Дисертації з теми "Wireless communication systems"
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1
Kodikara, Patabandi C. K. "Multimedia communications over 3G wireless communication systems." Thesis, University of Surrey, 2004. http://epubs.surrey.ac.uk/844270/.
Анотація:
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.
2
Jiang, Junyi. "Optical wireless communication systems." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/387239/.
Анотація:
In recent years, Optical Wireless (OW) communication techniques have attracted substantial attention as a benefit of their abundant spectral resources in the optical domain, which is a potential solution for satisfying the ever-increasing demand for increased wireless capacity in the conventional Radio Frequency (RF) band. Motivated by the emerging techniques and applications of OW communication, the Institute of Electrical and Electronics Engineers (IEEE) had released the IEEE standard 802.15.7 for short-range optical wireless communications, which categorised the Physical layer (PHY) of the OW communication into three candidate-solutions according to their advantages in different applications and environments: 1) Physical-layer I (PHY I): Free Space Optical (FSO)communication employs high-intensity Light Emitting Diodes (LEDs) or Laser Diodes (LDs) as its transmitter. 2) Physical-layer II (PHY II) uses cost-effective, low-power directional white LEDs for the dual function of illumination and communication. 3) Physical III (PHY-III) relies on the so-called Colour-Shift Keying (CSK) modulation scheme for supporting high-rate communication. Our investigations can be classified into three major categories, namely Optical Orthogonal Frequency Division Multiplexing (OFDM) based Multiple-Input Multiple-Output (MIMO) techniques for FSO communications in the context of PHY I, video streaming in PHY-II and the analysis and design of CSK for PHY-III. To be more explicit, in Chapter 2 we first construct a novel ACO-OFDM based MIMO system and investigate its performance under various FSO turbulence channel conditions. However, MIMO systems require multiple optical chains, hence their power consumption and hardware costs become substantial. Hence, we introduced the concept of Aperture Selection (ApS) to mitigate these problems with the aid of a simple yet efficient ApS algorithm for assisting our ACO-OFDM based MIMO system. Since the channel conditions of indoor Visible Light Communication (VLC) environments are more benign than the FSO-channels of Chapter 2, directional white LEDs are used to create an “attocell” in Chapter 3. More specifically, we investigate video streaming in a multi-Mobile Terminals (MTs) indoor VLC system relying on Unity Frequency Reuse (UFR) as well as on Higher Frequency Reuse Factor based Transmission (HFRFT) and on Vectored Transmission (VT) schemes. We minimise the distortion of video streaming, while satisfying the rate constraints as well as optical constraints of all the MTs. In Chapter 4 we analyse the performance of CSK relying both on joint Maximum Likelihood (ML) Hard-Detection (HD), as well as on the the Maximum A posteriori (MAP) criterion-based Soft-Detection (SD) of CSK. Finally, we conceive both two- stage and three-stage concatenated iterative receivers capable of achieving a substantial iteration gain, leading to a vanishingly low BER.
3
Alhartomi, Mohammed. "Collaborative optical wireless communication systems." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/13153/.
4
Toni, Laura <1982>. "Adaptive wireless multimedia communication systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2117/1/Laura_Toni_tesi.pdf.
Анотація:
In recent years, due to the rapid convergence of multimedia services, Internet and wireless communications, there has been a growing trend of heterogeneity (in terms of channel bandwidths, mobility levels of terminals, end-user quality-of-service (QoS) requirements) for emerging integrated wired/wireless networks. Moreover, in nowadays systems, a multitude of users coexists within the same network, each of them with his own QoS requirement and bandwidth availability. In this framework, embedded source coding allowing partial decoding at various resolution is an appealing technique for multimedia transmissions. This dissertation includes my PhD research, mainly devoted to the study of embedded multimedia bitstreams in heterogenous networks, developed at the University of Bologna, advised by Prof. O. Andrisano and Prof. A. Conti, and at the University of California, San Diego (UCSD), where I spent
eighteen months as a visiting scholar, advised by Prof. L. B. Milstein and Prof. P. C. Cosman. In order to improve the multimedia transmission quality over wireless channels, joint source and channel coding optimization is investigated in a 2D time-frequency resource block for an
OFDM system. We show that knowing the order of diversity in time and/or frequency domain can assist image (video) coding in selecting optimal channel code rates (source and channel code rates). Then, adaptive modulation techniques, aimed at maximizing the spectral efficiency, are investigated as another possible solution for improving multimedia transmissions. For both slow and fast adaptive modulations, the effects of imperfect channel estimation errors are evaluated, showing that the fast technique, optimal in ideal systems, might be outperformed by the slow adaptive modulation, when a real test case is considered. Finally, the effects of co-channel interference and approximated bit error probability (BEP) are evaluated in adaptive modulation techniques, providing new decision regions concepts, and showing how the widely used BEP
approximations lead to a substantial loss in the overall performance.
5
Toni, Laura <1982>. "Adaptive wireless multimedia communication systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/2117/.
Анотація:
In recent years, due to the rapid convergence of multimedia services, Internet and wireless communications, there has been a growing trend of heterogeneity (in terms of channel bandwidths, mobility levels of terminals, end-user quality-of-service (QoS) requirements) for emerging integrated wired/wireless networks. Moreover, in nowadays systems, a multitude of users coexists within the same network, each of them with his own QoS requirement and bandwidth availability. In this framework, embedded source coding allowing partial decoding at various resolution is an appealing technique for multimedia transmissions. This dissertation includes my PhD research, mainly devoted to the study of embedded multimedia bitstreams in heterogenous networks, developed at the University of Bologna, advised by Prof. O. Andrisano and Prof. A. Conti, and at the University of California, San Diego (UCSD), where I spent
eighteen months as a visiting scholar, advised by Prof. L. B. Milstein and Prof. P. C. Cosman. In order to improve the multimedia transmission quality over wireless channels, joint source and channel coding optimization is investigated in a 2D time-frequency resource block for an
OFDM system. We show that knowing the order of diversity in time and/or frequency domain can assist image (video) coding in selecting optimal channel code rates (source and channel code rates). Then, adaptive modulation techniques, aimed at maximizing the spectral efficiency, are investigated as another possible solution for improving multimedia transmissions. For both slow and fast adaptive modulations, the effects of imperfect channel estimation errors are evaluated, showing that the fast technique, optimal in ideal systems, might be outperformed by the slow adaptive modulation, when a real test case is considered. Finally, the effects of co-channel interference and approximated bit error probability (BEP) are evaluated in adaptive modulation techniques, providing new decision regions concepts, and showing how the widely used BEP
approximations lead to a substantial loss in the overall performance.
6
Yamashita, Shota. "Coexistence of Wireless Communication and Non-communication Systems." Kyoto University, 2018. http://hdl.handle.net/2433/232420.
7
Lukama, L. "Diversity systems for future wideband wireless communication systems." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249495.
8
Nordberg, Jörgen. "Signal enhancement in wireless communication systems /." Ronneby : Department of Telecommunications and Signal Processing, Blekinge Institute of Technology, 2002. http://www.bth.se/fou.
9
Sepasian, Mojtaba. "Multibiometric security in wireless communication systems." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/5081.
Анотація:
This thesis has aimed to explore an application of Multibiometrics to secured wireless communications. The medium of study for this purpose included Wi-Fi, 3G, and WiMAX, over which simulations and experimental studies were carried out to assess the performance. In specific, restriction of access to authorized users only is provided by a technique referred to hereafter as multibiometric cryptosystem. In brief, the system is built upon a complete challenge/response methodology in order to obtain a high level of security on the basis of user identification by fingerprint and further confirmation by verification of the user through text-dependent speaker recognition. First is the enrolment phase by which the database of watermarked fingerprints with memorable texts along with the voice features, based on the same texts, is created by sending them to the server through wireless channel. Later is the verification stage at which claimed users, ones who claim are genuine, are verified against the database, and it consists of five steps. Initially faced by the identification level, one is asked to first present one’s fingerprint and a memorable word, former is watermarked into latter, in order for system to authenticate the fingerprint and verify the validity of it by retrieving the challenge for accepted user. The following three steps then involve speaker recognition including the user responding to the challenge by text-dependent voice, server authenticating the response, and finally server accepting/rejecting the user. In order to implement fingerprint watermarking, i.e. incorporating the memorable word as a watermark message into the fingerprint image, an algorithm of five steps has been developed. The first three novel steps having to do with the fingerprint image enhancement (CLAHE with 'Clip Limit', standard deviation analysis and sliding neighborhood) have been followed with further two steps for embedding, and extracting the watermark into the enhanced fingerprint image utilising Discrete Wavelet Transform (DWT). In the speaker recognition stage, the limitations of this technique in wireless communication have been addressed by sending voice feature (cepstral coefficients) instead of raw sample. This scheme is to reap the advantages of reducing the transmission time and dependency of the data on communication channel, together with no loss of packet. Finally, the obtained results have verified the claims.
10
Parand, Farivar. "Cellular optical wireless communications systems." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270654.
11
Xia, Bin, and 夏斌. "Enhanced techniques for broadband wireless communications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29144231.
12
Liu, Lingjia. "On delay-sensitive communication over wireless systems." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2725.
13
Erkal, Hakan. "Optimization Of Energy Harvesting Wireless Communication Systems." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613937/index.pdf.
Анотація:
In an energy harvesting communication system, energy is derived from outside sources and becomes partially available at different points in time. The constraints induced by this property on energy consumption plays an active role in the design of efficient communication systems. This thesis focuses on the optimal design of transmission and networking schemes for energy harvesting wireless communication systems. In particular, an energy harvesting transmitter broadcasting data to two receivers in an AWGN broadcast channel assuming that energy harvests and data arrivals occur at known instants is considered. In this system, optimal
packet scheduling that achieves minimum delay is analyzed. An iterative algorithm, DuOpt, that achieves the same structural properties as the optimal schedule is proposed. DuOpt is proved to obtain the optimal solution when weaker user data is ready at the beginning. A dual problem is defined and shown to be strictly convex. Taking advantage of the dual problem, uniqueness of the solution of the main problem is proved. Finally, it is observed that DuOpt is almost two orders of magnitude faster than the SUMT (sequential unconstrained minimization technique) algorithm that solves the same problem.
14
Mazzaro, Gregory James. "Time-Frequency Effects in Wireless Communication Systems." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-09292009-115014/.
Анотація:
Time-frequency effects in wireless communication systems caused by narrowband resonances and coupled with device nonlinearities are revealed as new sources of co-site interference, exploited for the metrology of bandpass circuits, and employed to linearize amplitude-modulated transmissions. The transient properties of bandpass filters are found to last much longer than traditional time/bandwidth rules-of-thumb. The cause of this long-tail behavior is attributed to the coupled-resonator structure of the filter circuit. A solution method which uses lowpass prototyping is developed to reduce, by a factor of two, the complexity of the differential equation set describing a narrowband filter's transient response. Pulse overlap caused by the frequency dependence of long tails produced by filters is shown to cause intersymbol interference and intermodulation distortion in RF front-ends during frequency-hopped communications. The same properties which cause the ISI and IMD are used to develop three new transient methods for measuring resonant circuit parameters and a one-port method for extracting the operating band of a filter. A new signal-processing technique which combines time- and frequency-selectivity, Linear Amplification by Time-Multiplexed Spectrum, is developed to reduce IMD associated with amplitude modulation. Distortion reduction is demonstrated experimentally for multisines up to 20 tones.
15
Ng, Wing Kwan. "Energy efficient and secure wireless communication systems." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42810.
Анотація:
Orthogonal frequency division multiple access (OFDMA),
multiple--input multiple--output (MIMO), and base station (BS)
cooperation are the core techniques for the next generation wireless
communication systems. As the communication systems evolve, both
service providers and users are demanding not only high data rates,
but also energy efficiency and data security. As a result, it is
necessary to design novel resource allocation algorithms that meet
these new needs. This dissertation develops four resource allocation
algorithms which are tailored for different design goals and
communication environments.
For systems employing the combination of OFDMA and
decode-and-forward (DF) relaying technologies, we propose a novel
resource allocation algorithm for secure communication. The proposed
algorithm takes into account artificial noise generation to combat a
passive multiple antenna eavesdropper and the effects of imperfect
channel state information at the transmitter (CSIT).
Subsequently, we investigate the energy efficiency of OFDMA systems
which also provide communication security. We formulate the resource
allocation algorithm design as a non-convex optimization problem.
By exploiting the properties of fractional programming, the
considered non-convex optimization problem is transformed to an
equivalent convex optimization problem with a tractable solution,
which can be obtained with an iterative algorithm.
Thirdly, we study resource allocation for energy efficient
communication in OFDMA downlink networks with a large number of
transmit antennas. Our proposed resource allocation algorithm takes
into account the circuit power consumption, imperfect CSIT, a
minimum data rate requirement, and a maximum tolerable channel
outage probability.
Lastly, we propose a resource allocation algorithm for energy efficient communication in OFDMA downlink networks with cooperative
BSs. The resource allocation algorithm design problem is formulated
as a non-convex optimization problem which takes into account the
circuit power consumption, the limited backhaul capacity, and the
minimum required data rate for joint BS zero-forcing beamforming
(ZFBF) transmission. By using the concept of perturbation function,
we show that the duality gap in the considered system is always zero
under some general conditions, despite the non-convexity of the
primal problem. Thus, an efficient closed-form power allocation
solution for maximization of the energy efficiency of data
transmission is derived.
16
Samaras, Konstantinos. "Performance analysis of wireless infrared communication systems." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300127.
17
Sarkar, Md Zahurul Islam. "Information-theoretic security in wireless communication systems." Thesis, Queen's University Belfast, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579767.
Анотація:
The security in wireless communication networks is an important issue due to the mobility of users and network components, and the fact that the wireless medium is susceptible to eavesdropping and fraud. Motivated by the importance of security in the wireless communication networks, we study the secrecy capacity and secure outage performance of wireless channels in the presence of single as well as multiple eavesdroppers. At first, we study the effect of fading on the secrecy capacity and see, how we can achieve high data rates with reliability in spite of harsh wireless channel subject to the fading. Then, we study the effect of correlation on the secrecy capacity and quantify the loss of secrecy capacity of fading channels due to correlation. Since, the diversity is traditionally exploited to combat the fading in wireless systems. Therefore; secondly, we study the effect of channel diversity on the secrecy capacity of fading channels. This study is also useful to see, how we can overcome the loss of secrecy capacity due to correlation and obtain the target secrecy rate by improving the capacity of main channel exploiting diversity combining. We also investigate the effect of spatial multiplexing on the secrecy capacity and secure outage performance of keyhole multiple-input multiple-output (MIMO) channel. In addition, an achievable secrecy capacity region is developed using secret dirty-paper coding (SDPC) scheme to study the effect of transmit diversity on the secrecy capacity. Since, the group-oriented applications often require same data to be conveyed to multiple users simultaneously, and the traditional multicasting does not provide a secure framework for authentication and privacy for multicast sessions, the lack of which is currently preventing the large-scale deployment of group-oriented applications. Therefore, finally we study secure wireless multicasting and investigate the effect of fading and channel diversity on the secrecy multicast capacity.
18
Jalali, Sammuel. "Wireless Channel Equalization in Digital Communication Systems." Scholarship @ Claremont, 2012. http://scholarship.claremont.edu/cgu_etd/42.
Анотація:
Our modern society has transformed to an information-demanding system, seeking voice, video, and data in quantities that could not be imagined even a decade ago. The mobility of communicators has added more challenges. One of the new challenges is to conceive highly reliable and fast communication system unaffected by the problems caused in the multipath fading wireless channels. Our quest is to remove one of the obstacles in the way of achieving ultimately fast and reliable wireless digital communication, namely Inter-Symbol Interference (ISI), the intensity of which makes the channel noise inconsequential.
The theoretical background for wireless channels modeling and adaptive signal processing are covered in first two chapters of dissertation.
The approach of this thesis is not based on one methodology but several algorithms and configurations that are proposed and examined to fight the ISI problem. There are two main categories of channel equalization techniques, supervised (training) and blind unsupervised (blind) modes. We have studied the application of a new and specially modified neural network requiring very short training period for the proper channel equalization in supervised mode. The promising performance in the graphs for this network is presented in chapter 4.
For blind modes two distinctive methodologies are presented and studied. Chapter 3 covers the concept of multiple "cooperative" algorithms for the cases of two and three cooperative algorithms. The "select absolutely larger equalized signal" and "majority vote" methods have been used in 2-and 3-algoirithm systems respectively. Many of the demonstrated results are encouraging for further research.
Chapter 5 involves the application of general concept of simulated annealing in blind mode equalization. A limited strategy of constant annealing noise is experimented for testing the simple algorithms used in multiple systems. Convergence to local stationary points of the cost function in parameter space is clearly demonstrated and that justifies the use of additional noise. The capability of the adding the random noise to release the algorithm from the local traps is established in several cases.
19
Liu, Yi. "The performance of future wireless communication systems." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:a2f0b75e-3b0d-406e-af1b-6c5038c18fae.
Анотація:
Multimedia services provided through wireless networks, such as mobile television and video calls, have recently attracted great attention. These systems require higher data rates, better communication quality, and wider channel bandwidth compared with traditional wireless network services, such as voice calling and text messaging. In response to these demands, multiple-input multiple-output (MIMO) employing multiple antennas at both transmitter and receiver, has been investigated in recent years. Nevertheless, the major impediment in MIMO based wireless systems is the cost of the hardware due to the requirement of the complete radio frequency (RF) chain for each transmit and receive path. One technique named antenna subset selection has been proposed which can reduce the hardware complexity, for example, provide and smaller number of RF chains which are reconfigurable to serve multiple antennas, but retain good communication performance, such as increasing data rates and improving communication quality. On the other hand, network service providers have in recent years established wideband communication systems in order to provide more services and higher bandwidth to customers. However, this development lowers the communication link quality, since signals transmitted in wideband communication systems suffer frequency-selective fading. In order to reduce the fading, orthogonal frequency division multiplexing (OFDM) as a potential infrastructure in the fourth generation mobile communication networks is developed. Referring to the cost-performance ratio, an attractive future wireless system named antenna selection based MIMO-OFDM is considered to be widely utilized in civil wireless communications in near future. The working theory of antenna selection based MIMO-OFDM systems can be simply represented as that a data stream at each selected transmit/receiver antenna is sent/receive over a number of narrow band orthogonal subcarriers. This thesis addresses analysis of wireless channel and performance investigation of future wireless communication systems, such as MIMO and OFDM structures. Moreover, a novel significantly low computational complexity algorithm is introduced in this thesis, which is proposed for antenna selection MIMO-OFDM systems on the basis of multiple selection criteria. It is shown that the proposed selection algorithm clearly reduces the computational complexity load of the selection process and efficiently selects the optimum antenna subset of antenna selection MIMO-OFDM systems. The thesis concludes by outlining the advantage of the proposed antenna selection technique and points out its potential role in future wireless communications.
20
Butt, Muhammad Fasih Uddin. "Self-concatenated coding for wireless communication systems." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/159633/.
Анотація:
In this thesis, we have explored self-concatenated coding schemes that are designed for transmission over Additive White Gaussian Noise (AWGN) and uncorrelated Rayleigh fading channels. We designed both the symbol-based Self-Concatenated Codes considered using Trellis Coded Modulation (SECTCM) and bit-based Self- Concatenated Convolutional Codes (SECCC) using a Recursive Systematic Convolutional (RSC) encoder as constituent codes, respectively. The design of these codes was carried out with the aid of Extrinsic Information Transfer (EXIT) charts. The EXIT chart based design has been found an efficient tool in finding the decoding convergence threshold of the constituent codes. Additionally, in order to recover the information loss imposed by employing binary rather than non-binary schemes, a soft decision demapper was introduced in order to exchange extrinsic information with the SECCC decoder. To analyse this information exchange 3D-EXIT chart analysis was invoked for visualizing the extrinsic information exchange between the proposed Iteratively Decoding aided SECCC and soft-decision demapper (SECCC-ID). Some of the proposed SECTCM, SECCC and SECCC-ID schemes perform within about 1 dB from the AWGN and Rayleigh fading channels’ capacity. A union bound analysis of SECCC codes was carried out to find the corresponding Bit Error Ratio (BER) floors. The union bound of SECCCs was derived for communications over both AWGN and uncorrelated Rayleigh fading channels, based on a novel interleaver concept. Application of SECCCs in both UltraWideBand (UWB) and state-of-the-art video-telephone schemes demonstrated its practical benefits. In order to further exploit the benefits of the low complexity design offered by SECCCs we explored their application in a distributed coding scheme designed for cooperative communications, where iterative detection is employed by exchanging extrinsic information between the decoders of SECCC and RSC at the destination. In the first transmission period of cooperation, the relay receives the potentially erroneous data and attempts to recover the information. The recovered information is then re-encoded at the relay using an RSC encoder. In the second transmission period this information is then retransmitted to the destination. The resultant symbols transmitted from the source and relay nodes can be viewed as the coded symbols of a three-component parallel-concatenated encoder. At the destination a Distributed Binary Self-Concatenated Coding scheme using Iterative Decoding (DSECCC-ID) was employed, where the two decoders (SECCC and RSC) exchange their extrinsic information. It was shown that the DSECCC-ID is a low-complexity scheme, yet capable of approaching the Discrete-input Continuous-output Memoryless Channels’s (DCMC) capacity. Finally, we considered coding schemes designed for two nodes communicating with each other with the aid of a relay node, where the relay receives information from the two nodes in the first transmission period. At the relay node we combine a powerful Superposition Coding (SPC) scheme with SECCC. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second transmission period after re-encoding it, again, using a SECCC encoder. At the destination, the amalgamated block of Successive Interference Cancellation (SIC) scheme combined with SECCC then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput.
21
Moço, Andreia Vieira. "Cooperative diversity schemes for wireless communication systems." Master's thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/2055.
Анотація:
Mestrado em Engenharia Electrónica e TelecomunicaçõesA presente dissertação insere-se na área das comunicações sem fios, ou mais especificamente na temática da diversidade cooperativa. Neste trabalho é feito o estudo, implementação e avaliação do desempenho de esquemas de diversidade cooperativa de baixa complexidade para sistemas de comunicação móvel. Estes esquemas são mapeados em modelos de simulação baseados em OFDMA e são completamente simulados em CoCentric System Studio. Os resultados obtidos com os modelos desenvolvidos mostram que os esquemas de diversidade cooperativa atenuam os efeitos do desvanecimento induzido pela propagação multipercurso, aumentando desta forma a capacidade e cobertura dos sistemas wireless. Os ganhos são particularmente altos quando as perdas de percurso são consideráveis, como é o caso das zonas urbanas densas. ABSTRACT: This dissertation is inserted into the wireless communication, or more specifically, into the cooperative diversity field. within this thesis, the performance of low-complexity cooperative diversity schemes projected for mobile communication systems are studied, implemented and evaluated. These schemes are mapped into simulation models based on OFDMA and are fully simulated in the CoCentric System Studio environment. The obtained results show that the proposed cooperative schemes for the uplink communication mitigate fading induced by multipath propagation, thereby increasing the capacity and coverage of wireless systems. Cooperation gains are particularly high when multipath losses are considerable, as is the case for dense urban regions.
22
Liu, Feng. "Lifetime maximization through adaptive power allocation in reconfigurable system design for wireless systems /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?ECED%202009%20LIU.
23
Wang, Wenye. "Location management techniques for next generation wireless systems." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/13289.
24
Fan, Ho Yin. "MIMO detection schemes for wireless communication /." View Abstract or Full-Text, 2002. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202002%20FAN.
Анотація:
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002.Includes bibliographical references (leaves 64-66). Also available in electronic version. Access restricted to campus users.
25
Arredondo, Alberto. "Downlink beamforming for mobile communications." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035934.
26
Mundi, Anuj V. "PLC-WiFi hybrid broadband Internet deployment and security /." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006964.
27
Zhang, Mingliu. "Wireless communication for sparse and rural areas." Diss., Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/zhang/ZhangM0807.pdf.
28
Zhang, Lu. "Decentralized cooperative communication for wireless relaying networks." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 202 p, 2009. http://proquest.umi.com/pqdweb?did=1885757461&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
29
Wang, Yan. "Low power design for wireless communication system /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20WANG.
Анотація:
Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 171-179). Also available in electronic version. Access restricted to campus users.
30
Dong, Lu. "MIMO Selection and Modeling Evaluations for Indoor Wireless Environments." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19767.
Анотація:
Array-to-array, or multiple-input multiple-output (MIMO), links are known to provide extremely high spectral efficiencies in rich multipath environments, such as indoor wireless environments. The selection of a subset of receiver array antennas for a MIMO wireless link has been studied by many as a way to reduce cost and complexity in a MIMO system while providing diversity gain. Combined with a switched multi-beam beamformer, it becomes the beam selection system that can gain high signal-to-interference
ratio (SIR) improvement in an interference-imited environment.
The objective of this research is to evaluate the performance of low-complexity antenna or beam subset selection methods for small MIMO networks. The types of networks include (1) point-to-point MIMO links with out-of-system interference, (2)multi-user networks with a single, but possibly spatially distributed access point. We evaluate various selection techniques on measured indoor channels, which has not been done before. We propose a new practical selection metric, the peak-to-trough ratio of orthogonal frequency division multiplexing (OFDM) training symbols. We also compare antenna and beam selection on measured indoor channels under more general conditions than has previously been done. Finally, we consider some channel modeling issues associated with beamformers. We investigate the validity of three types of statistical MIMO channel models. A new beamformer is designed based on the ideal of the ``Weichselberger model.'
31
Zhang, Jun. "Power control in wireless ad hoc networks /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CSED%202007%20ZHANG.
32
Aggarwal, Pankaj. "Mobile authentication in wireless systems." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010839.
33
Wang, Shendi. "Efficient transmission design for machine type communications in future wireless communication systems." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23647.
Анотація:
With a wide range of potential applications, the machine type communication (MTC) is gaining a tremendous interest among mobile network operators, system designers, MTC specialist companies, and research institutes. The idea of having electronic devices and systems automatically connected to each other without human intervention is one of the most significant objectives for future wireless communications. Low data rate transmission and the requirement for low energy consumption are two typical characteristics for MTC applications. In terms of supporting low cots MTC devices, industrial standards will be more efficient if designers can re-use many features of existing radio access technologies. This will yield a cost effective solution to support MTC in future communication systems. This thesis investigates efficient MTC waveform and receiver designs for superior signal transmission quality with low operational costs. In terms of the downlink receiver design, this thesis proposes a novel virtual carrier (VC) receiver system for MTC receivers, which aims to reduce the maximum bandwidth to improve the data processing efficiency and cost-efficiency by using analogue filters to extract only sub-carriers of interest. For the VC receiver systems, we thus reduce the sampling rate in order to reduce the number of subsequent processing operations, which significantly reduces the analogue-to-digital converter (ADC) cost and power consumption while providing high signal to interference noise ratio (SINR) and low bit to error rate (BER) to support low data rate MTC devices. Our theoretical equations account for the interference effect of aliasing on the sub-carrier location, and this helps the system designer to evaluate what kind of filters and receiver sampling rate can be used to balance the energy cost and detection performance. In terms of the uplink waveform design, considering the enhanced number of MTC devices in the future communication systems, i.e. the fifth generation (5G) communications, the same tight synchronisation as used in today appears not to be cost-effective or even possible. Synchronisation signals, which aim to provide a perfect time or frequency synchronisation in the current fourth generation (4G) communication systems (known as the long-term evolution, LTE), is much more costly for low data rate MTC transmissions. The system bandwidth will be significantly reduced if a base station tries to synchronise all received signals among hundreds or thousands MTC devices in one transmission time period. In terms of relaxing the synchronisation requirements, this thesis compares and analyses the side-lobe reduction performance for several candidate multi-carrier waveforms to avoid these problems. We also propose the infinite impulse response universal filtered multi-carrier (UFMC) system and the overlap and add UFMC system, which significantly reduce the processing complexity compared with the state of the art UFMC techniques. This thesis derives closed-form expressions for the interference caused by time offsets between adjacent unsynchronised MTC users. Our analytical equations can be used in both simple and complex time-offset transmission scenarios, and enable the system designer to evaluate the SINR, the theoretical Shannon capacity and the BER performance.
34
Bala, Erdem. "Multichannel, multiuser and multiple antenna wireless communication systems." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 184 p, 2007. http://proquest.umi.com/pqdlink?did=1251904851&Fmt=7&clientId=79356&RQT=309&VName=PQD.
35
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.
36
Liu, Jianhua. "System design and signal processing for OFDM-based wireless communication systems." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006701.
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Azim, Ali Waqar. "Signal Processing Techniques for Optical Wireless Communication Systems." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAT059/document.
Анотація:
Le spectre radiofréquence (RF) diminue en raison d'une augmentation de la demande d'applications sans fil. Par conséquent, il existe une demande importante de régions de spectre alternatifs pour les communications afin d'incliner le spectre RF conventionnel. Dans ce contexte, les communications optiques sans fil (OWC) sont explorées comme un candidat potentiel pour compléter les communications RF. Le travail actuel se concentre sur les techniques d'atténuation des déficiences et les approches de modulation efficaces en énergie pour OWC. Dans un premier temps, on étudie le rapport de puissance crête à moyenne (PAPR) pour le multiplexage par répartition orthogonale de la fréquence optique (O-OFDM) et on présente deux techniques de réduction de PAPR orientées vers la décision. La complexité de ces méthodes est comparativement plus faible que celle des autres méthodes de réduction PAPR, tandis que leurs performances sont également analogues à celles des autres alternatives. Deuxièmement, une approche d'accès multiple par répartition en fréquence optique-porteuse unique (O-SCFDMA), appelée O-SCFDMA sans symétrie d'Hermitain (HSFO-SCFDMA) est proposée. Ce dernier évite la symétrie hermiatienne normalement attendue pour d'autres O-OFDM et Approches O-SCFDMA. Les résultats de la simulation affirment que HSFO-SCFDMA est plus efficace que toute autre approche O-SCFDMA pour OWC et manifeste le plus faible PAPR parmi les autres alternatives. Troisièmement, la performance du précodage est analysée pour l'O-OFDM (LACO-OFDM) asymétriquement en couches. Deux types de précodage sont utilisés, à savoir le précodage par transformée de Fourier et le précodage par transformée d'Hartley. Il est établi que le LACO-OFDM précodé a transformée Hartley présente le PAPR le plus faible et est moins vulnérable à la distorsion non linéaire introduite par les diodes électroluminescentes (LED), mais le rapport signale sur bruit (SNR) augmente ( électrique et optique à la fois) en raison de la structure en couches qui est plus élevée que le LACO-OFDM conventionnelleThe radio-frequency (RF) spectrum is dwindling due to an increase in the demand of wireless applications. Hence, there is substantial demand of alternative spectrum regions for communications to recline the conventional RF spectrum. In this context, optical wireless communications (OWC) is explored as a likely candidate to supplement the RF communications. The current work focuses on impairment mitigation techniques and energy-efficient modulation approaches for OWC. Firstly, the peak-to-average power ratio (PAPR) for optical-orthogonal frequency division multiplexing (O-OFDM) is studied and two decision-directed PAPR reduction techniques are presented. The complexity of these methods is comparatively lower than other PAPR reduction methods, whilst, their performance is likewise analogous with other alternatives. Secondly, an optical-single-carrier frequency division multiple access (O-SCFDMA) approach, referred to as Hermitain symmetry free O-SCFDMA (HSFO-SCFDMA) is proposed, that averts Hermiatian symmetry which is normally expected for other O-OFDM and O-SCFDMA approaches. The simulation results affirm that HSFO-SCFDMA is more efficient than any other O-SCFDMA approach for OWC and manifests the lowest PAPR among the other alternatives. Thirdly, the performance of precoding is analyzed for layered asymmetrically clipped O-OFDM (LACO-OFDM). Two types of precoding are employed, i.e., Fourier transform precoding and Hartley transform precoding. It is established that Hartley transform precoded LACO-OFDM exhibits the lowest PAPR and is less vulnerable to non-linear distortion introduced by the light emitting diodes (LEDs), howbeit, the signal-to-noise ratio (SNR) increase (both electrical and optical) owing to the layered structure is higher than conventional LACO-OFDM
38
Shum, Chin Yiu. "Detecting, locating, and tracking mobile user within a wireless local area network." HKBU Institutional Repository, 2013. http://repository.hkbu.edu.hk/etd_ra/1512.
39
McNair, Janise Yvette. "Handoff techniques for next generation wireless multimedia systems." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/15971.
40
Chen, Yingying, and 陳穎穎. "Micro-mobility management for next-generation wireless network." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29148212.
41
Guo, Xiaoyong. "Space-time code design for wireless communication systems." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 168 p, 2010. http://proquest.umi.com/pqdweb?did=1992441381&sid=9&Fmt=2&clientId=8331&RQT=309&VName=PQD.
42
Fang, Zuyuan. "Bandwidth allocation in wireless AD HOC networks /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?COMP%202004%20FANG.
Анотація:
Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 112-119). Also available in electronic version. Access restricted to campus users.
43
Wang, Hao Chen Biao. "Transceiver design issues for wireless multicarrier communication systems." Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2004. http://wwwlib.umi.com/cr/syr/main.
44
Wu, Peiran. "Transceiver optimization for broadband cooperative wireless communication systems." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/55220.
Анотація:
Cooperative broadband communications is a promising technique to improve the reliability, throughput, and coverage of the next generation wireless communication systems. Single-carrier transmission with frequency-domain equalization (SC-FDE) and orthogonal frequency-division multiplexing (OFDM) are the prevailing block based broadband schemes widely adopted in major wireless standards. Traditionally, these broadband schemes are deployed for point-to-point communications without the cooperation of any intermediate transmission nodes. However, as the communication systems evolve, both service providers and users are demanding higher data rates and non-seamless connection over large areas. As a result, it is necessary to design novel transceiver architectures that meet these stringent requirements. This dissertation proposes four such cooperative transceiver designs which are tailored for different communication scenarios. Firstly, for single-user SC-FDE broadband systems with multiple multi-antenna amplify-and-forward (AF) relays, we optimize the relay beamforming (rBF) filters and destination equalization filter based on the minimum mean-square error (MSE) criterion under an aggregate relay transmit power constraint. We also propose suboptimal rBF schemes which perform close to the optimal rBF scheme. Subsequently, we investigate single-user SC-FDE broadband MIMO AF relay systems. By exploiting the properties of the block-circulant channel matrices and the majorization theory, the problem is transformed into an equivalent power optimization problem with scalar variables. An alternating optimization algorithm is devised to obtain the optimal solution for the source and relay power allocation. Thirdly, we study a robust transceiver design for multiuser broadband systems with multiple single-antenna AF relays and in the presence of channel estimation errors. Our proposed design treats multiuser SC-FDE and OFDM based systems in a unified manner, where the goal is to maximize the network ABR subject to different types of relay power constraints. Lastly, we propose a robust transceiver design for single-user SC-FDE based multi-hop full-duplex decode-and-forward relay systems. The optimization problem is formulated as the minimization of the sum MSE or maximum MSE of different hops which takes into account the loopback interference of the full-duplex relays. We propose two algorithms to solve the resulting non-convex power allocation problems based on sequential geometric programming and alternating optimization, respectively.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
45
Liang, Yangwen. "Beamforming schemes for next generation wireless communication systems." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37957.
Анотація:
Multiple-input multiple-output (MIMO) and relaying are two promising techniques which will be employed in next generation wireless communication systems. Transmit beamforming (BF) and receive combining are simple yet popular methods for performance enhancement for MIMO and/or relaying. This thesis investigates several BF schemes for MIMO and relaying systems.
For systems combining MIMO and orthogonal frequency division multiplexing (MIMO-OFDM) technology, we propose a novel time-domain BF (TD-BF) scheme which uses cyclic BF filters (C-BFFs). Both perfect and partial channel state information at the transmitter are considered. The C-BFFs are optimized for maximum average mutual information per sub-carrier and minimum average uncoded bit error rate. We show that TD-BF has a more favorable performance/feedback rate trade-off than previously proposed frequency-domain BF schemes.
Secondly, BF for one-way cooperative networks with multiple multi-antenna amplify-and-forward relays in frequency-nonselective channels is considered. The source BF vector and the amplify-and-forward BF matrices at the relays are optimized for maximization of the signal-to-interference-plus-noise ratio (SINR) at the destination under three different power constraints. We show the benefits of having multiple antennas at the source and/or multiple multi-antenna relays.
Subsequently, we investigate filter-and-forward BF (FF-BF) for one-way relay networks in frequency-selective channels. For the processing at the destination, we investigate two different cases: a simple slicer, and a linear equalizer (LE) or a decision-feedback equalizer (DFE). For both cases, we optimize the FF-BF matrix filters at the relays for maximization of the SINR under a transmit power constraint, and for the first case we consider additionally optimization of the FF-BF matrix filters for minimization of the total transmit power under a quality of service constraint.
Leveraging results from one-way relaying, we also investigate FF-BF for two-way relay networks. For the simple slicer case, we show that the optimization problems are convex. For the LE/DFE case, we establish an upper and an achievable lower bound for an SINR max-min problem.
46
Chi, En Huang. "QoS-aware resource allocation in wireless communication systems." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43303.
Анотація:
With the rapid growth in demand for wireless communications, service providers are expected to provide always-on, seamless and ubiquitous wireless data services to a large number of users with different applications and different Quality of Service (QoS) requirements. The multimedia traffic is envisioned to be a concurrent mix of real-time traffic and non-real-time traffic. However, radio spectrum is a scarce resource in wireless communications. In order to adapt to the changing wireless channel conditions and meet the diverse QoS requirements, efficient and flexible packet scheduling algorithms play an increasingly important role in radio resource management (RRM).
Much of the published work in RRM has focused on exploiting multi-user and multi-channel diversities. In this thesis, we adopt an adaptive cross layer approach to exploit multi-application diversity in single-carrier communication systems and additionally, multi-bit diversity in multi-carrier communication systems. Efficient and practical resource allocation (RA) algorithms with finer scheduling granularity and increased flexibility are developed to meet QoS requirements. Specifically, for single-carrier communication systems, we develop RA algorithms with flow and user multiplexing while jointly considering physical-layer time-varying channel conditions as well as application-layer QoS requirements. For multi-carrier communication systems, we propose a bitQoS-aware RA framework to adaptively match the QoS requirements of the user application bits to the characteristics of the narrowband channels.
The performance gains achievable from the proposed bitQoS-aware RA framework are demonstrated with suboptimal algorithms using water-filling and bit-loading approaches. Efficient algorithms to obtain optimal and near-optimal solutions to the joint subcarrier, power and bit allocation problem with continuous and discrete rate adaptation, respectively, are developed. The increased control signaling that may be incurred, as well as the computational complexity as a result of the finer scheduling granularity, are also taken into consideration to establish the viability of the proposed RA framework and algorithms for deployment in practical networks. The results show that the proposed framework and algorithms can achieve a higher system throughput with substantial performance gains in the considered QoS metrics compared to RA algorithms that do not take QoS requirements into account or do not consider multi-application diversity and/or multi-bit diversity.
47
Zeng, Yu. "Adaptive modulation schemes for optical wireless communication systems." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3837/.
Анотація:
High-speed wireless optical communication links have become more popular for personal mobile applications. This is a consequence of the increasing demand from the personal information service boom. Compared to the radio frequency domain, optical wireless communication offers much higher speeds and bit rates per unit power consumption. As stated by the official infrared standard IrDA optical communication enjoys much lower power consumption than Bluetooth, with an inherent security feature while in Line of Sight (LOS) applications. There are also drawbacks such as the infrared radiation cannot penetrate walls as radio frequencies do and interference from the background contribute to the channel dispersions. Focus on the modulation aspects of the optical wireless communication, this thesis try to improve the channel immunity by utilising optimised modulation to the channel. Modulation schemes such as on off keying (OOK), pulse amplitude modulation (PAM) and pulse position modulation (PPM) and pulse position and amplitude modulation PAPM schemes have been validated. The combined power and bandwidth requirements suggest that the adaptive modulation schemes can provide reliability when deployed in a real time channel, resulting in improved system performance. As a result, an adaptive modulation technique is proposed. Extensive simulations of severe noise distraction have been carried out to validate the new scheme. The simulation results indicate that the new scheme can provide increased immunity against channel noise fluctuation at a relatively low complexity. The scheme obtained formed a basis to support reliable mobile optical wireless communication applications. The adaptive scheme also takes the real time channel conditions into account, which is different from existing schemes. Guaranteed system performance can be secured without compromising power and bandwidth efficiency. This is also a new approach to realise reliable optical wireless links. Fuzzy logic control module has been developed to match the adaptive pattern.
48
Balasubramanyam, Ramkumar. "Adaptive iterative multiuser detection for wireless communication systems." Thesis, University of Greenwich, 2008. http://gala.gre.ac.uk/8203/.
Анотація:
Wireless multi-user communication systems that operate in a low signal to interference noise ratio (SINR) region are studied in this thesis. This thesis examines a class of wireless communication systems that employs an adaptive receiver for multi-user symbol detection that operates in a low SINR (< 5 dB) region. Since the knowledge of channel-parameter estimates is unavailable at the receiver, a pilot (training) sequence is applied in the communication system, to learn the channel state information (CSI) at the receiver. In studying the classical view of a DFE, the mean square error (MSE) behaviour follows the bit error rate (BER) performance. Certain original results are obtained using the classical adaptive DFE to achieve minimum MSE, employing the least mean square (LMS) algorithm. The results thus obtained for an uncoded adaptive receiver system are applied to a coded system, transmitting either recursive systematic code (RSC) or turbo-code through a spread-spectrum multiuser multiple-path channel, which are referred to as two-stage and three-stage systems respectively in this thesis. The following claims are made based on the findings of this thesis: 1. It is known that a receiver implementing DFE can mitigate symbol-interference completely at high SINR. An adaptive LMS DFE realizes this by adapting the forward and backward filter coefficients with respective step-size constants. The classical approach to realizing interference mitigation was to set the forward and backward adaptation constants as the same. While this approach has provided interference mitigation at high SINR, it has been shown in this thesis that such an approach does not yield complete interference mitigation, even at high SINR. Instead, using different step-size constants at the backward and forward step-size constants provides the required optimality. 2. A decision feedback detector (DFD) mitigates the effects of interference on the information symbols that are transmitted through this communication channel. This thesis shows that an adaptive (LMS) DFD, using unequal compared to equal step-size constants to update the forward and backward filter coefficients, has a steady-state MSE improvement for an uncoded frequency selective communication channel. This thesis shows that, when the knowledge of CSI is not assumed to be known at a wireless receiver, a three-stage receiver has a BER performance improvement and operates at a lower SINR, without any additional computational complexity compared to a two-stage receiver.
49
Ali, Saqib. "Non-linearity mitigation in wireless broadband communication systems." Thesis, Lancaster University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543952.
50
Hashim, Mohamed H. "Dynamic impact of vegetation on wireless communication systems." Thesis, University of Surrey, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426023.