Cognitive radio (CR) is a novel wireless communication approach that may alleviate the looming spectrum-shortage crisis. Orthogonal frequency division multiplexing (OFDM) is an attractive modulation candidate for CR systems. In this thesis, we study resource allocation (RA) for OFDM-based CR systems using both aggressive and protective sharing. In aggressive sharing, cognitive radio users (CRUs) can share both non-active and active primary user (PU) bands. We develop a model that describes aggressive sharing, and formulate a corresponding multidimensional knapsack problem (MDKP). Low-complexity suboptimal RA algorithms are proposed for both single and multiple CRU systems. A simplified model is proposed which provides a faster suboptimal solution. Simulation results show that the proposed suboptimal solutions are close to optimal, and that aggressive sharing of the whole band can provide a substantial performance improvement over protective sharing, which makes use of only the non-active PU bands. Although aggressive sharing generally yields a higher spectrum-utilization efficiency than protective sharing, aggressive sharing may not be feasible in some situations. In such cases, sharing only non-active PU bands is more appropriate. When there are no fairness or quality of service (QoS) considerations among CRUs, both theoretical analysis and simulation results show that plain equal power allocation (PEPA) yields similar performance as optimal power allocation in a multiuser OFDM-based CR system. We propose a low-complexity discrete bit PEPA algorithm. To improve spectrum-utilization efficiency, while considering the time-varying nature of the available spectrum as well as the fading characteristics of wireless communication channels and providing QoS provisioning and fairness among users, this thesis introduces the following novel algorithms: (1) a distributed RA algorithm that provides both fairness and efficient spectrum usage for ad hoc systems; (2) a RA algorithm for non-real-time (NRT) services that maintains average user rates proportionally on the downlink of multiuser OFDM-based CR systems; and (3) cross-layer RA algorithms for the downlink of multiuser OFDM-based CR systems for both real-time (RT) services and mixed (RT and NRT) services. Simulation results show that the proposed algorithms provide satisfactory QoS to all supported services and perform better than existing algorithms designed for multiuser OFDM systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The aim of the thesis is to find out the most suitable channel estimation algorithms for the existing MIMO-OFDM SDR platform. Starting with the analysis of several prevalent channel estimation algorithms, MSE performance are compared under different scenarios. As a result of the hardware independent analysis, the complexvalued matrix computations involved in the algorithms are decomposed to real FLoating-point OPerations (FLOPs). Four feasible algorithms are selected for hardware dependent discussion based on the proposed hardware architecture. The computational latency is exposed as a manner of case study.

ABSTRACT In the past decade there has been a steady growth in development and implementation of wireless Local Area Networks and emerged as in the largest sectors of the telecommunication industry. Wireless local area network (WLANs) provides connectivity, mobility, and much higher performance and achievable data rate. WLAN is a new medium of access technology in the Local Area Network (LAN) world. Mostly WLAN applications are used in public sectors such as airports, banks, hotels, offices, city centres because of the flexibility of the people. Orthongonal Frequency Division Multiplexing OFDM has been adopted by IEEE 802.11’s standard as a transmission technique for high data rate in WLANs. Now IEEE 802.11 standard has been expanded to a family of WLAN standards. 802.11a and 802.11g both are used Orthongonal Frequency Division Multiplexing (OFDM) but operate in different frequency bands. It is shown that 802.11a provides high speed throughout the entire coverage area and long term solution however it does not provide better solution in most cases as compared to IEEE 802.11g. Matlab Simulation model based on IEEE 802.11a/g using different modulation and demodulation techniques such as BPSK, QPSK and QAM to analysis the best performance of IEEE 802.11a/g with implementation of OFDM. Keywords: Orthongonal Frequency Division Multiplexing (OFDM), IEEE 802.11s family, Wireless Local Area Network, Simulation, MATLAB / Summary The objective of this research is to examine the performance of the IEEE 802.11a and IEEE 802.11g WLAN comparing through OFDM modulation techniques. It is found that IEEE 802.11a/g provides similar quality except IEEE 802.11g provides wider range but range is the controversial topic in WLAN medium. In the other hand IEEE 802.11a provides more channels in 5 GHz bands as well as have a good enough signal qualities but there is range limitation factor. Range limitation in the enterprise and public sectors can be adjusting through installations more APs. The main disadvantage of the 802.11g is the frequency band is common and interference from the other networking technology such as Bluetooth, 2.04 GHz cordless phone and IEEE 802.11a avoid this interference because its operate in 5.GHz bands. Consequently, all the simulation is a comparison between simulated BER for a computer system and theoretical BER for serial systems it has been proved through simulation results that theoretical BER and simulated BER under AWGN are good agreement with each other. It means that I and Q points on constellation are much closer to each other the data error can be reduced as well as transmission easily influenced to noise. 64 QAM modulations are much better than 16 QAM when BER decrease SNR will be increase because signal is stronger than noise. 64 QAM modulations need higher bandwidth and give an excellent data rates as compared to 16 QAM.

This paper focuses on the design of a simple Time Division Multiple Access (TDMA) signaling structure for the Link Dependent Adaptive Radio (LDAR) prototype wireless radio communication system to meet the timing requirements of the iNET standard. Built for aeronautical telemetry, LDAR adapts its modulation and coding scheme based on the channel condition in real time. In this paper, a simple protocol for transmission of Command Message and Data Message between Ground Station and Test Article is discussed. This protocol includes all analysis for the continuous adaptation of modulation scheme and coding rate to maximize throughput while ensuring a minimum level of link quality. This project was a collaborative effort between Morgan State University and Georgia Tech Research Institute and is a continuation of our previously published work on LDAR.

Abstract The multiple–input multiple–output (MIMO) technique, applying several transmit and receive antennas in wireless communications, has emerged as one of the most prominent technical breakthroughs of the last decade. Wideband MIMO parameter estimation and its applications to the MIMO orthogonal frequency division multiplexing (MIMO–OFDM) channel estimation and mobile positioning are studied in this thesis. Two practical MIMO channel models, i.e., correlated-receive independent-transmit channel and correlated-transmit-receive channel, and associated space-time parameter estimation algorithms are considered. Thanks to the specified structure of the proposed training signals for multiple transmit antennas, the iterative quadrature maximum likelihood (IQML) algorithm is applied to estimate the time delay and spatial signature for the correlated-receive independent-transmit MIMO channels. For the correlated-transmit-receive MIMO channels, the spatial signature matrix corresponding to a time delay can be further decomposed in such a way that the angle of arrival (AOA) and the angle of departure (AOD) can be estimated simultaneously by the 2-D unitary ESPRIT algorithm. Therefore, the combination of the IQML algorithm and the 2-D unitary ESPRIT algorithm provides a novel solution to jointly estimate the time delay, the AOA and the AOD for the correlated-transmit-receive MIMO channels. It is demonstrated from the numerical examples that the proposed algorithms can obtain good performance at a reasonable cost. Considering the correlated-receive independent-transmit MIMO channels, channel coefficient estimation for the MIMO–OFDM system is studied. Based on the parameters of the correlated-receive independent-transmit MIMO channels, the channel statistics in terms of the correlation matrix are developed. By virtue of the derived channel statistics, a joint spatial-temporal (JST) filtering based MMSE channel estimator is proposed which takes full advantage of the channel correlation properties. The mean square error (MSE) of the proposed channel estimator is analyzed, and its performance is also demonstrated by Monte Carlo computer simulations. It is shown that the proposed JST minimum mean square error (MMSE) channel estimator outperforms the more conventional temporal MMSE channel estimator in terms of the MSE when the signals in the receive antenna array elements are significantly correlated. The closed form bit error probability of the space-time block coded OFDM system with correlation at the receiver is also developed by taking the channel estimation errors and channel statistics, i.e., correlation at the receiver, into account. Mobile positioning in the non-line of sight (NLOS) scenarios is studied. With the knowledge of the time delay, the AOA and the AOD associated with each NLOS propagation path, a novel geometric approach is proposed to calculate the MS's position by only exploiting two NLOS paths. On top of this, the least squares and the maximum likelihood (ML) algorithms are developed to utilize multiple NLOS paths to improve the positioning accuracy. Moreover, the ML algorithm is able to estimate the scatterers' positions as well as those of the MSs. The Cramer-Rao lower bound related to the position estimation in the NLOS scenarios is derived. It is shown both analytically and through computer simulations that the proposed algorithms are able to estimate the mobile position only by employing the NLOS paths.

Cette thèse étudie la possibilité d'appliquer les techniques de modulations multiporteuses de type OFDM dans les futurs systèmes de communications par satellite. Elle traite notamment du problème de synchronisation au niveau récepteur pour les systèmes de diffusion par satellite en bande Ka. L'objectif est de proposer une structure de réception ayant besoin du moins de ressources possibles pour synchroniser afin d'optimiser l'efficacité spectrale du système et obtenir un gain par rapport à un système monoporteuse. Une première partie du travail consiste à proposer et valider la structure de synchronisation. Ses performances en termes d'efficacité spectrale sont ensuite évaluées et comparées avec celles du DVB-S et du DVB-S2. Pour finir une étude de la complexité calculatoire de la structure proposée est menée. Les sources d'erreurs de synchronisation ayant été identifiées et leur impact sur les performances du système évalué, il s'avère que, mis à part l'erreur de fréquence horloge, les autres erreurs de synchronisation doivent être estimées et corrigées. La transmission en mode continu dans un système de diffusion par satellite permet l'utilisation d'une structure bouclée de type Non-Data-Aided en réception pour corriger les erreurs de synchronisation. Ceci évite l'utilisation de pilotes et permet ainsi d'améliorer l'efficacité spectrale du système. Cependant, cette structure de type aveugle nécessite une première étape de synchronisation grossière afin de limiter les interférences intersymboles et inter-porteuses pouvant conduire à une non convergence des boucles. Le procédé de synchronisation global s'effectue donc en deux étapes : une étape de synchronisation grossière utilisant l'intervalle de garde et quelques pilotes, suivie d'une étape de synchronisation plus fine utilisant des boucles de type Non-Data-Aided. L'étape de synchronisation grossière est dimensionnée (durée de l'intervalle de garde et nombre de pilotes) pour atteindre les performances d'estimation nécessaires à la convergence des boucles de la structure de synchronisation fine, tout en optimisant l'efficacité spectrale. L'efficacité spectrale obtenue est comparée avec celle des systèmes DVB-S et DVB-S2. Les performances de l'étape de synchronisation fine, en termes de dégradation du taux d'erreur binaire due aux erreurs de synchronisation, sont évaluées en l'absence puis en présence de bruit de phase. Les points de fonctionnement de la structure proposée sont donnés en utilisant les gabarits de bruit de phase des normes DVB-S2 et DVB-SH. Un gabarit de bruit de phase de Wiener conduisant aux gigues acceptées par le DVBS2 à l'entrée du décodeur est établi. Le temps d'accrochage, ainsi que la complexité calculatoire, de la structure proposée sont également évalués. / This thesis studies the applicability of OFDM techniques for future satellite telecommunications systems. In particular, he treats the synchronization problem at the receiver for satellite broadcasting systems in Ka band. The system uses QAM modulation with M phase stages and works in continuous mode, at small signal to noise ratio (typically at Eb/N0 = 0dB). The main objective of this thesis is to propose a receiver synchronization structure using as least resources as possible in order to optimize spectral efficiency. Two studies are carried out. The first study consists of proposing and validating a synchronization structure in the aim of optimizing spectral efficiency. The second study evaluates the performance of this structure then, compares it with existing standards such as DVB-S and DVB-S2 in terms of spectral efficiency. For first study, synchronization errors have been identified and their impact on system performance evaluated. These results prove that excepting clock frequency error, other synchronization errors have to be estimed and corrected. The transmission in continuous mode for fixed satellite broadcasting system allows the use of NDA (Non-Data-Aided) loop structure in order to avoid the use of pilots, then improve spectral efficiency. However, these algorithms need a coarse synchronization stage in order to limit interference terms. So, the synchronization includes a coarse stage in order to limit interference terms and a finer stage in order to improve system performance. For coarse synchronization stage, simulation results prove that algorithms using guard interval give better performance than whom using pilots. The second study evaluates performance of the proposed structure. In coarse synchronization stage, this evaluation allows to specify guard interval length then, calculate and compare system performance in terms of spectral efficiency with its in DVB-S and DVB-S2 standards. Then, performance evaluation of fine synchronization stage allows to calculate degradations of the proposed structure in the absence and in presence of phase noise models, one of important parameters in a telecommunications system. This stage allows not only to define operating points of the proposed structure in presence of phase noise models in existing standards but also to define phase noise mask of Wiener model supported by this structure. Finally, a study on the hanging time of the proposed structure allows to evaluate the time neccesary to this structure, based on blind algorithms, to be converged. Another study also evaluates the complexity of this structure. This study shows that the synchronization structure proposed in this thesis uses little resources both in terms of spectral efficiency and number of calculations.

In mobile communication channels information symbols are transmitted through a communication channel that is prone to fading and multipath propagation. At the receiver, the effect of multipath propagation is reduced by a process called channel equalization. Channel equalization relies on an accurate estimate of the channel state information (CSI). This estimate is obtained using a channel estimation algorithm. Mobile WiMAX is a recently released technology that makes use of an orthogonal frequency division multiplexing (OFDM) based physical layer to transmit information over a wireless communication channel. In this dissertation, frequency and time domain channel estimation methods typically used in classical OFDM systems, using block and comb type pilot insertion schemes, were analyzed and adopted for mobile WiMAX. Least squares (LS) and linear minimum mean square error (LMMSE) channel estimation methods were considered in the case of block type pilot insertion. In the case of comb type pilot insertion, piecewise constant, linear, spline cubic as well as discrete Wiener interpolation methods were considered. A mobile WiMAX simulation platform was developed as part of the dissertation to evaluate and compare the performance of these different channel estimation methods. It was found that the performance of the channel estimation methods, applied to a real world mobile WiMAX simulation platform, conforms to the expected performance of the corresponding classical OFDM channel estimation methods found in literature. / Dissertation (MEng)--University of Pretoria, 2009. / Electrical, Electronic and Computer Engineering / unrestricted

The integration of Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques has become a preferred solution for the high rate wireless technologies due to its high spectral efficiency, robustness to frequency selective fading, increased diversity gain, and enhanced system capacity. The main drawback of OFDM-based systems is their susceptibility to impairments such as Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), Symbol Timing Error (STE), Phase Noise (PHN), and fading channel. These impairments, if not properly estimated and compensated, degrade the performance of the OFDM-based systems In this thesis, a system model for MIMO-OFDM that takes into account the effects of all these impairments is formulated. Using this system model, we de-rive Cramer-Rao Lower Bounds (CRLBs) for the joint estimation of deterministic impairments in MIMO-OFDM system, which show the coupling effect among different impairments and the significance of the joint estimation. Also, Bayesian CRLBs for the joint estimation of random impairments in OFDM system are derived. Similarly, we derive Hybrid CRLBs for the joint estimation of random and deterministic impairments in OFDM system, which show the significance of using Bayesian approach in estimation. Further, we investigate different algorithms for the joint estimation of all impairments in OFDM-based system. Maximum Likelihood (ML) algorithms and its low complexity variants, for the joint estimation of CFO, SFO, STE, and channel in MIMO-OFDM system, are proposed. We propose a low complexity ML algorithm which uses Compressed Sensing (CS) based channel estimation method in a sparse fading sce-nario, where the received samples used for estimation are less than that required for a Least Squares (LS) or Maximum a posteriori (MAP) based estimation. Also, we propose MAP algorithms for the joint estimation of the random impairments, PHN and channel, utilizing their statistical knowledge which is known a priori. Joint estimation algorithms for SFO and channel in OFDM system, using Bayesian framework, are also proposed in this thesis. The performance of the estimation methods is studied through simulations and numerical results show that the performance of the proposed algorithms is better than existing algorithms and is closer to the derived CRLBs.

This thesis introduces performance analysis on the effect of using orthogonal polyphase spreading sequences in the uplink scenario of Code Division Multiple Access (CDMA) systems, with the use of two novel dynamic code allocation algorithms to exploit the cross-correlation properties of the spreading sequences. The analysis is also extended to the cooperative communication world, where a cooperative uplink technique is presented that builds on the results and conclusions achieved in the conventional uplink scenario. Theoretical analysis and simulation results are given to highlight the performance gains achieved using the proposed techniques. As Multiple-Input Multiple-Output (MIMO) systems have been increasingly studied and researched in the recent literature to accommodate for the high demand of current and future generations of wireless communications, this thesis follows the same pattern and investigates a new MIMO transmission technique, namely, Spatial Modulation. The thesis then proposes new novel Spatial Modulation enhancement techniques that focus on utilising more of the available system resources for further performance improvements.

Recently, orthogonal frequency-division multiplexing (OFDM) has been adopted for high-speed wireless communications due to its robustness against multipath fading. However, one of the main fundamental drawbacks of OFDM systems is the high peak-to-average-power ratio (PAPR). Several techniques have been proposed for PAPR reduction. Most of these techniques require transmitter-based (pre-compensated) processing. On the other hand, receiver-based alternatives would save the power and reduce the transmitter complexity. By keeping this in mind, a possible approach is to limit the amplitude of the OFDM signal to a predetermined threshold and equivalently a sparse clipping signal is added. Then, estimating this clipping signal at the receiver to recover the original signal. In this work, we propose a Bayesian receiver-based low-complexity clipping signal recovery method for PAPR reduction. The method is able to i) effectively reduce the PAPR via simple clipping scheme at the transmitter side, ii) use Bayesian recovery algorithm to reconstruct the clipping signal at the receiver side by measuring part of subcarriers, iii) perform well in the absence of statistical information about the signal (e.g. clipping level) and the noise (e.g. noise variance), and at the same time iv is energy efficient due to its low complexity. Specifically, the proposed recovery technique is implemented in data-aided based. The data-aided method collects clipping information by measuring reliable 
data subcarriers, thus makes full use of spectrum for data transmission without the need for tone reservation. The study is extended further to discuss how to improve the recovery of the clipping signal utilizing some features of practical OFDM systems i.e., the oversampling and the presence of multiple receivers. Simulation results demonstrate the superiority of the proposed technique over other recovery algorithms. The overall objective is to show that the receiver-based Bayesian technique is highly recommended to be an effective and practical alternative to state-of-art PAPR reduction techniques.