Decentralized distributed node time-frequency phase synchronization method

Abstract

The invention relates to a radar communication technology, and discloses a decentralized distributed node time-frequency phase synchronization method, which comprises a time synchronization step: sending signals from an initial radar station to complete a first round-trip cycle until all radar stations receive and transmit signals twice; each radar station obtains a time synchronization error estimation value of signals sent by two adjacent stations so as to carry out time synchronization correction; a frequency and phase synchronization step: starting to send a signal carrying the carrier frequency and the initial phase from the initial radar station to complete a second round-trip cycle until all radar stations transmit and receive signals carrying the carrier frequency and the initial phase twice; and each radar station obtains a carrier frequency estimation value and a phase estimation value of sending signals from two adjacent stations, the carrier frequency estimation value serves as a synchronous frequency, the two phase estimation values of the two adjacent stations are added to serve as a synchronous phase, and frequency and phase correction is performed by using the synchronous frequency and the synchronous phase.

Description

Technical Field

[0001] The present invention relates to radar communication technology, and in particular to a time-frequency phase synchronization technology among multiple radar base stations. Background Art

[0002] In recent years, with the advancement of electronic hardware technology and signal processing algorithms, radar technology has also been developing continuously. Various new radar systems are also emerging, among which MIMO radar system is more representative. MIMO radar can be divided into two types: centralized and distributed. MIMO radar has many advantages over traditional radar, but the synchronization problem between multiple radars will have an adverse effect on the performance of fusion detection. Based on this, it is necessary to study the synchronization problem of distributed radar and its solution.

[0003] In order to solve the multi-radar synchronization problem in a targeted manner, the size of the synchronization error must first be estimated and compensated before the radar system officially works. Therefore, as a radar, it is necessary to study the radar synchronization error estimation and compensation method. Most of the existing synchronization methods only stay at error analysis and compensation methods for a single error, but for distributed radars, the synchronization errors of time frequency and phase exist simultaneously and affect each other. At present, there are few relevant materials on how to comprehensively study the compensation methods of these three errors. Therefore, it is necessary to study the synchronization problem of distributed radars in combination with their distribution characteristics and signal forms.

[0004] For radar synchronization technology, the key is to simulate the parameters of the radar when it is working, and then use a suitable synchronization system and algorithm to estimate the synchronization errors of its time, frequency and phase, and finally compensate them during formal operation. We can start with the factors that affect synchronization in the radar system, such as the different time bases between stations affecting time synchronization, and the signal transmission distance and carrier frequency errors affecting frequency and phase synchronization. We can also start with the known information of the radar base station, such as the relatively unchanged distance between stations, the relatively unchanged error size during working time, and other characteristics to estimate and eliminate errors. This paper combines the above two ideas to study the modeling and estimation methods of synchronization errors, design a round-trip error synchronization system, and construct a time-frequency-phase estimation and compensation system.

[0005] The synchronization problem is a traditional and challenging problem in radar multi-station signal processing. Among them, the time synchronization error includes the fixed time difference between the time bases of the stations and the delay difference in the link when the hardware equipment transmits and receives signals. It ultimately causes the base station to have a deviation in delay ranging; the frequency and phase errors are caused by the different frequency sources between the base stations and the phase deviation from the initial phase when the signal propagates to the receiving radar site. At present, domestic research on synchronization problems has made great progress in theoretical analysis, but there are still many application problems that need to be further studied and solved. The existing synchronization method requires the designation of a central radar site, and the remaining radar sites are used as slave radar sites. The central radar site is used as the core control to synchronize the time, frequency and phase. It is necessary for the central radar site and the slave radar site to send signals in both directions to obtain the relative synchronization error between the two. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a more efficient time-frequency phase synchronization method for the situation where the existing synchronization error estimation and compensation require the designated central radar site to send information in both directions.

[0007] The technical solution adopted by the present invention to solve the above technical problems is a decentralized distributed node time-frequency phase synchronization method, which eliminates the central radar site through a round-trip signal path, and obtains the relative synchronization error between the two radar sites by sending signals in both directions. The first round-trip cycle performs time synchronization error correction, and the second round-trip cycle estimates the carrier frequency and the phase difference to achieve frequency-phase synchronization, including the following steps:

[0008] Round-trip loop path planning steps: count all radar sites and complete round-trip loop path planning; the round-trip loop path is to start from the starting radar site, transmit the signal in one direction, pass through all radar sites, and then return to the starting radar site, forming a one-way loop; then start from the starting radar site, transmit the signal in one direction in the opposite direction, pass through all radar sites, and then return to the starting radar site, forming a loop in the opposite direction;

[0009] Time synchronization steps: Send signals from the starting radar site to complete the first round-trip cycle until all radar sites have sent and received signals twice; each radar site obtains the estimated value of the time synchronization error of the signals sent by the two adjacent sites, and then performs time synchronization correction to achieve time synchronization of all radar sites;

[0010] Frequency and phase synchronization steps: Starting from the starting radar site, a signal carrying the carrier frequency and initial phase is sent to complete the second round-trip cycle until all radar sites have sent and received signals carrying the carrier frequency and initial phase twice; each radar site obtains the carrier frequency estimation value and phase estimation value of the signals sent from the two adjacent sites, uses the carrier frequency estimation value as the synchronization frequency, adds the two phase estimation values ​​of the two adjacent sites as the synchronization phase, and uses the synchronization frequency and synchronization phase to perform frequency and phase correction to achieve frequency and phase synchronization of all radar sites.

[0011] Since the present invention is aimed at estimating and compensating the synchronization problem of fixed base stations, it is necessary to measure the error between each station before work. Therefore, a decentralized distributed node time-frequency-phase synchronization method is adopted, and each station is allowed to send and receive signals clockwise and counterclockwise respectively. According to the error modeling method, the relationship between the signal cycles is used to estimate the size of the synchronization error so that it can be eliminated in subsequent work. Compared with the existing synchronization method, the method of the present invention removes the central node, can effectively synchronize the three aspects of time, frequency and phase, and has practical applicability.

[0012] The beneficial effects of the present invention are as follows: through the round-trip signal receiving and sending link, the need for coordinated control with a certain radar site as the core is eliminated, and synchronization between stations is performed two by two as the core, which is more flexible and variable, and improves the anti-interference and risk resistance capabilities of the distributed radar network. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The figure is a flow chart of the round-trip time-frequency phase synchronization method.

[0014] Figure 2 This is a diagram of the signal propagation path during a round trip.

[0015] Figure 3 This is the time synchronization error curve remaining after the instance passes time synchronization.

[0016] Figure 4 This is the frequency synchronization error curve remaining after the example passes the frequency synchronization.

[0017] Figure 5 This is the residual phase synchronization error curve after the example passes through phase synchronization. DETAILED DESCRIPTION

[0018] For a better description, the following definitions are first made:

[0019] Distributed radar: a network consisting of multiple radar sites in different locations but working together. Through network connection and collaborative work, it breaks through the limitation of a single radar at a single angle and achieves high-precision, all-round monitoring and tracking of targets. Generally, the signal waveforms emitted by this radar need to have good orthogonal characteristics so that the radar can determine the source of the signal when receiving it.

[0020] Synchronization error: refers to the time frequency and phase errors caused by different time bases and frequency sources of each device and the phase deviation of the sampling point from the original signal phase in the collaborative work of multiple radars. These errors will cause delays and phase deviations from the true value when receiving and processing signals.

[0021] Pulse compression: A radar technology that transmits a wide pulse signal, receives and processes the echo, and then outputs a narrow pulse. To achieve the effect of pulse compression, the transmitted wide pulse is encoded and processed by a matched filter in the receiver. The advantages of pulse compression radar are that it can achieve a large range and has a high range resolution.

[0022] The key element of the present invention is to construct a system architecture for bidirectional signal reception and transmission between stations through a round-trip method. Through the round-trip signal path, the central radar site is eliminated, and various errors are introduced into the signal propagation process, and then estimated and eliminated by the algorithm. Pulse compression is used to measure the time synchronization error. The first round-trip cycle performs time synchronization error correction; the second round-trip cycle estimates the carrier frequency and the phase difference to achieve frequency and phase synchronization.

[0023] The specific implementation of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] like Figure 2 As shown, there are K radar sites in total, and the signal is transmitted from radar site 1 to radar site K in a clockwise direction, and from K to 1 in a counterclockwise direction. For radar site i, the adjacent radar site in the clockwise direction is i+1, and the adjacent radar site in the counterclockwise direction is radar site i-1. Exceptionally, the adjacent radar site in the clockwise direction of radar site K is radar site 1, and the adjacent radar site in the direction of radar site 1 is radar site K. The path of the round-trip cycle is: starting from radar site 1, passing through radar sites 2, 3, ..., K-1, K in turn clockwise, and finally from radar site K to radar site 1, completing the clockwise closed loop, and then starting from radar site 1, passing through radar sites K, K-1, ..., 3, 2 in turn counterclockwise, and finally from radar site 2 to radar site 1, completing the counterclockwise closed loop, that is, one round-trip cycle is completed. Similarly, one round-trip cycle can also be completed by first going counterclockwise and then clockwise. Or taking other radar sites as the starting point of the path, the round-trip cycle can be completed in the same way.

[0025] Figure 2 The figure shows a simple scenario where the radar sites are distributed in a ring shape. In the actual scenario, the round-trip loop path can be arranged based on the ranging results after the ranging between the radar sites is completed.

[0026] The round-trip time-frequency phase synchronization method is as follows Figure 1 As shown, the following steps are included:

[0027] Step 1: K radar stations send signals clockwise and counterclockwise in turn to complete the first round-trip cycle until all radar stations have sent and received signals twice. At this point, each radar station obtains the estimated value of the time synchronization error of the signals sent by the two adjacent stations, and thus performs time synchronization correction to achieve time synchronization.

[0028] Specifically, take the case where adjacent radar sites i-1 and i send signals clockwise and radar site i obtains an estimated value of time synchronization error as an example:

[0029] The transmitting station i-1 transmits a signal, such as a linear frequency modulation signal LFM, to the receiving station i;

[0030] Receiving station i performs pulse compression on the received LFM signal to obtain the time when the signal has the highest amplitude value, thereby obtaining the propagation delay t i-1,i , and the signal theory propagation delay Compare the actual measured delay with the theoretical value and use the difference as the estimated value of the time synchronization error. i-1,i is the distance from transmitting station i-1 to receiving station i, and c is the speed of light.

[0031] The estimated value of the step time synchronization error is used to perform delay correction on the signal in the subsequent frequency and phase synchronization work, which greatly reduces the impact of the time synchronization error on the frequency and phase synchronization work.

[0032] Step 2: K stations send signals carrying carrier frequency and initial phase clockwise and counterclockwise to complete the second round-trip cycle until all radar stations have sent and received twice. At this time, each radar station estimates the carrier frequency and phase of the signals sent from the two adjacent stations, uses the estimated carrier frequency as the synchronization frequency, and adds the two phase estimation values ​​as the synchronization phase. Specifically:

[0033] When rotating counterclockwise, the transmitting station i constructs the transmitting waveform with the carrier frequency and initial phase of the formal operation as reference, and the carrier frequency is set to ω c , the initial phase is set to Transmitting station i transmits a signal carrying carrier frequency ω to receiving station i-1 c and initial phase The signal can be expressed as a(t) is the baseband signal Receiving station i-1 obtains the estimated value of the signal carrier frequency and phase estimate

[0034] In clockwise direction, the transmitting station i transmits the signal with carrier frequency ω to the receiving station i+1. c and initial phase The receiving station i+1 obtains the estimated value of the signal carrier frequency and phase estimate

[0035] Radar site i estimates the carrier frequency As the synchronization frequency, the phase estimate and phase estimate Added as the final synchronization phase

[0036] The carrier frequency estimation is obtained by using the fast Fourier transform FFT after down-converting the received signal; the phase estimation is specifically: in, y n is the nth sampling value in the received signal; get the estimated carrier frequency size and phase value Then, construct a new signal

[0037] In the round-trip process, taking a certain node as a reference, the sum of the signal propagation distances of other nodes in the clockwise and counterclockwise loops is equal, and because the phase error has the following relationship with the propagation time:

[0038]

[0039] Among them, const means constant value, cw means clockwise direction, and ccw means counterclockwise direction. The two summing ranges are the radar stations where the signal propagates clockwise and counterclockwise respectively. Therefore, the theoretical sum of the clockwise phase estimate and the counterclockwise phase estimate of each station is equal. Each station uses this phase sum as the synchronization phase.

[0040] The following is an implementation example. The number of radar sites is set to 3. The OFDM waveform is used for the transmitted and received signals. Time, frequency and phase errors are added. The signal bandwidth and sampling rate are about 100MHz, and the time width is about 30us. Using this method, the time synchronization error is first estimated and eliminated, and then the frequency and phase are measured again in a round-trip cycle. The deviation between the measured error size and the actual error size is as follows: Figure 2 , 3 , as shown in Figure 4. Figure 3 This is the error angle curve after the interference is not suppressed by this method. It can be seen from the comparison that this method can effectively estimate the size of the synchronization error.

[0041] The above simulation experiments verify the effectiveness and reliability of this method.

[0042] In summary, the decentralized distributed node time-frequency phase synchronization method eliminates the need for a central node in the synchronization system. It uses the round-trip signal transmission and reception between radar sites to estimate the synchronization error and compensate for it, which greatly improves the anti-interference ability of the radar network. It has a good effect in the distributed radar synchronization calibration and provides assistance for the fusion detection of distributed radars and other tasks.

Claims

1. A decentralized distributed node time-frequency phase synchronization method, characterized in that: The following steps are involved: Round-trip loop path planning steps: count all radar sites and complete round-trip loop path planning; the round-trip loop path is to start from the starting radar site, transmit the signal in one direction, pass through all radar sites, and then return to the starting radar site, forming a one-way loop; then start from the starting radar site, transmit the signal in one direction in the opposite direction, pass through all radar sites, and then return to the starting radar site, forming a loop in the opposite direction; Time synchronization steps: starting from the starting radar site, the signal is sent to complete the first round-trip cycle until all radar sites have sent and received signals twice; each radar site obtains the estimated value of the time synchronization error of the signals sent by the two adjacent sites, and then performs time synchronization correction to achieve time synchronization of all radar sites; Frequency and phase synchronization steps: Starting from the starting radar site, a signal carrying the carrier frequency and initial phase is sent to complete the second round-trip cycle until all radar sites have sent and received signals carrying the carrier frequency and initial phase twice; each radar site obtains the carrier frequency estimation value and phase estimation value of the signals sent from the two adjacent sites, uses the carrier frequency estimation value as the synchronization frequency, adds the two phase estimation values ​​of the two adjacent sites as the synchronization phase, and uses the synchronization frequency and synchronization phase to perform frequency and phase correction to achieve frequency and phase synchronization of all radar sites.

2. The method according to claim 1, characterized in that: In the round-trip path planning step, when counting all radar sites, the distances between the radar sites are measured, and the round-trip path planning is completed based on the distances between the radar sites.

3. The method according to claim 1, characterized in that: In the time synchronization step, the receiving station i receives the signal from the transmitting station i-1, and the time synchronization error estimate is calculated as follows: the receiving station i performs pulse compression on the received signal to obtain the time at which the signal has the highest amplitude value, thereby obtaining the actual propagation delay t i-1,i ; According to the distance l between the receiving station i and the transmitting station i-1 i-1,i Calculate the theoretical propagation delay τ = l i-1,i / c, c is the speed of light; The actual propagation delay t i-1,i Subtract the theoretical propagation delay τ from the actual propagation delay and use the difference as the estimated value of the time synchronization error.

4. The method according to claim 1, characterized in that: In the frequency and phase synchronization step, the signal carrying the carrier frequency and the initial phase is sent at the carrier frequency ω c and initial phase Constructing the transmit waveform for reference a(t) is the baseband signal and t is the time variable.

5. The method according to claim 4, characterized in that: In the frequency and phase synchronization step, the received signal is down-converted and then the carrier frequency estimate is obtained using the fast Fourier transform FFT. Phase estimate Among them, y n is the nth sample value in the received signal, and the total number of samples is N.

6. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to claim 1 are implemented.

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