Distributed Coordination Function Research Articles

AP-based CW Synchronization Scheme in IEEE 802.11 WLANs

In this paper, an optimal CW (Contention Window) synchronization scheme is proposed in IEEE 802.11 WLANs. IEEE 802.11 WLANs operates with DCF (Distributed Coordination Function) mode for the MAC (Medium Access Control). In DCF, CW becomes the minimum CW according to the success of data transmissions and increases exponentially due to the collisions. In this situation, the smaller value of the minimum CW can increase the collision probability because stations have higher opportunity to access the medium. On the other hand, the higher value of the minimum CW will delay the transmission, which can result in the network performance degradation. In IEEE 802.11, since the base minimum CW value is a fixed value depending on the hardware or standard, it is difficult to provide the optimal network performance that can be determined by the flexible CW value according to the number of active stations. In addition, the synchronization of optimal CW is required among mobile stations to adapt the network parameters. Especially for the newly joined stations such as moving or turning on stations, they need to adapt the minimum CW value to get the optimal network performance. The shorter the adaptation time is, the better the network performance can maintain. Therefore, in this paper, AP (Access Point) calculates the optimal CW and shares it with mobile stations using beacon and probe response messages for the fast CW synchronization. Extensive simulation results show that the proposed scheme outperforms the previous schemes in terms of the network throughput and adaptation time. Â

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.

Qualitative Analysis of dual MAC in Multihop Adhoc Wireless Network

Multihop adhoc wireless networks offer great challenges for protocol designers. Stations in such networks are constrained by factors like low power, limited bandwidth, link errors and collisions. Changes are needed at various levels of the protocol stack, most importantly at the media access layer(MAC). This paper emphasizes in minimizing the collisions, and take care of the hidden and exposed problems in multihop wireless networks. The MAC with Distributed Coordination Function(DCF)does not scale well in such networks. We introduce Point Coordination Function(PCF)in the region of high traffic areas, and discuss its effect on network performance. To improve network scalability and throughput, we propose the design of dual MAC. This work discusses architecture and working of the dual MAC. Performance results of the network using MAC are presented, and compared with that of pure DCF operation.

Weighted Greedy Approach for Low Latency Resource Allocation on V2X Network

In Vehicular ad-hoc networks (VANETs), resource allocation has become one of the primary tasks. Thus, a system should be well-designed so that information could be transmitted reliably and efficiently. As vehicular communication has several characteristics, efficient resource allocation scheme for D2D communications is highly required in VANET. The network topology changes rapidly as the vehicles are moving fast on the road and this makes it harder to communicate among the vehicles by predicting the best available channel. So as to overcome these issues, the proposed technique is offered in which the channel availability is predicted based on the novel mechanism like contention latency prediction using interframe spaces like Short interframe space, Distributed Coordination Function interframe space, Pointed Coordination Function and scattering based greedy weight matrix method. The implementation of this greedy mechanism in turn enhances the prediction probability of best channels that are available. Thus, the best available channel offered using greedy weight matrix scheme thereby estimates the decision probability at which the collision for available channel is computed. Thus, from this the best available channel is provided to the requested user. At last, the performance analysis is made in terms of packet delivery ratio, throughput, delay, reliability, and rate of message loss and is compared with existing techniques to prove the effectiveness of proposed strategy.

Improving the Throughput in Lightly Disturbed IEEE 802.11 DCF Saturated Network Using the Fragmentation Mechanism Under Basic Access Mode

The IEEE 802.11 is the most dominating protocol in the wireless local area networks and in which, the fundamental mechanism to access the channel is called distributed coordination function (DCF). As this mechanism is random, the calculation of the performance metrics for IEEE 802.11 networks is focused on the determination of probabilities such as collision probability and successful transmission probability. Recently, there are performance studies in the literature are based on the mathematical models developed using the Markov chains, which model the DCF mechanism with fragmentation in IEEE 802.11 network under imperfect channel. Yet, these models suffer with high collision probability and low successful transmission probability and as a result, the transmission with fragmentation is not recommended at all in the IEEE 802.11 basic DCF networks when the bit error rate is low $$\left( {BER < 5 \times 10^{ - 5} } \right)$$ . In order to solve this, a new analytical model of the basic DCF mechanism with fragmentation is presented in this paper to accurately evaluate throughput metric in the lightly disturbed IEEE 802.11 network at $$BER = 10^{ - 5}$$ under saturated traffic. Analytical results show that our model significantly improves the throughput of the IEEE 802.11 DCF network compared with existing model and hence, provides a higher throughput than that is improved with the request to send/clear to send (RTS/CTS) mode, regardless to network size.

Performance of distributed coordination function for serving IoT applications

The Internet of Things (IoT) interconnects “things” and autonomously exchanges data between them. It is expected that there are more than seven billion of connections interconnected by low-power wide-area (LPWA) networks to support IoT services before 2025. Several LPWA technologies are gaining popularity recently, such as LoRa and NB-IoT. Despite of their advertised advantages over conventional technologies such as low power, long range, and cheap module, several studies and field tests shows that they cannot communicate in long-range, the DIY supporting modules are not really power efficient, and the development are rather expensive. While commercial IoT networks have yet to be widely deployed, many smart connected devices use WiFi-based connectivity. This motivates us to study and evaluate the performance of WiFi’s medium access protocol for this new use case of IoT. In the experiment, our proposed analytical model is evaluated against a custom-made Monte Carlo simulation. The result shows that our model is accurate in estimating the system performance in term of normalized throughput.

Device-Selective Energy Request in RF Energy-Harvesting Networks

In a Wireless Local Area Network (WLAN), devices have limited battery capacity. To improve the energy efficiency, we propose a new Medium Access Control (MAC) protocol to perform selective energy transfer request based on the amount of residual energy of a device in a WLAN with IEEE 802.11 Distributed Coordination Function (DCF). By supplying the energy only to the device requiring energy harvesting, the deterioration in network throughput during energy harvesting in a wireless network is minimized. We present a new energy Markov chain model to analyze the throughput and the energy efficiency of the proposed method. We confirm that the throughput and the energy efficiency of the proposed method is improved.

Quality of Services Based on Intelligent IoT WLAN MAC Protocol Dynamic Real-Time Applications in Smart Cities.

The future directions and challenges for 6G-enabled wireless communication for IoT applications are mainly focused on quality of service (QoS). The selection criteria of mobility management (MM) protocol are mainly the total duration of the delay and packet loss rate during the MM procedure. This is called intelligent handover (IH) to designate a relay with a minimum delay. To solve the problem of handover, media access control (MAC) protocols are used to provide an intelligent protocol for QoS in real-time application in mobility. Moreover, changing the parameter to find the best protocol for mobile stations in WLAN is a good choice. This paper proposed a new QoS structure for the point coordination function that is based on a new intelligent enhanced distribution coordination function that suites with dynamic real-time applications and services. The paper addresses the distributed coordination function (DCF) with QoS-based intelligent mobility management in stations and other scenarios with enhanced distribution coordination function (EDCF) to find the result of throughput, retransmission attempts, delay, and data droop. In this paper, the remote topology comprises a few remote stations and one base station within the remote LAN. All remote stations are found that each station can distinguish a transmission from any other station, and there is portability within the proposed intelligent framework.

CFFD-MAC: A Hybrid MAC for Collision Free Full-Duplex Communication in Wireless Ad-Hoc Networks

Infrastructure-less (sometimes known as ad-hoc) networking paradigm is very appealing and potentially shaping its future into almost all emerging networks (i.e., IoT, wireless sensor networks, vehicular ad-hoc networks, emergency, and tactical radio networks, etc.). However, when conventional networking protocols are used, such networks often perform poorly, mainly because of interference within the network and limited network throughput. Recent advancements in wireless communications have enabled full-duplex (FD) operation by suppressing self-interference, which can theoretically double the network throughput. However, conventional medium access control (MAC) protocols like carrier-sense multiple access with collision avoidance (CSMA/CA) favor half-duplex (HD) operation and fail to benefit from FD transmission opportunities. This article proposes a novel hybrid MAC protocol for full-duplex ad-hoc networks. The proposed MAC combines time division multiple access (TDMA) and IEEE 802.11 distributed coordination function (DCF) strengths in chains of time-slotted contention-based control frames and collision-free data frames. The aim is to fully utilize FD transmission opportunities to increase network throughput. The proposed protocol modifies request-to-send (RTS) and clear-to-send (CTS) frames in IEEE 802.11 DCF MAC to form FD-RTS/CTS frames. These frames are used to enable collision-free FD communications among neighbors. The proposed scheme mitigates conventional MAC issues like hidden-node problem (HNP) and exposed-node problem (ENP). It also allows concurrent FD data transmissions in a collision-free manner. The model is generic and can be applied to any ad-hoc wireless network. In this article, the design is applied to a single channel ad-hoc network with FD transceivers. We compared the proposed design with IEEE 802.11 CSMA/CA protocol with both HD and FD transceivers. The simulation results show a 30% gain in throughput, reduced latency, and fairness among participating wireless nodes.

Intelligent CW Selection Mechanism Based on Q-Learning (MISQ)

Mobile ad hoc networks (MANETs) consist of self-configured mobile wireless nodes capable of communicating with each other without any fixed infrastructure or centralized administration using the medium radio. Wireless technology is based on standard IEEE.802.11. The IEEE 802.11 Distributed Coordination Function (DCF) MAC layer uses the Binary Exponential Backoff (BEB) algorithm to deal with wireless network collisions. BEB is considered effective in reducing the probability of collisions but at the expense of numerous network performance measures, such as throughput and packets delivery ratio, mainly in high traffic load. Deep Reinforcement Learning (DRL) is a DL technique in which an agent can achieve a goal by interacting with the environment. In this paper, using one of the DRL models, we propose Q-learning (QL) to optimize MAC protocols' performance based on the contention window (CW) in MANETs. The intelligent proposed MISQ takes into account the number of packets to be transmitted and the collisions committed by each station to select the appropriate contention window. The performance of the proposed mechanism is evaluated by using in-depth simulations. The outputs indicate that the intelligent proposal mechanism learns various MANETS environments and optimizes performance over standard MAC protocol. The performance of MISQ is evaluated in various networks with throughput, channel access delay, and packets delivery rate as performance measures.

Performance Analysis of Synchronous Multi-Radio Multi-Link MAC Protocols in IEEE 802.11be Extremely High Throughput WLANs

The representative media access control (MAC) mechanism of IEEE 802.11 is a distributed coordination function (DCF), which operates based on carrier-sense multiple access with collision avoidance (CSMA/CA) with binary exponential backoff. The next amendment of IEEE 802.11 being developed for future Wi-Fi by the task group-be is called IEEE 802.11be, where the multi-link operation is mainly discussed when it comes to MAC layer operation. The multi-link operation discussed in IEEE 802.11be allows multi-link devices to establish multiple links and operate them simultaneously. Since the medium access on a link may affect the other links, and the conventional MAC mechanism has just taken account of a single link, the DCF should be used after careful consideration for multi-link operation. In this paper, we summarize the DCFs being reviewed to support the multi-radio multi-link operation in IEEE 802.11be and analyze their performance using the Markov chain model. Throughout the extensive performance evaluation, we summarize each MAC protocol’s pros and cons and discuss essential findings of the candidate MAC protocols.

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.

Performance analysis and evaluation of IEEE 802.11 distributed coordination function using OPNET

This paper discusses the distributed coordination function (DCF) access mechanism which is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme. Simulation projects for different DCF performance parameters have been built using the OPNET network simulator. The projects are mainly basic service set (BSS) topology simulated under different parameter values (data rate, fragmentation, RTS/CTS, number of nodes, and load condition). Simulation results show when the DCF access mechanism is better under what load condition, and how to choose the best fragmentation threshold and other access-mechanism specific parameters according to the network conditions. Simulation results were validated against a theoretically calculated maximum throughput (the simulation maximum throughput was about 70% of the theoretically calculated maximum throughput).

Performance analysis of an adaptive OFDMA‐based CSMA/CA scheme on a wireless network

The conventional carrier-sense multiple access/collision avoidance (CSMA/CA) IEEE 802.11 protocol uses the rigid binary exponential backoff algorithm of the distribution coordination function (DCF) for channel access. The protocol poorly performs under loss by wireless links with high packet error rates and dense networks with numerous collisions from hidden nodes. Furthermore, the scheme is not cognisant of the state of the wireless link in its operation. This work develops hybrid adaptive orthogonal frequency division multiple access (OFDMA) CSMA/CA (hybrid AO–CSMA/CA) protocol that adapts the backoff and congestion window size according to the knowledge of the wireless channel conditions to mitigate against the effects of the loss by wireless links. The protocol utilises OFDM for effective resource allocation and solving the problem of the hidden terminal node on an OFDMA IEEE 802.11-based wireless network. The teletraffic performance analysis of the developed protocol is investigated in terms of throughput and delay metrics on a real dynamic Markovian wireless channel. The performance results indicate that the developed hybrid protocols perform better than the DCF protocol on the lossy wireless communication links.

A WLAN Uplink Collision-Resolving Scheme Using Multi-User Beamforming Technique

To effectively improve the throughput of the IEEE contention-based wireless local area network (WLAN) system, many uplink medium access control layer (MAC) protocols based on multi-user multiple-input multiple-output (MU-MIMO) technology have been proposed. However, a common problem of these approaches is that many physical layer (PHY) operations, e.g., synchronization, are not considered. As a result, existing methods may find difficulties in real-world implementation. In this article, we propose a simple yet practical uplink scheme for systems with multiple antennas. The main idea is to conduct multi-user beamforming (MU-BF) at an access point such that it can resolve collided signals from multiple competitive users; the proposed scheme can effectively reduce the upstream collision probability and improve system throughput. The other distinct advantage of the proposed scheme is that the MAC protocol of the original IEEE 802.11 standard, i.e., distributed coordination function (DCF), can remain unchanged. The mathematical analysis of system performance is also presented and verified. Simulations show that the proposed scheme significantly outperforms conventional WLAN systems.

Q Learning Algorithm with Network Coding in Multi Path Transfer Protocol for Wireless Mesh Network

In a wireless mesh network, the network coding algorithm used to improve network efficiency. In this paper, we have implemented the Q-learning algorithm with CSMA/CA as in distributed co-ordination function along with multi-path transfer protocol (MPTP). The functioning of CSMA/CA is based on physical carrier sensing. Q-learning algorithm, along with network coding, is implemented to achieve better throughput. Our proposed method has used to reduce the packet loss and to minimize the end to end delay of the network communication. Also, it will improve the possibility of receiver buffer blocking.

A multi-channel load awareness-based MAC protocol for flying ad hoc networks

Flying ad hoc network (FANET) is a promising and special mobile Ad hoc network, connecting large number of flying unmanned aerial vehicles (UAVs) on battlefield through wireless link. Designing a multi-priority traffic differentiated medium access control (MAC) protocol with low delay, large capacity, high flexibility, and strong scalability is a great challenge in the researches and applications of FANETs. In order to overcome the disadvantages in IEEE 802.11 distributed coordination function (DCF) and time division multiple access (TDMA) protocols, a novel multi-channel load awareness-based MAC protocol for FANETs is presented in this paper. The multi-priority queueing and service mechanism, and the multi-channel load-based backoff mechanism involved in the protocol are intensively described. We further model the multi-priority queueing and service mechanism by the multi-class queueing theory, and model the backoff mechanism using the Markov chain model. Simulation results show that the protocol can differentiate services for different priorities in FANETs according to real-time channel state, providing effective QoS guarantee for transmissions of various information, and the network bandwidth resource is efficiently utilized.

Effects of Retransmission Limit on the Performance of Centralized Random Backoff

Previous studies showed that the packet collision probability in the 802.11 Distributed Coordination Function (DCF) can approach zero by adopting Centralized Random Backoff (CRB), which improves the total throughput performance. Moreover, it was reported that wireless networks using CRB maintain a high level of compatibility to legacy wireless local area networks (WLANs) when they coexist. However, little attention has been paid to relations between the performance of CRB and the retransmission limit, although the number of retransmission limit is an essential parameter that must be carefully chosen when implementing CRB for efficient WLANs. This article presents more realistic Markov chain models, and studies the impact of retransmission limit on the performance of CRB. These relations are also investigated by Monte Carlo simulation in more practical scenarios. Results show the trade-off that the total throughput increases with the retransmission limit when the number of nodes is larger than 15; whereas, the channel access opportunities in the mixed network scenario are more unevenly distributed between nodes as the retransmission limit increases. It is also shown in the simulation results that the throughput degradation caused by the hidden node problem is alleviated as the retransmission limit increases.

SatOpt Partition: Dividing Throughput-Stability Region for IEEE 802.11 DCF Networks

This article investigates the throughput stability of nonsaturated 802.11 networks with distributed coordination function (DCF). We find that this throughput stability exhibits distinct characteristics in two different regions (or scopes) of parameter settings: the maximum stable throughput is higher than the saturation throughput and lasts for a long duration (say, in order of months) in one region, while the former is bounded by the latter in another region. Our core contribution is an innovative approach (called SatOpt partition) that can identify these two regions quickly and accurately, by a comparison between the saturated and optimal attempt rates. Our partition approach is suitable for a wide range of 802.11 DCF contention window settings, while our partition result is unique. Further, for 802.11 DCF standard settings, we predict the maximum stable throughput successfully, and reveal that it is often higher than the saturation throughput. We verify our approach via the widely adopted 802.11 DCF ns2 simulator (mostly with typical 802.11 DCF standard settings). We speculate that this two-region stability property should be inherent for any random-access networks. This suggests that the research on the throughput-stability problem should differentiate regions of parameter settings and failing to do so might produce inconsistent results. This study is expected to take a critical step toward solving the throughput-stability problem.

Throughput and delay analysis for IEEE 802.11 multi-hop networks considering data rate

In an IEEE 802.11 Distributed Coordination Function–based wireless network with multiple hops, a node operates on its own with several predefined data rates (i.e. following modulation and coding schemes). Moreover, the IEEE 802.11 Distributed Coordination Function node’s communication is characterized by transmission and carrier-sensing distances. The transmission one is, in general, reverse proportional to the data rate. Meanwhile, the carrier distance keeps constant regardless of the modulation and coding scheme. Therefore, when a node has a high transmission rate, within its carrier-sensing range, the number of nodes may increase. The previous works have not yet extensively investigated the impact of data rates on such a scenario. This article addresses that issue aiming to quantify the network performance of the multi-hop IEEE 802.11 networks. As a solution, we propose the mathematical expressions, which consider data rates, for end-to-end throughputs, as well as delays in the network with string topology. We confirm the expressions’ correctness by presenting the quantitative agreements between the analytical and simulation results.