Enhanced Distributed Coordination Access Research Articles

An Intelligent Method for Bandwidth Utilization in IEEE 802.11e Wireless LAN

IEEE 802.11 Wireless LAN, popularly known as WiFi, has become the admired source of internet connectivity for most of the offices as well as organizations. Due to the rapid growth of multimedia data and VoIP and also to provide better quality of service (QoS), bandwidth and management of bandwidth have become important factors in 802.11 wireless LAN. In 802.11 wireless LAN, Enhanced Distributed Coordination Access (EDCA) mechanism provides QoS with service differentiation by setting different priority to different traffic types. Some of the available methods provide priority based on user category also. In this paper we have proposed an intelligent bandwidth management technique based on the user priority value, traffic priority value and the bandwidth requirement value. By combining these three values, a new metric called request weight value is calculated. Based on this request weight value, dynamically bandwidth is allocated to the users. From the simulation results, we have seen that the proposed method performs well in proper utilization of bandwidth among the available users.

Saturation Throughput Analysis of IEEE 802.11e EDCA Through Analytical Model

The IEEE 802.11e EDCA is designed to provide quality of support for real time applications with stringent latency and throughput requirements. Theoretical frameworks for analysis of throughput performance of wireless LAN employing exponential back-off exist extensively. Several models rely on simplification assumptions that preclude their direct applicability to the enhanced distributed coordination access (EDCA) which uses heterogeneous protocol parameters, while other models are exceedingly complex to analyze. In this paper, a tractable analytical model is proposed for saturation throughput of the IEEE 802.11e EDCA. The prioritization through channel access parameters including the AIFS and contention window is catered for within a three dimensional Markov chain. The integration of back-off counter freezing and retry limit enhance the models precision. Its validation is done by simulation on NS-2. Practical applicability of the model is established based on accuracy and computational efficiency. The model is utilized for throughput analysis of the EDCA under saturated traffic loads.

Introducing an Adaptive Method to Tune Initial Backoff Window (-ATM) in IEEE 802.11 Wireless Networks

IEEE802.11 access protocol uses CSMA/CA in its Medium Access control layer as the main access function, which carries several deficiencies. In these networks, as the number of active stations increases, delay and throughput degrade severely. As far as throughput and service delay are vital elements in Quality of Service (QoS) determination, such degradation could lead to intolerable situations and reduce the efficiency of WLANs. Networks (WLANs). Studies proved this problem arises due to constant initial backoff windows size ( ), which is an important parameter in determination of network behavior. In this paper, we introduce a new method to tune this parameter adaptively according to changes in channel load. In this method, we do tune this parameter after every transmission using a feedback from transmission channel. Later it will be proven that applying this method in MAC layer enhances network stability; delay trend in all traffic classes exhibits a considerable reduction when compared with simple Enhanced Distributed Coordination Access (EDCA) scenarios. Also throughput exhibits a salient improvement in level. In other word, QoS improves. Especially, with the aid of this method, delay variations in all decrease considerably and more smoothen delay trends are achieved.

A random adaptive method to adjust MAC parameters in IEEE802.11e WLAN

The IEEE 802.11e standard is proposed to provide QoS support in WLAN by providing prioritized differentiation of traffic. Since all the stations in the same priority access category (AC) have the same set of parameters, when the number of stations increases, the probability of different stations in the same AC choosing the same values will increase, which will result in collisions. Random adaptive MAC (medium access control) parameters scheme (RAMPS) is proposed, which uses random adaptive MAC differentiation parameters instead of the static ones used in the 802.11e standard. The performance of RAMPS is compared with that of enhanced distributed coordination access (EDCA) using NS2. The results show that RAMPS can reduce collision rate of the AC and improve the throughput by using adaptive random contention window size and inter-frame spacing values. RAMPS ensures that at any given time, several flows of the same priority have different MAC parameter values. By using the random offset for the inter-frame spacing value and the backoff time, RAMPS can provide intra-AC differentiation. The simulation results show that RAMPS outperforms EDCA in terms of both throughput and end-to-end delay irrespective of the traffic load.

Extended EDCA for delay guarantees in wireless local area networks

Despite their very broad diffusion, IEEE 802.11 Wireless Local Area Networks (WLANs) are not able to provide service differentiation and to support real-time multimedia applications, due to their channel access methods. To overcome these limitations, the 802.11e working group has proposed the Enhanced Distributed Coordination Access (EDCA) scheme, which achieves service differentiation on a statistical basis by properly mapping user Quality of Service (QoS) requirements to channel contention parameters. Such a scheme will be included in the emerging 802.11n standard and in the revision of the 802.11 standard. However, it has been widely demonstrated that, especially at high network loads, EDCA does not provide an effective usage of the channel capacity. In particular, it is unable to provide a bounded delay service to all kinds of multimedia flow because flows with lower channel access priorities are starved to advantage only those with the highest priority. To fix this undesired behavior and improve wireless LAN performance, this paper proposes a new Extended EDCA (E 2DCA) scheme, that is compliant with 802.11e specifications. By exploiting a closed-loop control algorithm, E 2DCA performs a distributed dynamic bandwidth allocation, providing guarantees on average/absolute delays to real-time media flows, regardless of their priorities. Moreover, an innovative Call Admission Control (CAC) procedure has been developed. Using the ns-2 simulator, the effectiveness of the algorithm has been investigated in realistic network scenarios, involving a mix of audio, video, and FTP flows, at several network loads and with random losses. Results have shown that the proposed scheme is able to provide a bounded delay service to multimedia flows in a wide range of network loads and frame loss ratios.

Energy efficient feedback-based scheduler for delay guarantees in IEEE 802.11e networks

Energy saving algorithms for 802.11 Wireless LAN (WLAN) are basically based on keeping in a low-power state the Wireless Network Interface Card (WNIC) whenever a wireless station does not have frames to be transmitted/received. This can severely affect the QoS of the service provided to higher layers due to the transient time needed to switch from a low-power to a high-power state. Recently, the 802.11e Working Group (WG) has proposed a set of innovative functionalities in order to provide QoS in WLANs. In particular, the core of the 802.11e proposal is the Hybrid Coordination Function (HCF), which has a HCF Controlled Channel Access (HCCA) and an Enhanced Distributed Coordination Access (EDCA). In this paper, an innovative HCCA-based algorithm, which will be referred to as Power Save Feedback Based Dynamic Scheduler (PS FBDS), has been proposed to provide bounded delays while ensuring energy saving. Using ns-2 simulations, it has been shown that PS FBDS is able to provide a good trade-off between QoS and power saving at both low and high network loads.

Evaluation of Contention-Based EDCA for IEEE 802.11e Wireless LAN

The legacy IEEE 801.11 doesn’t support QoS streams with priorities. It since causes some QoS demanding applications such as VoIP, Video streaming to be limited in its usefulness. Enhancements have been made to the MAC layer by the new 802.11e standard to support prioritized and parameterized QoS. The work of this paper is to simulate the new scheme and modify the existing OPNET WLAN MAC model to satisfy the 802.1le standard. The modification includes adding four access category queues, AP beacon with EDCA parameters, AC queue switcher and an internal collision handler to evaluate the contention-based channel access mechanism, called enhanced distributed coordination access (EDCA) in the current 802.1le. The performance of those new schemes has been compared with DCF of the 802.11 standard via simulation results. It clearly indicates the IEEE 802.11 EDCA function can effectively provide QoS differentiation.