Distributed Coordination Function Protocol Research Articles

Fair and efficient resource allocation in IEEE 802.11ah WLAN with heterogeneous data rates

For dense wireless LANs (WLANs), IEEE 802.11ah has specified restricted access window (RAW) as the channel access scheme. Here the competing stations (STAs) are divided into groups and STAs belonging to each group attempt to access the channel during their designated RAW slot by invoking the distributed coordination function (DCF) protocol. This paper describes an analytical model to evaluate the throughput performance of IEEE 802.11ah WLAN, when STAs use distinct data rates and the RAW mechanism is implemented for medium sharing. When STAs are grouped randomly (i.e., without considering their data rates), a group will contain STAs operating at distinct data rates. Since all these STAs simultaneously contend for channel access based on DCF protocol, the throughput of high data rate STAs are down-equalized to that of lower data rate STAs; thus the aggregate network throughput is degraded significantly. To resolve the resulting performance anomaly problem, we consider data rate based grouping where STAs operating at the same data rate are grouped together. We describe an algorithm for implementing data rate based grouping at the access point (AP). Further, we describe an analytical procedure to find the network throughput under data rate based grouping. Through numerical and experimental investigations, we establish that data rate based grouping can significantly improve the aggregate network throughput performance, as compared to the conventional random grouping strategy. Further, we use Jain’s fairness index (JFI) to establish that data rate based grouping can also provide fair resource allocation among the STAs operating at distinct data rates, by ensuring that all the competing STAs in the network achieve throughput proportional to their data rates.

Adaptive Centralized Random Access for Collision Free Wireless Local Area Networks

Packet collisions caused by the standard Distributed Coordination Function (DCF) protocol in wireless local area networks (WLANs) have been a challenging problem leading to congestion and reduced throughput. To solve this problem, we propose a novel backoff state generation algorithm, called adaptive virtual backoff algorithm (AVBA), operating in an access point. The virtual contention window size in the algorithm is automatically adjusted based on the number of synchronized active nodes in a cell. Backoff counts generated by AVBA operating in the access point are sent by the access point to each active node in the cell to try to synchronize transmissions and minimize packet collisions. The evaluation results show that the AVBA improves the throughput performance compared to the existing collision resolution techniques, such as the deterministic backoff and centralized random backoff (CRB), when the number of active nodes is large. Moreover, the results show that it maintains a high level of fairness in terms of channel access opportunities between nodes using AVBA and nodes using the DCF protocol when they coexist in a mixed wireless network scenario.

Hybrid ARQ-Based Fairness Enhancement in Uplink WLAN

Per-station fairness is one of the important and challenging issues in wireless local area network based on a contention-based medium access control protocol. The unfairness problem among stations having different channel qualities is caused by the imbalance in access probability and outage probability among them. In this paper, we investigate the per-station fairness by resolving the imbalance in the above two factors through the enhanced distributed coordination function (DCF) adopting hybrid automatic repeat request (HARQ), named the DCF-H. We suggest adopting the HARQ with Chase combining as a solution for the imbalance in the outage probability on top of the loss differentiation mechanism which resolves the imbalance in the access probability. We also analyze the performance of the DCF-H by proposing a new Markov chain model and derive a closed-form expression of system throughput, delay, and outage probability. We compare the performance of the DCF-H with that of the conventional DCF protocols and find out that the DCF-H not only guarantees the near-perfect per-station fairness but also improves the whole system performance, such as throughput, delay, and outage probability.

Asymptotic performance modelling of DCF protocol with prioritized channel access

Abstract Recently, the modification of the DCF (Distributed Coordination Function) protocol by the prioritized channel access was proposed to resolve the problem that the DCF performance worsens exponentially as more nodes exist in IEEE 802.11 wireless LANs. In this paper, an asymptotic analytical performance model is presented to analyze the MAC performance of the DCF protocol with the prioritized channel access.

Enhancing MAC performance of DCF protocol for IEEE 802.11 wireless LANs

Abstract The DCF (Distributed Coordination Function) is the basic MAC (Medium Access Control) protocol of IEEE 802.11 wireless LANs and compatible with various IEEE 802.11 PHY extensions. The performance of the DCF degrades exponentially as the number of nodes participating in the DCF transmission procedure increases. To deal with this problem, we propose a simple, however efficient modification of the DCF by which the performance of the DCF is greatly enhanced.

Exploiting anomalous slots for multiple channel access in IEEE 802.11 networks

The execution process of the IEEE 802.11 distributed coordination function (DCF) exhibits non-accessible time slots preceded by transmissions (successful and collision). Those slots are “anomalous” due to the inaccessibility of channel for transmission. For improving network performance, a station attempts to successfully transmit more frames in less time, which, in turn, increases the number of anomalous slots. Consequently, increased number of anomalous slots results in reduced performance improvement. In this paper, we exploit the anomalous slots for improving the performance of the DCF protocol. The anomalous slots allow the stations to know the channel status much ahead of the slot's actual time of occurrence. By leveraging the channel status, each station schedules anomalous transmissions during anomalous slots. We integrate the concept of anomalous transmission with the DCF protocol for designing a modified medium access control protocol, namely ANT, for wireless local area networks (WLANs). Following Felemban and Ekici's modeling approach, we analyze the theoretical performance of the ANT protocol in WLANs. Analytical results show that the ANT protocol decreases the average medium access delay by 80% and 65%, respectively, under the basic and the RTS/CTS access modes compared with that in the DCF protocol, while it increases the network throughput as well.

Packet-Centric Trade-off and Unfair Success Region in IEEE 802.11 WLANs

In this paper, we present a packet-centric analytical study of carrier sense multiple access with collision avoidance (CSMA/CA)-based medium access in wireless local area networks, specifically using the IEEE 802.11 distributed coordination function (DCF). The packet-centric viewpoint of analysis adds a new dimension of insights over those available in the existing body of knowledge in this domain. We propose an absorbing Markov chain-based model for analyzing the behavior of head-of-line frames of each station in such networks. We generalize the long-term and short-term unfairness induced by the randomness of the DCF protocol and depict the actual unfair success region to be avoided in fair resource allocation schemes. One of the primary objectives of any CSMA/CA-based medium access control (MAC) protocol is to increase the frame delivery probability, while reducing the average delay of delivery. With such considerations, we show a tradeoff relationship between the delivery probability and access delay with respect to the maximum retransmission limit in a packet-centric approach. We numerically evaluate the packet-centric behavior of the DCF protocol for single-hop single access point networks involving both the saturated and unsaturated stations, imperfect wireless channel, and varying payload sizes.

IEEE 802.11ac/ad 무선 LAN의 적응형 MCS 구현 연구

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.

Using Markov Chain Model to Evaluate the Performance of EDCA Protocol Under Saturation and Non-Saturation Conditions

Nowadays, there is a significant increment of internet usage in public locations such as airports, restaurants and bus stations. Ease of extension and low costs make wireless networks more suitable than wire networks in these public locations. Providing quality of service (QOS) is the main challenge that wireless networks face. IEEE802.11e is developed to support QOS for real time applications. It uses the Enhanced Distributed Channel Access (EDCA) protocol rather than the Distributed Coordination Function (DCF). EDCA protocol uses four queues in its MAC layer. These queues have different priorities and serve different types of data (video, voice, best effort and background). On the other hand, DCF protocol has only one queue for all types of data. In this paper, a new Markov chain model is proposed for the EDCA protocol, which works in saturation and non-saturation conditions. The Markov chain model covers the difference between the station and the access point (AP). Also, it presents how the AP is considered as the bottleneck of the network, and it hinders the wireless network to serve more voice users with supporting QOS. The throughput of stations and AP are calculated for different data types. In addition to that, an adjusting contention window mechanism is proposed to enhance the capacity of wireless networks to support more voice users.

Evaluating The Performance for DCF Protocol and EDCA Protocol

Nowadays supporting quality of service (QOS) for real time application is the main challenge of the wireless area network. 802.11standards use distributed Coordination Function (DCF) protocol and Enhanced Distributed Channel Access (EDCA) protocol in the MAC layer. DCF protocol has only one queue for different data types, it deals with data depending on the arriving time. There is no priority to serve real time applications faster. However EDCA protocol has four queues and each queue works with specific data type. Voice, video, best effort and background are the different queues in the EDCA protocol. Different parameters and priorities are defined for each queue. The voice queue reserves the highest priority and serves its data first. In this paper QOS parameters are measured for both DCF and EDCA protocol by using OPNET simulation. The QOS parameters must reach the requirements to support QOS. The results show how QOS parameters do not reach the requirements when using DCF protocol. The values of the end to end delay and the packet loss percentage are 0.514second, 19.04% respectively. But, when using EDCA protocol the end to end delay becomes 0.0624 second and the percentage of the packet loss decreases until reach 0.00617%. So the QOS parameters achieve requirements with EDCA protocol and support QOS.

Modelling collision alleviating DCF protocol with finite retry limits

IEEE 802.11-based wireless ad hoc networks are well suited for critical scenarios such as rescue operations during natural calamities, military applications on battle fields and so on where the existing infrastructure fails. In these networks, since nodes have limited battery power, the reduction in packet collision is very important, otherwise the nodes have to spend more energy for packet transmission. In these wireless networks, the packet transmission procedure plays a pivotal role in performance. Several packet transmission procedures represented with Markov chain models have been suggested by the authors to improve the network performance. However, these procedures have not been suitable for dense networks due to the high collision rate. A new packet transmission procedure for the IEEE 802.11 distributed coordination function (DCF) protocol is proposed to reduce the number of collisions and enhance the throughput of wireless networks. A mathematical framework is carried out for transmission probability and performance analysis is presented showing that the new procedure greatly enhances the network performance and as a result can be applied in the design and performance optimisation of wireless network protocols.

Development of Collision Alleviating DCF Protocol with Efficient Backoff Algorithm for Wireless Ad hoc Networks

Ad hoc networks have been proposed for emergency communication wherein the required infrastructure is unavailable. However, a major concern in Ad hoc networks is collisions. Even in infrastructure based wireless networks, when the number of contending nodes is high, more number of frame collisions occur which leads to drastic reduction in network performance. In all IEEE 802.11 based wireless and Ad hoc networks, the backoff algorithm dynamically controls the contention window of the nodes experiencing collisions. Even though several algorithms such as Binary Exponential Backoff, Double Increment Double Decrement backoff, Exponential Increase Exponential Decrease backoff, Hybrid Backoff, Binary Negative Exponential Backoff etc. have been proposed in the literature to enhance the performance of IEEE 802.11 Distributed Coordination Function (DCF) protocol, most of them have not been developed for real- traffic scenarios. Also the packet collision rate is high using these algorithms. So, in this paper, a new Contention Window based Multiplicative Increase Decrease Backoff (CWMIDB) algorithm is proposed for the DCF protocol to alleviate the number of collisions. Furthermore, the packet transmission procedure of the DCF protocol is modified to avoid channel capture effect and this is represented with a Markov chain model. A simple mathematical model is developed for transmission probability considering the non-saturated traffic and channel errors. Results show that the proposed CWMIDB algorithm provides superior quality-of-service parameters over existing backoff algorithms.

Distributed Coordination Function Protocol with Unequal Frame Error Rates

This letter provides an analysis of the saturation throughputs of the individual stations (STAs) in a distributed coordination function (DCF) network. Compared with the previous DCF models, our new proposed model is suitable for more general environments where the frame error rates (FERs) are different depending on the transmitting STAs and the numbers of retransmission attempts. Numerical analyses show that FERs significantly affect the STAs' throughputs.

A MAC Throughput in the IEEE 802.11ac over Error-Prone Channel

This paper analyzes a MAC (Medium Access Control) layer throughput over error-prone channel in the IEEE 802.11ac-based wireless LAN with DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme, using theoretical analysis method. The MAC saturation throughput is evaluated by using a PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables. When the PER is 10-2 and the number of aggregated MPDUs in each A-MPDU is 20, it is identified that the MAC layer throughput of IEEE 802.11ac can be maximally attained up to a 92.8% of physical transmission rate.

Modeling IEEE 802.11 DCF with Finite Retry Limits

The IEEE 802.11 is the dominating standard for wireless local area networks (WLANs). IEEE 802.11 uses Distributed Coordination Function (DCF) protocol with Binary exponential backoff (BEB) algorithm for packet transmission. In WLANs, the performance metrics such as throughput and end-to-end delay greatly depend on packet transmission procedure. The packet transmission procedure can be represented with a Markov chain model. Till now, several Markov chain models have been developed for evaluating the performance of IEEE 802.11 wireless networks. Yet, these models cannot truthfully calculate the performance of the network. Moreover, the existing models suffer with high packet collisions resulting in degradation of throughput particularly under congested environments. In order to overcome this, a new packet transmission procedure for DCF protocol is introduced in this paper considering both packet retry limits and transmission errors. A mathematical analysis is carried out for transmission probability and the throughput of the network is analyzed. Simulation results show significant improvement in throughput of DCF protocol under basic access and request-to-send/clear-to-send (RTS/CTS) access mechanisms using the proposed model when compared with the existing models Keywords: DCF, IEEE 802.11, Markov chain model, Throughput. .

Performance analysis of collision alleviating distributed coordination function protocol in congested wireless networks – a Markov chain analysis

IEEE 802.11 is the most popular wireless local area network (WLAN) standard in use. WLANs support broadband multimedia communication and hence providing quality of service requirements such as good throughput and minimum end-to-end delay are the two main challenging issues in designing of WLAN protocols for supporting real-time applications. Until now, several Markov chain models have been developed to evaluate and to enhance the performance of the IEEE 802.11 distributed coordination function (DCF) protocol. However, these models cannot accurately predict the performance of the network. Also, the existing models suffer with high packet collisions resulting in degradation of throughput and end-to-end delay particularly under congested environments. This study proposes an exact Markov chain model to accurately predict the performance of the wireless networks. To alleviate the collisions and to avoid channel capture effect, the authors introduce a post-backoff stage to provide inter packet backoff (IPB) delay between successive packet transmissions. The analysis is carried out by considering the non-saturated traffic and the impact of channel errors because of Rayleigh fading. Results show significant improvement in throughput and reduction in delay using the proposed model when compared with the existing models.

Design and evaluation of a contention-based high throughput MAC with delay guarantee for infrastructured IEEE 802.11 WLANs

This paper proposes a complete solution of a contention-based medium access control in wireless local networks to provide station level quality of service guarantees in both downstream and upstream directions. The solution, based on the mature distributed coordination function protocol, includes a new fixed contention window backoff scheme, a tuning procedure to derive the optimal parameters, a super mode to mitigate the downstream bottleneck at the access point, and a simple admission control algorithm. The proposed system guarantees that the probabilityof the delay bound violation is below a predefined threshold. In addition, high channel utilization can be achieved at the same time. The numerical results show that the system has advantages over the traditional binary exponential backoff scheme, including efficiency and easy configuration.

Performance Analysis of IEEE 802.11e (EDCF) and IEEE 802.11(DCF) WLAN Incorporating Different Physical Layer Standards

Medium access coordination function basically implements the distributed coordination function (DCF) which provides support to best effort services but limited to QoS services. Subsequently, a new standard, namely enhanced distributed channel access (EDCA) is reported. The IEEE 802.11e (EDCA) defines MAC procedures to support QoS requirements which specifies distributed contention based access scheme to access the shared wireless media. This paper evaluates the performance of EDCA based IEEE 802.11 WLAN for various access categories (ACs) using OPNET™ Modeller 14.5. Further, the computed results are compared with DCF protocols in terms of QoS parameters. Furthermore, the simulative observation is reported at data rate of 54 Mbps using different physical layer protocols such as IEEE 802.11a/b/g to stumble on the best one to be implemented with EDCF to achieve improved QoS.

DCF Throughput Analysis of IEEE 802.11a/g/n-based Mobile LAN over Correlated Fading Channel

This paper explores a MAC (Medium Access Control) layer throughput with DCF (Distributed Coordination Function) protocol in the IEEE 802.11a/g/n-based mobile LAN. It is evaluated in Rayleigh fading wireless channel, using theoretical analysis method. The DCF throughput performance is analyzed by using the number of stations with both variable payload size and mobile speed on the condition that fading margin and transmission probability are fixed. In the IEEE 802.11n, A-MSDU (MAC Service Data Unit Aggregation) scheme is considered and number of subframe is used as the variable parameter. It is identified that MAC efficiency of IEEE 802.11n is the best out of four schemes.

Single Hop IEEE 802.11 DCF Analysis Revisited: Accurate Modeling of Channel Access Delay and Throughput for Saturated and Unsaturated Traffic Cases

Analytical models for IEEE 802.11 Distributed Coordination Function (DCF) play important roles in performance estimation, protocol optimization and admission control for wireless networks utilizing this MAC protocol. While a myriad of models for IEEE 802.11 DCF channel access delay and throughput exist, such models' accuracy is generally limited to rather narrow ranges of scenario parameters. Our investigations single out the inaccuracy in modeling the backoff process as the primary reason for the said deviations. In this paper, we introduce two highly accurate models for IEEE 802.11 DCF protocol in a single-hop setting under both saturated and unsaturated traffic loads. First, a crucial augmentation to the classical model proposed by Bianchi is presented for the saturation load analysis to account for channel state during the backoff countdown process, resulting in a highly accurate estimation of collision probability, channel throughput and channel access delay. We then extend this accurate model to unsaturated traffic cases through an iterative approach which similarly results in highly accurate performance metric estimations for a wide range of parameters. Both models have been evaluated through simulations and in comparison with existing analytical models.