JP2009210382A - Pulse radar and method for equivalent time sampling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine whether a pulse radar is in a distance-measurable state, even when external noise exists in the periphery of the pulse radar. <P>SOLUTION: A sampling circuit 6 acquires frame signals, by performing equivalent time sampling on received pulses received by a receiving circuit 5. A noise-determining part 7 detects a noise-determining region, in which the pulses reflected by a target do not overlap one another in the time base of the frame signals acquired by the sampling circuit 6, and determines whether distance measurements by frame signals are possible, on the basis of frame signals in the noise-determining region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an equivalent time sampling pulse radar, and more particularly to noise determination.

  In a general equivalent time sampling pulse radar, a distance is calculated based on a round-trip propagation time until a transmitted pulse signal is reflected by a target to be measured and received. For example, Patent Document 1 discloses an equivalent time sampling pulse radar that transmits a pulse to the outside in a wide band and samples a received waveform received in the wide band with a wide band sampling pulse.

Japanese National Patent Publication No. 10-511182

  Incidentally, external noise is superimposed on a transmission pulse received by an actual equivalent time sampling pulse radar (hereinafter referred to as pulse radar) in addition to a transmission pulse transmitted from the transmission antenna to the outside. For example, a method of observing a differential waveform between a waveform received at the current timing and a waveform received at the previous timing, even in an environment where external noise is superimposed There is. However, such a method is effective when the external environment does not change relatively at the time of receiving both waveforms, and is not necessarily effective when the pulse radar itself moves.

  The present invention has been made in view of such circumstances, and an object of the present invention is to easily determine whether or not distance measurement is possible even when external noise exists around the pulse radar. It is to be.

  In order to solve this problem, the first invention provides an equivalent time sampling pulse radar. The equivalent time sampling pulse radar includes a transmission circuit, a reception circuit, a sample circuit, and a noise determination unit. The transmission circuit transmits a transmission pulse to the outside. The reception circuit receives a reception pulse including at least a pulse reflected by the target among the transmission pulses transmitted by the transmission circuit. The sample circuit acquires a frame signal by sampling the received pulse received by the receiving circuit for an equivalent time. The noise determination unit detects a noise determination region in which the pulse reflected by the target is not superimposed on the time axis of the frame signal acquired by the sample circuit, and based on the frame signal in the noise determination region, distance measurement using the frame signal It is determined whether or not it is possible.

  Here, in the first invention, it is preferable that the transmission circuit delays the transmission timing of the transmission pulse at a predetermined timing. In the first invention, it is preferable to further include a sweep circuit that generates a sweep pulse that defines a timing at which the sample circuit samples the equivalent time. The sweep circuit includes a ramp wave generator, an offset wave generator, and an adder. The ramp wave generator repeatedly generates a ramp wave according to a rectangular wave that is periodically turned on and off. The offset wave generator repeatedly generates an offset wave obtained by temporally offsetting the rectangular wave. The adder repeatedly generates the sweep pulse by adding the ramp wave and the offset wave.

  The second invention provides an equivalent time sampling method. This equivalent time sampling method has first to fifth steps. In the first step, a transmission pulse is transmitted to the outside. The second step receives a reception pulse including at least a pulse reflected by the target among the transmission pulses transmitted in the first step. In the third step, a frame signal is acquired by sampling the reception pulse received in the second step for an equivalent time. The fourth step detects a noise determination region in which the pulse reflected by the target is not superimposed on the time axis of the frame signal acquired in the third step, and the frame signal is determined based on the frame signal in the noise determination region. It is determined whether or not distance measurement is possible.

  Here, in the second invention, it is preferable that the second step delays the transmission timing of the transmission pulse at a predetermined timing.

  According to the present invention, a noise determination region where a pulse reflected by a target is not superimposed is detected. Since the frame signal in this region is manifested as pure external noise in which the pulse reflected by the target is not superimposed, it is possible to easily determine whether or not distance measurement is possible by determining this.

(Noise judgment)
Prior to description of a specific configuration of an equivalent time sampling pulse radar (hereinafter simply referred to as pulse radar) according to the present embodiment, first, a noise determination mechanism according to the present embodiment will be described with reference to FIGS. 1 and 2. To do. FIG. 1 is an explanatory diagram relating to a noise determination area, which is a frame signal (baseband waveform) sampled by a pulse radar. The noise determination region refers to a temporal region in which transmission pulses (including those reflected by the target) are not superimposed on the sampled frame signal. The frame signal is a long-period reception pulse obtained by extending the reception pulse received by the pulse radar on the time axis.

  In the frame signal in the noise determination area, a noise floor (his noise), which is an external noise, becomes obvious. Noise floor is a general term for noise that has a main component in a high frequency range. This is noise caused by the longitudinal vibration of the tape. The noise floor of the present embodiment is external noise that is received until a transmission pulse transmitted to the outside returns to the pulse radar again as a reception pulse via the target.

  FIG. 2 is an explanatory diagram of a noise determination method. The determination of noise is performed based on the frame signal in the noise determination area shown in FIG. Specifically, it is determined whether distance measurement is possible by determining whether the voltage (amplitude) of the frame signal in the noise determination area exceeds a predetermined threshold value. The predetermined threshold includes a + (plus) side value (+ noise judgment threshold) and a-(minus) side value (-noise judgment threshold), and the absolute values of both values are the same. It is.

  For example, as shown in FIG. 5A, when the voltage of the frame signal in the noise determination region does not exceed any determination threshold value, that is, when the external noise mixed in the frame signal is negligibly small, Judge that distance measurement is possible. In addition, as shown in FIG. 4B, when the voltage of the frame signal in the noise determination region exceeds one of the determination threshold values, that is, when the external noise mixed in the frame signal cannot be ignored, Judge that distance measurement is possible.

(Equivalent time sampling pulse radar)
FIG. 3 is a block diagram of a pulse radar that implements the method shown in FIGS. This equivalent time sampling radar includes a reference clock generator 1, a transmission circuit 2, a sweep circuit 3, a sample pulse generator 4, a reception circuit 5, a sample circuit 6, and a noise determination unit 7. FIG. 4 is a diagram showing signal waveforms at points A to G shown in FIG.

  The reference clock generator 1 generates a rectangular reference clock (point A in FIG. 4) that is repeatedly turned on and off at a constant period. The reference clock is a repetitive waveform in which an H level (ON) and an L level (OFF) are alternately switched at a predetermined interval. In the present embodiment, the timing of changing from the H level to the L level is referred to as “change timing”.

  The transmission circuit 2 transmits a transmission pulse to the outside at a change timing of the reference clock generated by the reference clock generator 1, that is, a timing at which the reference clock changes from the H level to the L level. The transmission circuit 2 is mainly composed of a transmission antenna (not shown). First, at each change timing of the reference clock generated by the reference clock generator 1, a transmission pulse radiated to the outside from the transmission antenna is generated. Specifically, the transmission pulse is generated in one shot at the timing when the reference clock input to the transmission circuit 2 falls. The transmission pulse generated by the transmission circuit 2 is radiated from the transmission antenna to the outside through a band-pass filter or the like provided to limit the communication band defined by domestic laws and regulations.

  The sweep circuit 3 generates a sweep pulse that defines the timing at which the sample circuit 6 samples the equivalent time. The sweep circuit 3 includes a sweep clock generator 31, a pulse wave generator 32, an offset wave 33, and an adder 34. The sweep clock generator 31 repeatedly generates a rectangular sweep clock (point B in FIG. 4) whose voltage is periodically turned on and off according to the period of the reference clock described above. In this embodiment, the cycle of the sweep clock is an integral multiple of that of the reference clock.

  The pulse wave generator 32 repeatedly generates a ramp wave (point C in FIG. 4) according to the cycle of the sweep clock. The voltage level of the ramp wave in this embodiment increases linearly until the sweep clock falls, and is reset to 0 when the sweep clock falls. The offset wave generator 33 repeatedly generates an offset wave (point D in FIG. 4) obtained by temporally offsetting the rectangular wave. The offset wave in this embodiment has the same cycle as the sweep clock, but the off period is short and the on period is long. That is, the timing at which the voltage falls is the same, but the timing at which the voltage rises is early.

  The adder 34 repeatedly generates a sweep pulse (point E in FIG. 4) by adding the ramp wave from the ramp wave generator 32 and the offset wave from the offset wave generator 33. The voltage level of the sweep pulse increases with time as in the case of the ramp wave, but greatly increases at the rising edge of the offset wave. The sweep pulse generated here is used to create a noise determination region.

  The sample pulse generator 4 generates a rectangular sample pulse (point F in FIG. 4) based on the sweep pulse generated by the sweep circuit 3 and the reference clock generated by the reference clock generator 1. This generation is achieved by delaying (extending) the reference clock generated by the reference clock generator 1 in accordance with the voltage level indicated by the sweep pulse generated by the sweep circuit 34. In the present embodiment, the delay amount of the reference clock is increased as the voltage of the sweep pulse increases.

  The reception circuit 5 receives a reception pulse (point F in FIG. 4) including at least a pulse reflected by the target among the transmission pulses transmitted by the transmission circuit 2. The receiving circuit 5 is mainly composed of a receiving antenna (not shown) or the like, and an external pulse is received as a received pulse by the receiving antenna and is input to the sample circuit 6 through a band pass filter or the like.

  The sample circuit 6 obtains a frame signal (point G in FIG. 4) obtained by expanding the received pulse on the time axis by performing equivalent time sampling of the received pulse received by the receiving circuit 5. Specifically, according to the change timing of the sample pulse generated by the sample pulse generator 4, the voltage of the reception pulse received by the reception circuit 5 is temporarily held to perform equivalent time sampling. The sample timing of the reception pulse is the timing when the sample pulse falls. The generated long-period received pulse is used for target ranging. In this embodiment, one frame is assumed to be about 25 ms.

  The noise determination unit 7 detects a noise determination region in which the pulse reflected by the target is not superimposed on the time axis of the frame signal acquired by the sample circuit 6. The noise determination region may be detected by observing the waveform of the acquired frame signal. For example, a sweep pulse indicating a delay amount of timing for generating a sample pulse temporarily is used in this embodiment (FIG. 4). (E point) may be temporarily reduced. Thereby, the sample circuit 6 can sample the state before the transmission pulse reflected by the target reaches the reception circuit 5, and can intentionally set the noise determination region.

  The noise determination unit 7 determines whether distance measurement using this frame signal is possible based on the frame signal in the noise determination region. The determination includes a method of measuring a frequency in the corresponding region, a method of comparing with a statistical result value, and the like. In this embodiment, the voltage (amplitude) of the frame signal in the noise determination region as shown in FIG. Determines whether or not distance measurement is possible by determining whether or not the value exceeds a predetermined threshold value.

  When it is determined that distance measurement is impossible beyond the threshold, the frame signal acquired by the sample circuit 6 is discarded. On the other hand, if it is determined that the distance can be measured without exceeding the threshold, the target (failure) that is the object of distance measurement based on the frame signal acquired by the sample circuit 6 by the subsequent processing circuit (not shown). Ranging). As is well known, the distance to the target T is uniquely calculated based on a time value that forms a positive peak or a negative peak due to an obstacle.

  Thus, according to the present embodiment, the noise determination unit 7 detects a noise determination region in which the pulse reflected by the target is not superimposed. Since the frame signal in this region is manifested as pure external noise in which the pulse reflected by the target is not superimposed, it is possible to easily determine whether or not distance measurement is possible by determining this.

  The noise determination unit 7 in the present embodiment is a unit (hardware) included in the pulse radar of FIG. 3, but is not limited to this, and the same function may be realized by software processing. In that case, units that define periodic timing such as the reference clock generator 1 and the sweep clock generator 31 are not necessarily required as hardware.

  In the present embodiment, by providing the sweep circuit 3, as shown in FIG. 5A, the noise determination region is periodically formed in the received pulse. However, in this case, since many noise determination areas are included in one frame, the distance measurement time per frame becomes long. Therefore, by shortening the cycle of the sweep pulse generated by the sweep circuit 3, the distance measurement time per frame is shortened as shown in FIG. At this time, although the noise determination area is also shortened, the transmission circuit 2 is controlled so as to delay (or not transmit) the transmission timing of the transmission pulse at a predetermined timing, thereby periodically changing the noise determination area. It can be ensured and noise can be determined.

  Furthermore, the sample pulse generated by the sample pulse generator 4 in the present embodiment is generated based on the sweep pulse. However, the present invention only needs to detect a noise determination region and perform noise determination using this region. . Specifically, it is possible to increase / decrease sequentially at a constant rate for each cycle based on the change timing of the reference clock, or to select at random for each cycle. For example, a sample pulse having a fall at a time of ± δ, ± 2δ, ± 3δ,... From the fall timing t of the reference clock may be generated. Alternatively, a sample pulse that falls at the time of + δ, −2δ, + 3δ,... From the trailing edge t of the reference clock may be generated.

  In the present embodiment, the transmission circuit and the reception circuit are provided as separate bodies, but the present invention only needs to be able to receive and transmit a pulse radar. Therefore, the transmission antenna and the reception antenna may be an integrally formed antenna. In this case, the pulse radar is configured to separate the pulse at the time of transmission and the pulse at the time of reception in terms of time or frequency.

Illustration of the noise judgment area Explanatory diagram regarding noise judgment method Equivalent time sampling pulse radar configuration diagram The figure which shows the waveform in AG point shown in FIG. Explanatory diagram showing variations of the noise judgment area

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reference clock generator 2 Transmission circuit 3 Sweep circuit 4 Sample pulse generator 5 Reception circuit 6 Sample circuit 7 Noise judgment part

Claims (5)

In equivalent time sampling pulse radar,
A transmission circuit for transmitting a transmission pulse to the outside;
A receiving circuit for receiving a reception pulse including at least a pulse reflected by a target among the transmission pulses transmitted by the transmission circuit;
A sample circuit that obtains a frame signal by sampling the reception pulse received by the reception circuit by an equivalent time; and
Of the time axis of the frame signal acquired by the sample circuit, a noise determination region in which a pulse reflected by the target is not superimposed is detected, and distance measurement by the frame signal is performed based on the frame signal in the noise determination region. An equivalent time sampling pulse radar comprising: a noise determination unit that determines whether or not   The equivalent time sampling pulse radar according to claim 1, wherein the transmission circuit delays the transmission timing of the transmission pulse at a predetermined timing. A sweep circuit that generates a sweep pulse that defines a timing at which the sample circuit samples the equivalent time;
The sweep circuit comprises:
A ramp generator that repeatedly generates a ramp wave in response to a rectangular wave that periodically turns on and off;
An offset wave generator that repeatedly generates an offset wave that is temporally offset from the rectangular wave;
The equivalent time sampling pulse radar according to claim 1, further comprising an adder that repeatedly generates the sweep pulse by adding the ramp wave and the offset wave. In the equivalent time sampling method,
A first step of transmitting a transmission pulse to the outside;
A second step of receiving a reception pulse including at least a pulse reflected by a target among the transmission pulses transmitted in the first step;
A third step of acquiring a frame signal by sampling the reception pulse received in the second step by an equivalent time;
From the time axis of the frame signal acquired in the third step, a noise determination region where a pulse reflected by the target is not superimposed is detected, and according to the frame signal in the noise determination region, according to the frame signal And a fourth step for determining whether or not distance measurement is possible.   5. The equivalent time sampling method according to claim 4, wherein the second step delays the transmission timing of the transmission pulse at a predetermined timing.

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