Development of Ultra Wideband Radio System for
Short-Range Radar Applications
By Kazutaka Kamimura*, Yasushi Aoyagi*2, Sadao Matsushima*,
Kouji Horikawa*2, Hiroyuki Itohara* and Yoichi Iso*
Recently ultra wideband (UWB) radio systems have been extensively consideredin the field of intelligent transport systems (ITS) and communications since Feb.
2002, when the United States Federal Communication Commission (FCC) mitigated its restrictions on noise emission levels to permit UWB radio. Taking notice of automotive
short range radar (SRR) in the sub-millimeter wave radio band (22~29 GHz), the authors havebeen researching and developing this technology and, have taken part in a joint study consortium led by the National Institute of Information and Communication Technology (NICT). As aresult of these activities, the authors have successfully developed a UWB multi-function systemthat features pulse position modulation (PPM) for data communication as well as radar function.
The system consists of an antenna, transmitter, receiver, and baseband part. The authors developed the baseband part, which plays a key roll for ranging and communication functions as well
as a radio frequency (RF) part. The baseband part was adopted by the NICT, and the system
was demonstrated at IWUWB 2005, the international UWB conference held in Dec. 2005. In thedemonstration system, the authors also supported the design of an RF receiver, while the otherparts, including the antenna and RF transmitter devices, were provided by the NICT. The systemsimultaneously realized both ranging detection at a resolution of less than 10 cm and a communication function up to 1 Mbps. The authors report the structure and performance of the developed system as well as an outline and trends in UWB radio systems.

ABSTRACT1.

INTRODUCTIONUWB radio has attracted attention in high-speed data
communication with a very weak signal, of the samelevels as emission noise from electrical equipment
because of its ultra wideband frequency from several hundred MHz to several GHz. While UWB realizes high-speed
communication by varying pulse position (PPM) or bymodulating data by phase (PM), amplitude (AM) or frequency (FM), it also realizes very high-resolution radarwith a ranging resolution of less than 10 cm owing to thefeature of very short pulse (impulse). Recently UWB radio
has been actively researched by many institutes andindustries, with focus on a number of applications: highspeed wireless personal area network (WPAN), sensor
networks with low power consumption in the microwave
radio band, and automotive SRR in the sub-millimeterband (22~29 GHz) and millimeter band (77~81 GHz).
UWB SRR is considered a key device to survey aroundautomobiles for the prevention of traffic accidents andcasualties, and specifically is expected to detect targets
with high resolution for other automobiles and pedestri* G C G r. , C o m p o n e n t s a n d A d v a n c e d I n t e r c o n n e c t
Technologies Dept., Ecology and Energy Lab., R&D Div.
*2 WS Gr., FITEL Photonics Lab., R&D Div.

ans within 20 m in a wide angle. At the end of 2005, automotive UWB SRR was brought to market in Europe for the
first time in the world.
The 22~29 GHz UWB SRR system consists of multiple
radar units with antenna (for example, 8 units), and estimates the exact position of a target by triangulation.
Figure 1 shows possible applications for UWB SRR.
Major applications of UWB SRRs are adaptive cruise control (ACC) with Stop & Go, parking assistance, and warning in blind spots. In the figure, ACC indicates different
applications in the millimeter radio band (77 GHz) todetect range up to 200 m which will be equipped withUWB SRR.
In this paper, the authors report on standardization
trends in UWB, and developments including impulse genBlind spot

Intersection
Side crash

Rear crash
Park-aid
pre-crash

Parking &low-speed
backupRear collision
warning

Figure 1

ACC withstop & go
Side crash

Blind spot

Collision
warning

ACC(77 GHz)

Collision
avoidance
Intersection

Possible applications for 24-GHz UWB radar.

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Development of Ultra Wideband Radio System for Short-Range Radar Applications

2.

TRENDS OF STANDARDIZATION AND
REGULATION FOR UWB RADIOSYSTEM

2.1 ITU-R TG1/8
In ITU-R, TG1/8 was established from 2003 to Oct. 2005
for the international standardization of UWB. Especiallyfor the microwave radio band, the usage of bands
between 3.1 and 10.6 GHz was mainly discussed. The
permitted radiation level was recommended to be 20 dB
lower than the level permitted by the FCC. However, it
was also approved that the authorities of each country or
region can establish their own domestic UWB regulations.
The spectrum masks proposed by Europe, the USA andJapan are attached for reference. For the millimeter wave
radio band, the treatment for the protection band
(23.6~24 GHz) is particularly being discussed at TG1/8
for the decrease in UWB radiation to protect other existing
radio systems, while Europe and the USA has alreadypermit UWB radiation under their own restrictions. Other
counties, including Japan, China and Korea, are to study
their own spectrum masks.
2.2 Trends in the USA
The frequency allocation for UWB in the USA is shown in
Table 1. The other related regulations are as follows:(1) -10 dB bandwidth shall be within 22 to 29 GHz(2) The radiation level in the protection band
(23.6~24 GHz) shall be decreased gradually by 2005,2010 and 2015.
(3) Frequency hopping modulation and stepped frequency modulation are also to be made available in theband between 23.12 and 29 GHz except for the protection band, on the following conditions: that themethods have a -10 dB bandwidth of more than
10 MHz; that the maximum average radiation power
and peak radiation level is higher than 24.075 GHz;and that the devices operate only when the automobile engine is running.
Table 1

FCC frequency allocation.

Frequency in MHz

EIRP* in dBm

960~1,610-75.3

1,610~23,120-61.3

23,120~23,600-41.3

23,600~24,000-61.3

24,000~29,000-41.3*effective isotropic radiated power (EIRP)

2.3 Trends in Europe
Figure 2 shows the spectrum mask in Europe. The shortrange device (SRD) band is assigned for Doppler-shiftmeasurement of automotive radar, apart from wideband

spread spectrum frequencies. In Jan. 2005, the EC committee issued an order that allows automotive radar in the
24-GHz band until 2013 and bans the introduction of
applications other than automotive radar for the 24-GHz
band. The 77~81-GHz band is also considered for use
after 2013.
24 GHz SRD band

+20
+10
EIRP (dBm)eration/detection for high-resolution ranging, data modulation/demodulation for simultaneous ranging and data
communication, and system evaluation.

0

23.6 〜 24 GHz
Passive band

-10

SRR carrier

-20
-30
-40

22.625 GHz

25.625 GHz
24. 125 GHz-50

Figure 2

European Telecommunications Standards Institute(ETSI) spectrum mask.

2.4 Status in Japan
In Japan, the frequency band around 26.5 GHz is being
proposed in order to avoid the protection band.
Enactment of regulations for sub-millimeter band UWB is
still a task for the authorities. The Ministry of Internal
Affairs and Communications (MIC) held a public hearing
on this issue in Mar. 2006.

3.

DEVELOPMENT OF TECHNICALELEMENTS FOR UWBIn this section, the development of technical elements are
introduced including impulse generation, reception anddetection in UWB radar.
3.1 UWB pulse generation
Capacitors and switches are widely used to generate
impulses. Though a switch is useful for on/off switching ofoscillators for UWB communication, a costly control circuit is needed for high-speed switching. Recently, lowvoltage differential signaling (LVDS) is becoming popular
to generate high-speed signals for serial interfaces,
because LVDS features low voltage, which reduces theload for high-speed data generation, and handles differential signals which reduce the influence of commonmode noise. As the authors focused on the feature of
LVDS for high-speed data transmission and its controllability, it was decided to apply LVDS to generate stable
UWB pulse.
Figure 3 shows a method of impulse generation with
LVDS. The differential signals consist of N (negative) andP (positive) signals for offset voltage Vo. The desired
impulse can be generated by picking up only P, and bythen cutting off the DC component of P with a DC blocker
such as a capacitor. If P-N>0 then “1” is transmitted, and
if P-N<0 then “0” is transmitted. By changing data seriesof “0” and “1”, impulses can be generated for timing at
will. For example, an impulse of 320 ps width can be gen-

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Development of Ultra Wideband Radio System for Short-Range Radar Applications

erated from 1 bit by a differential pulse of 400~800 mV in
amplitude (or 800~1600 mVpp) when the LVDS data rate
is 3.125 Gbps.
An example of an impulse generated by this method isshown in Figure 4 for time domain and Figure 5 for frequency domain.
2)Selectone polarity
polarity (for(for example
example Positive)2)Select one
positive )
N
P

VV

oﬀset
V00 : Oﬀset
0

1

0

00

00 0 0 1 1 0 00; 0; LVDS
LVDSdata
data
line
lin

V
V

Figure 3

Impulse generated with LVDS.

3.2 RF Circuit
Though a double-balance mixer can be applied for converting UWB pulse signals, it causes a carrier-leakage ofthe local oscillator (LO) signal for lack of isolation performance. To avoid this problem, the authors adopted an RF
switch to reinforce isolation of the double-balance mixer.
Waveguides are widely used to build the circuit for the
sub-millimeter and millimeter radio wave bands becauseof good transmission performance (low attenuation), but
size increases. Thus the authors adopted coaxial RF
devices to build the circuit.

3.2.1 RF Transmitter
Figure 6 (a) shows a block diagram of the RF transmitter.
An RF pulse of the desired frequency (26.5 GHz) can beobtained by mixing baseband impulse and phase lockoscillator (PLO) output at 26.5 GHz via a switch at the
double-balance mixer. Then, through a band pass filter(BPF) and power amplifier, the desired pulse power of at
26.5 GHz can be caused to radiate from the Tx antenna.
In the actual configuration, a coaxial cable is connected
between transmitter output and receiver input to replace
RF wave radiation in the air because of licensing issues.
3.2.2 RF Receiver
Figure 6 (b) shows a block diagram of the RF receiver.
The RF signal received by the Rx antenna is amplified bya low noise amplifier (LNA), and is converted to a baseband signal with a device such as an in-phase quadrature(IQ) demodulator, mixer or diode. The authors adopted adiode-type detector for cost reduction. With the detector,
the RF signal is demodulated to a baseband video signal
after limiting the bandwidth by a BPF. Detection performance varies by the type of diode, and the authors chosea tunnel diode for good sensitivity and response. Figure 7
shows an example of the video signal detected.

（a）RF transmitter

High speed SW

PLO

Tx antenna

PA

BPF

DBM

（b）RF receiver

Baseband partRx antenna

LNA

Figure 6

Figure 4

BPF

Video detector

Schematic diagram of RF parts of radar.

Typical time domain signal.

Input pulse width: 1 ns
Detection pulse width: 1.01 ns

Figure 7

Figure 5

Typical video signal detected.

Typical frequency domain signal.

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Development of Ultra Wideband Radio System for Short-Range Radar Applications

4.

UWB MULTI-FUNCTION SYSTEM FORRANGING AND COMMUNICATIONThe UWB multi-function system developed in this work is
introduced in this section. While the system has radar
function with impulse, it also realizes a communication
function by adding PPM at the same time. The RF partdescribed in this section was developed on our own,
however, and is not identical to the RF part adopted in thedemonstration system.
4.1 Summary of UWB Multi-function
The outline of the system is shown in Figure 8 and Figure
9, and Table 2 shows the main specifications of the radardeveloped here. In the transmitter (Tx), each baseband
impulse is generated in a pulse repetition cycle, eitherwith or without delay of a time-slot depending on thedesired data (“0” or “1”) to modulate. The generated
baseband impulse is converted to an RF pulse of thedesired frequency (26.5 GHz) mixing with the carrier signal. The RF pulse is amplified by the LNA and radiatedfrom the Tx antenna. The RF signal reflected from the target is received by the Rx antenna, amplified by the LNA
and then detected by a wave detector (for example, a tunnel diode). The output signal is branched to the ranging
circuit for the distance measurement transaction and tothe communication circuit for the data demodulationtransaction.
4.2 Development of Baseband Part
To realize a UWB multi-function system, a baseband partwith a signal transaction function should be developed aswell as the elements introduced in the previous sections.
In the development of the baseband part, the authors
decided to use a high-performance all-purpose field programmable gate array (FPGA) for efficiency and more
rapid development. As well, an embedded CPU was
adopted for low-speed signal transaction and as an interface with an external PC. The transmitter, ranging circuitand communication circuit of the baseband part are introduced in this section.
4.2.1 Transmitter Part
The modulation method of the transmitter part is introduced here. Depending on data, the impulse is generated
either without delay (when the data code is “0”) or with adelay of dT (when the data code is “1”), where dT ismuch smaller than the pulse repetition cycle, T.
4.2.2 Ranging Circuit
An ordinary impulse radar detects an echo from the target
by converting the received RF signal to a low frequency
and sampling the signal with an analog digital converter(ADC). Because the developed system uses PPM for data
communication, the pulses are not always transmitted ina constant interval. In the ranging circuit, the influence ofdelay by PPM is removed by compensating for the time ofdelay (dT). The circuit also has an averaging function for
amplitude of each range information, and the averaging

number is variable. The circuit judges the presence of thetarget by comparing the averaged signal in the range
information to a threshold value. The distance of thecounterpart transmitter/receiver can also be estimatedfrom the above range information.
4.2.3

Communication Circuit (Data Demodulation
Circuit)In the communication circuit, the detected signal isjudged either “H” or “L” directly by a comparator. The
threshold value for the comparator is variable and easilychanged. Figure 10 shows the flow of data demodulation.
The received signal is judged either “H” or “L” by a comparator, using the following process: wait for the first “H”
reception; count the time (Tcount) until the next “H” reception; compare Tcount with pulse repetition cycle (T). If Tcount< T, the data is reset to 0, but if Tcount > T the data is set
to 1. If Tcount = T the data keeps its previous state. In acase where Tcount > 2T, the counter pauses as there is nodata transmission and waits for another “H” to come. Afterdata is demodulated, the counter is reset and restarts
counting.

5.

EVALUATION OF DEVELOPED SYSTEM

The evaluations of the proprietary system and the demonstration system for the NICT consortium are introduced inCommunication data

Radar and data
modulator/demodulator

Figure 8

Tx

Tx

Rx

Rx

Ranging

Radar andRadar
anddataData
modulator/demodulator

Block diagram of the communications and ranging
device.
Tx antenna

Upconversion
Upconversion

Impulse generator

TargetTargetSampling trigger information

Rx circuitry
Rx
CircuitryRx antenna

Ranging
Ranging
Communication
Communication

Detector

LNA
LNA

Base band

Figure 9
Table 2

Schematic diagram of multi-function radar.
Performance specification of the developed radar.

Parameter

Specification

Pulse shape

Uni-polar rectangular pulse

Pulse repetition frequency

1 MHz

Pulse width

1 ns

Rx frequency

26.5 GHz

Distance coverage

24 m

Distance resolution

15 cm, 7.5 cm

Modulation

Binary-PPM

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Pulse repetition period; T

Development of Ultra Wideband Radio System for Short-Range Radar Applications

Conventional
Conventional
radar
Radar
targetRadar
device target
Radar
deviceTd
Td

Multi -functional
SRR
deviceMuti-functional
Muti-functional
TargetTarget++Receiver
ReceiverdevicedeviceTrigger for counter
Count intervals
Betweenbetween pulses.
pulses.

TTddTimingTiming
oﬀset
Oﬀset
for
For
correct
correct
rangingranging
�
T
dT

Td
Td
Td
Td

d=1 TTd
��=ʻ1'dTcountT count=T=+�T
data=1
data=1d='0 TTd
��=ʻ0'dTcountT-T
Tcount=T=-�
data=0data=0T
TcountcountData@Rx

T -��
T-dT
00

T
T T
T+dTd
+�T
previous data1
Previous

Figure 10 Flow of communication and ranging procedure.

the data becomes “1” when the driver applies the brake.
For synchronization of the receiver, an additional 8 bits
are prepared for the preamble. Thus, 16 bits of data (preamble and information) make a frame. The graphical userinterface (GUI) is shown in Figure 11. The parameters canbe set up from the console (shown in the center). The signal reflected from the target in raw waveform is indicatedat the upper left. The table at the upper right indicatesnumerical peaks (maximum 20) with distance and intensity of reflected signal from the target. The lower side (withpictures of automobiles) indicates the status of communication: reception from other vehicle in left side, and transmission from own vehicle in right side. The demonstration
showed that communication was performed without disturbing the ranging function.

the first and second parts, respectively.
5.1 Experimental Result of Ranging Function
The ranging performance is evaluated by LVDS impulse.
Three coaxial cables of different length were preparedand connected directly from the RF transmitter to the RF
receiver to simulate echo from the target, instead of RF
radiation from the antenna. The result of these measurements is shown in Table 3, where the velocity factor of
coaxial cable is 0.7 and the ranging resolution mode is 15
cm, and demonstrates that the function works accurately
within the resolution.
Table 3

Target ranging results (resolution = 15 cm).

Cable length (cm)Result (cm)100

101.43200

187.14300

301.43

5.2 Experiment with Multi-function System
The demonstration system consists of an antenna, RFtransmitter, RF receiver and baseband part. The baseband part in the developed system was adapted to thedemonstration by the NICT UWB consortium. The RF
receiver was developed by the NICT in cooperation withthe authors. The other parts were provided by the NICT.
The system was demonstrated at IWUWBT2005 the international UWB conference held in Dec. 2005, and showedthat the impulse for ranging can be also utilized for data
communication. The demonstration attracted attention
there. The baseband part has two operational modes, theproprietary mode and the demonstration mode. Here, theperformance of the demonstration system is introduced
as a result of experiments. For data communication, visual information for the automobile including direction indicators (blinkers), brake-lamps, and hazard lamps are
assumed to be transmitted to the other automobiles toremind drivers to acknowledge the behavior or intentionof other automobiles. Data slots with 8 bits are prepared
and assigned to the above information. For example,
information on the brakes is assigned to the first bit, andFigure 11 Screen of measurement result.

Figure 12 UWB communication and ranging demonstration
device.

6.

CONCLUSION

The authors have successfully developed a UWB-based
short range radar system in the 22~29 GHz band. It is thefirst system in Japan that realizes multi-function for highresolution ranging and low-speed data communication.
The system is expected to contribute to road safety.
The baseband part of the developed system was adopt-

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Development of Ultra Wideband Radio System for Short-Range Radar Applications

ed in a demonstration by the NICT UWB consortium andplayed a core role in a demonstration at the international
UWB conference in Dec. 2005. The demonstration attracted the attention. Following the development, the authors
plan to conduct research toward a small-size low-cost
product for UWB SRR.

REFERENCES
1) “Commission enables cars to be equipped with road safety technology,” eSafety Support, (2005).
2) “New Distronic Plus Helps in Stop-and-Go Traffic,” MercedesBenz, News Release 2006, (2006).
3) Martin Kunert, Reiner Doerfler, Werner Hosp, and Christian Preis:“24 GHz UWB short range radars for vehicular applications,”
MWE2003, (2003), 110.
4) “About system maintenance for the use of a ultra wideband (UWB),”
MIC, (2005). (in Japanese)
Online: http://www.kisei-kaikaku.go.jp/minutes/wg/2005/1205/
item051205_02.pdf
5) “ S E C O N D R E P O RT A N D O R D E R A N D S E C O N D
MEMORANDUM OPINION AND ORDER,” FCC, NEWS, (2004).
6) “ECC Decision of 12 November 2004 on the frequency bands to be
designated for the temporary introduction of Automotive Short
Range Radars,” ECC/DEC/(04)’10, (2004).
7) “A summary of an opinion submitted for UWB committee report (aplan) and a way of thinking of a UWB radio system committee,”
MIC, (2006). (in Japanese)
Online: http://www.soumu.go.jp/joho_tsusin/policyreports/joho_tsusin/uwb_wlsystem/pdf/060320_1_si2.pdf
8) Yasushi Aoyagi, Kazutaka Kamimura, Ryuji Kohno, “UWB Multifunctional System for Communication and Ranging,” IWUWBT2005,(2005), 87.

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