Narrowband communication time synchronization method and system

Abstract

The invention relates to the technical field of communication, in particular to a narrowband communication time synchronization method and system. The method is applied to a narrowband communication system comprising a time synchronization initiating end and at least one time synchronization receiving end, and comprises the following steps: the time synchronization initiating end measures and stores independent unidirectional transmission delay for each time synchronization receiving end by performing bidirectional message interaction with the at least one time synchronization receiving end; the time synchronization initiating end periodically broadcasts and sends a time synchronization broadcast frame, the time synchronization broadcast frame comprises compensation time information for the at least one time synchronization receiving end, and the compensation time information is generated based on the local time of the time synchronization initiating end and the corresponding independent one-way transmission delay; and the at least one time synchronization receiving end receives the time synchronization broadcast frame, extracts respective compensation time information, and adjusts the local time according to the compensation time information. The method can realize accurate time synchronization, and has the characteristics of high precision and strong applicability.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a method and system for narrowband communication time synchronization. Background Technology

[0002] In multi-point distributed measurement and control automation applications, the system requires extremely high time synchronization accuracy for the communication system. Therefore, the communication system needs to solve the problem of accurate time synchronization between the transmitting and receiving ends. Satellite system synchronization schemes (BeiDou, GPS, etc.) are greatly affected by weather, region, environment, and mission factors, and their reliability cannot be guaranteed. Rubidium atomic clocks can only keep time, not achieve network-wide time synchronization, and their cost is very high. In power systems, SDH (Synchronous Digital Hierarchy) fiber optic channels are widely used for time synchronization. Broadband communication systems use the Ethernet communication protocol at the application layer, and through the PTP (Precise Time Protocol), a high-precision time synchronization mechanism and message interaction processing are used to achieve sub-microsecond accurate time synchronization between the transmitting and receiving ends through hardware and software cooperation. In the PTP protocol, the message sending rate directly affects the synchronization accuracy. Increasing the sending rate of the PTP protocol's Sync and Delay_Req messages helps to calibrate the clock more frequently, thereby obtaining higher clock accuracy, which can usually reach the sub-microsecond level. Sync and Delay_Req are typically tens to over a hundred bytes, and increasing them to 64 times per second would estimate bandwidth usage at around 100kbps. However, in application scenarios such as multi-point distributed measurement and control automation, communication bandwidth is only in the tens of kbps range, which is considered narrowband communication. Due to bandwidth limitations, it cannot support Ethernet protocols, thus preventing precise time synchronization.

[0003] In summary, how to design a time synchronization method suitable for narrowband communication to address this challenge is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] Therefore, it is necessary to provide a narrowband communication time synchronization method and system that can achieve precise time synchronization, which has the characteristics of high precision and strong applicability, to address the above-mentioned technical problems.

[0005] To achieve the above-mentioned objectives of this invention, the technical solution adopted is as follows: A narrowband communication time synchronization method, applied to a narrowband communication system including a time synchronization initiator and at least one time synchronization receiver, includes the following steps: The time synchronization initiator interacts bidirectionally with the at least one time synchronization receiver to measure and store the independent one-way transmission delay for each time synchronization receiver. ; The time synchronization initiator periodically broadcasts time synchronization broadcast frames, each containing compensation time information for the at least one time synchronization receiver. The compensation time information is based on the local time of the time synchronization initiator and the corresponding independent one-way transmission delay. generate; The at least one time synchronization receiver receives the time synchronization broadcast frame, extracts its own compensation time information, and adjusts its local time accordingly.

[0006] Preferably, the time synchronization initiator measures the unidirectional transmission delay. The steps include: The time synchronization initiator broadcasts the first time synchronization frame to the time synchronization receiver and records the first transmission time T0 through FPGA hardware logic. After receiving the first time synchronization frame, the time synchronization receiver immediately replies with a response data frame through FPGA hardware logic; The time synchronization initiator receives the response data frame and records the first reception time T1 through FPGA hardware logic, and calculates the one-way transmission delay. The records for T0 and T1 are both implemented by latching a hardware timestamp when a valid edge of the frame start signal is detected at the physical layer or MAC layer of the communication interface.

[0007] Furthermore, the FPGA hardware logic integrates a free-running counter to generate the hardware timestamp; the clock source of the free-running counter is 50 MHz, and the resolution is 20 ns.

[0008] Furthermore, both the compensation time information and the local time adopt a format combining coarse and fine scales; the coarse scale is used to represent the number of milliseconds since the start time, and the fine scale is generated by dividing the clock of the coarse scale by 64kHz, with the smallest scale being 1 / 64 microsecond.

[0009] Furthermore, the format of the time synchronization broadcast frame includes: a coarse scale high-order field common to all time synchronization receivers; and at least one site-specific compensation field, each of which corresponds to a specific time synchronization receiver and includes coarse scale low-order and fine scale for that time synchronization receiver, the coarse scale low-order and fine scale together constituting the independent one-way transmission delay. The generated compensation time information.

[0010] Furthermore, the steps for the time-synchronization receiver to adjust its local time include: Calculate the difference between the compensated time information and the local time of the time synchronization receiver. ; A maximum adjustment step is preset; Determine the difference Is the absolute value less than the maximum adjustment step? If so, adjust the local time to the correct position all at once; If not, then the difference will be... If it is considered abnormal, no adjustments will be made for the time being, and multiple judgments will be made based on the timing information of subsequent cycles.

[0011] Furthermore, the maximum adjustment step is calculated and determined based on the maximum relative frequency deviation of the quartz crystal oscillators of the time synchronization initiator and the time synchronization receiver, which is 40ppm, and the transmission period of the time synchronization broadcast frame, which is 2s.

[0012] Furthermore, the narrowband communication specifically refers to a wireless or wired serial link with a physical layer data rate of less than or equal to 64 kbps and which does not support Ethernet frame structure or UDP / IP protocol stack.

[0013] A narrowband communication precise time synchronization system is applied to a narrowband communication system including a time synchronization initiator and at least one time synchronization receiver, comprising a bidirectional message exchange module, a time compensation module, and a local time adjustment module; The bidirectional message interaction module is used to control the time synchronization initiator to perform bidirectional message interaction with at least one time synchronization receiver, and to measure and store the independent one-way transmission delay for each time synchronization receiver. ; The time compensation module is used to control the time synchronization initiator to periodically broadcast time synchronization broadcast frames. Each time synchronization broadcast frame contains compensation time information for the at least one time synchronization receiver. The compensation time information is based on the local time of the time synchronization initiator and the corresponding independent one-way transmission delay. generate; The local time adjustment module is used to control the at least one time synchronization receiver to receive the time synchronization broadcast frame, extract their respective compensation time information, and adjust their local time accordingly.

[0014] Preferably, the time synchronization initiator includes a first FPGA, which is configured to record a first transmission time T0 and a first reception time T1 by latching an internal counter during the bidirectional message interaction; the at least one time synchronization receiver includes a second FPGA, which is configured to immediately reply with a response data frame after receiving a time synchronization frame from the time synchronization initiator during the bidirectional message interaction.

[0015] The beneficial effects of this invention are as follows: This invention provides a narrowband communication time synchronization method that involves bidirectional interaction between the time synchronization initiator and each time synchronization receiver to measure and store the independent one-way transmission delay for each receiver. Furthermore, in subsequent periodically broadcast time synchronization frames, each receiver's unique compensation time information is packaged. This solves the problems of traditional one-way broadcast time synchronization failing to compensate for delays, or the PTP protocol being unable to operate on narrowband links. This invention effectively eliminates synchronization accuracy differences caused by varying communication distances between stations, transmission link lengths, and even low-speed movement within stations. This invention also sends time synchronization information to all receivers in a single broadcast operation, and each receiver only needs to extract its own compensation information to complete the adjustment. This mechanism integrates independent compensation information for multiple nodes into a single broadcast, resulting in high synchronization efficiency and significantly saving communication bandwidth. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating a narrowband communication time synchronization method in one embodiment; Figure 2 This is a schematic diagram of the precise synchronization process in narrowband communication in one embodiment; Figure 3 This is a schematic diagram of the time synchronization frame format broadcast by the transmitting end in one embodiment. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] Example 1 like Figure 1 As shown, a narrowband communication time synchronization method is applied to a narrowband communication system including a time synchronization initiator and at least one time synchronization receiver, comprising the following steps: The time synchronization initiator interacts bidirectionally with the at least one time synchronization receiver to measure and store the independent one-way transmission delay for each time synchronization receiver. ; The time synchronization initiator periodically broadcasts time synchronization broadcast frames, each containing compensation time information for the at least one time synchronization receiver. The compensation time information is based on the local time of the time synchronization initiator and the corresponding independent one-way transmission delay. generate; The at least one time synchronization receiver receives the time synchronization broadcast frame, extracts its own compensation time information, and adjusts its local time accordingly.

[0019] This invention designs a narrowband communication precise time synchronization method. This method has accurate time synchronization, low bandwidth overhead, and can achieve point-to-point or point-to-multipoint time synchronization without relying on the Ethernet protocol. Compared with the traditional one-way broadcast time synchronization method, the time synchronization accuracy can be improved from milliseconds to sub-microseconds. It can be applied to multi-point distributed measurement, measurement and control automation or related scenarios, ensuring measurement accuracy and significantly improving the accuracy of automatic control.

[0020] In one specific embodiment, such as Figure 2 As shown, the time synchronization initiator measures the one-way transmission delay. The steps include: The time synchronization initiator broadcasts the first time synchronization frame to the time synchronization receiver and records the first transmission time T0 through FPGA hardware logic. After receiving the first time synchronization frame, the time synchronization receiver immediately replies with a response data frame through FPGA hardware logic; The time synchronization initiator receives the response data frame and records the first reception time T1 through FPGA hardware logic, and calculates the one-way transmission delay. The records for T0 and T1 are both implemented by latching a hardware timestamp when a valid edge of the frame start signal is detected at the physical layer or MAC layer of the communication interface.

[0021] In one specific embodiment, the FPGA hardware logic integrates a free-running counter for generating the hardware timestamp; the clock source of the free-running counter is 50 MHz, and the resolution is 20 ns.

[0022] In one specific embodiment, both the compensation time information and the local time adopt a format combining coarse and fine scales; the coarse scale is used to represent the number of milliseconds since the start time, and the fine scale is generated by dividing the clock of the coarse scale by 64kHz, with the smallest scale being 1 / 64 microsecond.

[0023] In one specific embodiment, the format of the time synchronization broadcast frame includes: a coarse scale high-order field common to all time synchronization receivers; and at least one site-specific compensation field, each of the site-specific compensation fields corresponding to a specific time synchronization receiver and including coarse scale low-order and fine scale for that time synchronization receiver, the coarse scale low-order and fine scale together constituting the independent one-way transmission delay. The generated compensation time information.

[0024] In one specific embodiment, the step of adjusting its local time at the time synchronization receiver includes: Calculate the difference between the compensated time information and the local time of the time synchronization receiver. ; A maximum adjustment step is preset; Determine the difference Is the absolute value less than the maximum adjustment step? If so, adjust the local time to the correct position all at once; If not, then the difference will be... If it is considered abnormal, no adjustments will be made for the time being, and multiple judgments will be made based on the timing information of subsequent cycles.

[0025] In one specific embodiment, the maximum adjustment step is calculated and determined based on the maximum relative frequency deviation of the quartz crystal oscillators of the time synchronization initiator and the time synchronization receiver (40ppm) and the transmission period of the time synchronization broadcast frame (2s).

[0026] In one specific embodiment, the narrowband communication is a wireless or wired serial link with a physical layer data rate of less than or equal to 64 kbps and which does not support Ethernet frame structure or UDP / IP protocol stack.

[0027] Example 2 More specifically, the time synchronization initiator, through bidirectional message interaction with the at least one time synchronization receiver, measures and stores the independent one-way transmission delay for each time synchronization receiver. To achieve precise synchronization, the time synchronization initiator must first obtain the independent one-way transmission delay between itself and each time synchronization receiver. This delay may vary between different receiving ends due to differences in communication distance and link characteristics.

[0028] In a preferred embodiment, delay The measurement process is as follows: The time synchronization initiator broadcasts a first time synchronization frame (or delay measurement request frame) to all time synchronization receivers.

[0029] The time synchronization initiator incorporates a first FPGA hardware logic. When the first time synchronization frame is transmitted, the first FPGA immediately latches its internal hardware timestamp upon detecting the first valid edge of the frame start signal, recording it as the first transmission time T0. This process is completed at the physical layer or MAC layer, avoiding time jitter introduced by CPU polling or driver layer interrupt responses.

[0030] The time synchronization receiver has a built-in second FPGA hardware logic. After receiving the first time synchronization frame, the second FPGA immediately replies with an acknowledgment data frame (without CPU intervention).

[0031] When the first FPGA at the time synchronization initiator receives the response data frame, it also latches the hardware timestamp when it detects the start edge of the frame, which is recorded as the first reception time T1.

[0032] The time synchronization initiator calculates the loopback time based on T0 and T1, and assumes that the uplink and downlink communication systems are symmetrical, thereby calculating the one-way transmission delay. .

[0033] The time synchronization initiator performs the above process once for each time synchronization receiver (or distinguishes different responses by address), thereby measuring and storing the independent time synchronization data for each receiver. value.

[0034] To achieve high-precision time synchronization, the configuration used in this embodiment is as follows: FPGA Timestamp Hardware: Both the time synchronization initiator and receiver FPGAs integrate a 64-bit free-running counter. The clock source for this counter is, for example, 50 MHz, which allows for a time resolution of up to 20 ns, providing the hardware foundation for sub-microsecond synchronization. T0 and T1 are the latch values ​​for this counter.

[0035] Time format: In order to simultaneously meet the requirements of long period time range and nanosecond-level precision, all local time or compensated time information adopts a format that combines coarse and fine scales.

[0036] Coarse scale: For example, using 6 bytes to represent the number of milliseconds since a certain agreed start time (such as January 1, 2000, 00:00:00). 6 bytes can satisfy the use of more than 1000 years without exceeding the limit.

[0037] Fine scale: Generated by dividing a coarse scale clock (e.g., 1ms) by 64k, with a minimum scale of 1 / 64 microsecond (approximately 15.625 ns), matching the 20 ns resolution of the FPGA.

[0038] In this embodiment, the periodic synchronous broadcast is implemented as follows: The time synchronization initiator periodically initiates time synchronization, for example, by setting a synchronization period of 2 seconds.

[0039] In each synchronization cycle, the time synchronization initiator assembles a time synchronization broadcast frame. The design of this broadcast frame is key to achieving the "independent compensation" and "low bandwidth consumption" of this invention.

[0040] like Figure 3 As shown, the format of this time synchronization broadcast frame includes: Synchronization header and checksum: used for frame delimitation and error checking. Coarse scale high bits (common): the high-order part of the 6-byte coarse scale, identical to all receivers, representing the main body of the current time. At least one station-specific compensation field: if there are N time synchronization receivers in the system, the broadcast frame can contain N (or M, M...) compensation fields. N) Compensation Fields. Each compensation field corresponds to a specific time synchronization receiver (e.g., distinguished by address index or pre-allocated slot). This "site-specific compensation field" contains a "coarse scale low bit" and a "fine scale" for that specific receiver. The time value composed of these two fields, i.e., the "compensated time information," is based on the current local time of the time synchronization initiator, plus the receiver-specific one-way transmission delay measured in step one. And generated.

[0041] In this embodiment, if the current time of the initiator is The compensation time to be sent to receiver i The initiator will The scale is split into coarse low-order and fine scale, and then filled into the corresponding dedicated fields.

[0042] The time synchronization initiator broadcasts the assembled time synchronization broadcast frame to all receivers via the FPGA.

[0043] In this embodiment, the time adjustment at the receiving end is implemented as follows: all time synchronization receivers in the system receive the time synchronization broadcast frame. After successful verification, each time synchronization receiver extracts its own "site-specific compensation field" from the broadcast frame based on its own ID or address, and combines it with the common "coarse scale high bits" to reconstruct its own "compensation time information" (i.e., The receiving end will combine this compensation time information with its own local time. Compare and calculate the difference. .

[0044] The anti-abnormal adjustment algorithm executed at the receiving end is as follows: the receiving end pre-sets a "maximum adjustment step". This step is set based on the maximum cumulative deviation that may occur between the clocks of the transmitting and receiving ends between two synchronization cycles (e.g., 2 seconds). For example, if both the transmitting and receiving ends use 20ppm quartz crystal oscillators, the maximum relative frequency deviation is 40ppm. Within a 2-second period, the maximum deviation is... This allows you to set the maximum adjustment step (e.g., set it to 80). (or a slightly larger threshold). The receiver judges the difference. absolute value Is it less than the maximum adjustment step?

[0045] Scenario 1: The deviation is less than the maximum adjustment step. This indicates that the deviation is within the normal crystal oscillator drift range. The receiver performs a "one-time adjustment," meaning it directly adjusts the local time. Set as compensation time .

[0046] Scenario 2: Greater than or equal to the maximum adjustment step. This indicates a possible single time anomaly (e.g., data frame reception delay caused by strong interference). In this case, the receiver will not adjust its local time temporarily and will... If the value is considered an anomaly, it is discarded, and the system waits for the next time synchronization period (e.g., 2 seconds later) for the time synchronization broadcast frame, and performs multiple checks and confirmations.

[0047] Through the above steps, the method in this embodiment avoids software processing jitter by using FPGA hardware timestamps (step one); and by measuring and storing independent... (Step 1) and apply it to the compensation time information (Step 3), eliminating the difference in physical link delay between different sites; by carrying the dedicated compensation information of multiple nodes in a single broadcast frame (Step 3), the bandwidth overhead is greatly reduced; and by using the maximum step-based adjustment algorithm (Step 4), the stability of synchronization is improved.

[0048] In summary, this embodiment can achieve high-precision (e.g., sub-microsecond level) point-to-multipoint time synchronization under narrowband communication conditions, meeting the stringent requirements of scenarios such as multi-point distributed measurement and measurement and control automation.

[0049] Example 3 A narrowband communication precise time synchronization system is applied to a narrowband communication system including a time synchronization initiator and at least one time synchronization receiver, comprising a bidirectional message exchange module, a time compensation module, and a local time adjustment module; The bidirectional message interaction module is used to control the time synchronization initiator to perform bidirectional message interaction with at least one time synchronization receiver, and to measure and store the independent one-way transmission delay for each time synchronization receiver. ; The time compensation module is used to control the time synchronization initiator to periodically broadcast time synchronization broadcast frames. Each time synchronization broadcast frame contains compensation time information for the at least one time synchronization receiver. The compensation time information is based on the local time of the time synchronization initiator and the corresponding independent one-way transmission delay. generate; The local time adjustment module is used to control the at least one time synchronization receiver to receive the time synchronization broadcast frame, extract their respective compensation time information, and adjust their local time accordingly.

[0050] In one specific embodiment, the time synchronization initiator includes a first FPGA, which is configured to record a first transmission time T0 and a first reception time T1 by latching an internal counter during the bidirectional message interaction; the at least one time synchronization receiver includes a second FPGA, which is configured to immediately reply with a response data frame after receiving a time synchronization frame from the time synchronization initiator during the bidirectional message interaction.

Claims

1. A method for time synchronization of narrowband communication, applied to a narrowband communication system comprising one time synchronization initiator and at least one time synchronization receiver, characterized in that, The method comprises the following steps: The time-synchronization initiator measures and stores an independent one-way transmission delay for each time-synchronization receiver by performing bidirectional message interaction with the at least one time-synchronization receiver ; The time-synchronization initiating end periodically broadcasts a time-synchronization broadcast frame, which contains compensation time information for the at least one time-synchronization receiving end, and the compensation time information is based on the local time of the time-synchronization initiating end and the corresponding independent one-way transmission delay generating; The at least one time synchronization receiving end receives the time synchronization broadcast frame, extracts the respective compensation time information, and adjusts the local time thereof according to the compensation time information.

2. The method of claim 1, wherein, initiating a measurement of the one-way transmission delay from the time comprises: The time synchronization initiating end broadcasts a first time synchronization frame to the time synchronization receiving end, and records the first sending time T0 through FPGA hardware logic; After receiving the first time synchronization frame, the time synchronization receiving end immediately replies a response data frame through FPGA hardware logic; The time pair initiates the receiving of the response data frame, and records the first receiving time T1 through FPGA hardware logic, and calculates the one-way transmission delay ; wherein the recording of the T0 and T1 is achieved by latching the hardware time stamp when the effective edge of the frame start signal is detected at the physical layer or MAC layer of the communication interface.

3. The method of claim 2, wherein, The FPGA hardware logic is internally integrated with a free running counter for generating the hardware time stamp; the clock source of the free running counter is 50MHz, and the resolution is 20ns.

4. The method of claim 1, wherein, The compensation time information and the local time both adopt a format combining coarse scale and fine scale; the coarse scale is used for representing the millisecond number since the starting time, and the fine scale is generated by 64k frequency division of the clock of the coarse scale, and the minimum scale is 1 / 64 microsecond.

5. The method of claim 1, wherein, The format of the time-synchronization broadcast frame comprises: a coarse-scale high-order field common to all time-synchronization receivers; and at least one site-specific compensation field, each of which corresponds to a specific time-synchronization receiver and contains a coarse-scale low-order and a fine-scale for the time-synchronization receiver, which together form a time-synchronization compensation value based on the independent one-way transmission delay generated compensation time information.

6. The method of claim 1, wherein, The step of adjusting the local time of the time synchronization receiving end comprises: calculating a difference between the compensation time information and a local time of the time synchronization receiving end ; A maximum adjustment step is preset; Determine the difference Is the absolute value less than the maximum adjustment step? If yes, the local time is adjusted to the position at one time; If not, the difference value is considered as an exception, and is not adjusted temporarily and is judged repeatedly by using the time adjustment information of the following period.

7. The method of claim 6, wherein, The maximum adjustment step is determined according to the maximum relative frequency deviation 40ppm of the quartz crystal oscillator of the time synchronization initiating end and the time synchronization receiving end and the sending period 2s of the time synchronization broadcast frame.

8. The method of claim 1, wherein, The narrowband communication is specifically wireless or wired serial link with physical layer data rate less than or equal to 64kbps and without supporting Ethernet frame structure or UDP / IP protocol stack.

9. A narrowband communication precise time synchronization system, characterized in that, The application is applied to a narrowband communication system comprising one time synchronization initiating end and at least one time synchronization receiving end, and comprises a bidirectional message interaction module, a time compensation module, and a local time adjustment module. The bidirectional message interaction module is used for controlling the time transfer initiator to measure and store the independent one-way transmission delay for each time transfer receiver by performing bidirectional message interaction with the at least one time transfer receiver ; The time compensation module is used for controlling the time synchronization initiating end to periodically broadcast a time synchronization broadcast frame, the time synchronization broadcast frame containing compensation time information for the at least one time synchronization receiving end respectively, the compensation time information being based on the local time of the time synchronization initiating end and the corresponding independent one-way transmission delay generating; The local time adjustment module is used for controlling the at least one time synchronization receiving end to receive the time synchronization broadcast frame, extract the respective compensation time information, and adjust the local time thereof according to the compensation time information.

10. The system of claim 9, wherein, The time synchronization initiating end comprises a first FPGA, and the first FPGA is configured to record the first sending time T0 and the first receiving time T1 through the way of latching the internal counter in the bidirectional message interaction; the at least one time synchronization receiving end comprises a second FPGA, and the second FPGA is configured to immediately reply a response data frame after receiving the time synchronization frame from the time synchronization initiating end in the bidirectional message interaction.

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