Abstract This thesis considers data transmission in a full-duplex (FD) multiuser multiple-input multiple-output (MU-MIMO) system, where a FD capable base station (BS) bidirectionally communicates with multiple half-duplex (HD) users in downlink (DL) and uplink (UL) channels using the same radio resources. The main challenge in FD communications is how to deal with the self-interference (SI) between transmit and receive antennas at the BS. The work carried out in the thesis is motivated by recent advanced techniques in hardware design demonstrating that the SI can be suppressed to a degree that possibly allows for FD transmission in cellular networks. In particular, this thesis attempts to explore the potential gains in terms of the spectral efficiency (SE) and energy efficiency (EE) that can be brought by the FD MU-MIMO model. As the first of its kinds, the thesis aims to present a solid mathematical framework and report interesting results that foster research on wireless communications in general and FD communications in particular. For the FD system of interest the major challenge is due to the SI and co-channel interference from users in the UL channel to the ones in the DL channel, resulting in the coupling between the two channels. As a result we are concerned with the problem of joint transmit processing design to maximize the SE and EE subject to certain power constraints. Since the design problems are natually non-convex, it is difficult to find the globally optimal solutions or even when possible it is not practically appealing. Our contributions to solving these design problems are on the development of several iterative algorithms that can obtain locally optimal solutions. The proposed algorithms are built upon a framework of local optimization strategies such as the sequential parametric convex approximation and the Frank-Wolfe methods. In special cases closed-form designs are also presented. The reported results show that when the SI is sufficiently suppressed the considered FD MU-MIMO system with the proposed SE designs achieves a significantly better SE but consumes more energy, compared to the HD counterpart. In terms of EE the proposed EE scheme is superior to the proposed SE design. Moreover, in the low transmit power region, the EE design achieves a worse EE than the HD system but a better one in the high trasmit power regime when the SI power is low. / Tiivistelmä Tämä väitöskirja käsittelee datansiirtoa samanaikaisesti kaksisuuntaisessa (full-duplex, FD) usean käyttäjän moniantennijärjestelmässä (MU-MIMO), jossa FD-kykyinen tukiasema on yhtä aikaa yhteydessä vuorosuuntaisten (half-duplex, HD) käyttäjien kanssa laskevalla (DL) ja nousevalla (UL) siirtotiellä käyttäen samoja radioresursseja. FD-kommunikaation suurin haaste liittyy lähetys- ja vastaanottoantennien välisen omahäiriön (SI) hallintaan. Tässä työssä hyödynnetään tuoreita tutkimustuloksia, joissa edistyneillä häiriönvaimennustekniikoilla on kyetty vaimentamaan omahäiriö tasolle, jolla FD-lähetys solukkoverkoissa on toteutuskelpoista. Tässä työssä tutkitaan etenkin mahdollisia FD MU-MIMO –järjestelmän tuomia suorituskykyparannuksia spektrinkäytön tehokkuudessa (SE) ja energiatehokkuudessa (EE). Väitöskirjalla on uutuusarvoa matemaattisessa suorituskykyarvioinnissa ja työn mielenkiintoiset tulokset edistävät jatkotutkimusta aiheen ympärillä. Tutkittavan FD-järjestelmän merkittävänä haasteena on omahäiriön ja muiden käyttäjien siirtosuuntien välisen samankanavan häiriön yhteisvaikutus, jonka johdosta siirtosuunnat kytkeytyvät toisiinsa. Tämä johtaa lähetysprosessoinnin yhteisoptimointiin, jossa spektri- ja energiatehokkuus pyritään maksimoimaan määritetyillä tehorajoituksilla. Nämä suunnitteluongelmat eivät ole luonteeltaan konvekseja, joten niihin on vaikeaa löytää globaalisti optimaalisia ratkaisuja ja vaikka onnistuisikin niin ne eivät yleensä ole käytännöllisiä. Työssä esitetään useita iteratiivisia algoritmejä, joilla saavutetaan paikallisesti optimaalisia ratkaisuja. Ehdotetut algoritmit pohjautuvat paikallisten optimointistrategioiden viitekehykseen, jossa käytetään esimerkiksi peräkkäistä parametristä konveksiapproksimaatiota ja Frank-Wolfe –menetelmiä. Erityistapauksissa suljetun muodon ratkaisut on myös esitetty. Raportoidut tulokset osoittavat, että omahäiriön ollessa riittävästi vaimennettu mallinnetulla järjestelmällä saavutetaan spektrinkäytön optimointimielessä huomattavaa etua HD-verrokkiin lisääntyneen energian kulutuksen kustannuksella. Energiatehokkuuden optimointiin pohjautuvalla strategialla puolestaan päästään suurempiin suorituskykyetuihin. Pienillä lähetystehoilla energiatehokkuus voi kuitenkin olla HD-järjestelmää alempi, mutta vastaavasti suurten lähetystehojen alueella tilanne on päinvastainen kunhan omahäiriön teho on tarpeeksi alhainen.

Cooperative relay systems have emerged as promising techniques to boost the performance of wireless systems. Recent studies have confirmed that interferences, co-channel interferences (CCIs) and self-interferences, have a huge impact on cooperative relay systems and can cause significant performance degradation. Two problems were observed in this research. Firstly, previous studies on performance analysis of Amplify-and-Forward (AF) relay systems in presence of CCIs have only focused on a specific interference channel model. However, in practical design scenarios, such an assumption is not a realistic proposition. Secondly, analyses of overheads introduced by a time-based relay selection protocol in distributed cooperative systems have been based on an over-pessimistic assumption where all packets involved in a collision are destroyed. Nevertheless, collisions due to the protocol overheads cause the system performance to be degraded but this does not mean that the failure of end-to-end transmission certainly occurs. The thesis aims to analyse the performance of practical cooperative relay systems in the presence of CCIs and self-interferences, by developing exact mathematical methods. A new unified mathematical method for AF relay systems in presence of a random number of arbitrary non-identical CCIs was developed. The obtained new approach derived in terms of a moment generating function of the aggregate interferences' power led to the derivation of new explicit expressions. The new results greatly simplify evaluation of average error rates over diverse practical interference scenarios. Moreover, a new exact mathematical analysis for distributed cooperative relay systems employing a time-based relay selection protocol based on an accurate interference model was presented. This approach led to the derivation of new exact expressions for the spectral efficiency which accounts for both self-interferences and the protocol overheads as well as for different fading scenarios and arbitrary relay locations. This approach provided several advantages over direct approaches, one of which is that it significantly simplified averaging-out the joint random variables involved.

With the tremendous growth in the mobile data traffic, the demand for highdata rate is increasing rapidly, and higher frequency resources shall be exploredto alleviate the congestion in the overcrowded spectrum, thus, the millimeterwave (mmWave) frequency resource ranging from 30 GHz to 300 GHz has beenrecognized as a nature fit for the fifth-generation (5G) and beyond network. Tocompensate the severe path-loss in the mmWave band as well to realize theefficient transmissions by applying the low-cost architecture, it is of intereststo investigate the beamforming schemes with large-scale antenna arrays andthe full-duplex (FD) relaying strategy, which are indispensable in the operationof directional signal transmission and the efficient spectrum utilization inthe mmWave transmission, respectively. However, the self-interference (SI)occurring between the separate antenna arrays is the main impediment inrealizing a FD wireless node while considering the simultaneous transmission andreception.This thesis project aims to design efficient hybrid beamforming algorithms toimprove spectral efficiency and eliminate SI. The orthogonal matching pursuit(OMP)-based hybrid analog-digital beamforming design, and the alternatingdirection method of multipliers (ADMM)-based schemes are explored to improvethe spectral efficiency and eliminate the SI in this work. Moreover, a fast ADMMenabledhybrid precoding approach with SI cancellation is proposed to achievethe efficient performance and superior convergence compared with the existingschemes, as it is verified by the presented numerical simulations. / Med den enorma tillväxten i den mobila datatrafiken ökar efterfrågan påhög datahastighet snabbt, och högre frekvensresurser ska undersökas för attminska trängseln i det överbefolkade spektrumet, vilket innebär att Volymvågens(mmwave) frekvensresurs, som sträcker sig från 30 GHz till 300 GHz, har erkäntssom en naturlig resurs för den femte generationen (5G) och utanför nätverket.För att kompensera den allvarliga förlusten av tågläge i mmwave-bandet ochför att förverkliga de effektiva sändningarna genom att tillämpa den billigaarkitekturen.Det är av intresse att undersöka strålformningsprogrammen medstorskaliga antennmatriser och strategin för återutläggning av hela duplex (FD),som är oumbärliga för att driva den direkta signal överföringen och det effektivaspektrumutnyttjandet i mmwave-transmissionen.separata antennmatriser är etthuvudhinder för att förverkliga en trådlös nod från FD samtidigt som manöverväger samtidig överföring och mottagning.Syftet med detta avhandlingsprojekt är att utforma effektiva kombineradestrålformningsinformationsalgoritmer för att förbättra spektraleffektiviteten ocheliminera SI. Den ortogonala matchande jakten (OMP)-baserad hybrid analogdigitalstrålformning, och metoden med alternerande riktning för multiplikatorer(ADMM)-baserade system utforskas för att förbättra spektraleffektiviteten ochelimineraSI i det här arbetet. Dessutom föreslås en snabb, adMM-aktiveradhybrid förkonditionering med SI-annullering för att uppnå effektiv prestandaoch överlägset konvergens jämfört med de befintliga systemen, eftersom denkontrolleras av de presenterade numeriska simuleringarna.

In heterogeneous dense networks where spectrum is shared, users' privacy remains one of the major challenges. On a multi-antenna relay-assisted multi-carrier interference channel, each user shares the spectral and spatial resources with all other users. When the receivers are not only interested in their own signals but also in eavesdropping other users' signals, the cross talk on the spectral and spatial channels becomes information leakage. In this paper, we propose a novel secrecy rate enhancing relay strategy that utilizes both spectral and spatial resources, termed as information leakage neutralization. To this end, the relay matrix is chosen such that the effective channel from the transmitter to the colluding eavesdropper is equal to the negative of the effective channel over the relay to the colluding eavesdropper and thus the information leakage to zero. Interestingly, the optimal relay matrix in general is not block-diagonal which encourages users' encoding over the frequency channels. We proposed two information leakage neutralization strategies, namely efficient information leakage neutralization (EFFIN) and local-optimized information leakage neutralization (LOPTIN). EFFIN provides a simple and efficient design of relay processing matrix and precoding matrices at the transmitters in the scenario of limited power and computational resources. LOPTIN, despite its higher complexity, provides a better sum secrecy rate performance by optimizing the relay processing matrix and the precoding matrices jointly. The proposed methods are shown to improve the sum secrecy rates over several state-of-the-art baseline methods.

The master thesis deals with G.fast and G.mgfast transmission technologies, including their parameters. The work deals with the principle of vector DMT modulation and the possibility of time duplex TDD and full-duplex FDX in two-way communication used in these technologies. The following is a description of the line using the KHM model, which is suitable for simulations in the transmission band using G.fast and G.mgfast technologies. Subsequently, the disturbing effects of crosstalk at the near end of NEXT and the far end of FEXT and their elimination with these technologies are discussing. Part of the work explains supporting calculations to determine the SNR and bit allocation to calculate the baud rate. The work describes the methods of compensation of crosstalk FEXT and NEXT, which affect the resulting baud rate. The work also includes an application for simulation of transmission speed as a function of distance for G.fast and G.mgfast technologies, allowing changing input parameters and adjusting the transmission bandwidth based on G.9700 and G.9701 standards. Also, in work, an application is created to display the compensation of the influence of the transmitted signal crosstalk FEXT and NEXT, which allow the import of measured crosstalk between individual participants. The issue of influencing crosstalk for accurate measurements in the laboratory is also discussing. An application in the MATLAB environment is creating to display the measured characteristics.

In heterogeneous dense networks where spectrum is shared, users' privacy remains one of the major challenges. On a multi-antenna relay-assisted multi-carrier interference channel, each user shares the spectral and spatial resources with all other users. When the receivers are not only interested in their own signals but also in eavesdropping other users' signals, the cross talk on the spectral and spatial channels becomes information leakage. In this paper, we propose a novel secrecy rate enhancing relay strategy that utilizes both spectral and spatial resources, termed as information leakage neutralization. To this end, the relay matrix is chosen such that the effective channel from the transmitter to the colluding eavesdropper is equal to the negative of the effective channel over the relay to the colluding eavesdropper and thus the information leakage to zero. Interestingly, the optimal relay matrix in general is not block-diagonal which encourages users' encoding over the frequency channels. We proposed two information leakage neutralization strategies, namely efficient information leakage neutralization (EFFIN) and local-optimized information leakage neutralization (LOPTIN). EFFIN provides a simple and efficient design of relay processing matrix and precoding matrices at the transmitters in the scenario of limited power and computational resources. LOPTIN, despite its higher complexity, provides a better sum secrecy rate performance by optimizing the relay processing matrix and the precoding matrices jointly. The proposed methods are shown to improve the sum secrecy rates over several state-of-the-art baseline methods.

In-band full duplex is a new duplexing scheme that allows radio nodes to transmit and receive, utilizing the same frequency and time resources. The implementation of in-band full duplex was not feasible in practice, due to the effect of self-interference. But then, advances in signal processing made it possible to reduce this effect. However, the system level performance of in-band full duplex has not been investigated thoroughly.Through computer simulations, we investigate the performance of in-band full duplex, for indoor 5G small cell wireless networks. We examine the performance of in-band full duplex in comparison to dynamic and static time division duplexing. Additionally, we analyze the performance of the duplexing schemes with two interference mitigation techniques, namely beamforming and interference cancellation.Our results indicate that for highly utilized wireless networks, in-band full duplex should be combined with beamforming and interference cancellation, in order to achieve a performance gain over traditional duplexing schemes. Only then, in-band full duplex is considered advantageous, at any network utilization, and any downlink to uplink traffic demand proportion. Our results also suggest that in order to achieve a performance gain with in-band full duplex in both links, the transmit power of the access points should be comparable to the transmit power of the mobile stations. / Inomband hel duplex är en ny typ av duplexmetod som tillåter radionoder att sända och ta emot i samma frekvensoch tidsresurs. Att implementera inomband hel duplex har fram tills nu inte ansetts praktiskt genomförbart till följd av självstörningar. Framsteg inom signalbehandling har dock gjort det möjligt att begränsa denna självstörningseffekt. Emellertid har systemprestanda av inomband hel duplex inte undersökts tillräckligt noga i tidigare verk.Inomband hel duplex och dess prestanda för trådlösa 5G småcellsnätverk inomhus har studerats med hjälp av datasimuleringar och jämförts med dynamisk och statisk tidsdelning. Utöver detta har prestanda för de olika duplexmetoderna med avseende på två tekniker för störningsundertryckning, lobformning och störningseliminering, också undersökts.Våra resultat indikerar att för trådlösa nätverk med högt radioresursutnyttjande bör inomband hel duplex kombineras med lobformning och störningseliminering för att uppnå en prestandavinst jämfört med traditionella duplexmetoder. Bara då kan inomband hel duplex anses vara fördelaktig oberoende av radioresursutnyttjande och andelen upp- och nedlänkstrafik.Resultaten tyder också på att sändareffekten för radioaccesspunkterna bör vara jamförbar med den för mobilenheterna för att en prestandavinst med inomband hel duplex ska kunna uppnås. / Wireless networks, In-band full duplex, Static-time division duplexing, Dynamic-time division duplexing, Interference mitigation techniques, small cell, 5G, mmWave bands, Beamforming, Interference cancellation.