Recent technology has involved TCP in wireless applications even if it was originally designed to work over wired links. It is well known that wireless links are usually characterized by phenomena like shadowing, multipath propagation and path loss that cause an increase in the bit error rate. Moreover,TCP protocol was supposed to interpret all the losses as due to congestion because of it was designed to work over wired networks. All these problems caused by the wireless application of TCP usually degrade TCP performances. In order to improve TCP behavior over wireless links several solutions have been proposed in literature as: the split connection approach, the end-to-end approach and the link-layer approach. Starting from the link-layer solution that have been studied by Barman and Matta, the main contribution of this thesis is the study of the effects of different modulation formats on the maximum achievable value of an objective function, defined as the ratio between the TCP throughput and a cost function. Appropriate power management and error correction techniques are assumed to improve the link reliability observed by TCP and increase the objective function performance accordingly.

During the past years, TCP has proven to be unable to perform properly in wireless environments, with high bandwidth-delay product paths and bandwidth variation. The recent development of advanced 3G networks and services makes it necessary to find ways to improve TCP’s efficiency and resource utilization, as well as improve the user’s experience and reduce latency times. This report presents a proxy-based solution called Radio Network Feedback, which aims at improving the performance of TCP over 3G networks. The solution proposes the use of a proxy to split the TCP connection between remote servers and mobile terminals. It manages to adapt the parameters of the connection to the wireless link characteristics, by making use of the information provided by the Radio Network Controller. The results are evaluated through a set of simulations that compare the performance of Radio Network Feedback to that of TCP. The simulation results show that the Radio Network Feedback solution greatly improves the link utilization when used over wireless links, compared to TCP. It manages to reduce latency times, especially during Slow Start and after and outage. It also succeeds in maintaining reduced buffer sizes,and properly adapts to varying network conditions.

This thesis considers the development of the software for an, newly developed, embedded real-time control system, based on a Periferal Interface Controller (PIC). The control system is developed to be used for several different applications. In this thesis work, software for two different applications are developed. The first task is a time controlled system, while the other task is implementation of aPI-/PID-controller. A user interface is also developed and implemented. The time controlled system is an automatic horse feeder, which is used for feeding horses at certain predefined points in time. A barrier, which control when the horses are to be fed, is controlled by an electrical motor. The control signal from the control system is a digital signal, which allows the electrical motor to open the barrier and feed the horses. When this is done, the barrier closes and the system waits for the next point in time when the horses are to be fed. The PI-/PID-controller is to be used for positioning of proportional valves. The application for the positioning system is to control hydraulic systems, e.g. cranes on mobile units. The user interface consists of a keyboard, an LCD-display and a user menu. Different user menus are developed for the different applications. In the horse feeder system the user interface allows the supervisor to change the points in time when to feed the horses and in the PI-/PID-controller system the user interface allows the supervisor to change the regulator parameters. The software for the time controlled application is tested for a real horse feeder system which, together with the developed software, has a planned production start in spring 2005. To test the PI-/PID-controller an alternate test system is used, due to problems with the proportional valves. The test system is based on an electrical motor. The task in this test system is to control the motor axis angle with the PI-/PID-controller. / Detta examensarbete går ut på att utveckla mjukvara till ett, nyutvecklat, inbyggt styrsystem, som baseras på en Periferal Interface Controller (PIC-processor). Styrsystemet är utvecklat för att kunna användas inom flera olika applikationsområden. I detta examensarbete utvecklas mjukvara för två olika applikationer; dels en ren tidsstyrning och dels utvecklas en PI-/PID-regulator. Utöver detta utvecklas även ett användargränssnitt. Användningsområdet för tidsstyrningen är en hästutfodrare, vilken skall användas för att utfodra hästar vid definierade tidpunkter. En spärr, som reglerar när hästarna skall utfodras, regleras med hjälp av en elmotor. Utsignalen från styrsystemet är en digital signal, som tillåter elmotorn att öppna spärren och därmed utfodras hästarna. När detta är utfört stängs åter spärren och systemet väntar tills nästa tidpunkt när matning skall ske. PI-/PID-regulatorn är främst avsedd att användas för positionering med hjälp av proportionalventiler. Applikationen skall användas för styrning av hydrauliska system, exempelvis kranar på mobila enheter. Användargränssnittet består av ett tangentbord, en LCD-display och en användarmeny. Olika användarmenyer för de olika applikationerna utvecklas. I applikationen med hästutfodringsmaskinen tillåts användaren att, via användargränssnittet, ändra de tidpunkter då matning skall ske, medan användaren tillåts att ändra regulatorparametrarna i applikationen med PI-/PID-regulatorn. Mjukvaran för tidsstyrningsapplikationen testas även på en prototyp av en fodermatare som, tillsammans med styrsystemet och den utvecklade mjukvaran, har en planerad produktionsstart under våren 2005. För att testa PI-/PID-regulatorn används ett alternativt testsystem, på grund av problem med proportionalventilen. Testsystemet är baserat på en elmotor och regleruppgiften är att reglera motoraxelvinkeln med hjälp av PI-/PID-regulatorn.

This thesis project was carried out at Scania in Södertälje. The aim was to develop a model for the air temperature in a truck cabin. The model should simulate the truck temperature as it would have been measured by the Automatic Climate Controller’s (ACC’s) temperature sensor. Apart from the actual cabin temperature model, models for the heater and cooler systems also had to be developed. The model was developed in Simulink and is intended to be used in real-time ”hardware-inloop” simulations at Scania’s integration laboratory. For that purpose, simplicity of the model is given priority over high accuracy. Both black- and white-box techniques to model the cabin air temperature where developed and evaluated. Both techniques resulted in a model with acceptable performance. The main problem with the white-box model was a non-symmetry in the cabin temperature dynamics. This problem was solved by using variable parameters in the white-box model. The results of this thesis project shows possible approaches to do more accurate models of the cabin air temperature. The white-box model, in particular, is suitable to enhance in order to improve the performance.

In this thesis, the problem of finding the jointly Scheduling, Power and Rate allocation for Wireless ad hoc networks is considered. The motivation for this study is limiting multiuser interference in order to increase the total utility, throughput, and spatial reuse of the system. One such algorithm is realized for an S-TDMA (Spatial reuse-Time Division Multiple Access) environment where all communication links share the same frequency band and are power limited. Strong levels of interference inherent to wireless ad hoc network can not be overcome by computationally expensive power control algorithm. Therefore a scheduling algorithm becomes essential to coordinate the transmissions of the users in order to guarantee nonconflicting transmission and an efficient spatial reuse. In this work, firstly an algorithm that tries to simultaneously optimize routing, power/rate control and scheduling for a network composed by fixed nodes and channel gain depend only on distances, is developed. Then, with some modifications, the developed procedure handles node mobility and time-varying flat-fading channel. Numerical results indicate that both ones increase the performances of the system. Furthermore a formulation suitable for the study of energy-constrained networks is introduced. Finally this work investigates the use of multiuser detectors (MUD) in an ad hoc network environment. We demonstrate that multiuser detectors in the terminals give substantial improvements to the total network utility, even when we use very simple schemes for scheduling transmissions.

Routing within a telecommunication network defines how the traffic flow is mapped on the network topology. The increasing commercial importance of the Internet together with a rising number of real-time applications make of the routing mechanisms as essential feature in the control of the network performance. The routing mechanisms involved allow to assign the network capacities, more or less efficiently, to the demands or requests of traffic. The routing choice has a direct impact on the existence and location of congestion within the network. A high level of congestion may decrease the grade of service (increased delays, packet losses, call blocking, etc). Today several mechanisms are proposed to increase the routing control and to optimize the network performance, without introducing complexity in the network management but keeping the actual routers configuration. In this Thesis, we addressed the problem of local balancing in networks that use shortest path routing. In particular, starting from a given network topology, we are aimed in finding the link-distance metric assignment to all links in the network that minimize the maximum utilization and therefore minimize the congestion. Since it has shown that optimizing the weight setting for a given demand of traffic between routers is NP-hard, we resorted to a local search heuristic. This method has been considered for OSPF and ECMP routing disciplines, and we have found a weight set that are within a few percent from that of the optimal general routing where the flow for each demand is optimally distributed over all path between source and destination.

A steering aid system called active steering is evaluated by simulating different driving events. The active steering solution, which is taken from a scientific paper, has been implemented in Matlab/Simulink. A vehicle model, also implemented in Matlab/Simulink, is used to form a total system and to compare the two systems: a conventional vehicle and a controlled vehicle. The input to the vehicle model is the steering wheel angle performed by the driver. Simulations are made for a constant speed and a specific changeable road adhesion coefficient. The control system takes the yaw rate as input and derives a steering angle contribution to be added to the drivers command. The motivation for this work is to understand and characterize the response of a vehicle with a complementary steering system. Specific driving events are considered for the simulations such as a wind force disturbance and a severe double lane change. The response of the controlled vehicle is similar to the response of the conventional vehicle for nominal driving, but the steering aid system reduces the effect of wind force disturbances. Improved stability is obtained for the vehicle during slippery road driving.

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The aim of this master´s thesis is to investigate if it is possible to extract more dynamic information out of physical signals from nuclear reactor noise measurements than what is possible today. This was achieved by investigating methods to examine and determine the process signal quality, and studying the corresponding transfer function. Accurate measurements of for example the core stability and the control system interference are required for detailed process diagnostics. By analysing real reactor signals, (here neutron flux and reactor pressure), it is observed that they are correlated. Becuase the structure of the real system is not perfectly known, two hypothesis have been made regarding the real system. Identification of the transfer function of the two simulated systems have been done using Matlab with process noise added to the system, with measurement noise added to the system, and with feedback added to the system. The identification models ARX (Auto Regression Moving Average), AR (a special case of ARX) and BJ (Box-Jenkin) have been used. From the results, it follows difficult to adapt a good transfer function using the ARX model to data. This is because of bad coherence. When identifying the transfer function using a spectrum, an AR model, a good approximation was seen, since the approximation does agree well with the spectral estimate. Here the input is not used. When identifying using an uncorrelated noise vector as input, we get a bias in the approximation, since the output can not be fully explained by the input signal.

Most of the real-time applications use user data protocol (UDP) as their transport protocol. The reason is that UDP does not provide flow control or error recovery and does not require connection management. Consequently it is a fast protocol suitable for applications that only need to transmit little data or for delay sensitive applications. Nevertheless, UDP has a major drawback, if some packets are dropped then there is no way to recover them. Some applications as video or audio could accept lower quality and most of the times the lost of some packets is less critic than the delay introduced by error recovery methods. Since more applications with real-time constraints such as video image and audio are introduced both over the wired Internet and over wireless some improvements should be made in order to obtain better performance. The main contribution of this thesis is to study an intermediate solution providing more reliability to the communication between applications running on top of UDP and at the same time support its fast connection quality using already existing protocols. In order to obtain it, real-time transport protocol (RTP) has been chosen as upper level protocol (to provide ”flowcontrol”) and an adaptive forward error correction (AFEC) technique has been studied (to provide error management). The idea of AFEC is to inject an adaptive amount of redundancy packets in every sent block (or datagram) in order to achieve a desired recovery rate at the receiver without using any retransmission mechanism. The sender dynamically uses feedback information from the receiver to decide the optimal amount of redundancy to introduce in every sent block. This decision task is managed by a control system at the sender side. Using the network simulator, ns-2, the performance of three different controllers using AFEC is evaluated. The results show in various scenarios that the amount of discarded blocks due to the corruption of some of its packets (block loss probability after decoding) decrease considerably when the AFEC mechanism is introduced.