Geographic routing and location services

Participants : Selma Boumerdassi, Pascale Minet, Paul Muhlethaler.

Thanks to its scalable nature, geographic routing is an interesting alternative to topological routing for ad-hoc networks. In fact, in order to set up such a network, each node needs to know the location of the others and location services are in charge to provide such an information.

Two kinds of location services have been provided using either a flooding or a rendez-vous, a node in the network being chosen as a server for the rendez-vous. In the scope of our research, we have proposed different mechanisms based on social groups and/or communities and studied their impact on the control traffic of various protocols. For example, based on the simulations of SLS and SFLS using NS-2, we have demonstrated that the social behaviour of nodes has a strong impact on location services and therefore that next-generation location services should take the relationships between the network users into account.

Optimized Broadcast Scheme for Mobile Ad hoc Networks

Participants : Ahmed Amari, Nadjib Achir, Paul Muhlethaler.

In this training we propose an optimized broadcasting mechanism, which uses very limited signaling overhead. The main objective is to select the most appropriate relay nodes according to a given cost function. Basically, after receiving a broadcast packet each potential relay node computes a binary code according to a given cost function. Then, each node starts a sequence of transmit/listen intervals following this code. In other words, each 0 corresponds to a listening interval and each 1 to a transmit interval. During this active acknowledgment signaling period, each receiver applies the following rule: if it detects a signal during any of its listening intervals, it quits the selection process, since a better relay has also captured the packet. Finally, we split the transmission range into several sectors and we propose that all the nodes within the same sector use the same CDMA orthogonal spreading codes to transmit their signals. The CDMA codes used in two different sectors are orthogonal, which guarantees that the packet is broadcast in all possible directions.