CN102801469B - Optical fiber time frequency hybrid transmission method - Google Patents

Abstract

The invention discloses an optical fiber time frequency hybrid transmission method. The method comprises the following steps that: a master station normally transmits a 10MHz frequency signal to a slave station, a narrow negative pulse is interpolated into a previous periodic signal high level within a whole second, and the frequency signal is calibrated in the whole second; the slave station restores the frequency signal by employing combinational logic and restores a timing signal through a trigger after identifying special calibration; the slave station simultaneously returns the received time frequency hybrid transmission signal to the master station in an original sample mode, wherein the hybrid transmission signal is used for the loopback time delay measurement of the master station; the master station restores the timing signal from the returned signal according to the method of the slave station, dynamically measures the time delay of the restored timing signal and a local timing signal, and combines with the fixed time delay of the equipment to calculate the phase precompensation of a frequency scale signal in one second; and the master station realizes uniform phase compensation in the next second by utilizing the calculated phase compensation, so that the restored frequency and timing signal of the slave station are synchronous with those of the master station. The optical fiber time frequency hybrid transmission method has the advantages of time service precision, low cost, convenient cascade connection and plug and play function.

Description

A kind of optical fiber time frequency hybrid transmission method

Technical field

This method relates to one and utilizes optical fiber link to carry out frequency and time mixing transmission, realizes the method (mixing transmission method hereinafter referred to as time-frequency) of strange land time service simultaneously and Frequency Transfer.The method has that precision is high, cost is low, facilitates cascade, the advantage of plug and play.

Background technology

Each large state is all in develop actively oneself split-second precision and frequency integrated system in the world, the more famous mainly space-based decorum, the gps system of the such as U.S., Muscovite GLONASS, the dipper system etc. that the Galileo system in Europe and China are building.Meanwhile, split-second precision frequency networks based on optical-fiber network is also the important component part building time-frequency system, not only can be competent at high-precision temporal frequency transmission work, also mutually can supplement, mutually support with space-based time-frequency network, form air-ground integrated high accuracy time-frequency network.Compare with space-based the time frequency system, fiber channel has the advantages such as transmission quality is reliable and stable, relative closure, anti-interference, transmission characteristic change is slow, can effectively administer.Therefore, transmit occasion at the more high-precision time-frequency of needs, utilize the better optical fiber of channel to carry out the more high-precision time and Frequency Transfer becomes inevitable choice.

The method utilizing optical fiber to carry out time synchronized at present comprises pre-compensating method and two-way Time transfer receiver method, existing method is the clock correction measured between time-frequency central station and terminal station and compensates, terminal use can only obtain time synchronizing signal, i.e. synchronous pps pulse per second signal.As terminal use wishes to obtain the frequency signal ensureing short-term stability and long-term stability simultaneously, then need to utilize the pulse per second (PPS) of acquisition or local secondary oscillator (constant-temperature crystal oscillator or rubidium atomic clock) of time difference signal servo.

Summary of the invention

Technical problem: the object of this invention is to provide a kind of utilize optical fiber link to realize new method that high accuracy time-frequency mixes biography.The method adopts and the special demarcation of transmitted frequency marking being realized to Time Transmission, realizing time-delay precompensation by measuring poor, that utilization the compensates frequency marking phase place method of time-delay calculation frequency plot second, ensure that the high accuracy that time delay is transmitted.In this method, slave station simultaneously recovery time and frequency signal from the light signal received, and to live again frequency signal without the need to local Secondary Clock servo, therefore there is the advantage that system configuration is simple, facilitate application of the manystage cascade connection and plug and play.

Technical scheme: optical fiber time frequency hybrid transmission method of the present invention comprises the following steps:

A). whole second is demarcated: main website normally transmits 10MHz frequency signal to slave station, carries out special demarcation in the place 10MHz cycle whole second;

B) after the special demarcation of slave station identification, remove mark and recover normal frequency signal, be required frequency standard signal, and with this frequency standard signal for clock, exporting second along obtaining timing signal in the mark cycle, completing time service; While standing in recovery frequency marking and timing signal, to the mixed number of delivering a letter of time-frequency that main website former state passback receives, measure for main website loopback delay;

C). frequency marking phase compensation amount calculates: the phase compensation of frequency marking is for offsetting the impact of forward direction overall delay, and namely in one second time, phase place shifts to an earlier date total amount and is equivalent to delay volume;

D). frequency marking phase place electrical domain compensation: main website utilized delay unit to coordinate 10MHz clock before electro-optical conversion, realized uniform phase compensation within next second, make slave station recover frequency and timing signal synchronous with main website.

Described special demarcation is special demarcation is encode to whole cycle second, the hopping edge invariant position of cataloged procedure hold period signal, only inserting the rising edge that a narrow negative pulse is used to refer to next cycle in 10MHz periodic signal high level centre position is pulse per second (PPS) rising edge.Receiving terminal utilizes combinational logic to remove negative pulse mark recovery normal frequency signal, and according to mark position, using the frequency signal recovered as clock signal, utilizes sequential logic to recover timing signal.

Beneficial effect: whole scaling method second frequency when optical fiber link achieves that the present invention proposes first is mixed to be passed, the frequency signal that slave station can be demarcated from optical fiber link directly obtains frequency and timing signal, to live again frequency time signal without the need to servo Secondary Clock, the mixing of high-precision time-frequency can be realized at a lower cost and transmit.The method have unifying datum, stability high, facilitate cascade, be easy to ensure that time-frequency mixes the long-term stability of biography and the advantage of short-term stability simultaneously.

Method of the present invention is adopted to test equipment model machine at laboratory environment, its test block diagram as shown in Figure 2, the pulse per second (PPS) that benchmark rubidium atomic clock exports and 10MHZ frequency signal inject central station, the time-frequency that central station utilizes the present invention to propose is mixed wears method, utilize the optical fiber link of about 25Km that frequency time signal is delivered to terminal station, the pps pulse per second signal recovered in terminal station and clock source pps pulse per second signal utilize time interval measuring instrucment table SRS620 to carry out real-time matching measurement, thus obtain time service error.The 10MHZ frequency signal directly exported in the 10MHZ frequency signal utilizing SRS620 to be recovered in terminal station and rubidium atom is compared and is measured, thus measures the performance of Frequency Transfer.

Accompanying drawing explanation

Fig. 1 is that fundamental diagram is transmitted in optical fiber frequency time of the present invention mixing.

Fig. 2 is optical fiber frequency time mixing transmission equipment experiment test block diagram of the present invention.

Fig. 3 is the time service error testing structure of experiment test.

Fig. 4 is the Frequency Transfer Stabilily parameter result of experiment test.

Embodiment

(a). whole second is demarcated: main website normally transmits 10MHz frequency signal to slave station, carries out special demarcation in the place 10MHz cycle whole second, and scaling method diagram is shown in Fig. 1.After the special demarcation of slave station identification, remove mark and recover normal frequency signal, be required frequency standard signal.And with this frequency marking for clock, exporting second along obtaining timing signal in the mark cycle, completing time service.While standing in recovery frequency marking and timing signal, to the mixed number of delivering a letter of time-frequency that main website former state passback receives, measure for main website loopback delay.

(b). loopback delay is measured: main website recovers timing signal according to the method for above-mentioned slave station from return path signal, and utilize internal time interval measurement unit dynamic measurement recover the time delay T of timing signal and local timing signal _m, time delay T _mdeduct the two-way total fixed delay τ of terminal device _c, obtain bidirectional fiber link propagation delay T _dp, T _dp=T _m-τ _c, τ _chave nothing to do with optical fiber link length.

(c). main website is timed to slave station recovery timing signal One Way Delay second calculating T local second _f: main website calculates fiber lengths L, forward and backpropagation delay inequality δ thus the optical fiber link forward-propagating time delay P obtained from main website to slave station _f, add forward direction fixed delay τ _fobtain required unidirectional overall delay T _f.

L=T _dp·C/(2n)，δ=D _λc(λ _f-λ _R)L

P _f=(T _dp+ δ)/2, T _f=P _f+ τ _f(formula 1)

Wherein, C is vacuum light speed, and n represents optical fibre refractivity, D _{λ c}represent central wavelength abbe number, λ _fand λ _rrepresent that main website is to slave station forward direction and reverse laser carrier wavelength respectively.

(d). frequency marking phase compensation amount calculates: the phase compensation of frequency marking is for offsetting forward direction overall delay T _fimpact, namely in one second time, phase place shifts to an earlier date total amount and is equivalent to delay volume T _fophase compensation is completed by the means of delay compensation, and delay volume adopts digital form to realize, and resolution is 10ps.

(e). frequency marking phase place electrical domain compensation: main website have employed the signal of telecommunication delay unit that resolution is 10ps before electro-optical conversion.Main website utilizes delay unit to coordinate 10MHz clock, within 10M the cycle of next second, evenly choose several cycles, and each cycle shifts to an earlier date 10ps successively, and keeps scalar period constant.Thus ensure that frequency signal that slave station recovers with main website same-phase and recover second timing signal and main website synchronous.

As shown in Figure 2, optical fiber time-frequency of the present invention mixes transmission method, comprises the following steps:

(a). main station system powers up, and is sent to slave station according to local frequency marking and second in timing signal demarcation 10MHz frequency signal whole cycle second.

(b). slave station is removed frequency marking and is marked and to obtain required frequency signal from the signal received, then produces timing signal required second according to frequency signal and mark position, and the fibre circuit signal former state simultaneously received is looped back to main website.

(c). main website extracts with reference to timing signal second according to the method that slave station is identical from loopback signal, and utilizes internal time interval measurement unit to measure local timing and the time interval with reference to timing.

(d). in main website, bonding apparatus fixed delay, according to the total One Way Delay of formula 1 accurate Calculation main website to slave station.

(e). according to certain filter rule, try to achieve frequency marking phase compensation amount by One Way Delay.

(f). main website utilizes this to determine frequency marking benchmark and signal of telecommunication delay unit realizes uniform phase place electrical domain compensation within next second, completes simultaneously and demarcates whole second.

(g). get back to step (b), so repeatedly.

Claims (2)

1. an optical fiber time frequency hybrid transmission method, is characterized in that the method comprises the following steps:

A). whole second is demarcated: main website normally transmits 10MHz frequency signal to slave station, carries out special demarcation in the place 10MHz cycle whole second;

B) after the special demarcation of slave station identification, remove mark and recover normal frequency signal, be required frequency standard signal, and with this frequency standard signal for clock, exporting second along obtaining timing signal in the mark cycle, completing time service; While standing in recovery frequency marking and timing signal, to the mixed number of delivering a letter of time-frequency that main website former state passback receives, measure for main website loopback delay; Described loopback delay is measured: main website recovers timing signal according to the method for above-mentioned slave station from return path signal, and utilize internal time interval measurement unit dynamic measurement recover the time delay T of timing signal and local timing signal _m, time delay T _mdeduct the two-way total fixed delay τ of terminal device _c, obtain bidirectional fiber link propagation delay T _dp, T _dp=T _m-τ _c, τ _chave nothing to do with optical fiber link length;

Main website is timed to slave station recovery timing signal One Way Delay second calculating T local second _f: main website calculates fiber lengths L, forward and backpropagation delay inequality δ thus the optical fiber link forward-propagating time delay P obtained from main website to slave station _f, add forward direction fixed delay τ _fobtain required unidirectional overall delay T _f;

$L=T_{\mathrm{dp}}\·C/\left(2n\right),\mathrm{\δ}=D_{{\mathrm{\λ}}_c}({\mathrm{\λ}}_f-{\mathrm{\λ}}_R)L$

P _f=(T _dp+ δ)/2, T _f=P _f+ τ _fformula 1

Wherein, C is vacuum light speed, and n represents optical fibre refractivity, represent central wavelength abbe number, λ _fand λ _rrepresent that main website is to slave station forward direction and reverse laser carrier wavelength respectively;

C). frequency marking phase compensation amount calculates: the phase compensation of frequency marking is for offsetting the impact of forward direction overall delay, and namely in one second time, phase place shifts to an earlier date total amount and is equivalent to delay volume;

D). frequency marking phase place electrical domain compensation: main website utilized delay unit to coordinate 10MHz clock before electro-optical conversion, realized uniform phase compensation within next second, make slave station recover frequency and timing signal synchronous with main website.

2. optical fiber time frequency hybrid transmission method according to claim 1, it is characterized in that described special demarcation is encoded to whole cycle second, the hopping edge invariant position of cataloged procedure hold period signal, only inserting the rising edge that a narrow negative pulse is used to refer to next cycle in 10MHz periodic signal high level centre position is pulse per second (PPS) rising edge; Receiving terminal utilizes combinational logic to remove negative pulse mark recovery normal frequency signal, and according to mark position, using the frequency signal recovered as clock signal, utilizes sequential logic to recover timing signal.