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.T...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.展开更多
In the case of electric or tram traction vehicles, the energy for propulsion purposes, as well as all other purposes, is processed and delivered via traction substations. Knowledge of the course of traction substation...In the case of electric or tram traction vehicles, the energy for propulsion purposes, as well as all other purposes, is processed and delivered via traction substations. Knowledge of the course of traction substation loading, especially at the stage of its design, is an extremely important issue because of the choice of the processing equipment of the main circuit or protection devices. In the range of investigations of railway traction substation B in vicinity of Cracow （Poland）, the measurements of current load in hours 4：00 a.m.-8：00 p.m. were realized. The measurements for the analysis were chosen from those realized between 6：00 a.m.-8：00 a.m. （the morning rush time）. Due to the sampling of 2 h summit with a frequency of 2 kHz, the recorded data set contains 1.44 ~ 107 elements. Therefore, the necessary transformation of data was to lower frequency 1 Hz, 10 Hz and 50 Hz. The results of the analysis presented below indicate the effect of such conduct on the obtained results for the parameters of time series models. In view of the unsatisfactory effects of the polynomial approximation, there is a need to seek a more efficient approximation method for achieving the optimum compatibility with the measured process. Continued research should lead to the formulation of procedures, which will determine an acceptable accuracy of the expected variability of traction substation loads.展开更多
基金Sponsored by the National Natural Science Foundation and Civil Aviation Administration of China (Grant No. 61101122)the Fundamental Research Funds for the Central Universities (Grant No. HIT. NSRIF. 2010090)+1 种基金the China Postdoctoral Science Foundation (Grant No. 20100471079)the Heilongjiang Province Postdoctoral Science Foundation (Grant No. LBH-z10127)
文摘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.
文摘In the case of electric or tram traction vehicles, the energy for propulsion purposes, as well as all other purposes, is processed and delivered via traction substations. Knowledge of the course of traction substation loading, especially at the stage of its design, is an extremely important issue because of the choice of the processing equipment of the main circuit or protection devices. In the range of investigations of railway traction substation B in vicinity of Cracow （Poland）, the measurements of current load in hours 4：00 a.m.-8：00 p.m. were realized. The measurements for the analysis were chosen from those realized between 6：00 a.m.-8：00 a.m. （the morning rush time）. Due to the sampling of 2 h summit with a frequency of 2 kHz, the recorded data set contains 1.44 ~ 107 elements. Therefore, the necessary transformation of data was to lower frequency 1 Hz, 10 Hz and 50 Hz. The results of the analysis presented below indicate the effect of such conduct on the obtained results for the parameters of time series models. In view of the unsatisfactory effects of the polynomial approximation, there is a need to seek a more efficient approximation method for achieving the optimum compatibility with the measured process. Continued research should lead to the formulation of procedures, which will determine an acceptable accuracy of the expected variability of traction substation loads.
