Incentive Mechanisms in Multi-Hop Wireless Networks

In multi-hop wireless networks, data packets are relayed in several wireless hops from their source to their destination. Based on whether a fixed infrastructure is used or not, we can distinguish two types of multi-hop wireless networks: pure ad hoc and multi-hop cellular networks. Pure ad hoc networks do not rely on any fixed infrastructure; hence, the packet relaying service has to be provided solely by the end user devices. Multi-hop cellular networks rely on a set of base stations that are connected to a high speed backbone network; here, data packets have to be relayed by end user devices from the source to the backbone and from the backbone to the destination. Multi-hop cellular networks are a potential evolution of both voice-centric networks such as GSM and data-centric networks such as CDPD or IEEE 802.11. The proper operation of both types of network requires the end users to collaborate. However, collaboration is not individually beneficial for the users, because it consumes resources such as battery power, memory, and CPU cycles, and it does not provide any immediate advantages (serving others does not guarantee for the user that he will be served as well). Indeed, if the majority of the users collaborate, a selfish user can parasitically take advantage of this by using the network without contributing to it. While the problem is the same in both pure ad hoc and multihop cellular networks, the solutions can be very different. This difference mainly stems from the different set of assumptions that can be made in the two cases. In particular, in multi-hop cellular networks, the operator(s) of the backbone can be considered as a trusted authority, which can – at least to some extent – control the operation of the network by implementing various security measures, while in pure ad hoc networks, the existence of such a trusted authority cannot be assumed. In this paper, we present our ongoing work on the design of mechanisms that stimulate collaboration of end users in both pure ad hoc and multi-hop cellular networks. We put the emphasis on stimulating packet forwarding, as this is one of the most fundamental services that end users should provide to each other.