Adaptive medium access control for VoIP services in IEEE 802.11 WLANs

Abstract- Voice over Internet Protocol (VoIP) is an important service with strict Quality-of-Service (QoS) requirements in Wireless Local Area Networks (WLANs). The popular Distributed Coordination Function (DCF) of IEEE 802.11 Medium Access Control (MAC) protocol adopts a Binary Exponential Back-off (BEB) 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 adaptive MAC 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 is investigated and compared to the original DCF using the network simulator NS-2. The performance results reveal that the adaptive scheme is able to achieve the higher throughput and medium utilization as well as lower access delay and packet loss probability than the original DCF

A control theoretic approach to achieve proportional fairness in 802.11e EDCA WLANs

This paper considers proportional fairness amongst ACs in an EDCA WLAN for provision of distinct QoS requirements and priority parameters. A detailed theoretical analysis is provided to derive the optimal station attempt probability which leads to a proportional fair allocation of station throughputs. The desirable fairness can be achieved using a centralised adaptive control approach. This approach is based on multivariable statespace control theory and uses the Linear Quadratic Integral (LQI) controller to periodically update CWmin till the optimal fair point of operation. Performance evaluation demonstrates that the control approach has high accuracy performance and fast convergence speed for general network scenarios. To our knowledge this might be the first time that a closed-loop control system is designed for EDCA WLANs to achieve proportional fairness

A Dynamic Multimedia User-Weight Classification Scheme for IEEE_802.11 WLANs

In this paper we expose a dynamic traffic-classification scheme to support multimedia applications such as voice and broadband video transmissions over IEEE 802.11 Wireless Local Area Networks (WLANs). Obviously, over a Wi-Fi link and to better serve these applications - which normally have strict bounded transmission delay or minimum link rate requirement - a service differentiation technique can be applied to the media traffic transmitted by the same mobile node using the well-known 802.11e Enhanced Distributed Channel Access (EDCA) protocol. However, the given EDCA mode does not offer user differentiation, which can be viewed as a deficiency in multi-access wireless networks. Accordingly, we propose a new inter-node priority access scheme for IEEE 802.11e networks which is compatible with the EDCA scheme. The proposed scheme joins a dynamic user-weight to each mobile station depending on its outgoing data, and therefore deploys inter-node priority for the channel access to complement the existing EDCA inter-frame priority. This provides efficient quality of service control across multiple users within the same coverage area of an access point. We provide performance evaluations to compare the proposed access model with the basic EDCA 802.11 MAC protocol mode to elucidate the quality improvement achieved for multimedia communication over 802.11 WLANs.Comment: 15 pages, 8 figures, 3 tables, International Journal of Computer Networks & Communications (IJCNC

무선 랜 매체접근제어 (MAC) 효율화 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 이광복.In this dissertation, we develop medium access control (MAC) efficiency improvement schemes for IEEE 802.11 wireless local area networks. In part I of this dissertation, we develop a contention window (CW) control scheme for practical IEEE 802.11 wireless local area networks (WLANs) that have node heterogeneity in terms of the traffic load, transmission rate, and packet size. We introduce activity probability, i.e., the probability that a node contends for medium access opportunities at a given time. We then newly develop a performance analysis model that enables analytic estimation on the contention status including the collision probability, collision time, back-off time, and throughput with comprehensive consideration of node heterogeneity. Based on the newly developed model, we derive the theoretically ideal contention status, and develop a CW control scheme that achieves the ideal contention status in an average sense. We perform extensive NS-3 simulations and real testbed experiments for evaluation of both the proposed performance analysis model and CW control scheme. The results show that the proposed model provides accurate prediction on the contention status, and the proposed CW control scheme achieves considerable throughput improvement compared to the existing schemes which do not comprehensively consider node heterogeneity. In part II of this dissertation, we propose a sounding control scheme for IEEE 802.11ac multi-user multiple-input multiple-output (MU-MIMO). The proposed scheme comprehensively considers the long-term characteristics of a network environment including the downlink traffic loads and channel coherence times of wireless links, and jointly determines the sounding node set and sounding interval to maximize the long-term expected MU-MIMO throughput gain in consideration of sounding overhead. To this end, we analytically formulate an MU-MIMO throughput gain maximization problem considering the network environment and sounding overhead. We conduct MIMO channel measurement in practical WLAN environments, and evaluate the performance of the proposed scheme by employing the real channel data traces. Simulation results verify that the proposed scheme adaptively determines the sounding node set and sounding interval according to the network environment, and outperforms the existing scheme which considers the channel coherence times only. In part III of this dissertation, we develop an adaptive group ID (GID) control scheme to mitigate idle power consumption at nodes in IEEE 802.11ac wireless local area networks (WLANs) supporting multi-user multiple input multiple output (MU-MIMO). We analytically derive the expected idle power consumption at nodes sharing common GIDs, revealing that it has relations with their downlink (DL) traffic loads. Based on the analysis, we formulate an idle power consumption minimization problem, and develop an efficient algorithm to reduce the computational complexity. Simulation results reveal that idle power consumption becomes extremely severe when an access point (AP) has a large number of associated nodes. The proposed scheme assigns GIDs in consideration of DL traffic loads, thus considerably mitigating idle power consumption compared to random GID overloading.1 Introduction 1 1.1 Activity Probability Based Performance Analysis and Contention Control for IEEE 802.11 WLANs 1 1.2 Sounding Node Set and Sounding Interval Determination for IEEE 802.11ac MU-MIMO 3 1.3 Adaptive Group ID Control for Idle Power Consumption Mitigation in IEEE 802.11ac WLANs 5 2 Activity Probability Based Performance Analysis and Contention Controlfor IEEE 802.11 WLANs 7 2.1 DCF and Contention Window control 7 2.2 Activity Probability-Based Performance Analysis Model 8 2.2.1 System Description 8 2.2.2 Activity Probability-Based Throughput Estimation 10 2.2.3 Determination of Activity Probabilities 14 2.2.4 Considering Aggregate MAC Protocol Data Unit (A-MPDU) 16 2.3 Contention Window Control 18 2.3.1 Genie-Aided Ideal Contention Window Control 18 2.3.2 Proposed Contention Window Control 22 2.4 Performance Evaluation 29 2.4.1 Evaluation of Proposed Performance Analysis Model 29 2.4.2 Evaluation of Proposed Contention Window Control 34 2.4.3 Testbed Experiments 43 3 Sounding Node Set and Sounding Interval Determination for IEEE 802.11ac MU-MIMO 48 3.1 MU-MIMO in IEEE 802.11ac 48 3.2 System Description 50 3.3 MIMO Channel Characteristics in real IEEE 802.11ac WLANs 51 3.4 Proposed Sounding Control 54 3.4.1 Derivation of TG (Ts) and TO (Ts) 55 3.4.2 Efficient Determination of Sounding Node Set and Sounding Interval 57 3.5 Performance Evaluation 59 4 Adaptive Group ID Control for Idle Power Consumption Mitigation in IEEE 802.11ac WLANs 65 4.1 Group ID and Power Saving Mechanism in IEEE 802.11ac MU-MIMO 65 4.2 Proposed GID Control 67 4.2.1 System Description 67 4.2.2 Definition of GID Overloading Node Set and Idle Power Consumption Minimization Problem 68 4.2.3 Efficient GID Overloading Algorithm 71 4.3 Performance Evaluation 75 5 Conclusion 80 Abstract (In Korean) 88Docto

Class-Based Weighted Window for TCP Fairness in WLANs

The explosive growth of the Internet has extended to the wireless domain. The number of Internet users and mobile devices with wireless Internet access is continuously increasing. However, the network resource is essentially limited, and fair service is a key issue in bandwidth allocation. In this research, the focus is on the issue of fairness among wireless stations having different number and direction of flows for different required bandwidth to ensure that fair channel is fairly shared between wireless stations in the same class of bandwidth. It is shown that the current WLANs allocate bandwidth unfairly. It is also identified that the cause of this problem of unfairness is the TCP cumulative ACK mechanism combined with the packet dropping mechanism of AP queue and the irregular space for each wireless station in AP queue. The proposed method allocate converged bandwidth by introducing a Class-Based Weighted Window method which adjusts the TCP window size based on the current conditions of the network and according to the network’s requirements. This method works in wireless stations without requiring any modification in MAC. It can guarantee fair service in terms of throughput among wireless users whether they require the same or different bandwidth.Wireless LAN, TCP, Fairness