CN117471405A

CN117471405A - Anti-interference method for vehicle millimeter wave radar

Info

Publication number: CN117471405A
Application number: CN202311463451.4A
Authority: CN
Inventors: 刘吉祥; 张龙涛
Original assignee: Lisheng Intelligent Technology Shanghai Co ltd
Current assignee: Lisheng Intelligent Technology Shanghai Co ltd
Priority date: 2023-11-06
Filing date: 2023-11-06
Publication date: 2024-01-30

Abstract

The invention discloses an anti-interference method of a vehicle millimeter wave radar, which comprises the following steps: s1) obtaining a linear frequency modulation continuous wave of DDMA by adopting N _TX The radar transmitting antennas make Doppler frequencies of the transmitting antennas mutually equal and transmit millimeter waves; s2) performing two-dimensional FFT on the echo signals to obtain a distance-Doppler spectrogram; s3) processing each distance independently, and finding out a plurality of peaks after the constant false alarm rate is detected; only N of the same target is found _TX The individual peaks are identified as true targets. The anti-interference method for the vehicle millimeter wave radar provided by the invention adopts random prime number DDMA codes, the number of codes is more, and the background noise is not raised under the condition of interference.

Description

Anti-interference method for vehicle millimeter wave radar

Technical Field

The invention relates to a radar anti-interference method, in particular to a vehicle millimeter wave radar anti-interference method.

Background

Along with the wider and wider application of millimeter wave radars, the mutual interference problem among radars is inevitably encountered by the vehicle-mounted millimeter wave radars. The mutual interference between radars can be summarized as follows: co-channel interference and scanning interference.

The main current anti-interference schemes are as follows:

the method for detecting the interference point in the fast time dimension has the defect of common anti-interference effect.

Method two, a single chirp (code pulse technique, alias chirp) makes a short-time fourier transform, detects the interference frequency based on a time spectrum, and has the disadvantage of too large calculation amount.

The method three, slow time dimension uses pseudo-random phase coding to homogenize noise into bottom noise, the disadvantage is as follows:

1) The number of pseudo-random sequences with low cross-correlation is limited and not well found;

2) Noise is obviously improved after the interference is homogenized into the background noise, the detection probability of the real echo is reduced, and the real echo can be submerged.

The above methods generally need to be combined, but have shortcomings, so that improvement on the anti-interference method of the vehicle millimeter wave radar is needed.

Disclosure of Invention

The invention aims to solve the technical problem of providing an anti-interference method for a vehicle millimeter wave radar, which has more codes and can not raise the background noise under the condition of interference.

The invention provides an anti-interference method for a vehicle millimeter wave radar, which aims to solve the technical problems and comprises the following steps: s1) obtaining a linear frequency modulation continuous wave of DDMA by adopting N _TX The radar transmitting antennas make Doppler frequencies of the transmitting antennas mutually equal and transmit millimeter waves; s2) performing two-dimensional FFT on the echo signals to obtain a distance-Doppler spectrogram; s3) processing each distance independently, and finding out a plurality of peaks after the constant false alarm rate is detected; only N of the same target is found _TX The individual peaks are identified as true targets.

Further, the step S1 includes:

finding N _TX The prime number constitutes the vector Code, and a constant C and satisfies the following condition

C≥1；

The Code is rounded over the entire doppler spectrum by:

Code＝round(C*Code)；

the first element in the Code is then set to 0:

Code(1)＝0；

calculating the cumulative sum to obtain the angular frequency omega of each antenna DDMA code:

ω＝cumsum(Code)；

obtaining the initial Phase of the nth Chirp of each transmitting antenna:

Phase＝2*π*ω*n/N _Chirp n∈(1,N _Chirp )；

N _FFT for slow time dimension FFT point number, N _Chirp For the number of Chirp, the control radar encodes with this Phase when transmitting Chirp.

Further, every time there is a real target, N appears on the range-Doppler spectrum _TX A number of peaks, and a difference in position between each peak is equal to a value in Code; other peaks on the range-doppler spectrum are identified as interference peaks.

Further, the current frame starts from the step of searching for codes after being processed, or a plurality of groups of codes are selected to be searched offline, and then one group is selected randomly for the next frame to use.

Compared with the prior art, the invention has the following beneficial effects: the anti-interference method for the vehicle millimeter wave radar provided by the invention adopts random prime number DDMA codes, the number of codes is more, and the background noise is not raised under the condition of interference. In addition, the present invention may be conveniently used in combination with method one, method two.

Drawings

FIG. 1 is a Doppler spectrum of a real target in an embodiment of the invention;

fig. 2 is a doppler spectrum of the vehicle millimeter wave added interference in the embodiment of the present invention;

fig. 3 is a graph of a peak searching result of the vehicle millimeter wave CFAR in the embodiment of the present invention;

fig. 4 is a diagram of a decoding result of the vehicle millimeter wave DDMA in the embodiment of the present invention.

Detailed Description

The invention is further described below with reference to the drawings and examples.

The invention provides an anti-interference method for a vehicle millimeter wave radar, wherein the radar waveform is linear frequency modulation continuous wave of DDMA (Doppler-Division Multiple-Access), namely Doppler division multiple Access. The Doppler frequencies of the individual transmit antennas are made to be mutually equal and the Doppler frequencies are changed differently every frame. A two-dimensional FFT of the echo signal results in a range-doppler spectrum. For each distance, a plurality of peaks can be found after CFAR (Constant False-Alarm Rate) detection. Only the peak conforming to the Doppler code emitted by the radar itself is the true echo of the radar itself, and other peaks are all interference. Thus, the anti-interference purpose is achieved.

Let the number of radar transmitting antennas be N _TX Slow time dimension FFT point number N _FFT The number of Chirp is N _Chirp 。

Then N can be found at this time _TX The prime numbers constitute the vector Code, and a constant C and satisfy the following condition:

C≥1

the Code is rounded to the whole Doppler frequency spectrum through the following method, so that the frequency spectrum utilization rate can be effectively improved, and the decoding accuracy rate can be improved.

Code＝round(C*Code)

The first element in the Code is then set to 0.

Code(1)＝0

Calculating the cumulative sum to obtain the angular frequency omega of each antenna DDMA code

ω＝cumsum(Code)

Thus, the initial Phase of the nth Chirp of each transmitting antenna is obtained

Phase＝2*π*ω*n/N _Chirp n∈(1,N _Chirp )

The radar encodes at this Phase when transmitting Chirp.

After two-dimensional FFT is performed on the echo signals, a distance-Doppler diagram can be obtained, and N appears on the diagram when a real target exists on a single distance dimension _TX The number of peaks, and the difference in position between each peak is equal to the value in Code. There may also be several interference peaks on this figure. Only N of the same target is found _TX The individual peaks are considered to be real targets and the other peaks are considered to be interference to be rejected.Thus, the anti-interference purpose is achieved.

After the frame is processed, the step of searching the codes begins again, or a plurality of groups of codes can be searched offline and then a group of codes is randomly selected for the next frame to use.

A specific example is given below, let N _Chirp ＝N _FFT ＝512。N _TX =3. There is a real target at 0 doppler frequency and 10 disturbances are randomly present.

Step 1: randomly extracting 3 numbers from a prime number table

Code＝[3,5,7]

Step 2: calculating constant C

C＝sum(Code)/N _FFT ＝34.1333

Step 3, rounding the Code

Code＝round(C*Code)＝[102,171,239]

Step 4, the first number in the code is set to 0

Code＝[0,171,239]

Step 5, calculating the angular frequency

ω＝cumsum(Code)＝[0,171,410]

Step 6, calculating the code Phase

Phase＝2*π*ω*n/N _Chirp n∈(1,N _Chirp )

Step 7, encoding the phase to the initial phase of the transmitting antenna

Step 8, receiving echo signal and down-converting

Step 9: 2-dimensional FFT and extraction of a single range-dimensional Doppler spectrum

9.1 Doppler spectrum is shown in figure 1 when there is only one real target.

9.2 Doppler spectrum when 10 disturbances are set is shown in FIG. 2.

Step 10: CFAR, as shown in fig. 3.

Step 11: it can be seen with ω decoding that only one real object is detected and other spurious objects are discarded, as shown in fig. 4.

While the invention has been described with reference to the preferred embodiments, it is not intended to limit the invention thereto, and it is to be understood that other modifications and improvements may be made by those skilled in the art without departing from the spirit and scope of the invention, which is therefore defined by the appended claims.

Claims

1. The anti-interference method for the vehicle millimeter wave radar is characterized by comprising the following steps of:

s1) obtaining a linear frequency modulation continuous wave of DDMA by adopting N _TX The radar transmitting antennas make Doppler frequencies of the transmitting antennas mutually equal and transmit millimeter waves;

s2) performing two-dimensional FFT on the echo signals to obtain a distance-Doppler spectrogram;

s3) processing each distance independently, and finding out a plurality of peaks after the constant false alarm rate is detected; only N of the same target is found _TX The individual peaks are identified as true targets.

2. The method for anti-interference of vehicle millimeter wave radar according to claim 1, wherein the step S1 comprises:

C≥1；

The Code is rounded over the entire doppler spectrum by:

Code＝round(C*Code)；

the first element in the Code is then set to 0:

Code(1)＝0；

ω＝cumsum(Code)；

obtaining the initial Phase of the nth Chirp of each transmitting antenna:

Phase＝2*π*ω*n/N _Chirp n∈(1，N _Chirp )；

N _FFT is slow timeDimension FFT points, N _Chirp For the number of Chirp, the control radar encodes with this Phase when transmitting Chirp.

3. The method for anti-interference of vehicle millimeter wave radar according to claim 2, wherein each time there is a real target, N appears on the range-doppler spectrum _TX A number of peaks, and a difference in position between each peak is equal to a value in Code; other peaks on the range-doppler spectrum are identified as interference peaks.

4. The method for anti-interference of vehicle millimeter wave radar according to claim 2, wherein the step of searching for codes is resumed after the current frame is processed, or a plurality of groups of codes are selected to be searched off-line, and then a group is randomly selected for the next frame.