Enhanced Distributed Channel Access Research Articles

Performance Evaluation of 802.11ax OFDMA Through Theoretical Analysis and Simulations

With the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) in 802.11ax, the role of the Access Point (AP) in Wi-Fi networks changes significantly, thanks to the opportunity of implementing more complex scheduling logic to handle Downlink (DL) traffic flows and simultaneously act as coordinator of Multi User (MU) Uplink (UL) transmissions. In this context, it becomes necessary to develop reliable network analysis and simulation tools that allow for an in-depth investigation of the trade-offs involved in the usage of OFDMA, especially considering that the standard leaves much of the actual scheduling algorithmic details to vendor-specific implementation. In this work we present a series of results highlighting how several network settings have an impact on throughput and Head-of-Line Delay, in a network that employs multiple 802.11ax features such as OFDMA and the MU Enhanced Distributed Channel Access (EDCA) Parameter Set, while also containing legacy devices. The results are obtained via both the newly re-designed ns-3 wifi module and an original analytical framework, based on the well-established Bianchi 802.11 model.

Modulo N Backoff Scheme for Effective QoS Differentiation and Increased Bandwidth Utilization in IEEE 802.11 Networks

The paper presents a new modulo N channel access scheme for wireless local area networks (WLANs). The novel solution derives from the distributed coordination function (DCF) of the IEEE 802.11 standard, further elaborated as enhanced distribution channel access (EDCA) by the 802.11e draft specification. The main innovation concerns improvement of the binary exponential backoff scheme used for collision avoidance in 802.11 networks. The most appealing feature of the new modulo N backoff scheme is that it outperforms the original 802.11 solution in terms of channel utilization ratio under any traffic conditions. Furthermore, the modulo N proposal can be naturally augmented with QoS differentiation mechanisms like 802.11e extensions. The prioritized modulo N scheme achieves better throughput-delay characteristics for multimedia traffic when compared with the original 802.11e proposal. At the same time, the new solution retains backward compatibility and includes all features which have made IEEE 802.11 networks extremely popular nowadays.

Performance Analysis of IEEE 802.11p Protocol in IoV under Error-Prone Channel Conditions

The complexity of the channel condition in the Internet of vehicles (IoV) may increase the bit error rate (BER) of the intelligent vehicle terminals, resulting in data transmission failures or errors. Therefore, it is necessary to improve the performance of communication protocols under error-prone channel conditions. This article investigates the influence of the access categories’ (ACs) performance with channel errors by using four A C s to cause service differentiation based on the enhanced distributed channel access (EDCA) mechanism of the IEEE 802.11p. To address the error-prone characteristics of the channel and unsaturated traffic conditions, a three-dimensional Markov model is developed first, followed by an analysis of the characteristics and mutual transition probabilities of the seven classes of states in the model, and then, the steady-state equations of the system are developed to derive the steady-state distribution to study system performance. The model considers the backoff phase, the freezing of the backoff counter, the retransmission limit, the probability of collisions occurring, the size of the maximum and minimum contention window, and the number of interframe intervals. These parameters are chosen to meet the requirements for the protocol to operate, while also preventing overestimation of throughput and avoiding having packets being served all the time. We derive expressions for the throughput and delay of A C s under the conditions of error channels and unsaturated traffic. The impact of channel errors on the throughput and delay of A C s is evaluated by numerical simulation. Numerical results show that too many stations in the system will increase the average access delay and decrease throughput. The increase in BER will seriously decrease the performance of high-priority A C s . The throughput of the A C s is also modeled to vary with frame length and BER, and the variation curves of the optimal frame lengths for A C 3 and A C 2 were obtained.

A Semi-Markov Process Model for Performance Evaluation of DSRC Vehicular Safety Communication

In this study, a new semi-Markov process (SMP)-based model is devised to evaluate the IEEE 802.11p enhanced distributed channel access (EDCA) broadcast performance for vehicular safety communication. Differing from the existing SMP analytical models, the proposed model takes the virtual collision among various prioritized access categories (ACs) inside each vehicle into consideration. Moreover, in contrast to the Markov chain-based models, our model is simpler but with approximate accuracy. Concretely, we first capture the behavior of each AC’s backoff entity using SMP. Then, the parameters of interest in the vehicular ad hoc network (VANET) such as packet transmission probability, conditional collision probability, and saturation throughput are derived. Finally, via MATLAB simulations, we demonstrate that the newly developed model achieves comparable accuracy in calculating these output parameters while its complexity and computation time is around one-tenth of that of the Markov chain-based models. Therefore, the proposed model is more suitable for real-time performance analysis of IEEE 802.11p EDCA safety communication in a freeway scenario.

Effect of service differentiation on QoS in IEEE 802.11e enhanced distributed channel access: a simulation approach

The enhanced distributed channel access (EDCA) protocol is a supplement to IEEE 802.11 medium access control (MAC), ratified by IEEE 802.11e task group to support quality of service (QoS) requirements of both data and real-time applications. Previous research show that it supports priority scheme for multimedia traffic but strict QoS is not guaranteed. This can be attributed to inappropriate tuning of the medium access parameters. Thus, an in-depth analysis of the EDCA protocol and ways of tuning medium access parameters to improve QoS requirements for multimedia traffic is presented in this work. An EDCA model was developed and simulated using MATLAB to assess the effect of differentiating contention window (CW) and arbitration inter-frame space (AIFS) of different traffic on QoS parameters. The optimal performance, delay, and maximum sustainable throughput for each traffic type were computed under saturation load. Insight shows that traffic with higher priority values acquired most of the available channels and starved traffic with lower priority values. The AIFS has more influence on the QoS of EDCA protocol. It was also observed that small CW values generate higher packet drops and collision rate probability. Thus, EDCA protocol provides mechanism for service differentiation which strongly depends on channel access parameters: CW sizes and AIFS.

Throughput-Based Mapping Algorithm for Video Streaming over IEEE 802.11e WLAN

IEEE 802.11e utilizes the Enhanced Distributed Channel Access (EDCA) protocol to provide quality of service (QoS) support over WLANs. However, under EDCA, all video data are allocated to the same access category (AC) queue, irrespective of their coding importance. Consequently, the quality of the transmitted video may be severely degraded under heavy traffic load conditions. The literature contains several queue mapping mechanisms based on the settings of the AC queues, such as contention window size, for improving the video transmission quality over IEEE 802.11e WLANs. However, these mechanisms fail to consider the effect of the dequeuing time on the video delivery performance. Accordingly, the present study proposes a new queue mapping algorithm, designated as the throughput-based mapping algorithm (TMA), for improving the video transmission quality and reducing the video delay by dynamically allocating the video data packets to different AC queues based on their length and throughput such that the probability of the dequeuing time being reduced is increased. In implementing the proposed approach, the throughputs of the AC queues are analyzed using two Markov chain models. The simulation results show that TMA outperforms previously proposed static and dynamic queue mapping schemes in terms of a reduced AC queue length, an improved PSNR (peak signal-to-noise ratio), and a shorter transmission delay.

Reliable and QoS aware routing metrics for wireless Neighborhood Area Networking in smart grids

Smart Grid networks use data collected from sensors in evaluating the current system state to make optimal resource distribution decisions and facilitate two-way energy exchange. Efficient and timely communication between smart grid assets using high efficiency and reliable Neighborhood Area Network (NAN) for the last-mile can play a significantly important role. For this requirement, wireless mesh networking can be used to offer scalable, flexible and resilient wireless connectivity. Despite significant advantages and tremendous applications, smart grid NANs are vulnerable to security and reliability issues during electric power delivery. After being compromised by an adversary, cascading-failure-induced disasters may disrupt the power grid from a remote location; customer’s private information may become vulnerable if accessed illegally; the adversary may also compromise selected nodes (change the normal behavior of a node to malicious behavior) and thus fail the critical mission of the Supervisory Control and Data Acquisition (SCADA) system. Moreover, the Enhanced Distributed Channel Access (EDCA) mechanism of IEEE 802.11e wireless technology can be leveraged for service differentiation based routing among flows of differing priorities. Routing decisions in mesh networks are based on routing metrics which have been the focus of research for the past decade. However, NANs offer a different implementation scenario from traditional mesh infrastructures and also necessitate the need for differentiated quality of service. In this paper, we discuss how state-of-the-art routing metrics have limitations for the NAN scenario, especially for EDCA based differentiated access. Moreover, we propose and design a secure and EDCA based contention-aware routing approach - iRoute, for 802.11e based wireless NANs which enables the selection of reliable routes that also satisfy QoS requirements (low contention, high throughput routes). Simulation-based performance evaluation of the proposed approach shows that it can provide significantly better performance in terms of throughput and delay for NAN communication.

Service Differentiation in IEEE 802.11ah WLAN under Restricted Access Window based MAC protocol

The restricted access window (RAW) based channel access scheme proposed for IEEE 802.11ah wireless LAN (WLAN) divides the stations (STAs) in the network into groups and allocates RAW slots for each group of STAs. In this way, the STAs belonging to each group can attempt to access the medium during their designated RAW slot by invoking the enhanced distributed channel access (EDCA) protocol. This paper describes an analytical model to evaluate the saturation throughput of IEEE 802.11ah WLAN under the RAW based scheme, when STAs carry traffic of distinct access categories (ACs) and use the EDCA protocol for medium sharing. However, when groups are formed by randomly selecting the STAs, i.e., if random grouping (RG) scheme is employed, each group will contain STAs carrying traffic of distinct ACs. This will lead to starvation and degraded throughput performance for the low priority class STAs, since they have to contend with high priority class STAs within the same group during the RAW slot assigned. To resolve this issue, we propose an algorithm to realize priority class based grouping (PCG), in which the STAs belonging to the same ACs are grouped together. We also describe an analytical model to evaluate the saturation throughput of the network under the proposed PCG scheme. We establish that saturation throughput of the network and the relative service differentiation ratio of the lower priority class STAs can be significantly improved under the proposed PCG scheme compared to the conventional RG scheme.

Starvation avoidance-based dynamic multichannel access for low priority traffics in 802.11ac communication systems

Using optimally wide channels in 802.11ac networks has been the topic of various research work. Nevertheless, the efficiency of both Static and Dynamic Multichannel Access methods (SMA and DMA) is a challenging issue, since they employ the Enhanced Distributed Channel Access (EDCA) to provide the Quality of Service (QoS). Indeed, EDCA enables QoS through service differentiation between priority (Voice and Video) and non-priority (Besteffort and Background) traffics. Consequently, the concept of priority may severely starve non-priority traffics from channel access, and lead to an unfair bandwidth allocation. In this paper, we highlight the starvation issue of non-priority traffics in 802.11ac networks. Thereby, we propose a Starvation avoidance DMA (SDMA) method by means of 80 and 160 MHz channel bonding. The individual throughput is measured for comparing SDMA and DMA methods. The obtained results show a significant improvement in throughput of non-priority traffics, while maintaining the throughput level of priority traffics.

Highest Cost First-Based QoS Mapping Scheme for Fiber Wireless Architecture

The combination of a high-speed wireless network with passive optical network technologies has led to the evolution of a modern integrated fiber wireless (FiWi) access network. Compared to broadband wireless networks, the FiWi network offers higher bandwidth with improved reliability and reduced maintenance costs due to the passive nature of passive optical network (PON). Since the quality of service (QoS) is a baseline to deploy high-speed FiWi broadband access networks, therefore, it is essential to analyze and reduce the typical problems (e.g., bandwidth and delay) in the high-speed next-generation networks (NGANs). This study investigates the performance of a fiber wireless architecture where a 10-Gigabit-capable passive optical network (XGPON) and fifth generation of wireless local area network (WLAN) (i.e., IEEE 802.11ac) are integrated. Both technologies take benefits from each other and have pros and cons concerning the QoS demands of subscribers. The proposed work offers a very flexible QoS scheme for the different types of services of 5G WLAN and XGPON with the help of the highest cost first (HCF) algorithm, which leads to reduced upstream delays for delay-sensitive applications. The simulation results show that the HCF algorithm boosts the performance of the dynamic bandwidth assignment (DBA) scheme and results in up to 96.1%, 90.8%, and 55.5% reduced upstream (US) delays for video: VI(T2), background: BK(T3), and best effort: BE(T4) traffic in enhanced-distributed-channel-access (EDCA) mode. Compared to earlier work, the HCF and immediate allocation with the colorless grant (IACG) DBA combination results in the reduction of up to 54.8% and 53.4% mean US delays. This happens because of 50% to 65% better bandwidth assignment by the IACG DBA process due to efficient mapping by the HCF algorithm.

Performance analysis of randomized arbitration interframe space tuning algorithm for enhanced distributed channel access in IEEE 802.11p based vehicular network

AbstractThe Internet of Vehicle (IoV) aims to provide efficient vehicular communication by enhancing connectivity and user safety. IEEE 802.11p, a medium access control protocol, plays a vital role in the IoV protocol stack, which uses the enhanced distributed channel access (EDCA) method for channel contention. To deal with safety and nonsafety vehicular applications, EDCA adopts four access categories (AC), and each AC manages the channel access based on the priority of packets along with the contention window size and arbitration interframe spacing number (AIFSN). However, these contention parameters are fixed for each AC, and it does not account the real‐time network traffic. Hence, the fine‐tuning of AIFSN values and maintaining strict priority are challenging tasks for the highly dynamic vehicular network. To address these issues, this article proposes a novel probabilistic approach, namely, the randomized AIFSN tuning (RAT) algorithm for EDCA. It updates AIFSN value for every retransmission based on the vehicle density and contention intensity by preserving the strict priority behavior of the AC queues. A three‐dimensional Markov model is developed to analyze the proposed algorithm in terms of collision probability and throughput. The proposed RAT algorithm is simulated using the NS3 network simulator along with simulations for urban mobility (SUMO) for the real‐time traffic, and results are compared with other related algorithms in terms of packet loss, goodput, packet delivery ratio, and delay of each AC queue. These results reveal that the proposed RAT algorithm outperforms related algorithms under varying vehicle density.

Perbandingan Metode Antrian Paket HTB dan EDCA Untuk Layanan Multimedia Pada WLAN IEEE 802.11n

The development of wireless technology continues to improve quality and increase the speed of data transfer into one important factor that is considered. Each year, wireless technology users continue to increase and communication service needs also experience tremendous traffic surge. The impact of high traffic intensity of data sent can lead to increased data queue and transient transmission network. The problem of network crunch resulting from a high amount of queue data may affect service performance. To get the solution, in this study was tested using Hierarchy Token Bucket (HTB) and Enhanced Distributed Channel Access (EDCA) on 802.11n wireless network. Queuing tests are performed on four types of traffic: voice, video, best effort (BE) and background (BG). Assessment of QoS of HTB and EDCA is based on throughput and delay parameters. The results obtained from throughput testing of the mean value of each data packet, the results show that the EDCA method is better than HTB method. The best throughput results are given on Best Effort(BE) traffic. While on the delay test by using HTB and EDCA method, obtained the average of EDCA delay smaller in multimedia data packet for Video and Voice. In conclusion, the results show that the EDCA method is better than HTB.

Adaptive Networking Control Method for 5G VANET Nodes

With the development of Internet and Internet of Things, 5G has opened a new era of interconnection, and the technology of Vehicle Ad-hoc Network (VANET) has attracted great attention from all walks of life. However, the MAC protocol proposed at present has many drawbacks in supporting real-time services. To solve this problem, Hybrid MAC protocol, ET-MAC, came up with this paper by combining the Enhanced Distributed Channel Access (EDCA) and Time Division Multiple Access (TDMA) defined in IEEE 802.11p technology. Then, a performance comparison with the MAC protocol of the TDMA is performed in a simulation experiment to evaluate the function of the protocol. Finally, the simulation experiment proves that ET-MAC protocol is obviously superior to the MAC protocol based on TDMA is based on transmission delay, network throughput and packet loss rate, and more suitable for the current situation of high-density vehicle network in urban environment.

Improving Fairness in IEEE 802.11 EDCA Ad Hoc Networks Based on Fuzzy Logic

Wireless ad hoc network is a self-configurable and dynamically distributed network in which stations can move freely. In the ad hoc network, some flows have difficulty in accessing the channel due to contention at both the medium-access control (MAC) and link layers. The IEEE 802.11 protocol is currently the de facto standard for wireless networks. It uses enhanced distributed channel access (EDCA) method to access the transmission environment of each type of data flow. The size of the contention window (CW) in EDCA is related to the probability of accessing the channel of each flow. In our approach, useful information is obtained from the physical, MAC, and link layers. A fuzzy logic system is then used to adjust the size of CW to rely on such value, thereby improving the fairness index of data flows (voice, video, best effort) in IEEE 802.11 EDCA. The simulation results show that the proposed method can improve the throughput and fairness index of data flows.

A Priority-Based Cross-Layer Design for Future VANETs Through Full-Duplex Technology

Among all requirements for vehicle-to-everything (V2X) communications, successful delivery of packets with small delay is of the highest significance. Especially, the delivery of a message before a potential accident (i.e. emergency message) should be guaranteed. In this work, we propose a novel cross-layer design to enhance the delivery of emergency messages so that accidents can be further avoided. Particularly, in the PHY layer, imperfect full-duplex (FD) simultaneous transmitting and sensing is analysed and dynamic thresholds for determining the channel status before and during transmissions are mathematically formulated. Then a novel FD MAC protocol, named priority-based multiple access (PBMA), based on prioritised messaging between different vehicles is proposed. Average collision probability, collision duration, waiting time as well as successful delivery rate of the system are formulated too. The delivery performance of emergency messages is also mathematically derived. In addition, comparisons have been made among three different mechanisms. Benchmark is the DSRC standard which uses half-duplex (HD) technology with enhanced distributed channel access (EDCA) protocol. We also compare our proposed protocol with FD EDCA. Simulations have verified the accuracy of our analysis. They have also illustrated the delivery of emergency messages has been enhanced by deploying our proposed design.

Performance evaluation of the IEEE 802.11n random topology WLAN with QoS application

The IEEE 802.11n supports high data rate transmissions due its physical layer Multiple Input ‎Multiple Output (MIMO) advanced antenna system and MAC layer enhancement features (frame ‎aggregation and block acknowledgement). As a result this standard is very suitable for multimedia ‎services through its Enhanced Distributed Channel Access (EDCA). This paper focuses on ‎evaluating the Quality of Service (QoS) application on the performance of the IEEE 802.11n ‎random topology WLAN. Three different number of nodes (3, 9 and 18) random topology with one ‎access point are modeled and simulated by using the Riverbed OPNET 17.5 Modular to ‎investigate the Wireless Local Area Network (WLAN) performance for different spatial streams. ‎The result clarified the impact of QoS application and showed that its effect is best at the 18 node ‎number topology. For a 4x4 MIMO, when QoS is applied and with respect to the no QoS ‎application case, simulation results show a maximum improvement of 86.4%, 33.9%, 52.2% and ‎‎68.9% for throughput, delay, data drop and retransmission attempts, respectively. ‎

Combining contention‐based access and dynamic service period allocation for performance improvement in IEEE 802.11ad mmWave WLAN

SummaryIn IEEE 802.11ad millimeter wave wireless LANs, the directional multi‐giga bit stations (DMGSTAs) use contention‐based access periods (CBAPs) and scheduled service periods (SPs) for medium access. The STAs carrying non‐QoS traffic use CBAPs, while SPs are allocated for STAs carrying high QoS applications. During CBAP, the STAs use enhanced distributed channel access (EDCA) scheme. Further, 802.11ad advocates dynamic allocation of SP for guaranteed data transmission based on a centralized polling scheme. The standard advocates that the coverage area around the access point can be divided into several sectors, and the total CBAP shall be divided among the sectors on a time sharing basis. The STAs residing within a sector simultaneously contend during the CBAP fraction of that sector. However, such STAs have to defer their transmission attempts and wait for the designated CBAP fraction of the succeeding beacon interval (BI), if the residual time in the current CBAP fraction is not sufficient for a frame transmission. This leads to very high delay and reduced throughput. The objective of this paper is to propose an efficient hybrid medium access control scheme, where the deferred STAs during CBAP are scheduled again by utilizing the unallocated slots in the SP of the same BI. We describe an analytical model for the throughput and the average frame delay, under the proposed scheme, and compare the performance against the legacy scheme, where the STAs use CBAP alone for channel access. The analytical and simulation results establish that the proposed scheme significantly improves the throughput and reduces the average frame delay.

An Adaptive EDCA Selfishness-Aware Scheme for Dense WLANs in 5G Networks

To keep pace with the current rapid evolution of mobile data requirements, IEEE 802.11 was evolved to provide more desirable performance to fulfill the needs of fifth-generation (5G) and Internet of Things (IoT) networks. It provides two different access contention-based schemes; Distributed Coordination Function (DCF) which not differentiates between different services, and Enhanced Distributed Channel Access (EDCA) which provides differentiation between various services through four priority Access Categories (ACs). The dilemma of the conventional IEEE 802.11 networks is the static assignation of parameters in DCF and EDCA regardless of the number of associated stations and no matter what kind of service is required by each station (i.e., the activity of ACs). Consequently, this led to a significant degradation in the performance of the network, especially in the case of ultra-dense load network. Therefore, in this paper, we introduce a novel algorithm for EDCA considering a dynamic assignation of Arbitration Inter-Frame Space Number (AIFSN) and guidance Contention Window (CW) depending on the number of associated stations and ACs activeness status. Based on the analytical models of EDCA, a game-theoretic method is proposed to make each associated station adapts its transmission probability within the guidance CW. The purpose of guidance CW is a pre-stage to detect the selfish stations which pick up a very low CW to maximize its throughput regardless of the overall network throughput. Simulation results show that the proposed game-based algorithm can obtain higher performance than the standard 802.11 networks in terms of normalized throughput, data dropped during retransmissions limit threshold exceeding, and mean average delay for sensitive delay applications.

RTS Threshold Variation Study on Contention-based IEEE 802.11n EDCA for Real-time Services

As a “wide-deployed” wireless local area networks (WLANs) standard, the IEEE 802.11n was designed to support a high data transmission rate (up to 600 Mbps) and maintain a compatibility with the previous versions. Due to a substantial demand of real-time data services, such as VoIP and video conference, an enhanced quality of service (QoS) mechanism become crucially important. The IEEE 802.11n standard inherits the enhanced distributed channel access (EDCA) mechanism from the IEEE 802.11e, as the MAC layer improvement. It classifies the traffic into four different classes of data, called access categories (ACs). However, EDCA still suffers from a data packet collision, caused by hidden nodes problems. The packet loss ratio and end-to-end delay increase along with the escalation of real-time traffic. To address the issue, we conduct a simulation in Riverbed Modeler 17.5 environment with a 128, 256, 512, and 1,024 Bytes of request to send (RTS) threshold variation value to overcome a collision caused by hidden nodes problem. The result shows that the 512 Bytes of RTS threshold value gives the best QoS output among them all.

Resource Allocation and QoS Guarantees for Real World IP Traffic in Integrated XG-PON and IEEE802.11e EDCA Networks

Globally, there is a significant rise in the number of connected devices. Every device has an access to wide variety of telecom services among which voice, video and best effort (BE) contribute significantly. There is a noticeable growing trend towards upstream BE traffic besides real time e-services that demand high quality of service (QoS). Converged next-generation fiber-wireless (FiWi) access networks composed of next-generation passive optical network (XG-PON) and 802.11n based wireless local area network (WLAN) has emerged as a suitable choice to provide high quality and affordable e-services to plenty of subscribers as they possess both high bandwidth and flexibility. In this paper, we study the performance of the integrated network architecture which combines XG-PON and enhanced distributed channel access (EDCA) under real time bursty traffic derived from the current global IP traffic distribution. The joint tuning of various crucial parameters of both XG-PON and EDCA with incorporation of an efficient deficit dynamic bandwidth algorithm (DBA) at optical line terminal (OLT) is done by exhaustive simulations in network simulator-3 (NS-3). Through intensive simulations and tuning, we are able to achieve a end-to-end delay performance of <; 150 ms for voice, <; 500 ms for video and a few seconds for BE upto full capacity. Also, a packet loss ratio (PLR) of <; 3% and <; 6% is achieved for voice and BE respectively upto full load. For voice PLR is <; 1% upto 60% total offered load. Further, it is observed that the fine tuning of key parameters has also resulted in increased bandwidth for dominant BE services. Therefore, this optimized network architecture is 20% more fair to BE services as compared to the conventional integrated FiWi architectures.