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Conventional data networks are based on a layered architecture, in which a layer implements some aspect of the network while hiding the detailed implementation from the other layers. The introduction of wireless networks has created a need to violate this layered discipline to create cross-layer designs or adaptations. Such cross-layer adaptations optimize the performance of wireless networks by using information from any layer in the network. The key problem is that ad-hoc implementations of cross-layer adaptations introduce complex interactions between layers and thus reduce the level of modularity and abstraction in the network's implementation. This gives rise to a significant increase in complexity. We demonstrate that a new software architecture is able to provide a systematic framework that helps us to implement a wide variety of cross-layer adaptations while preserving to a significant degree the modularity found in the existing network's implementation. To develop such an architecture, we first create a taxonomy of possible cross-layer adaptations. The taxonomy allows a precise description of a wide variety of cross-layer adaptations. Thus our taxonomy can serve as a framework for developing a cross-layer architecture. We develop the software architecture by creating two architectures, a conceptual one and a concrete one. We first develop a conceptual architecture, which shows the key mechanisms that are required to implement cross-layer adaptations. This architecture helps us to understand how we can implement cross-layer adaptations by using our architectural framework. We then develop a concrete architecture, which shows how we can implement such a conceptual architecture on real wireless systems. This architecture addresses more detailed implementation issues. We design the concrete architecture for Hydra, which is a flexible wireless network testbed. We then show that our architecture is generic enough to allow us to support a wide set of cross-layer architectures. We evaluate the proposed architecture by performing three case studies, each of which implements a cross-layer adaptation within Hydra based on the concrete architecture. The case studies allow us to implement and evaluate the key mechanisms provided by our architectural framework. We also implement each cross-layer adaptation by using a conventional approach, in which one layer performs the cross-layer adaptation directly communicating with other layers and other nodes. Comparing both the implementation techniques allows us to evaluate how our architectural framework supports a wide variety of cross-layer adaptations while reducing the complexity of implementation of cross-layer adaptations. / text

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M. Tech. Electrical Engineering. / Widespread deployment of wireless local area networks (WLANs) and a gradual increase in streaming applications have brought about a demand for improved Quality of Service (QoS) in wireless networks. The IEEE 802.11e standard was proposed to provide QoS mechanisms for assigning high priority to delay-sensitive applications. However, Internet traffic is still dominated by TCP based applications, and the negative effects of the IEEE 802.11e service differentiation scheme on TCP performance in the presence of high priority traffic are becoming a challenging issue. TCP has been found to perform poorly in wireless networks, including IEEE 802.11e; more applications with higher QoS demands use UDP in the transport layer than TCP. Therefore, the QoS of low priority traffic in 802.11e is not guaranteed in networks highly loaded with high priority traffic. This is aggravated by the class differentiation introduced in current QoS protocols, which results in TCP applications being starved during high traffic load. The motivation of this work is to enhance the interaction between the TCP and MAC protocols in order to improve TCP performance in WLANs.

Nowadays more and more sensors are being incorporated into trucks. All of these sensors are interfaced with the ECU’s using wires. This increases the cost and complexity of installing the sensors. One alternative is to make the connection wireless. Therefore, AB Volvo technologies are researching on how to develop such a system. Currently it is at the initial stages. This thesis is a small part of this research.The main aim of this thesis is to identify the best gateway position for such a wireless sensor network at the chassis of the truck. To achieve this, a test platform was built, tests were performed and empirical link analysis was done. The platform makes use of an open source operating system called Contiki OS and uses IEEE 802.15.4 compliant transceivers. All the tests were conducted on a stationary truck. Moreover, all the tests conducted had 3 variables and they are gateway position, transmission power and truck mode.From the results obtained it was found that 2 gateway positions out of the total 3 tested are equally good. Furthermore, it was found that truck modes didn’t have any impact on the wireless link.

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