This thesis looks at new methods of achieving reliable data communication in wireless communication systems using different antenna transmission optimization methods. In particular, the problems of exploitation of MIMO communication channel diversity, secure downlink beamforming techniques, adaptive beamforming techniques, resource allocation methods, simultaneous power and information transfer and energy harvesting within the context of multi-antenna wireless systems are addressed.

In this thesis, multicell coordination for wireless cellular networks is studied, whereby various approaches have been conducted to tackle this issue. Firstly, the coverage probability and e ective capacity in downlink multiple-input multiple-output (MIMO) cellular system are considered. Two scenarios are investigated; in the rst scenario, it is assumed that the system employs distance-based fractional power control with no multicell coordination. For the second scenario, it is assumed that the system implements multicell coordinated beamforming so as to cancel inter-cell interference. The base stations (BS) are modelled as randomly uniformly distributed in the area according to Poisson point process (PPP). Using tools from stochastic geometry, tractable, analytical expressions for coverage probability and e ective capacity are derived for both scenarios. Secondly, an adaptive strategy for inter-cell interference cancellation and coordination is proposed for downlink multicarrier cellular random networks. The adaptive strategy coordinates and cancels the interference on the both frequency and spatial domains. Based on this adaptive strategy, two interference management schemes have been proposed. The adaptation process is implemented based on measured instantaneous signal-to-interference and noise ratio (SINR) of the considered user. Furthermore, the locations of base stations BSs are modelled as an independent spatial PPP. Using tools from stochastic geometry, the proposed schemes have been analytically evaluated. Analytical expressions for coverage probability are derived for both schemes. In addition, an expression for average rate has been derived using the coverage probability analysis. Thirdly, low complexity algorithms for user scheduling have been proposed for coordinated MIMO multicell network. The algorithms consist of two stages: multicell scheduling stage and precoding stage. The algorithm works on sequential distributive manner. Two variants of multicell scheduling are proposed. The rst algorithm has less complexity but leads to more di erence in sum rate among cells. While the second algorithm results in better fairness in terms of system performance but causes frequent signalling among the cells. Moreover, the algorithm is extended to multimode selection in addition to the user selection. Finally, an adaptive coordination scheme for energy-effeicient resource allocation has been developed for orthogonal frequency division multiple access (OFDMA) cellular networks. The proposed scheme consists of centralised and distributed stages for allocating resources to cell-edge and cell-centre users, respectively. The optimisation problems are formulated as integer linear fractional and integer linear problems for the first stage and second stages, respectively. The spectral-energy trade-o is analysed under the constraint of fairness among users. In summary, the research work presented in this thesis reveals statistical approach to analyse the multicell coordination in random cellular networks. It also offers insight into the resource allocation and scheduling problems within multicell coordination framework, and how to solve them with a certain objective.

Managing interference is the main technical challenge in wireless networks. Multiple input multiple output (MIMO) methods are key components to overcome the interference bottleneck and deliver higher data rates. The most efficient MIMO techniques require channel state information (CSI). In practice, this information is inaccurate due to errors in CSI acquisition, as well as mobility and delay. CSI inaccuracy reduces the performance gains provided by MIMO. When compounded with uncoordinated intercell interference, the degradation in MIMO performance is accentuated. This dissertation investigates the impact of CSI inaccuracy on the performance of increasingly complex interference limited networks, starting with a single interferer scenario, continuing to a heterogeneous network with a femtocell overlay, and finishing with a clustered multicell coordination model for randomly deployed transmitting nodes. First, this dissertation analyzes limited feedback beamforming and precoded spatial multiplexing over temporally correlated channels. Assuming uncoordinated interference from one dominant interferer, using Markov chain convergence theory, the gain in the average successful throughput at the mobile user is shown to decrease exponentially with the feedback delay. The decay rate is amplified when the user is interference limited. Interference cancellation methods at the receiver are shown to mitigate the effect of interference. This work motivates the need for practical MIMO designs to overcome the adverse effects of interference. Second, limited feedback beamforming is analyzed on the downlink of a more realistic heterogeneous cellular network. Future generation cellular networks are expected to be heterogeneous, consisting of a mixture of macro base stations and low power nodes, to support the increasing user traffic capacity and reliability demand. Interference in heterogeneous environments cannot be coordinated using traditional interference mitigation techniques due to the on demand and random deployment of low power nodes such as femtocells. Using tools from stochastic geometry, the outage and average achievable rate of limited feedback MIMO is computed with same-tier and cross-tier interference, and feedback delay. A hybrid fixed and random network deployment model is used to analyze the performance in a fixed cell of interest. The maximum density of transmitting femtocells is derived as a function of the feedback rate and delay. The detrimental effect of same-tier interference is quantified, as the mobile user moves from the cell-center to the cell-edge. The third part of this dissertation considers limited coordination between randomly deployed transmitters. Building on the established degrading effect of uncoordinated interference on practical MIMO methods, and the analytical tractability of random deployment models, interference coordination is analyzed. Using multiple antennas at the transmitter for interference nulling in ad hoc networks is first shown to achieve MIMO gains using single antenna receivers. Clustered coordination is then investigated for cellular systems with randomly deployed base stations. As full coordination in the network is not feasible, a random clustering model is proposed where base stations located in the same cluster coordinate. The average achievable rate can be optimized as a function of the number of antennas to maximize the coordination gains. For multicell limited feedback, adaptive partitioning of feedback bits as a function of the signal and interference strength is proposed to minimize the loss in rate due to finite rate feedback. / text

Abstract Uplink resource allocation strategies in modern cellular networks are studied in this thesis. With the presence of multiple antenna transmission, multiple base station (BS) coordination and multicarrier techniques, the resource allocation problem is reformulated and jointly optimized over a large set of variables. The focus is on the sum power minimization with per user rate constraints. A centralized multicarrier coordinated cellular network with multiple antennas implemented at the BS side is considered, where BSs can be adaptively clustered to detect signals from one mobile station (MS). The power, subcarrier, beamforming vector and BS cluster (BSC) are the design variables to be jointly optimized to satisfy the rate constraint per user. The first considered scenario is a simple single carrier multicell system. The power control problem with per user rate constraint can be optimally solved by the proposed algorithm, where power vector, BSC and beamforming vectors are separately updated until the sum power converges. The scenario is extended to more complicated multicarrier systems. The resource allocation problem is non-deterministic polynomial-time hard (NP-hard). Suboptimal algorithms are proposed to tackle the problem. To get more insights to the performance gap between the proposed algorithms and the capacity achieving bound, the scenario is specified to a single cell system with nonlinear receiver so that the calculation of the lower bound is possible. Efficient geometric aided fast converging power minimization algorithms are proposed to calculate the power bound of the multiple access channel (MAC) with per user rate constraint. By comparing the capacity achieving lower bound with the proposed algorithm, the BSW that starts from full rate allocation looks promising to have a good tradeoff between the convergence speed and the sum power consumption. Besides the resource allocation algorithms in the cellular network, the physical modeling and corresponding design of the network itself are also considered. The radio propagation in the elevation domain is modeled and considered. The diversity gain from the elevation domain is achieved by extra degree of freedom of beamforming in elevation domain. The antenna array can be either a uniform linear array or a uniform planar array with elements placed horizontally. The proposed power control algorithms are simulated in the 3D network scenarios. The effects of antenna array design in different propagation scenarios are compared. / Tiivistelmä Työssä tutkitaan ylälinkin resurssien kohdentamisstrategioita matkapuhelinverkoissa. Olettaen koordinointi useiden monikantoaaltotekniikoita käyttävien moniantennitukiasemien (BS) välillä, resurssien kohdentamisongelma muotoillaan uudelleen ja optimoidaan yli suuren joukon optimointimuuttujia. Erityisesti keskitytään yhteenlasketun tehon minimointiongelmaan käyttäjäkohtaisien siirtonopeusrajoitteiden kanssa. Työssä oletetaan keskitetty koordinointi useiden monikantoaaltotekniikoita käyttävien moniantennitukiasemien välillä, joten tukiasemat voidaan adaptiivisesti ryhmitellä yhden matkaviestimen signaalin havannointia varten. Lähetysteho, kantoaaltoallokaatio, keilanmuodostus ja tukiasemaklusterointi ovat ongelman muuttujia, jotka optimoidaan yhdessä siten, että käyttäjäkohtaiset siirtonopeusrajoitteet täyttyvät. Ensimmäinen käsitelty tapaus on yksinkertainen yhden operaattorin monisolujärjestelmä. Tehonsäätöongelma käyttäjäkohtaisten siirtonopeusrajoitusten kanssa voidaan optimaalisesti ratkaista ehdotetulla algoritmilla, jossa lähetysteho, keilanmuodostusvektorit ja tukiasemaklusterointi päivitetään erikseen, kunnes yhteenlaskettu teho suppenee. Tarkastelu laajennetaan monimutkaisempaan monikantoaaltojärjestelmään. Kun käyttäjäkohtainen siirtonopeustavoite kiinnitetään, ongelma voidaan vastaavasti hajottaa osittaisiksi alikantoaaltokohtaisiksi osaongelmiksi, jossa kukin osaongelma voidaan optimaalisesti ratkaista. Jos alikantoaaltokohtaista siirtonopeustavoitetta ei ole kiinnitetty, tehonsäätöongelmasta tulee ei-polynomisesti monimutkainen. Optimaalisia algoritmeja ehdotetaan ongelman ratkaisemiseksi. Jotta voitaisiin saada tietoa todellisesta suorituskykyerosta ehdotettujen algoritmien ja kapasiteettioptimaalisen rajan välillä, vertailu tehdään yhden solun simulointimallissa epälineaarisen vastaanottimen kanssa siten, että kapasiteettioptimaalisen alarajan laskeminen on mahdollista. Tätä varten kehitetään tehokas geometria-avusteinen ja nopeasti konvergoituva algoritmi tehon minimointia varten käyttäjäkohtaisten siirtonopeusrajoitusten kanssa. Vertaamalla kapasiteettioptimaalista alarajaa ehdotettujen algoritmien suorituskykyyn huomataan, että ehdotettu BSW algoritmi on hyvä kompromissi konvergoitumisnopeuden ja tehonkulutuksen välillä. Matkapuhelinverkkojen resurssienkohdentamisalgoritmien lisäksi työssä huomioidaan myös verkon fyysinen mallintaminen ja vastaava suunnittelu. Työssä mallinnetaan radiokanavan ominaisuudet myös korkeustasossa, joka mahdollistaa diversiteetin hyödyntämisen korkeustason keilanmuodostuksessa. Antenniryhmä voi olla joko yhtenäinen lineaarinen ryhmä tai yhtenäinen tasoryhmä, jossa antennielementit on sijoitettu tasoon. Ehdotettuja tehonsäätöalgoritmeja simuloidaan kolmiulotteisessa verkkoskenaarioissa, jossa verrataan antenniryhmäsuunnittelun vaikutuksia eri radiokanavaskenaarioissa.