Enhancing the support of multi-hopping in IEEE 802.11 ad-hoc networks.

摘要

The IEEE 802.11 standard for medium access control in wireless local area networks has been adopted as the de-facto medium access control standard in wireless multi-hop ad-hoc networks. The 802.11 standard documents clearly declare "an ad-hoc architecture" as supported. However, this does not mean that the 802.11 protocol automatically supports multi-hop mobile ad-hoc networks, of which multi-hop connectivity is an important feature. In fact, several researchers have pointed out the deficiencies of 802.11 in multi-hop networks. Accordingly, the 802.11 protocol needs to be enhanced to yield an acceptable performance in multi-hop ad-hoc networks.; In this thesis, we study the inefficiency encountered when using the IEEE 802.11 protocol in multi-hop ad-hoc networks. Specifically, two major drawbacks are observed, low system throughput and instability. We support this study with an analytical model as a proof of concept and to aid in further understanding of the system behavior. Then, we propose an overlay algorithm on top of the IEEE 802.11 protocol that enhances its performance in terms of the system throughput and stability. The algorithm makes use of specific stations serving as virtual access points (VAPs). Their role is to discipline the interaction among multiple overlapping 802.11 Independent Basic Service Sets (IBSSs) that operate on the same frequency channel. Such mode of operation, in which multiple IBSSs overlap each other, can be translated into a general multi-hop ad-hoc network. The effects of several algorithm parameters on the system performance have been studied. A performance model for the VAPA algorithm is finally provided to basically describe the system throughput when the algorithm is overlaid on top of 802.11. Such model can be used to design various algorithm parameters to optimize an 802.11 system that deploys the VAPA algorithm as a new protocol sublayer.; Both mathematical and simulation results have shown that with the current 802.11 protocol, performance in multi-hop networks is highly inefficient and unstable. When applying the VAPA new protocol sublayer that regulates the interaction between the overlapping IBSS's, the saturation throughput has improved and gained more stability. These results contribute to the potential for the 802.11 in mobile ad-hoc networks.