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1
Rohani-Mehdiabadi, Bijan. "Frequency discriminator detection in frequency-selective fading environments." Thesis, Curtin University, 1998. http://hdl.handle.net/20.500.11937/451.
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In recent years, millions of customers all over the world have been subscribing to mobile telephony services which are based on modern digital transmission. At the high transmission bit rates that these systems use, the mobile radio channel exhibits frequency-selective fading characteristics. Under such conditions, the received signal could experience significant intersymbol interference (ISI) from severe distortion to the waveform of the received baseband signal. Therefore, such techniques as adaptive waveform equalisation or adaptive maximum likelihood sequence estimation (MLSE) are used in modern digital mobile radio telephone systems to combat this undesirable ISI. These adaptive schemes have almost always been used in conjunction with coherent demodulation in the receivers.This study examines the application of noncoherent demodulation, in the form of frequency discriminator detection, as an alternative to coherent demodulation. The GSM (Global System for Mobile Communications) standard has been used as the basis for this investigation. It has been shown analytically that in the presence of frequency-selective fading, a propagation environment common to the GSM system, the use of frequency discriminator detection gives rise to nonlinear ISI in the demodulated signal. It has also been shown that frequency-selective fading could cause large unwanted "spikes" to appear in the demodulated signal, thus leading to a severe degradation in the bit-error-rate (BER) performance. Consequently, several waveform distortion cancellation schemes for combatting the nonlinear ISI have been formulated. The BER performances of these proposed schemes, under various propagation conditions, have been studied by computer simulation.Furthermore, it has been observed that the undesirable "spikes", that occur in the demodulated signal due to frequency-selective fading, could be suppressed by the use of inverse-limiting in conjunction with frequency discriminator detection. As a result, an effective adaptive detection scheme has been formulated, based on modelling the combination of the GMSK modulator, the mobile channel, the frequency discriminator, and any transmit and receive fitters, as a finite-state machine. The transmitted data is then detected using an MLSE. The BER performance of this proposed adaptive detection scheme has been extensively investigated by computer simulation. This has been carried out assuming various propagation conditions, including the two-ray fading channel model with equal path powers and relative delays of up to four bit periods, the maximum relative delay considered in the GSM system. Also, the effectiveness of the proposed adaptive detection scheme in combatting IS] has been investigated by computer simulation based on the six-ray GSM empirical propagation models for typical urban (TU), hilly terrain (HT) and rural area (RA) environments. The computer simulated results confirm that the voice grade performance required for the GSM system could be achieved by the proposed adaptive detection scheme in all the recommended GSM propagation models considered. Furthermore, the BER performance of the receiver remains unaffected by a carrier frequency offset of up to 2 kHz.
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Rohani-Mehdiabadi, Bijan. "Frequency discriminator detection in frequency-selective fading environments." Curtin University of Technology, School of Electrical and Computer Engineering, 1998. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=12148.
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In recent years, millions of customers all over the world have been subscribing to mobile telephony services which are based on modern digital transmission. At the high transmission bit rates that these systems use, the mobile radio channel exhibits frequency-selective fading characteristics. Under such conditions, the received signal could experience significant intersymbol interference (ISI) from severe distortion to the waveform of the received baseband signal. Therefore, such techniques as adaptive waveform equalisation or adaptive maximum likelihood sequence estimation (MLSE) are used in modern digital mobile radio telephone systems to combat this undesirable ISI. These adaptive schemes have almost always been used in conjunction with coherent demodulation in the receivers.This study examines the application of noncoherent demodulation, in the form of frequency discriminator detection, as an alternative to coherent demodulation. The GSM (Global System for Mobile Communications) standard has been used as the basis for this investigation. It has been shown analytically that in the presence of frequency-selective fading, a propagation environment common to the GSM system, the use of frequency discriminator detection gives rise to nonlinear ISI in the demodulated signal. It has also been shown that frequency-selective fading could cause large unwanted "spikes" to appear in the demodulated signal, thus leading to a severe degradation in the bit-error-rate (BER) performance. Consequently, several waveform distortion cancellation schemes for combatting the nonlinear ISI have been formulated. The BER performances of these proposed schemes, under various propagation conditions, have been studied by computer simulation.Furthermore, it has been observed that the undesirable "spikes", that occur in the demodulated signal due to frequency-selective fading, could be ++suppressed by the use of inverse-limiting in conjunction with frequency discriminator detection. As a result, an effective adaptive detection scheme has been formulated, based on modelling the combination of the GMSK modulator, the mobile channel, the frequency discriminator, and any transmit and receive fitters, as a finite-state machine. The transmitted data is then detected using an MLSE. The BER performance of this proposed adaptive detection scheme has been extensively investigated by computer simulation. This has been carried out assuming various propagation conditions, including the two-ray fading channel model with equal path powers and relative delays of up to four bit periods, the maximum relative delay considered in the GSM system. Also, the effectiveness of the proposed adaptive detection scheme in combatting IS] has been investigated by computer simulation based on the six-ray GSM empirical propagation models for typical urban (TU), hilly terrain (HT) and rural area (RA) environments. The computer simulated results confirm that the voice grade performance required for the GSM system could be achieved by the proposed adaptive detection scheme in all the recommended GSM propagation models considered. Furthermore, the BER performance of the receiver remains unaffected by a carrier frequency offset of up to 2 kHz.
3
Gifford, Wesley M. (Wesley Michael) 1979. "Diversity with practical channel estimation in arbitrary fading environments." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16698.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 79-83).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
This thesis presents a framework for evaluating the bit error probability of Nd-branch diversity combining in the presence of non-ideal channel estimates. The estimator structure is based on the maximum likelihood (ML) estimate and arises naturally as the sample mean of Np pilot symbols. The framework presented requires only the evaluation of a single integral involving the moment generating function of the norm square of the channel gain vector, and is applicable to channels with arbitrary distribution, including correlated fading. Analytical results show that the practical ML channel estimator preserves the diversity order of an Nd-branch diversity system, contrary to conclusions in the literature based upon a model that assumes a fixed correlation between the channel and its estimate. Finally, the asymptotic signal-to-noise ratio (SNR) penalty due to estimation error is investigated. This investigation reveals that the penalty has surprisingly little dependence on the number of diversity branches.
by Wesley M. Gifford.
S.M.
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Yan, Ming. "Antenna array receiver design and analysis in fast fading environments /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3022209.
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Luong, Dung Viet Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Optimal training sequence design for MIMO-OFDM in spatially correlated fading environments." Awarded by:University of New South Wales. Electrical Engineering & Telecommunications, 2009. http://handle.unsw.edu.au/1959.4/44513.
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Multiple Input Multiple Output with Orthogonal Frequency Division Multiplexing (MIMOOFDM) has been widely adopted as one of the most promising air interface solutions for future broadband wireless communication systems due to its high rate transmission capability and robustness against multipath fading. However, these MIMO-OFDM advantages cannot be achieved unless the channel state information (CSI) can be obtained accurately and promptly at the receiver to assist coherent detection of data symbols. Channel estimation and training sequence design are, therefore, still open challenges of great interest. In this work, we investigate the Linear Minimum Mean Square Error (LMMSE) channel estimation and design nearly optimal training sequences for MIMO-OFDM systems in spatially correlated fading. We, first, review the LMMSE channel estimation model for MIMO-OFDM in spatially correlated fading channels. We, then, derive a tight theoretical lower bound of the channel estimation Mean Square Error (MSE). By exploiting the information on channel correlation matrices which is available at the transmitter, we design a practical and nearly optimal training sequence for MIMO-OFDM systems . The optimal transmit power allocation for training sequences is found using the Iterative Bisection Procedure (IBP). We also propose an approximate transmit power allocation algorithm which is computationally more efficient than the IBP while maintaining a similar MSE performance. The proposed training sequence design method is also applied to MIMO-OFDM systems where Cyclic Prefixing OFDM (CP-OFDM) is replaced by Zero Padding OFDM - OverLap-Add method (ZP-OFDM-OLA). The simulation results show that the performance of the proposed training sequence is superior to that of all existing training sequences and almost achieves the MSE theoretical lower bound.
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Laneman, J. Nicholas. "Channel estimation and equalization for spread-response precoding systems in fading environments." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42673.
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Prabhakaran, Preetha. "Performance evaluation of mobile ad hoc networks in realistic mobility and fading environments." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001159.
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Svasti-Xuto, Usa. "Performance analyses of frequency-hopped spread-spectrum multiple access systems in fading environments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32771.pdf.
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Annamalai, Annamalai. "Accurate and efficient analysis of wireless digital communication systems in multiuser and multipath fading environments." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ37328.pdf.
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Liou, Anthony En-Lee. "Characterization of fading and polarization state dispersion on fixed wireless links in suburban macrocell environments." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/14716.
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Growing use of point-to-multipoint fixed wireless networks to support network access and system automation in suburban macrocell environments has prompted regulators to re-allocate various bands between 200 MHz and 2 GHz to such applications. Links in such networks are usually obstructed by
buildings and foliage and are classified as non-line-of-sight. Although it is well-known that such links are susceptible to fading caused by windblown trees and foliage, most past efforts to characterize fading
on such links have focused on frequency bands at 1.9 GHz and above. Here, we study how the depth and rate of fading in the 220, 850 and 1900 MHz bands vary with distance and time-averaged wind speed in a representative macrocell environment. We observed that while the signal fading is relatively severe at 1.9GHz, the depth of fading drops rapidly as the carrier frequency decreases. However, the rate of
fading is effectively independent of either the average wind speed or the carrier frequency. Further, polarization diversity on narrowband wireless links has traditionally been characterized in terms of the fading statistics and the cross-correlation between the fading signals on each branch. A complementary
approach, which is independent of the polarization states of the diversity receiving antennas, is to
characterize the manner in which the polarization states observed at the receiver disperse across the Poincaré sphere. First, by simulation, we show that when the fading signals observed on orthogonal
diversity branches follow ideal Ricean statistics, the distribution of polarization states on the Poincaré sphere is well-approximated by a Fisher distribution whose concentration parameter is: (1) determined by the corresponding Ricean K-factors and the cross-correlation coefficient between the diversity
branches, and (2) a good indicator of the level of cross-polar discrimination (XPD). Finally, from measurements collected in a typical suburban macrocell environment at 1.9GHz, we show that: (1) the means of the polarization state distributions also tends to follow a Fisher distribution and (2) the Fisher concentration parameter is negatively correlated with the average wind speed. Development of a model applicable to a broad range of environments will require additional data from other sites and
measurement configurations.
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Kiessling, Mario [Verfasser]. "Statistical Analysis and Transmit Prefiltering for MIMO Wireless Systems in Correlated Fading Environments / Mario Kiessling." Aachen : Shaker, 2004. http://d-nb.info/1172613060/34.
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Bejjenki, Praneeth Kumar, Muneeb Ahmed Goraya, and Syed Fovad Moid. "OPTIMIZED FUZZY BASED POWER CONTROL STRATEGY IN COGNITIVE RADIO NETWORKS IN MULTI FADING PROPAGATION ENVIRONMENTS." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-4160.
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In this thesis we have considered a cognitive radio network (CRN) with a pair of primary user (PU) and secondary user (SU) in spectrum sharing networks in path-loss and without path-loss propagation environments under identically distributed m-Nakagami fading channel. The thesis consists of three parts. In the first part we propose an optimized Takagi-Sugeno Fuzzy Inference System (FIS) based power control strategy in cognitive radio networks (CRN) in spectrum sharing network in without path-loss propagation environment. The second part proposes an optimized Takagi-Sugeno FIS based power control strategy in cognitive radio networks in spectrum sharing network in path-loss propagation environment. For without path-loss propagation environment the proposed FIS takes the interference channel gain ratio between SU transmitter (CUtx) and PU receiver (PUrx) and Signal to Noise Ratio (SNR) towards PU transmitter (PUtx) as antecedents and outputs the power scaling factor for SU. For path-loss propagation environment the proposed FIS takes the relative distance ratio between CUtx and PUrx and SNR towards PUtx as antecedents and outputs the power scaling factor for SU. The output power scaling factor is used to vary the transmit power of SU such that it does not degrade the quality of service (QoS) of PU link. The third part presents an implementation of orthogonal frequency division multiplexing (OFDM) transmission technique in CRN. The OFDM technique has intellectual attractive features like coping with the inter symbol interference (ISI), while providing increasing spectral efficiency and improved performance. This can be used in emergency conditions where transmission requires reliability and high data rate. The OFDM transmission technique is applied towards SU transmitter in CRN, which enables SU to utilize the spectrum efficiently under various fading environments. Spectrum sharing networks in with and without path-loss propagation environments and OFDM transmission were tested for bit error rate (BER) performance after fading effects from m-Nakagami fading channel. We conclude that by applying Takagi-Sugeno Fuzzy Inference System (FIS) based power control strategy we can improve the BER performance of PU when compared with no power control strategy and with other fuzzy based power control technique. OFDM transmission technique gives us better data rate and slightly improved BER in CRN hence making it suitable for use in emergency conditions.mobile: 0735032048 (Muneeb Goraya)
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Gui, Xiang, and 歸翔. "A technique for performance improvement of DS SS systems operating in fading and jamming environments." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31236923.
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Gui, Xiang. "A technique for performance improvement of DS SS systems operating in fading and jamming environments /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20294062.
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Lichtenstein, Joseph. "Low computational complexity bit error rate simulation for personal communications systems in multipath and fading environments." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06102009-063138/.
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Phua, Cheng Tatt Valance. "A communication protocol framework for wireless sensor networks in industrial environments." University of Western Australia. School of Computer Science and Software Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0179.
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[Truncated abstract] Developing wireless sensor network communication protocols for industrial environments is a challenging task. The wireless channel conditions in industrial environments are harsher as a result of multipath propagation of radio signals within an environment where the mechanics of the surrounding industrial activities often lead to severe small-scale fading effects. The design of network protocols to function in such an environment needs to provide a robust communication platform for the wireless sensor nodes, while optimizing the utilization of the limited node resources available. As existing general MAC protocols for wireless sensor networks do not work well under harsh channel conditions, we address this problem in this thesis by proposing a medium access control (MAC) protocol framework for wireless sensor networks in industrial environments. To describe the impact of an automated industrial site on small-scale fading effects in an industrial indoor wireless network, we use a site-specific ray-tracer for predicting signal propagation based on building blue prints to simulate the signal propagation paths through an industrial site with periodically moving objects. We found that in a fully automated industrial site, the periodic movements of objects with constant velocities result in an approximately periodic distribution of fading periods in the channel. Based on this finding, we propose a link state dependent TDMA-based MAC protocol for wireless sensor networks designed for automated industrial applications. ... This technique also conserves energy and maximizes packet integrity as the sensor nodes avoid performing network activities when the channel is sampled to be affected by fading. As a measure for fault-tolerance, we also propose a dynamic link reconstruction technique that allows sensor nodes to reconstruct new parent links when their present links are severely affected by fading. MAC protocols that adopt active buffering in fading-affected channels suffer bufferoverflow and latency issues as a result of the postponement of scheduled transmissions during periods when the channel is in a fade. Consequently, time-sensitive data packets that may contain critical information may miss their deadlines in a severely affected fading channel. Hence, we propose a general fading-aware data management (FADE) MAC protocol extension that uses buffer nodes to offload the memory buffer off sensor nodes in the network and prioritizes traffic based on a simple proposed priority scheme. The FADE extension provides a balance balance between minimum end-to-end latency for critical event reporting, high packet delivery guarantee, low energy consumption, and minimum buffer requirements on the sensor nodes. In summary, this thesis presents the design, implementation, and evaluation of all our proposed network protocols that are combined as a framework for wireless sensor networks in industrial environments.
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Portelinha, Junior Francisco Martins. "Avaliação do desempenho de redes de rádios cognitivos em ambientes com desvanecimento = Performance evaluation of cognitive radio networks in fading environments." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/259708.
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Orientador: Paulo CardieriDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Mestre em Engenharia Elétrica
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Ibanez, Marc B. (Marc Benedict). "Cellular power control in a fading environment." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11297.
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Banik, Tuhin. "Spatial fading characteristics of VHF broadcast signals in an urban environment." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=61679.
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Wu, Yating. "Code tracking for direct-sequence spread-spectrum systems under multiuser environment and multipath fading channels /." access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ee-b30082602f.pdf.
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Thesis (Ph.D.)--City University of Hong Kong, 2009."Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 105-111)
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Hamilton, Benjamin Russell. "Low-Overhead Opportunistic Routing for Wireless Ad Hoc and Sensor Networks in a Fading Environment." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19749.
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The development of miniaturized radio and sensing technologies have
enabled the deployment of large quantities of wireless sensors
capable of forming multi-hop networks. Emerging applications of this
technology such as surveillance and disaster monitoring have
throughput and efficiency requirements not met by current routing
algorithms. These requirements are also shared by ad-hoc networks.
Early routing protocols for these wireless networks were based on
algorithms designed for wired networks. Geographic routing (routing
based on position), was proposed. These algorithms perform poorly
since they do not account for the fading and interference effects of
wireless channels. Recent protocols that have attempted to account
for the wireless channel focus on single-hop situations and are not
readily extensible to multi-hop networks.
In this thesis we present a framework for routing based on a
distributed routing decision and provide several example protocols.
This framework provides a cross-layer design where the routing
decision is decided through silent negotiation between candidate
relays. We investigate the performance and parameters of this
framework. We then present an example protocol using this framework
which provides low-overhead opportunistic routing using cooperative
diversity. This protocol uses the intrinsic characteristics of the
wireless channel to achieve diversity while still maintaining
relatively low overhead. An adaptation of the protocol for
heterogeneous networks equipped with multiple antennas has also been
discussed and evaluated through simulations. We also investigate
another protocol based on this framework using the product of the
instantaneous packet reception rate and the marginal progress
towards the destination as a routing metric, offering enhanced
throughput.
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Eleftheriou, Evangelos Carleton University Dissertation Engineering Electrical. "Adaptive filtering in a time-varying environment with applications to equalization of fading HF channels." Ottawa, 1985.
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Kline, Elizabeth A. "Multi-variant analysis of real-world environmental variables affecting image fading on outdoor synthetic inkjet substrates /." Online version of thesis, 2006. https://ritdml.rit.edu/dspace/handle/1850/2845.
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Spyrou, Evangelos. "Performance analysis of wireless LAN signals transmitted over a ricean fading channel in a pulsed-noise preference environment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sep%5FSpyrou.pdf.
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Thesis (M.S. in Electrical Engineering and M.S. in Systems Engineering)--Naval Postgraduate School, Sept. 2004.Thesis Advisor(s): R. Clark Robertson. Includes bibliographical references (p. 67-68). Also available online.
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Shih, Wan-Chun. "Performance analysis of variable code rate signals transmitted over frequency-nonselective, slowly fading channels in a pulse-interference environment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FShih.pdf.
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Kosa, Irfan. "Performance of IEEE 802.11a wireless LAN standard over frequency-selective, slowly fading Nakagami channels in a pulsed jamming environment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FKosa.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2002.Thesis advisor(s): R. Clark Robertson, Tri Ha. Includes bibliographical references (p. 107-108). Also available online.
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Soelaiman, Adi Dharma, and Rina Pudjiastuti. "A Survays On Fading Channel Over West - Java Area for Flight Test Radio Telemetering Purposes." International Foundation for Telemetering, 1988. http://hdl.handle.net/10150/615047.
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International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, NevadaThis paper discusses one approach to determine a characteristic of West - Java's air and ground segment as a block-box to accomodate radio waves propagation, especially in L-band ranges, by evaluating both the topographical data and radio reception pattern as measured from ground based telemetry receiving-end system. All the measured signals are random and assumed to be stationair and ergodic. In order to characterize the channel for polarization diversity reception, some statistical analysis are applied to the signal strength measured of both - RHCP and LHCP components of 1531 MHz propagated waves as transmitted fr om NC212-200 PK-NZJ-aircraft. Some computer calculated correlograms of measured data are shown herewith, it is focused for a certain radio corridor at radial 265E relative to the ground based receiving antenna. More over some curves of predicted multipath gain factor are also presented to gain more theoretical back ground. When this paper is written, a further field experiments on the matter concerned is beeing conducted.
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Law, Eugene. "HOW WELL DOES A BLIND, ADAPTIVE CMA EQUALIZER WORK IN A SIMULATED TELEMETRY MULTIPATH ENVIRONMENT." International Foundation for Telemetering, 2004. http://hdl.handle.net/10150/604926.
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International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, CaliforniaThis paper will present the results of experiments to characterize the performance of a blind, adaptive constant modulus algorithm (CMA) equalizer in simulated telemetry multipath environments. The variables included modulation method, bit rate, received signal-to-noise ratio, delay of the indirect path relative to the direct path, amplitude of the indirect path relative to the direct path, and fade rate. The main measured parameter was bit error probability (BEP). The tests showed that the equalizer usually improved the data quality in the presence of multipath.
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Osman, Taha Mohammed. "FADI : a fault-tolerant environment for distributed processing systems." Thesis, Nottingham Trent University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388867.
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Chow, Jocelyn. "Performance analysis of a QAM multitone-on-FM system at and above the FM threshold in a non-frequency-selective slowly fading environment." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0019/NQ54404.pdf.
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Haghdad, Mehdi, and Kamilo Feher. "SMART ANTENNA (DIVERSITY) AND NON-FEEDBACK IF EQUALIZATION TECHNIQUES FOR LEO SATELLITE COMMUNICATIONS IN A COMPLEX INTERFERENCE ENVIRONMENT." International Foundation for Telemetering, 2003. http://hdl.handle.net/10150/605382.
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International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, NevadaAn improved performance smart diversity was invented to improve the signal performance in a combined selective fading, Additive White Gaussian Noise (AWGN), Co-channel interference (CCI) and Doppler shift environment such as the LEO satellite channel. This system is also applicable to aeronautical and telemetry channels. Smart diversity is defined here as a mechanism that selects at each moment the best branch in a n-branch diversity system based on the error quality with no default branch and no prioritization. The predominant novelty of this discovery is the introduction of multi level analog based Pseudo Error Detectors (PSED) in every branch. One of the advantages of PSED is that it is a non redundant error detection system, with no requirement for overhead and no need for additional valuable spectrum. This research was motivated by problems in LEO satellite systems due to low orbit and high relative speed with respect to the ground stations. The system is independent of the modulation techniques and is applicable to both coherent and non-coherent detections. The results from simulations using dynamic simulation techniques and hardware measurements over dynamic channels show significant improvement of both the Bit Error Rate (BER) and the Block Error Rate (BLER).
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Araújo, Filho Mário Silva de. "AVALIAÇÃO DOS NÍVEIS DE FADIGA EM TRABALHADORES DE ENFERMAGEM DE UM HOSPITAL ESCOLA." Pontifícia Universidade Católica de Goiás, 2018. http://tede2.pucgoias.edu.br:8080/handle/tede/4074.
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The objective of this study was to evaluate the fatigue levels of nursing professionals at a Hospital Escola de Goiânia, whose specific objectives were to outline the sociodemographic profile, evaluate the fatigue levels associated with the work environment, and compare fatigue levels with variables sociodemographic. Methods; An analytical cross-sectional study with a quantitative approach, with 25 nurses and 94 technicians in nursing. Discussion; it was identified that 97.5% of the interviewees are female, most of them between 20 and 35 years old, who have a double working day, and between 1 and 5 years of nursing service, of which 53.1 % presented fatigue. Conclusion; the study suggests the occurrence of fatigue is associated with the stressful situations experienced by the nursing professional in their work practice, as well as the exposure to physical and biological risks, in addition to the long and painful working days.
O estudo teve como objetivo geral avaliar os níveis de fadiga dos profissionais de enfermagem em um Hospital Escola de Goiânia, teve como objetivos específicos traçar o perfil sociodemográfico, avaliar os níveis de fadiga associados ao ambiente de trabalho e comparar os níveis de fadiga com as variáveis sociodemográficas. Métodos; estudo transversal analítico com abordagem quantitativa, tendo como participantes 25 Enfermeiros e 94 Técnicos em enfermagem A coleta de dados foi realizada entre os meses de junho a agosto de 2017 e ocorreu durante todos os turnos, mediante liberação pela chefia de enfermagem do setor e assinatura do Termo de Consentimento Livre e Esclarecido. Discussão; identificou-se que 97,5% dos entrevistados são do sexo feminino, em sua maioria com faixa etária entre 20 e 35 anos, que possuem dupla jornada de trabalho, e entre 1 a 5 anos de serviço na enfermagem, sendo que 53,1% apresentaram quadro de fadiga. Conclusão; o estudo sugere a ocorrência de fadiga está associada as situações estressantes vivenciadas pelo profissional de enfermagem em sua prática laboral, bem como a exposição a riscos físicos e biológicos, somados as longas e penosas jornadas de trabalho.
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Silva, Marta Sofia Mendonça da. "Ambiente físico hospitalar: a influência no burnout, stress, fadiga e satisfação no trabalho dos profissionais de saúde." Master's thesis, Universidade de Évora, 2018. http://hdl.handle.net/10174/23264.
Full textAbstract:
Este estudo teve como objetivo compreender se as três dimensões da Teoria do Design de Suporte (Ulrich, 1991; 2001), perceção de controlo, suporte social e dis-tração positiva, proporcionadas pelo ambiente hospitalar influenciam a satisfação no trabalho, fadiga, stress e burnout dos profissionais de saúde. A amostra deste estudo foi composta por 141 profissionais de saúde, dos quais 41 eram médicos/as e 96 en-fermeiros/as de 5 serviços hospitalares de 2 Edifícios diferentes de um Hospital Enti-dade Pública Empresarial (EPE) em Portugal. Utilizou-se uma grelha de observação do espaço para caracterizar os espaços utilizados pelos profissionais de saúde e um questionário de autopreenchimento. Os resultados da investigação indicam que existe uma influência da qualidade do ambiente hospitalar no bem-estar dos profissionais de saúde, embora os resultados não tenham sido maioritariamente significativos; Abstract:
The purpose of this study was to understand if the three dimensions of the Ulrich’s Theory of Supportive Design (Ulrich, 1991, 2001) perception of control, social support and positive distraction, provided by the hospital physical environment have an influence on the levels of job satisfaction, fatigue, stress, and burnout, of healthcare professionals. The sample was composed by 141 healthcare professionals, from whom 41 were medical doctors, and 96 were nurses, working in 5 hospital services of 2 different buildings that belong to a Public Hospital Entity Business (EPE) in Portugal. An observation grid to characterize the hospital spaces used by health professionals and a self-completion questionnaire were used. The results of the research indicate that there is an influence of the environment on health professionals, although with non-significant results.
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Moreto, Jéferson Aparecido. "Estudo da corrosão e corrosão-fadiga em ligas de Al e Al - Li de alta resistência para aplicação aeronáutica." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-22102012-112635/.
Full textAbstract:
A indústria aeronáutica está constantemente à procura de materiais que ofereçam benefícios em termos de redução de peso, desempenho e custo. Corrosão e fadiga em ligas de alumínio são questões importantes na avaliação da vida útil em estruturas de aeronaves e na gestão de frotas. O objetivo deste trabalho foi avaliar os processos de corrosão e corrosão-fadiga nas ligas 2198-T851 e 7081-T73511, que são promissoras substitutas das ligas 2524-T3 e 7050-T7451 normalmente utilizada pela indústria aeronáutica. As técnicas de potencial de circuito aberto (PCA), polarização potenciodinâmica, polarização potenciodinâmica em eletrodo cilíndrico rotatório, espectroscopia de impedância eletroquímica (EIE), eletrodo vibratório de alta resolução (SVET) e mapeamento de potencial (SKP) foram utilizadas para esclarecer e quantificar os mecanismos de corrosão destas ligas de alumínio. Os ensaios de fadiga e corrosão-fadiga foram realizados com uma razão de carga (R) de 0,1 e frequência de 15 Hz em ar e 0,1 Hz em meio de névoa salina. As amostras, antes e após os testes de corrosão e corrosão-fadiga foram analisadas usando microscopia eletrônica de varredura (MEV). As características localizadas das quatro ligas estão essencialmente relacionadas com a existência de compostos intermetálicos que, devido à sua natureza diferente, podem ser catódicos ou anódicos em relação à matriz de alumínio. Os resultados de corrosão-fadiga mostraram uma ligeira redução no limite de fadiga para as ligas da série 2XXX e 7XXX. Essa redução pode ser atribuída à formação de cavidades de corrosão (pites). Considerando o estágio de propagação de trinca, o ambiente salino aumentou a taxa de crescimento de trinca para um mesmo intervalo de fator de intensidade de tensão.The aircraft industry is constantly looking for improved materials which offer benefits in terms of performance, weight and cost savings. Corrosion and fatigue of aluminium alloys are major issues in the service life assessment of aircraft structures and in the management of aging air fleets. The aim of this study was to evaluate the corrosion and corrosion fatigue processes of 2198-T851 and 7081-T73511 aluminium alloys, which are promising substitutes for the base line 2524-T3 and 7050-T7451 aluminium alloys normally used in aircraft fabrication. Open circuit potential monitoring (OCP), potentiodynamic polarization, potentiodynamic polarization in rotating cylindrical electrode, eletrochemical impedance spectroscopy (EIS), Scanning vibrating electrode technique (SVET) and Scanning Kelvin Probe (SKP) techniques have been used to clarify and quantify the corrosion mechanisms of these Al alloys. Fatigue and corrosion fatigue tests were carried out an applied stress ratio (R) of 0.1, 15 Hz frequency for air and 0.1 Hz frequency for salt spray using a sinusoidal wave form in all cases. The specimens, before and after corrosion and corrosion-fatigue testing were analyzed using scanning electron microscope (SEM). The localised features of all the four alloys are essentially related to the existence of intermetallics that, due to their different nature, may be cathodic or anodic sites in relation to the Al matrix. SEM and EDS analysis allowed to identify the intermetallics that are more active in determining the corrosion behavior of the specimens. The fatigue corrosion results show a slightly reduction in the fatigue life limit by chloride environment for the 2XXX and 7XXX aluminium alloys in each aged condition might be partially attributed to the formation of corrosion pits. Considering the crack propagation stage, the saline environment increased the fatigue crack growth rate for the same range of stress intensity factor.
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Barbosa, José Fernando Cárdenas. "Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-27062017-111140/.
Full textAbstract:
Main extrinsic and intrinsic modifiers factors of crack growth rate in AA7050-T7451 were assessed in order to provide tools for aeronautical structures designers. These tools cover most necessary information to project aircraft\'s structures using the studied alloy, under damage tolerance philosophy. The experimental methodology consisted of use CT specimens, on TL and LT rolling direction to test its behavior under different conditions of stress ratio, force waveform, and the environment. The stress ratio values were 0.1 and 0.5, the force waveform used were sine and trapezoidal or Dwell under normal air laboratory conditions and salt fog 3.5%NaCl weight in order to simulate the marine environment. In Dwell tests, results were checked with the electrical potential drop technique (DCPD) in addition to the crack opening displacement (COD) method. Using the Walker coefficients, calculated on the present research, could be projected accurately the crack propagation behavior on Paris region and do fatigue life predictions using da/dN and S-N diagrams for different stress ratio values. The corrosion environment increases both crack growth rate and ΔKth due to oxides formation on the crack path that generates a crack closure effect. Dwell carrying makes decrease the crack growth rate by decreasing the slope of the Paris line on log (da/dN) versus log (ΔK) curve, instead of shifting down the line as occurs on titanium alloys. Rolling direction change from LT to TL increase the FCG rate in both threshold and Paris region, where the rate change use to be small.Os principais fatores modificadores extrínsecos e intrínsecos da taxa de propagação de trincas na liga AA7050-T7451 foram avaliados para fornecer subsídios para projetistas de estruturas aeronáuticas, com base na filosofía de tolerância ao dano. A metodologia experimental consistiu em ensaiar corpos de prova do tipo compact tension (CT) da liga nas direções de laminação TL e LT, para verificar seu comportamento sob diferentes razões de tensões, forma de onda e condição ambiente. Os valores de razão de tensão estudados foram 0,1 e 0,5, as formas de onda foram senoidal e trapezoidal ou de Dwell, em condições normais de laboratório, ao ar, e névoa salina 3,5% NaCl, em massa, para simular um ambiente marinho. No caso dos ensaios Dwell, os resultados foram conferidos pelo método de queda de potencial eléctrico (QPE), além do método de flexibilidade elástica. Usando os coeficientes de Walker calculados a partir dos resultados obtidos, pôde-se projetar com precisão o comportamento da propagação de trinca na região de Paris e prever a vida em fadiga usando os diagramas da/dN e S-N para diferentes valores da razão de tensões. O ambiente corrosivo aumenta tanto a taxa de propagação de trinca, quanto o valor de ΔKth por causa da formação de óxidos na trajetória da trinca, que geram um efeito de fechamento sobre a mesma. Quanto à forma de onda, verificou-se que o carregamento Dwell diminui a taxa de propagação de trinca, diminuindo a inclinação das curvas log (da/dN) versus log (ΔK) na região de Paris, ao invés de deslocá-la paralelamente como ocorre com ligas de titânio. A mudança da direção de laminação de LT para TL aumenta a taxa de propagação de trinca por fadiga (PTF) tanto na região de threshold, quanto na região de Paris, onde a mudança de taxa é pequena.
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Kirsch, Alessandra. "Politique agricole commune, aides directes de l'agriculture et environnement : analyse en France, en Allemagne et au Royaume-Uni." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCG001/document.
Full textAbstract:
La distribution des aides directes de la PAC bénéficie-t-elle aux exploitations agricoles les plus favorables à l’environnement ? Suite à un état de l’art sur les méthodes d’évaluation environnementales existantes, le développement d’une méthode originale a permis de classer des exploitations agricoles du RICA en fonction de leurs effets sur l'environnement à partir d’une série d’indicateurs agro-environnementaux. Ces classes ont ensuite été mises en relation avec les montants d'aides perçus à l’hectare. Les résultats sont traités pour 3 OTEX (céréales et oléo-protéagineux, bovins lait, bovins viande). Associée à un examen approfondi des réformes de la PAC depuis 1992, cette étude empirique permet de prendre du recul sur les conséquences des décisions politiques. Il apparait que si les aides du 2nd pilier sont orientées en faveur des exploitations les plus favorables à l’environnement, leur poids reste trop faible par rapport aux aides du 1er pilier, dont les paiements par hectare sont plus élevés dans les exploitations moins vertueuses. Ceci est lié en grande partie au poids des DPU dans les paiements directs, et au choix français de baser leur calcul par rapport à l’historique de l’exploitation. C’est pourquoi les simulations de la redistribution des aides du 1er pilier à horizon 2019 montrent que le rééquilibrage de ces aides entre les exploitations par une harmonisation nationale contribuera à niveler les écarts de paiements directs du 1er pilier par hectare entre les exploitations. La comparaison avec le Royaume-Uni et l’Allemagne montre les effets de la subsidiarité, notamment lors du découplage : l’harmonisation des paiements découplés en permet aux exploitations les plus favorables à l’environnement de toucher des paiements directs par hectare plus élevésDoes the CAP direct payment distribution benefit to the most environmentally friendly farms? Following an environmental assessment state of the art, a set of environmental indicators has been created to rank farms on their potential environmental impacts using FADN datas. Then, these classes have been connected with the amounts of direct payments received. Results are processed on three types of farm (specialized in cereals and oilseeds, meat cows and milk cows). Associated with a comprehensive study of the reforms of the CAP since 1992, this empirical study allows to stand back on the consequences of the political decisions. It seems that if the 2nd pillar direct payments are directed in favour of the more environmental friendly farms, their weight remains too low compared with the aids of the 1st pillar, which are higher in the less virtuous farms. This is largely connected to the weight of the DPU in the direct payments, and to the French choice to base their calculation with regard to the history of the farm. That is why the simulations of the redistribution of the subsidies of the 1st pillar on horizon 2019 show that the rebalancing of these payments between the farms by a national harmonization will contribute to level the gap of 1st pillar direct payments by hectare between french farms. The comparison with the United Kingdom and Germany shows the effects of the subsidiarity, in particular during the decoupling: the harmonization of the decoupled payments allows the most environmental friendly farms to get higher direct payments per hectare
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Ghandour-Haidar, Soukayna. "Estimation de canal à évanouissements plats dans les transmissions sans fils à relais multibonds." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT102.
Full textAbstract:
Cette thèse traite de l'estimation d'un canal de communication radio-mobile multi-bond. La communication entre l'émetteur et le récepteur est ainsi faite par l'intermédiaire de relais (de type « Amplify and-Forward ») en série. Les différents éléments (émetteurs, relais, récepteurs) peuvent être fixes ou mobiles. Chaque lien de communication (chaque bond) est modélisé par un canal de Rayleigh à évanouissements plats, avec un spectre Doppler issu de deux environnements possibles de diffusion : en deux dimensions (2D, amenant le spectre en U de Jakes), ou en trois dimensions (3D, amenant un spectre Doppler plat). L'objectif majeur de la thèse est l'estimation dynamique du canal global issue de la cascade des différents liens. A cette fin, la cascade de canaux est approchée par une modèle auto-régressif du premier ordre (AR (1)), et l'estimation est réalisée à l'aide d'un algorithme standard, le filtre de Kalman. La méthode couramment utilisée dans la littérature pour fixer le paramètre du modèle AR(1) est basée sur un critère de « corrélation matching » (CM). Cependant, nous montrons que pour des canaux à variations lentes, un autre critère basé sur la minimisation de la variance asymptotique (MAV) de la sortie du filtre de Kalman est plus approprié. Pour les deux critères, CM et MAV, cette thèse donne une justification analytique en fournissant des formules approchées de la variance d'estimation par le filtre de Kalman, ainsi que du réglage optimal du paramètre du modèle AR(1). Ces formules analytiques sont données en fonctions des fréquences Doppler et du rapport signal sur bruit, pour les environnements de diffusion 2D et 3D, quel que soit le nombre et le type de bonds (fixe-mobile ou mobile-mobile). Les résultats de simulations montrent un gain considérable en termes de l'erreur quadratique moyenne (MSE) de l'estimateur de canal bien réglé, en particulier pour le scénario le plus courant de canal à évanouissements lentsThis thesis deals with the estimation of the multihop Amplify-and-Forward relay communications. The various objects (transmitter, relays, receivers) can be fixed or mobile. Each link is modeled by a flat fading Rayleigh channel, with a Doppler spectrum resulting from two-dimensional (2D, leading to the U-shape Dopller spectrum) or three-dimensional (3D, leading to a flat Doppler spectrum) scattering environments. The cascade of channel hops is approximated by a first-order autoregressive (AR(1)) model and is tracked by a standard estimation algorithm, the Kalman Filter (KF). The common method used in the literature to tune the parameter of the AR(1) model is based on a Correlation Matching (CM) criterion. However, for slow fading variations, another criterion based on the off-line Minimization of the Asymptotic Variance (MAV) of the KF is shown to be more appropriate. For both the CM and MAV criteria, this thesis gives analytic justification by providing approximated closed-form expressions of the estimation variance in output of the Kalman filter, and of the optimal AR(1) parameter. The analytical results are calculated for given Doppler frequencies and Signal-to-Noise Ratio for both scattering environments, whatever the number and type of transmission hops (Fixed-to-Mobile or Mobile-to-Mobile). The simulation results show a considerable gain in terms of the Mean Square Error (MSE) of the well tuned Kalman-based channel estimator, especially for the most common scenario of slow-fading channel
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CHANDRA, MUDITA. "PERFORMANCE ANALYSIS OF TURBO CODES IN FADING ENVIRONMENTS." Thesis, 2016. http://dspace.dtu.ac.in:8080/jspui/handle/repository/14972.
Full textAbstract:
Turbo codes belong to the class of convolutional error correcting codes used in wireless data
transmission applications like mobile communications, deep-sea communications, satellite
communications and other power constrained fields. Turbo Decoder consists of concatenation of
decoders based on Maximum a posteriori algorithm. Turbo decoding is an iterative principle
where the constituent decoders pass extrinsic information to each other with an interleaver or
deinterleaver in between. The performance of turbo codes approaches the Shannon limit making
them most sought after in current wireless applications. Simulations of Turbo code performance
under different parameters and different situations like number of iterations, different encoder
structures, interleaver types, puncturing has been done. The performance of turbo codes was
simulated in Rayleigh and Rician fading channels. The turbo codes have shown a considerably
remarkable performance with variations in parameters and environments.
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He, Yue-Jing, and 何岳璟. "Modeling of Radio Multipath Fading Channels in Picocellular and Microcellular Environments." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/44860459932304519197.
Full textAbstract:
碩士國立交通大學
電信工程系
88
In this thesis, we present the hybrid model to research the characteristic of multipath fading in picocell (indoor) and microcell (urban). It is composed of 2-dimension adaptive site-specific model and scattering model. Adaptive site-specific model comprises the reflection, scattering and transmission effect of boundary in the transmission environment. Scattering model can be used to describe the scattering field as a result of random distribution of scattering object and the rough surface boundary. It is found that this treatment can decrease the number ray-tree levels of the site-specific model and saves a lot of computational time. In addition to accurately predicting mean field strength, the hybrid model can effectively quantify the contribution of scattering field (relative to mean value) with the relative scattering factor r. A large amount of experiment data at many different sites (2.44GHz for picocell, 900MHz for microcell) shows that a Nakagami distribution describes the fading distribution well in picocellular and microcellular environment. After measuring live on the spot, we find that in the picocell: (1) r = 0.65~0.72 if the receiving or transmitting antenna is in a heavy cluttering environment; (2) r = 0.26~0.35 if the receiving or transmitting antenna is in a light cluttering environment. While in microcell model, r = 0.1~0.2 because both transmitting and receiving are in light cluttering environment, it can model the statistical characteristic of multipath fading in different environment effectively.
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Li, Jing Yang, and 李景洋. "Diversity transmission techniques for framed ALOHA communication system in fading environments." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/30994630531238204979.
Full text
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Chen, Chia-Yi, and 陳家溢. "On the Behavior of Noncoherent Delay-Locked Loops in Mutipath Fading Environments." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/81330537851198065714.
Full textAbstract:
碩士國立交通大學
電信研究所
85
Noncoherent {\it delay-locked loops} (DLL) are often employed to track the code phase of the pseudo noise (PN) sequence used in a direct-sequence spread spectrum (DS/SS) system. In a wireless radio communication environment, the performence of a noncoherent DLL is affected not only by additive white Gaussian noise (AWGN) but also by multipath fading. This thesis investigates the behavior of noncoherent DDLs in a class of simple time-varying fading channels. Numerical method is used to solve the transition probability density function (pdf) of the tracking error and to study the transient behavior of a noncoherent loop. Detailed discussion on the numerical problems encountered in the course of deriving the desired solution is provided. {\it Mean time to lose lock} (MTLL) and {\it tracking error} are the two major performance measures of concern to us. Because the code phase error can be modeled as a renewal process, {\it Renewal Process Approach} (RPA) can be applied to analyze the performance of tracking loops. In a time-varying channel, however, we find that stationary analysis using RPA does not lead to correct estimates of the MTLL and the tracking error. We also analyze the performance of a class of code tracking loops called improved DLL that has a wider S-curve, larger pull-in and lock-in ranges.
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Hiep, Le Hoang, and 黎黃協(Le Hoang Hiep). "Developing An Algorithm of Signal Scheduling Management for Heterogeneous Networks over Fading Environments." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/3au66b.
Full textAbstract:
博士大葉大學
電機工程學系
103
In this dissertation, an efficient algorithm target tracking is studied using mobile sensor network in a heterogeneous network (HetNet). The purpose of the research focuses on a method which attempt to approach an optimal sensor scheduling to track a moving target such that it minimizes the measurement error, reduces the sensor usage cost and satisfies the constraints under consideration. In this study, a wireless Heterogeneous Network (HetNet) is considered as a fading propagation environment. To model for this kind of channel, authors applied m-Nakagami distribution as an efficient distribution for a fading propagation. Accordingly, the Kalman filter technique to predict position of target in posteriori state is applied. A new algorithm was proposed to recognize a most likely trajectory of this mobile user and to minimize resource consumption by scheduling an efficient moving for the mobile sensor network. A simulation for the case of three mobile sensors track a target moving, e.g. a mobile user, was considered. The position and velocity of target were assumed given in the initial state, then these sensors transmitted the measured information of target in recent state to a base station every time length. Based on received data of this priori state measurement, a management system embedded in base station would predict the posteriori state of target. Next, the base station transmitted commands to control these sensors move properly such that tracking system does not miss the target. In this simulation, total distance of itinerary of sensors represented resource consumption. Numerical results presented that the purposed algorithm gets a better performance than regular one by spending less executing time and estimated trajectory of target was almost similar to regular one. Keywords: mobile target tracking, wireless sensor network, Kalman filter, heterogeneous network, m-Nakagami.
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Svasti-Xuto, Usa. "Performance analyses of frequency-hopped spread-spectrum multiple access systems in fading environments." Thesis, 1996. http://hdl.handle.net/1828/8223.
Full textAbstract:
The focus of this dissertation is the performance analyses of two classes of frequency-hopped
spread-spectrum multiple access (FH-SSMA) systems in various fading
environments.
The capacity of Viterbi’s FH-SSMA system is evaluated under three types of
fading, namely Rician, shadowed Rician, and Nakagami fading. The results of recent
experiments have indicated that these fading phenomena occur in various environments
where the FH-SSMA system may be implemented. In this dissertation, the deletion
probability for each fading scenario is derived. Subsequently, the system capacity is
analyzed in terms of maximum number of users versus average bit error rate. The effect
of a change in the signal-to-noise ratio level on the system capacity is also demonstrated.
For Rician fading, it is found that the capacity of the system with a Rician factor of 2 dB
is reduced by 13 percent as compared to the capacity of the non-fading case. For
shadowed Rician fading, three shadowing scenarios are considered: light, average, and
heavy. It is shown that the light and the average shadowing scenarios provide only a
slight decrease in the capacity, while the heavy shadowing scenario renders a capacity
identical to that for the Rayleigh fading case. Finally, for Nakagami fading the capacity is
found to decrease by 50 percent as the fading parameter is reduced to 0.5.
The performance of a cellular frequency-hopped spread-spectrum multiple access
system is studied under an indoor environment. It is demonstrated how the system
capacity, given in terms of the number of users per cell, is affected by the number of cells
in the system. Also, the influence of the delay spread, which is the result of multipath
propagation, is investigated. The analysis focuses on a worst-case scenario where a user receives both the desired and interfering signals with equal power levels. This scenario
applies to both the downlink and the uplink. It is shown that the system capacity is
reduced drastically as the number of adjacent interfering cells increases from one to three.
Previous work concerning the indoor multipath propagation assumed that the number of
paths is fixed, the path delays are uniformly distributed, and the path gains are equal. In
this dissertation, a more realistic channel model derived from actual impulse response
measurements by Saleh and Valenzuela is employed. The model consists of clusters of
rays with constant cluster and ray arrival rates and power-delay time constants. The
system performance is shown to be affected strongly by the change in the power-delay
time constants, yet only slightly influenced by the variation in the arrival rates of the rays
and clusters. In addition, the degradation in the system performance due to the delay
spread becomes more severe as the transmission rate increases.Graduate
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CHIU, KAI-MING, and 邱開明. "Investigating in the System Performance of UWB Systems Operating over Frequency Selective Fading Environments." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/40947489659973830053.
Full textAbstract:
碩士大葉大學
電信工程學系碩士在職專班
95
The Federal Communications Commission (FCC) has allocated 7,500MHz spectrum for unlicensed use of ultra-wideband (UWB) devices in the 3.1 to 10.6 GHz frequency band. The UWB techniques belong to the protocol of 802.15.3a, that is, the UWB will be the most one technical applied in the wireless communication systems. Especially, it is one of the most important fechnique for application in military service, since the base station is not needed for the UWB system. The UWB communication methods will be the most adaptive application for small enterprises since it owns the unlicensed spectrum. Thus, the UWB wireless communication technique will be adopted in this paper for studing in order to research and dervelop some added applications in private area. Combining the high dense multiple access of AIRMA (analog impulse radio multiple access) with DIRMA (Digital impulse radio multiple access) will be held in this study. Some of the theories of UWB system will be derived by using the theory means. Hence, the advantages for the UWB technique will be cleared, and some of the results from this investigation will be provided to apply in the real world applications. Besides, the operation environments with frequency sclectve fading channel are also combined with the analysis of the system performance.
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Shih-Tan, Wang, and 王世坦. "Outage Performance of Maximal Ratio Combining Technique Working over the Environments of Fading Channel." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/25632199874091997541.
Full textAbstract:
碩士大葉大學
電信工程學系碩士在職專班
93
The Nakagami fading distribution is assumed in this thesis for investigating the outage performance of digital communication with MRC (maximal ratio combining) diversity technique. Besides, the phenomena of CCI (co-channel interference), frequency selective channel, and the random communication branch are also considered in here. In this thesis some new formulae of outage performance are proposed. The numerical results obviously show that not only the characteristics parameters of the channel model, but the number of branch also affect the performance of wireless radio systems over CCI environments.
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Annamalai, Annamalai Jr. "Accurate and efficient analysis of wireless digital communication systems in multiuser and multipath fading environments." Thesis, 1999. https://dspace.library.uvic.ca//handle/1828/8687.
Full textAbstract:
Testimonies of “wireless catching up with wireline” have begun. However, the nonstationary and hostile nature of the wireless channel impose the greatest threat to reliable data transmission over wireless links. The performance of a digital modulation scheme is degraded by many transmission impairments including fading, delay spread, co-channel interference and noise. Two powerful techniques for improving the quality of service over the wireless network are investigated: diversity reception and adaptive error control schemes. Owing to the growing interest in wireless communications, the importance of exact theoretical analysis of such systems cannot be understated. In light of these considerations, this dissertation focuses on accurate and efficient analysis of wireless digital communication systems in multiuser and multipath fading environments.
The evaluation of error probabilities in digital communication systems is often amenable to calculating a generic error probability of the form Pr {X ≤ 0}, where X is a random variable whose probability distribution is known. We advocate a simple numerical approach based on the Fourier or Laplace inversion formulas and Gauss-Chebychev quadratures (GCQ) for computing this error probability. Using this result, and by formulating the outage probability of cellular mobile radio networks in the framework of statistical decision theory, we can unify the outage performance analysis for cellular mobile radio systems in generalized fading channels without imposing any restrictions on the desired signal and interferers statistics.
Next, we develop two unified analytical frameworks for evaluating the bit or symbol error probability (SER) of a broad class of coherent, differentially coherent and noncoherent digital communication systems with diversity reception in generalized fading channels. The exact SER is mostly expressed in terms of a single finite-range integral, and in some cases in the form of double finite-range integrals. Virtually “exact” closed-form expressions (in terms of a rapidly converging series) are also derived. This offers a convenient method to perform a comprehensive study of all common diversity combining techniques (maximal-ratio combining (MRC), equal-gain combining (EGC), selection combining (SDC) and switched combining (SWC)) with different modulation formats in a myriad of fading scenarios. In particular, our unified approach based on characteristic function (CHF) method allows us to unify the above problem in a single common framework. Nevertheless, the moment generating function (MGF) method often yields a more concise solution than the CHF approach in the analysis of MRC, SDC and SWC diversity systems.
Subsequently, we examine the performance of a maximum amplitude selection diversity (MA/SD) rake receiver configuration in indoor wireless channels. The proposed low-complexity receiver structure is practically appealing because of its simplicity as well as its ability to operate effectively even at high signalling rates. We have also devised a robust packet combining mechanism to enhance the throughput and delay performance of spread-spectrum radio networks without incurring a substantial penalty in receiver complexity. A simple indirect method to estimate the channel state condition for successful implementation of a self-reconfigurable automatic repeat-request (ARQ) system, such as mixed-mode ARQ protocol or adaptive packet length strategy in a slowly varying mobile radio environment is also studied.Graduate
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Wen, Hsieh Tai, and 謝岱彣. "On the Impact of CFO for an MC-DS-CDMA System in Weibull Fading Environments." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/09335079770363173618.
Full textAbstract:
博士大葉大學
電機工程學系
98
On the basis of CFO (carrier frequency offset) point of view, the system performance results from the analysis by adopting the channel scenarios characterized as Weibull fading for an MC-DS-CDMA (multi-carrier direct-sequence coded-division multiple-access) system are proposed in this article. Moreover, an approximate simple expression with the criterion of BER (bit error rate) versus SNR (signal-to-noise ratio) method is derived for an MC-DS-CDMA system combining with MRC (maximal ratio combining) diversity based on the MGF (moment generating function) formula of Weibull statistics, and it associates with an alternative expression of Gaussian Q-function. In addition, the other point of view on the BER performance evaluation of an MC-DS-CDMA system is not only the assumption of both single-user and multi-user cases applied, but the phenomena of PBI (partial band interference) is also included. Furthermore, with several of the system parameters, such as CFO values, ε, Weibull fading parameter, β, user number, K, spreading chip number, N, branch number, L, and the PBI values, JSR, etc., are compared with each other in the numerical results in order to validate the accuracy in the derived formulas. To the best of author’s knowledge, it is a brain fresh idea proposed in this paper to evaluate the system performance for an MC-DS-CDMA system on the point of the CFO view over Weibull fading.
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Lin, Yung-Jeng, and 林永正. "Impact of Multipath Fading on the Quality of Signal Transmission in High Speed Railway Environments." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/78150295175371650660.
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HUNG, CHUN-TIEN, and 洪春田. "Study on the Performance of NC-MFSK with Selective Combining Diversity over Weibull Fading Environments." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/21605773189259607114.
Full textAbstract:
碩士大葉大學
電信工程學系碩士在職專班
93
The methods applied to improve the receiver of wireless communication system with digital modulation combines and diversity combining manners are investigated in this thesis. The channel fading phenomena exist in the modulation schemes are also considered in this study. There are some of the famous and most assumption channel model introduced in my study. The main reason for adopting the Weibull distribution in my study is it has the shape parameter can be applied to characterize the channel fading. On the other hands, the performance of average LCR (level crossing rates) and AFD (average fading durations) for the simplest combining diversity, SC (selection combining), are also evaluated in here. In fact, in this paper some of the formulas of BER (bit error rate) performance are proposed for the SC diversity with noncoherent MFSK (M-ary frequency shift keying) and DQPSK (difference quaternary phase shift keying) over Weibull fading environments.
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Tu, Wen Sheng, and 杜文生. "The Combining Diversity Techniques Frequently Applied in Wireless Radio System over Frequency Selective Fading Environments." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/86289807712821102908.
Full textAbstract:
碩士大葉大學
電信工程學系碩士在職專班
95
The channel capacity of dual-branch MRC (maximal ratio combining) diversity system over correlated waveform intensity, which is characterized as correlated-Nakagami-m fading (the power is modeled as the correlated-Gamma statistics), is evaluated in this paper. The formulas of channel capacity performance are provided with a pdf (probability density function)-based approach. The pdf of sum of Gamma variates based on the representation of the Moschopoulos single gamma series is adopted in the report. The corresponding expressions for Rayleigh fading are obtained as a special case of Nakagami-m fading. Finally, the numerical examples are presented for illustrating the purpose of the validation of the channel capacity equations derived in this paper.