In frequency-hopping (FH) system, the signal is not only impaired by receiver thermal noise, but also impaired by jamming, interference or multipath fading. Therefore, diversity techniques are used to reduce these impairments. Two systems are considered in this thesis, the first one is fast frequency-hopping/M-ary frequency-shift-keying (FFH/MFSK) System and the second one is fast frequency-hopping multiple access/M-ary frequency-shift-keying system (FFHMA/MFSK) System. In the first system, we consider three cases, multitone jamming (MTJ), broad-band noise jamming (BBN) and partial-band noise jamming (PBN).In the second system, we consider multiuser cases with multiple access interference, frequency-selective fading, and AWGN channels. In this thesis, two modified diversity combining methods are proposed. These methods are modified product and Order Statistics-Normalized Envelope Detection (OSNED) methods by adding the reliable order statistics. From simulation results, these methods can effectively combat multitone jamming and partial-band noise jamming. When comparing with product and OSNED in multiple access interference channel and frequency-selective fading channels, the proposed methods have better performance at high SNR. The proposed methods also do not need the additional side information as hard limiting majority vote (HLMV) and soft limiting combiner (SLC) needed.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Phase-locked loop (PLL) frequency synthesizers used for high-speed data transmission must rapidly hop and lock to new frequencies. The fundamental problem is that the settling time depends inversely on the loop bandwidth, and increasing the bandwidth causes unwanted noise interference and stability problems for the circuit. We demonstrate the feasibility of replacing the analog integrator in the PLL with a digital integrator. This circuit has advantages of increased hopping speed, ability to compensate for temperature drift and system stability. PLL lock-in was demonstrated in a prototype circuit designed and built with both discrete components and with a programmable logic device.

L'objectif de cette thèse est d'étudier la faisabilité et les performances d'un synthétiseur de fréquences agile pour les transmissions multi-bandes multi-utilisateurs destinées aux systèmes de transmission fournissant un très grand débit tout en répondant aux exigences de faible consommation et d'intégration facile. Dans ce contexte, les solutions classiques de synthétiseur de fréquences ne sont pas applicables et il est nécessaire de développer de nouvelles structures qui génèrent les fréquences centrales en permanence. La commutation d'une fréquence à l'autre peut se faire alors très rapidement par simple modification de la configuration des multiplexeurs. Dans la première partie de ce travail nous nous consacrons à l'analyse d'une telle architecture à fort potentiel. Une partie de sa structure est réalisée en technologie conventionnelle BiCMOS afin de valider sa faisabilité ainsi que le fonctionnement des solutions schématiques développées. Grâce à la caractérisation des composants, une analyse de la structure complète est réalisée. Cependant, la complexité de la structure du synthétiseur proposé fait de sorte qu'il existe pour les fréquences générées un grand nombre de fréquences parasites qui induisent des interférences entre utilisateurs. La réduction de leurs effets sur la transmission est l'objet de la deuxième partie de notre travail. Deux solutions numériques de réduction des interférences sont proposées. Elles permettent de rendre le design de la partie analogique moins contraignant en allégeant le cahier des charges et nous ont ainsi permis de simplifier l'architecture du synthétiseur. / The aim of this thesis is to study the feasibility and the performances of a fast switching frequency synthesizer designed for high debit multi-band multi-user transmission and used in transmission systems requiring a low consumption and an easy IC integration. In this context, the use of the classical synthesizer structures does not apply and there is a need to develop new architectures capable of generating all the frequencies permanently. Thus, the switching between frequencies can be easily done by changing multiplexors' state.In the first part of this study, we focus on the analysis of such high potential OL architecture. The main part of the proposed structure is implemented in a conventional BiCMOS technology in order to validate its feasibility and the operation of the developed blocks. Thanks to the measurements of the OL components, a complete analysis of the synthesizer is made. However, the complexity of the architecture of the proposed synthesizer induces the generation of large number of parasitic frequencies, creating interferences between the active users. The reduction of their effect on the transmission is the subject of the second part of the manuscript. Two digital methods are proposed to reduce the interferences. Lowering the requirements on the analog part, they allow a simplified design. This property was used to reduce the complexity of the frequency synthesizer.

Aiming to achieve the better efficiency in the use of bandwidth (spectral efficiency), as well as a compromise with the energy utilized in the process (power efficiency), the service operators are obliged to change the way in which the information is conveyed. The simplicity of the OOK modulation format has always been the main reason for using it in optical communications. Hence, once the coherent technologies had reached the maturity from a commercial point of view, they have become real alternatives to extend the capacity of networks. In this thesis, the performance of single and multirate FFH-OCDMA networks based on coherent modulation formats is addressed. The following modulation formats are assumed: binary and quadrature phase shift keying (BPSK and QPSK). For single rate networks, BPSK or QPSK are used as the modulation format for all users. For multirate networks, on the other hand, BPSK and QPSK modulation formats are employed for low and high rate transmission users, respectively. For both networks, new bit error rate (BER) formalisms regarding the main deleterious source in OCDMA are derived, namely multipleaccess interference (MAI). The mathematical formalism developed here accounts for any kind of users\' signal waveforms (which are accurately accounted for at the desired user\'s receiver). As a result, it can be successfully used to carry out performance analysis of any OCDMA network. Moreover, it is shown that both low and high rate users can surprisingly achieve similar BER levels. In addition, it is demonstrated that incoherent OOK-based networks are not good candidates for future single and multirate FFH-OCDMA implementations in this interference limited scenario. On the other hand, our results pave the way for BPSK- and QPSK -based networks, which are seen as potential candidates for next generation passive optical networks (NG-PON2), where higher data rates and a vast amount of users will be major network requirements. / No intuito de alcançar uma melhor eficiência no uso da largura de banda (eficiência espectral), bem como um compromisso com a energia utilizada no processo de transmissão de informações (eficiência em potência), as operadoras de serviços estão sendo obrigadas a alterar o modo em que a informações estão sendo transmitidas. Neste sentido, a simplicidade do formato de modulação OOK sempre foi a principal razão para a sua utilização em sistemas de comunicações ópticas. Assim, uma vez que a tecnologia coerente tem alcançado a maturidade do ponto de vista comercial, estas são reais alternativas para aumentar a capacidade das redes de comunicação ópticas. Nesta tese, são avaliados os desempenhos de redes FFH-OCDMA convencionais e de múltiplas taxas baseadas em formatos de modulação coerentes. Os seguintes formatos de modulação assumidos são: modulação por chaveamento de fase binário e por quadratura (BPSK e QPSK). Para redes convencionais, BPSK e QPSK são utilizados como formatos de modulação para todos os usuários. Por outro lado, para redes de múltiplas taxas de transmissão, os formatos de modulação BPSK e QPSK são empregados para baixas e altas taxas, respectivamente. Para ambas as redes, foram derivados novos formalismos matemáticos considerando a principal fonte deletéria de desempenho em OCDMA, comumente chamada de MAI, no cálculo da BER. Os formalismos matemáticos desenvolvidos são generalizados para quaisquer tipos de formas de onda empregada nos sinais dos usuários (as quais são contabilizadas precisamente no receptor do usuário de interesse). Como resultados, o formalismo matemático pode ser utilizado com sucesso para realizar a análise de desempenho de qualquer rede OCDMA. Adicionalmente, é demonstrado que ambos os usuários em baixa ou alta taxa de transmissão podem surpreendentemente alcançar níveis similares de BER. Concomitantemente, é observado que redes incoerentes baseadas em OOK não são boas candidatas para implementações convencionais e de múltiplas taxas de transmissão considerando esse cenário limitado por interferência. Por outro lado, os resultados trilham o caminho para redes baseadas em BPSK e QPSK, as quais são potenciais candidatas para a próxima geração de redes ópticas passivas (NG-PON2), onde os maiores requisitos são as altas taxas de transmissão e grande capacidade de inserção simultânea de usuários.

Asynchronous multiplexing schemes are efficient than synchronous schemes, in a bursty traffic environment of multiple access local area network (LAN), as fixed bandwidth is not allocated among the users and there is no access delay. Fiber- Optic Code-Division Multiple Access (FO-CDMA) is one such asynchronous multiplexing scheme suitable for high speed LAN networks. While FO-CDMA offers potential benefits it also faces challenges in three diverse areas which are 1) coding algorithms and schemes 2) advanced encoding and decoding hardware and 3) network architecture. In this thesis, as a solution to the first challenge, we propose the design and construction of a new family of codes, wavelength/time multiple-pulses-per-row (W/T MPR) codes. These codes have good cardinality, spectral efficiency and minimal cross-correlation values. Performance analysis of the W/T MPR codes is carried out and found to be superior to other codes. In unipolar 1-D Optical Orthogonal Codes (OOCs) proposed by Salehi et al., the ratio of code length/code weight grows rapidly as the number of users is increased for a reasonable weight. Hence, for a given pulse width, the data rate decreases or in other words for a given data rate very narrow pulses have to be used, because of which dispersion effects will be dominant. To overcome the drawbacks of non-linear effects in large spread sequences of 1-D unipolar codes in FO-CDMA networks, several two-dimensional codes have been proposed. Wavelength-time (W/T) encoding of the two-dimensional codes is practical in FO-CDMA networks. W/T codes reported so far can be classified mainly into two types: 1) hybrid sequences, where one type of sequence is crossed with another to improve the cardinality and correlation properties and 2) matrix codes, 1-D sequences converted to 2-D codes or 2-D codes by construc- tion, to reduce the ’time’ spread of the sequences/codes. Prime-hop and eqc/prime W/T hybrid codes have been proposed where one type of sequence is crossed with another to improve the cardinality and correlation properties. Other constructions deal with conversion of 1-D sequences to 2-D codes either by using Chinese remainder theorem or folding GoLomb rulers. W/T single-pulse-per-row (W/T SPR) codes are 2-D codes constructed using algebraic method Addition Modulo Group operation. Motivation for this work: To design a family of 2-D codes which have the design choice of length of one dimension over the other, and also have better cardinality, spectral efficiency and also low cross-correlation values (thereby have low BER) than that of the reported unipolar 2-D codes. In this thesis, we describe the design principles of W/T MPR codes, for in- coherent FO-CDMA networks, which have good cardinality, spectral efficiency and minimal cross-correlation values. Another feature of the W/T MPR codes is that the aspect ratio can be varied by trade off between wavelength and temporal lengths. We lay down the necessary conditions to be satisfied by W/T MPR codes to have minimal correlation values of unity. We analytically prove the correlation results and also verify by simulation (of the codes) using Matlab software tool. We also discuss the physical implementation of the W/T MPR FO-CDMA network with optical encoding and decoding. We show analytically that when distinct 1-D OOCs of a family are used as the row vectors of a W/T MPR code, it will have off-peak autocorrelation equal to ‘1’. An expression for the upper bound on the cardinality of W/T MPR codes is derived. We also show that 1-D OOCs and W/T SPR codes are the limiting cases of W/T MPR codes. Starting with distinct 1-D OOCs, of a family, as row vectors, we propose a greedy algorithm, for the construction of W/T MPR codes and present the repre- sentations of the results. An entire W/T MPR code family, generated using greedy algorithm, is simulated for various number of interfering users. Performance analysis of the W/T MPR codes and their limiting cases is carried out for various parameter variations such as the dimensions of wavelength, time and weight of the code. We evaluate the performance in terms of BER, capacities of the networks, temporal lengths needed (to achieve a given BER). Multiple access interference (MAI) signal can be reduced, by using a bistable optical hard-limiter device in the W/T MPR code receiver, by eliminating those signal levels which exceed a certain preset level. Performance analysis of the W/T MPR codes and their limiting cases is studied for various parameter variations. For given wavelength × time dimensions, we compare various W/T codes, whose cardinalities are known, and show that W/T MPR family of codes have better cardinality and spectral efficiency than the other (reported) W/T codes. As W/T MPR codes are superior to other W/T codes in terms of cardinality, spectral efficiency, low peak cross-correlation values and at the same time have good performance, makes it a suitable coding scheme for incoherent FO-CDMA access networks.

Aiming to achieve the better efficiency in the use of bandwidth (spectral efficiency), as well as a compromise with the energy utilized in the process (power efficiency), the service operators are obliged to change the way in which the information is conveyed. The simplicity of the OOK modulation format has always been the main reason for using it in optical communications. Hence, once the coherent technologies had reached the maturity from a commercial point of view, they have become real alternatives to extend the capacity of networks. In this thesis, the performance of single and multirate FFH-OCDMA networks based on coherent modulation formats is addressed. The following modulation formats are assumed: binary and quadrature phase shift keying (BPSK and QPSK). For single rate networks, BPSK or QPSK are used as the modulation format for all users. For multirate networks, on the other hand, BPSK and QPSK modulation formats are employed for low and high rate transmission users, respectively. For both networks, new bit error rate (BER) formalisms regarding the main deleterious source in OCDMA are derived, namely multipleaccess interference (MAI). The mathematical formalism developed here accounts for any kind of users\' signal waveforms (which are accurately accounted for at the desired user\'s receiver). As a result, it can be successfully used to carry out performance analysis of any OCDMA network. Moreover, it is shown that both low and high rate users can surprisingly achieve similar BER levels. In addition, it is demonstrated that incoherent OOK-based networks are not good candidates for future single and multirate FFH-OCDMA implementations in this interference limited scenario. On the other hand, our results pave the way for BPSK- and QPSK -based networks, which are seen as potential candidates for next generation passive optical networks (NG-PON2), where higher data rates and a vast amount of users will be major network requirements. / No intuito de alcançar uma melhor eficiência no uso da largura de banda (eficiência espectral), bem como um compromisso com a energia utilizada no processo de transmissão de informações (eficiência em potência), as operadoras de serviços estão sendo obrigadas a alterar o modo em que a informações estão sendo transmitidas. Neste sentido, a simplicidade do formato de modulação OOK sempre foi a principal razão para a sua utilização em sistemas de comunicações ópticas. Assim, uma vez que a tecnologia coerente tem alcançado a maturidade do ponto de vista comercial, estas são reais alternativas para aumentar a capacidade das redes de comunicação ópticas. Nesta tese, são avaliados os desempenhos de redes FFH-OCDMA convencionais e de múltiplas taxas baseadas em formatos de modulação coerentes. Os seguintes formatos de modulação assumidos são: modulação por chaveamento de fase binário e por quadratura (BPSK e QPSK). Para redes convencionais, BPSK e QPSK são utilizados como formatos de modulação para todos os usuários. Por outro lado, para redes de múltiplas taxas de transmissão, os formatos de modulação BPSK e QPSK são empregados para baixas e altas taxas, respectivamente. Para ambas as redes, foram derivados novos formalismos matemáticos considerando a principal fonte deletéria de desempenho em OCDMA, comumente chamada de MAI, no cálculo da BER. Os formalismos matemáticos desenvolvidos são generalizados para quaisquer tipos de formas de onda empregada nos sinais dos usuários (as quais são contabilizadas precisamente no receptor do usuário de interesse). Como resultados, o formalismo matemático pode ser utilizado com sucesso para realizar a análise de desempenho de qualquer rede OCDMA. Adicionalmente, é demonstrado que ambos os usuários em baixa ou alta taxa de transmissão podem surpreendentemente alcançar níveis similares de BER. Concomitantemente, é observado que redes incoerentes baseadas em OOK não são boas candidatas para implementações convencionais e de múltiplas taxas de transmissão considerando esse cenário limitado por interferência. Por outro lado, os resultados trilham o caminho para redes baseadas em BPSK e QPSK, as quais são potenciais candidatas para a próxima geração de redes ópticas passivas (NG-PON2), onde os maiores requisitos são as altas taxas de transmissão e grande capacidade de inserção simultânea de usuários.