Arrangement and method for measuring distance between devices in a radio system

Abstract

Arrangement for distance measurement between devices in a radio system, wherein at least a first receiver-side FMCW device (2) and a second transmitter-side FMCW device (2') are arranged in the radio system as devices, wherein the first receiver-side FMCW device (2) has an output for outputting a baseband signal, characterized in that a signal strength determination arrangement (1) is arranged which extracts an envelope from a narrowband baseband signal, samples the extracted envelope at specific times in terms of its amplitude and determines a signal strength value for each sample, and determines a maximum signal strength value from the signal strength values ​​determined in a specified time interval, which arrangement is connected to the output for outputting a baseband signal of the first receiver-side FMCW device (2),that the arrangement for determining the signal strength (1) has an output (16) for outputting the determined maximum signal strength value, that this output is connected to a subsequent distance determination arrangement (3) and that the distance determination arrangement (3) has an output (17) for outputting a value for the distance measurement.,

Description

[0001] The invention relates to an arrangement for measuring distances between devices in a radio system, wherein at least a first receiver-side FMCW device and a second transmitter-side FMCW device are arranged in the radio system, wherein the first receiver-side FMCW device has an output for outputting a baseband signal.

[0002] The invention also relates to a method for measuring distances between devices in a radio system, wherein a broadband FMCW signal of a first FMCW frequency ramp generated by a second transmitter-side FMCW device is received by a first receiver-side FMCW device, wherein the received broadband FMCW signal of the first FMCW frequency ramp is mixed by means of a second FMCW frequency ramp generated in the receiver-side FMCW device and a narrowband baseband signal is generated.

[0003] The present description concerns a distance measurement, for example between a transmitter and a receiver in a radio system, generally between two devices within a radio system, whereby the distance measurement must satisfy a specified accuracy when measuring a distance.

[0004] Such devices, transmitters or receivers in the radio systems can also be mobile stations and operate using various standards known from the state of the art, such as WLAN (wireless local area network), Bluetooth (industry standard according to IEEE 802.15.1) or Zigbee (extension of the IEEE 802.15.4 standard).

[0005] Such distance measurement or distance determination with sufficiently high accuracy, for example, in a range between approximately 2 and 5 m, is necessary, for example, in systems in which the position of a mobile station or person is to be determined in an environment with multiple rooms. For more precise location of persons within a room, accuracies of approximately 1 to 2 m are typically required, while in an example of autonomous control or autonomous driving of a forklift in a factory hall, accuracies of less than 50 cm are required.

[0006] According to the state of the art, such a distance measurement for radio location is often carried out using a method for determining a signal strength (RSSI; received signal strength indicator), whereby measurement errors can occur, particularly in environments with multipath propagation.

[0007] The main problem with this type of distance measurement is determining the shortest distance, for example, between a stationary transmitter and a mobile receiver using a so-called line-of-sight (LOS). In a real environment, however, radio signals are reflected by obstacles and thus received in a delayed and attenuated form. These unwanted reflected signals (NLOS), which deviate from the ideal line-of-sight (LOS) signal path, overlay the received signal and thus reduce the accuracy of the distance measurement.

[0008] State-of-the-art solutions for distance and position measurement are known which are either based on measuring the signal propagation time and determining the distance via the propagation speed of the signals or on measuring the signal strength and determining the distance via the decrease in signal strength with increasing distance between transmitter and receiver.

[0009] DE 101 55 251 A1 discloses a method for determining the distance between a base station and at least one transponder, in which a signal from a base station oscillator is transmitted from the base station. The object to be achieved is to demonstrate a particularly simple method with which it is possible to determine the distance to a transponder up to the near range in an alternative manner. To achieve this object, it is provided that, based on the signal received from the base station, a phase-coherent signal is generated and transmitted in the transponder by means of an oscillating oscillator, that the distance is determined in the base station based on the phase-coherent signal received from the transponder, wherein the oscillator is excited in a quasi-phase-coherent manner with the received signal to generate the phase-coherent signal.

[0010] DE 196 46 228 A1 discloses a method for determining the distance between two objects. In this method, an FMCW radar signal is emitted from one object, the signal reflected by the second object is recorded, and the difference signal is formed from both signals, which is then evaluated using the maximum entropy method. The proposed solution is to use the well-known FMCW principle to take advantage of the fact that the intermediate frequencies to be evaluated, especially for objects at close range, lie in a range that is significantly different from the frequency of the emitted signal and lies within the range of the frequency deviation of the emitted signal. This can be adjusted so that, on the one hand, the circuitry required for evaluating and detecting one or more targets remains low, even at close range, and, on the other hand, the resolution is sufficient.

[0011] US 2016 / 0 291 130 A1 discloses a radar system and relates in particular to the detection of interference in a frequency-modulated continuous wave (FMCW) radar system. The problem to be solved is to know when interference occurs so that mitigation and / or avoidance techniques can be applied. To solve this problem, a frequency-modulated continuous wave (FMCW) radar system is provided, comprising a receiver configured to generate a digital intermediate frequency signal and an interference monitoring component coupled to the receiver to receive the digital intermediate frequency signal, wherein the interference monitoring component is configured to monitor at least one subband in the digital intermediate frequency signal for interference, wherein the at least one subband does not comprise a radar signal.

[0012] So-called time-of-flight-based systems are known, which can be pulse-based or frequency-modulated. Pulse-based systems can use ultra-wideband (UWB) technology, for example, while frequency-modulated systems can use frequency-modulated continuous wave (FMCW) radar. Examples of such frequency- or pulse-based systems are shown in A. Strobel, R. Eickhoff, A. Ziroff, and F. Ellinger, "Comparison of pulse and FMCW-based radiolocation for indoor tracking systems," 2010 Future Network & Mobile Summit, Florence, 2010, pp. 1-8.

[0013] These systems are specially designed and optimized to enable the most precise distance measurement possible. A disadvantage of these systems is that both approaches require complex signal processing to determine the signal propagation time, as well as circuits for the precise synchronization of all participating stations or devices in the network. In multipath environments, these systems can distinguish unwanted incoming reflected signals (NLOS) from the desired direct signal (LOS) up to a theoretical resolution threshold.

[0014] Systems for determining the distance between devices in a radio system, which work by means of signal strength measurement, are present in practically all implementations of standardized, narrowband communication systems such as WLAN, Bluetooth, Zigbee.

[0015] In such systems, a signal processing unit in the device or transceiver typically provides a so-called signal strength value, which is also used to determine the distance. The state of the art for these methods can be found in the publications by W. Xue, W. Qiu, X. Hua, and K. Yu, "Improved Wi-Fi RSSI Measurement for Indoor Localization" in IEEE Sensors Journal, vol. 17, no. 7, pp. 2224-2230, April 1, 2017, or J. Neburka et al., "Study of the performance of RSSI-based Bluetooth Smart indoor positioning" in 26th International Conference Radioelektronika (RADIOELEKTRONIKA), Kosice, 2016, pp. 121-125.

[0016] This signal strength value is determined during the transmission of data over a narrowband channel in the so-called preamble, which is described, for example, in US 2013 0278416 “Methods for locating individuals in an emergency condition using an ad-hoc network and devices thereof”.

[0017] These systems do not require extensive signal analysis and are very simple in design. However, in multipath environments, this method of distance determination is very inaccurate because it cannot distinguish between unwanted reflected signals (NLOS) and directly received signals (LOS) when determining distance.

[0018] The disadvantages of this known state-of-the-art technology are that delay-based systems are specialized, complex systems that require complex signal processing and circuitry to synchronize all stations. As a result, these systems incur high costs in both development and manufacturing and consume high power. Furthermore, such systems are difficult to integrate due to their large size.

[0019] Current systems that use signal strength measurements for distance measurement utilize commercially available, narrowband communication systems and are therefore cost-effective. However, since signal strength is only determined for signals in a small frequency band, usually on the current radio channel with a bandwidth of a few tens of MHz, and only for short periods of time, such as in the preamble of a data packet, which for Wi-Fi typically covers a period of a few tens of microseconds, the information content of the signal strength value is very low. Thus, unwanted multipath propagation of the signals has a strong influence on the distance measurement result.

[0020] In addition, the signal strength value is subject to strong fluctuations, for example depending on the current position of a device in a room, which means that the accuracy of the distance measurement is very low in environments with multipath propagation.

[0021] A prior art direct conversion receiver is disclosed in the context of a continuous wave radar at https: / / de.wikipedia.org / wiki / Dauerstrichradar. With this direct conversion receiver, the high-frequency received signal, after being amplified, is directly superimposed with a portion of the transmitted signal in a mixer, thus transforming it into a baseband signal. The downstream amplifier operates in the low-frequency range.

[0022] DE 10 2011 075 824 A1 discloses a radar system for motor vehicles and a method for carrying out measurements using FMCW radar.

[0023] The task to be solved by this publication is to create a method for carrying out measurements using FMCW radar, in which the assignment of a detected relevant object to the class “obstacle” can be improved.

[0024] To achieve this objective, the system comprises at least one radar sensor and a control unit, wherein the measurements are performed using the FMCW radar with at least two frequency modulation ramps. For each measurement, a transmitted signal is mixed with a received signal, and a peak value of a spectrum of the mixed signal is determined. Furthermore, an expansion indicator value is determined depending on the deviations of the determined peak values ​​of the measurements from a mean value of the determined peak values ​​of the measurements.

[0025] Due to the known disadvantages of the state of the art explained above, there is a need for a suitable solution for measuring the distance between devices in a radio system with improved characteristics.

[0026] The object of the invention is to provide an arrangement and a method for measuring the distance between devices in a radio system, whereby an accurate and robust measurement is achieved using the principle of signal strength measurement and whereby the complexity of the system and its costs are low.

[0027] The problem is solved by an arrangement having the features according to claim 1 of the independent claims. Further developments are specified in the dependent claims 2 to 4.

[0028] The problem is also solved by a method having the features according to claim 5 of the independent patent claims. Further developments are specified in the dependent patent claims 6 to 10.

[0029] The main application of the present invention is precise and robust distance measurement within local positioning systems, for example, for locating people, objects, or vehicles in locally limited areas with multipath propagation, such as indoor spaces or industrial halls. Due to the low complexity and cost of the proposed solution, consumer applications are also conceivable, such as use in so-called location-based gaming. Another application could be in guiding or directing people, for example, during a tour of museums, locating products in a supermarket, or guiding blind people.

[0030] By utilizing the principle of signal strength measurement, the complexity of a distance measurement and / or positioning system is greatly reduced, while maintaining high accuracy using the presented solution.

[0031] The invention provides that a first receiver-side FMCW device and a second transmitter-side FMCW device are arranged in a radio system, wherein the first receiver-side FMCW device has an output for outputting a baseband signal. Alternatively, for example, a stationary FMCW transmitter can be arranged as the second transmitter-side FMCW device and a mobile FMCW device can be arranged as the first receiver-side FMCW device in the radio system. A further alternative consists in using one FMCW transceiver each as the first receiver-side mobile FMCW device and the second transmitter-side stationary FMCW device.

[0032] Typically, such FMCW devices can be components or subassemblies of stationary or mobile higher-level devices within a radio system, whereby these devices, such as smartphones, tablets or laptops, communicate with each other using common standards such as WLAN, Bluetooth or Zigbee.

[0033] Depending on the requirements, a first receiver-side FMCW device may, for example, comprise a receiving antenna, an input amplifier, a mixer with a frequency ramp generator, and a baseband amplifier. Optionally, a bandpass filter can also be arranged after the baseband amplifier.

[0034] A second transmitter-side FMCW device comprises, for example, a transmitting antenna and a driver stage connected to a frequency ramp generation arrangement.

[0035] Alternatively, for example, an FMCW transceiver may include all listed components of the transmitter-side FMCW device and the receiver-side FMCW device.

[0036] It is provided that with the first receiver-side FMCW device or an FMCW transceiver, an arrangement for determining signal strength is also arranged which extracts an envelope from a narrowband baseband signal, samples the extracted envelope at specific times in terms of its amplitude and determines a signal strength value for each sample, and determines a maximum signal strength value from the signal strength values ​​determined in a specified time interval, the input of which arrangement is connected to the output of the receiver-side FMCW device for outputting a baseband signal.

[0037] According to the invention, it is further provided that the arrangement for determining the signal strength has an output for outputting the determined maximum signal strength value, that this output is connected to a subsequent distance determination arrangement and that the distance determination arrangement has an output for outputting a value for the distance measurement.

[0038] It is also provided that the arrangement for determining signal strength comprises at least one envelope detector, a sampling arrangement, and a comparison arrangement. Advantageously, a memory is also arranged in the arrangement for determining signal strength.

[0039] The envelope detector is designed to extract an envelope from the baseband signal output at the output of the receiver-side FMCW device or at the output of the FMCW transceiver. The amplitude of this extracted envelope is sampled in the sampling arrangement, and the maximum signal strength value determined during this sampling is stored in the memory and output at the output of the signal strength determination arrangement to provide a signal strength value.

[0040] It is also planned to arrange a distance determination device, which is connected to the output for outputting a signal strength value. The maximum signal strength value output by the signal strength determination device corresponds best to the signal of the direct signal path (LOS) and is therefore converted in the distance determination device into a value for the distance to be determined during the distance measurement and output at the output for outputting a distance value of the distance determination device. For this purpose, known algorithms are used in the distance determination device to convert the maximum signal strength value into a distance to be determined.

[0041] The method involves extracting an envelope from a broadband FMCW signal in a mixer stage using a locally generated FMCW frequency ramp signal into a narrowband baseband signal. Since the maximum amplitude of this envelope best matches the signal from the direct signal path (LOS), the envelope is sampled at regular time intervals, and a signal strength value is determined for each sampling point. The maximum of these determined signal strength values ​​is determined, and the maximum signal strength value is output for further processing. This further processing is carried out, as already described, using a known algorithm for converting the maximum signal strength value into a distance to be determined. Algorithms such as a path loss model, fingerprinting, a Kalman filter, or a particle filter can be used for this purpose.

[0042] It is further proposed to generate the frequency ramp required for the FMCW signal in the form of a linearly rising ramp. Alternatively, the FMCW signal can be generated in the form of a linearly falling ramp. In a further alternative, the FMCW signal can be generated from an initially rising part followed by a subsequently falling part, or from a falling part followed by a subsequently rising part of a frequency ramp.

[0043] In a further embodiment, it is provided that the baseband signal of the first receiver-side FMCW device or of the FMCW transceiver is filtered by means of a band filter before output in order to eliminate interference components of the signal.

[0044] It is also intended that the envelope curve is sampled at regular intervals, controlled by a clock or timer.

[0045] Furthermore, it is also provided that the envelope is sampled over a period of time which corresponds at least to the period of time of an FMCW frequency ramp signal, i.e. until an FMCW frequency ramp is completely finished.

[0046] The above-explained features and advantages of this invention will be better understood and appreciated after careful study of the following detailed description of the preferred, non-limiting exemplary embodiments of the invention with the accompanying drawings, which show: Fig. 1: a schematic representation of an arrangement according to the invention for measuring distances between devices in a radio system, Fig. 2a - 2d: a representation of several diagrams of different signals at different points in the arrangement according to Fig. 1 and Fig. 3: a diagram comparing the achievable accuracies for a distance measurement according to the prior art and the inventive solution for measuring the distance between two devices in a radio system.

[0047] The basic idea behind the method is that different obstacles such as walls or windows reflect radio waves in different ways at different frequencies, which changes the behavior of the radio channel and thus the type and number of reflections across the frequency or frequency range.

[0048] Such effects are described, for example, in P. Ali-Rantala, L. Ukkonen, L. Sydanheimo, M. Keskilammi, and M. Kivikoski, “Different kinds of walls and their effect on the attenuation of radiowaves indoors” in IEEE Antennas and Propagation Society International Symposium, Vol. 3, June 2003, pp. 1020 - 1023.

[0049] According to the invention, signal strength measurements are continuously performed across a wide frequency band, and measured values ​​are generated. From these measured values, the measured value corresponding to the highest measured signal strength, i.e., the maximum signal strength, is selected. This highest measured signal strength corresponds to the desired direct signal (LOS). Using this highest measured signal strength, the distance is subsequently determined using an algorithm for converting a signal strength value into a distance and output as the value for the distance measurement.

[0050] It is intended that a distance measurement according to the invention between devices in a radio system is carried out by means of an arrangement for determining the signal strength 1, an upstream FMCW transceiver 2 and a downstream stage for implementing an algorithm for determining the distance, hereinafter referred to as distance determination arrangement 3, as described in the Fig. 1 is shown in a possible embodiment.

[0051] Such an FMCW transceiver 2, 2', which can transmit or receive high-frequency, broadband FMCW signals, has a frequency ramp generation arrangement 4, 4', by means of which a frequency ramp, as described for example in the Fig. 2a, a frequency ramp that increases over time is generated for the FMCW signal. Furthermore, a driver stage 5, 5' and a transmitting antenna 6, 6' are provided, via which the generated FMCW signal can be radiated. The frequency range in which such an FMCW transceiver 2, 2' is typically operated is, for example, between 2 GHz and 80 GHz.

[0052] The FMCW transceiver 2, 2' transmits an FMCW signal of a broadband, for example, linearly increasing first frequency ramp in the bandpass range, i.e., a signal modulated onto a carrier frequency, via the transmitting antenna 6, 6'. A bandwidth of this FMCW signal greater than 100 MHz is selected. Alternatively, such a frequency ramp can also be generated in the frequency ramp generation arrangement 4, 4' with a linearly decreasing frequency or can be a sequence of a linearly increasing ramp followed by a linearly decreasing ramp, or vice versa. The exact form of the frequency ramp is not limited by the invention and can be selected accordingly by a person skilled in the art.

[0053] In the example of Fig. 1, such an FMCW signal is to be generated in the FMCW transceiver 2' by means of the frequency ramp generation arrangement 4' and the driver stage 5' and radiated via the transmitting antenna 6'.

[0054] The FMCW signal thus generated and radiated via the transmitting antenna 6' is received by an identically constructed FMCW transceiver 2 via its receiving antenna 7. The received FMCW signal passes from the receiving antenna 7 via an input amplifier stage 8, in which the FMCW signal is amplified, to a mixer stage 9.

[0055] It is intended that the FMCW transceivers 2 and 2' are at least roughly synchronized with each other in time, so that a mixing of a frequency ramp of the FMCW received signal with a frequency ramp of a locally generated FMCW signal can take place in the mixer stage 9 of the FMCW transceiver 2. By means of the coarse temporal synchronization, it is ensured that the first FMCW frequency ramp of the FMCW received signal and a locally generated second FMCW frequency ramp overlap at least in a large temporal range, as is exemplified in the Fig. 2a. In the Fig. Figure 2a shows a plot of frequency (ordinate) versus time (abscissa) with a black solid line representing the first transmitted FMCW frequency ramp, while the dot-dot line shows the second locally generated FMCW frequency ramp.

[0056] Due to the difference in propagation time between the first and the second frequency ramp, a signal with a constant frequency is produced at the output of the mixer stage 9, as described, for example, in N. Joram, B. Al-Qudsi, J. Wagner, A. Strobel and F. Ellinger, “Design of a multi-band FMCW radar module” in 2013 10th Workshop on Positioning, Navigation and Communication (WPNC), Dresden, 2013, pp. 1-6.

[0057] This output signal from mixer stage 9 is processed by a baseband amplifier 10, so that the signal with the constant frequency is output at the output of baseband amplifier 10. The mixing process in mixer stage 9 converts a broadband high-frequency signal at the output of the input amplifier stage into a narrowband baseband signal at the output of baseband amplifier 10. This signal can optionally be limited in its bandwidth by means of a filter 11.

[0058] In a multipath environment, in addition to the first frequency ramp of the direct signal path (LOS), frequency ramps of reflected signals are also received, which are smaller in amplitude and have longer propagation times. These unwanted signals overlap with the signal of the direct signal path in the time domain, creating beats in the baseband and thus an envelope whose amplitude is not constant, i.e., varies over time, as described in the Fig. Figure 2b shows the amplitude (ordinate) plotted against a time axis (abscissa). Here, each point in time of the baseband signal corresponds to a different frequency in the bandpass range. The reason for the variation in the amplitude of the envelope over time is that multipath propagation can lead to shadowing and thus signal cancellation.

[0059] The envelope of this baseband signal is extracted by an envelope detector 12 arranged in the arrangement for signal strength determination 1, for example a Fig. 2c shows the curve of the amplitude (ordinate) over time (abscissa) at the output of the envelope detector 12.

[0060] This envelope detection can be carried out digitally, by processing sample values, or analogously, for example with a diode detector or an AGC amplifier (AGC; English: automatic gain control), to whose control input the envelope is directly applied.

[0061] It is intended that the envelope is sampled periodically, which is consistent with the Fig. 2d shown points on the extracted envelope. The Fig. Figure 2c depicts the amplitude (ordinate) of the extracted envelope curve over time (abscissa). The maximum signal strength value to be determined is indicated by the arrow. At specified times or periodically, values ​​of the current signal strength, i.e., signal strength values, are determined using sampling arrangement 13.

[0062] The first signal strength value sampled in this way is stored in memory 14 of the arrangement for signal strength determination 1. All signal strength values ​​subsequently sampled by the sampling arrangement 13 are compared in the comparison arrangement 15 with the signal strength value last stored in memory 14. If a comparison in the comparison arrangement determines that the signal strength value currently output by the sampling arrangement 13 is greater than the signal strength value currently stored in memory 14, this greater signal strength value is stored in memory 14. The signal strength value previously stored in memory 14 is overwritten, for example, with the new signal strength value. In this way, the maximum of the signal strength values ​​is determined over a specified time interval. This time interval is advantageously selected such that it corresponds to the duration of the superposition of the two frequency ramps.This operation of determining the maximum signal strength value can be performed using an analog or digitally sampled signal strength value of the envelope.

[0063] After the time interval has elapsed or the ramp of the FMCW signal has ended, the determined maximum signal strength value is read from the memory 14 and output at the signal strength value output 16.

[0064] This maximum signal strength value is further processed in the distance determination arrangement 3 downstream of the signal strength determination arrangement 1.

[0065] The conversion of the maximum signal strength value into a value to be determined according to the invention for a distance between the devices can be carried out using known algorithms.

[0066] A first algorithm that can be used is the so-called path loss model, which is described, for example, in Atreyi Bose and Chuan Heng Foh, "A practical path loss model for indoor WiFi positioning enhancement," 2007 6th International Conference on Information, Communications & Signal Processing, Singapore, 2007, pp. 1-5. In this path loss model, the attenuation of a radio signal and thus the signal strength at the receiver are described in the form of an equation as a function of the distance between transmitter and receiver.

[0067] A second algorithm that can be used is so-called fingerprinting, which is described in D. Wang, Y. Zhou, Y. Wei and T. Pei, "Distributed multi-object localisation by consensus on compressive sampling received signal strength fingerprints," in IET Communications, vol. 9, no. 14, pp. 1738-1745, 2015. Fingerprinting involves recording the signal strength values ​​of all existing transmitters whose positions are fixed and known, for example in the form of a grid at many different locations in the measurement scenario, and storing the signal strength values ​​determined in this way in a database. To measure the distance, a current signal strength value is later assigned to a position in space using the values ​​stored in the database, the so-called fingerprints.

[0068] An algorithm such as a Kalman filter or a particle filter can also be used. A description of a method using a Kalman filter can be found in W. Li, D. Gong, M. Liu, J. Chen and D. Duan, "Adaptive robust Kalman filter for relative navigation using global position system," in IET Radar, Sonar & Navigation, vol. 7, no. 5, pp. 471-479, June 2013. A description of a method using a particle filter can be found in P. Yang and W. Wu, "Efficient Particle Filter Localization Algorithm in Dense Passive RFID Tag Environment," in IEEE Transactions on Industrial Electronics, vol. 61, no. 10, pp. 5641-5651, Oct. 2014.

[0069] Such methods involve recording a large number of signal strength measurements per distance or position, and selecting the values ​​with the lowest error probability. With a Kalman filter, this selection is based on a previously created state-space model. With a particle filter, the selection is typically based on measurements from a different measurement system used simultaneously for motion prediction, such as an inertial measurement system (inertial navigation system).

[0070] After the maximum signal strength value has been processed by the distance determination arrangement 3, for example by means of one of the methods mentioned above, a value for the distance determined by the arrangement for measuring the distance between devices in a radio system is output at its distance value output 17.

[0071] The Fig. 3 shows a diagram comparing the achievable accuracies for a distance measurement according to the prior art and the inventive solution for measuring the distance between two devices in a radio system.

[0072] The accuracy of the distance measurement in meters at different measurement times or positions of an FMCW device 2 is shown. The accuracy of the measurements using the inventive solution is represented by a solid black line, while the accuracy of the measurements according to the prior art is shown by a dashed line. A measurement index with numbers from 1 to 15 is shown on the abscissa of the coordinate system, representing 15 different measurements at 15 different times at different positions of the FMCW device 2 within the measurement environment. The determined measurement deviation in meters is shown on the ordinate.

[0073] The state-of-the-art measurement corresponds to a conventional distance measurement between two radio nodes or devices using a signal strength measurement in a narrowband system.

[0074] For the measurement, a first FMCW transceiver 2' was installed as a transmitter at a fixed location, and a second FMCW transceiver 2 was installed as a receiving station in an interior space with moderate multipath propagation. In this example, the measurement was performed in an office space with an adjacent foyer.

[0075] The narrowband system of the prior art shows strong fluctuations in the accuracy of the measured distance for different positions of the FMCW receiving station 2, which result in a higher measurement deviation, while the system according to the invention with the presented method provides significantly more stable measured values.

[0076] The repeatability for this measurement scenario is 4.9 m for the narrowband system and 2.7 m for the presented arrangement, thus demonstrating that an accurate and robust distance measurement is achieved by means of the proposed invention.

[0077] An application example for the present invention is described below.

[0078] In an industrial hall, the positions of power tools, such as a cordless screwdriver, are to be determined. For this purpose, FMCW transmitter stations 2' are installed at known positions within the industrial hall. These stations generate and transmit a first ramp-shaped FMCW signal. Each tool to be located is attached to an FMCW receiver 2. The arrangement thus corresponds to the illustration in the Fig. 1. Alternatively, an FMCW transceiver 2 can be attached to each tool to be located.

[0079] Due to the fact that such tools are typically battery-operated and have a rather small size, the presented arrangement is very well suited for distance measurement by means of FMCW signal strength determination, since no complex signal processing is necessary and the receiving unit 2 can thus be designed small and power-saving.

[0080] Data packets are exchanged between transmitting and receiving stations 2' and 2' via any communication interface, e.g., Wi-Fi, thus establishing the required rough time synchronization. This ensures that the FMCW receiving station 2 always knows when a distance measurement begins and which FMCW transmitting station 2' is currently transmitting.

[0081] In the example, three FMCW transmitting stations 2' are installed, each transmitting an FMCW signal in sequence. These FMCW signals are received by the FMCW receiving station 2 on the power tool and converted into three signal strength values ​​according to the described method. Since the positions of the FMCW transmitting stations 2' are known, three distances can be calculated from the three signal strength values, for example, using the path loss model.

[0082] Using a triangulation method (geometrically speaking, the intersection of three circles with radii of the determined distances), the three determined distances can now be converted into a coordinate and thus a position of the tool to be located in the industrial hall. The determined tool position can then be transmitted from the tool to a central infrastructure unit via any communication interface, e.g., Wi-Fi, and evaluated there.

[0083] In summary, the core of the present invention can be seen in an arrangement and a method for measuring distances between devices in a radio system, wherein a signal strength is determined using a broadband radio-frequency signal from an FMCW transceiver, thus achieving immunity to multipath propagation and interference in the radio channel. The changing properties of the radio channel at different frequencies are exploited, and a maximum signal strength is determined, which corresponds to the direct signal path (LOS) between the transmitting and receiving stations and thus the desired shortest distance.

[0084] The advantages of the present invention lie in particular in the fact that the distance measurement method combines the advantages of the FMCW principle with the signal strength principle for distance and position determination. This achieves greater accuracy and robustness in multipath environments compared to conventional signal strength measurement, while the required setup exhibits low system complexity.

[0085] In contrast to narrowband communication systems, the signal strength value determined using this method is very little affected by narrowband interference signals. In an FMCW system, narrowband interference signals are converted back into a ramp after being mixed with a ramp, which is largely removed by the baseband filter.

[0086] The present invention is suitable for various applications, such as systems with very high distance measurement accuracy and high power consumption. Alternatively, the invention can be used in systems with lower distance measurement accuracy in power-saving solutions.

[0087] Existing components of an FMCW transceiver can be utilized with the invention. Furthermore, the signal processing for the time-of-flight measurement can be switched on or off as required. The same applies to the distance determination unit.

[0088] The present invention makes it possible to use all known common methods for converting the signal strength value into distances and positions in the arrangement, such as a path loss model, fingerprinting, a Kalman filter or a particle filter. LIST OF REFERENCE SYMBOLS 1 Arrangement for signal strength determination 2.2' FMCW device (transceiver / transmitter / receiver) 3 Distance determination arrangement 4, 4' frequency ramp generation arrangement 5.5' driver stage 6, 6' transmitting antenna 7, 7' receiving antenna 8, 8' input amplifier stage 9, 9' mixing stage 10 baseband amplifiers 11 filters 12 Envelope detector 13 Scanning arrangement 14 storage 15 Settlement order 16 Signal strength value output 17 Distance value output

Claims

[1] Arrangement for measuring the distance between devices in a radio system, wherein at least a first receiver-side FMCW device (2) and a second transmitter-side FMCW device (2') are arranged in the radio system, wherein the first receiver-side FMCW device (2) has an output for outputting a baseband signal, characterized bythat a signal strength determination arrangement (1) is arranged which extracts an envelope from a narrowband baseband signal, samples the amplitude of the extracted envelope at specific times and determines a signal strength value with each sample, and determines a maximum signal strength value from the signal strength values ​​determined in a specified time interval, which is connected to the output for outputting a baseband signal of the first receiver-side FMCW device (2), that the signal strength determination arrangement (1) has an output (16) for outputting the determined maximum signal strength value, that this output is connected to a downstream distance determination arrangement (3), and that the distance determination arrangement (3) has an output (17) for outputting a value for the distance measurement. [2] Arrangement according to claim 1, characterized bythat the arrangement for determining signal strength (1) has an envelope detector (12), a scanning arrangement (13) and a comparison arrangement (15). [3] Arrangement according to claim 1 or 2, characterized by that the arrangement for determining signal strength (1) has a memory (14) and that the memory (14) is connected to the comparison arrangement (15) and the output (16) for outputting a signal strength value. [4] Arrangement according to one of claims 1 to 3, characterized by that the first receiver-side FMCW device (2) and / or the second transmitter-side FMCW device (2') is an FMCW transceiver (2'). [5] Method for measuring the distance between devices in a radio system, wherein a broadband signal of a first FMCW frequency ramp generated by a second transmitter-side FMCW device (2') is received by a first receiver-side FMCW device (2), wherein the received broadband signal of the first FMCW frequency ramp is mixed by means of a second FMCW frequency ramp generated in the receiver-side FMCW device (2) and a narrowband baseband signal is generated, characterized bythat an envelope is extracted from the narrowband baseband signal, that the extracted envelope is sampled in its amplitude at specific times, with a signal strength value being determined for each sample, that a maximum signal strength value is determined from the signal strength values ​​determined in this way in a defined time interval and that by means of this maximum signal strength value, a value for the distance measurement is generated and output using an algorithm for converting this signal strength value into a distance. [6] Method according to claim 5, characterized by that the first FMCW frequency ramp and the second FMCW frequency ramp are generated in a linearly increasing or linearly decreasing manner or in a sequence of a linearly increasing and subsequently linearly decreasing frequency ramp or vice versa. [7] Method according to claim 5 or 6, characterized bythat the narrowband baseband signal is filtered to limit its bandwidth before extracting the envelope. [8] Method according to one of claims 5 to 7, characterized by that the sampling takes place at fixed, equally spaced times. [9] Method according to one of claims 5 to 8, characterized by that the specified time interval corresponds to the duration of an FMCW frequency ramp. [10] Method according to one of claims 5 to 9, characterized by that the determined maximum signal strength value is stored in a memory (14).

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