Research On Medium Access Control And Cluster Routing Protocols In Low Voltage Power Line Carrier Network

Power line networks are the most widely used networks in the world. Low-voltage power line carrier networks utilize the existing power line resource without installing additional communication lines,which have the advantages of high reliability of physical access, wide coverage, convenience of application, low cost of network installation and maintenance, and always on line etc.. However, since the lack of network layout planning strategy to adapt to the actual site, reliable real-time medium access control and routing protocols, the wide application of the low-voltage power line carrier network is restrained currently. To make Low-voltage power line carrier networks work further effectively, this dissertation investigates the media access control, network topology discovery and clustered routing problems. The main contributions are listed as follows.For the low efficiency and poor real-time data packet retransmission in the case of large-scale nodes in traditional media access control protocol, a time-slot medium access control protocol based on power line frequency synchronization is obtained. According to the line-frequency signal covering the entire network, the protocol employs the AC power frequency (50Hz or 60HZ) zero-crossing signal to obtain clock synchronization of all carrier nodes to reduce network collision probability by Priority Sensing, competition withdrawing and probability p reservation notification. This protocol can avoid network congestion and ensure the real-time data in the retransmission through fixed competition windows and raising retransmission priority level mechanisms.For the difficulty of time-varying characteristics in network planning, a minimum signal strength attenuation based topology discovery algorithm is proposed. Firstly, a minimum spanning tree model in terms of the signal attenuation strength and adjacency relations between the nodes is established. Then a genetic simulated annealing based discovery algorithm is developed to find the high-performance topology in the whole network. The algorithm makes use of convergence acceleration of genetic algorithms and avoids local optimum of simulated annealing. But this algorithm may produce a number of topological links which may lead to complex structure. To improve this algorithm, a concept of degree-constrained is adopted to simplify the topology , achieve effective network planning and enhance network reliability.Regarding to a large number of the cluster heads and the only single path connected two clusters in the traditional cluster algorithm, a novel clustering algorithm and network reconfiguration method based on signal strenghth is presented, in which the attenuation descending order of signal strenghth and multi-path among the clusters is used. The results show that the number of the cluster heads and time delays is reduced, inter-cluster communication paths increased effectively and network reliability is enhenced.Aiming at the unreliable link proplem caused by channel interference and time-varying, a dynamic routing algorithm with reliability assurance based on clusters is given to achieve minimun transmission delay and packet loss rate, in which a multi-path routing strategy is used to avoid routing failures resulted from failure of the best path and improve network reliability. To enhance the efficiency of optimal routing search, a genetic and ant colony combined algorithm is provided. Compared with only genetic and only ant colony algorithm, the results show that the proposed algorithm can achieve the much better performance such as average time delay,Package delivery rate and network throughput .