| Summary: | 碩士 === 國立交通大學 === 資訊科學系所 === 93 === In mobile ad hoc networks (MANETs), broadcasting is a common operation for providing network functions, such as route discovery and source paging. However, an uncontrolled broadcast, which is also called blind flooding, is inefficient and may lead to heavy redundancies, contentions and collisions, and is commonly referred to as a “broadcast storm” [1]. Although this problem has been addressed extensively, most studies suffer with respect to balance between coverage performance and rebroadcasting efficiency. In a counter-based scheme, a mobile node determines the rebroadcast probability based on the node density in its neighborhood, but does not include the distance concepts which helps improve the Expected Additional Coverage (EAC) [1]. This investigation proposes several algorithms to solve broadcast storm problem. The DISCOUNT scheme combines both DIStance-based and COUNTter-based schemes. The DIS_RAD distinguishes different Random Assessment Delays (RAD) from border nodes to interior ones. The DISCOUNT-RS further improve the performance of the mentioned algorithms. The basic idea of these algorithms is that give nodes closer to the border should have a higher rebroadcast probability since they create better Expected Additional Coverage (EAC) values. Here, a distance threshold is adopted to distinguish between interior and border nodes. Two distinct RADs are applied to the border and interior nodes, with the border nodes having shorter RADs than the interior nodes. Based on this change, the two rebroadcast probabilities are derived for the nodes located at the border annulus and those located at the interior circle. The analytical results indicate that the proposed scheme indeed provides a higher rebroadcast probability for border nodes and a lower rebroadcast probability for interior nodes compared with the counter-based scheme. The simulation results demonstrate that the proposed “DIS_RAD” scheme works much better than the counter-based scheme. The probability analysis model also confirms the validity of the simulation results. The most important, the proposed scheme can keep good balance between reachability and rebroadcast efficiency in various network densities. Therefore, the dynamic adjust counter threshold according to network densities is not necessary.
|
|---|
