Range finder, receiver

Abstract

To provide a ranging device that uses frequency division multiplexing.SOLUTION: A ranging device according to the present invention comprises a transmitter and N receivers. The transmitter transmits N kinds of frequency-modulated pulse waves differing in center frequency. The n-th receiver includes an IQ conversion unit, an amplitude suppression unit, a bandwidth limiting unit, and a pulse compression unit. The IQ conversion unit converts the received n-th kind of pulse wave to a baseband IQ signal. The amplitude suppression unit includes a wave detector, an attenuation amount calculator, a delay unit, and a suppresser. The wave detector detects the amplitude of a receive signal. The attenuation amount calculator calculates the amount of attenuation for attenuating a portion of the receive signal that is larger than a prescribed amplitude to the prescribed amplitude. The suppresser causes the receive signal to be attenuated on the basis of the amount of attenuation, and obtains a suppressed signal. The bandwidth limiting unit attenuates the frequency component other than the baseband and obtains a bandwidth limited suppression signal. The pulse compression unit performs, on the bandwidth limited suppression signal, pulse compression that corresponds to frequency modulation, and obtains a compressed receive signal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a distance measuring device and a receiver using pulse waves. [Background technology]

[0002] Distance measuring devices that use pulse waves, such as sonar and radar, measure the distance to a reflecting object by transmitting sound waves or radio waves to understand the surrounding environment and measuring the time it takes for the waves to reflect off a nearby object and be received again. The update rate of the measurement results varies depending on the measurement distance range; the longer the distance range, the longer the reception time and the slower the update rate. A decrease in the update rate results in a slower ability to follow changes in the surrounding environment. Furthermore, if the distance measuring device is moving, there is a limit to the speed of movement. This tendency is particularly noticeable in distance measuring devices that use sound waves, which travel slowly.

[0003] Furthermore, in ranging technology, pulse compression processing is used to improve distance resolution and extend the maximum detection distance. Known pulse compression techniques include those shown in Patent Documents 1 and 2 and Non-Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-85167 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-247615 [Non-patent literature]

[0005] [Non-Patent Document 1] JE Cilliers, JC Smit: Pulse Compression Sidelobe Reduction by Minimization of Lp-Norms, IEEE Trans. AERO, Vol. 43, No. 3, pp. 1238-1247, July 2007. Summary of the Invention [Problem to be solved by the invention]

[0006] Due to the nature of distance measuring devices that use pulse signals, it is unavoidable to secure reception time according to the measurement distance range. Therefore, a multiplexing method is required to allow for this and perform measurements in parallel during the reception time.

[0007] Code division multiplexing (CDMA) is a promising candidate for the multiplexing method. CDMA has the advantage that it can transmit and receive multiple mutually orthogonal codes, such as M-sequence codes, at the same time and frequency, and is the method adopted in second and third generation mobile phones. Figure 1 shows an example of a multiplexing method for improving the update rate in CDMA. In Figure 1, four orthogonal code sequences A to D are prepared, and measurements are performed by dividing the repetition period (= reception time) into four. This means that, theoretically, the update rate can be four times higher than usual.

[0008] However, when this multiplexing method is used in a ranging device, side lobes that occur during despreading affect detection performance. Figure 2 shows the effect of side lobes on detection performance. Figure 2(A) shows the result of transmitting code sequence A and then despreading using the same code sequence A at the receiving end. By despreading using the same code sequence, a peak signal is detected. Figure 2(B) shows the result of transmitting the same code sequence A, but despreading using code sequence B at the receiving end. Although a peak signal is not detected due to orthogonality, side lobes appear. These side lobes are unnecessary waves for measurements using code sequence B, and can cause false detection and loss of the target object.

[0009] CDMA also has a sidelobe reduction technology that uses complementary codes. This is a method of simultaneously transmitting and receiving two code sequences that cancel each other out except for the peak signal after despreading, and then adding the two signals together after despreading each, thereby reducing components other than the peak signal. However, complementary codes require the simultaneous transmission of two signals, and if there is only one transmitting device (e.g., a transducer), the signals will interfere with each other within the transmitting device, making this ineffective. Using multiple transmitting devices can reduce or avoid sidelobes, but the disadvantage is that multiple transmitting devices are required, making the equipment larger.

[0010] Another multiplexing method is frequency division. Figure 3 shows an example of a multiplexing method for improving the update rate in frequency division. This replaces the codes in Figure 1 with frequencies, and similar to Figure 1, theoretically it can be expected to have the effect of quadrupling the update rate.

[0011] In the case of frequency division multiplexing, the degree of separation from the transmitted signal in other measurements is determined by the performance of the band-limiting filter. To improve separation, it is desirable to make the spacing between adjacent frequencies as wide as possible and to make the attenuation (= the ratio of the transmitted signal to the receiver noise floor) as small as possible.

[0012] However, due to the physical constraints of the transmitting device and, when using radio waves, restrictions imposed by the Radio Law, there are limitations on the frequency range that can be used. This means that the spacing between adjacent frequencies cannot be made too large. Furthermore, the ratio of the transmitted signal to the receiver noise floor is generally very large. For example, even if the leakage of the transmitted signal from the transmitting device is limited to +20 dBm using a limiter or the like, it is not uncommon for the noise level at the receiver to be around -100 dBm. In other words, in this case, an attenuation of 120 dB or more is required. While this value is not impossible to achieve, depending on the spacing between adjacent frequencies (i.e., the frequencies that need to be removed), the circuit size could become very large.

[0013] The frequency division multiplexing method, which theoretically can improve the update rate, has the above-mentioned problems. The present invention has been made in consideration of these circumstances, and an object of the present invention is to provide a distance measuring device using the frequency division multiplexing method. [Means for solving the problem]

[0014] The distance measuring device of the present invention includes a transmitter and N receivers, where N is an integer equal to or greater than 2 and n is an integer equal to or greater than 1 and equal to or less than N. The transmitter transmits N types of frequency-modulated pulse waves with different center frequencies at predetermined timing. The nth receiver includes an IQ conversion unit, an amplitude suppression unit, a band limiting unit, and a pulse compression unit. The IQ conversion unit converts the received nth type of pulse wave into a baseband IQ signal and outputs a baseband received signal. The amplitude suppression unit includes a detector, an attenuation amount calculator, a delay unit, and a suppressor. The detector detects the amplitude of the received signal. The attenuation amount calculator calculates an attenuation amount for attenuating portions of the received signal that are greater than a predetermined amplitude to the predetermined amplitude. The delay unit delays the received signal until processing by the detector and attenuation amount calculator is complete. The suppressor attenuates the received signal delayed by the delay unit based on the attenuation amount and outputs a suppression signal. The band limiting unit attenuates frequency components other than the baseband included in the suppression signal and outputs a band-limited suppression signal. The pulse compressor performs pulse compression corresponding to frequency modulation on the band-limited suppressed signal to obtain a compressed received signal. [Effects of the Invention]

[0015] According to the distance measuring device of the present invention, since the received signal is frequency modulated, the band-limited suppressed signal is also frequency modulated. Then, pulse compression corresponding to the frequency modulation is performed on the band-limited suppressed signal, so that the desired signal can be detected. Therefore, a distance measuring device using frequency division multiplexing can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows an example of a multiplexing scheme for improving the update rate in CDMA. [Figure 2]A diagram showing the effect of side lobes on detection performance. [Figure 3] FIG. 10 is a diagram showing an example of a multiplexing scheme for improving the update rate in frequency division. [Figure 4] FIG. 2 is a diagram showing an example of the functional configuration of a distance measuring device according to the present invention. [Figure 5] 4 is a diagram showing an example of the amplitude of a received signal detected by a detector 120. FIG. [Figure 6] 10 is a diagram for explaining the process of calculating the amount of attenuation in an attenuation amount calculator 130. FIG. [Figure 7] 10A and 10B are diagrams showing examples of suppressed signals obtained by attenuating a received signal based on an attenuation amount. [Figure 8] FIG. 10 is a diagram showing an example of a band-limited suppressed signal. [Figure 9] 9 is a diagram showing an example of a compressed received signal obtained from the band-limited suppressed signal of FIG. 8. [Figure 10] FIG. 10 is a diagram showing a compressed received signal when there is no band limiting section. [Figure 11] FIG. 10 is a diagram showing a compressed received signal when only a second band-limiting section is arranged instead of the band-limiting section. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail. Components having the same functions are given the same numbers, and duplicated explanations will be omitted. [Example]

[0018] 4 shows an example of the functional configuration of the distance measuring device of the present invention. The distance measuring device 10 includes a transmitter 300 and N receivers 2001, ..., 200 N , a transmitting / receiving device 400. The distance measuring device 10 may also include a timing controller 600 and an output switcher 500. N is an integer of 2 or more, and n is an integer of 1 or more and N or less. The transmitting / receiving device 400 is, for example, a transducer or an antenna, and transmits pulse waves generated by the transmitter 300 into space, receives the pulse waves reflected by an object, converts them into electrical signals, and transmits them to receivers 2001, ..., 200. N Send to.

[0019] The transmitter 300 transmits N types of frequency-modulated pulse waves with different center frequencies at predetermined timings. For example, the transmitter 300 includes a signal generating unit 310. The signal generating unit 310 generates N types of frequency-modulated pulse waves with different center frequencies F1, F2, ..., F N It outputs a frequency modulated (FM) pulse wave by switching between them in sequence. Frequency modulation is a modulation method that changes the frequency while transmitting a pulse wave. For example, it is a modulation method that generates pulses with a pulse width of 1000 μs (1 ms) while changing the frequency by a width of 20 kHz (sweep frequency width).

[0020] The timing for outputting the pulse wave may be predetermined. The predetermined timing may be set in the transmitter 300 itself, or may be set in the timing controller 600, and the transmitter 300 may generate the pulse wave according to instructions from the timing controller 600. Note that "predetermined timing" is not limited to a fixed timing. It also includes varying the intervals at which different types of pulse waves are transmitted according to a predetermined rule. Figure 3 shows an example in which four frequencies, F1 to F4, are set, and the transmission signal is output during the time indicated as the "transmission interval." For example, if the frequency difference between adjacent center frequencies is 30 kHz and the frequency sweep width in frequency modulation is 20 kHz, there will be a frequency difference of at least 10 kHz between adjacent pulse waves of different types of frequency modulation.

[0021] nth receiver 200 n The receiver 200 includes an IQ conversion unit 210, an amplitude suppression unit 100, a band limiting unit 260, and a pulse compression unit 270. n The receiver 200 may also include a second band limiting unit 265. The pulse wave is assumed to be a signal detected by a sensor such as a transducer and converted into an electrical signal. The IQ conversion unit 210 converts the received n-th type of pulse wave into a baseband IQ signal, and outputs a baseband received signal. In order to convert the n-th type of pulse wave into a baseband IQ signal, the receiver 200 nThe IQ conversion unit 210 has a center frequency F n Receivers 2001,...,200 N The configuration of each IQ converter 210 is the same. n Each one can output a baseband received signal corresponding to one type of pulse wave.

[0022] The amplitude suppression unit 100 includes a detector 120, an attenuation calculator 130, a delay unit 140, and a suppressor 150. The detector 120 receives a received signal as an input and outputs a suppression signal. The detector 120 detects the amplitude of the received signal. More specifically, the detector 120 detects the received signal, which is a baseband IQ signal, and outputs a detection signal corresponding to the level of the received signal, thereby detecting the amplitude of the received signal. FIG. 5 shows an example of the amplitude of the received signal detected by the detector 120. The horizontal axis of FIG. 5 represents time (μsec), and the vertical axis represents the magnitude (dB) of the received signal. In FIG. 5, an adjacent frequency signal of 20 dB exists between 3100 and 4000 μsec, and a desired signal of −80 dB exists between 4000 and 4400 μsec. As explained with reference to FIG. 3, another type of pulse wave is transmitted while the reflected pulse wave is being detected. The example in Figure 5 shows a case where a received signal (adjacent frequency signal) based on a leakage signal of another type of pulse wave overlaps with a received signal (desired signal) based on a detected reflected pulse wave. In the example in Figure 5, -90 dB is set as the "predetermined amplitude." The "predetermined amplitude" can be set in advance to a small amplitude that prevents the side lobes after pulse compression from exceeding the noise level. Figures 5 to 11 show simulation results. In these simulations, the desired signal and adjacent frequency signal are both LFM pulses with a sweep frequency width of 20 kHz, and the difference in center frequency is 30 kHz.

[0023] The attenuation amount calculator 130 calculates the attenuation amount for attenuating a portion of the received signal that is greater than a predetermined amplitude to the predetermined amplitude. That is, in the case of FIG. 5, the attenuation amount calculator 130 calculates the attenuation amount for attenuating the amplitude from 3100 to 4400 μsec to the predetermined amplitude. FIG. 6 is a diagram for explaining the process of calculating the attenuation amount in the attenuation amount calculator 130. The horizontal axis of FIG. 6 represents time (μsec) and the vertical axis represents attenuation (dB). As shown in FIG. 6, the attenuation amount calculator 130 simply inverts the detected signal so that the attenuation amount for the amplitude corresponding to the predetermined amplitude becomes 0 dB. Then, the attenuation amount calculator 130 sets the attenuation amount for the zero attenuation region, which is the signal portion greater than 0 dB, to 0 dB.

[0024] The delay unit 140 delays the received signal until the processing by the detector 120 and the attenuation amount calculator 130 is completed. The suppressor 150 attenuates the received signal delayed by the delay unit 140 based on the attenuation amount calculated by the attenuation amount calculator 130, and outputs a suppression signal. FIG. 7 shows an example of a suppression signal obtained by attenuating the received signal based on the attenuation amount. The horizontal axis of FIG. 7 represents time (μsec), and the vertical axis represents the magnitude (dB) of the suppression signal. It can be seen that the suppressor 150 attenuates the amplitude from 3100 to 4400 μsec to a predetermined amplitude.

[0025] The band limiting unit 260 attenuates frequency components other than the baseband included in the suppression signal and outputs a band-limited suppression signal. The band limiting unit 260 attenuates only adjacent frequency signals in the suppressed received signal using a band limiting filter. n Then, the IQ conversion unit 210 has a center frequency F n Since the frequency band used is 100 kHz, the adjacent frequency signal will be a frequency component outside the baseband. Therefore, it is sufficient to attenuate frequency bands that cannot be part of the baseband. Figure 8 shows an example of a band-limited suppression signal. The horizontal axis of Figure 8 represents time (μsec), and the vertical axis represents the amplitude (dB) of the band-limited suppression signal. Figure 8 shows that the adjacent frequency signal is even lower than the specified amplitude. Note that the attenuation of the adjacent frequency signal is set to 80 dB here.

[0026] The pulse compressor 270 performs pulse compression corresponding to frequency modulation on the band-limited suppressed signal to obtain a compressed received signal. FIG. 9 shows an example of a compressed received signal obtained from the band-limited suppressed signal of FIG. 8. The horizontal axis of FIG. 9 represents time (μsec), and the vertical axis represents the magnitude (dB) of the compressed received signal. The example of FIG. 9 shows that the desired signal is successfully detected. Examples of "pulse compression corresponding to frequency modulation" include the technology disclosed in Non-Patent Document 1. The pulse compressor 270 may use existing pulse compression technology corresponding to frequency modulation, such as that disclosed in Non-Patent Document 1. Alternatively, the pulse compressor 270 may increase the amplitude of the signal obtained by pulse compression according to the amplitude and attenuation of the signal to obtain a compressed received signal. For example, a threshold may be set in advance, and the amplitude of the portion of the signal obtained by pulse compression that exceeds the threshold may be increased according to the attenuation. In the example of FIG. 9, if the compressed desired signal exceeds the set threshold, the amplitude of only the exceeding range may be increased according to the attenuation. Having the ability to increase the amplitude facilitates subsequent ranging processing. The amplitude is increased to a degree that makes it easier to carry out the subsequent distance measurement process.

[0027] In the distance measuring device 10, the received signal is frequency modulated, and therefore the band-limited suppressed signal is also frequency modulated. Then, pulse compression corresponding to the frequency modulation is performed on the band-limited suppressed signal, so the desired signal can be detected. Therefore, a distance measuring device using frequency division multiplexing can be provided, and the update rate can be improved.

[0028] FIG. 10 shows a compressed received signal without a band-limiting section, and FIG. 11 shows a compressed received signal with only a second band-limiting section instead of a band-limiting section. In both figures, the horizontal axis represents time (μsec) and the vertical axis represents the magnitude (dB) of the compressed received signal. If band-limiting section 260 were not present (FIG. 10), the remaining components of the adjacent frequency signal would be detected as being larger than the noise floor. Furthermore, if second band-limiting section 265 were inserted before amplitude suppression section 100 instead of band-limiting section 260 (FIG. 11), the remaining components of the adjacent frequency signal would still be detected. To obtain the desired results, it is desirable to include at least band-limiting section 260.

[0029] However, if the adjacent frequency signal and the desired signal completely overlap, the entire desired signal will be attenuated when the suppression signal is generated, so a second band-limiting unit 265 may also be provided. The second band-limiting unit 265 attenuates frequency components other than the baseband contained in the received signal output by the IQ conversion unit 210, and generates the received signal to be input to the amplitude suppression unit 100.

[0030] Alternatively, the timing controller 600 may change the interval at which different types of pulse waves are transmitted. By changing the interval at which pulse waves are transmitted, it is possible to avoid the phenomenon in which adjacent frequency signals and the desired signal always completely overlap. In this way, each frequency (F1 to F n ) measurement timing can be slightly changed each time to avoid constant degradation of detection performance.

[0031] When the output switch 500 is also provided, the output switch 500 selects the receivers 2001, . . . , 2002 in consideration of the timing at which the transmitter 300 outputs the pulse wave. N If the timing controller 600 is also provided, the output selector 500 may obtain information on the timing of outputting the pulse wave from the timing controller 600. [Explanation of symbols]

[0032] 10 Range finder 100 Amplitude suppression unit 120 Detector 130 Attenuation calculator 140 Delay 150 Suppressor 200 Receiver 210 IQ conversion unit 260 Bandwidth limiting unit 265 Second bandwidth limiting unit 270 Pulse compression section 300 Transmitter 310 signal generating unit 400 transmitting / receiving device 500 Output switcher 600 Timing controller

Claims

1. A ranging device comprising a transmitter and N receivers, N is an integer of 2 or more, n is an integer of 1 or more and N or less, The transmitter transmits N types of frequency-modulated pulse waves with different center frequencies at predetermined timings, The nth receiver is an IQ conversion unit that converts the received n-th type pulse wave into a baseband IQ signal and outputs a baseband received signal; an amplitude suppression unit having a detector, an attenuation amount calculator, a delay unit, and a suppressor, which receives the received signal as an input and outputs a suppression signal; a band limiting unit that attenuates frequency components other than the baseband included in the suppression signal and outputs a band-limited suppression signal; a pulse compression unit that performs pulse compression corresponding to the frequency modulation on the band-limited suppressed signal to obtain a compressed received signal; Equipped with The detector detects the amplitude of the received signal; the attenuation amount calculator calculates an attenuation amount for attenuating a portion of the received signal having an amplitude greater than a predetermined amplitude to the predetermined amplitude; the delay unit delays the received signal until the processing by the detector and the attenuation amount calculator is completed; The suppressor attenuates the received signal delayed by the delay device based on the attenuation amount, and outputs the suppression signal. A distance measuring device characterized by:

2. 2. The distance measuring device according to claim 1, a timing controller for controlling the predetermined timing at which the transmitter transmits the pulse wave; The timing controller changes the intervals at which different types of pulse waves are transmitted. A distance measuring device characterized by:

3. 2. The distance measuring device according to claim 1, The receiver also includes a second band limiting unit; The second band limiting unit attenuates frequency components other than the baseband included in the received signal output by the IQ conversion unit, and outputs the received signal as the received signal to be input to the amplitude suppression unit. A distance measuring device characterized by:

4. 4. A distance measuring device according to claim 1, The pulse compressor increases the amplitude of the signal obtained by pulse compression in accordance with the amplitude of the signal and the amount of attenuation, thereby obtaining a compressed received signal. A distance measuring device characterized by:

5. A receiver for receiving a frequency modulated pulse wave, an IQ conversion unit that converts a pulse wave having a predetermined center frequency into a baseband IQ signal and outputs a baseband received signal; an amplitude suppression unit having a detector, an attenuation amount calculator, a delay unit, and a suppressor, which receives the received signal as an input and outputs a suppression signal; a band limiting unit that attenuates frequency components other than the baseband included in the suppression signal and outputs a band-limited suppression signal; a pulse compression unit that performs pulse compression corresponding to the frequency modulation on the suppression signal to obtain a compressed received signal; Equipped with The detector detects the amplitude of the received signal; the attenuation amount calculator calculates an attenuation amount for attenuating a portion of the received signal having an amplitude greater than a predetermined amplitude to the predetermined amplitude; the delay unit delays the received signal until the processing by the detector and the attenuation amount calculator is completed; The suppressor attenuates the received signal delayed by the delay device based on the attenuation amount, and outputs the suppression signal. A receiver characterized by:

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