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Kodikara, Patabandi C. K. "Multimedia communications over 3G wireless communication systems". Thesis, University of Surrey, 2004. http://epubs.surrey.ac.uk/844270/.
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This thesis addresses the transmission of video over third generation radio access networks. The first part of the thesis investigates the capabilities of Universal Terrestrial Radio Access Networks (UTRAN) in terms of the provision of multimedia communications. The error performance and traffic requirements of real-time video transmission over circuit switched and packet switched connections are examined. The effect of network parameter settings upon video performances is evaluated, and optimum radio bearer configurations for the transmission of video are derived. A method of estimating received video quality after transmission over error prone environments is developed. The quality estimation is based on a distortion model, which accurately models the overall distortion seen in decoder frame reconstruction. This includes quantisation distortion, concealment distortion, and error propagation. Based on the developed performance model, optimum MTU (Maximum Transfer Unit) size for efficient wireless video communications over a packet switched access network is derived. The second part of the thesis investigates quality enhancement techniques for multimedia traffic transmitted over wireless channels. Quality enhancement is achieved at three levels of the transmission process: link level, application level and system level. Link level quality enhancement techniques are designed to optimise the allocation of link level parameter values according to the media characteristics. A novel Unequal Error Protection scheme and a novel Unequal Power Allocation scheme are designed to exploit the inherent diversity in the subjective importance of different sections of compressed media. The algorithms are developed and analysed for transmission of video over 3G wireless systems. The effectiveness of these algorithms is demonstrated through the results of simulated transmission over a UMTS channel. Application level quality enhancement techniques are designed to explore the time-varying nature of the wireless channel. A number of link adaptation schemes are proposed for real time video communication and real-time video streaming over 3G wireless systems. These algorithms are designed to enhance the perceptual video quality, and the system utilisation. This is achieved by adapting the allocated radio network parameters and the source parameters, according to a feedback channel condition. Simulation results show a significant performance improvement compared to non-adaptive schemes. Finally, system level adaptation techniques are designed for efficient radio resource allocation in multi-user scenarios. Two adaptive resource allocation schemes are proposed and analysed for real-time video communications in a UMTS system. The proposed algorithms are shown to provide improved performances in terms of average received video quality and user satisfaction. Key words: Wireless Communication, Multimedia communication. Video Transmission.
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Athukorala, Lakshman. "Miniaturised bandpass filters for wireless communications". Thesis, University of Westminster, 2012. https://westminsterresearch.westminster.ac.uk/item/8z606/miniaturised-bandpass-filters-for-wireless-communications.
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The wireless industry has seen exceptional development over the past few decades due to years of sustained military and commercial enterprise. While the electromagnetic spectrum is becoming increasingly congested, there is a growing tendency to strive for higher bandwidths, faster throughputs, greater versatility, compatibility and interoperability in current and emerging wireless technologies. Consequently, an increasingly stringent specification is imposed upon the frequency utilization of wireless devices. New challenges are constantly being discovered in the development and realization of RF and microwave filters, which have not only sustained but fuelled microwave filter research over the many years. These developments have encouraged new solutions and techniques for the realization of compact, low loss, highly selective RF and microwave bandpass filters. The theme of this dissertation is the realization of planar compact performance microwave and RF bandpass filters for wireless communication systems. The work may be broadly categorised into three sections as follows. The first section presents a novel compact planar dual-mode resonator with several interesting and attractive features. Generally, planar microwave dual-mode resonators are known to half the filter footprint. However, it is found that the proposed resonator is capable of achieving further size reductions. In addition the resonator inherently possesses a relatively wide stopband as the lowest spurious harmonic resonance is observed at thrice the fundamental frequency. Properties of this resonator, such as these and more are explored in depth to arrive at an accurate electrical equivalent circuit, which is used as the basis for high order filter design. The application of these resonators in the design of bandpass filters is the subject of the second section. A general filter design procedure based on the equivalent circuit is presented to assist the design of all-pole filters. Alternatively, it is shown that generalised Chebyshev filters with enhanced selectivity may be developed with cross coupled resonator topologies. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section explores the possibility of employing these resonators in the development of frequency tunable bandpass filters. Preference is given to varactor diodes as the tuning element due to the numerous qualities of this device in contrast to other schemes. In particular, interest is paid to center frequency tuned filters with constant bandwidth. Tunable filters constructed with the dual-mode resonator are shown to have a relatively wide tuning range as well as significantly higher linearity in comparison to similar published works. In line with the previous section, experimental verification is presented to support and supplement the discussions.
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Stanković, Veljko. "Multi-user MIMO wireless communications". [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985258039.
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Schmitt, Michael Philipp. "ARQ systems for wireless communications". Phd thesis, [S.l. : s.n.], 2002. http://elib.tu-darmstadt.de/diss/000269.
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Kim, Kihong. "Interference Mitigation in Wireless Communications". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7647.
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The primary objective of this thesis is to design advanced interference resilient schemes for asynchronous slow frequency hopping wireless personal area networks (FH-WPAN) and time division multiple access (TDMA) cellular systems in interference dominant environments. We also propose an interference-resilient power allocation method for multiple-input-multiple-output (MIMO) systems.
For asynchronous FH-WPANs in the presence of frequent packet collisions, we propose a single antenna interference canceling dual decision feedback (IC-DDF) receiver based on joint maximum likelihood (ML) detection and recursive least squares (RLS) channel estimation. For the system level performance evaluation, we propose a novel geometric method that combines bit error rate (BER) and the spatial distribution of the traffic load of CCI for the computation of packet error rate (PER). We also derived the probabilities of packet collision in multiple asynchronous FH-WPANs with uniform and nonuniform traffic patterns.
For the design of TDMA receivers resilient to CCI in frequency selective channels, we propose a soft output joint detection interference rejection combining delayed decision feedback sequence estimation (JD IRC-DDFSE) scheme. In the proposed scheme, IRC suppresses the CCI, while DDFSE equalizes ISI with reduced complexity. Also, the soft outputs are generated from IRC-DDFSE decision metric to improve the performance of iterative or non-iterative type soft-input outer code decoders.
For the design of interference resilient power allocation scheme in MIMO systems, we investigate an adaptive power allocation method using subset antenna transmission (SAT) techniques. Motivated by the observation of capacity imbalance among the multiple parallel sub-channels, the SAT method achieves high spectral efficiency by allocating power on a selected transmit antenna subset. For 4 x 4 V-BLAST MIMO systems, the proposed scheme with SAT showed analogous results. Adaptive modulation schemes combined with the proposed method increase the capacity gains. From a feasibility viewpoint, the proposed method is a practical solution to CCI-limited MIMO systems since it does not require the channel state information (CSI) of CCI.
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Anderson, Alan John. "Channel prediction in wireless communications". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/16188.
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Knowledge of the channel over which signals are sent is of prime importance in modern wireless communications. Inaccurate or incomplete channel information leads to high error rates and wasted bandwidth and energy. Although active channel measurement is commonly used to gain channel knowledge, it can only accurately represent the channel at the time the measurement was taken, makes energy and bandwidth demands, and adds significant complexity to the radio system. Due to the highly time variant nature of wireless channels, active measurements become invalid almost as soon as they are taken, making alternative approaches to predicting future behaviour highly attractive. Such systems would allow maximum advantage to be taken of the limited bandwidth available and make significant power savings. This thesis investigates a number of complementary technologies, leading towards a channel prediction scheme suitable for mobile devices. As a first step towards channel prediction, anomaly detection is investigated within periodic wireless signals to establish when radical changes in the channel occur. In pre- vious experiments, long monotonic sequences had been observed to coincide with certain anomalies but not others when using Kullback-Leibler Divergence (KLD) analysis, possibly allowing the characterisation of anomaly types. An investigation is described to explain the origin of these features in a rigorous mathematical sense. A proof is given for the causes of the monotonic sequences, followed by a discussion of the types of signal anomaly which would underly such a feature and the value of this information. The second part describes a novel channel characterisation method which uses a class of Recurrent Neural Network (RNN) called an Echo State Network (ESN). Using this tool, a channel characterisation system can be constructed without an explicit statistical or mathematical model of the wireless environment, relying instead on observed data. This approach is much more convenient than existing models which require detailed information about the wireless system's parameters and also allows for new channel classifications to be added easily. It is able to achieve double the correct classification rate of a conventional statistical classifier, and is computationally simple to implement, making it ideal for inclusion on low-power mobile devices. Following their successful use in characterisation, ESNs are used in the final part in an investigation into channel prediction in a number of different scenarios. They were however found to be unable to produce useful predictions for all but the most trivial channel models. An alternative method is described for indoor environments using an approach inspired by ray tracing. It is simple and computationally lightweight to implement, again making it suitable for mobile devices. Simulation results show that it can outperform pilot-assisted methods by a significant margin, while not wasting bandwidth on channel measurement.
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Shaheem, Asri. "Iterative detection for wireless communications". University of Western Australia. School of Electrical, Electronic and Computer Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0223.
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[Truncated abstract] The transmission of digital information over a wireless communication channel gives rise to a number of issues which can detract from the system performance. Propagation effects such as multipath fading and intersymbol interference (ISI) can result in significant performance degradation. Recent developments in the field of iterative detection have led to a number of powerful strategies that can be effective in mitigating the detrimental effects of wireless channels. In this thesis, iterative detection is considered for use in two distinct areas of wireless communications. The first considers the iterative decoding of concatenated block codes over slow flat fading wireless channels, while the second considers the problem of detection for a coded communications system transmitting over highly-dispersive frequency-selective wireless channels. The iterative decoding of concatenated codes over slow flat fading channels with coherent signalling requires knowledge of the fading amplitudes, known as the channel state information (CSI). The CSI is combined with statistical knowledge of the channel to form channel reliability metrics for use in the iterative decoding algorithm. When the CSI is unknown to the receiver, the existing literature suggests the use of simple approximations to the channel reliability metric. However, these works generally consider low rate concatenated codes with strong error correcting capabilities. In some situations, the error correcting capability of the channel code must be traded for other requirements, such as higher spectral efficiency, lower end-to-end latency and lower hardware cost. ... In particular, when the error correcting capabilities of the concatenated code is weak, the conventional metrics are observed to fail, whereas the proposed metrics are shown to perform well regardless of the error correcting capabilities of the code. The effects of ISI caused by a frequency-selective wireless channel environment can also be mitigated using iterative detection. When the channel can be viewed as a finite impulse response (FIR) filter, the state-of-the-art iterative receiver is the maximum a posteriori probability (MAP) based turbo equaliser. However, the complexity of this receiver's MAP equaliser increases exponentially with the length of the FIR channel. Consequently, this scheme is restricted for use in systems where the channel length is relatively short. In this thesis, the use of a channel shortening prefilter in conjunction with the MAP-based turbo equaliser is considered in order to allow its use with arbitrarily long channels. The prefilter shortens the effective channel, thereby reducing the number of equaliser states. A consequence of channel shortening is that residual ISI appears at the input to the turbo equaliser and the noise becomes coloured. In order to account for the ensuing performance loss, two simple enhancements to the scheme are proposed. The first is a feedback path which is used to cancel residual ISI, based on decisions from past iterations. The second is the use of a carefully selected value for the variance of the noise assumed by the MAP-based turbo equaliser. Simulations are performed over a number of highly dispersive channels and it is shown that the proposed enhancements result in considerable performance improvements. Moreover, these performance benefits are achieved with very little additional complexity with respect to the unmodified channel shortened turbo equaliser.
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Zyambo, Emmanuel Baleke. "High-speed wireless infrared communications". Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275377.
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Parand, Farivar. "Cellular optical wireless communications systems". Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270654.
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Leuca, Magdalena. "Security issues in wireless communications". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10266.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (leaves 99-103).
by Magdalena Leuca.
M.Eng.
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Joshi, Harita. "Modulation for optical wireless communications". Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/55521/.
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Diaz, Ariel Gomez. "Ultrafast indoor optical wireless communications". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:2bd2257f-ae58-40f0-a10f-04e7b5336519.
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Traffic from wireless and mobile devices is predicted to increase 10-fold between 2014 and 2019, surpassing wired data traffic by 2016. Given the expected radio frequency (RF) capacity crunch, this growing wireless demand will have to be met using a variety of new technologies exploiting other parts of the electromagnetic spectrum. Promising research areas include the Millimetre Band as well as Optical Wireless Communications (OWC). Millimetre Band demonstrations have accomplished ultrafast multi-Gigabit links, making use of state-of-the-art fibre transmission systems. However, complex opto-electronic (OE) interfaces are required to convert the optical carrier into Millimetre wireless signals. To avoid these interfaces, an all-optical transparent network is proposed here, spanning over both the fibre and OWC domains, in order to deliver ultrahigh data rates to mobile end-users in indoor environments. This is supported by the recent deployment of fibre-to-the-home (FTTH) networks creating the potential for Terabit aggregate connections at the user's doorstep. Therefore, infrared fibre-wireless-fibre (FWF) links are studied to support data rates over 100 Gb/s in nomadic applications. The link coverage is achieved via narrow beam beamsteering over a wide field-of-view (FOV) using suitable localization and tracking techniques. The proposed model is inherently bidirectional and transparent, i.e. independent of the data rate and modulation format. In this thesis, the potential for ultrafast wide coverage OWCs using SMF-based transceivers and coherent transmission is demonstrated. A record data rate of 418 Gb/s and 209 Gb/s with a wide FOV of θFOV=±30° and θFOV=±20°, respectively, is shown at a free space range of 3 m. To the best of our knowledge, this is the fastest demonstration of an indoor wireless link that offers practical room-scale coverage. The automated alignment of this FWF link is also demonstrated with the design and implementation a mm-accurate localization and tracking system. Finally, architectures for point-to-multipoint communications are explored in order to adapt the system to multiple users.
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Sohaib, Sarmad. "Energy efficient cooperative wireless communications". Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/energy-efficient-cooperative-wireless-communications(a852e1e2-04ad-4311-8004-53babe529e1b).html.
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Cooperative diversity exploits the broadcast nature of wireless channels and uses relays to improve link reliability. Most cooperative communication protocols are assumed to be synchronous in nature, which is not always possible in wireless communication. Also the relay nodes are assumed to be half duplex which in turn reduces the spectral efficiency. In this thesis, we first present a novel asynchronous cooperative communication protocol exploiting polarization diversity, which does not require synchronization at the relay node. Dual polarized antennas are employed at the relay node to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased throughput rate. Capacity analysis of the proposed scheme ascertains the high data rate as compared to conventional ANF. Bit error rate (BER) simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes. Considering channel path loss, the proposed scheme consume less total transmission energy as compared to ANF and non-cooperative scheme in more practical distance range. Thus the proposed scheme is suitable for high rate and energy efficient relay-enabled communication. In addition to that, we also present a novel power allocation scheme for multiple relay nodes that results in efficient cooperative multiple-input multiple-output (MIMO) communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation and non-cooperative scheme. Optimal relay positioning with proposed energy allocation scheme is also explored to maximize the capacity.
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Dong, Chen. "Buffer-aided multihop wireless communications". Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/364737/.
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In this thesis, we propose a suite of buffer-aided transmission schemes designed for a multihop link or for a three-node network by exploiting the characteristics of buffer-aided transmissions. Our objective is to improve the end-to-end BER, outage probability, throughput and energy dissipation. Specifically, we firstly proposed and studied a buffer-aided multihop link (MHL), where all the relay nodes (RNs) are assumed to have buffers for temporarily storing their received packets. Hence, the RNs are operated under the so-called store-and-forward (SF) relaying scheme. As a benefit of storing packets at the RNs, during each time-slot (TS), the best hop having the highest signal-to-noise ratio (SNR) can be activated from the set of those hops that have packets awaiting transmission in the buffer. A packet is then transmitted over the best hop. This hop-selection procedure is reminiscent of selection (SC) diversity, which is referred to here as multi-hop diversity (MHD), when assuming that each hop experiences both propagation pathloss and independent identically distributed (i.i.d) flat Rayleigh fading. In order to make the channel activation practical, a MAC layer implementation is proposed and several closed-form formulas are derived for its characterization. Then we studied the buffer-aided multihop link, when assuming that each hop experiences both propagation pathloss and independent non-identically distributed (i.n.i.d) at Nakagami-m fading. Both BPSK as well as M-ary quadrature amplitude modulation (MQAM) are employed. During each TS, the MHD scheme activates the specific hop's transmission, whose signal-to-noise ratio (SNR) cumulative distribution function (CDF) gives the highest ordinate value amongst all the available hops. The next packet is then transmitted over the selected hop. This CDF-aware MHD scheme is suitable for operation in the scenarios, where the different hops may have different length, hence resulting in different average SNRs, and/or experience different types of fading. This MHD scheme is also capable of achieving the maximum attainable diversity gain provided by the independent fading experienced by the different hops. Then the benefits of adaptive modulation are exploited, where the number of bits transmitted in each TS is affected both by the channel quality and the buffer fullness. During each TS, the criterion used for activating a specific hop is that of transmitting the highest number of bits (packets). When more than one hops are capable of transmitting the same number of bits, the particular hop having the highest channel quality (reliability) is activated. Hence we refer to this regime as the Maximum Throughput Adaptive Rate Transmission (MTART) scheme. Additionally, a new MAC layer protocol is proposed for implementing our MTART management. Finally, we propose and study a routing scheme, namely the Buffer-aided Opportunistic Routing (BOR) scheme, which combines the benefits both opportunistic routing and MHD transmission. It is conceived for the transmission of information in a Buffer-aided Three-node Network (B3NN) composed of a Source Node (SN), a buffer-aided Relay Node (RN) and a Destination Node (DN). When applying opportunistic routing, each packet is transmitted from SN to DN either directly or indirectly via a RN based on the instantaneous channel quality. When applying MHD transmission, the RN is capable of temporarily storing the received packets, which facilitates transmission over three links, namely the SR, RD and SD links. In this network, the three channels define a 3D channel probability space (CPS), which is divided into four regions representing the activation-region of the three channels and an outage region. Then the instantaneous channel quality values map to a specific point in this 3D channel space. The BOR scheme relies on the position of this point to select the most appropriate channel in the 3D CPS for its transmission. In comparison to the benchmark schemes considered in the literature, the BER, the OP, throughput and/or energy dissipation of our proposed systems are significantly improved.
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Othman, Noor Shamsiah. "Wireless speech and audio communications". Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/64488/.
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The limited applicability of Shannon’s separation theorem in practical speech/audio systems motivates the employment of joint source and channel coding techniques. Thus, considerable efforts have been invested in designing various types of joint source and channel coding schemes. This thesis discusses two different types of Joint Source and Channel Coding (JSCC) schemes, namely Unequal Error Protection (UEP) aided turbo transceivers as well as Iterative Source and Channel Decoding (ISCD) exploiting the residual redundancy inherent in the source encoded parameters. More specifically, in Chapter 2, two different UEP JSCC philosophies were designed for wireless audio and speech transmissions, namely a turbo-detected UEP scheme using twin-class convolutional codes and another turbo detector using more sophisticated Irregular Convolutional Codes (IRCC). In our investigations, the MPEG-4 Advanced Audio Coding (AAC), the MPEG-4 Transform-Domain Weighted Interleaved Vector Quantization (TwinVQ) and the Adaptive MultiRate WideBand (AMR-WB) audio/speech codecs were incorporated in the sophisticated UEP turbo transceiver, which consisted of a threestage serially concatenated scheme constituted by Space-Time Trellis Coding (STTC), Trellis Coded Modulation (TCM) and two different-rate Non-Systematic Convolutional codes (NSCs) used for UEP. Explicitly, both the twin-class UEP turbo transceiver assisted MPEG-4 TwinVQ and the AMR-WB audio/speech schemes outperformed their corresponding single-class audio/speech benchmarkers by approximately 0.5 dB, in terms of the required Eb/N0, when communicating over uncorrelated Rayleigh fading channels. By contrast, when employing the MPEG-4 AAC audio codec and protecting the class-1 audio bits using a 2/3-rate NSC code, a more substantial Eb/N0 gain of about 2 dB was achieved. As a further design alternative, we also proposed a turbo transceiver employing IRCCs for the sake of providing UEP for the AMR-WB speech codec. The resultant UEP schemes exhibited a better performance when compared to the corresponding Equal Error Protection (EEP) benchmark schemes, since the former protected the audio/speech bits according to their sensitivity. The proposed UEP aided system using IRCCs exhibits an Eb/N0 gain of about 0.4 dB over the EEP system employing regular convolutional codes, when communicating over AWGN channels, at the point of tolerating a SegSNR degradation of 1 dB. In Chapter 3, a novel system that invokes jointly optimised ISCD for enhancing the error resilience of the AMR-WB speech codec was proposed and investigated. The resultant AMR-WB coded speech signal is protected by a Recursive Systematic onvolutional (RSC) code and transmitted using a non-coherently detected Multiple-Input Multiple-Output (MIMO) Differential Space-Time Spreading (DSTS) scheme. To further enhance the attainable system performance and to maximise the coding advantage of the proposed transmission scheme, the system is also combined with multi-dimensional Sphere Packing (SP) modulation. The AMR-WB speech decoder was further developed for the sake of accepting the a priori information passed to it from the channel decoder as extrinsic information, where the residual redundancy inherent in the AMR-WB encoded parameters was exploited. Moreover, the convergence behaviour of the proposed scheme was evaluated with the aid of both Three-Dimensional (3D) and Two-Dimenstional (2D) EXtrinsic Information Transfer (EXIT) charts. The proposed scheme benefitted from the exploitation of the residual redundancy inherent in the AMR-WB encoded parameters, where an approximately 0.5 dB Eb/N0 gain was achieved in comparison to its corresponding hard speech decoding based counterpart. At the point of tolerating a SegSNR degradation of 1 dB, the advocated scheme exhibited an Eb/N0 gain of about 1.0 dB in comparison to the benchmark scheme carrying out joint channel decoding and DSTS aided SP-demodulation in conjunction with separate AMR-WB decoding, when communicating over narrowband temporally correlated Rayleigh fading channels. In Chapter 4, two jointly optimized ISCD schemes invoking the soft-output AMRWB speech codec using DSTS assisted SP modulation were proposed. More specifically, the soft-bit assisted iterative AMR-WB decoder’s convergence characteristics were further enhanced by using Over-Complete source-Mapping (OCM), as well as a recursive precoder. EXIT charts were used to analyse the convergence behaviour of the proposed turbo transceivers using the soft-bit assisted AMR-WB decoder. Explicitly, the OCM aided AMR-WB MIMO transceiver exhibits an Eb/N0 gain of about 3.0 dB in comparison to the benchmark scheme also using ISCD as well as DSTS aided SP-demodulation, but dispensing with the OCM scheme, when communicating over narrowband temporally correlated Rayleigh fading channels. Finally, the precoded soft-bit AMR-WB MIMO transceiver exhibits an Eb/N0 gain of about 1.5 dB in comparison to the benchmark scheme dispensing with the precoder, when communicating over narrowband temporally correlated Rayleigh fading channels.
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Cao, Ping. "UWB antennas for wireless communications". Thesis, University of Liverpool, 2013. http://livrepository.liverpool.ac.uk/14715/.
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This thesis focuses on four inter-related research topics on the design and analysis of compact planar ultra wide-band (UWB) monopole antennas for future wireless communications, namely, a planar super-wide-band (SWB) monopole antenna, a planar UWB antenna with band-notched characteristics, a planar UWB antenna with reconfigurable band-rejection features, and a planar UWB multiple-input and multiple-output (MIMO) antenna. A novel Mickey-mouse shaped planar monopole antenna with SWB performance is proposed and investigated. Three different techniques for bandwidth enhancement are implemented. The antenna is evolved from the traditional circular monopole antenna and has achieved an impedance bandwidth of more than 100:1 and a stable radiation patterns over a wider bandwidth. The design of a compact planar UWB monopole antenna (22 mm × 34 mm), incorporated with five m-shaped resonators (MSRs) at different positions, to achieve quintuple-band-notched performance is presented. The frequency-domain performance (in term of reflection coefficients, realized gain, efficiency, and radiation pattern), and time-domain performance (in term of pulse responses and fidelity), are investigated by simulation and measurement. The results show that the proposed UWB antenna has approximately omnidirectional radiation patterns and excellent band-notched behaviours and good time domain performance with the fidelity of more than 85.5% in the pulse response. A planar UWB monopole antenna with reconfigurable band-notched characteristics is also introduced. The band rejection is realized by incorporating two co-directional split ring resonators (CSRR) on the radiator element. Switches are added to the CSRR structures to achieve the reconfigurability. The proposed antenna can operate at different switching states including a UWB state, single and dual band-notched states with good rejection behaviours. Good radiation patterns and gain values are also obtained for different switching states. This compact wideband antenna can be very good candidate for a wide range of mobile portable applications. A compact planar UWB-MIMO antenna (60 mm × 45 mm) is presented for wireless applications. The wideband isolation of more than 15 dB is achieved by etching a new trident-like slot on the ground plane of the antenna. An equivalent circuit have been introduced for analysis and the diversity performances are studied. The results show that the proposed MIMO antenna is a very good candidate for wireless applications. The study of these four special antennas has demonstrated that, using various techniques, the planar monopole antenna can be an excellent choice for a wide range of wireless communication applications.
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Almoualem, Firas, i Firas Almoualem. "SDR - Based Resilient Wireless Communications". Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/625342.
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As the use of wireless technologies increases significantly due to the ease of deployment, the cost-effectiveness and the increase in bandwidth, there is a strong need to make the wireless communications reliable, secure, and resilient to attacks or faults (malicious or natural). Wireless communications are inherently prone to attacks due the open access to the medium. However, current wireless protocols have addressed the privacy issues, but have failed to provide effective solutions against denial of service attacks, session hijacking and jamming attacks. The goal of this research is to provide a resilient wireless communication system against these type of attacks.
In this thesis, we present a resilient wireless communications architecture based on Moving Target Defense (MTD), Software Defined Radio (SDR), and Software Defined Networking (SDN). The approach achieves the resilient operations by randomly changing the runtime characteristics of the wireless communication channels in order to make it extremely difficult to be succeeded in launching attacks. The runtime characteristics that can be changed include the packet size, the network address, the modulation type, and the operating frequency of the channel. In addition, the lifespan for each configuration will be random. To reduce the overhead in switching between two consecutive configurations, we use two radio channels, one is designated as an active channel while the second is designated as a standby channel. The standby channel is used if the attacker was successfully in attacking the active channel. This will harden the wireless communications attacks because the attackers need to figure out the configuration being used and then launch an attack before the current configuration is changed. Our experimental results and evaluation show that our approach can tolerate a wide range of attacks against wireless networks.
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Alhalabi, Ashraf S. A. <1985>. "Device-To-Device Wireless Communications". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/7845/1/Thesis_%D9%90Ashraf.pdf.
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The main topic investigated in this thesis is related to characterization of the performance of D2D wireless networks. Given this broad objective, analytical framework models based on stochastic geometry have been proposed. One of them deals with the study of the coverage probability of both cellular networks and D2D networks whereas the others are related to dynamic mobility models in which the effects of blockages on the link lifetime have been studied. On the other hand, the experimental activity based on UWB using passive tags has been presented in which a localization system based on the ultra-wideband (UWB) technology and high-level architectures to improve the cyclists safety has been proposed.
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Gong, P. "Energy efficient and secure wireless communications for wireless sensor networks". Thesis, City, University of London, 2017. http://openaccess.city.ac.uk/18026/.
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This dissertation considers wireless sensor networks (WSNs) operating in severe environments where energy efficiency and security are important factors. This main aim of this research is to improve routing protocols in WSNs to ensure efficient energy usage and protect against attacks (especially energy draining attacks) targeting WSNs. An enhancement of the existing AODV (Ad hoc On-Demand Distance Vector) routing protocol for energy efficiency, called AODV-Energy Harvesting Aware (AODVEHA), is proposed and evaluated. It not only inherits the advantages of AODV which are well suited to ad hoc networks, but also makes use of the energy harvesting capability of sensor nodes in the network. In addition to the investigation of energy efficiency, another routing protocol called Secure and Energy Aware Routing Protocol (ETARP) designed for energy efficiency and security of WSNs is presented. The key part of the ETARP is route selection based on utility theory, which is a novel approach to simultaneously factor energy efficiency and trustworthiness of routes in the routing protocol. Finally, this dissertation proposes a routing protocol to protect against a specific type of resource depletion attack called Vampire attacks. The proposed resource-conserving protection against energy draining (RCPED) protocol is independent of cryptographic methods, which brings advantage of less energy cost and hardware requirement. RCPED collaborates with existing routing protocols, detects abnormal sign of Vampire attacks and determines the possible attackers. Then routes are discovered and selected on the basis of maximum priority, where the priority that reflects the energy efficiency and safety level of route is calculated by means of Analytic Hierarchy Process (AHP). The proposed analytic model for the aforementioned routing solutions are verified by simulations. Simulations results validate the improvements of proposed routing approaches in terms of better energy efficiency and guarantee of security.
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Chan, Wing Chau. "Performance limits of MIMO wireless communications /". View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20CHANW.
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Kim, JoonBeom. "Iterative Channel Estimation for Wireless Communications". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14064.
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The main objective of this dissertation is to present the structural design, performance evaluation, and complexity reduction of iterative joint channel estimation and data detection receivers. One of the main technical challenges in advanced wireless communications stems from the characteristics of a wireless channel, e.g., time selectivity of a channel, mobility of users, and multipath propagation. Channel estimation is essential for achieving reliable information transmission for practical wireless communication applications. Numerous channel estimation structures have been developed for different underlying channels using pilot-symbol assisted modulation (PSAM) approaches. However, since pilot symbols carry no data information, the time and the power spent on pilot symbols degrades the efficiency and the throughput of the system. Therefore, it is necessary to minimize the pilot insertion ratio without degrading the error performance. This motivates our research on iterative joint channel estimation and data detection receivers with full- and reduced- or low-complexity.
In this thesis, we first propose an iterative channel estimator (ICE), based on a maximum a posteriori (MAP) algorithm, for single-carrier systems with PSAM structures. In contrast to existing MAP channel estimators, the proposed channel estimator has a lower computational complexity, which increases linearly with the modulation alphabet size. The computational complexity is reduced by exploiting a survivor in an efficient manner, while achieving comparable error performance to a full complexity receiver. For orthogonal frequency division multiplexing (OFDM) systems, we also propose novel signal constellations to facilitate channel estimation without pilot symbol transmission, and analyze the bit error rate for the proposed constellations. We also develop a suitable joint channel estimation and data detector with full- and low-complexity for the proposed constellations. This low-complexity ICE achieves an error performance comparable to the ICE with full-complexity. Finally, for vertical Bell Laboratories layered space-time OFDM systems, we propose an ICE based on a PSAM structure for time-varying multipath fading channels. By exploiting the statistical properties of a wireless channel, we also develop a method to suppress intercarrier interference due to the channel time selectivity, and propose a low-complexity ICE that exploits a priori information in an efficient manner.
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Tsimbalo, Evgeny. "Energy-constrained wireless communications for IoT". Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.723512.
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Pakravan, Mohammad M. Reza. "Broadband indoor wireless communications using infrared". Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/9534.
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In this thesis, we discuss the issue of using infrared light as a carrier for broadband indoor wireless networks. We discuss the infrared channel and show how it differs from conventional radio frequency channel. Noise sources for this environment and the practical ways of reducing their harmful effects are discussed. We determine the safety levels for the radiated power of an IR transmitter and we show how the system should be designed to operate within the safety limits. We introduce a computer-simulation algorithm to find the impulse response of an indoor infrared channel and discuss several implementation issues for the algorithm. Using the simulation software, we investigate temporal and spatial distributions of the channel, e.g., the delay spread of impulse response and the total received optical power. We use the results of the simulations to investigate the effects of receiver rotation on the channel properties. We propose an angular diversity as a mean for performance improvement in an infrared receiver. Simulating the noise sources and signal sources in a typical indoor environment, we see how diversity improves the signal-to-noise ratio in a receiver with the angular diversity reception.
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Pham, Tien D. "Adaptive antennas in multipath wireless communications". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq35282.pdf.
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Zamiri-Jafarian, Hossein. "Adaptive MLSDE receivers for wireless communications". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0001/NQ41537.pdf.
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Zuazola, Garcia. "Miniature antennas for mobile wireless communications". Thesis, University of Kent, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.591097.
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The subject of this this has been to produce new antermas suitable for use in Radio-over- Fibre Remote Antenna Units or in Mobile Equi pment which might be used at the other end of the link. Several new antennas have been developed and assessed for their suitable application to RoF systems. The antennas were: (i) a multiband PIFA developed previously in the ROSETTE project and modified here to exhibit an improved match when integrated with a ground plane for ceiling mounting. (ii) A cost effective microstrip array directive antenna for street illumination in the Manhattan Scenario. Beam coverage was controlled by electronic shaping and mechanical tilting. (iii) A new compact PIFA design for use in mobile equipment or sectorized base stations where a slotted structure is used to achieve a sharp edge defined operating bandwidth which allows the antenna to act as a filter, thus reducing component count and insertion loss in the transceiver front end. The antenna has been integrated with a larger handset sized ground plane and its insensitivity to this mounting has been demonstrated. (iv) the antenna in (iii) has been implemented in a 3 sector cluster and interference between sector beams by pattern overlap has been characterized. (v) A new compact PIFA working in the 3-5GHz sub-bands of the FCC UWB band has been described and demonstrated to offer useful performance and exhi bit a useful band pass fil tering characteristic reducing the need for a frontend filter in UW8 systems. (vi) A size reduced PIFA has been presented and studied where the rear ground plane was replaced by a strip element FSS tuned to 450Hz. This was demonstrated to improve performance at that band and the antenna was shown to offer a gain that compared well to a standard PlFA between I and 100Hz. The work described has been undertaken over 3 EU funded projects and the thesis begins with a brief overview of the relevant parts of those projects, particularly how antenna match is of importance at the Remote Antenna Unit of a Radio-over-Fibre system as poor input isolation and reflection can cause ringing in the bidirectional amplifiers associated with the duplex transmission. The new antennas developed for application in mobile equipment are shown to be compact (in relation to electrical size) and are considered in terms of their input bandwidth and efficiency.
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Muller, Andreas. "Message passing algorthms in wireless communications". Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.544340.
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Muller, Andreas. "Message passing algorithms in wireless communications". Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.544339.
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McDiarmid, Alisdair. "Anonymous communications in wireless access networks". Thesis, University of Strathclyde, 2006. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21649.
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The growth of mobile communications systems over the past decade indicates a trend towards an always-on, ubiquitously networked society. This increase in communications availability leads to a corresponding increase in information gathered, processed, and transmitted over these networks. Some of this information is loosely considered by users of these systems to be private, and in some cases, even the general pattern of use of network services could be regarded as revealing personal information. Therefore, along with growth in communications comes growth in privacy concerns. One approach to protecting users' privacy is to offer anonymity: the ability to blend into a crowd, such that any communications cannot be attributed to a particular real identity. This research study investigates two aspects of providing anonymity in mobile networks: in services, and for network access. Anonymous mobile service provision is approached by analysing several fixed-network approaches to anonymous communications, and examining how they can be reapplied to mobile systems. A set of conclusions and recommendations for future implementations are contributed, along with a case study of providing anonymous location-based services for mobile systems. Being able to connect to a network while remaining truly anonymous is a novel concept, only made possible by the untethered nature of mobile communications. Analysis of the practical requirements for achieving such service is presented, and a solution is proposed, based on a new approach to mobile network service provision called the Digital Marketplace. To support this approach to network access, the fair and reliable operation of the market is ensured by securing its protocol operation. Further modifications to this scheme are proposed, in order to enable fully anonymous network access.
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Xia, Bin, i 夏斌. "Enhanced techniques for broadband wireless communications". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29144231.
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Ghandi, Mohammad Mahdi. "Layered video coding for wireless communications". Thesis, University of Essex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426012.
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Mai, Huiheng. "Iterative channel estimation for wireless communications". Thesis, University of York, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433681.
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Dhomeja, Sheyam Lal. "CDMA communications over wireless infrared channels". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287004.
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Nordberg, Jörgen. "Signal Enhancement in Wireless Communications Systems". Doctoral thesis, Ronneby : Blekinge Institute of Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-00229.
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Digital Wireless communications has been one of the fastest growing communication techniques during the last decade. Today there exists several different communication systems that use wireless techniques. They share one common property that they transmit data through a radio interface. The radio channel is a tough channel that will both distort and disturb the transmitted signal in various ways. In Jörgen Nordberg's PhD-thesis "Signal Enhancement in Wireless Communications Systems" several different signal enhancement schemes are presented. They have the objective to minimize the impact of the channel. The main part of this thesis presents work on interference cancellation, i.e. how to reduce the impact of other interfering signals on the channel of interest. This is achieved by utilizing the spatial domain, i.e. the receiver is using several antennas to receive the transmitted signals. By using a multitude of antennas techniques like spatial diversity, adaptive antenna arrays, signal separation and beamforming can be applied to combat the interfering signals. In the single antenna case there is often a need to do channel equalization. Since, channel equalization is an inverse filtering, it will often result in estimation of equalization filter parameters of very high order. To reduce the both the complexity and improve the convergence speed of the equalization filter parameter estimation subband processing techniques can be used. In this case the received signal is separated up into different frequency bands (subbands) and decimated according to the bandwidth of the signal. The channel equalization problem is then solved for each subband at a lower sampling rate. Hence, the channel equalization problem is transformed from estimating the parameters of a high order filter into estimating several filter of much lower order.Ett av områdena inom telekommunikation som har ökat mest de senaste åren är radio kommunikation. Det finns många olika varianter av trådlösa radio system, men de har alla en sak gemensamt, de överför information/data via ett radiogränssnitt. Signaler som sänds över en radiokanal kommer på grund av många olika anledningar att bli störda eller distorderade. I Jörgen Nordbergs doktorsavhandling ?Signal Enhancement in Wireless Communication Systems? presenteras flera metoder för att förbättra kvaliten i de mottagna signalerna vilket ger betydande kvalitetsförbättring. Huvuddelen av denna doktorsavhandling behandlar interferensundertrycking, d.v.s. hur man undertrycker oönskad störning på den egna radiokanalen. Dessa metoder är baserade på användning av flera antenner i mottagaren. Genom att ta emot signalerna med flera antenner så kan metoder såsom diversitetskombinering, adaptiva antenner, lobformning, signal separation användas för att förbättra kvaliteten i den mottagna signalen. Om mottagaren har en antenn så behövs oftast kanalutjämning för att förbättra den mottagna signalen och undertrycka intersymbolinterferens. Eftersom kanalutjämning är en typ av inversfiltrering leder detta ofta till estimering av filterparametrar av hög ordning. Estimeringsproblem av hög ordning leder ofta till komplexitetsproblem och konvergensproblem hos estimerings algoritmen. För att motverka dessa problem så presenteras i denna avhandling en kanalutjämnare som är baserad på subbandsteknik. I denna kanalutjämnare så delas den mottagna signalen upp i flera frekvensband (subband) som decimeras till en takt som motsvarar subbandets bandbredd varefter filterparametrarna estimeras i denna lägre takt. Därvid har estimeringsproblemet delats upp i flera små problem som kan hanteras enklare.
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Jensen, Michael A., i Michael D. Rice. "SPACE-TIME CODING FOR WIRELESS COMMUNICATIONS". International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/605605.
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International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, CaliforniaSignal fading and intersymbol interference created by multipath propagation have traditionally limited the throughput on wireless communications systems. However, recent research has demonstrated that by using multiple antennas on both transmit and receive ends of the link, the multipath channel can actually be exploited to achieve increased communication throughput over single-antenna systems. This paper provides an introductory description of such multi-antenna communications systems, focusing on basic explanations of how they achieve capacity gains. Computed and measured capacity results are used to demonstrate the potential of these systems.
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Wang, Kezhi. "Performance analysis for cooperative wireless communications". Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/66981/.
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Cooperative relaying has been proposed as a promising solution to mitigate and combat the deleterious effects of fading by sending and receiving independent copies of the same signal at different nodes. It has attracted huge attention from both industry and academia. The purpose of this thesis is to provide an analytical performance evaluation of the cooperative wireless systems while taking some realistic conditions into consideration. To achieve this, first, performance analysis of amplify-and-forward (AF) relaying using pilot-aided maximum likelihood estimation is studied in this thesis. Both disintegrated channel estimation (DCE) and cascaded channel estimation (CCE) are considered. Based on this analysis, optimal energy allocation is proposed. Then, performance analysis for AF relaying corrupted by interferers are investigated. Both randomly distributed and fixed interferers are considered. For random interferers, both the number and the locations of the interferers are random while for fixed interferers, both the number and the locations are fixed. Next, multihop relaying and multiple scattering channels over α - μ fading are analyzed. Channels with interferences and without interferences are considered. Exact results in the form of one-dimensional integral are derived. Also, approximate results with simplified structure and closed-form expressions are provided. Finally, a new hard decision fusion rule that combines arbitrary numbers of bits for different samples taken at different nodes is proposed. The best thresholds for the fusion rules using 2 bits, 3 bits and 4 bits are obtained through simulation. The bit error rate (BER) for hard fusion rule with 1 bit is provided. Numerical results are presented to show the accuracy of our analysis and provide insights. First, they show that our optimal energy allocation methods outperform the conventional system without optimal energy allocation, which could be as large as several dB’s in some cases. Second, with the increase of signal-to-interference-plus-noise ratio (SINR) for AF relaying with interference, the outage probability decreases accordingly for both random and fixed interferers. However, with the change of interference-to-noise ratio (INR) but with the SINR fixed, the outage probability for random interferers change correspondingly while the outage probability for fixed interferers remains almost the same. Third, our newly derived approximate expressions are shown to have acceptable performances in approximating outage probability in wireless multihop relaying system and multiple scattering channel considering interferences and without interferences. Last, our new hard decision fusion rule is shown to achieve better performance with higher energy efficiency. Also they show that there is a tradeoff between performance and energy penalty in the hard decision fusion rule.
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Yuan, Wei Wen. "Optical wireless communications for micro-machines". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d0f2c779-fc66-4436-a831-fa65e1b36d5b.
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The main objective of this thesis is to develop a communication system that can minimize the micro-machine size and power consumption and maximize the link range and the number of micro-machines that can communicate simultaneously with the base station. Several possible communication systems are compared, including RF communications and active and passive free space optical communications. A directed, half duplex LOS link using a Ferroelectric liquid crystal (FLC) or multiple quantum well (MQW) modulating retroreflector-base passive uplink is then examined in more detail. Two potential geometries are described. In a broad-beam system, light from a source is broadcast to all micro-machines within the field of view (FOV). However, simulations show that the performance is unacceptable for most applications. In a narrow-beam system, light is holographically steered to active micro-machines within the same FOV. Therefore, the link budget has been improved. For a BER not exceeding 10-9, the 850 nm LC narrowbeam system can support maximum range of 146 m at a data rate of 10kbits/s, and the 1525 nm MQW narrowbeam system can support a maximum range of 34 m at a data rate of 10Mbits/s, when the transmitted power in the diffracted beam of the positive first order is 0.5 mW. Experiments have been carried out to verify the model. These were initially carried out with MQW Modulating RetroReflector (MRR). Results were then be used to modify the characteristics of these components in the model. Available components and discrete electronics have been used to set up a simple retro-reflecting link. Experiments have been performed at a limited data rate of 1 kbits/s over a limited range of 1m due to creating a uniform interrogation beam spot, and the active area of the receiver of 1 mm diameter. An algorithm to find the MQW MRR within the FOV is designed and tested.
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Mao, Chunxu. "Integrated filtering antennas for wireless communications". Thesis, University of Kent, 2017. https://kar.kent.ac.uk/69475/.
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In traditional radio frequency (RF) front-end subsystems, the passive components, such as antennas, filters, power dividers and duplexers, are separately designed and cascaded via the 50 Ω interfaces. This traditional approach results in a bulky and heavy RF front-end subsystem, and suffers from compromised efficiency due to the losses in the interconnections and the mismatching problems between different components. The frequency responses of the antennas such as the frequency selectivity and bandwidth are usually degraded, especially for microstrip antennas. To improve the frequency responses and reduce the size of RF front ends, it is important to investigate novel highly integrated antennas which exhibit multiple functions such as radiation, filtering, power dividing and combining or duplexing, simultaneously. In this thesis, several innovative designs of compact, multi-functional integrated an-tennas/arrays are proposed for wireless communication applications. First, new methods of designing integrated filtering antenna elements with broadband or dual-band performance are investigated. These antennas also feature high frequency selectivity and wideband harmonic suppression. Based on these studies, several integrated filtering array antennas with improved gains and frequency responses are developed for the first time. Compared with traditional array antennas, these proposed antennas exhibit improved bandwidths, out-of-band rejection and wideband harmonic suppression. The application of the filtering antennas in millimeter-wave (mm-Wave) frequency band is also investigated as it can potentially reduce the cost of the mm-Wave front-end subsystems significantly while providing the improved impedance bandwidth. The integrated design techniques are further developed to design novel dual-port highly integrated antennas with filtering and duplexing functions integrated. Such a new concept and the prototypes could find poten-tial applications in wireless communication systems and intelligent transportation system (ITS). In this thesis, comprehensive design methodologies and synthesis methods are provid-ed to guide the design of the integrated filtering antennas. The performance is evaluated with the help of full-wave electromagnetics (EM) simulations. All of the prototypes are fabricated and tested for validating the design concepts. Good agreement between the simulation and measurement results is achieved, demonstrating the integrated antennas have the advantages of compact size, flat gain performance, low losses and excellent harmonic suppression performance. These researches are important for modern wireless communication systems.
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Ahmad, Zaheer. "Video header compression for wireless communications". Thesis, University of Surrey, 2006. http://epubs.surrey.ac.uk/843682/.
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The delivery of high quality video to wireless users depends on achieving high compression efficiency and high robustness to wireless channel errors. Research on these topics has led to the introduction of a number of video codec standards. However, most of these standards incorporate redundant syntactical information that renders the video more susceptible to channel errors, and reduces the compression efficiency. This thesis presents a new approach to video compression that removes most of the problems associated with the excess syntax, a header compressor and decompressor is placed adjacent to encoder and decoder respectively. The compressor removes the excess header redundancy and decompressor regenerates the original header using already stored reference. The thesis investigates the syntactical header information of video coding standards MPEG-4 and H.264. The analysis shows that the overheads in small video packet may contribute up to 50% of the texture data. The video packet header fields are classified as static and dynamic. Based on the header analysis, a comprehensive header compression scheme is designed for MPEG-4 and H.264 video packets. For a practical scenario, simulations of video packets are carried out including the compressed IP/UDP/RTP overheads. The ROHC (RObust Header Compression) standard compresses the IP/UDP/RTP headers. In this thesis, ROHC parameters have been optimised for transmission over 3GPP simulated downlink channel. Furthermore, an improvement in the ROHC U-mode has been proposed to reduce the effects of unnecessary packet loss due to false context damage. Results show better video quality and lower packet loss rates with proposed scheme. The efficiency of the proposed video header compression scheme is evaluated with different combinations of encoding parameters. Experiments show the using the proposed video header compression scheme, up to 95% of header redundancy may be removed. Extensive simulations illustrate improvements in video quality due to the proposed header compression scheme under various channel conditions. The video quality is further enhanced by using a header-compression based unequal error protection scheme. The bits saved due to header compression can be utilised adaptively to protect the critical data at a fixed transmission rate. The results show significant improvement in objective and subjective video quality.
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Spilling, Anders Gil. "Self-organisation in future wireless communications". Thesis, University of Bristol, 2000. http://hdl.handle.net/1983/1d349f3a-d733-4a03-9d18-9e04d0c44aa1.
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Alizadeh, Ardalan. "Cognitive Communications for Emerging Wireless Systems". University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1470226402.
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Wu, Yue. "Active filter design for wireless communications /". The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486474078051051.
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Pinheiro, João Paulo Rocha. "Wideband power amplifier for wireless communications". Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/21658.
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Mestrado em Engenharia Eletrónica e TelecomunicaçõesEm anos recentes, com o desenvolvimento das tecnologias de telecomunicações, a alocação do espetro de frequências tem crescido consideravelmente. Os utilizadores finais exigem aparelhos capazes de operar com tecnologias que suportam taxas de transmissão cada vez mais elevadas (3G e 4G LTE) com compatibilidade com tecnologias como 2G GSM e 2.5G GPRS. Para que um telemóvel possa operar com todas as referidas tecnologias necessita de até 5 PAs para cada uma, resultando em maiores custos e espaço ocupado devido ao numero de dispositivos usados, para não mencionar o problema logístico para o fabricante do telemóvel já que cada um destes dispositivos ´e, por norma, produzido por diferentes fabricantes. Como as referidas tecnologias têm de coexistir, é necessário que as estações base continuem a receber e transmitir sinais no largo espetro de frequências alocado. O PA numa estacão base é o elemento mais dissipativo e a necessidade de usar diversos amplificadores implica, além do custo dos componentes, um elevado consumo de potência DC que se traduz em custos de energia substanciais para a empresa de telecomunicações. Portanto, o uso de um transmissor para cada frequência central está a tornar-se inaceitável. Um amplificador de banda larga capaz de operar dentro do espetro de frequências alocado e de suportar todas as normas de cada tecnologia, garantindo elevados níveis de potência de saída, linearidade e eficiência pode ser a solução para estes problemas. Esta tese foca-se no estudo do amplificador de banda larga. É apresentada uma comparação teórica de diversas arquiteturas de amplificadores de banda larga e é descrito e analisado o projeto e teste de um amplificador adaptado relativamente. São ainda conduzidos testes de depuração por forma a determinar as razões para a diferença observada entre as simulações e o os resultados medidos.
In recent years, with the development of telecommunication technologies, the frequency spectrum allocation has grown considerably. End users are requiring devices capable of operating with technologies supporting increasingly high data rates (3G and 4G LTE) with backward compatibility with technologies such as 2G GSM and 2.5G GPRS. For a mobile phone to work with all the referred technologies it must have up to ve PAs for each one, resulting in higher costs and occupied space due to the number of devices used, not to mention the logistic problem for the phone manufacturer since each of these devices is usually produced by di erent manufacturers. Since the referred technologies have to coexist, base stations are required to keep receiving and transmitting signals in the broad frequency spectrum allocated. A PA in a base station is the most dissipative element, and the need for several ampli ers implies, other than component cost, high DC power consumption which translates into substantial energy costs for a telecommunication company. Therefore, the use of a transmitter for each center frequency is becoming unacceptable. A wideband ampli er capable of operating within the allocated frequency spectrum and supporting all technology standards, granting high output power levels, linearity and e ciency can be the solution for these problems. This thesis focus on the study of the wideband ampli er. A theoretical comparison of several wideband ampli er architectures is presented and the design and testing of a reactively matched ampli er is further described and analyzed. Debugging tests are conducted in order to determine the reasons for the diferences observed between simulations and the measured results.
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Elissaios, Georgios. "Array communications in wireless sensor networks". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/11482.
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Mengot, Azibananye Massem. "Antenna array calibration in wireless communications". Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/11476.
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Krishnamurthy, Srikanth V. "System aspects of broadband wireless communications /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9820861.
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Chan, Chiu Lun. "Antennas for spectrum efficient wireless communications /". View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20CHANC.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 68-72). Also available in electronic version. Access restricted to campus users.
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Wang, Chengzhou. "CMOS power amplifiers for wireless communications /". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3112826.
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Peel, Christian B. "Studies in multiple-antenna wireless communications /". Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd331.pdf.
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Alresheedi, Mohammed Thamer. "Adaptation techniques in optical wireless communications". Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/6396/.
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The need for high-speed local area networks to meet the recent developments in multimedia and video transmission applications has recently focused interest on optical wireless communication. Optical wireless systems boast some advantages over radio frequency (RF) systems, including a large unregulated spectrum, freedom from fading, confidentiality and immunity against interference from electrical devices. They can satisfy the dual need for mobility and broadband networking. However, optical wireless links are not without flaws. They are affected by background noise (artificial and natural light sources) and suffer from multipath dispersion. The former can degrade the signal-to-noise ratio, while the latter restricts the maximum transmission rate available. The aim of this thesis is to investigate a number of techniques to overcome these drawbacks and design a robust high-speed indoor optical wireless system with full mobility. Beam delay and power adaptation in a multi-spot diffusing system is proposed in order to increase the received optical signal, reduce the delay spread and enable the system to operate at higher data rates. The thesis proposes employing angle diversity receivers and imaging diversity receivers as in order to reduce background noise components. Moreover, the work introduces and designs a high-speed fully adaptive optical wireless system that employs beam delay, angle and power adaptation in a multi-spot diffusing configuration and investigates the robustness of the link design in a realistic indoor office. Furthermore, a new adaptive optical wireless system based on a finite vocabulary of stored holograms is introduced. This method can effectively optimise the spots’ locations and reduce the design complexity of an adaptive optical wireless system. A fast adaptation approach based on a divide-andconquer methodology is proposed and integrated with the system to reduce the time required to identify the optimum hologram. The trade-off between complexity and performance enhancement of the adaptive finite holograms methods compared with the original beam power and angle adaptation is investigated.