Using wireless networking for vehicular

environment: IEEE 802.11a standard

performance

Janis Jansons, Arturs Barancevs

Department of Transport Electronics and Telematics

Riga Technical University

Riga, Latvia

janis.jansons_1@rtu.lv

Abstract - This paper present evaluation of wireless

networking based on IEEE 802.11a standard for use in a

vehicular environment. This standard is well-known and

widely used to provide indoor wireless communication for

stationary or slow moving users. Despite of this initial

application we analyzed this wireless communication

standard to understand basic performance and suitability

for Intelligent Transportation Systems (ITS) providing a

ubiquitous mobile INTERNET access. The experimental

results we acquired using National Chiao Tung

University- network simulator (NCTUns) -

simulation/emulation tool for evaluating the performance

of vehicle to infrastructure communication in variable

mobility scenarios.

Keywords-WLAN, IEE802.11a, NCTUns, vehicular

networking

I. INTRODUCTION

In the last decade a great efforts have been made to

provide Internet access in almost every place where it is

required. Different communication systems like WLAN,

WiMax, and GSM/UMTS provide wireless Internet access

for variety of applications. Mobile Internet access to every

day becomes more urgent and successful development of

mobile wireless technology increases the ability to create

high throughput and low cost networks for the user in-

motion. Providing ITS with stable wireless Internet

connection has become an attractive research field for many

years. Among the many technologies proposed for ITS,

wireless vehicular communication, covering vehicle-to-

vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-

to-person (V2P) communication, aims to increase drivers and

passengers comfort, road safety and transport efficiency and

provide ubiquitous wireless connectivity to the Internet. With

the assistances from these different means of communication,

driver and pedestrian can quickly obtain useful and/or

emergent traffic or entertainment information on the roads at

a low cost. For this reason, stable and reliable wireless

communication has become a very important technology for

developing ITS.

However the main task now is to choose the best

option of providing secure wireless communication and make

it usable in vehicular environments, because there appear

some meaningful difficulties. In vehicular environments users

are not static, they change velocity and there are also

numerous users which constantly change their location. In this

research we propose to look through the possibilities of using

some of the IEEE 802.11 wireless standards. We made

analyze to apply wireless networking standard IEEE 802.11a

for providing wireless networking connection in a vehicular

environment. Also we will explain why we prefer that option

over now among users so popular GSM/UMTS wireless

internet connections which can seem much more suitable for

outdoor [1].

In this paper, we use integrated simulation platform

NCTUns 6.0 to evaluate wireless technology, namely IEEE

802.11a wireless Local Area Network (WLAN). The 802.11a

WLAN allows data rates up to 54 Mbps while 802.11p is

designed especially for ITS for short message communication

and provides two times less throughput. To obtain results, we

analyzed the capabilities of these technologies in vehicle to

infrastructure scenario.

This paper constructs as follows: After the

introduction the problem in Section 1, Section 2 provides

some information about the related work. Then, Section 3

describes our research tasks. After then, in Section 4 and 5

presents some main future of the IEEE802.11a standard and

simulation tool accordingly. After demonstrating the

simulation results in Section 6, Section 7 summarizes this

paper.

II. RELAITED WORKS

Previous works that we used for this research lies

mostly in the fields of using of NCTUns software support in

advantages of easy modeling and simulating of plenty

various environments for commercial aims or education.

Also specific researches are made for vehicular networking,

V2I, V2V, C2I communications, IEEE802.11 in-motion and

others. Mostly they are made to improve the safety and keep

driver aware of conditions and situations [1][6][9-13].

From the side of researches about standards of IEEE

802.11 family, mostly the researches are made to describe,

test and estimate possibilities and advantages for using local

access points in local city objects, such as restaurants,

offices, public places and many others. For vehicular

environments and wide traffic objects more common is to

still use a GPS navigation system which can provide location

and time information and send short information

packages/messages. But it cannot provide permanent

connection to the network and internet. Anyway this is the

most investigated system for communication for vehicular

environments. As there is new IEEE 802.11p standard

specially for using in ITS there are first researches, for

example [4][7][13] specialized in describing benefits and

possibilities for this standard.

Our goal is to show possibilities and advantages of

IEEE 802.11a which is quite specific topic. Similar research

[11] evaluates realistic urban speeds and environments,

observing that performance at very low speeds is degraded

due to the presence of null zones. They vary the modulation

scheme and analyze the spread of resulting throughputs.

Gained results of research [11] have implications for

multimedia and other real-time applications that will utilize

vehicle-to-roadside connectivity.

The idea of using that standard is quite unusual and

there is good way to point out that it is also a good

opportunity to make less expensive traffic communication

systems. And as we are trying to prove good features of IEEE

802.11a then these systems can be much more accessible and

much easier to implement.

III. RESEARCH TASK

Main task of this research is to review standard

IEEE 802.11a points of view for its use in vehicular

environments. We will module road situations and present

test results using NCTUns simulation software. We have to

observe advantages and benefits of chosen WLAN between

other systems, for example WAVE. Also we are showing the

possibility of using standard IEEE 802.11a in road situations

instead of others and IEEE 802.11p. The most important

advantage that has the standard IEEE 802.11a is that it is

very outspread and popular, and it is possible to use almost

any device to connect to the access point using through this

standard. This standard is using lots of existing infrastructure.

We will make several experiments using this

standard and will test the throughput by changing speed of

vehicles and by changing the traffic from non-busy to busy.

Results will be evaluated and will calculate the goodput of

the standard and it will be visible which aspects are affecting

the systems goodput, stability and wireless data transfer rate

for our needs.

IV. IEEE 802.11A

The 802.11a standard uses the same core protocol as

the original standard and operates in 5 GHz band. 802.11a

uses a 52-subcarrier orthogonal frequency-division

multiplexing (OFDM) with a maximum raw data rate up to

54 Mbps, which more realistic achievable throughput is

around the mid-20 Mbps. The data rate can be reduced to 48,

36, 24, 18, 12, 9 then 6 Mbps if required. 802.11a originally

had 12/13 non-overlapping channels, 12 that can be used

indoor and 4/5 of the 12 that can be used in outdoor point to

point configurations. Recently many countries of the world

are allowing operation in the 5.47 to 5.725 GHz Band as a

secondary user using a sharing method derived in 802.11h.

This will add another 12/13 Channels to the overall 5 GHz

band enabling significant overall wireless network capacity

enabling the possibility of 24+ channels in some countries.

802.11a is not interoperable with 802.11b as they operate on

separate bands, except if using equipment that has a dual

band capability. Most enterprise class Access Points have

dual band capability.[2][3][5]

Using the 5 GHz band in 802.11a gives standard a

significant advantage, since the 2.4 GHz band is heavily used

until the point of being crowded. Degradation caused by such

conflicts can cause frequent dropped connections and

decreasing the quality of service. However, this frequency

also have a disadvantage: The effective overall range of

802.11a is slightly less than that of 802.11b/g; 802.11a

signals cannot penetrate as far as those for 802.11b because

they are absorbed more readily by walls and other solid

objects in their path and because the path loss in signal

strength is proportional to the square of the signal frequency.

On the other hand, OFDM has fundamental propagation

advantages when in a high multipath environment, such as an

indoor office, and the higher frequencies enable the building

of smaller antennas with higher RF system gain which

counteract the disadvantage of a higher band of operation.

The increased number of usable channels give 802.11a

significant aggregate bandwidth and reliability advantages

over other similar standards of this family[2][3][5].

Advantages that are more referable in Intelligent

Transportation Systems are popularity, ease to use and a low

systems price. The new standard 802.11p is now suited

especially for vehicular environment required to support

Intelligent Transportation Systems (ITS) applications. This

includes data exchange between high-speed vehicles and

between the vehicles and the roadside infrastructure in the

licensed ITS band of 5.9 GHz It has a twice less maximum

data rate than 802.11a – 27 Mbps although its working range

is up to 1000 meters. This standard is made to mostly provide

with short messages and broadcasting information, as in our

case we are trying to provide with stable connection to the

internet [4][7][8][13].

V. SIMULATION TOOL - NCTUNS

NCTUns uses a novel kernel-reentering simulation

methodology. As a result, NCTUns provides several unique

advantages that cannot be so easily achieved by traditional

network simulators.[8]

As the user manual says that NCTUns can provide

more realistic wireless physical modules that consider the

used modulation scheme, the used encoding/decoding

schemes, the received power level, the noise power level, the

fading effects, and the derived BER (Bit Error Rate) for

802.11(a), 802.11(b), 802.11(p), GPRS, 802.16(d) fixed

WiMAX, 802.16(e) mobile WiMAX, 802.16(j) relay

WiMAX, and DVB-RCST satellite networks. These

advanced physical-layer modules can generate more realistic

results but at the cost of more CPU time required finishing a

simulation. Depending on the requirements of simulation

speed and result precision, a user can choose possibilities to

use the basic physical-layer modules or the advanced

physical-layer modules.[8]

Manual claims that NCTUns can simulate various

protocols such as IEEE 802.3 CSMA/CD MAC, IEEE

802.11 (a)(b)(e)(p) CSMA/CA MAC, the learning bridge

protocol used by switches, the spanning tree protocol used by

switches, IP, Mobile IP, RIP, OSPF, UDP, TCP, HTTP, FTP,

Telnet, etc. It simulates the DiffServ QoS protocol suite, the

optical light-path setup protocol, the RTP/RTCP/SDP

protocol suite. It simulates the IEEE 802.16(d)(e)(j) WiMAX

PMP protocol suites and the 802.16(d) mesh mode protocol

suite. It simulates the DVBRCST protocol suite.[8]

NCTUns runs on Linux. NCTUns software provides

a highly-integrated and professional GUI environment.

NCTUns users can easily draw, conduct and test different

kinds of network simulations and also evaluate gained

results. The NCTUns GUI program is capable of:

• Drawing network topologies

• Configuring the protocol modules used inside a node 3

• Configuring the parameter values used inside a protocol

module

• Specifying the initial locations and moving paths of mobile

nodes

• Plotting network performance graphs

• Playing back the animation of a logged packet transfer trace

• Pasting a map graph on the background of the network

topology

• Constructing a road network for wireless vehicular network

simulations

• More ...[8]

VI. TESTS AND EXPERIMENTAL RESULTS

A: description

In the beginning we have to draw our topology

which is going to be as a simple situation where we will try

to pass access point with one client. We will choose speed

and client will go through the access points zone. Our

topology will consist of Host, 802.11a access point and a

802.11a (infrastructure mode) client. Host and access point is

connected by point-to-point link. But client is connected to

access point by wireless node. To packet transfer could

become possible all clients and access point have to be in one

subnet. We can start our tests only when client and access

point are in one subnet and ip addresses are generated. Our

access points range is 200 meters. For our tests client have to

go through the zone where data transfer is possible, that is

400 meters. Speed of moving client (considered as vehicle)

will be 20, 50, 70, 100 kmph. Wireless speed is 54Mbps as a

maximum of standard 802.11a. Our tests results will be

evaluated by sending UDP pockets from client to host trough

the access point. Number of clients will be increased still

having only one access point which will have to process

incoming packets. Size of the packets is 1500 bytes, which is

largest possible, but its variable. Host will receive these

packets and it will be possible to evaluate the throughput and

goodput, which in our case is more important measurement.

Each of client machines and host need to have sending and

receiving protocols generators, for packets to be generated,

send and received. We will use rtg protocol for receiving and

stg for sending. Using these protocols will increase packet

loss ratio, because packets sending option is not depending

on any outside aspects. This protocol doesn’t wait for

delivery confirmation and just send next packets. Sent and

received packet count will be different and we will rely our

measurements on received packet count. A little shortage of

NCTUns modeling is that it does not have a Rate Adaption

Algorithm so throughput will not be impacted by distance

between access point and client as long as the client is in

zone of accessibility.

B: Creating the topology

NCTUns software has four working modes: Draw

Topology, Edit Property, Run Simulation, Play Back. In first

mode we choose Host, 802.11(a) access point and 802.11(a)

mobile node (infrastructure mode) from toolbar. We connect

Host and access point using point-to-point connection.

Clients are connected to access point using wireless nodes

from toolbar. Also in their mode is important to set up the

moving path of clients and define moving speeds. When we

change to Edit Property mode NCTUns is forming a subnet

for access point and mobile nodes. Then IP addresses are

formed for Host and clients. As we know the addresses we

can now insert a packet generator for sending UDP packets.

It is made by adding an application to mobile station. In

command window we define the protocol that we use, packet

size, traffic length, mode, options, and receiver’s ip address.

In our case we send UDP packets with size 1500 bytes per

amount of time which have to be enough to enter and cross

the access zone. As the IP addresses are generated we need

to define host address where packets will be sent. Generator

is also made for Host. Host will just use rtg and receive any

size of packets and from any client. We use Node Editor to

interact on different layers. We set up our data rate to

maximum possible in 802.11a that is 54Mbps in every

mobile node and also in access point. Also here we choose

data which we want to inspect after simulation. In our case

we will depend on outgoing and incoming packets as results

for our test. We determine wireless node connectivity by

distance which range will be 200 meters. That makes

working zone to cross 400 meters. By running the simulation

we will receive modulated data and access them in play back

mode using Plot Graph from control panel. In Play Back

mode is also possible to view visually how data transfer is

managed when clients are passing the access point.

C: Goodput

The main measurement for those tests will be

goodput. We will calculate it using number of received

packets in second, packet size, and amount of time when

these packets was received. In that way the object of our

research will be average amount of received data depending

on clients moving speed and number of connected clients.

D: Test results

We started the tests by simplest topology with only

one client. Moving speed was changing from 20 kmph up to

90 kmph. As we assumed from theoretical approach

difference between sent and received amount of data is quite

large. The main reason for that is specifies of stg. As we are

measuring from received packets in our case the big data loss

is not so important. In Figure 1 we can see difference

between sent and received amount of packets in time, which

is necessary to go through the access zone. Our subject is one

client moving with speed 20 kmph.

Figure 1. Number of sent and received packets in amount of time.

Further in our calculations we use only received

packets data, so results would be more „lifelike”.

We tested topology with one client moving with 20,

50, 70 and 90 kilometers per hour. We see that peak number

of received packets is similar in all simulations. Main value

that is changing is time which client spends in access zone,

where it can send packets. As faster the client moves into a

zone, the slower it should reach the peak of possible number

of packets to send. In our simulations we see that it takes 2

seconds to reach peak point with every speed. The reason

why goodput is decreasing is that using higher speed client

spends less time in access zone. Less time in access zone

means that client has to switch access points more often and

every time client has to lose goodput to reach peak with the

next access point.

In Figure 2 we can see that by increasing moving

speed from 20 kmph up to 90 kmph our goodput is

decreasing from 14.3 Mbps to 12.1 Mbps. We have to point

out that now only one client is connected. As we know that

our data rate is 54 Mbps there is visible how this number is

decreased and what is rate that is possible to use in this kind

of situation.

Figure 2. Goodput with one client

When we added more clients goodput decreased

even more, so we can see that number of clients is also

important for data rate. In next figure 3 we see goodput

depending on number of accessed clients in different speed

situations from 20 kmph to 90 kmph. We have to point out

that this goodput is what host can provide to receive packets,

but this amount is going to split for every user. If goodput is

not decreasing so meaningfully for incoming packets for

host, it is decreasing more rapidly for every user when new

user gets access to the subnet. So we can say that amount of

data what host can process is divided for every client.

Figure 3. Goodput depending on number of clients

In our tests when we tried to increase the number of

accessed clients we found out that it is hard to provide good

data throughput for more than 5 clients at the same time.

When we try to ad 6 and more clients to the subnet access

became unstable and clients could send packets only

periodically with gapes between sending sessions. Also this

big amount cause some small gapes in traffic when no

packets was received from none of the users. In figure 4 we

can see how unstable is packet sending for each of the six

users when they are moving with speed 20 kmph.

Figure 4. Sent packets

It is hard to provide the same conditions for each

client. And as clients are moving faster as harder is to send

something and access is shaking more. From that we can

observe that there is this limit which can one access point

provide. More than five clients can’t get stable and usable

wireless internet connection.

CONCLUSION

From our test results we can see that it is possible to

use 802.11a standard in vehicular environments to provide

stable wireless internet connection with average goodput over

10 Mbps with a condition that one access point holds not

more than five clients. If number of clients increases it is still

possible to send broadcasting information and shorter

messages about traffic, safety or advertisement. Experimental

results showed that goodput is not so related to speed of the

client and network is till stable even if it is moving with 90

kmph and more. When more than 6 clients are trying to

access and they are moving from different sides and with

different speeds, still some of the clients can get almost good

data rate, but in just some cases. For example if they are

closest to the access point, but the system how priorities are

distributed is not so clear. Similar research [11] was also

based on sending UDP packets with throughput rates 10 and

30 Mbps, and 7 and 45 kmph speeds. Their gained results

show that even with two clients moving towards each other

signal strength is not so stable all time period while they are

in access point’s zone. The main observation which is similar

to ours is that moving with greater speed leaves less time in

access point’s zones so decreases useful connections

percentage. The main difficulty is switching to another access

point, because that makes drop throughput and reach its peak

point many times while moving. Even harder is to keep stable

connection when there are more users with different moving

speeds and directions. It is hard to analyze which will get

connection good enough and who will just be able to

exchange with broadcasting information or nothing.

REFERENCE

[1] P. Mähönen, J. Riihijärvi, M. Petrova, and Z. Shelby, „Hop-by-Hop

Toward Future Mobile Broadband IP,” IEEE Communications Magazine,

March 2004, pp.138-146.

[2] International IEEE 802.11 working group project timeline

http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm

[3] IEEE Standarts Association, „802.11a”, 1999.

[4] M. Weigle, „Standarts: WAVE/DSRC/802/11p,” Old Dominion

University, 2008.

[5] National Instruments „WLAN - 802.11 a,b,g and n,” Apr 11, 2008.

[6] Motion Mobility Services „Designing WLAN (802.11) to Support Tablet

PC Mobility,” 2007.

[7] V. P. Harigovindan, A. V Babu, L. Jacob, „Ensuring fair access in IEEE 802.11p – based vehicle-to-infrastructure networks,” EURASIP Journal on

Wireless Communications and Networking 2012:168, 2012.

[8] S.-Y. Wang, C-L. Chou, and C.-C. Lin „The GUI User Manual for the

NCTUns 6.0 Network Simulator and Emulator,” 2009.

[9] H. Yuan, Y. Ling, H. Sun , W. Chen, „Research on channel estimation

for OFDM receiver based on IEEE 802.11a,” Industrial Informatics, 2008. [10] R. Gass, J. Scott, C. D. Thomson, „Measurements of In-Motion 802.11

Networking,” 7th IEEE Workshop on Mobile Computing Systems and

Application, 2006. [11] D. N. Cottingham, I. J. Wassell, R. K. Harle, „Performance of IEEE

802.11a in Vehicular Contexts,” Vehicular Technology Conference, 2007.

VTC2007-Spring. IEEE 65th, pp.854-858. [12] A. Acharya, A. Misara, and S. Bansal, „High-Performance

Architectures for IP-Based Multihop 802.11 Networks,” IEEE Wireless

Commun., Oct. 2003, pp. 22–28. [13] Rohde & Schwarz „WLAN 802.11p Measurements for Vehicle to

Vehicle (V2V) DSRC,” 2009.