Real-time applications are sensitive to conditions such as transmission delay and jittering. To cut down on the influence generated by the WLAN handoff process, three parts of WLAN （wireless local area networks） han...Real-time applications are sensitive to conditions such as transmission delay and jittering. To cut down on the influence generated by the WLAN handoff process, three parts of WLAN （wireless local area networks） handoff： handoff triggering, access point selection and the fast handoff algorithm are investigated. A fast handoff solution totally based on the station is proposed and it is composed of three parts： a handoff triggering mechanism based on dynamic threshold adjustment; an AP selection criterion based on probe delay; a fast handoff algorithm with differentiated channel selection and a dynamic cache. The station based solution is independent with AP＇s collaboration and avoids any changes in the IEEE 802. l l protocol. It is robust and has very good extensibility. Through tests and evaluation in a hotspot WLAN, the solution effectively reduces handoff latency and user experience of real-time applications is enhanced.展开更多
基于IEEE 802.11协议标准的无线局域网(wireless local area network,WLAN)由于其成本低、速度快、灵活方便等特点,目前已得到广泛的应用。由于WLAN的覆盖范围较小,当用户位置发生移动而离开当前WLAN范围进入新的WLAN覆盖范围时,用户将...基于IEEE 802.11协议标准的无线局域网(wireless local area network,WLAN)由于其成本低、速度快、灵活方便等特点,目前已得到广泛的应用。由于WLAN的覆盖范围较小,当用户位置发生移动而离开当前WLAN范围进入新的WLAN覆盖范围时,用户将会在多个WLAN覆盖范围内进行切换(handoff)。WLAN的切换过程是复杂的,执行该过程需要消耗网络大量的信令和进程负载。文中首先研究分析了WLAN的切换过程,分别对WLAN切换的触发、探寻、接入认证和重关联四个阶段的原理进行了总结;然后进一步分析了各个阶段的时延产生机制,并对整个切换过程各阶段的时延进行了总结和对比分析;最后,基于以上研究和分析,分别从平滑切换策略和快速切换策略两个方面,总结了基于IEEE 802.11标准的WLAN的切换方案的研究,并对这些研究的优劣进行了简要探讨。展开更多
Applying IEEE802.11MAC protocols in baltery-powered devices make power consumption critical demand upon implementation.A statistical study on operator/bit usage,the weight of operator and operator type in the programs...Applying IEEE802.11MAC protocols in baltery-powered devices make power consumption critical demand upon implementation.A statistical study on operator/bit usage,the weight of operator and operator type in the programs has been done,including converting the MAC functions from SDL to C to ASM with tow RISC targts. The study shows that implementing MAC. functions should consider real-time protocol re3quirements by dividing MAC functions into sets. We enhance the set of time-critical functions implemented to dedicated hardwere and the set of non-time-critical functions implemented to software run with embedded processor. This heterogeneous system is proposed in consideration of our study results to reduce popwer consumption.展开更多
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
The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are m...The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.展开更多
基金The National Natural Science Foundation of China(No.90604003,60603067)
文摘Real-time applications are sensitive to conditions such as transmission delay and jittering. To cut down on the influence generated by the WLAN handoff process, three parts of WLAN （wireless local area networks） handoff： handoff triggering, access point selection and the fast handoff algorithm are investigated. A fast handoff solution totally based on the station is proposed and it is composed of three parts： a handoff triggering mechanism based on dynamic threshold adjustment; an AP selection criterion based on probe delay; a fast handoff algorithm with differentiated channel selection and a dynamic cache. The station based solution is independent with AP＇s collaboration and avoids any changes in the IEEE 802. l l protocol. It is robust and has very good extensibility. Through tests and evaluation in a hotspot WLAN, the solution effectively reduces handoff latency and user experience of real-time applications is enhanced.
文摘基于IEEE 802.11协议标准的无线局域网(wireless local area network,WLAN)由于其成本低、速度快、灵活方便等特点,目前已得到广泛的应用。由于WLAN的覆盖范围较小,当用户位置发生移动而离开当前WLAN范围进入新的WLAN覆盖范围时,用户将会在多个WLAN覆盖范围内进行切换(handoff)。WLAN的切换过程是复杂的,执行该过程需要消耗网络大量的信令和进程负载。文中首先研究分析了WLAN的切换过程,分别对WLAN切换的触发、探寻、接入认证和重关联四个阶段的原理进行了总结;然后进一步分析了各个阶段的时延产生机制,并对整个切换过程各阶段的时延进行了总结和对比分析;最后,基于以上研究和分析,分别从平滑切换策略和快速切换策略两个方面,总结了基于IEEE 802.11标准的WLAN的切换方案的研究,并对这些研究的优劣进行了简要探讨。
文摘Applying IEEE802.11MAC protocols in baltery-powered devices make power consumption critical demand upon implementation.A statistical study on operator/bit usage,the weight of operator and operator type in the programs has been done,including converting the MAC functions from SDL to C to ASM with tow RISC targts. The study shows that implementing MAC. functions should consider real-time protocol re3quirements by dividing MAC functions into sets. We enhance the set of time-critical functions implemented to dedicated hardwere and the set of non-time-critical functions implemented to software run with embedded processor. This heterogeneous system is proposed in consideration of our study results to reduce popwer consumption.
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.
文摘The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters.
