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Today, wireless communications are an essential part of our everyday life. Both the number of users and their demands for wireless data have increasedtremendously during the last decade. Multiantenna communicationsis a promising solution to meet this ever-growing traffic demands. However, impairments that exist in most practical communication networks may substantially limit the performance of a multiantenna system. The characterizationof such a performance loss and how to minimize that are still largelyopen problems. The present thesis addresses this important research gap. Inparticular, we focus on three major impairments of a multiantenna cellularnetwork: impairment in the channel state information (CSI), interference andimpairment in the transceiver hardware components.To fully realize the benefits of multiantenna communications, the users need to acquire a certain level of information about their propagation environment; that is, their corresponding CSI. In practice, the CSI is not known bythe users and should be acquired by allocating part of the network resourcesfor pilot transmission. This problem is mainly important in the systems with a large number of antennas, as in general the required network resources for CSI acquisition scales with the number of transmitting antennas. Theproblem of CSI acquisition in a single-cell multiuser multiple-input multipleoutput(MIMO) system is addressed in this thesis. A linear spatial precodingand combining scheme for pilot transmission is proposed. This scheme requiresless number of network resources for channel estimation compared tothe conventional schemes. The gains of the proposed scheme are characterized by finding an upper-bound and a lower-bound on the channel estimation error.Moreover, as an ultimate performance metric, an achievable sum-rate ofthe network is formulated and analyzed numerically.Due to the broadcast nature of the wireless channels, the performanceof the users in a network is intertwined; the desired signal of one user mayinterfere other users. Hence, the interference is another major impairment inwireless communication systems. In this thesis, the practical challenges of aninterference management technique, namely MIMO interference alignment isinvestigated by implementation on a multiuser MIMO testbed. Then, in thecontext of interference alignment, the problem of optimal power allocation forpilot and data transmission is studied and verified by the measurements.The impairment in the hardware components of the transceivers, that is, any deviation of the components from their ideal behavior, degrades the performance of a communication system. In particular, the impact of nonlineartransmitter power amplifiers (PA)s is investigated in this thesis. First, consideringa memoryless third-order polynomial model for the PAs, a model forthe transmitted nonlinear distortion signal from a multiantenna transmitter isproposed and validated by measurements. This model implies that the spatialdirection of the transmitted distortion is dependent on the spatial directionof the desired signal. Then, this model is extended for a general arbitrary order polynomial model. Exploiting the developed distortion model, the energyefficiency of a multiantenna system operating at millimeter wave frequenciesis studied. / <p>QC 20170523</p>

This thesis presents a technique for the detection of spread spectrum signals, of arbitrary form, even when the signal power spectral density (PSD) is well below the surveillance receiver noise spectral density, using a pair of antennas with broadband (1 GHz or more) receivers. Cross correlating the outputs of two receivers, spatially separated by a distance of the order of one metre or more, produces a cross correlation function (ccf) in which the noise components are spread uniformly over the whole width while the signal component, the narrow autocorrelation function (acf) of the spread spectrum signal, is concentrated near to the centre. The acf is displaced from the centre of the ccf by a small time shift equal to the time difference of arrival of the signal at the two antennas. A simple time domain filter can select a narrow centre portion of the ccf, rejecting the remainder which contains only noise. Taking the Fourier transform of this windowed ccf produces the &quot;time domain filtered cross spectral density&quot; (TDFCSD), in which the signal to noise ratio is independent of receiver bandwidth. Spread spectrum signals can then be both detected and characterised in an extremely sensitive broadband system by threshold detection applied to the magnitude of this TDFCSD. High resolution direction fmding can then be achieved by estimating the time difference of arrival at the two antennas from the phase slope of the appropriate part of the TDFCSD. An analysis of the performance of this dual receiver system is presented. A computer simulation illustrates the signal processing involved and shows excellent agreement with the analysis. An analysis of the detection performance of this system acting in an electronic support measure (ESM) role and comparison with other systems shows that, in addition to being able to obtain more information, this system can offer significantly greater sensitivity than a crystal video receiver. Acousto-optic correlation may be used to perform the cross correlation and time domain filtering of wideband signals in real time, with final processing of the much reduced data set to obtain and analyse the TDFCSD being carried out digitally. A novel non-heterodyning space integrating architecture capable of forming the true correlation function using the zeroth diffraction orders from acousto-optic cells was invented, the operation of which is not explained by the commonly used methods of analysis. By looking again at the acousto-optic interaction, it is shown that there is considerable information in the zeroth diffraction order and a unified theory of one dimensional space integrating correlators is developed, in which many known architectures can be treated as special cases of a general all order correlator. Because of practical difficulties in using a space integrating correlator to obtain the TDFCSD for continuous inputs, later work concentrated on time integrating correlation. Theoretical analysis and practical results are presented for a time integrating acousto-optic correlator, demonstrating that it gives itself naturally to the signal processing operations required and could be used in a real surveillance system making use of the TDFCSD for detection and direction finding.