Dissertations / Theses on the topic 'High Mobility Environments'
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1
Qu, Ming. "Experimental studies of wireless communication and GNSS kinematic positioning performance in high-mobility vehicle environments." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/50953/1/Ming_Qu_Thesis.pdf.
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In order to support intelligent transportation system (ITS) road safety applications such as collision avoidance, lane departure warnings and lane keeping, Global Navigation Satellite Systems (GNSS) based vehicle positioning system has to provide lane-level (0.5 to 1 m) or even in-lane-level (0.1 to 0.3 m) accurate and reliable positioning information to vehicle users. However, current vehicle navigation systems equipped with a single frequency GPS receiver can only provide road-level accuracy at 5-10 meters. The positioning accuracy can be improved to sub-meter or higher with the augmented GNSS techniques such as Real Time Kinematic (RTK) and Precise Point Positioning (PPP) which have been traditionally used in land surveying and or in slowly moving environment. In these techniques, GNSS corrections data generated from a local or regional or global network of GNSS ground stations are broadcast to the users via various communication data links, mostly 3G cellular networks and communication satellites.
This research aimed to investigate the precise positioning system performances when operating in the high mobility environments. This involves evaluation of the performances of both RTK and PPP techniques using: i) the state-of-art dual frequency GPS receiver; and ii) low-cost single frequency GNSS receiver.
Additionally, this research evaluates the effectiveness of several operational strategies in reducing the load on data communication networks due to correction data transmission, which may be problematic for the future wide-area ITS services deployment. These strategies include the use of different data transmission protocols, different correction data format standards, and correction data transmission at the less-frequent interval.
A series of field experiments were designed and conducted for each research task.
Firstly, the performances of RTK and PPP techniques were evaluated in both static and kinematic (highway with speed exceed 80km) experiments. RTK solutions achieved the RMS precision of 0.09 to 0.2 meter accuracy in static and 0.2 to 0.3 meter in kinematic tests, while PPP reported 0.5 to 1.5 meters in static and 1 to 1.8 meter in kinematic tests by using the RTKlib software. These RMS precision values could be further improved if the better RTK and PPP algorithms are adopted. The tests results also showed that RTK may be more suitable in the lane-level accuracy vehicle positioning. The professional grade (dual frequency) and mass-market grade (single frequency) GNSS receivers were tested for their performance using RTK in static and kinematic modes. The analysis has shown that mass-market grade receivers provide the good solution continuity, although the overall positioning accuracy is worse than the professional grade receivers.
In an attempt to reduce the load on data communication network, we firstly evaluate the use of different correction data format standards, namely RTCM version 2.x and RTCM version 3.0 format. A 24 hours transmission test was conducted to compare the network throughput. The results have shown that 66% of network throughput reduction can be achieved by using the newer RTCM version 3.0, comparing to the older RTCM version 2.x format. Secondly, experiments were conducted to examine the use of two data transmission protocols, TCP and UDP, for correction data transmission through the Telstra 3G cellular network. The performance of each transmission method was analysed in terms of packet transmission latency, packet dropout, packet throughput, packet retransmission rate etc. The overall network throughput and latency of UDP data transmission are 76.5% and 83.6% of TCP data transmission, while the overall accuracy of positioning solutions remains in the same level. Additionally, due to the nature of UDP transmission, it is also found that 0.17% of UDP packets were lost during the kinematic tests, but this loss doesn't lead to significant reduction of the quality of positioning results. The experimental results from the static and the kinematic field tests have also shown that the mobile network communication may be blocked for a couple of seconds, but the positioning solutions can be kept at the required accuracy level by setting of the Age of Differential. Finally, we investigate the effects of using less-frequent correction data (transmitted at 1, 5, 10, 15, 20, 30 and 60 seconds interval) on the precise positioning system. As the time interval increasing, the percentage of ambiguity fixed solutions gradually decreases, while the positioning error increases from 0.1 to 0.5 meter. The results showed the position accuracy could still be kept at the in-lane-level (0.1 to 0.3 m) when using up to 20 seconds interval correction data transmission.
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Edwards, Michael. "Characterization of Fillite as a Planetary Soil Simulant in Support of Rover Mobility Assessment in High-Sinkage/High-Slip Environments." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/292.
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This thesis presents the results of a research program characterizing a soil simulant called Fillite, which is composed of alumino-silicate hollow microspheres harvested from the pulverized fuel ash of coal-fired power plants. Fillite is available in large quantities at a reasonable cost and it is chemically inert. Fillite has been selected by the National Aeronautics and Space Administration (NASA) Glenn Research Center to simulate high-sinkage/high-slip environment in a large test bed such as the ones encountered by the Spirit rover on Mars in 2009 when it became entrapped in a pocket of soft, loose regolith on Mars. The terms high-sinkage and high-slip used here describe the interaction of soils with typical rover wheels. High-sinkage refers to a wheel sinking with little to no applied force while high-slip refers to a spinning wheel with minimal traction.
Standard material properties (density, specific gravity, compression index, Young's modulus, and Poisson's ratio) of Fillite were determined from a series of laboratory tests conducted in general accordance with ASTM standards. Tests were also performed to determine some less standard material properties of Fillite such as the small strain shear wave velocity, maximum shear modulus, and several pressure-sinkage parameters for use in pressure-sinkage models. The experiments include an extensive series of triaxial compression tests, bender element tests, and normal and shear bevameter tests.
The unit weight of Fillite on Earth ranges between 3.9 and 4.8 kN/m3, which is similar to that of Martian regolith (about 3.7 - 5.6 kN/m3) on Mars and close to the range of the unit weight of lunar regolith (about 1.4 - 2.9 kN/m3) on the Moon. The data presented here support that Fillite has many physical and mechanical properties that are similar to what is known about Martian regolith. These properties are also comparable to lunar regolith. Fillite is quite dilatant; its peak and critical angles of internal friction are smaller than those of most other simulants. Smaller shear strength, coupled with much smaller bulk unit weight as compared to other simulants, results in smaller bearing and shearing resistances allowing for better simulation of the intended high-sinkage, high-slip behavior for rover mobility studies.
The results of the normal bevameter tests were used to determine parameters for two models available in the literature - the Bekker model and the New Model of Mobility (N2M) model. These parameters were then used to predict the sinkage of a Spirit rover wheel if the rover were to be used on Fillite. The predicted sinkage of a Spirit rover wheel in Fillite was 84% of the wheel diameter, which was within the observed sinkage of 50 to 90% of the wheel diameter of the Spirit rover on Mars. Shear bevameter tests were also performed on Fillite to assess the shear stresses and shear deformations imparted by wheels under torsional loads. The results compared well to the estimated shear stresses and deformations of Martian soil caused by the wheels of the Spirit rover. When compared to other simulants (e.g. GRC-1), the pressure-sinkage and shear stress-shear deformation behaviors of Fillite confirm that Fillite is more suitable for high-sinkage and high-slip rover studies than other typical simulants derived from natural terrestrial soils and rocks.
3
Savoie, Courtney Beth Young. "Arsenic Mobility and Compositional Variability in High-Silica Ash Flow Tuffs." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1012.
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Volcanic rocks typically have only low to moderate arsenic concentrations, none-the-less, elevated levels of arsenic in ground waters have been associated with pyroclastic and volcaniclastic rocks and sediments in many parts of the world. The potential for arsenic leaching from these deposits is particularly problematic as they often comprise important water-bearing units in volcanic terrains. However, the role that chemical and mineralogical variations play in controlling the occurrence and mobility of arsenic from pyroclastic rocks is largely unexplored.
This study uses chemical and X-ray diffraction data to characterize and classify 49 samples of ash-flow tuffs, and 11 samples of tuffaceous sediments. The samples exhibit a range of devitrification and chemical weathering. Total and partial digestion, and water extractions of samples are used to determine the total, environmentally available, and readily leachable fractions of arsenic present in all tuff samples. Leaching experiments were also performed with buffered solutions to determine the influence of elevated pH levels on arsenic mobility.
The 49 tuff samples have a mean arsenic content of 7.5 mg kg-1, a geometric mean arsenic content of 4.8 mg kg-1, a median arsenic content of 5.2 mg kg-1, and a maximum arsenic concentration of 81 mg kg-1. The mean and median values are 2.8 - 4.4x the average crustal abundance of 1.7 mg kg-1 (Wedepohl, 1995), and consistent with previously reported values for volcanic glasses and felsic volcanic rocks (Onishi and Sandell, 1955; Wedepohl, 1995), although the maximum arsenic content is higher than previously reported (e.g., Casentini et al., 2010; Fiantis et al., 2010; Nobel et al., 2004). In addition, the arsenic concentrations of tuffs were found to be highly heterogenous, both between and within individual units, and in some cases, individual outcrops.
Results of whole rock and leachate analyses indicate that there is no significant difference in the total arsenic content of tuffs as a result of devitrification or weathering, but both devitrified and weathered tuffs contain higher levels of environmentally available arsenic than unweathered glassy tuffs. Glassy tuffs did not produce any readily leachable arsenic, while individual devitrified and weathered tuffs both generated aqueous concentrations that exceeded regulatory limits after 18 hours. Leaching of weathered tuffs produced higher levels of arsenic at high (~9-11) pH than in tests conducted at circum-neutral pH. Devitrified and glassy tuffs showed no increase in leachable arsenic with increasing pH.
The results of this study indicate that devitrification and weathering processes determine the host phases, degree of adsorption, and overall mobility of arsenic from ash-flow tuffs. Tuffs that have undergone different types of alteration are likely to have different host phases of arsenic, and different mechanisms that mobilize arsenic into the environment. Potential host phases and mobility mechanisms are discussed, and a conceptual model of arsenic behavior in ash-flow tuffs is proposed.
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Kim, Samuel H. "Addressing thermal and environmental reliability in GaN based high electron mobility transistors." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52244.
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AlGaN/GaN high electron mobility transistors (HEMTs) have appeared as attractive candidates for high power, high frequency, and high temperature operation at microwave frequencies. In particular, these devices are being considered for use in the area of high RF power for microwave and millimeter wave communications transmitter applications at frequencies greater than 100 GHz and at temperatures greater than about 150 °C. However, there are concerns regarding the reliability of AlGaN/GaN HEMTs. First of all, thermal reliability is the chief concern since high channel temperatures significantly affect the lifetime of the devices. Therefore, it is necessary to find the solutions to decrease the temperature of AlGaN/GaN HEMTs. In this study, we explored the methods to reduce the channel temperature via high thermal conductivity diamond as substrates of GaN. Experimental verification of AlGaN/GaN HEMTs on diamond substrates was performed using micro-Raman spectroscopy, and investigation of the design space for devices was conducted using finite element analysis as well. In addition to the thermal impact on reliability, environmental effects can also play a role in device degradation. Using high density and pinhole free films deposited using atomic layer deposition, we also explore the use of ultra-thin barrier films for the protection of AlGaN/GaN HEMTs in high humidity and high temperature environments. The results show that it is possible to protect the devices from the effects of moisture under high negative gate bias stress testing, whereas devices, which were unprotected, failed under the same bias stress conditions. Thus, the use of the atomic layer deposition (ALD) coatings may provide added benefits in the protection and packaging of AlGaN/GaN HEMTs.
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Ong, Felicia Li Chin. "Heterogeneous Networking for Beyond 3G system in a High-Speed Train Environment. Investigation of handover procedures in a high-speed train environment and adoption of a pattern classification neural-networks approach for handover management." Thesis, University of Bradford, 2016. http://hdl.handle.net/10454/12341.
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Based on the targets outlined by the EU Horizon 2020 (H2020) framework, it is expected that heterogeneous networking will play a crucial role in delivering seamless end-to-end ubiquitous Internet access for users. In due course, the current GSM-Railway (GSM-R) will be deemed unsustainable, as the demand for packet-oriented services continues to increase. Therefore, the opportunity to identify a plausible replacement system conducted in this research study is timely and appropriate. In this research study, a hybrid satellite and terrestrial network for enabling ubiquitous Internet access in a high-speed train environment is investigated. The study focuses on the mobility management aspect of the system, primarily related to the handover management. A proposed handover strategy, employing the RACE II MONET and ITU-T Q.65 design methodology, will be addressed. This includes identifying the functional model (FM) which is then mapped to the functional architecture (FUA), based on the Q.1711 IMT-2000 FM. In addition, the signalling protocols, information flows and message format based on the adopted design methodology will also be specified. The approach is then simulated in OPNET and the findings are then presented and discussed. The opportunity of exploring the prospect of employing neural networks (NN) for handover is also undertaken. This study focuses specifically on the use of pattern classification neural networks to aid in the handover process, which is then simulated in MATLAB. The simulation outcomes demonstrated the effectiveness and appropriateness of the NN algorithm and the competence of the algorithm in facilitating the handover process.
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Uppoor, Sandesh. "Understanding and Exploiting Mobility in Wireless Networks." Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00912521.
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Le degré de pénétration du marché des appareils intelligents tels que les smartphones et les tablettes avec les technologies de communication embarquées comme le WiFi, 3G et LTE a explosé en moins d'une décennie. En complément de cette tendance technologique, les appli- cations des réseaux sociaux ont virtuellement connecté une grande partie de la population, en génèrant une demande de trafic de données croissant vers et depuis l'infrastructure de com- munication. Les communications pervasive ont aussi acquis une importance dans l'industrie automobile. L'émergence d' une gamme impressionnante d' appareils intelligents dans les véhicules permettant services tels que assistance au conducteur, infotainment, suivi à dis- tance du vehicule, et connectivité àux réseaux sociaux même en déplacement. La demande exponentielle de connectivité a encore défié les fournisseurs de services de télécommunications pour répondre aux attentes des utilisateurs du réseau à grande vitesse. L'objectif de cette thèse est de modéliser et comprendre la mobilité dynamique des utilisateurs à grande vitesse et leurs effets sur les architectures de réseau sans fil. Compte tenu de l' importance du développement de notre étude sur une représentation réal- iste de la mobilité des véhicules, nous étudions tout d'abord les approches les plus populaires pour la génération de trafic routier synthétique et discutons les caractéristiques des ensem- bles de données accessibles au public qui decrivent des mobilités véhiculaires. En utilisant l'information des déplacements de la population dans une région métropolitaine, les données du réseau routier détaillées et des modèles réalistes de conduite microscopiques, nous pro- posons un jeux de données de mobilité véhiculaire original qui redéfinit l'état de l'art et qui replie la circulation routière de facon realiste dans le temps et dans l'espace. Nous étudions ensuite l'impact des dynamiques de mobilité du point de vue de la couverture cellulaire en présence d'un déploiement réel des stations de base. En outre, en examinant les effets de la mobilité des véhicules sur les réseaux autonomes, nous voyons des possibilités pour les futurs paradigmes de réseaux hétérogènes. Motivés par l'évolution dynamique dans le temps de la mobilité des véhicules observée dans notre jeux de données, nous proposons également une approche en ligne pour prédire les flux de trafic macroscopiques. Nous analysons les paramètres affectant la prédiction de la mobilité en milieu urbain. Nous dévoilons quand et où la gestion des ressources réseau est plus crucial pour accueillir le trafic généré par les utilisateurs à bord. Ces études dévoilent des multiples opportunités de gestion intelligente des transports, soit pour construire de nouvelles routes, soit pour l'installation de bornes de recharge électriques, ou pour la conception de systèmes de feux de circulation intelligents, contribuant ainsi à la planification urbaine.
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Benigni, Paolo. "Trapped Ion Mobility Spectrometry coupled to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for the analysis of Complex Mixtures." FIU Digital Commons, 2017. https://digitalcommons.fiu.edu/etd/3547.
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Analytical Characterization of complex mixtures, such as crude oil, environmental samples, and biological mixtures, is challenging because of the large diversity of molecular components. Mass spectrometry based techniques are among the most powerful tools for the separation of molecules based on their molecular composition, and the coupling of ion mobility spectrometry has enabled the separation and structural elucidation using the tridimensional structure of the molecule. The present work expands the ability of analytical chemists by furthering the development of IMS-MS instrumentation by coupling Trapped Ion Mobility Spectrometry to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (TIMS-FT-ICR MS). The TIMS-FT-ICR MS platform combines the high-resolution separation of TIMS, which has mobility resolving powers up to 400, and ultra-high mass resolution of FT-ICR MS, with mass resolving power over 1,000,000. This instrumentation allows the assignment of exact chemical composition for compounds in a complex mixture, as well as measurement of the collision cross-section of the molecule. Herein, the principles of the TIMS separation and its coupling to FT-ICR MS are described, as well as how the platform can be applied to targeted analysis of molecules, and untargeted characterization of complex mixtures.
Molecular standards were analyzed by TIMS-MS in order to develop a computational workflow that can be utilized to elucidate molecular structure, using the measured collision cross-section of the ion. This workflow enabled identification of structural, cis/trans isomers, and chelated molecules and provides the basis for unsupervised structural elucidation of a complex mixture, and in particular for the elucidation of hydrocarbons from fossil fuels. In summary, this work presents the coupling of TIMS-FT-ICR MS and provides examples of applications as a proof of concept of the potential of this platform for solving complex analytical challenges.
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Krämer, Dennis [Verfasser], Michael [Akademischer Betreuer] Bau, Andrea [Akademischer Betreuer] Koschinsky, Gregor [Akademischer Betreuer] Borg, and Thomas [Akademischer Betreuer] Kuhn. "Mobility of High-Technology Metals in Earth’s Surface Environment : A Study on Siderophore-Promoted Mobilization and Implications for the Extractive Hydrometallurgy of some Critical Metals / Dennis Krämer. Betreuer: Michael Bau. Gutachter: Michael Bau ; Andrea Koschinsky ; Gregor Borg ; Thomas Kuhn." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2015. http://d-nb.info/1095233416/34.
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JHANG, LUN-YUAN, and 張掄元. "Reduced-complexity OFDM signal detection under high mobility environments." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/05136578910983662760.
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碩士南開科技大學
電機與資訊工程研究所
99
In orthogonal frequency division multiplexing (OFDM) system, the intercarrier interference (ICI) causes significant performance degradation. The successive interference cancellation (SIC) has been proved to have an excellent performance for mitigating the ICI in OFDM system. However, since the complexity of SIC is proportional to the number of OFDM subcarrier N, the realization of this detector becomes impractical, especially when large number of subcarrier is considered. In this thesis, a modified successive interference cancellation (SIC) algorithm which is referred to as qSIC is proposed for high mobility OFDM system. The qSIC algorithm not only significantly reduces the computational complexity of SIC algorithm, but its performance also approaches the performance of conventional SIC algorithm. Furthermore, a fast matrix inversion for qSIC was purposed. In qSIC, the pseudo-inverse of the (2j+1)-dimensional matrices are repeatedly calculated and successively padded with zero columns. This means that the taken (2j+1)-square matrices are mostly non-full-rank. Thus this leaves room for improvement in decreasing computational complexity. The presented fast matrix inverse can obtain reliable and accurate approximations in the qSIC simulation cases.
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Liu, Ju-Chieh, and 劉如傑. "Channel Tracking Techniques for the High-Mobility Wireless Access in Vehicular Environments." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/89250474019104851485.
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碩士國立中正大學
通訊工程研究所
95
The industrial standard of Wireless Access Vehicular Environment (WAVE), or called the IEEE 802.11p standard, is an example of the orthogonal frequency division multiplexing (OFDM) technique applied to the high-mobility environment. In addition to the multipath effect, the high-mobility environment introduces severe fading to the received signals. Tracking of the channel state information becomes the critical issue for such high-mobility system. Based one the conventional decision-directed channel tracking (DDCT) algorithm, we proposes a modified decision-directed channel tracking (MDDCT) algorithm. Our proposed algorithm is shown to have approximately equal uncoded bit error rate (BER) to that of the conventional DDCT algorithm, but have significant lower packet error rate than that of the conventional DDCT algorithm under a variety of high-mobility environments. After comparing the error patterns of the uncoded bits that are demodulated by the conventional and our MDDCT algorithms, we observe that our MDDCT algorithm mitigates the burst error; hence, the following error correction decoder works more effectively to improve its packet error rate. Finally, our MDDCT is of very low complexity, and is of practical use.
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Li, Ying-Hao, and 李英豪. "A Study on WCDMA Power Control Algorithms under Very High Mobility Environments." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/82908467543040163001.
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Wu, Chong-Wei, and 吳崇瑋. "Code-Decision Directed Iterative ICI Mitigation Techniques for OFDM System in High Mobility Environments." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/03178160436623977944.
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碩士國立中央大學
通訊工程研究所
99
Orthogonal frequency-division multiplexing (OFDM) is a technique well suited for wireless broad-band communications.A drawback of OFDM is its sensitivity to time-varying channel effect in a mobile receiving environment with significant Doppler spread. In this scenario, the orthogonality between subcarriers is destroyed and the inter-carrier interference (ICI) is thus arised.In this thesis, we propose a modified iterative ICI mitigation method, which incorporates code-decision direct and an approximate maximum-likelihood detection, to improve the performance of a OFDM receiver in high-mobility environemt .
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Surabhi, G. D. "On Orthogonal Time Frequency Space Modulation for Wireless Communications." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4461.
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Future wireless communication systems are envisioned to support diverse requirements that include high mobility application scenarios such as high-speed trains, and vehicle-to-vehicle and vehicle-toinfrastructure communications. The dynamic nature of wireless channels in such scenarios makes them doubly-dispersive in nature. Orthogonal time frequency space (OTFS) modulation is a recent two-dimensional (2D) modulation technique specially suited for doubly-dispersive wireless channels. A fundamental feature of OTFS modulation is that the information symbols in OTFS modulation are multiplexed in delay-Doppler domain rather than in time-frequency domain as done in conventional multicarrier modulation techniques. An advantage of signaling in the delay-Doppler domain is that a channel rapidly varying in time manifests as a slowly varying sparse channel when viewed in the delay-Doppler domain, which simplifies channel estimation in rapidly time varying wireless channels. In this thesis, we focus on various fundamental and key aspects of OTFS modulation, which include asymptotic diversity analysis, peak-to-average power ratio analysis, design of low-complexity equalizers, OTFS based multiple access systems, and the performance of OTFS in millimeter wave (28 GHz and 60 GHz) channels in the presence of oscillator phase noise.
First, we provide a formal analysis of the asymptotic diversity order achieved by OTFS modulation in doubly-dispersive channels. Our analysis and simulations show that the asymptotic diversity order of OTFS modulation with maximum likelihood detection is one. We propose a phase rotation scheme for OTFS that achieves full diversity in the delay-Doppler domain. We extend the diversity analysis and the proposed phase rotation scheme to OTFS in multiple-input-multiple-output (MIMO) setting as well. We also propose the use of space-time coding to achieve full diversity in both spatial and delay-Doppler domains. We present an analysis of the peak-to-average-power ratio (PAPR) performance of OTFS modulation. We derive an upper bound on the maximum PAPR in OTFS and analytically characterize the complementary cumulative distribution function of the PAPR of OTFS.
Design of low-complexity equalizers is an important requirement for communication in fading channels. We propose low-complexity linear equalizers for OTFS signal detection in doublydispersive channels in both SISO and MIMO settings. The proposed equalizers exploit the block circulant nature of the OTFS channel matrix and achieve exact solutions at a significantly lower complexity compared to that of the conventional approach. We finally consider OTFS based multiple access (OTFS-MA), where delay-Doppler bins serve as the resource blocks for multiple access, in contrast to conventional multiple access schemes where resource blocks are defined in the TF plane. We carry out a comprehensive investigation of key issues in OTFS-MA, such as signal detection , channel estimation , and PAPR characteristics on the multiuser uplink, and compare them with those of OFDMA and SC-FDMA. Finally, we address the problem of high oscillator phase noise in millimeterwave communication systems. We investigate the effect of phase noise on the performance of OTFS modulation in mmWave communications and show that the OTFS is robust to oscillator phase noise.
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Lin, Wei-cheng, and 林韋丞. "Synchronization for DVB-T in High-mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/24722855096619877379.
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碩士國立中央大學
通訊工程研究所
96
OFDM technique is adopted in many standards, including DVB-T, since it exhibits outstanding characteristics in terms of efficiency in spectral utilization, simplicity in equalization and immunity in Inter-Symbol-Interference (ISI). However OFDM system performance is sensitive to synchronization errors including symbol timing offset, carrier frequency offset and sampling clock frequency offset. Typical methods exploiting the correlation of cyclic-prefix in time domain and the correlation of continual pilots in frequency domain have been proposed for estimating and correcting the synchronization errors for OFDM systems. In these methods the channel model is generally assumed to be static, i.e., the transmitter and receiver are in stationary positions and the channel impulse response is time invariant. This assumption is violated especially when the receiver and/or transmitter are in high-mobility environment, i.e., the channel impulse response becomes time varying significantly. In this thesis, we focus on studying on the synchronization problems of DVB-T system when the receiver is in mobility as high as to 300 km/hr. In this scenario, significant time-varying channel impulse response due to large Doppler spread is noticed which causes the loss of subcarrier orthogonality and signal correlation, and the performance of typical synchronization algorithms is evaluated. Finally, a synchronization method, which is more suitable to high-mobility reception, is designed for DVB-T receiver. The implementation of synchronization systems is verified with Modelsim tool and real-time implementation on FPGA hardware.
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Chang, Wei-Hsuan, and 張維軒. "A WiMAX Baseband Transceiver for High Mobility Environment." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/50898248259799112299.
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碩士國立清華大學
電機工程學系
96
This thesis is focus on a MIMO-OFDM system, which uses space frequency block coding algorithm for high mobility environment. An inner transmitter and receiver for IEEE 802.16e uplink specification is designed to implement this algorithm. In order to model a high mobility environment, ITU-VA channel model, which is constituted by 3GPP, is used for the simulation. Additionally, Jakes model is added to simulate the high mobility environment. Compare with space time block code and space frequency block code, space frequency block code has better performance in outdoor environment with high mobility. Thus, this thesis propose a SFBC decoding algorithm to against Doppler effect. An 2x2 SFBC-OFDM is defined in IEEE 802.16e standard. The simulation result shows that Doppler effect can be alleviated through this algorithm. In general SFBC system, the adjacent channel responses are assumed constant. However, channel responses are not constant in real communication systems, especially in high mobility environment. The variation between adjacent channel responses causes interference while decoding, so the error will occur in high SNR. Thus, an interference cancellation method is needed to solve this problem. The demapping result is sent back to the SFBC decoder for the interference cancellation. The simulation result shows that this cancellation can prevent error floor in high SNR region. In order to implement this system, we designed an inner transmitter platform for high speed emulation. This platform consist hardware part and software part. Some complicated operations can be implement in hardware, so the emulation time can be reduced. Furthermore, the receiver is designed in software, so the user can change or replace the receiving method easily. If designer want to develop a new receiving algorithm, it can save the development time. Additionally, this platform is built on the webpage, so everyone can use this platform from anywhere through the internet.
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Yeh, Kao-Fa, and 葉高發. "Optimizing UMTS Performance in High Speed Mobility Environment." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/7t6k62.
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碩士國立臺北科技大學
電腦與通訊研究所
97
Third Generation Mobile communication system using wideband code division multiple access (WCDMA) technology. Netork providers served one after another. We usually name for 3rd Generation Mobile communication. Netork operators enable voice、data、high speed downlink access services(HSDPA). According variety of serves incress. The subscribe request rigorous handover algorithm.Therefor those Handover algorithm are currently being standardized in 3GPP for Release 99 and R5.This article introduced “Handover Algorithm difference”and proposed “Apposite Handover Algorithm” for High Speed rail environment. Finally, we provided internal real mobile network measured data result in high speed rail environment for research and conclusion.
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Lin, Hong-Yi, and 林弘毅. "A MIMO-OFDM Baseband Engine for High Mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/82800494641140257700.
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碩士國立清華大學
電機工程學系
97
In this thesis, a MIMO-OFDM system which is designed for high mobility environment is proposed. In order to fight with the time varying channel, the system uses space frequency block coding (SFBC) algorithm to obtain additional diversity gain without any extra communication resource. Furthermore, a flexible and low complexity intercarrier interference (ICI) mitigation module is also proposed in the thesis. Doppler Effect causes ICI in high mobility environment. The ICI destroys orthogonality between subcarriers and degrades the system performance. In other words, the channel matrix is not a diagonal matrix anymore, non diagonal elements are the equivalent ICI factors and need to be eliminated. The channel matrix estimation uses a linear approximation algorithm. In order to adapt the module to MIMO systems, the proposed method substitutes for ZF ICI compensation algorithm to mitigate the ICI. So as to avoid calculating the inverse matrix, we take subtraction instead of inversion computation. The computational complexity can be reduced from O(N3) to O(N). The module can be applied not only in SISO systems but also in MIMO systems flexibly. The proposed SFBC-OFDM baseband transceiver is constructed by SystemC language. The receiver includes a timing synchronization module, a carrier frequency offset estimation and compensation module, a channel estimation module, a SFBC decoder with soft output, and a flexible and low complexity ICI mitigation module. In order to model a high mobility environment, ITU-VA channel model, which is constituted by 3GPP, is employed for the simulation. Also, Jakes’ model is added to simulate the high mobility environment. According to the simulation result, the proposed SFBC-OFDM system with ICI mitigation obtains about 3dB gain after ICI compensation in the high mobility environment.
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Basnet, Modick Bahadur, and 莫迪. "Self-optimizing algorithms for LTE system in high mobility environment." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/527sy6.
Full textAbstract:
博士元智大學
通訊工程學系
104
This dissertation is concerned with three self-optimizing algorithms all of which pertain to improve the performance of LTE system in high mobility environment. These algorithms include: a self-optimizing power control and receive antenna number selection (SOPCRAS) algorithm for high mobility MIMO-SC-FDMA transceiver and a self-optimizing beamforming null control (SOBNC) algorithm to improve the signal-to-interference-plus-noise ratio (SINR) for LTE uplink transceiver. LTE standard requires adequate performance for UE velocities up to 350 km/h, however, even with a good channel estimation method LTE performance in velocities above 100 km/h suffers with intense fading channel dispersion. LTE data rate performance depends on channel quality index (CQI) value which can be supported by maintaining certain SINR threshold to keep BLER<10-1. This dissertation proposes SOPCRAS algorithm to minimize the uplink power and inter-cell interference (ICI) of LTE uplink MIMO-SC-FDMA transceivers in high-mobility environments. In SOPCRAS algorithm, an MIMO-based self-optimization power controller is used to adjust the transmit power adaptively to minimize the UE transmit power and select minimum number of receiver antenna at eNB to satisfy BLER < 10-1 in extended vehicular A (EVA) channel for velocities in the range of 0~300 km/h. The throughput and power consumption of the SOPCRAS algorithm are compared numerically with open loop power control (OLPC) method in which the UE transmit power is adjusted in accordance with AWGN performance. Co-channel interference (CCI) has tremendous impact on the performance of heterogeneous networks (HetNets). The proposed SOPCRAS algorithm will increase the transmit power of transceivers with the interference power adaptively to maintain the BLER less than 10-1 if the transmit power is less than the upper bound of transmitter. A novel SOBNC algorithm based on the estimation of the SINR and angular spread is proposed in this dissertation which adapts the null width and depth of uniform linear array (ULA) to the changing environments. The SOBNC algorithm is initiated to reject the interference if the transmit power reaches the upper bound of transmitter. Finally, it has shown that the SOBNC can maintain the SINR level of eNB receiver at required threshold as per changing environments and its performance is superior to the conventional fixed null scheme.
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Lan, Yi-Yao, and 藍義堯. "Frequency Synchronization for OFDM System in Very High Mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/41333352586889337624.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
96
This thesis emphasize on frequency synchronization for OFDM in very high mobility environment. The very high mobility environment for TAIWAN HIGH SPEED RAIL (300km/hr) leads to critical doppler effect, so the channel will cause fast fading and multipath interference (doubly selective channel).The mismatch between transmitter and receiver and doppler effect will bring about carrier frequency offset. In order to working OFDM technique in very high mobility environment, we propose multiple sections training symbol method、weighting method and prediction mode method to resist time-variant channel and then do carrier frequency offset estimation。After we finish carrier frequency offset estimation, we do frequency compensation to reach whole frequency synchronization.
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LEE, CHIN-CHUN, and 李靖群. "Channel Identification of OFDM System in Very High Mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/33496862415888669817.
Full textAbstract:
碩士國立暨南國際大學
通訊工程研究所
96
This thesis probes for the very high mobility environment mainly. In medium or low mobility environment，we usually assume that the channel is time-invariant during each OFDM symbol which we transmit and demodulate. Because the very high mobility environment for TAIWAN HIGH SPEED RAIL (300km/hr) leads to critical doppler effect，the system suffers from the fast fading effect severely. In OFDM used large FFT points transmission architecture，the channel will change during each OFDM symbol.The bit error rate of conventional transmission and demodulation for time-variant channel will increase substantially ,so the major issues that how to transmit pilots and demodulate in receiver to decrease the bit error rate. This thesis uses ML channel estimation to estimate channel value and do interpolation in time domain to modify the channel situation. Finally ，we Use linear minimum mean square error equalizer to resist ICI effect. Besides , the channel is impossible to be known in real environment,so using power detection to distinguish the longest channel impulse length and noise location is the other major issue.
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Chang, Ya-Fen, and 張雅芬. "Cellular IP-based mobility management in very high speed railway environment." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/70097750689455964140.
Full textAbstract:
碩士國立暨南國際大學
電機工程學系
94
In this thesis, we analyzed the signaling cost for Cellular IP operating in either non-grouping or grouping case. We have both considered the Routing Update procedure for Active users and Location Update procedure for Idle users. We can easily know that grouping management for users in high speed train would be beneficial in Cellular IP network. It is because all passengers have the same mobility behavior and when grouping them together a lot of signaling could be saved. Moreover, we also consider the cost associated with group management, which includes the signaling sent for user to join and leave the group. We have provided a general mathematical model and method for the evaluation process.
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Chen, Shu-Yu, and 陳書妤. "Inter-Carrier Interference Cancellation for DVB-T in High-Mobility Environment." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/54419272123123653256.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
97
OFDM is a nucleus system of DVB-T. This system successfully eliminated the ISI effect and multi-path interference by using multi-carriers and inserting cyclic-prefix. In high-mobility environment, DVB-T signals pass the time-varying channel, and a loss of sub-carrier orthogonality due to Doppler spread of received signals leads to inter-carrier interference (ICI).This ICI effect degrades the maximum allowed velocity of reception. For eliminating this ICI effect due to high-mobility reception, this thesis modifies other’s methods and introduces a method about channel estimation and equalization, which is suitable high-mobility reception. This thesis refers to the DVB-T standard, and further makes it suitability for high mobility environment. By using ICI cancellation, and comparing three different scheme (Traditional, iterative ICI cancellation, and Taylor series-like) for channel and ICI estimation. In addition, we aim at low SIR ratio part which is influenced by ICI to add ML detection, which can improve the performance and reduce bit error rate.
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Chih-Hua, Hsu, and 徐志華. "A Study of Adaptive Modulation with OFDM In High Mobility Environment." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/83772941712345144430.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
95
The fundamental technology of adaptive modulation is to advance data throughput。The principle is receiver adjusts modulation level for next transmission depend on channel condition，i.e. when the channel condition is appropriate，it use high modulation level； when the channel is unfavorable，it use low modulation level，For example QPSK or BPSK。 OFDM (Orthogonal Frequency Division Multiplexing) can improve data throughput in the limited bandwidth。It transmits orthogonal sub-carriers in the limited bandwidth。OFDM can resist multi-path，ISI etc.. If we combine adaptive modulation and OFDM technology，we can get higher data throughput than single technology. Traditional adaptive modulation with OFDM have single transmission direction only and many assumptive conditions。For example，there is a perfect channel between transmitter and receiver。Another is modulation level in the modulated frame mustn''t affect by channel，i.e. the receiver can demodulate the level of modulation accurately. However these assumptive conditions were not true in the real world。 We propose a new algorithm for adaptive modulation with OFDM。We calculate pilot''s BER to adjust modulation level for next transmission，and decide which modulation level we use to demodulate it。 Other topic is to separate many blocks in a OFDM symbol。Each block has different modulation level then we can get maximum data throughput。
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Roni, Harmoko Habibi, and 林忠良. "Low Complexity Detection Algorithms for OFDM System under High Mobility Environment." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/35743906264403919203.
Full textAbstract:
碩士國立暨南國際大學
通訊工程研究所
97
In orthogonal frequency division multiplexing (OFDM) system, the intercarrier interference (ICI) causes significant performance degradation. A well-known interference cancellation technique called successive interference cancellation (SIC) has been proved to have an excellent performance for mitigating the ICI in OFDM system. However, since the complexity of SIC is proportional to the number of OFDM subcarrier N, the realization of this detector becomes impractical, especially when large number of subcarrier is considered. In this thesis, a modified successive interference cancellation (SIC) algorithm which is referred to as qSIC is proposed for high mobility OFDM system. The proposed low complexity qSIC algorithm only requires the computational complexity of order O(N(q+1)2.376), where N is the number of subcarrier and q is the number of neighborhood subcarrier. The qSIC algorithm not only significantly reduces the computational complexity of SIC algorithm, but its performance also approaches the performance of conventional SIC algorithm. Furthermore, the lattice reduction aided zero forcing (LR-ZF) and lattice reduction aided minimum mean square error (LR-MMSE) algorithm that were purposed for MIMO system are also studied. Using computer simulations, we also verify that lattice reduction algorithm not only significantly increases the performance of the conventional ZF and MMSE equalizer but its performance also approaches the performance of the optimal maximum likelihood (ML) detector. For this reason, we adopt the LR-ZF to the OFDM system and in order to decrease the computational complexity of LR-ZF, we also present the modified LR-ZF that excludes the swap operation of LLL algorithm.
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Shih, Pao-chen, and 施寶鎮. "Channel Estimation and Equalization for DVB-T in High-mobility Environment." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/62842899722177665736.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
95
DVB-T is an OFDM system, which exhibits outstanding characteristics in terms of simplicity in combating multi-path transmission and efficiency in spectral utilization. The ISI effect results from the multi-path interference could be successfully eliminated by the insertion of cyclic-prefix and the use of multi-carriers. In high-mobility environment, DVB-T signals pass the time-varying channel, and a loss of sub-carrier orthogonality due to Doppler spread of received signals leads to inter-carrier interference (ICI).This ICI effect degrades the maximum allowed velocity of reception. For eliminating this ICI effect due to high-mobility reception, this thesis modifies other’s methods and introduces a method about channel estimation and equalization, which is suitable high-mobility reception. Some ICI estimation schemes, which using first order linear model to approximate the channel variations, have been developed. This thesis compares three different schemes of ICI estimation, which two is first order model and the other is second order model, and iteratively repeats ICI cancellation to improve the maximum allowed velocity of reception. This modified method improves the normalized Doppler frequency from 8.6% to 13% for DVB-T signals in 8K mode、16QAM、code-rate=1/2.
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Hsu, Hua-Lin, and 徐華璘. "Channel Estimation and Equalization for multiple antennas OFDM System in High-mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/40862646414350085067.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
96
DVB-T is an OFDM system, which exhibits outstanding characteristics in terms of simplicity in combating multi-path transmission and efficiency in spectral utilization. The ISI effect results from the multi-path interference could be successfully eliminated by the insertion of cyclic-prefix and the use of multi-carriers. In high-mobility environment, DVB-T signals pass the time-varying channel, and a loss of sub-carrier orthogonality due to Doppler spread of received signals leads to inter-carrier interference (ICI).This ICI effect degrades the maximum allowed velocity of reception. For eliminating this ICI effect due to high-mobility reception, this thesis modifies other’s methods and introduces a method about channel estimation and equalization, which is suitable high-mobility reception. In this thesis, we refer to the DVB-T standard, and further make it suitability for high mobility environment.We use multiple antennas technique and ICI cancellation,compares three different scheme for channel and ICI estimation. This thesis proposed method improve the maximum allowed velocity as high as 250km/h for DVB-T receiver with SISO in 8K mode、16QAM、code-rate=1/2,and multiple antennas DVB-T reception improve the maximum allowed velocity more then 300km/h.Finally, reception use group pilot estimation technique SISO-DVB-T-like can work as 300km/h.
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Chuang, Ming-Dao, and 莊明道. "Performance Evaluation on Orthogonal Frequency Division Multiplexing System in Very High Mobility Environment." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/87156629519673657864.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
95
In very high mobility environments, it is easy for the receiver to have large Doppler effects. The influence on the system caused by fast fading is very large. The traditional non-time-varying channels may increase bit error rate. According to fast fading channels, we use decoding methods aim at time-varying channels at receiver ( ML channel estimation or MMSE channel estimation + time-domain interpolation refinement + LMMSE equalizer ) to do performance evaluation. Pilot symbols at transmitter use comb type and block type to transmit. We compute overall pilot symbol ratios at least to transmit for tolerable bit error rate, and compare to traditional receiver which doesn’t consider time-varying channels. In high-speed trains environment, we can use partial known information, for example, predictability of progress routes of train, every multipath delay spread of channel impulse response known characteristics for the complexity reduction and the performance advance. Besides these, we also discuss channel impulse response longest delay spread grid of ML and MMSE channel estimation which sets inaccuracy to see the influence.
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Wang, Yi-Yuan, and 王易垣. "The Improved ICI Self-Cancellation Method in OFDM Systems for High Mobility Environment." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/8753wc.
Full textAbstract:
碩士國立臺北科技大學
電機工程系研究所
97
This thesis is to investigate the solutions for inter-carrier interference (ICI) cancellation due to Doppler shifts caused by time-variant highly mobile channel in the OFDM system. In conventional OFDM receiver, the energy of each subcarrier will leak to adjacent subcarriers which destroys the orthogonality between subcarriers in time-variant channel. This will result in the increased bit-error rate (BER) and raised error floor as well. The approaches for ICI cancellation can be categorized into three types including frequency-domain equalizer, time-domain window algorithm, and self-cancellation. The pre-mapping algorithm is an improved ICI self-cancellation method with low complexity without loss of bandwidth efficiency. An ICI self-cancellation method based on pre-mapping algorithm was proposed in this thesis. By using new pre-mapping matrix, the proposed method can improve the system performance without increasing much system complexity. Computer simulation results show that the proposed method is good in system performance, complexity and bandwidth efficiency.
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Lin, Chien-Yang, and 林見陽. "A Study on Turbo Equalizer Combined with OFDM System in Very High Mobility Environment." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/00249150746128543502.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
95
Turbo equalization is a new method which combines channel equalization and channel coding .It is different from traditional equalization. The performance of turbo equalizer (TE) with single carrier system in very high mobility environment is excellent. So we try to use TE combined with multicarrier system ,such as Orthogonal Frequency Division Multiplexing (OFDM), in very high mobility environment. OFDM system would suffer gravely from Intercarrier Interference effect (ICI) in very high mobility environment, so we hope that TE could help OFDM system lower its Bit Error Rate (BER). At first, we simulate TE combined with OFDM system with small FFT (Fast Fourier Transform) size in very high mobility environment to make sure about its feasibility. Then we substitute the low FFT size for higher FFT size. Secondly, we use the high speed rail’s characterization of the fixed path to demonstrate two kinds of channel information for channel estimation. In the end, we change the ratio of data symbols and training segments in frame format in order to improve our system useful data rate.
30
Wu, Yi-Lin, and 吳宜霖. "A Study on Slot Synchronization of W-CDMA System in Very High Mobility Environment." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/13034695058344783658.
Full text
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Yuan, Wen-Hao, and 袁文浩. "A Study on Channel Estimation Algorithms for WCDMA System in Very High Mobility Environment." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/01774728996074187961.
Full text
32
Lee, Yi-Hua, and 李怡樺. "Improvement of Inter-Carrier Interference Mitigation Technology for OFDM System in High-mobility Environment." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/95221031095694753288.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
98
The core of DVB-T is OFDM system. By using multi-carriers and inserting cyclic prefix, this technology successfully eliminated the ISI effect and multi-path interference. In high-mobility environment, when DVB-T signals pass through the time-varying channel, the receive signals will have Doppler spread that can loss of sub-carrier orthogonality and cause the ICI. This ICI effect degrades the maximum allowed velocity of reception. To overcome the ICI which caused by the high-mobility, this thesis modifies other’s methods and introduces a method about the channel estimation and elimination of ICI which is suitable for high mobility reception. This thesis refers to the DVB-T standard, and further modifies it to suit in high-mobility environment. In high-mobility environment, the performance of wireless OFDM communication systems is degraded and limited by inter-carrier-interference (ICI) phenomenon. In this paper we proposed an algorithm based on maximum-likelihood criterion with improved performance in mitigation of ICI.
33
Huang, Xiang-yuan, and 黃祥原. "Practical Channel Tracking and Signal Recovery for the OFDM System Under High-Mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/16209554312044403159.
Full textAbstract:
碩士國立中正大學
通訊工程研究所
96
WAVE (IEEE802.11p) standard is proposed to use in high-mobility environment and used OFDM as the modulation scheme. Because of the high-mobility, the received signal is interfered by the multipath and Doppler. The time-variant fading channel model is considered. In this paper, a channel tracking and recovery technique is proposed for high-mobility environment. With an initial channel estimation based on preamble by Least Square (LS) algorithm, the channel frequency response is tracked by adaptive filters. We can find some conclusions after analyzing simulations. The first, Recursive Least Square (RLS) algorithm, robust Recursive Least Square (rRLS) algorithm, and Adaptive forgetting factor Recursive Least Square (AFRLS) algorithm can efficiently slow down the phenomenon of error floor than Least Mean Square(LMS) algorithm, Normalized Least Mean Square(NLMS) algorithm, and Adaptive step size Least Mean Square(ASLMS) algorithm. The second, rRLS, RLS, and AFRLS have better performance when under the environment of accelerating the speed of vehicle or increasing the packet length. The third, After a comparison of robust Recursive Least Square (rRLS) algorithm, Recursive Least Square (RLS) algorithm, and Adaptive forgetting factor Recursive Least Square (AFRLS) algorithm can find that rRLS have better performance than RLS and rRLS have lower computation complexity than AFRLS. Finally, we can find the best value of forgetting factor of RLS by [5] under the time-variant fading channel model.
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Liao, Keng-te, and 廖耕德. "Improvment of Channel Estimation and Equalization for MISO OFDM System in High Mobility Environment." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/23018288731098586695.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
99
OFDM systems exhibit advantageous characteristics in combating multi-path transmission and spectral efficiency, which use cyclic-prefix to overcome the inter-symbol interference (ISI) effect caused in multi-path transmission and multi-carriers with orthogonality to achieve high spectral efficiency. In high mobility environment, when the orthogonal multi-carrier signal passes through time-varying channel, inter-carrier interference (ICI) is resulted due to the loss of orthogonality of subcarriers. The degradation of the system performance due ICI is proportional to the Doppler spread, and thus a limitation in the velocity of the mobile receiver is inferred in OFDM systems. In this thesis we study on using transmitter diversity to improve the performance of OFDM systems in high mobility environment. We propose a modification of the transmitter diversity technique in DVB-T2 standard, which is designed originally for fixed reception, to make it more suitable for high mobility reception. vi
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Cheng, Chia-Chen, and 鄭佳臻. "Channel Tracking and Signal Recovery of the MIMO-OFDM System Under High-Mobility Environment." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/39190176809544785575.
Full textAbstract:
碩士國立中正大學
通訊工程學系
98
The multiple antennas and OFDM technologies are being considered as a possible solution to provide high data rate for the high-throughput wireless local area network (WLAN). Channel model is time-variant fading channel due to the multipath and doppler effects in high-mobility wireless environment. Based on the spatial channel model, several channel tracking and signal recovery techniques are compared in this thesis. Initially, least squared (LS) criterion is exploited to the received long training sequences in the preamble of IEEE 802.11n frame. Several adaptive channel tracking algorithms follow to track the variation of the channel/weight frequency responses. Our simulation results show that using recursive least square algorithm to track the variation of the channel frequency responses is yield better performance than to track the variation of the weight frequency responses. The ordered successive interference cancellation algorithm can be utilized to improve performance at the cost of higher computational complexity.
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Chen, Hsuan-Yu, and 陳鏇羽. "Study of self-optimization power control algorithms for MIMO downlink transceiver in high mobility environment." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/kqdzx2.
Full textAbstract:
碩士元智大學
通訊工程學系
104
The study of self-optimizing power control (SOPC) algorithm for high mobility MIMO-OFDM transceiver is the main purpose of the research report. The objective of SOPC is to make the downlink MIMO-OFDM transceiver to minimize transmit power and optimize average throughput under different channel quality indicator (CQI), user speed and antenna mode autonomously. The major research items of the project include the design of SOPC mechanism for downlink MIMO-OFDM transceiver; generation of the training data for adaptive network fuzzy inference system (ANFIS) controller through the simulations of blocking error rate (BLER) of downlink MIMO-OFDM transceiver over high mobility extended vehicular channel A (EVA) channel; the performance of the high mobility MIMO-OFDM transceiver using SOPC is compared with the traditional CQI-based method. Simulation results show the proposed algorithm can provide the better average throughput under high mobility environments.
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Ting, Hao-Hsuan, and 丁浩軒. "A Study of Turbo Equalization on WCDMA and OFDM Systems in Very High Mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/48393607614248676573.
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Chen, Po-Hong, and 陳伯紘. "A Study on Timing Synchronization in Frame for OFDM Systems in Very-High Mobility Environment." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/61035439709680966891.
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Wu, Wei-Li, and 吳偉立. "Feasible Study of Using STC Algorithms in MIMO Wireless Communications in Very High Mobility Environment." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/39736558623570595518.
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Lopes, Inês Mariana Lemos. "Software-defined connectivity in a mobile environment." Master's thesis, 2020. http://hdl.handle.net/10773/29545.
Full textAbstract:
Broadband Internet access on trains has become an expected service for passengers,
and the rise in quality demand has been posing a challenge to service
providers. There are solutions for Internet access on trains that lack the
flexibility and redundancy needed for an improved QoS in the network. Thus,
this dissertation studies two new load balancing solutions, one distributed and
the other centralized. In an emulated train network, routers of each car communicate
their network statistics to other nodes of the network, to be used
in load balancing decisions. In the distributed solution, each router has the
capacity to make load balancing decisions, while in the centralized solution,
an onboard controller makes those decisions. The latter solution is based on
load balancing in an SDN environment. In this system, a remote entity aggregates
the passengers’ traffic and forwards it to an external network, or to the
Internet. The systems must provide an improved quality of experience to the
passengers on the train and the total avaliable bandwidth should be distributed
evenly by all cars. Requirements were established for the systems, which were
developed after an in-depth analysis of solutions for Internet access on board
found in the literature. After obtaining the results of the performance tests, it
was concluded that the systems improve the QoE of the passengers, as long
as the network conditions are approximately constant for an extended period.O acesso à Internet de banda larga em comboios tornou-se num serviço esperado por parte dos passageiros e o aumento na exigência de qualidade tem constituído um desafio para os prestadores de serviços. Existem soluções de acesso à Internet em comboios que carecem da flexibilidade e redundância necessárias para uma melhor qualidade de serviço na rede. Assim, esta dissertação estuda duas novas soluções de balanceamento de carga, uma distribuída e outra centralizada. Numa rede de comboio emulada, routers de cada carruagem comunicam as suas estatísticas de rede para outros nós da rede, para posteriormente serem tomadas decisões de balanceamento de carga. Na solução distribuída, cada router tem capacidade de tomar decisões de balanceamento de carga, enquanto que na solução centralizada, um controlador dentro do comboio toma essas decisões. Esta última solução baseiase num balanceamento de carga em ambiente SDN. Neste sistema, uma entidade remota agrega o tráfego dos passageiros e encaminha-o para uma rede externa, ou para a Internet. Os sistemas devem proporcionar uma qualidade de experiência melhorada aos passageiros do comboio e a largura de banda total disponível deve ser distribuída mais uniformememente por todas as carruagens. Requisitos foram estabelecidos para os sistemas, que foram desenvolvidos após uma análise aprofundada das soluções de acesso à Internet em comboios encontradas na literatura. Após a obtenção dos resultados dos testes de desempenho, concluiu-se que as duas soluções melhoram o QoE dos passageiros, desde que as condições da rede sejam aproximadamente constantes durante um certo período.
Mestrado em Engenharia de Computadores e Telemática
41
Huang, Wen-Yu, and 黃文昱. "Design and FPGA Implementation of An Improved Inter-Carrier Interference Mitigation Scheme for OFDM Systems in High-Mobility Environment." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/54186969516007197659.
Full textAbstract:
碩士國立中央大學
通訊工程研究所
98
In high-mobility environment, the performance of wireless OFDM communication systems is limited by inter-carrier-interference (ICI) phenomenon and ICI effect is more serious with higher velocity of receiver. To overcome ICI which is caused by the high mobility, in this thesis we present an improved ICI mitigation scheme based on maximum-likelihood criterion. We take DVB-T system for example and finally implement the algorithm we propose with FPGA.