This project is concerned with transporting real-time multimedia information via multihop mobile ad hoc channels. The major problem with transmitting real-time information over these channels is the issue of link reliability. A fundamental issue in multihop wireless ad hoc networks is that network performance can degrade rapidly as the number of hops increases. This is mainly the result of the contention for accessing the same channel (i.e., using the Carrier Sense Multiple Access protocol), which tends to increase as the signal hops through a larger number of intermediate nodes. At the same time, nodes located far from each other can simultaneously transmit packets (i.e., by being outside the contention range) and thus, the throughput performance does not drop sharply as the hop-count (number of hops from source to destination) becomes relatively large. To improve the quality of the video reception we propose a cross-layer feedback control mechanism that allows the application layer to adapt itself to a dynamically changing network topology. Such a mechanism could be based on a form of cross-layer feedback from the network layer to the application layer. In particular, information about the transmission path, such as hop-count or an occurrence of link breakage, can provide valuable information to the source node about the transmission link as far as ad hoc routing is concerned. For instance, in ad hoc routing protocols such as AODV (Ad hoc On demand Distance Vector), each node maintains a routing table for an entry (destination) with the hop-count and sequence number . In addition, a link breakage can also be detected by looking at the routing table information and/or control messages of the routing protocol. If a route change is the consequence of a link breakage, any intermediate node (between the source and destination) detecting the link breakage to the next hop, will send the route error (RERR) message back to the source node. The source node therefore may use the reception of RERR as an indication of a link breakage.
Figure 2: Cross-layer design with AODV routing protocol.
