近年来随着核电技术、无线通信技术、EMC技术的发展,基于WLAN的无线通信技术已经在核电站得到了越来越广泛的应用。VoWLAN(Voice over WLAN)是一种利用WLAN来传输VoIP(Voice over Internet Protocol)帧的技术,VoWLAN技术是对VoIP的扩展...近年来随着核电技术、无线通信技术、EMC技术的发展,基于WLAN的无线通信技术已经在核电站得到了越来越广泛的应用。VoWLAN(Voice over WLAN)是一种利用WLAN来传输VoIP(Voice over Internet Protocol)帧的技术,VoWLAN技术是对VoIP的扩展和更新,将VoIP无线化,使用户能更方便更直接地进行语音通信,这也使VoWLAN技术在核电站得到了普遍应用,而Qos(Quality of Service)则为网络通信建立一个有保证的传输系统。本文介绍了VoWLAN的关键技术及影响VoWLAN的Qos的主要原因,阐述了时延、抖动、丢包等影响Qo S的机理和改进方法。展开更多
随着计算技术的快速发展,移动终端以其便携和移动的特性越来越多的应用于分布式虚拟环境当中。在支持移动终端的分布式虚拟环境中,切换是体现移动终端交互特性以及移动特性的关键问题。传统的切换策略大多以Received Signal Strength In...随着计算技术的快速发展,移动终端以其便携和移动的特性越来越多的应用于分布式虚拟环境当中。在支持移动终端的分布式虚拟环境中,切换是体现移动终端交互特性以及移动特性的关键问题。传统的切换策略大多以Received Signal Strength Indication(RSSI)作为是否需要进行切换的唯一依据,但是由于获得RSSI的信道扫描阶段较为耗时不能满足分布式虚拟环境中用户对实时性的要求。针对这个问题,给出了在WLAN环境下支持移动终端的分布式虚拟环境中一种基于用户QoS的切换策略。该方法通过对应用层可检测的特征进行分析,结合用户QoS综合作为信道扫描时机的判定条件。通过减少扫描次数,达到降低扫描延迟的目的,并在扫描/切换过程中采用DR(Dead Reckoning)算法来降低系统延迟造成的用户跳变感。试验证明,该方法较传统的切换策略更为灵活,对系统造成的延迟更小,并能很好的满足用户QoS需求。展开更多
In order to achieve the Quality of Service(QoS) provisioning and efficient resource utili-zation in cellular network and Wireless Local Area Network(WLAN) integration,an Integrated Ser-vice-Based Call Admission Contro...In order to achieve the Quality of Service(QoS) provisioning and efficient resource utili-zation in cellular network and Wireless Local Area Network(WLAN) integration,an Integrated Ser-vice-Based Call Admission Control(ISB-CAC) scheme is proposed in this paper.The integrated network is modeled by using multi-dimensional Markov chains.The numerical analysis is presented to evaluate the important performance measures such as the blocking probability of originating calls,the dropping probability,and the average transfer time,etc.The steady-state probabilities of the multi-dimensional Markov chains are obtained by using an iterative approach,and the CAC pa-rameters are optimally designed.The analytical model is validated by the computer simulation.It is shown that compared with the conventional WLAN-First Call Admission Control(WF-CAC) scheme,the proposed ISB-CAC scheme not only provides better QoS for mobile users but also utilizes the bandwidth resources more efficiently.展开更多
文摘近年来随着核电技术、无线通信技术、EMC技术的发展,基于WLAN的无线通信技术已经在核电站得到了越来越广泛的应用。VoWLAN(Voice over WLAN)是一种利用WLAN来传输VoIP(Voice over Internet Protocol)帧的技术,VoWLAN技术是对VoIP的扩展和更新,将VoIP无线化,使用户能更方便更直接地进行语音通信,这也使VoWLAN技术在核电站得到了普遍应用,而Qos(Quality of Service)则为网络通信建立一个有保证的传输系统。本文介绍了VoWLAN的关键技术及影响VoWLAN的Qos的主要原因,阐述了时延、抖动、丢包等影响Qo S的机理和改进方法。
文摘随着计算技术的快速发展,移动终端以其便携和移动的特性越来越多的应用于分布式虚拟环境当中。在支持移动终端的分布式虚拟环境中,切换是体现移动终端交互特性以及移动特性的关键问题。传统的切换策略大多以Received Signal Strength Indication(RSSI)作为是否需要进行切换的唯一依据,但是由于获得RSSI的信道扫描阶段较为耗时不能满足分布式虚拟环境中用户对实时性的要求。针对这个问题,给出了在WLAN环境下支持移动终端的分布式虚拟环境中一种基于用户QoS的切换策略。该方法通过对应用层可检测的特征进行分析,结合用户QoS综合作为信道扫描时机的判定条件。通过减少扫描次数,达到降低扫描延迟的目的,并在扫描/切换过程中采用DR(Dead Reckoning)算法来降低系统延迟造成的用户跳变感。试验证明,该方法较传统的切换策略更为灵活,对系统造成的延迟更小,并能很好的满足用户QoS需求。
基金Supported in part by the National Grand Fundamental Research Program of China (973 Program) (No. 2007CB-310606)the Specialized Foundation for the Achievements Transformation of Science and Technology of Jiangsu Province (No. BA2006101)
文摘In order to achieve the Quality of Service(QoS) provisioning and efficient resource utili-zation in cellular network and Wireless Local Area Network(WLAN) integration,an Integrated Ser-vice-Based Call Admission Control(ISB-CAC) scheme is proposed in this paper.The integrated network is modeled by using multi-dimensional Markov chains.The numerical analysis is presented to evaluate the important performance measures such as the blocking probability of originating calls,the dropping probability,and the average transfer time,etc.The steady-state probabilities of the multi-dimensional Markov chains are obtained by using an iterative approach,and the CAC pa-rameters are optimally designed.The analytical model is validated by the computer simulation.It is shown that compared with the conventional WLAN-First Call Admission Control(WF-CAC) scheme,the proposed ISB-CAC scheme not only provides better QoS for mobile users but also utilizes the bandwidth resources more efficiently.
