Dissertations / Theses on the topic 'Channel estimation errors'
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Yadav, A. (Animesh). "Space-time constellation and precoder design under channel estimation errors." Doctoral thesis, Oulun yliopisto, 2013. http://urn.fi/urn:isbn:9789526202143.
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Abstract Multiple-input multiple-output transmitted signal design for the partially coherent Rayleigh fading channels with discrete inputs under a given average transmit power constraint is consider in this thesis. The objective is to design the space-time constellations and linear precoders to adapt to the degradation caused by the imperfect channel estimation at the receiver and the transmit-receive antenna correlation. The system is partially coherent so that the multiple-input multiple-output channel coefficients are estimated at the receiver and its error covariance matrix is fed back to the transmitter. Two constellation design criteria, one for the single and another for the multiple transmit antennae are proposed. An upper bound on the average bit error probability for the single transmit antenna and cutoff rate, i.e., a lower bound on the mutual information, for multiple transmit antennae are derived. Both criteria are functions of channel estimation error covariance matrix. The designed constellations are called as partially coherent constellation. Additionally, to use the resulting constellations together with forward error control codes requires efficient bit mapping schemes. Because these constellations lack geometrical symmetry in general, the Gray mapping is not always possible in the majority of the constellations obtained. Moreover, different mapping schemes may lead to highly different bit error rate performances. Thus, an efficient bit mapping algorithm called the modified binary switching algorithm is proposed. It minimizes an upper bound on the average bit error probability. It is shown through computer simulations that the designed partially coherent constellation and their optimized bit mapping algorithm together with turbo codes outperform the conventional constellations. Linear precoder design was also considered as a simpler, suboptimal alternative. The cutoff rate expression is again used as a criterion to design the linear precoder. A linear precoder is obtained by numerically maximizing the cutoff rate with respect to the precoder matrix with a given average transmit power constraint. Furthermore, the precoder matrix is decomposed using singular-value-decomposition into the input shaping, power loading, and beamforming matrices. The beamforming matrix is found to coincide with the eigenvectors of the transmit correlation matrix. The power loading and input shaping matrices are solved numerically using the difference of convex functions programming algorithm and optimization under the unitary constraint, respectively. Computer simulations show that the performance gains of the designed precoders are significant compared to the cutoff rate optimized partially coherent constellations without precodingTiivistelmä Väitöskirjassa tarkastellaan lähetyssignaalien suunnittelua osittain koherenteissa Rayleigh-häipyvissä kanavissa toimiviin monitulo-monilähtöjärjestelmiin (MIMO). Lähettimen keskimääräinen lähetysteho oletetaan rajoitetuksi ja lähetyssignaali diskreetiksi. Tavoitteena on suunnitella tila-aikakonstellaatioita ja lineaarisia esikoodereita jotka mukautuvat epätäydellisen kanavaestimoinnin aiheuttamaan suorituskyvyn heikkenemiseen sekä lähetin- ja vastaanotinantennien väliseen korrelaatioon. Tarkasteltavien järjestelmien osittainen koherenttisuus tarkoittaa sitä, että MIMO-kanavan kanavakertoimet estimoidaan vastaanottimessa, josta niiden virhekovarianssimatriisi lähetetään lähettimelle. Työssä esitetään kaksi konstellaatiosuunnittelukriteeriä, toinen yhdelle lähetinantennille ja toinen moniantennilähettimelle. Molemmat kriteerit ovat kanavan estimaatiovirheen kovarianssimatriisin funktioita. Työssä johdetaan yläraja keskimääräiselle bittivirhetodennäköisyydelle yhden lähetinantennin tapauksessa sekä rajanopeus (cutoff rate), joka on alaraja keskinäisinformaatiolle, usean lähetinantennin tapauksessa. Konstellaatioiden käyttö yhdessä virheenkorjauskoodien kanssa edellyttää tehokaita menetelmiä, joilla bitit kuvataan konstellaatiopisteisiin. Koska tarvittavat konstellaatiot eivät ole tyypillisesti geometrisesti symmetrisiä, Gray-kuvaus ei ole yleensä mahdollinen.Lisäksi erilaiset kuvausmenetelmät voivat johtaa täysin erilaisiin bittivirhesuhteisiin. Tästä johtuen työssä esitetään uusi kuvausalgoritmi (modified bit switching algorithm), joka minimoi keskimääräisen bittivirhetodennäköisyyden ylärajan. Simulointitulokset osoittavat, että työssä kehitetyt konstellaatiot antavat paremman suorituskyvyn turbokoodatuissa järjestelmissä kuin perinteiset konstellaatiot. Työssä tarkastellaan myös lineaarista esikoodausta yksinkertaisena, alioptimaalisena vaihtoehtona uusille konstellaatioille. Esikoodauksen suunnittelussa käytetään samaa kriteeriä kuin konstellaatioiden kehityksessä eli rajanopeutta. Lineaarinen esikooderi löydetään numeerisesti maksimoimalla rajanopeus kun rajoitusehtona on lähetysteho. Esikoodausmatriisi hajotetaan singulaariarvohajotelmaa käyttäen esisuodatus, tehoallokaatio ja keilanmuodostusmatriiseiksi, jonka havaitaan vastaavan lähetyskorrelaatiomatriisin ominaisvektoreita. Tehoallokaatiomatriisi ratkaistaan numeerisesti käyttäen difference of convex functions -optimointia ja esisuodatusmatriisi optimoinnilla unitaarista rajoitusehtoa käyttäen. Simulaatiotulokset osoittavat uusien esikoodereiden tarjoavan merkittävän suorituskykyedun sellaisiin rajanopeusoptimoituihin osittain koherentteihin konstellaatioihin nähden, jotka eivät käytä esikoodausta
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Menon, Rekha. "Impact of Channel Estimation Errors on Space Time Trellis Codes." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/36490.
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Space Time Trellis Coding (STTC) is a unique technique that combines the use of multiple transmit antennas with channel coding. This scheme provides capacity benefits in fading channels, and helps in improving the data rate and reliability of wireless communication. STTC schemes have been primarily designed assuming perfect channel estimates to be available at the receiver. However, in practical wireless systems, this is never the case. The noisy wireless channel precludes an exact characterization of channel coefficients. Even near-perfect channel estimates can necessitate huge overhead in terms of processing or spectral efficiency. This practical concern motivates the study of the impact of channel estimation errors on the design and performance of STTC.
The design criteria for STTC are validated in the absence of perfect channel estimates at the receiver. Analytical results are presented that model the performance of STTC systems in the presence of channel estimation errors. Training based channel estimation schemes are the most popular choice for STTC systems. The amount of training however, increases with the number of transmit antennas used, the number of multi-path components in the channel and a decrease in the channel coherence time. This dependence is shown to decrease the performance gain obtained when increasing the number of transmit antennas in STTC systems, especially in channels with a large Doppler spread (low channel coherence time). In frequency selective channels, the training overhead associated with increasing the number of antennas can be so large that no benefit is shown to be obtained by using STTC.
The amount of performance degradation due to channel estimation errors is shown to be influenced by system parameters such as the specific STTC code employed and the number of transmit and receive antennas in the system in addition to the magnitude of the estimation error. Hence inappropriate choice of system parameters is shown to significantly alter the performance pattern of STTC.
The viability of STTC in practical wireless systems is thus addressed and it is shown that that channel estimation could offset benefits derived from this scheme.
Master of Science
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Zhu, Chao. "Performance Analysis of Minimum Selection GSC with Channel Estimation Errors in Rayleigh Fading Channels." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1250184723.
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Baykas, Tuncer. "Effects of spatial correlation and channel estimation errors on the performance of space-time block coded systems." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6147.
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Today's wireless communication systems require more efficiency in terms of data rate. One of the ways to improve channel capacity of such systems is to utilize diversity. Space-time block codes provide transmit diversity gain without any significant increase in complexity of systems. However in some cases, the gain by utilizing diversity decreases due to some factors. In this work we studied two of these factors and their effects to several space-time block coded systems. The first factor is the spatial correlation among channels and the second factor is channel estimation errors. Both of these factors are experienced in real life situations. The systems under consideration are 2, 3 and 4 antenna orthogonal and quasi-orthogonal space-time block coded systems. We have also compared the results with the maximum ratio combining schemes with 2 and 4 receiver antennas.
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Chong, Lucy Lok-Kwan. "The effects of channel estimation errors on wideband CDMA systems with path, frequency, time, and space diversity /." 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?p3029641.
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Irshad, Yasir. "On some continuous-time modeling and estimation problems for control and communication." Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-26129.
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The scope of the thesis is to estimate the parameters of continuous-time models used within control and communication from sampled data with high accuracy and in a computationally efficient way.In the thesis, continuous-time models of systems controlled in a networked environment, errors-in-variables systems, stochastic closed-loop systems, and wireless channels are considered. The parameters of a transfer function based model for the process in a networked control system are estimated by a covariance function based approach relying upon the second order statistical properties of input and output signals. Some other approaches for estimating the parameters of continuous-time models for processes in networked environments are also considered. The multiple input multiple output errors-in-variables problem is solved by means of a covariance matching algorithm. An analysis of a covariance matching method for single input single output errors-in-variables system identification is also presented. The parameters of continuous-time autoregressive exogenous models are estimated from closed-loop filtered data, where the controllers in the closed-loop are of proportional and proportional integral type, and where the closed-loop also contains a time-delay. A stochastic differential equation is derived for Jakes's wireless channel model, describing the dynamics of a scattered electric field with the moving receiver incorporating a Doppler shift.The thesis consists of five main parts, where the first part is an introduction- Parts II-IV are based on the following articles:
Part II - Networked Control Systems
1. Y. Irshad, M. Mossberg and T. Söderström. System identification in a networkedenvironment using second order statistical properties.
A versionwithout all appendices is published as Y. Irshad, M. Mossberg and T. Söderström. System identification in a networked environment using second order statistical properties. Automatica, 49(2), pages 652–659, 2013.
Some preliminary results are also published as M. Mossberg, Y. Irshad and T. Söderström. A covariance function based approachto networked system identification. In Proc. 2nd IFAC Workshop on Distributed Estimation and Control in Networked Systems, pages 127–132, Annecy,France, September 13–14, 2010
2. Y. Irshad and M. Mossberg. Some parameters estimation methods applied tonetworked control systems.A journal submission is made. Some preliminary results are published as Y. Irshad and M. Mossberg. A comparison of estimation concepts applied to networked control systems. In Proc. 19th Int. Conf. on Systems, Signals andImage Processing, pages 120–123, Vienna, Austria, April 11–13, 2012.
Part III - Errors-in-variables Identification
3. Y. Irshad and M. Mossberg. Continuous-time covariance matching for MIMOEIV system identification. A journal submission is made.
4. T. Söderström, Y. Irshad, M. Mossberg and W. X. Zheng. On the accuracy of acovariance matching method for continuous-time EIV identification. Provisionally accepted for publication in Automatica.
Some preliminary results are published as T. Söderström, Y. Irshad, M. Mossberg, and W. X. Zheng. Accuracy analysis of a covariance matching method for continuous-time errors-in-variables system identification. In Proc. 16th IFAC Symp. System Identification, pages 1383–1388, Brussels, Belgium, July 11–13, 2012.
Part IV - Wireless Channel Modeling
5. Y. Irshad and M. Mossberg. Wireless channel modeling based on stochasticdifferential equations .Some results are published as M. Mossberg and Y. Irshad. A stochastic differential equation forwireless channelsbased on Jakes’s model with time-varying phases, In Proc. 13th IEEEDigitalSignal Processing Workshop, pages 602–605, Marco Island, FL, January4–7, 2009.
Part V - Closed-loop Identification
6. Y. Irshad and M. Mossberg. Closed-loop identification of P- and PI-controlledtime-delayed stochastic systems.Some results are published as M. Mossberg and Y. Irshad. Closed-loop identific ation of stochastic models from filtered data, In Proc. IEEE Multi-conference on Systems and Control,San Antonio, TX, September 3–5, 2008
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Karim, Md Anisul. "Weighted layered space-time code with iterative detection and decoding." Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1095.
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Multiple antenna systems are an appealing candidate for emerging fourth-generation wireless networks due to its potential to exploit space diversity for increasing conveyed throughput without wasting bandwidth and power resources. Particularly, layered space-time architecture (LST) proposed by Foschini, is a technique to achieve a significant fraction of the theoretical capacity with a reasonable implementation complexity. There has been a great deal of challenges in the detection of space-time signal; especially to design a low-complexity detector, which can efficiently remove multi-layer interference and approach the interference free bound. The application of iterative principle to joint detection and decoding has been a promising approach. It has been shown that, the iterative receiver with parallel interference canceller (PIC) has a low linear complexity and near interference free performance. Furthermore, it is widely accepted that the performance of digital communication systems can be considerably improved once the channel state information (CSI) is used to optimize the transmit signal. In this thesis, the problem of the design of a power allocation strategy in LST architecture to simultaneously optimize coding, diversity and weighting gains is addressed. A more practical scenario is also considered by assuming imperfect CSI at the receiver. The effect of channel estimation errors in LST architecture with an iterative PIC receiver is investigated. It is shown that imperfect channel estimation at an LST receiver results in erroneous decision statistics at the very first iteration and this error propagates to the subsequent iterations, which ultimately leads to severe degradation of the overall performance. We design a transmit power allocation policy to take into account the imperfection in the channel estimation process. The transmit power of various layers is optimized through minimization of the average bit error rate (BER) of the LST architecture with a low complexity iterative PIC detector. At the receiver, the PIC detector performs both interference regeneration and cancellation simultaneously for all layers. A convolutional code is used as the constituent code. The iterative decoding principle is applied to pass the a posteriori probability estimates between the detector and decoders. The decoder is based on the maximum a posteriori (MAP) algorithms. A closed-form optimal solution for power allocation in terms of the minimum BER is obtained. In order to validate the effectiveness of the proposed schemes, substantial simulation results are provided.
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Karim, Md Anisul. "Weighted layered space-time code with iterative detection and decoding." School of Electrical & Information Engineering, 2006. http://hdl.handle.net/2123/1095.
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Master of Engineering (Research)Multiple antenna systems are an appealing candidate for emerging fourth-generation wireless networks due to its potential to exploit space diversity for increasing conveyed throughput without wasting bandwidth and power resources. Particularly, layered space-time architecture (LST) proposed by Foschini, is a technique to achieve a significant fraction of the theoretical capacity with a reasonable implementation complexity. There has been a great deal of challenges in the detection of space-time signal; especially to design a low-complexity detector, which can efficiently remove multi-layer interference and approach the interference free bound. The application of iterative principle to joint detection and decoding has been a promising approach. It has been shown that, the iterative receiver with parallel interference canceller (PIC) has a low linear complexity and near interference free performance. Furthermore, it is widely accepted that the performance of digital communication systems can be considerably improved once the channel state information (CSI) is used to optimize the transmit signal. In this thesis, the problem of the design of a power allocation strategy in LST architecture to simultaneously optimize coding, diversity and weighting gains is addressed. A more practical scenario is also considered by assuming imperfect CSI at the receiver. The effect of channel estimation errors in LST architecture with an iterative PIC receiver is investigated. It is shown that imperfect channel estimation at an LST receiver results in erroneous decision statistics at the very first iteration and this error propagates to the subsequent iterations, which ultimately leads to severe degradation of the overall performance. We design a transmit power allocation policy to take into account the imperfection in the channel estimation process. The transmit power of various layers is optimized through minimization of the average bit error rate (BER) of the LST architecture with a low complexity iterative PIC detector. At the receiver, the PIC detector performs both interference regeneration and cancellation simultaneously for all layers. A convolutional code is used as the constituent code. The iterative decoding principle is applied to pass the a posteriori probability estimates between the detector and decoders. The decoder is based on the maximum a posteriori (MAP) algorithms. A closed-form optimal solution for power allocation in terms of the minimum BER is obtained. In order to validate the effectiveness of the proposed schemes, substantial simulation results are provided.
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Potter, Chris. "Modeling Channel Estimation Error in Continuously Varying MIMO Channels." International Foundation for Telemetering, 2007. http://hdl.handle.net/10150/604490.
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ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, NevadaThe accuracy of channel estimation plays a crucial role in the demodulation of data symbols sent across an unknown wireless medium. In this work a new analytical expression for the channel estimation error of a multiple input multiple output (MIMO) system is obtained when the wireless medium is continuously changing in the temporal domain. Numerical examples are provided to illustrate our findings.
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Hunter, Brandon. "Channel Probing for an Indoor Wireless Communications Channel." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/64.
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The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.
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Arvidsson, Pontus. "Channel Estimation Error Model for SRS in LTE." Thesis, KTH, Signalbehandling, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-53769.
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In 3GPP long term evolution (LTE), sounding is used to gain a wideband estimate of the uplink channel. This channel estimate may then be used for several radio resource management related applications such as frequency selective scheduling and beam forming. Code division multiplexing (CDM) enables several users to broadcast sounding reference signals (SRS) simultaneously on the same time and frequency resource. As the multiplexed users may interfere with one another there is a trade-off between having users broadcast SRS as often as possible to get a frequent channel estimate and getting higher quality estimates with a lower periodicity. To assess this trade-off one must have a good understanding of what causes the errors in the channel estimate so that the sounding resource may be used as efficiently as possible. This thesis proposes a method to model the channel estimation error with sounding for use in a system simulator environment. The method consists of estimating a standard deviation with a per-resource-block resolution of the channel estimates as a function of received signal powers of interfering users as well as the target user and background noise. This estimated estimation error may then, in the system simulator, be applied to a known ideal channel estimate as noise. The main limiting source of error is shown to beinterference, both from sounding users in the same cell and in others as well as some effects of limited frequency resolution. Simulation results indicate that a cleverly designed sounding resource handler is needed to fully utilize the possible gains of sounding.
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Chi, Xuan. "The Impact of Channel Estimation Error on Space-Time Block and Trellis Codes in Flat and Frequency Selective Channels." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/33963.
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Recently multiple antenna systems have received significant attention from researchers as a means to improve the energy and spectral efficiency of wireless systems. Among many classes of schemes, Space-Time Block codes (STBC) and Space-Time Trellis codes (STTC) have been the subject of many investigations.Both techniques provide a means for combatting the effects of multipath fading without adding much complexity to the receiver. This is especially useful in the downlink of wireless systems. In this thesis we investigate the impact of channel estimation error on the performance of both STBC and STTC.
Channel estimation is especially important to consider in multiple antenna systems since (A) for coherent systems there are more channels to estimate due to multiple antennas and (B) the decoupling of data streams relies on correct channel estimation. The latter effect is due to the intentional cross-talk introduced into STBC.
Master of Science
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Avan, Muhammet. "Joint Frequency Offset And Channel Estimation." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/2/12610149/index.pdf.
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In this thesis study, joint frequency offset and channel estimation methods for
single-input single-output (SISO) systems are examined. The performance of
maximum likelihood estimate of the parameters are studied for different training
sequences. Conventionally training sequences are designed solely for the channel
estimation purpose. We present a numerical comparison of different training
sequences for the joint estimation problem. The performance comparisons are made
in terms of mean square estimation error (MSE) versus SNR and MSE versus the
total training energy metrics. A novel estimation scheme using complementary
sequences have been proposed and compared with existing schemes. The proposed
scheme presents a lower estimation error than the others in almost all numerical
simulations. The thesis also includes an extension for the joint channel-frequency
offset estimation problem to the multi-input multi-output systems and a brief
discussion for multiple frequency offset case is also given.
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Law, Eugene L. "Estimating the Characteristics of the Aeronautical Telemetry Channel during Bit Error Events." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/608759.
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International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, NevadaThis paper presents estimated aeronautical telemetry channel characteristics during bit error events. A T-39 aircraft was flown around various test corridors while transmitting a filtered 10 Mb/s pseudo-noise (PN) sequence binary phase shift keying (BPSK) signal. The received signal was down converted to 70 MHz, digitized when trigger criteria were met, and stored for later analysis. Received signal strength was also recorded. The first step in data analysis consisted of dividing the fast Fourier transform (FFT) of the recorded signal by the FFT of the expected signal. The received signal strength data was then used to correct for flat fade effects. The resulting signal is the difference (dB) between the expected signal at the receiver intermediate frequency (IF) output and the measured receiver IF output during the error event. This difference is the aeronautical telemetry channel characteristic. The characteristics of this difference signal were then matched against a 2-ray and 3-ray multipath fading model with reflected signal amplitude and path delay as the variables.
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Yasami, Keyvan. "Effect of Channel Estimation Error on Performance of Physical Layer Network Coding." Fogler Library, University of Maine, 2011. http://www.library.umaine.edu/theses/pdf/YasamiK2011.pdf.
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Kim, Yongsub. "Estimation and equalization of time-selective fading channels." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14925.
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Sadough, Seyed Mohammad Sajad. "Ultra wideband OFDM systems : channel estimation and improved detection accounting for estimation inaccuracies." Paris 11, 2008. http://www.theses.fr/2008PA112001.
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Les travaux présentés dans cette thèse se situent dans le cadre de la transmission OFDM appliqué au contexte Ultra Large Bande (UWB). L’objectif principal va être l’estimation du canal de propagation et la conception de récepteurs en prenant en compte la connaissance non idéale du canal. On propose d’abord une approche semi-aveugle d’estimation du canal qui bénéficie de la parcimonie du canal UWB dans le domaine des ondelettes pour réduire le nombre de paramètre à estimer. Ensuite, on propose des structures de réception itérative où la conception du détecteur prend en compte la présence des erreurs d’estimation de canal. La détection au sens maximum de vraisemblance (MV) est améliorée en modifiant sa métrique de détection pour le cas où le canal est estimé de manière imparfaite. La métrique MV améliorée ainsi obtenue nous permet de remettre en question le schéma de détection de type turbo MAP dans un contexte BICM et l’adapter à la connaissance imparfaite du canal. De plus, on dérive les débits de coupure atteignables (achievable outage rates) avec le détecteur MV améliorée ou un détecteur MV désadapté (utilisant les estimés de canal comme s’il s’agissait des vraies) qu’on comparera avec un détecteur théorique défini comme étant le meilleur récepteur possible en présence d’erreurs d’estimation de canal. Enfin, un récepteur itératif à complexité réduite basé sur un filtrage MMSE et l’annulation parallèle d’interférence (turbo-PIC) est introduit et ensuite adapté à la connaissance imparfaite du canal. Il est important de souligner que les améliorations proposées dans cette thèse n’impliquent pas une augmentation sensible de la complexité au niveau du récepteurThe aim of this thesis is to study the problem of iterative data detection in an ultra wideband (UWB) OFDM system, where the receiver disposes only of an imperfect (and possibly poor) estimate of the unknown channel parameters. First, we propose an efficient receiver jointly estimating the channel and the transmitted symbols in an iterative manner. This receiver is based on a wavelet representation of the unknown channel and exploits the sparseness property of UWB channels in the wavelet domain to reduce the receiver’s computational complexity. Second, we rely on the statistics characterizing the quality of the channel estimation as a mean to integrate the imperfect channel knowledge into the design of iterative receivers. In this way, we formulate an improved maximum likelihood (ML) detection metric taking into account the presence of channel estimation errors. A modified iterative MAP detector is derived by an appropriate use of this metric. The results are compared to those obtained by using the classical mismatched ML detector, which uses the channel estimate as if it was the perfect channel. Furthermore, we calculate the achieved throughputs associated to both improved and mismatched ML detectors, in terms of achievable outage rates. Finally, we propose an improved low-complexity iterative detector based on soft parallel interference cancellation and linear MMSE filtering where we takes into account the presence of channel estimation errors in the formulation of the detector. The important point is that the performance improvements reported in this thesis are obtained while imposing practically no additional complexity to the receiver
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Savaux, Vincent. "Contribution to multipath channel estimation in an OFDM modulation context." Phd thesis, Supélec, 2013. http://tel.archives-ouvertes.fr/tel-00988283.
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In wireless communications systems, the transmission channel between the transmitter and the receiver antennas is one of the main sources of disruption for the signal. The multicarrier modulations, such as the orthogonal frequency division multiplexing (OFDM), are very robust against the multipath effect, and allow to recover the transmitted signal with a low error rate, when they are combined with a channel encoding. The channel estimation then plays a key role in the performance of the communications systems. In this PhD thesis, we study techniques based on least square (LS) and minimum mean square error (MMSE) estimators. The MMSE is optimal, but is much more complex than LS, and requires the a priori knowledge of the second order moment of the channel and the noise. In this presentation, two methods that allow to reach a performance close to the one of LMMSE while getting around its drawback are investigated. In another way, a third part of the presentation investigates the errors of estimation due to the interpolations.
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Pachai, Kannu Arun. "Communications over noncoherent doubly selective channels." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1173887288.
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Razavi, Sabah. "Channel Estimation Error, Oscillator Stability And Wireless Power Transfer In Wireless Communication With Distributed Reception Networks." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-dissertations/508.
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This dissertation considers three related problems in distributed transmission and reception networks. Generally speaking, these types of networks have a transmit cluster with one or more transmit nodes and a receive cluster with one or more receive nodes. Nodes within a given cluster can communicate with each other using a wired or wireless local area network (LAN/WLAN). The overarching goal in this setting is typically to increase the efficiency of communication between the transmit and receive clusters through techniques such as distributed transmit beamforming, distributed reception, or other distributed versions of multi-input multi-output (MIMO) communication. More recently, the problem of wireless power transfer has also been considered in this setting.
The first problem considered by this dissertation relates to distributed reception in a setting with a single transmit node and multiple receive nodes. Since exchanging lightly quantized versions of in-phase and quadrature samples results in high throughput requirements on the receive LAN/WLAN, previous work has considered an approach where nodes exchange hard decisions, along with channel magnitudes, to facilitate combining similar to an ideal receive beamformer. It has been shown that this approach leads to a small loss in SNR performance, with large reductions in required LAN/WLAN throughput. A shortcoming of this work, however, is that all of the prior work has assumed that each receive node has a perfect estimation of its channel to the transmitter.
To address this shortcoming, the first part of this dissertation investigates the effect of channel estimation error on the SNR performance of distributed reception. Analytical expressions for these effects are obtained for two different modulation schemes, M-PSK and M2-QAM. The analysis shows the somewhat surprising result that channel estimation error causes the same amount of performance degradation in ideal beamforming and pseudo-beamforming systems despite the fact that the channel estimation errors manifests themselves quite differently in both systems.
The second problem considered in this dissertation is related to oscillator stability and phase noise modeling. In distributed transmission systems with multiple transmitters in the transmit cluster, synchronization requirements are typically very strict, e.g., on the order of one picosecond, to maintain radio frequency phase alignment across transmitters. Therefore, being able to accurately model the behavior of the oscillators and their phase noise responses is of high importance. Previous approaches have typically relied on a two-state model, but this model is often not sufficiently rich to model low-cost oscillators. This dissertation develops a new three-state oscillator model and a method for estimating the parameters of this model from experimental data. Experimental results show that the proposed model provides up to 3 dB improvement in mean squared error (MSE) performance with respect to a two-state model.
The last part of this work is dedicated to the problem of wireless power transfer in a setting with multiple nodes in the transmit cluster and multiple nodes in the receive cluster. The problem is to align the phases of the transmitters to achieve a certain power distribution across the nodes in the receive cluster. To find optimum transmit phases, we consider a iterative approach, similar to the prior work on one-bit feedback for distributed beamforming, in which each receive node sends a one-bit feedback to the transmit cluster indicating if the received power in that time slot for that node is increased. The transmitters then update their phases based on the feedback. What makes this problem particularly interesting is that, unlike the prior work on one-bit feedback for distributed beamforming, this is a multi-objective optimization problem where not every receive node can receive maximum power from the transmit array. Three different phase update decision rules, each based on the one-bit feedback signals, are analyzed. The effect of array sparsity is also investigated in this setting.
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Ng, Jimmy Hon-yuen. "Estimation of error rates and fade distributions on a Rayleigh fading channel with additive white Gaussian noise." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26318.
Full textAbstract:
Several characteristics of the Rayleigh fading channel are examined. A digital Rayleigh fading simulator is used to generate the (fading) signal envelope from which various statistics are derived.
Based on the simulation results, a simple model is proposed in order to estimate the block error rate of a block of N data bits transmitted over the Rayleigh fading channel in the presence of additive white Gaussian noise. This model gives an average estimation error of about 4 % over the range of blocksizes N = 63, 127, 255, 511, 1023, 2047 (bits), average signal-to-noise ratios 70 = 5 to 35 (dB) and fading frequencies f[sub D] = 10 to 90 (Hz) corresponding to vehicle speeds of 8 to 71 MPH at a radio carrier frequency of 850 MHz. A second somewhat more complex model for estimating the block error rate is found to yield a lower average estimation error of 2.4 % over the same set of simulated data.
The probability distributions of the fade rate and the fade duration are also examined. Empirical models are derived for the estimation of the probability mass function of the fade rate and the probability density function of the fade duration. These empirical models allow fairly accurate estimates without the need for cosdy and time-consuming simulations.
The probability of m-bit errors in an N-bit block is an important parameter in the design of error-correcting codes for use on the mobile radio channel. However, such probabilities are difficult to determine without performing extensive simulation or field trials. An approach to estimate them empirically is proposed.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Chan, Raymond. "Channel Prediction for Adaptive Modulation in Wireless Communications." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/34118.
Full textAbstract:
This thesis examines the benefits of using adaptive modulation and coding in terms of spectral efficiency and probability of bit error. Specifically, we examine the performance enhancement made possible by using linear prediction along with channel estimation in conjunction with adaptive modulation. We begin this manuscript with basic fundamentals of our study, followed by a detailed view of simulations, their results, and our conclusions from them. The study includes simulations in slow and moderately fast flat fading Rayleigh channels.
We present our findings regarding the advantages of using predictive measures to foresee the state of the channel and make adjustments to transmissions accordingly.
In addition to finding the general advantages of channel prediction in adaptive modulation, we explore various ways to adjust the prediction algorithm when we are faced with high Doppler rates and fast fading.
By the end of this work, we should have a better understanding of when channel prediction is most valuable to adaptive modulation and when it is weakest, and how we can alleviate the problems that prediction will have in harsh environments.Master of Science
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Medawar, Samer. "Pipeline Analog-Digital Converters Dynamic Error Modeling for Calibration : Integral Nonlinearity Modeling, Pipeline ADC Calibration, Wireless Channel K-Factor Estimation." Doctoral thesis, KTH, Signalbehandling, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95507.
Full textAbstract:
This thesis deals with the characterization, modeling and calibration of pipeline analog-digital converters (ADC)s. The integral nonlinearity (INL) is characterized, modeled and the model is used to design a post-correction block in order to compensate the imperfections of the ADC. The INL model is divided into: a dynamic term designed by the low code frequency (LCF) component depending on the output code k and the frequency under test m, and a static term known as high code frequency (HCF) component depending solely on the output code k. The HCF is related to the pipeline ADC circuitry. A set of adjacent piecewise linear segments is used to model the HCF. The LCF is the dynamic term depending on the input signal characteristics, and is modeled using a polynomial with frequency dependent coefficients. Two dynamic calibration methodologies are developed to compensate the imperfections of the pipeline ADC. In the first approach, the INL model at hand is transformed into a post-correction scheme. Regarding the HCF model, a set of gains and offsets is used to reconstruct the HCF segments structure. The LCF polynomial frequency dependent coefficients are used to design a bank of FIR filters which reconstructs the LCF model. A calibration block made by the combination of static gains/offsets and a bank of FIR filters is built to create the correction term to calibrate the ADC. In the second approach, the calibration (and modeling) process is extended to the upper Nyquist bands of the ADC. The HCF is used directly in calibration as a look-up-table (LUT). The LCF part is still represented by a frequency dependent polynomial of which the coefficients are used to develop a filter bank, implemented in the frequency domain with an overlap-and-add structure. In brief the calibration process is done by the combination of a static LUT and a bank of frequency domain filters. The maximum likelihood (ML) method is used to estimate the K-factor of a wireless Ricean channel. The K-factor is one of the main characteristics of a telecommunication channel. However, a closed-form ML estimator of the Kfactor is unfeasible due to the complexity of the Ricean pdf. In order to overcome this limitation, an approximation (for high K-factor values) is induced to the Ricean pdf. A closed-form approximate ML (AML) for the Ricean K-factor is computed. A bias study is performed on the AML and the bias derived value is used to improve the AML estimation, leading to a closed-form bias compensated estimator (BCE). The BCE performance (in terms of variance, bias and mean square error (MSE)) is simulated and compared to the best known closed-form moment-based estimator found in the literature. The BCE turns to have a superior performance for low number of samples and/or high K-factor values. Finally, the BCE is applied on real site wireless channel measurements in an urban macro cell area, using a 4-antenna transmit/receive MIMO system.QC 20120528
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Yapici, Yavuz. "A Bidirectional Lms Algorithm For Estimation Of Fast Time-varying Channels." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613220/index.pdf.
Full textAbstract:
Effort to estimate unknown time-varying channels as a part of high-speed mobile communication systems is of interest especially for next-generation wireless systems. The high computational complexity of the optimal Wiener estimator usually makes its use impractical in fast time-varying channels. As a powerful candidate, the adaptive least mean squares (LMS) algorithm offers a computationally efficient solution with its simple first-order weight-vector update equation. However, the performance of the LMS algorithm deteriorates in time-varying channels as a result of the eigenvalue disparity, i.e., spread, of the input correlation matrix in such chan nels. In this work, we incorporate the L MS algorithm into the well-known bidirectional processing idea to produce an extension called the bidirectional LMS. This algorithm is shown to be robust to the adverse effects of time-varying channels such as large eigenvalue spread. The associated tracking performance is observed to be very close to that of the optimal Wiener filter in many cases and the bidirectional LMS algorithm is therefore referred to as near-optimal. The computational complexity is observed to increase by the bidirectional employment of the LMS algorithm, but nevertheless is significantly lower than that of the optimal Wiener filter. The tracking behavior of the bidirectional LMS algorithm is also analyzed and eventually a steady-state step-size dependent mean square error (MSE) expression is derived for single antenna flat-fading channels with various correlation properties. The aforementioned analysis is then generalized to include single-antenna frequency-selective channels where the so-called ind ependence assumption is no more applicable due to the channel memory at hand, and then to multi-antenna flat-fading channels. The optimal selection of the step-size values is also presented using the results of the MSE analysis. The numerical evaluations show a very good match between the theoretical and the experimental results under various scenarios. The tracking analysis of the bidirectional LMS algorithm is believed to be novel in the sense that although there are several works in the literature on the bidirectional estimation, none of them provides a theoretical analysis on the underlying estimators. An iterative channel estimation scheme is also presented as a more realistic application for each of the estimation algorithms and the channel models under consideration. As a result, the bidirectional LMS algorithm is observed to be very successful for this real-life application with its increased but still practical level of complexity, the near-optimal tracking performa nce and robustness to the imperfect initialization.
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Mahmoud, Hisham A. "Advanced Transceiver Algorithms for OFDM(A) Systems." Scholar Commons, 2009. http://scholarcommons.usf.edu/etd/3757.
Full textAbstract:
With the increasing advancements in the digital technology, future wireless systems are promising to support higher data rates, higher mobile speeds, and wider coverage areas, among other features. While further technological developments allow systems to support higher computational complexity, lower power consumption, and employ larger memory units, other resources remain limited. One such resource, which is of great importance to wireless systems, is the available spectrum for radio communications. To be able to support high data rate wireless applications, there is a need for larger bandwidths in the spectrum. Since the spectrum cannot be expanded, studies have been concerned with fully utilizing the available spectrum. One approach to achieve this goal is to reuse the available spectrum through space, time, frequency, and code multiplexing techniques. Another approach is to optimize the transceiver design as to achieve the highest throughput over the used spectrum.
From the physical layer perspective, there is a need for a highly flexible and efficient modulation technique to carry the communication signal. A multicarrier modulation technique known as orthogonal frequency division multiplexing (OFDM) is one example of such a technique. OFDM has been used in a number of current wireless standards such as wireless fidelity (WiFi) and worldwide interoperability for microwave access (WiMAX) standards by the Institute of Electrical and Electronics Engineers (IEEE), and has been proposed for future 4G technologies such as the long term evolution (LTE) and LTE-advanced standards by the 3rd Generation Partnership Project (3GPP), and the wireless world initiative new radio (WINNER) standard by the Information society technologies (IST). This is due to OFDM’s high spectral efficiency, resistance to narrow band interference, support for high data rates, adaptivity, and scalability.
In this dissertation, OFDM and multiuser OFDM , also known as orthogonal frequency division multiple access (OFDMA), techniques are investigated as a candidate for advanced wireless systems. Features and requirements of future applications are discussed in detail, and OFDM’s ability to satisfy these requirements is investigated. We identify a number of challenges that when addressed can improve the performance and throughput of OFDM-based systems. The challenges are investigated over three stages. In the first stage, minimizing, or avoiding, the interference between multiple OFDMA users as well as adjacent systems is addressed. An efficient algorithm for OFDMA uplink synchronization that maintains the orthogonality between multiple users is proposed. For adjacent channel interference, a new spectrum shaping method is proposed that can reduce the out-of-band radiation of OFDM signals. Both methods increase the utilization of available spectrum and reduce interference between different users.
In the second stage, the goal is to maximize the system throughput for a given available bandwidth. The OFDM system performance is considered under practical channel conditions, and the corresponding bit error rate (BER) expressions are derived. Based on these results, the optimum pilot insertion rate is investigated. In addition, a new pilot pattern that improves the system ability to estimate and equalize various radio frequency (RF) impairments is proposed.
In the last stage, acquiring reliable measurements regarding the received signal is addressed. Error vector magnitude (EVM) is a common performance metric that is being used in many of today’s standards and measurement devices. Inferring the signal-to-noise ratio (SNR) from EVM measurements has been investigated for either high SNR values or data-aided systems. We show that using current methods does not yield reliable estimates of the SNR under other conditions. Thus, we consider the relation between EVM and SNR for nondata-aided systems. We provide expressions that allow for accurate SNR estimation under various practical channel conditions.
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Yuksekkaya, Mehmet. "Implementation And Performance Analysis Of The Dvb-t Standard System." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12606904/index.pdf.
Full textAbstract:
Terrestrial Digital Video Broadcasting (DVB-T) is a standard for wireless broadcast of MPEG-2 video. DVB-T is based on channel coding algorithms and uses Orthogonal Frequency Division Multiplexing (OFDM) as a modulation scheme.
In this thesis, we have implemented the standard of ETSI EN 300 744 for Digital Video Broadcasting in MATLAB. This system is composed of the certain blocks which include OFDM modulation, channel estimation, channel equalization, frame synchronization, error-protection coding, to name a few of
such blocks. We have investigated the performance of the complete system for different wireless broadcast impairments. In this performance analysis, we have considered Rayleigh fading multi-path channels with Doppler shift and framing
synchronization errors and obtained the bit error rate (BER), and channel minimum square error performances versus different maximum Doppler shift values, different channel equalization techniques and different channel estimation
algorithms. Furthermore, we have investigated different interpolations methods for the interpolation of channel response. It is shown that minimum mean-square error (MMSE) type equalization has a better performance in symbol estimation compared to zero forcing (ZF) equalizer. Also linear interpolation in time and low pass frequency interpolation, for time frequency interpolation of channel response can be used for practical application.
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Nilsson, Lucas. "Estimation of Ship Properties for Energy Efficient Automation." Thesis, Linköpings universitet, Reglerteknik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-133557.
Full textAbstract:
One method to increase efficiency, robustness and accuracy of automatic control, is to introduce mathematical models of the system in question to increase performance. With these models, it is possible to predict the behavior of the system, which enables control according to the predictions. The problem here is that if these models do not describe the dynamics of the system well enough, this method could fail to increase performance. To address this problem, one idea is to estimate the dynamics of the system during operation, using methods for system identification, signal processing and sensor fusion. In this thesis, the possibilities of estimating a ship's dynamics during operation have been investigated. The mathematical model describing the dynamics of the ship is a graybox model, which is based on the physical and mechanical relations. This model's properties are therefore described by physical quantities such as mass and moment of inertia, all of which are unknown. This means that, when estimating the model, these physical properties will be estimated. For a systematic approach, first a simulation environment with a 4-degrees-of-freedom ship model has been developed. This environment has been used for validation of system identification methods. A model of a podded propulsion system has also been derived and validated. The methods for estimating the properties of the ship have been analyzed using the data collected from the simulations. For system identification and estimation of ship properties, the influence of measurement noise and potential of detecting a change in dynamics has been analyzed. This has been done through Monte Carlo simulations of the estimation method with different noise realizations in the simulations, to analyze how the measurement noise affects the variance and bias for the estimates. The results show that variance and bias vary a lot between the parameters and that even a small change in dynamics is visible in some parameter estimates when only ten minutes of data have been used. A method based on cumulative summation (CUSUM) has been proposed and validated to analyze if such a method could yield fast and effective detection of system deviations. The results show that the method is rather effective a with robust detection of changes in the dynamics after about four minutes of data collection. Finally, the methods have been validated on data collected on a real ship to analyze the potential of the methods under actual circumstances. The results show that the particular data is not appropriate for this kind of application along with some additional problems that can yield impaired results.Genom att inkludera matematiska modeller som beskriver ett systems dynamik i styrningsalgoritmer, kan man åstadkomma en automatisk styrning med förbättrad effektivitet, robusthet och noggrannhet. Med dessa modeller går det att förutsäga beteendet hos systemet och därmed öppnas också möjligheten att använda sig av detta i styrningen. Problemet är att om dessa modeller inte beskriver systemets dynamik tillräckligt bra kan prestandan istället sänkas genom dessa metoder. Den här sortens problem kan man lösa genom att aktivt skatta systemets dynamik under körning, med hjälp av metoder för systemidentifiering, signalbehandling och sensorfusion. I denna exjobbsrapport har möjligheterna att skatta ett skepps girdynamik undersökts. Den matematiska modell som beskriver skeppets dynamik är en grålådemodell som baserar sig på fysikaliska och mekaniska samband. Denna modells egenskaper beskrivs därför av fysikaliska storheter så som massa, tröghetsmoment och tyngdpunkt, vilka alla är okända. Detta innebär att vid modellskattning skattas dessa fysikaliska storheter, vilka kan vara av stort intresse. En simuleringsmiljö med en skeppsmodell med fyra frihetsgrader har skapats och använts för att validera metoder för systemidentifiering. En modell av ett roterbart framdrivningssystem har också härletts och inkluderats i simuleringsmodellen. Vid systemidentifiering och skattning av skeppets egenskaper har dels inverkan av mätbrus analyserats samt även möjligheter till att detektera skillnader i dynamik. Detta har gjorts med Monte Carlo-simuleringar av skattningsmetoden med olika brusrealiseringar för att analysera hur mätbrus påverkar variansen och metodfelet hos skattningarna. Resultaten visar att vissa parametrar skattas med större noggrannhet och hos dessa kan därmed en förändring i dynamik identifieras när endast tio minuter av data har använts. En metod baserad på kumulativ summering av residualer har formulerats och validerats, detta för att undersöka om en sådan metod kan ge snabb och effektiv detektion av systemförändringar. Resultat visar på robusthet i att detektera skillnader i dynamik efter ungefär fyra minuter av datainsamling. Slutligen har metoderna validerats på data insamlad på ett riktigt skepp för att undersöka potentialen under verkliga omständigheter. Resultaten visar att just denna data inte är lämplig för denna applikation samt några problem som kan leda till försämrade resultat.
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Shang, Lei, and lei shang@ieee org. "Modelling of Mobile Fading Channels with Fading Mitigation Techniques." RMIT University. Electrical and Computer Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061222.113303.
Full textAbstract:
This thesis aims to contribute to the developments of wireless communication systems. The work generally consists of three parts: the first part is a discussion on general digital communication systems, the second part focuses on wireless channel modelling and fading mitigation techniques, and in the third part we discuss the possible application of advanced digital signal processing, especially time-frequency representation and blind source separation, to wireless communication systems. The first part considers general digital communication systems which will be incorporated in later parts. Today's wireless communication system is a subbranch of a general digital communication system that employs various techniques of A/D (Analog to Digital) conversion, source coding, error correction, coding, modulation, and synchronization, signal detection in noise, channel estimation, and equalization. We study and develop the digital communication algorithms to enhance the performance of wireless communication systems. In the Second Part we focus on wireless channel modelling and fading mitigation techniques. A modified Jakes' method is developed for Rayleigh fading channels. We investigate the level-crossing rate (LCR), the average duration of fades (ADF), the probability density function (PDF), the cumulative distribution function (CDF) and the autocorrelation functions (ACF) of this model. The simulated results are verified against the analytical Clarke's channel model. We also construct frequency-selective geometrical-based hyperbolically distributed scatterers (GBHDS) for a macro-cell mobile environment with the proper statistical characteristics. The modified Clarke's model and the GBHDS model may be readily expanded to a MIMO channel model thus we study the MIMO fading channel, specifically we model the MIMO channel in the angular domain. A detailed analysis of Gauss-Markov approximation of the fading channel is also given. Two fading mitigation techniques are investigated: Orthogonal Frequency Division Multiplexing (OFDM) and spatial diversity. In the Third Part, we devote ourselves to the exciting fields of Time-Frequency Analysis and Blind Source Separation and investigate the application of these powerful Digital Signal Processing (DSP) tools to improve the performance of wireless communication systems.
29
Lau, Buon Kiong. "Applications of Adaptive Antennas in Third-Generation Mobile Communications Systems." Thesis, Curtin University, 2002. http://hdl.handle.net/20.500.11937/2019.
Full textAbstract:
Adaptive antenna systems (AAS's) are traditionally of interest only in radar and sonar applications. However, since the onset of the explosive growth in demand for wireless communications during the 1990's, researchers are giving increasing attention to the use of AAS technology to overcome practical challenges in providing the service. The main benefit of the technology lies in its ability to exploit the spatial domain, on top of the temporal and frequency domains, to improve on transceiver performance. This thesis presents a unified study on two classes of preprocessing techniques for uniform circular arrays (UCA's). UCA's are of interest because of their natural ability to provide a full azimuth (i.e. 360') coverage found in typical scenarios for sensor array applications, such as radar, sonar and wireless communications. The two classes of preprocessing techniques studied are the Davies transformation and the interpolated array transformations. These techniques yield a mathematically more convenient form - the Vandermonde form - for the array steering vector via a linear transformation. The Vandermonde form is useful for different applications such as direction-of-arrival (DOA) estimation and optimum or minimum variance distortionless response (MVDR) beamforming in correlated signal environment and beampattem synthesis. A novel interpolated array transformation is proposed to overcome limitations in the existing interpolated array transformations. A disadvantage of the two classes of preprocessing techniques for UCA's with omnidirectional elements is the lack of robustness in the transformed array steering vector to array imperfections under certain conditions. In order to mitigate the robustness problem, optimisation problems are formulated to modify the transformation matrices.Suitable optimisation techniques are then applied to obtain more robust transformations. The improved transformations are shown to improve robustness but at the cost of larger transformation errors. The benefits of the robustification procedure are most apparent in DOA estimation. In addition to the algorithm level studies, the thesis also investigates the use of AAS technology with respect to two different third generation (3G) mobile communications systems: Enhanced Data rates for Global Evolution (EDGE) and Wideband Code Division Multiple Access (WCDMA). EDGE, or more generally GSM/EDGE Radio Access Network (GERAN), is the evolution of the widely successful GSM system to provide 3G mobile services in the existing radio spectrum. It builds on the TDMA technology of GSM and relies on improved coding and higher order modulation schemes to provide packet-based services at high data rates. WCDMA, on the other hand, is based on CDMA technology and is specially designed and streamlined for 3G mobile services. For WCDMA, a single-user approach to DOA estimation which utilises the user spreading code and the pulse-shaped chip waveform is proposed. It is shown that the proposed approach produces promising performance improvements. The studies with EDGE are concerned with the evaluation of a simple AAS at the system and link levels.Results from, the system and link level simulations are presented to demonstrate the effectiveness of AAS technology in the new mobile communications system. Finally, it is noted that the WCDMA and EDGE link level simulations employ the newly developed COST259 directional channel model, which is capable of producing accurate channel realisations of macrocell environments for the evaluation of AAS's.
30
Lau, Buon Kiong. "Applications of Adaptive Antennas in Third-Generation Mobile Communications Systems." Curtin University of Technology, Australian Telecommunications Research Institute, 2002. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=12983.
Full textAbstract:
Adaptive antenna systems (AAS's) are traditionally of interest only in radar and sonar applications. However, since the onset of the explosive growth in demand for wireless communications during the 1990's, researchers are giving increasing attention to the use of AAS technology to overcome practical challenges in providing the service. The main benefit of the technology lies in its ability to exploit the spatial domain, on top of the temporal and frequency domains, to improve on transceiver performance. This thesis presents a unified study on two classes of preprocessing techniques for uniform circular arrays (UCA's). UCA's are of interest because of their natural ability to provide a full azimuth (i.e. 360') coverage found in typical scenarios for sensor array applications, such as radar, sonar and wireless communications. The two classes of preprocessing techniques studied are the Davies transformation and the interpolated array transformations. These techniques yield a mathematically more convenient form - the Vandermonde form - for the array steering vector via a linear transformation. The Vandermonde form is useful for different applications such as direction-of-arrival (DOA) estimation and optimum or minimum variance distortionless response (MVDR) beamforming in correlated signal environment and beampattem synthesis. A novel interpolated array transformation is proposed to overcome limitations in the existing interpolated array transformations. A disadvantage of the two classes of preprocessing techniques for UCA's with omnidirectional elements is the lack of robustness in the transformed array steering vector to array imperfections under certain conditions. In order to mitigate the robustness problem, optimisation problems are formulated to modify the transformation matrices.Suitable optimisation techniques are then applied to obtain more robust transformations. The improved transformations are shown to improve robustness but at the cost of larger transformation errors. The benefits of the robustification procedure are most apparent in DOA estimation. In addition to the algorithm level studies, the thesis also investigates the use of AAS technology with respect to two different third generation (3G) mobile communications systems: Enhanced Data rates for Global Evolution (EDGE) and Wideband Code Division Multiple Access (WCDMA). EDGE, or more generally GSM/EDGE Radio Access Network (GERAN), is the evolution of the widely successful GSM system to provide 3G mobile services in the existing radio spectrum. It builds on the TDMA technology of GSM and relies on improved coding and higher order modulation schemes to provide packet-based services at high data rates. WCDMA, on the other hand, is based on CDMA technology and is specially designed and streamlined for 3G mobile services. For WCDMA, a single-user approach to DOA estimation which utilises the user spreading code and the pulse-shaped chip waveform is proposed. It is shown that the proposed approach produces promising performance improvements. The studies with EDGE are concerned with the evaluation of a simple AAS at the system and link levels.
Results from, the system and link level simulations are presented to demonstrate the effectiveness of AAS technology in the new mobile communications system. Finally, it is noted that the WCDMA and EDGE link level simulations employ the newly developed COST259 directional channel model, which is capable of producing accurate channel realisations of macrocell environments for the evaluation of AAS's.
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Lin, Yu-Ting, and 林玉婷. "MIMO Signal Detection in the Presence of Channel Estimation Errors." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/30227411867232736630.
Full textAbstract:
碩士國立交通大學
電信工程研究所
98
The multiple-input multiple output (MIMO) technology promises significant capacity increase over conventional single-input single-output systems. Most investigations on MIMO signal detection, however, assume perfect channel state information (CSI), which is difficult, if not impossible, to realize in practice. Earlier studies have shown that that the performance of MIMO detection schemes will suffer from severe degradation in the presence of channel estimation errors. In this thesis, the effects of imperfect CSI on two MIMO signal detectors, namely, the Particle-Swarm-Driven Cross-Entropy (PSD-CE) based detector and the QRD-$M$ detector, are studied, and new detector structures that take into account the CSI error are proposed. The PSD-CE detector tries to estimate and refine the `a posteriori probability distribution' of the transmitted signal location given the received vector. The distribution is estimated by sampling over the neighborhood of the received vector and is iteratively updated to the one which has the minimum cross entropy with respect to the current distribution. It is further modified by applying the concept of Particle Swarm Optimization to render a mixture of probability distribution. QRD-M, on the other hand, is an efficient tree-search based detector. It prunes the earch tree to reduce the number of surviving paths with minimum performance loss. Since the minimum Euclidean distance criterion is no longer suitable for both detectors in the presence of channel estimation errors, the proposed MIMO detectors take into account the imperfect CSI effect by averaging the estimation errors to obtain a new decoding metric. Numerical examples are given to demonstrate the performance improvement which is attained with insignificant complexity increase.
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Lee, Wen-Ming, and 李汶洺. "Optimal Channel Prediction for Training Overhead Reduction in LTE-A Uplink under Channel Estimation Errors." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/99329437505918947192.
Full textAbstract:
碩士國立交通大學
電信工程研究所
100
Energy efficiency is a critical demand in the design of next generation wireless communication systems such as Long Term Evolution (LTE). In this thesis, we study the problem of training overhead reduction for LTE uplink transmission, in which the Single-Carrier Frequency Division Multiple Access (SC-FDMA) modulation is adopted. Motivated by the fact that samples of real-world wireless channels are typically correlated in time, we propose to exploit such temporal correlation to develop a new channel prediction scheme for training overhead reduction. More specifically, assuming that the receiver has acquired a set of channel estimates, based on the linear minimum mean square error (LMMSE) rule, during a few training phases, we develop a LMMSE based channel prediction scheme which explicitly takes account of the effect of channel estimation errors. A closed-form formula for the optimal channel predictor is derived, and the achievable MSE performance is the analytically characterized. The achievable post-detection SNR performance when the predicted channels are employed in the LMMSE equalizer design is also studied. Computer simulations are used to illustrate the performances of the proposed scheme.
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Lin, Dingyi. "Performance analysis of Viterbi decoding in Rayleigh fading with channel estimation errors." Thesis, 2006. http://hdl.handle.net/2429/18293.
Full textAbstract:
Previous studies on the effect of channel estimation errors on the bit error rate (BER) performance of Viterbi decoding (VD) concern various types of fading channels with additive white Gaussian noise (AWGN), modulation and interleaving schemes. Pairwise error probabilities (PEP) have been derived using Laplace transform. Studies of VD on fading channels with impulsive noise and perfect channel estimation are also available in the literature. In this thesis, the BER performance of unquantized VD with BPSK is analyzed for a frequency-nonselective slow Rayleigh fading channel with AWGN and Gaussian distributed channel estimation errors. Closed-form expressions for the PEP are derived. Upper bound and lower bound on the BER are obtained. It is shown that channel estimation errors have the same effect on BER as channel noise. Computer simulation results show that the upper bound is fairly tight. In practice, the channel might be estimated using pilot symbols, together with various interpolation filters. It is shown that the channel estimation error variances are usually unequal for different data symbol positions. The BER performance of VD optimized for unequal estimation error variances is compared with that of VD optimized for equal variances using computer simulation. The BER performance of VD in Rayleigh fading and impulsive noise with channel estimation error is also studied. The optimal metrics are derived for VD in Rayleigh fading with Gaussian channel estimation errors, for Laplacian noise and Gaussian mixture noise. The BER performances of VD’s for various scenarios are compared.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Liu, Chia-Chieh, and 劉家杰. "The Performance of STBC-VBLAST with Interference Cancellation and Channel Estimation Errors." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/9myy5s.
Full textAbstract:
碩士國立臺北科技大學
電腦與通訊研究所
94
Vertical Bell Labs Layered Space-Time (VBLAST) is a spatial multiplexing scheme and can provide huge data rate by using multiple antennas. At the receiver of VBLAST, a successive processing, nulling and interference cancellation, which consumes high computation to reconstruct the information, is required. Therefore, we propose a method, partial interference cancellation (PIC), to reduce the complexity. By this way, the number of the layers required to be cancelled are evaluated first. After canceling only these layers, the performance will still be close to that of the original VBLAST, and the computation can be reduced. On the other hand, the BER of VBLAST is not good enough. Although increasing the number of receive antenna N can enlarges the diversity order and improves the performance, it is not suitable for downlink transmission where the receiver has limited resource (e.g. power and size). As a result, the space-time block coding (STBC), an effective transmit diversity scheme, can be utilized on the first detected layers to provide the diversity gain. This system incorporating the STBC and VBLAST schemes is called STBC-VBLAST. Different form the traditional combination of STBC and VBLAST (parallel STBC), the STBC encoders are applied into only a few layers of VBLAST in STBC-VBLAST, which are detected first, and dominates the system performance. Thus, the system performance can be improved by the increased diversity. Additionally, in order to make our analysis be close to the real environment, the channel state information (CSI) is assumed non-perfect in STBC-VBLAST scheme. We apply training sequence to estimated CSI. Finally, the derivation of BER for STBC-VBLAST with interference cancellation and channel estimation errors is proposed. It is helpful for the system design.
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chien-yu, lin, and 林倩羽. "Design of Robust Receiver for Space-Time Block Coded Multi-user MIMO System under Channel Estimation Errors." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/05547305823968857905.
Full textAbstract:
碩士國立交通大學
電信工程系所
96
It is well known that space-time block coding (STBC) has emerged as a popular technique in multiple-input multiple-output (MIMO) wireless communication, especially for multi-user cases. Several linear receiver algorithms have been developed for such a system where multi-access inference (MAI) causes a problem. A common shortcoming of all these techniques, however, is that they are all developed based on the perfect channel assumption. Channel estimation errors do happen in practical situations due to the limited training symbols or severe fading channels. In this thesis, new robust linear receivers for joint space-time decoding and interference rejection in orthogonal space-time block coded multi-user MIMO systems are proposed for combating imperfect channel estimation. The proposed receivers are developed based on the constrained optimization design which can be transformed to an equivalent unconstrained one by the generalized sidelobe canceller (GSC) technique. By using the perturbation techniques, the channel estimation error term can be incorporated into the receiver design. We also apply the successive interference cancellation (SIC) mechanism for further performance enhancement. Numerical simulations confirm the robustness of the proposed receiver when compared with the other existing techniques.
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Basri, Amir Ali. "Wireless Communication over Fading Channels with Imperfect Channel Estimates." Thesis, 2008. http://hdl.handle.net/1807/16745.
Full textAbstract:
In wireless communication systems, transmitted signals are corrupted by fading as well as noise. The receiver can benefit from the estimates of fading channels to detect the transmitted symbols. However, in practical wireless systems channel information cannot be estimated perfectly at the receiver. Therefore, it is crucial to examine the effect of channel estimation error on the structure and performance of the receivers. In the first part of the thesis, we study single-user systems with single-antenna reception over fading channels in the presence of Gaussian-distributed channel estimation error. By using the statistical information of the channel estimation error, we will derive the structure of maximum-likelihood receivers for a number of different modulation formats and then analyze their performance over fading channels. In the second part of the thesis, we consider the uplink of multi-user wireless systems with multi-antenna reception. For conventional diversity combining techniques such as maximal ratio combining and optimum combining we analyze the performance degradation due to imperfect channel estimates in the presence of multiple interfering users for several fading channels. By investigating the probability density function of the output signal-to-interference ratio, we will derive analytical expressions for several performance measures such as the average signal-to-interference ratio, outage probability and average bit-error probability. These expressions quantify performance degradation due to channel estimation error.
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Liao, Jing-Luen, and 廖經倫. "The Impact of Estimation Error on Channel Estimation-Based Equalizer for UWA Channel." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/68785692990239570269.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
99
Underwater acoustic channels are generally recognized as one of the most difficult communication media in use today. The ocean is a time and spatially varying propagation environment. The underwater acoustic propagation is best supported at low frequencies, and the bandwidth available for communication is extremely limited. The underwater acoustic communication differ from RF communication in two aspects: One is the long multipath delay time that containing ten to hundreds of symbols, and the other is the rapid time variation of underwater acoustic channel. The receiver structure that has been found useful in many applications is a decision-feedback equalizer(DFE). Due to the nature of the propagation channel, the required signal processing is often prohibitively complex, to reduce computational complexity of signal processing, the receiver structures that are matched to the physical channel characteristics are investigates. A channel estimation-based equalization which relies on an adaptive channel estimation to compute its parameters, this estimation is used to cancel the post-cursor ISI before the linear equalization. The impact of estimation error on the channel estimation-based equalizer are investigated.
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Huang, Chun-Fu, and 黃俊富. "Effects of Channel Estimation Error on the BER Performance of OFDM Systems in Multipath Rayleigh Slowly Fading Channels." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/30489132297639351425.
Full textAbstract:
碩士淡江大學
電機工程學系碩士班
95
In this thesis, we study the effects of channel estimation error on the bit error probability of orthogonal frequency division multiplexing (OFDM) systems in multipath Rayleigh slowly fading channels. The channel estimation errors come from the additive white Gaussian noise (AWGN) and intercarrier interference (ICI) caused by the residual frequency offset (CFO) We derive the bit error rate (BER) formulas for BPSK, QPSK, 16-QAM, and64-QAM modulation schemes to characterize the performance degradation resulting from imperfect channel state information (CSI). Without complex numerical integrals in our BER formulas, they can be evaluated easily and accurately. Simulation results verify the correctness of our theoretical analysis.
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Chang, Huei-Ya, and 張惠雅. "Trellis Code Design for Combined Channel Estimation and Error Correction." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/44792420463766323966.
Full textAbstract:
碩士國立交通大學
電信工程研究所
99
In this thesis, we attempt to decrease the decoding complexity of self-orthogonal tree-structure codes designed for combined channel estimation and error correction by fitting them into a trellis structure subject to an upper bound on the number of trellis states at each level. Specifically, we provide an algorithm to compress the tree-structure codes into a trellis structure by selectively merging tree nodes. Simulations show that the more the merged nodes, the less the memory consumption and decoding complexity, but the worse the performance. A trade-off among these factors can therefore be controlled by a proper choice of maximum number of trellis states.
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Fu, Po-Chun, and 傅柏鈞. "Channel Estimation Error and SIR Distribution for 5G Uplink Transmission." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/31951196604366091378.
Full textAbstract:
碩士國立交通大學
電信工程研究所
104
Our proposed 5G multipath division multiple access (MDMA) system is an interferencelimited system. As in the previous CDMA system, the signal to interference (SIR) distribution has a major impact on the system capacity. However, the performance of channel estimation affects SIR distribution as well. In this thesis, for the massive MISO antenna based system, the combined behavior of channel estimation and data detection in multiuser detection are investigated. In order to evaluate the system performance, the key parameters which affect system behavior can be obtained from analysis and simulation. These parameters are important for the research and development of the future 5G cellular system.
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Lu, Yuan-Chieh, and 呂元介. "Carrier Frequency Offest Estimation Bounds with Channel Estimation Error for OFDM Multi-Relay Systems." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/vn8pre.
Full textAbstract:
碩士國立東華大學
電機工程學系
105
With increasingly high demand for communication and transmission, the cooperative relay network system can contribute to high-speed, high-volume and high-quality requirements, and not only can Orthogonal Frequency Division technology improve the transmission rate, but it also can resist the multi-path channel attenuation. Because of the orthogonality of the signal, however, the orthogonal frequency multiplier will degrade the system performance. Hence, this thesis is dedicated to the application in the orthogonal frequency division multiplexing multiple relay system with channel estimation error under the carrier frequency offset estimation limit. In this thesis, we first derive the mathematical formula of the carrier frequency offset (CFO) estimation of the relay network system under the known parameters, namely Fisher Information Matrix (FIM). Then, the parameters in the channel are replaced by the sum of the estimated channel and the channel error, and the corresponding Fisher information matrix is corrected by using the estimation model of the random transformation, and the Cramer-Rao bound (CRB). Finally, we will observe the results obtained by different parameters to observe the channel estimation error on the carrier frequency offset estimation. The results of the simulation can be used as an important reference for future comparison and future design of a relay network system. Keyword：Cooperative Communication、MIMO 、OFDM、Relay Network、Carrier Frequency Offset、CRLB。
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Ruan, Ting-Liang, and 阮庭亮. "Carrier Frequency Offset Estimation Bounds with channel Estimation error for OFDM-based Relay Networks." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/kew24n.
Full textAbstract:
碩士國立東華大學
電機工程學系
102
Cooperative relay network system in which future mobile communication system plays an important role. The orthogonal frequency division multiplexing technology can provide higher transmission rates and resistance multipath channel fading. However, the carrier frequency offset will cause the orthogonal frequency division multiplexing signals orthogonality damage and reduce system performance. Therefore, this paper will focus on applied orthogonal frequency division multiplexing system relay network with a carrier frequency of the channel estimation error under the offset estimation performance analysis. We first derive the relay network system known in the carrier frequency offset estimate channel parameters under the Fisher information matrix. Generation will be one of the channel parameters and then replaced by the sum of the channel and the channel estimation error. Through random estimation error model, we can fix the corresponding Fisher information matrix, and then calculate the Cramer-Rao bound. In addition, we also simulate different parameters through to observe the channel estimation error on the carrier frequency offset estimate the impact. The simulation results can be provided as an important reference for future design relay network system.
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Shih-Chang, Chen, and 陳世昌. "Channel Estimation Error Tolerable Multiuser Detection for DS-CDMA UWB Systems." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/30915896587560012188.
Full text
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Nwaekwe, Chinwe M. "Channel estimation in a two-way relay network." Thesis, 2011. http://hdl.handle.net/10155/174.
Full textAbstract:
In wireless communications, channel estimation is necessary for coherent symbol detection.
This thesis considers a network which consists of two transceivers communicating
with the help of a relay applying the amplify-and-forward (AF) relaying scheme. The
training based channel estimation technique is applied to the proposed network where
the numbers of the training sequence transmitted by the two transceivers, are different.
All three terminals are equipped with a single antenna for signal transmission and reception.
Communication between the transceivers is carried out in two phases. In the
first phase, each transceiver sends a transmission block of data embedded with known
training symbols to the relay. In the second phase, the relay retransmits an amplified
version of the received signal to both transceivers. Estimates of the channel coefficients
are obtained using the Maximum Likelihood (ML) estimator. The performance analysis
of the derived estimates are carried out in terms of the mean squared error (MSE) and
we determine conditions required to increase the estimation accuracy.UOIT
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Chen, Yi-Hsin, and 陳詒欣. "QPSK-modulated Code Design for Combined Channel Estimation and Error Correction on a Frequency-selective Fading Channel." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/29506456345560987669.
Full textAbstract:
碩士國立交通大學
電信工程研究所
99
In this thesis, we design and examine the QPSK-modulated codes for combined channel estimation and error protection over frequency-selective channels. We found that when QPSK modulation is considered, phase information of the channel coefficients is more essential than the respective amplitude information, particularly for the blind receiver we are interested in. Under the assumption that the unknown phases are synchronized among different channel taps, we establish a close-form-expressed union bound for the error performance and later use it as a criterion to search for the optimal code design. Our simulations show that the QPSK-modulated codes can provide an acceptable improvement over the BPSK-modulated codes.
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Li, Sheng-Hung, and 李聖弘. "Performance Analysis of Relay Selection in Two-Way Relay Networks with Channel Estimation Error." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/8msjk8.
Full textAbstract:
碩士國立中山大學
通訊工程研究所
103
The impact of channel estimation errors is investigated in two-way relay networks (TWRNs) with two different channel state information (CSI) estimation schemes, namely, cascaded and separate. In the cascaded scheme, the relay node is selected on the basis of the CSI of the individual channels between the source nodes and the relay node. In the separate scheme, relay node selection is based on the CSI of the cascaded channel between the two source nodes. For both estimation schemes, the effect of the CSI estimation error on the outage probability is examined by Cramer-Rao lower bound. Contrary to previous reports, the source nodes in the TWRN are assumed to yield different estimation errors. Numerical results confirm the validity of the derived expression and indicate that the presence of different estimation errors at the two source nodes can significantly influence the performance of the TWRN. However, we extend the relay selection problem to non-reciprocal TWRNs. We propose a selection scheme based on the concept of censoring rule, in which each relay node can decide whether the received signal should be forwarded. This method can save a level of transmission power and maintain the diversity gain without gathering all of the CSI between the source nodes and relay nodes at a central node. The effectiveness of the proposed scheme is evident in the simulation results.
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Huang, Yu-Hsuan, and 黃鈺軒. "Performance Analysis of Uplink MIMO-NOMA Systems in the Presence of Channel Estimation Error." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/trcybe.
Full textAbstract:
碩士國立中央大學
通訊工程學系
106
This paper analyzes the performance of Non-orthogonal multiple access (NOMA) in the presence of channel estimation error for an uplink Multiple Input Multiple Output (MIMO) system with N antennas at base station (BS) and one transmit antenna per 2N users. We investigate the performance of perfect and imperfect channel estimation by utilizing two different beamforming weight matrices methods, which are zero-forcing (ZF) and minimum mean square error (MMSE). In each situation, the calculation of capacity is derived from the signal to interference plus noise ratio (SINR), and then we examine the performance through those data. Furthermore, the perfect successive interference cancellation (SIC) can be utilized when the channel state information (CSI) is perfect, but it cannot be achieved in the presence of channel estimation error. By comparing the performance of simulation results, we notice that without perfect CSI, the MMSE beamforming is a better choice in the uplink NOMA system since MMSE offers better sum capacity and bit error rate.
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Jiang, Zhengwei. "Performance of Full-rate Full-diversity Space-time Codes Under Quantization and Channel Estimation Error." Thesis, 2010. http://hdl.handle.net/1807/25640.
Full textAbstract:
In this work, we investigate the performance of full-rate full-diversity space-time codes (FRFD-STCs) under practical conditions. In this thesis, we first discuss the performance of FRFD-STCs in the moderate SNR region. We also compare FRFD-STCs with spatial multiplexing, using the same transmission rate, for both un-coded and coded systems. The results show that spatial multiplexing is as good as FRFD-STCs with channel coding. Secondly, we investigate the issue of quantization, i.e. the effect of the quantization error in the space-time encoding matrix. Our analysis and results show that the performance loss is negligible. Finally, we propose two receiver structures in the presence of imperfect channel state information (CSI). The two receivers use the VEM module as the channel estimator and MIMO detector respectively. Both receivers are of low complexity, and have better performance than the methods proposed previously.
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Wu, Chia-Lung, and 吳佳龍. "Systematic Code Design for Combined Channel Estimation and Error Correction and Its Maximum-Likelihood Decoding." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/26108324808807951686.
Full textAbstract:
博士國立交通大學
電信工程系所
97
A traditional communication system uses separate training sequence for the estimation of channel state information (CSI) at the receiver. This channel estimation will then be used as a base for error correction through channel codes. In applications that channel estimation at the receiver is either of infeasibly high complexity or statistically impossible, noncoherent system design apparently becomes the due selection. At this background, we study the coding scheme that can be applied in an environment that the channel coefficients are completely unknown to both the transmitters and receivers. We subsequently investigate efficient decoding algorithms for our proposed codes. In fact, the coding technique that combines channel estimation and error correction has received attention recently, and has been regarded as a promising approach to counter the effects of multi-path fading. It has been shown by simulation that a proper code design that jointly considers channel estimation can improve the system performance subject to a fixed code rate as compared to a conventional system which performs channel estimation and error correction separately. Nevertheless, the major obstacle that prevents the practice of such coding technique is that the existing codes are mostly searched by computers, and subsequently exhibit no apparent structure for efficient decoding. Hence, the operation-intensive exhaustive search becomes the only decoding option, and the decoding complexity increases dramatically with codeword length. In this dissertation, a systematic construction is derived for a class of structured codes that support joint channel estimation and error correction. The extension designs that take into consideration the varying characteristic of channels and multiple-input multiple-output channels are also discussed. Simulations show that our codes have comparable performance to the best simulated-annealing-based computer-searched codes. Moreover, the systematically constructed codes can now be maximum-likelihoodly decoded with respect to the unknown-channel criterion in terms of a newly derived recursive metric for use by the priority-first search decoding algorithm. Thus, the decoding complexity is significantly reduced as compared with that of an exhaustive decoder.
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Wang, Chenyuan. "Performance evaluation and enhancement for AF two-way relaying in the presence of channel estimation error." Thesis, 2012. http://hdl.handle.net/1828/3954.
Full textAbstract:
Cooperative relaying is a promising diversity achieving technique to provide reliable transmission, high throughput and extensive coverage for wireless networks in a variety of applications. Two-way relaying is a spectrally efficient protocol, providing one solution to overcome the half-duplex loss in one-way relay channels. Moreover, incorporating the multiple-input-multiple-output (MIMO) technology can further improve the spectral efficiency and diversity gain. A lot of related work has been performed on the two-way relay network (TWRN), but most of them assume perfect channel state information (CSI). In a realistic scenario, however, the channel is estimated and the estimation error exists. So in this thesis, we explicitly take into account the CSI error, and investigate its impact on the performance of amplify-and-forward (AF) TWRN where either multiple distributed single-antenna relays or a single multiple-antenna relay station is exploited.
For the distributed relay network, we consider imperfect self-interference cancellation at both sources that exchange information with the help of multiple relays, and maximal ratio combining (MRC) is then applied to improve the decision statistics under imperfect signal detection. The system performance degradation in terms of outage probability and average bit-error rate (BER) are analyzed, as well as their asymptotic trend. To further improve the spectral efficiency while maintain the spatial diversity, we utilize the maximum minimum (Max-Min) relay selection (RS), and examine the impact of imperfect CSI on this single RS scheme. To mitigate the negative effect of imperfect CSI, we resort to adaptive power allocation (PA) by minimizing either the outage probability or the average BER, which can be cast as a Geometric Programming (GP) problem. Numerical results verify the correctness of our analysis and show that the adaptive PA scheme outperforms the equal PA scheme under the aggregated effect of imperfect CSI.
When employing a single MIMO relay, the problem of robust MIMO relay design has been dealt with by considering the fact that only imperfect CSI is available. We design the MIMO relay based upon the CSI estimates, where the estimation errors are included to attain the robust design under the worst-case philosophy. The optimization problem corresponding to the robust MIMO relay design is shown to be nonconvex. This motivates the pursuit of semidefinite relaxation (SDR) coupled with the randomization technique to obtain computationally efficient high-quality approximate solutions. Numerical simulations compare the proposed MIMO relay with the existing nonrobust method, and therefore validate its robustness against the channel uncertainty.Graduate