IEEE 802.11 Systems in the Automotive Domain: Challenges and

Solutions

Alaa Mourad

, Mohamad Omar Al Kalaa

, Hazem Refai

and Peter Adam Hoeher

BMW AG, Munich, Germany

Electrical and Computer Engineering, University of Oklahoma, Tulsa, OK, U.S.A.

Information and Coding Theory Lab, University of Kiel, Kiel, Germany

Keywords:

Infotainment, WLAN, Wireless Coexistence, Automotive Domain, 2.4 GHz ISM Band, Intra-vehicle

Interference, IEEE 802.11, Wi-ﬁ.

Abstract:

Customer demand for infotainment systems has garnered great attention from car manufacturers. System fea-

tures have become a decisive factor when choosing among car models. As consumers become more dependent

on their portable electronic devices (e.g., mobile phones, tablets), they expect to have seamless integration of

their devices inside their cars. This allows them to use the same features supported by their phones in the cars.

Car manufacturers aim to make their infotainment systems user-friendly. A key factor to achieve this goal is

facilitating a wireless connection between mobile phones and car computers. IEEE 802.11 systems are the

most popular candidate to provide high data rate connections utilizing the unlicensed industrial, scientiﬁc and

medical (ISM) radio band. However, due to the limited available spectrum and the high density of devices

inside the car, the achieved throughput could be strongly affected by interference and coexistence challenges.

Furthermore, strong interference between the networks in different cars plays a crucial role in the automotive

domain. This paper highlights the interference problem between IEEE 802.11 systems in cars. Two solu-

tions in the 802.11n standard, namely transmission power control (TPC) and multiple input multiple output

(MIMO) techniques, are discussed. Results show that both techniques could improve system performance.

Transmission power control is essential to control radiation to surrounding environment.

1 INTRODUCTION

Car infotainments systems have improved dramati-

cally in the past years. Changes have been driven by

customer demand to stay connected and to enjoy var-

ious applications in their cars. Infotainments systems

have attracted the interest of big technology compa-

nies like Google and Apple, and both companies have

developed new platforms for cars–Android Auto and

CarPlay, respectively. This innovation is expected to

lead to growth of connected cars. This growth is not

unlike the transition of cell phone use for calling and

texting to their widespread use of innovative func-

tions.

The number of accidents related to cell phone

use while driving has increased dramatically in recent

years. According to a study from the National Safety

Council in the USA (National Safety Council, 2013),

nearly 26 percent of all crashes involve drivers talk-

ing and texting on cell phones. One key advantage

of new infotainment systems is that seamless integra-

tion of new functions utilizing wireless connections is

expected to reduce the number of accidents resulting

from cell phone use while driving.

A number of wireless systems have rapidly mi-

grated into the automotive industry in recent years as

a part of infotainment systems. WLAN

, Bluetooth

and Kleer (Kleer, 2007) are among the most widely

used in the 2.4 GHz ISM band. Bluetooth is used

mainly for hands-free calling and music streaming,

while Kleer is used for high quality music stream-

ing. WLANs are used to provide Internet connec-

tivity for vehicle passengers using a shared connec-

tion to cellular networks. The WLAN use in cars is

not restricted to Hotspots, several applications rely

on WLAN–like screen mirroring using Wi-Fi direct

Notably, Android auto and CarPlay functions will use

WLAN, Wi-Fi and 802.11 will be used interchangeably

in this paper

It was standardized by IEEE as 802.15.1, now it is man-

aged by Bluetooth special interest group (SIG)

Called also Wi-Fi P2P

Mourad, A., Kalaa, M., Refai, H. and Hoeher, P.

IEEE 802.11 Systems in the Automotive Domain: Challenges and Solutions.

DOI: 10.5220/0006232700410051

In Proceedings of the 3rd International Conference on Vehicle Technology and Intelligent Transport Systems (VEHITS 2017), pages 41-51

ISBN: 978-989-758-242-4

Wi-Fi direct to enable wireless connection between

cell phones and car computers. This feature makes

them more user-friendly by alleviating the need for

wired connection (e.g., USB).

Currently, the number of cars equipped with

WLAN is minimal and is restricted to premium-

priced automobiles. This exclusivity will likely

change relatively soon due to the attractiveness of

WLAN for various applications and the availability of

high supported data rate. According to a report from

GSMA (Sbd, 2012), all new cars will have WLAN by

2025. Consequently, millions of new overlapped ba-

sic subscriber sets (OBSSs) will coexist with current

networks, moreover they are mobile with different

speeds, which makes any kind of network planning

not possible. Unlike indoor scenarios (e.g. ofﬁces,

homes), interference between vehicle WLANs is ex-

tremely high due to weak attenuation of car bodies.

Simulations and measurements in (Blesinger et al.,

2013; Blesinger et al., 2012) show that the attenu-

ation of car bodies and windows is very low; mean

path loss does not exceed 85 dB at 50 m distance

around the car. This demonstrates the severity of

coexistence problems in this domain. Several fac-

tors affect path loss (e.g., antenna position and win-

dow type), which should be taken into account by

car manufacturers. Mutual interference between con-

current 802.11 systems in cars is studied in (Pfeif-

fer et al., 2014). Measurements validate the notion

that the achieved throughput is strongly affected by

the WLAN connection in a neighboring car. When

both 2.4 GHz and 5 GHz ISM bands are considered,

the results show that the interference in the 2.4 GHz

band is higher due to the lower path loss. A study on

the effectiveness of WLAN in vehicles is presented in

(Heddebaut et al., 2004). The objective was to charac-

terize radio frequency (0.7-6 GHz) propagation inside

vehicles. Measurements show that mean attenuation

ranges from a few decibel to more than 40 dB, de-

pending on the antenna positions. As such, good link

quality for WLAN inside the vehicle should not be

difﬁcult to achieve. In (Kukolev et al., 2015), chan-

nel measurements are conducted inside the vehicle in

the frequency band 5.8 GHz. The primary focus is

centered on IEEE 802.11p standard for both intra-

vehicle and out-of-vehicle environments. The mea-

sured power delay proﬁle (PDF) is described using a

double exponential model; delay spread is small re-

sulting in negligible effect on inter-symbol interfer-

ence (ISI).

In (Lin et al., 2013), a performance study of intra-

vehicle wireless sensor networks (IVWSN) based on

Bluetooth low energy and ZigBee under Wi-Fi and

Bluetooth interference is presented; performance of

both IVWSNs signiﬁcantly degrades when Wi-Fi in-

terference is introduced. Although the interference

from the surrounding networks is not considered, it

will deﬁnitely increase its inﬂuence. In previous

work (Mourad et al., 2016), test drives were con-

ducted to investigate WLAN performance in the ve-

hicles. Highway and city center test drives in Ger-

many demonstrate that achieved throughput inside

the car under test is strongly affected by interference

from surrounding networks. Currently, WLANs are

primarily found in ofﬁces, homes, and public areas,

as noted earlier, the number of cars equipped with

WLAN is still limited.

In this work, the focus is on WLAN used for info-

tainment applications in vehicles, which is expected

to be widely spread before the vehicular Ad-Hoc net-

work (VANET). Having WLANs in vehicles will es-

calate the coexistence problem in the ISM bands. A

consequence of millions of new mobile OBSSs, per-

formance of the surrounding ﬁxed Hotspots will be

strongly affected. The high density of devices in ve-

hicles and their mobility, in addition to low inser-

tion loss between neighboring cars make this domain

unique.

Wi-Fi has been studied in various indoor/outdoor

scenarios and under many attenuation scenarios.

However, studies of vehicular environment are lim-

ited. Consequently, this paper provides a ﬁrst step into

investigating Wi-Fi performance in realistic vehicle

coexistence scenario. The main contribution of this

paper is to study how the WLANs in two neighboring

cars affect each other and to discuss solutions lever-

aging the most recent WLAN standard –802.11n– at

2.4 GHz. To accomplish this, two cars are parked

near to each other and two WLANs are established

in them. Throughput and power values are collected

and analyzed. Both TPC and MIMO techniques are

discussed.

The IEEE 802 community has recently recognized

this issue in the sake of increased demand by car man-

ufacturers. A new study group, namely wireless au-

tomotive coexistence, has been established under the

working group 802.19. The groups effort focuses on

wireless coexistence, optimizing the 802.11 and Blue-

tooth parameter settings for the automotive domain.

The remainder of this paper is organized as fol-

lows. Section 2 presents brieﬂy the IEEE 802.11

standards family. Section 3 describes the measure-

ments setup and the baseline, while section 4 shows

the measurement results. In section 5, the results are

discussed, and the paper is concluded in section 6.

VEHITS 2017 - 3rd International Conference on Vehicle Technology and Intelligent Transport Systems

Figure 1: WLAN channels in the 2.4 GHz ISM band.

Table 1: IEEE 802.11 Standards.

Standard Description Status

IEEE 802.11 2.4 GHz, up to 2

Mbps

Finished

1997

IEEE 802.11b 2.4 GHz, DSSS,

up to 11 Mbps

Finished

1999

IEEE 802.11a 5 GHz, OFDM, up

to 54 Mbps

Finished

1999

IEEE 802.11g 2.4 GHz, OFDM,

up to 54 Mbps

Finished

2003

IEEE 802.11n 2.4 GHz and 5

GHz, OFDM,

up to 600 Mbps,

MIMO

Finished

2009

IEEE

802.11ac

5 GHz, MU-

MIMO in down-

link, up to 1300

Mbps

Finished

2013

IEEE

802.11ax

2.4 GHz and 5

GHz, OFDMA,

MU-MIMO for

both downlink

and uplink

Under

devel-

opment,

expected

2019

2 IEEE 802.11 SYSTEMS

IEEE 802.11 systems provide wireless connectivity

for various portable devices. The standards deﬁne

both the MAC layer speciﬁcation and the physical

layer techniques. Table 1 shows IEEE 802.11 stan-

dards, as well as a short description about each and

the year of release. Systems operate in both 2.4 and

5 GHz ISM unlicensed bands. Speciﬁcally in the 2.4

GHz band, 83.5 MHz are available, ranging from 2.4

to 2.483 GHz. Fourteen channels –22 MHz each– are

deﬁned in the standard, as shown in Fig. 1. Only three

channels (1, 6 and 11) are not overlapped. Thus, these

channels are used most frequently.

Coordination functions are used to control channel

access. Two functions are deﬁned in the standard: 1)

distributed coordination function (DCF) and 2) point

coordination function (PCF). The DCF, which is most

commonly used, is based on the carrier sense multiple

access/collision avoidance (CSMA/CA) channel ac-

cess method. The device initiates transmission only in

the event that it senses the medium idle for a time pe-

riod (i.e., inter frame space [IFS]). After receiving the

packet, the receiver then sends an acknowledgment to

the transmitter. Given that the transmitter does not re-

ceive an acknowledgment after a certain period, the

transmitter will repeat the transmission up to a certain

maximum number before deferring the transmission,

in such a case, the packet is lost.

The carrier sense is composed of two different

functions: 1) clear channel assessment (CCA) and 2)

network allocation vector (NAV). While the CCA in-

dicates if the medium is busy for the current frame,

the NAV reserves the medium for the transmission

of frames following the most current transmission.

Moreover, CCA is initiated based on two entities:

1) preamble detection (PD) and 2) energy detection

(ED). Preamble detection is used to sense other Wi-

Fi signals by detecting and decoding the preamble of

these signals. If the station detects additional Wi-Fi

signals, the medium should be marked busy through-

out the time required for current frame transmission.

Required time could be established from the Physi-

cal Layer Convergence Procedure header length ﬁeld.

According to the standard, PD threshold used in Wi-

Fi is set to -82 dBm. ED is used to detect other sys-

tem signals, like Bluetooth, that share the medium

with Wi-Fi or with corrupted Wi-Fi transmissions that

cannot be decoded. In contrast to PD, the necessary

time for the current transmitted frame is unknown.

As such, the device should check the medium for

each time slot, verifying that energy is still present.

The ED threshold used in Wi-Fi equals -62 dBm

in a 20 MHz channel, allowing fairness in sharing

the medium among various 802.11 systems and ad-

ditional non-802.11 systems that share the same unli-

censed frequency band.

The new 802.11ax standard, which is still un-

der development, aims at improving the throughput

in the event of high density OBSSs as stated in the

project authorization request (PAR): “This amend-

ment deﬁnes standardized modiﬁcations to both the

IEEE 802.11 physical layers (PHY) and the IEEE

802.11 medium access control layer (MAC) that en-

able at least one mode of operation capable of sup-

porting at least four times improvement in the aver-

age throughput per station (measured at the MAC data

service access point) in a dense deployment scenario,

while maintaining or improving the power efﬁciency

per station.” 802.11ax is the ﬁrst 802.11 standard to

support multi-user MIMO in both downlink and up-

link. Moreover, the standard improves coexistence

and spatial reuse by differentiating between inter-BSS

and intra-BSS frames using a new ﬁeld in the frame

called BSS color (Stacey, 2015).

IEEE 802.11 Systems in the Automotive Domain: Challenges and Solutions

Table 2: Measurement Parameters.

Test cars BMW X6 2016 and Toy-

ota Camry 2003

WLAN boards Mikrotik Router boards

(RB953GS) with R11e-

2HPnD radio cards

Power measurement

hardware

PXIe-1075 chassis

equipped with a PXIe-

5663 vector network

analyzer

AP position Middle console or

driver’s footwell

Station position middle back seat

Standard 802.11n

Channel width 20 MHz

Trafﬁc type UDP

Channel number 11

Channel center fre-

quency

2.62 GHz

Scenario Downlink

Link throughput Maximum achievable

Antenna gain 4 dBi

Nonetheless, this new standard does not consider

mobile Hotspots with speeds higher than 6 mph, due

to the small market share of automotive at the time

when the new group was formed. Regardless, it is ex-

pected that consumer electronic devices will not sup-

port this standard before year 2020, which is already

notably late for the problem addressed in this paper.

3 MEASUREMENT SETUP AND

BASELINE

Measurements are determined using Mikrotik Router

boards (RB953GS) equipped with R11e-2HPnD ra-

dio cards. The Mikrotik boards are fully conﬁgurable,

enabling power level and number of RF chains ad-

justments. WLAN connection is established between

two boards, one acting as an access point (AP) and

the other as a station. Their operating system facili-

tated bandwidth tests using both TCP and UDP traf-

ﬁc. The standard 802.11n with 20 MHz channel width

was chosen for all measurements, as it is the most re-

cent standard operating in the 2.4 GHz band. Mea-

surement parameters are summarized in Table 2.

To deﬁne ground-truth throughput using the

boards, measurements had to be conducted in ane-

choic chamber. Ground-truth throughput identiﬁes

board performance and acts as a reference for mea-

surements in cars. Initially, two networks working on

the same channel were established. Distance between

Figure 2: Test setup in the chamber.

the AP and the station is 1.5 m, and the distance be-

tween station 1 and station 2 is 1 m. These measures

hold true for APs, as seen in the Fig. 2. Power was

set to 16 dBm for both networks. A 60-second aver-

age was used, and throughput remained stable at near

average. Results are shown in Table 3. The achieved

throughput was 62.8 Mbps for the SISO case for both

networks. For the MIMO case (2x2), 121 Mbps and

116.8 Mbps were the achieved values for networks

1 and 2, respectively. When two networks share the

medium, network throughput for both is quite simi-

lar, and the sum of both throughputs is slightly lower

than the maximum throughout for one pair. The drop

in total throughput –compared to the case when ei-

ther network functions independently– occurs when a

second transmitter joins the channel, which increases

the probability of corrupted transmission. This in turn

leads to a decrease in the throughput. These ﬁndings

substantiate work presented in (Rajab et al., 2015).

Throughout the experiment, two cars were parked

parallel to one other, with 1.5 m separation distance

between them, see Fig. 3. To simulate a real life sce-

nario, two cars from different manufacturers –BMW

X6 2016 and Toyota Camry 2003– were used. Ad-

ditionally, two positions of AP –middle console and

driver’s footwell– were considered. The station was

mounted on the middle console of the back seat, as

shown in Figures 4 and 5. In this case, both LOS

and NLOS for propagation inside the car were consid-

ered. A bandwidth test was performed for both SISO

and MIMO (2x2) to establish a baseline for through-

put without interference in the two cars for both posi-

tions of access point (footwell position is not shown

in the ﬁgures). Transmission power was tuned from 0

dBm to 16 dBm with 2 dB step size. For middle con-

sole position, in both cars the maximum throughput

was achieved for the SISO case, following the obser-

VEHITS 2017 - 3rd International Conference on Vehicle Technology and Intelligent Transport Systems

Figure 3: The test setup with the two cars.

Figure 4: Board positions in the BMW, the AP is on middle

console.

vations reported in Table 3. For the MIMO case, a

slight reduction in throughput was achieved for low

power levels. For the footwell position, a slight re-

duction (e.g., 5-10 Mbps) in throughput compared to

middle console position is visible for all power levels,

especially in MIMO case.

A National Instruments (NI) PXIe-1075 chassis

equipped with a PXIe-5663 vector signal analyzer

(VSA) was used to collect power levels. The device

was mounted in several positions inside the cars. Data

were collected using LabView software developed at

the University of Oklahoma (Balid et al., 2016). The

VSA was conﬁgured to sweep the entire band (i.e.,

2.4-2.483 GHz) with a resolution bandwidth (e.g., the

fast-Fourier transform (FFT) bin size) of 100 KHz.

Spectrum sweep ran for ten seconds at each mea-

surement point, and then data were post-processed in

MATLAB to calculate probability distribution func-

tion (PDF) of the received power for different cases.

PDFs were used to draw insights from the results.

Notably, results could vary given an alternative

hardware implementation scheme and car model than

the ones used in our setup. However, our results

should be regarded as representative of available com-

mercial devices and cars.

Table 3: Measurement results in anechoic chamber.

Network 1 Network 2

Description

Antenna

Mode

Throughput Antenna

Mode

Throughput

1x1 62.8 N/A N/A

only net-

work 1 is

active

2x2 121 N/A N/A

only net-

work 1 is

active

N/A N/A 1x1 62.8

only net-

work 2 is

active

N/A N/A 2x2 116.8

only net-

work 2 is

active

1x1 30.5 1x1 29.5

both net-

works are

active

2x2 57.5 2x2 55.9

both net-

works are

active

1x1 33.1 2x2 55.9

both net-

works are

active

2x2 60.1 1x1 30.5

both net-

works are

active

Figure 5: Boards position in the Toyota, the AP is on middle

console.

4 MEASUREMENTS RESULTS

In this section, throughput measurements for various

scenarios are presented; results are explained and an-

alyzed using power measurements. In order get rid

of small variations in throughput, sixty seconds av-

erage is used for each power level. Measurements

IEEE 802.11 Systems in the Automotive Domain: Challenges and Solutions

−140 −130 −120 −110 −100 −90 −80 −70 −60 −50 −40

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Power [dBm]

PDF

In Toyota

In BMW

Figure 6: Background noise in both cars.

were repeated four times, which was enough to get

low standard deviation around the mean (< 5Mbps).

Average values, in addition to the standard deviation

around the means, are presented in the ﬁgures. Mea-

surements were taken in a location where no active

WLANs or other systems are performing in the same

band. This is veriﬁed by spectrum sweep prior to the

test. Fig. 6 shows the PDF of received power in both

cars when all the networks are inactive, noise mean is

approximately

-102 dBm and the VSA is positioned on the middle

console. Fig. 7 and Fig. 8 show the achieved through-

put for a transmission power ranging from 0 dBm to

16 dBm with 2 dB step size in both cars for SISO and

MIMO cases, respectively. Continuous lines repre-

sent middle console position, while dashed lines rep-

resent footwell position.

4.1 AP on Middle Console

In the SISO case and for power levels above 4 dBm,

the sum of throughputs in both cars is slightly lower

than the maximum achieved when only one network

is active. These results are similar to when both net-

works operate in the chamber and demonstrate that

when transmission power is relatively high, through-

put is divided between the cars as a result of sharing

the medium. This means that when multiple cars with

WLANs operating on the same channel are located

near each other (e.g., during a trafﬁc jam) through-

put will be divided between them, resulting in a dra-

matic reduction. Notably, a power level of 16 dBm

is not the maximum-allowed transmission power, as

limits depend on local regulations (e.g., in Germany

19 dBm is the maximum allowed by regulation of-

0 2 4 6 8 10 12 14 16

Power [dBm]

Throughput [Mbps]

In Toyota (Middle console)

In Bmw (Middle console)

In Toyota (Footwell)

In BMW (Footwell)

Figure 7: Throughput as a function of power for both AP

positions, SISO in both cars.

0 2 4 6 8 10 12 14 16

100

Power [dBm]

Throughput [Mbps]

In Toyota (Middle console)

In BMW (Middle console)

In Toyota (Footwell)

In BMW (Footwell)

Figure 8: Throughput as a function of power for both AP

positions, MIMO in both cars.

ﬁces). For power levels below 4 dBm, throughput

in both cars rises, meaning that both networks can

transmit more often at the same time. When decreas-

ing power, probability of sensing an idle medium in-

creases and leads to an increase in throughput. No-

tably, maximum throughput is not achieved even for a

power level of 0 dBm. This result could be due to of

low SINR values, which leads to erroneous transmis-

sions when both networks transmit simultaneously.

Trends similar to those found in the SISO case are

found in MIMO, see Fig. 8. Nevertheless, for low

power levels, throughput in both cars tends to increase

slightly, primarily due to low power. Probability of

bad link quality for two streams increases; therefore,

VEHITS 2017 - 3rd International Conference on Vehicle Technology and Intelligent Transport Systems

more errors are likely to occur.

Fig. 9 and Fig. 10 illustrate results when power is

high in one car (i.e., set to 16 dBm) relative to differ-

ent power levels in the second car. The same trend is

visible in both ﬁgures. As power decreases through-

put in the car with lower power decreases, as well.

This can be explained by the fact that a car with the

higher power has more chance to transmit by sensing

the idle medium when compared to a car with lower

power. For a power level of 0 dBm, throughput is re-

duced to approximately 20 Mbps in the car with lower

power. This demonstrates unfairness in sharing the

medium when various power levels are used by dif-

ferent car manufacturers. The same behavior is also

observed in the MIMO case. (Figures are not included

in an effort to avoid repeated information.)

Fig. 11 presents results when MIMO is used in

one car (i.e., Toyota) and SISO in another car (i.e.,

BMW), which could be the case in different car mod-

els. The two networks share the medium evenly in a

way similar to that described in previous cases. For

example, at a power level of 16 dBm, the MIMO net-

work achieves 63 Mbps (i.e., almost half the maxi-

mum achieved without interference); the SISO net-

work achieves 30 Mbps (i.e., almost half the maxi-

mum without interference). Increases in throughput

are similar for power levels below 4 dBm.

Fig. 12 shows the PDF of received power in the

BMW vehicle when only the network in Toyota is

active with different transmission power. VSA was

positioned on the middle console (similar to AP posi-

tion) as seen in Fig. 13. For a transmission power

of 5 dBm, all packets were received with a power

lower than -82 dBm. This phenomenon explains why

throughput starts to rise in both cars at around (4-5

dBm). Given 0 dBm transmission power, networks

should not sense each other and, therefore, through-

put should rise to high value. However, low SINR

could still lead to erroneous transmissions. As afore-

mentioned, power PDFs are used only for compari-

son. Received power by the boards could be different

due to various RF front-ends. In addition, PD thresh-

old could vary depending on chip manufacturer, even

when a threshold of -82 dBm is deﬁned in the stan-

dard.

Fig. 14 compares the PDF of total power in both

cars when the network in each is active independently

and transmission power is set to 16 dBm. Clearly, the

channel is quite symmetric. Received power in the

BMW is slightly higher than that in Toyota, which

could be the reason for higher throughput in Toyota,

especially in the SISO case.

0 2 4 6 8 10 12 14 16

Power in BMW [dBm]

Throughput [Mbps]

In Toyota

In BMW

Figure 9: Throughput as a function of power in BMW,

power in Toyota is ﬁxed to 16 dBm, SISO in both cars.

0 2 4 6 8 10 12 14 16

Power in Toyota [dBm]

Throughput [Mbps]

In Toyota

In BMW

Figure 10: Throughput as a function of power in Toyota,

power in BMW is ﬁxed to 16 dBm, SISO in both cars.

4.2 AP in Footwell

In both cars, the access point was positioned in the

driver’s footwell, as shown in Fig. 15. No LOS

between AP and the station led to a minor reduc-

tion of throughput without interference, especially for

MIMO. Fig. 7 illustrates that the trend in throughput

is similar to that of the middle console. However, it

is clear that at the higher power level (e.g., approxi-

mately 6 dBm) throughput starts to rise for both net-

works when compared to middle console. This phe-

nomenon can be interpreted by higher path loss be-

tween the two access points (and stations) in the two

cars. In the ﬁrst position, the majority of the signals

IEEE 802.11 Systems in the Automotive Domain: Challenges and Solutions

0 2 4 6 8 10 12 14 16

100

Power [dBm]

Throughput [Mbps]

In Toyota

In BMW

Figure 11: Throughput as a function of power, MIMO in

Toyota, SISO in BMW.

−140 −130 −120 −110 −100 −90 −80 −70 −60 −50 −40

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Power [dBm]

PDF

16 [dBm]

10 [dBm]

5 [dBm]

0 [dBm]

Figure 12: PDF of received power in BMW for four trans-

mission power levels in Toyota, AP and VSA are on middle

console.

are propagating through windows, which have low at-

tenuation at this frequency.

In the second position, there are numerous re-

ﬂections inside the car, so the signals reach the other

car with lower power levels. At power level 0 dBm,

throughput reached 43 Mbps in the BMW and around

57 Mbps in the Toyota. For MIMO (2x2), throughput

in both networks was lower than the middle console

position. This result is related to the absence of LOS

and the multi-path propagation inside the car.

The VSA was positioned separately in the

footwell of both cars to record power values, as seen

Figure 13: VSA position on middle console in BMW.

−140 −130 −120 −110 −100 −90 −80 −70 −60 −50 −40

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Power [dBm]

PDF

In Toyota

In BMW

Figure 14: Received power in both cars for middle console

position, the transmission power is set to 16 dBm.

in Fig. 16. Fig. 17 shows the PDF of total power

for footwell position in both cars. In this position,

the channel is asymmetric and the probability of

receiving higher power level in the BMW is higher

than that of the Toyota. Therein lies the explanation

for higher throughput in the Toyota.

Finally, Fig. 18 demonstrates the PDFs of total

power in the BMW for middle console and footwell

positions. Transmission power for the network in

Toyota in both cases is set to 16 dBm. It is clear

from the ﬁgures that regarding the middle console

case, received power from the network in Toyota is

much higher than that of the footwell case. This ex-

plains why throughput rises at a lower power level for

VEHITS 2017 - 3rd International Conference on Vehicle Technology and Intelligent Transport Systems

Figure 15: AP position in the driver’s footwell.

Figure 16: VSA position in the driver’s footwell in Toyota.

footwell. Most packets in the middle console case are

received at power levels between -90 and -70 dBm;

footwell position reception is at power levels between

-78 and -100 dBm. It is clear that PDF is much wider

for Footwell due to the richer multi-path environment,

which makes packets arrive with wider power levels.

5 DISCUSSION

Consumer demand is cause for increased interest in

Wi-Fi for both car manufacturers and big technology

companies. In addition relying on Bluetooth for all

intra-car applications is not possible due to low sup-

ported data rates. The main purpose of this work is to

attract interest to this new Wi-Fi usage domain. Con-

sumers have come to expect the same connectivity

services in their cars as they enjoy in their homes and

ofﬁces –especially due to the wide use of social media

applications. Improvement in infotainment systems

decreases the use of cellular phones while driving,

hopefully reducing the number of accidents caused by

−140 −130 −120 −110 −100 −90 −80 −70 −60 −50 −40

0.01

0.02

0.03

0.04

0.05

0.06

Power [dBm]

PDF

InToyota

In BMW

Figure 17: PDF of received power in both cars for footwell

position, the transmission power is set to 16 dBm.

−140 −130 −120 −110 −100 −90 −80 −70 −60 −50 −40

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Power [dBm]

PDF

Middle console

Footwell

Figure 18: Power received in BMW in two different posi-

tions, the transmission power is 16 dBm in Toyota.

cell phone use.

The automobile Wi-Fi domain is different than

other domains, thus previous research performed in

building environments cannot be easily extended to

the automobile domain. One major difference is the

large number of devices assembled in a restricted

space. For example, some car manufacturers will

have more than three access points in a single car for

different applications. Furthermore necessary coordi-

nation among the applications is not an easy task due

to the complexity of automobile design. Also, the ef-

fect of mobility requires detailed investigation.

In the proposed test setup, two cars were parked

parallel to one other with 1.5 m separation. In order to

study more practical scenarios, similar measurements

IEEE 802.11 Systems in the Automotive Domain: Challenges and Solutions

were performed with a 5.2 m distance between the

cars. This separation emulates a free spot between

them. Another investigated scenario was when the

cars are parked in a line with 2.5 m distance. Simi-

lar results were achieved for all tests. Power distribu-

tion shows only a small decrease in power value (e.g.,

approximately 5-10 dB) when comparing tests.

The presented measurements show that given

most vehicles are equipped with WLANs in the near

future, millions of new mobile Hotspots will be trav-

eling our roadways. Unlike networks in building envi-

ronments, these Hotspots will radiate extremely high

energy to surrounding cars. There is concern about

the performance of surrounding Hotspots. One im-

portant example is hospitals, which were studied in

(Al Kalaa et al., 2016). Hospitals utilize sensitive de-

vices with BLE and ZigBee systems that operate in

the 2.4 ISM band. In the event that hundreds of cars

are parked in hospital parking, access points will most

likely affect the wireless systems inside the hospitals.

Two solutions under the standard 802.11n um-

brella are discussed in this paper, namely MIMO and

power control. In (Herbert et al., 2014), a wireless

channel inside the car was studied. Results demon-

strated that the spatial correlation is well deﬁned; thus

deployment of MIMO antenna arrays should be ef-

fective in vehicles. The spatial multiplexing tech-

nique deﬁned in the standard was used in the measure-

ments. Although two data streams were transmitted

simultaneously, a second antenna and RF front-end

is needed, which increase the cost. To date, not all

cellular phones support MIMO, due to limited space

and increased cost. Limiting transmission power is

essential for reducing interference to the surrounding

networks. However, power should not be so low as to

affect link quality inside the car, especially given that

passenger devices can be located anywhere in the car.

It is important to mention that this procedure should

be standard in all cars. Not doing so leads to unfair-

ness in sharing the medium, as measurements demon-

strate above. National and international regulatory of-

ﬁces should take action to this end.

Two positions of AP are discussed, namely mid-

dle console and footwell. Given footwell position, at-

tenuation between the cars is higher. Different AP

positions were discussed in (Blesinger et al., 2012)

and footwell position was proposed to reduce the in-

terference to the surrounding cars. Directive antennas

could be beneﬁcial for this purpose as well. However,

in this study, only the downlink is considered. User

devices can be located anywhere in the car, thus not

controlled by car manufacturers.

One possible solution for this problem is to ofﬂoad

sensitive application trafﬁc, like video streaming to

the 5 GHz ISM band. Regardless, the 5 GHz band

has some challenges. The car environment is consid-

ered outdoors, and most available channels cannot be

used without radar detection and dynamic frequency

selection. Both of these are difﬁcult to implement

in a moving vehicle. In addition, coexistence with

LTE in the unlicensed band (LTE-U) or license as-

sisted access (LAA) could affect WLAN performance

in the ISM band. Coexistence between WLAN and

LTE-U/LAA remains an ongoing discussion among

the IEEE 802 and 3GPP communities.

6 CONCLUSION AND FUTURE

WORK

Future cars are projected to be equipped with ad-

vanced infotainments systems with options and capa-

bilities similar to those currently available in homes

and ofﬁces. Autonomous cars will allow passengers

to efﬁciently use their in-car time for working or en-

tertaining. Seamless integration of passengers’ con-

sumer electronic devices is a key. 802.11 systems are

the most promising systems to achieve this integra-

tion, providing relatively high data rates in the unli-

censed ISM frequency bands.

This work highlights the coexistence problem in

the automotive domain, focusing on 802.11 systems

used for infotainment applications. Performed mea-

sures show that interference between networks in cars

will be very high compared to building environments.

MIMO techniques could be used to boost the achieved

data rates by spatial multiplexing; in addition MIMO

could also be used to improve robustness by means

of spatial diversity. On the other hand optimal tuning

of transmission power is essential to guarantee good

coverage inside the car and to reduce the interference

with surrounding networks.

The effect of vehicle mobility is a work in

progress, as it is quite important to understand the

difference to other indoor/outdoor scenarios. Coex-

istence of Bluetooth and Wi-Fi in this domain is quite

interesting and could lead to future work. It has yet to

be determined whether or not hands-free calling us-

ing Bluetooth will work when several WLAN signals

with relatively high power level are present. In addi-

tion, analyzing applications used in infotainment sys-

tems is necessary to determine necessary data rates

for each application. Answers offer a better idea of

the severity of throughput reduction due to interfer-

ence.

VEHITS 2017 - 3rd International Conference on Vehicle Technology and Intelligent Transport Systems

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