On Optimizing Backoff Counter Reservation and Classifying Stations for the IEEE 802.11 Distributed Wireless LANs (original) (raw)
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EBA: An Enhancement of the IEEE 802.11 DCF via Distributed Reservation
IEEE Transactions on Mobile Computing, 2005
The IEEE 802.11 standard for Wireless Local Area Networks (WLANs) employs a Medium Access Control (MAC), called Distributed Coordination Function (DCF), which is based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The collision avoidance mechanism utilizes the random backoff prior to each frame transmission attempt. The random nature of the backoff reduces the collision probability, but cannot completely eliminate collisions. It is known that the throughput performance of the 802.11 WLAN is significantly compromised as the number of stations increases. In this paper, we propose a novel distributed reservationbased MAC protocol, called Early Backoff Announcement (EBA), which is backward compatible with the legacy DCF. Under EBA, a station announces its future backoff information in terms of the number of backoff slots via the MAC header of its frame being transmitted. All the stations receiving the information avoid collisions by excluding the same backoff duration when selecting their future backoff value. Through extensive simulations, EBA is found to achieve a significant increase in the throughput performance as well as a higher degree of fairness compared to the 802.11 DCF.
A simple and effective backoff scheme for the IEEE 802.11 MAC protocol
2005
Wireless Local Area Networks (WLANs) based on the IEEE 802.11 have been widely implemented in most commercial products available in the market. This paper proposes a simple and effective contention window-resetting scheme, named Double Increment Double Decrement (DIDD), to improve the performance of the contention based IEEE 802.11 Distributed Coordination Function (DCF). An alternative mathematical analysis for the proposed scheme is developed based on elementary conditional probability arguments rather than bi-dimensional Markov chains. Performance results are presented to identify the improvement of DIDD in terms of throughput and packet drop comparing to the Binary Exponential Backoff (BEB) utilized in the legacy IEEE 802.11 DCF.
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.
The IEEE 802.11 Distributed Coordination Function in Small
International Journal of wireless …, 2003
The IEEE 802.11 standards for wireless local area networks define how the stations of an ad-hoc wireless network coordinate in order to share the medium efficiently. This work investigates the performance of such a network by considering the two different access mechanisms proposed in these standards. The IEEE 802.11 access mechanisms are based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol using a binary slotted exponential backoff mechanism. The basic CSMA/CA mechanism uses an acknowledgment message at the end of each transmitted packet, whereas the request to send/clear to send (RTS/CTS) CSMA/CA mechanism also uses a RTS/CTS message exchange before transmitting a packet. In this work, we analyze these two access mechanisms in terms of throughput and delay. Extensive numerical results are presented to highlight the characteristics of each access mechanism and to define the dependence of each mechanism on the backoff procedure parameters.
IEEE 802.11 distributed coordination function (DCF): analysis and enhancement
2002
Being a part of IEEE project 802, the 802.11 medium access control (MAC) is used to support asynchronous and time bounded delivery of radio data packets. It is proposed that a distributed coordination function (DCF), which uses carrier sense multiple access with collision avoidance (CSMA/CA) and binary slotted exponential backoff, be the basis of the IEEE 802.11 WLAN MAC protocols. This paper proposes a throughput enhancement mechanism for DCF by adjusting the contention window (CW) resetting scheme. Moreover, an analytical model based on Markov chain is introduced to compute the enhanced throughput of 802.11 DCF. The accuracy of the model and the enhancement of the proposed scheme are verified by elaborate simulations
Wireless Networks, 2011
In conventional IEEE 802.11 medium access control protocol, the distributed coordination function is designed for the wireless stations (WSs) to perform channel contention within the wireless local area networks (WLANs). Packet collision is considered one of the major issues within this type of contention-based scheme, which can severely degrade network performance for the WLANs. Research work has been conducted to modify the random backoff mechanism in order to alleviate the packet collision problem while the WSs are contending for channel access. However, most of the existing work can only provide limited throughput enhancement under specific number of WSs within the network. In this paper, an adaptive reservation-assisted collision resolution (ARCR) protocol is proposed to improve packet collision resulting from the random access schemes. With its adaptable reservation period, the contention-based channel access can be adaptively transformed into a reservation-based system if there are pending packets required to be transmitted between the WSs and the access point. Analytical model is derived for the proposed ARCR scheme in order to evaluate and validate its throughput performance. It can be observed from both analytical and simulation results that the proposed protocol outperforms existing schemes with enhanced channel utilization and network throughput.
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.
Hashing Based Distributed Backoff (HBDB) Mechanism for IEEE 802.11 Wireless Networks
J. Internet Serv. Inf. Secur., 2015
Binary Exponential Backoff (BEB) is the De-facto mechanism for contention control in IEEE 802.11 Wireless LAN. The exponential growth of Contention Window (CW) in all BackOff (BO) stages and randomness in BO selection causes unnecessary waiting time, high collision rate and unfairness in accessing the channel among the nodes. To overcome these anomalies, this paper proposes Hashing Based Distributed Backoff (HBDB) algorithm. It allows a node to dynamically adopt different CW values based on the collision probability. To choose unique collision probability value, linear probing is used. The simulation results show the effectiveness of the proposed algorithm in linear and random topologies under low, medium and high traffic scenarios.
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.
Performance Analysis of Backoff Algorithm in IEEE 802.11 Networks
ijser.org
The primary Medium Access Control (MAC) technique of IEEE 802.11 is called Distributed Coordination Function (DCF). This protocol adopts a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with a binary exponential backoff (BEB) algorithm to access the channel. The protocol performance mainly depends on backoff procedure which reduces the probability of collision. With BEB, waiting time of a node gets doubled after every unsuccessful transmission. This introduces fast-growing retransmission delays for the backlog traffic. In a mobile ad hoc network (MANET), it would be worthwhile to slow down the growth-rate of waiting time because the nodes communicating in a MANET might move out of collision range while waiting for retransmission. Moreover, DCF reduces the Contention Window to the initial value after each successful transmission which essentially assumes that each successful transmission is an indication that the system is under low traffic loading. In this paper analyzed the problem with existing Backoff Algorithm.