Download or read book Simulation of a DS CDMA System for Performance Analysis Over Different Channel Conditions written by Marcelo Guillen and published by . This book was released on 1994 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Analysis of Adaptive Chaos based DS CDMA System with Imperfect Channel Estimation written by Meher Krishna Patel and published by . This book was released on 2017 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents the analysis of chaos-based direct sequence code division multiple access (DS-CDMA) systems under imperfect channel estimation environments. Chaos-based CDMA systems are studied extensively in the last few decades, but their performances under imperfect channel estimation conditions are never studied. The main motivation of the thesis is to fill this research gap under various possible conditions. The thesis focuses on three main objectives. The first objective is to determine the effect of spreading sequences in channel estimation processes. Here performances of channel estimators in the presence and absence of chaotic spreading sequences are investigated. The second objective is to study the performances of imperfect channel estimations in chaos based CDMA systems under various fading conditions. This part mainly focuses on the various factors which deteriorate the performance of the systems. The third objective focuses on the various techniques which can improve the performances of the systems. In this part various available techniques for CDMA systems are studied under imperfect channel estimation environments. It is concluded that performances of all the available chaos based CDMA systems significantly depend on performances of channel estimators. Analytical simulation results in the thesis show that performance degradation in available systems due to various fading channels can be significantly improved by using channel estimators.

Download or read book Performance Analysis and Simulation of a Direct Sequence CDMA System for Various Spreading Sequences written by Girish-Kumar K. N. and published by . This book was released on 2000 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Analysis of Asynchronous Multi carrier DS CDMA System Using Different 2 D Spreading Codes in Fading Channels written by 劉清平 and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Analysis of CDMA Systems in a Multipath Fading Channel written by Thomas Eng and published by . This book was released on 1995 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Analysis of Coherent DS CDMA System in Correlated Rayleigh Fading Channel with Rake Combining written by Liu Li and published by . This book was released on 2002 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Analysis of 2 Dimensional Spreading Codes for MC DS CDMA Wireless System Over Fading Channels written by and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Search Algorithms and Applications written by Nashat Mansour and published by BoD – Books on Demand. This book was released on 2011-04-26 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt: Search algorithms aim to find solutions or objects with specified properties and constraints in a large solution search space or among a collection of objects. A solution can be a set of value assignments to variables that will satisfy the constraints or a sub-structure of a given discrete structure. In addition, there are search algorithms, mostly probabilistic, that are designed for the prospective quantum computer. This book demonstrates the wide applicability of search algorithms for the purpose of developing useful and practical solutions to problems that arise in a variety of problem domains. Although it is targeted to a wide group of readers: researchers, graduate students, and practitioners, it does not offer an exhaustive coverage of search algorithms and applications. The chapters are organized into three parts: Population-based and quantum search algorithms, Search algorithms for image and video processing, and Search algorithms for engineering applications.

Download or read book Performance Evaluation of Different DS CDMA Receivers Using Chaotic Sequences written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 sequences called chaotic sequences for DS-CDMA system. These sequences are generated by chaotic maps. First of all, chaotic sequences are easy to generate and store. Only a few parameters and functions are needed even for very long sequences. In addition, an enormous number of different sequences can be generated simply by changing its initial condition. . Chaotic sequences are deterministic, reproducible, uncorrelated and random-like, which can be very helpful in enhancing the security of transmission in communication. This Thesis investigates the performance of chaotic sequences in DS-CDMA communication systems using various receiver techniques. 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 and Volterra receiver using chaotic sequences and the performance have been compared with gold sequences.

Download or read book Performance Evaluation of a DS CDMA Packet Transmission System Under Rician Fading Channel Conditions written by Christodoulos Argyrides and published by . This book was released on 2001 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Downlink Performance Analysis of DS CDMA System with Base Station Diversity written by Hemabh Shekhar and published by . This book was released on 2002 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis we study the performance of DS-CDMA downlink with base station diversity (BSD), since most of the works till date have concentrated on uplink. A BSD architecture is considered with three base stations (BSs) per cell and its performance compared against the conventional cellular network with one BS per cell. A mobile station (MS) will be connected to multiple BSs in its cell. In downlink each BS will transmit same data to the MS using certain power control scheme. Three power control schemes have been studied. One scheme distributes the power equally among all the BSs communicating to a certain MS, maintaining a constant transmit power. Second scheme maintains a constant power at the MS receiver taking into account the path loss. Third scheme analyzed is the famous water filling solution to compute the transmitted power in each BS-MS channel keeping the total power level constant. This scheme will have the advantage that transmitted power from each base station will be changed adaptively based on the channel SNR and interference conditions to provide maximum channel capacity. However it has been concluded from this work that this scheme is suitable for a MIMO system unlike this work which considers a MISO system. A conventional matched filter receiver is implemented at the MS. The communication channel has been modeled to have AWGN, frequency non-selective fast rayleigh multipath fading, considering the effect of path loss and MAI.

Download or read book THE CODING SPREADING TRADEOFF PROBLEM IN FINITE SIZED SYNCHRONOUS DS CDMA SYSTEMS written by and published by . This book was released on 2005 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation provides a comprehensive analysis of the coding-spreading tradeoff problem in finite-sized synchronous DS-CDMA systems. In contrast to the large system which has a large number of users, the finite-sized system refers to a system with a small number of users. Much work has been performed in the past on the analysis of the spectral efficiency of synchronous DS-CDMA systems and the associated coding-spreading tradeoff problem. However, most of the analysis is based on the large-system assumptions. In this dissertation, we focused on finite-sized systems with the help of numerical methods and Monte-Carlo simulations. Binary-input achievable information rates for finite-sized synchronous DS-CDMA systems with different detection/decoding schemes on AWGN channel are numerically calculated for various coding/spreading apportionments. We use these results to determine the existence and value of an optimal code rate for a number of different multiuser receivers, where optimality is in the sense of minimizing the SNR required for reliable multiuser communication. Our results are consistent with the well-known fact that all coding (no spreading) is optimal for the maximum a posteriori receiver. Simulations of the LDPC-coded synchronous DS-CDMA systems with iterative multiuser detection/decoding and MMSE multiuser detection/single-user decoding are also presented to show that the binary-input capacities can be closely approached with practical schemes. The coding-spreading tradeoff is examined using these LDPC code simulation results, where agreement with the information-theoretic results is demonstrated. We extend our work to the DS-CDMA systems on two idealized Rayleigh flat-fading channels: the chip-level flat-fading (CLFF) and the (code) symbol-level flat-fading (SLFF). These models represent ideal fast fading and slow fading channels, respectively. Both information-theoretic results and LDPC code simulation results are presented to show the effects of channel fading on system performance and the coding-spreading tradeoff. It is shown that fast fading can be beneficial to system performance under the condition of perfect channel state information at receiver, but slow fading is very harmful. Slow fading also increases the importance of coding greatly, compared to the AWGN and fast fading. Finally, we present some comparisons with large-system results on AWGN and CLFF channels, which show both consistencies and discrepancies.

Download or read book Performance Evaluation of DS CDMA Receivers Using Genetic Algorithm written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Performance Analysis of Decorrelating Detectors for Dual rate Synchronous DS CDMA Systems Over Frequency selective Rayleigh Fading Channels written by Xiangtao Li and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, the performance of a decorrelating-based multiuser detector for frequency-selective channels is discussed. The users transmit data at two different rates are instead of one single rate. According to their transmission rates, the users are classified into two groups, a group of high rate users and a group of low rate users. It is assumed that over the time interval [0, T o], the low rate users transmit one bit, while the high rate users transmit M bits of information. At the receiving end, two types of decorrelators are examined to decode the signals: a low rate decorrelator (LRD) and a high rate decorrelator (HRD). The LRD makes a decoding decision for every T o seconds and views one high rate user as M effective low rate users. The HRD makes a decision for every T 1 = T o / M seconds and detects a bit from a low rate user M times during the time interval[0, T o]. The signals from the two groups are transmitted over frequency-selective multipath Rayleigh fading channels. The maximal ratio combining (MRC) technique is used in two parts of the receivers. First, the multipath diversity and MRC diversity reception method are utilized in the receivers to combat against the multipath fading. Secondly, in HRD, MRC is employed to implement a soft decoding rule for the low rate users. The error probability and asymptotic multiuser efficiency for both types of decorrelators will be evaluated and the simulation results given. It can be seen in the simulation results that the LRD is superior to the HRD in the performance for both low rate and high rate users.

Download or read book Modeling and Analysis of Cellular CDMA Forward Channel written by Jan E. Tighe and published by . This book was released on 2001-03 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, we develop the forward channel model for a DS-CDMA cellular system operating in a slow-flat Rayleigh fading and log normal shadowing environment, which incorporates the extended Hata model to predict median path loss. Forward error correction is integrated into the model by applying convolution encoding with soft-decision decoding. The worst-case probability of bit error for a mobile user at the edge of the center cell of a seven-cell cluster is developed using Gaussian approximation. In estimating the probability of bit error, we develop a statistical model, which approximates the sum of d multiplicative chi-square(two degrees of freedom)- log normal random variables as a multiplicative chi-square(with 2d degrees of freedom)-log normal random variable. Using this approximation, we examine the performance of the cellular system under a range of shadowing conditions, for various user capacities and with antenna sectoring as they compare with Monte Carlo simulated results. Next, we modify our worst-case performance analysis to accommodate users that are distributed in the cell according to a specified distribution and compare results with the worst-case performance. Finally, we introduce fast power control into the forward channel and explore system performance with power control under a range of operatng conditions as it compares with the fixed-power performance.

Download or read book Multicarrier CDMA Versus DS CMDA written by Pushkar R. Apte and published by . This book was released on 1998 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of Bandwidth Efficient DS CDMA Systems written by Jun Wang and published by . This book was released on 1993 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis studies the modulation and coding aspects of bandwidth efficient direct-sequence CDMA systems. The novel concepts proposed and investigated are: DS-CDMA employing combined modulation schemes; MFSK/DS-CDMA employing orthogonal codes; and DS-CDMA employing permutation modulation. Under each concept, one or more schemes are developed and examined. The first concept suggests that two or more modulation schemes can be considered together as a combined modulation in a DS-CDMA system. By combining two modulation schemes, the signal energy per symbol for a given bit energy is increased. This in turn increases the system power efficiency and also the bandwidth efficiency. By combining MFSK and MPSK, we proposed the MFSK-MPSK/DS-CDMA scheme. By combining MFSK and differential MPSK, we proposed the MFSK-DMPSK/DS-CDMA scheme. The second concept can be thought of as an application of the first. By combining MFSK and the orthogonal PN codes, we proposed the MFSK-OC/DS-CDMA scheme. It is found in this thesis that the orthogonal code concept has many significant applications in both performance improvement and complexity reduction in DS-CDMA systems. An analysis also shows that the ideal orthogonality of the codes can be relaxed with very little performance degradation. Thus, quasi-orthogonal codes can be used in practical applications. In the third concept, permutation modulation is applied to the DS-CDMA systems and it is proved to be a very powerful scheme in fading channels. By using the multi-tone FSK scheme, we proposed the MT-FSK/DS-CDMA system. In a fading channel, this system introduces an implicit diversity, and thus is robust in mobile environments. The concept of orthogonal codes are used here to reduce the implementation complexity. By using a simple frequency tone selection rule, we further proposed a novel scheme, namely OMT-FSK/DS-CDMA in which all symbols are orthogonal each other. For the proposed schemes, performance analyses are made over AWGN and fading channels with and without FEC coding. Computer simulation is done for the MFSK-OC/DS-CDMA and MT-FSK/DS-CDMA systems.