The use of Code Division Multiple Access (CDMA) technology for cellular radio and personal communications has ushered in a new era wherein the benefits of CDMA can be directly applied to voice transmission. In particular, the resistance to multipath and graceful degradation of performance (voice quality) in the presence of multiple access interference are the significant benefits of CDMA. Spectral efficiency is a key issue in mobile communications. The use of vocoders reduces the average bit transmission rate for each user, thereby reducing the bandwidth necessary to transmit the speech of each user. Qualcomm-Code Excited Linear Prediction (QCELP) algorithm provides a way to implement a variable rate vocoder which could reduce the average bit rate by a factor of two. This thesis describes a software implementation of the QCELP algorithm and the integration of the vocoder with the CDMA transmission and reception segments. A subjective performance analysis of the vocoder, using a Mean Opinion Score (MOS) test on the speech quality under various channel conditions including 1-Ray and 2-Ray Rayleigh fading environments is performed. Objective quality measures such as Signal-to-Noise Ratio (SNR), Segmental SNR (SSNR) and the Coherence Function (CF) are also investigated for comparison with the subjective analysis results. / Master of Science

We consider the transmission of correlated sources over a multiple access channel(MAC). Multiple access channels are important building blocks in many practical communication systems, e.g., local area networks(LAN), cellular systems, wireless multi-hop networks. Thus this topic has been studied for last several decades. One recent motivation is estimating a random field via wireless sensor networks. Often the sensor nodes are densely deployed resulting in correlated observations. These sensor nodes need to transmit their correlated observations to a fusion center which uses this data to estimate the sensed random field. Sensor nodes have limited computational and storage capabilities and very limited energy. Since transmission is very energy intensive, it is important to minimize it. This motivates our problem of energy efficient transmission of correlated sources over a sensor network. Sensor networks are often arranged in a hierarchical fashion. Neighboring nodes can first transmit their data to a cluster head which can further compress information before transmission to the fusion center. The transmission of data from sensor nodes to their cluster-head is usually through a MAC. At the fusion center the underlying physical process is estimated. The main trade-off possible is between the rates at which the sensors send their observations and the distortion incurred in estimation at the fusion center. The availability of side information at the encoders and/or the decoder can reduce the rate of transmission. In this thesis, the above scenario is modeled as an information theoretic problem. Efficient joint source-channel codes are discussed under various assumptions on side information and distortion criteria. Sufficient conditions for transmission of discrete/continuous alphabet sources with a given distortion over a discrete/continuous alphabet MAC are given. We recover various previous results as special cases from our results. Furthermore, we study the practically important case of the Gaussian MAC(GMAC) in detail and propose new joint source-channel coding schemes for discrete and continuous sources. Optimal schemes are identified in different scenarios. The protocols like TDMA, FDMA and CDMA are widely used across systems and standards. When these protocols are used the MAC becomes a system of orthogonal channels. Our general conditions can be specialized to obtain sufficient conditions for lossy transmission over this system. Using this conditions, we identify an optimal scheme for transmission of Gaussian sources over orthogonal Gaussian channels and show that the Amplify and Forward(AF) scheme performs close to the optimal scheme even at high SNR. Next we investigate transmission of correlated sources over a fast fading MAC with perfect or partial channel state information available at both the encoders and the decoder. We provide sufficient conditions for transmission with given distortions. We also provide power allocation policies for efficient transmission. Next, we use MAC with side information as a building block of a hierarchical sensor network. For Gaussian sources over Gaussian MACs, we show that AF performs well in such sensor network scenarios where the battery power is at a premium. We then extend this result to the hierarchical network scenario and show that it can perform favourably to the Slepian-Wolf based source coding and independent channel coding scheme. In a hierarchical sensor network the cluster heads often need to send only a function of the sensor observations to the fusion center. In such a setup the sensor nodes can compress the data sent to the cluster head exploiting the correlation in the data and also the structure of the function to be computed at the cluster head. Depending upon the function, exploiting the structure of the function can substantially reduce the data rate for transmission. We provide efficient joint source-channel codes for transmitting a general class of functions of the sources over the MAC.

In this thesis, we investigate in detail, certain important problems in cryptography and coding theory. In the first part of this thesis, we discuss the number field sieve and compare the two ways in which the sieving step is implemented -one method using the line sieve and the other using the lattice sieve. We discuss why the lattice sieve performs better than the line sieve in the presence of large primes -this has not been attempted before. In the second part of this thesis, we design low-correlation CDMA sequences over the Quadrature Amplitude Modulation (QAM) alphabet. The sequences proposed in this thesis have the lowest value of the maximum correlation parameter as compared to any other family in the literature. In the third part of this thesis, we design large families of optimal two-dimensional optical orthogonal codes for optical CDMA. The size of these codes is larger than any other code in the literature.

Direct-Sequence Code Division Multiple Access (DS-CDMA), over the last few years, has become a popular technique and finds a place in many modern communication systems. The performance of this technique is closely linked to the signature (or spreading) sequences employed in the system. In the past, there have been many successful attempts by research groups to construct families of signature sequences that offer the potential gains promised by theoretical bounds. In this thesis, we present constructions of families of signature sequences over the AM-PSK and QAM alphabet with low correlation. In this thesis, we construct a family of sequences over the 8-ary AM-PSK constella- tion, Family AOpt(16) that is asymptotically optimal with respect to the Welch bound on maximum magnitude of correlation for complex sequences. The maximum magnitude of correlation for this family, θmax, is upper bounded by √N , where N is the period of the sequences. The 8-ary AM-PSK constellation is a subset of the 16-QAM constellation. We also construct two families of sequences over 16-QAM, Family A16A, and Family A16,B , with the maximum magnitude of correlation upper bounded by √2√N . We construct a family, A(M 2), of sequences over the 2m+1-ary AM-PSK constellation of period N = 2r- 1 and family size (N + 1)/2m-1 . The 2m+1-ary AM-PSK constellation is a subset of the M 2-QAM constellation with M =2m . The maximum nontrivial normalized correlation parameter is bounded above by θmax < a √N where a ranges from 1.34 in the case of M 2 = 16 to √5 for large m. Apart from low correlation values, the family possesses several interesting and useful features. In Family A(M 2), users have the ability to transmit 2m bits of data per period of the spreading sequence. The sequences in Family A(M 2) are balanced; all points from the 2m+1-ary AM-PSK constellation occur approximately equally often in sequences of long period. The Euclidean distance between the signals assigned to a particular user in A(M 2), corresponding to different data symbols, is larger than the corresponding value for the case when 2m+1-PSK modulation and spreading is used. Perhaps most interestingly, Family A(M 2) permits users on the reverse link of a CDMA system to communicate asynchronously at varying data rates by switching between different QAM constellations. Family A(M 2) is compatible with QPSK sequence families S(p) in the sense that the maximum correlation magnitude is increased only slightly if one adds sequences from (p) S(p)\ S(0) to Family A(M 2). We also construct families of sequences over AM-PSK that tradeoff data rate per sequence period and θmax for a given family size. We have extended the construction of sequences over AM-PSK constellation to construct sequences over the M 2-QAM constellation for M =2m . The QAM sequence families, Families (AM 2), have size, data rate and minimum squared Euclidean distance same as the corresponding AM-PSK construction but have higher values of θmax. Also included in the thesis are constructions for large families of sequences over the M 2-QAM alphabet.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho, alÃm dos capÃtulos que envolvem a teoria e definiÃÃes, foi basicamente divido em trÃs estudos: Primeiro (capÃtulo 4), apresentamos uma investigaÃÃo numÃrica do desempenho de um filtro passa-banda totalmente Ãptico composto por um acoplador direcional duplo seguido de duas grades de Bragg simetricamente iguais gravadas nos seus braÃos de saÃda. Esta configuraÃÃo caracteriza um InterferÃmetro de Michelson com caracterÃsticas de um filtro add/drop. As caracterÃsticas de transmissÃo (T), taxa de extinÃÃo (XR) e âcrosstalkâ (XT) foram estudadas a partir da aplicaÃÃo de um sinal CW (onda contÃnua) na entrada do dispositivo. A teoria de modos acoplados e o mÃtodo de Runge Kutta de 4a ordem foram aplicados, respectivamente para resolver as equaÃÃes diferenciais acopladas. Este à o primeiro estudo feito considerando a nÃo linearidade do acoplador e a linearidade das grades de Bragg. O dispositivo apresenta um comportamento altamente nÃo-linear em funÃÃo do defasamento entre as amplitudes dos feixes refletidos e em funÃÃo da potÃncia de entrada. Num segundo momento (capÃtulo 5) apresentamos a propagaÃÃo e chaveamento de pulsos ultracurto (~2ps) usando um interferÃmetro de Michelson de Fibras Ãpticas. Neste estudo o desempenho do interferÃmetro à estudado como uma funÃÃo das caracterÃsticas nÃo lineares do acoplador e das grades de Bragg. Os estudos numÃricos foram feitos a partir das equaÃÃes de modos acoplados resolvidas usando o mÃtodo de Runge-Kutta de 4 ordem. As caracterÃsticas de chaveamento do pulso foram analisadas em funÃÃo da potÃncia de entrada e do defasamento aplicado em uma das grades de Bragg. As caracterÃsticas de transmissÃo (T), coeficiente de ExtinÃÃo (XR), âcrosstalkâ (XT), fator de compressÃo (FC). Utilizamos trÃs valores de potÃncia de entrada: abaixo da potÃncia critica (P0=1W), igual a potÃncia crÃtica (P0=1,73W) e acima da potÃncia crÃtica (P0=1,95W). AtravÃs deste estudo, pode-se verificar que a transmissÃo, taxa de extinÃÃo, âcrosstalkâ e fator de compressÃo dependem da potÃncia da bombeio inserida no dispositivo e da defasagem aplicada. O interferÃmetro de Michelson em fibras implementa componente de grande importÃncia para aplicaÃÃes em redes Ãpticas, como os demultiplexadores add/drop. Este dispositivo tem atraÃdo bastante interesse no campo das telecomunicaÃÃes devido a sua alta capacidade de taxas de transmissÃo. Num terceiro momento foi apresentado um estudo de simulaÃÃo numÃrica do desempenho da codificaÃÃo e decodificaÃÃo de pulsos Ãpticos curtos (ps) em sistemas OCDMA (Optical Code Division Multiple Access â acesso VIII mÃltiplo por divisÃo de cÃdigo no domÃnio Ãptico) baseado em FBG (Fiber Bragg Grating â grade de Bragg em fibra Ãptica) onde os cÃdigos sÃo inseridos atravÃs de saltos discretos na fase Ãptica (Â&#960;). Para geraÃÃo de pulsos codificados foram utilizados cÃdigos de Gold obtidos analiticamente. Analisamos como a inserÃÃo de cÃdigos adicionais afetam a autocorrelaÃÃo e correlaÃÃo cruzada. O interferÃmetro de Michelson inicialmente estudado no capÃtulo 4 foi utilizado para propagaÃÃo e chaveamento de sinais codificados. Baseados nas caracterÃsticas de TransmissÃo (T) e Taxa de extinÃÃo (XR) fizemos um estudo do dispositivo como multiplexador /demultiplexador add/drop na recuperaÃÃo de pulsos codificados. / This work, in addition the chapters which involves both theory and definitions, was basically divided three studies: First (chapter 4),we present a numerical investigation of the performance of a bandpass filter composed of an all-optical directional coupler, followed by two double bars Bragg recorded symmetrically equal outputs in their arms. This configuration features a Michelson interferometer with characteristics of an add/ drop filter. The transmission characteristics (T), extinction rate (XR) and "crosstalk" (XT) were studied based on the application of a CW signal (continuous wave) into the device. Theory of coupled modes and the Runge Kutta fourth order were applied respectively to solve the coupled differential equations. This is the first study considering the nonlinearity of the coupler and the linearity of Bragg gratings. The device features a highly nonlinear behavior as a function of dephasing between the amplitudes of the reflected beams and depending on the input power. In a second step (section 5), the propagation and switching of ultrashort pulse (~ 2PS) Michelson interferometer using an optical fiber. In this study the performance of the interferometer is studied as a function of the nonlinear characteristics of the coupler and Bragg gratings. The numerical studies were made from the coupled mode equations solved using the Runge-Kutta 4th order. The pulse switching characteristics were analyzed as a function of input power and applied to one dephasing Bragg gratings. The transmission characteristics (T), extinction coefficient (XR), "crosstalk" (XT), the compression factor (CF)and shape of the pulses were analyzed for different values of phase and different input powers. We use three values of input power: below the critical power (1W = P0), equal to the critical power (P0 = 1.73W) and above the critical power (P0 = 1.95W). Through this study, it is found that the transmission rate of extinction, "crosstalk" and compression factor depends on the power of the pump device inserted into the gap and applied The Michelson interferometer fiber implement major component with applications in optical networks, such as demultiplexers add/drop. This device has attracted considerable interest in the field of telecommunications due to its ability of high transmission rates. In the third place was presented a numerical simulation study of the performance of encoding and decoding of short optical pulses (ps) systems OCDMA (Optical Code Division Multiple Access based on FBG (Fiber Bragg Grating ) where codes are inserted through discrete jumps in the optical phase ( &#960;). For generation of coded pulses were used Gold codes obtained analytically. We look at how the inclusion of additional codes affect the autocorrelation and cross correlation.The Michelson interferometer initially studied Chapters 4 was used for propagation and switching of encrypted signals. Based on the characteristics of transmission (T) and extinction rate (XR) did a study of the device as multiplexer/demultiplexer add / drop in the recovery of coded pulses.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper describes a system of Total Border Surveillance, which is cost effective, closes existing gaps and is less manpower intensive than the current techniques. The system utilizes a fleet of commercially available aircraft converted to unmanned capability, existing GPS and surveillance systems and autonomous ground stations to provide the desired coverage.

H.264/AVC encoder complexity is mainly due to variable size in Intra and Inter frames. This makes H.264/AVC very difficult to implement, especially for real time applications and mobile devices. The current technological challenge is to conserve the compression capacity and quality that H.264 offers but reduce the encoding time and, therefore, the processing complexity. This thesis applies machine learning technique for video encoding mode decisions and investigates ways to improve the process of generating more general low complexity H.264/AVC video encoders. The proposed H.264 encoding method decreases the complexity in the mode decision inside the Inter frames. Results show, at least, a 150% average reduction of complexity and, at most, 0.6 average increases in PSNR for different kinds of videos and formats. / by Paula Carrillo. / Thesis (M.S.C.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.

Zhao Fei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 87-89). / Abstracts in English and Chinese. / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Multirate Scheme --- p.2 / Chapter 1.1.1 --- VSF Scheme --- p.3 / Chapter 1.1.2 --- Multicode Scheme --- p.5 / Chapter 1.2 --- Multicode CDMA System --- p.7 / Chapter 1.2.1 --- System Model --- p.7 / Chapter 1.2.2 --- Envelope Variation of Multicode Signal --- p.9 / Chapter 1.2.3 --- Drawback of Multicode Scheme --- p.11 / Chapter 1.3 --- Organization of the Thesis --- p.13 / Chapter 2. --- Related Work on Minimization of PAP of Multicode CDMA --- p.15 / Chapter 2.1 --- Constant Amplitude Coding --- p.16 / Chapter 2.2 --- Multidimensional Multicode Scheme --- p.22 / Chapter 2.3 --- Precoding for Multicode Scheme --- p.25 / Chapter 2.4 --- Summary --- p.26 / Chapter 3. --- Multicode CDMA System with Constant Amplitude Transmission --- p.27 / Chapter 3.1 --- System Model --- p.28 / Chapter 3.2 --- Selection of Hadamard Code Sequences --- p.31 / Chapter 3.3 --- The Optimal Receiver for the Multicode System --- p.37 / Chapter 3.3.1 --- The Maximum-Likelihood Sequence Detector --- p.38 / Chapter 3.3.2 --- Maximum A Posteriori Probability Detector --- p.41 / Chapter 4. --- Multicode CDMA System Combined with Error-Correcting Codes --- p.45 / Chapter 4.1 --- Hamming Codes --- p.46 / Chapter 4.2 --- Gallager's Codes --- p.48 / Chapter 4.2.1 --- Encoding of Gallager's Codes --- p.48 / Chapter 4.2.2 --- Multicode Scheme combined with Gallager's Code --- p.52 / Chapter 4.2.3 --- Iterative Decoding of the Multicode Scheme --- p.55 / Chapter 4.3 --- Zigzag Codes --- p.59 / Chapter 4.4 --- Simulation Results and Discussion --- p.62 / Chapter 5. --- Multicode CDMA System with Bounded PAP Transmission --- p.68 / Chapter 5.1 --- Quantized Multicode Scheme --- p.69 / Chapter 5.1.1 --- System Model --- p.69 / Chapter 5.1.2 --- Interference of Code Channels --- p.71 / Chapter 5.2 --- Parallel Multicode Scheme --- p.74 / Chapter 5.2.1 --- System Model --- p.74 / Chapter 5.2.2 --- Selection of Hadamard Code Sequences --- p.75 / Chapter 6. --- Conclusions and Future Work --- p.82 / Chapter 6.1 --- Conclusions --- p.82 / Chapter 6.2 --- Future Work --- p.84 / Bibliography --- p.87

Abstract The primary mission of the Finnish Air Force is to ensure a continuous surveillance and policing of the national airspace. The wartime mission is defensive counter-air fighter operations. Implementation of the air surveillance is carried out mainly with air surveillance radars – policing and defensive actions with fighters. A foundation to a well-executed flight operation is a situation awareness. Pilots have to have a real time air picture in their use, i.e., exact information of the own and enemy’s fighters, and instructions of the mission command. The later has to have information for example about the remaining flight time of the fighters. To keep up the situation awareness the fighters participating the flight operation and the mission command on the ground are connected via real time robust communications system. In this thesis, the system development of the experimental SIHTI (Suomen ilmavoimien hajaspektritietovuo) spread spectrum data link fulfilling the national requirements is considered from the requirement specification to the performance measurements of the airproof prototype. The SIHTI system, which has to be secure, robust and having good LPD/LPI (Low Probability of Detection/Low Probability of Interception) properties has to enable bidirectional transmission between fighters and base stations as well as the fighters themselves. The SIHTI system has to operate in the case when many of similar nets are operating simultaneously in the same region and under heavy jamming. The system concept and its implementation has to be configurable so that an end user and a maintenance of the system can affect on the performance of the system only via parameters and changes in algorithms. In this thesis, it will be shown that the experimental SIHTI prototype with minor changes can fulfil the set requirements. / Tiivistelmä Suomen ilmavoimien perustehtävä on kansallisen ilmatilan jatkuva valvonta ja vartiointi sekä sodan aikana ilmatilan puolustus. Ilmatilan valvonta hoidetaan pääasiassa ilmavalvontatutkilla – vartiointi ja puolustus sotilaskoneilla. Sotilaskoneiden tehokkaan toiminnan edellytyksenä on tilannetietoisuus. Lento-operaatioon osallistuvilla tahoilla tulee olla käytettävissä ajan tasalla oleva ilmatilannekuva eli tarkat tiedot omista ja vastapuolen koneista, taistelujohdon toimintaohjeet sekä tietoa muun muassa operaatioon osallistuvien koneiden jäljellä olevasta toiminta-ajasta. Tilannetietoisuuden ylläpitäminen edellyttää, että lento-operaatioon osallistuvia lentokoneita ja maassa olevaa taistelujohtoa yhdistää reaaliaikainen varmatoiminen tiedonsiirtoyhteys. Tässä väitöskirjassa tarkastellaan kansallisen sotilasilmailun tarpeet täyttävän lentokelpoisen SIHTI (Suomen ilmavoimien hajaspektritietovuo) -hajaspektritiedonsiirtokoejärjestelmän järjestelmäkehitystä aina vaatimusmäärittelystä lentokelpoisen koelaitteiston suorituskykymittauksiin. Turvallisen, varmatoimisen ja vaikeasti tiedusteltavan tiedonsiirtojärjestelmän tulee mahdollistaa niin lentokoneiden kuin lentokoneiden ja maa-asemien välinen kaksisuuntainen sanomansiirto useiden lähekkäin toimivien verkkojen tapauksessa hyvinkin voimakkaassa tahallisessa häirinnässä. Tiedonsiirtojärjestelmässä ja sen toteutuksessa tulee olla myös riittävä määrä muunneltavuutta, jotta järjestelmän loppukäyttäjä ja järjestelmän ylläpitäjä pystyvät parametri- ja algoritmimuutoksin vaikuttamaan järjestelmän suorituskykyyn. Väitöskirjassa osoitetaan, että FH/DS-CDMA (Frequency Hopping / Direct Sequence Code Division Multiple Access)- ja TDMA (Time Division Multiple Access) -monikäyttömenetelmiin pohjautuva SIHTI-koejärjestelmä pystyy pienin muutoksin täyttämään sille asetetut vaatimukset.

Future wireless networks will have applications that require many devices to be connected to the network. Non-orthogonal multiple access (NOMA) is a promising multiple access scheme that allows more users to simultaneously transmit in a common channel than orthogonal signaling techniques. This overloading allows for high spectral efficiencies which can support the high demand for wireless access. One notable NOMA scheme is low-density spreading (LDS), which is a code domain multiple access scheme. Low density spreading operates like code division multiple access (CDMA) in the sense that users use a spreading sequence to spread their data, but the spreading sequences have a low number of nonzero chips, hence the term low-density. The message passing algorithm (MPA) is typically used for multi-user detection (MUD) of LDS systems. The MPA detector has complexity that is exponential to the number of users contributing to each chip. LDS systems suffer from two inherent problems: high computational complexity, and vulnerability to multipath channels. In this thesis, these two problems are addressed. A lower complexity MUD technique is presented, which offers complexity that is proportional to the number of users squared. The proposed detector is based on minimum mean square error (MMSE) and parallel interference cancellation (PIC) detectors. Simulation results show the proposed MUD technique achieves reductions in multiplications and additions by 81.84% and 67.87% with a loss of about 0.25 dB with overloading at 150%. In addition, a precoding scheme designed to mitigate the effects of the multipath channel is also presented. This precoding scheme applies an inverse channel response to the input signal before transmission. This allows for the received signal to eliminate the multipath effects that destroy the low-density structure.