机会网络中节点相遇的时-空特征

Spatial and temporal characteristics of node intercontacts in opportunistic networks

节点相遇特征是构建机会网络节点运动模型、实现数据机会转发的基础,也是研究机会网络的动态拓扑演化规律,指导网络部署,特别是移动节点部署的重要依据.以4个实测数据集为对象,研究了基于节点度的节点相遇空间特征:节点度分布很不均衡;随着节点度的增加,任意相遇次数按照幂律递增,核心节点比孤僻节点对消息传输成功率的贡献更大;研究了基于任意相遇时间间隔的节点相遇时间特征:多数任意相遇时间间隔和相遇持续时间都很小,相遇持续时间较小的记录对消息传输成功率影响较大,而相遇持续时间达到一定值后,时间的增长对消息传输成功率的贡献可以忽略不计.这些时空特征对于构建机会数据传递方法,解决无网络覆盖或覆盖不佳区域的通信难题具有重要意义.

The characteristics of node intercontacts are the basis for the model construction of node movement and the data retransmission in opportunistic networks, and they are also important guidance of the evolving pattern investigation of the dynamic opportunistic network to- pology and the network deployment, especially for the deployment of mobile nodes. In this article, we studied the spatial and temporal characteristics of node intercontacts based on the node degrees of 4 practical datasets. The results revealed that the distribution of node degrees was highly heterogeneous. The arbitrary intercontact times increased with the node degree in a power-law relation, and the core nodes exhibited a greater contribution to the data transmission efficiency compared to the isolated ones. The results also showed short arbitrary intercontact intervals and durations. When the duration exceeded a threshold level, the positive impact of node intercontactson success rate of data transmission decreased, and the intercontact duration increased and became saturated. These spatial and temporal characteristics play crucial roles in constructing method of opportunistic transmission to solve communication problems under such scenarios as having no network coverage or having no good coverage.