Enhancing IEEE 802.11 MAC in congested environments (original) (raw)

Collision-Aware Adaption of Contention Window in 802 . 11 e Wireless Lan

2009

One of the key challenges in designing a quality of service (QOS) scheme for IEEE 802.11 wireless LANs (WLANS) is reducing collisions and improving throughput. Existed Adaptive contention windows mechanisms can reduce collisions of all traffic. However, adaptive contention window algorithms cannot guarantee the absolute priority of the high-priority traffic. Especially in the heavy loading, low-priority traffics will introduce unnecessary collisions and cause unsuccessful transmission. Our scheme aims to share the transmission channel efficiently and to provide the absolute differentiated traffic scheme. Relative priorities are provisioned by adjusting the range of the back-off timer of low-priority traffic class taking into account both applications requirements and network conditions. We demonstrate the effectiveness of our solution by comparing with existing approaches through extensive simulations. Results show that our scheme reduces frame delay as well when traffic load is hea...

Modeling and analysis of slow CW decrease for IEEE 802.11 WLAN

14th IEEE Proceedings on Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003., 2003

~Ihsrruci-~rhe IEEE 802.1 I Medium Access Control (MAC) protucol provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium, which may introduce a lot of collisions in ease of overloaded active stations. Slow Contention Window (CW) decrease scheme is a simple and efficient solution for this problem. In this paper, we use an analytical model to compare the slow CW decrease scheme t u the IEEE 802.11 MAC protocol. Several parameters are invcrtigdted such as thc number of Svations, the initial CW size. the decrease factor value. the maximum bdckoff stage and the coexistence with the RequestToSend and ClearToSend (RlSICTS) mechanism. The results show that the slow CW decl-ease scheme can efficiently improve the throughput of IEEE 802.11. a n d that the throughput gain is higher when the -decrease hctor is larger. Moreover, the initial CW size and maximum backoff stage also affect tlie performance of slow CW decrease scheme. K q w i r d s -IEEE X02.11; DCF; slow CW decrease scheme; ~r s m s

The Novel Contention Window Control Scheme for IEEE 802.11 Mac Protocol

The IEEE 802.11 medium access control (MAC) protocol defines a contention-based distribution channel access mechanism that shares the wireless medium for mobile stations. In this paper, we present a novel back off mechanism, which divides contention window range to the different level based on the history of channel status. Instead of doubling and resetting the CW, we change the CW range by taking into account last three channel states. We test the new scheme against legacy IEEE 802.11 with NS-2 network simulator. The simulation results have shown 30.77% improvement in packet delivery ratio and 31.76% in delay and 30.81% in throughput compared to the IEEE 802.11 DCF.

Determinist Contention Window Algorithm for IEEE 802.11

2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005

With the widespread IEEE 802.11 networks use, strong needs to enhance Quality of Service (QoS) has appeared. The IEEE 802.11 Medium Access Control (MAC) protocol provides a contention-based distributed channel access mechanism that allow for wireless medium sharing. This protocol involves a significant collision rate as the network gets fairly loaded. Although the Contention Window (CW) is doubled after each collision, active stations may randomly select a backoff Timer value smaller than the preceding one. This is obviously sub-optimal since the backoff values should rather increase after each collision in order to further space between successive transmissions and thus absorbing the growing contending flows. In this paper, we propose a novel backoff mechanism, namely "Determinist Contention Window Algorithm (DCWA)", which further separates between the different backoff ranges associated to the different contention stages. Instead of just doubling the upper bound of the CW, DCWA increases both backoff range bounds (i.e., upper and lower bounds). On the other hand, after each successful transmission the backoff range is readjusted by taking into account current network load and past history. Simulation results show that DCWA outperforms both the Distributed Coordination Function (DCF) and the Slow Decrease (SD) scheme in terms of responsiveness to network load fluctuations, network utilization, and fairness among active stations.

Modeling and analysis of slow CW decrease IEEE 802.11 WLAN

2003

Performance limits and analysis of contention-based IEEE 802.11 MAC

2006

Abstract Recent advance in IEEE 802.11 based standard has pushed the wireless bandwidth up to 600Mbps while keeping the same wireless medium access control (MAC) schemes for full backward compatibility. However, it has been shown that the inefficient protocol overhead casts a theoretical throughput upper limit and delay lower limit for the IEEE 802.11 based protocols, even the wireless data rate goes to infinitely high.

Performance evaluation and enhancement of the CSMA/CA MAC protocol for 802.11 wireless LANs

1996

The IEEE 802.11 protocol for wireless local area networks adopts a CSMA/CA protocol with exponential backoff as medium access control technique. As the throughput performance of such a scheme becomes critical when the number of mobile stations increases, in this paper we propose an adaptive contention window mechanism, which dynamically selects the optimal backoff window according to the estimate of

A Novel Contention Window Control Scheme for IEEE 802.11 WLANs

ietejournal, 2012

In the IEEE 802.11 standard, network nodes experiencing collisions on the shared medium need a mechanism that can prevent collisions and improve the throughput. Furthermore, a backoff mechanism is used that uniformly selects a random period of time from the contention window (cw) that is dynamically controlled by the Binary Exponential Backoff (BEB) algorithm. Prior research has proved that the BEB scheme suffers from a fairness problem and low throughput, especially under high traffic load. In this paper, we present a new backoff control mechanism that is used with the IEEE 802.11 distributed coordination function (DCF). In particular, we propose a dynamic, deterministic contention window control (DDCWC) scheme, in which the backoff range is divided into several small backoff sub-ranges. In the proposed scheme, several network levels are introduced, based on an introduced channel state vector that keeps network history. After successful transmissions and collisions, network nodes change their cw based on their network levels. Our extensive simulation studies show that the DDCWC scheme outperforms four other well-known schemes: Multiplicative Increase and Linear Decrease, Double Increment Double Decrement, Exponential Increase Exponential Decrease, and Linear/Multiplicative Increase and Linear Decrease. Moreover, the proposed scheme, compared with the IEEE 802.11 DCF, gives 30.77% improvement in packet delivery ratio, 31.76% in delay, and 30.81% in throughput.

Performance Impact of CSMA/CA on the throughput of IEEE 802.11 Networks

A wireless LAN is a LAN that uses the air as a medium of transmission to permit data transmission among fixed, or moving computers. The MAC layer of 802.11 employs the carrier sense multiple access/collision avoidance (CSMA/CA) to provide reliable frame transmission. This paper presents the impact of CSMA/CA on the performance of IEEE 802.11 networks. We measure the IEEE 802.11 wireless network throughput from a number of hosts to the access point (AP). The paper shows the factors that lead the difference between theoretical and measured throughput

History Based Contention Window Control in IEEE 802.11 MAC Protocol in Error Prone Channel

Journal of Computer Science, 2010

Problem statement: IEEE 802.11 Medium Access Control (MAC) protocol is one of the most implemented protocols in this network. The IEEE 802.11 controls the access to the share wireless channel within competing stations. The IEEE 802.11 DCF doubles the Contention Window (CW) size for decreasing the collision within contending stations and to improve the network performances but it is not good for error prone channel because the sudden CW rest to CW min may cause several collisions. Approach: The research to date has tended to focus on the current number of active stations that needs complex computations. A novel backoff algorithm is presented that optimizes the CW size with take into account the history of packet lost. Results: Finally, we compare the HBCWC with IEEE 802.11 DCF. The simulation results have shown 24.14, 56.71 and 25.33% improvement in Packet Delivery Ratio (PDR), average end to end delay and throughput compared to the IEEE 802.11 DCF. Conclusion: This study showed that monitoring the last three channel status achieve better delay and throughput that can be used for multimedia communications.

Enhancing IEEE 802.11 MAC in congested environments (original) (raw)

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