Digital Signal Processing Research Program

Contains table of contents for Section 2, an introduction, reports on twenty-two research projects and a list of publications.Sanders, a Lockheed-Martin Corporation Contract BZ4962U.S. Army Research Laboratory Contract DAAL01-96-2-0001U.S. Navy - Office of Naval Research Grant N00014-93-1-0686National Science Foundation Grant MIP 95-02885U.S. Navy - Office of Naval Research Grant N00014-96-1-0930National Defense Science and Engineering FellowshipU.S. Air Force - Office of Scientific Research Grant F49620-96-1-0072U.S. Navy - Office of Naval Research Grant N00014-95-1-0362National Science Foundation Graduate Research FellowshipAT&T Bell Laboratories Graduate Research FellowshipU.S. Army Research Laboratory Contract DAAL01-96-2-0002National Science Foundation Graduate FellowshipU.S. Army Research Laboratory/Advanced Sensors Federated Lab Program Contract DAAL01-96-2-000

Channel Identification Using Chaos for an Uplink/Downlink Multicarrier Code Division Multiple Access System, Journal of Telecommunications and Information Technology, 2010, nr 1

A scheme of chaotic spreading sequence for multicarrier code division multiple access system (MC-CDMA) is proposed to estimate the transmission channel. This system spreads spectrum and identifies the channel, simultaneously. The proposed scheme uses a chaotic sequence generated by a logistic map as a training signal and estimate channel parameters according to dynamics of the chaotic sequence. Encoding data by chaotic sequences is first built and then the orthogonal codes are used to spread the encrypted data for multiusers scheme. At the reception, first the channel parameters are identified using a training chaotic sequence in order to equalize the received data, and then the encrypted information is decoded for the desired user. The studies reveal that the proposed system (chaos plus orthogonal codes) significantly outperforms the Walsh-Hadamard code spreading in MC-CDMA system. The performance of the system is considered in the multiuser case by means of simulation. The simulation result shows that the proposed chaotic code spreading approach for channel identification achieves significant improvement in the channel identification, comparing to using others training sequence or the least square method

Digital Signal Processing Research Program

Contains table of contents for Section 2, an introduction, reports on twenty research projects and a list of publications.Lockheed Sanders, Inc. Contract BZ4962U.S. Army Research Laboratory Grant QK-8819U.S. Navy - Office of Naval Research Grant N00014-93-1-0686National Science Foundation Grant MIP 95-02885U.S. Navy - Office of Naval Research Grant N00014-95-1-0834U.S. Navy - Office of Naval Research Grant N00014-96-1-0930U.S. Navy - Office of Naval Research Grant N00014-95-1-0362National Defense Science and Engineering FellowshipU.S. Air Force - Office of Scientific Research Grant F49620-96-1-0072National Science Foundation Graduate Research Fellowship Grant MIP 95-02885Lockheed Sanders, Inc. Grant N00014-93-1-0686National Science Foundation Graduate FellowshipU.S. Army Research Laboratory/ARL Advanced Sensors Federated Lab Program Contract DAAL01-96-2-000

Techniques in secure chaos communication

In today's climate of increased criminal attacks on the privacy of personal or confidential data over digital communication systems, a more secure physical communication link is required. Chaotic signals which have bifurcation behavior (depending on some initial condition) can readily be exploited to enhance the security of communication systems. A chaotic generator produces disordered sequences that provide very good auto- and cross- correlation properties similar to those of random white noise. This would be an important feature in multiple access environments. These sequences are used to scramble data in spread spectrum systems as they can produce low co-channel interference, hence improve the system capacity and performance. The chaotic signal can be created from only a single mathematical relationship and is neither restricted in length nor is repetitive/ cyclic. On the other hand, with the progress in digital signal processing and digital hardware, there has been an increased interest in using adaptive algorithms to improve the performance of digital systems. Adaptive algorithms provide the system with the ability to self-adjust its coefficients according to the signal condition, and can be used with linear or non-linear systems; hence, they might find application in chaos communication. There has been a lot of literature that proposed the use of LMS adaptive algorithm in the communication arena for a variety of applications such as (but not limited to): channel estimation, channel equalization, demodulation, de-noising, and beamforming. In this thesis, we conducted a study on the application of chaos theory in communication systems as well as the application of adaptive algorithms in chaos communication. The First Part of the thesis tackled the application of chaos theory in com- munication. We examined different types of communication techniques utilizing chaos theory. In particular, we considered chaos shift keying (CSK) and mod- ified kind of logistic map. Then, we applied space-time processing and eigen- beamforming technique to enhance the performance of chaos communication. Following on, we conducted a study on CSK and Chaos-CDMA in conjunction with multi-carrier modulation (MCM) techniques such as OFDM (FFT/ IFFT) and wavelet-OFDM. In the Second Part of the thesis, we tried to apply adaptivity to chaos com- munication. Initially, we presented a study of multi-user detection utilizing an adaptive algorithm in a chaotic CDMA multi-user environment, followed by a study of adaptive beamforming and modified weight-vector adaptive beam- forming over CSK communication. At last, a study of modified time-varying adaptive filtering is presented and a conventional adaptive filtering technique is applied in chaotic signal environment. Twelve papers have been published during the PhD candidature, include two journal papers and ten refereed conference papers

Analysis of Chaos-Based Coded Modulations under Intersymbol Interference

Ministerio de Educación y CienciaMinisterio de Ciencia e InnovaciónMinisterio de IndustriaComunidad de Madri

Program of the 3rd International Conference on Signal Processing and Communication Systems, Omaha, Nebraska, 28-30 September 2009

10 sessions; 2 poster sessions. Schedule and Table of Contents

Performance Evaluation of DS-CDMA Receivers Using Genetic Algorithm

Direct sequence-code division multiple access (DS-CDMA) technique is used in cellular systems where users in the cell are separated from each other with their unique spreading codes. In recent times DS-CDMA has been used extensively. These systems suffers from multiple access interference (MAI) due to other users transmitting in the cell, channel inter symbol interference (ISI) due to multipath nature of channels in presence of additive white Gaussian noise(AWGN). Spreading codes play an important role in multiple access capacity of DS-CDMA system. M-sequences, gold sequences etc., has been traditionally used as spreading codes in DS-CDMA. These sequences are generated by shift registers and periodic in nature. So these sequences are less in number and also limits the security. This thesis presents an investigation on use of new type of DS CDMA receiver called Genetic Algorithm based DS-CDMA receiver. Genetic Algorithm is robust optimization technique and does not fall into local minima hence this gives better weight optimization of any system. This Thesis investigates the performance of GA based DS-CDMA communication using gold code sequences. Extensive simulation studies demonstrate the performance of the different linear and nonlinear DS-CDMA receivers like RAKE receiver, matched filter (MF) receiver, minimum mean square error (MMSE) receiver using gold sequences and the performance have been compared with GA based receiver

Digital Signal Processing Research Program

Contains table of contents for Section 2, an introduction, reports on twenty-one research projects and a list of publications.U.S. Navy - Office of Naval Research Grant N00014-93-1-0686Lockheed Sanders, Inc. Contract P.O. BY5561U.S. Air Force - Office of Scientific Research Grant AFOSR 91-0034National Science Foundation Grant MIP 95-02885U.S. Navy - Office of Naval Research Grant N00014-95-1-0834MIT-WHOI Joint Graduate Program in Oceanographic EngineeringAT&T Laboratories Doctoral Support ProgramDefense Advanced Research Projects Agency/U.S. Navy - Office of Naval Research Grant N00014-89-J-1489Lockheed Sanders/U.S. Navy - Office of Naval Research Grant N00014-91-C-0125U.S. Navy - Office of Naval Research Grant N00014-89-J-1489National Science Foundation Grant MIP 95-02885Defense Advanced Research Projects Agency/U.S. Navy Contract DAAH04-95-1-0473U.S. Navy - Office of Naval Research Grant N00014-91-J-1628University of California/Scripps Institute of Oceanography Contract 1003-73-5

Kaotik haberleşme sistemlerinde gözü kapalı kanal denkleştirme

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu çalışmada, SISO ve MIMO kaotik haberleşme sistemlerinde gözü kapalı kanal denkleştirme problemi ele alınmıştır. SISO FIR filtreler olarak modellenen kanalların denkleştirilmesi için uyarlamalı özyinelemeli ve yinelemeli olmayan uyarlamalı iki algoritma geliştirilmiştir. SISO algoritmalarının ilkinde denkleştirici IIR ikincisinde ise FIR uyarlamalı bir filtre olarak tasarlanmıştır. Algoritmalar, kaotik işaretlerin kısa süreli öngörülebilirliklerinden yaralanılarak çıkartılmıştır. Algoritmaların performansları detaylı simülasyonlar yapılarak tespit edilmiştir. Geliştirilen algoritmaların literatürde sıklıkla kullanılan MNPE yönteminden daha yüksek performans sağladıkları gösterilmiştir. Uyarlamalı özyinelemeli algoritma en iyi denkleştirme sonuçlarını vermesine rağmen önemli iki sınırlamaya sahiptir. Yinelemeli olmayan uyarlamalı algoritma performansın bir miktar düşmesi karşılığında bu iki sınırlamayı kaldırmaktadır. Ayrıca, yinelemeli olmayan algoritma optimum sabit filtre ile kıyaslanmış ve algoritmanın optimum sabit filtreye oldukça yakın sonuçlar verdiği gösterilmiştir. Daha sonra, MIMO klasik haberleşme sistemleri için geliştirilen kavramlara benzer bir şekilde, SISO kaotik haberleşme durumunda kullanılan maliyet fonksiyonu MIMO durumuna uyarlanarak elde edilen gözü kapalı bir kanal denkleştirme algoritması önerilmiştir. Algoritma geliştirilmeden önce, MIMO bir kanal için mükemmel denkleştirmeyi gerçekleştirebilecek bir denkleştiricinin varlığı ve tekliği için gerek ve yeter koşullar tespit edilmiştir. Kanalın bilindiği varsayılarak optimum sabit filtre tasarlanmıştır. Literatürde MIMO kaotik haberleşme sistemleri için geliştirilen bir algoritma olmadığından algoritmanın performansı optimum sabit filtrenin performansı ile kıyaslanmıştır. Simülasyonlar vasıtasıyla, MIMO uyarlamalı denkleştiricinin giriş işaretlerini doğru bir şekilde kestirdiği ve önerilen algoritmanın optimum sabit filtreye oldukça yakın sonuçlar verdiği gösterilmiştir.In this study, blind channel equalization problem for SISO and MIMO chaotic communication systems is investigated. An adaptive autoregressive filter and a non-recursive adaptive filter are developed for equalizing SISO channels that are modelled as FIR filters. Equalizer is designed as an adaptive IIR filter in the first SISO algorithm while it is modelled as an adaptive FIR filter in the second algorithm. Algorithms are derived by exploiting short time predictability of chaotic signals. Simulation results are provided to demonstrate effectiveness of the proposed adaptive algorithms. Proposed algorithms are shown to give better equalization results compared to the frequently used MNPE method. Even though the adaptive autoregressive algorithm gives the best equalization results, it has two serious limitations. Non-recursive adaptive algorithm avoid these limitations at the cost of slightly decreased performance. In addition, the non-recursive algorithm was compared to the optimum filter and it was shown to exhibit performance similar to that of optimum filter. Finally, similar to blind equalization methods for MIMO classical communication systems, a novel blind channel equalization algorithm is developed for MIMO chaotic communication systems by modifying the cost function used in SISO chaotic equalization algorithms. Existence and uniqueness conditions fort he MIMO reconstruction filters are investigated before deriving the adaptive MIMO algorithm. An optimum fixed filter is developed for MIMO chaotic communication systems. Since there do not exist a method for comparison, the proposed algorithm is compared to the optimum fixed filter. That the adaptive MIMO equalizer estimates the input signals correctly and it gives results very close to that of the optimum fixed filter are shown via simulations

On the Realization of Non-Linear Pseudo-Noise Generator for various Signal Processing and Communication Applications

In digital communication systems and digital signal processing, the design of pseudo-noise (PN) sequences having good correlation properties has been one of the most important development steps. Its well-known application areas include spread spectrum communications, Multiuser Communications, Digital Signal Processing for reduction of power spectral density, mitigation of Multiple Access Interference (MAI) and improvement of signal to noise ratio (SNR) respectively. In this paper a performance of non- linear PN code generator for interference rejection improvement of signal to noise ratio in signal processing applications have been studied.  The signal of interest can be considered to be a digitally controlled wide band digital chaotic signal, which has been implemented by conventional PN code generators.  The proposed technique can be used as an alternative code for improvement in signal to noise ratio, interference rejection, spreading code for various signal processing and communication applications.  The proposed scheme has been implemented using matlab as a simulation tool.  Power spectral density, auto-correlation and cross-correlation property have been thoroughly studied and has been compared with conventional scheme and are presented in the paper. Keywords: PN Code Generator, Spread Spectrum Modulation, Auto-correlation, Cross-correlation, Power Spectral Density