CN1455533A - Time synchronous method for multi-carrier CDMA system - Google Patents
Time synchronous method for multi-carrier CDMA system Download PDFInfo
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Abstract
The method includes: 1) storing the known synchronous train sequence IFFI changing result into buffer storage in advance, 2) carrying on correlation for received synchronous train sequence with synchronous time slot and train sequence in buffer storage and within search window, carrying on correlation operation to obtain a serial correlation output result, 3) derivating out energy of correlation output result, 4) utilizing a filter set to carry on filter processing for a serial obtained energy, 5) arranging filtered correlation output energy in sequence from big to small and starting cancellation sidelobe for correlation peak value from the maximum value, 6) searching out frame head position by searching forward and 7) adjusting framke boundary as per framke head position and removing cyclic prefix of OFDM data symbol to restore initial position for it.
Description
Technical field
The present invention relates to a kind of MC-CDMA (MC-CDMA) system, relate in particular to a kind of method for synchronizing time that is used for MC-CDMA system.
Background technology
The MC-CDMA technology combines the advantage of OFDM (OFDM) technology and code division multiple access (CDMA) technology, can resist multipath fading effectively, improves the availability of frequency spectrum, reduces message transmission rate.Just because of these advantages, the MC-CDMA technology is considered to one of otherwise effective technique of following wireless broadband communication.But another characteristic of ofdm system has also been inherited by the MC-CDMA system, and is very responsive to frequency shift (FS).Therefore, simultaneous techniques is a critical problem of MC-CDMA system.
Simultaneous techniques comprises time synchronized (sign synchronization, frame synchronization) and Frequency Synchronization.In the MC-CDMA system, data are the unit transmission with the frame, therefore must determine the original position of each frame exactly, and system just can communicate by letter reliably.So time synchronized is as synchronous primary link, the accuracy that the accuracy of its estimation is synchronous with direct contributive rate.
The time synchronized scheme of existing multicarrier system, major part all is based on the processing of Cyclic Prefix.The precision of timing estimation depends on the length of Cyclic Prefix, and length is long more, and timing estimation is accurate more, yet the efficiency of transmission of the long more system of Cyclic Prefix is low more, as seen has contradiction between the two.In addition, in multidiameter fading channel, Cyclic Prefix very easily is subjected to the interference of multipath, and the accuracy that obtains timing estimation will be subjected to very big influence, is difficult for guaranteeing the correctness of time synchronized thus based on the method for synchronous of Cyclic Prefix.
Summary of the invention
At the problem that exists in the existing time synchronized scheme, the present invention proposes a kind of method for synchronizing time that is used for MC-CDMA system, and described method comprises step:
The first step is stored in the IFFT transformation results of known synchronous training sequence in the buffer in advance;
Second step, in search window, the synchronous training sequence of the synchronization slot that receives and training sequence in the buffer are carried out relevant, related operation control by given thresholding, continues in search window slip then and asks relevant, obtains a series of relevant output results thus;
In the 3rd step, asking is correlated with exports result's energy;
In the 4th step, utilize single order infinite impulse response digital filter group that a series of relevant output energy of gained is carried out Filtering Processing;
The 5th step, with the descending ordering of filtered relevant output energy,, leave out the correlation peak secondary lobe from the value of maximum, till finding out several values, remember these several values and corresponding sampling point position thereof;
The 6th step in this several value, was a benchmark with maximum corresponding sampling points position, searched forward and benchmark be separated by front position in the certain limit, i.e. frame head position;
The 7th step, adjust frame boundaries according to determined frame head position, remove the Cyclic Prefix of OFDM data symbol, recover the original position of OFDM data symbol.
For fear of the defective of multicarrier system based on cyclic prefix method, we utilize synchronous training sequence to carry out time synchronized in the MC-CDMA system.The short frame design of MC-CDMA system's employing of the present invention, each frame is provided with special-purpose synchronization slot, by once searching for Synchronous Processing, acquisition comprises the correlation energy output of frame synchronization and sign synchronization initial estimation information, follow the tracks of the variation of channel so effectively, guaranteed the synchronous reliability of each frame time.Because relevant output energy is subjected to The noise, further adopts single order infinite impulse response (IIR) digital filter bank, relevant output energy is carried out Filtering Processing, thereby guaranteed the accuracy of time synchronized.Here, the known array design that constitutes synchronization slot has very big flexibility, synchronous training sequence is designed to have the Gold sign indicating number sequence of sharp-pointed autocorrelation performance here, can effectively resist interference.
Description of drawings
Further describe the present invention with reference to the accompanying drawings and in conjunction with the embodiments, wherein:
Fig. 1 is the block diagram of MC-CDMA band processing system;
Fig. 2 is the frame structure of MC-CDMA;
Fig. 3 is the more detailed block diagram of time synchronized unit;
Fig. 4 is the more detailed block diagram of filter unit.
Embodiment
Describe the present invention with reference to the accompanying drawings in detail.
Fig. 1 is the block diagram of MC-CDMA band processing system, and it comprises a transmitter 101 and a receiver 102.Transmitter 101 provides user data to be sent, and user data is through being merged into frequency domain multi-carrier OFDM symbolic frame after the spectrum-spreading unit 103 and from the synchronous training sequence in frame synchronization training sequence source 104.Each frequency domain multi-carrier OFDM symbol is for conversion into time domain multi-carrier OFDM symbol by IFFT (invert fast fourier transformation) unit 105, sends into multipath channel 107, finishes base band and sends processing.In receiver 102, at first from the time domain multi-carrier OFDM symbol that receives, extract synchronous training sequence, send into time synchronized unit 108, finish obtaining of frame timing estimation information in time domain.According to frame timing estimation information,, determine the original position of multi-carrier OFDM symbol at the Cyclic Prefix of the time domain multi-carrier OFDM symbol of deleting cyclic prefix unit 109 deletion receptions.Enter FFT (fast fourier transform) unit 110 then and be transformed into the frequency-domain OFDM symbol, the final data symbol recovers the user data that transmitter provides through despread unit 111.Method for synchronizing time of the present invention is finished in the time synchronized unit 108 of the receiver 102 shown in the figure, will specify hereinafter.
Fig. 2 is the frame structure schematic diagram of system.The synchronization slot that the synchronous training sequence that is produced by frame synchronization training sequence source 104 constitutes is inserted into periodically from the customer traffic of spectrum-spreading unit 103 to IFFT unit 105, constitutes to send Frame.Comprise a synchronization slot and N user data time slot in each frame.In frame alignment time slot, synchronous training sequence is that the form with the OFDM symbol exists, and is known for receiver.Can several synchronous OFDM symbols be set according to performance requirements in frame alignment time slot.Each synchronous OFDM symbol adopts Gold sign indicating number sequence to generate, and utilizes the strong autocorrelation performance of sign indicating number to obtain frame and symbol timing estimation.
Fig. 3 is the more detailed block diagram of time synchronized of the present invention unit 108.Local frame synchronization training sequence source 301 corresponding to and generation and transmitter in the identical synchronous training sequence in source 104, pass through IFFT and be transformed into time-domain symbol C (n), leave in the buffer 302.For the time domain multi-carrier OFDM symbol r (n) that receives, at first to carry out separating of synchronizing sequence and data symbol in synchronizing sequence, data separating unit 303, the synchronous training sequence R (n) that separates directly sends into relevant treatment unit 304, the data symbol part then postpones processing unit 305 through one and postpones to obtain s (n), handles behind the timing estimation information acquisition again.Relevant treatment unit 304 adopts slip relevant treatment principle, in length is the search window of L, with the synchronous training sequence R (n) that separates with leave C (n) in the buffer 302 in and grip altogether and carry out related calculation, the search window length L is set according to the multipath channel environmental parameter.In order to reduce the data volume of carrying out relevant treatment, an initial accumulative frequency z (satisfying 2 power) is set, utilize relevant the adding up of given thresholding TH control, the TH size is determined according to signal to noise ratio and initial accumulative frequency z, whether the energy of judging the output that the z correlations adds up is greater than TH, if just continue relevant adding up greater than TH, otherwise the output of being correlated with is set to null value.The related operation formula is as follows:
D=1 wherein, 2 ... .L,
Initial accumulative frequency z, Λ (d) is the relevant output that adds up, NF
FTEqual the number of sub carrier wave of system.Λ (d) obtains relevant output energy M (d) through squaring cell 306, then the M ' that obtains by filter unit 307 of M (d) (d), the filter here adopts the first order IIR digital filter.With (d) input sequencing deletion correlation peak secondary lobe unit 308 of M ', this L M ' sort from big to small (d), the over-sampling rate of taking into account system, think that the neighbouring sample value is the correlation peak secondary lobe in certain sampled distance, begin successively with its correlation peak secondary lobe deletion, to reduce the probability of miscarriage of justice of the secondary lobe position being thought the frame head position from maximum.The processing procedure of controller 309 control deletion correlation peak secondary lobes, before obtaining m be worth till, remember this m value and corresponding sampling point position thereof, here will based on the suitable m value of hardware implementation complexity selection (m＜＜L).This m value and corresponding sampling point position thereof are sent into frame head position output unit 310, are benchmark with maximum corresponding sampling points position, search with benchmark forward and are separated by w with interior front position, be i.e. the frame head position
The big I of w is set according to the time delay expansion of channel.In deletion cyclic prefix unit 311, according to the frame synchronization position
Leave out the Cyclic Prefix of OFDM data symbol s (n) in each data slot in a frame, promptly determined the original position of OFDM data symbol, carry out FFT again.
Fig. 4 is the specific implementation block diagram of filter unit 307.The selection of filter will be eliminated noise as much as possible, guarantees hard-wired simply again, and we adopt the first order IIR digital filter here.The relevant output energy M (d) that enters filter unit is earlier through a serial to parallel conversion, the first order IIR filtering device group that is L by a size then, at last through a parallel serial conversion export M ' (d).Here, the relevant output energy M (d) of each sampled point in the search window, d=1,2, ... .L is to there being a first order IIR filtering device, this filter only carries out filtering to the relevant output energy of identical sampling point position in the search window, is different from the additive method median filter the relevant output of all sampled points in search window energy is carried out filtering.The selection of the factor alpha of first order IIR filtering device will be considered the ability of filter filtering noise, and factor alpha is more little, and iir filter filtering noise ability is strong more, but the renewal speed in path will be slack-off.Because it is very simple that the first order IIR filtering device is realized, the implementation complexity of whole filter unit 307 depends on the length L of search window.
In the present invention,, not only can reduce the data volume of carrying out relevant treatment, guarantee to obtain timing estimation accurately, and the number of the memory that takies is reduced, reduce hardware spending with the minimum of computation amount by relevant the adding up of given thresholding control.Single order infinite impulse response (IIR) digital filter techniques is applied to the frame synchronization algorithm of MC-CDMA system, the relevant output energy in the search window is carried out filtering, can eliminate the influence of noise effectively timing estimation.Introduce the operation of deletion correlation peak secondary lobe, can reduce the probability of miscarriage of justice of the sampling location of correlation peak secondary lobe being thought the frame head sampling location, greatly improve the timing estimation precision.With the corresponding sampling location of maximal correlation peak value is benchmark, searches the frame head position forward, like this, even first footpath not in the sampling location of maximal correlation peak value correspondence, this operation also can guarantee the correctness of frame head position.
Claims (12)
1. method for synchronizing time that is used for MC-CDMA system comprises step:
(i) the IFFT transformation results with known synchronous training sequence is stored in the buffer in advance;
(ii) in length is the L search window, carry out relevant with training sequence in the buffer synchronous training sequence of the synchronization slot that receives, related operation is controlled by given thresholding TH, continues then to slide in search window and asks relevant, obtains a series of relevant output results thus;
(iii) ask relevant output result's energy;
(iv) utilize single order infinite impulse response digital filter group that a series of relevant output energy of gained is carried out Filtering Processing;
(v),, leave out the correlation peak secondary lobe, before finding out, till m value, remember this m value and corresponding sampling point position thereof from the value of maximum with the descending ordering of filtered relevant output energy;
(in this m value, be benchmark vi), search with benchmark forward and be separated by w, be i.e. the frame head position with interior front position with maximum corresponding sampling points position;
(vii) adjust frame boundaries, remove the Cyclic Prefix of OFDM data symbol, recover the original position of OFDM data symbol according to determined frame head position.
2. according to the process of claim 1 wherein that described known synchronous training sequence is the OFDM sign format.
3. according to the method for claim 2, wherein said OFDM symbol adopts GOLD sign indicating number sequence to generate.
4. also comprise step according to the process of claim 1 wherein before (ii) in step:
The time domain multi-carrier OFDM symbol that receives is carried out separating of synchronizing sequence and data symbol in synchronizing sequence, data separating unit, the synchronous training sequence of separating so just can directly be sent into the relevant treatment unit and be correlated with, the data symbol part then postpones processing unit through one and postpones, and handles behind the timing estimation information acquisition again.
5. according to the method for claim 1, the search window length L is set according to the multipath channel environmental parameter.
6. according to the process of claim 1 wherein (ii), the synchronous training sequence of the synchronization slot that receives and the conjugation of the training sequence in the buffer are carried out related calculation in step.
7. according to the method for claim 1, wherein (ii) in step, an initial accumulative frequency z is set, z satisfies 2 power, utilize relevant the adding up of given thresholding TH control, whether judge output energy that the z correlations adds up greater than TH, if just continue relevant adding up greater than TH, otherwise the output of being correlated with is set to null value.
8. according to the method for claim 7, wherein given thresholding TH is relevant with initial accumulative frequency z with signal to noise ratio.
9. according to the method for claim 1, wherein in step Filtering Processing principle (iv) be: all to a single order infinite impulse response digital filter should be arranged, this filter only carries out filtering to the relevant output energy of identical sampling point position in the search window to the relevant output energy of each sampled point in the search window.
10. according to the method for claim 1, and the step of deletion correlation peak secondary lobe (v) also comprise: the over-sampling rate of taking into account system, think that the neighbouring sample value is the correlation peak secondary lobe in certain sampled distance.
11. according to the process of claim 1 wherein m＜＜L.
12. according to the method for claim 1, with the sampled point of benchmark at interval w can set according to the time delay expansion of channel.
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| CN100388639C (en) * | 2004-08-18 | 2008-05-14 | 中兴通讯股份有限公司 | Multi-path time-delay estimating method for direct spread-spectrum CDMA system |
| CN100389582C (en) * | 2004-07-26 | 2008-05-21 | 南京邮电学院 | Synchronous method of orthogonal freuency division multiplex in broadband radio insertion system |
| CN1741424B (en) * | 2004-08-23 | 2010-05-05 | 中兴通讯股份有限公司 | PHS base station up TCH frame static error code testing method |
| CN1878157B (en) * | 2005-06-07 | 2010-09-29 | 中兴通讯股份有限公司 | Method for realizing OFDM system synchronization using circulating prefix |
| CN1798003B (en) * | 2004-12-22 | 2010-09-29 | 方正通信技术有限公司 | Initial synchronization method in subzone search of CDMA communication system |
| CN101034970B (en) * | 2006-03-08 | 2010-10-20 | 北京中电华大电子设计有限责任公司 | Valve value self-adaptive selection synchronization signal detection method and device |
| CN1972271B (en) * | 2006-10-19 | 2010-11-10 | 北京邮电大学 | A synchronization method of MIMO-OFDM system |
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| US5991330A (en) * | 1997-06-27 | 1999-11-23 | Telefonaktiebolaget L M Ericsson (Pub1) | Mobile Station synchronization within a spread spectrum communication systems |
| CN1329410A (en) * | 2001-01-18 | 2002-01-02 | 深圳市中兴集成电路设计有限责任公司 | Small region search method in code division multiple address communication system |
| US6738437B2 (en) * | 2001-03-15 | 2004-05-18 | Qualcomm Incorporated | Symbol recovery from an oversampled hard-decision binary stream |
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| CN100388639C (en) * | 2004-08-18 | 2008-05-14 | 中兴通讯股份有限公司 | Multi-path time-delay estimating method for direct spread-spectrum CDMA system |
| CN1741424B (en) * | 2004-08-23 | 2010-05-05 | 中兴通讯股份有限公司 | PHS base station up TCH frame static error code testing method |
| CN1798003B (en) * | 2004-12-22 | 2010-09-29 | 方正通信技术有限公司 | Initial synchronization method in subzone search of CDMA communication system |
| CN101164309B (en) * | 2005-03-10 | 2015-04-08 | 高通股份有限公司 | Method and device for placing collection window for FFT |
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