Enhanced Distributed Coordination Function Research Articles

Link Reliable On-Demand Multipath Distance Vector Routing for Reliable Video Streaming in MANET

Background: Due to the generic feature of AOMDV, it is widely used in Long-Term Evolution (LTE) networks such as the Internet which requires new challenges to deploy conversational real-time applications like VoIP (Voice over IP) and video conferencing. Objective: In AOMDV, the multiple routes between any source and destination pair are selected based on minimal hop count which does not ensure reliable video content delivery as the communicating nodes along the paths are prone to link failures and route breaks. Methods: To overcome such problems, the Link Reliable On-demand Multipath Distance Vector (LROMDV) is proposed by modifying the Ad hoc On-demand Multipath Distance Vector (AOMDV). Results: The LROMDV uses an enhanced Cumulative Expected Transmission Count (enh-CETX) for selecting multiple routes between any source and destination pair to avoid link failures and route breaks in Long-Term Evolution (LTE) networks. Conclusion: The performance of LROMDV on H.264/MPEG-4 AVC video streaming under both Distributed Coordination Function (DCF) and Enhanced Distributed Coordination Function (EDCF) using NS2.34 and Enhanced EvalVid framework is evaluated and the simulation result shows the effectiveness of LROMDV.

TSCH Multiple Slotframe Scheduling for Ensuring Timeliness in TS-SWIPT-Enabled IoT Networks

This paper presents a time-slotted channel hopping (TSCH) multiple slotframe scheduling (TMSS) protocol to ensure the timeliness of energy harvesting and data transmission for sensor devices with different transmission periods in Internet of Things (IoT) networks enabled with time-switching simultaneous wireless information and power transfer (TS-SWIPT). The TMSS uses a modified three-step 6P transaction to allocate power and data cells within the slotframe. The sensor device sets the slotframe length equal to the transmission period and estimates the number of power and data cells for allocation in the configured slotframe and requests cell allocation to the hybrid access point (HAP). Upon request from a sensor device, the HAP executes a cell-overlapping prevention (COP) algorithm to resolve the cell-overlapping problem and responds to the sensor device with a candidate cell list. Upon receiving the response from HAP, the sensor device determines its power and data cells by referring to the cell list. We conducted experimental simulations and compared the TMSS performance to that of the legacy TSCH medium access control (MAC) with a single slotframe and the harvest-then-transmit-based modified enhanced distributed coordination function (EDCF) MAC protocol (HE-MAC). The results showed that TMSS outperforms legacy TSCH MAC and HE-MAC in terms of delay, effective throughput and energy utilization.

A New Buffer and Energy Based Scheduling Scheme for Supporting QoS in MANETs

Today, the original IEEE 802.11 standard has several problems in providing Quality of Service in MANETs. A single FIFO queue is used in best effort manner and it does not support QoS. The upcoming IEEE 802.11e was drafted to overcome these drawbacks. In this paper we describe a new multiple queuing system with an adaptive scheduling taking into account the states of buffers and energy consumption in a mobile ad hoc network. The proposed scheduling scheme uses dynamic weights for each queue. We study the performance of this scheme and compare it with the original IEEE 802.11b and the upcoming IEEE 802.11e. We show through simulations that the proposedbuffer and energy based scheduling scheme improves overall end-to-end throughput, and gives better results than the original 802.11b and the Enhanced Distributed Coordination Function (EDCF), in terms of delay and total received and lost packets, as well as support service differentiation over multi-hop ad hoc networks.

H.264/MPEG-4 AVC Video Streaming Evaluation of LR-EE-AOMDV Protocol in MANET

Deployment of conversational real-time applications like VoIP (Voice over IP) and videoconferencing require new challenges in Long-Term Evolution (LTE) networks such as Internet. Quality of video delivered over the Internet has been determined in terms of Quality-of-Service (QoS) and Quality-of-Experience (QoE). QoS includes packet delivery ratio, average end-to-end delay, throughput, routing overhead, etc. QoE is a qualitative measure of videos transmitted over Internet. In this paper, we evaluate the performance of Link Reliable Energy Efficient Ad hoc On-demand Multipath Distance Vector (LR-EE-AOMDV) routing on H.264/MPEG-4 AVC video streaming under both Distributed Coordination Function (DCF) and Enhanced Distributed Coordination Function (EDCF) using NS2.34 and Enhanced EvalVid framework. Simulation results show that the LR-EE-AOMDV performs better than AOMDV and OMMRE-AOMDV.

Improved QoS in WLAN Using IEEE 802.11e

In this paper, a detailed overview of the new attributes of a long term effective standard IEEE 802.11e to aid Quality of Service (QoS) with Wireless Local area Networks (WLANs) is presented. We address Medium Access Control (MAC) enhancements revealed in the present 802.11e draft standards by centering the problems with the legacy 802.11 standard. Cutting edge mechanisms for QoS assistance, specifically Enhanced Distributed Coordination Function (EDCF) and Hybrid Coordination Function (HCF), defined within the 802.11e drafts are usually evaluated. The effectiveness of new schemes is layed out via simulation outcomes.

Latency and Jitter Analysis for IEEE 802.11e Wireless LANs

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.

The Performance Evaluation of IEEE 802.11e for QoS Support in Wireless LANs

During the past few years the widespread use of the wireless local area networks (WLANs) communication technique is one of the most popular technologies in data telecommunications and networking. With the increasing variety of multimedia applications, it is needed to develop a mechanism for the quality of service (QoS) to support different types of traffic. The IEEE 802.11 protocol has achieved worldwide acceptance with WLANs with minimum management and maintenance costs. However, IEEE 802.11 can only provide a best effort service and does not support the QoS. In this paper, we pay attention to the enhanced distributed coordination function (EDCF) of WLANs. First, we modify the Ziouva and Antonakopoulous's (ZA's) model and then extend the model to support EDCF. We study the behavior of the station within a Markov chain model, and present a more accurate analysis of the EDCF and also study the saturation throughput when the maximum load that the system can support is reached. The numerical results show that the modified model has a better performance than the ZA's model under an ideal channel scenario.

Video streaming transmission: performance modelling over wireless local area networks under saturation condition

Transmitting delay-sensitive video streaming over IEEE 802.11e wireless local area networks (WLANs) is becoming increasingly popular. However, the transmission of real-time video streaming is very challenging because of the time-varying wireless channels and video content characteristics. The authors propose an accurate model to assess the perceived quality of video streaming over WLANs with enhanced distributed coordination function (EDCF) mechanism. The analytical model considers not only the packet loss caused by wireless interference and channel fading, but also the effects of loss from channel access competition. Based on the Markov chain, the authors then present the discrete probability distribution of medium access control (MAC) layer packet service time by using the signal transfer function of the generalised state transition diagram. Moreover, the coding relation of lost video frames is also explored in the performance analysis of the proposed model. Simulations based on Network Simulator 2 (NS-2) are conducted to verify the performance of the analytical model. The results show that the proposed model provides superior accuracy for the perceived quality of MPEG-4 video streaming over IEEE 802.11e EDCF-based WLANs.

The performances study of IEEE 802.11e to support QoS in channel error environment

ABSTRACTOne of the most important functions in IEEE 802.11e is enhanced distributed coordination function (EDCF). EDCF is an enhanced version of IEEE 802.11 distributed coordination function (DCF) which provides a priority scheme by differentiating the inter‐frame space and the initial window size. We proposed a modified Markov chain model to study the EDCF priority scheme. We have theoretically analyzed the saturation throughput and delay by using the modified Markov chain model in non‐ideal channel scenario. We also have compared it with the Markov chain model that exists under ideal channel scenario. Simulations are also conducted to validate analytical results. Our study shows that the modified model under ideal channel scenario is better than that in channel error scenario. Copyright © 2011 John Wiley & Sons, Ltd.

MIMO-Based Collision Avoidance in IEEE 802.11e Networks

In response to the growing market demand for high-performance wireless local area networks (WLANs) with quality-of-service (QoS) support, the IEEE 802.11 standard adopts the 802.11e as the medium access protocol and 802.11n-based products, which utilize multiple-input-multiple-output (MIMO) transmission systems. The medium access collision avoidance of IEEE 802.11e, even with IEEE 802.11n at the physical layer, still utilizes the enhanced distributed coordination function (EDCF) mechanism. It is known that collisions cause significant performance degradation in IEEE 802.11e EDCF-based systems. In this paper, we utilize the multiple spatial channels of MIMO technology to propose collision-mitigation enhancements to the IEEE 802.11e EDCF. The key idea of the scheme, which is called MIMO-based EDCF (M-EDCF), is the sharing of the spatial channels during the medium contention period, i.e., instead of accessing the medium using all the spatial channels, the accessing nodes use a subset of the available spatial channels. As the number of concurrent spatial channels used is less than or equal to the spatial degree of freedom, receivers can decode the transmitted signals of different medium access contenders and then coordinate their responses to avoid potential collisions. The spatial channel sharing also enables transmitters to sense the medium and terminate if they detect other ongoing medium access attempts. Simulation results show that the M-EDCF scheme substantially reduces medium access collisions. Based on the preliminary results, an adaptive optimized length of the collision-avoidance window is derived. The performance of the M-EDCF scheme based on optimized online spatial channel sharing demonstrates that the scheme further reduces medium access collisions and boosts medium utilization.

A Novel Prioritization Scheme to Improve QoS in IEEE 802.11e Networks

IEEE 802.11 WLAN utilizes a distributed function at its MAC layer, namely, DCF to access the wireless medium. Due to its distributed nature, DCF is able to guarantee working stability in a wireless medium while maintaining the assembling and maintenance cost in a low level. However, DCF is inefficient in dealing with real-time traffics due to its incapability on providing QoS. IEEE 802.11e was introduced as a supplementary standard to cope with this problem. This standard introduces an Enhanced Distributed Coordination Function (EDCF) that works based on diff-Serve model and can serve multiple classes of traffics (by using different prioritizations schemes). With the emergence of new time-sensitive applications, EDCF has proved to be yet inefficient in dealing with these kinds of traffics because it could not provide network with well-differentiated QoS. In this study, we propose a novel prioritization scheme to improve QoS level in IEEE 802.11e network. In this scheme, we replace Uniform PDF with Gamma PDF, which has salient differentiating properties. We investigate the suitability and superiority of this scheme on furnishing network with well-differentiated QoS using probabilistic analysis. We strengthen our claims by extensive simulation runs.

A supporting service differentiation multichannel MAC protocol for wireless ad hoc networks

Providing service differentiation by using distributed control at the MAC layer is an effective mechanism for supporting Quality of Service (QoS) in wireless ad hoc networks. However, existing QoS-capable MAC protocols have been designed in single channel environments. Multichannel technology has been demonstrated to significantly increase network capacity, reduce chances of contention and collision of data transmission. So, QoS guarantee is easier to achieve by using multichannel technology. In this paper, we devise a supporting service differentiation multichannel MAC protocol. Two interfaces are used, an interface staying at common control channel is responsible for assigning data channel and another can dynamically switch channel for data transmission. In the common control channel, different priority flows adopt different backoff parameters to access channel to acquire data channel assignment chance. Simulation results show the protocol outperforms Enhanced Distributed Coordination Function (EDCF) of IEEE 802.11e.

A new call admission control method for providing desired throughput and delay performance in IEEE802.11e wireless LANs

The draft IEEE 802.11e standard aims at providing quality of service (QoS) support in 802.11 wireless local area networks (WLANs). Enhanced distributed coordination function (EDCF), being the fundamental medium access control mechanism in IEEE 802.11e, can only provide service differentiation but offers no QoS guarantees. While service differentiation does not perform well under high traffic load conditions, call admission control (CAC) becomes necessary in order to provide and support the QoS of existing calls. In this paper, we first analyze the saturation throughput and mean access delay performance of differentiated service provided by EDCF. Specifically, we investigate the impact of transmission opportunity (TXOP) and wireless channel errors on the performance of the EDCF. Based on the results from this analysis, we propose a new CAC algorithm that provides the desired throughput and access delay performance. Simulated performance results demonstrate the effectiveness of the proposed CAC algorithm

Proportional Service Differentiation in Wireless LANs Using Spacing-based Channel Occupancy Regulation

In this paper, we propose Spacing-based Channel Occupancy Regulation (SCORE) MAC protocol for wireless LANs that provides proportional service differentiation in terms of normalized throughput. As shown by our system model and simulation study, SCORE provides consistent, scalable and adjustable proportional differentiation for any network size, any service class distribution, any node data rate and any packet size. Compared to state-of-the-art prioritized service differentiation schemes like Enhanced Distributed Coordination Function (EDCF), SCORE can quantitatively control the channel sharing between different service classes. Moreover, SCORE obtains significant performance improvements in terms of higher network throughput, higher transmission efficiency, lower medium access delay and lower delay jitter.

Dynamic polling mechanism for enhancing voice transmission in IEEE 802.11e wireless LANs

In this paper, we propose a Dynamic Polling Mechanism (DPM) to enhance the system capacity in supported voice stations over IEEE 802.11e based WLANs, which employs Hybrid Co-ordination Function (HCF) to detect the silence and talkspurt alternation of voice stations and dynamically adds and removes the voice station IDs in the polling list. Apart from the existing dynamic polling mechanisms, the DPM detects the silence-to-talkspurt alternation by the reception of the first packet of each talkspurt, which contends to access channel with high Enhanced Distributed Co-ordination Function (EDCF) priority in Contention Period (CP). An analytical model is presented to investigate the access delay of the voice packets transmitted in CP and the system capacity in supported voice stations. The numerical and simulation results show that the performance of the DPM significantly outperforms that of conventional static polling mechanism. In addition, through exploring the impact of the DPM on the throughput of data stations, we conclude that the performance of the DPM can be optimised by configuring the first packet of each talkspurt with the highest EDCF priority.

A delay based backoff scheme for WLAN with QoS guarantee and its performance

Based on the Distributed Coordination Function (DCF) and the Enhanced DCF (EDCF) mechanisms in IEEE 802.11 and 802.11e, a novel backoff scheme for Wireless Local Area Network (WLAN) is proposed. The scheme is to solve the problem of the packet loss and the decrease of performance due to the increasing Contention Window (CW) when there are continuous collisions. In the proposed scheme, the CW of the packet will change dynamically with different delay for the different traffics. Mathematic formulas are presented to indicate the relationship between the CW and the delay character. The performance of the new scheme is also discussed with simulation results. The results show that it helps WLAN system handle multimedia simultaneously.

Sliding contention window (SCW): towards backoff range-based service differentiation over IEEE 802.11 wireless lan networks

A number of works have tried to adjust the contention window in order to provide differentiated quality of service in IEEE 802.11-based wireless networks. By giving different service classes different CWs, the distribution of backoff intervals (chosen randomly, on the interval [O, CW]) will reflect the desired service classes. However, these protocols cannot deliver firm service guarantees while maintaining high network utilization, particularly under congested network conditions. In this article we propose a new MAC protocol featuring a sliding CW (SCW) for each network flow. The SCW dynamically adjusts to changing network conditions, but remains within a per-class predefined range in order to maintain a separation between different service classes. Each flow's SCW reacts based on the degree to which class-defined QoS metrics are satisfied. Simulation results show that compared to the enhanced distributed coordination function (EDCF) scheme of 802.11e, SCW consistently excels, in terms of network utilization, strict service separation, and service-level fairness.

Performance analysis for IEEE 802.11e EDCF service differentiation

Having been originally developed as an extension of the wired local area networks, IEEE 802.11 lacks support for quality-of-service (QoS) and differential services. Since its introduction, various extensions and modifications have been studied to address this current need and the IEEE 802.11 Task Group E is responsible for developing a QoS-aware MAC protocol that considers several service differentiation mechanisms. However, the performance of service differentiation has only been evaluated by simulation. The analytical model that calculates the differential service performance corresponding to the contention parameter configuration has not been found yet. In this paper, we first briefly explain the enhanced distributed coordination function (EDCF) access method of IEEE 802.11e. We then introduce an analytical model, which can be used to calculate the traffic priority, throughput, and delay corresponding to the configuration of multiple DCF contention parameters under the saturation condition. A detailed simulation is provided to validate the proposed model. Finally, using the analytical model, we analyze the effect on service differentiation for each contention parameter. The contention parameters can be configured appropriately at each station to achieve specific needs of service differentiation for applications.

Enhancement of QoS Differentiation Over IEEE 802.11 WLAN

IQD, a distributed coordination function (DCF) with integrated quality of service (QoS) differentiation, is proposed in this letter to enhance QoS over IEEE 802.11 WLAN. DCF does not support any QoS differentiation. Enhanced DCF (EDCF) only supports delay differentiation. IQD can achieve both delay and packet-loss-rate differentiation by differentiating the initial window size and the retry limit. Simulation results show that IQD performs better than DCF and EDCF in enhancing QoS, and the proposed analytical model is valid.

Saturation Throughput Analysis of IEEE 802.11e Enhanced Distributed Coordination Function

The IEEE 802.11 Task Group E will soon approve the 802.11e standard for medium access control (MAC) layer quality-of-service (QoS) enhancements to the 802.11 protocol, and it is widely believed that these enhancements will allow 802.11 technology to form the foundation of high-bandwidth vertically integrated networks. At the heart of 802.11e is a modified contention-based access mechanism, named the enhanced distributed coordination function (EDCF). In this paper, we propose and validate an analytical model for the saturation throughput of EDCF. Key to the accuracy of our model is a treatment of the postcollision period, which has been ignored by all previous 802.11 models. With results from the ns-2 simulator, we show that our model can accurately predict throughput over a wide range of scenarios, and thereby demonstrate its usefulness as a predictive tool for use in QoS provision. With context provided by our analytical model, we discuss the primary throughput differentiation mechanisms of EDCF.