This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has conten...This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst（TB）. When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.展开更多
A series of very successful Continuous Very Long Baseline Interferometry Campaigns(CONT) have been carried out at irregular intervals since 1994.One of the goals is to support high-resolution earth rotation studies.Th...A series of very successful Continuous Very Long Baseline Interferometry Campaigns(CONT) have been carried out at irregular intervals since 1994.One of the goals is to support high-resolution earth rotation studies.The most recent CONT08 campaign was conducted with a network of 11 observatories at an increased recording rate of 512 Mbit per second over a fortnightly time span,from which stronger diurnal variations of the Earth Rotation Parameters(ERP) have been detected.We compared the high-frequency ERP from VLBI and GPS observations during CONT02,CONT05 and CONT08 with the atmospheric angular momentum functions derived from the National Centers for Environmental Prediction/National Center for Atmospheric(NCEP/NCAR) during these periods.We attribute the detected diurnal discrepancies between the theoretical models and the CONT08 observations to atmospheric excitations.展开更多
基金Supported by National Natural Science Foundation of China (No. 60472078 and No. 90604013).
文摘This paper proposes a modification to distributed coordination function （DCF） to improve the channel utilization in IEEE 802.11 wireless local area networks （ WLANs）. In the modified DCF, when a station has contended for the channel, it may transmit multiple data frames continuously to the same destination, which is called transmission burst（TB）. When the maximum number of data packets transmitted continuously in a TB is set to be 2, the performance is expected to be the best. The theoretical analysis and simulation results show that compared with the standard DCF, the modified DCF can increase the throughput and decrease the delay of the WLAN, and the modification does not introduce any additional control overhead.
基金supported by the National Natural Science Foundation of China (10973031)National High-Tech Research and Development Program of China (2008AA12A210)100 Talents Program of the Chinese Academy of Sciences
文摘A series of very successful Continuous Very Long Baseline Interferometry Campaigns(CONT) have been carried out at irregular intervals since 1994.One of the goals is to support high-resolution earth rotation studies.The most recent CONT08 campaign was conducted with a network of 11 observatories at an increased recording rate of 512 Mbit per second over a fortnightly time span,from which stronger diurnal variations of the Earth Rotation Parameters(ERP) have been detected.We compared the high-frequency ERP from VLBI and GPS observations during CONT02,CONT05 and CONT08 with the atmospheric angular momentum functions derived from the National Centers for Environmental Prediction/National Center for Atmospheric(NCEP/NCAR) during these periods.We attribute the detected diurnal discrepancies between the theoretical models and the CONT08 observations to atmospheric excitations.
