Method for measuring location of communication device using frequency modulation continuous wave (FMCW) radar

Abstract

An existing method for measuring the location of a communication device using an FMCW radar uses a frequency carried by the communication device, and uses a method for calculating the difference between the frequency of a transmission signal of the FMCW radar and the frequency of a carrier wave carried by the communication device. However, in the process of identifying the frequency difference, the frequency of the reciprocal of the unit chirp time length is only measured as the resolution, and an accurate frequency is unable to be measured. In order to solve the above problem, the invention of the present application transmits a continuous chirp signal from the FMCW radar by using the FMCW radar and a frequency modulation tag, calculates an intermediate signal (IF) which is the difference in frequency between signals received at the same time, and demodulates an accurate modulation frequency f_m, thereby quickly and accurately measuring the distance between the FMCW radar and the communication device.

Description

Method for measuring the location of a communication device using FMCW (FREQUENCY MODULATION CONTINUES WAVE) radar

[0001] The present invention relates to a technology for precisely measuring location using a communication device. More specifically, it relates to a technology for improving the location accuracy of a communication device by utilizing signal processing technology.

[0002] Prior to the filing of the present invention, a technology related to an interrogator and a communication device including the same was disclosed. This technology includes an interrogator that outputs an interrogation signal consisting of a series of unit chirp signals varying from a first frequency to a second frequency, and a backscatter tag that receives the interrogation signal, modulates the frequency thereof, and forms and provides a tag signal.

[0003] Another prior art discloses a method and device for performing communication based on backscattering in a wireless communication system. The technology includes an interrogator that outputs an interrogation signal consisting of a series of unit chirp signals varying from a first frequency to a second frequency, and a backscatter tag that receives the interrogation signal, modulates the frequency thereof, and forms and provides a tag signal, and the interrogator is disclosed to receive the tag signal and demodulate the tag signal.

[0004] Conventional methods for measuring the location of communication devices using FMCW radar utilize the frequency returned from the communication device, calculating the difference in frequency between the FMCW radar transmission signal and the carrier wave returned from the communication device. However, in the process of identifying the frequency difference, the resolution is measured only with the reciprocal frequency of the unit chirp time length, and thus the exact frequency cannot be measured. For this reason, the resolution for identifying the frequency difference is limited, which may cause errors in the distance measurement of the communication device.

[0005] The present invention seeks to eliminate distance measurement errors between FMCW radar and the communication device that occur due to inability to accurately measure the difference in frequency as described above.

[0006] The above communication device may include either an active frequency modulation tag having a receiving antenna and a transmitting antenna that modulate a received signal and generate a return signal, or a passive frequency modulation tag that receives a radar signal, modulates the signal, and returns the signal.

[0007] In the present invention, a frequency modulation tag is used as the same term as the above communication device.

[0008] In addition, the FMCW radar may be configured with a signal generator that generates various types of transmission signals, a transmission antenna that transmits the generated signals, a reception antenna that receives the signals, and a signal processing unit. In some cases, the signal generator and the transmission antenna, the reception antenna that receives the signals, and the signal processing unit may be provided separately.

[0009] The composition of the invention to solve the above problem is as follows.

[0010] Using FMCW radar and frequency modulation tags,

[0011] The present invention provides a method for measuring a position of a communication device using an FMCW radar, characterized in that the FMCW radar calculates an intermediate signal (IF), which is a difference in the frequency of a signal transmitted and simultaneously received from a continuous chirp signal, and a tag signal, which is an intermediate signal of a carrier wave returned from a frequency modulation tag by a continuous chirp signal, is a sum of a modulation frequency f_m and a distance frequency f_r representing a distance due to a time shift, and in order to calculate the modulation frequency f_m of the tag signal from the FMCW radar, the FMCW radar calculates the modulation frequency f_m by subtracting the frequency of the nearest neighboring reflected signal smaller than the maximum peak frequency from the maximum peak frequency of the tag signal modulated from the frequency modulation tag located among the neighboring reflected signals located at an integer multiple of the reciprocal frequency of the unit chirp time length in the frequency domain.

[0012] Additionally, using FMCW radar and frequency modulation tags,

[0013] A method for calculating a distance frequency indicating a distance between the FMCW radar and a frequency modulation tag from a tag signal transmitted from a frequency modulation tag, the method comprising: demodulating a sync function of a tag signal received from the frequency modulation tag using modulation frequency spectrum leakage characteristic values ​​of a tag signal that does not overlap with a periodic peripheral reflection signal frequency centered on a maximum peak frequency of a signal modulated from the frequency modulation tag located between the periodic peripheral reflection signal frequencies in the frequency domain; and calculating a distance frequency by subtracting the modulation frequency from the center frequency of the demodulated sync function.

[0014] Additionally, using FMCW radar and frequency modulation tags,

[0015] In a method for measuring the distance between the FMCW radar and the frequency modulation tag,

[0016] A radar transmission signal generation step for generating a radar transmission signal in the above FMCW radar; and

[0017] A carrier wave transmission step of receiving a radar transmission signal generated in the radar transmission signal generation step from the tag receiving antenna provided in the frequency modulation tag, modulating the frequency by f_m in the modulation unit provided in the frequency modulation tag, and transmitting the modulated signal from the tag transmission antenna of the frequency modulation tag; and

[0018] A signal receiving step for receiving a modulated signal transmitted in the carrier transmission step from a receiving antenna provided in the FMCW radar; and

[0019] A reception frequency preprocessing step for generating an intermediate signal by mixing the frequency transmitted from the FMCW radar and the frequency received from the FMCW radar to calculate the sum of the distance frequency and the modulation frequency, which are the differences between the frequency transmitted from the FMCW radar and the frequency received in the signal receiving step; and

[0020] A frequency domain conversion step of converting the intermediate signal generated in the above reception frequency preprocessing step into a frequency domain; and

[0021] A separation frequency confirmation step for confirming the frequency of the surrounding reflection signal periodically located in the intermediate signal of the frequency domain converted in the above frequency domain conversion step and the tag signal modulated in the frequency modulation tag; and

[0022] A method for measuring the position of a communication device using an FMCW radar is provided, including calculating the modulation frequency f_m by subtracting the frequency of the nearest peripheral reflection signal that is smaller than the maximum peak frequency of the tag signal among the peripheral reflection signals periodically located at the maximum peak frequency of the tag signal modulated in the frequency modulation tag.

[0023] Additionally, using FMCW radar and frequency modulation tags,

[0024] In a method for measuring the distance between the FMCW radar and the frequency modulation tag,

[0025] A radar transmission signal generation step for generating a radar transmission signal in the above FMCW radar; and

[0026] A carrier wave transmission step of receiving a radar transmission signal generated in the radar transmission signal generation step from the tag receiving antenna provided in the frequency modulation tag, modulating the frequency by f_m in the modulation unit provided in the frequency modulation tag, and transmitting the modulated signal from the tag transmission antenna of the frequency modulation tag; and

[0027] A signal receiving step for receiving a modulated signal transmitted in the carrier transmission step from a receiving antenna provided in the FMCW radar; and

[0028] A reception frequency preprocessing step for generating an intermediate signal by mixing the frequency transmitted from the FMCW radar and the frequency received from the FMCW radar to calculate the sum of the distance frequency and the modulation frequency, which are the differences between the frequency transmitted from the FMCW radar and the frequency received in the signal receiving step; and

[0029] A frequency domain conversion step of converting the intermediate signal generated in the above reception frequency preprocessing step into a frequency domain; and

[0030] A separation frequency confirmation step for confirming the frequency of the surrounding reflection signal periodically located in the intermediate signal of the frequency domain converted in the above frequency domain conversion step and the tag signal modulated in the frequency modulation tag; and

[0031] The present invention provides a method for measuring the position of a communication device using an FMCW radar, which includes demodulating a sync function of a signal received from a frequency modulation tag using modulation frequency spectrum leakage characteristic values ​​of a signal received from a frequency modulation tag that do not overlap with the surrounding reflected signal frequencies periodically positioned around the maximum peak frequency of a tag signal modulated from the frequency modulation tag in the frequency domain, and calculating the center frequency of the demodulated sync function as the sum of the distance frequency and the modulation frequency.

[0032] In addition, a method for measuring the position of a communication device using an FMCW radar is provided, characterized in that a value obtained by subtracting a modulation frequency (f_m) from the center frequency in the frequency domain is calculated as a distance frequency f_r indicating the distance.

[0033] In addition, a method for measuring a position of a communication device using an FMCW radar is provided, characterized in that the radar signal generated from the FMCW radar is any one of a periodic repetition of two or more continuous chirp signals, an intermittent periodic repetition of two or more continuous chirp signals, a discontinuous and periodic repetition of two or more chirp signals, and a discontinuous and intermittent periodic repetition signal of two or more chirp signals.

[0034] In addition, a method for measuring the position of a communication device using an FMCW radar is provided, characterized in that the reciprocal of the above f_r is calculated as a time delay according to distance and multiplied by the speed of light to calculate the distance between the FMCW radar and a frequency modulation tag.

[0035] The present invention is an invention having the effect of providing a technology capable of quickly and accurately measuring the distance between an FMCW radar and a single or multiple fixed or moving frequency modulation tags having a frequency modulation function by using an FMCW radar and a frequency modulation tag having a frequency modulation function according to the configuration of the invention as described above.

[0036] Figure 1 is a conceptual diagram and internal configuration diagram of the FMCW radar and communication device (tag, frequency conversion tag) of the present invention.

[0037] Figure 2 is a configuration diagram of the FMCW radar and multiple communication devices (tags) of the present invention.

[0038] Figure 3 is a signal graph in the time domain of communication signals used in the FMCW radar of the present invention and a plurality of communication devices.

[0039] Figure 4 shows the types of signals (chirp signals and their modified signals) that can be used for distance measurement in the FMCW radar of the present invention.

[0040] Figure 5 is a comparison graph in the frequency domain of the intermediate signal reception result using an existing FMCW radar and a frequency conversion tag and the intermediate signal reception result using an FMCW radar and a frequency conversion tag using a continuous chirp signal of the present invention.

[0041] Fig. 6 is a graph showing a tag signal of a frequency conversion tag received by the FMCW radar of the present invention in the frequency domain and calculating the modulation frequency (f_m) of the frequency conversion tag.

[0042] Fig. 7 is a graph of a sync function graph of a frequency conversion tag reception signal demodulated using a spectrum leakage feature point that displays the tag signal of a frequency conversion tag received by the FMCW radar of the present invention in the frequency domain.

[0043] Fig. 8 is a diagram illustrating a signal processing sequence of a tag signal of a frequency conversion tag received by the FMCW radar of the present invention.

[0044] FIG. 9 is a conceptual diagram for measuring the distance of a plurality of frequency conversion tags from the FMCW radar using the FMCW radar of the present invention and a plurality of frequency conversion tags.

[0045] FIG. 10 is a drawing showing the measurement of the positions of multiple tags on a plane using the FMCW radar of the present invention and multiple frequency conversion tags.

[0046] Fig. 11 is a graph showing the results of calculating the sync function of individual tag signals to measure the positions of multiple tags on a plane using the FMCW radar of the present invention and multiple frequency conversion tags.

[0047] FIG. 12 is an explanatory diagram of a case where a frequency conversion tag is fixed to a moving object and a case where a frequency conversion tag is fixed to a stationary object using the FMCW radar and two frequency conversion tags of the present invention.

[0048] Fig. 13 is a graph showing a tag signal in the frequency domain when a frequency conversion tag of the present invention is fixed to a moving object.

[0049] FIG. 14 is an explanatory diagram of a case where a frequency conversion tag is fixed to a moving object and a case where a frequency conversion tag is fixed to a stationary object using the FMCW radar and a plurality of frequency conversion tags of the present invention.

[0050] FIG. 15 is an explanatory diagram illustrating signals exchanged when measuring the distance between an FMCW radar and a frequency conversion tag using the FMCW radar and one frequency conversion tag of the present invention.

[0051] Fig. 16 is an embodiment for detecting the position of a frequency conversion tag in 2D or 3D space.

[0052] Fig. 17 is another embodiment for detecting the position of a frequency conversion tag in 2D or 3D space.

[0053] Fig. 18 is another embodiment of the present invention for simultaneously detecting a fixed frequency conversion tag and a moving frequency conversion tag in a 2D or 3D space.

[0054] The operational effects generated by the above-described composition of the present invention are explained using drawings as follows.

[0055] Figure 1 is a conceptual diagram and an internal configuration diagram of an FMCW radar and a communication device (tag, frequency conversion tag) of the present invention. The upper figure illustrates the concept of an FMCW radar and a communication device exchanging signals with each other, and the lower figure illustrates the configuration of the FMCW radar and the communication device in a conceptual diagram, respectively. The FMCW radar is composed of a transmitter for transmitting a signal to the communication device, a receiver for receiving a signal returned from the communication device, and a position measurement algorithm for calculating position information from the received signal. The communication device is composed of a transmit / receive antenna and a modulation unit, and can further include a separate control signal to control the modulation unit, and the transmit / receive antennas can be configured separately as a transmit antenna and a receive antenna. The FMCW radar can utilize various types of chirp signals, and for this purpose, it is equipped with a chirp signal generator, and the generated chirp signal is propagated through a splitter to a transmit antenna. The transmit signal transmitted through the splitter to a mixer is multiplied by a receive signal received through the receive antenna in the mixer to generate an intermediate signal (IF). The generated IF signal is converted into a signal in the frequency domain and separated into a peripheral reflection signal (noise signal) and a communication device signal (tag signal). The communication device signal separated in this way is demodulated by using the sync function of the communication device signal by utilizing the spectrum leakage characteristic frequency to accurately measure the location of the communication device. Any device that is composed of a receiving antenna, a modulation unit, and a transmitting antenna can be used as the communication device, and it is more convenient to use if it is in the form of a tag that can be simply attached and used. In the present application invention, the tag can be used with the same expression as the communication device, but in order to distinguish it from a tag without a general frequency conversion function, it is also used with the same meaning to describe it as a frequency modulation tag.

[0056] For frequency modulation, the modulation unit of the tag modulates by repeatedly switching between two or more impedance values. The modulation unit can switch the impedance value according to the value of an externally input control signal, and various means can be used to adjust the control signal, such as the output of a voltage-controlled oscillator (VCO), switching between multiple fixed oscillators, or directly generating it in a separate processor (such as an MCU).

[0057] Figure 2 is a configuration diagram of the FMCW radar and a plurality of communication devices (tags) of the present invention. A plurality of frequency conversion tags that receive a radar chirp signal generated by the FMCW transmit a frequency that is converted differently for each tag, and the FMCW radar receives this transmitted signal to separate and recognize each tag, and calculates the distance for each tag.

[0058] Fig. 3 is a time domain signal graph of a communication device carrier received by the FMCW radar of the present invention. The signal generated by the FMCW radar is reflected by objects, buildings, and things existing in space and is received by the FMCW radar with a certain time delay (dt), and the return signal of the communication device (frequency conversion tag) is received by the FMCW radar after being separated from the object, building, and thing signals by the modulated frequency signal while going through an internal frequency conversion. However, since it is a time domain, it can be confirmed that multiple signals can be overlapped and measured on the X-axis representing the same time. However, since the Y-axis values ​​representing each frequency do not overlap, these signals can be measured separately in the frequency domain.

[0059] Figure 4 illustrates the types of signals (chirp signals and their modified signals) that can be used for distance measurement in the FMCW radar of the present invention. A chirp signal refers to a signal whose frequency changes linearly over time. The frequency need not change linearly over the entire period, and it includes signals that can be repeated periodically, and whose increasing and decreasing portions may or may not be symmetrical. Figure 4 illustrates that various types of chirps can be used partially or fully. The present invention can use chirp signals of other types than those shown in Figure 4 as needed, and signals can be generated and used discontinuously or continuously, continuously discontinuously, or discontinuously discontinuously as needed. These signals can be used periodically by repeating for a certain period of time. In Figure 4, the continuous chirp signal can adjust the number of chirps and the duration of the chirps. As the number of chirps increases, the frequency resolution increases, allowing for the operation of larger tags. Increasing the chirp length allows for the observation of tags at greater distances. Conversely, decreasing the number and length of chirps allows for faster updates of tag location information. The appropriate continuous chirp signal setting can be selected depending on the technology's application environment.

[0060] Fig. 5 is a comparative graph in the frequency domain of the intermediate signal reception result using the existing FMCW radar and frequency conversion tag and the intermediate signal reception result using the FMCW radar and frequency conversion tag using the continuous chirp signal of the present invention. Fig. 5 (a) shows that the communication device signal with 40 Hz frequency modulation is expressed at the same frequency as the ambient reflection signal (noise, noise) generated by nearby surrounding objects (clutter) in the FMCW radar, and the signal size is small and cannot be recognized. (b) The communication device signal with 40 Hz frequency modulation is expressed separately from the ambient reflection signal under the continuous chirp interrogation method. At this time, the distance accuracy of the communication device is the same as that of the existing FMCW radar. (60 cm for 250 MHz frequency band).

[0061]

[0062] The continuous chirp radar transmission method with continuous chirp signal processing added to the FMCW radar effectively separates the tag FSK signal from the surrounding reflected signals in the frequency domain.

[0063] Compared to the conventional FMCW that uses an intermittent single chirp signal c(t), the continuous chirp interrogation method utilizes a radar transmission signal that is a multiple continuous chirp signal.

[0064]

[0065] Here, c(t) represents a single chirp, T represents the chirp duration, N represents the number of chirp repetitions, and * represents convolution. That is, s(t) is the signal in the lower left of Fig. 5, which is the signal in which the chirp c(t) is repeated N times with period T.

[0066] When this radar transmission signal reflects from an ambient reflector (i.e., clutter), the propagation delay is reflected to become s(t-dt), where dt is the round-trip propagation delay time between the radar and the clutter. In the continuous chirp interrogation method, the radar transmission signal received after reflecting from clutter is simply the time-shifted radar transmission signal, so it maintains the period T. Therefore, the radar intermediate signal (IF) of the clutter (ambient reflection signal, measurement noise) is represented by a peak at an integer multiple of 1 / T Hz frequency (because a signal with period T is represented as a sum of integer multiples of 1 / T Hz frequencies), and all other frequency components that are not integer multiples of 1 / T Hz become 0. This applies to all clutter noise, i.e., all noise is concentrated in the same set of frequencies.

[0067] On the other hand, the reflected signal (backscatter signal, communication device signal) from the communication device is modulated with FSK (Frequency Shift Keying) to change its frequency based on the FMCW radar transmission signal. Specifically, the signal returned from the communication device is expressed by the following equation.

[0068] s(t-dt) *

[0069] Interrogation signal FSK

[0070] (period T) (period 1 / fm)

[0071] Here, f_m is the modulation frequency of FSK, and its period is 1 / f_m, which is different from the period T of the FMCW radar chirp signal. As a result, the period of the communication device signal becomes the least common multiple of T, which is a new period other than T, and 1 / f_m. As a result of this frequency modulation, the communication device carrier is expressed at a frequency that is not an integer multiple of 1 / T during the process of being converted to an intermediate signal, and is therefore separated from the clutter noise and displayed in the frequency domain. The separation of the communication device signal and the clutter (surrounding reflected signals, noise) can be confirmed in Fig. 5.

[0072] Fig. 6 is a graph illustrating the FMCW radar and frequency conversion tag reception signal of the present invention in the frequency domain to calculate the modulation frequency (f_m) of the frequency conversion tag. The frequency conversion tag reception signal is a signal that includes a frequency change (f_r) due to time delay and a frequency change (f_m) due to frequency modulation performed within the frequency conversion tag. Therefore, if the frequency difference f_m due to frequency modulation can be calculated, the frequency change f_r due to time delay can be calculated and the distance can be calculated using this.

[0073] The first step to obtain an accurate estimate of the distance frequency f_r, that is, the frequency change due to time delay, is to remove the influence of f_m from the intermediate frequency (IF) signal. While the modulation frequency can be designed when designing a communication device, in reality, f_m is not always constant due to the instability of the oscillator, so it must be measured in real time and used. For example, a crystal oscillator has a deviation of approximately 500 ppm in various environments, and even when configuring an oscillator circuit such as an LCR circuit, changes occur due to temperature. Therefore, when calculating f_r using the designed f_m frequency without actual measurement, a large distance error of more than 24.6 cm was measured.

[0074] The position tracking method of the present invention can accurately measure f_m by the following method without prior knowledge of the modulation speed of the communication device or the environment in which the communication device is installed. In order to accurately identify f_m, f_r can be measured based on the principle of using a multi-chirp signal (s(t-dt)) with a period T, i.e., a propagation delay due to a distance difference between the FMCW radar and the communication device. f_m has a period of 1 / f_m. As an FSK signal, the s(t-dt) signal is frequency-shifted by f_m. By this frequency shift, the intermediate signal (IF) of the communication device signal is displayed at a position f_m away from the 1 / T Hz integer multiple frequency peak, as shown in Fig. 6. Therefore, f_m can be accurately calculated in real time through the frequency difference with the 1 / T Hz integer multiple frequency peak adjacent to the communication device signal.

[0075] To remove f_m, first nullify the clutter noise to 0, and then shift the communication device signal to the nulled frequency range, which will remove f_m. This is because removing f_m from the communication device signal places the signal at an integer multiple of 1 / T Hz where the clutter noise is.

[0076] Fig. 7 is a graph showing a demodulated sync function graph of a frequency conversion tag reception signal using spectrum leakage feature points that display the tag signal of the frequency conversion tag received by the FMCW radar of the present invention in the frequency domain. The center frequency of the sync function represents the sum of the distance frequency and the modulation frequency. By accurately removing the modulated frequency f_m using the method discussed above, the location of the communication device (frequency conversion tag) can be calculated.

[0077] The measured maximum peak signal of the intermediate signal of the communication device is expressed in 1 / T Hz intervals, so it may not be the exact f_r+f_m. The exact f_r+f_m is found by finding the center frequency of the sync function. The peak error frequency is indicated as df in Figure 7.

[0078] To solve these problems and achieve more accurate position measurement, the present invention utilizes the spectral leakage characteristics of the discrete Fourier transform (DFT) for a time-limited signal. The DFT of a signal with a period of T and a frequency of f_r exhibits peaks at multiples of 1 / T Hz, and the envelope of its spectral leakage becomes a sinc function centered at f_r (i.e., TSinc(pi*T(f-fr))). Therefore, to accurately identify f_r, the envelope sinc function must be accurately identified. To this end, the positioning method zero-pads a signal of duration T in the time domain to the size of T_pad. This is a sinc interpolation method in the frequency domain. As shown in Figures 8(c)-(e), the center of the sinc function is located at f_r. Consequently, given the sinc interpolation result as shown in Figure 8(e), f_r is obtained as the frequency with the maximum peak amplitude. The computational complexity of the overall positioning method is O(NlogN), where N is the number of samples, and its computational complexity is the same as that of the FFT. In other words, the positioning method maintains the complexity of the existing FMCW, which necessarily performs the FFT, while achieving high accuracy.

[0079] FIG. 8 is a flowchart illustrating a signal processing procedure for a tag signal of a frequency conversion tag received by an FMCW radar of the present invention. (a) After f_m is identified and removed in real time at an intermediate frequency (IF), (b) an Inverse Fast Fourier Transform (IFFT) is applied to a separated signal containing only f_r (including spectral leakage). (c) In the time domain of the signal resulting from the IFFT, (d) a signal segment of duration T is zero-padded, where (e) an FFT (Fast Fourier Transform) is performed to obtain an envelope sinc function, and f_r is calculated as the frequency of the maximum peak amplitude.

[0080] Fig. 9 is a conceptual diagram of measuring the distance of a plurality of frequency conversion tags from an FMCW radar using the FMCW radar and a plurality of frequency conversion tags of the present invention. Each tag (frequency conversion tag, communication device) signal has a different distance frequency f_r and modulation frequency f_m, and the intermediate signal (IF) thereof is expressed at different frequencies f_r+f_m.

[0081] FMCW radar is equipped with a wideband receiver (wideband receiving antenna) that analyzes multiple different tag intermediate signals (IFs) in the frequency domain, thereby simultaneously measuring the precise locations of tags that are independently expressed at different frequencies depending on the distance and modulation frequency. Figure 9 illustrates this. The range frequency f_r is determined by the physical distance between the tag and the FMCW radar, and each tag is frequency modulated with a different modulation frequency f_m, so that the tags are distinguished and the distance is measured.

[0082] Fig. 10 is a graph and photograph showing the position of multiple tags on a plane using the FMCW radar of the present invention and multiple frequency conversion tags. The positions of the tags are measured very accurately. The result is not shown by scanning the tags one by one, but rather, the result is shown by having multiple tags arranged in two dimensions simultaneously generate carrier waves in response to the transmission signal of the FMCW radar, receiving the generated carrier waves in the wideband receiving unit of the FMCW radar, converting them to intermediate frequencies, and then simultaneously recognizing each tag in the frequency domain and calculating the distance using the method described above.

[0083] Figure 11 is a graph showing the results of calculating the sync function of the received tag signals from individual frequency conversion tags to measure the plane positions of multiple tags using the FMCW radar of the present invention and multiple frequency conversion tags. By accurately measuring the distance frequency of each tag through the center frequency of the sync function, the precise distance between the radar and the tags can be calculated.

[0084] The method for tracking the location of a communication device (tag, frequency conversion tag) of the present invention can simultaneously track the location of both stationary and moving communication devices with a single FMCW radar transmission. This is possible because each communication device is configured to generate a different modulation frequency f_m. The different modulation frequencies f_m also function as IDs (identifiers) that distinguish the communication devices.

[0085] That is, the period 1 / f_m of the modulation frequency of each communication device is set to be distinct from the period T of the FMCW radar transmission signal s(t). As a result, each communication device is effectively separated from the clutter, as shown in FIG. 6, and can be expressed in separate frequency peaks that do not overlap, as shown in FIG. 11. The position tracking method acquires communication device signals with different FSK frequencies returning from multiple communication devices using a wideband receiver, and analyzes the intermediate signal (IF) thereof in the frequency domain, thereby measuring the exact positions of the communication devices independently expressed in different frequencies according to the distance and modulation frequency in the frequency domain. The f_m of each communication device can be set to a corresponding frequency interval so as to allow for the frequency error of the crystal oscillator used. Each f_m can include all frequencies that are not integer multiples of 1 / T Hz, and its value can be lower or higher than 1 / T Hz.

[0086] FIG. 12 is a diagram illustrating a case where a frequency-converting tag is fixed to a moving object and a case where a frequency-converting tag is fixed to a stationary object using an FMCW radar and two frequency-converting tags of the present invention. Unlike a stationary communication device, a moving communication device induces a Doppler frequency f_d and a time-varying range frequency f_r(t). As the communication device moves, the Doppler frequency f_d is added on top of f_m. f_d operates fundamentally in the same way as f_m in the intermediate frequency (IF) signal, appearing as a 1 / T Hz integer multiple peak offset by the amount f_m+f_d instead of f_m. This can be easily removed by measuring the distance from the 1 / T Hz integer multiple peak and shifting the IF signal in the negative direction by that frequency, similar to the f_m removal method described above. On the other hand, the range frequency f_r(t), which varies over time, causes frequency dispersion of the peak, as shown in FIG. 13(b).

[0087] Since the fixed frequency conversion tag does not have a variable element f_d, there is no frequency dispersion, as shown in Fig. 13(a). This can be used to distinguish between moving tags and fixed tags.

[0088] The frequency dispersion increases as the movement of the communication device increases. The positioning method can track f_r(t) with an accuracy of less than 1 centimeter through detailed time analysis. The positioning of a moving communication device can distinguish between a moving communication device and a stationary communication device through the frequency dispersion proportional to the communication device speed. For sub-centimeter positioning, when a moving communication device is defined as having a movement of >1 cm within the duration of the FMCW radar transmission signal s(t), the peaks with a frequency dispersion of 1.4 Hz or more are identified.

[0089] The positioning of a mobile communication device is basically the same design principle as that of a stationary communication device: the mobile communication device signal f_m is removed, an IFFT is performed (Fig. 8(a)-(c)), and the distance frequency (i.e., f_r(t)) is reconstructed in the time domain. That is, each signal fragment (duration T) of f_r(t) in Fig. 8(c) represents the position at the corresponding time, and zero padding is performed to represent the exact position at that time (Fig. 8(d),(e)).

[0090] By using the FMCW radar of the present invention, it is possible to observe the frequency dispersion of multiple tag peaks to determine whether the tag is moving or stationary.

[0091] Additionally, the moving speed of a tag can be measured by measuring the magnitude of the frequency dispersion. To precisely track the position of a moving tag, the same positioning process is used as for a stationary tag. However, to precisely recover the tag's positional changes over time, an IFFT can be performed, including the tag peak, spectral leakage, and its frequency dispersion.

[0092] Figure 14 is a diagram illustrating a case where a frequency conversion tag is fixed to a moving object and a case where a frequency conversion tag is fixed to a stationary object using an FMCW radar and multiple frequency conversion tags of the present invention. In a situation where there are multiple moving tags and fixed tags, after distinguishing whether each tag is moving or fixed, location recognition is performed according to the classification. In this case as well, the wideband receiving unit of the FMCW radar can measure the locations of multiple moving tags and fixed tags simultaneously.

[0093] Figure 15 is a diagram illustrating signals exchanged when measuring the distance between an FMCW radar and a frequency conversion tag using the FMCW radar and one frequency conversion tag of the present invention. One-dimensional distance can be measured by using one FMCW radar.

[0094] Fig. 16 is an embodiment for detecting the position of a frequency conversion tag in 2D or 3D space. By using two or more FMCW radars, the position of a tag in a plane or space can be calculated. To this end, a master FMCW radar and a slave FMCW radar are provided, and the distance to the tag measured by each is transmitted to the master FMCW radar to determine the position of the tag in a plane or space.

[0095] Fig. 17 is another embodiment for detecting the position of a frequency conversion tag in 2D or 3D space. A method is used to calculate the position of a tag by providing a separate position calculation controller without distinguishing between a master and slave FMCW radar. Each radar may be connected to a controller capable of post-processing and transmitting / receiving radar information, such as a mini PC or Raspberry Pi. The controller can transmit radar IF signals or measured distance information for each tag to the position calculation controller via wired or wireless communication, and can receive instructions from the position calculation controller to change the continuous chirp signal settings (length per chirp and total number of chirps). The position calculation controller can display or store position information using information received from the radar, and can instruct the continuous chirp signal settings to be changed according to environmental changes.

[0096] Fig. 18 is another embodiment of the present invention for simultaneously detecting fixed and moving frequency conversion tags in 2D or 3D space. This is an explanatory diagram to explain that the positions of moving tags and fixed tags can be determined in the same way when determining the positions of tags on a plane or in space. Since the frequency dispersion of moving tags is measured in space, tags that move in the same way can be measured. The use of multiple radars for trilateration can simultaneously track the positions of multiple fixed and moving tags. Here, moving tags are affected by different Doppler frequencies f_d for each radar depending on the direction of movement. To cope with this, each radar can set the modulation frequency f_m and the distance frequency f_r interval of each tag so that it can correspond to the maximum Doppler frequency.

[0097] (drawing symbol)

[0098] 100: Position measurement system for communication devices using FMCW radar

[0099] 200: FMCW radar

[0100] 210: Chirp signal generator

[0101] 220: Signal separator

[0102] 230: Transmission antenna

[0103] 240: Receiving antenna

[0104] 250: Signal mixer

[0105] 260: Distance or position measurement algorithm

[0106] 300: Communication device (frequency conversion tag)

[0107] 310: Transmitting and receiving antenna

[0108] 320: Modulation section

[0109] The invention of this application is a technology that can be industrially applied as a method for measuring the location of a communication device using communication technology.

Claims

1. Using FMCW radar and frequency modulation tags, A method for measuring a position of a communication device using an FMCW radar, characterized in that the FMCW radar calculates an intermediate signal (IF) which is a difference in the frequency of a signal transmitted and simultaneously received from the continuous chirp signal, and the tag signal which is an intermediate signal of a carrier wave returned from the continuous chirp signal by the frequency modulation tag is a sum of a modulation frequency f_m and a distance frequency f_r which represents a distance due to a time shift, and in order to calculate the modulation frequency f_m of the tag signal from the FMCW radar, the FMCW radar subtracts the frequency of the nearest neighboring reflection signal smaller than the maximum peak frequency from the maximum peak frequency of the tag signal modulated from the frequency modulation tag which is located among neighboring reflection signals located at an integer multiple of the reciprocal frequency of the unit chirp time length in the frequency domain to calculate the modulation frequency f_m.

2. Using FMCW radar and frequency modulation tags, A method for calculating a distance frequency indicating a distance between the FMCW radar and a frequency modulation tag from a tag signal transmitted from the frequency modulation tag, the method comprising: demodulating a sync function of a tag signal received from the frequency modulation tag using modulation frequency spectrum leakage characteristic values ​​of a tag signal that does not overlap with the peripheral reflection signal frequencies that are periodically positioned, centered on a maximum peak frequency of a signal modulated from the frequency modulation tag that is positioned between the peripheral reflection signal frequencies that are periodically positioned in the frequency domain, and calculating the distance frequency by subtracting the modulation frequency from the center frequency of the demodulated sync function.

3. Using FMCW radar and frequency modulation tags, In a method for measuring the distance between the above FMCW radar and the frequency modulation tag, A radar transmission signal generation step for generating a radar transmission signal from the above FMCW radar; and A carrier wave transmission step of receiving a radar transmission signal generated in the radar transmission signal generation step from the tag receiving antenna provided in the frequency modulation tag, modulating the frequency by f_m in the modulation unit provided in the frequency modulation tag, and transmitting the modulated signal from the tag transmission antenna of the frequency modulation tag; and A signal receiving step for receiving a modulated signal transmitted in the carrier transmission step from a receiving antenna equipped in the FMCW radar; and A reception frequency preprocessing step for generating an intermediate signal by mixing the frequency transmitted from the FMCW radar and the received frequency to calculate the sum of the distance frequency and the modulation frequency, which are the differences between the frequency transmitted from the FMCW radar and the frequency received in the signal receiving step; and A frequency domain conversion step of an intermediate signal that converts the intermediate signal generated in the above reception frequency preprocessing step into a frequency domain; and A separation frequency verification step for verifying the frequency of the surrounding reflection signal that is periodically located in the intermediate signal of the frequency domain converted in the above frequency domain conversion step and the tag signal modulated in the frequency modulation tag; and A method for measuring the position of a communication device using an FMCW radar, comprising calculating the modulation frequency f_m by subtracting the frequency of the nearest peripheral reflection signal smaller than the maximum peak frequency of the tag signal among the peripheral reflection signals periodically located at the maximum peak frequency of the tag signal modulated in the frequency modulation tag.

4. Using FMCW radar and frequency modulation tags, In a method for measuring the distance between the above FMCW radar and the frequency modulation tag, A radar transmission signal generation step for generating a radar transmission signal from the above FMCW radar; and A carrier wave transmission step of receiving a radar transmission signal generated in the radar transmission signal generation step from the tag receiving antenna provided in the frequency modulation tag, modulating the frequency by f_m in the modulation unit provided in the frequency modulation tag, and transmitting the modulated signal from the tag transmission antenna of the frequency modulation tag; and A signal receiving step for receiving a modulated signal transmitted in the carrier transmission step from a receiving antenna equipped in the FMCW radar; and A reception frequency preprocessing step for generating an intermediate signal by mixing the frequency transmitted from the FMCW radar and the received frequency to calculate the sum of the distance frequency and the modulation frequency, which are the differences between the frequency transmitted from the FMCW radar and the frequency received in the signal receiving step; and A frequency domain conversion step of an intermediate signal that converts the intermediate signal generated in the above reception frequency preprocessing step into a frequency domain; and A separation frequency verification step for verifying the frequency of the surrounding reflection signal that is periodically located in the intermediate signal of the frequency domain converted in the above frequency domain conversion step and the tag signal modulated in the frequency modulation tag; and A method for measuring the position of a communication device using an FMCW radar, comprising: demodulating a sync function of a signal received from a frequency modulation tag using modulation frequency spectrum leakage characteristic values ​​of the signal received from the frequency modulation tag that do not overlap with the surrounding reflected signal frequencies periodically positioned around the maximum peak frequency of the tag signal modulated from the frequency modulation tag in the frequency domain; and calculating the center frequency of the demodulated sync function as the sum of the distance frequency and the modulation frequency.

5. In any one of paragraphs 1 to 4, A method for measuring the position of a communication device using an FMCW radar, characterized in that the distance frequency f_r is calculated by subtracting the modulation frequency (f_m) from the center frequency in the frequency domain.

6. In any one of paragraphs 1 to 4, A method for measuring position of a communication device using an FMCW radar, characterized in that the radar signal generated from the above FMCW radar is any one of a periodic repetition of two or more continuous chirp signals, an intermittent periodic repetition of two or more continuous chirp signals, a discontinuous periodic repetition of two or more chirp signals, and a discontinuous and intermittent periodic repetition signal of two or more chirp signals.

7. In paragraph 5, A method for measuring position of a communication device using an FMCW radar, characterized in that the distance between the FMCW radar and a frequency modulation tag is calculated by multiplying the speed of light by the reciprocal of the above f_r, which is calculated as a time delay according to distance.

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