Wi-Fi Direct is a promising technology for the support of device-to-device communications (D2D) on commercial mobile devices. However, the standard as-it-is is not sufficient to support the real deployment of networking solutions entirely based on D2D such as opportunistic networks. In fact, WiFi Direct presents some characteristics that could limit the autonomous creation of D2D connections among users' personal devices. Specifically, the standard explicitly requires the user's authorization to establish a connection between two or more devices, and it provides a limited support for inter-group communication. In some cases, this might lead to the creation of isolated groups of nodes which cannot communicate among each other. In this paper, we propose a novel middleware-layer protocol for the efficient configuration and management of WiFi Direct groups (WiFi Direct Group Manager, WFD-GM) to enable autonomous connections and inter-group communication. This enables opportunistic networks in real conditions (e.g., variable mobility and network size). WFD-GM defines a context function that takes into account heterogeneous parameters for the creation of the best group configuration in a specific time window, including an index of nodes' stability and power levels. We evaluate the protocol performances by simulating three reference scenarios including different mobility models, geographical areas and number of nodes. Simulations are also supported by experimental results related to the evaluation in a real testbed of the involved context parameters. We compare WFD-GM with the state-of-the-art solutions and we show that it performs significantly better than a Baseline approach in scenarios with medium/low mobility, and it is comparable with it in case of high mobility, without introducing additional overhead.

翻译：Wi-Fi Direct是一种有望在商用移动设备上支持设备间通信（D2D）的技术。然而，现标准本身不足以支持完全基于D2D（如机会网络）的网络解决方案的实际部署。事实上，WiFi Direct存在一些可能限制用户个人设备间自主建立D2D连接的特性。具体而言，该标准明确要求用户授权才能建立两个或多个设备之间的连接，并且对群组间通信的支持有限。在某些情况下，这可能导致形成无法相互通信的孤立节点群。本文提出了一种新型中间件层协议，用于高效配置和管理WiFi Direct群组（WiFi Direct Group Manager, WFD-GM），以实现自主连接和群组间通信。这使得机会网络能在真实条件下（如可变移动性和网络规模）运行。WFD-GM定义了一个上下文函数，该函数综合考虑异构参数（包括节点稳定性指数和功率水平），在特定时间窗口内创建最优群组配置。我们通过模拟三种参考场景（包含不同移动模型、地理区域和节点数量）来评估协议性能。模拟结果还得到了实际测试平台中相关上下文参数评估的实验结果支撑。我们将WFD-GM与现有解决方案进行对比，结果表明：在中等/低移动性场景下，其性能显著优于基线方法；在高移动性场景下，性能与之相当且未引入额外开销。