FMCW traffic radar anti-synchronous interference method

Abstract

This application relates to a method for resisting co-frequency asynchronous interference in FMCW traffic radar. It utilizes a composite modulation scheme combining inter-frame frequency hopping, inter-frame pulse position pseudo-random code modulation, and inter-pulse phase pseudo-random code modulation to achieve anti-interference. With the increasing number of traffic radars, including vehicle-mounted and roadside radars, even though multiple radars operate simultaneously in the same area, this co-frequency asynchronous method ensures stable and reliable operation of each radar, accurately acquiring target distance, speed, and angle information, providing accurate data for intelligent driving or traffic management and monitoring.

Description

Technical Field

[0001] This application relates to the field of radar technology, specifically to a method for resisting co-frequency asynchronous interference in FMCW traffic radar. Background Technology

[0002] Radar, with its high precision, high stability, and all-weather environmental information sensing capabilities, has been widely applied in the transportation sector. FMCW (Frequency Modulated Continuous Wave) traffic radar can detect the distance, speed, and angle of targets in real time, and is widely used in short-range detection applications such as intelligent assisted driving and traffic management. For example, in speeding detection, radar senses vehicle speed through Doppler frequency; if the speed exceeds a threshold, it triggers a camera to capture the image, ensuring road safety. Furthermore, with the increasing use of FMCW traffic radar in vehicles such as Forward Collision Warning (FCW), Automatic Emergency Braking (AEB), Adaptive Cruise Control (ACC), Blind Spot Detection (BSD), and Lane Change Assist (LCA), as well as in roadside applications such as traffic flow statistics, road occupancy, average vehicle speed, and intelligent traffic light timing control, the number of vehicles and roadside infrastructure using FMCW radar has grown significantly. This has led to a substantial increase in the number of vehicles equipped with radar and the resulting asynchronous interference between radars operating on the same frequency. This interference can affect the radar's accurate detection, leading to the appearance of false targets or the inability to correctly detect real targets.

[0003] To enable multiple radars to operate normally and reliably in the same area simultaneously, relevant universities, research institutes and other institutions have proposed many anti-interference design methods, but these methods cannot solve the interference problem of FMCW traffic radar operating at the same frequency and asynchronously. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this application provides an FMCW traffic radar anti-co-frequency asynchronous interference method. With the increasing number of traffic radars, including vehicle-mounted radars and roadside radars, even though multiple radars operate simultaneously in the same area, the use of this co-frequency asynchronous method can ensure that each radar operates stably and reliably, accurately acquiring the distance, speed, and angle information of the target, and providing accurate data information for intelligent driving or traffic management and monitoring.

[0005] The first aspect of this application provides a method for resisting co-frequency asynchronous interference in FMCW traffic radar. The radar detection period T is modulated with pseudo-random code, and T is uniformly distributed between [T1, T2]. The inter-frame pulse pseudo-random modulated transmission signal is generated according to T and radiated to the outside through the transmission antenna. Different radars will not have long-term synchronous transmission signals due to different detection period modulation methods, thereby achieving the purpose of resisting co-frequency asynchronous interference in the time dimension.

[0006] Optionally, the detection period T is generated as shown in the following formula:

[0007] T = T1x + T2(1-x);

[0008] In the formula, T represents the pulse interval, T1 represents the minimum period, T2 represents the maximum period, and x represents a random number uniformly distributed in [0 to 1].

[0009] Optionally, the sweep time of the transmitted linear frequency modulated continuous wave signal is T. m Then its expression is:

[0010]

[0011] In the formula, f i For carrier frequencies; i = 0, 1, ..., M-1, representing M different starting frequencies; A T B is the amplitude of the transmitted signal; B is the bandwidth of the FM signal; k = -B / T m This is the frequency modulation slope; This is the initial phase of the transmitted signal.

[0012] Optionally, if the relative distance between the radar and the target is R, the relative velocity is v, and the delay of the transmitted signal returning to the receiver after reflection from the target is τ(t) = 2(R-vt) / c, then the expression for the echo signal is:

[0013]

[0014] Optionally, after mixing the echo signal and the local oscillator signal, a low-pass filter is applied to obtain the beat frequency signal, which is expressed as follows:

[0015]

[0016] In the formula, if i≠j, the difference frequency signal falls outside the receiver bandwidth. After being processed by the receiver frequency filter, it will not cause interference. Only when i=j, that is, the signal transmitted by this radar, can it be correctly received by the receiver and the echo of the target be obtained.

[0017] Optionally, the mathematical expression for inter-pulse phase pseudo-random code modulation is:

[0018]

[0019] Where a(t) is a binary pseudo-random code, taking values ​​of +1 and -1, where 1 represents S. T The phase of (t) remains unchanged; taking -1 indicates that S T The phase of (t) is increased by 180°.

[0020] Optionally, the autocorrelation function of the a(t) random code is:

[0021]

[0022] A pseudo-random code with excellent autocorrelation performance has a peak value only when it is perfectly autocorrelated with itself, and the other values ​​are small and close to 0. Only when it is perfectly autocorrelated can the Doppler signal complete effective accumulation and the spectrum has obvious peak values. Otherwise, it exhibits noise characteristics and is equivalent to thermal noise.

[0023] The technical solution provided in this application may include the following beneficial effects:

[0024] With the increasing number of traffic radars, including vehicle-mounted radars and roadside radars, even though multiple radars are operating simultaneously in the same area, the use of the same frequency asynchronous method can ensure that each radar operates stably and reliably, accurately acquiring the distance, speed, and angle information of the target, and providing accurate data information for intelligent driving or traffic management and monitoring.

[0025] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a block diagram illustrating the anti-co-frequency asynchronous interference principle of the FMCW traffic radar in this application embodiment;

[0028] Figure 2 This is the anti-co-frequency asynchronous interference waveform of the traffic radar in the embodiments of this application;

[0029] Figure 3 This is a schematic diagram of inter-frame random pulse positions generated by pseudo-random code modulation in an embodiment of this application;

[0030] Figure 4 This is a schematic diagram illustrating the selection of different starting frequencies for pseudo-random codes in the embodiments of this application;

[0031] Figure 5 This is a schematic diagram of pseudo-random code phase modulation in an embodiment of this application;

[0032] Figure 6 This is a simulation diagram of the autocorrelation of a 128-point random code in an embodiment of this application;

[0033] Figure 7 This is a simulation diagram of the cross-correlation of two 128-point pseudo-random codes in an embodiment of this application;

[0034] Figure 8 This is a flowchart of the anti-interference and data processing of the FMCW traffic radar in the embodiments of this application. Detailed Implementation

[0035] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0036] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0037] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0038] The technical solutions of the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0039] This embodiment provides a transmitting signal generator that generates a set of detection periods T,<Fstart、Fend> The waveform is generated by pseudo-random composite modulation, and the phase of the transmitted waveform is modulated according to the binary pseudo-random code generated by the pseudo-random code generator. One path is radiated outward through the transmitting antenna, and the other path is input to the receiver as the local oscillator signal. The receiving antenna receives the echo signal reflected from the target and mixes it with the local oscillator signal in the receiver. Then, in the processor, analog-to-digital conversion is performed through AD sampling, and the digital signal undergoes signal preprocessing, pseudo-random code phase correlation demodulation, and spectrum analysis to obtain target distance and speed information. Traffic radar has multiple receiving channels. Using multi-channel data, the direction of arrival (DOA) estimation algorithm is used to obtain the target's angle information, which can be converted into the target's lane information. This information is noisy data, and there is an error between the detected value and the true value. A tracking filter method is used to reduce the error and make the filtered value closer to the true value.

[0040] This invention provides a method for combating co-channel asynchronous interference in FMCW traffic radar. The invention relates to a radar architecture that integrates radar waveform analysis, transmitter, receiver, and signal processing to jointly combat co-channel asynchronous interference. A block diagram is shown below. Figure 1 As shown. The waveform is synchronously triggered by a pseudo-random pulse, synchronously received by the receiver, frequency filtered, and then the pseudo-random code phase-correlation reception is completed in signal processing. First, a set of waveforms is designed, such as... Figure 2 As shown, specifically, a detection period T has an effective transmission time Tr, consisting of N pulse repetition periods (PRTs). Each PRT is divided into idle time, rise time, and fall time. The waveform change comprises three parts: the first effective time Tr remains constant, while the detection period T varies according to a Gaussian or uniform distribution, achieving inter-frame pulse position pseudo-random code modulation in time. This ensures that the radar echo signal and co-frequency asynchronous interference fall within the same time interval with a low probability, suppressing co-frequency asynchronous interference in the time dimension. Each RPT is a chirp with a <start frequency (Fstart) and an <end frequency (Fend)>. The radar waveform is designed into multiple sets.<Fstart、Fend> A set of data is selected within a coherent accumulation period (CPI).<Fstart、Fend> By using pseudo-random code selection and switching, inter-frame frequency hopping is achieved at the frequency level, suppressing co-frequency and asynchronous interference in the frequency dimension. N PRTs are phase-modulated using a binary pseudo-random code of length N; when the code is 0, phase modulation is 0, and when the code is 1, phase modulation is Pi. During reception, pseudo-random code correlation demodulation is performed. Only correlated pseudo-random codes can be correctly correlated and demodulated; uncorrelated pseudo-random codes exhibit noise characteristics after demodulation. The transmitter consists of a pseudo-random code generator that generates a pseudo-random synchronization signal to trigger the transmission signal. The receiver performs pulse-level synchronization reception and frequency filtering reception, and the signal processor performs pseudo-random code phase modulation correlation demodulation of the transmitted signal.

[0041] Figure 1 This is a block diagram illustrating the principle of a traffic radar. The radar detection period T uses pseudo-random code modulation, with T uniformly distributed between [T1, T2]. A transmit signal with inter-frame pulse position pseudo-random modulation is generated according to T and radiated outwards via the transmitting antenna. Due to differences in the detection period modulation methods, different radars will not experience prolonged synchronization of transmitted signals in the time dimension, thus achieving the purpose of resisting co-frequency asynchronous interference in the time dimension.

[0042] The method for generating T is shown in the following formula:

[0043] T = T1x + T2(1-x)

[0044] In the formula, T represents the pulse interval, T1 represents the minimum period, T2 represents the maximum period, and x represents a random number uniformly distributed in the range of [0 to 1].

[0045] The interval T between pulse a and pulse b in the figure is randomly distributed between T1 and T2, with the greatest uncertainty, and has good anti-synchronous ability in the time dimension.

[0046] Let the sweep time of the transmitted linear frequency modulated continuous wave signal be T. m Then its expression is:

[0047]

[0048] In equation (1): f i For carrier frequencies; i = 0, 1, ..., M-1, representing M different starting frequencies, A T B is the amplitude of the transmitted signal; B is the bandwidth of the FM signal; k = -B / T m This is the frequency modulation slope; This is the initial phase of the transmitted signal. Different starting frequencies, such as... Figure 4

[0049] Let the relative distance between the radar and the target be R, the relative velocity be v, and the delay of the transmitted signal returning to the receiver after reflection from the target be τ(t) = 2(R - vt) / c. Then the expression for the echo signal is:

[0050]

[0051] After mixing the echo signal and the local oscillator signal and low-pass filtering, the expression for the resulting beat frequency signal is: S I (t)=A M cos{2π(f i -f j )t+2πf i τ(t)+2πkτ(t)t-πk[τ(t)] 2} , (0 <t<Tm (3)

[0052] In equation (3), if i ≠ j, the difference frequency signal falls outside the receiver bandwidth. After being processed by the receiver frequency filter, it will not cause interference. Only when i = j, that is, the radar's transmitted signal, can it be correctly received by the receiver and the target's echo be obtained.

[0053] The mathematical expression for inter-pulse phase pseudo-random code modulation is:

[0054]

[0055] Where a(t) is a binary pseudo-random code, taking values ​​of +1 and -1, where 1 represents S. T The phase of (t) remains unchanged; taking -1 indicates that S T Adding 180° to the phase of a(t), the autocorrelation function of the random code a(t) is:

[0056]

[0057] A pseudo-random code with excellent autocorrelation performance only exhibits a peak value when it is perfectly autocorrelated with itself; otherwise, the value is small, close to 0. Only when perfectly autocorrelated can the Doppler signal achieve effective accumulation and have a significant peak in the spectrum; otherwise, it exhibits noise characteristics, equivalent to thermal noise.

[0058] The radar generates a transmission waveform according to the above parameters, and then transmits it via an auxiliary signal. Figure 1 After being amplified by the power amplifier, the signal is transmitted through the transmitting antenna. The receiving antenna receives the reflected echo from the target, amplifies it with low noise, and mixes it with the local oscillator. Synchronous reception is then achieved, thus completing the time-domain anti-co-frequency asynchronous interference function. For co-frequency asynchronous interference entering the reception timing sequence, since each RPT transmit signal has a different starting frequency, the difference frequency echo cannot be properly amplified and received by the receiver's frequency filtering circuit, thereby completing the anti-co-frequency asynchronous interference function in the frequency domain. For waveforms that simultaneously satisfy synchronous reception and frequency filtering reception, due to the phase modulation of the inter-pulse pseudo-random code, only waveforms completely correlated with the local pseudo-random code will form autocorrelation peaks, see [reference needed]. Figure 6 Otherwise, only noise spectrum Figure 7 It cannot form a clear peak.

[0059] Only the echo reflected from the target can be correctly processed by the radar. Other co-channel and asynchronous interference is completely suppressed due to the three measures mentioned above, and cannot cause significant interference. Therefore, the target information detected by the radar is that of the real target. The target echo signal is filtered and amplified before being transmitted to an AD converter. After AD sampling, it is transmitted to the processing equipment. After signal preprocessing, pseudo-random code modulation, phase correlation, and demodulation, it is sent to the spectrum analysis module for spectrum analysis. Each PRT (Phase-Reflection Test) produces a set of spectrum analysis results. After N PRTs, a spectrum analysis matrix is ​​formed. Performing two-dimensional spectrum analysis on the one-dimensional spectrum matrix yields the Range-Doppler two-dimensional matrix of a receiving channel. Incoherent accumulation between multiple receiving channels improves the signal-to-noise ratio and enhances the radar's detection range. The accumulated Range-Doppler two-dimensional matrix is ​​fed into both the noise floor estimation module and the two-dimensional CFAR constant false alarm rate (CFAR) detection module. The noise floor estimation result serves as the input to the CFAR detection module. The CFAR module can estimate the clutter environment in which the radar is located in real time, and maximize the detection probability while keeping the false alarm rate constant. After detection, the target's R and V information, as well as the complex echo information of each channel, including the amplitude and phase information of the channel, are obtained. The complex echo information of multiple channels is fed into the DOA estimation module. The DOA estimation module uses a spatial spectrum estimation algorithm to accurately calculate the target's direction of arrival. Especially for dense targets, the high-resolution spatial spectrum estimation technology can quickly and accurately obtain the target's angle information. Thus, the target's RCS, range R, velocity V, and angle θ are obtained.

[0060] Each radar detection cycle obtains the target's RCS, range R, velocity V, and angle θ. The RCS, range R, velocity V, and angle θ of the same target in different cycles are correlated. These are correlated using trajectory association algorithms such as nearest neighbor or JPDA joint probability density association. For each target, trajectory prediction is performed based on its motion equations. The predicted trajectory is then filtered against matched targets using a filtering algorithm such as the improved EKF. Once the trajectory is stably established, the target is output. For targets without correlation, the predicted value is used. If there is no correlation for several consecutive radar cycles, the target is lost. The process of trajectory establishment, prediction, correlation, filtering, and output is repeated for targets detected in new detection cycles. See the flowchart below. Figure 8 After filtering, the target's error variance is reduced, improving the accuracy and precision of the measurement. This provides a stable data source for data processing in the traffic management radar application layer and for the application functions of vehicle-mounted radar, supporting correct decision-making and the execution of appropriate actions, making traffic smarter, more efficient, and safer, and making vehicles safer, more convenient, more efficient, and more energy-saving.

[0061] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, and improvements made within the spirit and scope of this application are included within the scope of protection of this application.

Claims

1. A method for resisting co-frequency asynchronous interference in FMCW traffic radar, characterized in that, The radar detection period T uses pseudo-random code modulation, with T uniformly distributed between [T1, T2]. A pseudo-randomly modulated inter-frame pulse signal is generated according to T and radiated outwards via the transmitting antenna. Different radars, due to variations in their detection period modulation methods, will not experience prolonged synchronization of transmitted signals in the time dimension, thus achieving the goal of resisting co-frequency asynchronous interference in the time dimension. T = T1x + T2(1-x); In the formula, T represents the pulse interval, T1 represents the minimum period, T2 represents the maximum period, and x represents a random number uniformly distributed in [0~1]. One detection period T includes N pulse repetition periods, each pulse repetition period being a linear frequency modulated continuous wave signal with a <start frequency and end frequency>. Within one coherent accumulation period, a set of <start frequency and end frequency> is selected and switched by pseudo-random code selection, realizing inter-frame frequency hopping from the frequency dimension and suppressing co-frequency asynchronous interference in the frequency dimension. The N pulse repetition periods within the coherent accumulation period are phase modulated using a binary pseudo-random code with a code length of N.

2. The FMCW traffic radar anti-co-frequency asynchronous interference method as described in claim 1, characterized in that, The sweep time of the transmitted linear frequency modulated continuous wave signal is T. m Then its expression is: In the formula, f i For carrier frequencies; i = 0, 1, ..., M-1, representing M different starting frequencies; A T B is the amplitude of the transmitted signal; B is the bandwidth of the FM signal; k = -B / T m This is the frequency modulation slope; This is the initial phase of the transmitted signal.

3. The FMCW traffic radar anti-co-frequency asynchronous interference method as described in claim 2, characterized in that, The relative distance between the radar and the target is R, the relative velocity is v, and the delay of the transmitted signal returning to the receiver after reflection from the target is τ(t) = 2(R-vt) / c. Then the expression for the echo signal is:

4. The FMCW traffic radar anti-co-frequency asynchronous interference method as described in claim 3, characterized in that, After mixing the echo signal and the local oscillator signal and low-pass filtering, the expression for the resulting beat frequency signal is: S I (t)=A M cos{2π(f i -f j )t+2πf i τ(t)+2πkτ(t)t-πk[τ(t)] 2 } , (0<t<T m ) In the formula, if i≠j, the difference frequency signal falls outside the receiver bandwidth. After being processed by the receiver frequency filter, it will not cause interference. Only when i=j, that is, the signal transmitted by this radar, can it be correctly received by the receiver and the echo of the target be obtained.

5. The FMCW traffic radar anti-co-frequency asynchronous interference method as described in claim 4, characterized in that, The mathematical expression for inter-pulse phase pseudo-random code modulation is: Where a(t) is a binary pseudo-random code, taking values ​​of +1 and -1, where 1 represents S. T The phase of (t) remains unchanged; taking -1 indicates that S T The phase of (t) is increased by 180°.

6. The FMCW traffic radar anti-co-frequency asynchronous interference method as described in claim 5, characterized in that, The autocorrelation function of the a(t) random code is: A pseudo-random code with excellent autocorrelation performance has a peak value only when it is perfectly autocorrelated with itself, and the other values ​​are small and close to 0. Only when it is perfectly autocorrelated can the Doppler signal complete effective accumulation and the spectrum has obvious peak values. Otherwise, it exhibits noise characteristics and is equivalent to thermal noise.

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