Protocols and architecture for wireless ad hoc networks

The subject of this dissertation is ad hoc wireless networks. In such networks packets are relayed over multiple hops to reach their destination. In order to operate ad hoc networks several protocols, for media access control, power control, routing, and transport are needed. This dissertation is concerned with the development and evaluation of such protocols, and the associated architecture of the protocol stack. We take a holistic approach to the problems in ad hoc networks.; Transmission power control is important because of the fundamental nature of the wireless network that it is interference limited. Transmission power control has the potential to increase a network's traffic carrying capacity, reduce energy consumption, and reduce the end-to-end delay. We start by postulating general design principles for power control based on the effect of transmit power on various performance metrics. These are used to design a set of protocols which attempt to optimize different performance metrics, as all the metrics cannot be simultaneously optimized in general. Some of these protocols have been implemented in the Linux kernel in an architecturally appropriate manner. Extensive testing was not possible due to the limitations of the current generation of hardware, and so performance results obtained through NS2 simulations are used to illustrate the potential benefits of the power control protocols.; Next we investigate the transport layer in static multihop wireless networks. Based on an experimental study and statistical analysis, we make recommendations on modifications to TCP for use in ad hoc wireless networks. We suggest clamping the congestion window, turning off RTS-CTS and turning on the TCP selective acknowledgment on, among other things. Our recommendations are based on experimental testing of all possible combinations of these and other modifications on nine different topologies of up to six hops, with several runs of each experiment. The results are analyzed through statistical techniques to arrive at the recommendations suggested above. This work has also resulted in the development of a set of tools to automate the process of experimentation, data collection, processing and presentation.; Our work at the routing layer is motivated by the difficulty in implementing on-demand routing protocols for ad hoc networks in common operating systems. It provides an API and its implementation in Linux as a user-space library (ASL), which facilitates implementation of on-demand routing protocols. It has been used to implement a few routing protocols.; Then this dissertation addresses the important issues of cross-layer design and system architecture. We make the case for a cautionary approach to designing cross-layer schemes and protocols. Some examples are given to illustrate how cross-layer design can lead to unintended interactions which could actually degrade system performance.; Given the increased interest in cross-layer design, we provide the outline of a general approach to protocols and layering. A central feature of our suggested model is that each layer have its own sets of addresses, and the interaction between the layers be enforced strictly through inter-layer services. We illustrate how the generalized stack solves many problems cleanly.; The dissertation concludes by describing the design and implementation of an ad hoc networking software module, which provides certain basic services necessary for configuring and operating ad hoc networks.