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Energy consumption is one of the most crucial issues in wireless sensor networks since sensor nodes are commonly battery-driven. Recently, several aggregation methods have been proposed to save energy by reducing the number of transmissions from source to the sink. They assumed a single sink for aggregation of data. In this paper, we propose an aggregation scheme for wireless sensor networks with multiple sinks. In our scheme, each node caches the gradient information collected from its local neighbors to determine the aggregation point for merging data to be delivered to multiple sinks. The experimental results show that our scheme can reduce the number of transmissions and thus save the energy more than the greedy incremental tree scheme and the shortest path scheme.

Improving the performance of delay-constrained video streaming over wireless networks is one of the most important issues for various multimedia-related applications, as well as for the efficient overall utilization of the wireless medium. In this paper, we propose a scheme for adaptive admission control and scheduling for frame-based multimedia traffic in the 802.11 wireless local area networks. The conventional scheduler used for IEEE 802.11e is not suitable for VBR traffic such as MPEG-4 because only a single fixed TXOP is allocated from the hybrid Coordinator. In our scheme, we divide an MPEG flow into three different classes of video-frames depending on the user-QoS, and Our scheme is distributed admission control for each divided video-frame types and poll scheduling adaptive admission control for the flow.

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