The objective of this dissertation is to investigate the factors that influence the design of wide-area wavelength division multiplexing (WDM) optical networks. Wide-area networks are presented as communication networks capable of transporting voice and data communication over large geographical areas. These networks typically span a whole country, region or even continent.The rapid development and maturation of WDM technology over the last decade have been well-received commercially and warrants the development of skills in the field of optical network design.The fundamental purpose of all communication networks and technologies is to satisfy the demand of end-users through the provisioning of capacity over shared and limited physical infrastructure. Consideration of the business aspects related to communications traffic and the grooming thereof are crucial to developing an understanding of customer requirements in terms of the selection and quality of services and applications. Extensive communication networks require complex management techniques that aim to ensure high levels of reliability and revenue generation.An integrated methodology is presented for the design of wide-area WDM optical networks. The methodology harnesses physical, logical, and virtual topologies together with routing and channel assignment (RCA) and clustering processes to enhance objectivity of the design process. A novel approach, based on statistical clustering using the Ward linkage as similarity metric, is introduced for solving the problem of determining the number and positions of the backbone nodes of a wide-area network, otherwise defined as the top level hub nodes of the multi-level network model. The influence of the geographic distribution of network traffic, and the intra/inter-cluster traffic ratios are taken into consideration through utilisation of modified gravity models and novel network node weighting. / Dissertation (MEng)--University of Pretoria, 2005. / Electrical, Electronic and Computer Engineering / unrestricted

Cette thèse décrit l'état de l'art des sondes et nanoparticules fluorescents traditionnels utilisés en imagerie de fluorescence ainsi que le développement de nouveaux nanomatériaux à base de polymère à empreinte moléculaire, aussi dénommé ‘anticorps plastique’, pour le ciblage et la bioimagerie. En biologie et en médecine, il y a un besoin constant de diagnostiquer diverses maladies pour leur éventuel traitement et prévention. Une distribution anormale et un taux élévé de glycosylation (e.g. acides hyaluronique et sialique) à la surface ou dans les cellules sont indicateurs d’une infection ou d’un cancer. Généralement, l’imagerie par fluorescence permet de visualiser, localiser et quantifier les biomarqueurs de pathologie mais à l’heure actuelle, il n’existe pas d’outil analytique fiable pour cibler spécifiquement les molécules de glycosylation car les anticorps et les lectines vendus dans le commerce ont une faible affinité et sélectivité vis-à-vis de ces cibles. Dans ce contexte, les polymères à empreintes moléculaires (MIPs) pourraient apporter une solution. Les MIPs sont des récepteurs synthétiques possédant des affinités et sélectivités comparables à ceux des anticorps, mais exhibant une stabilité physique, thermique et chimique bien plus accrue. De plus, leur fabrication est peu coûteuse et ne nécessite pas de tuer des animaux comme pour l’obtention des anticorps biologiques. Dans cette thèse, nous avons optimisé et synthétisé des MIPs biocompatibles pour leur utilisation en bioimagerie afin de détecter et quantifier l’acide hyaluronique et l’acide sialique sur les cellules et les tissus de peau humaine. L’acide glucuronique, une composante de l’acide hyaluronique et l’acide N-acétylneuraminique, l’acide sialique le plus commun, ont été utilisés comme molécules ‘patron’, générant des MIPs très sélectifs envers leur cible en milieu aqueux. Deux types de nanoparticules de MIPs fluorescents ont été synthétisés: (1) en incorporant un colorant rhodamine polymérisable dans la solution de pré-polymérisation et (2) en encapsulant des boîtes quantiques InP/ZnS générant ainsi des MIPs de type cœur-coquille. Pour cela, nous avons adopté une stratégie innovante qui consiste à synthétiser les coquilles de MIPs directement autour des boîtes quantiques en utilisant l’énergie de l’onde fluorescente émise par l’excitation des points quantiques, pour initier la polymérisation. Un protocole d'immunocoloration standard a ensuite été optimisé afin d’imager des kératinocytes humains fixés et vivants ainsi que des tissus de peau, par microscopie à épifluorescence et confocale. Les résultats étaient similaires à ceux obtenus par la méthode de référence utilisant une protéine biotinylée reconnaissant l'acide hyaluronique. L'imagerie multiplex en combinant deux MIPs couplés à deux couleurs de boîtes quantiques et l’imagerie des cellules cancéreuses ont également été démontrées. Bien que les MIPs n’étaient pas cytotoxiques aux concentrations utilisées pour la bioimagerie, la toxicité des différentes composantes du MIP pourrait être un frein à leur utilisation dans le domaine biomédical. Afin de rendre ces MIPs plus ‘inoffensifs’, nous avons supprimé l’amorceur de polymérisation, une molécule considérée comme toxique. Les MIPs ont été synthétisés en employant des monomères qui s’auto-initient sous l’effet de l’UV ou de la chaleur. La spécificité et la sélectivité des MIPs obtenus étaient similaires à ceux préparés avec des amorceurs. En conclusion, cette thèse décrit la première utilisation des MIPs comme anticorps synthétique pour la bioimagerie de fluorescence. Ce travail ouvre la voie à de nouvelles applications en détection, diagnostique et thérapie par des MIPs. / This thesis describes the state of the art in nanomaterials-based targeted bioimaging and introduces molecularly imprinted polymers, also termed ‘plastic antibodies’ as novel biorecognition agents for labeling and imaging of cells and tissues. In fundamental biology and medical diagnostics, there is a constant need to localize and quantify specific molecular targets. Abnormal glycosylation levels or distributions of hyaluronan or sialic acids on cells are indicators of infection or malignancy. In general, bioimaging with fluorescent probes enables the localization and qualitative or quantitative determination of these pathological biomarkers. However, no reliable tools for the recognition of glycosylation sites on proteins exist, because the commercially available antibodies or lectins have poor affinity and selectivity for these targets. In this context, tailor-made molecularly imprinted polymers (MIPs) are promising synthetic receptor materials since they present a series of advantages over their natural counterparts such as the ease and low cost of preparation and their physical and chemical stability. Thus, MIPs could provide a robust and specific imaging tool for revealing the location/distribution, time of appearance and structure of glycosylation sites on/in cells, which would lead to a better insight of the tremendously diverse biological processes in which these molecules are involved. Herein, we describe the synthesis of water-compatible MIPs for the molecular imaging of hyaluronan and sialylation sites on cells and tissues. Since molecular imprinting of entire biomacromolecules like oligosaccharides is challenging, we opted for what is commonly called the ‘epitope approach’, which was inspired by nature. The monosaccharides, glucuronic acid and N-acetylneuraminic acid were imprinted, and the resulting MIPs were able to bind these molecules when present and accessible on the terminal unit of hyaluronan and sialylation sites. Fluorescent MIPs were synthesized as rhodamine-labeled nanoparticles and as MIP-coated InP/ZnS core-shell quantum dot (QD) particles. For the coating of the QDs, a novel versatile solubilization and functionalization strategy was proposed, which consists of creating polymer shells directly on QDs by photopolymerization using the particles as individual internal light sources. A standard immunostaining protocol was then successfully adapted for the application of the fluorescently labeled MIPs to image fixed and living human keratinocytes and skin tissues, by epifluorescence and confocal fluorescence microscopy. The results were comparable to those obtained with a reference method where staining was done with a biotinylated hyaluronic acid binding protein. Multiplexed and cancer cell imaging were also performed, demonstrating the potential of molecularly imprinted polymers as a versatile biolabeling and bioimaging tool. Although the MIPs were not cytotoxic at the concentrations used for bioimaging, in order to render them generally applicable in biomedicine, where toxicity of the polymerization precursors is a matter of concern, we suppressed the initiator, a toxic chemical. Initiator-free MIPs were thus synthesized by using monomers that can self-initiate under UV irradiation or heat. The specificity and selectivity of the obtained MIPs were as good as the ones prepared with initiators. In conclusion, we have demonstrated for the first time the great potential of MIPs as synthetic antibody mimics for bioimaging. The possibility to associate other functionalities such as QDs and additionally attach drugs to the same material appears rather straightforward due to the synthetic polymeric nature of MIPs, which paves the way to new potential applications in theranostics.

The integration of Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques has become a preferred solution for the high rate wireless technologies due to its high spectral efficiency, robustness to frequency selective fading, increased diversity gain, and enhanced system capacity. The main drawback of OFDM-based systems is their susceptibility to impairments such as Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), Symbol Timing Error (STE), Phase Noise (PHN), and fading channel. These impairments, if not properly estimated and compensated, degrade the performance of the OFDM-based systems In this thesis, a system model for MIMO-OFDM that takes into account the effects of all these impairments is formulated. Using this system model, we de-rive Cramer-Rao Lower Bounds (CRLBs) for the joint estimation of deterministic impairments in MIMO-OFDM system, which show the coupling effect among different impairments and the significance of the joint estimation. Also, Bayesian CRLBs for the joint estimation of random impairments in OFDM system are derived. Similarly, we derive Hybrid CRLBs for the joint estimation of random and deterministic impairments in OFDM system, which show the significance of using Bayesian approach in estimation. Further, we investigate different algorithms for the joint estimation of all impairments in OFDM-based system. Maximum Likelihood (ML) algorithms and its low complexity variants, for the joint estimation of CFO, SFO, STE, and channel in MIMO-OFDM system, are proposed. We propose a low complexity ML algorithm which uses Compressed Sensing (CS) based channel estimation method in a sparse fading sce-nario, where the received samples used for estimation are less than that required for a Least Squares (LS) or Maximum a posteriori (MAP) based estimation. Also, we propose MAP algorithms for the joint estimation of the random impairments, PHN and channel, utilizing their statistical knowledge which is known a priori. Joint estimation algorithms for SFO and channel in OFDM system, using Bayesian framework, are also proposed in this thesis. The performance of the estimation methods is studied through simulations and numerical results show that the performance of the proposed algorithms is better than existing algorithms and is closer to the derived CRLBs.

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The rapid advancements in semiconductor technology have led to constant shrinking of transistor sizes as per Moore's Law. Wireless communications is one field which has seen explosive growth, thanks to the cramming of more transistors into a single chip. Design of these systems involve trade-offs between performance, area and power. Fast Fourier Transform is an important component in most of the wireless communication systems. FFTs are widely used in applications like OFDM transceivers, Spectrum sensing in Cognitive Radio, Image Processing, Radar Signal Processing etc. FFT is the most compute intensive and time consuming operation in most of the above applications. It is always a challenge to develop an architecture which gives high throughput while reducing the latency without much area overhead. Next generation wireless systems demand high transmission efficiency and hence FFT processor should be capable of doing computations much faster. Architectures based on smaller radices for computing longer FFTs are inefficient. In this thesis, a fully parallel unrolled FFT architecture based on novel radix-4 engine is proposed which is catered for wide range of applications. The radix-4 butterfly unit takes all four inputs in parallel and can selectively produce one out of the four outputs. The proposed architecture uses Radix-4^3 and Radix-4^4 algorithms for computation of various FFTs. The Radix-4^4 block can take all 256 inputs in parallel and can use the select control signals to generate one out of the 256 outputs. In existing Cooley-Tukey architectures, the output from each stage has to be reordered before the next stage can start computation. This needs intermediate storage after each stage. In our architecture, each stage can directly generate the reordered outputs and hence reduce these buffers. A solution for output reordering problem in Radix-4^3 and Radix-4^4 FFT architectures are also discussed in this work. Although the hardware complexity in terms of adders and multipliers are increased in our architecture, a significant reduction in intermediate memory requirement is achieved. FFTs of varying sizes starting from 64 point to 64K point have been implemented in ASIC using UMC 130nm CMOS technology. The data representation used in this work is fixed point format and selected word length is 16 bits to get maximum Signal to Quantization Noise Ratio (SQNR). The architecture has been found to be more suitable for computing FFT of large sizes. For 4096 point and 64K point FFTs, this design gives comparable throughput with considerable reduction in area and latency when compared to the state-of-art implementations. The 64K point FFT architecture resulted in a throughput of 1332 mega samples per second with an area of 171.78 mm^2 and total power of 10.7W at 333 MHz.

Scheduling policies adopted for statistical multiplexing should provide delay differentiation between different traffic classes, where each class represents an aggregate traffic of individual applications having same target-queueing-delay requirements. We propose scheduling to optimally balance weighted mean instanteneous queue lengths and later weighted mean cumulative queue lengths as an approach to delay differentiation, where the class weights are set inversely proportional to the respective products of target delays and packet arrival rates. In particular, we assume a discrete-time, two-class, single-server queueing model with unit service time per packet and provide mathematical frame-work throughout our work. For iid Bernoulli packet arrivals, using a step-wise cost-dominance analytical approach using instantaneous queue lengths alone, for a class of one-stage cost functions not necessarily convex, we find the structure of the total-cost optimal policies for a part of the state space. We then consider two particular one-stage cost functions for finding two scheduling policies that are total-cost optimal for the whole state-space. The policy for the absolute weighted difference cost function minimizes the stationary mean, and the policy for the weighted sum-of-square cost function minimizes the stationary second-order moment, of the absolute value of the weighted difference of queue lengths. For the case of weighted sum-of-square cost function, the ‘iid Bernoulli arrivals’ assumption can be relaxed to either ‘iid arrivals with general batch sizes’ or to ‘Markovian zero-one arrivals’ for all of the state space, but for the linear switching curve. We then show that the average cost, starting from any initial state, exists, and is finite for every stationary work-conserving policy for our choices of the one-stage cost-function. This is shown for arbitrary number of class queues and for any i.i.d. batch arrival processes with finite appropriate moments. We then use cumulative queue lengths information in the one-step cost function of the optimization formulation and obtain an optimal myopic policy with 3 stages to go for iid arrivals with general batch sizes. We show analytically that this policy achieves the given target delay ratio in the long run under finite buffer assumption, given that feasibility conditions are satisfied. We take recourse to numerical value iteration to show the existence of average-cost for this policy. Simulations with varied class-weights for Bernoulli arrivals and batch arrivals with Poisson batch sizes show that this policy achieves mean queueing delays closer to the respective target delays than the policy obtained earlier. We also note that the coefficients of variation of the queueing delays of both the classes using cumulative queue lengths are of the same order as those using instantaneous queue lengths. Moreover, the short-term behaviour of the optimal myopic policy using cumulative queue lengths is superior to the existing standard policy reported by Coffman and Mitrani by a factor in the range of 3 to 8. Though our policy performs marginally poorer compared to the value-iterated, sampled, and then stationarily employed policy, the later lacks any closed-form structure. We then modify the definition of the third state variable and look to directly balance weighted mean delays. We come up with another optimal myopic policy with 3 stages to go, following which the error in the ratio of mean delays decreases as the window-size, as opposed to the policy mentioned in the last paragraph, wherein the error decreases as the square-root of the window-size. We perform numerical value-iteration to show the existence of average-cost and study the performance by simulation. Performance of our policy is comparable with the value-iterated, sampled, and then stationarily employed policy, reported by Mallesh. We have then studied general inter-arrival time processes and obtained the optimal myopic policy for the Pareto inter-arrival process, in particular. We have supported with simulation that our policy fares similarly to the PAD policy, reported by Dovrolis et. al., which is primarily heuristic in nature. We then model the possible packet errors in the multiplexed channel by either a Bernoulli process, or a Markov modulated Bernoulli process with two possible channel states. We also consider two possible round-trip-time values for control information, namely zero and one-slot. The policies that are next-stage optimal (for zero round-trip-time), and two-stage optimal (for one-slot round-trip-time) are obtained. Simulations with varied class-weights for Bernoulli arrivals and batch arrivals with Poisson batch sizes show that these policies indeed achieve mean queueing delays very close to the respective target delays. We also obtain the structure for optimal policies with N = 2 + ⌈rtt⌉ stages-to-go for generic values of rtt, and which need not be multiple of time-slots.

Orthogonal frequency division multiplexing (OFDM) in next generation wireless systems provides high downlink data rates by employing frequency-domain scheduling and rate adaptation at the base station (BS). However, in order to control the significant feedback overhead required by these techniques, feedback reduction schemes are essential. Best-m feedback is one such scheme that is implemented in OFDM standards such as Long Term Evolution. In it, the sub channel (SC) power gains of only the m strongest SCs and their corresponding indices are fed back to the BS. However, two assumptions pervade most of the literature that analyze best-m feedback in OFDM systems. The first one is that the SC gains are uncorrelated. In practice, however, the SC gains are highly correlated, even for dispersive multipath channels. The second assumption deals with the treatment of unreported SCs, which are not fed back by the best-m scheme. If no user reports an SC, then no data transmission is assumed to occur. In this thesis, we eschew these assumptions and investigate best-m feedback in OFDM systems with correlated SC gains. We, first, characterize the average throughput as a function of correlation and m. A uniform correlation model is assumed, i.e., the SC gains are correlated with each other by the same correlation coefficient. The system model incorporates greedy, modified proportional- fair, and round robin schedulers, discrete rate adaptation, and non-identically distributed SC gains of different users. We, then, generalize the model to account for feedback delay. We show in all these cases that correlation degrades the average throughput. We also show that this effect does not arise when users report all the SC power gains to the BS. In order to mitigate the reduction in the average throughput caused by unreported SCs, we derive a novel, constrained minimum mean square error channel estimator for the best-m scheme to estimate the gains of these unreported SCs. The estimator makes use of the additional information, which is unique to the best-m scheme, that the estimated SC power gains must be less than those that were reported. We, then, study its implications on the downlink average cell throughput, again for different schedulers. We show that our approach reduces the root mean square error and increases the average throughput compared to several approaches pursued in the literature. The more correlated the SC gains, greater is the improvement.

Photonic bandgap structures have provided promising platform for miniaturization of modern integrated optical devices. In this thesis, a photonic crystal based ring resonator (PCRR) is proposed and optimized to exhibit high quality factor. Also, force sensing application of the optimized PC ring resonator and Dense Wavelength Division Multiplexing (DWDM) application of the PCRR are discussed. Finally fabrication and characterization of the PCRR is presented. A photonic crystal ring resonator is designed in a hexagonal lattice of air holes on a silicon slab. A novel approach is used to optimize PCRR to achieve high quality factor. The numerical analysis of the optimized photonic crystal ring resonator is presented in detail. For all electromagnetic computations Finite Difference Time Domain (FDTD) method is used. The improvement in Q factor is explained by using the physical phenomenon, multipole cancellation of the radiation held of the PCRR cavity. The corresponding mathematical frame work has been included. The forced cancellation of lower order radiation components are verified by plotting far held radiation pattern of the PCRR cavity. Then, the force sensing application of the optimized PCRR is presented. A high sensitive force sensor based on photonic crystal ring resonator integrated with silicon micro cantilever is presented. The design and modelling of the device, including the mechanics of the cantilever, FEM (Finite Element Method) analysis of the cantilever beam with PC and without PC integrated on it. The force sensing characteristics are presented for forces in the range of 0 to 1 N. For forces which are in the range of few tens of N, a force sensor with bilayer cantilever is considered. PC ring resonator on the bilayer of 220nm thick silicon and 600nm thick SiO2 plays the role of sensing element. Force sensing characteristics of the bilayer cantilever for forces in the range of 0 to 10 N are presented. Fabrication and characterization of PCRR is also carried out. This experimental work is done mainly to understand practical issues in study of photonic crystal ring resonators. It is proved that Q factor of PCRR can be signi cantly improved by varying the PCRR parameters by the proposed method. Dense Wavelength Division Multiplexing (DWDM) application of PC ring resonator is included. A novel 4-channel PC based demultiplexer is proposed and optimized in order to tolerate the fabrication errors and exhibit optimal cross talk, coupling efficiency between resonator and various channels of the device. Since the intention of this design is, to achieve the device performance that is independent of the unavoidable fabrication errors, the tolerance studies are made on the performance of the device towards the fabrication errors in the dimension of various related parameters. In conclusion we summarize major results, applications including computations and practical measurements of this work and suggest future work that may be carried out later.

This thesis presents an introduction to the design and simulation of a novel class of integrated photonic phased array switch elements. The main objective is to use nano-electromechanical (NEMS) based phase shifters of cascaded under-etched slot nanowires that are compact in size and require a small amount of power to operate them. The structure of the switch elements is organized such that it brings the phase shifting elements to the exterior sides of the photonic circuits. The transition slot couplers, used to interconnect the phase shifters, are designed to enable biasing one of the silicon beams of each phase shifter from an electrode located at the side of the phase shifter. The other silicon beam of each phase shifter is biased through the rest of the silicon structure of the switch element, which is taken as a ground. Phased array switch elements ranging from 2×2 up to 8×8 multiple-inputs/multiple-outputs (MIMO) are conveniently designed within reasonable footprints native to the current fabrication technologies. Chapter one presents the general layout of the various designs of the switch elements and demonstrates their novel features. This demonstration will show how waveguide disturbances in the interconnecting network from conventional switch elements can be avoided by adopting an innovative design. Some possible applications for the designed switch elements of different sizes and topologies are indicated throughout the chapter. Chapter two presents the design of the multimode interference (MMI) couplers used in the switch elements as splitters, combiners and waveguide crossovers. Simulation data and design methodologies for the multimode couplers of interest are detailed in this chapter. Chapter three presents the design and analysis of the NEMS-operated phase shifters. Both simulations and numerical analysis are utilized in the design of a 0º-180º capable NEMS-operated phase shifter. Additionally, the response of some of the designed photonic phased array switch elements is demonstrated in this chapter. An executive summary and conclusions sections are also included in the thesis.