Zugl.: Aachen, Techn. Hochsch., Diss.

Spectral efficiency is one of the most important measures of the performance of wireless communication systems owing to scarcity and cost of the radio spectrum. The increase in spectral efficiency provides higher data rates to the user, lower network cost to the operator, coverage extension and higher service reliability as well. Intercell interference due to frequency reuse is one of the key impairments in wireless systems. Multiple-input multiple-output (MIMO) technique has been developed to enhance the desired signal power (and hence mitigating the effects of intercell interference) and with employing simple linear signal processing technique, can strongly mitigate the interference resulting from co-channel users. This technique is mainly used to achieve spatial diversity for boosting the communication link reliability by combating fading, and providing spatial multiplexing to increase data rates without extra bandwidth by exploiting multipath. Distributed antenna system (DAS) has recently gained substantial interest due to its ability to reduce transmitted power thereby lowering the out-of-cell interference effects, maximise the coverage and improve the spectral efficiency. The combination of MIMO techniques with DAS, so-called distributed MIMO (D-MIMO) systems, is now being exploited and largely succeeded to fulfil the services of the fourth generation (4G) wireless systems. Very recently, one of crucial significance approach to reducing the radiated power and improving spectral efficiency to cope with fifth generation (5G) wireless systems is the use of large-scale MIMO (also referred to as massive MIMO) technology, which utilizes a large number of antennas, i.e., tens to hundreds, typically at the base station (BS) side. Presently, in the light of the rapid evolution of wireless systems into 5G, the integration of wireless power transfer (WPT) with newly wireless systems has seen a great deal of attention as a potential solution for powering energy-constrained wireless systems, especially with shortening communication links by emerging new technologies, e.g., D-MIMO and massive MIMO. This thesis is devoted to investigating and comparing the performance of three different MIMO systems. More specifically, the thesis focuses on analysing the spectral efficiency of a comprehensive model of self-powered MU-MIMO systems employing linear ZF technique at the BS for both perfect and imperfect channel state information (CSI) cases. The results demonstrate the impact of practical channel impairments, e.g., spatial correlation, shadowing and co-channel interference (CCI), and system parameters, e.g., the number of BS and user antennas, signal to noise ratio (SNR) and channel estimation error, on the spectral efficiency of the system. Besides, from a spectral efficiency perspective, a proposed model of a combination of MIMO and massive MIMO technologies with DAS in the presence of linear receivers at the processing unit (PU) is considered and compared to a centralised MIMO (CMIMO) system. The obtained results provide a wide range of insights into the effects of system parameters on the spectral efficiency and reveal that the proposed distributed MIMO system outperforms the C-MIMO system. In the context of wireless powered MIMO systems, this work investigates the performance of a power beacon (PB)-assisted wireless powered C-MIMO system, including one multi-antenna BS and a number of single-antenna users powered by randomly deployed PBs in the presence of ZF receiver at the BS. Also, two modes for radiation from the PBs are assumed and compared, one is the beamforming radiation mode (BRM), and the other is the isotropic radiation mode (IRM).

Cette thèse se focalise sur le concept du radar MIMO co-localisé. L'acronyme MIMO -- pour Multiple-Input Multiple-Output -- indique l'utilisation de plusieurs émetteurs et de plusieurs récepteurs, tandis que le terme co-localisé signifie que ces éléments sont étroitement espacés. Chaque émetteur envoie une forme d'onde qui lui est propre : un radar MIMO émet donc simultanément un ensemble de signaux.Cette thèse a ainsi pour but d'établir une méthodologie permettant de générer cet ensemble de signaux, tout en respectant certaines contraintes opérationnelles. Cela nous permettra de déterminer les apports éventuels de ce radar. Nous nous sommes intéressés en particulier aux codes de phase, pour des raisons de couplage (qu'on peut traduire ici par la capacité, lors du traitement, à distinguer la position angulaire d'une cible de sa distance).La méthodologie proposée se synthétise simplement en une modélisation sous la forme d'un problème d'optimisation. Contrairement à la littérature et à des précédents résultats théoriques, nous avons décidé d'évaluer l'orthogonalité des signaux émis par le radar en différentes directions, et non l'orthogonalité des signaux élémentaires. Ce problème, plus réaliste, est malheureusement non-convexe et à grande échelle : un benchmark sur différentes méthodes d'optimisation nous a permis de constater l'efficacité des algorithmes basées sur le gradient.Optimiser cette orthogonalité sous-entend l'utilisation de filtres adaptés. Cependant, en pratique, le traitement radar s'effectue à l'aide de filtres désadaptés. Nous suggérons ainsi un problème d'optimisation jointe, permettant de générer de manière simultanée un ensemble de formes d'onde (pour le radar MIMO, entre autres) et les filtres désadaptés associés. Des simulations ont permis de montrer l'efficacité de la méthode. Celle-ci est en particulier préférable aux algorithmes cycliques habituellement utilisés. / This thesis deals with coherent MIMO radars. MIMO stands for Multiple-Input Multiple-Output, meaning that several transmitters and several receivers are used, closely-spaced in a coherent MIMO radar. Each transmitter has its own signal, providing waveform diversity. This thesis aims for defining a way to generate a set of sequences, specific for this radar, while satisfying practical constraints. It may help to determine the potential contribution of a MIMO radar. Only phase codes are concerned here, because they suffer less from the range/angle coupling effect.A simple framework is introduced, based on an optimisation problem.While literature often involves the orthogonality of the elementary signals (because of theoretical aspects), it is suggested to consider the orthogonality of signals from different directions of the surveillance space. Unfortunately, the obtained optimisation problem is non-convex and has a lot of variables. A benchmark on a simpler problem notifies us that gradient-based algorithms are surprisingly efficient.An optimisation of the correlation function corresponds to a processing with matched filters. However, in practice, mismatched filters are usually employed. A joint optimisation problem is suggested accordingly, in order to generate simultaneously a set of sequences (e.g. MIMO radar signals) and their associated mismatched filters. Obtained results are quite promising : as expected, a joint optimisation seems to perform better than a cyclic one, usually employed.

In this dissertation a computationally efficient cognitive multiple-input multiple-output (MIMO) orthogonal frequency division duplexing (OFDM) detector is designed to decode perfect space-time coded signals which are able maximize the diversity and multiplexing properties of a rich fading MIMO channel. The adaptive nature of the cognitive detector allows a MIMO OFDM communication system to better meet to needs of future wireless communication networks which require both high reliability and low run-time complexity depending on the propagation environment. The cognitive detector in conjunction with perfect space-time coding is able to achieve up to a 2 dB bit-error rate (BER) improvement at low signal-to-noise ratio (SNR) while also achieving comparable runtime complexity in high SNR scenarios.

Smart building's benefits range from improving comfort of occupant, increased productivity, reduction in energy consumption and operating costs, lower CO2 emission, to improved life cycle of utilities, efficient operation of building systems, etc. [65]. Hence, modern building owners are turning towards smart buildings. However, the current smart buildings mostly are not capable of achieving the objectives they are designed for and they can improve a lot better [22]. Therefore, a new technology called, Internet of Things, or IoT, is combined with the smart buildings to improve their performance [23]. IoT is the inter-networking of things embedded with electronics, software, sensors, actuators, and network connectivity to collect and exchange data, and things in this definition is anything and everything around us and even ourselves. Using this technology, e.g. a door can be a thing and can sense how many people have passed it's sensor to enter a space and let the lighting system know to prepare appropriate amount of light, or the HVAC (Heating Ventilation Air Conditioning) system to provide desirable temperature. IoT will provide a lot of useful information that before that accessibility to it was impossible, e.g., condition of water pipes in winter, which helps avoiding damages like frozen or broken pipes. However, despite all the benefits, IoT suffers from being vulnerable to cyber attacks. Examples have been provided later in Chapter 1. In this project among building systems, HVAC system is chosen to be automated with a new control method called MPC (Model Predictive Control). This method is fast, very energy efficient and has a lower than 0.001 rate of error for regulating the space temperature to any temperature that the occupants desire according to the results of this project. Furthermore, a PID (Proportional–Integral–Derivative) controller has been designed for the HVAC system that in the exact same cases MPC shows a much better performance. To design controllers for HVAC system and set the temperature to the desired value a method to automate balancing the heat flow should be found, therefore a thermal model of building should be available that using this model, the amount of heat, flowing in and out of a space in the building disregarding the external weather would be known to estimate. To automate the HVAC system using the programming languages like MATLAB, there is a need to convert the thermal model of the building to a mathematical model. This mathematical model is unique for each building depending on how many floors it has, how wide it is, and what materials have been used to construct the building. This process is needs a lot of effort and time even for buildings with 2 floors and 2 rooms on each floor and at the end the engineer might have done it with error. In this project you will see a software that will do the conversion of thermal model of buildings in any size to their mathematical model automatically, which helps improving the HVAC controllers to set temperature to the value occupants desire and avoid errors and time loss which is put both into calculations and troubleshooting. In addition, a test environment has been designed and constructed as a cyber physical system that allows us to test the IoT- enabled control systems before implementing them on real buildings, observe the performance, and decide if the system is satisfying or not. Also, all cyber threats can be explored and the solutions to those attacks can be evaluated. Even for the systems that are already out there, there is an opportunity to be assessed on this testbed and if there is any vulnerability in case of cyber security, solutions would be evaluated and help the existing systems improve. / Master of Science / Buildings function as shelters more than any thing else, and this has allowed humans to use it as a space to store important things like private and important information. Therefore, this space should be safe and secure from any vulnerabilities for occupants and their information. Smart buildings, have made a great difference in increasing the comfort level of occupants, but they haven’t been greatly successful achieving their objectives [50]. Therefore, a new technology called, Internet of Things, or IoT, is combined with the smart buildings to improve their performance [23]. IoT is the inter-networking of things embedded with electronics, software, sensors, actuators, and network connectivity to collect and exchange data, and things in this definition is anything and everything around us and even ourselves. Internet of Things (IoT) has helped improving the smart buildings and getting a considerable amount of energy efficiency [27]. But adding Internet of Things has added a network of things connected to internet, which gives the cyber hackers an opportunity to hack the buildings, and get access to the information stored inside the building or put even occupants lives in danger. Therefore, in this thesis the following items have been contributed: • Designing and programming a novel control system for HVAC system of the buildings (Model Predictive Control): This is a new method to control HVAC system of buildings and in comparison with the methods available in the market, it is the most energy efficient, it is faster, and it has a lower error rate in following the desired temperature of the occupants. • Design and construction of IoT- enabled smart building testbed: Since cyber attacks make buildings vulnerable, the author believes it is better to build a test environment to simulate the buildings and the control methods that are used inside the buildings, and try to evaluate performance of the control methods before implementing them on real buildings. Also, by installing IoT sensors inside the test environment, the engineers can perform some cyber attack tests, and also evaluate the solutions for each attack on the testbed. • Design and program a software to convert thermal model of buildings to mathematical model : In designing a new control method for HVAC system of buildings, the first required information is the thermal model of the buildings. Eventually, there is a need to program. Thus, the thermal model should be converted to a mathematical model. However, there is a heavy manual calculation behind it that is really overwhelming, tiring, with a high possibility of error, and time-consuming even for a very small sized building. Therefore, automating this process in terms of a software that takes the information of thermal model of buildings as an input and giving the output of the mathematical model of building is a considerable achievement.

This thesis is split into two parts: first a statistical analysis of multi-hop MIMO relay networks, followed by a simulation of the perfomance of a P25 SISO multi-hop relay network. The basis of the MIMO section is the developement of an end to end statistical model of the multiple relay channel. This end to end model simplifies the statistics involved, making the analysis of systems with large numbers of relays and antennas more practical. A partial system model is obtained. This is exact for a multiple input single output network and can be used to describe the received signal at a single antenna in a multiple output system. We go on to look at the relationship between end to end system parameters and the paramters of individual inter-relay channels. The SISO section contains a characterisation of BER for P25 relay chains. The effect of the SNR at each relay node, the nature of the channel and the number of relay hops on the BER is determined. Furthermore, the performance trends are compared for a range of common relaying protocols, including amplify and forward and two types of decode and forward.

The spatial modulation (SM) concept combines, in a novel fashion, digital modulation and multiple antenna transmission for low complexity and spectrally efficient data transmission. The idea considers the transmit antenna array as a spatial constellation diagram with the transmit antennas as the constellation points. To this extent, SM maps a sequence of bits onto a signal constellation point and onto a spatial constellation point. The information is conveyed by detecting the transmitting antenna (the spatial constellation point) in addition to the signal constellation point. In this manner, inter-channel interference is avoided entirely since transmission is restricted to a single antenna at any transmission instance. However, encoding binary information in the spatial domain means that the number of transmit antennas must be a power of two. To address this constraint, fractional bit encoded spatial modulation (FBE—SM) is proposed. FBE–SMuses the theory of modulus conversion to facilitate fractional bit rates over time. In particular, it allows each transmitter to use an arbitrary number of transmit antennas. Furthermore, the application of SM in a multi-user, interference limited scenario has never been considered. To this extent, the average bit error rate (ABER) of SM is characterised in the interference limited scenario. The ABER performance is first analysed for the interference-unaware detector. An interference-aware detector is then proposed and compared with the cost and complexity equivalent detector for a single–input multiple–output (SIMO) system. The application of SM with an interference-aware detector results in coding gains for the system. Another area of interest involves using SM for relaying systems. The aptitude of SM to replace or supplement traditional relaying networks is analysed and its performance is compared with present solutions. The application of SM to a fixed relaying system, termed dual-hop spatial modulation (Dh-SM), is shown to have an advantage in terms of the source to destination ABER when compared to the classical decode and forward (DF) relaying scheme. In addition, the application of SM to a relaying system employing distributed relaying nodes is considered and its performance relative to Dh-SM is presented. While significant theoretical work has been done in analysing the performance of SM, the implementation of SM in a practical system has never been shown. In this thesis, the performance evaluation of SM in a practical testbed scenario is presented for the first time. To this extent, the empirical results validate the theoretical work presented in the literature.

Multiple-InputMultiple-Output (MIMO) systems promise higher data rates and better quality of service for wireless communications, by using multiple antennas at both the transmitter and receiver. However, applying MIMO technology at small portable wireless devices is faced with the problem of mutual coupling between antenna elements due to the limited space to put multiple antennas. It is shown in the literature that the mutual coupling degrades the MIMO performance. For a given channel matrix and a known mutual coupling model, using antenna impedance matching network(s) between the coupled antenna array and its load or source network is proposed by recent studies to counteract the mutual coupling effects and maximise the MIMO performance. There are two issues with the existing matching techniques. First, they employ a model based on open-circuit voltages that separates the channel matrix and the mutual coupling model. This model is not valid except for a limited types of antennas (e.g. half-wavelength dipoles). Secondly, there is no solution among existing approaches that are capable of adapting to variations of the channel matrix. This thesis focuses on the mutual coupling problem at the receiver. We first examine the most common approaches to model the mutual coupling. For instance, we compare various definitions of coupling matrix available in the literature, analyse their relationship and clarify when we can use them. The mutual coupling effects on MIMO performance metrics and impedance matching are also investigated using the conventional open-circuit voltage based model and a new method called receiving mutual impedances. Then we propose the idea of having an adaptive uncoupled impedance matching technique which tunes the antenna impedance loads to compensate the effects of the propagation channel and mutual coupling together by directly dealing with the received signals. The mutual coupling model is unknown, but it is included implicitly by using the voltages across the real parts of the antenna load impedances to estimate the total effects. Assuming identical impedance loads for all receive antennas, several optimisation techniques such as Gradient-based, Newton-Raphson, and random search methods are investigated to implement such an adaptive impedance match. We found the random search method to be a simple and robust solution in comparison to other approaches. Finally, we extend this adaptive matching technique to non-identical termination case, in which all load impedances are tuned individually. The performance of the adaptive matching networks are compared with the conventional termination scenarios such as: characteristic impedance match, and self-impedance conjugate match. Simulation results for a 3 × 3 MIMO system under different propagation scenarios show that both identical and non-identical adaptive impedance matching networks are capable of optimising the performance in the presence of strong mutual coupling and time variations of the channel. The adaptive non-identical match gives a significant improvement in the mean capacity (more than 20% compared to conventional terminations for 0.05λ element separation) at the expense of a longer convergence time compared to the identical match.

Over the past decade, wireless sensor networks have gained more research attention for their potential applications in healthcare, defense, environmental monitoring, etc. Due to the strict energy limitation in the sensor node, techniques used for energy saving are necessary for this kind of network. MIMO technology is proven to be an effective method of increasing the channel capacity and supporting higher data rate under a fixed power budget and bit-error-rate requirement. So, wireless sensor networks and MIMO technology are combined and investigated in this thesis. The key contributions of this thesis are detailed below. Firstly, the extended total energy consumption equations for different transmission modes in cluster-based wireless sensor networks are derived. The transmitting energy consumption and the circuit energy consumption are taken into account in both intra-cluster and inter-cluster phases respectively. Secondly, a resource allocation framework is proposed for cluster-based cooperative MIMO on consideration of circuit energy. By introducing two adjusting parameters for the transmitting energy and the time slot allocation between intra-cluster and inter-cluster phases, this framework is designed to achieve the maximum data throughput of the whole system whilst maintaining the capacity and outage probability requirement in these two phases respectively. Thirdly, on comparison of various transmission modes in wireless sensor networks, a relatively energy-efficient mode switching framework is proposed for both single-hop and multi-hop transmissions. Based on the destination and the neighboring nodes’ path-loss, the source node can decide which transmission mode, SISO or cooperative MISO, single-hop or multi-hop, should be chosen. Conditions for each mode switching are investigated. The possible existing area of the cooperative nodes and the relaying nodes can be obtained from this framework.

Approved for public release; distribution unlimited / This thesis investigates the fundamentals of Multiple-Input-Multiple-Output (MIMO) radio communication systems with space-time codes. A MIMO system was design using the Alamouti space-time code. The modulation technique was binary phase-shift keying (BPSK). Matlab with Simulink was used to simulate the design, which was tested in both an additive white Gaussian noise (AWGN) channel and in a multipath fading channel with AWGN. Theoretical performance was derived for both channels and compared to simulated results. The original receiver design was changed to incorporate a maximal-ratio combiner (MRC) receiving technique with channel state information (CSI). The theoretical performance for this design was determined and compared to simulated and published results. / Lieutenant Commander, Canadian Navy