Relay selection schemes for store-carry and forward relaying based on optimal stopping theory

New challenges have been brought by applications with high device density, such as the large number of supportable devices and long device battery lives. The store-carry and forward scheme can be used to address these issues, but its performance relies on the schemes of relay selection or routing. Existing methods using utility metric are able to mitigate this problem to some extent, but still suffer from incomplete information as the device density increases. By formulating the relay selection problem into two optimal stopping problems from energy efficiency and time efficiency, respectively, the energy-optimal forwarding and time-energy forwarding are proposed, which allow each source device to select the best relay based on the information it can acquire. Simulation results show that the proposed schemes can provide better performance in terms of the energy consumption and transmission delay compared to both random transmission and epidemic routing.