<p>The WCDMA air interface, used in the third generation mobile communication systems, is currently being evolved to improve the uplink, i.e. the radio links carrying traffic from the mobile user to the fixed network. An enhanced uplink concept is being developed to meet the expected needs from future applications like multimedia and video-streaming. This thesis studies interference management when high bit rates are introduced in the enhanced uplink. The study is performed through theoretical assessments and simulations using WCDMA system simulators.</p><p>An optimization scheme using a basic system throughput based scheduling is derived to attain a theoretical assessment of bit rate limits. The throughput optimization is achieved at the expense of user-experienced fairness. Users located on cell coverage area overlap show to be most complicated to manage.</p><p>The need for interference management is primary when the network deployment consists of small cells while coverage requirements are most essential when the cell size increases. By exploiting the benefits of directional antennas the antenna tilt can be tuned to increase performance resulting in increased bit rates, increased system throughput and increased resource efficiency. The improvements are attained without trade-offs and the different components of the study concur unanimously.</p>

<p><b>Keywords </b>: <i>Conjugate gradient fast Fourier transform (CG-FFT), Discrete complex image method (DCIM), Electric field integral equation (EFIE), Frequency selective surfaces (FSS), Generalized pencil-of-functions (GPOF), Green’s function (GF), Method of moments (MoM), Prony’s method (PM), Sommerfeld integral (SI), Two-dimensional generalized exponential integral (2D-GEI)</i></p><p>As the need for more frequency spectrum drives the design of antennas and other microwave components at higher frequencies, compact but electrically large microwave components are beginning to appear. Since a significant share of these components comprises scatterers etched on planar stratified layers, efficient tools analyzing and optimizing such structures are invaluable. The work carried out here is in fact a continuation of the research performed in the past at the Department of Electronics and Telecommunications at the Norwegian University of Science and Technology in Trondheim, Norway.</p><p>The conventional method of moments for analyzing and optimizing scatterers in stratified media is simple in formulation but computationally very intensive. Moreover, the computer memory usage of the software based on conventional MoM is high. Both these factors have so far limited the application of conventional MoM to electrically small and simpler stratified structures. Therefore, the present work focuses on introducing and implementing an improved space domain MoM for large radiating or scattering structures etched on planar stratified media. The space domain method of moments is selected due to its simplicity and potential for further improvements when compared with the spectral domain method of moments.</p><p>The major areas of space domain MoM such as finding spectral Green's functions, deriving spatial Green’s functions, matrix formulation and matrix inversion are addressed.</p><p>The existing methods are evaluated with respect to their pros and cons. In addition, in order to extract the scattering parameters a few simple de-embedding techniques are introduced. We have attempted to optimize each stage of the conventional space domain MoM such that it can handle electrically large scatterers in planar stratified media. Each method is discussed independently and proved to be performing well compared with the corresponding method applied in conventional space domain MoM. In deriving spectral Green’s functions, a novel formulation of transmission line theory is applied easing the analytical derivation and the software implementation significantly. A robust form of discrete complex image method (DCIM) is used in deriving spatial Green’s functions from the corresponding spectral Green’s functions. DCIM is an accurate and efficient way of evaluating Sommerfeld integrals without resorting to multi-dimensional numerical integration.</p><p>The accuracy and efficiency of DCIM are affirmed by applying it to simple scatterers. The outcome of DCIM is a sum of complex exponential functions. These are then used to calculate the impedance matrices of MoM. It is also shown that when using mixed potential integral formulation, the original four-dimensional numerical integration can be simplified to two-dimensional integration with no loss of accuracy, thus reducing the mathematical complexity during matrix filling phase. Nevertheless, some of the complex exponential functions can lead to two-dimensional singular integrals. These singular two- dimensional generalized exponential integrals(2D-GEI) are efficiently handled by generalizing an innovative numerical integration method, thus saving the processing time further. The last but most important operation of MoM, the matrix inversion is achieved by using an iterative algorithm known as conjugate gradient method. It is then combined with fast Fourier transform to exploit the space invariant property present in the impedance matrices of MoM. A new compact formulation of the matrices is also presented to facilitate the programing task. To our knowledge, this is the first time such formulation is presented explicitly. A brief chapter is reserved for de-embedding of scattering parameters from the surface current densities resulting from MoM.</p><p>In order to present the thesis as a collection of self-containing and independent chapters, results are included in each chapter whenever it is appropriate. These partial results confirm the accuracy and the efficiency of each method introduced in the corresponding chapter before we move on to the next. The conclusion on the overall method introduced in this work is that the space domain method of moments combined with the discrete complex image method and the conjugate gradient fast Fourier transform presents a very powerful tool for analyzing and optimizing large arbitrary stratified structures. However, to be competitive with commercial products based on either spectral domain method of moments or finite element methods, further improvements in its implementation and methodology are needed. Few improvements such as more efficient implementation of the entire method, inclusion of surface wave contribution in DCIM, integration of non-uniform basis and testing functions and need for better de-embedding techniques are already identified at the end of this work.</p><p>Finally we hope that this work clarifies some important issues relating to space domain method of moments when applied to large scatterers etched on planar stratified media and encourages the further research on this particular method.</p>

<p>Currently, there is a great interest in panel absorber design where porous components are excluded due to environmental and cleaning considerations. For such absorbers, the challenge is to increase the natural, viscous losses to attain an acceptable absorption bandwidth. This dissertation presents two new perforated panel absorber concepts, where the viscous energy dissipation has been enhanced by the use of non-traditional design of the perforations.</p><p>The first concept is a perforated panel where the perforations has been shaped as small horns. The inner part of the horns have dimensions comparable to microperforated panels. The purpose of the design is to increase the surface area of the opening, increase the flow velocity in the inner part of the horn, and offer a better impedance match to the incoming wave. The concept has been investigated primarily by calculations using the Finite Difference Method. The results indicate that a relatively large absorption bandwidth can be obtained for a horn with wide outer radius and small inner radius.</p><p>The second concept is a double perforated panel, consisting of two parallel, perforated plates separated by a small distance, typically 0.1 – 0.3 mm. The main part of the energy dissipation takes place in the small gap between the plates. Both perforated and slitted variants have been investigated by simulations and experiments. For the slitted palne case, absorption bandwidths equivalent to microperforated panels has been observed. The slitted variant can also be designed to be adjustable, allowing tha lateral distance between the slites in the two plates to be varied. This offers two special features: The maximum absorption coefficient can be adjusted from unity to almost zero, and the resonance frequency can be shifted. A frequency shift of one actave at normal sound incidence has been obtained. </p>

<p>A rapid growth of new satellite systems utilizing the Ka-band (27 – 40 Ghz) and even higher frequencies is expected in the coming years. The services offered will include broadband communication, interactive broadcasting, multimedia applications, interconnection of local area networks and Internet connectivity. Many of the new systems will use technologies as multiple spot-beams, onboard processing, and switching of packets between beams and inter satellite links. Because of congestion in the lower bands such ad C (4 – 8 Ghz) and Ku-band (12 – 18 Ghz), numerous of these services will use Ka-band. One additional advantage to the spectrum availability at Ka-band is the potential of smaller terminals compared to those used in lower frequency bands.</p><p>Several mobile satellite systems have recently started operation and more are planned or scheduled for implementation within a few years to provide personal and data communication at L-band (1 – 2 Ghz) and S-band (2 – 4 Ghz) frequencies. The systems will utilize different orbit types, for example low, medium or geostationary earth orbits, to provide voice and data services to mobile users.</p><p>Understanding of the propagation aspects is important for successful design of a satellite system obtaining the targeted service quality and availability. For systems operating above about 10 Ghz, attenuation caused by hydrometeor effects is the dominant propagation impairment on line-of-sight (LOS) links. For mobile communications systems operating at lower frequencies, the impairments resulting from multipath propagation, shadowing and blockage from obstacles on the ground severely affect the radio signals. Estimation of dynamic propagation is essential for the design of reliable and spectrum efficient communication systems. The system can adapt the transmission methodology that maximizes the throughput of information and optimizes the delivery time. The design of such mitigation techniques will depend on the dynamics and how often the events occur.</p><p>The research conducted in this study on mobile propagation effects of terrain at L-band has led to an improved three-state channel model for land mobile satellite systems. The time spent in each of the states is quite realistic, facilitating better simulation of the performance of communication systems. A new methodology was developed to perform large area coverage estimation by calculating satellite visibility for low earth orbit and geostationary constellations based on digital terrain maps. The procedure takes into account large terrain obstacles and procedures a gross overview of the potential area covered with one or several satellites. A photogrammetric technique to assess performance of non-geostationary orbit (NGSO) systems in mid- and high latitude urban areas was used to estimate channel fading and diversity improvement. Some measurements of the maximum obtainable call duration for the Iridium system are included as well.</p><p>The studies on atmospheric propagation effects between 20 and 60 Ghz included analyses of fade and inter-fade duration statistics, which are important when evaluating fade mitigation techniques and estimating system outages. Fade duration measurements were analyzed and an effort made to find a common statistical fade duration model. Based on this work, a new prediction method for fade durations on satellite-earth paths was developed. This ability to forecast rain attenuation was investigated with the aid of statistical prediction methods and terrestrial measurements on a 60 Ghz link. Finally, beacon measurements at 50 Ghz from Italsat F1 were used to test and compare available scintillation prediction models.</p><p>The work has improved the ability to estimate and simulate propagation effects on mobile and fixed satellite system performance. </p>

Currently, there is a great interest in panel absorber design where porous components are excluded due to environmental and cleaning considerations. For such absorbers, the challenge is to increase the natural, viscous losses to attain an acceptable absorption bandwidth. This dissertation presents two new perforated panel absorber concepts, where the viscous energy dissipation has been enhanced by the use of non-traditional design of the perforations. The first concept is a perforated panel where the perforations has been shaped as small horns. The inner part of the horns have dimensions comparable to microperforated panels. The purpose of the design is to increase the surface area of the opening, increase the flow velocity in the inner part of the horn, and offer a better impedance match to the incoming wave. The concept has been investigated primarily by calculations using the Finite Difference Method. The results indicate that a relatively large absorption bandwidth can be obtained for a horn with wide outer radius and small inner radius. The second concept is a double perforated panel, consisting of two parallel, perforated plates separated by a small distance, typically 0.1 – 0.3 mm. The main part of the energy dissipation takes place in the small gap between the plates. Both perforated and slitted variants have been investigated by simulations and experiments. For the slitted palne case, absorption bandwidths equivalent to microperforated panels has been observed. The slitted variant can also be designed to be adjustable, allowing tha lateral distance between the slites in the two plates to be varied. This offers two special features: The maximum absorption coefficient can be adjusted from unity to almost zero, and the resonance frequency can be shifted. A frequency shift of one actave at normal sound incidence has been obtained.

A rapid growth of new satellite systems utilizing the Ka-band (27 – 40 Ghz) and even higher frequencies is expected in the coming years. The services offered will include broadband communication, interactive broadcasting, multimedia applications, interconnection of local area networks and Internet connectivity. Many of the new systems will use technologies as multiple spot-beams, onboard processing, and switching of packets between beams and inter satellite links. Because of congestion in the lower bands such ad C (4 – 8 Ghz) and Ku-band (12 – 18 Ghz), numerous of these services will use Ka-band. One additional advantage to the spectrum availability at Ka-band is the potential of smaller terminals compared to those used in lower frequency bands. Several mobile satellite systems have recently started operation and more are planned or scheduled for implementation within a few years to provide personal and data communication at L-band (1 – 2 Ghz) and S-band (2 – 4 Ghz) frequencies. The systems will utilize different orbit types, for example low, medium or geostationary earth orbits, to provide voice and data services to mobile users. Understanding of the propagation aspects is important for successful design of a satellite system obtaining the targeted service quality and availability. For systems operating above about 10 Ghz, attenuation caused by hydrometeor effects is the dominant propagation impairment on line-of-sight (LOS) links. For mobile communications systems operating at lower frequencies, the impairments resulting from multipath propagation, shadowing and blockage from obstacles on the ground severely affect the radio signals. Estimation of dynamic propagation is essential for the design of reliable and spectrum efficient communication systems. The system can adapt the transmission methodology that maximizes the throughput of information and optimizes the delivery time. The design of such mitigation techniques will depend on the dynamics and how often the events occur. The research conducted in this study on mobile propagation effects of terrain at L-band has led to an improved three-state channel model for land mobile satellite systems. The time spent in each of the states is quite realistic, facilitating better simulation of the performance of communication systems. A new methodology was developed to perform large area coverage estimation by calculating satellite visibility for low earth orbit and geostationary constellations based on digital terrain maps. The procedure takes into account large terrain obstacles and procedures a gross overview of the potential area covered with one or several satellites. A photogrammetric technique to assess performance of non-geostationary orbit (NGSO) systems in mid- and high latitude urban areas was used to estimate channel fading and diversity improvement. Some measurements of the maximum obtainable call duration for the Iridium system are included as well. The studies on atmospheric propagation effects between 20 and 60 Ghz included analyses of fade and inter-fade duration statistics, which are important when evaluating fade mitigation techniques and estimating system outages. Fade duration measurements were analyzed and an effort made to find a common statistical fade duration model. Based on this work, a new prediction method for fade durations on satellite-earth paths was developed. This ability to forecast rain attenuation was investigated with the aid of statistical prediction methods and terrestrial measurements on a 60 Ghz link. Finally, beacon measurements at 50 Ghz from Italsat F1 were used to test and compare available scintillation prediction models. The work has improved the ability to estimate and simulate propagation effects on mobile and fixed satellite system performance.

<b>Keywords </b>: Conjugate gradient fast Fourier transform (CG-FFT), Discrete complex image method (DCIM), Electric field integral equation (EFIE), Frequency selective surfaces (FSS), Generalized pencil-of-functions (GPOF), Green’s function (GF), Method of moments (MoM), Prony’s method (PM), Sommerfeld integral (SI), Two-dimensional generalized exponential integral (2D-GEI) As the need for more frequency spectrum drives the design of antennas and other microwave components at higher frequencies, compact but electrically large microwave components are beginning to appear. Since a significant share of these components comprises scatterers etched on planar stratified layers, efficient tools analyzing and optimizing such structures are invaluable. The work carried out here is in fact a continuation of the research performed in the past at the Department of Electronics and Telecommunications at the Norwegian University of Science and Technology in Trondheim, Norway. The conventional method of moments for analyzing and optimizing scatterers in stratified media is simple in formulation but computationally very intensive. Moreover, the computer memory usage of the software based on conventional MoM is high. Both these factors have so far limited the application of conventional MoM to electrically small and simpler stratified structures. Therefore, the present work focuses on introducing and implementing an improved space domain MoM for large radiating or scattering structures etched on planar stratified media. The space domain method of moments is selected due to its simplicity and potential for further improvements when compared with the spectral domain method of moments. The major areas of space domain MoM such as finding spectral Green's functions, deriving spatial Green’s functions, matrix formulation and matrix inversion are addressed. The existing methods are evaluated with respect to their pros and cons. In addition, in order to extract the scattering parameters a few simple de-embedding techniques are introduced. We have attempted to optimize each stage of the conventional space domain MoM such that it can handle electrically large scatterers in planar stratified media. Each method is discussed independently and proved to be performing well compared with the corresponding method applied in conventional space domain MoM. In deriving spectral Green’s functions, a novel formulation of transmission line theory is applied easing the analytical derivation and the software implementation significantly. A robust form of discrete complex image method (DCIM) is used in deriving spatial Green’s functions from the corresponding spectral Green’s functions. DCIM is an accurate and efficient way of evaluating Sommerfeld integrals without resorting to multi-dimensional numerical integration. The accuracy and efficiency of DCIM are affirmed by applying it to simple scatterers. The outcome of DCIM is a sum of complex exponential functions. These are then used to calculate the impedance matrices of MoM. It is also shown that when using mixed potential integral formulation, the original four-dimensional numerical integration can be simplified to two-dimensional integration with no loss of accuracy, thus reducing the mathematical complexity during matrix filling phase. Nevertheless, some of the complex exponential functions can lead to two-dimensional singular integrals. These singular two- dimensional generalized exponential integrals(2D-GEI) are efficiently handled by generalizing an innovative numerical integration method, thus saving the processing time further. The last but most important operation of MoM, the matrix inversion is achieved by using an iterative algorithm known as conjugate gradient method. It is then combined with fast Fourier transform to exploit the space invariant property present in the impedance matrices of MoM. A new compact formulation of the matrices is also presented to facilitate the programing task. To our knowledge, this is the first time such formulation is presented explicitly. A brief chapter is reserved for de-embedding of scattering parameters from the surface current densities resulting from MoM. In order to present the thesis as a collection of self-containing and independent chapters, results are included in each chapter whenever it is appropriate. These partial results confirm the accuracy and the efficiency of each method introduced in the corresponding chapter before we move on to the next. The conclusion on the overall method introduced in this work is that the space domain method of moments combined with the discrete complex image method and the conjugate gradient fast Fourier transform presents a very powerful tool for analyzing and optimizing large arbitrary stratified structures. However, to be competitive with commercial products based on either spectral domain method of moments or finite element methods, further improvements in its implementation and methodology are needed. Few improvements such as more efficient implementation of the entire method, inclusion of surface wave contribution in DCIM, integration of non-uniform basis and testing functions and need for better de-embedding techniques are already identified at the end of this work. Finally we hope that this work clarifies some important issues relating to space domain method of moments when applied to large scatterers etched on planar stratified media and encourages the further research on this particular method.

The WCDMA air interface, used in the third generation mobile communication systems, is currently being evolved to improve the uplink, i.e. the radio links carrying traffic from the mobile user to the fixed network. An enhanced uplink concept is being developed to meet the expected needs from future applications like multimedia and video-streaming. This thesis studies interference management when high bit rates are introduced in the enhanced uplink. The study is performed through theoretical assessments and simulations using WCDMA system simulators. An optimization scheme using a basic system throughput based scheduling is derived to attain a theoretical assessment of bit rate limits. The throughput optimization is achieved at the expense of user-experienced fairness. Users located on cell coverage area overlap show to be most complicated to manage. The need for interference management is primary when the network deployment consists of small cells while coverage requirements are most essential when the cell size increases. By exploiting the benefits of directional antennas the antenna tilt can be tuned to increase performance resulting in increased bit rates, increased system throughput and increased resource efficiency. The improvements are attained without trade-offs and the different components of the study concur unanimously.

Diss. Univ. Zürich, 2004. / Buchhandelsausg. der Diss. Zürich, 2004. Literaturverz.

<p>The ability to construct software, call it a functional ciphertext, which can be remotely executed in encrypted form as an entirely self-contained unit, has the potential for some interesting applications. One such application is the construction of autonomous mobile agents capable of entering into certain types of legally binding contracts on behalf of the sender. At a premium in such circumstances is the ability to protect secret cryptographic keys or other secret information, which typically is necessary for legally binding contracts. Also important is the ability to do powerful computations, that are more than just one-off secure function evaluations.</p><p>The problem of constructing computation systems that achieve this, has been attempted by many to little or no avail. This thesis presents three similar cryptographic systems that take a step closer to making such encrypted software a reality.</p><p>First is demonstrated how one can construct mappings from finite automata, that through iteration can do computations. A stateless storage construction, called a Turing platform, is defined and it is shown that such a platform, in conjunction with a functional representation of a finite automaton, can perform Turing universal computation. </p><p>The univariate, multivariate, and parametric ciphers for the encryption of multivariate mappings are presented and cryptanalyzed. Cryptanalysis of these ciphers shows that they must be used very carefully, in order to resist cryptanalysis. Entirely new to cryptography is the ability to remotely and securely re-encrypt functional ciphertexts made with either univariate or multivariate encryption.</p><p>Lastly it is shown how the ciphers presented can be applied to the automaton representations in the form of mappings, to do general encrypted computation. Note: many of the novel constructions in this thesis are covered by a patent application.</p>