A major consideration for mobile WiMAX is seamless handoff. The British English term for transferring a cellular call is handover whereas the Americans prefer to call it handoff. Cellular-based standards have the advantage of many years experience in handover for voice calls, while for broadband mobility in itself is no mean feat, and handover is still a challenge. Mobile IP, with "slow" handover, will be fine for web-browsing but not good enough for decent voice quality. Many services require the appearance of seamless connections (VoIP, VPNs, etc). Much of the complexity (and latency) in the cellular network is from maintaining these connections across cell boundaries. Handovers in wireless technologies have always been a challenging topic of discussion. According to the mobility framework of IEEE 802.16e, a Mobile Station (MSS) should scan the neighbouring Base Stations (BSs) for selecting the best BS for a potential handover. However, the standard does not specify the number of BSs to be scanned leaving room for unnecessary scanning. Moreover, prolonged scanning also interrupts data transmissions thus degrading the QoS of an ongoing connection. Reducing unnecessary scanning is an important issue. This thesis proposes a scheme to reduce the number of BSs to scan, thus improving the overall handover performance. Simulation results show that the proposed hybrid predictive BS selection scheme for potential scanning activities is more effective than the conventional IEEE 802.16e handover scheme in terms of handover delay and resource wastage. Before the actual handover process, there is scope of reducing the total number of iterations of message exchanges occurring between the mobile MSS, the SBS and the neighbouring BSs which are potential targets for handover. Simulations prove that it takes upto 700 ms to decide the target BS before initiating the handover process with it. There are multiple message exchanges to choose a set of potential target BSs from all the neighbouring BSs. A few more messages flow between the MSS, SBS and potential target BSs to choose the best candidate BS for handover. The many stages and messages waste time and could be reduced. This thesis discusses some ways to reduce them and backs it up with simulation results.

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

yes / This paper describes the characterization and design of energy efficient user terminal transceiver power amplifier. To reduce the design of bulky external circuitry, the load modulation technique is employed. The design core is based on the combination of Class B and Class C that includes quarter wavelength transformer at the output to perform the load modulation. The handset transceiver for this power amplifier is designed to operate over the frequency range of 3.4GHz to 3.6GHz mobile WiMAX band. The performances of the load modulation amplifier are compared with conventional Class B amplifier. The results of 30dBm output power and 53% power added efficiency are achieved.

This Thesis is an embodiment of some research work carried out towards achieving faster and more reliable handover techniques in a Mobile WiMAX (Worldwide Interoperability for Microwave Access) network. Handover, also called handoff, is the critical mechanism that allows an ongoing session in a cellular mobile network like WiMAX to be seamlessly maintained without any call drop as the Mobile Station (MS) moves out of the coverage area of one base station (BS) to that of another. Mobile WiMAX supports three different types of handover mechanisms, namely, the hard handover, the Fast Base Station Switching (FBSS) and the Micro-Diversity Handover (MDHO). Out of these, the hard handover is the default handover mechanism whereas the other two are the optional schemes. Also, FBSS and MDHO provide better performance in comparison to hard handover, when it comes to dealing with the high-speed multimedia applications. However, they require a complex architecture and are very expensive to implement. So, hard handover is the commonly used technique accepted by the mobile broadband wireless user community including Mobile WiMAX users. The existing Mobile WiMAX hard handover mechanism suffers from multiple shortcomings when it comes to providing fast and reliable handovers. These shortcomings include lengthy handover decision process, lengthy and unreliable procedure of selecting the next BS, i.e., the target BS (TBS) for handover, occurrence of frequent and unwanted handovers, long connection disruption times (CDT), wastage of channel resources, etc. Out of these, reducing the handover latency and improving the handover reliability are the two issues that our present work has focused on. While the process of selecting the TBS for handover adds to the overall delay in completing the process of handover, choosing a wrong TBS for handover increases the chance of further unwanted handovers to occur or even a call drop to occur. The latter greatly hampers the reliability of a handover. In order to contribute to the solution of the above two problems of slow handover and unreliable handover, this Thesis proposes and investigates three handover techniques, which have been called Handover Techniques 1, 2 and 3, respectively. Out of these three techniques, the first two are fully MS-controlled while the third one is a dominantly serving BS-controlled. In Handover Techniques 1 and 2, which share between them some amount of commonness of ideas, the MS not only itself determines the need for a handover but also self-tracks its own independent movement with respect to the location of the (static) neighboring BSs (NBS). N both these handover techniques, the MS performs distance estimation of the NBSs from the signal strength received from the NBSs. But they (the two handover techniques) employ different kinds of “lookahead” techniques to independently choose, as the TBS, that NBS to which the MS is most likely to come nearest in the future. Being MS-controlled, both Handover Technique 1 and Handover Technique 2 put minimal handover-related workload on their respective SBSs who thus remain free to offer services to many more MSs. This interesting capability of the two handover techniques can increase the scalability of the WiMAX network considerably. In Handover Technique 3, which is a BS-controlled one with some assistance received from the MS, the SBS employs three different criteria or parameters to select the TBS. The first criterion, a novel one, is the orientation matching between the MS’s direction of motion and the geolocation of each NBS. The other two criteria are the current load of each NBS (the load provides an indication of a BS’s current QoS capabilities) and the signal strength received by the MS from each NBS. The BS assigns scores to each NBS against each of the three independent parameters and selects the TBS, which obtains the highest weighted average score among the NBSs. All three handover techniques are validated using simulation methods. While Handover Techniques 1 and 2 are simulated using Qualnet network simulator, for Handover Technique 3, we had to design, with barest minimum capability, our own simulation environment, using Python. Results of simulation showed that for Handover Techniques 1 and 2, it is possible to achieve around 45% improvement (approx) in the overall handover time by using the two proposed handover techniques. The emphasis in the simulation of the Handover Technique 3 was on studying its reliability in producing correct handovers rather than how fast handovers are. Five different arbitrary pre-defined movement paths of the MS were studied. Results showed that with orientation matching or orientation matching together with signal strength, reliability was extremely good, provided the pre-defined paths were reasonably linear. But reliability fell considerably when relatively large loads were also considered along with orientation matching and signal strength. Finally, the comparison between the proposed handover techniques in this Thesis and few other similar techniques in Mobile WiMAX proposed by other researchers showed that our techniques are better in terms providing fast, reliable and intelligent handovers in Mobile WiMAX networks, with scalability being an added feature.

Avec l’évolution rapide des technologies réseaux et télécoms radios mobiles, les chercheurs sont actuellement en train de préparer l’arrivée d’une nouvelle génération baptisée 4G. Le réseau de 4ème génération qui est encore l’objet de travaux de recherche vise à améliorer l’efficacité spectrale et à augmenter la capacité de gestion du nombre des mobiles dans une même cellule. Il tend à offrir des débits élevés en situation de mobilité à grande ou faible vitesse. Il vise aussi à permettre et à faciliter l’interconnexion et l’interopérabilité entre différentes technologies existantes en rendant transparent à l’utilisateur le passage entre les réseaux. Enfin, il vise à éviter l’interruption des services durant le transfert intercellulaire, et à basculer l’utilisation vers le tout IP. Dans ce contexte, nous nous sommes intéressés en premier lieu aux problématiques de la QoS en situation de mobilité au sein d’une technologie candidate à la 4G (WiMAX mobile) pour du trafic temps-réel. Pour cela, nous avons comparé la performance de plusieurs protocoles de mobilité dans le contexte du Handover de niveau 2 et de niveau 3 et plus. Nous avons pour cela fait varier les modèles de mobilité, les configurations et les scénarios. Enfin, nous avons modélisé un algorithme décisionnel qui gère le Handover dans le WiMAX mobile en fonction de plusieurs paramètres d’entrées. Au travers de ces études, nous avons dégagé des protocoles de mobilité qui offrent un niveau de QoS acceptable pour un trafic temps-réel dans le cadre des scénarios envisagés. En deuxième lieu, nous nous sommes concentrés sur les problèmes d’interconnexion et d’interopérabilité entre les réseaux en tenant compte de la mobilité et du Handover vertical entre deux technologies. Pour cela, nous avons proposé de comparer des protocoles de mobilité puis de les combiner afin de diminuer les délais des trafics temps-réel au cours du Handover. Au niveau de l’interconnexion, nous avons proposé des modèles entre WiMAX mobile et de nombreux autres standards (802.11e, UMTS, DVB-S/RCS, LTE). Outre les solutions d’interconnexion, nous avons également mis en évidence la ou les combinaisons de protocoles de gestion de la mobilité qui permettent de garantir de la QoS. / With the rapid evolution of mobile radio telecommunications and networks technologies, researchers are currently preparing the arrival of a new generation called 4G. The 4th generation network aims to improve spectral efficiency and increase capacity to manage a large number of mobiles in a cell. It tries to provide high flow rates under high or low mobility. It also aims to enable and facilitate the interconnection and the interoperability between different technologies allowing transparent transition between networks. Finally, it aims to avoid interruption of services during the handover, and to switch an all-IP system. In this context, we are concerned first with QoS and mobility issues in Mobile WiMAX for the real-time traffic. We compared the performance of several mobility protocols in the context of the level 2 and level 3+ handovers. Several mobility models, configurations and scenarios were considered. Finally, we modeled a decision algorithm that manages the handover in mobile WiMAX based on several input parameters.Through these studies, we have identified mobility protocols that provide an acceptable QoS level for real-time traffic under the proposed scenarios. Secondly, we focused on the problems of interconnection and interoperability between networks, taking into account the mobility and vertical handovers between two technologies. For this, we proposed to compare mobility protocols or combine them to reduce delays for real-time traffic during the handover. We also proposed interconnection models between mobile WiMAX and many other standards (802.11e, UMTS, DVB-S/RCS, LTE). Besides interconnection solutions, we also highlighted the combination or combinations of management mobility protocols that can guarantee QoS.

The fundamentals for continued growth of broadband wireless remain sound. According to the Ericsson’s official forecasts, the addressable global market of wireless internet broadband connectivity reaches to 320 million users by the end of 2010. The opportunity for BWA/WiMAX to serve those who want to switch to broadband service is huge in many parts of the world where wireline technologies may not be feasible.The current document (Capacity and Cell-range Estimation for Multitraffic Users in Mobile WiMAX) is prepared as a master’s program final thesis to peruse the service provision capabilities of Mobile WiMAX innovate technology in more details. An elaborate excerpt of the technical subjects of IEEE-802.16e-2005 standard is gathered in the first chapter to provide the reader with a practical concept of Mobile WiMAX technology. The following chapter is aimed to collect the required knowledge for WiMAX planning problem. An innovate methodology to calculate the system’s actual throughput and a traffic model for mixed application users are proposed with a step by step description to derive an algorithm to determine the maximum number of subscribers that each specific Mobile WiMAX sector may support. The report also contains a Matlab code –enclose in the appendix– that tries to implement the entire algorithm for different system parameter and traffic cases to ease the Mobile WiMAX planning problem. The last chapter introduces the mostly used propagation models that suit the WiMAX applications.The presented methodology would help those operators that plan to implement a wide coverage network in a city. Using the introduced methodology, service providers will be able to estimate the number of base stations and hence the network investment and profitability. / Uppsatsnivå: D

Yes / RF power amplifiers in mobile WiMAX transceivers operate in an inherently nonlinear manner. It is possible to amplify the signal in the linear region, and avoid distortion, using output power back-off; however, this approach may suffer significant reduction in efficiency and power output. This paper investigates the use of Doherty techniques instead of back-off, to simultaneously achieve good efficiency and acceptable linearity. A 3.5 GHz Doherty RFPA has been designed and optimized using a large signal model simulation of the active device, and performance analysis under different drive levels. However, the Doherty EVM is generally poor for mobile WiMAX. Linearity may be improved by further digital pre-distortion, and a simple pre-distortion method using forward and reverse AM-AM and AM-PM modeling. Measurements on the realized amplifier show that this approach satisfies the EVM requirements for WiMAX base stations. It exhibits a PAE over 60%, and increases the maximum linear output power to 43 dBm, whilst improving the EVM.

Yes / Fourth generation systems require the use of both amplitude and phase modulation to efficiently utilize the available spectrum and to obtain high data rates, hence imposing stringent requirements on the power amplifier in terms of efficiency and linearity and requires the power amplifier to operate linearly and efficiently. The B3G base station transceiver Doherty power amplifier was designed to operate over the frequency range of 3.47GHz to 3.53GHz mobile WiMAX band using Freescale¿s N-Channel Enhancement-Mode Lateral MOSFET Transistor, MRF7S38010HR3; The performances of the Doherty amplifier are compared with that of the conventional Class AB amplifier. The results of 43 dBm output power and 66% power added efficiency are achieved.

Made available in DSpace on 2016-04-04T18:31:28Z (GMT). No. of bitstreams: 1 Adriano Almeida Goes.pdf: 1890295 bytes, checksum: 24b4098cee62cc9c7d9d7e7d523ea3c2 (MD5) Previous issue date: 2009-10-30 / This work proposes a methodology for intelligent distribution of traffic between users and cells in a mobile network with adaptive modulation. In this dissertation a new method of handover to enable the proposal for load balancing traffic, serving as support for the planning and design of these networks. An example of this case is the IEEE802.16e adopted as a platform in this work. As developed a simulation platform that contains the requirements necessary to analyze and compare the current method of handover with the proposed method under different topologies. The results show a gain in the effective data rate of the cell 25% of the proposed method of handover for the current method of handover. Index: IEEE802.16e, Load Balance, Handover, mobile WiMAX / Este trabalho prop?e uma metodologia para distribui??o inteligente de usu?rios e tr?fego entre c?lulas de uma rede m?vel com modula??o adaptativa. Para isso foi proposto nesta disserta??o um m?todo de Handover que viabiliza a proposta de balanceamento de tr?fego servindo de apoio para o planejamento e dimensionamento destas redes, Como ? o caso da IEEE802.16e, plataforma utilizada neste trabalho. Foi desenvolvida uma plataforma de simula??o que cont?m os requisitos necess?rios para analisar e comparar o m?todo atual de Handover com o m?todo proposto sob topologias diferentes. Os resultados mostram um ganho efetivo na taxa de dados geral da c?lula de 25% do m?todo de Handover proposto em rela??o a m?todo de Handover atual.