Development of Future Short Range Radar

Development of Future Short Range Radar

Technology

Karl M. Strohm, Hans-Ludwig Bloecher, Robert Schneider, Josef Wenger

1 DaimlerChrysler AG, Research & Technology, Wilhelm-Runge-Str. 11, 89081 Ulm, Germany, Tel. +497315052025

Abstract — First ca rs equipped with 24 GHz Short Ra nge Ra da r (SRR) systems in combina tion with 77 GHz Long Ra nge Ra da r (LRR) system will enter the ma rket in autumn 2005 enabling new safety and comfort functions. In Europe the 24 GHz ultra wideband (UWB) frequency band is tempora lly a llowed only till end of June 2013 with a limitation of the car parc penetration of 7%. From middle of 2013 new cars have to be equipped with SRR sensors which opera te in the frequency ba nd of 79 GHz (77 GHz to 81 GHz). The development of the 79 GHz SRR technology within the Germa n government (BMBF) funded project KOKON will be described.

I.I NTRODUCTION

World Health Day on 7 April 2004 was dedicated to the theme of road safety. This was due to the fact, that every year, according to the statistics, 1.2 million people are known to die in road accidents worldwide and as many as 50 million are injured. With the slogan “Road Safety is No Accident” attention was drawn to the fact that road traffic injuries can be prevented if governments and others take action [1].

Within the European Union more than 40,000 fatalities and 1.7 million injuries are caused by road accidents each year. The European Commission (EC) has set, in its White Paper on the Common Transport Policy of September 2001 [2], an ambitious target to reduce road deaths by 50% by the end of 2010.

The European Commission, has identified automotive short range radar systems, as a significant technology for the improvement of road safety in Europe. SRR at 24 GHz is one of the key topics of the e-Safety programme of the EC and is seen as a major instrument to improve road safety.

In this paper an overview of the actual automotive radar frequency regulation issues is given, the current status of 24 GHz short range radar systems is presented, and the development towards future SRR technology is discussed.

II.A UTOMOTIVE RADAR FREQUENCY REGULATIONS

A consortium of automobile manufacturers and suppliers known as the SARA (Short Range Automotive Radar F requency Allocation) Consortium is working on for the worldwide frequency allocation for 24 GHz UW

B automotive radar. In the USA, approval of the 24 GHz band was already granted unlimited in time and system numbers in 2002 by the US regulation authorities.

In Europe, on 17 January 2005 the European Commission approved the decision on allocation of the 24 GHz frequency band for automotive short-range radar [3]. According to this decision the frequency band of 21.625-26.625 GHz is allocated for the temporary use of UWB automotive short range radar from 1 July 2005 until 30. June 2013. Included is the task to work towards an early introduction of equipment operating in the 79 GHz band by means of research and development programme.

From mid of 2013 new cars have to be equipped with SRR sensors which operate in the frequency range between 77-81 GHz (79 GHz band). The 79 GHz frequency band was designated for the use of automotive short range radars in the ECC decision (ECC/DEC/(04)03) [3] from 19 March 2004. F ollowing regulations are fixed:

79 GHz frequency range (77-81 GHz) is designated

for Short Range Radar (SRR) equipment on a non-

interference and non-protected basis with a maximum

mean power density of -3 dBm/MHz e.i.r.p.

associated with an peak limit of 55 dBm e.i.r.p

the maximum mean power density outside a vehicle resulting from the operation of one SRR equipment

shall not exceed -9 dBm/MHz e.i.r.p

the 79 GHz frequency range (77-81 GHz) should be made available as soon as possible and not later than

January 2005

The European approach of a temporary use of 24 GHz with a transition to 79 GHz is called “packaged solution” (Fig. 1) to make an early contribution to the enhancement

of road safety possible and to give the time for the development of the 79 GHz technology which is not yet mature for SRR sensors.

Fig. 1. "Package solution" for automotive short range radar in Europe.

The European 24 GHz SRR standard (document: ETSI EN 302 288 [4]) has been completed recently. The drafting process of the European 79 GHz SRR standard

(document: ETSI EN 302 264 [4]) has started and is still ongoing.

III.24GH Z S HORT R ANGE R ADAR

Monitoring the surroundings of cars with sensors gathers useful information for safety and comfort applications. Radar appears to be the best sensor principle, because alternatives like video, laser, and ultrasound may have difficulties under bad weather conditions, when they are needed most. Additionally radar offers the vehicle manufacturers a stylistic advantage of mounting behind a plastic bumper that can be considered nearly transparent to the radar signal without requiring specific cut-outs or similar accommodations.

As shown in Fig. 2 short range radar sensors can enable

a variety of applications:

?ACC support with Stop&Go functionality ?Collision warning

?Collision mitigation

?Blind spot monitoring

?Parking aid (forward and reverse)

?Lane change assistant

?Rear crash collision warning

Collision warning

Collision

mitigation Blind spot detection

Stop & Go for ACC Parking aid

Precrash

Backup

Parking aid Blind spot

detection

Lane change

assistant

Rear crash

collison

Fig. 2. Short Range Radar – different kinds of applications. Especially the combination of LRR and SRR provides valuable data for advanced driver assistance systems (ADAS). Part of this will be realized for the first time in the future Mercedes Benz S-Class, which will celebrate its world premiere in autumn of 2005. In the new S-Class two radar systems are offered to monitor the traffic situation in front of the vehicle: a newly developed short range radar based on 24 GHz technology works in tandem with the tried and proven 77-GHz radar employed in the DISTRONIC proximity cruise control system [5]. The two systems complement each other well: Whereas the DISTRONIC radar is designed to be able to track three motorway lanes over a distance of up to 150 metres with an angle of nine degrees, the new 24-GHz radar uses an angle of 80 degrees to monitor the immediate area up to 30 metres in front of the vehicle (Fig. 3).

The radar technology will be used to determine the distance to vehicles ahead (F ig. 4), warn drivers when they get too close, and provide the necessary braking power if it appears that a collision is unavoidable. In those situations where drivers are forced to brake, the new Brake Assist PLUS system will calculate and generate the braking force needed for a given situation

within fractions of a second.

Fig. 3. Combination of LRR and SRR for advanced safety features.

While the conventional Brake Assist requires a reflex activation of the brake pedal, the new system recognises the driver’s intention to brake when he or she puts clear pressure on the pedal, after which it automatically optimises the braking pressure. One of the key preconditions for preventing rear-end collisions is thus fulfilled: the best possible braking deceleration for each

situation.

F ig. 4. Short range radar observing the area in front of the motorcar.

Mercedes-Benz has conducted extensive tests with the new technology, in both a driving simulator and under real conditions: The driving-simulator tests involved a total of 100 drivers, each of whom drove for 40 minutes and were confronted with several critical situations on motorways and rural roads, whereby emergency stops were the only way to prevent an accident. The result was that 44 % of the simulated drives taken with conventional brake technology resulted in accidents, but only 11 % of those in which Brake Assist PLUS was used.

What is more, the combination of the new Brake Assist PLUS and PRE-SAFE? made possible a higher level of occupant protection. In addition to tried-and-tested PRE-SAF E? functions such as seatbelt tightening and seat repositioning, the future S-Class will also be equipped with new multi-contour seats with cushions and backrests that automatically inflate if an accident threatens. Thus a comprehensive safety system will be activated before a threatening accident has a chance to happen.

The 24 GHz SRR sensors used in the new S-class are based on a pulsed radar concept according to Fig. 5 [6]. The RF front end (transceiver) consists of the transmit circuitry, the receive circuitry and the control and processing circuits. An object at range R is detected by measuring the elapsed time between a transmitter pulse and a correlated received signal. With this time-gated

correlation receiver architecture detection range of 0.2 to 30 m, a range (object) resolution of 15 cm and a range accuracy of 7.5 cm can be achieved. Up to 10 objects with range, bearing and velocity information can be classified.

The individual sensors are connected via a local network to the radar decision unit which is on its part connected via the car controller area network (CAN) bus to the different electronic control units of the car.

Fig. 5. Simplified shematic diagram of a 24 GHz SRR front-end according [6].

IV.F UTURE S HORT R ANGE R ADAR D EVELOPMENT

In the ECC Decision of 19 March 2004

(ECC/DEC/(04)03) it was decided that the 79 GHz

frequency range (77-81 GHz) is designated for Short

Range Radar (SRR) [3]. Already in the year 2009 a report

has to be made about the development status of 79 GHz

SRR technology [3].

The ECC frequency regulation forces the development

of 79 GHz SRR sensors within a time frame of only 8.5

years. Considering the development cycles of

automobiles this is a very short time period.

The transition from 24 GHz to 79 GHz causes an

increase in frequency and a reduction of wavelength by

the factor 3.3. The smaller wavelength λ enables reduced

antenna size and spacing (~λ) and lower effective antenna

area (~λ2). The higher frequency yields increased

atmospheric and bumper losses. With higher frequencies

semiconductor power output decreases (roughly 20 dB per decade), parasitic effects are more stringent, and packaging and testing are more difficult.

The development plan towards the introduction of 79

GHz SRR sensors is shown in Fig. 6. Sensor-Vehicle-Time schedule

Development

Development

Integration

Rollout

F ig. 6. Time schedule for the development and rollout of 79 GHz SRR sensors.

Essential features of future 79 GHz radar sensor systems are:

?low chip and component costs ?low assembly costs

?improved performance

?reduced power consumption

?improved electrostatic discharge (ESD)/

electromagnetic interference (EMI) ?high update rates

The historical path in the electronics industry for reducing cost, and improving and increasing functionality, has been to migrate toward IC-based solutions. Therefore in the first phase an effective and powerful chip technology has to be developed. With the funding of the German Ministry of Education and Research (BMBF) the joint research project “Automotive high frequency electronics – KOKON” [7] was started in September 2004. The KOKON consortium consists of two semiconductor companies (Atmel and Infineon), two automotive radar sensor manufacturers (Bosch and

Continental Temic), and one automobile company

(DaimlerChrysler) supported by institutes and universities.

Silicon Germanium (SiGe) has been identified as the chip technology which may fulfill the technological

requirements and the cost constraints and which might be

an alternative to GaAs [8]. Within the KOKON project

the development of both 77 GHz LRR and 79 GHz SRR

radar chip technology is investigated. As spin-off cost

reduction and performance improvement of 77 GHz LRR

sensors are expected.

The specifications for 79 GHz SRR systems are:

?F requency 79 GHz

?Bandwidth 4000 MHz

?Maximum field of view +/- 80°

?Range 30 m

?Range Accuracy +/- 5 cm

?Bearing accuracy +/- 5°

With the allowed bandwidth B of 4 GHz the achievable

range resolution ΔR is according to the range resolution

equation

B c

R 2=Δ (1) 3.75 cm. In Equation (1) the factor ? is due to the two-way travel time.

With Silicon Germanium heterobipolar transistors (SiGe HBT) nowadays transit frequencies f T of 300 GHz and f max of 350 GHz have been reported by an IBM research group [9]. Infineon which is partner of the KOKON consortium has achieved up to now f T of 225 GHz and f max of 300 GHz [10]. These transit frequencies are sufficient high for the realization of 77 and 79 GHz radar MMICs.

A key device of a radar transceiver is the voltage controlled oscillator (VCO). Using the Infineon technology fully integrated SiGe VCOs with powerful output buffer for 77 GHz automotive radar system have been demonstrated [11]. The data of this VCO (F ig. 7) are:

?chip size: 0.8 x 1.2 mm2,

?center frequency: 77 GHz,

?tuning range: 6.7 GHz,

?phase noise: -97dBc/Hz at 1 MHz offset frequency,

?output power (2 outputs): 18.5 dBm

?single power supply: -5.5 V

?power consumption: 1.2 W

Fig. 7. Photograph of the 77 GHz SiGe VCO Chip (0.8 mm x 1.2 mm) according to [11].

Also a low-noise and high-gain double-balanced mixer for 76.5 GHz automotive radar front-ends in SiGe bipolar technology has been realized using the Infineon technology [12]. The data of the active mixer are: ?Chip size: 550 x 450 μm2

?Gain (65 – 90 GHz): > 24 dB

? 1 dB Compression Point (In/Out): - 30 dBm/- 4 dBm

?SSB Noise F igure (72–82 GHz): < 14 dB (IF > 10kHz)

?Supply Voltage: - 5 V

?Supply Current: 60 mA

?

Additional key elements like LNA, frequency divider etc. have also been demonstrated. The final goal will be to fully integrate a 79 GHz SRR transceiver front-end on a single chip.

VI.C ONCLUSION

F irst cars equipped with 24 GHz short range radar sensors will be available in autumn 2005 with already remarkable active safety features. Additional driver assistance functions based on SRR sensors are expected in near future. In Europe the designated SRR frequency band at 24 GHz is allocated for temporary use with a transition to 79 GHz (77-81 GHz) no later than 1 July 2013. Therefore the development of 79 GHz SRR was started with high priority. SiGe HBT technology has the potential to realize cost effective “radar on chip” solutions.

A CKNOWLEDGEMENT

The authors wish to acknowledge the funding of the German Ministry of Education and Research (BMBF) within the KOKON project and all partners and subcontractors of the KOKON consortium who contributed to this work.

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