Applications of Millimeter-Wave Sensors in ITS

by Shigeaki Nishikawa* and Hiroshi Endo*

There is considerable public and private support for intelligent transport systems

ABSTRACT (ITS), which promise spectacular improvements in road traffic safety and transpor-

tation efficiency. This paper deals with research efforts relating to radar sensors using millimeterwave technology, which is fundamental to enabling the all-weather operation of ITS. One of these isfor an automotive radar and is used for forward looking and to detect the distance and relative
velocity of vehicles ahead. The other is a radar for infrastructure (right-of-way installation) and isused to detect obstructions and vehicles. Both use spread-spectrum (SS) technology, which offers
outstanding performance in separation and detection of multiple vehicles. The automotive radar has
multiple receiving antennas to determine the direction in which the target lies, using a method
whereby the angle is calculated by comparing the power of the signals.

1.

INTRODUCTION

Intelligent transport systems (ITS) are under active development worldwide as a means of reducing loss of life andlimiting economic and environmental costs. In Japan, theMinistry of Construction and other government agencies
have been carrying out a variety of projects since the1970s, but in July 1996 these were unified into a national
project. This was jointly announced as a "Basic Guidelines on the Promotion of ITS" by five government agencies--The National Police Agency, The Ministry of International Trade and Industry, The Ministry of Transport, The
Ministry of Posts and Telecommunications and The Ministry of Construction. The scheme proposed 20 user services, and serves as a blueprint for efficient and systematic R & D and commercial introduction.
This paper reports on applications of millimeter-wave
sensors in ITS, specifically an automotive millimeter-wave
radar using spread-spectrum (SS) technology, and an
obstacle and vehicle detection radar for installation on theroad right-of-way.

* ITS Technology Center, Yokohama Research Lab., R&D Div.

2.

Automotive Millimeter-Wave Radar
Using SS Technology

2.1 Automotive Radar and Its Applications
Of the wide range of technologies used in ITS, millimeterwave technology is an important element applicable tothe sensors (radar) and communications. Because its performance is particularly unaffected by weather, it has attracted attention as a replacement for infrared laser radarsystems currently in use, and is itself nearly ready for commercial launch.
Automotive millimeter-wave radars are used in suchapplications as forward looking to warn drivers of dangers, and studies are under way on using it to measure
the distance to vehicles ahead and to maintain constantintervals between vehicles. It is hoped that the wider useof automotive millimeter-wave radar will reduce serious
traffic accidents that so frequently occur on limited-accesshighways in foggy or snowy conditions.
In addition, automotive millimeter-wave radars could be
used to monitor the driver's "dead zone", and serve as aperipheral monitoring sensor in the automated cruisingsystems of the future. Studies are also under way in ITS
areas besides vehicles, such as detection of obstacles on
the road, detection of moving vehicles, etc.
Systems applying automotive millimeter-wave radar
include collision avoidance and cruise control featuring
interval control, and development is under way towardcommercially viable products.1) Table 1 shows typical per-1

formance requirements for a radar for autonomous intelligent cruise control (AICC). The main issue is the provision of wide-range angle measuring capability.

Table 1

Typical AICC Radar Performance Requirements

Maximum range

100 ~ 120 (m)Relative velocity± 200 (km/h)

Range accuracy± 3 % (min ± 1 m)

Relative velocity accuracy± 3 % (min ± 1 km/h)

Figure 1 shows the hardware configuration of the prototype radar. A 1-GHz intermediate frequency band signal
is modulated by a PN sequence in the IF circuit. The spreadsignal is up-converted to 76.5 GHz in the RF circuit, andis then transmitted from the transmitter antenna.
This transmitted signal is then reflected from an object
in front of the radar, and received by the three receiver

14 ~ 20 (˚)

Field of view

2.2

Features of SS Method, and Prototype Configuration and Specifications
Considered for automotive radars, the SS method has anumber of features that make it easy to achieve the following characteristics: 2)~7). Accurate distance measurement;. Separation and detection of multiple vehicles locatedin the range direction;. Accurate measurement of reception power; and. Interference eliminating capability.
It is reported that, in the FMCW method, ranging isgoverned by the linearity of the local millimeter-wave transmitter, whereas in the SS method, even when the phasenoise characteristics of the transmitter are poor, compensation is provided by the mixer, making it more advantageous in the development of millimeter-wave transmitters.4)
For the reasons mentioned above, the SS method wasconsidered more suitable for automotive radar, and it wasused in the development of the millimeter-wave radar.
Table 2 shows the specifications of the prototype radar.
Table 2

Specifications of Prototype Radar

Item

Specifications

Modulation method

Direct-sequence SS

Frequency

76.5 GHz

Bandwidth

480 MHz

Output power–2 dBmPN sequence

M-sequence, 127 chips
Chip rate: 24 Mchip/s

Antennas

Tx: 1 (11˚ (AZ))
Rx: 3 (4˚ (AZ))

Range

100 m

Relative velocity±200 km/h

With respect to angle measurement, a method was
adopted whereby the signals were received by three antennas of different directionality. The power information
received by each is detected at the stage of SS signal
demodulation, and angle information is taken from theiramplitude intensity ratios.

2

Figure 1

Hardware configuration

antennas. After each of the received signals is selectedsequentially at the switch provided in the RF circuit, it isdown-converted to the IF signal by the local signal of themillimeter-wave used in the up-converter and sent to thesignal processor, which comprises, in addition to the control circuitry, the following algorithms:. object detection algorithm,. object tracking algorithm, and. angle measurement algorithm
The radar detects the distance, the relative velocity andthe reflected power of multiple objects using object detection algorithm. In the object tracking algorithm, multiple
objects are tracked based on the features of values instantaneously measured, which are then time-stream processed and assigned to the objects. In the angle measurement algorithm, the output data of the object tracking
algorithm for the identical object received by each receiving antenna are selected, and amplitude information basedon received power is compared, analyzed and processed
to estimate the angle of the object.
2.3 Performance Evaluation
Figure 2 shows the evaluation system for field test. The
RF unit of the prototype radar was mounted near the front
grille, and the IF and signal processing units were positioned inside the cabin. The situation evaluated was recorded on video tape.
The first items of performance evaluated were for distance and relative velocity on a limited-access highway
straight-away, using a passenger vehicle as the target. Figure 3 shows the results, which confirmed that the prototype radar could provide stable measurements of the distance and relative velocity of a vehicle in front at ranges of
up to 100 m. A separate static test confirmed that distance measurements were accurate to within approximately ±1 m. Evaluations were also conducted using a
number of passenger vehicles as the targets, and similar

Furukawa Review, No. 18. 1999

Relative
velocity

Figure 2

Figure 4

Evaluation system

Example of angle, distance and relative velocity
measurements

totype radar was capable of stable measurement of theangle of a passenger vehicle running approximately 40 m
ahead within a range of ±4°.

Figure 3

Example of distance and relative velocity measurements

performance was confirmed for each of them.
Next the performance of the angle measurement
method was evaluated on a curved section of limited-access highway having a radius of approximately 300 m.
Figure 4 shows the results, which confirmed that the pro-

Figure 5

2.4 Accuracy and Range of Angle Measurements
The accuracy of the angle measurement method wasevaluated by a test conducted under four sets of static
conditions: with a vehicle placed at orientation θ of 3 and4°, and distance L of 30 and 40m. Figure 5 shows theresults. The white squares on the plots represent measured values, while the vertical lines show the width of thevehicle at each distance. In all cases, it was confirmedthat the measured value was within the vehicle width range.
The tests demonstrate that stable angle measurements
were possible up to a range of approximately 40 m. Sincewith the method adopted here it is essential that stabledetection of a single object be provided almost simultaneously by a plurality of antennas, reception sensitivity
must be such that, in an automotive radar for which small
size is essential, reception is possible even in the regionof low antenna gain. With respect to achieving the required

Results of static observations

3

angle measurement performance, further consideration,
extending to the method adopted here, is an issue remaining for the future.

3. MILLIMETER-WAVE SENSORS FOR ITSINFRASTRUCTURE
3.1 ITS and AHS
Table 3 shows the 20 user services that are incorporated
within the overall concept of ITS. Of these, VICS (vehicle
information and communication system) and ETC (electronic toll collection) are already largely practicable, andwill be followed by AHS (advanced cruise-assist highway
system).
AHS is the most technologically sophisticated system
within ITS, and is intended, by means of equipment in-

Table 3

ITS Development Areas and User Services

Development Areas
1 Upgrading
navigation systems

User Services Provided(1) Provision of route guidance
traffic information(2) Provision of destination-related
information

2 Electronic tollcollection systems(3) Electronic toll collection

3 Assistance forsafe driving(4) Provision of driving androad conditions information(5) Danger warnings(6) Assistance for driving(7) Automated highway systems

4 Optimization of
traffic management(8) Optimization of traffic flow
(9) Provision of traffic restriction
information on accident management

5 Support forroad management(10) Improvement of maintenance
operations(11) Management of special permittedcommercial vehicles(12) Provision of roadway
hazard information

6 Support for(13) Provision of public transport information
public transportation(14) Assistance for public transport
operations and operations management
7 Improving operating (15) Assistance for commercial vehicle
efficiency ofoperations management
commercial vehicles(16) Automated platooning ofcommercial vehicles
8 Support forpedestrians(17) Pedestrian route guidance(18) Vehicle-pedestrian accident avoidance

9 Support for
emergency vehicle
operation

4(19) Automatic emergency notification(20) Route guidance for emergency vehicles
and support for relief activities

stalled on the road right-of-way, to improve safety by reducing accidents and promote economic efficiency andenvironmental protection by increasing transportation efficiency. In the United States, AHS tends to be understoodin the sense of automated cruising, but in Japan it is understood to comprise three levels of support: "i" for provision of information, "c" for control support, and "a" for automated cruising, so that these may, so to speak "progress"
as actual services are made practicable. Automated cruising, in particular, places the onus for traffic accidents on
the infrastructure (installations on the right-of-way), andthus requires that major legal and societal hurdles be surmounted, to say nothing of technical problems, but prior
to that, at the "i" and "c" levels, fully practicable systems
can be configured. Furthermore studies in Japan are proceeding with reference not only to limited-access toll roads,
but also to the ordinary highway network.
September 1996 saw the establishment of the Advanced Cruise-Assist Highway System Research Association, of which Furukawa Electric, together with 20 othermajor manufacturers, is a member. Under contact with the
Public Works Research Institute of the Ministry of Construction, this organization is working on a wide range of
AHS R & D activities, including establishing the AHS concept, system design, and major factor technologies. The
developmental effort concentrates on right-of-way infrastructure, but allocation and coordination between infrastructure-based functions and vehicle-based functions isa major issue and is an object of study.
3.2 Detection of Obstacles on the Road
Implementation of AHS requires the following broad categories of equipment and functions:. Collection and recognition of information by sensors
installed on the right-of-way. Information processing and control by local sensors. Transmission of information by road-to-vehicle com
munication equipment. Management of traffic information by wide-area andlocal centers.
Among right-of-way sensors, which form a major partof equipment for the implementation of AHS, sensors fordetermining road conditions are fundamental. That is to
say they tie in the detection of obstructions--fallen objects
on the road, stopped vehicles, bicycles, pedestrians andthe like--with danger warnings and control assistance, andby keeping informed of all moving vehicles, serve to ascertain traffic conditions, warn of danger and assist in control. They are required to function in all types of weather,including heavy fog and heavy rain. Various types of sensors--using visible light, infrared rays, laser light and radio
waves--have all been considered, but object detection
sensors using radio waves have a number of distinct advantages over those using light in the visible or infrared
range, including:. Very little absorption by fog, snow, rain, etc., making
all-weather systems possible;. Excellent environment resistance with respect to dust
and mud.

Furukawa Review, No. 18. 1999

Within the radio spectrum, the use of millimeter waves(30-300 GHz) was found to offer a number of advantages
over microwaves (3-30 GHz), including:. Higher directionality, reducing spurious operation andinterference;. More compact and lightweight equipment, particularly
antennas;. Greater Doppler shift, improving the accuracy of velocity measurement;. Wider band for higher range resolution;. Comparatively high attenuation in air, reducing interference when two systems are installed close together,and thereby allowing a number of systems to coexist.
The detection area required for infrastructure-based
sensors depends on the service provided, but may betaken, typically, to be approximately 12 m (or 3 traffic lanes)in the transverse direction and about 100 m in the length
direction. For such an area to be covered by a single radar, the millimeter-wave beam must scan. Scanning may
be effected either mechanically or electronically, but given
the budgetary constraints, mechanical scanning is the mostpractical method at the current state of the art.
The installation position was also considered--whether
to mount the radar equipment high (on gantries or overpasses about 5 m or more above the road surface), or
lower (on roadside poles or atop guard rails at a height ofabout 1 m). At the higher position it was found that toachieve a 12-m-wide detection area from near to far distances required 2-dimensional scanning of the millimeterwave. This greatly increased the measurement time withmechanical scanning and was therefore impractical. Mounting at the lower height, as shown in Figure 6, however, it
was possible to cover the detection area with a horizontal
1-dimensional scan, so that the system was feasible interms of measurement time.

Millimeter-wave
sensorDriver unit for scanning
Data analyzing unit

Figure 6

Millimeter-wave sensor installed on road right-ofway

It is necessary to bear in mind, however, that if there
happens to be a large vehicle in the foreground of theobject to be detected, the possibility that the waves will beblocked and detection impossible is greater for the lower
position that the higher. Based on the above factors, themost practicable method is to install the radar at the lower
position, on the roadside at a height of about 1 m above
the road surface, and to provide 1-dimensional left-rightmechanical scanning. In future it may well be possible toadopt high-speed 1- or 2-dimensional electronic scanning,or to install a larger number of low-cost millimeter-wave
radars.
The ability to detect multiple objects is an important function of obstruction and vehicle detection sensors used in
AHS. As noted in Section 2 above, the spread-spectrum
radar now under development by Furukawa Electric features comparatively simple separation and detection ofmultiple vehicles in the range direction, and is therefore
well suited to AHS applications.

4.

CONCLUSION

The authors are working on millimeter-wave radar for the
ITS market, which is expected to enjoy considerable
growth. Measurement of distance and relative velocity is
described as related to spread-spectrum (SS) millimeterwave radar for automotive applications. Activities relating
to obstruction and vehicle detection radar for right-of-way
installation are also described.

ACKNOWLEDGMENT
We would like to express our sincere thanks to Prof. Ryuji
Kohno of Yokohama National University for his continued
guidance.

REFERENCES

1) T.Tokoro: "Automotive radar and its applications", Journalof the 1997 IEICE, Vol.80, No.9, (1997), 917. (in Japanese)
2) J.Detlefsen, et al.: "System aspects and design of an automotive collision warning PN code radar using wavefront reconstruction", IEEE MTT-S Digest, (1992), 625.
3) K.Hasimoto et al.: "Evaluation of fundamental performancefor 60GHz automotive radar using SS method", Proceeding of
the 1996 IEICE General Conference, (1996), B-115. (in Japanese)
4) H.Endo et al.: "76GHz automotive radar using SS method",
Proceeding of the 1997 IEICE General Conference, (1997),
SA-4-5. (in Japanese)
5) S.Noda et al.: "A study on automotive millimeter-wave radarusing SS technique", Proceeding of the 1997 IEICE General
Conference, (1997), SA-4-4. (in Japanese)
6) Y.Hanada and R.Kohno: "Evaluation of angle detection performance of SS radar system using multi-beam antenna", Proceeding of the 1997 IEICE General Conference, (1997), SA4-1. (in Japanese)
7) Y.Aoyagi et al.: Evaluation of angle measurement system of
76GHz automotive SS radar", Transaction of IEICE A, Vol.J81A, No.4, (1998), 607. (in Japanese)
Manuscript received on July 17, 1998.

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