JP2002014159A - FM-CW radar device - Google Patents

Abstract

(57) [Problem] To provide an FM-CW radar device which is less susceptible to radio wave interference between a plurality of radars of the same type. SOLUTION: An FM-CW signal is distributed to a transmission carrier signal and a local signal by a coupler. The distributed transmission carrier signal is phase-modulated by a phase modulator in two phases of 0 degree and 180 degrees by a phase modulation code from a code generator, and is radiated as a transmission signal from a transmission antenna to space. The transmitted signal radiated into the space is reflected by the target, received by the receiving antenna, and output to the mixer as a received signal. The mixer mixes the received signal with the local signal and outputs it to a phase demodulator. The phase demodulator converts the mixed reception signal to 0 degree and 1 degree by a phase demodulation code obtained by time-delaying the phase modulation code from the code generator by a delay circuit.
Phase demodulation into two phases of 80 degrees.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW radar device used in an in-vehicle millimeter-wave radar system or the like.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional FM-CW radar. Conventional FM-CW radar technology is described in, for example, "Radar Technology" (Institute of Electronics and Communication Engineers). In FIG. 4, 1 is an FM-CW signal generator, 2 is a coupler, 3 is a transmitting antenna, 4 is a receiving antenna, 5 is a mixer, 6 is a low-pass filter, 7 is a frequency detector, 8 is a calculator, 101 is FM. -CW signal, 102 is a transmission signal, 103 is a local signal, 104 is a reception signal,
105 is a beat signal.

Next, the conventional operation will be described. FM-
For example, the FM-CW signal 101 generated by the CW signal generator 1 and whose frequency changes with a triangular wave having a substantially constant cycle,
The signal is distributed to the transmission signal 102 and the local signal 103 by the coupler 2. The distributed transmission signal 102 is transmitted by the transmission antenna 3
, Is reflected to an object (for example, a vehicle) not shown, is received by the receiving antenna 4, and is received by the receiving signal 1.
04 is output to the mixer 5.

The received signal 104 is mixed with the local signal 103 by a mixer 5 and output to a low-pass filter 6, where a fundamental wave component, ie, a beat signal 105
Is selected and sent to the frequency detector 7. The frequency detector 7 calculates the frequency fbu of the rising phase beat signal 105 and the frequency fb of the falling phase beat signal 105 in the frequency signal of the transmission signal 102 as shown in the following equations.
d is detected and output to the computing unit 8.

Fbu = (4 × R × DF × Fm−2 × V × F0) / C (1) fbd = (4 × R × DF × Fm + 2 × V × F0) / C (2)

Where R is the distance to the target, C is the speed of light,
DF is the frequency deviation width, Fm is the modulation signal frequency, F0 is the center frequency of the transmission wave, and V is the relative speed between the target and the radar device.

The arithmetic unit 8 calculates the distance R to the object (not shown) and the relative velocity V from the relationship between the frequency fbu of the rising phase beat signal 105 and the frequency fbd of the falling phase beat signal 105 by the following equation. Ask.

R = (C / (8 × DF × Fm)) × (fbu + fbd) (3) V = (C / (4 × F0)) × (fbd−fbu) (4)

[0009]

As described above, the conventional FM-CW radar device has an advantage that it can detect the distance and speed of an object with a relatively simple structure, and is therefore used for a vehicle-mounted radar or the like. However, there is a problem that a plurality of radars of the same type are susceptible to radio wave interference. In particular, in the case of an on-vehicle radar device, the measured distance to the opponent's vehicle and the relative speed are used to prevent collision with the opponent's vehicle. There is a problem that the speed cannot be detected.

The present invention has been made to solve such a conventional problem, and a plurality of radars of the same type can be realized with a simple configuration without impairing the advantage of the conventional FM-CW radar apparatus. An object of the present invention is to provide an FM-CW radar device that is less susceptible to radio wave interference between them.

[0011]

Means for Solving the Problems FM-CW of the first invention
The radar apparatus has a thermal noise generating means for generating a thermal noise signal, a code generating means for generating a random code sequence from the thermal noise signal, and an FM-CW for generating an FM-CW signal.
Signal generation means, FM-CW transmission wave generation means for generating the FM-CW signal into a two-phase modulated FM-CW transmission wave with the random code sequence, and the FM-CW signal
A transmission antenna for transmitting a transmission wave in a target direction, a reception antenna for receiving a reflected wave from the target, and a reception signal of the reception antenna mixed with a part of the FM-CW signal, and the mixed reception signal Receiving means for performing phase demodulation into two phases by the random code sequence.

According to a second aspect of the present invention, there is provided an FM-CW radar apparatus comprising: a code generating means for generating a pseudo-random code sequence;
FM-CW signal generating means for generating a CW signal;
FM-CW for generating an M-CW signal into a two-phase FM-CW transmission wave modulated by the pseudo random code sequence
Transmission wave generation means, a transmission antenna for transmitting the FM-CW transmission wave in a target direction, a reception antenna for receiving a reflected wave from the target, and a reception signal of the reception antenna for a part of the FM-CW signal. And mixes the received signal thus mixed with the pseudo random code sequence.
Receiving means for performing phase demodulation into a phase.

According to a third aspect of the present invention, there is provided the FM-CW radar device according to the first and second aspects, wherein the extracting means for extracting the frequency of the beat signal from the frequency components of the output signal from the receiving means, Frequency detecting means for detecting the frequency of the beat signal output from the extracting means, and calculating means for calculating the distance and speed to the target reflecting the FM-CW transmission wave from the output signal of the frequency detecting means. It is provided with.

According to a fourth aspect of the present invention, in the FM-CW radar apparatus according to the first, second and third aspects, the delay means for delaying the code sequence signal from the code generation means for a predetermined time and outputting the delayed signal to the reception means. Is provided.

According to a fifth aspect of the present invention, in the FM-CW radar apparatus according to the first aspect, the thermal noise generating means is configured to detect a time when the FM-CW transmission wave reflected from the target located at the maximum detection distance arrives at the receiving antenna. This is to generate thermal noise having a frequency bandwidth substantially equal to the reciprocal.

According to a sixth aspect of the present invention, in the FM-CW radar apparatus according to the first aspect, the code generation means may include a code length of the random code sequence being equal to or less than a reciprocal of a maximum frequency of the beat signal. The repetition occurs for a time substantially equal to one phase of the FM-CW signal.

According to a seventh aspect of the present invention, in the FM-CW radar apparatus according to the second aspect, the code generation means may generate the pseudo-random code sequence with a code length equal to or less than a reciprocal of a maximum frequency of the beat signal. The repetition occurs for a time substantially equal to one phase of the FM-CW signal.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram of an FM-CW radar apparatus according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 9 denotes a phase modulator, 10 denotes a phase demodulator, 11 denotes a code generator, and 11a denotes thermal noise generation. Circuit, 1
1b is a comparator, 11c is a storage circuit, 12 is a delay circuit, 106 is a transmission carrier signal, 107 is a phase modulation code, 108 is a phase demodulation code, 109 is a thermal noise signal, 11
0 is a random code. In addition, 1-8, 101-10
5 is the same as that shown in FIG.

Next, the operation of the present invention will be described. FM-C
The FM-CW signal 101 whose frequency changes with a triangular wave having a substantially constant period, for example, generated by the W signal generator 1 is transmitted by the coupler 2 to the transmission carrier signal 106 and the local signal 103.
And distributed to. The distributed transmission carrier signal 10
Reference numeral 6 denotes a phase modulator 9, which is phase-modulated in two phases of 0 degree and 180 degrees, that is, spectrum spread by a phase modulation code 107 from a code generator 11, and radiated as a transmission signal 102 from a transmission antenna 3 to space.

The transmission signal 102 radiated into the space is reflected by a target (not shown) (for example, in the case of an on-vehicle radar, a vehicle running ahead of the own vehicle), is received by the reception antenna 4, and is received by the reception antenna 104. Is output to the mixer 5.
The mixer 5 converts the received signal 104 into the local signal 1
03 and outputs to the phase demodulator 10. The phase demodulator 10 demodulates the mixed reception signal into two phases of 0 degrees and 180 degrees by a phase demodulation code 108 obtained by time-delaying the phase modulation code 107 from the code generator 11 by the delay circuit 12, and performs a low-pass filter. 6 is output.

The time delay Tdr of the delay circuit 12 is the time Tmax at which the radio wave reflected from a target (not shown) at the maximum detection distance Rmax arrives at the receiving antenna 4, that is, the delay amount substantially equal to the time represented by the following equation. It is.

Tmax = 2 × Rmax / C (5)

On the other hand, the thermal noise generation circuit 11a
A thermal noise having a frequency bandwidth substantially equal to the reciprocal of max is generated, and a thermal noise signal 109 is output to the comparator 11b. The thermal noise signal 109 is compared by a comparator 11b at a constant voltage level, for example, 0 volt, and is binarized as "1" when the phase modulation code is positive and "0" when the phase modulation code is negative. It is converted into a random code 110 and output to the storage circuit 11c. The storage circuit 11c stores a random code 1
10 is stored for a period of time substantially equal to the reciprocal Tfb of the preset maximum frequency of the beat signal 105 in synchronization with the start point of the rising phase or the falling phase of the frequency of the transmission signal 102. The signal 107 is repeatedly output to the phase modulator 10 and the delay circuit 12 as a symbol 107.

That is, the phase modulation code 107 has a clock cycle Tcp of almost Tmax and a code cycle Tco of almost Tf.
The random code sequence b is a signal that is repeatedly output for each phase of the frequency rise or fall of the transmission signal 102. The phase demodulation code 108 is a signal delayed from the phase modulation code 107 by the delay time Tdr of the delay circuit 12.

FIG. 2 shows the thermal noise signal 109, random code 1
FIG. 10 is a diagram illustrating a relation between a phase modulation code 107 and a phase demodulation code 108 on a time axis.

The signal from the phase demodulator 10 input to the low-pass filter 6 selects and extracts only the fundamental wave component, that is, the beat signal 105, and sends it to the frequency detector 7. The beat signal 105 is the phase demodulator 1
0, which is a correlation output between the phase demodulation code 108 and the received signal 104,
When the time difference of the phase modulation applied to 04 is zero, the amplitude becomes maximum.

That is, the phase demodulation code 108 is substantially T-phase with the phase modulation code 107 which performs phase modulation on the transmission signal 102.
Since the time difference of the received signal 104 is substantially equal to Tmax (the target distance (not shown) is substantially equal to the maximum detection distance Rmax), the amplitude becomes maximum because the time difference Tdr equals to the maximum. Furthermore, the clock cycle Tcp is also almost Tma.
Since the distance is x, the correlation can be obtained in a range of the distance to the target from almost zero to twice the maximum detection distance Rmax.

FIG. 3 shows the target distance and the beat signal 10.
FIG. 6 is a diagram showing a relationship between amplitudes of a fifth example. However, in FIG. 3, for simplicity, the chip rate Tcp and the delay time Tdr of the delay circuit 12 are assumed to be equal to Tmax. Further, the amplitude of the received signal 104 is inversely proportional to the square of the distance to the target, but is set to 1.0 regardless of the target distance.

Note that the frequency detector 7 outputs the transmission signal 102
Beat signal 105 of the rising phase in the frequency signal of
The arithmetic unit 8 detects the frequency fbu of the rising phase beat signal 105 and the frequency fbd of the falling phase beat signal 105 from the frequency fbu of the rising phase beat signal 105 and the frequency fbd of the falling phase beat signal 105, respectively.
This is for obtaining a distance R and a relative speed V to an object (not shown), and performs the same processing as that described in the related art.

In the first embodiment, the code sequence is a random code sequence generated from thermal noise, but may be a generally used pseudo-random code sequence such as an M sequence. Although this pseudo random code sequence is not generated from thermal noise, a pseudo random code sequence is stored in advance in a memory, and the pseudo random code sequence is read from the memory to generate a pseudo random code sequence. It was done.

The present invention relates to an FM-CW which is spectrum-spread with a random code sequence or a pseudo-random code sequence.
Since the transmission wave is transmitted and the correlation process is performed upon reception, in the correlation process, a code pattern different from the code sequence generated by itself (for example,
If 110101) is received, the amplitude after the correlation processing is suppressed, so that even if the amplitude of the own signal and the signal of the other radar are the same at the antenna input, the amplitude of the own signal after the correlation processing is Is relatively larger than the amplitude of the signals of the other radars, so that they are less susceptible to mutual radio interference. In the case of an on-vehicle radar, for example, the distance to the vehicle ahead and the relative speed can be measured. In addition, there is an effect that it can be realized at low cost because only one system is required for the reception channel.

[0032]

According to the present invention, F-spread spectrum with a random code sequence or pseudo-random code sequence is used.
Since the M-CW transmission wave is transmitted and the correlation processing is performed upon reception, there is an effect that mutual radio interference is less likely to occur even in an environment where many radars of the same type, such as a vehicle-mounted radar, are present.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM-CW radar device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a phase modulation code and a phase demodulation code on a time axis.

FIG. 3 is a diagram illustrating an example of a distance to a target and an amplitude of a beat signal.

FIG. 4 is a block diagram showing a conventional FM-CW radar device.

[Explanation of symbols]

1 FM-CW signal generator, 3 transmitting antenna, 4 receiving antenna, 5 mixer, 6 low-pass filter, 7 frequency detector, 8 arithmetic unit, 9 phase modulator, 10 phase demodulator, 11 code generator, 11a thermal noise Generating circuit, 11b
Comparator, 11c storage circuit, and 12 delay circuit.

Claims (7)

[Claims] 1. A thermal noise generating means for generating a thermal noise signal, a code generating means for generating a random code sequence from the thermal noise signal, and an FM-CW generating an FM-CW signal
Signal generation means, FM-CW transmission wave generation means for generating the FM-CW signal into a two-phase modulated FM-CW transmission wave with the random code sequence, and the FM-CW signal
A transmission antenna for transmitting a transmission wave in a target direction, a reception antenna for receiving a reflected wave from the target, and a reception signal of the reception antenna mixed with a part of the FM-CW signal, and the mixed reception signal Receiving means for performing phase demodulation into two phases by the random code sequence. 2. A code generator for generating a pseudo-random code sequence, an FM-CW signal generator for generating an FM-CW signal, and two-phase modulation of the FM-CW signal by the pseudo-random code sequence. FM-CW transmission wave generating means for generating an FM-CW transmission wave; a transmission antenna for transmitting the FM-CW transmission wave in a target direction; a reception antenna for receiving a reflected wave from the target; Receiving means for mixing a received signal with a part of the FM-CW signal and demodulating the mixed received signal into two phases by the pseudo-random code sequence. Device. 3. An extracting means for extracting a frequency of a beat signal from a frequency component of an output signal from the receiving means, and a frequency detecting means for detecting a frequency of the beat signal output from the extracting means. 3. An FM-CW laser according to claim 1, further comprising: a calculating means for calculating a distance and a speed to a target reflecting the FM-CW transmission wave from an output signal of the frequency detecting means. -Device. 4. The FM according to claim 1, further comprising delay means for delaying the code sequence signal from said code generation means for a predetermined time and outputting to said reception means.
-CW radar device. 5. The thermal noise generating means generates thermal noise having a frequency bandwidth substantially equal to the reciprocal of the time when an FM-CW transmission wave reflected from a target located at a maximum detection distance arrives at a receiving antenna. The FM-C according to claim 1,
W radar device. 6. The code generating means repeatedly generates the random code sequence for a time whose code length is equal to or less than the reciprocal of the maximum frequency of the beat signal and which is substantially equal to one phase of the FM-CW signal. 2. The FM-CW radar device according to claim 1, wherein: 7. The code generating means repeats the pseudo-random code sequence for a time whose code length is equal to or less than the reciprocal of the maximum frequency of the beat signal and which is substantially equal to one phase of the FM-CW signal. 3. The method of claim 2, wherein
The FM-CW radar device as described in the above.