CN101883070A - Method for OFDM time synchronization by using superimposed training sequence - Google Patents
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- 230000005540 biological transmission Effects 0.000 claims abstract description 14
- 238000006243 chemical reaction Methods 0.000 claims description 11
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Abstract
The invention aims to provide a method for carrying out OFDM time synchronization by utilizing a superposed training sequence, which enhances the correlation performance of time synchronization by designing a training sequence structure and a corresponding synchronization algorithm. The OFDM synchronous training sequence adopts a method of being superposed on the cyclic prefix of the transmission data, does not increase extra transmission cost, and further reduces the interference between the training sequence and the transmission data because 0 is inserted into the training sequence.
Description
Technical field
The present invention relates to the OFDM technical field, particularly relate to a kind of overlying training sequence that utilizes and carry out method for synchronizing time.
Background technology
OFDM is a kind of special multi-carrier modulation technology, and it utilizes the orthogonality of intercarrier further to improve the availability of frequency spectrum, and can resist narrow band interference and multipath fading.The subcarrier of OFDM by a plurality of quadratures can increase the width of code element with the data parallel transmission of serial, reduces the frequency band that single code element takies, the frequency selective fading that the opposing multipath causes; Can effectively overcome intersymbol interference, the reduction system is applicable to the high speed data transfer in multi-path environment and the fading channel to the requirement of balancing technique; And channel utilization is very high, and this point is particularly important in frequency spectrum resource limited wireless environment.
But, realize that there is technical difficult point in ofdm system, wherein very important one is that system is very high to synchronous requirement because it to timing error than the single-carrier technology sensitivity many.The if symbol timing offset is excessive, makes the length of the length sum of side-play amount regularly and maximum delay expansion less than Cyclic Prefix, can produce intersymbol interference, destroys the integrality of OFDM symbol, reduces the performance of system.We can say that the estimation of symbol timing offset accurately is the key that realizes ofdm system.
Fig. 1 is the block diagram of a general purpose O FDM baseband system.Row modules such as preface are trained in transmitting terminal serial to parallel conversion among Fig. 1, source encoding, mapping, OFDM baseband modulation and stack, represent the process of OFDM baseband modulation; The serial to parallel conversion of receiving terminal among Fig. 1, synchronously, OFDM base band demodulating, channel estimating and modules such as channel compensation, inverse mapping and parallel serial conversion, represent OFDM base band demodulating process; Channel is a multipath channel among Fig. 1; Synchronization module among Fig. 1 promptly is the part that realizes the OFDM time synchronized.
Common OFDM time synchronized scheme has two kinds:
(1) training sequence is synchronous as the OFDM of pilot tone.This method takies a data transmitting element with training sequence separately as data message, and receiving terminal obtains the purpose that correlation peak is realized time synchronized by the related operation to pilot tone.Utilize the method for pilot tone can guarantee to obtain good synchronization performance, but, reduced the efficiency of transmission of system because pilot tone has taken transmission resources.
(2) OFDM that training sequence is superimposed upon on the data is synchronous.These class methods are transmitted with the stack of OFDM symbol after training sequence being multiply by a power division factor (having reduced energy) more simultaneously, reduced the needed transmission resources of pilot tone, improved efficiency of transmission, but the problem that this method exists training sequence and transmission data to interfere with each other.Referring to document: Tufvesson F., Faulkner M., Hoeher P., Edfors O..OFDM time and frequency synchronization by spreadspectrum pilot technique[J] .Commun.Theory Mini-Conference.Jun, 1999.vol.5:115-119.The someone proposes training sequence is superimposed upon method on the Cyclic Prefix again subsequently, has reduced the interference of training sequence with the transmission data.Referring to document: Tang Youxi, Yan Chunlin. a kind of OFDM time, frequency synchronization method [P]. 02133996.1 open day on June 14th, 2006 of number of patent application, publication number CN1259780C.But this series methods is owing to reduced the energy of training sequence, and the performance of anti-multipath interference aspect descends to some extent.
Summary of the invention
Order of the present invention provides a kind of training sequence structure and corresponding synchronization algorithm thereof at the deficiencies in the prior art.OFDM synchronous training sequence of the present invention adopts the method that is superimposed upon on the transmission datacycle prefix, does not increase extra transport overhead, and the structure of combined training sequence is divided into time synchronized synchronously thick and synchronously thin.
, may further comprise the steps based on described training sequence structure according to method for synchronous of the present invention:
A. at the satisfactory training sequence of formation of making a start, promptly training sequence length equals the length of Cyclic Prefix.Get coded sequence negative and get conversion such as conjugation after form training sequence m (k).
B. training sequence m (k) is superimposed upon on the Cyclic Prefix of baseband OFDM signal, and sends into channel.
C. receiving terminal is sought the position of correlation peak with the signal that the receives related operation that is shifted.Wherein, received signal at first will be carried out shift transformation in correlation window, carries out related operation with known training sequence m (k) again after the conversion.
Described steps A comprises:
With coded sequence a get negative, get conjugation, get computing such as negative conjugation after, according to structure shown in Figure 2, form training sequence.Wherein, choosing of coded sequence a has generality, chooses the sequence of correlated performance excellence usually.
Described step B comprises:
With training sequence m[k] multiply by
ρ is the power division factor, and the definition power division factor equals the energy of overlying training sequence and the ratio of gross energy (that is: the energy sum of the energy of training sequence and burst), and the Cyclic Prefix with superposed positions multiply by again
After, the two addition is finished the process of overlying training sequence.
Described step C comprises:
Received signal is carried out as shown in Figure 4 reconfiguration according to formula (1) and formula (2) in correlation window.
r1(n)＝-1×r*(n) (1)
Wherein, the time domain data of r (n) for receiving, r1 (n) is the negative conjugation of r (n), and G is the length of Cyclic Prefix, and * is a conjugate operation.
Data are through carrying out related operation with known training sequence m (k) according to 3 formulas after the deformation process.
Wherein m (k) is known training sequence, and G is the length of Cyclic Prefix, and a (n) is that b (n) is the correlated results of slip correlation window through the data after formula 1 and formula 2 distortion, and * is a conjugate operation.
From correlated results, find maximum correlation, determine that the position of maximum correspondence in receiving data promptly finish timing synchronization.
The invention has the advantages that: in time domain training sequence only is superimposed upon on the Cyclic Prefix of transmission data, structure by the project training sequence, on the basis that does not change coded system, introduce new correlation, and in conjunction with new related algorithm, strengthen the antijamming capability of timing synchronization, improved synchronous accuracy.
Above-mentioned other purposes of the present invention and the further applicable scope of feature thereof can be known in following detailed description and learn.But these detailed explanations and the embodiment that is mentioned only supply illustration, are not to be construed as limiting the invention, and those of skill in the art are to be understood that other version.
Description of drawings
Fig. 1 is the ofdm system structural representation according to overlying training sequence of the present invention.Among the figure, 1 is string and modular converter, and 2 is the source encoding module, 3 is mapping block, and 4 is OFDM baseband signal generation module, and 5 is the training sequence laminating module, 6 is parallel serial conversion module, and 7 is channel module, and 8 are string and modular converter, 9 is synchronization module, 10 is OFDM baseband signal demodulation module, and 11 is channel estimating and channel compensation block, and 12 are the inverse mapping module, 13 is decoder module, and 14 is parallel serial conversion module.
Fig. 2 is according to training sequence structure schematic diagram of the present invention.Among the figure, 15 is coded sequence, usually selects coding with good correlation, and 16 is 15 to get the sequence after the conjugation, and 17 is 16 to get the sequence after the negative value, and 18 is 15 to get the sequence after the negative value.By 15,16,17 and 18 4 parts common composing training sequence m (k).
Fig. 3 is the transmission signal structure schematic diagram according to overlying training sequence of the present invention.Among the figure, 19 for multiply by
Training sequence, 20 for multiply by at the overlying training sequence place
Cyclic Prefix, 21 is initial data.
Fig. 4 is the structural change schematic diagram of receiving end data in correlation window that the present invention proposes.
Fig. 5 is training sequence and the synchronized algorithm synchronizing signal schematic diagram under multipath channel thereof that the present invention proposes.
Fig. 6 is the method and the synchronous accuracy curve comparison diagram of employing conventional method under multipath channel that system adopts the present invention to carry.Wherein, conventional method is meant that training sequence just is made up of the coded sequence repeat replication, through conjugation, get calculation process such as negative value, the receiving end synchronized algorithm is directly will receive data and training sequence to carry out the associated shift computing, relevant calculation expression is similar to formula (3), just changes a (n) into received signal r (n).
Fig. 7 is that system is under identical simulated environment, when not having overlying training sequence and the error rate comparison diagram during overlying training sequence.Wherein overlying training sequence is divided into the training sequence of stack this patent training sequence that proposes and the traditional structure that superposes.Traditional structure is meant that training sequence is to be repeated to place by coded sequence, does not pass through calculation process such as negate.
Embodiment
Below with reference to the accompanying drawings the preferred embodiments of the present invention are described in detail.
Step 1: establishing ofdm system sub-carriers number is N=512, and circulating prefix-length is 128.Original serial data forms parallel data through module 1, behind the RS coding of every group of data through module 2, carries out the i.e. mapping of QPSK modulation; Data are carried out the IFFT computing and are generated the Cyclic Prefix of data correspondence respectively in OFDM baseband modulation module; Selection cycle is N
Pn=31 m sequence is in the end mended 0 back to constitute length is 32 coded sequence for one, make a start coded sequence got computings such as conjugation, negate after, form the training sequence of structure as shown in Figure 2, be designated as m[K] k ∈ [0,127]; Training sequence be multiply by
ρ=0.3, the energy of training sequence accounts for 30% of gross energy in the expression Cyclic Prefix.Training sequence is superimposed upon on the Cyclic Prefix of first group of data in the overlying training sequence module, the Cyclic Prefix that is applied multiply by
Data are sent into channel through behind the parallel serial conversion.Still to select length be 31 m sequence to overlying training sequence in conventional method, in the end mends 0 back to constitute length be 32 coded sequence for one, will be not do not repeat to place through the coded sequence of calculation process such as negate to form training sequence.
Step 2: data are subjected to the interference of multipath effect and Gaussian noise in channel.Wherein, the multipath number is 20, and maximum doppler frequency is 200Hz.
Step 3: receiving end will receive data carry out serial to parallel conversion after, data are sent into synchronization module.Synchronization module carries out related operation according to formula (3) after the data based formula of the reception in the correlation window (1) and formula (2) are carried out data conversion again.Wherein, the length of relevant sliding window equals the length of training sequence, is 128 in this example.
The invention performance evaluation
According to above-mentioned implementation step, can obtain net synchronization capability shown in Figure 6.By relatively finding, repeat the method for synchronous of method for synchronous and the training sequence structure that proposes based on the present invention of the training sequence of displacement structure based on coded sequence, under identical signal to noise ratio condition, the improvement structure that the present invention proposes and the synchronous accuracy of synchronized algorithm are apparently higher than traditional algorithm.Along with the increase of signal to noise ratio, the rate of climb of the improvement structure that the present invention proposes and the synchronous accuracy curve of synchronized algorithm also is higher than conventional method.As seen from Figure 7, improvement structure that this patent proposes and synchronized algorithm are compared with conventional method the influence of error rate of system and are differed very little, and improvement structure that this patent proposes and synchronized algorithm slightly are better than conventional method to the influence of error rate of system.
More than disclosed only be the preferred embodiments of the present invention, can not limit the scope of the present invention with this certainly.Be appreciated that the equivalent variations that the essence that limits in the appended claims according to the present invention and scope are done, still belong to the scope that the present invention is contained.
Claims (1)
1. utilize overlying training sequence to carry out the OFDM method for synchronizing time, this method comprises the steps:
Step 1 determines to send the frame structure of data, determines the length of Cyclic Prefix, the length of training sequence, and the length of training sequence equals the length of Cyclic Prefix usually;
It is the coded sequence a (k) of training sequence length 1/4th that step 2 is selected length, type of coding generally select the autocorrelation performance excellence, length is smaller or equal to the sign indicating number type of training sequence length 1/4th, if selected code length is littler than training sequence length 1/4th, then supply with 0;
Step 3 is carried out the coded sequence a (k) in the step 2 conjugation, is got computing such as negative value, forms [a (k) a
*(k)-a
*(k)-and a (k)] the training sequence m (k) of structure, wherein, * is for getting conjugation;
Step 4 is superimposed upon the training sequence m (k) that obtains in the step 3 on the Cyclic Prefix of transmission data;
Step 5 time synchronized: will carry out related operation through the data of channel, wherein, receive data and at first carry out reconfiguration according to formula (1) and formula (2) in correlation window, the data after the conversion are carried out related operation with known training sequence according to formula (3) again.Correlated results is compared, find the position of maximum related value, i.e. sync bit;
r1(n)＝-1×r*(n) (1)
Wherein, the time domain data of r (n) for receiving, r1 (n) is the negative conjugation of r (n), G is the length of Cyclic Prefix, and * is a conjugate operation, and m (k) is known training sequence, a (n) is that b (n) is the correlated results of slip correlation window through the data after formula 1 and formula 2 distortion.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102291360A (en) * | 2011-09-07 | 2011-12-21 | 西南石油大学 | Superimposed training sequence based optical OFDM (Orthogonal Frequency Division Multiplexing) system and frame synchronization method thereof |
| GB2515854A (en) * | 2013-07-04 | 2015-01-07 | Sony Corp | Transmitter and receiver and methods of transmitting and receiving |
| CN104702542A (en) * | 2013-12-04 | 2015-06-10 | 武汉邮电科学研究院 | Signal generation device, data recovery device, signal generation method, and data recovery method |
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2009
- 2009-05-09 CN CN2009101414357A patent/CN101883070A/en active Pending
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102291360A (en) * | 2011-09-07 | 2011-12-21 | 西南石油大学 | Superimposed training sequence based optical OFDM (Orthogonal Frequency Division Multiplexing) system and frame synchronization method thereof |
| GB2515854A (en) * | 2013-07-04 | 2015-01-07 | Sony Corp | Transmitter and receiver and methods of transmitting and receiving |
| GB2515801A (en) * | 2013-07-04 | 2015-01-07 | Sony Corp | Transmitter and receiver and methods of transmitting and receiving |
| GB2515861A (en) * | 2013-07-04 | 2015-01-07 | Sony Corp | Transmitter and receiver and methods of transmitting and receiving |
| US10404507B2 (en) | 2013-07-04 | 2019-09-03 | Sony Corporation | Implicit signaling in OFDM preamble with embedded signature sequence, and cyclic prefix and postfix aided signature detection |
| US10999111B2 (en) | 2013-07-04 | 2021-05-04 | Saturn Licensing Llc | Implicit signalling in OFDM preamble with embedded signature sequence, and cyclic prefix and postfix aided signature detection |
| US11496345B2 (en) | 2013-07-04 | 2022-11-08 | Saturn Licensing Llc | Implicit signaling in OFDM preamble with embedded signature sequence, and cyclic prefix and postfix aided signature detection |
| CN104702542A (en) * | 2013-12-04 | 2015-06-10 | 武汉邮电科学研究院 | Signal generation device, data recovery device, signal generation method, and data recovery method |
| CN104702542B (en) * | 2013-12-04 | 2018-03-16 | 武汉邮电科学研究院 | Signal generation device and Data Recapture Unit and its method |
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Application publication date: 20101110 |