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Some Issues On Multiuser Detection In Ds Cdma Systems
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Book Synopsis Some Issues on Multiuser Detection in DS-CDMA Systems by : Zhiwei Mao
Download or read book Some Issues on Multiuser Detection in DS-CDMA Systems written by Zhiwei Mao and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, direct-sequence code-division multiple access (DS-CDMA) systemswith multiuser detectors used at receiver are investigated and two kinds of multiuser detectors are developed for DS-CDMA systems. In the investigation of DS-CDMA systems using multiuser detectors at receiver, a study on the performance of the system is presented, where heterogeneous traffic with different transmission rates and quality of service (QoS) requirements is supported. The effects of some realistic factors, such as imperfect power control and the existence of multiple cells, on the system performance are studied. In addition, algorithms are proposed to deal with the forward link power allocation problem based on the measurements of random characteristics of the received signals. This power allocation problem is formulated as a constrained optimization problem. To make the problem easy to solve, an additional appropriate constraint is proposed. Two methods are developed to identify the feasible region of this constrained optimization problem.The first proposed multiuser detector is an adaptive minimum mean-squared-error(MMSE) detector. Particularly, it is desirable for the cases where communication channelshave severe near-far problem, and thus the convergence rates of adaptive MMSE detectorsfor users with different power are quite different. To improve the convergence ratesof adaptive MMSE detectors for weak power users, the interference effects of the strongpower user signals are subtracted from the received signal successively. The method to estimatethe parameters required in the proposed detector is also developed. It is shown thatthe proposed detector achieves fast convergence rates in various near-far scenarios. Otherstudies conducted include the transient mean-squared-error (MSE) analysis to explain thedifferent convergence rates of adaptive MMSE detectors for users with different power, and the bit-error-rate (BER) performance analysis for the proposed detector. The second proposed multiuser detector is a set of semi-blind linear parallel interferencecancellation (PIC) detectors for the reverse link of multiple-cell systems, where only information about intra-cell users is available. To decrease the interference from inter-cellusers whose information is unavailable to the receiver, the inter-cell user signal subspace is identified first by making use of the available information about intra-cell users. The eigen vectors and eigen values of this signal subspace are then used in the traditional linear PIC structure, in place of the unknown inter-cell users' signature codes and signal amplitudes. Based on this idea, three detection schemes are proposed. In addition, an efficient adaptation implementation method is developed, and the performance of the proposed detectorsis studied. The proposed detectors are shown to be suitable for practical implementations and have satisfactory performance.
Book Synopsis Multi-user Detection for Multi-rate DS/CDMA Systems by : Jinwen Ma
Download or read book Multi-user Detection for Multi-rate DS/CDMA Systems written by Jinwen Ma and published by . This book was released on 2000 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: Wireless cellular communication is witnessing a rapid growth in market, technology and range of services. Current and future demands for wireless communication services motivate the need for handling multi-media traffic types. In a multimedia communication system, users with different and even time-varying rates and quality of services (QoS) requirements, such as voice, image and data, must be accommodated. The use of Spread Spectrum modulation with Code Division Multiple Access (CDMA) technology is an attractive approach for economical spectrally efficient and high quality cellular and personal communication services. This dissertation explores the technologies of applying different interference cancellation techniques to multi-rate CDMA systems that serve users with different QoS. Multiple Access Interference (MAI) and multipath propagation are the major issues in wireless communication systems. It is also true for multi-rate CDMA systems. Multi-user detection has been shown to be effective in combating the near-far problem and providing superior performance over conventional detection method. In this dissertation, we combine both linear minimum mean squared error (LMMSE) detector, nonlinear decision feedback detector, with other signal processing techniques, such as array processing and multipath combining, to create effective near-far resistant detectors for multi-rate CDMA systems. Firstly, we propose MMSE receivers for synchronous multi-rate CDMA system and compare the performance with the corresponding multi-rate decorrelating detectors. The multi-rate decorrelating detector is optimally near-far resistant and easy to implement. The proposed linear MMSE multi-rate receiver can be adaptively implemented only with the knowledge of the desired user. Due to the fact that MMSE detector offers best trade-off between the MAI cancellation and noise variance enhancement, it is shown that multi-rate MMSE receiver can offer better performance than the multi-rate decorrelator when the interfering users' Signal to Noise Ratio (SNR) is relatively low comparing to the desired user's SNR. Secondly, the asynchronous multi-rate CDMA system, we propose multi-rate multi-shoot decorrelating detectors and multi-rate multi-shot MMSE detectors. The performance of multi-shot detectors can be improved monotonically with increasing the number of stacked bits, but a great computational complexity is going to be introduced in order to get better performance. A debiasing method is introduced to multi-rate multi-shot linear detectors. Debiasing method optimizes multi-rate detectors based on the multi-rate multi-shot model. Debiasing multi-shot MMSE detector for multi-rate signals can offer performance than the corresponding debiasing multi-shot decorrelating detector. Thirdly, we propose linear space-time receivers for multi-rate CDMA systems. The minimum mean-squared error criteria is used. We perform a comparative study on the multi-rate receiver which uses either multipath (temporal) processing or array (spatial) processing, and the one which uses both array and multipath (space-time) processing. The space-time receiver for the multi-rate CDMA signals give us the potential of improving the capacity of multi-rate systems. The space-time processing combined with multiuser detection have the advantages of combating multipath fading through temporal processing, reducing MAI through MMSE method and provide antenna or diversity gain through spatial processing and increasing the capacity of the multi-rate CDMA systems. Lastly, the group-wise interference cancellation methods are proposed for multi-rate CDMA signals. The non-linear decision feedback detection (DFD) schemes are used in the proposed receivers. The proposed interference cancellation schemes benefit from the nature of the unequal received amplitudes for multi-rate CDMA signals. Users with same data rate are grouped together. Users with the highest data-rate are detected first. Interference between the groups is cancelled in a successive order. The results show that the group-wise MMSE DFD yields better performance than multi-rate linear MMSE detector and multi-rate decorrelating detector, especially for highly loaded CDMA systems.
Book Synopsis Frequency-Domain Multiuser Detection for CDMA Systems by : Paulo Silva
Download or read book Frequency-Domain Multiuser Detection for CDMA Systems written by Paulo Silva and published by CRC Press. This book was released on 2022-09-01 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Future broadband wireless communication systems are expected to be able to offer new and powerful services enabling fast transmission rates of several tens of Mbit/s. This is an ambitious challenge especially for mobile communication systems since these systems should be able to cope with severely time dispersive channels, associated to the signal multipath propagation. Moreover, these systems should have high spectral and power efficiencies, as well as high capacity and flexibility. Spread spectrum techniques, particularly coded division multiple access (CDMA) techniques allow high capacity and flexibility, continuous transmission requiring low-peak power requirements for the amplifiers, as well as some robustness against fading and time-dispersion effects associated with the multipath propagation. When employed in prefix assisted (PA) block transmission schemes combined with frequency-domain receiver implementations they become especially interesting for broadband wireless systems. In Frequency-Domain Multiuser Detection for CDMA Systems the use of PA block transmission is considered in the context of both DS (Direct Sequence) and MC (Multicarrier) CDMA schemes. The main goal is the study of frequency-domain multiuser detection techniques with iterative signal detection/decoding techniques, also in combination with estimation and cancelation of nonlinear distortion effects. The receiver structures are suitable to scenarios with high interference levels and strongly time-dispersive channels.
Book Synopsis Multiuser detection for DS-CDMA systems using optimization methods by : Xianmin Wang (Ph. D.)
Download or read book Multiuser detection for DS-CDMA systems using optimization methods written by Xianmin Wang (Ph. D.) and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Several new multiuser detectors are developed for different direct-sequence codedivision multiple-access (DS-CDMA) application environments. The first detector is based on a semidefinite-programming (SDP) relaxation technique. In this detector, maximum likelihood (ML) detection is achieved by 'relaxing' the associated combinatorial problem into an SDP problem, which leads to a detector of polynomial complexity. It is shown that the SDP-relaxation (SDPR) based detector can be obtained by solving a dual SDP problem which leads to improved efficiency. Computer simulations demonstrate that the SDPR detector offers near-optimal performance with much reduced computational complexity compared with that of the ML detector proposed by Verdu for both synchronous and asynchronous DS-CDMA systems. The second detector is based on a recursive convex programming (RCP) approach. In this detector, ML detection is carried out in two steps: first, the combinatorial problem associated with ML detection is relaxed to a convex programming problem, and then a recursive approach is used to obtain an approximate solution for ML detection. Efficient unconstrained relaxation approach is proposed for the proposed detector to reduce the involved computational complexity. Computer simulations demonstrate that the proposed detectors offer near-optimal detection performance which is superior to that offered by many other suboptimal detectors including the SDPR detector. However, the computational complexity involved in the proposed detectors is much lower relative to that involved in Verdu's ML detector as well as our SDPR detector. The third detector entails a subspace estimation-based constrained optimization approach for channel estimation in DS-CDMA systems with multipath propagation channels. The proposed approach offers an improved approximation for the noise iii subspace compared with that offered by several existing algorithms. Computer simulations show that the performance of the proposed detector offers nearly the same performance as that of existing subspace detectors but leads to a significant reduction in the amount of computation. Relative to some existing constrained optimization methods, the proposed detector offers a significantly improved performance while requiring a comparable amount of computation. The fourth detector is proposed based on a vector constant-modulus (VCM) approach. This detector is designed for DS-CDMA systems with multipath propagation channels where the effective signatures observed at receiver are distorted by multipath propagation and aliasing concurrently. In this detector, detection is carried out by solving a linear constrained optimization problem whose objective function is formulated based on the VCM criterion. Two adaptation algorithms, namely, the constrained stochastic gradient algorithm and the recursive vector constant-modulus algorithm, are developed. Analysis are presented to investigate the performance of the proposed detector. Computer simulations show that the proposed detectors are able to suppress multiuser interference and inter-symbol interference effectively. More importantly, they offer robust detection performance against the effective signature distortion caused by aliasing at the receiver.
Book Synopsis Multiuser Detection in DSSS Systems by : Shahzadi Mahnoor
Download or read book Multiuser Detection in DSSS Systems written by Shahzadi Mahnoor and published by LAP Lambert Academic Publishing. This book was released on 2014-05-28 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: Direct sequence code division multiple access (DS-CDMA) is a popular wireless technology in DS-CDMA communications, all of the users' signal overlap in time and frequency and cause mutual interference. The capacity of Direct Sequence Code Division Multiple Access (DS-CDMA) is limited by Multiple Access Interference (MAI) instead of thermal noise. Commercial CDMA systems such as the ones based on IS-95 standard regard MAI as additive noise and employ matched filter detectors. This technique limits the number of users that can be supported in DS-CDMA system to less than 10% of the spreading gain. Moreover the bit error rates for individual users degrade rapidly with an increase in number of users. The conventional DS-CDMA detector follows single user detection strategy in which each user is detected separately without regard for the other users. A better strategy is multi-user detection, where information about multiple users is used to improve detection of each individual user. A number of important multiuser detectors have been proposed here. The content of the book is in following sequence.
Book Synopsis Frequency-Domain Multiuser Detection for CDMA Systems by : Paulo Silva
Download or read book Frequency-Domain Multiuser Detection for CDMA Systems written by Paulo Silva and published by CRC Press. This book was released on 2022-09-01 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: Future broadband wireless communication systems are expected to be able to offer new and powerful services enabling fast transmission rates of several tens of Mbit/s. This is an ambitious challenge especially for mobile communication systems since these systems should be able to cope with severely time dispersive channels, associated to the signal multipath propagation. Moreover, these systems should have high spectral and power efficiencies, as well as high capacity and flexibility. Spread spectrum techniques, particularly coded division multiple access (CDMA) techniques allow high capacity and flexibility, continuous transmission requiring low-peak power requirements for the amplifiers, as well as some robustness against fading and time-dispersion effects associated with the multipath propagation. When employed in prefix assisted (PA) block transmission schemes combined with frequency-domain receiver implementations they become especially interesting for broadband wireless systems. In Frequency-Domain Multiuser Detection for CDMA Systems the use of PA block transmission is considered in the context of both DS (Direct Sequence) and MC (Multicarrier) CDMA schemes. The main goal is the study of frequency-domain multiuser detection techniques with iterative signal detection/decoding techniques, also in combination with estimation and cancelation of nonlinear distortion effects. The receiver structures are suitable to scenarios with high interference levels and strongly time-dispersive channels.
Book Synopsis Subspace Multiuser Detection in DS-CDMA Communication Systems and Its Applications by : Yong-Suk Moon
Download or read book Subspace Multiuser Detection in DS-CDMA Communication Systems and Its Applications written by Yong-Suk Moon and published by . This book was released on 1999 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis On the Use of Antenna Arrays and Multiuser Detection for DS/CDMA Systems by : Sang Gook Kim
Download or read book On the Use of Antenna Arrays and Multiuser Detection for DS/CDMA Systems written by Sang Gook Kim and published by . This book was released on 2000 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Combined Adaptive Multiuser Detection for DS-CDMA System by : Yishu Guo
Download or read book Combined Adaptive Multiuser Detection for DS-CDMA System written by Yishu Guo and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Multiuser Detection and Channel Estimation for DS-CDMA Systems by : Alexander Lampe
Download or read book Multiuser Detection and Channel Estimation for DS-CDMA Systems written by Alexander Lampe and published by . This book was released on 2003 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Space-time Multiuser Detection of Multi-carrier DS-CDMA Systems by : James Bruce Whitehead
Download or read book Space-time Multiuser Detection of Multi-carrier DS-CDMA Systems written by James Bruce Whitehead and published by . This book was released on 2001 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Advances in Multiuser Detection by : Michael L. Honig
Download or read book Advances in Multiuser Detection written by Michael L. Honig and published by John Wiley & Sons. This book was released on 2009-08-31 with total page 517 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Timely Exploration of Multiuser Detection in Wireless Networks During the past decade, the design and development of current and emerging wireless systems have motivated many important advances in multiuser detection. This book fills an important need by providing a comprehensive overview of crucial recent developments that have occurred in this active research area. Each chapter is contributed by noted experts and is meant to serve as a self-contained treatment of the topic. Coverage includes: Linear and decision feedback methods Iterative multiuser detection and decoding Multiuser detection in the presence of channel impairments Performance analysis with random signatures and channels Joint detection methods for MIMO channels Interference avoidance methods at the transmitter Transmitter precoding methods for the MIMO downlink This book is an ideal entry point for exploring ongoing research in multiuser detection and for learning about the field's existing unsolved problems and issues. It is a valuable resource for researchers, engineers, and graduate students who are involved in the area of digital communications.
Book Synopsis Multiuser Detection Employing Recurrent Neural Networks for DS-CDMA Systems by : Navern Moodley
Download or read book Multiuser Detection Employing Recurrent Neural Networks for DS-CDMA Systems written by Navern Moodley and published by . This book was released on 2006 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Design of Interference cancellation Receiver for CDMA with MIMO system by : Dr.P.Sreesudha,
Download or read book Design of Interference cancellation Receiver for CDMA with MIMO system written by Dr.P.Sreesudha, and published by Archers & Elevators Publishing House. This book was released on with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Multiuser Detection and Channel Estimation for DS-CDMA Systems by :
Download or read book Multiuser Detection and Channel Estimation for DS-CDMA Systems written by and published by . This book was released on 2004 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Adaptive Decision-feedback Multiuser Detection for DS-CDMA Systems by : Min Li
Download or read book Adaptive Decision-feedback Multiuser Detection for DS-CDMA Systems written by Min Li and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A Study of Multiuser Detection Algorithms for DS-Cdma Communications by : 陳特彬
Download or read book A Study of Multiuser Detection Algorithms for DS-Cdma Communications written by 陳特彬 and published by . This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
