The UMRR 24GHz Radar Sensor Family for Short and Medium Range Applications

Dr.-Ing. Ralph Mende, Managing Director

smart microwave sensors GmbH

Phone: +49 (531) 39023 0 / Fax: +49 (531) 39023 58 / ralph.mende@smartmicro.deMittelweg 7 – 38106 Braunschweig - Germany

www.smartmicro.de

Abstract The paper briefly describes the UMRR sensor family, which has been developed by smart microwave sensors GmbH. The sensor operates in the 24GHz ISM band and is applicable for Advanced Driver Assistance System functions in the automotive sector. It can run both in pulse- and in a number of narrowband FMCW modes. For the narrowband modes, a frequency approval is available. The opera-tion of those with respect to existing frequency regulations is discussed. Concept, technical and per-formance data of the sensor are given. I. Concept and Technical Data Design The name UMRR stands for Universal Medium Range Radar. The design targets of the UMRR sensor platform were mainly performance and flexibility, the intention was to cover a certain range of auto-motive applications, with the focus on high dynamic scenarios. The second design target has been to create a sensor which operates in accordance with existing frequency regulations, thus being conform with ETSI EN300-440 and FCC part 15 §§15.245 and 15.249, and other acts. To achieve this, narrowband waveforms were selected. The disadvantage of the limited range resolution (separation) is compensated using high resolution signal processing algo-rithms. The compensation, however, is limited to the theoretically possible values given by the band-width. Achieving practical resolution values being very close to the theoretical limits was one of the key issues during development. Key Performance Facts:

- Direct and simultaneous measurement of range, velocity and angle. - Short measurement time. - Good min. range, medium max. range (typ. 50-70m) (in FMCW Mode). - Conformity with ETSI and FCC frequency regulations in all narrowband modes. - One-Box-Design with integrated detection, tracking and communication software.

Key Flexibility Facts:

- UWB Pulse Mode and FMCW narrowband operation possible. - Multiple planar antenna designs available. - Stand alone or network operation.

CAN

Power

Sensor-Processor #1

DSP BoardRF Board

DSPA

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MixerAmpl.

SPITX RXA RXB

Data Logging

Internal SystemCommunication

Figure 1: Block Diagram and Photograph of the UMRR Radar Sensor

The 24GHz UMRR Radar Sensor Family for Short and Medium Range Applications.doc April 8, 2004

A sensor unit consists of two components: RF frontend module and DSP module. This is depicted in the block diagram in figure 1, a photograph is given on the right. The size of the device is only (including processor) 94x78x31mm (WxHxD). Waveforms The technical data of two example waveforms, corresponding to operational modes are provided be-low. It is possible to switch between the modes, the switching dead-time has a duration of one cycle.

Parameter UWB Pulse Mode Narrowband FMCW Mode Operation Principle UWB Pulsed Single chirp FMCW 3dB Bandwidth < 3GHz < 200MHz Minimum Range 0.25m 0.75m Maximum Range 15m 60m+ Cycle Time 8ms <30ms Velocity Interval -10…+10m/s -69.4...+69.4m/s Carrier Frequency 24.125GHz Maximum Transmit Power 20dBm Antenna Type Patch Antenna Field of View (Example) 40° (Azimut) x 13° (Elevation) Supply/Interface 12V/CAN

Table 1: UMRR Technical Data

As an example, an FMSK signal [2] is described in figure 2. This combination of FSK and LFM wave-form design principles offers the possibility of an unambiguous and simultaneous target range and velocity measurement. The transmit waveform consists in this case of at least two linear frequency modulated up-chirp or down-chirp signals (the intertwined signal sequences are called A and B). The two chirp signals will be transmitted in an intertwined sequence (ABABAB...), where the stepwise fre-quency modulated sequence A is used as a reference signal while the second up-chirp signal is shifted in frequency with . The received signal is down converted into base band and directly sampled at

the end of each frequency step. The combined and intertwined waveform concept is depicted in Fig-ure 3.

Shiftf

Descriptions of the Pulse Mode is not provided here, for details of a similar UWB system see [1] and [5]. RF Waveform and the corresponding detection and tracking software are thus quite flexible. UMRR can be optimized for different requirements, i.e. maximized object separation and/or maximum sensi-tivity etc., depending on the situation. To demonstrate the sensitivity of UMRR, some more numbers can be given. The typ. max. range on pedestrians is 45m, on bicycles 50m and on passenger cars 60-70m. The speed of the object has no influence on the maximum range. All parameters are measured during only one cycle. Typical Accuracy data are:

Range: Typical < 0.5m (under 10m, 10m…max. range: better than +- 1.25%). Velocity: Typical < 0.25km/h. Angle: Typical < 0.5 degree.

The radar is able to resolve (separate), handle and track multiple targets. To be separately detectable, in theory two objects of identical reflectivity must be different in at least one of the following parame-ters (B=100MHz, Tcycle = 30ms):

Range Difference >= 1.5m, Speed Difference >= 0.21m/s. The UMRR sensor achieves values close to the given figures. A separation in angle with one single sensor is not possible with the actual monopulse antenna concept.

The 24GHz UMRR Radar Sensor Family for Short and Medium Range Applications.doc April 8, 2004

II. Frequency Regulations Any device operating in the 24GHz ISM band must meet the existing regulations, which are given (for Europe) by the harmonized standards ETSI EN 300440-1 and –2 (and oth-ers). Hence using the 24GHz ISM band for automotive ap-plications is possible already today as long as those existing regulations can be fulfilled. For the UMRR sensor, operating in FMCW narrowband mode, the frequency ap-proval for many (including automotive) purposes was granted already more than one year ago by the German Frequency Allocation Authority, RegTP. The spectrum of the device´s transmit waveform is depicted on the right. Similar regulations are valid for the US (FCC part 15 §§15.245 and 15.249) and for most other countries in the world. Without violating those, a number of applications that require short or medium range coverage can be ful-filled, see the section below. Thus a UMRR sensor cover-ing a frequency band of less than 250MHz at 24GHz is applicable for automotive purposes in almost all countries that represent an important market for automo-tive OEMs.

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To obtain a frequency approval for an automotive sensor, national authorities need to be addressed. Even for UMRR, being compliant with the harmonized European ETSI stan-dards, additional national restrictions and regulations must be considered, at least for a few countries. From the tech-nical point of view, compliance can easily be proven, but the formal procedures are different in each nation. A lav-ish bureaucratic paperwork is the result. A number of authorities request test reports generated by accredited testing laboratories CETEKOM ICT Services GmbH, which are available for UMRR. However, not all functions can be handled by a sensor covering just such a narrow frequency band. For certain applications, like a parking aid function (and possibly certain others), a very low minimum range is necessary. In that special case the only practicable solution is an Ultra Wide Band (UWB) pulsed radar principle. See the spectrum analyzer plot on the right for an impression of the frequency band, covering more than 3GHz. At the moment it is not allowed to use such 24GHz sensors in UWBexception for the US), this fact being currently under discussion astrations. An exception solution for those radar applications is favThe proposed solution again being subject of additional restrictionssors limited).

The 24GHz UMRR Radar Sensor Family for Short and Medium Range Applications.doc

Figure 2: FMSK-2 Transmit Waveform0

Figure 3: FMSK-2 Transmit Spectrum

mt or (

Figure 4: UWB Transmit Spectrum

ode (with a special, time limited the European frequency admini-ed by the SARA consortium [6]. time and overall number of sen-

April 8, 2004

III. Example Automotive Applications

As stated above, a number of automotive sensing functions can be handled using narrow-band operation. One example is Blind Spot Surveillance. In combination with a Lane Change Support function the comfort oriented application provides assistance for the driver and has the poten-tial of reducing or eliminating a high percentage of collisions caused by inattentive lane change maneuvers. The sensor system monitors the presence of vehicles in a region beside the radar-equipped vehi-cle and has in addition to that a field of view ranging more than 50m back, and provides full coverage of at least three lanes.

It is of importance that the maximum range is not reduced for objects approaching at high relative speed (relative speeds of up to 250km/h are no problem with UMRR and have no effect on max. range). For detecting and indicating those to the driver, even 50m are experienced as “a short dis-tance” by most drivers. A second example application is a vehicle control related one: ACC plus Stop & Go, or ACC Support. In this case two UMRR sen-sors are placed behind the front bumper fascia. The comparatively wide field of view (40-50° in azimuth) allows for an excellent detec-tion of any obstacles at short or medium range. Again three lanes can be covered, this can lead to a significant improvement of the function of long range 77GHz ACC sensors, when the detection results of all radars are sub-ject to a sensor fusion. En-hanced features like follow-to-stop or stop-and-go become possible. More sensing functions have been under investigation. When discussing restraint systems related sensing functions, the applications Closing Velocity Sensing and Pre-Crash Firing for Reversi-ble Restraints can be covered with UMRR.

The 24GHz UMRR Radar Sensor Family for Short and Medium Range Applications.doc April 8, 2004

A different situation shows up when discussing radar based Parking Aid and possible other applica-tions requiring very high range resolution. The UMRR sensor would need to be switched to UWB op-eration. Although the function can be demonstrated, this operational mode has no frequency ap-proval. UMRR is in this case affected by the current bandwidth limitations just as competing sensor concepts. See the figures below for a demonstration of the detection of a small plastic tube at 5m range. The obstacle is detected by all three sensors, the well-matching range and angle data of the three UMRRs are superposed in the graphic on the right.

More applications, their requirements, typical practical problems of different 24GHz sensor designs are given in [3] and [4]. IV. References [1] Klotz, Michael; Rohling, Hermann: A high range resolution radar system network for parking aid applications International Conference on Radar Systems, Brest/France 1999. [2] Meinecke, Marc-Michael; Rohling, Hermann: Waveform Design Principles for Automotive Radar Systems German Radar Symposium, Berlin 2000. [3] Moritz; Pre-Crash Sensing – Its functional evaluation based on a platform radar sensor; SAE Technical Paper Series 2000-01-2718. [4] Hoess et. al.; The RadarNet Project 7th ITS World Congress, Torino, November 2000 [5] Skutek, Mekhaiel, Wanielik; A PreCrash System Based on Radar for Automotive Applications Intelligent Vehicle Conference 2003 Columbo/ Ohio [6] SARA Initiative, Volker Schmid, Wolfgang Lauer, Gerhard Rollmann; Ultra Wide Band 24GHz Radar Sensors for Innovative Automotive Applications; International Radar Symposium, Dresden 2003

The 24GHz UMRR Radar Sensor Family for Short and Medium Range Applications.doc April 8, 2004