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In Impulse Radio based Ultra Wide Band (UWB) systems, where sub-nano second pulses are used, synchronization is very challenging because of their short pulse duration and very low duty cycle. Coherent detection of ultra wide-band signals requires complex channel estimation algorithms. In impulse based UWB systems, suboptimal receivers that require no channel estimation are proposed for low data rate applications using non coherent detection of energy. This approach requires integrators that collect energy and detect the incoming stream of bits for detection and synchronization. These techniques yield reasonable performance when compared to coherent detection techniques that require complex hardware and dissipate more energy. Non-coherent detection is a promising technique for low complexity, low cost and low data rate ultra-wideband communication applications like sensor area networks. In the past, several attempts have been made to characterize the performance of the energy collection receivers for synchronization using various metrics that include time of arrival and BER measurements. A comprehensive study of the synchronization problem using Probability of False Alarm is limited. The current thesis attempts to characterize the synchronization problem using Probability of False Alarm and Probability of Detection under various channel models and also discusses the importance of the length of the integration window for energy collection receivers. The current work also focuses on the performance evaluation of synchronization for Impulse based UWB systems using energy capture method and modeling them using the Probability of False Alarm and Probability of Detection under various channel models. In these systems, the integration region of a receiver integrator significantly affects the bit error rate (BER) performance. The effect of the integration window on the performance of the algorithm is also studied. This work also discusses the trade-offs between complexity and precision in using these algorithms for synchronization of Impulse based Direct Sequence Ultra Wideband Systems (DS-UWB). Signal to Noise Ratio vs. Probability of Detection, Probability of False Alarm are plotted for different channel models. / Master of Science

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I denna uppsats betraktas två olika bandspridningstekniker och vilken påverkan de har på telekrigsförmågan. Uppsatsen svarar på frågan: Vilka möjligheter finns att bedriva signalspaning och störning mot radiokommunikation som använder bandspridningsteknikerna frekvenshopp eller direktsekvens? Inledningsvis beskrivs en modell för telekrig mot radiokommunikation, ”telekrigcykeln”. Därefter beskrivs principer för ett radiosystem samt de två bandspridningsteknikerna frekvenshopp och direktsekvens. Slutligen analyseras bandspridningsteknikernas påverkan med hjälp av telekrigcykeln och resultaten diskuteras. Uppsatsen kommer fram till att båda signalerna går att spana mot, direktsekvens innebär större svårigheter för signalspaningen än frekvenshopp. Störning av båda signalerna görs bäst med störsändare som befinner sig nära radiomottagaren, dock är det svårt att placera störsändare nära motståndarens mottagare. / This essay examines two spread-spectrum technologies and what their effects are on the electronic warfare ability. The essay seeks to answer this question: What are the possibilities for signals intelligence and communications jamming against radio communications using one of the two spread-spectrum technologies frequency-hopping and direct sequence? The essay initially describes a model for how electronic warfare against radio communication is conducted, “telekrigcykeln”. It then describes the principles of a radio system as well as the two spread-spectrum technologies frequency-hopping and direct sequence. Using the model “telekrigcykeln” the essay finally analyses and discusses the impact of the spread-spectrum technologies. The essay finds that it is possible to conduct signals intelligence towards both signals, however direct sequence pose bigger problems than frequency-hopping. Both signals are easiest to jam using a jammer in close proximity to the radio receiver. However, close-proximity jammers are harder to place close to the opponent’s receiver.

Approved for public release, distribution is unlimited / Direct-Sequence Spread Spectrum (DSSS) modulation is being advanced as the physical-layer basis for Seaweb undersea acoustic networking. DSSS meets the need for channel tolerance, transmission security, and multi-user access. This thesis investigates the performance of subspace-decomposition blind-equalization algorithms as alternatives to RAKE processing of DSSS signals. This approach is tailored for superior performance in time-dispersive and frequency-dispersive channels characteristic of ocean acoustic propagation. Transmitter and receiver structures are implemented in Matlab and evaluated with a statistics-based model of a doubly spread channel with additive noise. Receiver performance is examined using Monte Carlo simulation. Biterror rates versus signal-to-noise ratio are presented for various multipath assumptions, noise assumptions, and receiver synchronization assumptions. / Lieutenant, Hellenic Navy

A destilação é um processo de separação com uma alta demanda de energia, razão pela qual, através de diferentes épocas tem sido estudadas diferentes configurações. O problema da separação de misturas multicomponente pode envolver sequências de colunas de destilação convencionais. Neste caso, surge um problema combinatório a fim de projetar a sequência mais econômica de separação. Por outro lado, em anos recentes têm sido proposto o uso de equipamentos alternativos, sendo as colunas com paredes divididas uma opção bastante estudada que se caracterizam pela integração de 2 seções de colunas compartilhando um único condensador e um único refervedor. Estes equipamentos propõem diminuir o custo total de processo de separação de misturas multicomponentes. Neste trabalho apresenta-se um estudo econômico da separação de três misturas ternárias de Benzeno, Tolueno, P-xileno, comparando os projetos ótimos de sequências convencionais e de colunas de paredes divididas. Inicialmente, são definidas as variáveis de projeto para cada configuração por meio de uma análise de graus de liberdade. O dimensionamento é realizado inicialmente com o método não rigoroso de valor de fronteira. Finalmente, as sequências diretas e indiretas e as colunas de parede divididas são projetadas usando modelos rigorosos, baseados no método de ponto de bolha, programação matemática para resolver os problemas de otimização do Custo Total Anualizado TAC com variáveis contínuas e enumeração exaustiva para tratar o problema combinatório. São obtidos projetos ótimos para uma alimentação com três composições diferentes. A sequência indireta forneceu o melhor resultado para a alimentação rica no componente mais pesado (-58,35%) e no componente intermediário (-45,98%). Já a sequência direta foi a melhor quando a alimentação é rica em componente leve (-33,36%). A coluna com parede dividida teve o pior desempenho em todos os três casos estudados. / Distillation is a high-energy demand separation process, for that reason, alternative configurations have been studied through the ages. The separation problem of multicomponent mixtures may involve a sequence of conventional distillation columns. In this case, a combinatorial problem arises in order to design the most economical separation sequence. On the other hand, in recent years the use of alternative devices has been proposed. One of those options is the divided wall column, which is extensively studied, and is characterized by the integration of two column sections sharing a single condenser and a single reboiler. This equipment is sought to decrease the total cost of the separation process for multicomponent mixtures. This work presents an economic study for the separation of three ternary mixtures of benzene, toluene and p-xylene, comparing the optimum design of conventional sequences and divided wall columns. Initially, the design variables are defined for each configuration through a degrees of freedom analysis. The sizing is initially performed with the boundary value shortcut method. Then, the direct and indirect sequences, and divided wall columns are designed using rigorous models based on the bubble point method. Mathematical programming is used for solving the optimization problems of minimization of the total annualized cost (TAC) with continuous variables and exhaustive enumeration to handle the combinatorial issue. Optimal designs for three feeds with different compositions are obtained. The indirect sequence provided the best result for the feed rich in the heaviest component (-58.35 %) and in the intermediate component (-45.98 %). The direct sequence result was the best when the feed composition is rich in lighter component (-33.36 %). The divided wall column had the worst performance in all three cases studied.

¡@¡@Pseudo-noise (PN) code synchronizer is an essential element of direct-sequence code division multiple access (DS-CDMA) system because data transmission is possible only after the receiver accurately synchronizes the locally generated PN code with the incoming PN code. The code synchronization is processed in two steps, acquisition and tracking, to estimate the delay offset between the two codes. Recently, the adaptive LMS filtering scheme has been proposed for performing both code acquisition and tracking with the identical structure, where the LMS algorithm is used to adjust the FIR filter taps to search for the value of delay-offset adaptively. A decision device is employed in the adaptive LMS filtering scheme as a decision variable to indicate code synchronization, hence it plays an important role for the performance of mean acquisition time (MAT). In this thesis, only code acquisition is considered. ¡@¡@In this thesis, a new decision device, referred to as the weight vector square norm (WVSN) test method, is devised associated with the adaptive LMS filtering scheme for code acquisition in DS-CDMA system. The system probabilities of the proposed scheme are derived for evaluating MAT. Numerical analyses and simulation results verify that the performance of the proposed scheme, in terms of detection probability and MAT, is superior to the conventional scheme with mean-squared error (MSE) test method, especially when the signal-to-interference-plus-noise ratio (SINR) is relatively low. ¡@¡@Furthermore, an efficient and joint-adaptation code acquisition scheme, i.e., a smart antenna coupled with the proposed adaptive LMS filtering scheme with the WVSN test method, is devised for applying to a base station, where all antenna elements are employed during PN code acquisition. This new scheme is a process of PN code acquisition and the weight coefficients of smart antenna jointly and adaptively. Numerical analyses and simulation results demonstrate that the performance of the proposed scheme with five antenna elements, in terms of the output SINR, the detection probability and the MAT, can be improved by around 7 dB, compared to the one with single antenna case.

The system capacity of the direct-sequence code division multiple access (DS-CDMA) system is limited mainly due to the multiple access interference (MAI), this is basically due to the incomplete orthogonality of spreading codes between different users. In wireless communication environments, the use of DS-CDMA system over multipath channels will introduce the effect of inter-symbol interference (ISI), thus the system performance might degrade, dramatically. To circumvent the above-mentioned problems many adaptive multiuser detectors are proposed, such as the minimum mean square error (MMSE) criteria subject to certain constraints. Unfortunately, with the MMSE receiver it requires an extra training sequence, which decreases the spectral efficiency. To increase the spectral efficiency, the blind adaptive receivers are adopted. In the conventional approach the blind adaptive receiver is developed based on the linear constrained minimum variance (LCMV) criteria, which can be viewed as the constrained version of the minimum output energy (MOE) criteria. Other alternative of designing the blind adaptive receiver is to use the linear constrained constant modulus (LCCM) criteria. In general, the LCCM receiver could achieve better robustness due to the changing environment of channel. With the above-mentioned adaptive linearly constrained multi-user receivers, we are able to reduce the effects of ISI and MAI and achieve desired system performance. However, for worse communication link, the conventional adaptive multi-user detector might not achieve desired performance and suppress interference effectively. In this thesis, we consider a new approach, in which the pre-coder similar to the Orthogonal Frequency Division Multiplexing (OFDM) systems is introduced in the transmitter of the DS-CDMA system. In the receiver, by using the characteristics of pre-coder we could remove the effect of ISI, effectively, and follows by the adaptive multi-user detector to suppress the MAI. Two most common use pre-coders of the OFDM systems are the Cyclic Prefix (CP) or Zero Padding (ZP). Thus the pre-coded DS-CDMA systems associated with the adaptive blind linearly constrained receiver could be employed to further improve the system performance with the cost of decreasing the spectral efficiency.