The UMRR-S: A High-Performance 24GHz Multi Mode Automotive Radar Sensor for Comfort and Safety Applications

Transcription

1 The UMRR-S: A High-Perormance 24GHz Multi Mode Automotive Radar Sensor or Comort and Saety Applications Ralph Mende*, Marc Behrens*, Marc-Michael Meinecke**, Arne Bartels**, Thanh-Binh To** *smart microwave sensors GmbH Phone: +49 (531) / Fax: +49 (531) / ralph.mende@smartmicro.de Mittelweg Braunschweig - Germany **Volkswagen AG Phone: +49 (5361) / Fax: +49 (5361) / marc-michael.meinecke@volkswagen.de Letter Box Wolsburg - Germany Abstract The paper describes the UMRR-S sensor, which has been developed or automotive applications in a co-operation between Volkswagen AG and smart microwave sensors GmbH as a derivative o the UMRR platorm. The sensor is able to operate in the 24GHz ISM band and is applicable or Advanced Driver Assistance System unctions. It can run both in UWB Pulse- and in a number o Narrowband FMCW Modes. It can be part o a network ormed o several UMRR-S sensors, or integrated into an existing sensor network, or instance in combination with a 77GHz long range radar. Dierent types o antennae are available. Concept, technical and perormance data o the sensor are given. Advanced eatures like object generation out o individual radar relectors rom one physical object are described. I. Concept and Technical Data The name UMRR stands or Universal Medium Range Radar. The design targets o the UMRR sensor platorm were mainly lexibility and perormance. Flexibility: - UWB Pulse- and FMCW narrowband operation possible. - Multiple planar antenna designs available (independent o microwave module). - Stand alone or network operation. - No central ECU required or network operation. Perormance: - Direct an simultaneous measurement o range, velocity and angle. - Short measurement time. - Reasonable Minimum Range (0.75m), Medium maximum range (typ m). - Conormity with RegTP / ETSI EN requency regulations in FMCW narrowband mode. - One-Box-Design with integrated detection, tracking and communication sotware. Sensor-Processor #1 RF Board DSP Board Mixer Ampl. A DSP TX RXA RXB D SPI Data Logging CAN Power Internal System Communication Figure 1: Bloc Diagram and Photograph o the UMRR Radar Sensor

2 A sensor unit consists o two components: RF rontend module and DSP module. The planar antenna structure is made as the outermost layer o the microwave board. A dual RX antenna setup was selected to allow or monopulse based direct angle measurement. UMRR-S is a derivative o the UMRR platorm, and was customized or Volkswagen AG. A number o waveorms are selectable. Among those, UWB pulse mode and the FMSK-2 narrowband mode are o importance. The technical data o those example modes are provided below. It is possible to switch between the modes, the switching dead-time has a duration o one cycle. Parameter UWB Pulse Mode Narrowband Mode Operation Principle UWB Pulsed FMSK-2 3dB Bandwidth < 3GHz < 200MHz Minimum Range 0.25m 0.75m Maximum Range 15m 60m+ Cycle Time 8ms 25ms Velocity Interval m/s m/s Carrier Frequency GHz Maximum Transmit Power 20dBm Antenna Type Patch Antenna Field o View (Example) 40 (Azimut) x 13 (Elevation) Size (including processor) 94x78x31mm (WxHxD) Supply/Interace 12V/CAN Table 1: UMRR-S Technical Data No description o the UWB Pulsed operation shall be given here, or details o a similar system see [1]. The more interesting waveorm is the narrowband FMSK-2 signal, which is reerred to in most o the ollowing text. FMSK-2: this combination o FSK and LFM waveorm design principle oers the possibility o an unambiguous and simultaneous target range and velocity measurement. The transmit waveorm consist in this case o at least two linear requency modulated up-chirp or downchirp 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 requency modulated sequence A is used as a reerence signal while the second up-chirp signal is shited in requency with. The received Shit signal is down converted into base band and directly sampled at the end o each requency step. The combined and intertwined waveorm concept is depicted in Figure 3. T (t) T, B T, A A 0 B A B A Shit B Incr = N Sweep 1 Sweep t T Chirp As an example, the waveorm can be conigured as ollows: FMSK-2 (that means two intertwined chirps), = 200MHz, = 1MHz, N = 256. One o the outstanding advantages o this sweep Shit Figure 3: FMSK-2 Transmit Waveorm type o waveorm is the act that all parameters (range, velocity, angle) can be deduced in one measurement cycle rom only one intertwined chirp [2]. Beside the operational modes, the ield o view can easily be customized by selecting an appropriate antenna pattern. An example o a single sensor wide beam setup and a two sensor narrow ield o view setup can be seen in the pictures. One o the advantageous eatures is that the measurement o all parameters is possible even in the side lobe zones, this eect being very welcome, or in many applications the desired ield o view is deined in Cartesian co-ordinates as a rectangle in ront o a vehicle. Thereore antennae with intentionally designed side lobes can useully be applied.

3 Superposed Individual Sensors;UM RR-Fern01;25-Oct Y-Co-ordinate[m] X-Co-ordinate[m ] Figure 4: Example Single and Dual Sensor coniguration. Parameter Antenna Type 2 (let) Antenna Type 8 (right) 3dB Azimuth dB Elevation Table 2: Example Antenna Data II. Perormance Data To demonstrate the sensitivity o UMRR-S, the ollowing numbers can be given. The typ. max. range on pedestrians is 45m, on bicycles 50m and on passenger cars 60-70m. The speed o the object has no inluence on the maximum range. Typical Accuracy data are: Range: Typical < 0.5m (under 10m, 10m max. range: better than +-2%). 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, two objects o identical relectivity must be dierent in at least one o the ollowing parameters: Range Dierence >= 1.75m Speed Dierence >= 1.94km/h. Figure 5: Range Error [m] given or dierent positions. A separation in angle is not possible with the actual simple monopulse antenna concept. The graphics provide an impression o the accuracy igures o a single sensor. The wavy appearance o the results occur due to multi-path eects in the measurement scenario, using a corner relector. Accuracy is similar at higher ranges, while the data in the plots end at 15m.

4 Figure 6: Angular Error [deg] given or dierent positions. III. Special Features Length Estimation While a standard target detection procedure would normally search or peaks in a spectrum, the UMRR- S sotware uses more sophisticated algorithms. As an example, the radial extension (length) o a relector is estimated. Other than point relectors, normal relectors in an automotive environment (passenger cars, trucks etc.) usually have more than just one scatterer, hence more than one peak in a spectrum. The relectors o one physical object basically have the same relative velocity (it still depends on the illumination angle). To estimate the length o an object, an algorithm searches or a chain o local peaks. See Figures 7 and 8 or an example. In Figure 7 the blue lines indicate the estimated length value, the red lines correspond to the relative velocity. The (uniltered) length values show a reasonable correlation with the video picture. Figure 7: Length Estimation Demonstration Object Generation As a number o parameters (range, velocity, angle, level, length etc., it becomes possible to apply algorithms which interpret the detected set o relectors in each measurement cycle and estimate beside the accurate position and velocity vector - the shape (length and width) o the physical objects which consist o a set o individual scatterers. Beside the radar data, vehicle dynamics data are required. A sensor usion algorithm is applied. One good example or the object generation (in this case

5 it is even a classiication) is the detection o crashor other barriers at the edges o the road. Position, length and curve radius can be measured using radar only. The object generation in this case is simple, because a row o poles or other relectors can easily be detected by UMRR-S. Thereore in practice good results are achieved or guard rail detection and classiication (see also Figure 9). Vehicles and trucks can also be interpreted as objects and displayed as rectangles. IV. Automotive Applications or UMRR-S UMRR-S sensors have been installed in several test vehicles or various applications. As an example, a radar network consisting o two UMRR sensors has been implemented in an experimental car or testing the new technology in real street situations. The coniguration is depicted in Figure 4 on the right. A Figure 8: Spectrum, used or length estimation normal Autobahn situation was recorded, the interpreted data being shown in the ollowing igures (graphic: 60x40m). Figure 9: Interpreted Objects and photograph o the situation. A number o applications that require short or medium range coverage can be ulilled without violation o actual ETSI and FCC requency allocation rules. More applications, their requirements, typical practical problems o dierent 24GHz sensor designs are given in [3] and [4]. The perormanceoptimized UMRR-S sensor has been tested and can be applied or the unctions listed below. Sensor and Display (Comort): Vehicle Control related (Comort + Control): Restraint Systems related (Saety): Blind Spot Surveillance. ACC plus Stop & Go. Closing Velocity Sensing. Pre-Crash Firing or Reversible Restraints. V. Recent Developments The next step in the development o the UMRR platorm would be the modiication o the antenna concept to allow or angle measurement principles that provide true resolution (target separation) in angle. Furthermore it is possible to implement additional waveorms and signal processing principles, like or instance a Pulse Doppler measurement mode. The multi-mode capability being available, strategies need to be developed to exploit the advantages o their combination.

6 VI. Reerences [1] Klotz, Michael; Rohling, Hermann: "A high range resolution radar system network or parking aid applications" International Conerence on Radar Systems, Brest/France [2] Meinecke, Marc-Michael; Rohling, Hermann: Waveorm Design Principles or Automotive Radar Systems German Radar Symposium, Berlin [3] Moritz; Pre-Crash Sensing Its unctional evaluation based on a platorm radar sensor ; SAE Technical Paper Series [4] Hoess et. al.; The RadarNet Project 7 th ITS World Congress, Torino, November 2000