The growth of mobile handheld devices promotes sink mobility in an increasing number of wireless sensor networks (WSNs) applications. The movement of the sink may lead to the breakage of existing routes of WSNs, thus the routing recovery problem is a critical challenge. In order to maintain the available route from each source node to the sink, we propose an immune orthogonal learning particle swarm optimisation algorithm (IOLPSOA) to provide fast routing recovery from path failure due to the sink movement, and construct the efficient alternative path to repair the route. Due to its efficient bio-heuristic routing recovery mechanism in the algorithm, the orthogonal learning strategy can guide particles to fly on better directions by constructing a much promising and efficient exemplar, and the immune mechanism can maintain the diversity of the particles. We discuss the implementation of the IOLPSOA-based routing protocol and present the performance evaluation through several simulation experiments. The results demonstrate that the IOLPSOA-based protocol outperforms the other three protocols, which can efficiently repair the routing topology changed by the sink movement, reduce the communication overhead and prolong the lifetime of WSNs with mobile sink.
The fault-tolerant routing problem is important consideration in the design of heterogeneous wireless sensor networks (H-WSNs) applications, and has recently been attracting growing research interests. In order to maintainkdisjoint communication paths from source sensors to the macronodes, we present a hybrid routing scheme and model, in which multiple paths are calculated and maintained in advance, and alternate paths are created once the previous routing is broken. Then, we propose an immune cooperative particle swarm optimization algorithm (ICPSOA) in the model to provide the fast routing recovery and reconstruct the network topology for path failure in H-WSNs. In the ICPSOA, mutation direction of the particle is determined by multi-swarm evolution equation, and its diversity is improved by immune mechanism, which can enhance the capacity of global search and improve the converging rate of the algorithm. Then we validate this theoretical model with simulation results. The results indicate that the ICPSOA-based fault-tolerant routing protocol outperforms several other protocols due to its capability of fast routing recovery mechanism, reliable communications, and prolonging the lifetime of WSNs.
Time synchronisation plays an important role in time division multiple access (TDMA) wireless sensor networks (WSNs). Existing time synchronisation methods suffer from cumulative time error and the imbalance of time synchronisation precision, and those factors bring fluctuations to nodes' time and will become worse with the increase of hops, inducing more unstable communication links for sensor nodes. A dual time synchronisation method (DTSM) for WSNs is introduced, which is endowed with the maintenance of two running time sources per node, one for its parent and the other for its sons. This method eliminates the time fluctuations among nodes especially for the nodes with greater hops, so as to obtain more stable links for large-scale networks. This method is implemented on the SCSC-RFA1 platform and the results show its validity.Introduction: Wireless sensor networks (WSNs) can be widely used in many applications such as wild environment monitoring, industrial process detection and control and emergency detection and so on. As one of the key technologies for WSNs, time synchronisation is essential for time division multiple access networks and plays important roles in node localisation, data fusion, synchronised channel switching/hopping etc.Several time synchronisation protocols have been developed to deal with the special requirements of WSN applications. Some of the notable ones are the reference broadcast synchronisation algorithm [1], timing-sync protocol for sensor networks [2] and flooding time synchronisation protocol (FTSP) [3]. Some of the implementations for these protocols can achieve synchronisation precision of a few microseconds. However, most of these protocols are up against error accumulation and are sensitive to the dynamic network topology even for large-scale networks.Error accumulation and uneven distribution for multi-hop networks are depicted in Fig. 1. Node 0 acts as the time reference of the network and nodes 1-10 directly or indirectly synchronise to the reference. The line with an arrow represents the synchronisation relationship between two nodes and the end of the arrow points to the parent side. There are accumulation errors from node 5 to node 0 according to the increasing network hops and uneven error distribution between node 5 and node 10 as they synchronise to the reference from different paths.
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