Design and Development of Code Division Multiple Access Techniques for Various Communications and Signal Processing Applications

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Design and Development of Code Division Multiple Access Techniques for Various Communications and Signal Processing Applications

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Title: Design and Development of Code Division Multiple Access Techniques for Various Communications and Signal Processing Applications
Author: Sheikh, Javaid Ahmad (Scholar); Bhat, G. Mohiuddin (Guide)
Abstract: The goal for the next generation of mobile communication systems is to seamlessly integratewide variety of communication services such as high speed data, video and multimediatraffic as well as voice signals and high data rates with low bandwidth.Further, communication systems are to be power efficient.The technology needed to tackle these challenges to make theseservices available is popularly known as Code Division Multiple Access technology which is being employed in Third Generation (3G) and Fourth Generation 4G communication systems. One ofthe most promising approaches to 3G and 4G systemsis to combine a Wideband Code Division MultipleAccess (WCDMA) air interface with the fixed network of Global System for Mobilecommunications also called as Group Service Mobile (GSM). The work carried out in this thesis is concerned with the design and development of Code Division Multiple Access techniques for various Communications and Signal processing applications. The statistical properties of Pseudo- Noise (PN) codes have also been thoroughly studied. Chaotic signals have been generated using novel techniques. The main focus has been given on Multi- carrier and Multiuser CDMA communication systems. In a practical CDMA communication systems the transmitted signal is corrupted bymultiple access interference which is generated in a structured way rather than treating it asAdditive White Gaussian Noise (AWGN). The signal is further corrupted by AWGN at thefront end of the receiver; various techniques have been proposed in this thesis which exploits the characteristic properties of frequency selective channel like Rayleigh channel. The modeling of frequency selective channel has also been done. Beam forming and rake diversity combing has beenemployed.The bit error rate, correlation and power spectral density properties have been investigated atthe receiving end to evolve the performance of the proposed techniques. Spreading codes are widely employed in CDMA based communication systems and Signal Processing applications. Different techniques are being employed for the realization of PN codes. A novel spreading scheme for generation of PN- codes has been presented in this thesis. Performance evaluation of the non- linear PN code in terms of auto- correlation and cross- correlation properties has been evaluated and compared with conventional PN codes. Fourth generation mobile communications are being designed to support very high speed services of 100 Mbs to 1Gbs. For such high speed data transmissions, the channel becomes severely frequency selective due to time dispersion and the same system is not sufficient since the channel is both space and frequency dependent. To reduce Multiple Access Interference (MAI) and data transmission losses, beam forming technique using Antenna Array based DS- CDMA to overcome above mentioned problems has been proposed in this thesis. The performance of the proposed technique has been verified by computing Bit Error Rate (BER)versus Signal to Noise Ratio (SNR) which is related to variance. A new multi-user detection (MUD) technique has been proposed. In CDMA spreading is achieved by using long PN or other codes so as to achieve high processing gain to reduce the effect of jamming and multipath interference. However, high value of processing gain requires spreading code of large length. In the proposed technique a novel method has been proposed in which time domain spreading is achieved at two successive stages which results T x T spreading. Modern wireless communication systems based on CDMA techniques operate in environments that are interference, bandwidth, and multi- path fading limited. In order to combat these effects, complex receiver structures, such as those using complicated synchronization structures, demodulators, multi- user detectors and RAKE processors are often used. A Parallel Interference Cancellation (PIC) based CDMA system over Multipath Rayleigh fading channel has been proposed in this thesis. The proposed detector estimates and subtracts out all of the MAI for each user in parallel. Anovel Intermediate Frequency Hopping (IF- FH) Spread Spectrumtechnique for CDMA applications has been proposed and investigated. The proposed technique requires low speed frequency synthesizers and low power consumption as the whole system has been operated at intermediate frequency and consequently adds a new variant of frequency hopping spread spectrum called as Intermediate Frequency Hopping Spread Spectrum. The new scheme for the generation of digitally controlled chaotic signal for spreading in CDMA applications has been proposed in thisthesis. Chaotic Systems are dynamic systems which show complex behavior. One of the defining attributes of chaotic system is the sensitive dependence on initial conditions. Time series generated from chaotic systems are wide-band in nature and noise like in appearance. A chaotic based system Frequency Hopping Spread Spectrum for CDMA applications has been proposed in this thesis in which digital method has been used to generate the wide-band analog chaotic signal for signal spreading. A Pseudo Noise (PN) code controlled chaotic signal generator using real time Frequency Hopping Spread Spectrum technique has also been proposed. The proposed technique has a capability to initialize the chaotic signal generator which is necessary for predicting the future value for an authorized receiver. Some of the proposed schemes have been simulated using Matlab/Simulink simulation software for checking the efficacy and utility. The bit error rate and correlation properties have also been checked. Prototype hardware modules of some of the proposed schemes presented in this thesis have been developed for experimental investigation. The thesis concludes with a discussion over the results of the conducted work during the course of this research. Future scope of work in this thesis direction has been discussed. A bibliography of concerned literature consulted has also been presented.
URI: http://dspaces.uok.edu.in/jspui//handle/1/978
Date: 2012


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