scholarly journals Hybrid Control of Contention Window and Frame Aggregation for Performance Enhancement in Multirate WLANs

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
Muhammad Adnan ◽  
Eun-Chan Park
Keyword(s):  
Performance Enhancement ◽  
Hybrid Control ◽  
Transmission Rate ◽  
Local Area ◽  
Contention Window ◽  
Channel Access ◽  
Distributed Coordination ◽  
Frame Aggregation ◽  
Transmission Rates ◽  
Coordination Function

The IEEE 802.11 standard has been evolved to support multiple transmission rates in wireless local area networks (WLANs) to cope with diverse channel conditions and to increase throughput. However, when stations with different transmission rates coexist, the basic channel access mechanism of WLAN, distributed coordination function (DCF), not only fails to assure airtime fairness among competing stations but also decreases overall network throughput, because DCF was designed to provide fair opportunity of channel access, regardless of transmission rate. As an effective solution to this problem, we propose a hybrid control mechanism that integrates contention window control and frame aggregation. The former adjusts the size of contention window and differentiates the channel access opportunity depending on the transmission rates of stations. The latter controls the number of packets in the aggregated frame to tightly assure per-station airtime fairness with the reduced channel access overheads. Moreover, we derive an analytical model to evaluate the performance of the proposed mechanism in terms of throughput and fairness. Along with the analysis results, the extensive simulation results confirm that the proposed mechanism significantly increases the overall throughput by about three times compared to the conventional DCF, while assuring airtime fairness strictly.

scholarly journals Improving Energy Efficiency in Idle Listening of IEEE 802.11 WLANs

2016 ◽  
Vol 2016 ◽  
pp. 1-15 ◽  
Author(s):  
Muhammad Adnan ◽  
Eun-Chan Park
Keyword(s):  
Energy Efficiency ◽  
Ieee 802.11 ◽  
Power Saving ◽  
Local Area ◽  
Contention Window ◽  
Channel Access ◽  
Analysis Model ◽  
Frame Aggregation ◽  
Improve Energy Efficiency ◽  
Idle Listening

This paper aims to improve energy efficiency of IEEE 802.11 wireless local area networks (WLANs) by effectively dealing with idle listening (IL), which is required for channel sensing and is unavoidable in a contention-based channel access mechanism. Firstly, we show that IL is a dominant source of energy drain in WLANs and it cannot be effectively alleviated by the power saving mechanism proposed in the IEEE 802.11 standard. To solve this problem, we propose an energy-efficient mechanism that combines three schemes in a systematic way: downclocking, frame aggregation, and contention window adjustment. The downclocking scheme lets a station remain in a semisleep state when overhearing frames destined to neighbor stations, whereby the station consumes the minimal energy without impairing channel access capability. As well as decreasing the channel access overhead, the frame aggregation scheme prolongs the period of semisleep time. Moreover, by controlling the size of contention window based on the number of stations, the proposed mechanism decreases unnecessary IL time due to collision and retransmission. By deriving an analysis model and performing extensive simulations, we confirm that the proposed mechanism significantly improves the energy efficiency and throughput, by up to 2.8 and 1.8 times, respectively, compared to the conventional power saving mechanisms.

Enhanced Distributed Coordination Function of MAC for VoIP Services Using IEEE802.11 Networks

2012 ◽  
Vol 433-440 ◽  
pp. 2304-2309
Author(s):  
B. Suvarna Vignan ◽  
B. Lalu Naick
Keyword(s):  
Mac Protocol ◽  
Local Area ◽  
Contention Window ◽  
Collision Probability ◽  
Network Simulator ◽  
Distributed Coordination ◽  
Medium Access ◽  
Packet Collision ◽  
Distributed Coordination Function ◽  
Coordination Function

Voice over Internet Protocol (VoIP) is an important service with strict Quality-of-Service (QoS) requirements with in wireless local area networks. The popular Distributed Coordination Function (DCF) of IEEE802.11 Medium Access Control (MAC) protocol adopts Multiplicative Increase and linear Decrease procedure to reduce the packet collision probability in WLANs. In DCF, the size of contention window is doubled upon a collision regardless of the network loads. This paper presents an enhanced DCF scheme to improve the QoS of VoIP in WLANs. This scheme applies a threshold of the collision rate to switch between two different functions for increasing the size of contention window based on the status of network loads. The performance of this scheme investigated and compared to the original DCF using the network simulator NS-2. Under the high traffic loads the packet loss probability decreases with the enhanced DCF compared to the original DCF. Some other parameters like throughput and access delay is decreased with the enhanced DCF.

A MAC Throughput in the IEEE 802.11ac over Error-Prone Channel

2014 ◽  
Vol 631-632 ◽  
pp. 801-805 ◽  
Author(s):  
Ha Cheol Lee
Keyword(s):  
Wireless Lan ◽  
Transmission Rate ◽  
Mac Protocol ◽  
Transmission Probability ◽  
Packet Error Rate ◽  
Distributed Coordination ◽  
Medium Access ◽  
Ieee 802.11Ac ◽  
Coordination Function ◽  
Control Layer

This paper analyzes a MAC (Medium Access Control) layer throughput over error-prone channel in the IEEE 802.11ac-based wireless LAN with DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme, using theoretical analysis method. The MAC saturation throughput is evaluated by using a PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables. When the PER is 10-2 and the number of aggregated MPDUs in each A-MPDU is 20, it is identified that the MAC layer throughput of IEEE 802.11ac can be maximally attained up to a 92.8% of physical transmission rate.

scholarly journals Channel Assignment Mechanism for Multiple APs Cochannel Deployment in High Density WLANs

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Jianjun Lei ◽  
Jianhua Jiang ◽  
Fengjun Shang
Keyword(s):  
Channel Assignment ◽  
Loss Rate ◽  
Time Slot ◽  
Local Area ◽  
Network Capacity ◽  
Vertex Coloring ◽  
Distributed Coordination ◽  
Slot Allocation ◽  
Distributed Coordination Function ◽  
Coordination Function

In Wireless Local Area Networks (WLANs), cochannel deployment can bound channel access delay and improve network capacity due to mitigating the collision and interference among different Access Points (APs). In this paper, we present a network model and an interference model for multiple APs cochannel deployment and propose a channel assignment mechanism which formulates the channel assignment problem into a time slot allocation problem. Meanwhile, we assign the channel based on the vertex coloring algorithm and make extra polls by utilizing the time slot reservation strategy to improve the channel assignment. Furthermore, we optimize the polling list of APs through classifying the clients to improve the channel utilization. The simulation results show that our proposed algorithm can improve the performance in terms of network throughput, transmission delay, and packet loss rate compared with the DCF (Distributed Coordination Function) and TMCA algorithms.

scholarly journals Asymptotic performance modelling of DCF protocol with prioritized channel access

2017 ◽  
Vol 68 (6) ◽  
pp. 482-486
Author(s):  
Woo-Yong Choi
Keyword(s):  
Ieee 802.11 ◽  
Performance Model ◽  
Analytical Performance ◽  
Channel Access ◽  
Distributed Coordination ◽  
Asymptotic Performance ◽  
Performance Modelling ◽  
Distributed Coordination Function ◽  
802.11 Wireless Lans ◽  
Coordination Function

Abstract Recently, the modification of the DCF (Distributed Coordination Function) protocol by the prioritized channel access was proposed to resolve the problem that the DCF performance worsens exponentially as more nodes exist in IEEE 802.11 wireless LANs. In this paper, an asymptotic analytical performance model is presented to analyze the MAC performance of the DCF protocol with the prioritized channel access.

scholarly journals Decoupling-Based Channel Access Mechanism for Improving Throughput and Fairness in Dense Multi-Rate WLANs

2019 ◽  
Vol 12 (1) ◽  
pp. 3 ◽  
Author(s):  
Jianjun Lei ◽  
Ying Wang ◽  
Hong Yun
Keyword(s):  
Data Transmission ◽  
Local Area ◽  
Access Time ◽  
Channel Access ◽  
Distributed Coordination ◽  
Medium Access ◽  
Performance Anomaly ◽  
Network Utilization ◽  
Free Data ◽  
And Performance

Legacy IEEE 802.11 Medium Access Control (MAC) adopts the Distributed Coordination Function (DCF) mechanism, which provides the same access opportunity for all contenders. However, in dense multi-rate Wireless Local Area Networks (WLANs), the pure distributed control mechanism will cause high collision rate and performance anomaly, which results in low network utilization and wasting valuable channel resources. In this paper, we present a decoupling MAC mechanism (DMAC) based on the idea of contention/reservation to reduce collision and realize collision free data transmission. In proposed mechanism, the channel access time is partitioned into channel contention process and data transmission process. The proposed algorithm makes full use of the distributed random channel access mechanism and performs a centralized collision-free data transmission. Wherein, we also design an adaptive algorithm to adjust the length of the contention period to improve the channel utilization. Furthermore, we further propose two airtime fairness algorithms Improve-DMAC1 (I-DMAC1) and Improve-DMAC2 (I-DMAC2) for delay sensitive network and high throughput network scenarios, respectively, to solve the performance anomaly in multi-rate WLANs, based on DMAC. We verify the effectiveness of these decoupling algorithms through extensive simulations. Moreover, the simulation results show that the proposed algorithms achieve better performance than the 802.11 standard and other protocols.

A Markov Model for the IEEE 802.11 DCF under Limit Load

2011 ◽  
Vol 48-49 ◽  
pp. 29-33
Author(s):  
Sheng Guo Gao
Keyword(s):  
Markov Model ◽  
Load Condition ◽  
Packet Delay ◽  
Limit Load ◽  
Local Area ◽  
Distributed Coordination ◽  
Medium Access ◽  
802.11 Dcf ◽  
Significant Research ◽  
Coordination Function

Wireless Local Area Networks (WLANs) have been attracted significant research during the last few years. The primary medium access control (MAC) technique of 802.11 is called distributed coordination function (DCF). DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper proposes a new Markov model to analyze the CSMA/CA protocol and average packet delay. This model covers the finite load condition and saturation condition. The close agreement between the theoretical results and simulation results using NS-2 under reaffirms the accuracy of the analytical model.

scholarly journals Latency and Jitter Analysis for IEEE 802.11e Wireless LANs

2013 ◽  
Vol 2013 ◽  
pp. 1-9
Author(s):  
Sungkwan Youm ◽  
Eui-Jik Kim
Keyword(s):  
Local Area ◽  
Ieee 802.11E ◽  
Distributed Coordination ◽  
Mac Layer ◽  
Medium Access ◽  
Distributed Coordination Function ◽  
Packet Latency ◽  
Coordination Function ◽  
The Voice

This paper presents a numerical analysis of latency and jitter for IEEE 802.11e wireless local area networks (WLANs) in a saturation condition, by using a Markov model. We use this model to explicate how the enhanced distributed coordination function (EDCF) differentiates classes of service and to characterize the probability distribution of the medium access control (MAC) layer packet latency and jitter, on which the quality of the voice over Internet protocol (VoIP) calls is dependent. From the proposed analytic model, we can estimate the available number of nodes determining the system performance, in order to satisfy user demands on the latency and jitter.

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