Control Channel Interval Research Articles

Multi‐round elimination contention‐based multi‐channel MAC scheme for vehicularad hocnetworks

In this study, the authors propose a multi-round elimination contention-based multi-channel medium access control (VEC-MAC) scheme for vehicular ad hoc networks. In our proposed scheme, the control channel (CCH) interval is divided into three phases: roadside unit broadcast phase (BP), safety message BP (SBP) and service channel (SCH) reservation phase (RP). On the basis of this division, both the demand of safety-relevant applications and non-safety service applications can be satisfied. In addition, through the multi-round elimination contention in the SCH RP collision probability of transmissions significantly decreases and more successful reservations can be provided. Furthermore, the proposed multi-round elimination contention-based multi-channel MAC for VANETs (VEC-MAC) can adaptively adjust the length of the CCH interval (CCHI) and the value of the round number for the improvement of the system throughput. Theoretical analysis and simulation results exhibit the superiority of the proposed VEC-MAC in saturated throughput compared with the variable CCHI MAC and the wireless access in vehicular environment MAC.

Performance Evaluation of Adaptive Control Channel Interval in VANET Based on Network Simulation Model

Performance Evaluation of Adaptive Control Channel Interval in VANET Based on Network Simulation Model

APDM: An adaptive multi-priority distributed multichannel MAC protocol for vehicular ad hoc networks in unsaturated conditions

Vehicular ad hoc networks (VANETs) employ multichannel to provide a variety of safety and non-safety applications. Safety applications require reliable and timely transmission, while non-safety applications need high network throughput. IEEE 802.11p and IEEE 1609.4 protocol divide the bandwidth into seven channels. One control channel (CCH) is to serve safety applications and the other six service channels (SCHs) to serve non-safety applications. The IEEE 1609.4 protocol specifies an alternating scheme to allow vehicles to switch between two types of applications. However, the IEEE 1609.4 multichannel media access control (MAC) protocol has limitations on its capability of supporting either delay- or throughput-sensitive applications. In this paper, we propose an adaptive multi-priority distributed multichannel (APDM) MAC protocol for VANETs. Considering that in realistic VANETs, the queue of MAC layer is far from saturated. We assume that generated packets with different priorities arrive at the MAC layer in a Poisson manner. A Markov analytical model is conducted to optimize the packet transmission probabilities and adjust the ratio between CCH interval and SCH interval dynamically according to the real-time traffic in a distributed way. An M/M/1 queue model is then adopted to analyze the time performance. Extensive simulation results show that the APDM MAC protocol can ensure prioritized transmission of safety packets, reduce the transmission delay of packets and enhance the unsaturated and saturated throughput of SCHs.

To send or to defer? Improving the IEEE 802.11p/1609.4 transmission scheme

The IEEE 1609.4 protocol has been proposed to improve message delivery in Vehicular Ad Hoc Networks (VANETs) through its multi-channel usage. To ensure good performance for safety applications, during the first half of a synchronization interval, each vehicle tunes a dedicated Control CHannel (CCH) to exchange safety messages, and during the second half, either it stays on the CCH or switches to one of the six available Service CHannels (SCH). As demonstrated in the literature, such behavior leads safety messages to suffer from synchronous collisions at the start of the CCH interval, as well as from high end-to-end delays caused by the queue-up during the SCH intervals. To address these issues, we propose DMS, a Distributed MAC Scheduler that relies on the Optimal Stopping Theory to evenly balance the channel load by introducing tolerated deferring delays before sending a message. This ensures a higher reception probability and lower collision risks, while complying with Enhanced Distributed Channel Access (EDCA) access categories (ACs). Simulation study shows the ability of our approach to increase the reception rate of safety messages up to 25%, to decrease loses up to 47%, and to improve the load balancing during the CCH interval.

Optimizing the Control Channel Interval of the DSRC for Vehicular Safety Applications

Dedicated short-range communication (DSRC) technology has been adopted by the IEEE community to enable safety and nonsafety applications for vehicular ad hoc networks. To better serve these two classes of applications, the DSRC standard divides the bandwidth into seven channels. One channel, which is called the control channel (CCH), serves safety applications, and the other six channels, which are called service channels, serve nonsafety applications. The DSRC standard specifies a channel-switching scheme to allow vehicles to alternate between these two classes of applications. The standard also recommends that vehicles should visit the CCH every 100 ms, which is called the synchronization interval (SI), to send and receive their status messages. It is highly desirable that these status messages be delivered to the neighboring vehicles reliably and within an acceptable delay bound. It is obvious that increasing the time share of the CCH from the SI will increase the reliability of safety applications. In this paper, we propose two algorithms to optimize the length of the control channel interval (CCI) such that nonsafety applications have a fair share of the SI interval. One algorithm, which is called optimal channel access, is proposed to allow vehicles to access the channel with a derived optimal probability such that the successful transmission rate is maximized. The second algorithm, which is called the mobility- and topology-aware algorithm, is an adaptive scheme proposed to change the DSRC parameters based on the road and network conditions to allow the coexistence of safety and nonsafety applications on the DSRC. Vehicles will execute both algorithms in a distributed manner to achieve a high success rate within the selected CCI interval. The simulation results show that using the two new algorithms keeps the CCI below half of the SI in all scenarios while maintaining a high success rate for safety messages. This will give nonsafety applications the opportunity to work in the second half of the SI interval without jeopardizing the critical safety applications.

Adaptive Control Channel Interval in VANET Based on Mobility Model and Queuing Network Analysis

The dynamic of changing network topology and vehicle density in VANET are causing the dynamic of message traffic intensity. This situation requires adaptability of channel management to provide the channel capacity dynamically and proportionally. The length of CCH interval in VANET represents the capacity of channel or service rate of vehicles. The fixed pattern of CCH/SCH interval as published by IEEE 802.11p/1609.4 would become the constraint of adaptability of vehicles in VANETs. Moreover it would affect to VANET performance inefficient. This research proposes an adaptive scheme of CCH/SCH interval which proportional with density of vehicles based on the number of vehicle connected each other’s. To show how effective the proposed adaptive scheme of CCH/SCH interval can afford to improve of VANET performance (compared to fixed interval scheme of current IEEE standard), we analyze by combining mobility model and queuing network model. We assume that statistically there is a steady state of VANET topology which can be analyzed by using queuing network model. We specified the real map of highway in Bandung city along 10 Km length to achieve the representative experimental result. The various specified of speeds are: 70-90 Km/h, 90-110 Km/h, and 110-130Km/h, while the various of density of vehicle are 15, 30, 45, 60, 75, and 90 vehicles along 10Km length of highway. All of experiments performed in two main scenarios, i.e. the fixed CCH/SCH interval, and adaptive CCH/SCH interval which compared each other to see the improvement. The analytical result examined by simulation method. The experimental results show the improvement of adaptive CCH/SCH interval. The improvement of average delay is 10ms, and the improvement of system throughput is 450 kbps.

Efficient Channel Management Mechanism to Enhance Channel Utilization for Sensing Data Delivery in Vehicular Ad Hoc Networks

IEEE 1609.4 defines MAC layer implementation in a vehicular ad hoc network (VANET). In IEEE 1609.4 multichannel operation, the control channel interval (CCHI) and the service channel interval (SCHI) are defined such that service channels cannot be utilized during the CCHI, and vice versa, which leads to poor utilization of scarce spectrum resources. In this paper, we propose a multi-schedule-based channel switching mechanism to improve channel utilization and uniformly distribute channel load. In our proposed mechanism, four schedules are defined to switch between the control channel and service channels. Therefore, service channels can be utilized during the CCHI, and the control channel can be utilized during the SCHI. Moreover, control channel load is distributed throughout the whole sync interval. We compared our proposed MAC protocol with IEEE802.11p for wireless access in the vehicular environment using the OMNET++ 4.5 network simulator. In the simulation results, we determined that utilization of the service channel increased and contention on the control channel was reduced, compared with the legacy standard, especially in slow motion and high-density VANETs.

Performance Analysis of Connectivity Probability and Connectivity-Aware MAC Protocol Design for Platoon-Based VANETs

Vehicular ad hoc networks (VANETs) can provide safety and nonsafety applications to improve passenger safety and comfort. Grouping vehicles into platoons in VANETs can improve road safety and reduce fuel consumption. It is critical to design an efficient medium access control (MAC) protocol for platoon-based VANETs. Moreover, because of the space and time dynamics of moving vehicles, network connectivity is an important performance metric to indicate the quality of the network communications and the satisfaction of users. Unfortunately, network connectivity is often ignored in the design of existing MAC protocols for VANETs. In this paper, we study the connectivity characteristics and present a connectivity-aware MAC protocol for platoon-based VANETs. The connectivity probabilities are analyzed for vehicle-to-vehicle and vehicle-to-infrastructure communication scenarios in one- and two-way VANETs, respectively. A multipriority Markov model is presented to derive the relationship between connectivity probability and system throughput. Based on variable traffic status and network connectivity, a multichannel reservation scheme is adopted to dynamically adjust the length of the control channel interval and the service channel interval for the improvement of the system throughput. Analysis and simulation results show that the throughput increases with connectivity probability. However, with a further increase in connectivity probability, the throughput will decrease due to numerous channel contentions.

Research on Dynamic Bandwidth Partition Algorithm for Control Channel of Vehicular Ad-Hoc Networks

In IEEE 802.11p protocol of Vehicular Ad-Hoc network (VANET), the multiple channels are divided into one control channel (CCH) and six service channels (SCHs). CCH is used for broadcasting safety messages related to road conditions, so that CCH access algorithm has great influence on efficiency of VANET. This paper proposes a contention-free bandwidth partition algorithm, which can dynamically partition the CCH interval and bandwidth assigned to on board units (OBUs) located in vehicles according to real-time VANET environments. Meanwhile, a frequency hopping communication scheme based on chaos scrambling is applied to our algorithm to improve the reliability of VANET. The performance of proposed algorithm are verified by theoretical analysis, the results show that it is able to enhance the transmission efficiency of safety packets in CCH with high reliability.

A New Interference-Aware Dynamic Safety Interval Protocol for Vehicular Networks

In IEEE 802.11p/1609-based vehicular networks, vehicles are allowed to exchange safety and control messages only within time periods, called control channel (CCH) interval, which are scheduled periodically. Currently, the length of the CCH interval is set to the fixed value (i.e. 50ms). However, the fixed-length intervals cannot be effective for dynamically changing traffic load. Hence, some protocols have been recently proposed to support variable-length CCH intervals in order to improve channel utilization. In existing protocols, the CCH interval is subdivided into safety and non-safety intervals, and the length of each interval is dynamically adjusted to accommodate the estimated traffic load. However, they do not consider the presence of hidden nodes. Consequently, messages transmitted in each interval are likely to overlap with simultaneous transmissions (i.e. interference) from hidden nodes. Particularly, life-critical safety messages which are exchanged within the safety interval can be unreliably delivered due to such interference, which deteriorates QoS of safety applications such as cooperative collision warning. In this paper, we therefore propose a new interference-aware Dynamic Safety Interval (DSI) protocol. DSI calculates the number of vehicles sharing the channel with the consideration of hidden nodes. The safety interval is derived based on the measured number of vehicles. From simulation study using the ns-2, we verified that DSI outperforms the existing protocols in terms of various metrics such as broadcast delivery ration, collision probability and safety message delay.

An Efficient and Reliable MAC in VANETs

Vehicular Ad hoc Network (VANET) is developed to enhance the safety, comfort and efficiency of driving. The IEEE 802.11p/WAVE and IEEE 1609.4 family are standards intended to support wireless access in VANETs. In this paper, we propose an Efficient and Reliable MAC protocol for VANETs (VER-MAC) which allows nodes to broadcast safety packets twice during both the control channel interval and service channel interval to increase the safety broadcast reliability. By using the additional data structures, nodes can transmit service packets during the control channel interval to improve the service throughput.

A Scalable CSMA and Self-Organizing TDMA MAC for IEEE 802.11 p/1609.x in VANETs

vehicular ad hoc networks (VANETs) have been a key topic for research community and industry alike. The wireless access in vehicular environment standard employs the IEEE 802.11p/1609.4 for the Medium Access Control (MAC) layer implementation for VANETs. However, the carrier sense multiple access (CSMA) based mechanism cannot provide reliable broadcast services, and the multi-channel operation defined in IEEE 1609.4 divides the available access time into fixed alternating control channel intervals (CCH) and service channel (SCH) intervals, which may lead to the low utilization of the scarce resources. In this paper, a novel multichannel MAC protocol called CS-TDMA considering the channel access scheduling and channel switching concurrently is proposed. The protocol combines CSMA with the time division multiple access (TDMA) to improve the broadcast performance in VANETs. Meanwhile, the dwelling ratio between CCH and SCH changes dynamically according to the traffic density, resulting in the improvement of resource utilization efficiency. Simulation results are presented to verify the effectiveness of our mechanism and comparisons are made with three existing MAC protocols, IEEE MAC, SOFT MAC and VeMAC. The simulation results demonstrate the superiority of CS-TDMA in the reduction of transmission delay and packet collision rate and improvement of network throughput.

Dynamic Channel Coordination Schemes for IEEE 802.11p/1609 Vehicular Networks: A Survey

IEEE 802.11p/1609-based vehicular networks utilize a multichannel architecture to support vehicle-to-vehicle and vehicle-to-infrastructure communications. In the multi-channel architecture, the available channels in the 5 GHz spectrum are divided into one control channel (CCH) and multiple service channels (SCHs). Multiple SCHs are defined for nonsafety data transfer, while the CCH is used to broadcast safety messages called beacons and control messages (i.e., service advertisement messages). According to the channel coordination scheme, a radio interface alternately switches between the CCH and a specific SCH. The intervals during which a radio interface stays tuned to the CCH and SCH are called CCH and SCH intervals, respectively. Both intervals are set to a fixed value (i.e., 50 ms) in the standard. However, since the fixed-length intervals cannot be effective for dynamically changing traffic load, some dynamic interval division protocols have been recently proposed to support the dynamic adjustment of the CCH/SCH intervals for improving channel utilization. In this paper, we therefore provide a survey of dynamic interval division protocols for VANETs, discuss the advantages and disadvantages of them, and define some open issues and possible directions of future research.

Performance Analysis of a Multi-Channel MAC with Dynamic CCH Interval in WAVE System

To improve the throughput performance of the Wireless Access in Vehicular Environment (WAVE) system, we propose a multi-channel MAC protocol that is able to adaptively adjust the intervals of Control Channel (CCH) and Service Channel (SCH) according to the probability distribution of the reservation time for service packet in CCH Interval. Numerical results show that our protocol can significantly improve the performance of WAVE system.

Collision Control of Periodic Safety Messages With Strict Messaging Frequency Requirements

For safety messages in a vehicular networking environment, strict messaging frequency requirements exist. For instance, six out of eight cooperative vehicular safety applications, as chosen by the National Highway Traffic Safety Administration and the Crash Avoidance Metrics Partnership, require a minimum of 10 Hz, whereas the precrash sensing application requires an even higher frequency of 50 Hz, for messages that convey the positions of vehicles. Currently, the collisions of periodic safety message broadcasts for the IEEE Wireless Access in Vehicular Environment (WAVE) system are left to the IEEE 802.11p medium access control (MAC) to resolve. With small contention window sizes stipulated in the 802.11p amendment, however, the MAC offers only limited relief to the collision problem, particularly toward the beginning of the control channel (CCH) interval. In this paper, we show that application-level control of the message transmission phase is desirable, when the frequency adaptation is not allowed due to the application requirement. We demonstrate through simulation and analysis that the proposed technique achieves up to 50% higher message reception probability compared with that relying only on the 802.11p MAC. The proposed method works in the safety applications themselves; therefore, the existing standards need not be modified.

Adaptive Message Rate Control of Infrastructured DSRC Vehicle Networks for Coexisting Road Safety and Non-Safety Applications

Intelligent transport system (ITS) has large potentials on road safety applications as well as nonsafety applications. One of the big challenges for ITS is on the reliable and cost-effective vehicle communications due to the large quantity of vehicles, high mobility, and bursty traffic from the safety and non-safety applications. In this paper, we investigate the use of dedicated short-range communications (DSRC) for coexisting safety and non-safety applications over infrastructured vehicle networks. The main objective of this work is to improve the scalability of communications for vehicles networks, ensure QoS for safety applications, and leave as much as possible bandwidth for non-safety applications. A two-level adaptive control scheme is proposed to find appropriate message rate and control channel interval for safety applications. Simulation results demonstrated that this adaptive method outperforms the fixed control method under varying number of vehicles.

An IEEE 802.11p-Based Multichannel MAC Scheme With Channel Coordination for Vehicular Ad Hoc Networks

In recent years, governments, standardization bodies, automobile manufacturers, and academia are working together to develop vehicular ad hoc network (VANET)-based communication technologies. VANETs apply multiple channels, i.e., control channel (CCH) and service channels (SCHs), to provide open public road safety services and the improve comfort and efficiency of driving. Based on the latest standard draft IEEE 802.11p and IEEE 1609.4, this paper proposes a variable CCH interval (VCI) multichannel medium access control (MAC) scheme, which can dynamically adjust the length ratio between CCH and SCHs. The scheme also introduces a multichannel coordination mechanism to provide contention-free access of SCHs. Markov modeling is conducted to optimize the intervals based on the traffic condition. Theoretical analysis and simulation results show that the proposed scheme is able to help IEEE 1609.4 MAC significantly enhance the saturated throughput of SCHs and reduce the transmission delay of service packets while maintaining the prioritized transmission of critical safety information on CCH.

Modeling Broadcasting in IEEE 802.11p/WAVE Vehicular Networks

IEEE 802.11p/WAVE (Wireless Access in Vehicular Environments) is an emerging family of standards intended to support wireless access in Vehicular Ad Hoc Networks (VANETs). Broadcasting of data and control packets is expected to be crucial in this environment. Both safety-related and non-safety applications rely on broadcasting for the exchange of data or status and advertisement messages. Most of the broadcasting traffic is designed to be delivered on a given frequency during the control channel (CCH) interval set by the WAVE draft standard. The rest of the time, vehicles switch over to one of available service channels (SCHs) for non-safety related data exchange. Although broadcasting in VANETs has been analytically studied, related works neither consider the WAVE channel switching nor its effects on the VANET performance. In this letter, a new analytical model is designed for evaluating the broadcasting performance on CCH in IEEE 802.11p/WAVE vehicular networks. This model explicitly accounts for the WAVE channel switching and computes packet delivery probability as a function of contention window size and number of vehicles.

Cooperative multichannel management in IEEE 802.11p/WAVE vehicular ad hoc networks

The upcoming IEEE 802.11p/Wireless Access in Vehicular Environment (WAVE) standard is intended to provide wireless access to vehicles on the roads. According to it, safety/control messages are delivered on a given frequency during a common control channel (CCH) interval. The rest of the time, vehicles switch over one of available service channels (SCH) for non-safety-related data exchange. Despite the massive research effort onto reliable and timely dissemination solutions for safety-related data, few works have investigated non-safety data delivery when considering the WAVE features and capabilities. In this work, a simple and easy-to-deploy channel reservation scheme based on cooperation among vehicles has been designed, which fully leverages the 802.11p/WAVE multichannel capability. Simulation results show that the proposed solution, by adding just few modifications and little-to-none signalling overhead compared to the standard, is successful in improving the performance delivery of non-safety services under several network topologies and different traffic loads.