The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor
High-accuracy, short-range distance measurement is required in a variety of industrial applications e.g., positioning of robots in a fully automated production process, level measurement of liquids in small containers. An FMCW radar sensor is suitable for this purpose, since many of these applicatio...
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MDPI AG
2019-09-01
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| Series: | Sensors |
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| Online Access: | https://www.mdpi.com/1424-8220/19/18/3938 |
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| author | Akanksha Bhutani Sören Marahrens Michael Gehringer Benjamin Göttel Mario Pauli Thomas Zwick |
| author_facet | Akanksha Bhutani Sören Marahrens Michael Gehringer Benjamin Göttel Mario Pauli Thomas Zwick |
| author_sort | Akanksha Bhutani |
| collection | DOAJ |
| description | High-accuracy, short-range distance measurement is required in a variety of industrial applications e.g., positioning of robots in a fully automated production process, level measurement of liquids in small containers. An FMCW radar sensor is suitable for this purpose, since many of these applications involve harsh environments. Due to the progress in the field of semiconductor technology, FMCW radar sensors operating in different millimeter-wave frequency bands are available today. An important question in this context, which has not been investigated so far is how does a millimeter-wave frequency band influence the sensor accuracy, when thousands of distance measurements are performed with a sensor. This topic has been dealt with for the first time in this paper. The method used for analyzing the FMCW radar signal combines a frequency- and phase-estimation algorithm. The frequency-estimation algorithm based on the fast Fourier transform and the chirp-z transform provides a coarse estimate of the target distance. Subsequently, the phase-estimation algorithm based on a cross-correlation function provides a fine estimate of the target distance. The novel aspects of this paper are as follows. First, the estimation theory concept of Cramér-Rao lower bound (CRLB) has been used to compare the accuracy of two millimeter-wave FMCW radars operating at 60 GHz and 122 GHz. In this comparison, the measurement parameters (e.g., bandwidth, signal-to-noise ratio) as well as the signal-processing algorithm used for both the radars are the same, thus ensuring an unbiased comparison of the FMCW radars, solely based on the choice of millimeter-wave frequency band. Second, the improvement in distance measurement accuracy obtained after each step of the combined frequency- and phase-estimation algorithm has been experimentally demonstrated for both the radars. A total of 5100 short-range distance measurements are made using the 60 GHz and 122 GHz FMCW radar. The measurement results are analyzed at various stages of the frequency- and phase-estimation algorithm and the measurement error is calculated using a nanometer-precision linear motor. At every stage, the mean error values measured with the 60 GHz and 122 GHz FMCW radars are compared. The final accuracy achieved using both radars is of the order of a few micrometers. The measured standard deviation values of the 60 GHz and 122 GHz FMCW radar have been compared against the CRLB. As predicted by the CRLB, this paper experimentally validates for the first time that the 122 GHz FMCW radar provides a higher repeatability of micrometer-accuracy distance measurements than the 60 GHz FMCW radar. |
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| last_indexed | 2024-04-11T21:41:26Z |
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| spelling | doaj.art-cd61d366e6374fcfa5c9780e1e9f78682022-12-22T04:01:35ZengMDPI AGSensors1424-82202019-09-011918393810.3390/s19183938s19183938The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar SensorAkanksha Bhutani0Sören Marahrens1Michael Gehringer2Benjamin Göttel3Mario Pauli4Thomas Zwick5Institute of Radio Frequency Engineering and Electronics, Karlsruhe Institute of Technology, Campus South, Engesserstrasse 5, 76131 Karlsruhe, GermanyInstitute of Radio Frequency Engineering and Electronics, Karlsruhe Institute of Technology, Campus South, Engesserstrasse 5, 76131 Karlsruhe, GermanyInstitute of Radio Frequency Engineering and Electronics, Karlsruhe Institute of Technology, Campus South, Engesserstrasse 5, 76131 Karlsruhe, GermanyWellenzahl Radar- und Sensortechnik GmbH & Co. KG, Im Vogelsand, 76131 Karlsruhe, GermanyInstitute of Radio Frequency Engineering and Electronics, Karlsruhe Institute of Technology, Campus South, Engesserstrasse 5, 76131 Karlsruhe, GermanyInstitute of Radio Frequency Engineering and Electronics, Karlsruhe Institute of Technology, Campus South, Engesserstrasse 5, 76131 Karlsruhe, GermanyHigh-accuracy, short-range distance measurement is required in a variety of industrial applications e.g., positioning of robots in a fully automated production process, level measurement of liquids in small containers. An FMCW radar sensor is suitable for this purpose, since many of these applications involve harsh environments. Due to the progress in the field of semiconductor technology, FMCW radar sensors operating in different millimeter-wave frequency bands are available today. An important question in this context, which has not been investigated so far is how does a millimeter-wave frequency band influence the sensor accuracy, when thousands of distance measurements are performed with a sensor. This topic has been dealt with for the first time in this paper. The method used for analyzing the FMCW radar signal combines a frequency- and phase-estimation algorithm. The frequency-estimation algorithm based on the fast Fourier transform and the chirp-z transform provides a coarse estimate of the target distance. Subsequently, the phase-estimation algorithm based on a cross-correlation function provides a fine estimate of the target distance. The novel aspects of this paper are as follows. First, the estimation theory concept of Cramér-Rao lower bound (CRLB) has been used to compare the accuracy of two millimeter-wave FMCW radars operating at 60 GHz and 122 GHz. In this comparison, the measurement parameters (e.g., bandwidth, signal-to-noise ratio) as well as the signal-processing algorithm used for both the radars are the same, thus ensuring an unbiased comparison of the FMCW radars, solely based on the choice of millimeter-wave frequency band. Second, the improvement in distance measurement accuracy obtained after each step of the combined frequency- and phase-estimation algorithm has been experimentally demonstrated for both the radars. A total of 5100 short-range distance measurements are made using the 60 GHz and 122 GHz FMCW radar. The measurement results are analyzed at various stages of the frequency- and phase-estimation algorithm and the measurement error is calculated using a nanometer-precision linear motor. At every stage, the mean error values measured with the 60 GHz and 122 GHz FMCW radars are compared. The final accuracy achieved using both radars is of the order of a few micrometers. The measured standard deviation values of the 60 GHz and 122 GHz FMCW radar have been compared against the CRLB. As predicted by the CRLB, this paper experimentally validates for the first time that the 122 GHz FMCW radar provides a higher repeatability of micrometer-accuracy distance measurements than the 60 GHz FMCW radar.https://www.mdpi.com/1424-8220/19/18/3938millimeter-wavefrequency modulated continuous wavefrequency estimationphase estimationCramér Rao lower boundmicrometer-accuracy range measurement |
| spellingShingle | Akanksha Bhutani Sören Marahrens Michael Gehringer Benjamin Göttel Mario Pauli Thomas Zwick The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor Sensors millimeter-wave frequency modulated continuous wave frequency estimation phase estimation Cramér Rao lower bound micrometer-accuracy range measurement |
| title | The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor |
| title_full | The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor |
| title_fullStr | The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor |
| title_full_unstemmed | The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor |
| title_short | The Role of Millimeter-Waves in the Distance Measurement Accuracy of an FMCW Radar Sensor |
| title_sort | role of millimeter waves in the distance measurement accuracy of an fmcw radar sensor |
| topic | millimeter-wave frequency modulated continuous wave frequency estimation phase estimation Cramér Rao lower bound micrometer-accuracy range measurement |
| url | https://www.mdpi.com/1424-8220/19/18/3938 |
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