The ABR point-to-multipoint connection is now playing a more important role. Many consolidation algorithms have been proposed to solve the consolidation noise problems and the slow transient response problem. But few timeout algorithms are proposed to handle the ¡§non-responsive¡¨ branches problems for the multicast connections. We proposed a timeout algorithm which can handle the ¡§non-responsive¡¨ branches problems and with a lower implementation complexity. Simulation results also show that the proposed timeout algorithm can efficiently handle the ¡§non-responsive¡¨ branches and can use the available bandwidth within a small period of time.

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International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / It is always desirable to transmit several data signals simultaneously. This paper discusses how one transmitter can transmit several data signals to several receivers at the same time in a Point to Multipoint communication system. Two novel schemes are proposed. One is communication with Multiple Phase Shift Keying(MPSK,e.g.8PSK),another is communication with Direct-Sequence Spread-Spectrum Multiple-Access(DS/SSMA). Their models are presented and their operations are illustrated. It is proved theoretically that the communication properties of DS/SSMA are better than those of another.

One of the currently explored strategies for interference avoidance and improving Signal to Noise Ratio (SNR) for mobile communication systems is Coordinated MultiPoint (CoMP) transmission. The general idea of the strategy is to let two or more base stations serve the same user. Due to delay factors, the channels from each serving base station needs to be predicted to obtain an adaptive CoMP system. In this thesis, a user interface is created to act as an experimental platform for a set of measured downlink channel data. The user interface supports editing of the channel data, model estimation, Kalman filtering and prediction and evaluation of the channel statistics. The user interface and the measured channel downlink data is then used to examine how well we can predict the weakest channel in a CoMP setup with three base stations. The predictions are carried out using an m-step Kalman predictor which uses an AR4 model, estimated from previous channel data. For the investigation, the user moves at pedestrian speed and the signals from the three different base stations use orthogonal Common Reference Signals (CRS). A comparison of different CRS patterns is also included in the investigation. It is concluded that 5 ms predictions of the weakest channel achieves a normalized mean squared error (NMSE) of -8 dB or lower provided that the weakest signal has an SNR of at least 5 dB and is no more than 15 dB lower than the combined received signal. Additionally, it is found that predictions are more accurate for CRS patterns spread over time than over subcarriers.

Applications such as video and audio streaming, online gaming, video conferencing, Voice over IP (VoIP) and File Transfer Protocol (FTP) demand a wide range of QoS requirements such as bandwidth and delay. Existing wireless technologies that can satisfy the requirements of heterogeneous traffic are very costly to deploy in rural areas and “last mile” access. Worldwide Interoperability for Microwave Access (WiMAX) provides an affordable alternative for wireless broadband access supporting a multiplicity of applications. The IEEE 802.16 standard provides specification for the Medium Access Control (MAC) and Physical (PHY) layers for WiMAX. A critical part of the MAC layer specification is scheduling, which resolves contention for bandwidth and determines the transmission order of users. It is imperative for a scheduling algorithm to have a multi-dimensional objective of satisfying QoS requirements of the users, maximizing system utilization and ensuring fairness among the users. In this thesis, we categorize and study various scheduling algorithms for the uplink traffic in WiMAX in view of these objectives. The algorithms are studied under different mixes of traffic and for various characteristics of the IEEE 802.16 MAC layer such as uplink burst preamble, frame length, bandwidth request mechanisms etc. Simulation results indicate that legacy algorithms are not suitable for the multi-class traffic in WiMAX as they do not explicitly incorporate the WiMAX QoS parameters. We provide recommendations for enhancing existing scheduling schemes in WiMAX, and shed light on some of the open issues that need to be addressed. / Thesis (Master, Computing) -- Queen's University, 2007-12-29 18:21:21.521

Network coding is a new research area with potential to reduce network resources. With network coding, intermediate nodes forward packets that are linear combinations of previously received packets. The type of networks we consider are vehicle mounted mobile tactical radio networks. Tactical communication may be required in areas where pre-deployed base stations are unavailable. Mobile ad hoc networks satisfy this requirement. Due to low antenna heights, network resources are scarce inmobile networks without base stations. Broadcast traffic, which disseminates information network-wide, is very important in tactical mobile networks. Multipoint relay flooding is a well-known technique for efficient distribution of broadcast traffic. It is therefore interesting to evaluate how much network coding can reduce the number of transmissions in a mobile ad hoc network. In this thesis we show that it is possible to further reduce the number of transmissions for Multipoints Relay flooding by using network coding. However, this improvement is largely theoretical - there has been no effort to evaluate this approach in practice.

The recent allocation and auctioning of the largest spectrum currently available has positioned Local Multipoint Distribution Service (LMDS) technology as a major contender in the race to provide broadband connectivity to customers. With the focus on solving the "Last Mile" problem, LMDS provides a significant reduction in both the time it takes for system deployment as well as the cost of the implementation. However, as with all emerging technologies, the lack of standardization and the risks involved in being the pioneer of an emerging market have resulted in a slower commercialization of such systems. The issues mentioned above served as the catalyst for this paper, to examine the factors that affect deployment strategies for an LMDS system in a rural commercial environment. In order to provide a better understanding of this technology, a review on the background issues in the areas of terrain, coverage/capacity, and networking will be presented. By evaluating these criteria, a strategy that can be employed to facilitate the implementation of LMDS systems is generated. Finally, the application of these methodologies will be demonstrated on a case study performed for a commercial environment in the county of South Boston, Virginia. Through evaluating the possible designs and the feasibility of the business case, it was determined that a point-to-multipoint system will best match the needs of the proposed location. / Master of Science

Asynchronous Transfer Mode (ATM) network is being deployed in carrier backbone. ATM can transmit a wide variety of traffic, such as video, voice, and data. Available Bit Rate (ABR) service is one of six ATM services, which is now under intensive research for its closed loop feedback control feature. ABR service supports two types of connections: unicast and multicast. There are also three types of multicast connections: point-to-multipoint, multipoint-to-point, and multipoint-to-multipoint. Multipoint communication is the exchange of information among multiple senders and multiple receivers, forming a multicast group. Examples of multicast applications include audio and video conferencing, video on demand, tele-metering, distributed games, and data distribution applications. In this dissertation, we focus on queuing and packet scheduling management for multipoint-to-point ABR connections. Although there are so many proposed fairness definitions for all ABR sources in a multipoint-to-point connection, there are still problems about queue lengths, queuing delays, and throughputs, when ABR sources are with variable-length packets. From the nature of VC-merge scheme on merged points in a multipoint-to-point connection, merged switches cannot transmit cell-stream of a packet out until the packet is completely and totally queued. If there is no complete packets queued, the switch can then choose an incomplete packet for cut-through forwarding for efficiency. Therefore, if the switch chooses a long packet from a branch that has smaller cell input rate, for cut-through forwarding, the throughput of output ports will experience severe oscillations. At the same time, ABR queue lengths will be also occupied with severe growth, and ABR cells will be experienced long queuing delays. We proposed a scheme, named MWTF (Minimum Waiting Time First), which is architecture-independent of any rate allocation schemes and fairness definitions, to resolve the problems by providing length of each packet to merged switches. Thereby the scheduler can choose an appropriate incomplete packet for cut-through forwarding, by selecting the packet that has the smallest packet waiting time. Simulation results show that merged switch has good performances. Throughput will be no severe oscillations and will be getting smoother. Also cells have smaller and smoother queuing delays in average, and the switches have much smaller queue lengths and smoother variations.

Dans cette thèse, nous proposons deux algorithmes multi-échelles pour la simulation de modèles géologiques de réservoir. Le premier algorithme relève des méthodes géostatistiques à deux points. Il s'agit d'une simulation séquentielle Gaussienne avec variable secondaire. Dans notre approche multi-échelle, la variable secondaire est supposée connue à une deuxième échelle, de résolution plus grossière. Elle représente alors la tendance ou moyenne de la variable principale. A partir d'une paramétrisation adéquate, on montre que le calage des propriétés du modèle géologique à l'échelle grossière est plus efficace que le calage de ces mêmes propriétés à l'échelle fine. Notre méthode est applicable aux variables continues et aux variables discrètes.Le deuxième algorithme est une adaptation d'un algorithme de synthèse de texture aux problèmes de réservoir. C'est un algorithme de simulation multipoints qui nécessite l'utilisation d'une image d'entrainement. Il permet de reproduire des objets géologiques de formes complexes comme des chenaux ou des réseaux de fractures. Comme tous les algorithmes multipoints, il requiert des temps de calcul important. Nous montrons alors comment l'introduction d'une échelle intermédiaire permet de diminuer ce temps de calcul et d'améliorer la reproduction des grandes structures. Nous testons deux techniques pour diminuer davantage encore le temps de calcul : le scan partiel de l'image d'entrainement ou l'organisation des informations extraites de cette même image. / In this manuscript, we propose two multiscale algorithms for the simulation of geological reservoir models.The first algorithm is based on two-points statistics methods. It is based upon the sequential Gaussian simulation with a secondary variable. In our multiscale approach, the scale of the secondary variable is considered as a second scale of coarser resolution. It represents the trend or the average of the primary variable. In the context of history-matching, it can be shown that adjusting the properties of the geological model at the coarse scale is more effective than doing the same at the fine scale provided a suitable parameterization technique is used. Our method holds for both continuous and discrete variables. The second algorithm is rooted in texture synthesis techniques developed in computer graphics and modified to cope with reservoir simulation. This is a multipoint simulation algorithm. As such, it requires the use of a training image. It permits to simulates complex geological objects like channels or networks of fractures. However, as all multipoint algorithms, it requires significant computation times. We show how the introduction of an intermediate scale reduces the computation time and improves the reproduction of large structures. We also test two techniques to further reduce the computation time: the partial scan of the training image and the preliminary organization of the information extracted from this image.

Structural shape optimisation is a field that has been studied since early on in the development of finite element methods. The sub-fields of shape and topology optimisation are continuously growing in industry and aim to leverage the benefits of technologies such as 3D printing and additive manufacturing. These fields are also being used to optimise designs to improve quality and reduce cost. Gradient-based optimisation is well understood as an efficient method of obtaining solutions. In order to implement gradient-based optimisation methods in the context of structural shape optimisation, sensitivities describing the change of the domain stiffness are required. To obtain the stiffness sensitivities, mesh deformation sensitivities are required. In this study, a mesh generating method is developed that provides mesh deformation sensitivities. For shape optimisation it is advantageous to employ an optimisation algorithm that allows for the manipulation of CAD geometry. This means that the CAD geometry is finalised upon completion of the optimisation process. This, however, necessitates the calculation of accurate sensitivities associated with non-linear geometries, such as NURBS (those present in CAD), by the mesher. The meshing method developed in this study is analogous to a linear truss system. The system is solved for static equilibrium through a geometrically non-linear finite element analysis using Newton’s method. Sensitivities are made available by Newton’s method for use in generating mesh sensitivities for the system. It is important for the mesher to be able to accurately describe the geometrical domain which approximates the geometry being modelled. To do so, nodes on the boundary may not depart from the boundary. Instead of prescribing all boundary nodes, this mesher frees the boundary nodes to move University of Pretoria ii Department of Mechanical and Aeronautical Engineering along, but not away from the boundary. This is achieved using multipoint constraints since they allow for an analytical relationship between boundary node movement and the boundary. Two multipoint constraint (MPC) methods are investigated for boundary discretisation, namely, the Lagrangian and master-slave elimination methods (MSEM). The MSEM presents several difficulties in obtaining convergence on non-linear boundaries in general when compared to the Lagrangian method. The MSEM has reduced computational requirements for a single Newton step, especially when direct solvers are used. However, when indirect solvers are implemented the time difference between the two MPC methods reduces significantly. For a “medium” curvature geometry the Lagrangian implementation has only a 6% time penalty. The Lagrangian method is selected as the preferred MPC method for implementation in the mesher to avoid the convergence problems associated with the MSEM. This is justified on the basis of reliability outweighing the 6% time penalty for what is intended to be a tool in the shape optimisation process. Analytical sensitivities are obtained for the truss system in order to account for the MPC boundaries. The analytical mesh sensitivities are proven to be accurate through comparison with numerical sensitivities. The method is demonstrated to be able to accurately described the mesh deformation throughout the domain for both uniform and non-uniform meshes in the presence of non-linear boundaries. / Dissertation (MEng)--University of Pretoria, 2020. / Mechanical and Aeronautical Engineering / MEng (Mech) / Unrestricted