Rayleigh fading通道下VANETs饱和吞吐量分析

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本文是一篇研究论文，针对"Vehicular Ad Hoc Networks (VANETs)"的饱和吞吐量分析在Rayleigh fading无线信道条件下的应用。作者是Wuwen Lai、Ning Guan、Han Liu和Hua Wang，他们均来自北京理工大学信息与电子学院。论文发表于2017年的第17届IEEE国际通信技术会议。在传统的VANETs性能评估中，特别是通过马尔科夫链模型，往往忽略了无线通信环境（如Rayleigh fading）对介质访问控制(Medium Access Control, MAC)操作的影响，以及车辆速度这一重要因素。然而，这些因素对于在高速移动环境中传播信息娱乐服务的网络性能至关重要。因此，论文的主要贡献在于提出了一种改进的马尔科夫链模型，该模型综合考虑了无线信道条件和车辆速度，以更精确地计算传输概率。通过这种改进的模型，作者能够对饱和吞吐量进行评估，它反映了在MAC操作、无线环境和车辆动态条件下的系统极限性能。相比于基础模型，新模型能够同时考虑这三个关键因素，从而提供更为准确的评估结果。因此，关键词包括VANETs、性能分析、MAC操作和无线信道模型，这表明该研究旨在提升对VANETs在实际复杂环境下通信能力的理解和预测。这篇论文对VANETs的优化设计具有重要意义，它扩展了现有理论，为如何在动态变化的无线环境中提高VANETs的效率和可靠性提供了新的见解。这对于未来VANETs的设计者和研究人员来说，无疑是一个有价值的工具，有助于提升网络的整体性能和用户体验。

176

2017 17th IEEE International Conference on Communication Technology

Saturated Throughput Analysis of Vehicular Ad Hoc Networks over Rayleigh-

Fading Channels

Wuwen Lai, Ning Guan, Han Liu, Hua Wang

School of Information and Electronics

Beijing Institute of Technology

Beijing, China

e-mail: {laiwuwen2013, guanning, 3120140335, wanghua}@bit.edu.cn

Abstract—Throughput is a key network performance for

disseminating infotainment services in Vehicular Ad Hoc

Networks (VANETs). However, when throughput is analyzed

by Markov chain, wireless channel conditions and vehicle

speed are not taken into account in modeling Medium Access

Control (MAC) operations. In this paper, we propose an

improved Markov chain model combining the above two

factors to calculate the transmission probability. The saturated

throughput is evaluated with considering MAC operations,

wireless channel conditions, and vehicle speed. Compared with

the basic model, our proposed model can accurately evaluate

the saturation throughput with consideration of the

aforementioned three factors simultaneously.

Keywords-VANETs; performance analysis; Markov chain;

Rayleigh fading

NTRODUCTION

In recent years, Vehicular Ad Hoc Networks (VANETs)

are experiencing a rapid development due to many emerging

applications in Intelligent Transportation System (ITS).

Safety applications, traffic efficiency enhancements and

information/entertainment (infotainment) services are three

kinds of emerging applications in VANETs. Distributed

Coordination Function (DCF) known as Carrier Sense

Multiple Access with Collision Avoidance (CSMA/CA)

protocol is adopted in IEEE 802.11p [1]. VANETs have

some unique characteristics: high mobility, fast changing

density, and unstable topology. Network communication

may become unstable due to these characteristics. Cluster-

based methods appear to be promising approaches to fix the

aforementioned problems, because nearby vehicles in the

same direction can be formed a cluster providing relatively a

stable unit for communication [2], [3].

Most works have focused on safety applications in

VANETs, which are aimed at avoiding the risk of car

accidents. Markov chain models usually are introduced to

analyze and evaluate network performances in disseminating

safety-related messages. Lately the focus in VANETs

research also turns to non-safety applications [4], especially

infotainment services. The combination of information and

entertainment services is called infotainment services, which

can enhance in-car users’ experience. Infotainment services

are more throughput-sensitive rather than delay-sensitive.

Throughput is a key performance metric to measure the

system effectiveness. In Bianchi seminal paper, a two-

dimensional Markov chain was proposed to estimate

saturated throughput for unicast transmission [5]. According

to Bianchi model, many improved Markov chain models

have been developed to discuss saturated or unsaturated

conditions. All models in [6]-[9] assumed that wireless

channel conditions in Physical layer (PHY) are ideal.

However, wireless channel quality has a significant impact

on throughput. Enhanced Markov chain models [10], [11]

have been designed with consideration a constant frame error

probability, but the constant frame error probability cannot

reflect the influence of detailed channel parameters (such as:

path loss exponent, the distance between sender and receiver,

and transmit power) on network performances. Some

analytical models were proposed with considering the effect

of detailed channel parameters on network performances in

[12], [13]. However, the transmission probabilities calculated

by Markov chain models still ignore channel quality.

In this paper, an analytical model is proposed to estimate

saturated throughput for basic access model in a cluster

considering both wireless channel conditions and MAC

operations. In this model, the transmission probability is

calculated with the wireless channel parameters. In addition,

the vehicle speed is also taken into account when calculating

the transmission probability, because vehicle mobility is an

important characteristic in VANETs. Extensive simulations

show that the proposed model is capable of accurately

depicting saturation throughput.

The rest of this paper is organized as follows. In Section

II, related work is described. In section III, System model

and throughput analysis are presented. In section IV,

simulation and numerical results are given. Finally,

conclusions are drawn in section V.

II.

ELATED

ORK

Dedicated Short-Range Communications (DSRC) has

become the standard for Vehicle-to-Vehicle (V2V)

communication, Vehicle-to-Infrastructure (V2I)

communication and hybrid communication. The DSRC

standard, also known as IEEE 802.11p, uses a 5.9 GHz

licensed spectrum. The MAC layer of IEEE 802.11p adopts

CSMA/CA mechanism. Markov chain has been used to

model the back-off procedure of CSMA/CA in many works.

Assuming ideal channel conditions and finite number of

terminals, an analytical model based on two-dimensional

Markov chain was developed to evaluate saturated

throughput both in basic access and Request-to-Send/Clear-

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