E-BEB Algorithm to Improve Quality of Service on Wireless Ad-Hoc Networks

The Medium Access Control (MAC) protocol is the main element which determines the system throughput in Wireless Local Area Networks (WLANs) IEEE 802.11 standard. The MAC technique of the IEEE 802.11 protocol is called Distributed Coordination Function (DCF). In DCF, stations contend for the use of the channel in distributed manner via the use of the Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) protocol. In the CSMA/CA protocol, each station sets up a Backoff time according to a randomly selected interval from zero to the Contention Window (CW) for an additional deferral time before transmitting. The random Binary Exponential Backoff (BEB) algorithm is used to randomize moments at which stations try to access the wireless medium. However, in the random Backoff mechanism, packet collisions are not entirely eliminated, and the system throughput decreases when the number of stations is large, and there is no fairness between stations. The BEB algorithm has a number of disadvantages; one crucial disadvantage is the problem of fairness. In this paper, we analyze the behavior of the BEB algorithm used in IEEE 802.11 standard. We propose an Enhanced Binary Exponential Backoff (E-BEB) algorithm to improve the fairness of the channel access for BEB algorithm. Our E-BEB algorithm adjusts the way of increase or decrease of the contention window CW based on the number of the frame which is sent successfully. We propose several configurations, and we use NS2 simulator to analyze the network's fairness of the channel access of the E-BEB algorithm. The simulation results show that compared with other algorithms like BEB or Improved BEB (IBEB), the E-BEB algorithm improves the fairness of the channel access and increases the network's throughput capacity; which is an valuable Quality of Service (QoS) parameter.

並列關鍵字

Ad-Hoc ； backoff algorithm ； CW ； DCF ； fairness ； QoS

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