CN102546509A - Carrier frequency offset estimation method based on chirp training sequence - Google Patents
Carrier frequency offset estimation method based on chirp training sequence Download PDFInfo
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- CN102546509A CN102546509A CN2011104453774A CN201110445377A CN102546509A CN 102546509 A CN102546509 A CN 102546509A CN 2011104453774 A CN2011104453774 A CN 2011104453774A CN 201110445377 A CN201110445377 A CN 201110445377A CN 102546509 A CN102546509 A CN 102546509A
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Abstract
The invention provides a carrier frequency offset estimation and time synchronization algorithm based on chirp training sequence. A transmitted training sequence is divided into three parts with equal lengths, wherein the second part and the third part are the complex conjugates of the first part respectively; the received training sequence through a multi-path channel is subjected to autocorrelation and anti-autocorrelation respectively, wherein when the multi-path channel is adopted, the anti-autocorrelation operation can be not only used for frequency offset estimation, but also can be used for time synchronization, and a decimal time frequency offset can be estimated according to the position of related result peak value; signals of the decimal time frequency offset after being compensated are subjected to delay and complex conjugate, two parts of signals pass through the same filter, and cross-correlation operation is performed so as to estimate integral time frequency offset; the frequency offset is subjected deflection compensation; at last iteration operation is performed till the frequency offset is estimated correctly.
Description
Technical field
The present invention relates to the frequency offset estimating algorithm of wireless communication technology field, the frequency offset estimating algorithm at particularly a kind of TD-SCDMA terminal is equally applicable to the frequency offset estimating of ofdm communication system.
Background technology
TD-SCDMA technology as one of the world's three big standards; Successfully moved towards commercial in China; And the research of TD-SCDMA technology was never stopped; Especially frequency offset estimating in the communication process and correction is research focus and difficult point always, and a lot of experts and scholar always enjoy it for this reason.
The unsteadiness of crystal oscillator, Doppler effect, there are deviation in centre frequency and local crystal oscillator frequency that multipath transmission etc. all can cause communication system to receive signal, Here it is carrier wave frequency deviation.The frequency deviation of carrier wave can cause the raising that receives the error rate, and serious meeting causes the decoded in error of signal, therefore must estimate and proofread and correct.Common bearing calibration is to make the local crystal oscillator frequency of correcting circuit follow the tracks of the reception signal frequency exactly; This is a frequency deviation correcting method ground part; Frequency offset correction be can not guarantee to carry out exactly, especially when signal process multipath channel, research concrete frequency offset estimating algorithm and design accurate frequency offset estimating circuit needed; Make receiver to carry out frequency-tracking automatically, carry out frequency offset estimating and compensation.Equally, the terminal receiver of TD-SCDMA system also must be carried out automatic frequency tracking, and especially up frequency offset estimating is with synchronously.Because the base station receives the signal that sends from a plurality of portable terminals simultaneously, they have nothing in common with each other at frequency deviation separately, and therefore common correcting algorithm can't be estimated and proofread and correct, and the time that needs the individual subscriber signal of assurance to arrive the base station like this is identical with frequency.
Therefore needing a kind of simple effective method, solve the frequency deviation stationary problem in the TD-SCDMA system, is frequency offset estimating and correction and solve the synchronous key of frequency deviation, and this patent has proposed the frequency offset estimating algorithm at a kind of TD-SCDMA terminal to this respect.
Summary of the invention
The object of the present invention is to provide the frequency offset estimating and the time synchronized algorithm at a kind of TD-SCDMA terminal.
To achieve these goals, provided by the invention based on Nonlinear Transformation in Frequency Offset Estimation and time synchronized algorithm in the TD-SCDMA system of chirp training sequence, the training sequence of transmission is divided into three isometric parts; If the training sequence that sends is the chirp signal; In order to tell the peak value of channel impulse response; Here
;
is the disperse factor (time-bandwidth product) of chirp signal, and training sequence can be expressed as like this
(1)
Therefore the training sequence that sends does
(3)
Wherein
(normalization of
) is total frequency deviation;
is fractional part of frequency offset;
is the integer frequency offset of
;
(normalization of
) is corresponding
time delay directly;
and
arranged so;
is the multipath tap number,
be multiple AWGN signal.
If do the relevant of different delay with local chirp sequence with the receiving sequence that contains the chirp sign indicating number that receives; So because the good correlation properties of chirp sign indicating number; Can make each correlation of acquisition receive single footpath channel and carrier wave frequency deviation with the time caused partially phase place rotate these three influences of taking advantage of sex factor; Therefore to each correlation carry out channel estimating based on known array can obtain comprising this directly respond and the carrier phase rotation and the time inclined to one side comprehensive response; But can't to channel impulse response and the time partially and carrier wave frequency deviation separate lotus root; Especially the time partially with the lotus root problem of separating of frequency deviation, and on different impulses, send upwards with chirp signal downwards can be well to the time inclined to one side and frequency deviation separate lotus root.This paper adopts earlier and receives the signal autocorrelation method and anti-correlation method is estimated carrier wave frequency deviation and the time is carried out synchronously; Then frequency deviation is proofreaied and correct; Next the signal after compensating fractional part of frequency offset postpones respectively and complex conjugate, and two parts of signals through identical filter, is carried out computing cross-correlation respectively then, estimates integer frequency offset; Then to the carrier integer frequency multiplication partially and the time estimate partially; Obtain total frequency offset estimating value at last and carry out compensate of frequency deviation simultaneously.
Carry out earlier the auto-correlation function computing to received signal
(4)
Therefore
But, when channel impulse response postpones to expand to a plurality of sample value, the peak of trigonometric equation be not special obviously, in order well to distinguish peak value, we have introduced anti-auto-correlation algorithm.
At first define anti-auto-correlation function: this algorithm needs two sequences; Second sequence is the complex conjugate that first sequence is overturn on time-domain; With the chirp signal is example; Suppose that first sequence (goes up the chirp signal) for
; So second sequence is
(the following chirp signal that a time delay is arranged), the anti-auto-correlation function that therefore receives signal
can be expressed as
Thereby anti-auto-correlation function has provided the variable of an impulse type, finds the position of impulse response, obtains phase place when being used for time synchronized, can obtain frequency deviation more accurately like this.
2. integer frequency offset
is estimated
The estimation of integer frequency offset, be equivalent to obtain earlier integral multiple the time inclined to one side, confirm integer frequency offset through peak, confirm integer frequency offset through peak value here.
In (8), obtain
The peak value that formula (9) obtains has surpassed the number of channel impulse response; In order to obtain integer frequency offset; We can set two other variable
and
equally; In this patent supposition they corresponding respectively be training sequence first and relevant (being equivalent to pass through filtering to
and
) of
and
, as
The peak of formula (10) with the time partially relevant with multidiameter; The amplitude square of
and
is approximately the form of
, and peak value satisfies following positions
(11)
Can estimate integer frequency offset through the distance of calculating between
and
peak value; But it is under the multipath situation, relatively more difficult.In order better to get the peak value of
and
; Set two thresholding factors
and
; Get two peak value threshold
and
; And during as
, make
; During as
; Make
; The purpose of doing like this is to reduce small leak to estimation effect, the noise reduction process that is equivalent to use in the channel estimation method.Then take after peak after treatment
and
correlation
(12)
Therefore total frequency deviation satisfies
3. through the signal behind total frequency offset correction do
Description of drawings
Fig. 1 is the theory diagram of training sequence
Fig. 2 is that the closure of frequency offset estimating realizes theory diagram
Fig. 3 is that fractional part of frequency offset is estimated and the compensation principle block diagram
Fig. 4 is integer frequency offset estimation and compensation and frequency offset correction block diagram
Embodiment
Below in conjunction with accompanying drawing frequency offset estimating provided by the invention and correcting algorithm are done corresponding the description.
As shown in Figure 1; The training sequence that sends is divided into three parts that length is L; Be respectively
,
and
; And corresponding X is last chirp signal to suppose
; The X* that
and
is corresponding is following chirp signal, satisfies like this
Therefore the training sequence that sends does
Wherein
is the disperse factor (time-bandwidth product) of chirp signal; In order to tell the peak value of channel impulse response,
is length and
of channel impulse response window here.
Fig. 2 is that frequency offset estimating realizes general frame figure, and the first step is estimated fractional part of frequency offset; Second step was carried out the fractional part of frequency offset compensation to the signal that receives; The 3rd step was estimated integer frequency offset; The 4th step integer frequency offset is to received signal estimated; The 5th step carried out iteration to frequency deviation and estimates; Above several steps constituted closed frequency offset estimating and compensation flow process, through after the iteration repeatedly, estimate comparatively accurately frequency deviation and proofread and correct.
Fig. 3 is the algorithm for estimating flow chart of fractional part of frequency offset estimator; At first with the training sequence process multipath channel of sending; Suppose channel impulse for
, the signal that receives of receiving terminal does so
Wherein
(normalization of
) is total frequency deviation;
is fractional part of frequency offset;
is the integer frequency offset of
;
(normalization of
) is corresponding
time delay directly;
and
arranged so;
is the multipath tap number,
be multiple AWGN signal.
The signal that receiving terminal is received is through autocorrelator and anti-autocorrelator, and the auto-correlation function that obtains receiving signal does
Wherein
is trigonometric equation.
And the anti-auto-correlation function that receives signal does
Here need define anti-auto-correlation function: this algorithm needs two sequences; Second sequence is the complex conjugate that first sequence is overturn on time-domain; With the chirp signal is example; Suppose that first sequence (goes up the chirp signal) for
; So second sequence is
(the following chirp signal that a time delay is arranged), the anti-auto-correlation function that therefore receives signal
can be expressed as formula (6).
In the formula (5); When channel impulse response postpones to expand to a plurality of sample value, the peak of trigonometric equation be not special obviously, in order well to distinguish peak value; Formula (6) has provided the variable of an impulse type; Find the position of impulse response, obtain phase place when being used for time synchronized, can obtain frequency deviation more accurately like this.The fractional part of frequency offset estimated value of estimating through the fractional part of frequency offset estimator like this does
The fractional part of frequency offset estimated value is used for the fractional part of frequency offset compensator, thereby the signal after the correction does through
Fig. 4 is the system flow block diagram of integer frequency offset estimation and frequency offset correction; The signal through after the fractional part of frequency offset correction that at first formula (8) is obtained postpones and complex conjugate operation, obtains
and
; To through delay and complex conjugate operation after signal pass through filter process respectively; The filtering signal here is taken as
; Be the first of training sequence, the signal behind wave filter satisfies
The peak of formula (9) with the time partially relevant with multidiameter; And the amplitude square of
and
is approximately the form of
, and peak value satisfies formula (10) position relation so
Here can estimate integer frequency offset through the distance of calculating between
and
peak value; But it is under the multipath situation, relatively more difficult.In order better to get the peak value of
and
, this patent is taked the output signal is handled.Set two thresholding factors
and
; Get two peak value threshold
and
; During as
, make
; During as
; Make
and
cross-correlation after the peak value of learning from else's experience is then handled
Output result to cross-correlator carries out the peak value detection, gets the position
of cross-correlation peak value like this as
and satisfies
Association type (7); Through the integer frequency offset estimator, the estimated value that obtains integer frequency offset
does
Therefore total frequency offset estimating value satisfies
Signal after proofreading and correct through the frequency offset correction device at last does
Claims (10)
1. Algorithm of Carrier Frequency Offset Estimation based on the chirp training sequence, the training sequence of transmission is divided into three isometric parts; The training sequence that passes through after the multipath channel that receives is carried out auto-correlation and anti-auto-correlation respectively, and the position according to the correlated results peak value estimates fractional part of frequency offset; Signal after compensating fractional part of frequency offset postpones respectively and complex conjugate, and two parts of signals through identical filter, estimates integer frequency offset respectively; Frequency deviation is compensated correction; Last interative computation estimates frequency deviation up to accurately.
2. frequency offset estimating algorithm according to claim 1; The training sequence that wherein sends satisfies shown in Figure 1; If the training sequence that sends is the chirp signal; And the signal length that satisfies every part is L; In order to tell the peak value of channel impulse response; Here
;
is the disperse factor of chirp signal, and the training sequence that obtains like this does
(1)
Therefore the training sequence that sends does
(2)。
3. frequency offset estimating algorithm according to claim 1; Suppose channel impulse for
, the reception signal of signal after through channel does so
4. frequency offset estimating algorithm according to claim 1, the auto-correlation function that receives signal does
Wherein
is trigonometric equation; When channel impulse response postpones to expand to a plurality of sample value; The peak of trigonometric equation be not special obviously; In order well to distinguish peak value, we have introduced anti-auto-correlation algorithm
(5)
Anti-auto-correlation function has provided the variable of an impulse type, finds the position of impulse response, obtains phase place when being used for time synchronized, can obtain frequency deviation more accurately like this.
6. according to the anti-auto-correlation of claim 4 definition: this algorithm needs two sequences; Second sequence is the complex conjugate that first sequence is overturn on time-domain; With the chirp signal is example; Suppose that first sequence (goes up the chirp signal) for
; So second sequence is
(the following chirp signal that a time delay is arranged), the upset auto-correlation function that therefore receives signal
can be expressed as formula (5).
9. frequency offset estimating algorithm according to claim 1; Signal after compensating fractional part of frequency offset postpones respectively and complex conjugate; Two parts of signals is respectively through identical filter (the filter here is the first of training sequence); Estimate integer frequency offset; We can set two other variable
and
equally; They are corresponding respectively is training sequence first and relevant (be equivalent to handle
and
and pass through filtering) of
and
, as
The peak of formula (9) with the time partially relevant with path delay; The amplitude square of
and
is approximately the form of
, and peak value satisfies following positions
(10)
Here can estimate integer frequency offset through the distance of calculating between
and
peak value; But under the multipath situation; Relatively more difficult; In order better to get the peak value of
and
; Set two thresholding factors
and
; Get peak value threshold
and
; During as
, make
; During as
; Make
cross-correlation of getting
and
then
Therefore the estimated value of frequency deviation does
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CN104104624A (en) * | 2013-04-10 | 2014-10-15 | 富士通株式会社 | Frequency difference estimation method, apparatus and system |
CN104735016A (en) * | 2015-03-19 | 2015-06-24 | 深圳市通创通信有限公司 | OFDM system fractional part of frequency offset estimation method and device based on multi-path channel |
CN111147123A (en) * | 2019-12-23 | 2020-05-12 | 东方红卫星移动通信有限公司 | Carrier synchronization method of low-orbit satellite broadband OFDM communication system |
CN113141245A (en) * | 2021-06-22 | 2021-07-20 | 中国人民解放军国防科技大学 | Time-frequency synchronization method, system, equipment and readable storage medium |
CN113783585A (en) * | 2021-09-13 | 2021-12-10 | 深圳市力合微电子股份有限公司 | Method for estimating sampling deviation based on Chirp correlation peak position deviation trend |
CN114337982A (en) * | 2022-03-16 | 2022-04-12 | 深圳市华普微电子有限公司 | Chirp pilot signal generation and time-frequency estimation method |
CN114726701A (en) * | 2022-05-16 | 2022-07-08 | 为准(北京)电子科技有限公司 | Frequency offset estimation method and device |
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US10009096B2 (en) | 2013-04-10 | 2018-06-26 | Fujitsu Limited | Method for estimating frequency offset, apparatus and system |
CN104104624A (en) * | 2013-04-10 | 2014-10-15 | 富士通株式会社 | Frequency difference estimation method, apparatus and system |
WO2014166390A1 (en) * | 2013-04-10 | 2014-10-16 | 富士通株式会社 | Method, device, and system for frequency offset estimation |
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CN104104624B (en) * | 2013-04-10 | 2018-02-16 | 富士通株式会社 | Frequency difference estimation method, device and system |
CN104038264A (en) * | 2014-04-22 | 2014-09-10 | 中国水产科学研究院渔业工程研究所 | Short wave communication system power automatic control method |
CN104735016A (en) * | 2015-03-19 | 2015-06-24 | 深圳市通创通信有限公司 | OFDM system fractional part of frequency offset estimation method and device based on multi-path channel |
CN111147123A (en) * | 2019-12-23 | 2020-05-12 | 东方红卫星移动通信有限公司 | Carrier synchronization method of low-orbit satellite broadband OFDM communication system |
CN113141245A (en) * | 2021-06-22 | 2021-07-20 | 中国人民解放军国防科技大学 | Time-frequency synchronization method, system, equipment and readable storage medium |
CN113783585A (en) * | 2021-09-13 | 2021-12-10 | 深圳市力合微电子股份有限公司 | Method for estimating sampling deviation based on Chirp correlation peak position deviation trend |
CN114337982A (en) * | 2022-03-16 | 2022-04-12 | 深圳市华普微电子有限公司 | Chirp pilot signal generation and time-frequency estimation method |
CN114337982B (en) * | 2022-03-16 | 2022-07-15 | 深圳市华普微电子有限公司 | Chirp pilot signal generation and time-frequency estimation method |
CN114726701A (en) * | 2022-05-16 | 2022-07-08 | 为准(北京)电子科技有限公司 | Frequency offset estimation method and device |
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Application publication date: 20120704 |