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The monitoring and study of the earth�s atmosphere is becoming an increasingly important task given the current uncertainties in climate prediction. Areas where lidar has been used to further understanding of the atmosphere include monitoring of greenhouse gases, global warming, stratospheric ozone depletion, photochemical smog and aerosol photochemistry. However, the potentially severe long term effects of anthropogenic aerosols on earth�s biosphere are poorly understood. This project seeks to apply state of the art laser technology to develop an innovative multiwavelength lidar system capable of providing new information and new insights into the field of tropospheric aerosol lidar. Several novel tunable laser and laser-like sources have been investigated and developed for the purpose of tropospheric aerosol lidar at The National Institute of Water and Atmospheric Research (Niwa), Central Otago. Multiwavelength operation in the visible and near infrared portion of the spectrum has been emphasised with the sources developed collectively spanning the wavelength interval of 400-1369 nm. The laser sources investigated were the LiF:F2+ colour centre, Titanium Sapphire (Ti:sapphire) and barium nitrate Raman lasers. In addition to the laser sources, the β-barium borate optical parametric oscillator (BBO OPO) was characterised. For each of the sources, lidar relevant aspects were studied. The results recorded include conversion efficiency with respect to the pump source, linewidth and tuning characteristics, beam quality, temporal behaviour, and device reliability and ruggedness. It was found that the LiF:F2+ laser offered significantly lower threshold, broader tuning and higher output pulse energies than the Ti:sapphire laser in the 900-1000 nm region. The high optical gain of the LiF:F2+ medium facilitated cavity optical alignment and operation of the system. The high gain also resulted in temporal behaviour well suited to the existing Niwa lidar detection scheme. When using a 5 ns pump source, amplified spontaneous emission (ASE) was found to limit the laser tuning range and efficiency. The barium nitrate Raman laser was based on a simple linear cavity arrangement which resulted in a compact and robust device with no moving components. The stimulated Raman scattering process offers relatively narrow linewidth laser operation at the first and second Stokes wavelengths of 1197 nm and 1369 nm respectively. This laser offered efficient operation once the high operation threshold was reached. Second harmonic generation was used to extend the number of potential lidar transmitter lines produced. The barium nitrate Raman laser possessed high beam divergence and a maximum of three discrete transmitter wavelengths. The BBO OPO used a type I collinear signal resonant configuration. A plane-plane cavity configuration with pump reflection was found to provide simplicity of design, low threshold, highly efficient operation and output pointing stability. The BBO OPO signal wavelength could be tuned over the wavelength interval of 400-700 nm. The disadvantage of the plane cavity was high output beam divergence. However, this was successfully brought within the required limits through the use of a 40 mm long cavity in conjunction with an expanding and collimating telescope. As a result of the study, a Tunable lidar Transmitter (TLT) system based on the BBO OPO was designed and constructed at the Physics Department. The TLT was computer-controlled using custom written software and constructed in a self contained modular manner with all required mechanical, electrical and optical components. A user manual was also written to accompany the TLT. The TLT was installed at Niwa and was successfully used to gather preliminary multiwavelength lidar data. The TLT BBO OPO threshold occurred for a pump energy of 5.2 mJ (10.6 MW/cm2) and had a maximum slope efficiency of 53%. Signal efficiency varied from 24-41-35% over the intervals of 410-500-600 nm. A maximum signal energy of 21 mJ was obtained for a signal wavelength of 492 nm when using the maximum available pump energy of 42 mJ. OPO signal linewidth varied from 0.1-1-8 nm over the signal wavelength intervals of 400-600-700 nm. The associated OPO finesse varied between 370 and 100 as the signal wavelength was tuned over the wavelength interval of 400-600 nm. The temporal behaviour of the BBO OPO was a slowly varying function of pump energy and closely followed the temporal behaviour of the pump laser, making it well suited to the existing Italian lidar detection and timing scheme.

Dans cette thèse, nous étudions les trois sujets suivants sur les systèmes de multiples entrées multiples sorties (MIMO) avec retour limité: Distorsion bout-à-bout: La première partie de la thèse présente l'impact conjoint des les nombres d'antenne, le ratio de bande passante de la source au canal, la corrélation spatiale et diversité dans le temps sur l'espérance de la distorsion optimale bout-à-bout dans les MIMO systèmes sans panne. En particulier, repose sur l'expression analytique pour tout les ratios du signal au bruit (SNR), l'expression asymptotique de l'espérance de la distorsion optimal bout-à-bout au SNR élevé est dérivé, composé de l'exposant de distorsion optimale et le facteur de distorsion optimale. Les résultats des simulations montrent que, à un SNR élevé pratique, l'analyse sur les impacts de l'exposant de distorsion optimale et le facteur de distorsion optimale explique le comportement de la distorsion optimale bout-à-bout. Les résultats présentés dans cette partie pourraient être les objectifs de performance pour les systèmes qui transmettent les sources analogique et en outre les directives sur la conception du système. Retour analogique du canal: Dans la seconde partie de cette thèse, nous proposons d'appliquer le codage bloc d'espace-temps orthogonal (OSTBC) sur retour analogique linéaire du canal. Considérant l'information du canal MIMO est une sorte de source vectorielle analogique, par rapport au retour du canal quantifié, le retour analogique linéaire a les avantages comme sans panne, l'adaptation automatique au canal et peu complexe. Il est prouvé que la méthode de transmission analogique linéaire OSTBC peutatteindre le borne de filtre adapté (MFB) sur SNR reçu. Par rapport en méthode analogique linéaire du codage bloc d'espace-temps circulant, la méthode linéaire analogique OSTBC obtient de meilleurs résultats à l'égard de SNR reçu et erreur quadratique moyenne (MSE) ; Par rapport en méthode de la quantification vectorielle aléatoire, les résultats des simulations montrent que sous une contrainte stricte de latence, leur performances sont proches à l'égard de l'erreur moyenne au sens et la méthode linéaire analogique OSTBC exécute encore mieux à l'égard erreur quadratique moyenne. Nous étudions également l'incidence de appliquer le retour linéaire analogique OSTBC au beamforming en liaison descendante pour multiutilisateurs MIMO et nous montrons que le retour linéaire analogique OSTBC peut rendre l'approche du système des performances optimales dans un temps de latence court. Multiplexage par couche: Dans la troisime partie de cette thèse, en considérant les systèmes avec des blocs courts, une nouvelle stratégie de multi-plexage par couches est proposée d'adapter un canal incertain par le codage couche-temps Walsh, l'annuleur d'interférence successif et HARQ signalisation. Comme l'illustrent les résultats de la simulation, en raison de ses performances proches mais beaucoup moins complexe, cette stratégie serait un bon substitut µa la stratégie de modulation QAM adaptive qui est largement utilise.

<p>The first part of the thesis (Part I) is devoted to find methods to describe transient behaviour of traffic processes, where the main emphasis is put on the description and analysis of excess periods and excess volumes of quite general stochastic processes. By assuming that traffic changes on different time scales, the transient characteristics such as excess periods could be important measures to describe periods of congestion on a communication link and moreover, the corresponding excess volume will represent lost information during such periods. Although the results obtained are of rather general nature, they provide some rather fundamental insight into transient characteristics of traffic processes. The distributions of the length of excess periods may then be expressed it terms of some excess probabilities that are related to the minimum of the process in the time interval considered. Similar relationsfor the excess volumes are harder to obtain and require the joint probability of the arrived volume and the minimum of the process in the same time interval.</p>

Multiple-input multiple-output (MIMO) antennas can be exploited to provide high data rate using a limited bandwidth through multiplexing gain. MIMO combined with orthogonal frequency division multiplexing (OFDM) could potentially provide high data rate and high spectral efficiency in frequency-selective fading channels. MIMO-OFDM technology has been widely employed in modern communication systems, such as Wireless Local Area Network (WLAN), Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX). However, most of the conventional schemes either are computationally prohibitive or underutilize the full performance gain provided by the inherent merits of MIMO and OFDM techniques. In the first part of this dissertation, we firstly study the channel matrix inversion which is commonly required in various MIMO detection schemes. An algorithm that exploits second-order extrapolation in the time domain is proposed to efficiently reduce the computational complexity. This algorithm can be applied to both linear detection and non-linear detection such as ordered successive interference cancellation (OSIC) while maintaining the system performance. Secondly, we study the complexity reduction for Lattice Reduction Aided Detection (LRAD) of MIMO-OFDM systems. We propose an algorithm that exploits the inherent feature of unimodular transformation matrix that remains the same for relatively highly correlated frequency components. This algorithm effectively eliminates the redundant brute-force lattice reduction iterations among adjacent subcarriers. Thirdly, we analyze the impact of channel coherence bandwidth on two LRAD algorithms. Analytical and simulation results demonstrate that carefully setting the initial calculation interval according to the coherence bandwidth is essential for both algorithms. The second part of this dissertation focuses on efficient multi-user (MU) scheduling and coordination for the uplink of WLAN that uses MIMO-OFDM techniques. On one hand, conventional MU-MIMO medium access control (MAC) protocols require large overhead, which lowers the performance gain of concurrent transmissions rendered by the multi-packet reception (MPR) capability of MIMO systems. Therefore, an efficient MU-MIMO uplink MAC scheduling scheme is proposed for future WLAN. On the other hand, single-user (SU) MIMO achieves multiplexing gain in the physical (PHY) layer and MU-MIMO achieves multiplexing gain in the MAC layer. In addition, the average throughput of the system varies depending on the number of antennas and users, average payload sizes, and signal-to-noise-ratios (SNRs). A comparison on the performance between SU-MIMO and MU-MIMO schemes for WLAN uplink is hence conducted. Simulation results indicate that a dynamic switch between the SU-MIMO and MU-MIMO is of significance for higher network throughput of WLAN uplink. / Graduation date: 2013

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 82-85). Also available on the World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 175-177).

The first part of the thesis (Part I) is devoted to find methods to describe transient behaviour of traffic processes, where the main emphasis is put on the description and analysis of excess periods and excess volumes of quite general stochastic processes. By assuming that traffic changes on different time scales, the transient characteristics such as excess periods could be important measures to describe periods of congestion on a communication link and moreover, the corresponding excess volume will represent lost information during such periods. Although the results obtained are of rather general nature, they provide some rather fundamental insight into transient characteristics of traffic processes. The distributions of the length of excess periods may then be expressed it terms of some excess probabilities that are related to the minimum of the process in the time interval considered. Similar relationsfor the excess volumes are harder to obtain and require the joint probability of the arrived volume and the minimum of the process in the same time interval.

This thesis studies a two-way relay network (TWRN), which consists of two single antenna source nodes and a multi-antenna relay node. The source nodes exchange information via the assistance of the relay node in the middle. The relay scheme in this TWRN is amplify-and-forward (AF) based analog network coding (ANC). A robust beamforming matrix optimization algorithm is presented here with the objective to minimize the transmit power at the relay node under given signal to interference and noise ratio (SINR) requirements of source nodes. This problem is first formulated as a non-convex optimization problem, and it is next relaxed to a semi-definite programming (SDP) problem by utilizing the S-procedure and rank-one relaxation. This robust beamforming optimization algorithm is further validated in a MATLAB-based orthogonal frequency-division multiplexing (OFDM) MIMO two-way relay simulation system. To better investigate the performance of this beamforming algorithm in practical systems, synchronization issues such as standard timing offset (STO) and carrier frequency offset (CFO) are considered in simulation. The transmission channel is modeled as a frequency selective fading channel, and the source nodes utilize training symbols to perform minimum mean-square error (MMSE) channel estimation. BER curves under perfect and imperfect synchronization are presented to show the performance of TWRN with ANC. It is shown that the outage probability of robust beamforming algorithm is tightly related to the SINR requirements at the source nodes, and the outage probability increases significantly when the SINR requirements are high.