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University, Diss., 2002--Kaiserslautern.

Zugl.: Ulm, Univ., Diss.

Downlink power control and beamforming designs in wireless system have been a recent research focus. To achieve reliable and efficient designs, good estimation of wireless channel knowledge is desired. However, the presence of uncertain channel knowledge due to constant changing radio environment will cause performance degradation in system designs. Thus the mismatches between the actual and presumed channel state information (CSI) may frequently occur in practical situations. Robust power control and beamforming were introduced considering the channel uncertainty. In this thesis, a new robust downlink power control solution based on worst-case performance optimization is developed. Our approach explicitly models uncertainties in the downlink channel correlation (DCC) matrices, uses worst-case performance optimization and guarantees that the quality of service (QoS) constraints are satisfied for all users using minimum amount of power. An iterative algorithm to find the optimum power allocation is proposed. The key in the iteration is the step to solve an originally non-convex problem to obtain worst-case uncertainty matrices. When the uncertainty is small enough to guarantee that the DCC matrices are positive semidefinite, we obtain a closed-form solution of this problem. When the uncertainty is large, we transform this intractable problem into a convex problem. Simulation results show that our proposed robust downlink power control using the approach of worst-case performance optimization converges in a few iterations and reduces the transmission power effectively under imperfect knowledge of the channel condition. / Thesis / Master of Applied Science (MASc)

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / What do you do when your downlink telemetry needs outstrip your downlink bandwidth capability? The telemetry needed to support construction and operation of the largest, most complex engineering project ever undertaken, the International Space Station (ISS), already requires utilization of the full capacity of the downlink S-band capacity, yet there are additional systems and capabilities still to be added by NASA and the International Partners. The ISS Command and Telemetry Team has developed a method of swapping packets of telemetry that are intended for special operations, while simultaneously sending essential systems telemetry and less critical telemetry that is needed on a continuous basis. To support this attempt to “make available all of the data at least some of the time” the team developed concepts for grouping telemetry into families that would always be selected as a group and then created a set of metadata associated with these groups. This metadata is pre-defined to support automated selection and scrubbing of telemetry to correspond to major upgrades in the command and control software for the ISS. The new process will at least double the effective S-band downlink bandwidth. It will also provide automated selection, scrubbing, reporting and verification of telemetry selections.

The newly defined NB-IoT standard currently lacks a toolkit and simulator. In order to develop algorithms for this new standard there is a need for channels and signals as reference during tests. MATLAB is commonly used for testing LTE signals and therefore the toolkit was developed in this environment. The toolkit focuses primarily on the Layer 1-relevant functionality of NB-IoT, the grid generation, encoding, rate-matching and modulation of channels. The simulator focuses on testing the developed toolkit in a virtual LTE NB-IoT environment. The virtual environment attempts to emulate a base station and a terminal. The path followed is scheduling, channel processing, grid generation, QPSK and OFDM modulation through a modeled channel, OFDM demodulation, channel estimation, equalisation, QPSK demodulation and reversal of channel processing. The simulator tests primarily the NPDSCH channel implementations. Measurements of bit error and block error rates were made and it was concluded that they follow the expected trends. More testing is required to validate the remaining channels. A sector equaliser and an interpolating equaliser were tested by measuring block error rate and checking constellation diagrams and it was concluded that the performance of the interpolation equaliser is more consistent. In order to improve the equalisation further the noise estimation must be reworked.

The coding and transmission of the massive datasets captured by Earth Observation (EO) satellites is a critical issue in current missions. The conventional approach is to use compression on board the satellite to reduce the size of the captured images. This strategy exploits spatial and/or spectral redundancy to achieve compression. Another type of redundancy found in such data is the temporal redundancy between images of the same area that are captured at different instants of time. This type of redundancy is commonly not exploited because the required data and computing power are not available on board the satellite. This paper introduces a coding scheme for EO satellites able to exploit this redundancy. Contrary to traditional approaches, the proposed scheme employs both the downlink and the uplink of the satellite. Its main insight is to compute and code the temporal redundancy on the ground and transmit it to the satellite via the uplink. The satellite then uses this information to compress more efficiently the captured image. Experimental results for Landsat 8 images indicate that the proposed dual link image coding scheme can achieve higher coding performance than traditional systems for both lossless and lossy regimes.

Cette étude porte sur l’allocation de ressources radio dans les réseaux LTE à forte mobilité. En particulier, il s’agit de concevoir des stratégies d’allocation de ressources capables d’améliorer la qualité de service des flux multimédia dans un contexte de forte mobilité des terminaux. Pour atteindre ces objectifs, l’étude a été menée en deux étapes. Dans un premier temps les travaux se sont déroulés dans un contexte où l’aspect forte mobilité n’a pas été pris en compte. Cela a permis de bien maitriser tous les aspects liés à l’allocation de ressources dans le LTE tout en proposant de nouvelles méthodes meilleures que celles existantes. Une fois cette tâche accomplie, l’aspect forte mobilité a été ajouté au problème et des stratégies adaptées à ce contexte ont été proposées. Néanmoins, dû aux différences entre les liens montants et descendants, l’étude a été menée dans les deux directions. Comme première contribution, nous avons conçu deux stratégies pour améliorer l’allocation de ressources sur la liaison descendante dans un contexte où la forte mobilité n’a pas été prise en compte. La première méthode est un mécanisme qui améliore cette allocation en particulier dans les scénarios d’overbooking en faisant un compromis entre l’équité, le débit global du système et les exigences de qualité de service des applications. La seconde stratégie permet non seulement de satisfaire aux contraintes de délais mais également de garantir un très faible taux de perte de paquets aux services de type multimédias. Les performances des systèmes proposés ont été évaluées par des simulations en les comparant à d’autres mécanismes dans la littérature. Les analyses ont démontré leur efficacité et révélé qu’elles obtenaient les meilleures performances. Notre deuxième contribution a permis d’améliorer l’allocation de ressources toujours dans un contexte de non prise en compte de la forte mobilité, mais cette fois ci sur le lien montant et pour des flux de type vidéo téléphonie. Nous avons conçu un nouveau protocole qui réduit de façon considérable les retards causés par l’allocation dynamique des ressources. L’idée consiste à allouer des ressources à ces trafics en utilisant une stratégie semi-persistante associée à un processus de pré-allocation. Les performances de notre méthode ont été évaluées par simulations et les résultats ont montré qu’elle fournissait le meilleur support en qualité de service. La dernière partie de nos travaux s’est intéressée au problème d’allocation de ressources dans les scénarios de fortes mobilités des terminaux. Dans cette partie, nous avons élaboré deux stratégies efficaces convenant aux scénarios véhiculaires. La première méthode est une technique permettant de maintenir le niveau de qualité de service nécessaire pour le bon fonctionnement des applications vidéo des utilisateurs ayant les vitesses les plus élevées. Elle consiste à déterminer en fonction des différentes vitesses des utilisateurs, le taux minimum de rapports CQI à envoyer à la station de base. Quant à la seconde stratégie, c’est un procédé d’ordonnancement opportuniste qui améliore la qualité de service des applications vidéo des utilisateurs ayant les vitesses les plus élevées. Avec cette stratégie, ces utilisateurs obtiennent une plus grande priorité et acquièrent ainsi beaucoup plus de ressources. / Abstract Our thesis focuses on issues related to resources allocation in LTE Networks. In particular the purpose of this study is to design efficient scheduling algorithms to improve the QoS of real time flows in a context of high mobility of the users. To reach this goal, the study has been carried out in two steps. At first, in order to have an expert knowledge of the key facets of LTE scheduling, we conducted the study in a context where the high mobility aspect of the node was not taken into account. This helped not only to critically analyze the literature but also to propose new schemes to improve QoS of real time applications. After that, the high mobility parameter has been added and innovative methods dealing with this context have been designed. Nevertheless due to the existing differences between the downlink and the uplink, the issue was tackled in each of the aforementioned directions. We firstly addressed the problem of improving the scheduling of downlink communications in a context where the high mobility was not taken into account. Two major methods have been designed for this purpose. The first one is an innovative scheme which improves resources assignment in overbooking scenarios by doing a trade-off between fairness, overall system through put and QoS requirements. The second one is an enhanced scheduling scheme which provides strict delay bounds and guarantees very low packet loss rate to multimedia flows. The performance of the proposed schemes have been evaluated by simulations and compared to other schemes in the literature. The analyses demonstrated their effectiveness and showed that they outperformed the existing ones. The second contribution concerned the problem of improving the scheduling of uplink communications in a context where the high mobility was not taken into account. We designed a novel scheduling protocol which improves resources allocation for videotelephony flows and reduces the delay caused by dynamic scheduling. It consists in scheduling such traffics using a semi-persistent strategy associated with a provisioning process. The performance of our proposed method have been evaluated by simulations and results demonstrated its effectiveness by showing that it improved videotelephony flows performance and provided the best QoS support compared to the dynamic scheduling.The last contribution addressed the problem of resources allocation in high mobility scenarios. In this part, the high mobility aspect was taken into account for designing suitable schemes for vehicular scenarios. We proposed in this way two efficient strategies. The first one is a technique which maintains the required level of QoS for supporting video users at high velocities. It consists in identifying depending on the UEs velocity, the minimum CQI reports rate in order to maintain the required QoS. The second proposed strategy is an opportunistic method which improves the performance of high speed video users. With this strategy, more priority are given to the UEs having the highest velocity. Simulations results demonstrated its effectiveness and showed that it improved the QoS support of video users having the highest velocity.

Strong demand for wireless communications encourages academic research centres and industrial electronics and communication companies to keep improving the performance, increase the speed, extend the coverage area and enlarge the baud rate and capacity. LTE (Long Term Evolution) and WiMAX (the Worldwide Interoperability Microwave Access) are recent solutions for most wireless technologies. LTE and WiMAX coverage range are one of the important factors that affect the quality of broadband access services and mobile cellular systems in wireless communication. Predicting and evaluating the path loss is essential in planning and designing cellular mobile systems. This thesis presents a comprehensive study of path loss on LTE and mobile WiMAX to achieve large throughputs and wide coverage at the Cell-edge. The thesis introduces, analyzes and compares the path loss values, based on LTE and WiMAX standard at one carrier frequency, namely 3.5GHz and a variation of distances in the range of 1 to 50 km, in flat rural, suburban and urban environments. The thesis discusses and implements the Okumura, Hata, Cost-231, Ericsson, Erceg, Walfish, Ecc-33, Lee and the simplified free space path loss models. The objectives of path loss evaluation results are to calculate the link budget, the power outage and the base station cell coverage area for mobile cellular systems. A femtocell (FMC) is a low cost low power cellular home base station, operating in licensed spectrum. Because of the requirement for high data rates and improved coverage indoors, FMC provides a solution to these requirements. FMC is deployed mainly indoors and sometimes outdoors at the cell-edge to increase the area of coverage, capacity and in order to enhance the received signal in the user’s premises. The thesis presents the interference, SINR and the probability of connection for the downlink with different numbers of FMCs based on LTE and WiMAX OFDMA. Moreover, comparisons of interference, SINR and probability of connection for three different numbers of FMCs and for three different indoor areas are presented. In addition, a comparison for the probability of connection with various threshold values and numbers of FMCs is simulated and presented in 3-D. The probability of connection for a varied number of FMCs is a guide study to find the appropriate number of FMCs that could serve a specific indoor area and the proper number of UEs in the specified area. The thesis also presents the interference, SINR and the probability of connection at the uplink for a user equipment device (UE) to an FMC with varied number of UEs based on LTE and WiMAX OFDMA. Moreover, comparisons of the interference, SINR and probability of connection for three different areas at the uplink are presented. Therefore, analyzing probability of connection with varied number of UEs is a worthy study in order to identify the appropriate number of UEs that could be served by a specific number of FMCs at a specific indoor location. The thesis presents and investigates the capacity of MIMO with the presence of FMCs to perform cancellation of co-channel interference. The research introduces algorithms to calculate the capacity of MIMO with the presence of FMCs by two models. The simulation results show that the capacity equations of model-2 give better results than the capacity equations of model-1. Therefore, model-2 is used for the interference cancellation of MIMO in the presence of MIMO. Interference cancellation is performed at the downlink when the signal is transmitted from FMC to UE by mitigating and cancelling the interference which comes from the neighbouring FMCs to the target UE. The thesis introduces, explains and applies a novel algorithm to calculate the capacity of MIMO at the presence of FMCs with interference cancellation by these channel equalizers ZF, MMSE, VBLAST ZF, VBLAST MMSE and VBLAST OFDM MMSE.

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