Improving protocol capacity by scheduling random access on WLANs
Improving protocol capacity by scheduling random access on WLANs
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DOI：
10.1007/s11235-008-9076-2
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发表时间：
2008-03
影响因子：
2.5
通讯作者：
X. Tian;Xiang Chen;T. Ideguchi;T. Okuda
中科院分区：
文献类型：
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作者：
X. Tian;Xiang Chen;T. Ideguchi;T. Okuda
由于无线局域网的带宽有限，MAC协议尤为重要。进行了大量的研究，提出的一些方案是有效的。具体来说，已经投入了相当大的努力来改进广泛使用的IEEE 802.11标准。先前的理论分析给出了IEEE 802.11 DCF吞吐量的上界远低于信道容量，并提出了相应的算法，可以实现接近上界的吞吐量。似乎我们不能指望用常规的方法来提高吞吐量。同时，除了吞吐量之外，DCF还存在公平性和QoS支持等问题。然而，除了少数混合协议外，大多数协议要么是基于争用模式，要么是基于调度模式，两者都不具备彼此的优点。本文提出了一种新的用于DCF（无控制节点）的MAC方案，该方案在低流量负载情况下动态适应流量变化而不降低延迟，在饱和情况下实现接近传输容量的高吞吐量。其关键思想是将虚拟帧划分为调度部分和竞争部分，并使每个节点在调度部分保留一个插槽。与传统的混合协议不同，除了队列长度之外，每个节点不必根据不断变化的流量负载有意地重置任何参数。该方案的一个显著特点是采用了一种新颖的方式，允许wlan在基于争用的模式下以低延迟工作，并在基于调度的模式下实现高吞吐量，而无需像以前的方案那样需要复杂的在线估计。这使得我们的方案更简单、更可靠。通过对仿真结果的分析，表明该方案可以在低延迟的情况下大大提高吞吐量。
The MAC protocol is important, especially for wireless LAN because of limited bandwidth. A great deal of research has been carried out and some of proposed schemes are effective. Specifically, considerable effort has been devoted to improving the IEEE 802.11 standard which is utilized widely. Previous theoretical analysis gave the upper bound of IEEE 802.11 DCF throughput which is far below the channel capacity and corresponding algorithm was proposed, which can achieve the throughput close to the upper bound. It seems that we cannot expect to enhance the throughput much more in a usual way. In the meantime, besides throughput, there are some other issues for DCF such as fairness and QoS support. However, except for several hybrid protocols, most proposals were either based on contention mode or schedule mode and neither of the two modes has possessed the good characters of the other.In this paper, we propose a new MAC scheme used for DCF (with no control node) that dynamically adapts to traffic changes without degradation of delay in the case of low traffic load and achieves high throughput which is close to transmission capacity in saturated case. The key idea is to divide the virtual frame into two parts, i.e., schedule part and contention part, and to enable each node to reserve a slot in schedule part. Unlike conventional hybrid protocols, every node does not have to intentionally reset any parameter according to the changing traffic load except its queue length. A distinguishing feature of this scheme is the novel way of allowing WLANs to work with low delay as in the contention-based mode and achieve high throughput as in the schedule-based mode without complicated on-line estimation required in previous schemes. This makes our scheme simpler and more reliable. Through an analysis of simulation results, we show that our scheme can greatly improve the throughput with low delay.