Dissertations / Theses on the topic 'Multiuser communication'
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1
Ma, Ming. "Multiuser mobile communication systems." Thesis, Lancaster University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289069.
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Al-Hussaibi, Walid Awad. "High capacity multiuser multiantenna communication techniques." Thesis, University of Sussex, 2011. http://sro.sussex.ac.uk/id/eprint/7489/.
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One of the main issues involved in the development of future wireless communication systems is the multiple access technique used to efficiently share the available spectrum among users. In rich multipath environment, spatial dimension can be exploited to meet the increasing number of users and their demands without consuming extra bandwidth and power. Therefore, it is utilized in the multiple-input multiple-output (MIMO) technology to increase the spectral efficiency significantly. However, multiuser MIMO (MU-MIMO) systems are still challenging to be widely adopted in next generation standards. In this thesis, new techniques are proposed to increase the channel and user capacity and improve the error performance of MU-MIMO over Rayleigh fading channel environment. For realistic system design and performance evaluation, channel correlation is considered as one of the main channel impurities due its severe influence on capacity and reliability. Two simple methods called generalized successive coloring technique (GSCT) and generalized iterative coloring technique (GICT) are proposed for accurate generation of correlated Rayleigh fading channels (CRFC). They are designed to overcome the shortcomings of existing methods by avoiding factorization of desired covariance matrix of the Gaussian samples. The superiority of these techniques is demonstrated by extensive simulations of different practical system scenarios. To mitigate the effects of channel correlations, a novel constellation constrained MU-MIMO (CC-MU-MIMO) scheme is proposed using transmit signal design and maximum likelihood joint detection (MLJD) at the receiver. It is designed to maximize the channel capacity and error performance based on principles of maximizing the minimum Euclidean distance (dmin) of composite received signals. Two signal design methods named as unequal power allocation (UPA) and rotation constellation (RC) are utilized to resolve the detection ambiguity caused by correlation. Extensive analysis and simulations demonstrate the effectiveness of considered scheme compared with conventional MU-MIMO. Furthermore, significant gain in SNR is achieved particularly in moderate to high correlations which have direct impact to maintain high user capacity. A new efficient receive antenna selection (RAS) technique referred to as phase difference based selection (PDBS) is proposed for single and multiuser MIMO systems to maximize the capacity over CRFC. It utilizes the received signal constellation to select the subset of antennas with highest (dmin) constellations due to its direct impact on the capacity and BER performance. A low complexity algorithm is designed by employing the Euclidean norm of channel matrix rows with their corresponding phase differences. Capacity analysis and simulation results show that PDBS outperforms norm based selection (NBS) and near to optimal selection (OS) for all correlation and SNR values. This technique provides fast RAS to capture most of the gains promised by multiantenna systems over different channel conditions. Finally, novel group layered MU-MIMO (GL-MU-MIMO) scheme is introduced to exploit the available spectrum for higher user capacity with affordable complexity. It takes the advantages of spatial difference among users and power control at base station to increase the number of users beyond the available number of RF chains. It is achieved by dividing the users into two groups according to their received power, high power group (HPG) and low power group (LPG). Different configurations of low complexity group layered multiuser detection (GL-MUD) and group power allocation ratio (η) are utilized to provide a valuable tradeoff between complexity and overall system performance. Furthermore, RAS diversity is incorporated by using NBS and a new selection algorithm called HPG-PDBS to increase the channel capacity and enhance the error performance. Extensive analysis and simulations demonstrate the superiority of proposed scheme compared with conventional MU-MIMO. By using appropriate value of (η), it shows higher sum rate capacity and substantial increase in the user capacity up to two-fold at target BER and SNR values.
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姍, 路., and Shan Lu. "Coding and decoding for multiuser communication systems." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12863897/?lang=0, 2014. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12863897/?lang=0.
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本論文は、多端子通信路に対するマルチユーザ符号化および復号の研究成果をまとめたものである。多重接続加算通信路による情報伝送において、複数ユーザの稼働状態を識別するための誤り訂正可能なシグネチャ符号の構成を論ず,全伝送率の高いシグネチャ符号の一般的な構成法を解明する.双方向中継通信路では、2ユーザターボ符号に対する復号の演算量を低減させる復号法を提案する。加法性白色ガウス雑音環境下では復号性能を劣化することなく、レイリーフェージング環境下では僅かな劣化にとどめながら、復号の演算量を約半分程度に低減することができる.Coding and decoding for multiuser communication systems are investigated. For MAAC, we propose a coding scheme of (k + 1)-ary error-correcting signature codes. We give binary and non-binary signature codes. They are the best error-correcting signature codes for MAAC, in the sense that they have highest sum rates known. For TWRC, we propose a low-complexity two-user turbo decoding scheme when turbo codes are applied in two users. The approximate decoding algorithm preserves low decoding complexity over the Gaussian TWRC, without much performance degradation.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
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Kang, Deokwon. "MIMO beamforming in multiuser wireless environments." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 81 p, 2009. http://proquest.umi.com/pqdweb?did=1885755741&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Kane, Roma. "Multiuser TDMA channel estimation." Diss., Columbia, Mo. : University of Missouri-Columbia, 2004. http://hdl.handle.net/10355/5810.
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Thesis (M.S.)--University of Missouri-Columbia, 2004.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (June 30, 2006) Vita. Includes bibliographical references.
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Bala, Erdem. "Multichannel, multiuser and multiple antenna wireless communication systems." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 184 p, 2007. http://proquest.umi.com/pqdlink?did=1251904851&Fmt=7&clientId=79356&RQT=309&VName=PQD.
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Balasubramanyam, Ramkumar. "Adaptive iterative multiuser detection for wireless communication systems." Thesis, University of Greenwich, 2008. http://gala.gre.ac.uk/8203/.
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Wireless multi-user communication systems that operate in a low signal to interference noise ratio (SINR) region are studied in this thesis. This thesis examines a class of wireless communication systems that employs an adaptive receiver for multi-user symbol detection that operates in a low SINR (< 5 dB) region. Since the knowledge of channel-parameter estimates is unavailable at the receiver, a pilot (training) sequence is applied in the communication system, to learn the channel state information (CSI) at the receiver. In studying the classical view of a DFE, the mean square error (MSE) behaviour follows the bit error rate (BER) performance. Certain original results are obtained using the classical adaptive DFE to achieve minimum MSE, employing the least mean square (LMS) algorithm. The results thus obtained for an uncoded adaptive receiver system are applied to a coded system, transmitting either recursive systematic code (RSC) or turbo-code through a spread-spectrum multiuser multiple-path channel, which are referred to as two-stage and three-stage systems respectively in this thesis. The following claims are made based on the findings of this thesis: 1. It is known that a receiver implementing DFE can mitigate symbol-interference completely at high SINR. An adaptive LMS DFE realizes this by adapting the forward and backward filter coefficients with respective step-size constants. The classical approach to realizing interference mitigation was to set the forward and backward adaptation constants as the same. While this approach has provided interference mitigation at high SINR, it has been shown in this thesis that such an approach does not yield complete interference mitigation, even at high SINR. Instead, using different step-size constants at the backward and forward step-size constants provides the required optimality. 2. A decision feedback detector (DFD) mitigates the effects of interference on the information symbols that are transmitted through this communication channel. This thesis shows that an adaptive (LMS) DFD, using unequal compared to equal step-size constants to update the forward and backward filter coefficients, has a steady-state MSE improvement for an uncoded frequency selective communication channel. This thesis shows that, when the knowledge of CSI is not assumed to be known at a wireless receiver, a three-stage receiver has a BER performance improvement and operates at a lower SINR, without any additional computational complexity compared to a two-stage receiver.
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WANG, SHU. "THE APPLICATION OF SUBSPACE TECHNOLOGIES IN WIRELESS COMMUNICATION SYSTEMS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1065704505.
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Wang, Ruifeng. "Spatial-temporal signal processing for multiuser CDMA communication systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0003/NQ42986.pdf.
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Khandaker, Muhammad Ruhul Amin. "Signal processing algorithms for multiuser MIMO relay communication systems." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/1797.
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The increasing demand for mobile applications such as streaming media, software updates, and location-based services involving group communications has prompted the need for wireless communication technologies that can support reliable high data rates. However, wireless channel is subject to signal fading that severely degrades the system spectral efficiency. By exploiting the spatial diversity, multiple-input multiple-output (MIMO) techniques can provide both theoretically attractive and technically practical solutions to combat channel fading. Moreover, in the case of long source-destination distance, single or multiple MIMO relay node(s) is necessary to combat the pathloss and/or shadowing effects of wireless channel and relay signals from the source to the destination.In this thesis, we focus on multiuser MIMO relay systems. We first present joint source, relay, and receiver optimization algorithms for the uplink system based on the minimum mean-squared error (MMSE) criterion subjecting to individual power constraints at the source and the relay nodes. The proposed algorithms outperform the existing techniques in terms of both MSE and bit-error-rate (BER). Next, in the downlink system, we consider multicasting multiple data streams among a group of users with the aid of a relay node, where all the nodes are equipped with multiple antennas. The downlink system performance is optimized subjecting to both power constraints at the source and the relay nodes and quality-of-service (QoS) constraints at the receivers.Then we present the duality between the uplink and the downlink of a multi-hop MIMO relay system. Based on this duality, we propose an optimal design of the source precoding matrix and relay amplifying matrices for multi-hop MIMO relay system with a nonlinear dirty paper coding (DPC)- based transmitter at the source node. The proposed nonlinear transmitter algorithm outperforms the existing decision feedback equalizer (DFE)-based receiver schemes.Multiuser MIMO relaying is then considered in an interference system where a group of transmitters communicate simultaneously with their desired destination nodes with the aid of multiple relay nodes, all equipped with multiple antennas. Transmit-relay-receive beamforming technique is exploited to minimize the total source and relay transmit power in conjunction with transmit power control such that a minimum QoS threshold is maintained at each receiver. The proposed scheme generalizes the existing single-hop MIMO interference systems and the single-antenna, dual-hop interference relay systems to the dual-hop interference MIMO relay systems with any number of source, relay, and destination nodes, all equipped with multiple antennas.The above algorithms are developed assuming that the instantaneous channel state information (CSI) knowledge of both the source-relay link and the relay-destination link is available at the scheduler. However, in practical relay communication systems, the instantaneous CSI is unknown, and therefore, has to be estimated. Hence, we finally propose a bandwidth efficient MIMO channel estimation algorithm that provides the destination node with full knowledge of all channel matrices involved in a dual-hop MIMO communication. The proposed approach attains smaller channel estimation error and is applicable for both one-way and two-way MIMO relay systems.
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Zheng, Gan. "Optimization in linear multiuser MIMO systems." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557923.
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Zheng, Gan, and 鄭淦. "Optimization in linear multiuser MIMO systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557923.
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Jones, Haley M., and Haley Jones@anu edu au. "On multipath spatial diversity in wireless multiuser communications." The Australian National University. Research School of Information Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20050202.152811.
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The study of the spatial aspects of multipath in wireless communications environments
is an increasingly important addition to the study of the temporal aspects
in the search for ways to increase the utilization of the available wireless channel
capacity. Traditionally, multipath has been viewed as an encumbrance in wireless
communications, two of the major impairments being signal fading and intersymbol
interference. However, recently the potential advantages of the diversity offered by
multipath rich environments in multiuser communications have been recognised.
Space time coding, for example, is a recent technique which relies on a rich scattering
environment to create many practically uncorrelated signal transmission
channels. Most often, statistical models have been used to describe the multipath
environments in such applications. This approach has met with reasonable success
but is limited when the statistical nature of a field is not easily determined or is
not readily described by a known distribution.¶
Our primary aim in this thesis is to probe further into the nature of multipath
environments in order to gain a greater understanding of their characteristics and
diversity potential. We highlight the shortcomings of beamforming in a multipath
multiuser access environment. We show that the ability of a beamformer to resolve
two or more signals in angle directly limits its achievable capacity.¶
We test the probity of multipath as a source of spatial diversity, the limiting
case of which is co-located users. We introduce the concept of separability to define
the fundamental limits of a receiver to extract the signal of a desired user from
interfering users signals and noise. We consider the separability performances of
the minimum mean square error (MMSE), decorrelating (DEC) and matched filter
(MF) detectors as we bring the positions of a desired and an interfering user closer
together. We show that both the MMSE and DEC detectors are able to achieve
acceptable levels of separability with the users as close as λ/10.¶
In seeking a better understanding of the nature of multipath fields themselves,
we take two approaches. In the first we take a path oriented approach. The
effects on the variation of the field power of the relative values of parameters such
as amplitude and propagation direction are considered for a two path field. The
results are applied to a theoretical analysis of the behaviour of linear detectors
in multipath fields. This approach is insightful for fields with small numbers of
multipaths, but quickly becomes mathematically complex.¶
In a more general approach, we take a field oriented view, seeking to quantify
the complexity of arbitrary fields. We find that a multipath field has an intrinsic
dimensionality of (πe)R/λ≈8.54R/λ, for a field in a two dimensional circular region, increasing only linearly with the radius R of the region. This result implies that there is no such thing as an arbitrarily complicated multipath field. That is, a field generated by any number of nearfield and farfield, specular and diffuse
multipath reflections is no more complicated than a field generated by a limited
number of plane waves. As such, there are limits on how rich multipath can
be. This result has significant implications including means: i) to determine a
parsimonious parameterization for arbitrary multipath fields and ii) of synthesizing
arbitrary multipath fields with arbitrarily located nearfield or farfield, spatially
discrete or continuous sources. The theoretical results are corroborated by examples
of multipath field analysis and synthesis.
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Kannan, Arumugam. "Communication Strategies for Single-User and Multiuser Slow Fading Channels." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19850.
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Technological progress in the field of wireless communications over the past few years has only been matched by the increasing demand for sophisticated services at lower costs. A significant breakthrough was achieved in the design of efficient wireless communication systems with the advent of the diversity concept. Spatial diversity exploits the availability of multiple spatial paths between the transmitter and receiver by placing antenna arrays at either end. In addition to improving the reliability of communication by creating redundant copies of the transmitted information at the receiver, wireless transceivers with multiple antennas exploit the spatial degrees of freedom to multiplex multiple streams of data and achieve significant gains in spectral efficiencies.
In this thesis, we design spatial diversity techniques for slow-fading wireless channels. There are two parts to this thesis: In Part I we propose spatial diversity techniques for point-to-point single-user wireless systems, while in Part II we propose multiuser cooperative diversity techniques for multiuser wireless communication systems.
In the first part, we propose a set of new wireless communication techniques for multiple-input, multiple-output (MIMO) channels over Rayleigh slow-fading wireless channels. We introduce MIMO transceivers that achieve high data rates and low error rates using a class of MIMO systems known as layered space-time (ST) architectures, which use low complexity, suboptimal decoders such as successive cancellation (SC) decoders. We propose a set of improved layered space-time architectures and show that it is possible to achieve near-optimal error performance over MIMO channels while requiring just SC decoding at the receiver. We show that these architectures achieve high rate and diversity gains. We also show that some of the proposed layered space-time architectures could find applications in multiple-access communications as low-complexity solutions for achieving near-optimum performance.
In the second part of this thesis, we propose novel techniques for cooperative communication between terminals in multiuser wireless communication systems. Cooperative communication is a concept where neighboring terminals share their antennas and signal processing resources to create a virtual transmit array . In addition to transmitting their own information, users in a cooperative communication system listen to transmission from other users and relay this information to the destination, thus creating multiple paths between transmitter and receiver. This form of diversity, known as cooperative diversity, helps improve the overall reliability of all the users in a network.
We start with a simple three node multiple-access system where two users are communicating with a common destination. We propose new high-rate cooperation strategies which achieve the full diversity gain offered by the cooperative channel for this simple system. We propose a new framework to address the tradeoff between cooperation and independent transmission over a multiple access channel and determine the conditions under which each idea is better than the other. Finally, we propose a high rate cooperation protocol which achieves the maximum diversity over a multiple access system with an arbitrary number of users and achieves high rates which scale favorably as the number of users increases.
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Eneh, Titus Ikechukwu. "Adaptive MMSE multiuser receivers in MIMO OFDM wireless communication systems." Thesis, University of Greenwich, 2011. http://gala.gre.ac.uk/8041/.
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In a bid to cope with challenges of increasing demand for higher data rate, better quality of service, and higher network capacity, there is a migration from Single Input Single Output (SISO) antenna technology to a more promising Multiple Input Multiple Output (MIMO) antenna technology. On the other hand, Orthogonal Frequency Division Multiplexing (OFDM) technique has emerged as a very popular multi-carrier modulation technique, thus it is considered as a promising solution to enhance the data rate of future broadband wireless communication systems. The first contribution of this thesis is the development of a low complexity adaptive algorithm that is robust against slow and fast fading channel scenarios, in comparison to the conventional individual parameter estimation by E. Teletar in his famous paper of 1999. Implementing the Adaptive MMSE Receivers in MIMO OFDM systems which I refer to (AMUD MIMO OFDM), combines the adaptive minimum mean square error multiuser receiver's scheme with prior information of the channel and interference cancelation in the spatial domain, achieves enhanced joint channel estimation and signal detection which makes the new technique effectively mobile. A mathematical analysis and simulation results to estimate the Information Capacity of Mobile Communication system with MMSE DFE and OFDM receivers were investigated. The capacity of a stationary channel with ISI is achievable by both the single carrier MMSE DFE and multicarrier modulation over narrow sub channels with OFDM receivers. The achieved capacity result shows that in both techniques single carrier and multicarrier, apart from different implementations are essentially identical when it comes to achievable criteria for information channel capacity. Lastly, AMUD MIMO OFDM were compared with both adaptive vector pre-coding and iterative system and their performance were fantastic, results shows that it will assure transmission over a high channel capacity.
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Lai, Lifeng. "Multiuser wireless networks the user cooperation perspective." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1186425130.
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Lunemann, Carolin. "Quantum cryptography : security analysis of multiuser quantum communication with embedded authentication." Master's thesis, Universität Potsdam, 2006. http://opus.kobv.de/ubp/volltexte/2007/1275/.
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Three quantum cryptographic protocols of multiuser quantum networks with embedded authentication, allowing quantum key distribution or quantum direct communication, are discussed in this work. The security of the protocols against different types of attacks is analysed with a focus on various impersonation attacks and the man-in-the-middle attack. On the basis of the security analyses several improvements are suggested and implemented in order to adjust the investigated vulnerabilities. Furthermore, the impact of the eavesdropping test procedure on impersonation attacks is outlined. The framework of a general eavesdropping test is proposed to provide additional protection against security risks in impersonation attacks.In der Diplomarbeit werden drei verschiedene quantenkryptographische Protokolle mit dem Schwerpunkt auf authentifizierten Quantennetzwerken analysiert. Die Sicherheit der Protokolle gegenüber verschiedenen Angriffen wird untersucht, wobei der Fokus auf kompletten Personifikationsattacken („impersonation attacks“) liegt. Auf Basis der Sicherheitsanalyse und den Netzwerkanforderungen werden entsprechende Verbesserungen vorgeschlagen. Um die Gefahr von Personifikationen realistisch abschätzen zu können, wird außerdem der Einfluss des Testablaufs analysiert. Um zusätzlichen Schutz gegen Personifikationsattacken zu gewährleisten, werden die Rahmenbedingungen für eine allgemeine Testspezifikation festgelegt.
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Castañeda, García Mario Hernán [Verfasser]. "Design of Multiuser Multiantenna Wireless Communication Systems / Mario Hernán Castaneda García." Aachen : Shaker, 2014. http://d-nb.info/1063264820/34.
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Foo, Justin. "Exploiting multiuser diversity with capture in wireless networks." University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0168.
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In a wireless network, owing to the time-varying nature of wireless channels, different mobile users typically experience peaks and troughs in channel quality at different times. This diversity in channel quality is known as multiuser diversity. With the aid of rate adaptation, multiuser diversity can be exploited by allowing the mobile user with the best channel to use the channel resource. However, in order to achieve this in most practical systems, the mobile users in the network must feed back their channel state information (CSI) to the transmitting user. In large networks, this feedback overhead can outweigh the multiuser diversity gain. In this thesis dissertation, a centralised wireless medium access control (MAC) scheme, namely Multiuser Diversity with Capture (MDC), is discussed as a solution to obviate the overhead problem. MDC explicitly employs the capture effect in radio receivers to reduce network overhead by allowing multiple mobile stations (MSs) with channels better than a nominal response threshold to simultaneously compete for the wireless channel. Owing to the capture effect, the base station (BS) can determine which MS has the best channel. In comparison with the Medium Access Diversity (MAD) scheme in the literature, the proposed MDC possesses the strong merit that the feedback overhead is independent of the number of MSs in the network. Several aspects of the MDC scheme are investigated in detail. An application of the MDC scheme based on the physical layer and parts of the MAC layer of the IEEE 802.11a standard is considered. A general analytical framework for the goodput performance of MDC is derived. Using this framework, the exact closed form solution for the expected goodput of MDC with rate adaptation over Rayleigh fading channels is calculated. The fairness performance of MDC in networks where some MSs experience better average channel conditions than others is also addressed. MSs with low average channel states tend to use the channel less often in MDC than MSs with high average channel states. This issue is tackled with Fairer Multiuser Diversity with Capture (FMDC), a variant of the MDC scheme designed to share the channel resource more equitably across all of the MSs in the network. In FMDC, instead of using the network-wide response threshold to decide whether to compete for the channel, each MS only competes for the channel when their channel state is greater than a threshold factor multiplied by their average channel state. Finally, the problem of adaptive optimisation of the response threshold for MDC and the threshold factor for FMDC is also considered. In the proposed solution, the response threshold and the threshold factor are adapted heuristically according to the estimated goodput performance of the system. The adaptive heuristic has importance in practical systems because the BS usually does not know the characteristics of the time varying channels of the MSs in the network.
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Causey, Richard Todd. "Blind multiuser detection based on second-order statistics." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/15486.
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Fung, Chun-yu, and 馮震宇. "Estimation of fading channel in DS-CDMA multiuser communications systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B27509023.
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Ngo, Hien Quoc. "Performance Bounds for Very Large Multiuser MIMO Systems." Licentiate thesis, Linköpings universitet, Kommunikationssystem, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-85240.
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The last ten years have seen significant advances of multiuser MIMO (MU-MIMO) in wireless communication. MU-MIMO is now being introduced in several new generation wireless standards (e.g.,LTE-Advanced, 802.16m). The number of users is increasing with more and more applications. At the same time, high transmission data rate and communication reliability are required. Furthermore, there is a growing concern about green communication which relates to the effects of the radiation emitted from wireless devices onthe human body. Therefore, the future MU-MIMO systems have to satisfy three main requirements: i) serving many autonomous users in the same time-frequency resource, ii) having high data rate and communication reliability, and iii) less energy consumption/radiation. These are seemingly contradictory requirements since the more users are served, the more interference the systems will suffer, or the more data rate is transmitted, the more power is required. MU-MIMO with very large antenna arrays seems to meet above demands and hence, it can be considered as a promising technology for next generation wireless systems. With very large antenna arrays (we mean arrays comprising say a hundred of antennas), the channel vectors are nearly-orthogonal and hence, multiuser interference can be significantly reduced. As a result, many users can be simultaneously served with high data rate. In particular, with coherent processing, transmit power can be reduced dramatically owing to array gain. In this thesis, we focus on the performance bounds of MU-MIMO with very large antenna arrays. We study the fundamental limits on the system performance when using large antenna arrays under practical constraints such as low complexity processing, imperfect channel state information, intercell interference, and finite-dimensional channels.
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Hijazi, Samer L. "Multi-user detection for multi-carrier communication systems." Diss., Manhattan, Kan. : Kansas State University, 2006. http://hdl.handle.net/2097/147.
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Sjöberg, Frank. "High speed communication on twisted-pair wires and low complexity multiuser detectors." Licentiate thesis, Luleå tekniska universitet, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18771.
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This thesis deals with two different topics: High speed communication on twisted pair wires (digital subscriber lines) and low complexity multiuser detectors. The major part of this thesis concerns a technique for high speed communication over the telephone network called Very high bit rate Digital Subscriber Line VDSL). VDSL is not standardized yet but it is intended to offer bit rates up to 52 Mbit per second on twisted-pair wires. An important problem in VDSL is crosstalk between wire pairs, especially Near End Cross Talk (NEXT). A novel duplex method, called Zipper, that mitigates NEXT is presented herein. Zipper is a flexible duplex method that has high duplex efficiency and offers compatibility with existing services. It is based on Discrete Multi Tone (DMT) modulation, and uses different subcarriers in the two different transmission directions. The method relies on an additional cyclic extension to ensure orthogonality between the transmission directions. Zipper achieves best performance when all transmitters in the access network are synchronized, but it can also operate in an asynchronous mode with only a small loss in performance. Another important issue for VDSL is the problem with Radio Frequency Interference (RFI). The copper wires can act as large antennas and hence can transmit and receive radio signals. Herein the problem of radio frequency signals interfering with VDSL systems (called RFI-ingress) is addressed. The proposed method for suppressing the RFI works in the frequency domain of the DMT-receiver and can be used by any DMT-based VDSL system. By modeling the RFI and measuring the disturbance on some unmodulated subcarriers we can extrapolate and subtract the disturbance on all the other subcarriers. For a typical scenario with an average Signal-to-Noise Ratio (SNR) of 30 dB without RFI, about 20 dB can be lost due to RFI, but with the presented RFI-canceller this SNR-loss is reduced to less than 1 dB. The last part of this thesis deals with low complexity multiuser detection in a direct sequence code division multiple access system. The Maximum Likelihood Sequence Detector (MLSD) gives very good performance but is known to be very computationally complex. The detector presented herein is a simple threshold detector that makes MLSD-decisions on some, but not necessarily all, bits. A pipelined structure of the detector is presented which is attractive from an implementation point of view, since it allows parallel processing of the data. Using a single-user matched filter detector as post processor, taking care of the previously undetected bits, a complete multiuser detector with very low complexity is achieved. This detector gives better performance than the decorrelator receiver for a limited number of simultaneous users, e.g. up to 25 users with a spreading factor of 127.Godkänd; 1998; 20070404 (ysko)
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Tasneem, Khawaja Tauseef. "Reduced Complexity Detection Techniques for Multi-Antenna Communication Systems." Thesis, University of Canterbury. Electrical and Computer Engineering, 2013. http://hdl.handle.net/10092/8611.
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In a multiuser system, several signals are transmitted simultaneously within the same frequency band. This can result in significant improvements both in spectral efficiency and system capacity. However, a detrimental effect of the shared transmissions (both in time and bandwidth), is that the signal received at the base station (BS) or access point (AP) suffers from cochannel interference (CCI) and inter-symbol interference (ISI). This situation presents challenges to receiver design. To combat the destructive nature of multipath fading, a receiver often employs multiple antennas to collect the faded superimposed versions of the transmitted signals. The multiple signals are combined and processed in such a way that the effects of CCI and ISI are minimized and the desired information is reliably recovered. The situation is even more challenging when the system is operating under overload, i.e. when there are fewer receive antennas than there are transmitted signals. Multiuser detection (MUD) is used to simultaneously estimate the information sent by the transmitters. To do this, the receiver exploits differences among the cochannel signals (through unique spatial signatures in this case).
We consider a cochannel communication system where multiple transmitted signals arrive at a receiver (equipped with multiple receive antennas) after propagating through a Rayleigh fading channel. It is assumed that the receiver is operating in an overloaded scenario. For such systems, an optimum maximum a posterior probability (MAP) detector estimates the transmitted signal by maximizing the probability of correct decision. The MAP detector reduces to the maximum likelihood (ML) detector when all the transmitted signals are equiprobable. The computational complexity of both MAP and ML detectors increases exponentially with the number of transmitted signals and the channel memory. For large systems suffering severe CCI and ISI, this is clearly not a good choice for real-time implementation due to the associated computational expenses. The main factors that influence the complexity of MAP / ML detection are: (i) the number of transmitted signals (or equivalently the number of users sharing the system resources), (ii) modulation alphabet size, and (iii) length of the channel memory. On the other hand, linear detection approaches fail to offer acceptable performance while other nonlinear sub-optimum approaches incur high computational costs for reasonably improved system performance and exhibit an irreducible error-floor at medium to high signal to noise ratio (SNR) values.
We develop receiver signal processing techniques for the frequency-flat fading channel (where all the multipaths of the transmitted signal arrive at the receiver within a symbol period). We develop an ant colony optimization (ACO) assisted soft iterative detection approach for binary phase-shift keying (BPSK) modulated signals which employs a simplified MAP criteria to extract the most probable signals from the search space. The structure of the receiver is such that it can continue operating under overloaded conditions. The technique achieves near maximum likelihood (ML) performance in critically loaded cases using much lower complexity. For the challenging case of overload it still offers performance close to ML at low to moderate SNR values. Second, an integrated framework comprising of ACO metaheuristic and a recursively defined ML search criteria is developed to handle multilevel modulations. The proposed receiver is capable of achieving near-ML performance for the considered system with significant savings in computational complexity. The receiver framework is independent of the system loading condition, and therefore it remains suitable for overloaded scenarios. Due to the branch and bound nature of the algorithm, an exact expression for the complexity cannot be determined. Instead, an upper bound on computational complexity is developed.
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Lo, Ernest Sze-Yuen. "Cooperation and multiuser resource allocation for spectral-efficient wireless networks /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?ECED%202008%20LO.
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Akho-Zahieh, Maryam Mahmoud. "Design and Analysis of Multicarrier Multicode Wavelet Packets Based CDMA Communication Systems with Multiuser Detection." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1149006699.
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Zhang, Dongbo. "Wireless multiuser communication systems diversity receiver performance analysis, GSMuD design, and fading channel simulator /." [Ames, Iowa : Iowa State University], 2007.
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Annamalai, Annamalai. "Accurate and efficient analysis of wireless digital communication systems in multiuser and multipath fading environments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ37328.pdf.
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Blunt, Shannon D. "Novel adaptive signal processing algorithms for wireless communications : echo cancellation and multiuser detection /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074375.
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Yue, Guosen. "Code optimization and analysis for multiple-input and multiple-output communication systems." Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/2758.
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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.
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Soydan, Yusuf. "Cluster Based User Scheduling Schemes To Exploit Multiuser Diversity In Wireless Broadcast Channels." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609941/index.pdf.
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Diversity methods are used to improve the reliability of the communication between
transmitter and receiver. These methods use redundancy to reduce the errors in the
communication link. Apart from the conventional diversity methods, multiuser
diversity has an aim of maximizing the sum capacity of a multi-user system. To
benefit from multiuser diversity, the opportunistic scheduling method grants the
channel access to the user which has the best channel quality among all users.
Therefore, the cumulative sum of the information sent to all users, which is the sum
capacity, is maximized in the long term.
Although the opportunistic scheduling maximizes the sum capacity, it has some
drawbacks such as the feedback load growing with the number of users and the
problem of fairness for the users which may have lower channel quality than some
other users. In this thesis, these two issues are investigated for the broadcast channels.
Feedback quantization, which gives partial information on the channel state, is
studied to mitigate the feedback load with a goal of little loss in the sum capacity.
The thresholds for the finite feedback quantization are determined to provide fairness and to reduce the feedback load at the same time. To provide fairness, users are
grouped into clusters and thresholds are optimized for each cluster. A method is
proposed by extending the one given by Floren et. al. to solve the mentioned
problems and the proposed method is compared with some other scheduling methods
in the literature.
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Axehill, Daniel. "Integer Quadratic Programming for Control and Communication." Doctoral thesis, Linköpings universitet, Reglerteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-10642.
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The main topic of this thesis is integer quadratic programming with applications to problems arising in the areas of automatic control and communication. One of the most widespread modern control methods is Model Predictive Control (MPC). In each sampling time, MPC requires the solution of a Quadratic Programming (QP) problem. To be able to use MPC for large systems, and at high sampling rates, optimization routines tailored for MPC are used. In recent years, the range of application of MPC has been extended to so-called hybrid systems. Hybrid systems are systems where continuous dynamics interact with logic. When this extension is made, binary variables are introduced in the problem. As a consequence, the QP problem has to be replaced by a far more challenging Mixed Integer Quadratic Programming (MIQP) problem, which is known to have a computational complexity which grows exponentially in the number of binary optimization variables. In modern communication systems, multiple users share a so-called multi-access channel. To estimate the information originally sent, a maximum likelihood problem involving binary variables can be solved. The process of simultaneously estimating the information sent by multiple users is called Multiuser Detection (MUD). In this thesis, the problem to efficiently solve MIQP problems originating from MPC and MUD is addressed. Four different algorithms are presented. First, a polynomial complexity preprocessing algorithm for binary quadratic programming problems is presented. By using the algorithm, some, or all, binary variables can be computed efficiently already in the preprocessing phase. In numerical experiments, the algorithm is applied to unconstrained MPC problems with a mixture of real valued and binary valued control signals, and the result shows that the performance gain can be significant compared to solving the problem using branch and bound. The preprocessing algorithm has also been applied to the MUD problem, where simulations have shown that the bit error rate can be significantly reduced compared to using common suboptimal algorithms. Second, an MIQP algorithm tailored for MPC is presented. The algorithm uses a branch and bound method where the relaxed node problems are solved by a dual active set QP algorithm. In this QP algorithm, the KKT systems are solved using Riccati recursions in order to decrease the computational complexity. Simulation results show that both the proposed QP solver and MIQP solver have lower computational complexity compared to corresponding generic solvers. Third, the dual active set QP algorithm is enhanced using ideas from gradient projection methods. The performance of this enhanced algorithm is shown to be comparable with the existing commercial state-of-the-art QP solver \cplex for some random linear MPC problems. Fourth, an algorithm for efficient computation of the search directions in an SDP solver for a proposed alternative SDP relaxation applicable to MPC problems with binary control signals is presented. The SDP relaxation considered has the potential to give a tighter lower bound on the optimal objective function value compared to the QP relaxation that is traditionally used in branch and bound for these problems, and its computational performance is better than the ordinary SDP relaxation for the problem. Furthermore, the tightness of the different relaxations is investigated both theoretically and in numerical experiments.This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the Linköping University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By choosing to view this material, you agree to all provisions of the copyright laws protecting it.
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Jaiswal, Suraj Kumar. "MIMO communication for ad hoc networks a cross layer approach /." Connect to this title, 2008. http://scholarworks.umass.edu/theses/111/.
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Deumal, Herraiz Marc. "Multicarrier communication systems with low sensibility to nonlinear amplification." Doctoral thesis, Universitat Ramon Llull, 2008. http://hdl.handle.net/10803/9137.
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Actualment estem entrant a una nova era de la informació amb gran demanda de sistemes de comunicació sense fils. Nous serveis com dades i video requereixen transmissions fiables d'alta velocitat, fins i tot en escenaris d'alta mobilitat. A més a més, la dificultat d'assignar el limitat espectre radioelèctric juntament amb la necessitat d'incrementar el temps de vida de les bateries dels terminals mòbils, requereix el diseny de transceptors que usin la potència i l'ampla de banda disponibles de manera eficient. Les comunicacions multiportadora basades en OFDM són capaces de satisfer la majoria d'aquests requeriments. Però, entre altres reptes, reduir la sensibilitat a la amplificació no-lineal és un factor clau durant el diseny. En aquesta tesi doctoral s'analitza la sensibilitat dels sistemes multiportadora basats en OFDM a l'amplificació no-lineal i es consideren formes eficients per superar aquest problema. La tesi s'enfoca principalment al problema de reduir les fluctuacions de l'envolupant del senyal transmès. En aquest sentit es presenta també un estudi de les mètriques de l'envolupant del senyal, PAPR i CM. A més a més, basant-nos en l'anàlisis presentat es proposen noves tècniques per sistemes OFDM i MC-SS. Per MC-SS, també es tracta el diseny d'una tècnica de postprocessament en forma de detector multiusuari per canals no-lineals.Actualmente estamos entrando en una nueva era de la información donde se da una gran demanda de sistemas de comunicación inalámbricos. Nuevos servicios como datos y vídeo requieren transmisiones fiables de alta velocidad, incluso en escenarios de alta movilidad. Además, la dificultad de asignar el limitado espectro radioeléctrico junto con la necesidad de incrementar el tiempo de vida de las baterías de los terminales móviles, requiere el diseño de transceptores que usen eficientemente la potencia y el ancho de banda disponibles. Las comunicaciones multiportadora basadas en OFDM son capaces de satisfacer la mayoría de dichos requerimientos. Sin embargo, entre otros retos, reducir su sensibilidad a la amplificación no-lineal es un factor clave durante el diseño. En esta tesis se analiza la sensibilidad de los sistemas multiportadora basados en OFDM a la amplificación no-lineal y se consideran formas eficientes para superar dicho problema. La tesis se enfoca principalmente al problema de reducir las fluctuaciones de la envolvente. En este sentido también se presenta un estudio de las métricas de la señal, PAPR y CM. Además, basándonos en el análisis presentado se proponen nuevas técnicas para OFDM y MC-SS. Para MC-SS, también se trata el diseño de un detector multiusuario para canales no-lineales.
We are now facing a new information age with high demand of wireless communication systems. New services such as data and video require achieving reliable high-speed transmissions even in high mobility scenarios. Moreover, the difficulty to allocate so many wireless communication systems in the limited frequency band in addition to the demand for long battery life requires designing spectrum and power efficient transceivers. Multicarrier communications based on OFDM are known to fulfill most of the requirements of such systems. However, among other challenges, reducing the sensitivity to nonlinear amplification has become a design key. In this thesis the sensitivity of OFDM-based multicarrier systems to nonlinear amplification is analyzed and efficient ways to overcome this problem are considered. The focus is mainly on the problem of reducing the envelope fluctuations. Therefore, a study of the signal metrics, namely PAPR and CM, is also presented. From the presented analysis, several new techniques for OFDM and MC-SS are proposed. For MC-SS, the design of a post-processing technique in the form of a multiuser detector for nonlinearly distorted MC-SS symbols is also addressed.
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Greig, Adam. "Design techniques for efficient sparse regression codes." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274917.
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Sparse regression codes (SPARCs) are a recently introduced coding scheme for the additive white Gaussian noise channel, for which polynomial time decoding algorithms have been proposed which provably achieve the Shannon channel capacity. One such algorithm is the approximate message passing (AMP) decoder. However, directly implementing these decoders does not yield good empirical performance at practical block lengths. This thesis develops techniques for improving both the error rate performance, and the time and memory complexity, of the AMP decoder. It focuses on practical and efficient implementations for both single- and multi-user scenarios. A key design parameter for SPARCs is the power allocation, which is a vector of coefficients which determines how codewords are constructed. In this thesis, novel power allocation schemes are proposed which result in several orders of magnitude improvement to error rate compared to previous designs. Further improvements to error rate come from investigating the role of other SPARC construction parameters, and from performing an online estimation of a key AMP parameter instead of using a pre-computed value. Another significant improvement to error rates comes from a novel three-stage decoder which combines SPARCs with an outer code based on low-density parity-check codes. This construction protects only vulnerable sections of the SPARC codeword with the outer code, minimising the impact to the code rate. The combination provides a sharp waterfall in bit error rates and very low overall codeword error rates. Two changes to the basic SPARC structure are proposed to reduce computational and memory complexity. First, the design matrix is replaced with an efficient in-place transform based on Hadamard matrices, which dramatically reduces the overall decoder time and memory complexity with no impact on error rate. Second, an alternative SPARC design is developed, called Modulated SPARCs. These are shown to also achieve the Shannon channel capacity, while obtaining similar empirical error rates to the original SPARC, and permitting a further reduction in time and memory complexity. Finally, SPARCs are implemented for the broadcast and multiple access channels, and for the multiple description and Wyner-Ziv source coding models. Designs for appropriate power allocations and decoding strategies are proposed and are found to give good empirical results, demonstrating that SPARCs are also well suited to these multi-user settings.
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Bogdanski, Jan. "Experimental multiuser secure quantum communications." Doctoral thesis, Stockholms universitet, Fysikum, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-26498.
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We are currently experiencing a rapid development of quantum information, a new branch of science, being an interdisciplinary of quantum physics, information theory, telecommunications, computer science, and many others. This new science branch was born in the middle of the eighties, developed rapidly during the nineties, and in the current decade has brought a technological breakthrough in creating secure quantum key distribution (QKD), quantum secret sharing, and exciting promises in diverse technological fields. Recent QKD experiments have achieved high rate QKD at 200 km distance in optical fiber. Significant QKD results have also been achieved in free-space. Due to the rapid broadband access deployment in many industrialized countries and the standing increasing transmission security treats, the natural development awaiting quantum communications, being a part of quantum information, is its migration into commercial switched telecom networks. Such a migration concerns both multiuser quantum key distribution and multiparty quantum secret sharing that have been the main goal of my PhD studies. They are also the main concern of the thesis. Our research efforts in multiuser QKD has led to a development of the five-user setup for transmissions over switched fiber networks in a star and in a tree configuration. We have achieved longer secure quantum information distances and implemented more nodes than other multi-user QKD experiments. The measurements have shown feasibility of multiuser QKD over switched fiber networks, using standard fiber telecom components. Since circular architecture networks are important parts of both intranets and the Internet, Sagnac QKD has also been a subject of our research efforts. The published experiments in this area have been very few and results were not encouraging, mainly due to the single mode fiber (SMF) birefringence. Our research has led to a development of a computer controlled birefringence compensation in Sagnac that open the door to both classical and quantum Sagnac applications. On the quantum secret sharing side, we have achieved the first quantum secret sharing experiment over telecom fiber in a five-party implementation using the "plug & play" setup and in a four-party implementation using Sagnac configuration. The setup measurements have shown feasibility and scalability of multiparty quantum communication over commercial telecom fiber networks.
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Basharati, Sarhad. "MIMO and Relay Systems Based on Multi-Amplitude Minimum Shift Keying." Thesis, University of Canterbury. Electrical and Computer Engineering, 2013. http://hdl.handle.net/10092/8491.
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This thesis describes the use of a multi-amplitude minimum shift keying (MAMSK) signal in various types of wireless communication system. A MAMSK signal is a bandwidth efficient modulation scheme obtained by superimposing ℳ minimum shift keying (MSK) signals with unequal amplitudes. The overall phase of a MAMSK signal is controlled by the phase of the largest component MSK signal which allows the use of a low-complexity differential detector. A closed form expression for the average bit error rate (BER) for coherent detection of an MAMSK in AWGN is derived and is shown to achieve the same BER as that of square constellation quadrature amplitude modulation (QAM) with the same average transmit power.
We describe the design and implementation of a STBC-based MIMO radio system in conjunction with MAMSK modulation. The proposed system provides high capacity data transmission by carrying information not only in the phases but also in the amplitude. Despite using a simple MAMSK differential receiver the system achieves performance within 1 dB of coherent detection. The existing MSK modems in conjunction with STBC could easily be modified to construct the proposed system.
The MAMSK modulation scheme is extended to a multiuser relaying network where two nodes cooperate in a half-duplex environment to achieve diversity gain. The cooperative scheme is based on superposition modulation using a decode-and-forward (DF) strategy. In the proposed scheme, each node simultaneously transmits its own and the relayed signals by superimposing one on the other. A MAMSK signal is an excellent choice for this type of cooperative communication due its being obtained by a superposition technique. The proposed system exploits the overall phase of a MAMSK signal which allows differential detection and as a result it provides the lowest decoding complexity and memory requirements among the existing superposition based cooperation schemes. The performance of the system is evaluated by simulation, where it is shown that the MAMSK cooperative system outperforms a conventional DF scheme in terms of both power and bandwidth efficiency.
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Zhang, Rong. "Non-orthogonal random waveform based multiuser communications." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/66594/.
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This thesis is aimed at providing a unified treatment of non-orthogonal random waveform based multiuser communications, commencing from the underlying theory and providing the way to sophisticated applications. In Chapter 2, we introduce the general framework of non-orthogonal random waveform based multiuser communications, where we focus our attention on the fundamental theory behind this topic. We then pay particular attention to three general application aspects, where the principle of non-orthogonal random waveform based multiuser communications may be exploited. These are applied to cellular systems in Chapter 3, to cooperative systems in Chapter 4 and they are combined with a practical Hybrid Automatic Repeat reQuest (HARQ) system in Chapter 5. In the cellular system scenario presented in Chapter 3, we discuss three design tradeoffs ofMulti-Carrier Interleave Division Multiple Access (MC-IDMA) with the aid of EXtrinsic Information Transfer (EXIT) charts. Based on the analysis of IDMA, we generalise the principle of nonorthogonal random waveform based multiuser communications, leading to the so-called Interleaved Random Code Division Multiple Access (IR-CDMA) concept. We also consider an interferencelimited cooperative system in Chapter 4, where we propose a novel Interleaved Random Space Time Code (IR-STC) scheme, which is specifically designed for aMulti-Source Cooperation (MSC) scenario. Furthermore, the network coding concept is also employed, when designing a coded MSC arrangement for the sake of improving the attainable energy efficiency. More specifically, the proposed Physical-layer Algebraic Network Coding (PANC) scheme implicitly inherits the random coding principle applied in a distributed manner. In Chapter 5, we proceed by proposing a novel SuperPosition Coding (SPC) aided multiplexed HARQ scheme for substantially improving the overall end-to-end transmission efficiency. In parallel to presenting our general framework of non-orthogonal random waveform based multiuser communications, we bear inmind that employing a powerfulMulti-User Detector (MUD) for maintaining a near-single-user performance is of high importance. Hence, in Chapter 6 we propose a novel so-called Harmony Search (HS) algorithm for joint iterative channel stimation, data detection and channel decoding. The algorithm proposed can be readily employed to replace all detection algorithms used throughout Chapters 3 to 5, when a high throughput is desired.
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Das, Suman. "Multiuser information processing in wireless communication." Thesis, 2000. http://hdl.handle.net/1911/17954.
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The available wireless bandwidth cannot keep pace with the amazing growth rate of wireless subscribers. Moreover, the higher data rate and superior quality of service demand of the increasingly popular multimedia services over wireless networks mandate efficient utilization of the channel. Unfortunately, the wireless channel is not very conducive towards error-free raw data transmission. Forward error correction schemes are therefore necessary for reliable information delivery.
Error correcting schemes rely on the addition of redundancy to information content. Therefore it is essential to know the limits of channels in order to design the most efficient wireless systems. Traditional Shannon capacity defines the maximum rate at which data can be perfectly transferred over a channel. But none of the practical error control schemes achieve zero error rate. Moreover, most of the wireless applications can tolerate certain bit error rates. We introduce the notion of distorted channel capacity that measures the maximum rate of data transfer over a channel under a given bit error rate criteria.
The performance of the various practical codes benchmarked against this measure reveals that only complex codes can perform close to the optimal bound. For example, convolutional codes of large constraint lengths perform much better than codes with smaller constraint lengths. The decoding complexity of the commonly deployed Viterbi algorithm, however, grows exponentially with the constraint length. We propose a new maximal weight basis decoding technique whose complexity is only quadratic in the constraint length and hence is better suited for real time systems deploying strong codes for error protection.
We finally investigate a computationally efficient implementation of a multiuser wireless receiver. The optimal joint decoding complexity of a coded multiuser system is exponential in the number of users. Our proposed iterative joint interference cancellation and decoding technique strikes a balance between the computational complexity and the receiver performance.
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Hosseini, Iraj. "Multiuser detection in TH-UWB communication systems." Master's thesis, 2009. http://hdl.handle.net/10048/501.
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Thesis (M. Sc.)--University of Alberta, 2009.Title from pdf file main screen (viewed on Aug. 14, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Communications, Department of Electrical and Computer Engineering, University of Alberta." Includes bibliographical references.
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"Maximum-likelihood detection for multiuser communication systems." 2001. http://library.cuhk.edu.hk/record=b6073346.
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Ma Wing Kin.Thesis (Ph.D.)--Chinese University of Hong Kong, 2001.
Includes bibliographical references (p. 150-155).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.
Abstracts in English and Chinese.
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Shen, Zukang. "Multiuser resource allocation in multichennel wireless communication systems." Thesis, 2006. http://hdl.handle.net/2152/2645.
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Cheng, Yong-Sheng, and 程勇昇. "Reduced-omplexity Multiuser Detection in Ultra-Wideband Communication." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/12605349614927816575.
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碩士國立中正大學
通訊工程研究所
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In the Ultra-Wideband (UWB) communication system, multiple access interference (MAI) is the main point to affect the performance of the bit error rate (BER). One of the traditional methods for the multiuser detection is the minimum mean square error (MMSE). It can efficiently decrease the MAI to gain the better performance, but it needs to calculate the matrix inverse. This calculation is too complex, so the method is not practice in the real-time system. Therefore, we take the two methods to improve the disadvantage, one is the multiuser multistage Wiener filter (MMWF) and the other is conjugate gradient (CG). The former uses the method decomposing the calculation of the matrix inverse to decrease the complex. And the latter is searching all the directions to find the optimum weight vector of the filter to avoid the calculation of the matrix inverse. Then, the performances of the two methods are almost equal to it of the MMSE, but the complex of the two methods is less than that of the MMSE. In Chapter 4, we will introduce the algorithm of the decision-feedback detection (DFD). This method is based on the MMSE or the MMWF and it can gain the better performance. Besides, its complex will not increase too much, because it can share the calculation results of the MMWF. Finally, we will simulate all the frameworks we introduced above in the computer. And we also simulate the results with two different spreading spectrum methods of UWB system in all kinds of the detecting filters.
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Linton, Lance. "Iterative and Adaptive Processing for Multiuser Communication Systems." Thesis, 2016. https://vuir.vu.edu.au/31027/.
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The huge demand of wireless communications has driven the requirement
for highly-efficient multiple-access communications schemes that
can accommodate multiple simultaneous users, yet provide performance
similar to single-user systems. Recently, iterative multiuser detection
schemes have shown to provide this high level of performance at a
manageable level of complexity. This thesis is concerned with iterative
detection of two non-orthogonal asynchronous access schemes: codedivision
multiple-access (CDMA); and interleave-division multiple-access
(IDMA).
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Xu, Gang. "Implementation issues of multiuser detection in CDMA communication systems." Thesis, 1999. http://hdl.handle.net/1911/17315.
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Multistage detectors have been accepted in designs for next generation CDMA base stations because they are less complex than some other multiuser detectors. In this thesis, we propose a differencing method to further reduce complexity. It achieves both high performance in the interference cancellation and computational efficiency. When interference cancellation converges, the difference of the detection vectors between two consecutive stages is mostly zero. We recode the estimation bits, mapping from $\pm1$ to 0 and $\pm2$. Bypassing all the zero terms saves computations. Multiplication by $\pm2$ can be easily implemented in hardware as arithmetic shifts. The system delay of a five-stage detector will be reduced by 75% with a satisfactory bit error rate. We also investigated fixed-point implementation issues and implemented this algorithm in a real-time system using both TI's TMS320C62 DSP and ASICs.
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Tekin, Ender Yener Aylin. "Information theoretic secrecy for some multiuser wireless communication channels." 2008. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2741/index.html.
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Jones, Haley M. "On multipath spatial diversity in wireless multiuser communications." Phd thesis, 2001. http://hdl.handle.net/1885/47290.
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The study of the spatial aspects of multipath in wireless communications environments is an increasingly important addition to the study of the temporal aspects in the search for ways to increase the utilization of the available wireless channel capacity. Traditionally, multipath has been viewed as an encumbrance in wireless communications, two of the major impairments being signal fading and intersymbol interference. However, recently the potential advantages of the diversity offered by multipath rich environments in multiuser communications have been recognised. Space time coding, for example, is a recent technique which relies on a rich scattering environment to create many practically uncorrelated signal transmission channels. Most often, statistical models have been used to describe the multipath environments in such applications. This approach has met with reasonable success but is limited when the statistical nature of a field is not easily determined or is not readily described by a known distribution. ¶ ...
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Elliott, Robert C. "Genetic algorithms for scheduling in multiuser MIMO wireless communication systems." Phd thesis, 2011. http://hdl.handle.net/10048/1876.
Full textAbstract:
Multiple-input, multiple-output (MIMO) techniques have been proposed to meet the needs for higher data rates and lower delays in future wireless communication systems. The downlink capacity of multiuser MIMO systems is achieved when the system transmits to several users simultaneously. Frequently, many more users request service than the transmitter can simultaneously support. Thus, the transmitter requires a scheduling algorithm for the users, which must balance the goals of increasing throughput, reducing multiuser interference, lowering delays, ensuring fairness and quality of service (QoS), etc.
In this thesis, we investigate the application of genetic algorithms (GAs) to perform scheduling in multiuser MIMO systems. GAs are a fast, suboptimal, low-complexity method of solving optimization problems, such as the maximization of a scheduling metric, and can handle arbitrary functions and QoS constraints. We first examine a system that transmits using capacity-achieving dirty paper coding (DPC). Our proposed GA structure both selects users and determines their encoding order for DPC, which affects the rates they receive. Our GA can also schedule users independently on different carriers of a multi-carrier system. We demonstrate that the GA performance is close to that of an optimal exhaustive search, but at a greatly reduced complexity. We further show that the GA convergence time can be significantly reduced by tuning the values of its parameters.
While DPC is capacity-achieving, it is also very complex. Thus, we also investigate GA scheduling with two linear precoding schemes, block diagonalization and successive zero-forcing. We compare the complexity and performance of the GA with "greedy" scheduling algorithms, and find the GA is more complex, but performs better at higher signal-to-noise ratios (SNRs) and smaller user pool sizes. Both algorithms are near-optimal, yet much less complex than an exhaustive search. We also propose hybrid greedy-genetic algorithms to gain benefits from both types of algorithms.
Lastly, we propose an improved method of optimizing the transmit covariance matrices for successive zero-forcing. Our algorithm significantly improves upon the performance of the existing method at medium to high SNRs, and, unlike the existing method, can maximize a weighted sum rate, which is important for fairness and QoS considerations.Communications
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Lai, Pao-Jen, and 賴寶仁. "Multiuser Detection and Bit Allocation Algorithms for Digital Communication System." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/87843354351302542656.
Full textAbstract:
碩士國立雲林科技大學
電子工程與資訊工程技術研究所
88
In this thesis, we develop low-complexity bit loading algorithms for ADSL and blind adaptive multiuser detection methods for synchronous direct-sequence CDMA (code division multiple access) systems. A variety of bit-loading algorithms have been examined in this thesis. We employ the table loop-up technique to avoid the computation of exponentiation. The binary search method is used to achieve fast convergence in log2(N) steps. We propose a class of low-complexity code-aided blind multiuser detectors by using an auxiliary vector orthogonal to the signature sequence of the desired user. Our simulation results indicate that the proposed multiuser detectors are robust with respect to various configurations of multi-access interference (MAI), ambient white noise, and correlation between signature sequences. We have also experimented with a number of multiuser detection schemes to gain better insight into synchronous multiuser communication.