Currently,the WLAN indoor positioning system attracts a lot of interests,not only because of the cheap implementation but also because of the high positioning accuracy comparing with other indoor positioning systems.The WLAN indoor positioning system contains two phases,which are offline phase and online phase.In the online phase,the WLAN equipment user(UE) has to access to the WLAN for the latest radio map and positioning software.Due to during the network allocation vector(NAV) duration,the WLAN channel is only reserved for one WLAN UE,others UEs' carrier accessing will be blocked.In addition,the blocked UE will make a retrial accessing,which will definitely introduce more traffic blocking to the WLAN.So In this paper,based on the analysis of the WLAN indoor positioning system architecture,a proper queuing model by using of the Extended Erlang B formula is proposed,which takes the retrial calling percentage into consideration in the proposed model.The simulation results show that the proposed method is more accurate and performs well to predict the blocking probability.
The effect of too much overhead caused by fixed neighborhood state update cycle on the whole network performance has been greatly alleviated by a neighborhood state dynamic update(NSDU) algorithm proposed for MANET in this paper.A local topology flapping metric(LTFM) has been established based on the changes of link connection to achieve the measurement of stability.The loop control theory has been adopted to establish the control model of the neighborhood state,so as to set up the mapping relationship with the topology change,based on which both the neighborhood state information exchange and the timeout of link with neighbors involved will be adjusted dynamically according to NSDU to ensure that the update cycle would regulate with the network environment in order to achieve the purpose of reducing the control overhead.The simulation results on NS2.34 with different nodes velocities,traffic generating rates and the network node densities shows that adopting NSDU,no matter based on a table-driven protocol or a on-demand one,would reduce the overhead effectively while hardly bring any obvious impacts on metrics of packet successful delivery rate and the average end-to-end delay as well.
