A Telematics System Using In-Vehicle UWB Communications

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A Telematics System using In-Vehicle
UWB Communications
I.J. Garcia Zuazola1, J.M.H. Elmirghani2 and J.C. Batchelor3
1Deusto Institute of Technology - DeustoTech, University of Deusto
2School of Electronic & Electrical Engineering, University of Leeds
3School of Engineering and Digital Arts, University of Kent
1Spain
2,3UK
1. Introduction
Owing to the rapid evolution in wireless and cellular communications usage, and the
resulting huge demand, new communications technologies are needed to support the cost
effective growth of mobile telephony and the tremendous increase in Internet data traffic in
new applications such as Telematics. New wireless communication technologies are
therefore needed for the delivery of enhanced applications, for example telematics services
to motorway users. This is targeted towards transforming wireless techniques to operate on:
fast moving vehicles with high impairments encountered at high data rates; small cellular
cells which are key to high data rate operation; and, more frequent cell handovers dictated
by speed and small cell size. This scenario can make use of data from inductive loops for
traffic (vehicular and data) monitoring, prediction, grooming and control.
Central base stations driving distributed antenna units will facilitate this new bandwidth
provision and Radio-over-Fibre (RoF) is a technology proposed to achieve transparent data
distribution. The replacement of coaxial cables with optical fibres is desirable. Fibre
transmission offers sufficient bandwidth with reduced loss over long distances and decreased
electromagnetic interference. Low loss Single Mode Fibre (SMF) is commonly deployed
outdoors while Multimode Fibre (MMF), with higher losses, is often pre-installed in buildings.
Unfortunately MMF is not of a quality that lends itself to broadband Radio-over-Fibre.
Two data transmission approaches meet the data rate requirements criteria, (i) high
performance Worldwide Interoperability for Microwave Access (WiMAX) approaches that
use an unlicensed spectrum band (5.470-5.725 GHz) for the motorway-to-vehicle
communication and (ii) the Ultra Wide Band (UWB) communications standard for
communication exchange from the vehicle to the in-vehicle applications. UWB in the
unlicensed lower band (3.168-4.752 GHz) offers multipath immunity.
WiMAX technology, based on the IEEE 802.16m standard, is of great interest to Intelligent
Transport Systems (ITS) due to the expected need for the delivery of peak rates of up to
1 Gbit/s at fixed speeds and 100Mbit/s to mobile users over micro-cells. Theoretically,
antennas are reciprocal, which means they are able to transmit and receive electromagnetic
waves with similar properties. Antennas play a key role in wireless communications; the
antenna performance is crucial to efficient electromagnetic propagation. Cost-effective while

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efficient antenna units have been assessed (Garcia et al., 2008) for Intelligent Transport
Systems (ITS) in a highway scenario. The antennas designed and tested served the WiMAX
standard over full-duplex bi-directional optical links.
UWB technology is of global interest in modern communication systems due to its potential
to deliver high speed data rate transmissions with excellent immunity to multipath
interference at low power consumption, low cost (Elmirghani et al., 2006) and simple
hardware configuration. The deployment of UWB inside vehicles can provide mobility and
connectivity to a host of passenger devices while significantly reducing the costs associated
with wiring. Vehicle chasses may contain large steel plates and antennas over ground
planes are favoured for ceiling mounts (Garcia et al., 2009).
Key potential applications include advanced ultra-high speed cellular communications to
vehicles, emergency services, ramp entry and variable speed control, and roadside
assistance notification. The systems can also provide live traffic information and triple play
services on in-car traffic information terminals or bespoke terminals.
In this work the following topics are discussed. First, a Telematics system, based on a
published patent GB2436909 is presented. In essence, WiMAX is used here in highways to
provide communication services to moving vehicles incorporating an in-vehicle UWB
network of 480 Mbps. Second, a detailed motorway-to-vehicle wireless communication
system using recent developments in RoF systems is introduced. This utilizes centralized
base stations driving a host of antenna units along a highway through Single Mode Fibre
(SMF). Third, a UWB wireless propagation analysis in an in-vehicle scenario is analysed.
The analysis is performed in the lower unlicensed band (3.168-4.752 GHz) of the allocated
Federal Communications Commission (FCC) spectrum that has an assigned band from 3.1
to 10.6 GHz (FCC, 2002). Finally, the design of a UWB antenna for an in-vehicle application
is described.
2. The telematics system
An attractive nature of a Telematics system is its capability to revolutionise transport using
the latest wireless communication technologies including computer networking and
communications infrastructure for delivering enhanced services to motorway users, Fig. 1.
This provides the users with live traffic information and multi-play services on in-car traffic
information terminals or bespoke systems.
The introduced Telematics system utilises RoF as a technology to achieve the modulated
carrier distribution. RoF brings the opportunity to simplify typical Base Station (BS)
deployments by making them part of the system backbone while being able to transmit over
long distances. In addition, among the advantages of using optical fibres are: bandwidth,
security, lack of interference and an extreme reduction in maintenance costs that is achieved
by centralisation.
The RoF term is used when light is modulated using a radio frequency (RF) information
carrying signal and is transmitted over optical fibre. The electromagnetic spectrum that can
in theory be used to modulate the light is typically of several GHz bandwidth for the
semiconductor lasers and several MHz for light emitting diodes (LEDs). Microwaves are
commonly used due to their reasonable coverage, high data rates and capacity using
moderate cells with low frequency reuse.

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(a) (b)
Fig. 1. A highway communication infrastructure (a) and an in-vehicle femtocell (b)
High capacity, Quality of Service (QoS) and data transfer communications are in demand.
Methods to meet these demands include techniques that range from the use of smaller
radius cells and the use of sectorisation, to the most recent use of multiple antennas in
spatial and/or frequency diversity configurations. For these systems it is desirable to have
easy integration and small package antenna units. Multiple Input Multiple Output (MIMO)
Antennas composed of three 120 sectors exploiting frequency diversity gain have been
reported in (Garcia et al., 2008). In the same way, wireless systems devices for the vehicle to
road intercommunication are usually of small profile. A tri-sector configuration antenna to
meet this demand has been reported in (Garcia et al., 2010).
Low cost RoF distribution deployed in-vehicles is of great interest, Fig. 1b. Unlike coaxial,
fibre lines are capable of providing electromagnetic interference free transmissions over the
distance. Centralisation of transceivers to a system backbone might complement with lower
engineering costs, both in deployment and maintenance.
Antennas play a key role in wireless transceivers as they are the last step to radiating energy
into the space. Miniature antennas are required for the in-vehicle application; the prototypes
will have to ensure a good system performance and be platform tolerant.
In the next section, the motorway-to-vehicle wireless communication system, the in-
vehicle wireless communication system including a UWB in-car wireless channel
analysis, and finally the design of an UWB antenna for in-vehicle applications are
introduced.
2.1 Motorway-to-vehicle communication system
In Telematics applications, an autonomous data collection and processing systems can
exploit recent advances in UWB, Worldwide Interoperability for Microwave Access
(WiMAX) and radio fibre technologies to provide data and multimedia services for vehicles
along sophisticated highways (Kerner et al., 2005). Traffic prediction systems are receiving
increased attention and are being evaluated and adopted in a variety of contexts
(Gunter & Grosmann, 2005). Communication between vehicles and vehicle to infrastructure
has also been explored using a range of technologies (Lee & Williams, 2000). Refined
highways hold sophisticated telematics infrastructure that includes fibre, inductive loops
buried, routers, switches and digital video cameras with number plate recognition systems
among others.
An example of a highway sensing and communication infrastructure is depicted in Fig. 1.

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Fig. 2. The Telematics system architecture
The motorway-to-vehicle wireless communication system is realised using various
components of the system architecture in Fig. 2, the RoF architecture.
In essence, the system architecture comprises a (virtual) central office (CO) which consists of
base station modules (BSM), circulators, attenuators, bidirectional optical transceivers
(BIDI TRX) and wavelength division multiplexers (WDM). Erbium-doped fibre amplifiers
(EDFAs) provide bi-directional amplification to compensate for losses due to long runs of
the single mode fibre (SMF). Optical add drop multiplexers (OADM) provide interfaces
between the fibre and the remote antenna units (RAUs).
The functional view of the RoF system is now detailed. The system employs a high
performance unlicensed 5.470-5.725 GHz WiMAX band directly modulated over a
bi-directional SMF link using remote units composed of three sector antennas
(Garcia et al., 2008) which aims to achieve a better capacity and coverage performance over
micro-cells, and is intended to support around 100 Mbps. The radio frequency (RF) signals
are directly modulated using a distributed feedback laser (DFL) contained in the BIDI TRX.
The signal generated is carried over the downlink SMF to a remote RAU site which converts
this optical signal to an RF signal by positive-intrinsic-negative photodiode with a
transimpedance amplifier (PIN-TIA) receiver with high sensitivity. For uplink transmission,
the wireless signal received from an RAU is amplified, converted into an optical form by a
DFB laser (chosen as an ideal device for SMF and long haul communications), and
transported uplink by the SMF to the CO where another PIN-TIA receiver in BIDI TRX
demodulates the optical signal into the RF.
2.2 In-vehicle communication system
UWB technology has gained huge interest globally due to its potential to deliver high data
rate and spatial capacity, with multipath immunity (Das et al., 2006; Way, 1989) and low
power, low cost design. The deployment of this wireless technology in vehicles will provide

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mobility and connectivity to a host of passenger devices while reducing significantly the
costs associated with wiring.
In addition, large vehicles can benefit from the use of low cost optical fibre communications.
A RoF system can be used as part of a distributed antenna system (DAS), (with centeralised
control) which supports the deployment of femtocellular access networks at 480Mbps
within airplanes, buses, coaches, cars, lorries, trains, trams and other transport vehicles.
Such a system can assist in the minimisation of radio frequency (RF) inference when
compared to coaxial cable links, simplifies the infrastructure and reduces engineering cost.
A high-level block diagram for the in-car system is depicted in Fig. 3.
Next, a study of a UWB system over RoF in an in-vehicle scenario is described in Section
2.2.1. Experimental results of the radio propagation within the car in a realistic environment
validate the system and are described in Section 2.2.2.


Fig. 3. The in-vehicle distributed antenna system
2.2.1 UWB RoF transmission in-vehicle
A feasibility study of an IEEE 802.15.3a UWB system based on Multi-Band Orthogonal
Frequency Division Multiplexing (MB-OFDM) transmitted over RoF inside a vehicle is
described. The in-vehicle system set-up includes a DV9110 Development Kit (DVK) from
Wisair Ltd and a Renault Extra Van that was used as a base for the experiments. Two
UWB transceivers were placed in the vehicle; one was used as an Access Point (AP) and
the other as fixed/Mobile Equipment (ME). Each transceiver had an integrated
monopole antenna of 2 dBi gain. The transceiver emits a short pulse of output power
80μW (Power Spectral Density PSD of -42 dBm/MHz max) containing the
WiMedia/MBOA Group 1 sub-band (3.168–4.752 GHz) and using a modulated signal
MB-OFDM quadrature phase shift keying (QPSK) at a varying physical data rate
between 53.3 Mbps and 480 Mbps.
The in-vehicle system design is depicted in Fig. 4 which shows the UWB RoF architecture.
A UWB radio at the central unit was directly modulated over an optical signal using a
Vertical Cavity Surface Emitting Laser (VCSEL) and then distributed over a MultiMode
Fibre (MMF) to a remote antenna unit where the transmitted modulated optical signal was
demodulated back to radio using a PhotoDetector (PD) and then propagated by the antenna

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into the space. A multimode fibre network was used for the UWB radio distribution due to
the large bandwidth, low loss and the ability of centralisation at a relatively low cost
(Garcia et al., 2005).
Results using Agilent ADS software demonstrate the feasibility of the RoF system. A
waveform generator was used to transmit/receive through the system. It used a signal
spectrum at 1 MHz narrow resolution bandwidth (RBW) filter within a Federal
Communications Commission (FCC) mask. The transmitted and received signals are
depicted in Fig. 5. They overlapped and showed good agreement.


Fig. 4. The complete UWB RoF femtocell
The measured output power was -41.3dBm; this agreed with the maximum UWB Effective
Isotropic Radiated Power (EIRP) allowance and the receiver sensitivity was -79.55 dBm. The
system Transmit (Tx) power budget was measured near 0dBm after compensating for a
power penalty (attributed to optical and RF devices loses) of 8.26dB.


Fig. 5. Transmitted/received UWB MB-OFDM signal
A Bit Error Rate (BER) test evaluated the performance of the system. The transmitter
produced OFDM UWB symbols that a receiver was capable of analysing; with/without

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multipath over an in-door channel. The resulting test for the down link is depicted in Fig. 6,
where an irrelevant BER difference between a referenced transmitter and the UWB RoF
full-duplex system is observed.


Fig. 6. The system Bit Error Rate (BER)
The results show the feasibility of the RoF system; this would allow extending UWB radio
signals over hundreds of meters distances, well enough for in-vehicle applications.
2.2.2 UWB in-car wireless propagation
Based on the MultiBand technique, the multiband UWB (MB-UWB) splits the spectrum into
sub-bands and uses conventional narrow band techniques, such as Orthogonal Frequency-
Division Multiplexing (OFDM), to transmit the information in each sub-band (Elmirghani et
al., 2006).
In this section, the propagation of a MB-UWB wireless system is studied within the in-car
environment.
Using the same wireless set-up as in Section 2.2.1 without the optical fibre distribution, each
transceiver was connected to a laptop for control and datalogging.
The cell size which is limited by the in-vehicle dimension was 0.9 metres in radius. The
access point was set in the middle of the ceiling of the car as the preferred location in
vehicles (Garcia et al., 2009); this ensures good power distribution and minimises field
exposure to occupants.
The maximum channel path loss (where the antennas are considered as part of the channel)
was measured at 33.53dB at 3.8GHz and the antenna mismatch or de-tuning is best at about
4cm away from the metallic in-car ceiling. A -91.30dBm noise floor was observed and an
Access Point (AP) UWB Development Kit (DVK) power of -43.42dBm (1MHz resolution
bandwidth, RBW) was employed.
Several channel analysis have been reported in (Garcia et al., 2009), this includes a rich
multipath in this application, high reflections, path delay changes in open and closed
environments with a possible Doppler dispersion, and the Inter-Symbol Interference (ISI) for
moving vehicles. A Bit Error Rate (BER) measurement was made to validate the system.

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The BER was set up having the Access Point (AP) and Mobile Equipment (ME)
intercommunicating reciprocally with each other. To predict the maximum achievable data
rate at the allowed BER, packets of certain known length were sent over the in-car channel
from the AP to the ME when the vehicle was stationary and then at different vehicle
velocities using the driver closed environment scenario. The received data is analysed and
recorded as BER in Figs. 7a and 7b respectively. Throughputs (capacity) for the same set up
are shown in Figs. 8a and 8b. Although there are fluctuations in the BER performance, an
average of 2.5x10-4 is obtained while the vehicle is stationary and BERs up to 3.2x10-2 are
measured at a speed of 120km/h.
The vehicle in motion (system closed) affects the BER results. The ISI mainly arising from
high reflections within the small car metallic chamber is conjectured to be aggravated by the
antenna instability due to the mobile vehicle vibration and interaction through the restricted
window area. This is translated into a collection of received variations in the amplitudes and
phases of differently delayed waves caused by further fading and multipath. The
interference of direct path and the reflected waves results in higher BERs.


(a) (b)
Fig. 7. BER as a function of distance (a) and BER as a function of mobility (b).


(a) (b)
Fig. 8. Capacity vs. distance (a) and Capacity vs. mobility (b).
An average of 115Mbps throughput is measured when stationary and up to 102Mbps at a
speed of 120km/h. The vehicle in motion affects the BER results due to the antenna
instability that is created while in motion. There was high multipath in-vehicle, and this, in

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the moving vehicle, resulted in ISI and caused higher BER measured at higher speeds. In the
same way, a lower data rate was achieved in motion.
3. UWB Antenna for in-vehicle applications
Planar Inverted-F Antennas (PIFAs) are well suited for integration inside vehicles. Their
chasses may contain large steel plates and antennas over ground planes are favoured for
ceiling mounts (Garcia et al., 2009). A UWB PIFA incorporating two shorting posts with
coupling gaps is presented. The antenna operates at the lower UWB band (3.168-4.752 GHz)
with a 3.57:1 VSWR and has a tailored impedance bandwidth and roll-off comparable to a
standard frontend Band Pass Filter (BPF). To bring down unit cost, there has been a drive to
simplify the hardware of UWB systems (Mohammad & Ismail 2008) and hardware could be
further reduced by the adoption of the UWB PIFA proposed here, because the commonly
deployed front-end BPFs would not be required. For the antenna to be implemented in car,
the antenna performance was verified when in close proximity to a large conducting plate.
Additionally, the elimination of the BPF with its associated insertion loss can offer power
savings from the vehicle´s battery especially when stationary.
Fig. 9 depicts the geometry of the UWB PIFA antenna. It consists of two planes, an etched
upper layer (A) and a bottom ground (B) separated by an air substrate (εr≈1).




Fig. 9. Geometry of the UWB PIFA
The A and B planes are capacitively coupled via the two pairs of pins (a & a’ and b & b’).
The dimensions of both posts a & b are 2.9 x 2.9 x 2.9 mm3 while posts a’ & b’ are 2.9 x 2.9 x
1.45 mm3. Coupling between planes A and B is achieved across the gaps in the posts.
The antenna is fed at the upper plane A using the inner core (0.51 mm) of a 50Ω rigid coax
cable with a total diameter of 2.16mm and 62mm length. The outer shield of the cable is

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attached to a grounding strip, D, electrically connected to B. The total volume of the antenna
is 19.58 x 15.75 x 5.53 mm3. The maximum dimension is smaller than 0.21λ at the lowest
frequency of operation.
A simulated parametric study of the capacitive gap is reported in (Garcia et al., 2010b)
where decreasing the gap between a and a' (or b and b') tended to improve the band-notch
depth and impedance roll-off. Therefore, adjusting the gap capacitance of the electrically
unconnected shorting posts allows a BPF like characteristic to be defined. An optimum
length value of a = b = 2.9 mm and, a' = b' = 1.45 mm was found to give a band-notch at
5.5GHz, a return loss (RL) of -5dB, roll-off of 0.18 and 0.03 dB/MHz and a -5dB S11
fractional bandwidth of 40%. The optimal value of the gap corresponds to 1.18mm.


Fig. 10. The UWB PIFA antenna
The reflection coefficient of the UWB antenna is shown in Fig. 10 compared to a standard
frontend BPF (RFlambda, n.d.). Compared to the commercially available BPF (2441MHz
pass-band rejection and 2dB insertion loss; roll-offs of 0.050dB/MHz and 0.031dB/MHz for
the lower and upper bands respectively), the UWB antenna has a lower 1108MHz pass-band
rejection and improves the roll-offs to 0.024dB/MHz and 0.030dB/MHz.
An antenna having a VSWR of 3.57 (5dB RL) can be calculated to present an equivalent
mismatch loss of 1.65dB (Kraus & Marhefka, 2001). Therefore, if the BPF and its associated
mismatch loss of 2dB was removed, then there will still be an overall reduction in loss of
0.8dB.
The measured 5dB return loss bandwidth of the proposed PIFA is 42.15% for the
3.168-4.860 GHz FCC UWB. To investigate the effect of attaching the antenna to a large
conducting plate in a car chassis, a larger ground plane of dimensions 510 x 800 x 0.75 mm3
was placed ¼ wavelength below the PIFA. Fig. 10 shows the S11 response.

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The far-field radiation patterns of the antenna including the large plane in polar form
(measured at 4.752 GHz) are depicted in Fig. 11. The patterns are essentially directional,
presenting a 120 half power beam-width (HPBW) and 1.53/1 front-to-back ratio in the
H-azimuth plane and similar value for the E-elevation. A gain of 7.11dBi was measured
with the E plane present.











Fig. 11. Radiation patterns of the antenna including the large ground plane

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4. Conclusion
This chapter has introduced new techniques and methodologies to support the cost effective
growth of mobile telephony and the tremendous increase in Internet data traffic in
Telematics for the delivery of enhanced services to highways users.
A Telematics system has been described based on a high performance WiMAX spectrum
using an unlicensed band (5.470-5.725 GHz) and recent developments in RoF systems as a
base for the delivery of wireless communications to motorway-to-vehicle applications. This
approach results in a relative low cost deployment and maintenance, extends the radio over
long distances and delivers peak rates of at least 1 Gbit/s to fixed users and 100Mbit/s to
mobile users over micro-cells.
Cost-effective while efficient narrow band tri-sector antenna units have been assessed for
Intelligent Transport Systems (ITS) in the presented highway scenario. The antennas served
the WiMAX standard over full-duplex bi-directional optical links (Garcia et al., 2008). These
antennas seem to be reasonably proficient for use in ITS due to their potential higher gains
and reduced spatial limitations. The low VSWR performance achieved by the use of these
narrow band antennas can improve the system link budget, which is translated into a
relatively higher coverage/throughput.
The Robustness to multipath interference offered by the unlicensed lower band
(3.168-4.752 GHz) UWB communication is to be exploited for in-vehicle communications.
Within this work a promising low cost RoF link to extend the UWB radio over relatively long
distances (i.e.: trains, trams and airplanes) has been introduced. The transmission was assessed
using a relatively inexpensive multimode RoF link. The transmission network was capable of
providing high data rates of 400-480Mbps at picocells of about a metre radius with
inconsiderable SNR degradation performance over fibre links of several hundred of meters.
In addition, a wireless propagation of UWB radio inside a vehicle is analysed. The analysis
of the UWB radio channel in-vehicles demonstrates that UWB is a very suitable and
promising technology for transmission networks able to provide high data rates of 400Mbps
within cars. Path loss was not of a significant level due to the short ranges that are
encountered within cars. However, the main attenuation might perhaps be due to
shadowing effects. High data rates were achieved in closed environment scenarios (Garcia et
al., 2009). As many new cars include air conditioning, it is not unreasonable to expect the
environment to be closed for the majority of the time.
A UWB antenna design example for an in-vehicle application has been introduced. The
results indicate that the presented antenna works satisfactorily in the unlicensed UWB band
and that the antenna element can be mounted on a large ground plane without degrading its
performance. Owing to the low volume of the design it can be easily integrated inside
vehicles in close proximity to the body.
5. Acknowledgment
This work was partially funded by the European Union.
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