CN110350998B - High-dynamic inter-station high-precision time frequency synchronization method - Google Patents

High-dynamic inter-station high-precision time frequency synchronization method Download PDF

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CN110350998B
CN110350998B CN201910720692.XA CN201910720692A CN110350998B CN 110350998 B CN110350998 B CN 110350998B CN 201910720692 A CN201910720692 A CN 201910720692A CN 110350998 B CN110350998 B CN 110350998B
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mobile station
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胡阳
周戌初
周益青
王玉达
李阿明
李名祺
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Shanghai Radio Equipment Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0644—External master-clock
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/001—Synchronization between nodes
    • H04W56/0015—Synchronization between nodes one node acting as a reference for the others
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
    • H04W56/005—Synchronisation arrangements compensating for timing error of reception due to propagation delay compensating for timing error by adjustment in the receiver

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Abstract

A high-precision time frequency synchronization method between stations under high dynamic condition is disclosed, wherein a mobile station sends an information frame and a synchronization code to a reference station, and the reference station obtains the arrival time of the reference station; the base station sends an information frame and a synchronous code to the mobile station, and the mobile station obtains the first arrival time of the mobile station; the reference station sends the information frame and the synchronous code to the mobile station again, and the mobile station obtains the second arrival time of the mobile station; calculating relative motion velocity and Doppler frequency between the reference station and the rover station; calculating time difference information between the base station and the mobile station, and adjusting the local time of the mobile station by the mobile station according to the time difference information to enable the mobile station and the base station to achieve time synchronization; and calculating crystal oscillator frequency difference information between the reference station and the mobile station, and adjusting the crystal oscillator frequency of the mobile station by the mobile station according to the crystal oscillator frequency difference information so that the mobile station and the reference station achieve frequency synchronization. The method obtains the time difference information between stations with high precision, and realizes the frequency synchronization of the reference station and the mobile station by detecting the carrier phase change rate between the stations.

Description

High-dynamic inter-station high-precision time frequency synchronization method
Technical Field
The invention relates to the field of digital communication, in particular to a high-precision time-frequency synchronization method between stations under high dynamic condition.
Background
The multi-carrier networking detection and cooperative control become important directions for the development of anti-air-raid anti-pilot weaponry, and a multi-carrier cooperative detection system can effectively improve the working distance and the measurement precision and is valued by researchers at home and abroad. In the cooperative networking communication and cooperative positioning among multiple carriers, the time and frequency of each carrier in the network need to be accurately synchronized, so that the high-precision positioning of a target can be realized. In the prior art, different devices are generally subjected to time synchronization by combining navigation satellite signals with a high-precision atomic clock, but the method has strong dependence on the navigation satellite signals, is easily interfered by the outside, has long preheating time and is not suitable for a missile-borne system. The time-frequency synchronization method based on the two-way communication can improve the anti-interference capability of the system, can obtain the time-frequency synchronization function by improving the original communication link to a certain extent, and can better adapt to the missile-borne application requirement under the condition of not increasing the hardware cost.
The existing literature studies the time-frequency synchronization method. Document 1 (xie shui, sun lingfeng, zhufeng, time-frequency center time synchronization method [ J ]. command information system and technology, 2016,7(1):58-62.) provides a plurality of time-frequency synchronization methods, compares the synchronization precision that can be achieved by various methods, and introduces the satellite-based co-view method in detail. The satellite common-view time frequency synchronization method can achieve nanosecond time synchronization precision, but the method is only suitable for time frequency synchronization with ground equipment, and the synchronization performance under the condition of high dynamic flight is not mentioned. The pseudolite self-organizing network time-frequency synchronization method proposed in document 2 (epoch method, billow, grand hitching, serenity, lugwarmy, pseudolite network time-frequency synchronization system design and implementation [ J ]. embedded technology, 2018,6(44):39-43) also adopts a bidirectional measurement method, but the method is not improved for high dynamic conditions and is not suitable for high dynamic scenes, and the method needs to continuously track signals, so that the anti-interference capability is weak, and the function is single. Patent 1 (beidou disciplined time service method and device, CN201811627948.4, 2018) provides a beidou disciplined time service method and device, which performs time synchronization by receiving beidou satellite signals, but does not describe the time synchronization accuracy that can be achieved. Patent 2 (a clock time-frequency integrated transmission method and device, CN201810916848.7, 2018) proposes a method for time and frequency transfer based on IRIG-B code, which performs transmission through RS485, multimode fiber, single-mode fiber, and the like, and is not applicable to wireless transmission.
Disclosure of Invention
The invention provides a high-precision time-frequency synchronization method between high-dynamic base stations, which adopts an improved RTT time synchronization method to obtain time difference information between the high-precision base stations and realizes frequency synchronization between a reference station and a mobile station by detecting the carrier phase change rate between the base stations.
In order to achieve the above object, the present invention provides a high-dynamic inter-station high-precision time-frequency synchronization method, which comprises the following steps:
the base station and the mobile station send information frames and synchronous codes according to a fixed time slot length delta T;
the mobile station sends information frame and synchronous code to the reference station, and the reference station obtains the TOAI；
The reference station sends information frame and synchronous code to the mobile station, and the mobile station obtains the first time TOA of the mobile stationR1；
The reference station sends the information frame and the synchronous code to the mobile station again, and the mobile station obtains the second time TOA of the mobile stationR2；
Calculating the relative motion velocity v and Doppler frequency f between the reference station and the rover stationd；
Figure BDA0002157080860000021
Figure BDA0002157080860000022
Wherein f iscIs the carrier frequency;
calculating time difference information epsilon between the base station and the rover station, and adjusting the local time of the rover station by the rover station according to the time difference information epsilon so that the rover station and the base station achieve time synchronization;
Figure BDA0002157080860000023
wherein, td1Timing the time from the starting time to the signal transmission time, t, for the reference stationp1Is the signal propagation time, t, at which the rover station transmits the information frame and the synchronization code to the reference stationp2Is the signal propagation time when the reference station sends information frame and synchronous code to the mobile station for the first time;
calculating crystal oscillator frequency difference information delta f between the reference station and the mobile station, and adjusting the crystal oscillator frequency of the mobile station by the mobile station according to the crystal oscillator frequency difference information delta f to enable the mobile station and the reference station to achieve frequency synchronization;
Figure BDA0002157080860000031
wherein f isoIs the crystal oscillation frequency, fnIn order to be the carrier frequency difference,
Figure BDA0002157080860000032
Figure BDA0002157080860000033
is the phase of the carrier wave and is,
Figure BDA0002157080860000034
and I and Q are signals of an in-phase branch I and a quadrature branch Q obtained after quadrature down-conversion is carried out on the radio frequency signal.
The invention makes the mobile station obtain the time difference information with the reference station through the mutual communication between the reference station and other mobile stations, thereby adjusting the local time to achieve the time synchronization with the reference station, and the time synchronization precision reaches the nanosecond level, and in addition, in the communication process, the frequency difference information between the mobile station and the reference station can be obtained, thereby adjusting the local crystal oscillator frequency to achieve the frequency synchronization with the reference station, and the frequency synchronization precision reaches 10-9Magnitude.
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FIG. 1 is a flow chart of a high-precision time-frequency synchronization method between stations under high dynamic conditions according to the present invention.
FIG. 2 is a schematic diagram of an embodiment of a high-precision time-frequency synchronization method between stations under high dynamics.
Detailed Description
The preferred embodiment of the present invention will be described in detail below with reference to fig. 1 and 2.
A common inter-station Time synchronization method is Round Trip Time (RTT) which is a bidirectional comparison method for performing measurement based on Time of Arrival (TOA). The working principle of the two-way comparison is that the error of the wireless signal in the path transmission is counteracted by utilizing the two-way pair transmitted by the TOAs of the two parties participating in the time synchronization, and the accurate time difference between the two parties is obtained through calculation. However, in the case of high dynamic conditions, the time difference measurement has errors due to the relative motion between the reference station and the mobile station, and the frequency difference measurement also has errors due to the doppler effect. Therefore, the invention adds a measuring process on the basis of the original RTT method and eliminates time difference and frequency difference under high dynamic state.
The invention adopts an improved RTT time synchronization method to obtain the time difference information between the high-precision stations and realizes the frequency synchronization of the reference station and the mobile station by detecting the carrier phase change rate between the stations.
The information is interacted between the reference station and the mobile station through a wireless radio frequency link, the physical layer works in a Time Division Multiple Access (TDMA) mode, each reference station and the mobile station send information frames with corresponding lengths according to a fixed time slot length, and the information frames are modulated by spread spectrum. In addition, a synchronization code for accurately calculating the arrival time is transmitted after each information frame.
As shown in FIG. 1, the present invention provides a high-dynamic inter-station high-precision time-frequency synchronization method, which comprises the following steps:
step S1, the rover station sends the information frame and the synchronous code to the reference station, and the reference station obtains the arrival time of the reference station;
the mobile station sends an information frame and a synchronous code to the reference station, the reference station receives the information frame, calculates the arrival time of the information frame by using the synchronous code and records the arrival time as the arrival time of the reference station;
step S2, the base station sends information frame and synchronous code to the mobile station, and the mobile station obtains the first arrival time of the mobile station;
the reference station sends an information frame and a synchronization code to the rover station, the information frame comprises the arrival time of the reference station calculated in the step S1, the rover station receives the information frame and obtains the arrival time of the reference station, and meanwhile, the arrival time of the information frame is calculated by the synchronization code and is recorded as the first arrival time of the rover station;
step S3, the base station sends the information frame and the synchronous code to the mobile station again, and the mobile station obtains the second arrival time of the mobile station;
the reference station sends the information frame and the synchronous code to the mobile station again, the mobile station receives the information frame, calculates the arrival time of the information frame by using the synchronous code and records the arrival time as the second arrival time of the mobile station;
step S4, calculating the relative motion speed and Doppler frequency between the reference station and the rover station;
calculating the relative motion speed and Doppler frequency between the current reference station and the current rover station through the first arrival time of the rover station and the second arrival time of the rover station;
step S5, calculating the time difference information between the base station and the rover station;
calculating time difference information between the base station and the mobile station through the relative movement speed information, the arrival time of the base station and the first arrival time of the mobile station, and adjusting the local time of the mobile station to enable the mobile station and the base station to achieve time synchronization;
step S6, calculating crystal oscillator frequency difference information between the reference station and the rover station;
in the process of despreading and demodulating an information frame, a mobile station performs related accumulation operation on IQ (in-phase branch I and quadrature branch Q signals obtained after orthogonal down-conversion is performed on radio frequency signals) signals collected by an AD (analog-to-digital conversion) chip and locally stored spread spectrum codes to finally obtain IQ integral values respectively, and current carrier phase information is calculated through the IQ integral values;
calculating carrier phase information at intervals of a certain time by the mobile station, calculating carrier frequency difference information according to the change rate of the carrier phase along with the time, and subtracting Doppler information caused by the speed from the carrier frequency difference and dividing the Doppler information by a frequency multiplication value (the ratio of the carrier frequency to the crystal oscillator frequency) to obtain the crystal oscillator frequency difference between the reference station and the mobile station;
and adjusting the crystal oscillator frequency of the mobile station according to the crystal oscillator frequency difference information so that the mobile station and the reference station can achieve frequency synchronization.
As shown in fig. 2, the calculation process of the present invention is described by taking 2 stations (1 reference station and 1 rover station) as an example, and can be generalized to 1 reference station and a plurality of rover stations in practical cases. Each rover and reference transmits frames of information in fixed 3ms slots, with the initial time difference between the rover and the reference being noted as epsilon.
Step S1, firstly, the rover station sends the information frame and the synchronous code to the reference station, the arrival time of the reference station measured by the reference station is TOAIWherein the signal propagation time is denoted as tp1。
Step S2, the base station sends the information frame and the synchronous code to the mobile station, the first time of arrival time of the mobile station measured by the mobile station is TOAR1Wherein the signal propagation time is denoted as tp2。
Step S3, the base station sends the information frame and the synchronous code to the mobile station again, the second time of arrival of the mobile station measured by the mobile station is TOAR2Wherein the signal propagation time is denoted as tp3。
Step S4, calculating the relative motion speed and Doppler frequency between the reference station and the rover station;
as can be seen from fig. 2:
TOAR2-TOAR1＝td2-td1-tp2+tp3 (1)
wherein, td1Timing the time from the starting time to the signal transmission time, t, for the reference stationd2Timing the reference station with the time from the start time to the second signal transmission time, td2-td1The propagation time t of the base station sending the information frame to the rover twice is 3msp2、tp3The difference of (2) is mainly influenced by the relative motion between stations, and if the relative motion speed is v, the change of the distance between two signal transmissions is v × 3ms, then:
tp3-tp2＝(v*3ms)/c (2)
wherein c is the speed of light, and the relative movement speed can be calculated by combining the formulas (1) and (2):
Figure BDA0002157080860000051
the doppler frequency between stations is then:
Figure BDA0002157080860000052
wherein f iscIs the carrier frequency.
Step S5, calculating the time difference information epsilon between the base station and the rover station;
as can be seen from fig. 2:
ε+TOAR1＝td1+tp2 (5)
ε+tp1＝TOAI (6)
then, the following equations (5), (6) can be obtained:
Figure BDA0002157080860000061
before RTT, a coarse synchronization process is usually performed between a reference station and a mobile station, synchronization accuracy varies according to transmission distance, usually in us magnitude, and a signal propagation distance error caused by this time is negligible, so it can be considered that t is tp3-tp2And ≈ v × 3ms)/c, where v can be calculated by formula (3).
And adjusting the time count of the mobile station through the calculated time difference epsilon between the stations so as to align the time of the reference station with the time of the mobile station.
Step S6, calculating crystal oscillator frequency difference information between the reference station and the rover station;
and in the information frame despreading and demodulation process, the mobile station performs correlation accumulation operation on the IQ signals acquired by the AD and the spread spectrum codes stored locally, finally obtains IQ integral values respectively, and calculates the current carrier phase information according to the IQ integral values.
The carrier phase is:
Figure BDA0002157080860000062
the rover is timed at intervalsThe carrier phase information is calculated according to the formula (8) and is recorded as T
Figure BDA0002157080860000063
The measured carrier frequency difference is:
Figure BDA0002157080860000064
wherein, n is the measurement times, the crystal oscillator frequency difference between the mobile station and the reference station is:
Figure BDA0002157080860000065
wherein f isoIs the crystal oscillation frequency.
The frequency of a crystal oscillator (generally a voltage-controlled crystal oscillator) of the rover station is adjusted through the calculated frequency difference deltaf of the crystal oscillator between the stations, so that the frequencies of the reference station and the rover station can be aligned.
The invention makes the mobile station obtain the time difference information with the reference station through the mutual communication between the reference station and other mobile stations, thereby adjusting the local time to achieve the time synchronization with the reference station, and the time synchronization precision reaches the nanosecond level, and in addition, in the communication process, the frequency difference information between the mobile station and the reference station can be obtained, thereby adjusting the local crystal oscillator frequency to achieve the frequency synchronization with the reference station, and the frequency synchronization precision reaches 10-9Magnitude.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (1)

1. A high-dynamic inter-station high-precision time frequency synchronization method is characterized by comprising the following steps:
the base station and the mobile station send information frames and synchronous codes according to a fixed time slot length delta T;
the mobile station sends the information frame and the synchronous code to the reference station, and the reference station obtains the time TOA of the information frame and the synchronous code arriving at the reference stationI；
The reference station sends the information frame and the synchronous code to the mobile station, and the mobile station obtains the time TOA of the first arrival of the information frame and the synchronous code at the mobile stationR1；
The reference station sends the information frame and the synchronous code to the mobile station again, and the mobile station obtains the time TOA of the second arrival of the information frame and the synchronous code at the mobile stationR2；
Calculating the relative motion velocity v and Doppler frequency f between the reference station and the rover stationd；
Figure FDA0002967754800000011
Figure FDA0002967754800000012
Wherein f iscIs the carrier frequency;
calculating time difference information epsilon between the base station and the rover station, and adjusting the local time of the rover station by the rover station according to the time difference information epsilon so that the rover station and the base station achieve time synchronization;
Figure FDA0002967754800000013
wherein, td1Timing the time from the starting time to the signal transmission time, t, for the reference stationp1Is the signal propagation time, t, at which the rover station transmits the information frame and the synchronization code to the reference stationp2Is the signal propagation time when the reference station sends information frame and synchronous code to the mobile station for the first time;
calculating crystal oscillator frequency difference information delta f between the reference station and the mobile station, and adjusting the crystal oscillator frequency of the mobile station by the mobile station according to the crystal oscillator frequency difference information delta f to enable the mobile station and the reference station to achieve frequency synchronization;
Figure FDA0002967754800000014
wherein f isoIs the crystal oscillation frequency, fnIn order to be the carrier frequency difference,
Figure FDA0002967754800000015
Figure FDA0002967754800000021
is the phase of the carrier wave and is,
Figure FDA0002967754800000022
and I and Q are signals of an in-phase branch I and a quadrature branch Q obtained after quadrature down-conversion is carried out on the radio frequency signal.
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