Recently, smartphones are commonly equipped with Wi-Fi direct modules, which can be used to support infrastructure-less communications. Considering an emergency scene, communication infrastructures are damaged or unable to operate. Affected people in the emergency site cannot communicate with each other and with the outside world until rescue personnel establishes an emergency network for them. In this paper, we aim to provide an emergency communication method based on Wi-Fi direct technology. Originally, Wi-Fi direct capable devices rely on a Wi-Fi direct group mechanism to operate. However, we observe that forming Wi-Fi direct groups may not be appropriated in the emergency scenario. Besides, Wi-Fi direct capable devices carried by affected people should operate in power saving mode when emergency. In this paper, we model the target scenario as an emergency Wi-Fi direct device scheduling (EWDS) problem. We then propose centralized and distributed schemes to solve the EWDS problem. The proposed schemes schedule devices' active and sleep timings with the guarantee that all devices can join the network within a bounded time and devices can exchanges packets with each other effectively. Furthermore, by the proposed distributed schemes, devices can operate locally and unsynchronized without a central controller. We evaluate the proposed schemes by simulations and prototyping implementation, and the results demonstrate the effectiveness of our designs.
