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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Receiver Design and Performance Study for Amplify-and-Forward Cooperative Diversity Networks with Reduced CSI Requirement

LIU, PENG 25 June 2014 (has links)
This thesis aims to tackle the theoretical challenges of characterizing the fundamental performance limits of amplify-and-forward (AF) cooperative networks and to resolve the practical challenges in the receiver design for AF systems. First of all, we study the Shannon-theoretic channel capacity which serves as a benchmark for practical wireless communications systems. Specifically, we derive exact expressions of the ergodic capacity in a single-integral form for general multi-branch AF relay networks with/without the direct link (DL). Moreover, we derive closed-form and tight upper bounds on the ergodic capacity, which facilitate the evaluation of the ergodic capacity. These expressions provide useful theoretical tools for the design of practical wireless AF relaying systems. We then tackle the practical challenges involved in the design of AF receivers, aiming to substantially reduce the channel state information (CSI) signaling overhead yet achieving satisfactory error performance. We take the maximum-likelihood (ML) and generalized likelihood ratio test (GLRT) approaches to develop detectors under four typical wireless communications scenarios with little/no knowledge of the CSI. Firstly, for a semi-coherent scenario where only the product of channel coefficients of each relay branch is known, we develop the ML symbol-by-symbol (SBS) detector, which reduces the instantaneous CSI signaling overhead by 50% while achieving comparable performance to the ideal coherent receiver. Secondly, for the noncoherent scenario with only the (second-order) channel statistics and noise variances, we develop a noncoherent ML SBS detector for AF networks employing differential modulations. Thirdly, for AF networks with only the knowledge of the noise variance, we develop a sequence detector using GLRT. Lastly, for a completely blind scenario where the instantaneous CSI, channel statistics, and noise variances are all unknown, we develop a GLRT-based sequence detector. The proposed detectors achieve significant performance improvements over the state-of-the-art counterparts. The conducted theoretical analysis and practical design will facilitate the design of reliable communications over wireless AF networks with reduced CSI requirement. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2014-06-25 16:48:05.912
2

A Proposal for Efficient Use of the Television Spectrum

Weiss, Martin 22 July 2002 (has links)
It is widely recognized that broadcast spectrum is utilized inefficiently. The principle technical cause of this inefficiency is inexpensive receiver design. In addition, the economics of the industry are such that users do not pay the opportunity costs of spectrum associated with these receivers. In this paper, I develop an approach that would internalize the spectrum opportunity costs so that consumers will make decisions that are economically more rational in terms of their choice of the program delivery channel.
3

New Results on Selection Diversity over Fading Channels

Zhao, Qiang 05 March 2003 (has links)
This thesis develops a mathematical framework for analyzing the average bit error rate performance of five different selection diversity combining schemes over slow, frequency non-selective Rayleigh, Nakagami-m and Ricean fading channels. Aside from the classical selection diversity, generalized selection combining and the "maximum output" selection methods, two new selection rules based on choosing the branch providing the largest magnitude of log-likelihood ratio for binary phase shift keying signals (with and without phase compensation in the selection process) are also investigated. The proposed analytical framework is sufficiently general to study the effects of dissimilar fading parameter and unequal mean received signal strengths across the independent diversity paths. The effect of branch correlation on the performance of a dual-diversity system is also studied. The accuracies of our analytical expressions have been validated by extensive Monte-Carlo simulation runs. The proposed selection schemes based on the log-likelihood ratio are attractive in the design of low-complexity rake receivers for wideband CDMA and ultra wideband communication systems. / Master of Science
4

Analytical Frameworks of Cooperative and Cognitive Radio Systems with Practical Considerations

Khan, Fahd Ahmed 08 1900 (has links)
Cooperative and cognitive radio systems have been proposed as a solution to improve the quality-of-service (QoS) and spectrum efficiency of existing communication systems. The objective of this dissertation is to propose and analyze schemes for cooperative and cognitive radio systems considering real world scenarios and to make these technologies implementable. In most of the research on cooperative relaying, it has been assumed that the communicating nodes have perfect channel state information (CSI). However, in reality, this is not the case and the nodes may only have an estimate of the CSI or partial knowledge of the CSI. Thus, in this dissertation, depending on the amount of CSI available, novel receivers are proposed to improve the performance of amplify-and forward relaying. Specifically, new coherent receivers are derived which do not perform channel estimation at the destination by using the received pilot signals directly for decoding. The derived receivers are based on new metrics that use distribution of the channels and the noise to achieve improved symbol-error-rate (SER) performance. The SER performance of the derived receivers is further improved by utilizing the decision history in the receivers. In cases where receivers with low complexity are desired, novel non-coherent receiver which detects the signal without knowledge of CSI is proposed. In addition, new receivers are proposed for the situation when only partial CSI is available at the destination i.e. channel knowledge of either the source-relay link or the relay-destination link but not both, is available. These receivers are termed as `half-coherent receivers' since they have channel-state-information of only one of the two links in the system. In practical systems, the CSI at the communicating terminals becomes outdated due to the time varying nature of the channel and results in system performance degradation. In this dissertation, the impact of using outdated CSI for relay selection on the performance of a network where two sources communicate with each other via fixed-gain amplify-and-forward relays is studied and for a Rayleigh faded channel, closed-form expressions for the outage probability (OP), moment generating function (MGF) and SER are derived. Relay location is also taken into consideration and it is shown that the performance can be improved by placing the relay closer to the source whose channel is more outdated. Some practical issues encountered in cognitive radio systems (CRS) are also investigated. The QoS of CRS can be improved through spatial diversity which can be achieved by either using multiple antennas or exploiting the independent channels of each user in a multi-user network. In this dissertation, both approaches are examined and in multi-antenna CRS, transmit antenna selection (TAS) is proposed where as in a multi-user CRS, user selection is proposed to achieve performance gains. TAS reduces the implementation cost and complexity and thus makes CRS more feasible. Additionally, unlike previous works, in accordance with real world systems, the transmitter is assumed to have limited peak transmit power. For both these schemes, considering practical channel models, closed-form expression for the OP performance, SER performance and ergodic capacity (EC) are obtained and the performance in the asymptotic regimes is also studied. Furthermore, the OP performance is also analyzed taking into account the interference from the primary network on the cognitive network.
5

Design and Implementation of a Pilot Signal Scanning Receiver for CDMA Personal Communication Services Systems

Blankenship, T. Keith III 04 May 1998 (has links)
In cellular and personal communications services (PCS) systems based on code division multiple access (CDMA), a pilot signal is used on the forward link for synchronization, coherent detection, soft handoff, maintaining orthogonality between base stations, and, in the future, position location. It is critical that the percentage of power allocated to the pilot signal transmitted by each base station be fixed properly to ensure the ability of the CDMA network to support subscriber demand. This thesis reports on the design and implementation of a prototype receiver for measuring pilot signals in CDMA PCS systems. Since the pseudonoise (PN) signal of the pilot channel is a priori information, the receiver searches for pilot signals by digitally correlating the received signal with this known, locally generated pilot signal. By systematically changing the phase of this locally generated pilot signal, the receiver scans the received signal to identify all possible signs of pilot signal activity. Large values of correlation indicate the presence of a pilot signal at the particular phase of the locally generated pilot signal. The receiver can also detect multipath components of the pilot signal transmitted from a given base station. One issue associated with this receiver is its ability to keep the signal power within the dynamic range of the analog-to-digital (A/D) converter at its input. This necessitated the design of an automatic gain control (AGC) mechanism, which is digitally implemented in this receiver. Simulation studies were undertaken to assist in the design and implementation of the pilot signal scanning receiver. These simulations were used to quantify how various non-idealities related to the radio frequency (RF) front-end and A/D converter adversely affect the ability of the digital signal processing algorithms to detect and measure pilot signals. Because the period of the pilot signal is relatively long, methods were developed to keep the receiver's update period as small as possible without compromising its detection ability. Furthermore, the high sampling rate required strains the ability of the digital logic to produce outputs at a rate commensurate with real-time operation. This thesis presents techniques that allow the pilot signal scanning receiver to achieve real-time operation. These techniques involve the judicious use of partial correlations and windowing the received signal to decrease the transfer rate from the A/D converter to the digital signal processor. This thesis provides a comprehensive discussion of these and other issues associated with the actual hardware implementation of the pilot signal scanning receiver. / Master of Science
6

Adaptive Thresholding for Detection of Radar Receiver Signals

Benson, Stephen R. 01 November 2010 (has links)
No description available.
7

A close range baseband radar transceiver for application in borehole radar systems

Van der Merwe, P.J. (Paulus Jacobus) 12 1900 (has links)
Thesis (PhD (Electrical and Electronic Engineering)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: A monostatic baseband radar is required with the capability of detecting close range targets that appear at distances comparable to the system’s resolution, without compromising the radar’s maximum range. The application in borehole radar imposes further constraints associated with the physical limitations and variable electromagnetic environment of different borehole diameters and conditions. This dissertation discusses the complete design process of the analog section of a monostatic radar that successfully addresses these issues. The proposed transceiver employs a series duplexing arrangement consisting of an antenna, transmitter, receiver and an isolation switch. An exponentially decaying tail is observed in the current flowing on a borehole radar antenna when excited by pulse waveforms. The characteristics of this tail depend strongly on the borehole environment. A measurement technique is developed that accurately quantifies this exponential decay by digitizing a logarithmic representation of the antenna current while it is operating in various boreholes. Transmitters are then designed to drive these antennas with waveforms that prevent the formation of current tails. This is achieved through the use of pole-zero networks or alternatively by generating certain asymmetric, bipolar waveforms. The transmitters are simultaneously designed to have an output impedance approximating a short circuit after the transient is generated. In the series configuration proposed here, the duplexing of the antenna between transmitter and receiver is then reduced to simply isolating the receiver during transmit-mode. The switch responsible for this isolation disconnects the receiver and presents a short circuit between antenna and transmitter during transmit-mode, while connecting the receiver terminals between the antenna and the short circuited transmitter terminals in receive-mode. The required close-in performance of the transceiver dictates that the transition between these two states of the isolation switch occur in a time similar to the duration of the transmitter waveform. The switching artefacts generated by the switch are consequently similar to the radar data signal. The isolation switch employs an innovative configuration (using both transistors and diodes) which accepts a single control signal and causes the switching artefacts to be generated as a common mode signal, while a differential path is created for the radar data signal which is being switched. This leads to effective suppression of the switching signal in the signal passed to the receiver. Dissipative filtering is advocated as a fundamental design principle for high fidelity receivers and it is shown how it can be applied by using constant impedance equalizers and diplexers as basic building blocks. This principle is used as the basis for the design of this transceiver's receivers, which incorporate both standard gain blocks and operational amplifiers. A complete borehole radar system, based on the transceiver developed here, was built and tested; resulting in the first known practical monostatic borehole radar system. Data obtained in field trials are presented and suggest that the monostatic system compares well with current state of the art bi-static systems. / AFRIKAANSE OPSOMMING: Die behoefte is geïdentifiseer vir 'n monostatiese basisbandradar wat oor die vermoë beskik om nabygeleë teikens op 'n afstand soortgelyk aan die resolusie van die stelsel waar te neem, sonder om die maksimum bereik van die stelsel in te kort. Die toepassing daarvan in 'n boorgatradarstelsel lei tot verdere vereistes vanweë die fisiese beperkings en veranderende elektromagnetiese omgewing van boorgate met verskillende deursnitte en toestande. Hierdie proefskrif is gemoeid met die volledige ontwerpsprosedure van die analoog gedeelte van 'n monostatiese radar wat al hierdie kwessies aanspreek. 'n Serie verbinding van antenne, sender, ontvanger en isolasieskakelaar word ingespan vir hierdie ontwerp. Eksponensieel wegsterwende stertjies word waargeneem in die antennestroom van 'n boorgatradarantenne wanneer dit aangedryf word deur puls golfvorms. 'n Meettegniek word ontwikkel wat hierdie eksponensiële verslapping noukeurig kan monitor deur 'n logaritmiese voorstelling van die antennastroom te versyfer terwyl dit ontplooi word in verskillende boorgate. Senders word dan ontwikkel om hierdie antennes aan te dryf met golfvorms wat juis die vorming van hierdie stertjies voorkom. Dit word bewerkstellig deur die gebruik van pool-zero netwerke of andersins deur die opwek van sekere asimmetriese, bipolêre golfvorms. Die senders se uittree-impedansies moet egter terselfdertyd ontwerp word om 'n kortsluiting te benader sodra die oorgang klaar opgewek is. Met die serie verbinding wat hier gebruik word, raak die vereiste tyddeling van die antenna tussen die sender en ontvanger dan bloot 'n geval van ontvanger-isolasie gedurende uitsaai-modus. Die skakelaar wat verantwoordelik is vir hierdie isolasie ontkoppel die ontvanger en vertoon soos 'n kortsluiting tussen sender en antenne tydens uitsaai-modus, maar verbind weer die terminale van die ontvanger tussen die antenne en kortgeslote senderterminale tydens ontvang-modus. Die vereiste kortafstand vermoë van die stelsel veroorsaak dat die tysduur van die oorgang tussen hierdie twee modusse soortgelyk is aan dié van die sender golfvorm en enige skakelverskynsels wat opgewek word deur die skakelaar is gevolglik soortgelyk aan die radardatasein self. Die isolasieskakelaar gebruik egter 'n innoverende konfigurasie (met transistors sowel as diodes) wat funksioneer met 'n enkele beheersein en die skakelverskynsels as gemene modus seine opwek, terwyl 'n differensiële seinpad geskep word vir die radardatasein wat geskakel word. Die skakelseine word gevolglik effektief onderdruk in die sein wat oorgedra word aan die ontvanger. Die gebruik van verkwistende filters word voorgestel as 'n fundamentele ontwerpsbeginsel vir hoëtrou ontvangers en daar word getoon hoe dit toegepas kan word met konstante impedansie vereffeningsbane en dipleksers. Hierdie beginsel is dan ook gebruik as basis vir die ontwerp van hierdie stelsel se ontvangers, wat gebruik maak van beide standard aanwinsblokke sowel as operasionel versterkers. 'n Volledige boorgatradarstelsel, gebaseer op die stelsel wat hier ontwikkel is, is gebou en getoets. Die gevolg is die eerste bekende, praktiese monostatiese boorgatradarstelsel. Data wat hiermee verwerf is word aangebied en dui daarop dat die monostatiese stelsel baie goed opweeg teen huidige bi-statiese stelsels.
8

Wireless receiver designs: from information theory to VLSI implementation

Zhang, Wei Zhang 06 October 2009 (has links)
Receiver design, especially equalizer design, in communications is a major concern in both academia and industry. It is a problem with both theoretical challenges and severe implementation hurdles. While much research has been focused on reducing complexity for optimal or near-optimal schemes, it is still common practice in industry to use simple techniques (such as linear equalization) that are generally significantly inferior. Although digital signal processing (DSP) technologies have been applied to wireless communications to enhance the throughput, the users' demands for more data and higher rate have revealed new challenges. For example, to collect the diversity and combat fading channels, in addition to the transmitter designs that enable the diversity, we also require the receiver to be able to collect the prepared diversity. Most wireless transmissions can be modeled as a linear block transmission system. Given a linear block transmission model assumption, maximum likelihood equalizers (MLEs) or near-ML decoders have been adopted at the receiver to collect diversity which is an important metric for performance, but these decoders exhibit high complexity. To reduce the decoding complexity, low-complexity equalizers, such as linear equalizers (LEs) and decision feedback equalizers (DFEs) are often adopted. These methods, however, may not utilize the diversity enabled by the transmitter and as a result have degraded performance compared to MLEs. In this dissertation, we will present efficient receiver designs that achieve low bit-error-rate (BER), high mutual information, and low decoding complexity. Our approach is to first investigate the error performance and mutual information of existing low-complexity equalizers to reveal the fundamental condition to achieve full diversity with LEs. We show that the fundamental condition for LEs to collect the same (outage) diversity as MLE is that the channels need to be constrained within a certain distance from orthogonality. The orthogonality deficiency (od) is adopted to quantify the distance of channels to orthogonality while other existing metrics are also introduced and compared. To meet the fundamental condition and achieve full diversity, a hybrid equalizer framework is proposed. The performance-complexity trade-off of hybrid equalizers is quantified by deriving the distribution of od. Another approach is to apply lattice reduction (LR) techniques to improve the ``quality' of channel matrices. We present two widely adopted LR methods in wireless communications, the Lenstra-Lenstra-Lovasz (LLL) algorithm [51] and Seysen's algorithm (SA), by providing detailed descriptions and pseudo codes. The properties of output matrices of the LLL algorithm and SA are also quantified. Furthermore, other LR algorithms are also briefly introduced. After introducing LR algorithms, we show how to adopt them into the wireless communication decoding process by presenting LR-aided hard-output detectors and LR-aided soft-output detectors for coded systems, respectively. We also analyze the performance of proposed efficient receivers from the perspective of diversity, mutual information, and complexity. We prove that LR techniques help to restore the diversity of low-complexity equalizers without increasing the complexity significantly. When it comes to practical systems and simulation tool, e.g., MATLAB, only finite bits are adopted to represent numbers. Therefore, we revisit the diversity analysis for finite-bit represented systems. We illustrate that the diversity of MLE for systems with finite-bit representation is determined by the number of non-vanishing eigenvalues. It is also shown that although theoretically LR-aided detectors collect the same diversity as MLE in the real/complex field, it may show different diversity orders when finite-bit representation exists. Finally, the VLSI implementation of the complex LLL algorithms is provided to verify the practicality of our proposed designs.
9

Fundamentals of molecular communication over microfluidic channels

Bicen, Ahmet Ozan 27 May 2016 (has links)
The interconnection of molecular machines with different functionalities to form molecular communication systems can increase the number of design possibilities and overcome the limited reliability of the individual molecular machines. Artificial information exchange using molecular signals would also expand the capabilities of single engineered cell populations by providing them a way to cooperate across heterogeneous cell populations for the applications of synthetic biology and lab-on-a-chip systems. The realization of molecular communication systems necessitates analysis and design of the communication channel, where the information carrying molecular signal is transported from the transmitter to the receiver. In this thesis, significant progress towards the use of microfluidic channels to interconnect molecular transmitter and receiver pairs is presented. System-theoretic analysis of the microfluidic channels are performed, and a finite-impulse response filter is designed using microfluidic channels. The spectral density of the propagation noise is studied and the additive white Gaussian noise channel model is developed. Memory due to inter-diffusion of the transmitted molecular signals is also modeled. Furthermore, the interference modeling is performed for multiple transmitters and its impact on the communication capacity is shown. Finally, the efficient sampling of the signal transduction by engineered bacterial receivers connected to a microfluidic channel is investigated for the detection of the pulse-amplitude modulated molecular signals. This work lays the foundation for molecular communication over microfluidic channels that will enable interconnection of engineered molecular machines.
10

Stratégies de détection MIMO d'ordre supérieur avec applications au relayage pour les réseaux 4G+ et 5G / Higher-order MIMO detection and half-duplex relay strategies for 4G+ and 5G networks

Thomas, Robin 09 December 2016 (has links)
Ce travail présente deux contributions clés dans le domaine des réseaux de communication sans fil 4G+/5G, en particulier dans le domaine de la détection MIMO d’ordre supérieur et le design (conception) de réseau relai semi-duplex. La première partie de ce travail de recherche s’intéresse au développement d’une stratégie de détection MIMO d’ordre supérieur pour les terminaux 4G+/5G existants et futurs, d’un point de vue à la fois théorique et pratique. Une nouvelle technique de décomposition QR Bloc de prétraitement est proposée pour un récepteur LTE dans un scénario limité à un seul utilisateur, interférence limitée, ainsi qu’un scénario point par point dont les résultats surlignent les avantages et inconvénients en performance et complexité. La deuxième partie de cette étude comprend une étude de faisabilité d’une stratégie de message novatrice à deux phases et trois parties pour un réseau relai semi-duplex à couche physique, qui comporte un codage de superposition et un décodage d’annulation d’interférence successif, conscient des interférences. Un point clé de cette étude était d’analyser la performance du schéma d’adaptation des liaisons proposées dans le régime non asymptotique et d’évaluer l’efficacité spectrale (ES) par rapport aux hypothèses théoriques des blocs d’asymptotiquement grandes longueurs. Une comparaison ES supplémentaire est également présentée, avec une transmission de relais à deux étapes non coopérative et une stratégie de transmission point à point. Les résultats obtenus révèlent les gains d'ES qui peuvent être obtenus en exploitant la coopération de couche physique entre le relais et la station de base. / The evolution of wireless communication networks has always been rapidly progressive partly due to the demands of today’s data hungry users. This dissertation presents two key contributions to the body of knowledge in the evolving area of physical layer 4G+/5G communication technologies, especially in the domain of Higher-order MIMO detection and half-duplex relay network design. The initial part of this research investigates the development of a higher-order MIMO detection strategy for existing and future 4G+/5G receivers, from both a theoretical and practical perspective. A novel pre-processing Block QR decomposition technique has been proposed for an LTE receiver in a single-user interference-limited scenario as well as a point-to-point scenario with the results highlighting the complexity advantages and limitations in performance. The second part of this study involves a practical feasibility study of a novel two-phase three-part-message strategy for a physical layer half-duplex relay network, which features superposition coding and interference-aware successive interference cancellation decoding. A key aim of this study was to analyze the performance of the proposed link adaptation scheme in the non-asymptotic regime (finite block-length and discrete constellation signaling), and evaluate the spectral efficiency (SE) against the theoretical assumptions of asymptotically large block-lengths. An additional SE comparison with a non-cooperative two-hop relay transmission and point-to-point transmission strategy is also presented. The resulting outcomes reveal the SE gains that can be had by exploiting physical layer cooperation between the relay and base station.

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