A decentralized distributed node time-frequency phase synchronization method

Abstract

The present invention relates to radar communication technology and discloses a decentralized distributed node time-frequency-phase synchronization method, comprising a time synchronization step: starting from a starting radar site, sending a signal to complete a first round-trip cycle until all radar sites receive and transmit signals twice; each radar site obtains a time synchronization error estimate of signals sent by two adjacent sites, thereby performing time synchronization correction; a frequency and phase synchronization step: starting from the starting radar site, sending a signal carrying a carrier frequency and an initial phase to complete a second round-trip cycle until all radar sites receive and transmit signals carrying the carrier frequency and the initial phase twice; each radar site obtains a carrier frequency estimate and a phase estimate of signals sent from two adjacent sites, uses the carrier frequency estimate as a synchronization frequency, adds two phase estimate values ​​of the two adjacent sites as a synchronization phase, and uses the synchronization frequency and synchronization phase to perform frequency and phase correction.

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, radar technology has continued to advance with advances in electronic hardware and signal processing algorithms. Various new radar systems have emerged, with MIMO radar being a particularly representative example. MIMO radars can be categorized as centralized or distributed. While MIMO radars offer many advantages over traditional radars, synchronization issues between multiple radars can negatively impact the performance of fusion detection. Therefore, it is necessary to study the synchronization issues of distributed radars and their solutions.

[0003] To effectively address the synchronization issue of multiple radars, the magnitude of synchronization errors must be estimated and compensated before the radar system officially begins operation. Therefore, research on radar synchronization error estimation and compensation methods is essential. Existing synchronization methods mostly focus on error analysis and compensation for a single error. However, for distributed radars, time, frequency, and phase synchronization errors coexist and interact with each other. Currently, there is limited research on how to comprehensively compensate for these three errors. Therefore, it is necessary to study the synchronization issues of distributed radars in light of their distribution characteristics and signal form.

[0004] The key to radar synchronization technology is to simulate the radar's operating parameters, then employ appropriate synchronization systems and algorithms to estimate the time, frequency, and phase synchronization errors, and finally compensate for these errors during actual operation. This approach can be addressed by considering factors affecting synchronization in the radar system, such as the impact of different time bases between stations on time synchronization, and the impact of signal transmission distance and carrier frequency errors on frequency and phase synchronization. Alternatively, errors can be estimated and eliminated by leveraging known information about radar base stations, such as the relatively constant distance between stations and the relatively constant magnitude of errors over operating time. This paper combines these two approaches to investigate synchronization error modeling and estimation methods, design a round-trip error synchronization system, and construct a time-frequency-phase estimation and compensation system.

[0005] Synchronization is a traditional yet challenging problem in multi-station radar signal processing. Time synchronization errors include fixed time differences between station time bases and differences in hardware delays during signal transmission and reception. This ultimately leads to deviations in delay ranging during base station measurement. Frequency and phase errors arise from differences in frequency sources between base stations, and the phase of the signal deviates from the initial phase when it propagates to the receiving radar site. While significant progress has been made in theoretical analysis of synchronization issues in China, many application challenges remain to be further studied and addressed. Existing synchronization methods require the designation of a central radar site, with the remaining sites acting as slaves. The central radar site acts as the core controller for time-frequency phase synchronization. This requires bidirectional signal transmission between the central and slave sites to determine the relative synchronization error between them. 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 in view of the situation that the existing synchronization error estimation and compensation require a 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. This method eliminates the need for a central radar site through a round-trip signal path. The relative synchronization error between two radar sites is determined by bidirectional signal transmission between the two radar sites. The first round-trip cycle corrects the time synchronization error, while the second round-trip cycle estimates the carrier frequency and phase difference to achieve frequency-phase synchronization. The method includes 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 a one-way signal transmission starting from the starting radar site, passing through all radar sites, and then returning to the starting radar site, forming a one-way loop; then starting from the starting radar site, the signal is transmitted in the opposite direction, passing through all radar sites, and then returning to the starting radar site, forming a loop in the opposite direction;

[0009] 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 the signal twice. Each radar site obtains the estimated time synchronization error between 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 the signal carrying the carrier frequency and initial phase twice; each radar site obtains the carrier frequency estimate and phase estimate of the signals sent from the two adjacent sites, uses the carrier frequency estimate as the synchronization frequency, and adds the two phase estimates of the two adjacent sites as the synchronization phase. The synchronization frequency and synchronization phase are used to perform frequency and phase correction to achieve frequency and phase synchronization of all radar sites.

[0011] Because this invention targets the estimation and compensation of synchronization issues for fixed base stations, it requires pre-measurement of the errors between each station. Therefore, a decentralized, distributed node time-frequency-phase synchronization method is employed. Each station transmits and receives signals in both clockwise and counterclockwise directions. Using error modeling, the relationship between the signals during the round-trip signal cycle is used to estimate the magnitude of the synchronization error, allowing for subsequent elimination. Compared to existing synchronization methods, this method eliminates the central node, effectively synchronizing time, frequency, and phase, making it highly practical.

[0012] The beneficial effects of the present invention are as follows: through the circular signal transmission and reception link, the need for coordinated control with a certain radar site as the core is eliminated, and the synchronization between stations is taken 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 flowchart 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 phase synchronization error curve remaining 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 of multiple radar stations operating in collaboration at different locations. Through network connectivity and collaborative operation, this technology transcends the single-angle limitations of a single radar, enabling high-precision, all-around monitoring and tracking of targets. Generally, the signal waveforms emitted by such radars must exhibit good orthogonality, enabling the radar to identify the signal's source.

[0020] Synchronization error: This refers to the time, frequency, and phase errors that occur when multiple radars work together due to differences in the time base and frequency sources of each device, as well as the phase deviation of the sampling point from the original signal phase. These errors will cause time 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 and then outputs a narrow pulse after receiving and processing the echo. To achieve the pulse compression effect, the transmitted wide pulse is encoded and processed by a matched filter in the receiver. The advantages of pulse compression radar are a long range and high range resolution.

[0022] The key element of this invention is the construction of a system architecture for bidirectional signal transmission and reception between stations, using a round-trip method. This round-trip signal path eliminates the need for a central radar station, introducing various errors into the signal propagation process, which are then estimated and eliminated using an algorithm. Pulse compression is used to measure time synchronization errors. The first round-trip cycle corrects the time synchronization error; the second round-trip cycle estimates the carrier frequency and phase difference, achieving frequency and phase synchronization.

[0023] The specific embodiments 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. Signals are transmitted clockwise from radar site 1 to radar site K, and counterclockwise from K to 1. For radar site i, its clockwise neighbor is radar site i+1, and its counterclockwise neighbor is radar site i-1. As an exception, radar site K's clockwise neighbor is radar site 1, and its counterclockwise neighbor is radar site K. The round-trip loop path is: starting from radar site 1, proceeding clockwise through radar sites 2, 3, ..., K-1, K, and finally from radar site K to radar site 1, completing the clockwise loop. Then, starting from radar site 1, proceeding counterclockwise through radar sites K, K-1, ..., 3, 2, and finally from radar site 2 to radar site 1, completing the counterclockwise loop, thus completing one round-trip loop. Similarly, a round-trip loop can be completed by first proceeding counterclockwise and then clockwise. Alternatively, a round-trip loop can be completed using the same method, starting from another radar site.

[0025] Figure 2 The figure shows a simple scenario where radar sites are distributed in a ring. In actual scenarios, the round-trip loop path can be arranged based on the ranging results after the ranging between radar sites is completed, and reasonable clockwise and counterclockwise signal receiving and sending paths can be arranged according to the ranging results.

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

[0027] Step 1: K radar stations transmit signals clockwise and counterclockwise in sequence, completing the first round-trip cycle until all radar stations have transmitted and received signals twice. At this point, each radar station obtains an estimated time synchronization error between the signals transmitted by its two neighboring stations, allowing it to perform time synchronization corrections and achieve time synchronization.

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

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

[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 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 between the transmitting station i-1 and the receiving station i, and c is the speed of light.

[0031] The step time synchronization error estimation value is used to perform time 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 transmit signals carrying the carrier frequency and initial phase clockwise and counterclockwise to complete the second round-trip cycle until all radar stations have transmitted and received signals twice. At this point, 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 estimates 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 carrier frequency of the signal and phase estimate

[0034] In clockwise direction, the transmitting station i transmits the carrier frequency ω to the receiving station i+1. c and initial phase The receiving station i+1 obtains the estimated carrier frequency of the signal 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] Carrier frequency estimation is obtained by using Fast Fourier Transform (FFT) after down-converting the received signal; 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, with a certain node as a reference, the sum of the signal propagation distances of other identical nodes in the clockwise and counterclockwise loops is equal, and because the phase error and propagation time have the following relationship:

[0038]

[0039] Where const represents a constant value, cw represents the clockwise direction, and ccw represents the counterclockwise direction. The two summation ranges represent the radar stations through which the signal propagates clockwise and counterclockwise, respectively. Therefore, the sum of the clockwise and counterclockwise phase estimates at each station is theoretically equal. Each station uses this phase sum as the synchronization phase.

[0040] The following is an implementation example. The number of radar stations is set to 3, and 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 approximately 100MHz, and the time width is approximately 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 and the actual error size is as follows: Figure 2 、 3 , as shown in 4. Figure 3 The error angle curve is shown in Figure 1. The error angle curve is shown in Figure 2. The error angle curve is shown in Figure 3. The error angle curve is shown in Figure 4. The error angle curve is shown in Figure 5. The error angle curve is shown in Figure 6. The error angle curve is shown in Figure 7. The error angle curve is shown in Figure 8. The error angle curve is shown in Figure 9. The error angle curve is shown in Figure 1.

[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 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 distributed radar fusion detection 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 a one-way signal transmission starting from the starting radar site, passing through all radar sites, and then returning to the starting radar site, forming a one-way loop; then starting from the starting radar site, the signal is transmitted in the opposite direction, passing through all radar sites, and then returning 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 the signal twice. Each radar site obtains the estimated time synchronization error between 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 the signal carrying the carrier frequency and initial phase twice; each radar site obtains the carrier frequency estimate and phase estimate of the signals sent from the two adjacent sites, uses the carrier frequency estimate as the synchronization frequency, and adds the two phase estimates of the two adjacent sites as the synchronization phase. The synchronization frequency and synchronization phase are used to perform frequency and phase correction to achieve frequency and phase synchronization of all radar sites.

2. The method according to claim 1, wherein: 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, wherein: In the time synchronization step, receiving station i receives the signal from transmitting station i-1, and the time synchronization error estimate is calculated as follows: receiving station i performs pulse compression on the received signal to obtain the time when 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 original value and use the difference as the estimated value of time synchronization error.

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

5. The method according to claim 4, wherein: 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.

Images