High-precision time synchronization method based on Doppler frequency shift

Abstract

The invention discloses a Doppler frequency shift-based high-precision time synchronization method, which comprises the following steps that: a common node sends a time synchronization request message to a time reference node, and when the time reference node receives the time synchronization request message, the time reference node records the time when the time synchronization request message reaches an air interface and estimates the Doppler frequency shift of the time synchronization request message; the time reference node replies a time synchronization response message, and when the common node receives the time synchronization response message replied by the time reference node, the time when the time synchronization response message reaches an air interface is recorded, and meanwhile, the Doppler frequency shift of the time synchronization response message is estimated; and the common node solves the time synchronization error between the common node and the time reference node by using the Doppler frequency shift of the time synchronization request message and the time synchronization response message and the transmission delay of the time synchronization request message and the time synchronization response message, thereby realizing time synchronization. The problem of asymmetry of message propagation paths is solved, and the time synchronization precision of the mobile ad hoc network is improved.

Description

Technical Field

[0001] The present application belongs to the field of wireless self-organizing network management and control technology, and in particular, relates to a high-precision time synchronization method based on Doppler frequency shift. Background Art

[0002] Time synchronization is the basis for efficient operation of wireless self-organizing networks, and is also an important means to improve network performance, ensure service quality, enhance security and promote efficient management. In recent years, with the development of distributed service applications in wireless self-organizing networks such as data fusion, deterministic scheduling and power allocation, the role of time synchronization in ensuring data consistency, distributed computing and collaboration has become increasingly prominent. For example, time synchronization ensures the consistency of event records and data packet timestamps in the network, which is crucial for applications that require accurate time information, such as environmental monitoring in sensor networks, positioning and tracking in military applications, etc. In application scenarios involving multiple nodes working together, such as distributed database updates or parallel computing, time synchronization is the basis for ensuring the smooth and correct execution of tasks.

[0003] Experts and scholars have proposed a variety of time synchronization protocols for wireless self-organizing network time synchronization. The earliest time synchronization protocol can be traced back to the Network Time Synchronization Protocol (NTP) proposed in 1985. This protocol belongs to the application layer protocol. Two nodes that need to be synchronized exchange time-stamped time synchronization messages, and use the forward and reverse timestamp message transmission delay difference to calculate the time synchronization error of the two nodes. However, since the NTP protocol timestamp is injected by the protocol layer, the message transmission delay is affected by multiple factors such as message processing delay, queuing delay, access delay, and physical layer processing delay, resulting in poor time synchronization accuracy of the NTP protocol, which can only achieve ms-level synchronization accuracy.

[0004] In order to eliminate protocol stack processing delays such as message processing delay, queuing delay and access delay, the IEEE organization proposed the Precision Time Synchronization (PTP) protocol - IEEE PTPv2 in 2002. Although this protocol belongs to the application layer protocol, it can achieve us-level time synchronization accuracy by injecting hardware timestamps at the physical layer and eliminating protocol stack processing delays. However, in highly dynamic scenarios, there is a problem of asymmetric propagation paths, which will greatly reduce the time synchronization accuracy of IEEE PTPv2.

[0005] The above NTP protocol and IEEE PTPv2 protocol both assume that the bidirectional propagation path is symmetrical, that is, the forward propagation delay and the reverse propagation delay are equal. However, in mobile wireless ad hoc networks, the movement of nodes causes the bidirectional propagation delay to be asymmetric, which greatly reduces the time synchronization accuracy of the NTP protocol and the IEEE PTPv2 protocol.

[0006] In order to solve the problem of poor time synchronization accuracy caused by the asymmetric propagation path in the wireless two-way time synchronization protocol, Japanese experts proposed the wireless two-way interference time synchronization (Wi-Wi) protocol in 2017. This protocol uses low-frequency wireless channels to exchange time synchronization protocol messages and calculate the time synchronization error of two nodes through the phase difference of forward and reverse message propagation. In theory, this protocol can achieve ps-level synchronization accuracy. However, the Wi-Wi protocol based on the phase information of the RF signal has the following problems that seriously affect its time synchronization accuracy: first, the phase ambiguity problem, that is, the phase difference has multiple possibilities of Δφ+2kπ, k=0,1,…; second, the poor anti-interference performance, that is, the phase estimation accuracy of the wireless RF signal is poor due to the influence of the interference signal. Summary of the invention

[0007] The purpose of this application is to provide a high-precision time synchronization method based on Doppler frequency shift, which uses the Doppler frequency domain of the two-way time synchronization signal to estimate the two-way radio frequency signal propagation delay difference caused by the relative motion of the nodes, solve the problem of poor time synchronization accuracy caused by the asymmetry of the propagation path of the two-way time synchronization protocol message, and improve the time synchronization accuracy of the high-mobility wireless self-organizing network.

[0008] The purpose of this application is achieved through the following technical solutions:

[0009] A high-precision time synchronization method based on Doppler frequency shift, the time synchronization method comprising:

[0010] S1: The common node sends a time synchronization request message to the time reference node. When the time reference node receives the time synchronization request message, it records the time when the time synchronization request message arrives at the air interface and estimates the Doppler frequency shift of the time synchronization request message.

[0011] S2: The time reference node replies with a time synchronization response message. When the common node receives the time synchronization response message replied by the time reference node, it records the time when the time synchronization response message arrives at the air interface and estimates the Doppler frequency shift of the time synchronization response message.

[0012] S3: Ordinary nodes use the Doppler frequency shift of time synchronization request messages and time synchronization response messages and the transmission delay of time synchronization request messages and time synchronization response messages to solve the time synchronization error between ordinary nodes and time reference nodes, thereby achieving time synchronization.

[0013] According to a preferred embodiment, in step S1, the time synchronization request message sent by the common node includes: the common node address, the time synchronization request message sequence number and the sending timestamp t1;

[0014] Ordinary nodes use physical layer hardware timestamping to inject the sending timestamp t1 into the time synchronization request message.

[0015] According to a preferred embodiment, in step S1, after the time reference node detects the radio frequency signal sent to the node,

[0016] First, the physical layer hardware is used to mark the time t2 when the corresponding RF signal arrives at the time reference node air interface, and the signal detection algorithm is used to estimate the Doppler frequency shift Δf of the corresponding signal. R ,

[0017] Then, the common node calculates the time t2 and Doppler frequency shift Δf of the RF signal arriving at the time reference node air interface. R and the message body are uploaded to the protocol stack.

[0018] According to a preferred embodiment, in step S2, the time synchronization response message replied by the time reference node includes: the common node address, the time synchronization request message sequence number, the time synchronization request message sequence number arrival time t2, the time synchronization request message Doppler frequency shift Δf R , time synchronization response message sending timestamp t3;

[0019] Furthermore, the sending timestamp of the time synchronization response message is injected by the physical layer hardware of the time reference node.

[0020] According to a preferred embodiment, in step S2, after a common node detects a radio frequency signal sent to the node,

[0021] First, the physical layer hardware is used to mark the time t4 when the RF signal arrives at the time reference node air interface, and the signal detection algorithm is used to estimate the Doppler frequency shift Δf of the corresponding RF signal. A ,

[0022] Then, the common node calculates the time t4 and Doppler frequency shift Δf of the RF signal arriving at the time reference node air interface. A and the message body are uploaded to the protocol stack.

[0023] According to a preferred embodiment, step S3 also includes: when the common node protocol stack receives the time synchronization response message, it performs a message legitimacy check. If the detection is consistent with the information maintained by this node, the legitimacy check passes; otherwise, the message is discarded.

[0024] According to a preferred embodiment, performing message legitimacy verification includes: detecting whether the common node address is consistent with the address of the current node, and whether the sequence number of the replied time synchronization request message is consistent with the sequence number of the time synchronization request message most recently sent by the current node;

[0025] According to a preferred embodiment, after the time synchronization response message passes the validity check,

[0026] Ordinary nodes parse the time synchronization response message to obtain the arrival time t2 of the time synchronization request message at the time reference node and the Doppler frequency shift Δf of the time synchronization request message. R , time synchronization response message sending time t3;

[0027] Combined with the time synchronization request message sending time t1 and the time synchronization request message transmission frequency f R , the time t4 of the time synchronization response radio frequency signal arriving at the time reference node air interface, the frequency f of the time synchronization response radio frequency signal A , you can get the time synchronization error between the common node and the time reference node.

[0028] According to a preferred embodiment, the time synchronization error between the common node and the time reference node is calculated by the following formula:

[0029]

[0030] Among them, T1(R) and T2(R) represent the signal processing delay of the time synchronization request message sending end and the signal processing delay of the receiving end; T1(A) and T2(A) represent the signal processing delay of the time synchronization response message sending end and the signal processing delay of the receiving end.

[0031] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application. After understanding the scheme of the present application, those skilled in the art can understand that there are multiple combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here.

[0032] Beneficial effects of this application:

[0033] The high-precision time synchronization method based on Doppler frequency shift proposed in the present invention can effectively solve the problem of asymmetric message propagation paths, improve the time synchronization accuracy of mobile self-organizing networks, and achieve ns-level synchronization accuracy under high mobility conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a principle diagram of a high-precision time synchronization method based on Doppler frequency shift proposed by the present invention.

[0035] Figure 2 3 is a schematic diagram of time synchronization performance of the high-precision time synchronization method based on Doppler frequency shift proposed by the present invention when the Doppler frequency shift estimation error is 0 Hz;

[0036] Figure 3 1 is a schematic diagram of time synchronization performance of the high-precision time synchronization method based on Doppler frequency shift proposed by the present invention when the Doppler frequency shift estimation error is 250Hz;

[0037] Figure 4 It is a schematic diagram of the relationship between Doppler frequency shift estimation error and time synchronization accuracy when the present invention is used. DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0039] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0040] The present application discloses a high-precision time synchronization method based on Doppler frequency shift, and the time synchronization method comprises the following steps.

[0041] Step S1: The common node sends a time synchronization request message to the time reference node. When the time reference node receives the time synchronization request message, it records the time when the time synchronization request message arrives at the air interface and estimates the Doppler frequency shift of the time synchronization request message.

[0042] Preferably, in step S1, the time synchronization request message sent by the common node includes: the common node address, the time synchronization request message sequence number and the sending timestamp t1; the common node injects the sending timestamp t1 into the time synchronization request message by means of physical layer hardware timestamping.

[0043] Preferably, in step S1, after the time reference node detects the radio frequency signal sent to the node, it first uses the physical layer hardware to mark the time t2 when the corresponding radio frequency signal arrives at the air interface of the time reference node, and uses the signal detection algorithm to estimate the Doppler frequency shift Δf of the corresponding signal. R Then, the common node calculates the time t2 and Doppler frequency shift Δf of the RF signal arriving at the time reference node air interface. R and the message body are uploaded to the protocol stack.

[0044] Step S2: The time reference node replies with a time synchronization response message. When the common node receives the time synchronization response message replied by the time reference node, it records the time when the time synchronization response message arrives at the air interface and estimates the Doppler frequency shift of the time synchronization response message.

[0045] Preferably, in step S2, the time synchronization response message replied by the time reference node includes: the common node address, the time synchronization request message sequence number, the time synchronization request message sequence number arrival time t2, the time synchronization request message Doppler frequency shift Δf R , the time synchronization response message sending timestamp t3; and, the sending timestamp of the time synchronization response message is injected by the physical layer hardware of the time reference node.

[0046] Preferably, in step S2, after the common node detects the radio frequency signal sent to the node, it first uses the physical layer hardware to mark the time t4 when the radio frequency signal arrives at the air interface of the time reference node, and uses the signal detection algorithm to estimate the Doppler frequency shift Δf of the corresponding radio frequency signal. A Then, the common node calculates the time t4 and Doppler frequency shift Δf of the RF signal arriving at the time reference node air interface. A and the message body are uploaded to the protocol stack.

[0047] Step S3: The common node uses the Doppler frequency shift of the time synchronization request message and the time synchronization response message and the transmission delay of the time synchronization request message and the time synchronization response message to solve the time synchronization error between the common node and the time reference node, thereby achieving time synchronization.

[0048] Preferably, step S3 also includes: after the common node protocol stack receives the time synchronization response message, it performs a message legitimacy check. If the detection is consistent with the information maintained by the node, the legitimacy check passes; otherwise, the message is discarded.

[0049] Furthermore, the message validity check includes: checking whether the common node address is consistent with the address of the current node, and whether the sequence number of the time synchronization request message replied is consistent with the sequence number of the time synchronization request message most recently sent by the current node;

[0050] Preferably, when the time synchronization response message passes the validity check,

[0051] Ordinary nodes parse the time synchronization response message to obtain the arrival time t2 of the time synchronization request message at the time reference node and the Doppler frequency shift Δf of the time synchronization request message. R , time synchronization response message sending time t3;

[0052] Combined with the time synchronization request message sending time t1 and the time synchronization request message transmission frequency f R , the time t4 of the time synchronization response radio frequency signal arriving at the time reference node air interface, the frequency f of the time synchronization response radio frequency signal A , you can get the time synchronization error between the common node and the time reference node.

[0053] Specifically, ordinary nodes can calculate the transmission delay Δt of RTT-R message and RTT-A R and Δt A :

[0054] Δt R =t2-t1=T1(R)+T2(R)+T Rp -δ

[0055] Δt A =t4-t3=T1(A)+T2(A)+T Ap +δ

[0056] Where, T1(R) and T1(A) are the signal processing delays of the RTT-R message and RTT-A message sender, T2(R) and T2(A) are the signal processing delays of the RTT-R message and RTT-A message receiver, T Rp and T Ap Indicates the air propagation delay of RTT-R and RTT-A messages.

[0057] Then, the common node can obtain the time synchronization error between itself and the time reference node by the following method.

[0058] Let L represent the distance between the common node and the time reference node at a given moment, and L1 represent the relative moving distance between the common node and the time reference node during the transmission of the RTT-R radio frequency signal. Then, the following equation can be obtained:

[0059]

[0060] L=[Δt R -T1(R)-T2(R)+δ]×c+L1 (1)

[0061] In the above two formulas, c represents the speed of light, f R Indicates the carrier frequency of the RTT-R radio frequency signal, which is known to the transmitter and receiver. R -T1(R)-T2(R)+δ]×c represents the propagation distance of RTT-R radio frequency signal; It indicates the relative moving speed between the common node and the time reference node at the time t2 when the RTT-R signal is received. Since the propagation time of the RF signal is short (usually in the order of ms), it can be considered that the relative moving speed between the two nodes remains unchanged during the propagation of the RF signal.

[0062] Let L2 represent the relative motion distance between the common node and the time reference node from the time t2 when the time reference node detects the RTT-R radio frequency signal to the time t3 when the time reference node replies with the RTT-A message.

[0063]

[0064] In the above formula It represents the relative moving speed between the common node and the time reference node at the time t4 when the RTT-A signal is received. Similarly, since the radio frequency signal propagation time in the air is short, it can be considered that the relative moving speed between the common node and the time reference node at the time t3 when the RTT-A message is sent is also v A .at this time It represents the average relative moving speed between the common node and the time reference node from t2 to t3.

[0065] Let L2 represent the relative moving distance between the common node and the time reference node during the RTT-A message transmission process, then we can get:

[0066]

[0067] L=(Δt A -T1(A)-T2(A)-δ)×c+L1+L2+L3 (2)

[0068] Combining equation (1) and equation (2), we can get:

[0069] [Δt R -T1(R)-T2(R)+δ]×c+L1=(Δt A -T1(A)-T2(A)-δ)×c+L1+L2+L3

[0070] Simplifying the above formula, the time error between the common node and the time reference node is:

[0071]

[0072] If the physical layer of the common node and the time reference node adopts the same bit rate, adjustment style, hardware clock frequency and signal processing architecture, it can be considered that T1(A)+T2(A)=T1(R)+T2(R), and the above formula can be simplified to:

[0073]

[0074] Otherwise, it is necessary to measure the processing delay when the physical layer signals of the ordinary node and the time reference node send and receive radio frequency signals for compensation.

[0075] Example 1

[0076] It is assumed that ordinary nodes and time reference nodes use the same physical layer signal processing architecture.

[0077] See also Figure 1,To achieve precise time synchronization, the ordinary node sends a time synchronization request (RTT-R) message to the time reference node, ,which contains the ordinary node address, the RTT-R message sequence number and the ,sending timestamp t1, where the RTT-R sending timestamp t1 of the ordinary ,node is injected by the underlying physical layer hardware.

[0078] After the time reference node receives the RTT-R message sent by the ordinary node, it records the message arrival time t2 when the signal is detected and estimates the signal Doppler frequency shift Δf R , and the message body is combined with the message arrival time t2 and the RF signal Doppler frequency shift Δf R Upload them to the time synchronization module together.

[0079] See also Figure 1 The time synchronization module of the time reference node parses the RTT-R message, obtains the common node address and RTT-R message sequence number, and then uses the same modulation mode and code rate as the RTT-R message to reply the RTT-A message, which contains the common node address, RTT-R message sequence number, RTT-R message arrival time t2, and RTT-R radio frequency signal Doppler frequency shift Δf R , RTT-A message sending timestamp t3, where the RTT-A message sending timestamp t3 is injected by the physical layer hardware of the time reference node.

[0080] When a common node receives the RTT-A message, it records the message arrival time t3 when it detects the signal and estimates the signal Doppler frequency shift Δf A , and the message body is combined with the message arrival time t3 and the RF signal Doppler frequency shift Δf A Upload them to the time synchronization module together.

[0081] The common node time synchronization module parses the RTT-A message and performs a validity check based on the common node address and RTT-R message sequence number in the RTT-A message. If both of the above items are consistent with the information maintained by this node, the validity check passes; otherwise, the message is discarded.

[0082] At this point, the common node can obtain the RTT-R message arrival time t2 and the RTT-R signal Doppler frequency shift Δf R , RTT-A message sending time t3. Combined with RTT-R message sending time t1 and RTT-R message transmission frequency f R , RTT-A RF signal TOA time t4, RTT-A RF signal frequency f A And other information.

[0083] Assuming that the common node and the time reference node use the same bit rate, adjustment style, hardware clock frequency and signal processing architecture, so T1(A)+T2(A)=T1(R)+T2(R), the common node can use the following formula to calculate the time error between itself and the time reference node.

[0084]

[0085] See also Figure 2 and Figure 3 , compare the high-precision time synchronization scheme based on Doppler frequency shift proposed in the present invention with the existing time synchronization method that does not use motion error compensation.

[0086] See also Figure 2 and Figure 3 , the existing time synchronization method without motion error compensation has a linear growth of time synchronization error as the relative moving speed of the nodes increases, while the high-precision time synchronization scheme based on Doppler frequency shift proposed in the present invention does not change with the change of the relative moving speed between nodes. In particular, when the Doppler frequency shift estimation error is 0Hz, the high-precision time synchronization method based on Doppler frequency shift proposed in the present invention can achieve zero-error time synchronization.

[0087] See also Figure 4 The time synchronization error of the high-precision time synchronization scheme based on Doppler frequency shift proposed in the present invention is linearly related to the Doppler frequency domain estimation error. The time synchronization error δ is linearly related to the Doppler frequency shift estimation error Δf d The numerical relationship is about δ = 0.004672 × Δf d .

[0088] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A high-precision time synchronization method based on Doppler frequency shift, characterized in that: The time synchronization method comprises: S1: The common node sends a time synchronization request message to the time reference node. When the time reference node receives the time synchronization request message, it records the time when the time synchronization request message arrives at the air interface and estimates the Doppler frequency shift of the time synchronization request message. S2: The time reference node replies with a time synchronization response message. When the common node receives the time synchronization response message replied by the time reference node, it records the time when the time synchronization response message arrives at the air interface and estimates the Doppler frequency shift of the time synchronization response message. S3: Ordinary nodes use the Doppler frequency shift of time synchronization request messages and time synchronization response messages and the transmission delay of time synchronization request messages and time synchronization response messages to solve the time synchronization error between ordinary nodes and time reference nodes, thereby achieving time synchronization.

2. The time synchronization method according to claim 1, characterized in that: In step S1, the time synchronization request message sent by the common node includes: the common node address, the time synchronization request message sequence number and the sending timestamp t1; Ordinary nodes use physical layer hardware timestamping to inject the sending timestamp t1 into the time synchronization request message.

3. The time synchronization method according to claim 1, characterized in that: In step S1, when the time reference node detects the radio frequency signal sent to the node, First, the physical layer hardware is used to mark the time t2 when the corresponding RF signal arrives at the time reference node air interface, and the signal detection algorithm is used to estimate the Doppler frequency shift Δf of the corresponding signal. R , Then, the common node calculates the time t2 and Doppler frequency shift Δf of the RF signal arriving at the time reference node air interface. R and the message body are uploaded to the protocol stack.

4. The time synchronization method according to claim 1, characterized in that: In step S2, the time synchronization response message replied by the time reference node includes: the common node address, the time synchronization request message sequence number, the time synchronization request message sequence number arrival time t2, the time synchronization request message Doppler frequency shift Δf R , time synchronization response message sending timestamp t3; Furthermore, the sending timestamp of the time synchronization response message is injected by the physical layer hardware of the time reference node.

5. The time synchronization method according to claim 1, characterized in that: In step S2, when a common node detects a radio frequency signal sent to the node, First, the physical layer hardware is used to mark the time t4 when the RF signal arrives at the time reference node air interface, and the signal detection algorithm is used to estimate the Doppler frequency shift Δf of the corresponding RF signal. A , Then, the common node calculates the time t4 and Doppler frequency shift Δf of the RF signal arriving at the time reference node air interface. A and the message body are uploaded to the protocol stack.

6. The time synchronization method according to claim 1, characterized in that: Step S3 also includes: when the common node protocol stack receives the time synchronization response message, it performs a message legitimacy check. If the detection is consistent with the information maintained by this node, the legitimacy check passes; otherwise, the message is discarded.

7. The time synchronization method according to claim 6, characterized in that: The message validity check includes: checking whether the common node address is consistent with the address of the current node, and whether the sequence number of the replied time synchronization request message is consistent with the sequence number of the time synchronization request message most recently sent by the current node.

8. The time synchronization method according to claim 6, characterized in that: When the time synchronization response message passes the validity check, Ordinary nodes parse the time synchronization response message to obtain the arrival time t2 of the time synchronization request message at the time reference node and the Doppler frequency shift Δf of the time synchronization request message. R , time synchronization response message sending time t3; Combined with the time synchronization request message sending time t1 and the time synchronization request message transmission frequency f R , the time t4 of the time synchronization response radio frequency signal arriving at the time reference node air interface, the frequency f of the time synchronization response radio frequency signal A , you can get the time synchronization error between the common node and the time reference node.

9. The time synchronization method according to claim 8, characterized in that: The time synchronization error between the common node and the time reference node is calculated by the following formula: Among them, T1(R) and T2(R) represent the signal processing delay of the time synchronization request message sending end and the signal processing delay of the receiving end; T1(A) and T2(A) represent the signal processing delay of the time synchronization response message sending end and the signal processing delay of the receiving end.

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