Mobile Ad Hoc NETworks (MANETs) are a special kind of wireless networks which allow a group of mobile nodes to set up and maintain a temporary network by themselves, without the support of any fixed infrastructure. These networks are useful for situations which require a rapid deployment in an infrastructureless location, or under emergency situations where communications are not available. They can be used in a large variety of scenarios, such as campus, museums, emergency rescues, and exploration missions.
Wireless networks are nowadays one of the most spread communication technologies. The demand of multimedia services over wireless networks, such as video on demand (VoD) or voice over IP (VoIP), has experienced a huge increase over last years. These multimedia services have certain Quality of Service (QoS) requirements which have to be accomplished. The amount of devices capable of maintaining wireless transmissions has grown as well. These features lead to a promising situation where the delivering of multimedia contents to mobile users through the establishment of MANETs can open new markets and services. Thus, the provision of QoS to the user over these networks must be a reality to success in the deployment of MANETs. Nonetheless, the inherent features of these networks make this issue certainly complicated. Since nodes are mobile, the network topology may change rapidly and unpredictably throughout time. Node mobility, short-life batteries, time-varying link capacity and a dynamic topology make the problem of providing QoS over MANETs rather complex and challenging.
Nodes can act as hosts or as routers to forward data from one node to another node not reachable in one hop. As they can move freely through the network, it is common to have link breakages, so alternative paths must be provided quickly. Furthermore, more stable and reliable paths should be preferred instead of just the shortest one.
The main objective of this thesis has been to develop new techniques, and to combine existing ones, to improve the performance of multimedia services over wireless Ad Hoc networks, focusing on the provision of video-streaming services over MANETs. Aspects such as multipath routing, network state monitoring, video characteristics, path classification, dynamic self-configuration, life-time of the routes, trust and reliability of the nodes within the forwarding paths, among others aspects, have been tackled.
We have designed an structure for MANET networks that includes the MMDSR (Multipath Multimedia Dynamic Source Routing) protocol, especially designed to improve the provision of VoD services over MANETs. MMDSR is a routing protocol able to establish multiple paths simultaneously between two nodes. The development has been based on an optimized cross-layer design, thus different layers of the protocol stack coordinate their actions to globally optimize the network benefits. The proposal includes dynamic mechanisms of autoconfiguration which depend on the network state. This dynamic behaviour is very relevant for MANETs, as they are very dynamic environments with scarce resources. Also, an improvement of the medium access mechanism of IEEE 802.11e has been proposed, diminishing probabilities of collision. The proposal also includes algorithms that take into account the node reliability, to promote higher cooperation among nodes to improve overall performance of MANETs. Also, a game-theoretical scheme has been incorporated to the routing algorithm to share resources among competing nodes maximising the whole benefit. An analytical model to estimate the route life-time has also been developed. It helps in a proactive way the routing schemes to take the proper decisions at precise moments. Different scenarios have been studied and simulation results of multiple video-streaming flows over MANETs have shown to improve the performance of the network compared to basic schemes such as plain DSR (Dynamic Source Routing), among others.
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