CN110266623A - A kind of LEO satellite communication systems carrier synchronization method based on 5G - Google Patents

A kind of LEO satellite communication systems carrier synchronization method based on 5G Download PDF

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CN110266623A
CN110266623A CN201910487070.7A CN201910487070A CN110266623A CN 110266623 A CN110266623 A CN 110266623A CN 201910487070 A CN201910487070 A CN 201910487070A CN 110266623 A CN110266623 A CN 110266623A
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period
signal
pss
estimation
value
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CN110266623B (en
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崔高峰
田丁
赵月
童建飞
王卫东
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Beijing University of Posts and Telecommunications
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Beijing University of Posts and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18517—Transmission equipment in earth stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Abstract

The invention discloses a kind of LEO satellite communication systems carrier synchronization method based on 5G, belongs to field of communication technology.First to current period, ground based terminal receives the primary synchronization signal that satellite issues by filter, is PSS time-domain signal by sample quantization and stores.Then filter receives the primary synchronization signal of next cycle and sample quantization is time-domain signal, in conjunction with the time-domain signal of upper a cycle, carries out the estimation of frequency deviation change rate, then carry out Estimation Optimization by Kalman Filter 1.The primary synchronization signal of current period is subjected to offset estimation, obtains frequency deviation value, in conjunction with the frequency deviation change rate estimated value of the primary synchronization signal, Estimation Optimization is carried out by Kalman Filter 2.Finally using the optimal estimation value of the optimal estimation value of current period frequency deviation change rate and frequency deviation, frequency deviation compensation is carried out to data-signal, realizes the digital signal after carrier synchronization, outgoing carrier synchronize.The present invention improves the robustness of estimated accuracy and carrier synchronization strategy, can be applied in the environment of low signal-to-noise ratio.

Description

A kind of LEO satellite communication systems carrier synchronization method based on 5G
Technical field
The invention belongs to field of communication technology, specifically a kind of LEO satellite communication systems carrier synchronization side based on 5G Method.
Background technique
For OFDM technology since spectrum efficiency is high, the advantages such as ability of anti-multipath is strong are widely used in land mobile system System, such as LTE, WiMax etc..5th Generation Mobile Communication System (5G) still uses core of the OFDM technology as physical layer transmission Technology, but OFDM technology is more sensitive to the carrier frequency offset of sending and receiving end, this is that limitation OFDM technology is mobile logical in satellite Widely applied main problem in letter.
Compared to land mobile communication system, low rail (Low Earth Orbit, LEO) satellite communication system has covering The features such as range is wide, not vulnerable to physical attacks and Effect of Natural Disaster, for being not easy to carry out land mobile communication system covering The disaster area etc. that region (such as high mountain, ocean and desert etc.) and land mobile communication system are destroyed, LEO satellite communication system Mobile communication service can be preferably provided, meanwhile, 3GPP is it is also proposed that using LEO satellite mobile communication system as land mobile Supplement, incorporate 5G communication standard formulate the considerations of within the scope of.
Ofdm signal is to transmit in the subchannel of multiple spectrum overlappings simultaneously, is carried in order to accurately receive every height Information on wave must assure that the orthogonality between subcarrier in receiving end, but Doppler effect can to receive signal hair Offset on raw frequency domain, destroys the orthogonality between receiving terminal carrier wave, leads to the sharply deterioration of receptivity, so carrier wave is same Step algorithm is one of the key technology that OFDM technology is applied to LEO satellite mobile communication system.
Since LEO satellite movement speed is fast, there are large scale time-varying frequency deviations between ground based terminal, this to receive and dispatch both ends Carrier synchronization face very big problem.Relative to land mobile communication system, the relative motion of high speed can generate large scale Doppler shift, the range of this offset estimation for requiring receiver to need to have sufficiently large, in addition, in LEO satellite communication system Middle Doppler shift can quickly be changed with the time, and the estimation of Doppler shift change rate will also be included in examining for carrier synchronization Consider range, Carrier Synchronization is the major issue that LEO satellite communication system needs to solve.
In terms of offset estimation, the Doppler shift sub-carrier interval in ofdm system is normalized, then Doppler Influence of the effect to ofdm system can be divided into integer frequency offset and fractional part of frequency offset, carry out small several times and integer frequency offset respectively Estimation be improve frequency offset estimation range important way.
In terms of the estimation of frequency deviation change rate, existing research considers according to the cyclic prefix or one in an ofdm system The extraction of frequency deviation rate of change information is carried out in a synchronization signal, although estimation range is considerably beyond the change of practical frequency deviation change rate Change range, but estimated accuracy is low, it is impossible to meet actual demands.In addition, due under the conditions of satellite communication path loss it is serious, Effective carrier synchronization can be carried out under Low SNR is also problem to be solved.
Summary of the invention
In order to facilitate merging for LEO satellite communication system and 5G land mobile communication system, the present invention provides one kind and is based on The LEO satellite communication system carrier synchronous method of 5G estimates large scale frequency deviation and frequency deviation by the primary synchronization signal that the period sends Change rate carries out the compensation of carrier wave frequency deviation, solves the problems, such as that OFDM technology is applied in LEO satellite communication system.
Specific step is as follows:
Step 1: being directed to current period, certain LEO satellite issues primary synchronization signal, and ground based terminal carries out time synchronization capture Then the position of the primary synchronization signal receives the primary synchronization signal by filter.
Primary synchronization signal is expressed from the next:
Wherein s (t) indicates the PSS time-domain signal that t moment transmitting terminal is sent, r (t) indicate t moment by after channel by frequency The PSS time-domain signal that the receiving end that inclined and white noise influences receives, θ0Indicate that t moment receiving end receives the initial phase of signal Offset, it is constant in the duration of OFDM symbol.fd(t) the Doppler shift value changed with moment t is indicated, by following formula table Show: fd(t)=fd+fa·t；fdIndicate initial Doppler frequency deviation value, faIndicate Doppler shift change rate.N (t) indicates t moment White Gaussian noise.
Step 2: the primary synchronization signal of current period is sampled by ADC, is quantified as PSS time-domain signal and is stored in It is local；
The sampling number of each OFDM symbol is N, then the duration T of each sampled pointsAre as follows:
fsFor sample frequency, Δ f is system subcarrier interval；
In t=kTsWhen, the signal received is quantified, the expression of PSS time-domain signal is obtained are as follows:
Wherein, s (k) is local transmitting terminal synchronous PSS time-domain signal sent in current period；K=0,1 ..., N- 1, ε=fd/ Δ f is normalization Doppler shift, γ=fa/(Δf·fs) it is normalization Doppler shift change rate.
Step 3: it is time-domain signal that filter, which receives the primary synchronization signal of next cycle and sample quantization, in conjunction with storage Upper a cycle time-domain signal, carry out the estimation of frequency deviation change rate, then by Kalman Filter 1 carry out Estimation Optimization.
The estimation procedure of frequency deviation change rate is as follows:
Firstly, being directed to m-th of period and the m-1 period, then the continuous PSS time domain sequences of two received are respectively rm-1(k) and rm(k):
εmFor the normalization Doppler shift in m-th of period, εm-1For the normalization Doppler shift in the m-1 period, and εm=εm-1+γmL, γmFor the normalization Doppler shift ε in m-th of periodmChange rate；L=fs·TPSSFor PSS time domain letter Number sending cycle duration TPSSInterior total number of sample points；θmIndicate that the initial phase of m-th of period receiving end reception signal is inclined It moves；θm-1Indicate that the m-1 period receiving end receives the initial phase offset of signal.
Then, receive two PSS time domain sequences are subjected to point-by-point conjugate multiplication, obtain time domain correlation sequence R (k):
Then, time domain correlation sequence R (k) is divided into two sections of front and back and carries out correlation, obtain correlation C1:
Finally, utilizing correlation C1Calculate the estimated value of the Doppler shift change rate in m-th of period；
Calculation formula are as follows:
I.e. the estimation range of Doppler shift change rate is (- Δ f/TPSS,Δf/TPSS], with the subcarrier spacing of system at Direct ratio, the sending cycle T with PSS time-domain signalPSSIt is inversely proportional.
The process of 1 Estimation Optimization of Kalman Filter is as follows:
Utilize the optimal estimation value of the frequency deviation change rate in the m-1 periodIt is counted by Kalman Filter 1 Calculate the optimal estimation value of m-th of period frequency deviation change rate
Wherein, optimal estimation valueInitial value is set at random；For the Doppler shift variation in m-th of period The measured value of rate, the estimated value of value and frequency deviation change rateIt is identical.
Kg1(m) it is kalman gain, is obtained by following formula:
Wherein R1For the system noise during Kalman Filter 1, Q1For the survey during Kalman Filter 1 Measure noise.P1(m-1) when being m-1 period Kalman Filter 1 optimal variance, initial value sets at random；For The prediction variance of m-th of period Kalman Filter 1.
To the optimal variance P in m-th of period1(m) be updated, for the m+1 period Kalman Filter 1 repeatedly Generation:
Step 4: the primary synchronization signal of current period is carried out offset estimation, frequency deviation value is obtained, in conjunction with the primary synchronization signal Frequency deviation change rate estimated value, pass through Kalman Filter 2 carry out Estimation Optimization.
The process of offset estimation is as follows:
The primary synchronization signal in m-th of periodIn, normalize Doppler shift εmFor decimal frequency multiplication Inclined εfWith integer frequency offset εiSum；Fractional part of frequency offset ε is carried out firstfEstimation:
By the primary synchronization signal r in m-th of periodm(k) the signal s (k) of transmission synchronous with local transmitting terminal is carried out point by point altogether Yoke is multiplied, and removes the modulation intelligence of synchronization signal, obtains time domain correlation sequence cm(k):
Then by time domain correlation sequence cm(k) it is divided into two parts and carries out correlation, obtains correlation C2:
Due to plural argument range be (- π, π], so fractional part of frequency offset is estimated by following formula:
Wherein arg { } indicates calculated complex argument.
Then by the primary synchronization signal r in m-th of periodm(k) it after compensating fractional part of frequency offset, then carries out integer frequency offset and estimates Meter:
By the compensated primary synchronization signal r of fractional part of frequency offsetc(k) sequence takes out N by FFT transform to frequency domainPSS=127 The reception frequency domain PSS sequence R of positionc(n), wherein n=0,1 ..., NPSS-1；Then integer frequency offset is obtained by following formula:
G is the auxiliary variable of cyclic shift；S (n) is that locally generated transmission signal s (k) synchronous with transmitting terminal is identical Frequency domain PSS sequence；
Then the Doppler shift estimated value in m-th of period is
The process of 2 Estimation Optimization of Kalman Filter is as follows:
Utilize the Doppler shift estimated value in the m-1 periodWith the optimal estimation value of frequency deviation change rateThe optimal estimation value of the Doppler shift in m-th of period is calculated by Kalman Filter 2
Wherein, optimal estimation valueInitial value is set at random；For the survey of the offset estimation value in m-th of period The estimated value of magnitude, value and Doppler shiftIt is identical.
Kg2(k) it is kalman gain, is obtained by following formula:
Wherein R2For the system noise during Kalman Filter 2, Q2For the measurement during Kalman Filter2 Noise.
P2(m-1) when being m-1 period Kalman Filter 2 optimal variance, initial value sets at random； For the prediction variance of m-th of period Kalman Filter 2.
To the optimal variance P in m-th of period2(m) be updated, for the m+1 period Kalman Filter 2 repeatedly Generation:
Step 5: using the optimal estimation value of the frequency deviation change rate of current period and the optimal estimation value of frequency deviation, to reception To data-signal carry out frequency deviation compensation to realize the digital signal after carrier synchronization, outgoing carrier synchronize.
For m-th of period, carrier synchronization calculation formula are as follows:
X (k) is after receiving current PSS and before next PSS arrival, and the time domain data after ADC received is believed Number, y (k) is the time domain data signal after carrier synchronization.
The present invention has the advantages that
1) a kind of, LEO satellite communication systems carrier synchronization method based on 5G passes through the main synchronous letter in 5G frame structure The estimation for number carrying out frequency deviation and frequency deviation change rate, is suitable for multicarrier system, mobile convenient for LEO satellite communication system and land 5G The fusion of communication system.
2) a kind of, LEO satellite communication systems carrier synchronization method based on 5G is completed big in a PSS duration Scale offset estimation carries out the estimation of Doppler shift change rate in a PSS sending cycle, improves estimated accuracy, and And Kalman filter is combined, the robustness of carrier synchronization strategy is improved, the strategy is made to can be applied to the ring of low signal-to-noise ratio In border.
Detailed description of the invention
Fig. 1 is the LEO satellite communication systems carrier synchronization schematic diagram the present invention is based on 5G；
Fig. 2 is a kind of LEO satellite communication systems carrier synchronization method flow chart based on 5G of the present invention；
Fig. 3 is distribution map of the PSS time-domain signal of the present invention in SSB.
Specific embodiment
Below in conjunction with attached drawing and example, the present invention is described in further detail.
A kind of LEO satellite communication systems carrier synchronization method based on 5G of the present invention, as shown in Figure 1, certain LEO satellite is sent out After primary synchronization signal is received by filter out, receives signal and pass through ADC, progress sample quantization is PSS time-domain signal, simultaneously The estimation of frequency deviation and frequency deviation change rate is carried out, specifically: two cadence of small several times and integral multiple is carried out in a PSS duration Estimation partially improves frequency offset estimation range；Frequency deviation change rate is carried out using two continuous PSS in a PSS sending cycle Estimation improves frequency deviation change rate estimated accuracy, is finally utilized respectively the stability that Kalman filter 1 and 2 improves estimation, realizes To the carrier synchronization of digital signal.
As shown in Figure 2, the specific steps are as follows:
Step 1: being directed to current period, certain LEO satellite issues primary synchronization signal, and ground based terminal carries out time synchronization capture Then the position of the primary synchronization signal receives the primary synchronization signal by filter.
Each primary synchronization signal is PSS time-domain signal in 5G system, is transmitted in synchronization/broadcast singal block (SSB), The time-frequency structure of SSB as shown in figure 3, as can be seen from the figure PSS occupies 127, the center subcarrier of SSB on frequency domain, when PSS occupies 1 OFDM symbol on domain, and the sending cycle of SSB is configurable, and for the robustness of system, the present embodiment is using transmission The highest configuration T of densityPSSThe every 5ms of=5ms, i.e. PSS sends primary.
It is influenced by large scale time-varying Doppler shift, receiving end receives the OFDM symbol comprising PSS can be by following formula table Show:
Wherein s (t) indicates the PSS time-domain signal that t moment transmitting terminal is sent, r (t) indicate t moment by after channel by frequency The PSS time-domain signal that the receiving end that inclined and white noise influences receives, θ0Indicate that t moment receiving end receives the initial phase of signal Offset, it is constant in the duration of OFDM symbol.fd(t) the Doppler shift value changed with moment t is indicated, by following formula table Show: fd(t)=fd+fa·t；fdIndicate initial Doppler frequency deviation value, faIndicate Doppler shift change rate.N (t) indicates t moment White Gaussian noise.
Step 2: the primary synchronization signal of current period is sampled by ADC, is quantified as time-domain digital signal and is stored in It is local；
The sampling number of each OFDM symbol is N, then the duration T of each sampled pointsAre as follows:
fsFor sample frequency, Δ f is system subcarrier interval；
In t=kTsWhen, the digital signal after sampling to analog signal indicates are as follows:
Wherein, s (k) is local transmitting terminal synchronous PSS time-domain signal sent in current period；K=0,1 ..., N- 1, ε=fd/ Δ f is normalization Doppler shift, γ=fa/(Δf·fs) it is normalization Doppler shift change rate.
Step 3: filter receives the primary synchronization signal of next cycle and sample quantization is time-domain digital signal, in conjunction with The time-domain digital signal of the upper a cycle of storage carries out the estimation of frequency deviation change rate, then is estimated by Kalman Filter 1 Meter optimization.
Since in LEO satellite mobile communication system, Doppler shift change rate is changed over time very slowly, the hair of PSS Sending the period is 5ms, interior during this period to think that Doppler shift change rate remains unchanged.Doppler shift change rate and PSS sequence Phase offset in time domain is related, in order to improve the estimated accuracy of frequency deviation change rate, (i.e. one in a big time scale A PSS sending cycle) carry out frequency deviation change rate estimation the phase offset in time domain can be accumulated, make algorithm for estimating to frequency deviation Change rate is more sensitive.
The estimation procedure of frequency deviation change rate is as follows:
Firstly, being directed to m-th of period and the m-1 period, then the continuous PSS time domain sequences of two received are respectively rm-1(k) and rm(k):
εmFor the normalization Doppler shift in m-th of period, εm-1For the normalization Doppler shift in the m-1 period, Under the influence of Doppler shift change rate, Doppler shift carries out linear accumulation: ε in PSS sending cyclem=εm-1+γmL, γmFor the normalization Doppler shift ε in m-th of periodmChange rate；L=fs·TPSSContinue for PSS time-domain signal sending cycle Duration TPSSInterior total number of sample points；θmIndicate that m-th of period receiving end receives the initial phase offset of signal；θm-1Indicate m- 1 period receiving end receives the initial phase offset of signal.
Then, receive two PSS time domain sequences are subjected to point-by-point conjugate multiplication, obtain time domain correlation sequence R (k):
Then, time domain correlation sequence R (k) is divided into two sections of front and back and carries out correlation, obtain correlation C1:
Finally, utilizing correlation C1Calculate the estimated value of the Doppler shift change rate in m-th of period；
Calculation formula are as follows:
I.e. the estimation range of Doppler shift change rate be (- 1/L, 1/L], i.e. (- Δ f/TPSS,Δf/TPSS], with system Subcarrier spacing it is directly proportional, the sending cycle T with PSS time-domain signalPSSIt is inversely proportional.
In LEO satellite mobile communication system, system needs work under the conditions of very low signal-to-noise ratio, Kalman filter It can be used for Doppler shift and the estimation of Doppler shift change rate to improve the stability of estimation, resist noise to estimation performance It influences, guarantees validity of the system under Low SNR.
The process of 1 Estimation Optimization of Kalman Filter is as follows:
Utilize the optimal estimation value of the frequency deviation change rate in the m-1 periodIt is counted by Kalman Filter 1 Calculate the optimal estimation value of m-th of period frequency deviation change rate
Wherein, For the predicted value of m-th of period frequency deviation change rate；Optimal estimation valueInitial value is set at random；For the measured value of the Doppler shift change rate in m-th of period, value and frequency deviation become The estimated value of rateIt is identical.
Kg1(m) it is kalman gain, is obtained by following formula:
Wherein R1For the system noise during Kalman Filter 1, Q1For the survey during Kalman Filter 1 Measure noise.P1(m-1) when being m-1 period Kalman Filter 1 optimal variance, initial value sets at random；For The prediction variance of m-th of period Kalman Filter 1.
To the optimal variance P in m-th of period1(m) be updated, for the m+1 period Kalman Filter 1 repeatedly Generation:
Step 4: the primary synchronization signal of current period is carried out offset estimation, Doppler shift value is obtained, it is same in conjunction with the master The frequency deviation change rate estimated value for walking signal carries out Estimation Optimization by Kalman Filter 2.
The process of offset estimation is as follows:
PSS is broadcasted by the period of 5ms, occupies the fixation N in 1 OFDM symbolPSS=127 subcarriers, it is assumed that be System has obtained sign synchronization, and the OFDM symbol where PSS is carried out bandpass filtering at this time, obtains m-th of period to be processed Primary synchronization signalIn, normalize Doppler shift εmFor fractional part of frequency offset εfWith integer frequency offset εi Sum；Fractional part of frequency offset ε is carried out firstfEstimation:
By the primary synchronization signal r in m-th of periodm(k) the signal s (k) of transmission synchronous with local transmitting terminal is carried out point by point altogether Yoke is multiplied, and removes the modulation intelligence of synchronization signal, obtains time domain correlation sequence cm(k):
Then by time domain correlation sequence cm(k) it is divided into two parts and carries out correlation, obtains correlation C2:
Due to plural argument range be (- π, π], so fractional part of frequency offset is estimated by following formula:
Wherein arg { } indicates calculated complex argument.
Then by the primary synchronization signal r in m-th of periodm(k) it after compensating fractional part of frequency offset, then carries out integer frequency offset and estimates Meter:
Integer frequency offset is obtained according to the offset of PSS sequence relevant peaks in a frequency domain, and fractional part of frequency offset is compensated Primary synchronization signal rc(k) sequence takes out N by FFT transform to frequency domainPSS=127 reception frequency domain PSS sequence Rc(n), wherein N=0,1 ..., NPSS-1；Then integer frequency offset is obtained by following formula:
S (n) is the identical frequency domain PSS sequence of locally generated transmission signal s (k) synchronous with transmitting terminal；
Then the Doppler shift estimated value in m-th of period is
The process of 2 Estimation Optimization of Kalman Filter is as follows:
Utilize the Doppler shift estimated value in the m-1 periodWith the optimal estimation value of frequency deviation change rateThe optimal estimation value of the Doppler shift in m-th of period is calculated by Kalman Filter 2
Wherein, For the Doppler shift predicted value in m-th of period；It is optimal Estimated valueInitial value is set at random；For the measured value of the offset estimation value in m-th of period, value and Doppler The estimated value of frequency deviationIt is identical.
Kg2(k) it is kalman gain, is obtained by following formula:
Wherein R2For the system noise during Kalman Filter 2, Q2For the measurement during Kalman Filter2 Noise.P2(m-1) when being m-1 period Kalman Filter 2 optimal variance, initial value sets at random；It is The prediction variance of m period Kalman Filter 2.
To the optimal variance P in m-th of period2(m) be updated, for the m+1 period Kalman Filter 2 repeatedly Generation:
Step 5: using the optimal estimation value of the frequency deviation change rate of current period and the optimal estimation value of frequency deviation, to reception To data-signal carry out frequency deviation compensation to realize the digital signal after carrier synchronization, outgoing carrier synchronize.
For m-th of period, carrier synchronization calculation formula are as follows:
X (k) is after receiving current PSS and before next PSS arrival, and the time domain data after ADC received is believed Number, y (k) is the time domain data signal after carrier synchronization.

Claims (5)

1. a kind of LEO satellite communication systems carrier synchronization method based on 5G, which is characterized in that specific step is as follows:
Step 1: being directed to current period, certain LEO satellite issues primary synchronization signal, and ground based terminal carries out time synchronization and captures the master Then the position of synchronization signal receives the primary synchronization signal by filter；
Primary synchronization signal is expressed from the next:
Wherein s (t) indicates the PSS time-domain signal that t moment transmitting terminal is sent, r (t) indicate t moment by after channel by frequency deviation and The PSS time-domain signal that the receiving end that white noise influences receives, θ0Indicate that the initial phase of t moment receiving end reception signal is inclined It moves, it is constant in the duration of OFDM symbol；fd(t) the Doppler shift value changed with moment t is indicated, by following formula table Show: fd(t)=fd+fa·t；fdIndicate initial Doppler frequency deviation value, faIndicate Doppler shift change rate；N (t) indicates t moment White Gaussian noise；
Step 2: the primary synchronization signal of current period is sampled by ADC, is quantified as PSS time-domain signal and is stored in local；
Step 3: it is time-domain signal that filter, which receives the primary synchronization signal of next cycle and sample quantization, in conjunction with the upper of storage The time-domain signal of a cycle carries out the estimation of frequency deviation change rate, then carries out Estimation Optimization by Kalman Filter 1；
The estimation procedure of frequency deviation change rate is as follows:
Firstly, being directed to m-th of period and the m-1 period, then the continuous PSS time domain sequences of two received are respectively rm-1 (k) and rm(k):
S (k) is local transmitting terminal synchronous PSS time-domain signal sent in current period；K=0,1 ..., N-1, εmIt is m-th The normalization Doppler shift in period, εm-1For the normalization Doppler shift in the m-1 period, and εm=εm-1+γmL, γm For the normalization Doppler shift ε in m-th of periodmChange rate；L=fs·TPSSWhen continuing for PSS time-domain signal sending cycle Long TPSSInterior total number of sample points；θmIndicate that m-th of period receiving end receives the initial phase offset of signal；θm-1Indicate m-1 A period receiving end receives the initial phase offset of signal；
Then, receive two PSS time domain sequences are subjected to point-by-point conjugate multiplication, obtain time domain correlation sequence R (k):
Then, time domain correlation sequence R (k) is divided into two sections of front and back and carries out correlation, obtain correlation C1:
Finally, utilizing correlation C1Calculate the estimated value of the Doppler shift change rate in m-th of period；
Calculation formula are as follows:
I.e. the estimation range of Doppler shift change rate is (- Δ f/TPSS,Δf/TPSS], the subcarrier spacing with system is at just Than sending cycle T with PSS time-domain signalPSSIt is inversely proportional；
The process of 1 Estimation Optimization of Kalman Filter is as follows:
Utilize the optimal estimation value of the frequency deviation change rate in the m-1 periodM is calculated by Kalman Filter 1 The optimal estimation value of a period frequency deviation change rate
Wherein, optimal estimation valueInitial value is set at random；For the Doppler shift change rate in m-th period Measured value, the estimated value of value and frequency deviation change rateIt is identical；
Kg1(m) it is kalman gain, is obtained by following formula:
Wherein R1For the system noise during Kalman Filter 1, Q1It makes an uproar for the measurement during Kalman Filter 1 Sound；P1(m-1) when being m-1 period Kalman Filter 1 optimal variance, initial value sets at random；For m The prediction variance of a period Kalman Filter 1；
To the optimal variance P in m-th of period1(m) it is updated, the iteration for the m+1 period Kalman Filter 1:
Step 4: the primary synchronization signal of current period is carried out offset estimation, frequency deviation value is obtained, in conjunction with the frequency of the primary synchronization signal Inclined change rate estimated value carries out Estimation Optimization by Kalman Filter 2；
Step 5: using the optimal estimation value of current period frequency deviation change rate and the optimal estimation value of frequency deviation, to the number received It is believed that number carrying out frequency deviation compensation to realize the digital signal after carrier synchronization, outgoing carrier synchronize.
2. a kind of LEO satellite communication systems carrier synchronization method based on 5G as described in claim 1, which is characterized in that institute The sampling number for stating each OFDM symbol in step 2 is N, then the duration T of each sampled pointsAre as follows:
fsFor sample frequency, Δ f is system subcarrier interval；
In t=kTsWhen, the signal received is quantified, the expression of PSS time-domain signal is obtained are as follows:
Wherein, ε=fd/ Δ f is normalization Doppler shift, γ=fa/(Δf·fs) it is normalization Doppler shift change rate.
3. a kind of LEO satellite communication systems carrier synchronization method based on 5G as described in claim 1, which is characterized in that step The process of offset estimation described in rapid four is as follows:
The primary synchronization signal in m-th of periodIn, normalize Doppler shift εmFor fractional part of frequency offset εfWith Integer frequency offset εiSum；
Fractional part of frequency offset ε is carried out firstfEstimation:
By the primary synchronization signal r in m-th of periodm(k) the signal s (k) of transmission synchronous with local transmitting terminal carries out point-by-point conjugation phase Multiply, remove the modulation intelligence of synchronization signal, obtains time domain correlation sequence cm(k):
Then by time domain correlation sequence cm(k) it is divided into two parts and carries out correlation, obtains correlation C2:
Due to plural argument range be (- π, π], so fractional part of frequency offset is estimated by following formula:
Wherein arg { } indicates calculated complex argument；
Then by the primary synchronization signal r in m-th of periodm(k) after compensating fractional part of frequency offset, then integer frequency offset estimation is carried out:
By the compensated primary synchronization signal r of fractional part of frequency offsetc(k) sequence takes out N by FFT transform to frequency domainPSS=127 Receive frequency domain PSS sequence Rc(n), wherein n=0,1 ..., NPSS-1；Then integer frequency offset is obtained by following formula:
G is the auxiliary variable of cyclic shift；S (n) is the identical frequency domain of locally generated transmission signal s (k) synchronous with transmitting terminal PSS sequence；
Then the Doppler shift estimated value in m-th of period is
4. a kind of LEO satellite communication systems carrier synchronization method based on 5G as described in claim 1, which is characterized in that step The process of 2 Estimation Optimization of Kalman Filter described in rapid four is as follows:
Utilize the Doppler shift estimated value in the m-1 periodWith the optimal estimation value of frequency deviation change rateIt is logical Cross the optimal estimation value that Kalman Filter 2 calculates the Doppler shift in m-th of period
Wherein, optimal estimation valueInitial value is set at random；For the measured value of the offset estimation value in m-th of period, The estimated value of value and Doppler shiftIt is identical；
Kg2(k) it is kalman gain, is obtained by following formula:
Wherein R2For the system noise during Kalman Filter 2, Q2It makes an uproar for the measurement during Kalman Filter 2 Sound；P2(m-1) when being m-1 period Kalman Filter 2 optimal variance, initial value sets at random；For m The prediction variance of a period Kalman Filter 2；
To the optimal variance P in m-th of period2(m) it is updated, the iteration for the m+1 period Kalman Filter 2:
5. a kind of LEO satellite communication systems carrier synchronization method based on 5G as described in claim 1, which is characterized in that step M-th of period, the calculation formula of carrier synchronization are directed to described in rapid five are as follows:
X (k) is the time domain data signal after ADC received after receiving current PSS and before next PSS arrival, y It (k) is the time domain data signal after carrier synchronization.
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