Yu-Liang Kuo

An admission control strategy for differentiated services in IEEE 802.11

With the provisioning of high-speed wireless LAN (WLAN) environments, traffic classes (e.g., VoIP or video-conference) with different QoS requirements will be introduced in future WLANs. The IEEE 802.11e draft is currently standardizing a distributed access approach, called the enhanced distributed coordination function (EDCF), to support service differentiation in the MAC layer. However, since each mobile station transmits data packets egotistically in a distributed environment, the QoS requirement of each traffic class may not be guaranteed. In this paper, we develop an admission control strategy to guarantee the QoS requirement of each traffic class. In order to provide a criterion for admission decision, we introduce an analytical model for EDCF to evaluate the expected bandwidth and the expected packet delay of each traffic class. The admission control strategy uses the performance measures derived from the analytical model to decide if a new traffic stream is permitted into the system. We validate the accuracy of the analytical model by using the ns-2 simulator. Some performance evaluations are also demonstrated to illustrate the effect of the proposed admission control strategy.

Bandwidth-Constrained Routing Problem in Wireless Ad Hoc Networks

The bandwidth-constrained routing problem (BCRP) asks for a route that has sufficient bandwidth for data transmission. When BCRP is defined for wired networks, it can be solved in polynomial time. On the other hand, when it is defined for wireless ad hoc networks, it is NP-complete if the underlying MAC protocol is TDMA-based or CDMA-over-TDMA-based. In this paper, we show that BCRP is still NP-complete, even if CSMA-based or contention-based CDMA MAC prot.ocols are used. Besides, we show that BCRP is polynomial-time solvable if the channel model is collision-free and the scheduling policy is FIFO. In wireless ad hoc networks, no MAC protocol was designed before, which would lead to a polynomial-time solution to BCRP. The results of this paper suggest a design for MAC protocols that can support QoS routing well.

Noncooperative admission control for differentiated services in IEEE 802.11 WLANs

The IEEE 802.11 working group has been developing a new distributed MAC, called the enhanced distributed function (EDCF), to support service differentiation in the IEEE 802.11 MAC protocol. Besides, highspeed WLAN environments are also expected to provide wireless Internet services in hot spots such as airports, parks, etc. Since there are usually multiple service providers competing for providing wireless network access in hot spots, mobile users are free to choose their own service providers. In this paper, we analyze the resource management problem in the competitive environment, in which the EDCF protocol is implemented in all access points (APs) and mobile stations. We formulate admission control as a game and prove the game owns a Nash equilibrium solution. Based on the game, a service provider not only fulfills, for the most part, the QoS satisfaction of ongoing flows but also increases its own revenue. We evaluate the performance by means of throughput, packet delay and bandwidth violation ratio.

Multirate Throughput Optimization With Fairness Constraints in Wireless Local Area Networks

In 802.11-based wireless local area networks (WLANs), it is difficult to simultaneously attain both high throughput and fairness for multirate traffic. There is a performance anomaly when there are stations whose data rates are much lower than the other stations, in which the aggregate throughput of the high-rate stations drastically degrades. The problem of maximizing the total throughput while maintaining time fairness among the competing stations was studied previously by the same authors. However, our previous solution sacrificed the throughput of low-rate stations. In this paper, we extend our previous work by solving the same optimization problem while maintaining both time fairness and throughput fairness. The optimization problem is formulated as a mixed-integer nonlinear programming problem. The two fairness constraints are maintained by means of changing the channel access probability and transmission time among the competing stations, which can be realized by adjusting their minimum contention window sizes and medium access control (MAC) frame sizes, respectively. A penalty function accompanied with a gradient-based approach is used to solve the problem, and its effectiveness is verified by computational experiments. The proposed solution is also compared with our previous solution in terms of convergence speed and total throughput.

Performance analysis of the enhanced distributed coordination function in the IEEE 802.11e

Recently, the IEEE 802.11 Task Group E is standardizing a distributed access approach, called the enhanced distributed coordination function (EDCF), to support service differentiation in WLANs. In EDCF, service differentiation is achieved by assigning different values of EDCF access parameters (e.g., the minimum contention window, the maximum contention window, and the arbitration interframe space) to different traffic classes. In order to satisfy specific QoS requirements for different traffic classes, a mathematical analysis turns to be helpful to analyze the system performance. In this paper, we provide an analytical model to study the expected bandwidth for each traffic class in EDCF. We validate the accuracy of the model by using the ns-2 simulator. Some performance evaluations are demonstrated in comparison with the IEEE 802.11 legacy MAC protocol. The model can be also used as guidelines for admission control or resource management schemes.

Bandwidth constrained routing problem in multi-hop wireless networks

The Bandwidth-Constrained Routing Problem (BCRP) asks for a route that has sufficient bandwidth for data transmission. When BCRP is defined for wired networks, it can be solved in polynomial time. On the other hand, when it is defined for multi-hop wireless networks, it is NP-complete if the underlying MAC protocol is TDMA-based or CDMA-over-TDMA-based. In this paper, we show that BCRP is still NP-complete, even if CSMA-based or contention-based CDMA MAC protocols are used. Besides, we show that BCRP is polynomial-time solvable if the underlying MAC protocol adopts CDMA channel model and FIFO scheduling policy. In multi-hop wireless networks, no MAC protocol was designed before which would lead to a polynomial-time solution to BCRP. The results of this paper suggest a design principle for MAC protocols that can support QoS routing well.

Multi-rate throughput optimization for wireless local area network anomaly problem

Due to varying wireless channel conditions, the IEEE 802.11 wireless local area network (WLAN) standard supports multiple modulation types to accommodate the tradeoff between data rate and bit error rate. In Heusse(2003), Rousseau, Berger-Sabbatel and Duda theoretically analyzed a performance anomaly when multi-rate stations with different modulation types exist in IEEE 802.11 WLANs. The performance anomaly is: the aggregate throughput of those stations transmitting at a higher data rate will dramatically degrade below the same level as that of those stations transmitting at a lower data rate. In this paper, we address the anomaly problem and formulate a nonlinear mixed integer programming problem to maximize the total aggregate throughput of all stations subject to that the channel occupancy times among the stations transmitting at different data rates are kept at a fairness ratio. With its aid, a single-hop WLAN can dynamically accommodate the resource access usage to maximize the system throughput in varying fading environments. We prove that the optimization problem is intractable and propose a heuristic solution based on a penalty function with gradient-based approach to solve it. We show the effectiveness of the approach via computational experiments and provide some useful guidelines to regulate the parameters needed for the approach.

QoS routing in mobile ad hoc networks based on the enhanced distributed coordination function

This paper proposes a QoS routing protocol (RP) for multimedia services in mobile ad hoc networks (MANETs). We adopt a new distributed MAC protocol, called enhanced distributed coordination function (EDCF), to support service differentiation. It requires a QoS RP to find routes with QoS guarantees. The proposed QoS RP discovers routes for source-destination transmission pairs with bandwidth and end-to-end delay guarantees. The procedures of neighborhood maintenance, QoS violation detection, and route maintenance are also presented in this paper. Furthermore, we introduce a new problem called hidden route problem, which arises because of existing routes that are hidden from the current route discovery procedure. This problem is also solved in the proposed QoS RP. We use the ns-2 simulation to evaluate the performance of the proposed QoS RP and compare it with other ad hoc QoS RPs. Simulation results show that the performance criteria, such as packet delivery ratio and average end-to-end delay, outperform other existing QoS RPs with the sacrifice of routing overhead under light load conditions.

Performance Evaluation for Next Generation Differentiated Services in Wireless Local Area Networks

With the provisioning of high-speed wireless LAN (WLAN) environments, multi- media services (e.g., VoIP and video-conference) with different QoS requirements will be available in next generation WLANs. Multimedia services could be categorized into multiple traffic classes and different priorities will be applied to access the wireless me- dium. The IEEE 802.11 working group has been developing a new generation distributed access protocol, called enhanced distributed channel access (EDCA), to support service differentiation in the 802.11 MAC layer. Service differentiation is achieved by assigning different values of EDCA access parameters (i.e., minimum contention window, maxi- mum contention window, and arbitration interframe space) to different traffic classes. To investigate the system performance under various network conditions, it is helpful to have a theoretical model for EDCA. In this paper, we introduce an analytical model for EDCA so that the saturation bandwidth can be estimated by closed-form formulas for each traffic class. We use ns-2 simulator to validate the analytical model. Some numeri- cal results are provided to evaluate the performance of EDCA. The numerical results demonstrate the corresponding effects for tuning different EDCA access parameters.