Download or read book Performance Evaluation of Multicode DS CDMA Systems with Multiusers Detection Over Nakagami m Fading Channels and Five Sequential Detectors written by and published by . This book was released on 2004 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Multiuser Detection and Performance Evaluation for Cellular DS CDMA Networks with Partial Information written by Liqing Zhang and published by . This book was released on 2003 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Coded Transmit Diversity in CDMA Over Nakagami m Fading Channels written by Ariel Sacramento and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Estimation of Fading Channel in DS Cdma Multiuser Communications Systems written by Chun-Yu Fung and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Estimation of Fading Channel in DS-CDMA Multiuser Communications Systems" by Chun-yu, Fung, 馮震宇, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of the Thesis Entitled Estimation of Fading Channel in DS-CDMA Multiuser Communications Systems submitted by Fung Chun Yu for the degree of Master of Philosophy at the University of Hong Kong in December 2002 Multipath fading and multiuser access interference are two major impairments in direct-sequence code-division multiple-access (DS-CDMA) systems. Efficient channel estimation and multiuser detection techniques play important roles in overcoming these deficiencies. This thesis is concerned with the design of a space-time (ST) blind adaptive receiver for DS-CDMA systems and the accompanied channel estimation algorithm. A new space-time decorrelating RAKE (ST-DRAKE) receiver is developed for blind reception of CDMA signals in frequency-selective fading channels. It has the advantage that only the knowledge of the desired user's signature waveform is required and therefore no transmission of training sequence is needed. The ST-DRAKE receiver consists of two parts. The first part is a set of constrained adaptive filters that are designed to suppress interference based on the minimum output energy criterion. These filters are implemented in a structure analogous to the general sidelobe canceller in array processing, which is implemented by a multistage Weiner filter is employed to reduce the complexity of the receiver. The second part of the ST-DRAKE receiver coherently combines the outputs of the constrained adaptive filters and gives an estimate of the transmitted signal. Simulation results show that the ST- DRAKE delivers significant performance improvement by exploiting the spatial diversity of the antenna array. The problem of estimating fast fading channels in the proposed receiver is also addressed. The time-varying channel is modeled as an autoregressive process and the Kalman filter is employed to estimate the time-varying channel coefficients. A robust Kalman filter based on the M-estimate cost function is also developed to suppress impulsive noise present in the received signals. Simulation results show that the Kalman filter provides more accurate channel estimate to the ST-DRAKE than using the decomposition method. Simulation results also show that the coupled receiver has a performance comparable to the optimum minimum mean-squared error receiver with known channel information. DOI: 10.5353/th_b2750902 Subjects: Code division multiple access Wireless communication systems
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.
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.
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.
Download or read book Multiuser Detection in CDMA Mobile Terminals written by Piero Castoldi and published by Artech House. This book was released on 2002 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: Here's an authoritative, cutting-edge resource that gives you a thorough understanding of CDMA transmission and detection. It offers practical guidance in designing interference-reducing multi-user receivers for mobile radio systems and multi-user adaptive modems for accessing satellite earth stations. The book provides in-depth descriptions of CDMA principles, and of linear and non-linear multi-user detection , and covers the fine details of the realization of a linear multi-user receiver.
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:
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.
Download or read book Advances in Multiuser Detection written by Michael L. Honig and published by John Wiley & Sons. This book was released on 2009-08-19 with total page 512 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.
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.
Download or read book Performance of Multicarrier DS CDMA Systems in a Nakagami Fading Channel written by Jifang Wang and published by . This book was released on 1998 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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:
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:
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 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:
