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IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as “virtual carrier sensing”). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the “virtual carrier sensing” implemented by RTS/CTS handshake cannot prevent all interference as we expect in theory. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. In this paper, we investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Two independent solutions are proposed in this paper. One is a simple enhancement to the IEEE 802.11 MAC protocol. The other is to utilize directional antennas. Simulation results verify that the proposed schemes indeed can help IEEE 802.11 resolve most interference caused by large interference range. 相似文献
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介绍了无线局域网IEEE802.11g标准,详细讲述了IEEE802.11g标准的概念、产生背景、特点、构件及体系结构、发展前景,并探讨了实现IEEE802.11 gWLAN所需的几项关键技术,同时分析了IEEE802.11g标准的网络性能. 相似文献
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Xiangyu Peng Letian Jiang Guozhi Xu 《Wireless Communications and Mobile Computing》2012,12(13):1165-1174
To estimate the system performance of RTS/CTS scheme in an error‐prone WLAN channel, this paper proposes a new three‐dimensional Markov model, which considers the impact of bit error on all kinds of frames, and both station short retry limit and long retry limit. The system performance parameters including saturation throughput, packet drop probability, drop time, and average delay are derived using the new Markov model. By comparing the numerical results with simulation results, the model is proved to be more accurate than previous work. The numerical results show that the channel bit error rate has a significant impact not only on system performance, but also on the sensitivity of other system parameters including network scale, channel data rate, and packet length. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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采用高温固相法合成了Si4+掺杂的BaZr(BO3)2:Eu红色发光荧光粉。激发光谱表明,不同Si4+掺杂浓度明显使电荷迁移态(CTS)向高能量的位置移动,且改善了样品的发光强度。分析认为,这是由于Si4+的电负性大于所取代的Zr4+,且Si4+的进入影响了Eu3+的配位数,提高了CTS向发光中心的能量传递几率。依据Judd-Ofelt理论计算的强度参数表明,随着Si4+掺杂浓度的增加,Eu3+所处格位的对称性明显降低,增大了Eu3+的跃迁几率,从而改善了发光强度。计算Eu3+间的能量传递几率发现,在掺杂浓度为5%时,Eu3+间的能量传递几率很小,其对荧光粉的发光影响不大。 相似文献
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目前的ASIC设计中,时钟偏移对同步数字电路的影响越来越大,它也越来越受到高速电路设计者的关注,因此如何解决它给电路带来的不利影响成了设计中的重要挑战、文章分析了时钟偏移的产生机理,然后提出了怎样使用CTS在时钟树中插入不同驱动能力的缓冲器,以平衡时钟网络,最后还分析了如何利用有用的时钟偏移来改善电路的时序。 相似文献
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用Encounter实现Mesh-Local-Tree结构的时钟设计流程 总被引:1,自引:0,他引:1
提出了一种实用的设计流程,即在Cadencd公司的Encounter环境中去实现对网格 本地树(MLT)时钟结构的综合与分析方法.对一个实际工业设计试验的数据表明:运用Clockmesh CRS的综合方式,MLT的时钟架构相对于单一的树结构能够实现更小的时钟偏差(114ps、 171ps).同时,将这种设计流程运用于其他设计中,以比较MLT和CTS不同的设计流程.结果显示,MLT的时钟架构可以实现更小的时钟偏差,同时还可以降低缓冲器的数量,这样也弥补了单一网格结构的功耗问题. 相似文献