Author: Eduardo J. Bolas
Publisher:
ISBN: 9781423507512
Category :
Languages : en
Pages : 111
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Book Description
In this thesis we investigate the usage of low rate codes primarily to provide the total bandwidth expansion required for a CDMA system. Comparing different combinations of coding and spreading with a traditional DS-CDMA, as defined in the IS-95 standard, allows the criteria to be defined for the best coding-spreading tradeoff in CDMA systems. The analysis of the coding-spreading tradeoff is divided into two parts. The first part is dedicated to the study of the deterministic components of the problem. This includes the different factors with non-random behavior that the system's designer can determine. The processing gain, the code characteristics and the number of users are well- defined variables that can determine the overall performance and can consequently affect the tradeoff. The second part of the study is dedicated to analyzing different combinations of coding and spreading with no ideal channel estimation and interference reduction techniques. Small-scale fading channel conditions are emulated through Nakagami-m distribution. Large-scale path loss was incorporated through the extended Hata model while Lognormal shadowing considered the fluctuations on the received power at points with the same distance to the transmitter. We assessed the performance of different combinations of coding and spreading considering in two cases: a worst-case scenario in which the mobile user was located at the corner of a hexagon cell in a seven-cell cluster and a more realistic scenario in which the user could be physically located anywhere in the cell, following a uniform probability distribution function. Furthermore, we investigated the improvement in performance generated by interference reduction techniques, such as sectoring and power control.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 268
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Book Description
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.
Author: Qinghua Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages : 290
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Book Description
Author: R. Michael Buehrer
Publisher: Morgan & Claypool Publishers
ISBN: 1598290401
Category : Code division multiple access
Languages : en
Pages : 192
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Book Description
This book covers the basic aspects of Code Division Multiple Access or CDMA. It begins with an introduction to the basic ideas behind fixed and random access systems in order to demonstrate the difference between CDMA and the more widely understood TDMA, FDMA or CSMA. Secondly, a review of basic spread spectrum techniques are presented which are used in CDMA systems including direct sequence, frequency-hopping and time-hopping approaches. The basic concept of CDMA is presented, followed by the four basic principles of CDMA systems that impact their performance: interference averaging, universal frequency reuse, soft handoff, and statistical multiplexing. The focus of the discussion will then shift to applications. The most common application of CDMA currently is cellular systems. A detailed discussion on cellular voice systems based on CDMA, specifically IS-95, is presented. The capacity of such systems will be examined as well as performance enhancement techniques such as coding and spatial filtering. Also discussed are Third Generation CDMA cellular systems and how they differ from Second Generation systems. A second application of CDMA that is covered is spread spectrum packet radio networks. Finally, there is an examination of multi-user detection and interference cancellation and how such techniques impact CDMA networks. This book should be of interest and value to engineers, advanced students, and researchers in communications.
Author: Mehul Motani
Publisher:
ISBN:
Category :
Languages : en
Pages : 310
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Book Description
Author: Francis Swarts
Publisher: Springer Science & Business Media
ISBN: 146155103X
Category : Technology & Engineering
Languages : en
Pages : 324
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Book Description
CDMA Techniques for Third Generation Mobile Systems presents advanced techniques for analyzing and developing third generation mobile telecommunication systems. Coverage includes analysis of CDMA-based systems, multi-user receivers, Turbo coding for mobile radio applications, spatial and temporal processing techniques as well as software radio techniques. Special emphasis has been given to recent advances in coding techniques, smart antenna systems, spatial filtering, and software implementation issues. Internationally recognized specialists contributed to this volume, and each chapter has been reviewed and edited for uniformity. CDMA Techniques for Third Generation Mobile Systems is an invaluable reference work for engineers and researchers involved in the development of specific CDMA systems.
Author: Kamil Sh. Zigangirov
Publisher: John Wiley & Sons
ISBN: 0471655481
Category : Technology & Engineering
Languages : en
Pages : 411
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Book Description
A comprehensive introduction to CDMA theory and application Code division multiple access (CDMA) communication is rapidly replacing time- and frequency-division methods as the cornerstone of wireless communication and mobile radio. Theory of Code Division Multiple Access Communication provides a lucid introduction and overview of CDMA concepts and methods for both the professional and the advanced student. Emphasizing the role CDMA has played in the development of wireless communication and cellular mobile radio systems, the author leads you through the basic concepts of mobile radio systems and considers the different principles of multiple access-time division, frequency division, and code division. He then analyzes three major CDMA systems-direct sequence (DS) CDMA systems, frequency hopped (FH) CDMA systems, and pulse position hopped (PPH) CDMA systems. Other topics covered include: * Spread spectrum (SS) technology * Forward error control coding * CDMA communication on fading channels * Pseudorandom signals * Information theory in relation to CDMA communication * CDMA cellular networks Complete with useful appendices providing analyses of the moments of CDMA system decision statistics, Theory of Code Division Multiple Access Communication is a ready reference for every engineer seeking an understanding of the history and concepts of this key communications technology.
Author: John B. Anderson
Publisher: Springer Science & Business Media
ISBN: 0306477920
Category : Technology & Engineering
Languages : en
Pages : 494
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Book Description
Coded Modulation Systems is an introduction to the subject of coded modulation in digital communication. It is designed for classroom use and for anyone wanting to learn the ideas behind this modern kind of coding. Coded modulation is signal encoding that takes into account the nature of the channel over which it is used. Traditional error correcting codes work with bits and add redundant bits in order to correct transmission errors. In coded modulation, continuous time signals and their phases and amplitudes play the major role. The coding can be seen as a patterning of these quantities. The object is still to correct errors, but more fundamentally, it is to conserve signal energy and bandwidth at a given error performance. The book divides coded modulation into three major parts. Trellis coded modulation (TCM) schemes encode the points of QAM constellations; lattice coding and set-partition techniques play major roles here. Continuous-phase modulation (CPM) codes encode the signal phase, and create constant envelope RF signals. The partial-response signaling (PRS) field includes intersymbol interference problems, signals generated by real convolution, and signals created by lowpass filtering. In addition to these topics, the book covers coding techniques of several kinds for fading channels, spread spectrum and repeat-request systems. The history of the subject is fully traced back to the formative work of Shannon in 1949. Full explanation of the basics and complete homework problems make the book ideal for self-study or classroom use.
Author: Guosen Yue
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Design and analysis of random-like codes for various multiple-input and multiple-output communication systems are addressed in this work. Random-like codes have drawn significant interest because they offer capacity-achieving performance. We first consider the analysis and design of low-density parity-check (LDPC) codes for turbo multiuser detection in multipath CDMA channels. We develop techniques for computing the probability density function (pdf) of the extrinsic messages at the output of the soft-input soft-output (SISO) multiuser detectors as a function of the pdf of input extrinsic messages, user spreading codes, channel impulse responses, and signal-to-noise ratios. Using these techniques, we are able to accurately compute the thresholds for LDPC codes and design good irregular LDPC codes. We then apply the tools of density evolution with mixture Gaussian approximations to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations which include different number of antennas, different channel models and different demodulation schemes. We also study the coding-spreading tradeoff in LDPC coded CDMA systems employing multiuser joint decoding. We solve the coding-spreading optimization based on the extrinsic information SNR evolution curves for the SISO multiuser detectors and the SISO LDPC decoders. Both single-cell and multi-cell scenarios will be considered. For each of these cases, we will characterize the extrinsic information for both finite-size systems and the so-called large systems where asymptotic performance results must be evoked. Finally, we consider the design optimization of irregular repeat accumulate (IRA) codes for MIMO communication systems employing iterative receivers. We present the density evolution-based procedure with Gaussian approximation for optimizing the IRA code ensemble. We adopt an approximation method based on linear programming to design an IRA code with the extrinsic information transfer (EXIT) chart matched to that of the soft MIMO demodulator.
Author: Ramesh Annavajjala
Publisher:
ISBN:
Category :
Languages : en
Pages : 145
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Book Description
Some of the challenges in the design of next generation wireless systems are providing high data rate multimedia services, increasing user capacity, improving reliability and range, terminal mobility, robustness to interference, limited spectrum availability, and transmission power constraints. The approaches that we take in this dissertation to address some of the aforementioned issues are cross-layer design and user cooperation. In the first part of the dissertation, on a wideband CDMA channel with a finite transmission bandwidth constraint, we consider the problem of optimal bandwidth allocation for source coding, channel coding and spread-spectrum modulation. For analytical tractability, we assume a memoryless Gaussian source with an optimum quantizer, a convolutional encoder with a soft-decision decoder, and a spread spectrum modulator with random spreading codes and a RAKE receiver. In the presence of both multiple access interference (MAI) and narrowband interference (NBI), for frequency-selective Nakagami fading channels, we derive upper and lower bounds on the end-to-end average source distortion. Since an exact expression for the average distortion is difficult to derive, we seek to obtain the three-tuple (i.e., source coding rate, channel coding rate, and spreading factor) that optimizes the upper and lower bounds on the average distortion. Under various channel conditions and interference levels, we numerically computed the optimum three-tuple, and verify the accuracy with system-level simulations. For small values of spreading factor, we show that the system performance is hurt by the self-interference of the user-of-interest, thus cautioning against aggressive channel coding. Since a multi-carrier DS-CDMA (or, simply MC-CDMA) system is more robust to NBI, we propose to employ an MC-CDMA system to improve the distortion performance on channels with severe NBI. For a fixed channel code rate, we then quantify the tradeoff between source coding and spreading for an MC-CDMA system. In the second part of the dissertation, we consider a parallel relay channel wherein the relay nodes help the source transmissions to provide improved reliability at the destination. With multiple relay nodes, we design and analyze robust noncoherent amplify-and forward receivers for use on rapidly varying Rayleigh fading channels with unknown instantaneous channel knowledge. Next, with a sum power constraint, we consider the problem of optimal transmit power allocation when only statistical knowledge, in terms of the average fading power, of the channel is available at the transmitting nodes. We quantify the improvements in both outage probability performance and asymptotic cooperation gain of various relaying protocols with optimal power allocation.
