Performance of a fixed reward incentive scheme for two-hop DTNs with competing relays

International audienceWe analyse the performance of an incentive scheme for two- hop DTNs in which a backlogged source proposes a fixed reward to the relays to deliver a message. Only one mes- sage at a time is proposed by source. For a given message, only the first relay to deliver this message gets the reward corresponding to this message thereby inducing a competi- tion between the relays. The relays seek to maximize the expected reward for each message whereas the objective of the source is to satisfy a given constraint on the probabil- ity of message delivery. We show that the optimal policy of a relay is of threshold type: it accepts a message until a first threshold and then keeps the message until it either meets the destination or reaches the second threshold. For- mulas for computing the thresholds as well as probability of message delivery are derived for a backlogged source. Ex- plicit expressions are obtained for this scenario in the limit- ing regime where the number of relays is large