Adapting mobility of observers for quick reputation assignment in a sparse post-disaster communication network

Researchers have proposed to use smart-phone based opportunistic networks for post-disaster communication where the smart-phones carried by the volunteers (also known as, nodes) are used to exchange the situational information from different corners of the disaster affected areas. In such scenario, some malicious nodes may try to intercept and manipulate the sensitive situational data with the intention of corruption and fraud. One way of preventing such corruption is to detect the malicious nodes based on their reputation and avoid them during data forwarding. In our earlier work [1], we proposed a dynamic reputation estimation technique where a group of trusted, independent, roving observer were assigned to specific affected zones. They randomly monitor, estimate the behavior of nodes in terms of their cooperation pattern as well as group-biasness and periodically publish a global node reputation matrix to help other nodes in selecting a suitable unselfish, unbiased and cooperative forwarder. In this paper, we suggested some improvement on the reputation collection mechanism proposed in our earlier work so that global reputation matrix can be generated quickly in a sparse network. In a post-disaster scenario, volunteers normally work around shelters; As a result, volunteers are found to be sparsely spread across the entire affected area. Observers, being unaware of the locations of volunteers or shelters, move around randomly within their designated zones to collect reputation of volunteers. Thus, the time taken to collect the reputation of all nodes in a specific zone is found to be quite large. Our objective, in this paper, is to adapt the mobility of an observer towards the more volunteer-rich areas in that zone so that maximum volunteers can be met in minimum time and the reputations may be collected quickly. Inspired by Ant colony based route selection algorithm we have implemented volunteer-concentration based adaptive mobility of the observers. The performance of the proposed scheme is evaluated using ONE simulator [13].