Space-based Automatic Dependent Surveillance-Broadcast(ADS-B)technology can eliminate the blind spots of terrestrial ADS-B systems because of its global coverage capability.However,the space-based ADS-B system faces n...Space-based Automatic Dependent Surveillance-Broadcast(ADS-B)technology can eliminate the blind spots of terrestrial ADS-B systems because of its global coverage capability.However,the space-based ADS-B system faces new problems such as extremely low Signal-toNoise Ratio(SNR)and serious co-channel interference,which result in long update intervals.To minimize the position message update interval at an update probability of 95%with full coverage constraint,this paper presents an optimization model of digital multi-beamforming for space-based ADS-B.Then,a coevolution method DECCG_A&A is proposed to enhance the optimization efficiency by using an improved adaptive grouping strategy.The strategy is based on the locations of uncovered areas and the aircraft density under the coverage of each beam.Simulation results show that the update interval can be effectively controlled to be below 8 seconds compared with other existing methods,and DECCG_A&A is superior in convergence to the Genetic Algorithm(GA)as well as the coevolution algorithms using other grouping strategies.Overall,the proposed optimization model and method can significantly reduce the update interval,thus improving the surveillance performance of space-based ADS-B for air traffic control.展开更多
I.Lenovo: refocus on PC operation On December 8th, 2004, Lenovo consummated a deal with IBM whereby Lenovo was to acquire IBM’s desktop and laptop PC unit and its R&D and procurement operations worldwide for the...I.Lenovo: refocus on PC operation On December 8th, 2004, Lenovo consummated a deal with IBM whereby Lenovo was to acquire IBM’s desktop and laptop PC unit and its R&D and procurement operations worldwide for the sum of US$1.25 billion. On May 1st 2005, Lenovo completed its acquisition of IBM’s PC Unit. "Using an analogy, our enterprise is well likened to a tortoise but our foreign competitor is more like a rabbit. Instead of racing against the rabbit heads-on, we would rather ride on its back and let it carry us forward," said former Lenovo Chairman Liu Chuanzhi.展开更多
文摘Space-based Automatic Dependent Surveillance-Broadcast(ADS-B)technology can eliminate the blind spots of terrestrial ADS-B systems because of its global coverage capability.However,the space-based ADS-B system faces new problems such as extremely low Signal-toNoise Ratio(SNR)and serious co-channel interference,which result in long update intervals.To minimize the position message update interval at an update probability of 95%with full coverage constraint,this paper presents an optimization model of digital multi-beamforming for space-based ADS-B.Then,a coevolution method DECCG_A&A is proposed to enhance the optimization efficiency by using an improved adaptive grouping strategy.The strategy is based on the locations of uncovered areas and the aircraft density under the coverage of each beam.Simulation results show that the update interval can be effectively controlled to be below 8 seconds compared with other existing methods,and DECCG_A&A is superior in convergence to the Genetic Algorithm(GA)as well as the coevolution algorithms using other grouping strategies.Overall,the proposed optimization model and method can significantly reduce the update interval,thus improving the surveillance performance of space-based ADS-B for air traffic control.
文摘I.Lenovo: refocus on PC operation On December 8th, 2004, Lenovo consummated a deal with IBM whereby Lenovo was to acquire IBM’s desktop and laptop PC unit and its R&D and procurement operations worldwide for the sum of US$1.25 billion. On May 1st 2005, Lenovo completed its acquisition of IBM’s PC Unit. "Using an analogy, our enterprise is well likened to a tortoise but our foreign competitor is more like a rabbit. Instead of racing against the rabbit heads-on, we would rather ride on its back and let it carry us forward," said former Lenovo Chairman Liu Chuanzhi.
