In this thesis, two-dimensional (2-D) direction-of-arrival (DOA) estimation problem is considered. Usually, DOA estimation is considered in one dimension assuming a fixed elevation angle. While this assumption simplifies the problem, both the azimuth and elevation angles, namely, the 2-D DOA estimates are required in practical scenarios. In this thesis, planar array structures are considered for 2-D DOA estimation. In this context, V-shaped arrays are discussed and some of the important features of these arrays are outlined. A new method for the design of V-shaped arrays is presented for both isotropic and directional beam patterns. The design procedure is simple and can be applied for both uniform and nonuniform V-shaped sensor arrays. Closed form expressions are presented for the V-angle in order to obtain isotropic angle performance. While circular arrays have the isotropic characteristics, V-shaped arrays present certain advantages due to their large aperture for the same number of sensors and inter-sensor distance. The comparison of circular and V-shaped arrays is done by considering the azimuth and elevation Cramer-Rao Bounds (CRB). It is shown that V-shaped and circular arrays have similar characteristics for the sensor position errors while the uniform isotropic (UI) V-array performs better when there is mutual coupling and the sources are correlated. In the literature, there are several techniques for 2-D DOA estimation. Usually, fast algorithms are desired for this purpose since a search in two dimensions is a costly process. These algorithms have a major problem, namely, the pairing of the azimuth-elevation couples for multiple sources. In this thesis, a new fast and effective technique for this purpose is proposed. In this technique, a virtual array output is generated such that when the ESPRIT algorithm is used, the eigenvalues of the rotational transformation matrix have the 2-D angle information in both magnitude and phase. This idea is applied in different scenarios and three methods are presented for these cases. In one case, given an arbitrary array structure, array interpolation is used to generate the appropriate virtual arrays. When the antenna mutual coupling is taken into account, a special type of array structure, such as circular, should be used in order to apply the array interpolation. In general, the array mutual coupling matrix (MCM) should have a symmetric Toeplitz form. It is shown that the 2-D DOA performance of the proposed method approaches to the CRB by using minimum number of antennas in case of mutual coupling. This method does not require the estimation of the mutual coupling coefficients. While this technique is effective, it has problems especially when the number of sources increases. In order to improve the performance, MCM is estimated in the third approach. This new approach performs better, but it cannot be used satisfactorily in case of multipath signals. In this thesis, the proposed idea for fast 2-D DOA estimation is further developed in order to solve the problem when mutual coupling and multipath signals jointly exist. In this case, real arrays with some auxiliary sensors are used to generate a structured mutual coupling matrix. It is shown that the problem can be effectively solved when the array structure has a special form. Specifically, parallel uniform linear arrays (PULA) are employed for this purpose. When auxiliary sensors are used, a symmetric banded Toeplitz MCM is obtained for the PULA. This allows the application of spatial smoothing and ESPRIT algorithm for 2-D DOA estimation. The proposed algorithm uses triplets and presents closed form paired 2-D DOA estimates in case of unknown mutual coupling and multipath signals. Several simulations are done and it is shown that the proposed array structure and the method effectively solve the problem.

PN code tracking plays a very important role in CDMA communication systems. In literature, the influences of multipath fading and of multiuser interference on PN code tracking are studied separately. The multipath fading influence is mitigated by combining a rake receiver and a channel estimator in the Delay-Locked Loop (DLL). The multiuser interference is overcome by incorporating a data estimator into the DLL. In the downlink, PN code tracking may suffer from the multipath fading influence. However, the multipath fading and the multiuser interference influences exist in the uplink. Unfortunately, sole use of the aforementioned methods cannot solve out both influences simultaneously. In this thesis, two new Coherent Decision-Directed Delay-Locked Loop (CDD-DLL) PN-Code tracking schemes are developed and either can overcome both influences. First, a channel and a data estimators are incorporated into the DLL inherent with a rake receiver. This new scheme works properly in an environment with multipath fading and multiuser interference. Second, the original CDD-DLL is combined with a multipath interference canceller (MPI) to reduce both influences. Analytical results are derived for the two schemes proposed and are validated with numerical simulations. Simulation results show that the conventional DLLs working in a multipath fading and multiuser interference environment can be significantly improved using the new schemes. Moreover, the latter outperforms the former because the multipath interference is cancelled completely.

Traditional routing protocols select paths based on static link weights and converge to new paths only when there is an outright reachability failure (such as a link or router failure). This design allows routing scale to hundreds of thousands of nodes, but it comes at the cost of functionality: routing provides only simple, single path connectivity. Networked applications in the wide-area, enterprise, and data center can all benefit from network protocols that allow traffic to be sent over multiple routes en route to a destination. This ability, also called multipath routing, has other significant benefits over single-path routing, such as more efficiently using network resources and recovering more quickly from network disruptions. This dissertation explores the design of an architecture for path selection in the network and proposes a "narrow waist" interface for networks to expose choice in routing traffic to end systems. Because most networks are also business entities, and are sensitive to the cost of routing traffic in their network, this dissertation also develops a framework for exposing paths based on their cost. For this purpose, this dissertation develops a cost model for routing traffic in a network. In particular, this dissertation presents the following contributions: * Design of path bits, a "narrow waist" for multipath routing. Our work ties a large number of multipath routing proposals by creating an interface (path bits) for decoupling the multipath routing protocols implemented by the network and end systems (or other network elements) making a choice for path selection. Path bits permit simple, scalable, and efficient implementations of multipath routing protocols in the network that still provide enough expressiveness for end systems to select alternate paths. We demonstrate that our interface is flexible and leads to efficient network implementations by building prototype implementations on different hardware and software platforms. * Design of path splicing, a multipath routing scheme. We develop, path splicing, a multipath routing technique, which uses random perturbations from the shortest path to create exponentially large number of paths with only a linear increase in state in a network. We also develop a simple interface to enable end systems to make path selection decisions. We present various deployment paths for implementing path splicing in both intradomain and interdomain routing on the Internet. * Design of low cost path-selection framework for a network. Network operators and end systems can have conflicting goals, where the network operators are concerned with saving cost and reducing traffic uncertainty; and end systems favor better performing paths. Exposing choice of routing in the network can thus, create a tension between the network operators and the end systems. We propose a path-selection framework where end systems make path selection decisions based on path performance and networks expose paths to end systems based on their cost to the network. This thesis presents a cost model for routing traffic in a network to enable network operators to reason about "what-if " scenarios and routing traffic on their network.

GNSS-Messungen werden neben systembedingten Fehlereinflüssen vor allem von den Auswirkungen der Mehrwegeausbreitung und Signalbeugung insbesondere in der Empfangsumgebung dominiert. Verschiedene Dienste z.B. der Landesvermessungsämter haben deshalb ein primäres Interesse daran, die Auswirkungen der Effekte möglichst gering zu halten oder aber genau bestimmen zu können, um Korrekturwerte zu generieren. Mehrwege- und Beugungseffekte lassen sich besonders innerhalb von Netzstrukturen gut bestimmen. Liegen Sollkoordinaten aller Beobachtungsstationen vor gelingt dies auch in Echtzeit. In der vorliegenden Arbeit werden neben einer detaillierten Beschreibung der jeweiligen Einflussgrößen auch Möglichkeiten aufgezeigt, die genannten Effekte zu erkennen und Maßnahmen zur Reduktion der Auswirkungen auf das Meßergebnis zu ergreifen. Kern der Untersuchungen ist ein zweistufiges Modell zur Reduzierung von Mehrwegeeffekten in Echtzeit innerhalb von (Referenz-) Stationsnetzen durch Bestimmung von Korrekturwerten für originale und abgeleitete Meßwerte pro Epoche, Station und Satellit.

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The continuous advancement in wireless communications technology demands new approaches to improving the capacity of existing radio links. The high data throughput required can be achieved by the complete utilization of space, time and polarization diversities inherent in any propagation environment. Among the different propagation scenarios, the indoor channels represent a particularly challenging problem given the number and complexity of interactions between the transmitted signal and the environment. This dissertation explores the interrelation between propagation physics and space-time-polarization diversity based on a novel high resolution channel sounding and reconstruction technique. First, a method to reconstruct the indoor complex channel response based on a limited set of samples and the elimination of the interference using deconvolution techniques is presented. Then, the results for the joint angle-of-arrival, delay characterization and depolarization of electromagnetic waves are presented. Finally, a novel approach to using depolarized multipath signals to boost the receiver signal-to-noise performance is presented. The current study shows that full utilization of the diversities of channel novel wireless systems can be proposed with significant improvement in capacity.

Multipath amplifier theory: In this thesis it is proven that the theoretical minimum noise measure of a multipath amplifier (an amplifier which has multiple parallel amplifiers) is achieved by using the optimum source impedance for the amplifier and the optimum gain for each amplification path. This optimum source impedance and gain can be calculated by using the optimum–loaded input network, i.e. by replacing each amplifier with its optimum source impedance. The resulting noise measure is the same as the minimum noise measure of the amplifiers used in the amplification paths. Whereas single–path amplifiers can achieve this minimum noise measure over narrow bandwidths, multipath amplifiers are theoretically able to achieve the minimum noise measure over very broad bandwidths. The theory is demonstrated by applying it to distributed amplifiers. In an ideal distributed amplifier, the magnitude of the optimum gain of the amplification paths decreases and the phase delay increases the farther the stage is from the input, with the decrease in gain being faster for higher frequencies. The challenge in designing broadband, low–noise, distributed amplifiers is to achieve optimum gain matching over broad bandwidths. Multipath amplifier design procedure: Based on the theory, a three step design and optimisation procedure is introduced. Firstly, unconditionally stable amplification paths are designed to have small minimum noise measures, then an input network is designed for optimum source impedance matching and lastly an output network is designed for gain matching. Multipath amplifier prototype: The theory and design procedure is demonstrated by optimising a 0.5–2 GHz distributed amplifier. An average noise measure of 0.3 dB is achieved, which is only 0.1 dB higher than the minimum noise measure of the amplification stages used. This increase is mainly due to transmission line loss and gain mismatch. Radio telescope feasibility: Multipath amplifiers break the trade–off between noise temperature, bandwidth and source termination that a single–path amplifier has, because they have much more design freedom when designing the input network. In general, the more paths, the larger the low–noise bandwidth, but the larger and more complex the amplifier. Roughly two to three amplification paths are required per octave of bandwidth for LNAs around 1 GHz. When the bandwidth is very narrow, a single path is sufficient. Multipath amplifiers have similar trade–offs between linearity and power consumption, between noise temperature and noise resistance, and between noise temperature and size to a single–path amplifier. Multipath amplifiers are therefore a feasible alternative for use in radio telescopes. / Thesis (Ph.D. (Space Physics))--North-West University, Potchefstroom Campus, 2011.

The continuous advancement in wireless communications technology demands new approaches to improving the capacity of existing radio links. The high data throughput required can be achieved by the complete utilization of space, time and polarization diversities inherent in any propagation environment. Among the different propagation scenarios, the indoor channels represent a particularly challenging problem given the number and complexity of interactions between the transmitted signal and the environment. This dissertation explores the interrelation between propagation physics and space-time-polarization diversity based on a novel high resolution channel sounding and reconstruction technique. First, a method to reconstruct the indoor complex channel response based on a limited set of samples and the elimination of the interference using deconvolution techniques is presented. Then, the results for the joint angle-of-arrival, delay characterization and depolarization of electromagnetic waves are presented. Finally, a novel approach to using depolarized multipath signals to boost the receiver signal-to-noise performance is presented. The current study shows that full utilization of the diversities of channel novel wireless systems can be proposed with significant improvement in capacity.

Multipath amplifier theory: In this thesis it is proven that the theoretical minimum noise measure of a multipath amplifier (an amplifier which has multiple parallel amplifiers) is achieved by using the optimum source impedance for the amplifier and the optimum gain for each amplification path. This optimum source impedance and gain can be calculated by using the optimum–loaded input network, i.e. by replacing each amplifier with its optimum source impedance. The resulting noise measure is the same as the minimum noise measure of the amplifiers used in the amplification paths. Whereas single–path amplifiers can achieve this minimum noise measure over narrow bandwidths, multipath amplifiers are theoretically able to achieve the minimum noise measure over very broad bandwidths. The theory is demonstrated by applying it to distributed amplifiers. In an ideal distributed amplifier, the magnitude of the optimum gain of the amplification paths decreases and the phase delay increases the farther the stage is from the input, with the decrease in gain being faster for higher frequencies. The challenge in designing broadband, low–noise, distributed amplifiers is to achieve optimum gain matching over broad bandwidths. Multipath amplifier design procedure: Based on the theory, a three step design and optimisation procedure is introduced. Firstly, unconditionally stable amplification paths are designed to have small minimum noise measures, then an input network is designed for optimum source impedance matching and lastly an output network is designed for gain matching. Multipath amplifier prototype: The theory and design procedure is demonstrated by optimising a 0.5–2 GHz distributed amplifier. An average noise measure of 0.3 dB is achieved, which is only 0.1 dB higher than the minimum noise measure of the amplification stages used. This increase is mainly due to transmission line loss and gain mismatch. Radio telescope feasibility: Multipath amplifiers break the trade–off between noise temperature, bandwidth and source termination that a single–path amplifier has, because they have much more design freedom when designing the input network. In general, the more paths, the larger the low–noise bandwidth, but the larger and more complex the amplifier. Roughly two to three amplification paths are required per octave of bandwidth for LNAs around 1 GHz. When the bandwidth is very narrow, a single path is sufficient. Multipath amplifiers have similar trade–offs between linearity and power consumption, between noise temperature and noise resistance, and between noise temperature and size to a single–path amplifier. Multipath amplifiers are therefore a feasible alternative for use in radio telescopes. / Thesis (Ph.D. (Space Physics))--North-West University, Potchefstroom Campus, 2011.

Backscatter radio - the broad class of systems that communicate using scattered electromagnetic waves - is the driving technology behind many compelling applications such as radio frequency identification (RFID) tags and passive sensors. These systems can be used in many ways including article tracking, position location, passive temperature sensors, passive data storage, and in many other systems which require information exchange between an interrogator and a small, low-cost transponder with little-to-no transponder power consumption. Although backscatter radio is maturing, such systems have limited communication range and reliability caused, in part, by multipath fading. The research presented in this dissertation investigates how multipath fading can be reduced using multiple antennas at the interrogator transmitter, interrogator receiver, and on the transponder, or RF tag. First, two link budgets for backscatter radio are presented and fading effects demonstrated through a realistic, 915 MHz, RFID-portal example. Each term in the link budget is explained and used to illuminate the propagation and high-frequency effects that influence RF tag operation. Second, analytic envelope distributions for the M x L x N, dyadic backscatter channel - the general channel in which a backscatter system with M transmitter, L RF tag, and N receiver antennas operates - are derived. The distributions show that multipath fading can be reduced using multiple-antenna RF tags and by using separate transmitter and receiver antenna arrays at the interrogator. These results are verified by fading measurements of the M x L x N, dyadic backscatter channel at 5.8 GHz - the center of the 5725-5850 MHz unlicensed industrial, scientific, and medical (ISM) frequency band that offers reduced antenna size, increased antenna gain, and, in some cases, reduced object attachment losses compared to the commonly used 902-928 MHz ISM band. Measurements were taken with a custom backscatter testbed and details of its design are provided. In the end, this dissertation presents both theory and measurements that demonstrate multipath fading reductions for backscatter-radio systems that use multiple antennas.