针对四轴飞行器很难通过运动控制来完成快速扩展随机树(Rapidly-exploring Random Tree,RRT)所生成运动轨迹的问题,提出动力学和运动学约束的RRT算法.采用固定最终状态和固定最终时间控制器改进算法,通过动力学和运动学约束产生四轴飞...针对四轴飞行器很难通过运动控制来完成快速扩展随机树(Rapidly-exploring Random Tree,RRT)所生成运动轨迹的问题,提出动力学和运动学约束的RRT算法.采用固定最终状态和固定最终时间控制器改进算法,通过动力学和运动学约束产生四轴飞行器可执行的路径,对比实际四轴飞行器行走的路径与期望的路径,对RRT重新布线,调节其行走路径,保证算法的渐近最优性.仿真实验及实物测试结果表明,该算法可以运用到四轴飞行器运动规划中,在实际应用中具有一定的价值.展开更多
This paper focuses on the instantiation of random oracles in public key encryption schemes. A misunderstanding in the former instantiations is pointed out and analyzed. A method of using this primitive as a substituti...This paper focuses on the instantiation of random oracles in public key encryption schemes. A misunderstanding in the former instantiations is pointed out and analyzed. A method of using this primitive as a substitution of random oracles is also proposed. The partial and full instantiations of random oracles in optimal asymmetric encryption padding （OAEP） implemented by pseudorandom functions are described and the resulted schemes are proven to be indistinguishable secure against adaptive chosen ciphertext attack （IND-CCA2） secure. Using this method, one can transform a practical public key encryption scheme secure in the random oracle model into a standard-model secure scheme. The security of the scheme is based on computational assumptions, which is weaker than decisional assumptions used in Cramer- Shoup like schemes.展开更多
随着物联网(IoT,internet of things)的快速发展,机器类型通信(MTC,machine type communication)在生活中的应用大幅增长,机器类设备(MTD,machine type device)的部署也越来越密集。在这种情况下,如果发生断电断网等突发情况,在设备通...随着物联网(IoT,internet of things)的快速发展,机器类型通信(MTC,machine type communication)在生活中的应用大幅增长,机器类设备(MTD,machine type device)的部署也越来越密集。在这种情况下,如果发生断电断网等突发情况,在设备通电的瞬间将会有大规模的MTD同时向基站发起接入,设备接入基站需要完成下行同步、接收系统消息和随机接入(RA,random access)等过程。然而基站所能分配的前导资源是有限的,无法满足如此庞大的接入需求,从而造成网络阻塞,影响设备的接入概率和接入时延。为了减轻RA的接入冲突,提出了一种基于上下行子帧和物理随机接入信道(PRACH,physical random access channel)配置的动态随机接入时机(RO,random access occasion)调整方案,以及针对时延要求高的部分MTD分配特定的前导资源,仿真结果表明该方案能够有效提高系统的吞吐量,降低设备的接入时延。展开更多
文摘针对四轴飞行器很难通过运动控制来完成快速扩展随机树(Rapidly-exploring Random Tree,RRT)所生成运动轨迹的问题,提出动力学和运动学约束的RRT算法.采用固定最终状态和固定最终时间控制器改进算法,通过动力学和运动学约束产生四轴飞行器可执行的路径,对比实际四轴飞行器行走的路径与期望的路径,对RRT重新布线,调节其行走路径,保证算法的渐近最优性.仿真实验及实物测试结果表明,该算法可以运用到四轴飞行器运动规划中,在实际应用中具有一定的价值.
基金Supported by the National Basic Research Program of China (973 Program) (2007CB311201)the National High-Technology Research and Development Program of China (863 Program) (2006AA01Z427)the National Natural Science Foundation of China (60673073)
文摘This paper focuses on the instantiation of random oracles in public key encryption schemes. A misunderstanding in the former instantiations is pointed out and analyzed. A method of using this primitive as a substitution of random oracles is also proposed. The partial and full instantiations of random oracles in optimal asymmetric encryption padding （OAEP） implemented by pseudorandom functions are described and the resulted schemes are proven to be indistinguishable secure against adaptive chosen ciphertext attack （IND-CCA2） secure. Using this method, one can transform a practical public key encryption scheme secure in the random oracle model into a standard-model secure scheme. The security of the scheme is based on computational assumptions, which is weaker than decisional assumptions used in Cramer- Shoup like schemes.
文摘随着物联网(IoT,internet of things)的快速发展,机器类型通信(MTC,machine type communication)在生活中的应用大幅增长,机器类设备(MTD,machine type device)的部署也越来越密集。在这种情况下,如果发生断电断网等突发情况,在设备通电的瞬间将会有大规模的MTD同时向基站发起接入,设备接入基站需要完成下行同步、接收系统消息和随机接入(RA,random access)等过程。然而基站所能分配的前导资源是有限的,无法满足如此庞大的接入需求,从而造成网络阻塞,影响设备的接入概率和接入时延。为了减轻RA的接入冲突,提出了一种基于上下行子帧和物理随机接入信道(PRACH,physical random access channel)配置的动态随机接入时机(RO,random access occasion)调整方案,以及针对时延要求高的部分MTD分配特定的前导资源,仿真结果表明该方案能够有效提高系统的吞吐量,降低设备的接入时延。
