Structure of Enhanced QoS for Vehicular Network

The current medium access control (MAC) protocol of the wireless access in vehicular environments (WAVE) system is based on IEEE 802.11 distributed coordination function (DCF) and enhanced distributed channel access (EDCA), which have drawbacks in supporting throughput-sensitive non-safety applications in vehicular ad-hoc network (VANET). In order to address the problem, we propose a novel MAC protocol, namely vehicular MESH network (VMESH), which is specifically designed for the control channel (CCH) and multiple service channels (SCHs) structure of WAVE. A synchronized and distributed beaconing scheme is employed in the VMESH protocol for the purposes of neighborhood awareness and dynamic resource reservation on SCHs. The advantages of the VMESH protocol in supporting the throughput-sensitive non-safety applications in VANET are shown through the theoretical analysis comparing to the current WAVE MAC.

With the onset of multimedia applications, Quality of Service (QoS) in 802.11-based wireless ad hoc networks has been an essential area to look into. Standard wireless protocols such as IEEE 802.11b and IEEE 802.11e have been deemed unsuitable for multimedia traffic transmission in an ad hoc (multihop) network environment due to the unique network characteristics. As an ad hoc network is infrastructureless and distributed in nature, it gives rise to several challenges in QoS provisioning. In this thesis, we focus on the research of three key areas on QoS in ad hoc networks namely, buffer management in the medium access control (MAC) layer, cross-layer design and flow admission control. Firstly, we study MAC layer buffer management in the IEEE 802.11e protocol. The IEEE 802.11e MAC protocol provides QoS for multimedia traffic by probabilistic priority queueing. Ad hoc networks tend to generate a large volume of network control packets for route maintenance and these control packets are typically queued in the highest priority queue. As a result, higher priority control traffic is always being served, consuming most of the bandwidth and results in poor network performance for data traffic. We examine this problem and propose a dynamic buffer management scheme to mitigate it. By setting different threshold levels in different priority queues, we allow lower priority data traffic to be served when the higher priority control traffic is deemed to be excessive. Simulation of our proposed scheme has shown that our approach yielded better network performance compared to the standard protocol in terms of packet delivery ratio and average delay. Secondly, we study the cross-layer interaction between the MAC and Network layers to identify its impact on QoS. We select the IEEE 802.11e MAC protocol and Ad-hoc On Demand Distance Vector (AODV) routing protocol in our study since they are standardized protocols for wireless networks. In IEEE 802.11e MAC protocol, lower priority traffic has a higher probability of being blocked. Hence, the MAC layer will inform the Network layer of a broken link through the link notification function. In this case, AODV will re-route the paths that traverse this link. As a result, higher priority traffic which shares the same link as the lower priority traffic will undergo the same re-routing procedures. We termed this phenomenon path correlation effect. Under high traffic load, the path correlation effect will be more intense and hence degrade the QoS of higher priority traffic. To break the path correlation effect, we propose a cross-layer design called the Bundled Virtual Circuit (BVC). Our proposed BVC scheme not only addresses the path correlation issues, but also provides priority treatment from the Network layer to the MAC layer. Through our simulations, our proposed cross-layer design approach is proven to provide better network performance than the 802.11e/AODV protocols in terms of packet delivery ratio and delay. Finally, we examine flow admission control at the routing layer in ad hoc networks. Standard routing protocols such as AODV performs routing on a shortest path basis. In the presence of multiple routes, hotspots are likely to form among the intermediate nodes and thus lead to network congestion. In addition, existing routes are not well-protected from the introduction of new routes. We propose a flow admission control algorithm to be used with AODV. Our algorithm allows routes to be created through available bandwidth and congestion estimation. During the route discovery phase, each node will be gauged on its estimated available bandwidth and its backlog of packets in the MAC buffer. If a node does not have sufficient bandwidth, or has too many backlogged packets compared to the requested flow rate, it will not participate in the route discovery process. From simulations, our new scheme is able to provide better network performance than the standard AODV protocol in terms of delay. Our work in this thesis focuses on QoS provisioning in ad hoc networks from the MAC and network layer perspectives. By studying the network characteristics and protocols’ behavior, we investigate the various problems of providing QoS in an ad hoc network environment and propose three different schemes to improve the QoS provisioning at the MAC and network layers. We believe that our work is able to provide some insights to the research area on QoS in ad hoc networks.

Providing quality-of-service- (QoS-) guaranteed video on demand (VOD) services over wireless access in vehicular environments (WAVEs) is a challenge as WAVE adopts enhanced distributive channel access (EDCA), a contention-based channel access mechanism, for air interface access control. This paper proposes a selective downlink scheduling (SDS) algorithm to enhance the quality of VOD for WAVE networks. According to the importance of video decoding, video packets are categorized into high and low priorities. The categorized packets are put into different queues in roadside units (RSUs) to contend for transmission opportunities. Aiming to improve video playback quality and reduce video playback delay, the proposed SDS algorithm schedules video packets based on their importance, playback deadline, and their real-time parameters of receiving onboard units (OBUs), such as velocity and remaining dwelling time. The effectiveness of SDS algorithm is verified by simulations.

WAVE(Wireless Access in Vehicular Environments) designed for vehicle communication has the features of a short initial link, low latency and high mobility. The success of data transmission in WAVE is affected by the priority and size of data and how many nodes are transmitting the data. In this paper, we tested and analyzed how the success rate of data transmission of each node varies according to the number of nodes, priority and size of data in various cases. Based on the simulation results, it is possible to confirm the success rate of data transmission and delay time for each node and the entire channel, and it can be determined how channel resources should be efficiently used considering these results.

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.

Recently, the IEEE 1609.4 Standard for Wireless Access in Vehicular Environments (WAVE) has been proposed to enhance the performance of vehicular networks with multi-channel operations that allow for the coexistence of safety-related and non-safety related vehicular applications. However, while the benefits of the multi-channel approach are clear, the impact of the IEEE 1609.4 channel scheduler on the performance of delay-constrained vehicular applications remains to be well explored by researchers. At present, the evaluation of 1609.4-based Vehicular Ad Hoc Networks (VANETs) constitutes an open issue due to the lack of simulation tools that can provide a complete modeling of the IEEE WAVE 802.11p/1609.4 stack. In this paper, we provide three key contributions pertaining to multi-channel VANETs. First, we describe our implementation of the IEEE 1609.4 protocol in the ns2 simulator, and we detail its current integration with the existing ns2 implementation of the 802.11p MAC protocol. Second, using our simulation model we propose an evaluation study of 1609.4-based VANETs, and we show that the tight channel synchronization issues foreseen by the protocol might have a dramatic impact on the performance of safety-related applications with strict delivery ratio and delay requirements. Third, we propose two new enhancements for the WAVE protocol stack to favor the dissemination of safety messages in multi-channel VANETs. The suggested algorithms are shown to greatly improve packet delivery ratio and delay of safety applications in single and multi-hop topologies, while preserving the synchronization scheme of the IEEE 1609.4 protocol.

The emergence of Intelligent Transport Systems has led to the development of a specific communications standard carried out by the IEEE: Wireless Access in Vehicular Environments (WAVE). However, this standard does not address certain critical security and real time application constraints, such as the platooning guidance of transport units. This paper presents an original proposal of medium access control protocol based on Non Cooperative Cognitive Radio techniques to obtain a mechanism which complies with the requirements of real time communications. The mechanism also offers other advantages, such as avoiding signalling and the capacity to adapt to channel conditions. The solution is applied to the problem of units merging a convoy. Comparison results between the proposal and Slotted-Aloha are included.

There has been keen interest in the literature recently on the IEEE wireless metropolitan area network (MAN) developed within IEEE 802.16. Through the use of flexible physical layer features and medium access control (MAC) layer mechanisms, this system can be used to deliver broadband voice and data into areas that may have a wide range of population densities, cell radii, propagation environments, and quality of service (QoS) requirements. The physical layer provides flexibilities of time or frequency domain duplexing, multiple bandwidths, adjustable subchannelization, scalable OFDM formats, adaptive coded modulation, and advanced antenna system. The IEEE 802.16 MAC layer offers a connection-oriented service to upper layers of the protocol stack. The QoS of each connection takes one of four levels: constant bit rate grant, real time polling, non-real-time polling, and best effort. The MAC layer also offers packing, fragmentation and ARQ. The MAC privacy sublayer performs authentication, key exchange and encryption of MAC packet data units. The MAC convergence sublayers at the top of the MAC enable Ethernet, ATM, TDM voice and IP (Internet Protocol) services to be offered. This presentation will endeavor to provide a high level overview of the system. It will discuss, from an information theoretic point of view, the key enablers of the system

Vehicular ad hoc networks (VANETS) are simply a collection of onboard units (OBUs) and roadside units (RSUs) that communicate using dedicated short-range communications (DSRC) utilizing 75 Mhz in 5.9 GHz frequency band for wireless access in vehicular environment (WAVE). The frequency channel layout of WAVE has been divided into seven channels, with one channel for service safety applications and the remaining for service non-safety applications. The nature of the VANET environment being dynamic, it is most likely that packet forwarding over varied time intervals may be disconnected, causing network delays. In such a case the message containing information needs to be with the current vehicle until a new intelligent node becomes active. Extensive studies have been conducted on the propagation of messages in vehicular networks. Although conventional methods are mainly focused on similar traffic, in this only high, low-density traffic is considered. The intelligent mobile node structure in NS-3 has been designed in such a way as to support 802.11 MAC with a single channel. However, this intelligent mobile node is not appropriate for WAVE multi-channel operation.

The research of vehicular networks has been studied for many years. In actual life, there are a few implementations of V2X communication system, majority of them are extremely expensive. Most importantly, detailed insight implementation procedure hasn't been provided for researches. In this paper, an efficient V2X communication system based on the IEEE 802.11p/1609.X protocol stack, also known as the Wireless Access in Vehicular Environment (WAVE) standard has been designed. In this system, a Dedicated Short Range Communication (DSRC) unit using low-cost and commercial hardware which can support the vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications is developed. Some specific driver adjustments based on the IEEE 802.11a driver are taken to assure compliance with the IEEE 802.11p protocol. Besides, the development of networking layer protocol is accomplished based on IEEE 1609.3. Furthermore, three safety applications and a performance evaluation subsystem have been developed on this platform. The subsystem can test the comprehensive performance of the communication unit in terms of Packet Loss Rate (PLR), throughput and end-to-end delay. Meanwhile enormous experiments are conducted to evaluate the performance of the communication prototype and different scenarios were designed to validate the practical function of the safety applications.

The vehicular ad-hoc network (VANET) is a promising technology in near future. VANET allows vehicles to communicate with each other and with roadside units (RSUs). Wireless Access in Vehicular Environment (WAVE), defined by IEEE, provides the Internet connectivity for vehicles as well as vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication. RSUs can form a wireless mesh network (WMN) as a backbone infrastructure to enhance the performance of VANET. However, WAVE supports only one-hop communications for IP packets in VANET, and existing researches do not consider the compatibility between VANET and WMN infrastructure formed by RSUs. We propose the extended WMN (ExWMN) which has the feasibility to extend WMN to VANET domain. In ExWMN, the vehicles can send IP packets to an access router by using the multi-hop capability of WMN. ExWMN uses the addressing scheme of WMN for the extended VANET domain and exploits geographical routing protocols instead of existing routing protocols of WMN due to VANET characteristics such as mobility and dynamically changing network topologies. ExWMN supports the compatibility between the extended VANET and a WMN infrastructure due to RSUs, which provide a bridging function between them. This paper presents the architecture and the detailed procedures of the ExWMN.

Dedicated Short Range Communications (DSRC) is a wireless communication standard intended for high speed secure communication between vehicles and the infrastructure. In order to overcome the limitations that vehicular environment imposes such as high mobility, IEEE published the 802.11p amendment widely known as Wireless Access in Vehicular Environment (WAVE). To the best of our knowledge, most of the WAVE stack implementations and studies that are carried out till now are simulator based. This paper majorly focuses on the implementation of IEEE 1609 WAVE /DSRC stack on a Linux based system that forms the backbone of vehicular communication. It dives deep into the changes and the development of new modules that have to be made in Linux kernel to cater the need for vehicular communication. We also discuss in brief about the various challenges faced and design decisions that were made in this process. Finally, we conclude by depicting the performance of our developed stack in comparison with commercially available stack in terms of packet losses.

Wireless Access in Vehicular Environments (WAVE) protocol stack is the most important protocol used to allocate spectrum for vehicular communication. The capabilities of WAVE to provide reliable exchange of safety information are questionable. In a previous work, we suggested a system that employs cognitive networks principles to increase the spectrum allocated to the control channel (CCH) by the IEEE 802.11p amendment, where all safety information is transmitted. However, the decision making process implemented in that work does not differentiate between contention levels and does not relate precisely the measured contention to the amount of needed spectrum, which leads to an inefficient utilization of the white spectrum. In order to assign the minimum necessary additional bandwidth to relieve the contention, we suggest in this paper a new system that quantifies contention into multiple levels of severity based on Fuzzy Logic and maps additional spectrum correspondingly. Simulations show the effectiveness of the system in allocating the minimum needed bandwidth to relieve contention, without affecting other QoS parameters such as delay and number of untransmitted packets.

For the influence of Internet, 802.11 lacks the definition over the MAC (medium access control) layer, user-data are switched via upper protocols and the switching point is located in the network layer. This redundant architecture has shortcomings on efficiency and is not propitious to guarantee QoS (quality of service). In this paper, we propose a novel user-data switching mechanism in the lower layer, viz. the MAC layer in 802.11. This mechanism modifies the traditional finite state machine, the header format of user-data and the communication primitives of MAC layer to achieve the goal of reducing user-data plane. Our simulations show this user-data mechanism can better the relay efficiency and improve the QoS.

Dedicated short range communication (DSRC) is the key component in intelligent transportation systems (ITS). The goal of this technology is to help driver and passengers getting multimedia services via wireless communication equipment during the movement of vehicle, so as to improve the traffic safety and enhance the transportation efficiency. The paper is focus on the DSRC baseband technical analysis and the application development. Based on the WLAN 802.11a architecture, we develop a new adaptive channel estimation algorithm that uses two kinds of feedback tracking and pilot aid to enhance wireless access ability in vehicular environments.