CN102006256A - Estimation method of integral multiple subcarrier frequency offset of robust - Google Patents
Estimation method of integral multiple subcarrier frequency offset of robust Download PDFInfo
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- CN102006256A CN102006256A CN2009100578735A CN200910057873A CN102006256A CN 102006256 A CN102006256 A CN 102006256A CN 2009100578735 A CN2009100578735 A CN 2009100578735A CN 200910057873 A CN200910057873 A CN 200910057873A CN 102006256 A CN102006256 A CN 102006256A
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Abstract
The invention discloses an estimation method of integral multiple subcarrier frequency offset of a robust. In the method, by means of a known frequency domain training sequence in an orthogonal frequency division multiplexing (OFDM) system and the cross-correlation characteristic between a received signal and a known ideal signal, a channel frequency domain response is obtained by descrambling; and after time frequency domain conversion, an offset value of the integral multiple carrier frequency offset is judged according to the amplitude value of the obtained channel time domain pulse response. The estimation method can realize full multiplexing of a fast Fourier transform (FFT) module in the OFDM system and is slightly affected by multi-path channel attenuation; and the estimation method has the characteristics of simple implementation, high judgment accuracy and the like, thus being applicable to any OFDM communication system with the training sequence.
Description
Technical field
The present invention relates to digital communicating field, particularly relate to the method for estimation of carrier frequency offset in a kind of OFDM (OrthogonalFrequency Division Multiplexing, OFDM) communication system.
Background technology
Ofdm system declines characteristics such as ability is strong and is widely used in the wide-band communication system with its availability of frequency spectrum height, anti-multipath, is particularly useful for the changeable Wireless Broadband Communication Systems of communication environments.While is just because of the technical characterstic of OFDM itself, OFDM modulation is to realize effective utilization to frequency spectrum by a plurality of mutually orthogonal sub-carrier signals of parallel modulation in effective band, and this has just caused ofdm system responsive unusually to the influence of carrier frequency offset.From normalized subcarrier bandwidth angle, divide the carrier frequency offset that is several times as much as subcarrier bandwidth can cause sub-carrier signal to leak on the adjacent sub-carrier on the one hand, destroy the orthogonality of each intercarrier, thereby produce inter-carrier interference (ICI); Integral multiple can cause effective carrier signal to be offset in the carrier frequency offset of subcarrier bandwidth on the other hand, causes the receiver can't be according to correct order recovery source signal.Therefore the carrier frequency synchronization technology is a key technology in the ofdm system.
Concerning general ofdm system, carrier frequency offset mainly is to be caused by the inconsistent of local frequency between the transmitter and receiver.But concerning the wireless OFDM system, the Doppler frequency shift that produces owing to the relative motion between the Receiver And Transmitter and the conversion of communication environments on every side also can produce certain carrier frequency offset, this frequency departure is less relatively, normally the branch several times of subcarrier bandwidth.Therefore integral multiple sub-carrier frequencies estimation of deviation technology mainly is inconsistent at local frequency and initial frequency deviation that produce.
Existing most of integral multiple sub-carrier frequencies estimation of deviation technology has all been utilized the their cross correlation that receives between frequency domain training signal and the desirable training signal, produce different reception frequency domain training by cyclic shift, judge the side-play amount of integer-time carrier wave frequency deviation by relatively more different sizes between the value mutually.But consider and transmit through after the dissemination channel, on amplitude and phase place, all can suffer the distortion effect of channel, therefore the adverse effect that all needed usually to eliminate propagation channel earlier before carrying out computing cross-correlation is to improve the accuracy of estimating, this has just increased the complexity that method of estimation realizes.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of method of estimation of integral multiple subcarrier frequency deviation of robust, can multiplexing ofdm system in FFT module commonly used, do not need to increase extra resource overhead, can eliminate the adverse effect of propagation channel simultaneously.
For solving the problems of the technologies described above, the method for estimation of the integral multiple subcarrier frequency deviation of robust of the present invention comprises the steps:
Step 1 is carried out the FFT conversion, and time-domain signal is transformed to frequency domain, obtains the frequency domain received signal;
Step 2 according to the desirable carrier wave mapping position of known frequency domain training sequence, is adjusted the initial mapping position of frequency domain training sequence, and is separated mapping in a positive and negative P reference carrier wave, obtain 2P+1 different received training sequence altogether;
Step 3 utilizes known desirable training sequence that 2P+1 received training sequence carried out Hadamard multiplication process, R '
p(k)=R
p(k) * S
H(k), wherein ,-P≤p≤P, ()
HConjugate operation is asked in expression;
Step 4 is carried out IFFT spatial transform frequently to the sequence after the Hadamard multiplication process, obtains 2P+1 time-domain signal sequence, r
p(n)=F
HR '
p(k), wherein, F represents fourier transform matrix;
Step 5 is obtained the amplitude of 2P+1 time-domain signal sequence respectively, and finds out these signal amplitude sequences maximum separately, and note is made M respectively
p, M
p=argmax (| r
p(n) |) ,-P≤p≤P;
Step 6 is at 2P+1 maximum M
pThe middle value M that seeks maximum
PmaxAnd corresponding sequence number p
Max,-P≤p
Max≤ P, p
MaxBe the subcarrier number that detects the corresponding skew of integral multiple subcarrier frequency deviation that obtains.
Adopt the FFT module that method of the present invention can multiplexing ofdm system, only need to increase the assessment function that a spot of resource just can realize integral multiple subcarrier frequency deviation.In addition, can effectively utilize the time-domain pulse response information of channel, and received training sequence is with the relevant information between the desirable training sequence, have realize simple, judgement accuracy height, characteristics such as estimation range is big, and anti-multipath influence of fading ability is strong; In wireless OFDM system complicated and changeable, can be applied well equally, be applicable to any ofdm communication system with training sequence.
Description of drawings
The present invention is further detailed explanation below in conjunction with accompanying drawing and embodiment:
Accompanying drawing is a method control flow chart of the present invention.
Embodiment
Be that example describes with CMMB (China Mobile Multimedia Broadcasting China Mobile multimedia broadcasting TV) system in the following description.Two kinds of frequency domain training sequences in the CMMB standard, have been defined: the pilot tone signal in synchronous training symbol in the beacon signal and the normal OFDM symbol.The subcarrier mapping position of these training sequences and transmission signals itself all are known.Use method of the present invention based on above-mentioned two kinds of frequency domain training sequences and can realize frequency offset estimating the integral multiple subcarrier bandwidth.
Method of the present invention is described as the frequency domain training signal with the synchronous training symbol in the beacon signal below, specifically comprise the steps:
Step 1 utilizes FFT module general in the ofdm system to realize the time-frequency domain conversation of signal, obtains the received signal of frequency domain.
Step 2, desirable carrier wave mapping position according to known synchronous training sequence, respectively in the initial carrier wave mapping position of positive and negative both direction slip, again according to desirable carrier wave mapping order, begin to separate the frequency-region signal that mapping receives from different initial carrier wave mapping position respectively, obtain a plurality of different received training sequences.
Suppose in the slip of positive negative direction for being symmetrically distributed, and maximum magnitude is P subcarrier, can separates so altogether to shine upon and obtain 2P+1 received training sequence.
Desirable carrier wave mapping position is shown below:
If there is not the carrier wave frequency deviation of integral multiple subcarrier bandwidth in received signal, separate according to desirable carrier wave mapping position so and shine upon the synchronous training sequence that the receiving sequence that obtains has just comprised to be influenced through channel fading, after carrying out the Hadamard multiplication process, can estimate to obtain the frequency domain response of fading channel with desirable training sequence.Otherwise because the carrier position that integral multiple subcarrier frequency deviation is brought skew, separating the receiving sequence that mapping obtains based on desirable carrier wave mapping position, still is a received signal at random that comprises the channel fading influence after carrying out the Hadamard multiplication process with desirable training sequence.Therefore by near the P carrier position that desirable carrier wave mapping initial position, horizontally slips as the carrier wave mapping initial position of receiving sequence, can get 2P+1 receiving sequence after separating mapping.
Step 3 is carried out the Hadamard multiplication process to separating 2P+1 receiving sequence obtaining of mapping with desirable training sequence.The R ' as a result of multiplication process
p(k) comprise the frequency domain response information of fading channel, and the frequency domain receiving sequence is with the frequency domain cross-correlation information between the desirable training sequence.Wherein have only one to be the frequency domain response of fading channel, other all are frequency-region signal at random.
R '
p(k)=R
p(k) * S
H(k) (formula 2)
Wherein ,-P≤p≤P, ()
HConjugate operation, R are asked in expression
p(k) receiving sequence that mapping obtains is separated in expression, the local known desirable training sequence of S (k) expression.
Step 4, utilizing channel frequency domain response and channel time domain impulse response is the right characteristic of Fourier transform, and the sequence after 2P+1 the Hadamard multiplication process is carried out the frequency spatial transform.The FFT module of this step in equally can multiplexing ofdm system.
Step 5 at 2P+1 burst that is transformed into time domain, wherein only has a time-domain response characteristic that has characterized channel, and the amplitude of its most powerful path is much larger than average signal strength.And other time domain sequences still are OFDM time-domain signal at random, and the maximum amplitude in its sequence should be fallen in PAPR (Peak-to-Average Power Ratio, the peak-to-average power ratio) scope of ofdm system with the ratio of average amplitude.Therefore can carry out maximum to the amplitude of each time domain sequences and detect, find out the maximum of amplitude in the sequence separately.
Step 6, the maximum amplitude to the 2P+1 sequence compares again, find out in 2P+1 the maximum maximum value with and corresponding carrier shift number.The integral multiple subcarrier number that this carrier shift number promptly is the carrier wave frequency deviation correspondence.So far finish the estimation of the carrier wave frequency deviation of integral multiple subcarrier bandwidth.
Above special case only is used to illustrate concrete application mode of the present invention, but the present invention does not limit to the CMMB system that is applied to.For general ofdm system with frequency domain training sequence, invention spirit of the present invention and actual content are suitable equally.
Claims (3)
1. the method for estimation of the integral multiple subcarrier frequency deviation of a robust is characterized in that, comprises the steps:
Step 1 is carried out the FFT conversion, and time-domain signal is transformed to frequency domain, obtains the frequency domain received signal;
Step 2 according to the desirable carrier wave mapping position of known frequency domain training sequence, is adjusted the initial mapping position of frequency domain training sequence and is separated mapping in a positive and negative P reference carrier wave, obtain 2P+1 different received training sequence altogether;
Step 3 utilizes known desirable training sequence that 2P+1 received training sequence carried out Hadamard multiplication process, R '
p(k)=R
p(k) * S
H(k), wherein ,-P≤p≤P, ()
HConjugate operation is asked in expression;
Step 4 is carried out IFFT spatial transform frequently to the sequence after the Hadamard multiplication process, obtains 2P+1 time-domain signal sequence, r
p(n)=F
HR '
p(k), wherein, F represents fourier transform matrix;
Step 5 is obtained the amplitude of 2P+1 time-domain signal sequence respectively, and finds out these signal amplitude sequences maximum separately, and note is made M respectively
p, M
p=argmax (| r
p(n) |) ,-P≤p≤P;
Step 6 is at 2P+1 maximum M
pThe middle value M that seeks maximum
PmaxAnd corresponding sequence number p
Max,-P≤p
Max≤ P, p
MaxBe the subcarrier number that detects the corresponding skew of integral multiple subcarrier frequency deviation that obtains.
2. method of estimation as claimed in claim 1 is characterized in that: the frequency domain training sequence that is adopted in the step 2 can be the synchronizing symbol in the ofdm system, also can be the pilot tone symbol in the ofdm system.
3. method of estimation as claimed in claim 1 is characterized in that: the carrier wave number P that is adopted in the step 2 sets according to the maximum frequency deviation scope that system can correct.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102238125A (en) * | 2011-06-21 | 2011-11-09 | 西安电子科技大学 | Integral multiple frequency offset estimation method of OFDM (orthogonal frequency division multiplexing) system with residual time bias |
| CN106230762A (en) * | 2016-07-26 | 2016-12-14 | 广州海格通信集团股份有限公司 | Doppler frequency offset estimation method and system |
| CN107438043A (en) * | 2016-05-26 | 2017-12-05 | 上海高清数字科技产业有限公司 | Leading symbol detects analytic method |
| CN110741588A (en) * | 2017-03-24 | 2020-01-31 | 诺基亚技术有限公司 | Spectrum utilization for independent NB-IoT carriers |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1490955A (en) * | 2003-09-19 | 2004-04-21 | 清华大学 | Method for obtaining rough estimate of frequency diviation by frequency domain PV sequence guidance |
| CN101447970A (en) * | 2008-11-14 | 2009-06-03 | 中国人民解放军理工大学 | Method for conducting LOFDM system timing and carrier synchronization utilizing training sequence |
-
2009
- 2009-09-03 CN CN2009100578735A patent/CN102006256A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1490955A (en) * | 2003-09-19 | 2004-04-21 | 清华大学 | Method for obtaining rough estimate of frequency diviation by frequency domain PV sequence guidance |
| CN101447970A (en) * | 2008-11-14 | 2009-06-03 | 中国人民解放军理工大学 | Method for conducting LOFDM system timing and carrier synchronization utilizing training sequence |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102238125A (en) * | 2011-06-21 | 2011-11-09 | 西安电子科技大学 | Integral multiple frequency offset estimation method of OFDM (orthogonal frequency division multiplexing) system with residual time bias |
| CN102238125B (en) * | 2011-06-21 | 2013-06-12 | 西安电子科技大学 | Integral multiple frequency offset estimation method of OFDM (orthogonal frequency division multiplexing) system with residual time bias |
| CN107438043A (en) * | 2016-05-26 | 2017-12-05 | 上海高清数字科技产业有限公司 | Leading symbol detects analytic method |
| CN107438040A (en) * | 2016-05-26 | 2017-12-05 | 上海高清数字科技产业有限公司 | Leading symbol detects resolver and method |
| CN107438040B (en) * | 2016-05-26 | 2020-09-29 | 上海高清数字科技产业有限公司 | Leading symbol detection and analysis device and method |
| CN106230762A (en) * | 2016-07-26 | 2016-12-14 | 广州海格通信集团股份有限公司 | Doppler frequency offset estimation method and system |
| CN106230762B (en) * | 2016-07-26 | 2019-06-18 | 广州海格通信集团股份有限公司 | Doppler frequency offset estimation method and system |
| CN110741588A (en) * | 2017-03-24 | 2020-01-31 | 诺基亚技术有限公司 | Spectrum utilization for independent NB-IoT carriers |
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Application publication date: 20110406 |