Slicing the battery pie: fair and efficient energy usage in device-to-device communication via role switching

By using device-to-device communication, opportunistic networks promise to fill the gap left by infrastructure-based networks in remote areas, to support communication in disaster and emergency situations, as well as to enable new local social networking applications. Yet, to become feasible in practice and accepted by the users, it is crucial that opportunistic communication is energy-efficient. In this paper, we measure and analyze the energy consumption of today's device-to-device communication technologies: Wi-Fi Direct, Bluetooth and WLAN-Opp (a solution based on the WLAN access point mode). We compare the energy consumption of individual operations such as neighbor discovery and connection establishment/maintenance across the different standards. We find that all of these technologies suffer from two problems. First, neighbor discovery is expensive and can quickly drain the battery if implemented carelessly. We analyze this by measuring the impact of scanning frequency on battery lifetime for the different technologies. Second, all technologies suffer from unfairness issues once a connection is established. The ``host'' of a connection consumes two to five times the energy of a "client". We propose strategies to increase fairness by alternating the hosting role among the peers. We compute the frequency of switching roles based on the distribution of the residual connection time, to achieve a good trade-off between fairness and switching cost.