CN106534035A - Timing synchronization method in low-orbit satellite communication system - Google Patents
Timing synchronization method in low-orbit satellite communication system Download PDFInfo
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- CN106534035A CN106534035A CN201611115883.6A CN201611115883A CN106534035A CN 106534035 A CN106534035 A CN 106534035A CN 201611115883 A CN201611115883 A CN 201611115883A CN 106534035 A CN106534035 A CN 106534035A
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- 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
- H04L27/2662—Symbol synchronisation
- H04L27/2665—Fine synchronisation, e.g. by positioning the FFT window
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- 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
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- 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
- H04L27/2662—Symbol synchronisation
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- Synchronisation In Digital Transmission Systems (AREA)
Abstract
The invention provides a timing synchronization method in a low-orbit satellite communication system. The timing synchronization method is characterized by comprising the following steps: selecting longest linear feedback shift register sequences to construct a training symbol, wherein the training symbol has two front and back reverse parts, the total length is N, the front half part N/2 is reverse to the back half part N/2, and meanwhile two parts N/4 in each N/2 part form conjugate antisymmetry; further improving a time domain structure of the training symbol, so that the time domain structure becomes a dual conjugate antisymmetry structure; and calculating the improved training symbol according to a timing synchronization measurement function to obtain a time domain measurement result. By adoption of the method, related peak values of timing positions can be eliminated, no platform effect is generated, and meanwhile the sidelobe phenomenon is also well inhibited.
Description
Technical field
The present invention relates to timing in LEO satellite communication systems technical field, more particularly to a kind of LEO satellite communication systems
Synchronous method.
Background technology
Satellite communication refers to setting on earth between the radio communication station of (including in ground, the water surface and lower atmosphere layer)
Make relay station forwarding using artificial earth satellite or launch radio wave, the communication carried out between two or more earth stations.
Satellite communication belongs to one kind of space radio communication, and compared with other communication modes, satellite communication has wide coverage, leads to
Letter capacity is big, distance is remote, do not limited by geographical conditions, it is stable and reliable for performance the advantages of, and with fiber optic communication, digital microwave telecommunication
Become the pillar of modern telecommunication together, obtained increasingly being widely applied.
According to the difference of satellite orbital altitude, satellite mobile communication system can be divided into stationary orbit (Geostationary
Orbit, GEO), middle orbit (Medium Earth Orbit, MEO) and low orbit (Low Earth orbit, LEO) these three.
Following communication needs to ensure to provide flexible multimedia service, therefore satellite to global any place, the user of any time
Communication is also faced with the challenge for supporting broadband high-speed multimedia service.GEO system technology matures, advantage of lower cost can be obtained
Larger coverage, but for wideband multimedia telecommunication satellite, high orbit means that transmission delay is big, launch cost
Also it is higher, and GEO geo-stationary orbit resource wretched insufficiencies at present, therefore people's one side consideration uses LEO satellite, separately
On the one hand using the transmission mechanism that band efficiency is high.The orbit altitude of LEO systems is low, lightweight, and the R＆D cycle is short, researches and develops into
This is low, while having the advantages that propagation delay time is short, link load is little, avoid the crowded of GEO tracks, has become the whole world in recent years
The study hotspot of satellite communication field.
Satellite mobile channel simultaneously has the feature of satellite channel and mobile channel, exist multipath effect, shadow effect,
Doppler effect, has a strong impact on the reliability of signal transmission.LEO satellite under complicated ground receiver environment, satellite-signal meeting
Blocked by building and trees, its channel has the characteristic of time-varying and decline again.As OFDM technology is to the efficient of frequency band
Using the rate of information throughput can be greatly improved；Experience geographical environment simultaneously during satellite communication transmission more complicated, OFDM's
The characteristics of anti-multipath, can weaken the negative effect of environment complicated and changeable to signal transmission.Therefore OFDM technology is led to satellite
Letter combines, and can play the advantage of OFDM technology, also complies with satellite communication development trend.
Although OFDM technology can effectively alleviate the nervous problem of LEO satellite band resource, which will to frequency synchronism
Ask very strict.As LEO satellite is very fast away from earth surface relatively near and translational speed, this will cause very considerable Doppler to be imitated
Should, so as to cause the time selective fading of channel.Doppler effect meeting for ofdm system, caused by satellite movement
Cause the destruction of orthogonality between subcarrier, cause inter-sub-carrier interference (Inter-channel Interference, ICI), from
And affect the effect of signal detection.Therefore study simultaneous techniquess effectively to suppress the Doppler effect in channel to LEO satellite
Ofdm system has very important realistic meaning.
It is one of two big shortcomings of OFDM technology to frequency deviation sensitivity, simultaneous techniquess are also one of key technology of OFDM.It is logical
Often ofdm system has carrier synchronization, sample-synchronous and Timing Synchronization, and in the synchronizing process of OFDM, it is fixed typically first to carry out
When synchronization.Timing Synchronization is for the original position for finding each OFDM symbol so that receiving terminal carries out FFT and transmitting terminal to be carried out
The window start/stop time of IFFT computings is identical, so as to realize correct demodulation.If Timing Synchronization is inaccurate may to affect to connect down
Come the offset estimation for carrying out, so that system Integral synchronous hydraulic performance decline, therefore Timing Synchronization is it is critical that link.State
Outer some scholars have been studied to this, and such as Schmid is in document [T.Schmidl, D.Cox.Robust Frequency
and Timing Synchronization for OFDM[J].IEEE Transactions on
Communications.1997,45(12):1613-1621.] in propose a kind of synchronous method based on training sequence, but from
In the timing metric analogous diagram of the algorithm it is seen that, the timing metric of Schmidl algorithms exist near peak point one it is little
Platform, which can be that the determination of the original position of symbol brings error.To this H.Minn document [H.Minn, M.Zeng,
V.K.Bhargava.On Timing Offset Estimation for OFDM Systems[J].IEEE
Communications Letters.2000,4(7):242-244.] in propose a kind of improvement project, eliminate platform effect
Should, but its timing metric contains secondary lobe, and when signal to noise ratio is relatively low, side lobe levels may exceed main lobe so as to cause timing mould
Paste.
The content of the invention
The technical problem to be solved is to provide the time synchronization method in a kind of LEO satellite communication systems,
Solve the problems, such as timing ambiguities.
The problem is not solved, the present invention provides the time synchronization method in a kind of Low-Orbit Satellite Communication system, including：
Step one, construction training symbol, the training symbol total length are accorded with for N, first half N/2 and latter half N/2
Number conversely, while two parts N/4 in each N/2 part is in conjugate antisymmetry；
Step 2, the spatial structure for improving training symbol, make the spatial structure become the structure of dual conjugate antisymmetry；
Step 3, the training symbol after improvement is calculated according to Timing Synchronization metric function, obtained time-domain metrics knot
Really.
Further, the step one includes：
Step S1：N/2+1 sequence is continuously sent using m-sequence generator, x is designated as0(k), k=0,1 ..., N/2；
Step S2：By x0(k) by a null value difference device, to x01 zero is inserted between adjacent two sequence of (k)
Original sequence is changed into N+1, is designated as x by value point1(k), k=0,1 ..., N；
Step S3：By x1K () filters x by a high pass filter1First sequence of (k), now original sequence
It is changed into N number of, is designated as x2(k), k=1 ..., N；
Step S4：By x2K () carries out N point IFFT, be designated as x (k), k=1 ..., N.
Further, the step 2 includes：
Step S5：By x (k) respectively by two different band filters, BPF is designated as1:N/4And BPFN/4+1:N/2, respectively
Retain the 1～N/4 and N/4+1～N/2 sequence of x (k), the sequence after the two band filters can be abbreviated respectively
For x1:N/4And xN/4+1:N/2, and which is taken conjugation respectively, obtain x* 1:N/4And x* N/4+1:N/2；
Step S6：X=x is abbreviated as respectively1:N/4、X*=x* 1:N/4, Y=xN/4+1:N/2、Y*=x* N/4+1:N/2, and according to [X；Y；
X*；Y*] mode arranged.
Further, the Timing Synchronization metric function isWherein, d is in displacement correlation window the
The sequence number of one sample, sk, k-th sample sequence after the improvement that k=1 ..., N are received for receiving terminal in training symbol,It is to X, Y*In N/4 training symbol difference
Carry out dual related operation and sue for peace,For the energy value of training symbol after improvement.
Further, in the training symbol, X (k)=- Y*(N/4-1-k), k=0,1 ..., N/4-1, wherein X and Y are common
Yoke antisymmetry.
The present invention is reconfigured using alternative method to training symbol, proposes a kind of new dual conjugation with this
Antisymmetric structure, can eliminate the correlation peak of timing position when the timing metric of sign synchronization is carried out, and will not go out
Existing platform effect, while secondary lobe phenomenon has also obtained good suppression.
Description of the drawings
Spatial structure figures of the Fig. 1 for the training symbol of the embodiment of the invention；
Spatial structure figures of the Fig. 2 for the training symbol after the improvement of the embodiment of the invention；
Fig. 3 is the schematic flow sheet of the construction training symbol of the embodiment of the invention.
Specific embodiment
Time synchronization method in the LEO satellite communication systems for providing to the present invention below in conjunction with the accompanying drawings being embodied as
Mode elaborates.
It is an object of the invention to provide a kind of design of new LEO satellite ofdm system Timing Synchronization, the program
On the basis of original H.Minn schemes, training symbol is reconfigured using alternative method, one kind is proposed with this
New structure, to the correlation peak that can eliminate timing position when the timing metric of sign synchronization is carried out, so as to solve
The certainly problem of H.Minn schemes timing ambiguities.
In the specific embodiment of the present invention, the new building method adopted to training symbol is included following several
Step：
The first step：Select suitable PN sequences (PN (pseudo noise) sequence) to construct training symbol.By PN in the present embodiment
The reason for sequence is clearly m-sequence (longest linear feedback shift register sequence), selection m-sequence is its own good phase
Characteristic is closed, the needs of timing accuracy are so just disclosure satisfy that.Therefore odd subcarriers are allowed, during subcarrier is sent,
For 0, even subcarriers send m-sequence, before so after the Fast Fourier Transform Inverse (IFFT), entirely symbol will become
Contrary two parts afterwards.Here might as well assume total length for N, first half N/2 and latter half N/2 conversely, while each N/2
Two parts N/4 in part is in conjugate antisymmetry.Their structures in time domain are as shown in figure 1, wherein X and Y opposes in conjugation
Claim, i.e.,
X (k)=- Y*(N/4-1-k), k=0,1 ..., N/4-1 (1)
Wherein X and Y is conjugate antisymmetry.
Second step：The spatial structure of training symbol is improved further.In order to further enhance the conjugation of training symbol in Fig. 1
Symmetry, the spatial structure of the training symbol in Fig. 1 can be revised as the form of Fig. 2.Now in training symbol, X and Y is common
Yoke antisymmetry, and X*、Y*Sequence obtained by being then respectively after being conjugated to X, Y.So X*With Y, Y*It is antisymmetry with X,
Therefore two distinct types of conjugate antisymmetric sequence is there is in whole sequence：①X*With Y, X and Y*, and 2. (X；Y) with
(Y*；X*)。
For the training symbol shown in Fig. 2, can determine according to the symmetrical characteristic construction of the conjugation of two half part is new
When synchronization metric function, Timing Synchronization metric function adopted here is：
Wherein, d be shift correlation window in first sample sequence number, sk, k=1 ..., N is receiving terminal after improving
K-th sample sequence in the training symbol for receiving,
It is to X, Y*In N/4 training symbol carry out dual related operation respectively and sue for peace,To train after improvement
The energy value of symbol.
It is not difficult to find out from above, two summation operations are contained in P (d), and one is X and X*, Y and Y*Conjugation, another is
X and Y, X*With Y*Conjugate antisymmetry.
As the training structure in Fig. 2 uses the structure of dual conjugate antisymmetry, thus with Schmidl and
The spatial structure of the training symbol proposed by H.Minn is compared, and its peak value after being sued for peace can be obvious, is not in
Platform effect, while secondary lobe phenomenon has also obtained good suppression.
Fig. 3 is refer to, is the schematic flow sheet for constructing training symbol.
Step S1：N/2+1 sequence is continuously sent using m-sequence generator, x is designated as0(k), k=0,1 ..., N/2.
Step S2：By x0(k) by a null value difference device, to x01 zero is inserted between adjacent two sequence of (k)
Original sequence is changed into N+1, is designated as x by value point1(k), k=0,1 ..., N.
Step S3：By x1K () filters x by a high pass filter (High-PassFilter, HPF)1The first of (k)
Individual sequence, now original sequence are changed into N number of, are designated as x2(k), k=1 ..., N.It is seen that, x2K the odd numbered sequences in () are
0, even order is m-sequence.
Step S4：By x2K () carries out N point IFFT, be designated as x (k), k=1 ..., N.The front N/2 of the sequence and rear N/2 parts
Conversely, while the front and rear part of each N/2 is in conjugate antisymmetry, its time-domain signal structure is as shown in Figure 1.
Step S5：By x (k) respectively by two different band filters (Band-Pass Filter, BPF), it is designated as
BPF1:N/4And BPFN/4+1:N/2, retain the 1～N/4 and N/4+1～N/2 sequence of x (k) respectively, after the two BPF
Sequence can be abbreviated as x respectively1:N/4And xN/4+1:N/2, and which is taken conjugation respectively, obtain x* 1:N/4And x* N/4+1:N/2。
Step S6：Sequence of this 4 length for N/4 is abbreviated as into X=x respectively1:N/4、X*=x* 1:N/4, Y=xN/4+1:N/2、
Y*=x* N/4+1:N/2, and according to [X；Y；Y*；X*] mode arranged, the time-domain signal structure in Fig. 2 is just obtained.
Also include：Training symbol is calculated according to the Timing Synchronization metric function in formula (2), can be compared
The more excellent time-domain metrics of training symbol that Schmidl and H.Minn are proposed are as a result, it is possible to eliminate the relevant peaks of timing position
Value, solves the problems, such as timing ambiguities.
The above is only the preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art
Member, under the premise without departing from the principles of the invention, can also make some improvements and modifications, and these improvements and modifications also should be regarded as
Protection scope of the present invention.
Claims (5)
1. the time synchronization method in a kind of Low-Orbit Satellite Communication system, it is characterised in that include：
Step one, construction training symbol, the training symbol total length is N, first half N/2 and latter half N/2 symbol phases
Instead, while two parts N/4 in each N/2 part is in conjugate antisymmetry；
Step 2, the spatial structure for improving training symbol, make the spatial structure become the structure of dual conjugate antisymmetry；
Step 3, the training symbol after improvement is calculated according to Timing Synchronization metric function, obtained time-domain metrics result.
2. the time synchronization method in Low-Orbit Satellite Communication system according to claim 1, it is characterised in that the step
Rapid one includes：
Step S1：N/2+1 sequence is continuously sent using m-sequence generator, x is designated as0(k), k=0,1 ..., N/2；
Step S2：By x0(k) by a null value difference device, to x01 zero point is inserted between adjacent two sequence of (k),
Original sequence is changed into into N+1, x is designated as1(k), k=0,1 ..., N；
Step S3：By x1K () filters x by a high pass filter1K first sequence of (), now original sequence are changed into N
It is individual, it is designated as x2(k), k=1 ..., N；
Step S4：By x2K () carries out N point IFFT, be designated as x (k), k=1 ..., N.
3. the time synchronization method in Low-Orbit Satellite Communication system according to claim 2, it is characterised in that the step
Rapid two include：
Step S5：By x (k) respectively by two different band filters, BPF is designated as1:N/4And BPFN/4+1:N/2, retain x respectively
K 1～the N/4 of () and N/4+1～N/2 sequence, the sequence after the two band filters can be abbreviated as respectively
x1:N/4And xN/4+1:N/2, and which is taken conjugation respectively, obtain x* 1:N/4And x* N/4+1:N/2；
Step S6：X=x is abbreviated as respectively1:N/4、X*=x* 1:N/4, Y=xN/4+1:N/2、Y*=x* N/4+1:N/2, and according to [X；Y；Y*；
X*] mode arranged.
4. the time synchronization method in Low-Orbit Satellite Communication system according to claim 1, it is characterised in that described fixed
When synchronization metric function beWherein, d be shift correlation window in first sample sequence number, sk,
K-th sample sequence after the improvement that k=1 ..., N are received for receiving terminal in training symbol,It is to N/4 training symbol difference in X, Y*
Carry out dual related operation and sue for peace,For the energy value of training symbol after improvement.
5. the time synchronization method in Low-Orbit Satellite Communication system according to claim 1, it is characterised in that the instruction
Practice in symbol, X (k)=- Y*(N/4-1-k), k=0, wherein 1 ..., N/4-1, X are conjugate antisymmetry with Y.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109861938A (en) * | 2018-12-31 | 2019-06-07 | 上海工程技术大学 | The method for inhibiting phase rotation error in signal of high data transmission efficiency |
| CN110519195A (en) * | 2019-08-02 | 2019-11-29 | 北京科技大学 | The method for wearing data transmission link timing synchronization in steel number energy simultaneous interpretation system |
| CN113162882A (en) * | 2021-04-02 | 2021-07-23 | 国网江苏省电力有限公司无锡供电分公司 | Self-correlation OFDM symbol synchronization method based on conjugate antisymmetric training sequence |
-
2016
- 2016-12-07 CN CN201611115883.6A patent/CN106534035B/en active Active
Non-Patent Citations (1)
| Title |
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| 张树娟: "卫星移动通信系统OFDM同步技术研究", 《中国优秀硕士学位论文全文数据库 信息科技辑》 * |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109861938A (en) * | 2018-12-31 | 2019-06-07 | 上海工程技术大学 | The method for inhibiting phase rotation error in signal of high data transmission efficiency |
| CN109861938B (en) * | 2018-12-31 | 2021-06-11 | 上海工程技术大学 | Method for suppressing phase rotation error in signal with high data transmission efficiency |
| CN110519195A (en) * | 2019-08-02 | 2019-11-29 | 北京科技大学 | The method for wearing data transmission link timing synchronization in steel number energy simultaneous interpretation system |
| WO2021022969A1 (en) * | 2019-08-02 | 2021-02-11 | 北京科技大学 | Method for timing synchronization of data transmission link symbols in steel-penetrating data and energy simultaneous transmission system |
| CN113162882A (en) * | 2021-04-02 | 2021-07-23 | 国网江苏省电力有限公司无锡供电分公司 | Self-correlation OFDM symbol synchronization method based on conjugate antisymmetric training sequence |
| CN113162882B (en) * | 2021-04-02 | 2023-02-28 | 国网江苏省电力有限公司无锡供电分公司 | Self-correlation OFDM symbol synchronization method based on conjugate antisymmetric training sequence |
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