Master of Science / Department of Electrical and Computer Engineering / William B. Kuhn / Crosstalk and electromagnetic interference (EMI) are constant problems in the design of RF circuits. There have been several studies to analyze and improve isolation of transmission lines, but the focus has been mainly on digital circuits or the isolation goals have been on the order of 40-60 dB. When the isolation goals are much more stringent, such as 80-100 dB, much of a designer’s time is still spent ensuring that a circuit meets isolation and EMI constraints. This typically involves the use of extensive metal shielding over a circuit board. This thesis presents results from an isolation and EMI study to provide a simple reference that can be applied to typical substrates, provided proper scaling is used between substrates. The results in this thesis are reported from DC to 30 GHz using a low cost 4-layer FR4 process. The changes in isolation between various transmission lines types are investigated while varying line separation and length. It is shown that isolation between ground-backed coplanar waveguide (GBCPW) and stripline traces can reach 100dB through L-band and 60dB through Ku-band for 1.3in traces separated by 150mils. Due to the heavy usage of filters in RF design, the isolation between edge-coupled bandpass filters is also studied. It is seen that isolation levels of 100dB through L-band by enclosing the filters within stripline technology is possible, provided that signal launches and layer transitions are carefully designed. Within the passband of the 20 GHz filter tested, the isolation is less but is still significantly improved by use of enclosed stripline. Lastly, a preliminary assessment of EMI is presented which focuses on radiation levels as well as variables that can degrade isolation performance. The data illustrated in this thesis can provide guidance in the early stages of RF circuit design to determine appropriate structures to meet given design requirements. It also helps to assess the degree to which additional metal shielding can be avoided in PC board systems that use multi-layer technologies.

In multiuser wireless communications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference management in multiuser wireless communication has received significant attention in the last decade, both in the academia and industry. The interference channel (IC) is one of the simplest information theoretic models to analyze the effect of interference on the throughput and secrecy of individual messages in a multiuser setup. In this thesis, the IC is studied under different settings with and without the secrecy constraint. The main contributions of the thesis are as follows: • The generalized degrees of freedom (GDOF) has emerged as a useful approximate measure of the potential throughput of a multiuser wireless system. Also, multiple antennas at the transmitter and receiver can provide additional dimension for signaling, which can in turn improve the GDOF performance of the IC. In the initial part of the thesis, a K-user MIMO Gaussian IC (GIC) is studied from an achievable GDOF perspective. An inner bound on GDOF is derived using a combination of techniques such as treating interference as noise, zero-forcing receiving, interference alignment (IA), and extending the Han-Kobayashi (HK) scheme to K users. Also, outer bounds on the sum rate of the K-user MIMO GIC are derived, under different assumptions of cooperation and providing side information to the receivers. The derived outer bounds are simplified to obtain outer bounds on the GDOF. The relative performance of these bounds yields insight into the performance limits of the multiuser MIMO GIC and the relative merits of different schemes for interference management. • Then, the problem of designing the precoding and receive filtering matrices for IA is explored for K-user MIMO (M × N) GIC. Two algorithms for designing the precoding and receive filtering matrices for IA in the block fading or constant MIMO IC with a finite number of symbol extensions are proposed. The first algorithm for IA is based on aligning a subset of the interfering signal streams at each receiver. As the first algorithm requires global channel knowledge at each node, a distributed algorithm is proposed which requires only limited channel knowledge at each node. A new performance metric is proposed, that captures the possible loss in signal dimension while designing the precoders. The performance of the algorithms are evaluated by comparing them with existing algorithms for IA precoder design. • In the later part of the thesis, a 2-user IC with limited-rate transmitter cooperation is studied, to investigate the role of cooperation in managing interference and ensuring secrecy. First, the problem is studied in the deterministic setting, and achievable schemes are proposed, which use a combination of interference cancelation, relaying of the other user’s data bits, time sharing, and transmission of random bits, depending on the rate of the cooperative link and the relative strengths of the signal and the interference. Outer bounds on the secrecy rate are derived, under different assumptions of providing side information to receivers and partitioning the encoded message/output depending on the relative strength of the signal and the interference. The achievable schemes and outer bounds are extended to the Gaussian case. For example, while obtaining outer bounds, for the Gaussian case, it is not possible to partition the encoded message or output as performed in the deterministic case, and the novelty lies in finding the analogous quantities for the Gaussian case. The proposed achievable scheme for the Gaussian case uses a combination of cooperative and stochastic encoding along with dummy message transmission. For both the models, one of the key techniques used in the achievable scheme is interference cancelation, which has two benefits: it cancels interference and ensures secrecy simultaneously. The results show that limited-rate transmitter cooperation can greatly facilitate secure communications over 2-user ICs.

The South African railway company makes use of a train wheel detection system to monitor the trains present on a particular track, noting their lengths, positions and speeds. Interference due to distorted traction currents cause havoc with this system rendering the information gathered unreliable. To combat this interference two paths are available to reduce the detection systems susceptibility. These paths include the addition of shielding between the railway track and the wheel detectors, which form the functional entities of the train wheel detection system, and the installation of a cable running parallel to the railway track with connections to it some distance before and after the position of the wheel detector. To verify these paths, high frequency experiments were performed in the lab as well as FEM simulations. To perform the high frequency experiments a source capable of producing the high frequency current needed was designed and constructed, along with a well shielded measurement system to enable the mapping of the flux density within the region occupied by and surrounding the wheel detector. The results of both the experimental measurements and simulations yielded that the interfering magnetic field could indeed be reduced through the use of the two available paths, when they are both applied separately and in combination. To obtain the greater reduction in the interfering field within the area occupied by and surrounding the wheel detector the paths should be used in combination. Therefore through the use of a shield that is constructed from a magnetic material and the installation of a parallel cable the train wheel detection system can be made more robust. / Prof. W.A Cronjé Prof. I.W. Hofsajer

In order to achieve Full Duplex (FD) communication, currently studied solutionsfor the commercial sector rely on advanced Self-Interferece Cancellation (SIC)techniques to remove the transmitted signal from the received one. This thesis expandsthe research of these techniques by evaluating their potential usage in militarycommunication scenarios where requirements and conditions are distinct,firstly, by identifying, categorizing and describing a set of previously proposedsic techniques and secondly, by performing a comprehensive simulation andanalysis of two suggested sic techniques as part of a FD transceiver. Though themajority of the considered SIC techniques was determined to be potentially implementablein military FD transceivers, some frequency-dependent techniquesand techniques prohibiting omnidirectional communication could not be used.The simulation and analysis of the two suggested SIC techniques show that undercertain conditions, such as limited transmission power and/or reflective environment,close to complete suppression could be realized even with high nonlineardistortion in the transmit chain.

Ce mémoire est scindé en deux parties. La première partie traite de l'estimation de l'optimum combiner. Traditionnellement, l'optimum combiner est estimé à travers l'estimation du canal du signal désiré et la matrice de covariance de l'interférence plus bruit. Dans cette première partie, on propose d'estimer l'optimum combiner à travers l'estimation de deux filtres séparés, à savoir un filtre qui suppose que la transmission est sans bruit (ce filtre prend en compte l'interférence mais pas le bruit) et un filtre qui suppose que la transmission est sans interférences (ce filtre prend en compte le bruit mais pas l'interférence). Néanmoins ce type d'estimation reste optimal seulement dans le cas où le récepteur est composé de deux antennes et/ou la transmission n'est perturbée que par une seule source d'interférence, indépendamment du nombre d'antennes. Le cas d'une transmission avec un récepteur à deux antennes et une source d'interférence est simulé puis implémenté sur une cible type DSP en virgule fixe au format 16 bits.La deuxième partie est dédiée à l'estimation aveugle du canal où deux méthodes sont proposées. Ces deux méthodes sont basées sur les moments d'ordre supérieurs. La première méthode est une extension de l'algorithme de Viterbi & Viterbi avec résolution de l'ambiguïté inter sous-porteuses, pour le cas d'une transmission basée sur une forme d'onde OFDM. La deuxième méthode est construite autour du principe de l'auto déconvolution. On propose aussi dans cette partie une extension aux systèmes MIMO par l'introduction d'un précodage et d'un postcodage spatio-temporel adapté à la méthode d'estimation du canal et au type de la transmission. Enfin une étude de cas d'utilisation de cette extension MIMO est donnée pour un système de transmission basé sur le standard IEEE 802.11. / This thesis is split into two parts. The first part deals with the estimation of the optimum combiner. Traditionally, the optimum combiner is estimated through the estimation of both the desired signal channel and the covariance matrix of interference plus noise.In this first part, we propose to estimate the optimum combiner by estimating two separate filters, namely a filter which assumes that the transmission is noiseless (taking into account the interference but not the noise) and a filter which assumes that the transmission is no interfered (taking into account the noise but not the interference). However this method of estimation is optimal only in the case where the receiver has two antennas and/or transmission undergone a single source of interference regardless of the number of antennas. The case of a transmission with a receiver equipped with two antennas and interfered by a single source of interference, is simulated and implemented on a fixed-point DSP target in 16 bit format.The second part is dedicated to the blind channel estimation where two methods are proposed. Both methods are based on the higher order moments. The first method can be viewed as an extension of the Viterbi & Viterbi algorithm, with inter subcarrier ambiguity solving, for the case of an OFDM waveform. The second method is built around the principle of self deconvolution. In this section, an extension to MIMO systems based on a space-time pre-coding and postcoding is introduced. Finally a case of application of this extension, for a MIMO transmission system based on the IEEE 802.11 standard, is analysed and simulated.

Research into the nature and content of visual long-term memory has investigated what aspects of its representation may account for the remarkable ability we have to remember large amounts of detailed visual information. One theory proposed is that visual memories are supported by an underlying structure of conceptual knowledge around which visual information is organized. However, findings in memory for visual information learned in a visual search task were not explained by this theory of conceptual support, and a new theory is proposed that incorporates the importance of episodic, task-relevant visual information into the organizational structure of visual memory. The current study examined visual long-term memory organization as evidenced by retroactive interference effects in memory for objects learned in a visual search. Four experiments were conducted to examine the amount of retroactive interference induced based on aspects in which interfering objects were related to learned objects. Specifically, episodically task-relevant information about objects was manipulated between conditions based on search instructions. Aspects of conceptual category, perceptual information (color), and context (object role in search) were examined for their contribution to retroactive interference for learned objects. Findings indicated that when made episodically task-relevant, perceptual, as well as conceptual, information contributed to the organization of visual long-term memory. However, when made episodically non-relevant, perceptual information did not contribute to memory organization, and memory defaulted to conceptual category organization. This finding supports the theory of an episodically defined organizational structure in visual long-term memory that is overlaid upon an underlying conceptual structure.

Decision, interference and inactivity of an administrative body in the Code of Administrative Justice and the choice of the type of action Abstract This thesis is focused on the concepts of decision, interference and inactivity which determine the material scope of the corresponding actions: action against decision (§ 65 of the Code of Administrative Justice), action against unlawful interference (§ 82 of the Code of Administrative Justice) and action due to inactivity (§ 79 of the Code of Administrative Justice). In this context, the overlaps between such actions arise as a result of problematic interpretation of these concepts: while decision often cannot be distinguished from interference, the type of inactivity and the subsequent choice of action depends on the nature of an act that is not performed. The thesis consists of five parts gradually acquainting with the problematic aspects of the structure of such actions. The introductory part is devoted to the historical context which focuses on a short period in the development of the regulations of administrative justice - between the years 1992 and 2002, i. e. the period immediately preceding the entry into force of the Code of Administrative Justice. The second part of this work is focused on the action against decision considering the concept of...

The fruit fly, Drosophila melanogaster is an exceptional model species for understanding both proximate and ultimate causes of variation in behaviour. Here, we have examined two behaviors: foraging and mating. We discuss these research projects in turn. Almost 40 years ago, the classic foraging behaviour polymorphism rover/sitter was first discovered. Recently, evidence has suggested that the polymorphism is maintained by negative frequency-dependent selection at the larval stage. In two separate experiments we failed to replicate negative frequency-dependence in the survival of rover and sitter larvae. However, we empirically demonstrated differences in burrowing behaviour between the rover and sitter morphs which may be a possible mechanism causing the negative frequency-dependent relationship between the morphs. Future replication of negative frequency-dependence is necessary if we are to understand the maintenance of this polymorphism in nature. We examined mating behaviour from the perspective of two mechanisms of sexual selection: female choice and male-male competition. The study of sexual selection requires careful isolation of these mechanisms. Owing to difficulties in experimental design, studies have yet to properly separate and quantify the individual effects of female choice and male-male competition in fruit flies. Here, we designed a novel arena to assess true female choice. We then used this arena to test the effect of male courtship interference on mating outcomes. However, due to an unforeseen amount of male harassment of females in the arena, we withhold any strong conclusions about the effect of male-male interference behaviour. We also attempt to demonstrate the potential for sexual selection on traits associated with interference behaviour in males. / Thesis / Master of Science (MSc)

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