JP2011099752A - Radar device - Google Patents

Abstract

An object of the present invention is to improve the detection performance of a target by matching the period of a response wave from the target with the period of Fourier transform.
A transmission time of a transmission pulse from a pulse generation circuit 5c is acquired by a pulse window synchronization circuit 7b of a synchronization circuit section 7 provided between a transmission circuit section 5 and a reception circuit section 6, and a transmission pulse is generated. At the timing, supply of sampling data from the serial-parallel conversion circuit 6c to the FFT circuit 6d is started. The end time of the FFT window is the time that has passed by the period of the transmission pulse from the start time of the window, the FFT sample data is acquired within the time of this window, and the received waveform is converted from the time axis data to the frequency axis. Convert to data. This makes it possible to match the period of the response wave from the target and the period of the FFT, convert raw data to the frequency domain without causing waveform distortion, and improve radar performance such as recognition performance and distance resolution. be able to.
[Selection] Figure 1

Description

  The present invention relates to a radar device that detects a target by Fourier transforming a response wave reflected by the target.

  In general, a radar apparatus radiates radio waves into space and receives reflected waves from an object, and processes the received signals to detect the presence and distance of a target. Some of such radar devices perform target recognition and distance measurement using the frequency spectrum of the received signal, and the frequency spectrum of the received signal is acquired by FFT (Fast Fourie Transform). .

  In general, the FFT operation of the observed waveform is performed using a window function. The window function is a process that applies weights to reduce the influence of discontinuities at the start and end of the window (window) that cuts out the waveform when cutting out a part of the periodic observation waveform and performing Fourier transform. In order to suppress the distortion of the spectrum, a direct current component and a low frequency component due to the window function processing are generated in the data after the window function processing.

  For this reason, in Patent Document 1, a frequency difference signal corresponding to a frequency difference between a transmission signal and a reception signal is sampled in a predetermined sampling section to generate first sampling data, and the first sampling data is generated near the center of the sampling section. The first window function processing for weighting the second weight smaller than the first weight from the center to the edge is obtained to obtain the second sampling data, and the average of the second sampling data is the first Subtracted from the sampling data, and the second window function processing by the same window function as the first window function processing is performed on the subtraction result to obtain the frequency detection data of the frequency difference signal. Thus, a technique for effectively removing low frequency components contained in sampling data of a frequency difference signal is disclosed.

JP 2008-298750 A

  However, in the conventional technique, when performing FFT using a window function, the period of the observed waveform is unknown, so the start position of the window is uniquely set based on the period of the observed waveform that is expected in design. is doing. For this reason, the period of the actual observation waveform and the sampling period of the FFT data do not necessarily coincide with each other, causing a discontinuous point and distorting the waveform, which is a cause of lowering the radar performance.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a radar device that can improve the target detection performance by matching the period of the response wave from the target with the period of Fourier transform. .

  In order to achieve the above object, a radar apparatus according to the present invention receives a response wave in which a transmitted wave radiated into space is reflected by a target, and detects the target by performing Fourier transform on the response wave data in a Fourier transform unit. A radar apparatus that synchronizes the transmission timing of the transmission wave and the sampling start timing of the Fourier transform data supplied to the Fourier transform unit, and sets a Fourier transform window width in accordance with the period of the transmission wave A window synchronization unit is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the period of the response wave from a target can be made to correspond with the period of a Fourier-transform, and the detection performance of a target can be improved.

Configuration diagram of radar equipment Explanatory drawing which shows the relationship between a transmission wave and a response wave, and the object area of FFT. Explanatory drawing showing the usage status of radar equipment Explanatory diagram showing response waves from multiple targets, serial-parallel conversion, and FFT interval Explanatory drawing which shows the power spectrum obtained by FFT Conceptual diagram showing threshold for texture recognition

Embodiments of the present invention will be described below with reference to the drawings.
A radar apparatus 1 shown in FIG. 1 is an antenna-separated radar that is mounted on a vehicle such as an automobile and includes a transmission antenna 2 and a reception antenna 3 as separate bodies. The radar apparatus 1 includes a transmission wave and a reception wave reflected by a target. This is a pulse radar device that performs object detection and distance measurement based on a time difference. In this embodiment, an example in which the present invention is applied to a pulse radar apparatus will be described. However, the present invention is not limited to a pulse radar, and a frequency-modulated continuous wave is transmitted and reflected by a target. It is also applied to an FMCW (Frequency Modulated Continuous Wave) type radar apparatus that obtains a beat signal with a response wave and performs object detection and distance measurement from the frequency difference of the beat signal.

  The radar apparatus 1 according to the present embodiment includes a transmission / reception front end unit 4 that performs output processing from the transmission antenna 2 and reception processing for a response wave of the reception antenna 3, and a transmission circuit unit that generates transmission pulses to be transmitted to the transmission / reception front end unit 4. 5, a receiving circuit unit 6 that processes a received wave from the transmission / reception front end unit 4, a synchronizing circuit unit 7 that performs synchronization processing between the transmitting circuit unit 5 and the receiving circuit unit 6, and a signal from the receiving circuit 6 The recognition processing unit 8 that performs recognition processing and distance measurement is mainly configured.

  The transmission / reception front end unit 4 generates an impulse radar signal by modulating the frequency band of the transmission pulse into the transmission band, and transmits the impulse radar signal to the space from the transmission antenna 2. The front end 4a receives a response wave reflected from the target via the reception antenna 3, and generates a clock to be supplied to the reception side RF front end 4b and the RF front ends 4a and 4b that demodulate the transmission band to the intermediate frequency band. And a clock generator 4c.

  The transmission circuit unit 5 transmits a clock generator 5a that generates a reference clock, a PLL (Phase Locked Loop) circuit 5b that generates a clock signal of an arbitrary frequency from the reference clock, and a rising edge of the clock signal generated by the PLL circuit 5b. A pulse generation circuit 5c for generating a pulse is provided.

  The reception circuit unit 6 includes an interface (IF) 6a that demodulates the response wave in the intermediate frequency band from the reception-side RF front end 4b to an AD conversion frequency, and AD conversion that performs AD conversion on the demodulated response wave Circuit 6b, serial-parallel conversion circuit 6c for serial-parallel conversion of AD-converted time-domain serial data (response wave data) to rearrange parallel data, time-domain data by FFT (Fast Fourier Transform) operation Is converted to frequency domain data, and a parallel / serial conversion circuit 6e is provided for converting the parallel data converted to the frequency domain into serial data.

  In addition, the radar apparatus 1 includes a synchronization circuit unit 7 between the transmission circuit unit 5 and the reception circuit unit 6. The synchronization circuit unit 7 receives as a trigger a frequency multiplication circuit 7a that multiplies the clock frequency from the PLL circuit 5b and synchronizes the sampling period of the AD conversion circuit 6b with the transmission pulse, and a transmission pulse from the pulse generation circuit 5c. And a pulse window synchronization circuit 7b for controlling the FFT series-parallel conversion circuit 6c.

  The radar apparatus 1 having the above configuration can perform FFT without requiring a window function by matching the period of the received waveform with the period of Fourier transform. Conventionally, the start position of the FFT window is uniquely set based on the period of the observation waveform expected in advance by design, and the discontinuity due to the discrepancy between the actual reception waveform period and the Fourier transform data sampling period. A point is generated and the waveform is distorted, which contributes to a decrease in radar performance.

  On the other hand, because the radar, in principle, emits radio waves and acquires the radio waves reflected by the target, when the target is stationary or nearly stationary, the period of the received signal is the transmission pulse. Match the period. Therefore, in this embodiment, by synchronizing the transmission time of the transmission pulse and the start time of the window for performing FFT, the FFT period is made to coincide with the period of the received wave, and distortion of the waveform after FFT is suppressed. Highly accurate object recognition and distance measurement.

  Specifically, the transmission time of the transmission pulse from the pulse generation circuit 5c is acquired by the pulse window synchronization circuit 7b of the synchronization circuit unit 7 provided between the transmission circuit unit 5 and the reception circuit unit 6, and the transmission pulse is generated. At this timing, the supply of sampling data from the serial-parallel conversion circuit 6c to the FFT circuit 6d is started. Also, the FFT window end time is the time that has passed by the period of the transmission pulse from the window start time, the FFT sample data is acquired within this window time, and the received waveform is converted from the time axis data. Convert to frequency axis data.

  The received waveform converted into frequency axis data is processed by the recognition processing unit 8 to recognize target information. The recognition processing unit 8 recognizes the target type based on the texture of the target such as the target position (distance to the target) and the difference between the moisture and the metal, and outputs the recognition result to a display device (not shown) to the driver. Present information. The type of the target is determined based on the difference in the frequency component of the reflected wave due to the difference between moisture and metal.

  Next, the detailed operation of the radar apparatus 1 will be described with reference to FIG. Prior to the operation of the radar apparatus 1, the number of FFT samplings is registered in advance in the FFT circuit 6d. The registered sampling number is set so that the time derived by the sampling time of the AD conversion circuit 6b × the number of samplings becomes the cycle of the transmission pulse.

  First, as shown in FIG. 2A, when a clock is generated by the PLL circuit 5b, a transmission pulse as shown in FIG. 2B is generated by the pulse generation circuit 5c at the rising edge of this clock. Are sent to the transmitting RF front end 4a. Then, an impulse-like signal frequency-modulated to the transmission band by the transmission-side RF front end 4a is emitted from the transmission antenna 2 into the air, and the emitted radio wave bounces back to the target, and a response wave as shown in FIG. Is received by the receiving antenna 3.

  The received response wave is demodulated from the transmission band to the intermediate frequency band by the reception-side RF front end 4b and converted into digital data through the AD conversion circuit 6b. The sampling period of the AD conversion circuit 6b is a period that is multiplied by the frequency multiplication circuit 7a to a multiple of 2 of the period of the transmission pulse from the sampling theorem.

  The AD-converted sampling data is input to the FFT circuit 6d via the serial / parallel conversion circuit 6c. At this time, with the generation of the transmission pulse of the pulse generation circuit 5c as a trigger, the pulse window synchronization circuit 7b instructs the serial-parallel conversion circuit 6c to start serial-parallel conversion, and for FFT by serial-parallel conversion of AD-converted digital data Acquisition of sample data begins.

  When the acquisition of FFT data reaches a preset number of samples (2 to the power of n), the FFT circuit 6d converts the digital data acquired so far from the time domain to the frequency domain. This makes it possible to prevent the distortion of the waveform after the FFT by matching the period of the response wave from the target and the period of the FFT, and to avoid reducing the amount of information of the raw data by using the window function. it can.

  The data converted into the frequency domain is subjected to recognition processing by the recognition processing unit 8 and then output to a display circuit (not shown) to display the distance to the target. More specifically, for example, as shown in FIG. 3, a person H1 and a vehicle C1 exist at a point of a distance A in front of the host vehicle C0 on which the radar apparatus 1 is mounted, and a distance B (B> A). An example will be described in which another person H2 exists at the point.

  When detecting a plurality of such different types of targets, a transmission wave (pulse) is transmitted with a period W as shown in FIG. As a result, the reflected wave from the point at the distance A as shown in FIG. 4B and the reflected wave from the point at the distance B as shown in FIG. 4C are superimposed, as shown in FIG. Such a response wave is received.

At this time, the reflected wave from the target at the distance A is received with a delay of time T1 from the start of transmission, and the reflected wave from the target at the distance of B is received with a delay of time T2 from the start of transmission. The In the radar apparatus 1 of this embodiment which is a pulse radar, the times T1 and T2 are given by the following equations. However, c in the following formula is the speed of light.
T1 = 2 × A / c, T2 = 2 × B / c

  Accordingly, the distances A and B are determined as the minimum and maximum distances that can be measured by the radar, or the distance of the desired detection range, and the time from the start of transmission to the start of serial-parallel conversion for FFT is determined as the start time T1. Then, as shown in FIG. 4 (e), after AD conversion of the response wave, the start time T1 is shifted by a time step Δt corresponding to the distance resolution (T1 + n × Δt; n = 0, 1, 2,...) Then, a series-parallel conversion is performed with the window width W, and FFT is performed to obtain a frequency component. Thereafter, when the start time T1 + n × Δt reaches the time T2, the first scan is terminated, and the second and subsequent scans are similarly performed.

  As shown in FIGS. 5A, 5B, 5C, and 5D, the frequency f is obtained at each timing of sampling start times T1, T1 + Δt, T1 + 2 × Δt,... An axial power spectrum P distribution is obtained. The frequency domain data obtained by the FFT of the response wave is mapped to the vector space, and the texture of the target is recognized.

  For example, as shown in FIG. 6, when the power spectrum distribution obtained by FFT is projected onto a vector plane with the frequencies f1 and f2 as axes, a region R1 indicating the frequency characteristics of the response wave with respect to moisture (human), metal A region R2 indicating a frequency characteristic for (vehicle) and a region R3 having a frequency characteristic that is not one of them are determined in advance by experiments or simulations as threshold values for determining the texture of the target. Then, the texture of the target is recognized by determining which region the frequency characteristics of the response wave actually obtained belong to.

  By this FFT analysis of the response wave, a reasonable texture such as moisture or metal is obtained, and when the target type is recognized as “human” or “vehicle”, the distance is obtained based on the FFT start time, and the texture is unknown. In the case of, “other” is output without calculating the distance. In other words, a transmission pulse is generated assuming the distance to the target, and if the response wave is valid, it is determined that there is an object at that distance. Can get the situation.

In the example of FIG. 3 described above, the target existing at the distance A and the target existing at the distance B can be correctly identified and the type and distance can be output as follows.
FFT start time Target distance T1 Human H1 + Vehicle C1 A
T1 + Δt Others No output T1 + 2 × Δt Others No output ・ ・ ・
・ ・ ・
T2 human H2 B

  As described above, in the present embodiment, the period of the response wave from the target and the period of the FFT are matched, and the raw data can be converted to the frequency domain without causing distortion of the waveform. Thus, the radar performance can be improved. In addition, since no window function is required for FFT, it is possible to simplify the hardware circuit and reduce costs.

DESCRIPTION OF SYMBOLS 1 Radar apparatus 5c Pulse generation circuit 6b AD conversion circuit 6c Serial / parallel conversion circuit 6d FFT circuit 7b Pulse window synchronous circuit 8 Recognition processing part

Claims (4)

A radar apparatus that receives a response wave reflected by a target from a transmission wave radiated into space, and detects the target by performing Fourier transform on the response wave data by a Fourier transform unit,
A window synchronization unit that synchronizes the transmission timing of the transmission wave and the sampling start timing of the Fourier transform data supplied to the Fourier transform unit and sets the window width of the Fourier transform according to the cycle of the transmission wave is provided. A radar device characterized by the above.   2. The radar apparatus according to claim 1, wherein the sampling number of the Fourier transform data is set such that a ratio between a period of sampling the response wave data and a transmission period of the transmission wave is a multiple of two.   3. The radar apparatus according to claim 1, wherein the type of the target is determined based on a frequency characteristic obtained by Fourier transforming the response wave data.   The radar apparatus according to claim 1, wherein the radar apparatus is a pulse radar apparatus that performs distance measurement based on a time difference between the transmission wave and the response wave.

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