Energy-efficient Data-gathering Mechanisms in Wireless Sensor Networks

无线传感器网络集成了计算能力、无线传输能力以及对物理世界的感知能力，具有广泛的应用范畴。在大规模的周期性数据收集型传感器网络中，如何高效的利用传感器节点的能量、保证网络长时间的运行是亟待解决的关键问题之一。然而，大量感知数据向汇聚节点逐步汇集的特性使得靠近汇聚节点的传感器节点成为“热点”，导致它们过早的耗尽能量，严重缩短了网络的生存时间。 本文首先研究在汇聚节点位置固定的场景下如何设计能量高效的数据收集机制，以均衡传感器节点之间的能量消耗，延长网络的生存时间；然后研究在汇聚节点可移动的场景下如何驱动汇聚节点自主的改变收集数据时的停留位置，以达到延长网络生存时间的目的。本文的主要贡献和创新性工作包括以下几点： （1）提出了一种应用于汇聚节点固定的传感器网络的数据收集机制。此机制按到达汇聚节点的跳数将传感器节点分级，并调度各个级别中的节点轮流负责收集全网数据并单跳发送给汇聚节点。此数据收集机制可以使距离汇聚节点远近不同的传感器节点间能量消耗均衡，减轻热点效应的影响，延长网络生存时间。 （2）提出了一种适用于可移动汇聚节点的自主式单步移动策略。在每个数据收集周期中，此策略通过让汇聚节点在能量较高的节点附近选择停留位置进行数据收集，并兼顾对剩余能量较低的节点的影响，以达到均衡节点间能量消耗的目的。此移动策略可以延长网络的生存时间，并对网络形状具有自适应能力。 （3）提出了一种适用于可移动汇聚节点的自主式多步移动策略。此策略在汇聚节点逐步趋近目标节点的过程中采用基于半象限的方法决定移动方向，而在到达目标节点附近时采用基于尝试的方法寻找最佳停留位置。此策略不仅可以延长网络的生存时间，还可适应网络规模较大以及传感器节点分布不均匀的应用环境。 （4）提出了一种基于地理位置信息的路由协议。此路由协议利用传感器节点到达汇聚节点的跳数和地理位置信息进行三级调度，将节点的数据收发操作分散在整个数据收集周期中，从而可以降低节点间的数据发送冲突，提高汇聚节点对全网数据的成功接收率，减少数据重传。Wireless sensor networks have the potentiality to innovate the manner in which we sense the real physical world. The envisioned applications of wireless sensor networks range widely. In large-scale periodically data-gathering applications, it is very important to utilizing node energy efficiently to prolong the lifetime of the networks. However, the aggregating character, which is caused by that all the sensor nodes report their sensed data towards a sink, usually makes the nodes close to the sink hotspots and drain of their energy quickly, which results in shortening the network lifetime seriously. This thesis addresses how to balance the energy consumption among sensor nodes and prolong network lifetime by designing an energy-efficient data-gathering mechanism for the sensor networks with a static sink and proposing two autonomous moving strategies for the sensor networks with a mobile sink. The main contributions and creativity are described as follows. Firstly, a data-gathering scheme, called Data Aggregating Ring (DAR) is proposed. In the DAR scheme, all the sensor nodes with different hop counts to the sink will participate in gathering all the sensed data and transferring them to the sink. Because all the nodes in the network partake of the heavy workload, the sensor nodes consume their energy almost equally and the hotspot problem can be significantly relieved, so that the DAR scheme can balance the energy consumption in a whole network range and extend the network lifetime dramatically. Secondly, an autonomous single-step moving strategy for mobile sinks is proposed. The moving strategy is called Ball-on-Stick Strategy (BoSS). In each reporting period, BoSS makes the sink move to the side of the node with the highest residual energy in the network and tries to consume the energy of the node as much as possible, and meanwhile, balance the energy consumption of the nodes with low energy to avoid exhausting them much earlier than others. BoSS can improve energy efficiency and prolong network lifetime; more¬over, it can provide adaptability to different network shapes. Thirdly, an autonomous multi-step moving strategy called Half-quadrant-based Moving Strategy (HUMS) is proposed. HUMS has the same basic idea with BoSS, but it focuses on the network where the sink cannot move very fast or the sensor nodes are deployed unevenly. In the course of approaching the destination node, the sink adopts a half-quadrant-based algorithm to choose the moving directions; when the sink is close to the destination node, it determines a sojourn position around it with an attempt-based mechanism. HUMS can not only alleviate the hotspot problem and extend the network lifetime, but also be employed in more diverse network environments than BoSS. Finally, a geographical routing protocol is proposed, which is called Geographical TDMA-like Routing (GTR). The GTR protocol makes good use of the long interval between two data-gathering periods in a low duty-cycle sensor network. It employs a three-level scheduling to disperse data transmissions to different timeslots to reduce transmission collisions so as to increase the packet reception rates at the sink

research on quality of service guarantee in community broadband network system with integrated services

社区宽带综合业务网络系统使用交换式以太网技术，在一个物理网络上为社区用户提供Internet接入、数字电视、IP电话等服务，对三网融合进行了实践性探讨。提出并实现了一套保证系统服务质量的方法，并在测试中取得了满意的效果