CN110782709A - High-precision clock redundancy backup method for civil aviation ADS-B ground station system - Google Patents

Abstract

The invention discloses a high-precision clock redundancy backup method for a civil aviation ADS-B ground station system. Three ground stations are set in the civil aviation management ADS-B ground station system, and each ground station includes a GPS receiver, an FPGA and a CPU. ;Three ground stations achieve high-precision clock redundancy backup by sharing the second pulse and sharing the UTC time. The technical scheme of the present invention realizes a high-precision clock redundancy backup design method for the civil aviation ADS-B ground station system. The method shares the UTC time through network multicast and the second pulse technology through discrete lines. When there is only one ADS-B ground station When GPS works normally, other ground stations of the whole system can work normally, which greatly improves the reliability of the system. In the case of GPS locking of multiple devices, the method simultaneously uses a high-precision time mean design to eliminate the error caused by the second pulse jitter of a single GPS receiver, so that the time stamp of the output message is more accurate.

Description

A high-precision clock redundancy backup method for civil aviation ADS-B ground station system

technical field

The invention relates to a high-precision clock redundancy backup method for a civil aviation ADS-B ground station system.

Background technique

Civil aviation vigorously promotes the technological transformation of the surveillance system, strives to build an integrated ADS-B operation system of sky, air and ground, and actively promotes the construction and operation of ADS-B. By the end of 2017, the layout of ADS-B ground facilities will be basically completed and the initial operation will begin; By the end of 2020, the airborne equipment retrofitting and ground ADS-B network construction will be fully completed, and a complete civil aviation ADS-B operation monitoring system and information service system will be built to provide full airspace monitoring means for air traffic and ADS-B for aviation enterprises. Information service; by the end of 2025, based on the experience of ADS-B operation and implementation, continuously improve the layout of ADS-B ground facilities and ground ADS-B network construction, and improve the safety level, airspace capacity, operation efficiency and service capability of civil aviation as a whole .

According to ED129B, the message output by the ADS-B ground station is required to meet the ASTERIX CAT021V2.1 standard, which clarifies the requirements of the ADS-B ground station for the receiving time of the message. The air traffic control data station uses the time of arrival (TOA, time of arrival) of the response signal sent by the aircraft to arrive at each ground receiving station to calculate the position of the aircraft based on the TDOA-based hyperboloid positioning algorithm. By comparing the position with the position information sent by the ADS-B airborne, false targets can be filtered out to achieve the purpose of ADS-B anti-spoofing. Therefore, how to determine the message acceptance time in the ADS-B ground station system is very important for the calculation of the position accuracy. In addition, the mean time between failures (MTBF) of indoor equipment in the ADS-B ground station system of civil aviation management is not less than 20000h, and the maintenance time (MTTR) of indoor equipment is not more than 30min. The equipment can work continuously for 7×24 hours, and the design life of the equipment is more than 15 years. Therefore, the use of redundant design to improve system stability is a necessary means in the development of ATC equipment.

In the civil aviation management ADS-B ground station system, there are three sets of ADS-B ground stations, and the three sets of equipment can work independently. In the actual operation process, two omnidirectional ground stations are master and backup machines of each other, and the directional ground stations work independently. In the process of using high-precision GPS, the ADS-B ground station equipment uses the UTC time output by the serial port of the GPS receiver as the time reference of each second, uses the second pulse signal of the GPS receiver as the reset signal of the high-precision time, and uses the GPS receiver The machine 100M inputs the clock as a high-precision time counting signal.

At present, in a multi-machine large-scale system using high-precision GPS, each set of equipment uses an independent GPS receiver. When the GPS receiver of machine A fails, machine A stops working and the system switches. When all GPS receivers are locked normally, each device works independently. The disadvantages of this method are as follows:

(1) When the main and standby machines are used in the system, if the GPS receiver of machine A is abnormal, the system can only switch to machine B. If other modules (non-GPS receivers) of machine B are abnormal at this time , the system will not work properly. Redundant design is not fully reflected, reducing system reliability.

(2) Due to the jitter in the pulse-per-second signal output by the high-precision GPS receiver, when multiple devices in the system work normally at the same time, the pulse-per-second of multiple devices is independent, so for the reception time of the same signal, the same system The data acceptance time calculated by different devices fluctuates greatly.

SUMMARY OF THE INVENTION

The present invention proposes a design method for high-precision clock redundancy backup of civil aviation ADS-B ground station system. The system targeted by the present invention includes components such as GPS receiver, FPGA, CPU, etc. Each component is connected through discrete, serial port, network, etc. Second pulse, shared UTC time means to achieve high-precision clock redundancy.

The purpose of this invention is to realize through the following technical solutions:

A high-precision clock redundancy backup method for a civil aviation ADS-B ground station system. Three ground stations are set in the civil aviation management ADS-B ground station system, and each ground station includes a GPS receiver, an FPGA and a CPU; The station realizes high-precision clock redundancy backup by sharing the second pulse and sharing the UTC time.

As a preferred way, the three ground stations share the UTC time through the network, and share the PPS second pulse through the discrete TTL interface.

As a preferred way, the connection relationship between the GPS receiver, FPGA and CPU of the ADS-B ground station is as follows:

a) The GPS receiver outputs a 100M clock signal to the FPGA;

b) The GPS receiver outputs a TTL level pulse-per-second signal and is connected to the FPGA and CPU at the same time;

c) The GPS receiver outputs a serial port signal of RS232 level to the CPU;

The external interface of ADS-B ground station is as follows:

a) ADS-B ground station outputs a 100M Ethernet signal;

b) ADS-B ground station outputs 1 channel TTL level second pulse signal;

c) The ADS-B ground station is connected to two TTL level second pulse signals.

As a preferred way, in order to realize multi-station high-precision clock redundancy processing, the time processing module running inside the CPU and the high-precision time stamping module running inside the FPGA need to cooperate to complete. The time processing module includes two functions: time source processing and second pulse processing. The time source processing completes the parsing of GPS NEMA0183 format packets and the maintenance of the time source status, and the second pulse processing completes the writing of the UTC time by the CPU to the FPGA. The FPGA high-precision time stamping module completes the calculation of high-precision time.

As a preferred way, the ADS-B ground station time processing module divides the time information into a local time source and a system time source, the local time source reflects the GPS receiver status of the device, and the system time source reflects the integrated status of all GPS receivers in the entire system; The time processing module accepts GPS messages through the serial port to process and maintain the local time source.

As a preferred way, the time processing module accepts GPS messages through the serial port to process and maintain the local time source. The specific steps are as follows:

Step 1: The ADS-B ground station time processing module receives the GPS receiver conforming to the NEMA0183 format message through the serial port, and caches it;

Step 2: The ADS-B ground station time processing module verifies the received message, and extracts the message type flag for the message that has passed the check;

Step 3: The ADS-B ground station time processing module obtains the GPS receiver taming state as the local time source state by solving the "TOD" message;

Step 4: The ADS-B ground station time processing module obtains the UTC time by solving the "GGA" message, and updates the local time according to the state of the local time source;

Step 5: The ADS-B ground station time processing module uses multicast technology to send local time source information to other ADS-B ground stations through the network, including the UTC time of the GPS receiver and the GPS taming state;

Step 6: The ADS-B ground station time processing module receives the time source information sent by other ADS-B ground stations through the network multicast technology, and selects the locked GPS receiver time as the system time source. If the GPS receivers of multiple devices are locked, the GPS time of the device with the smaller IP is selected as the system time source.

As a preferred method, the standard UTC time is used for the output messages of the ADS-B ground station, and the FPGA only introduces the second pulse signal of the GPS receiver, and cannot obtain the current UTC time. Therefore, the ADS-B ground station time processing module needs to be interrupted at the second pulse. Provide the current UTC time to the FPGA, the specific steps are as follows:

The ADS-B ground station time processing module accepts the GPS receiver second pulse interrupt and releases the semaphore, and the processing thread waiting for the semaphore will process it;

If the local time source status is valid, the ADS-B ground station time processing module preferentially selects and maintains the GPS time of the device;

If the local time source is invalid and the system time source is valid, the ADS-B ground station time processing module selects the system time source as the device GPS time and maintains it;

If both the local time source and the system time source are invalid, the ADS-B ground station time processing module uses the relationship between time continuity and second pulse to enter GPS failure maintenance.

The ADS-B ground station time processing module obtains the GPS status of the device and the GPS status of other devices and writes the UTC time into the FPGA through the data bus.

As a preferred method, considering the probability of data transmission errors, the FPGA needs to perform continuous judgment and range judgment on the time written by the time processing module; it is judged that the UTC time is updated through the FPGA, otherwise the FPGA uses the second pulse signal to automatically update the time.

As a preferred method, according to the requirements of the ED129B standard, the low-precision time requirement for the output message of the ADS-B ground station is 1/128s, and the high-precision jitter is less than 200ns. The ADS-B ground station cannot calculate the high-precision time of the message through software, so the message time of the ADS-B ground station is obtained by the FPGA of the decoding module. In order to improve the time accuracy, the FPGA high-precision time stamping module uses the 100MHz standard clock provided by the GPS receiver as the clock source; the FPGA high-precision time stamping module obtains the UTC absolute time from the CPU through the bus, and uses the second pulse signal as the high-precision counting trigger.

As a preferred way, considering that the GPS receiver status affects the pulse-per-second accuracy, the FPGA high-precision time stamping module needs to determine the status of the three GPS receivers in the ADS-B ground station system of the civil aviation management; Under the premise of eliminating the jitter error, the FPGA needs to perform averaging processing on the high-precision counts. The specific steps are as follows:

The FPGA connects to the local ground station GPS receiver second pulse signal and two other ground station GPS receiver second pulse signals at the same time, and uses three counters corresponding to three GPS receivers at the same time. The counter uses the clock source of the 100M clock provided by the machine. ;

高精度计数为

精度时间等于高精度计数与时钟周期的乘积；When the FPGA high-precision time stamping module receives the second pulse, the counter corresponding to the first second pulse will be cleared and start counting again; it is assumed that the arrival times of the three second pulses are T1, T2, and T3 respectively; The time count of two second pulses is N1, N2; then the time used by the FPGA is

High precision counting is

The precision time is equal to the product of the high precision count and the clock period;

After the ADS-B message is successfully decoded, the FPGA high-precision time stamping module adds the UTC absolute time written by the CPU and the high-precision time as the receiving time of the message, and generates a DMA interrupt request to the CPU, waiting for the CPU to read data.

The beneficial effects of the present invention are:

The technical scheme of the invention realizes a high-precision clock redundancy backup design method of the civil aviation ADS-B ground station system. The method shares the UTC time through network multicast and the second pulse technology through discrete lines. When there is only one ADS-B ground station When GPS works normally, other ground stations of the whole system can work normally, which greatly improves the reliability of the system.

In the case of GPS locking of multiple devices, the method uses high-precision time mean design to eliminate the error caused by the second pulse jitter of a single GPS receiver, so that the time stamp of the output message is more accurate.

Description of drawings

In order to explain the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore do not It should be regarded as a limitation of the scope, and for those of ordinary skill in the art, other related drawings can also be obtained according to these drawings without any creative effort.

Figure 1 is a block diagram of the clock sharing connection of the civil aviation ADS-B ground station system;

Fig. 2 is the time source processing flow chart of ADS-B ground station time processing module;

Fig. 3 is the second pulse processing flow chart of ADS-B ground station time processing module;

Fig. 4 is the processing flow chart of the FPGA high-precision time stamping module.

Detailed ways

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following.

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Accordingly, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in Figure 1, a high-precision clock redundancy backup method for the civil aviation ADS-B ground station system, the connection diagram of the high-precision clock redundancy backup design of the civil aviation ADS-B ground station system is shown in Figure 1. -B ground station system set up 3 ground stations (such as ground station A, ground station B and ground station C in Figure 1), each ground station includes GPS receiver, FPGA and CPU; 3 ground stations pass the shared seconds Pulse and shared UTC time means to achieve high-precision clock redundancy backup; in the case of only one ground station GPS receiver working normally, other ground stations in the entire system can work normally through sharing technology.

High-precision time average design: Multiple ADS-B devices can detect the second pulse signal of all devices in the system through the second pulse sharing technology. After multiple ground station GPS receivers are locked, the pulse-to-pulse jitter error is removed using the average value of the time-to-arrival counts of pulsars.

High-precision clock redundancy backup: Three ADS-B devices share UTC time through the network, share the second pulse through discrete signals, and enable other ground stations in the entire system to be able to use the sharing technology when only one ground station GPS receiver is working normally. normal work. The redundant design of the system is increased, and the reliability of the system is improved.

The three ground stations share UTC time through the network and PPS second pulse through discrete TTL interfaces.

The connection relationship between the GPS receiver, FPGA and CPU of the ADS-B ground station is as follows:

a) The GPS receiver outputs a 100M clock signal to the FPGA;

b) The GPS receiver outputs a TTL level pulse-per-second signal and is connected to the FPGA and CPU at the same time;

c) The GPS receiver outputs a serial port signal of RS232 level to the CPU;

The external interface of ADS-B ground station is as follows:

a) ADS-B ground station outputs a 100M Ethernet signal;

b) ADS-B ground station outputs 1 channel TTL level second pulse signal;

c) The ADS-B ground station is connected to two TTL level second pulse signals.

In order to realize the redundant processing of multi-station high-precision clocks, it is necessary to cooperate with the time processing module running inside the CPU and the high-precision time stamping module running inside the FPGA. The time processing module includes two functions: time source processing and second pulse processing. The time source processing completes the parsing of GPS NEMA0183 format packets and the maintenance of the time source status, and the second pulse processing completes the writing of the UTC time by the CPU to the FPGA. The FPGA high-precision time stamping module completes the calculation of high-precision time.

The ADS-B ground station time processing module divides the time information into local time sources and system time sources. The local time source reflects the GPS receiver status of the device, and the system time source reflects the comprehensive status of all GPS receivers in the entire system; the time processing module passes The serial port accepts GPS messages to process and maintain the local time source.

The time processing module accepts GPS messages through the serial port to process and maintain the local time source. The specific steps are as follows (as shown in Figure 2):

Step 1: The ADS-B ground station time processing module receives the GPS receiver conforming to the NEMA0183 format message through the serial port, and caches it;

Step 2: The ADS-B ground station time processing module verifies the received message, and extracts the message type flag for the message that has passed the check;

Step 3: The ADS-B ground station time processing module obtains the GPS receiver taming state as the local time source state by solving the "TOD" message;

Step 4: The ADS-B ground station time processing module obtains the UTC time by solving the "GGA" message, and updates the local time according to the state of the local time source;

Step 5: The ADS-B ground station time processing module uses multicast technology to send local time source information to other ADS-B ground stations through the network, including the UTC time of the GPS receiver and the GPS taming state;

Step 6: The ADS-B ground station time processing module receives the time source information sent by other ADS-B ground stations through the network multicast technology, and selects the locked GPS receiver time as the system time source. If the GPS receivers of multiple devices are locked, the GPS time of the device with the smaller IP is selected as the system time source.

The ADS-B ground station output message uses the standard UTC time, and the FPGA only introduces the second pulse signal of the GPS receiver, and cannot obtain the current UTC time, so the ADS-B ground station time processing module needs to provide the FPGA with the second pulse when the second pulse is interrupted. The current UTC time, as shown in Figure 3, the specific steps are as follows:

The ADS-B ground station time processing module accepts the GPS receiver second pulse interrupt and releases the semaphore, and the processing thread waiting for the semaphore will process it;

If the local time source status is valid, the ADS-B ground station time processing module preferentially selects and maintains the GPS time of the device;

If the local time source is invalid and the system time source is valid, the ADS-B ground station time processing module selects the system time source as the device GPS time and maintains it;

If both the local time source and the system time source are invalid, the ADS-B ground station time processing module uses the relationship between time continuity and second pulse to enter GPS failure maintenance.

The ADS-B ground station time processing module obtains the GPS status of the device and the GPS status of other devices and writes the UTC time into the FPGA through the data bus.

Considering the probability of data transmission errors, the FPGA needs to continuously judge the time written by the time processing module and judge the range; judge to update the UTC time through the FPGA, otherwise the FPGA uses the second pulse signal to automatically update the time.

According to the requirements of the ED129B standard, the low-precision time of the ADS-B ground station output message is required to be 1/128s, and the high-precision jitter is less than 200ns. The ADS-B ground station cannot calculate the high-precision time of the message through software, so the message time of the ADS-B ground station is obtained by the FPGA of the decoding module. In order to improve the time accuracy, the FPGA high-precision time stamping module uses the 100MHz standard clock provided by the GPS receiver as the clock source; the FPGA high-precision time stamping module obtains the UTC absolute time from the CPU through the bus, and uses the second pulse signal as the high-precision counting trigger.

Considering that the GPS receiver state affects the pulse-per-second accuracy, the FPGA high-precision time stamping module needs to determine the state of the three GPS receivers in the ADS-B ground station system of civil aviation management; under the premise that multiple GPSs are locked, In order to eliminate the jitter error, the FPGA high-precision time stamping module needs to average the high-precision counts, as shown in Figure 4. The specific steps are as follows:

The FPGA connects to the local ground station GPS receiver second pulse signal and two other ground station GPS receiver second pulse signals at the same time, and uses three counters corresponding to three GPS receivers at the same time. The counter uses the clock source of the 100M clock provided by the machine. ;

高精度计数为

高精度时间等于高精度计数与时钟周期的乘积；When the FPGA high-precision time stamping module receives the second pulse, the counter corresponding to the first second pulse will be cleared and start counting again; it is assumed that the arrival times of the three second pulses are T1, T2, and T3 respectively; The time count of two second pulses is N1, N2; then the time used by the FPGA is

High precision counting is

High precision time is equal to the product of high precision count and clock period;

After the ADS-B message is successfully decoded, the FPGA high-precision time stamping module adds the UTC absolute time written by the CPU and the high-precision time as the receiving time of the message, and generates a DMA interrupt request to the CPU, waiting for the CPU to read data.

The invention realizes high-precision time mean design and high-precision time backup design by means of sharing second pulse and sharing UTC time. The high-precision time average design uses the average value of the arrival time of the second pulse to remove the second pulse jitter error after the GPS locks of multiple ground stations. The high-precision time backup design enables other ground stations in the entire system to work normally through sharing technology under the condition that only one ground station GPS works normally, which greatly improves the reliability index of the equipment.

Although preferred embodiments of the present invention have been described, additional changes and modifications to these embodiments may occur to those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention. The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. It should be pointed out that any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall include within the protection scope of the present invention.

Claims (10)

1. A high-precision clock redundancy backup method for a civil aviation ADS-B ground station system is characterized by comprising the following steps:

3 ground stations are arranged in an ADS-B ground station system of the civil aviation air traffic control system, and each ground station comprises a GPS receiver, an FPGA and a CPU; and 3 ground stations realize high-precision clock redundancy backup by means of sharing pulse per second and UTC time.

2. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 1, characterized in that: and 3 ground stations share UTC time through a network and share PPS second pulse through a discrete TTL interface.

3. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 1, characterized in that: the connection relation among the GPS receiver, the FPGA and the CPU of the ADS-B ground station is as follows:

a) the GPS receiver outputs a 100M clock signal to the FPGA;

b) the GPS receiver outputs a path of second pulse signal of TTL level and simultaneously accesses the FPGA and the CPU;

c) the GPS receiver outputs a serial port signal of RS232 level to the CPU;

the external interface of the ADS-B ground station is as follows:

a) the ADS-B ground station outputs a path of 100M Ethernet signal;

b) the ADS-B ground station outputs 1 path of second pulse signals of TTL level;

c) and the ADS-B ground station accesses two paths of second pulse signals of TTL level.

4. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 1, characterized in that: the multi-station high-precision redundant processing needs to be completed by matching a time processing module running in a CPU (Central processing Unit) with a high-precision time marking module running in an FPGA (field programmable Gate array); the time processing module comprises two functions of time source processing and second pulse processing, wherein the time source processing completes the analysis of NEMA0183 format messages of the GPS and the maintenance of time source states, and the second pulse processing completes the writing of the CPU to UTC time of the FPGA high-precision time marking module; and the FPGA high-precision time marking module is used for finishing the calculation of high-precision time.

5. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 4, characterized in that: the ADS-B ground station time processing module divides the time information into a local time source and a system time source, wherein the local time source reflects the state of the GPS receiver of the equipment, and the system time source reflects the comprehensive state of all the GPS receivers in the whole system; and the time processing module receives the GPS message through the serial port to process and maintain the local time source.

6. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 5, characterized in that: the specific steps of the time processing module receiving the GPS message through the serial port to process and maintain the local time source are as follows:

step 1: the ADS-B ground station time processing module receives the message of the GPS receiver conforming to the NEMA0183 format through the serial port and caches the message;

step 2: the ADS-B ground station time processing module checks the received message and extracts a message type mark for the checked message;

and step 3: the ADS-B ground station time processing module obtains the taming state of the GPS receiver as a local time source state by solving the TOD message;

and 4, step 4: the ADS-B ground station time processing module obtains UTC time by solving the message GGA and updates the local time according to the local time source state;

and 5: the ADS-B ground station time processing module uses multicast technology to send local time source information to other ADS-B ground stations through a network, wherein the local time source information comprises UTC time of a GPS receiver and a GPS tame state;

step 6: the ADS-B ground station time processing module receives time source information sent by other ADS-B ground stations through a network multicast technology, and selects the locked GPS receiver time as a system time source.

7. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 6, characterized in that: the ADS-B ground station time processing module needs to provide the current UTC time for the FPGA when the pulse per second is interrupted, and the specific steps are as follows:

the ADS-B ground station time processing module receives the second pulse interruption of the GPS receiver and releases the semaphore, and waits for the processing thread of the semaphore to process;

if the local time source state is effective, the ADS-B ground station time processing module preferentially selects the GPS time of the equipment and maintains the GPS time;

if the local time source is invalid and the system time source is valid, the ADS-B ground station time processing module selects the system time source as the GPS time of the equipment and maintains the equipment;

if the local time source and the system time source are invalid, the ADS-B ground station time processing module enters GPS failure maintenance by utilizing the relation between time continuity and pulse per second;

and the ADS-B ground station time processing module acquires the GPS state of the equipment and the GPS states of other equipment and writes the UTC time into the FPGA through a data bus.

8. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 7, characterized in that: the FPGA needs to continuously judge the time written in by the time processing module and judge the range; and judging that the UTC time is updated through the FPGA, otherwise, automatically updating the time by the FPGA by using a pulse per second signal.

9. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 8, characterized in that: the FPGA high-precision time marking module uses a 100MHz standard clock provided by a GPS receiver as a clock source; the FPGA high-precision time marking module acquires UTC absolute time from the CPU through a bus, and meanwhile, a pulse per second signal is used as high-precision counting trigger.

10. The high-precision clock redundancy backup method for the civil aviation ADS-B ground station system according to claim 9, characterized in that: the FPGA high-precision time marking module is used for judging the states of 3 GPS receivers in an ADS-B ground station system of the civil aviation air traffic control system; on the premise that a plurality of GPS are in a locking state, in order to eliminate jitter errors, the FPGA needs to perform mean value processing on high-precision counts, and the method specifically comprises the following steps:

the FPGA simultaneously accesses a second pulse signal of a GPS receiver of the ground station and second pulse signals of two other ground station GPS receivers, and simultaneously uses three counters corresponding to the 3 GPS receivers, and the counters use a clock source to provide 100M clocks for the local machine;

after the FPGA high-precision time marking module receives the pulse per second, the pulse per second corresponding to the counter is cleared and counting is restarted; suppose the arrival times of the three second pulses are T1, T2 and T3 respectively; the time counts of the first two second pulses when the 3 rd second pulse arrives are N1, N2; then the time of FPGA use is

High precision count is

The high-precision time is equal to the product of the high-precision counter value and the clock period;

and after the ADS-B message is successfully decoded, the FPGA high-precision time marking module adds the UTC absolute time written by the CPU and the high-precision time to be used as the receiving time of the message, generates a DMA interrupt request to the CPU and waits for the CPU to read data.

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