The Research Of Stable Multi-layer Hierarchical Structure And Its Key Technologies In Ad Hoc Networks

As ad hoc networks'scale increasing constantly, scalability problem has been listed as one of the several problems urgent to be solved, and hierarchical structure has been a main solution to this problem. And researches on hierarchical structure have very high theory value and application value. At present, hierarchical structure includes two-layer hierarchical structure and multi-layer hierarchical structure. The scalability of present multi-layer hierarchical structure (MHS) is better than that of two-layer hierarchical structure, but MHS also exists some problems such as poor structure stability and large structure maintenance overheads. Aiming at above problems, a stable multi-layer hierarchical structure (SMHS) is proposed, and then SMHS's key technologies are researched in depth. The main research content includes the following four parts:(1) Aiming at the problems existing in MHS, stable multi-layer hierarchical structure (SMHS) and its clustering algorithm are proposed. SMHS adopts a new scheme that"a structure doesn't rely on some centered nodes apt to vary, but relies on some relatively stable clusters". As long as a node doesn't leave a cluster, its HID (Hierarchical ID) doesn't change with the cluster-representative's alteration, which improves structure's stability and furthers to reduce structure's maintenance overheads. Meanwhile, SMHS adopts a new scheme that"a high-layer virtual link is composed of some clusters with relatively low alternation frequencies", which improves the stability of a high-layer virtual link and then also reduces structure's maintenance overheads. SMHS's clustering algorithm includes bottom-layer clustering algorithm and high-layer clustering algorithm. The bottom-layer clustering is proceeded by the clustering criterion adopted by the typical clustering algorithm MSWCA which has the most comprehensive consideration on stability measurement in clustering algorithms with motion-correlativity consideration that is favorable for improving bottom-layer clusters'stability. And high-layer clustering is proceeded by making the biggest connectivity cluster-degree as its clustering criterion.(2) Aiming at the problem existing in SMHS's bottom-layer clustering algorithm that"it only considers on bottom-layer intracluster stability, but neglects bottom-layer intercluster stability", the bottom-layer improving method of stable multi-layer hierarchical structure (SMHS) that"bottom-layer clustering algorithm which enhances clusters'stability (BCAECS)"is proposed. Based on mobility prediction idea, BCAECS considers on bottom-layer intracluster stability, bottom-layer intercluster stability and bottom-layer clusters'optimization comprehensively, and it's adapted to different scenarios by adjusting weights, which improves bottom-layer clusters'stability and reduces bottom-layer clusters'maintenance overheads.(3) Aiming at the problem that SMHS doesn't exist a matched hierarchical routing protocol, the stable multi-layer hierarchical structure (SMHS) based hierarchical routing protocol (HRP) is proposed, which refers to the thought of a typical multi-layer hierarchical structure MHS based hierarchical routing protocol HSR and combines SMHS's characteristic. HRP's structure and high-layer virtual links have higher stability. It improves the protocol's reliability and also reduces the lost-packets'number and rerouting times, and then reduces the protocol's transmission delay and routing overheads. Meanwhile, HRP's structure maintenance overheads and position management overheads are relatively low, which also reduces the protocol's routing overheads.(4) To improve the stability of SMHS's bottom-layer clusters, the bottom-layer improving method of stable multi-layer hierarchical structure (SMHS) that"bottom-layer clusters with multi-hop radius are constructed, and a typical hybrid flat structure routing protocol ZRP with a wide application range is adopted as bottom-layer intracluster routing protocol"is proposed. The bottom-layer clustering algorithm with multi-hop radius can be achieved by a little modification of SMHS's bottom-layer clustering algorithm, so the bottom-layer clustering algorithm is not the research emphasis, but the bottom-layer intracluster routing protocol ZRP is. Aiming at the problem that"interzone-route maintenance scheme of SMHS's bottom-layer intracluster routing protocol ZRP makes ZRP have many lost packets'number and many route rediscovering times; the former makes ZRP's delivery ratio of data packets low, which makes ZRP's reliability low; the latter makes ZRP's transmission delay and routing overheads high.", the segment repair based bottom-layer intracluster routing protocol (SRBIRP) is proposed. In SRBIRP, each node saves multiple backup routes to each node in its intrazone by maintaining an intrazone topology structure based directed acyclic graph (DAG), and an interzone route is repaired by using backup segment-routes as much as possible. SRBIRP's interzone-route maintenance scheme reduces lost packets'number and route rediscovering times. It improves delivery ratio of data packets of the protocol and shows that SRBIRP improves the protocol's reliability, and it also reduces the transmission delay and routing overheads of the protocol.The above research work not only prompts developments of correlative theories such as clustering algorithms, hierarchical structure based hierarchical routing protocols and flat structure based routing protocols but also provides a better support to scalability of ad hoc networks.