Receiver

Abstract

To enable small level signals that become undetectable due to the application of pulse compression to large level signals to be detected.SOLUTION: A receiver according to the present invention receives a frequency-modulated pulse wave. The receiver according to the present invention comprises an IQ conversion unit, an amplitude suppression unit, and a pulse compression unit. The IQ conversion outputs a receive signal of a baseband. 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 the 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 delay unit causes the receive signal to be delayed until processing by the wave detector and the attenuation amount calculator is completed. The suppresser causes the receive signal having been delayed by the delay unit to be attenuated on the basis of the amount of attenuation, and outputs a suppressed signal. The pulse compression unit performs, on the suppressed signal, pulse compression that corresponds to frequency modulation, and obtains a compressed receive signal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a receiver in a distance measuring device such as a sonar or radar. [Background technology]

[0002] Distance measuring devices such as sonar and radar use sound waves or radio waves to measure the distance to nearby reflecting objects in order to understand the surrounding environment, and pulse compression processing is used to improve distance resolution and extend the maximum detection distance. A basic method uses a linear frequency modulated pulse wave as the transmitted signal, and calculates the cross-correlation function between the transmitted signal and the received signal on the receiving side. However, this method has the problem of generating unwanted waves (side lobes) with high signal levels in the time (distance) before and after the reflected signal from the target object, which affects the identification of small objects around the target object. Techniques known as solutions to this problem include those in Patent Documents 1 to 3 and Non-Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-85167 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-175552 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-247615 [Non-patent literature]

[0004] [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]

[0005] However, conventional techniques have limitations in their improvement due to imperfections in hardware, and when the received signal level is high, the side lobes exceed the noise floor of the receiver. This effect makes it impossible to detect low-level signals in close proximity to high-level signals, and is particularly noticeable in short-distance measurements where leakage of the transmitted signal has an adverse effect.

[0006] This will be explained in detail using Figures 1 and 2. Figure 1 shows the relationship between the received signal and the noise floor. Figure 1(A) shows the case when the received signal level is low, and Figure 1(B) shows the case when the received signal level is high. The side lobe suppression ratio X is the same in both cases. When the received signal level is low, as shown in Figure 1(A), only the peak signal after pulse compression appears at a level higher than the noise floor level. However, when the received signal level is high, as shown in Figure 1(B), the side lobes that depend on the pulse width before compression appear at a level higher than the noise floor level.

[0007] As an example of where this effect is most pronounced, Figure 2 shows an example of a received signal with a low-level signal present near the transmitted leakage signal. The horizontal axis of Figure 2 represents time (μsec), and the vertical axis represents the magnitude of the received signal (dB). Figure 2(A) shows the received signal before pulse compression. A 0 dB transmitted leakage signal exists between -1000 and 0 μsec, while a -80 dB signal exists between 0 and 400 μsec. In this example, the transmitted signal has a pulse width of 1000 μsec (1 ms), and a small object exists at a round-trip distance of 400 μsec. The nearby low-level signal should also have a width of 1000 μsec (1 ms), but a 600 μsec portion of the nearby low-level signal overlaps with the transmitted leakage signal. Figure 2(B) shows the result of pulse compression of the received signal from Figure 2(A). It can be seen that the nearby low-level signal cannot be detected due to the influence of the side lobes present near -10 dB.

[0008] Even when identifying small objects around a target object, the pulse waves reflected by the target object and the pulse waves reflected by the surrounding small objects are received overlapping each other. Therefore, as in the example of Figure 2, if the received pulse waves are converted to baseband received signals and pulse compressed, the received signals of the pulse waves reflected by the target object may not be detected due to the side lobes of the received signals. Therefore, an object of the present invention is to make it possible to detect low-level signals that would otherwise be undetectable if high-level signals were subjected to pulse compression. [Means for solving the problem]

[0009] A receiver of the present invention receives a frequency-modulated pulse wave. The receiver of the present invention includes an IQ conversion unit, an amplitude suppression unit, and a pulse compression unit. The IQ conversion unit converts the received pulse wave into a baseband IQ signal and outputs a baseband received signal. The amplitude suppression unit has a detector, an attenuation amount calculator, a delay unit, and a suppressor, and receives the received signal as input and outputs a suppression signal. 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 pulse compression unit performs pulse compression on the suppression signal corresponding to the frequency modulation, obtaining a compressed received signal. [Effects of the Invention]

[0010] According to the receiver of the present invention, the received signal is frequency modulated, and therefore the suppression signal is also frequency modulated. By performing pulse compression corresponding to the frequency modulation on the suppression signal, the side lobes that occur when pulse compression is performed on a high-level signal can be reduced to below the noise floor. Furthermore, since the attenuation of nearby low-level signals is small, performing pulse compression corresponding to the frequency modulation makes it possible to detect the low-level signals. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 10 is a diagram showing the relationship between a received signal and a noise floor. [Figure 2] FIG. 10 is a diagram showing an example of a received signal of a small level signal present near a transmitted leakage signal. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of a receiver. [Figure 4] 4 is a diagram showing an example of the amplitude of a received signal detected by a detector 120. FIG. [Figure 5] 10 is a diagram for explaining the process of calculating the amount of attenuation in an attenuation amount calculator 130. FIG. [Figure 6] 10A and 10B are diagrams showing examples of suppressed signals obtained by attenuating a received signal based on an attenuation amount. [Figure 7] FIG. 7 is a diagram showing an example of a compressed received signal obtained from the suppressed signal of FIG. 6; DETAILED DESCRIPTION OF THE INVENTION

[0012] 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]

[0013] FIG. 3 shows an example of the configuration of a receiver according to the present invention. Receiver 200 receives a frequency-modulated pulse wave. Receiver 200 includes an IQ converter 210, an amplitude suppressor 100, and a pulse compressor 260. As shown in FIG. 3, receiver 200 may also include an amplitude restorer 270. 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 converter 210 converts the received pulse wave into a baseband IQ signal, thereby outputting a baseband received signal. Frequency modulation (FM) is a modulation method that changes the frequency while transmitting a pulse wave. For example, this modulation method generates pulses with a pulse width of 1000 μs (1 ms) while changing the frequency by a 20 kHz width (sweep frequency width).

[0014] The amplitude suppression unit 100 includes a detector 120, an attenuation calculator 130, a delayer 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. As described above, a small-level signal present near a transmission leakage signal is an example of a small-level signal that becomes undetectable by applying pulse compression to a large-level signal, similar to identifying small objects around a target object. Furthermore, because the transmission leakage signal is very large, it is more difficult to detect a small-level signal present near the transmission leakage signal. Therefore, the following explanation will be given using a small-level signal present near the transmission leakage signal as an example. FIG. 4 shows an example of the amplitude of the received signal detected by the detector 120. The horizontal axis of FIG. 4 represents time (μsec), and the vertical axis represents the magnitude (dB) of the received signal. In Figure 4, a 0 dB transmission leakage signal exists between -1000 and 0 μs, while a -80 dB signal exists between 0 and 400 μs. The signal transmitted at 0 μs is reflected and is an adjacent low-level signal at 400 μs. In the example of Figure 4, -90 dB is set as the "predetermined amplitude." The "predetermined amplitude" can be set in advance to a small amplitude that will prevent the side lobes after pulse compression from exceeding the noise level. Figures 4 to 7 show simulation results.

[0015] The attenuation amount calculator 130 calculates the attenuation amount for attenuating the portion of the received signal that is greater than a predetermined amplitude to the predetermined amplitude. That is, in the case of FIG. 4, the attenuation amount calculator 130 calculates the attenuation amount for attenuating the amplitude up to 400 μsec to the predetermined amplitude. FIG. 5 is a diagram for explaining the process of calculating the attenuation amount in the attenuation amount calculator 130. The horizontal axis of FIG. 5 represents time (μsec) and the vertical axis represents attenuation amount (dB). As shown in FIG. 5, 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 area, which is the signal portion greater than 0 dB, to 0 dB.

[0016] 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. 6 shows an example of a suppression signal obtained by attenuating the received signal based on the attenuation amount. The horizontal axis of FIG. 6 represents time (μseconds), and the vertical axis represents the magnitude (dB) of the suppression signal. It can be seen that the suppressor 150 attenuates the amplitude up to 400 μseconds to a predetermined amplitude.

[0017] The pulse compressor 260 performs pulse compression corresponding to frequency modulation on the suppression signal to obtain a compressed received signal. FIG. 7 shows an example of the compressed received signal obtained from the suppression signal of FIG. 6. The horizontal axis of FIG. 7 represents time (μsec), and the vertical axis represents the magnitude (dB) of the compressed received signal. In the example of FIG. 7, it can be seen that both the transmission leakage signal and the adjacent low-level signal are detected. Examples of "pulse compression corresponding to frequency modulation" include the technology disclosed in Non-Patent Document 1. The pulse compressor 260 can use existing pulse compression technology corresponding to frequency modulation, such as that disclosed in Non-Patent Document 1. Even if two pulses overlap with a slight time difference, the two pulses can be compressed individually because they have different frequencies.

[0018] In the receiver of the present invention, the received signal is frequency modulated, and therefore the suppression signal is also frequency modulated. By performing pulse compression corresponding to the frequency modulation on the suppression signal, the side lobes that occur when pulse compression is performed on a high-level signal can be reduced to below the noise floor. Furthermore, since the attenuation of nearby low-level signals is small, pulse compression corresponding to the frequency modulation makes it possible to detect these low-level signals. This effect is achieved by utilizing the fact that pulse compression technology can compress the received signal even when the SNR (signal-to-noise power ratio) is very poor, and that compression is possible even for nearby signals as long as there is a slight time difference and no side lobes are generated.

[0019] The level of the transmission leakage signal that exceeds the "predetermined amplitude" is attenuated. However, by setting a threshold for the pulse-compressed signal and applying the signal level before compression to signals that exceed that value, it is possible to achieve a level close to that of the original received signal. Therefore, the receiver 200 may also include an amplitude restoration unit 270 that increases the amplitude of the compressed received signal according to the amplitude and attenuation of the compressed received signal. For example, a threshold may be set in advance, and the amplitude of the compressed received signal in the portion that exceeds the threshold may be increased according to the attenuation. In the example shown in FIG. 7, if the compressed transmission leakage signal and the adjacent low-level signal exceed the set threshold, the amplitude of only the exceeding range may be increased according to the attenuation. [Explanation of symbols]

[0020] 100 Amplitude suppression unit 120 Detector 130 Attenuation calculator 140 Delay 150 Suppressor 200 Receiver 210 IQ conversion section 260 Pulse compression section 270 Amplitude restoration section

Claims

1. A receiver for receiving a frequency modulated pulse wave, an IQ conversion unit that converts the received pulse wave into a baseband IQ signal and outputs the 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 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:

2. 2. The receiver of claim 1, An amplitude restoration unit that increases the amplitude of the compressed received signal in accordance with the amplitude of the compressed received signal and the amount of attenuation. Equipped with a receiver.

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