An efficient TDMA-based variable interval multichannel MAC protocol for vehicular networks

Vehicular Adhoc NETworks (VANETs) are the key to the future of intelligent transportation systems. An efficient MAC protocol is of greater importance to meet the strict deadlines of safety related applications in VANETs. This work introduces a novel TDMA-based variable interval multichannel MAC protocol (TM-MAC) for VANETs. TM-MAC employs TDMA along with variable interval multichannel scheduling for providing a reliable and efficient broadcast service over a lossy wireless medium. TM-MAC reduces transmission collisions thus making Control CHannel (CCH) more reliable and provides high throughput over Service CHannel (SCH) via maximum channel utilization. The scheduling strategy ensures that vehicles are assigned a slot instantaneously. Moreover there is a reduction of almost 50 % in number of vehicles incurring merging collisions when compared with VeMAC (Omar et al. in IEEE Trans Mob Comput 12(9):1724–1736, 2013), an existing and recently proposed TDMA based MAC protocol. This reduction in merging collisions increased the packet delivery ratio by almost 25 % when compared with VeMAC. Extensive simulations which were done over a realistic city scenario connote the superiority of TM-MAC over existing schemes for a wide range of traffic conditions.     

A bandwidth-efficient and fair CSMA/TDMA based multichannel MAC scheme for V2V communications

Designing QoS-aware medium access control (MAC) scheme is a challenging issue in vehicular ad hoc networks. Proportional fairness and bandwidth utilization are among the significant requirements that should be taken into account by a MAC scheme. In this paper, a bandwidth-efficient and fair multichannel MAC protocol is proposed to address these two requirements, specifically in vehicle-to-vehicle communications. The proposed scheme is based on clustering of vehicles and exploits time division multiple access (TDMA) method alongside the carrier sense multiple access with collision avoidance mechanism to allocate DSRC-based resources in a different manner from IEEE 802.11p/IEEE 1609.4 protocols. It divides each channel into aligned dynamic-sized time frames. In each time frame, in a fully TDMA-based period, transmission opportunities are assigned to vehicles letting them have dedicated transmissions on the service and control channels. The maximum number of transmission opportunities per each frame is determined by the cluster head (CH) based on a defined optimization problem which aims at maximizing both proportional fairness and bandwidth utilization. Furthermore, the bandwidth utilization is assumed to be enhanced more through reallocation of unused transmission opportunities in each time frame, using a proposed reallocation algorithm. The proposed MAC protocol is treated as a lightweight scheme such that various types of unicast, multicast and broadcast communications are possible within the cluster without involving the CH. Evaluation results show that the proposed scheme has more than 90 % achievement in terms of proportional fairness and bandwidth utilization simultaneously, and in this case, has a considerable superiority over TC-MAC. In addition, using the proposed scheme, the satisfaction level of vehicles is preserved appropriately.     

Performance modeling and analysis of the ADHOC MAC protocol for vehicular networks

The ADHOC MAC protocol is a classical MAC protocol for supporting reliable broadcast services in vehicular ad hoc networks (VANETs). This paper develops an analytical model for analyzing the access performance of the ADHOC MAC protocol. A Markov chain is first constructed to describe the number of vehicles which have acquired a timeslot successfully at the end of a frame when using the ADHOC MAC protocol. Based on the Markov model, an analytical model is then derived to describe the relationship between the frame length and the channel utilization. Based on the derived analytical model, an optimal frame length that maximizes the channel utilization is further obtained. Simulation experiments are conducted to verify the effectiveness of the analytical model.     

采用TDMA和CSMA混合MAC协议的时隙调整算法

由于车联网(VANET)拓扑动态变化,车辆高速移动以及不同服务质量要求,制定媒体接入控制(MAC)协议面临巨大挑战。在控制信道间隔内采用基于TDMA和CSMA的混合接入协议是最有效的MAC协议之一。基于TDMA和CSMA的混合MAC协议(T-C-MAC)能够依据车辆环境调整TDMA帧长度,并能有效地传输非安全消息。为了提高T-C-MAC协议的性能,提出了一种基于三跳邻居信息的时隙调整(THSA) 算法。通过有效地调整车辆传输时隙,基于THSA的MAC（THSA-MAC）协议能够有效地实施广播服务,提高了安全消息传输率。实验数据表明,THSA-MAC有效地提高了安全消息传递率。     

一种高效低时延的宽带电力线通信网多跳MAC协议

针对IEEE1901.1宽带电力线通信媒体接入控制(Medium Access Control,MAC)协议涉及到信标时隙利用不充分和控制开销过大等问题,提出了一种高效低时延的宽带电力线通信网多跳MAC协议(Efficient and Low Delay Multi-hop MAC,ELDM-MAC).采用基于节点层级号的信标时隙分配机制,根据邻居表和时隙分配信息计算能够提前进入到载波监听多路访问时隙(Carrier Sense Multiple Access,CSMA)的时间,减少了信标时隙的浪费,提高了信道利用率;同时采用基于拓扑信息的信标帧高效广播机制,删除不大于自身层级号的节点和大于且在两跳范围内的非子孙节点的时隙分配信息,降低了网络控制开销.仿真结果表明,ELDM-MAC协议在信道利用率、平均时延和控制开销等方面都优于IEEE1901.1 MAC协议,更适用于宽带电力线通信网络的实际应用场景.     

Performance Analysis for a New Medium Access Control Protocol in Wireless LANs

One fundamental issue in high-speed wireless local area networks (LANs) is to develop efficient medium access control (MAC) protocols. In this paper, we focus on the performance improvement in both MAC layer and transport layer by using a novel medium access control protocol for high-speed wireless LANs deploying carrier sense multiple access/collision avoidance (CSMA/CA). We first present a recently proposed distributed contention-based MAC protocol utilizing a Fast Collision Resolution (FCR) algorithm and show that the proposed FCR algorithm provides high throughput and low latency while improving the fairness performance. The performance of the FCR algorithm is compared with that of the IEEE 802.11 MAC algorithm via extensive simulation studies on both MAC layer and transport layer. The results show that the FCR algorithm achieves a significantly higher efficiency than the IEEE 802.11 MAC and can significantly improve transport layer performance.     

Saturation throughput analysis of a carrier sensing based MU-MIMO MAC protocol in a WLAN under fading and shadowing

In wireless local area networks (WLANs), the traditional carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol cannot use the full benefits from multiuser multiple-input multiple-output (MU-MIMO) technique due to random medium access of the users. In this paper, we propose a carrier sensing based MAC protocol for a MU-MIMO based WLAN with full utilization of MU-MIMO technique. By modeling the WLAN system under the proposed MAC protocol as a discrete time Markov chain, we develop an analytical model for computing the saturation throughput in presence of path loss, Rayleigh fading and log-normal shadowing. The analytical model is then validated via simulation. By means of numerical and simulation results, we demonstrate that the proposed MAC protocol significantly improves throughput performance than the traditional CSMA/CA MAC protocol. Further, we compare the performance of the proposed MAC protocol with a MU-MIMO MAC protocol called Uni-MUMAC protocol and find that the proposed MAC protocol performs better than the Uni-MUMAC protocol. We also explore the effect of some of the network and wireless channel parameters on the performance of the proposed MAC protocol.

     

RSU-coordinated multichannel MAC protocol in vehicular ad hoc network

A road side unit (RSU)-coordinated multichannel media access control (MAC) (RMM) protocol was proposed in vehicular ad hoc network,which aimed to improve the transmission efficiency of non-safety messages.Under the coordination of RSU,nodes had more opportunities to make SCH reservations on control channel,and the contention-free message transmissions were thus realized.The proposed RMM protocol could use the service channel during the whole synchronization interval for non-safety message transmissions,and thus the saturated network throughput and channel utilization were improved,and the transmission delay was reduced.Compared with other existing protocols,extensive analysis and simulation results demonstrate the superiority of the RMM protocol.     

Variable Beam Width Selection for Improving the Throughput of IEEE 802.11ad Wireless LAN in the Contention Based Access Period

The hybrid MAC protocol specified by IEEE 802.11ad for millimeter wave wireless LANs consist of carrier sense multiple access/collision avoidance (CSMA/CA) during the contention based access periods (CBAPs) and TDMA during the service periods. To provide channel access during CBAP, the coverage area around the access point (AP) can be divided into several quasi omni (QO) beam levels. When uplink channel access during CBAP is considered, every directional multigigabit station residing within a QO level uses CSMA/CA protocol for getting the transmission opportunity. With equal beam width receive QO levels at the AP, we present an analytical model to compute the uplink throughput of the network in the CBAP, by closely following the 802.11ad MAC protocol specifications. We demonstrate that PHY layer MCS (modulation and coding scheme) dependent adaptive selection of QO levels can improve the throughput performance. In the second part of the paper, we consider that PCP/AP can have at most three radios, each tuned to operate in non-overlapping frequency bands as specified by 802.11ad PHY. We establish that such an arrangement can lead to concurrent transmissions in the network and improve the uplink throughput performance.     

Mobility impact in IEEE 802.11p infrastructureless vehicular networks

Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. In this paper, we provide a comprehensive evaluation of mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay. An unfairness problem due to the relative speed is identified for both broadcast and unicast scenarios. We propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. The first scheme provides dynamic level of service priority via adaptation to the number of neighboring nodes, while the second scheme provides service priority based on node relative speed. Extensive simulation results demonstrate a significant impact of mobility on the IEEE 802.11p MAC performance, the unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.     

面向应用的车载自组织网络跨层多信道MAC协议

提出了一种面向应用的车载网络跨层多信道MAC协议。对来自应用层不同类型的消息进行实时统计,预测出最优控制信道周期,确保控制信道上安全消息的及时、可靠传输,同时采用预约机制实现消息在服务信道上的无竞争传输,提高服务信道的吞吐量。本协议适合饱和与非饱和的一般VANET环境,具有较低的计算复杂度,扩展性较好。与现存的其他协议相比较,仿真结果证实了所提协议的优越性。     

Model-based admission control for IEEE 802.11e enhanced distributed channel access

IEEE 802.11e enhanced distributed channel access (EDCA) is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this paper, a model-based admission control (MBAC) scheme that performs real-timely at medium access control (MAC) layer is proposed for the decision of accepting or rejecting requests for adding traffic streams to an IEEE 802.11e EDCA wireless local area network (WLAN). The admission control strategy is implemented in access point (AP), which employs collision probability and access delay measures from active flows to estimate throughput and packet delay of each traffic class by the proposed unsaturation analytical model. Simulation results prove accuracy of the proposed analytical model and effectiveness of MBAC scheme.     

Vehicle density based multihop broadcast protocol in VANET

In vehicular ad hoc networks (VANET), the medium access control (MAC) protocol was of crucial importance to provide time-critical multihop broadcast. Contemporary multihop broadcast protocols in VANET usually choose the farthest node in broadcast range as the forwarder to reduce the number of forwarding hops. However, it was demonstrated that the farthest forwarder may experience long contention delay in case of high vehicle density. An IEEE 802.11p-based multihop broadcast protocol vehicle density based forwarding (VDF) was proposed, which adaptively chose the forwarder according to the vehicle density. The evaluation results in safety warning and online game applications show that, VDF could shorten broadcast delay by achieving the proper trade-off between the contention delay and coverage speed.     

多信道车载网中基于时分多址的MAC改进算法

车载网(VANETs)需提供时延敏感的安全应用和非安全应用的通信服务.这就使得媒体接入控制(MAC)协议既要满足安全消息的时延和可靠率,又要保证非安全消息的服务信道利用率,给MAC的设计提出了挑战.为此,提出基于时分多址的MAC改进算法(I-TDMA-MAC).I-TDMA-MAC算法在每个同步帧内给每辆车分配两个子时隙,旨在提高无碰撞信道接入率和安全消息的传递率.同时,对空闲时隙采取重分配策略,并基于最短作业优先准则(SJF)给空闲时隙设置优先级,旨在提高服务信道利用率.仿真结果表明,提出的I-TDMA-MAC算法的安全消息传递率高达99%,当车流密度到达100 vehicle/km时,服务信道利用率接近于90%.     

Performance analysis of the IEEE 802.11 distributed coordinationfunction

The IEEE has standardized the 802.11 protocol for wireless local area networks. The primary medium access control (MAC) technique of 802.11 is called the distributed coordination function (DCF). The DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. In addition, it also applies to a combination of the two schemes, in which packets longer than a given threshold are transmitted according to the RTS/CTS mechanism. By means of the proposed model, we provide an extensive throughput performance evaluation of both access mechanisms of the 802.11 protocol     

Performance Analysis of Directional CSMA/CA for IEEE 802.15.3c under Saturation Environments

In this paper, the directional carrier sense multiple access/collision avoidance (CSMA/CA) protocol in the immediate acknowledgement mode for IEEE 802.15.3c is analyzed under saturation environments. For the analysis, a sensing region and an exclusive region with a directional antenna are computed probabilistically and a Markov chain model in which the features of IEEE 802.15.3c and the effects of using directional antennas are incorporated is analyzed. An algorithm to find the maximal number of concurrently transmittable frames is proposed. The system throughput and the average transmission delay are obtained in closed forms. The numerical results show the impact of directional antennas on the CSMA/CA media access control (MAC) protocol. For instance, the throughput with a small beamwidth of antenna is more than ten times larger than that for an omnidirectional antenna. The overall analysis is verified by a simulation. The obtained results will be helpful in developing an MAC protocol for enhancing the performance of mmWave wireless personal area networks.     

1-persistent DUAL channel local area network for integrated voice and data application

It is a well-known fact that the carrier sense multiple access with collission detection (CSMA/CD) protocol would suffer from throughput degradations and long packet delays at heavy loads due to excessive collisions and retransmissions, and thus is not suitable for voice/data integration. Recently, a new protocol called carrier sense multiple access with time-split collision detection and split channel reservation (CSMA-TCD-SCR) has been proposed¹ to improve the channel throughput of CSMA/CD protocol by splitting the common channel into dual channels, i.e. one for data transfer and the other for reservation. It has been shown that the CSMA-TCD-SCR protocol improves the channel throughput and stability performance significantly.¹ In this paper, we propose a 1-persistent dual-channel LAN (1P-DC-LAN) protocol with the tree algorithm for reservation, which is an extension of the CSMA-TCD-SCR protocol, for voice/data integration applications. Through approximate analytical modelling and computer simulations, it has been demonstrated that the 1P-DC-LAN protocol exhibits nearperfect scheduling throughputs for data transmission and highly bounded voice packet delays. In addition, the results were compared with IEEE 802.3 CSMA/CD and twin-channel CSMA/CD.     

Analytical modeling of bidirectional multi‐channel IEEE 802.11 MAC protocols

This paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd.     

Reservation CSMA/CD: a multiple access protocol for LAN's

A multiple-access protocol for local area networks is described. It is basically a hybrid of carrier-sense multiple access with collision detection (CSMA/CD) and the broadcast recognizing access method (BRAM). CSMA/CD, which is contention-based, works well under light traffic, but message collisions degrade system performance when the channel becomes heavily loaded. BRAM, which is collision-free, has no longer delays at low load, but its efficiency improves as the load increases. Performance models are developed for the hybrid protocol and for the Ethernet protocol, a proven commercial implementation of CSMA/CD-type protocols. It is found that the hybrid protocol gives better performance for a wide range of scenarios     

Impact of MAC frame length on energy efficiency in 6LowPAN

To reach necessary end-to-end connectivity between the Internet and wireless sensor networks （WSNs）, the Internet Engineering Task Force （IETF） IPv6 over low power wireless personal area network （6LowPAN） working group has been established and introduced an adaptation layer for integration of IEEE 802.15.4 physical layer/media access control （PHY/MAC） layers and the upper layers of any Intemet protocol （IP）-based networks, such as the Internet. The energy efficiency is one of the most important performance measures in WSNs because most sensor nodes are only battery powered so we should reduce the energy consumption to the lowest to extend the life of nodes. Therefore the determination of MAC frame length should be carefully considered since that the radio frequency （RF） module consumes most the energy of a sensor node meanwhile the MAC protocol is the direct controller of RF module. In this paper, we provide a star-shaped 6LowPAN non-beacon mode with unslotted carrier sense multiple access with collision avoidance （CSMA/CA） mechanism to access to the channel and model the stochastic behavior of a target end node as the M/G/1 queuing system. Analytical expressions for some parameters such as channel busy probability, packet loss probability and energy efficiency are obtained in this paper and our analytical results can clearly show the impact of MAC frame length on the energy efficiency of a target node in both ideal and lossy channel.