the residual self-interference component due to imperfect self-interference cancellation at the relays results in an end-to-end effective channel that is an all-pole frequency-selective channel. Also, by assuming the relay channels undergo frequency-selective fading, the outage probability analysis is performed and the performance is compared with the case when the relay channels undergo frequency-flat fading. The outage performance of this system is performed assuming that the destination employs an equalizer or a matched filter. For the case of a two-hop (single relay) full-duplex amplify-and-forward relaying system, the bounds on the outage probability are derived by assuming that the destination employs a matched filter or a minimum mean squared error decision feedback equalizer. For the case of a three-hop (two-relay) system with frequency-flat relay channels, the outage probability analysis is performed by considering the output SNR of different types of equalizers and matched filter at the destination. Also, the closed-form upper bounds on the output SNR are derived when the destination employs a minimum mean squared error decision feedback equalizer which is used in outage probability analysis. It is seen that for sufficiently high target rates, full-duplex relaying with equalizers is always better than half-duplex relaying in terms of achieving lower outage probability, despite the higher RSI. In contrast, since full-duplex relaying with MF is sensitive to RSI, it is outperformed by half-duplex relaying under strong RSI. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

Abstract In this thesis we study Full-Duplex (FD) cooperative networks from different perspectives, using concepts of information theory, communication theory and applied statistics. We provide a comprehensive performance analysis of cooperative communications systems operating with FD relays. We demonstrate that FD relaying is feasible even when experiencing strong self-interference, and we show its application under different scenarios. More importantly, the results attained through this work serve as a benchmark for design as well as deployment of current and future wireless communications technologies. Our first contribution is a comprehensive overview of the state-of-the-art on FD communications, more specifically on FD relaying, and we revisit some of the main properties of cooperative schemes. Another contribution comes from an extensive analysis of outage probability, throughput and energy efficiency of FD relaying over Rayleigh fading channels. Besides the mathematical framework introduced herein, we also show that in some cases cooperative Half-Duplex (HD) schemes achieve better performance than FD relaying with self-interference. Therefore, we draw a discussion on the trade-offs between HD and FD schemes as well as between throughput and energy efficiency. Then, we investigate the performance of FD relaying protocols under general fading settings, namely Nakagami-m fading. Our findings allow a better understanding of effects of the residual self-interference and line-of-sight on a FD relaying setup. Our final contribution lies on the performance analysis of secure cooperative networks relying on information theoretical metrics to provide enhanced privacy and confidentiality to wireless networks. Thus, we provide a comprehensive mathematical framework for composite fading channels. Even though experiencing strong self-interference, we demonstrate that FD relaying is feasible also under secrecy constraints, thus perfect secrecy can be achieved. / Tiivistelmä Tässä työssä tutkitaan kaksisuuntaisia (Full-Duplex, FD) yhteistoiminnallisia verkkoja informaatioteorian, tietoliikenneteorian ja sovelletun tilastotieteen näkökulmista. Työssä suoritetaan kattava suorityskykyarviointi yhteistoiminnallisten FD-välittimien muodostamassa tietoliikenneverkossa. FD-releointi osoitetaan toimintakelpoiseksi useissa toimintaympäristöissä ja sovelluksissa jopa voimakkaan omahäiriön vallitessa. Mikä tärkeintä, työssä saavutetut tulokset muodostavat vertailukohdan sekä nykyisten että tulevien langattomien verkkoteknologioiden suunnitteluun ja toteutukseen. Aluksi esitetään perusteellinen katsaus uusimpiin FD-tiedonsiirtomenetelmiin, etenkin FD-välitykseen, sekä kerrataan yhteistoiminnallisten tekniikoiden pääpiirteet. Seuraavaksi analysoidaan laajasti FD-välitinyhteyden luotettavuutta sekä spektrinkäyttö- ja energiatehokkuutta Rayleigh-häipyvissä radiokanavissa. Matemaattisen viitekehyksen lisäksi osoitetaan myös, että joissain tapauksissa yhteistoiminnalliset vuorosuuntaiset (Half-Duplex, HD) menetelmät ovat parempia kuin FD-releointi omahäiriön vallitessa. Niinpä työssä käydään keskustelua kaupankäynnistä HD- ja FD -menetelmien kesken kuten myös spektrinkäyttö- ja energiatehokkuuden kesken. Seuraavaksi tutkitaan FD-releoinnin suorityskykyä yleistetymmässä häipymäympäristössä eli Nakagami-m -kanavassa. Saavutetut tulokset auttavat ymmärtämään paremmin jäljelle jäävän omahäiriön ja näköyhteyslinkkien vuorovaikutussuhteet FD-välitinjärjestelmän suunnittelussa. Lopuksi käsitellään tietoturvattuja yhteistoiminnallisia verkkoja informaatioteoreettisin mittarein, joilla pyritään tarjoamaan langattomien verkkojen käyttäjille parempaa yksityisyyden suojaa ja luottamuksellisuutta. Tätä varten työssä esitetään perusteelliset matemaattiset puitteet yhdistettyjen häipyvien kanavien tutkimiseen. Tuloksena osoitetaan, että myös salassapitokriteerien kannalta on mahdollista käyttää voimakkaan omahäiriön kokemaa FD-releointia vahvan salauksen saavuttamiseen.

In the last decade, wireless applications have witnessed a tremendous growth. This can be envisioned in the surge of smart devices which became almost in everyone's possession, demand for high speed connection and the internet of things (IoT) along with its enabling technologies. Hence, the multiuser interference became the main limiting factor in wireless communications. Moreover, just like diamonds and emeralds, the electromagnetic spectrum is limited and precious. Therefore, the high data rate application may not be satisfied by our current technologies. In order to solve this spectrum scarcity problem, researchers have steered their focus to develop new techniques such as cognitive radio (CR) and in-band full-duplex (FD). However, these systems suffer from the interference problem that can dramatically impede their quality-of-service (QoS). Therefore, investigating communication techniques/systems that can relieve the interference adverse signature becomes imperative. Improper Gaussian signaling (IGS) has been recently shown to outperform the traditional proper Gaussian signaling (PGS) in several interference-limited systems. In this thesis, we use IGS in order to mitigate the interference issue in three different communication settings. IGS has the ability to control the interference signal dimension, and hence, it can be considered as one form of interference alignment. In the first part, we investigate an underlay CR system with in-band FD primary users (PUs) and one-way communication for the secondary user (SU). IGS is employed to alleviate the interference introduced by the SU on the PUs. First, we derive a closed form expression and an upper bound for the SU and PUs outage probabilities, respectively. Second, we optimize the SU signal parameters, represented in its power and the circularity coefficient, to achieve the design objectives of the SU while satisfying certain QoS constraints for the PU under instantaneous, average and partial channel state information (CSI). Finally, we provide some numerical results that demonstrate the advantages that can be reaped by using IGS to access the spectrum of the FD PUs. Specifically, with the existence of week PU direct channels and/or strong SU interference channels, PGS tends to use less transmit power while IGS uses more power along with increasing the signal impropriety. Part 2 studies the potential employment of IGS in FD cooperative settings with non-negligible residual self-interference (RSI). In this part, IGS is used in an attempt to alleviate the RSI adverse effect in full-duplex relaying (FDR). To this end, we derive a tight upper bound expression for the end-to-end outage probability in terms of the relay signal parameters. We further show that the derived upper bound is either monotonic or unimodal in the relay's circularity coefficient. This result allows for easily locating the global optimal point using known numerical methods. Based on the analysis, IGS allows FDR systems to operate even with high RSI. It is shown that, while the communication totally fails with PGS as the RSI increases, the IGS outage probability approaches a fixed value that depends on the channel statistics and target rate. The obtained results show that IGS can leverage higher relay power budgets than PGS to improve the performance, meanwhile it relieves its RSI impact via tuning the signal impropriety. In part 3, we investigate the potential benefits of adopting IGS in a two-hop alternate relaying (AR) system. Given the known benefits of using IGS in interference-limited networks, we propose to use IGS to relieve the inter-relay interference (IRI) impact on the AR system assuming no CSI is available at the source. In this regard, we assume that the two relays use IGS and the source uses PGS. Then, we optimize the degree of impropriety of the relays signal, measured by the circularity coefficient, to maximize the total achievable rate. Simulation results show that using IGS yields a significant performance improvement over PGS, especially when the first hop is a bottleneck due to weak source-relay channel gains and/or strong IRI.

In our thesis work, we analyze the performance analysis of a power domain NonOrthogonal Multiple Access (NOMA) system in which the closer user acts as fullduplex relaying to forward the signal to farther user. Because Nakagami-m distribution is a generalized case including the two common fading distributions as specialcases: Rayleigh distribution (m=1), Rician distribution (m>1). We assume that thesystem experiences Nakagami-m fading. Then, we have to analyze outage probabilityof NOMA system. Numerical results are provided for outage probability to show theeffect of system parameters on the performance of the NOMA system in full duplexrelaying over Nakagami-m fading.