Dissertations / Theses on the topic 'Multi-user detector'
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1
Shepherd, David Peter, and RSISE [sic]. "Optimisation of Iterative Multi-user Receivers using Analytical Tools." The Australian National University. Research School of Information Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20081114.221408.
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The objective of this thesis is to develop tools for the analysis and optimization of an iterative receiver. These tools can be applied to most soft-in soft-out (SISO) receiver components. For illustration purposes we consider a multi-user DS-CDMA system with forward error correction that employs iterative multi-user detection based on soft interference cancellation and single user decoding. Optimized power levels combined with adaptive scheduling allows for efficient utilization of receiver resources for heavily loaded systems.¶
Metric transfer analysis has been shown to be an accurate method of predicting the convergence behavior of iterative receivers. EXtrinsic Information (EXIT), fidelity (FT) and variance (VT) transfer analysis are well-known methods, however the relationship between the different approaches has not been explored in detail. We compare the metrics numerically and analytically and derive functions to closely approximate the relationship between them. The result allows for easy translation between EXIT, FT and VT methods. Furthermore, we extend the $J$ function, which describes mutual information as a function of variance, to fidelity and symbol error variance, the Rayleigh fading channel model and a channel estimate. These $J$ functions allow the \textit{a priori} inputs to the channel estimator, interference canceller and decoder to be accurately modeled. We also derive the effective EXIT charts which can be used for the convergence analysis and
performance predictions of unequal power CDMA systems.¶
The optimization of the coded DS-CDMA system is done in two parts;
firstly the received power levels are optimized to minimize the
power used in the terminal transmitters, then the decoder activation
schedule is optimized such that the multi-user receiver complexity is
minimized. The uplink received power levels are optimized for the system load using a constrained nonlinear optimization approach. EXIT charts are used to optimize the power allocation in a multi-user turbo-coded DS-CDMA system. We show through simulation that the optimized power levels allow for successful decoding of heavily loaded systems with a large reduction in the convergence SNR.¶
We utilize EXIT chart analysis and a Viterbi search algorithm to derive the optimal decoding schedule for a multi component receiver/decoder. We show through simulations that decoding delay and complexity can be significantly reduced while maintaining BER performance through optimization of the decoding schedule.
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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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Yeh, Chen-Chu Alex. "Minimum-error-probability equalization and multi-user detection." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12994.
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Silva, Mário Marques da. "Multi-User Detection for DS-CDMA Systems." Master's thesis, Instituto Superior Técnico, 1999. http://hdl.handle.net/11144/349.
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The main purpose in wireless communications is to allow high data rates, low delays, high net capacity and flexibility in services. The Direct Spreading – Code Division Multiple Access (DS-CDMA) technology is the main key to combat several sources of interference.
The Intersymbol Interference (ISI) tends to increase with the increase in the symbol rates. To combat the ISI, this thesis improve the ISI Cancellation System, named “Commutation Signaling”. Additionally, presents the use of DS-CDMA technology, and because all the spectrum is available to all users at the same time, there is Multiple Access Interference (MAI), which is caused because several spreading codes used by several users are not received by one reference user perfectly orthogonal.
This thesis studies Subtractive Multi-User Detectors (SIC – Successive Interference Cancellation, and PIC – Parallel Interference Cancellation) without and with the ISI Cancellation System – Commutation Signaling. Additionally, studies the detection with Noise Whitening Matched Filter (NWMF) that combats the MAI with the whitening of the interference power spectrum, and so, following the Single-User strategy, also without and with the ISI Cancellation System – Commutation Signaling.
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Al-Iesawi, Salah. "Adaptive implementation of turbo multi-user detection architecture." Thesis, University of Newcastle Upon Tyne, 2012. http://hdl.handle.net/10443/1494.
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MULTI-access techniques have been adopted widely for communications in underwater acoustic channels, which present many challenges to the development of reliable and practical systems. In such an environment, the unpredictable and complex ocean conditions cause the acoustic waves to be affected by many factors such as limited bandwidth, large propagation losses, time variations and long latency, which limit the usefulness of such techniques. Additionally, multiple access interference (MAI) signals and poor estimation of the unknown channel parameters in the presence of limited training sequences are two of the major problems that degrade the performance of such technologies. In this thesis, two different single-element multi-access schemes, interleave division multiple access (IDMA) and code division multiple access (CDMA), employing decision feedback equalization (DFE) and soft Rake-based architectures, are proposed for multi-user underwater communication applications. By using either multiplexing pilots or continuous pilots, these adaptive turbo architectures with carrier phase tracking are jointly optimized based on the minimum mean square error (MMSE) criterion and adapted iteratively by exchanging soft information in terms of Log-Likelihood Ratio (LLR) estimates with the single-user’s channel decoders. The soft-Rake receivers utilize developed channel estimation and the detection is implemented using parallel interference cancellation (PIC) to remove MAI effects between users. These architectures are investigated and applied to simulated data and data obtained from realistic underwater communication trials using off-line processing of signals acquired during sea-trials in the North Sea. The results of different scenarios demonstrate the penalty in performance as the fading induces irreducible error rates that increase with channel delay spread and emphasize the benefits of using coherent direct adaptive receivers in such reverberant channels. The convergence behaviour of the detectors is evaluated using EXIT chart analyses and issues such as the adaptation parameters and their effects on the performance are also investigated. However, in some cases the receivers with partial knowledge of the interleavers’ patterns or codes can still achieve performance comparable to those with full knowledge. Furthermore, the thesis describes implementation issues of these algorithms using digital signal processors (DSPs), such as computational complexity and provides valuable guidelines for the design of real time underwater communication systems.
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Baines, Steven John. "Linear multi-user detection in DS-CDMA cellular systems." Thesis, University of York, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263690.
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Abedi, Saied. "Genetic multi-user detection for code division multiple access systems." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/843016/.
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The origins of spread spectrum are in navigation and military systems. Techniques originally developed to reduce the effects of the intentional jamming also proved suitable for communications through dispersive channels in cellular applications. In 1949 the first time hoping spread spectrum multiple access system has been introduced by John Pierce. A direct-sequence spread spectrum system has been proposed by De Rosa-Rogoff later in 1950. He has also introduced the concept of processing gain. However the commercialisation of cellular direct-sequence code division multiple access (DS-CDMA) systems became possible only during the 1980's and 1990's. In 2000 and beyond we will be witness to the standardisation and commercialisation of wide band CDMA system with a bandwidth of 5 MHz or more. While CDMA presents a number of advantages for cellular mobile communications, it has its own drawbacks. Good air interface designs provide efficient solutions for the terrestrial cellular system. We first take a look at the problem of narrow-band and partial band interference suppression in a CDMA system. By using Poor's model for partial-band interference, some interference suppression techniques are analysed. Then the concept of hybrid genetic prediction is introduced which outperforms the nonlinear techniques in terms of SNR improvements. The performance of a CDMA system can be degraded by Multiple Access Interference (MAI) due to the presence of many users in the same bandwidth. After analysing the structure and performance of existing multi user detection techniques, a low complexity bit level detector is proposed to reduce MAI in synchronous CDMA (S-CDMA) system for an AWGN channel. It is shown how it is possible to reach almost the single user bound by combining detection theory and the fundamentals laws of evolution found in nature. Nonlinear mappings are added to the proposed detector to increase detector's performance by reducing the misleading effect of noise on the detection process. Then for Asynchronous CDMA (A-CDMA), a novel packet level genetic detector is proposed. The near-far resistance feature of the proposed detector is studied. The effect of different parameters of genetic engine i.e. chromosome length, gene's value or mutation and crossover probabilities on its performance are characterised. Different initialisation methods are introduced. For high bit rate CDMA system in multimedia applications in a dispersive CDMA channel, Inter Symbol Interference (ISI) becomes another highly important factor that degrades system performance. It is shown how it is possible to use a signal sub-space based detector as a core detector for a hybrid genetic Multi user detector.
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Fantuz, Mitchell. "Multi-User Detection of Overloaded Systems with Low-Density Spreading." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39600.
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Future wireless networks will have applications that require many devices to be connected to the network. Non-orthogonal multiple access (NOMA) is a promising multiple access scheme that allows more users to simultaneously transmit in a common channel than orthogonal signaling techniques. This overloading allows for high spectral efficiencies which can support the high demand for wireless access. One notable NOMA scheme is low-density spreading (LDS), which is a code domain multiple access scheme. Low density spreading operates like code division multiple access (CDMA) in the sense that users use a spreading sequence to spread their data, but the spreading sequences have a low number of nonzero chips, hence the term low-density. The message passing algorithm (MPA) is typically used for multi-user detection (MUD) of LDS systems. The MPA detector has complexity that is exponential to the number of users contributing to each chip. LDS systems suffer from two inherent problems: high computational complexity, and vulnerability to multipath channels. In this thesis, these two problems are addressed. A lower complexity MUD technique is presented, which offers complexity that is proportional to the number of users squared. The proposed detector is based on minimum mean square error (MMSE) and parallel interference cancellation (PIC) detectors. Simulation results show the proposed MUD technique achieves reductions in multiplications and additions by 81.84% and 67.87% with a loss of about 0.25 dB with overloading at 150%. In addition, a precoding scheme designed to mitigate the effects of the multipath channel is also presented. This precoding scheme applies an inverse channel response to the input signal before transmission. This allows for the received signal to eliminate the multipath effects that destroy the low-density structure.
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Zhu, Weihua. "Blind Equalization and Multi-User Detection in Asynchronous Space-Time Coded CDMA System." Cincinnati, Ohio : University of Cincinnati, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=ucin1092948594.
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Okada, Hiraku, Peter M. Grant, Ian W. Band, and Akira Ogawa. "Application of MMSE Multi-user Detection to CDMA Unslotted ALOHA System." IEEE, 2000. http://hdl.handle.net/2237/7806.
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Illangakoon, Chathura. "On joint source-channel decoding and interference cancellation in CDMA-based large-scale wireless sensor networks." IEEE, 2013. http://hdl.handle.net/1993/22019.
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Motivated by potential applications in wireless sensor networks, this thesis considers the problem of communicating a large number of correlated analog sources over a Gaussian multiple-access channel using non-orthogonal code-division multiple-access (CDMA). A joint source-channel decoder is presented which can exploit the inter-source correlation for interference reduction in the CDMA channel. This decoder uses a linear minimum mean square error (MMSE) multi-user detector (MUD) in tandem with a MMSE joint source decoder (JSD) for multiple sources to achieve a computational complexity that scales with the number of sources. The MUD and the JSD, then iteratively exchange extrinsic information to improve the interference cancellation. Experimental results show that, compared to a non-iterative decoder, the proposed iterative decoder is more robust against potential performance degradation due to correlated channel interference and offers better near far resistance.
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Hicks, James Edward. "Novel Approaches to Overloaded Array Processing." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28670.
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An antenna array is overloaded when the number of cochannel signals in its operating environment exceeds the number of elements. Conventional space-time array processing for narrow-band signals fails in overloaded environments. Overloaded array processing (OLAP) is most difficult when signals impinging on the array are near equal power, have tight excess bandwidth, and are of identical signal type. Despite the failure of conventional beamforming in such environments, OLAP becomes possible when a receiver exploits additional signal properties such as the finite-alphabet property and signal excess-bandwidth. This thesis proposes three approaches to signal extraction in overloaded environments, each providing a different tradeoff in performance and complexity. The first receiver architecture extracts signals from an overloaded environment through the use of MMSE interference rejection filtering embedded in a successive interference cancellation (SIC) architecture. The second receiver architecture enhances signal extraction performance by embedding a stronger interference rejection receiver, the reduced-state maximum aposteriori probability (RS-MAP) algorithm in a similar SIC architecture. The third receiver fine-tunes the performance of spatially reduced search joint detection (SRSJD) with the application of an energy focusing transform (EFT), a complexity reducing front-end linear pre-processor. A new type of EFT, the Energy Focusing Unitary Relaxed Transform (EFURT) is developed. This transform facilitates a continuous tradeoff between noise-enhancement and error-propagation in an SRSJD framework. EFURT is used to study the role of this tradeoff for SRSJD receivers in a variety of signal environments. It is found that for the environments studied in this thesis, SRSJD enjoys an aggressive reduction in interference at the expense of possible noise-enhancement.Ph. D.
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Annalingam, Dheveegar David. "Blind adaptive multi user interference cancellation detectors and antenna array for CDMA systems." Thesis, University of Sussex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435615.
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Mashwama, Derrick Bonginkosi. "Performance of turbo multi-user detectors in space-time coded DS-CDMA systems." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/5169.
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Includes bibliographical references (leaves 118-123).In this thesis we address the problem of improving the uplink capacity and the performance of a DS-CDMA system by combining MUD and turbo decoding. These two are combined following the turbo principle. Depending on the concatenation scheme used, we divide these receivers into the Partitioned Approach (PA) and the Iterative Approach (IA) receivers. To enable the iterative exchange of information, these receivers employ a Parallel Interference Cancellation (PIC) detector as the first receiver stage.
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Kao, Johnny Wei-Hsun. "Methods of artificial intelligence for error control coding and multi-user detection." Thesis, University of Auckland, 2010. http://hdl.handle.net/2292/5962.
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This thesis investigates error control coding and multi-user detection for a single and multi-user communication system using methods of artificial intelligence. The main motivation of the research is to improve on the drawbacks and the constraints of the existing decoding/detection algorithms by proposing alternative methods based on the principle of soft computing. This thesis contains two main parts: the first part investigates the decoding of convolutional codes using a recurrent neural network and a support vector machine on a classical single-user communication system, and the second part studies a multi-user detector for a CDMA system based on a support vector machine. In particular, this thesis investigates a chaos-based CDMA system and compares it with other conventional systems. The theoretical analysis of the proposed methods are studied in detail by mathematical modeling and numerical examples, where all relevant design parameters and issues are considered. A quantitative approach is used to measure and compare the performance of the system by a series of Monte-Carlo simulations. The regular methods for convolutional decoding such as the Viterbi and the Turbo algorithms are reviewed and compared with the proposed methods. It is shown that the recurrent neural network decoder has a similar performance to the conventional Viterbi decoder, while the complexity reduces from an exponential to a polynomial function with respect to the encoder size. The inherent parallel processing capability of this decoder makes it suitable for high data-rate applications. On the other hand, the support vector machine decoder can learn and adapt to the surrounding environment, hence it achieves an extra coding gain of 2dB over the Viterbi decoder under a Rayleigh fading channel. Furthermore, the semi-blind support vector machine detector has a comparable performance with the well-known MMSE detector, and it is suitable for the forward link. The complexity of the detector is made even simpler than a matched filter receiver once feature extraction is incorporated. The results from the thesis suggest that these proposed methodologies can effectively make the radio links smarter and more flexible for future wireless systems.
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Schepker, Henning F. [Verfasser]. "Compressive Sensing Multi-User Detection Approaches for Sporadic Communication / Henning F. Schepker." Aachen : Shaker, 2015. http://d-nb.info/1081885270/34.
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Hsu, Kai-Chieh Frank. "High-performance vector processing for multi-user detection in spread-spectrum communication." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0015/MQ52998.pdf.
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Kozal, Ahmed Sultan Bilal. "Multi user cooperation spectrum sensing in wireless cognitive radio networks." Thesis, Liverpool John Moores University, 2015. http://researchonline.ljmu.ac.uk/4474/.
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With the rapid proliferation of new wireless communication devices and services, the demand for the radio spectrum is increasing at a rapid rate, which leads to making the spectrum more and more crowded. The limited available spectrum and the inefficiency in the spectrum usage have led to the emergence of cognitive radio (CR) and dynamic spectrum access (DSA) technologies, which enable future wireless communication systems to exploit the empty spectrum in an opportunistic manner. To do so, future wireless devices should be aware of their surrounding radio environment in order to adapt their operating parameters according to the real-time conditions of the radio environment. From this viewpoint, spectrum sensing is becoming increasingly important to new and future wireless communication systems, which is designed to monitor the usage of the radio spectrum and reliably identify the unused bands to enable wireless devices to switch from one vacant band to another, thereby achieving flexible, reliable, and efficient spectrum utilisation. This thesis focuses on issues related to local and cooperative spectrum sensing for CR networks, which need to be resolved. These include the problems of noise uncertainty and detection in low signal to noise ratio (SNR) environments in individual spectrum sensing. In addition to issues of energy consumption, sensing delay and reporting error in cooperative spectrum sensing. In this thesis, we investigate how to improve spectrum sensing algorithms to increase their detection performance and achieving energy efficiency. To this end, first, we propose a new spectrum sensing algorithm based on energy detection that increases the reliability of individual spectrum sensing. In spite of the fact that the energy detection is still the most common detection mechanism for spectrum sensing due to its simplicity. Energy detection does not require any prior knowledge of primary signals, but has the drawbacks of threshold selection, and poor performance due to noise uncertainty especially at low SNR. Therefore, a new adaptive optimal energy detection algorithm (AOED) is presented in this thesis. In comparison with the existing energy detection schemes the detection performance achieved through AOED algorithm is higher. Secondly, as cooperative spectrum sensing (CSS) can give further improvement in the detection reliability, the AOED algorithm is extended to cooperative sensing; in which multiple cognitive users collaborate to detect the primary transmission. The new combined approach (AOED and CSS) is shown to be more reliable detection than the individual detection scheme, where the hidden terminal problem can be mitigated. Furthermore, an optimal fusion strategy for hard-fusion based cognitive radio networks is presented, which optimises sensing performance. Thirdly, the need for denser deployment of base stations to satisfy the estimated high traffic demand in future wireless networks leads to a significant increase in energy consumption. Moreover, in large-scale cognitive radio networks some of cooperative devices may be located far away from the fusion centre, which causes an increase in the error rate of reporting channel, and thus deteriorating the performance of cooperative spectrum sensing. To overcome these problems, a new multi-hop cluster based cooperative spectrum sensing (MHCCSS) scheme is proposed, where only cluster heads are allowed to send their cluster results to the fusion centre via successive cluster heads, based on higher SNR of communication channel between cluster heads. Furthermore, in decentralised CSS as in cognitive radio Ad Hoc networks (CRAHNs), where there is no fusion centre, each cognitive user performs the local spectrum sensing and shares the sensing information with its neighbours and then makes its decision on the spectrum availability based on its own sensing information and the neighbours’ information. However, cooperation between cognitive users consumes significant energy due to heavy communications. In addition to this, each CR user has asynchronous sensing and transmission schedules which add new challenges in implementing CSS in CRAHNs. In this thesis, a new multi-hop cluster based CSS scheme has been proposed for CRAHNs, which can enhance the cooperative sensing performance and reduce the energy consumption compared with other conventional decentralised cooperative spectrum sensing modes.
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Xu, Chong. "Reduced-complexity near-optimal Ant-Colony-aided multi-user detection for CDMA systems." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/206015/.
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Reduced-complexity near-maximum-likelihood Ant-Colony Optimization (ACO) assisted Multi-User Detectors (MUDs) are proposed and investigated. The exhaustive search complexity of the optimal detection algorithm may be deemed excessive for practical applications. For example, a Space-Time Block Coded (STBC) two transmit assisted K = 32-user system has to search through the candidate-space for finding the final detection output during 264 times per symbol duration by invoking the Euclidean-distance-calculation of a 64-element complex-valued vector. Hence, a nearoptimal or near-ML MUDs are required in order to provide a near-optimal BER performance at a significantly reduced complexity. Specifically, the ACO assisted MUD algorithms proposed are investigated in the context of a Multi-Carrier DS-CDMA (MC DS-CDMA) system, in a Multi-Functional Antenna Array (MFAA) assisted MC DS-CDMA system and in a STBC aided DS-CDMA system. The ACO assisted MUD algorithm is shown to allow a fully loaded MU system to achieve a near-single user performance, which is similar to that of the classic Minimum Mean Square Error (MMSE) detection algorithm. More quantitatively, when the STBC assisted system support K = 32 users, the complexity imposed by the ACO based MUD algorithm is a fraction of 1 × 10−18 of that of the full search-based optimum MUD. In addition to the hard decision based ACO aided MUD a soft-output MUD was also developed,which was investigated in the context of an STBC assisted DS-CDMA system using a three-stage concatenated, iterative detection aided system. It was demonstrated that the soft-output system is capable of achieving the optimal performance of the Bayesian detection algorithm.
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Khattak, Shahid. "Base station cooperation strategies for multi-user detection in interference limited cellular systems /." Dresden : Vogt, 2008. http://d-nb.info/990989542/04.
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Vollmer, Marius [Verfasser]. "Efficient Linear Multi User Detection Techniques for Third Generation Mobile Radio Systems / Marius Vollmer." Aachen : Shaker, 2005. http://d-nb.info/1181619866/34.
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LI, XIANGTAO. "PERFORMANCE ANALYSIS OF DECORRELATING DETECTORS FOR DUAL-RATE SYNCHRONOUS DS/CDMA SYSTEMS OVER FREQUENCY-SELECTIVE RAYLEIGH FADING CHANNELS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1028644891.
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Husseini, Orabi Ahmed. "Multi-Modal Technology for User Interface Analysis including Mental State Detection and Eye Tracking Analysis." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36451.
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We present a set of easy-to-use methods and tools to analyze human attention, behaviour, and physiological responses. A potential application of our work is evaluating user interfaces being used in a natural manner. Our approach is designed to be scalable and to work remotely on regular personal computers using expensive and noninvasive equipment.
The data sources our tool processes are nonintrusive, and captured from video; i.e. eye tracking, and facial expressions. For video data retrieval, we use a basic webcam. We investigate combinations of observation modalities to detect and extract affective and mental states.
Our tool provides a pipeline-based approach that 1) collects observational, data 2) incorporates and synchronizes the signal modality mentioned above, 3) detects users' affective and mental state, 4) records user interaction with applications and pinpoints the parts of the screen users are looking at, 5) analyzes and visualizes results.
We describe the design, implementation, and validation of a novel multimodal signal fusion engine, Deep Temporal Credence Network (DTCN). The engine uses Deep Neural Networks to provide 1) a generative and probabilistic inference model, and 2) to handle multimodal data such that its performance does not degrade due to the absence of some modalities. We report on the recognition accuracy of basic emotions for each modality. Then, we evaluate our engine in terms of effectiveness of recognizing basic six emotions and six mental states, which are agreeing, concentrating, disagreeing, interested, thinking, and unsure.
Our principal contributions include the implementation of a 1) multimodal signal fusion engine, 2) real time recognition of affective and primary mental states from nonintrusive and inexpensive modality, 3) novel mental state-based visualization techniques, 3D heatmaps, 3D scanpaths, and widget heatmaps that find parts of the user interface where users are perhaps unsure, annoyed, frustrated, or satisfied.
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Bian, Yan Qing. "Advanced multi-user direct-sequence code division multiple access (DS-CDMA) detection techniques for cellular communications." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398603.
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Yeo, Hong Kwang. "Development and implementation of multi-user detection (MUD) strategies for shallow water acoustic network (SWAN) telemetry." Thesis, University of Newcastle upon Tyne, 2001. http://hdl.handle.net/10443/3131.
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This thesis describes the development and implementation multi-user detection strategies for phase coherent Shallow Water Acoustic Network (SWAN) communication. Sea-trial experiments were carried out in the North Sea, 8 km near Noordwijk, Netherlands. The present demand for shallow water acoustic networks (SWAN) is driven by the need for environmental and other data acquisition from fixed and mobile measuring platforms located in the continental sea. Such networks require new, reliable and bandwidth-efficient data communication systems. Which maximises the use of the underwater channel for simultaneous transmissions. However, horizontal-link digital acoustic communication is limited by both environmental and system factors. Underwater acoustic channels are characterised by multipath propagation, which is due to signal reflection from the sea surface and the sea bottom. Due to wave motion, the multipath components undergo time-varying propagation delays, which result in signal fading and phase fluctuations in the received signal. Another problem with horizontal-link communication is that of the Doppler effect that arises as a result of relative motion between the transmitter and receiver. Receivers employing array processing with adaptive decision feedback equalisation schemes have been shown to be effective to tackle these problems. However, in a phase coherent SWAN, the base-station receiver has the added task of mitigating the effect of co-channel interference from users in the network. Although various multiple access protocols can be implemented to help ease the co-channel interferences, they usually utilises a significant amount of the limited channel resources. The constraints of SWAN communication lead to the need for multi-user detection strategies. The thesis proposes a number of novel multi-user detection strategies and presents the software architecture and practical implementation of these phase coherent multi-user receiver structures. Both simulation data and experimental real data were used to compare the performances of the proposed receiver structures. Successful implementation of the receiver system was demonstrated by field trail results for ranges up to 5km.
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Webber, Julian Leonard. "Performance enhancement of multi-user detectors for TD-CDMA by means of polarisation diversity and reduced computational complexity." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396658.
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Ganhão, Francisco José Dinis de Sousa Fernandes. "Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2014. http://hdl.handle.net/10362/12453.
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Dissertação para obtenção do Grau de Doutor em
Engenharia Electrotécnica e ComputadoresThe forthcoming generation of mobile communications, 5G, will settle a new standard for a larger bandwidth and better Quality of Service (QoS). With the exploding growth rate of user generated data, wireless standards must cope with this growth and at the same time be energy efficient to avoid depleting the batteries of wireless devices. Besides these issues, in a broadband wireless setting QoS can be severely affected from a multipath dispersive channel and therefore be energy demanding. Cross-layered architectures are a good choice to enhance the overall performance of a wireless system. Examples of cross-layered Physical (PHY) - Medium Access Control (MAC) architectures are type-II Diversity Combining (DC) Hybrid-ARQ (H-ARQ) and Multi-user Detection (MUD) schemes. Cross-layered type-II DC H-ARQ schemes reuse failed packet transmissions to enhance data reception on posterior retransmissions; MUD schemes reuse data information from previously collided packets on posterior retransmissions to enhance data reception. For a multipath dispersive channel, a PHY layer analytical model is proposed for Single-Carrier with Frequency Domain Equalization (SC-FDE) that supports DC H-ARQ and MUD. Based on this analytical model, three PHY-MAC protocols are proposed. A crosslayered Time Division Multiple Access (TDMA) scheme that uses DC H-ARQ is modeled and its performance is studied in this document; the performance analysis shows that the scheme performs better with DC and achieves a better energy efficiency at the cost of a higher delay. A novel cross-layered prefix-assisted Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme is proposed and modeled in this document, it uses principles of DC and MUD. This protocol performs better by means of additional retransmissions, achieving better energy efficiency, at the cost of higher redundancy from a code spreading gain. Finally, a novel cross-layered protocol H-ARQ Network Division Multiple Access (H-NDMA) is proposed and modeled, where the combination of DC H-ARQ and MUD is used with the intent of maximizing the system capacity with a lower delay; system results show that the proposed scheme achieves better energy efficiency and a better performance at the cost of a higher number of retransmissions. A comparison of the three cross-layered protocols is made, using the PHY analytical model, under normalized conditions using the same amount of maximum redundancy. Results show that the H-NDMA protocol, in general, obtains the best results, achieving a good performance and a good energy efficiency for a high channel load and low Signal-to-Noise Ratio (SNR). TDMA with DC H-ARQ achieves the best energy efficiency, although presenting the worst delay. Prefix-assisted DS-CDMA in the other hand shows good delay results but presents the worst throughput and energy efficiency.
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Wang, Beibei. "Improved Statistical Interference Suppression Techniques in Single and Multi-rate Direct Sequence Spread Spectrum Code Division Multiple Access Systems." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1173119961.
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Nguyen, Anh-Minh Ngoc. "High-Quality Detection in Heavy-Traffic Avionic Communication System Using Interference Cancellation Techniques." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29069.
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This dissertation focuses on quantifying the effects of multi-user co-channel interference for an avionic communication system operating in a heavy-traffic aeronautical mobile environment and proposes advanced interference cancellation techniques to mitigate the interference.
The dissertation consists of two parts. The first part of the work investigates the use of a visualization method to quantify and characterize the multi-user co-channel interference (multiple access interference) effects impinging on an avionic communication system. The interference is caused by complex interactions of thousands of RF signals transmitted from thousands of aircraft; each attempts to access a common communication channel, which is governed by a specific channel contention access protocol. The visualization method transforms the co-channel interference, which is specified in terms of signal-overlaps (signal collisions), from a visual representation to a matrix representation for further statistical analysis. It is found that the statistical Poisson and its cumulative distribution provide the best estimates of multi-user co-channel interference. It is shown, using Monte Carlo simulation, that the co-channel interference of a victim aircraft operating in the heavy-traffic environment could result in as high as eight signal-overlaps. This constitutes to approximately 83.4% of success rate in signal detection for the entire three thousand aircraft environment using conventional FSK receiver. One key finding shows that high-quality communications, up to 98.5% success rate, is achievable if only three overlapping signals can be decoded successfully. The interference results found in the first part set the stage for interference cancellation research in the second part.
The second part of the work proposes the use of advanced interference cancellation techniques, namely sequential interference cancellation (SIC) and parallel interference cancellation (PIC), as potential solutions to mitigating the interference effects. These techniques can be implemented in radio receivers to perform multi-signal decoding functionality to remove the required interferers (three overlapping signals) so that high-quality communication, as described in the first part, can be achieved. Various performance graphs are shown for B-FSK and B-PSK for both SIC and PIC techniques. One key finding is that the system performance can be improved substantially to an additional 15% in signal reception success rate by using SIC or PIC. This means that critical information transmitted from 450 aircraft (out of approximately three thousand aircraft in the environment) is preserved and successfully decoded. Multi-signal decoding using these interference cancellation receivers comes at a small penalty of 2 - 4.5 dBs in Eb/No when sufficient signal-to-interference (SIR) ratio (7-12 dB) is provided.Ph. D.
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Çelebi, Mehmet Bahadır. "On the Improvement of the Capacity of the Heterogeneous Networks with Link-Level and System-Level Approaches." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5353.
Full textAbstract:
Evolution of wireless services enabled the development of the advanced applications and shifted the paradigms of research in this field from voice to data centric. Such services are spreading like wildfire between users and hence, increasing the demand for large bandwidth. However, the frequency spectrum that is suitable for wireless mobile communications is already assigned to particular services from 400 MHz to several GHz. Also, allocating a large chunk of band continuously from the same part of the spectrum may not be possible due to spectral crowd. Therefore, meeting the demand for high data rate requiring wireless services within the accessible spectrum range becomes a challenging problem.
The spectrum allocation policies are discussed by regulatory authorities and academia, and the idea of spectrum sharing systems are addressed as a solution. For instance, heterogeneous networks (HetNets) increase the number of available resources and improve the spectrum accessing capabilities of the wireless communication systems. To achieve this, HetNet nodes are deployed within the coverage of the macrocell regions. Thus, spectral efficiency is boosted via spatial reuse of the same spectral resources. On the contrary, HetNets preclude to fully exploit the resources because of serious interference problems between macrocell and HetNet nodes. Thus, wireless networks of the future will observe interference from even a larger number of sources.
Due to co-channel HetNet deployment and denser frequency reuse, interference cancellation is expected to have significant importance for future wireless communication systems. The occupied resources can also be reused as a solution by conducting advanced signal processing algorithms at the receiver to increase the spectral efficiency. While doing so, the proposed approaches are expected to be easily integrated with the existing complementary approaches to improve the capacity further. Besides, new deployment strategies that allow spectrum access for non-licensed users to achieve larger bandwidth become important to increase the spectral efficiency of the HetNets.
Within the scope of the dissertation, new solutions are developed for the aforementioned problems of the next-generation wireless communication systems. First, an interference cancellation receiver that exploits the unique characteristics of current waveforms is developed in Chapter 2. Also the unknown model of interference is converted to a known model and new algorithms are proposed to recover the desired signal. Then, another perspective is brought into the subject by transforming the interference problem to an interference advantage in Chapter 3. The idea of co-existence of different types of signals are analyzed to bring another degree of freedom as a solution. The proposed approaches are integrated to the existing complementary approaches, such as interference coordination and power control, to improve the capacity further. Finally, a cooperation mechanism is suggested to facilitate the transmission of signal which has a large bandwidth by integrating the idle bands in Chapter 4. By this way, geo-spatially idle bands within the coverage area are utilized and spectral efficiency is increased.
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Ollivier, Benjamin. "Acoustique longue portée pour transmission et localisation de signaux." Thesis, Télécom Bretagne, 2016. http://www.theses.fr/2016TELB0413/document.
Full textAbstract:
Le positionnement d'objets sous-marins représente un enjeu stratégique pour des applications militaires, industrielles et scientifiques. Les systèmes de positionnement reposent sur des signaux de type SONAR « Sound Navigation and Ranging ». Plusieurs émetteurs synchrones avec des temps d'émission connus sont alors considérés, l'objectif étant que la position d'un récepteur se fasse en fonction des positions des émetteurs. Nous avons la main mise sur la détection des signaux en réception d'une part, et sur le choix des formes d'ondes à l'émission d'autre part. La méthode de détection, basée sur le filtrage adapté, se veut robuste aux différentes perturbations engendrées par le canal de propagation (pertes par transmission, multi-trajets) et par le système lui-même (environnement multi-émetteurs). De plus, la détection restreinte à une somme de tests d'hypothèses binaires, nécessite un fonctionnement en temps réel. A l'émission, les formes d'ondes doivent permettre d'identifier indépendamment les émetteurs les uns des autres. Ainsi les travaux portent essentiellement sur les modulations FHSS, les paramètres de construction de ces signaux étant alors choisis de sorte à optimiser la méthode de détection étudiée. Enfin, l'implémentation des algorithmes issus de ces travaux sur des systèmes embarqués a permis leur validation sur des données enregistrées, puis en conditions réelles. Ces essais ont été réalisés avec l'entreprise ALSEAMAR, dans le cadre de la thèse CIFRE-DGAThere is an increasing interest in underwater positioning system in industry (off-shore, military, and biology). In order to localize a receiver relative to a grid of transmitters, thanks to the knowledge of positions and transmission time, it needs to detect each signal and estimate the TOA (Time Of Arrival). Thus, a range between a transmitter and receiver can be deduced by estimation of TOA. When receiver knows three ranges at least, it can deduce its position by triangulation. This work takes into account signal detection, and waveform choice. Detection method, based on matched filter, needs to be robust face to propagation channel (transmission loss, multi-paths) and to the system (multi-users environment). Moreover, the detection structure, being a combination of binary hypothesis testing, must work in real time. In a CDMA context which requires to distinguish each transmitter, the FHSS (Frequency Hopped Spread Spectrum) modulation, allocating one code per user, is adapted. FHSS signals performance, depending of the number of frequency shifts N and the time-bandwidth product, are analyzed from detection criterion point of view. Moreover, detection method and adapted signal is tested in a shallow water environment.The research was supported by ALSEAMAR and DGA-MRIS scholarship
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Fares, Fares. "Traitement des signaux Argos 4." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0024/document.
Full textAbstract:
Cette thèse est dédié à l’étude de la problématique des interférences multi utilisateurs dans le système Argos et à la proposition des diverses techniques pour réduire les effets de ces interférences. Le système Argos est un système mondial de localisation et de collecte de données géo positionnées par satellite. Il permet à l’échelle mondiale de collecter et de traiter les données émises par des émetteurs installés sur la surface de terre. Ces émetteurs sont connus sous le nom de balises. Ces balises sont installées sur des voiliers, des stations météo, des bouées, ainsi que sur quelques animaux (phoques, penguins, etc.…). Le système Argos a été créé en 1978 par le Centre National des Études spatiales (CNES), l’agence spatiale américaine (NASA) et l’agence américaine d’étude de l’atmosphère et de l’océan (NOAA). Depuis sa création, le nombre de balises Argos n’a cessé d’augmenter afin de couvrir au mieux la couverture mondiale. Nous sommes orientés ainsi à la saturation de la bande d’émission et à la présence des interférences multi utilisateurs (MUI) provenant de la réception simultanée de plusieurs signaux émis par les balises. Cette MUI limite la capacité du système Argos et dégrade les performances en termes de Taux Erreur Bit (TEB). Actuellement, le système Argos n’est capable de traiter qu’un seul signal reçu à un instant donné. D’où, l’intérêt d’implanter des techniques au niveau du récepteur capable de réduire les effets des interférences et de traiter les signaux émis par toutes les balises. Plusieurs techniques de détection multi utilisateurs (MUD) ont été développées dans le cadre de cette problématique. Ces techniques sont principalement implantées dans les systèmes CDMA où des codes d’étalement sont utilisés afin de différencier entre les différents signaux. Ceci n’est pas le cas du système Argos où les signaux ne présentent pas des séquences d’étalement et que les bandes de fréquences pour ces différents signaux ne sont pas disjointes à cause de l’effet Doppler et donc, un recouvrement spectral au niveau du récepteur est très probable. Dans ce contexte, l’objectif du travail présenté dans cette thèse est d’étudier différentes techniques MUD appliquées au système Argos et d’évaluer ces techniques au niveau des performances en termes de TEB et de complexité d’implantation. Dans ce travail, nous présentons les différentes composantes du système Argos ainsi que son mode de fonctionnement. Ensuite, nous présentons la problématique dans le système Argos ainsi que les différentes solutions proposées. Parmi ces solutions, nous montrons celle basant sur l’implantation des techniques MUD au niveau du récepteur. Ces différentes techniques MUD sont alors présentées ainsi que les avantages et les inconvénients de chacune d’elles. Parmi les techniques possédant un bon compromis entre les performances d’une part et la complexité d’autre part, nous notons la technique d’annulation par série d’interférence (SIC). Dans cette technique, les signaux sont démodulés successivement suivant l’ordre décroissant des puissances. Cette technique nécessite une étape d’estimation des paramètres des signaux à chaque étape. L’impact d’une estimation imparfaite des différents paramètres est aussi étudié. Après l’étude des impacts des erreurs d’estimation, nous proposons des estimateurs adaptables au système Argos. Les performances de ces estimateurs sont obtenues en comparant les variances de leurs erreurs aux bornes de Cramer Rao (CRB). Enfin, nous terminons le travail par une conclusion générale des résultats obtenus et nous envisageons les perspectives des prochains travauxIn our thesis, we investigate the application of multi user detection techniques to a Low Polar Orbit (LPO) satellite used in the Argos system. Argos is a global satellite-based location and data collection system dedicated for studying and protecting the environment. User platforms, each equipped with a Platform Transmitter Terminal (PTT), transmit data messages to a 850 km LPO satellite. An ARGOS satellite receives, decodes, and forwards the signals to ground stations. All PTTs transmit at random times in a 100 kHz bandwidth using different carrier frequencies. The central carrier frequency f0 is 401.65 MHz. Due to the relative motion between the satellite and the platforms, signals transmitted by PTTs are affected by both a different Doppler shift and a different propagation delay. Thus, the Argos satellite receives overlapping signals in both frequency and time domains inducing Multiple Access Interference (MAI). One common approach to mitigate the MAI problem is to implement Multi User Detection (MUD) techniques at the receiver. To tackle this problem, several MUD techniques have been proposed for the reception of synchronous and asynchronous users. In particular, the Successive Interference Cancelation (SIC) detector has been shown to offer a good optimality-complexity trade-off compared to other common approaches such as the Maximum Likelihood (ML) receiver. In an Argos SIC receiver, users are decoded in a successive manner, and the signals of successfully decoded users are subtracted from the waveform before decoding the next user. This procedure involves a parameter estimation step and the impact of erroneous parameter estimates on the performance of Argos SIC receiver has been studied. Argos SIC receiver has been shown to be both robust to imperfect amplitude and phase estimation and sensitive to imperfect time delay estimation. The last part of our work focuses on the implementation of digital estimators for the Argos system. In particular, we propose a time delay estimator, a frequency estimator, a phase estimator and an amplitude estimator. These estimators are derived from the ML principle and they have been already derived for the single user transmission. In our work, we adapt successfully these estimators for the multi user detector case. These estimators use the Non Data Aided (NDA) cases in which no a priori information for the transmitted bits is required. The performance of these different estimators are compared to the Cramer Rao Bound (CRB) values. Finally, we conclude in our work by showing the different results obtained during this dissertation. Also, we give some perspectives for future work on Argos system
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Poliak, Sebastián. "Mobilní aplikace využívající hlubokých konvolučních neuronových sítí." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2018. http://www.nusl.cz/ntk/nusl-385895.
Full textAbstract:
This thesis describes a process of creating a mobile application using deep convolutional neural networks. The process starts with proposal of the main idea, followed by product and technical design, implementation and evaluation. The thesis also explores the technical background of image recognition, and chooses the most suitable options for the purpose of the application. These are object detection and multi-label classification, which are both implemented, evaluated and compared. The resulting application tries to bring value from both user and technical point of view.
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Ngo, Khac Hoang. "Non-coherent wireless communications : fundamental limits and system design." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC031.
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Dans les communications sans fil sur des canaux à évanouissement, en particulier à antennes multiples, la connaissance instantanée des coefficients de canal, appelés informations d’état de canal (CSI), est essentielle car elle permet d’adapter la transmission et la réception aux conditions actuelles du canal. La communication avec CSI a priori au niveau du récepteur est dite cohérente. En pratique, cependant, le CSI n’est pas disponible avant la communication et doit être estimé à un coût qui ne doit pas être ignoré, en particulier dans un environnement hautement mobile. Ainsi, la communication sans CSI a priori, également appelée communication noncohérente, est un cadre plus pratique et général. Cette thèse contribue à la compréhension des limites théoriques des communications noncohérentes, ainsi qu’à la conception d’un système de communication pratique noncohérent à évanouissement par bloc. Nous considérons trois scénarios: le canal point à point (P2P), le canal à accès multiple (MAC) et le canal de diffusion (BC).Dans la première partie, nous étudions les limites fondamentales des communications noncohérentes en termes de débit de données et de degrés de liberté (DoF) réalisables. Nous considérons un évanouissement par bloc générique dans lequel le canal a une entropie différentielle finie et un second moment fini. Nous établissons d’abord le DoF optimal pour le canal P2P noncohérent à entrées multiples et sorties multiples (MIMO) en utilisant l’approche de la dualité pour borner les informations mutuelles. Deuxièmement, en utilisant une approche de dualité similaire, nous dérivons la région de DoF optimale pour le MAC SIMO à deux utilisateurs, qui peut être obtenue par partage de temps entre des schémas à pilotes simples. Troisième, nous dérivons les régions débit et DoF réalisable pour le BC MIMO noncohérent avec un évanouissement spatialement corrélé en exploitant la diversité de corrélation de transmission, qui est la différence entre la corrélation subie par différents utilisateurs. Ce faisant, nous concevons soigneusement des schémas de transmission basés sur des pilotes et sur le partage de débit, la superposition de produits et une combinaison de ceux-ci pour transmettre efficacement des signaux dans les parties communes et mutuellement exclusives des sous-espaces de corrélation. Dans la deuxième partie, nous concevons la constellation et les schémas de détection efficaces pour les communications noncohérentes sur le canal d’évanouissement de type Rayleigh par bloc. Premièrement, nous proposons une constellation Grassmannienne structurée pour le canal P2P SIMO qui est simple à générer, a une efficacité d’empilement élevée, admet un étiquetage binaire simple mais efficace et permet une détection efficace douce et dure. Deuxièmement, nous étudions la conception de constellation conjointe pour le MAC MIMO. Nous introduisons des critères de conception simples et efficaces afin de minimiser l’erreur de détection conjointe et proposons quelques constructions de constellation simples. Troisièmement, nous proposons un schéma de détection souple multi-utilisateurs noncohérent pour le MAC SIMO à l’évanouissement de Rayleigh corrélé spatialement basé sur l’inférence approximative par propagation d’espérance. Ce schéma présente une complexité polynomiale dans la dimension du canal tout en produisant des marginaux postérieurs approximatifs par utilisateur précis conduisant à des performances d’erreur quasi-optimalesIn wireless communication over fading channels, especially multiple-antenna communication, the instantaneous knowledge of channel coefficients, so-called channel state information (CSI), is critical because it enables to adapt the transmission and reception to current channel conditions. The communication with a priori CSI at the receiver is said to be coherent. In practice, however, CSI is not granted for free prior to communication and needs to be estimated at a cost that should not be ignored, especially in a highly mobile environment. Thus, communication without a priori CSI, also known as noncoherent communication, is a more practical and general framework. This thesis contributes to the understanding of the theoretical limits of noncoherent communications, as well as the design of a practical noncoherent communication system in block fading. We consider three scenarios: the point-topoint (P2P) channel, the multiple-access channel (MAC), and the broadcast channel (BC).In the first part, we study the fundamental limits of noncoherent communications in terms of achievable data rate and degrees of freedom (DoF). We consider generic block fading in which the channel has finite differential entropy and finite second moment. First, we derive the optimal DoF for the noncoherent multiple-input multiple-output (MIMO) P2P channel by using the duality approach to bound the input-output mutual information. Second, using a similar duality approach, we derive the optimal DoF region for the two-user noncoherent single-input multiple-output (SIMO) MAC, which can be achieved by time sharing between simple pilot-based schemes. Third, we derive achievable rate and DoF regions for the noncoherent MIMO BC with spatially correlated fading by exploiting the transmit correlation diversity, which is the difference between the correlation experienced by different users. In doing so, we carefully design pilot-based transmission schemes based on rate splitting, product superposition, and a combination of them to effectively transmit signals in both the common and mutually exclusive parts of the correlation subspaces. In the second part, we design the constellation and efficient detection schemes for noncoherent communications over Rayleigh block fading channel. First, we propose a structured Grassmannian constellation for the SIMO P2P channel that is simple to generate, has high packing efficiency, admits a simple yet effective binary labeling, and allows for efficient soft and hard detection. Second, we investigate joint constellation design for the MIMO MAC. We introduce some simple and effective design criteria so as to minimize the joint detection error, and propose some simple constellation constructions. Third, we propose a noncoherent multi-user soft detection scheme for the SIMO MAC in spatially correlated Rayleigh fading based on expectation propagation approximate inference. This scheme has polynomial complexity in the channel dimension while producing accurate approximate per-user posterior marginals leading to near-optimal error performance
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Wu, sheng-quan, and 吳昇銓. "Orthogonal Decision-Feedback Detector (ODFD) for CDMA Multi-user Detection." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/67899744505316790570.
Full textAbstract:
碩士國立中興大學
電機工程學系
89
We propose a multi-user detection scheme for downlink channel and uplink link channel, including multi-path effect. The orthogonal decision-feedback detector (ODFD) employs a match filter bank matching to a set of orthogonal sequences, which are generating by Gram-Schmidt orthogonalisation procedure based on spreading codes. The ODFD algorithm involves only the orthonormal coefficient matrix, which require no frequent recalculations even when system parameters change. Successive decision-feedback detection is performed immediately at the output of the ODFD match filter bank without the transform matrix, which requires in the DDFD. For downlink channel, we considering the multi-path and fading effect, and we assume that there are 12 kinds of channels to simulation. To improve the system performance, two different types of RAKE receiver structures, equal gain combining RAKE and maximum ratio combining RAKE, are also considered for CDMA systems to mitigate multi-path fading effects of mobile channels. For uplink channel, the assumption are the same with downlink channel, the different is just the users are asynchronous each other. And in this thesis we comparison structure and algorithm complexity between ADDFD and AODFD.
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Wu, sheng-quan, and 張亞寧. "Orthogonal Decision-Feedback Detector (ODFD) for CDMA Multi-user Detection." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/05050716608149895145.
Full textAbstract:
碩士國立中興大學
電機工程學系
89
We propose a multi-user detection scheme for downlink channel and uplink link channel, including multi-path effect. The orthogonal decision-feedback detector (ODFD) employs a match filter bank matching to a set of orthogonal sequences, which are generating by Gram-Schmidt orthogonalisation procedure based on spreading codes. The ODFD algorithm involves only the orthonormal coefficient matrix, which require no frequent recalculations even when system parameters change. Successive decision-feedback detection is performed immediately at the output of the ODFD match filter bank without the transform matrix, which requires in the DDFD. For downlink channel, we considering the multi-path and fading effect, and we assume that there are 12 kinds of channels to simulation. To improve the system performance, two different types of RAKE receiver structures, equal gain combining RAKE and maximum ratio combining RAKE, are also considered for CDMA systems to mitigate multi-path fading effects of mobile channels. For uplink channel, the assumption are the same with downlink channel, the different is just the users are asynchronous each other. And in this thesis we comparison structure and algorithm complexity between ADDFD and AODFD.
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Huang, Zi-Yi, and 黃子益. "An Improved Multi-User Detector for Ds-CDMA system." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/71982824880834813076.
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碩士國立中山大學
電機工程學系研究所
86
Direct-sequence code-division multiple access (DS-CDMA) is one of several methods of multiplexing wireless users. In CDMA, all users use the same carrier frequency and may transmit signals simultaneously by assigning a distinct signature sequence to each user. The detector receives a signal composed of the sum of all users' signals, which overlap in time and frequency.A conventional DS-CDMA system treats each user separately as a signal, with the other users considered as multiple access interference (MAI) and is highly vulnerable to tjhe near-far effect. The optimum maximum likelihood detector jointly extracts user's messages by solving an optimization problem. Although the optimum detector improves the system performance significantly, the associated computational complexity increases exponentially with the number of users [7], which prohibits its practical use. Therefore, many suboptimum detectors, like MMSE detector, decorrelator detector and etc. have been proposed [9]-[18].In this paper, we use adaptive algorthm to implement the MMSE detector and use decision feedback structure to improve it. We compare the bit error rate of the proposed detector with those of the conventional, decorrelator. and MMSE detetors. The performance for relatively weak user by using the proposed adaptive decision feedback detector has been significantly improved.
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Li, Tzung-Cheng, and 李宗晟. "An Improved PDA Multi-User Detector for DS-CDMA UWB Systems." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/65927769982615811037.
Full textAbstract:
碩士國立中山大學
電機工程學系研究所
93
Ultra-Wideband technology has attracted interests of the researchers and commercial groups due to its advantage of high data rate, low complexity and low power consumption. The direct-sequence code division multiple access ultra wideband system (DS-CDMA UWB) is one of the proposal of IEEE 802.15.3a standard. By combing the power of both UWB and DS-CDMA techniques, the system could construct multiple access architecture using direct sequence method. In multi-user environment, the major problem of the receiver designing of conventional DS-CDMA system is multiple access interference(MAI). In DS-CDMA UWB system, the transmitted signal were interfered by inter-symbol interference(ISI) and neighbor symbol interference because of the multi-path channel characteristic. In this thesis, we use the training method to get the spreading waveform influenced by multi-path. Based on the information of spreading waveform, we use the block method to reformulate the received signal. We can separate the interference into multiple access interference and neighbor symbol interference. With Combining the interference cancellation, probabilistic data association (PDA) filter and sliding window techniques, we could eliminate the interference. In the computer simulation section, we compare the detection performance of sliding window PDA detector with conventional detector, and the simulation result shows that the improved PDA detector has better performance than others.
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Shepherd, David Peter. "Optimisation of Iterative Multi-user Receivers using Analytical Tools." Phd thesis, 2008. http://hdl.handle.net/1885/49357.
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The objective of this thesis is to develop tools for the analysis and optimization of an iterative receiver. These tools can be applied to most soft-in soft-out (SISO) receiver components. For illustration purposes we consider a multi-user DS-CDMA system with forward error correction that employs iterative multi-user detection based on soft interference cancellation and single user decoding. Optimized power levels combined with adaptive scheduling allows for efficient utilization of receiver resources for heavily loaded systems.¶ Metric transfer analysis has been shown to be an accurate method of predicting the convergence behavior of iterative receivers. EXtrinsic Information (EXIT), fidelity (FT) and variance (VT) transfer analysis are well-known methods, however the relationship between the different approaches has not been explored in detail. We compare the metrics numerically and analytically and derive functions to closely approximate the relationship between them. The result allows for easy translation between EXIT, FT and VT methods. Furthermore, we extend the $J$ function, which describes mutual information as a function of variance, to fidelity and symbol error variance, the Rayleigh fading channel model and a channel estimate. ... ¶
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Lin, Shin-Ji, and 林信吉. "The improvement on the performance of the Group MMSE Multi-user Detector." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/66439102764073978225.
Full textAbstract:
碩士國立臺北科技大學
電機工程系碩士班
91
The goal of this thesis is to investigate the Group MMSE multi-user detector technology applied on the DS-CDMA system and MT-CDMA system and to improve the performance of these systems. Since the complexity of the MMSE multi-user detector is related to the inverse matrix operation, in order to reduce the complexity and increase the practicality, the Group MMSE detector has been proposed. However, while the Group MMSE detector does reduce the complexity, it also increases the bit error rate. This thesis proposes two methods to lower the bit error rate for the Group MMSE detector. The first method is to apply the correlation matrix for choosing the user’s group in the original DS-CDMA system, so that the users with higher cross correlation are grouped together and those with lower cross correlation are allocated in the different groups. For the second method, to further reduce the interference of different groups, we apply the Group MMSE detector on the modified MT-CDMA structure. We make use of the multi-tone property of the MT-CDMA system, and let users of different groups propagate on the different carriers. By orthogonality of the carrier, we can reduce the mutual interferences between user groups, and thus lower the bit error rate.
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Lin, Kowei, and 林克威. "A Multi-user Detector for Synchronous CDMA communication Systems Based on EM Algorithm." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/27417219217471859878.
Full textAbstract:
碩士長庚大學
電機工程研究所
89
The maximum likelihood detection of superimposed signal in direct sequence code division multiple access (DS-CDMA) has a computational complexity, increased in exponential with numbers of active users, and its implementation is prohibitive even for a moderate number of users. Some research has applied expectation maximization (EM) algorithm to decompose the multiuser detection problem into a series of single-user problems, and presents an iterative computational efficient algorithm for detection of signals in synchronous CDMA system. The EM-based detector estimates each user’s signal to interference ratio (SIR) only by the property of cross-correlation of different users, but it does not reflect the actual SIR of each user. We propose a new detector, without increasing additional hardware circuit, can estimate signal to interference ratio (SIR) of different users directly by each user’s match filter output. Within estimated SIR, new detector changes its parameter dynamically to increase the performance of detection. Simulation result also shows that when near-far effect occurs or the power control is not perfect, the new detector can maintain performance without estimating signal amplitude of each user.
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Yang, Shih-Yang, and 楊石陽. "A Multi-user Detector Based on EM Algorithm for Synchronous CDMA Communication Systems Over." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/28896865849098321333.
Full textAbstract:
碩士長庚大學
電機工程研究所
90
The maximum likelihood detection of superimposed signal in direct sequence code division multiple access (DS-CDMA) has a computational complexity, increased in exponential with numbers of active users, and its implementation is prohibitive even for a moderate number of users. Some research has applied expectation maximization (EM) algorithm to decompose the multi-user detection problem into a series of single-user problems, and presents an iterative computational efficient algorithm for detection of signals in synchronous CDMA system. However the EM-based detector estimates each user’s signal to interference ratio (SIR) only by the property of cross-correlation of different users, but it does not reflect the actual SIR of each user. So，we propose a new algorithm called AISI algorithm ( Approximate ISR estimator by Side-lobe Information algorithm ) for improving the EM-based detector , The AISI algorithm can estimate signal to interference ratio (SIR) of different users directly by each user’s despreading filter output without increasing additional hardware circuit,. Within estimated SIR, new detector changes its parameter dynamically to increase the performance of detection. Our new detector also adds the novel idea of improved PIC that has different weight in each stage. By combining these two opinions，New detector changes its parameter dynamically in each stage to increase performance .At the end of this paper; we compare several kinds of multi-user detector. Simulation result also shows that when near-far effect occurs or not, the new detector still can have better performance than others.
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Lan, Hao-Yu, and 藍浩佑. "Low Complexity Multi-User Detector Design for Sparse Code Multiple Access in 5G networks." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/8qnx69.
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碩士國立臺灣大學
電子工程學研究所
106
Massive Machine Type Communications (mMTC) is one of the three major types of 5G use cases. In the coming era of Internet of Things (IoT), all devices will be connected. Currently there are several proposals for achieving this objective in the 3GPP standard meetings. One promising technology, called sparse code multiple access (SCMA), implements uplink grant-free non-orthogonal multiple access (NOMA) for mMTC networks. SCMA is derived from the low-density spread OFDM (LDS-OFDM) and has the advantages of low signaling overhead, low transmission latency, and high spectral efficiency. In this thesis, we focus on low complexity and high performance multiuser receiver design for SCMA systems. In the Chapter 3, we introduce the principle of SCMA and LDS systems and conduct physical layer simulation for AWGN channel and uplink multipath fading channel. To start with, we design the SCMA codebook and low-density signature (LDS) and analyze their BER performance and convergence behavior. It is worth mentioning that different spreading length, overloading ratio, receiver diversity and near-far effect are also taken into account in our analysis. In the Chapter 4, we design the low complexity multiuser detection for the basic SCMA system, including the factor graph and the message passing algorithm. To improve the convergence rate and reduce the MPA complexity of later iterations, SINR based Serial MPA (SS-MPA) and codebook cardinality reduction based MPA (CCR-MPA) are proposed. To validate the effectiveness of these two methods, we conduct simulations to show that SS-MPA converges faster than traditional methods on the uplink multipath fading channel and CCR-MPA reduces 50% to 80% complexity of conventional MPA while the characteristic of fixed complexity is retained to facilitate the realization of the hardware implementation. At the end of the thesis, we design the cost-efficient multiuser receiver for turbo sparse code multiple access (Turbo-SCMA) system. By iterative detection and decoding (IDD) and our proposed methods, the receiver achieves high BER performance and reduces a lot of memory usages and computational complexity compared with state state of the art method.
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Lee, Zheng-Xiu, and 李政修. "Performance Analysis and Improvement of Multi-user Detector Using Probabilistic Data Association in CDMA systems." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/2v45m8.
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碩士國立臺北科技大學
電機工程系所
93
The main purpose of this thesis is to improve the performance of multi-user detector using probabilistic data association in CDMA systems by reducing its computational complexity. The performance of multi-user detector using probabilistic data association is close to optimal multi-user detector, but its computational complexity is still higher than the linear MMSE multi-user detector. To reduce its computational complexity, the different initial settings of probabilistic data association are used in this thesis to analyze the effects of convergence time of this multi-user detector in synchronous and asynchronous CDMA systems. A new method has been proposed in this thesis. We set the initial values of probabilistic data association by using the soft decision of the output signals in MMSE or decorrelating multi-user detectors. It can reduce the computational complexity while maintain the same bit error rate in the CDMA systems. Finally, the new proposed method and other methods of fixed initial values of probability are applied to both the DS-CDMA system and slowly fading flat channel MC-CDMA system to verify its performance.
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Fu, Ray-Hsiang, and 傅瑞翔. "Multi-user Detector for DS-UWB System Using Constricted Selection Rake Receiver and Genetic Algorithms." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/r774q9.
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碩士國立臺北科技大學
電機工程系所
95
DS-UWB is one major technology employed in UWB system. However, for the multi-user application the multiple access interference (MAI) due to imperfect orthogonality between spreading codes induced by UWB dense multi-path degrades system performance. Though optimum multi-user detector (OMD) can achieve remarkable performance, its computational complexity is too high to implement. Therefore, many sub-optimal multi-user detectors (MUDs) have been proposed to compromise system performance and complexity, such as the genetic algorithm-based MUD (GA-MUD). Previous work combining the partial rake receiver (p-rake) and GA-MUD has been proposed, but its performance is still not attractive. Therefore, a CSRGA-MUD that combines the constricted selection rake receiver (cs-rake) and GA-MUD is proposed to improve BER performance further. Moreover, for seeking the best trade-off between BER performance and computational complexity, a CSRGA-MUD with lower computational complexity is also proposed.
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Wang, Qingsheng. "Power and performance trade-off in DS-CDMA receivers based on adaptive LMS-MMSE multi-user detector." Thesis, 2003. http://hdl.handle.net/10413/4212.
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Third generation cellular communication systems based on CDMA techniques have shown great scope for improvement in system capacity. Over the last decade, there has been significant interest in DS-CDMA detectors. The conventional detector, the optimal detector and a number of sub-optimal multi-user detectors (MUD) have been extensively analyzed in the literature. Recently, the reduction of power consumption in DS-CDMA systems has also become another important consideration in both system design and in implementation. In order to support wireless multimedia services, all CDMA-based systems for third generation systems have a large bandwidth and a high data rate, therefore the power consumed by the digital signal processor (DSP) is high. This thesis focuses on power consumption in the adaptive Minimum Mean Square Error (MMSE) detector which is based on the Least Mean Square (LMS) algorithm. This thesis presents a literature survey on MUD and adaptive filter algorithms. A system model of the quantized LMS-MMSE MUD is proposed and its performance is analyzed. The quantization effects in the finite precision LMS-MMSE adaptive MUD including the steady-state weight covariance, mean square error (MSE) and bit error rate (BER) versus wordlength of data and coefficient are investigated when both the data and filter coefficients are quantized. The effects of wordlength size on power consumption are investigated and the tradeoff between the power consumption and performance degradation and the optimal allocation of bits to data and to LMS coefficients under power constraint is presented.Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.
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Chin, Wan-Ying, and 秦婉瑛. "Noncoherent multi-user detection." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/896qh6.
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碩士國立中央大學
通訊工程學系
107
Wireless communications is required to transmit quantity of data more and more. An important studying topic is how to transmit the same quantity of data in a shorter period of time. Recently, two-way relaying is a popular subject, where two terminal nodes transmit to each other with the help of the relay node. Two-phase two-way relaying (TPTWR) using physical-layer coding is a bandwidth efficient technique. Several TPTWR schemes using differential phase-shift keying (DPSK) which avoid the rate loss due to pilot symbols were proposed. In this thesis ,we first focus on differential MPSK for TPTWR using decode and forward technique. We propose that the signal constellation of one terminal is the signal constellation of the other terminal rotated by an angle. For the noncoherent maximum-likelihood detector at the relay, we propose a distance measure for the transmitted signals of the two terminals. Based on the proposed distance, we find the optimal angles for both cases of using decision feedback or not. Then the noncoherent two-user detection at the relay is extended as noncoherent three-user detection. We apply these results to NOMA(non-orthogonal multiple access), and compare it with OMA(orthogonal multiple access) by computer simulation.
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Wang, Jinghan. "Multi-user Detection Techniques in Multi-antenna Systems." 2004. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2106200410081500.
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Wang, Jinghan, and 王璟瀚. "Multi-user Detection Techniques in Multi-antenna Systems." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/61864350144676531457.
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碩士國立臺灣大學
電信工程學研究所
92
In the thesis, we discuss several multi-antenna techniques in a wireless communication system. First, we consider the communication between a single transmitter and a single receiver by utilizing multiple antennas. Next, we discuss the multiuser detection (MUD) techniques in a CDMA system, and then we propose that the multiuser detection techniques can also be utilized in a multi-antenna system.
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Wen-Feng, Hu. "Performance Comparison of Multi-user Detection and Multi-Antenna Technique for Multi-user DS-CDMA UWB System." 2005. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1507200511223500.
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