Absrraet-The use of laptop and handheld computers in educational environments has changed the nature of teaching, introduciug new ways for students to interact with materials, teachers, and their classmates. Technological advances allow handheld devices to be equipped with faster processors and wireless interfaces, making the performance comparable to laptop Computers. In this paper we pmpose a simple but effective scheme according to which each student can visualize in realtime and store the captions of the ongoing lecture. The system is based on IEEE802.11b Multicast protocols and implements a redundant transmission mechanism to mitigate the errors due to the unreliable wireless channel.

Unmanned Aerial Vehicles (UAVs) severing as the relay is an effective technology method to extend the coverage. It can also alleviate the congestion and increase the throughput, especially applied in UAV networks. However, since the energy of UAVs is limited and the resources in UAV networks are scarce, how to optimize the network delay performance under these constraints should be well investigated. Besides, the relationship among different resources, e.g. power and bandwidth, is coupled which makes the optimization more complex. This article investigates the problem of joint power and bandwidth allocation in UAV backhaul networks, which considers both the delay performance and the resource utilization efficiency. Considering the heterogeneous locations characteristics of different UAVs, we formulate the optimization problem as a Stackelberg game. The relay UAV acts as the leader and extended UAVs act as followers. Their utility functions take both the delay durance and the resource consumption into account. To capture the competitive relationship among followers, the sub-game is proved to be an exact potential game and exists Nash equilibriums (NE). The Stackelberg Equilibrium (SE) is proved afterwards. We utilize a hierarchical learning algorithm (HLA) to find out the best resource allocation strategies, which also reduces the computational complexity. Simulation results demonstrate the effectiveness of the proposed method.