Modeles et strategies du handoff dans les reseaux ATM sans fil: Performances et choix (French text)

The main goal of our study is to analyze the handoff function in future wireless networks supporting multimedia traffic and a large number of mobile users.; The handoff procedure requires a radio channel change when a mobile moves from one cell to another. It can also require connection re-routing in order to maintain the user's communication path. All these procedures must provide an efficient bandwidth use as well as an acceptable handoff delay.; We propose to study the handoff function in the framework of ATM networks which are known to provide multimedia traffic handling within predefined criteria of service quality. In this framework, we present a new handoff strategy called hierarchical handoff, whose structure is derived from the analysis of previously proposed strategies. It turns out that this new strategy improves the overall quality of service.; The handoff strategies can be classified into two categories called simple and hybrid. The simple handoff procedures use a single handoff procedure whereas the hybrid ones combine the advantages of two simple strategies. In this respect, the hierarchical handoff is hybrid combining the partial re-routing and the virtual connection tree strategies. We compare this strategy with the previously proposed partial re-routing handoff procedure known to allow a more efficient bandwidth use and shorter handoff delay than all the other simple strategies. We also present a comparison with the two-phase handoff strategy which performs better than simple strategies.; Three performances measures are defined and estimated for the three handoff strategies. These measures are based on the expected bandwidth per call, the expected delay per call and the call blocking probability.; An analytical model is proposed to compute the expected bandwidth and delay per call for the three handoff strategies. We also propose a traffic model to evaluate the call blocking probability. This model is based on the use of reserved channels to handle handoff calls. This strategy can reduce the handoff blocking probability a sensitive parameter in the users perception of quality of service.; Numerical results are presented for data and voice traffics, for users with large and small mobility and different channel reservation schemes. In most cases, they show that the hierarchical handoff procedure gives lower expected bandwidth and delay per call as well as smaller handoff blocking probability in comparison with the two-phase and partial re-routing handoff strategies. We conclude the study by some recommendations about the use of these strategies in wireless ATM networks depending on the users mobility characteristics either broad or local.