Neigborhood discovery overhead in dual rate ad hoc networks

In mobile ad hoc networks when nodes are moving, the network topology will change. Such dynamic topology changes must be handled by the ad hoc network radio protocols. In order to do this the network nodes need to keep track of their local neighbourhoods. In this report, we first analyse the overhead cost of keeping such information updated and study at which network sizes and link data rates the overhead can be kept at a reasonable level. In this analysis, two message representations to send the necessary topology information are included, the OLSR Hello message format and a "minimal neighbourhood representation". Thereafter, a two mode waveform consisting of a high data rate mode and a significantly lower data rate mode is outlined and its overhead cost analysed. The aim is to use the lower data rate mode mainly to uphold connectivity and for sending essential information between network parts in a network that is fragmented at the high data rate mode. In this way low data rate links can be added to the network for network sizes far larger than a solely low rate network can handle. Also, the overhead needed for maintaining the necessary local neighbourhood topology information of the two mode waveform is shown to be acceptable if the minimal neighbourhood representation is used.