CN103297100A - Doppler change rate estimation method and system for OFDM (Orthogonal Frequency Division Multiplexing) system - Google Patents

Abstract

The invention provides a doppler change rate estimation method and system for an OFDM (Orthogonal Frequency Division Multiplexing) system. The doppler change rate estimation method comprises obtaining sampling point data of an OFDM symbol; performing self-correlation operation on a result obtained from self-correlation operation which is performed on a sampling point in an OFDM symbol cyclic prefix and a sampling point corresponding to the sampling point at the end of the OFDM symbol and a result obtained from self-correlation operation which is performed on the next sampling point of the sampling point and a sampling point corresponding to the next sampling point at the end of the OFDM symbol to obtain a correlation value; and obtaining a doppler change rate for the OFDM system according to the correlation value. The doppler change rate estimation method is low in complexity, can be utilized to estimate the doppler change rate of a multi-carrier OFDM system and is not sensitive to doppler frequency shift in the estimation process of the doppler change rate.

Description

A kind of doppler changing rate method of estimation and system for ofdm system

Technical field

The present invention relates to wireless communication technology field, relate in particular to a kind of doppler changing rate method of estimation and system for ofdm system.

Background technology

OFDM (OFDM, Orthogonal Frequency Division Multiplexing) is the wireless broadband communication technology of present main flow, as the core technology such as physical layer in numerous mobile communication standards such as LTE and Wimax.In order to make the system based on the OFDM technology in the application scenarios of some high mobilities, provide broadband wireless communications, such as: the low orbit satellite communication scenes, auxiliary and the control system of millimeter wave traffic, and the high-speed railway communication system, need design based on the doppler changing rate method of estimation of ofdm system.In these scenes, receive the influence that signal can be subjected to the Doppler frequency shift that becomes when quick.Be to guarantee the correct reception of signal, need estimate and compensate Doppler frequency shift and doppler changing rate.For example, in the low orbit satellite communication scenes, need the parameter of doppler changing rate to carry out prediction and the control of satellite orbit; In the auxiliary and control system, doppler changing rate can be used for estimating the acceleration of motion of the vehicles, thereby the motion conditions of the vehicles is predicted at millimeter wave traffic; In the high-speed railway communication system, obtain the prediction that doppler changing rate helps the Doppler frequency shift variation tendency, and the correct estimation of Doppler frequency shift is the significant process that guarantees the Frequency Synchronization of communication system reliability service.Therefore, need design based on the doppler changing rate method of estimation of ofdm system.

In the prior art, the method that is used for the estimating Doppler rate of change comprises: the Doppler frequency shift of maximum likelihood and doppler changing rate associating estimation approach, this method has defined the target function of a Doppler frequency shift and doppler changing rate two dimension combined optimization, carry out two-dimensional search then, be difficult to practicality to such an extent as to complexity is very high; Only be used for the maximum likelihood method that doppler changing rate is estimated, this method is by the means of integration, removed initial phase and Doppler frequency shift to the doppler changing rate estimation effect, this doppler changing rate method of estimation is stronger to the robustness of Doppler frequency shift, and complexity is lower; And FREFE (Frequency Rate Estimation through Frequency Estimation) method, this method hypothesis is in the process of the data packet transmission of a burst transfer, Doppler frequency shift is linear change, and doppler changing rate can calculate by the Doppler frequency shift estimated result of two ends pilot tone.

The problem that prior art exists is that above these methods only are applicable to the single carrier scene, and is not suitable for the OFDM scene of multicarrier, and said method needs to come the estimating Doppler rate of change based on a unmodulated carrier wave.Yet in prior OFDM system, as LTE, WiMax, ISDB-S etc., because the demand of channel estimating etc., pilot tone is to be placed on discretely on the specific temporal frequency Resource Block, rather than is placed on whole OFDM symbol or the subcarrier, thereby can't obtain unmodulated carrier wave, can't use above-mentioned existing method to come the rate of change of estimating Doppler.And prior art is not considered initial Doppler shift mostly, and very responsive to big Doppler frequency shift, and namely Doppler frequency shift can make a big impact to the estimation of this doppler changing rate.

Therefore, need a kind of doppler changing rate in can the estimating OFDM system, and to the insensitive method of initial Doppler frequency shift.

Summary of the invention

According to one embodiment of present invention, provide a kind of doppler changing rate method of estimation for ofdm system, comprising:

The baseband digital signal sampling number certificate of step 1), an OFDM symbol of acquisition;

Step 2), the sampled point in the described OFDM symbol cyclic prefix is carried out the result that autocorrelation operation obtains with its corresponding sampled point at described OFDM symbol end, carry out the result that autocorrelation operation obtains with the next sampled point of this sampled point with the corresponding sampled point of this next one sampled point at described OFDM symbol end, carry out autocorrelation operation and obtain correlation;

Step 3), obtain doppler changing rate for ofdm system according to described correlation.

In one embodiment, step 2) comprising:

Step 21), according to following formula sampled point is carried out autocorrelation operation with its corresponding sampled point at described OFDM symbol end, obtain P _Corr(k):

$P_{\mathrm{corr}}\left(k\right)=r_k{r}_{k+N}^{*},$

Wherein, k is sampled point sequence number and k ∈ [0, L-2], and L is the sampling number of Cyclic Prefix, and N is the sampling number of effective OFDM symbol, r _kRepresent that k receives signal,

Expression r _K+NConjugation;

Step 22), next sampled point is carried out autocorrelation operation with the corresponding sampled point of this next one sampled point at described OFDM symbol end, obtain P _Corr(k+1);

Step 23), according to following formula with step 21) result and the step 22 that obtain) result that obtains carries out autocorrelation operation, obtains correlation P ' _Corr(k):

$P_{\mathrm{corr}}^{\′}\left(k\right)=P_{\mathrm{corr}}\left(k\right)P_{\mathrm{corr}}^{*}(k+1),$

Wherein,

Expression P _Corr(k+1) conjugation.

In one embodiment, step 3) comprises according to following formula calculating normalization doppler changing rate:

$\hat{a}=\frac{1}{2\mathrm{\π}}\arg \left\{P_{\mathrm{corr}}^{\′}\left(k\right)\right\}.$

In a further embodiment, step 23) also comprise afterwards:

Step 24), that calculate correlation according to following formula and P ' _{Corr_sum}:

$p_{\mathrm{corr}\_\mathrm{sum}}^{\′}=\underset{k=0}{\overset{L-2}{\mathrm{\Σ}}}{P}_{\mathrm{corr}}^{\′}\left(k\right),$

Wherein, L is the sampling number of Cyclic Prefix.

Then, step 3) comprises according to following formula and obtains the normalization doppler changing rate:

$\hat{a}=\frac{1}{2\mathrm{\π}}\arg \left\{P_{\mathrm{corr}\_\mathrm{sum}}^{\′}\right\},$

Wherein, P ' _{Corr_sum}Be correlation and.

In one embodiment, also comprise before the step 1):

Step 0), the continuous signal that obtains is changed the acquisition baseband digital signal through A/D.

According to one embodiment of present invention, also provide a kind of doppler changing rate estimating system for ofdm system, comprising:

The device that is used for the sampling number certificate of an OFDM symbol of acquisition;

Be used for the sampled point of described OFDM symbol cyclic prefix is carried out the result that autocorrelation operation obtains with its corresponding sampled point at described OFDM symbol end, carry out the result that autocorrelation operation obtains with the next sampled point of this sampled point with the corresponding sampled point of this next one sampled point at described OFDM symbol end, carry out the device that autocorrelation operation obtains correlation; And

For the device that obtains according to described correlation for the doppler changing rate of ofdm system.

Adopt the present invention can reach following beneficial effect:

1), considered the signal model of OFDM, can be used for estimating the doppler changing rate of multi-carrier OFDM systems;

2), the influence of having removed initial Doppler frequency shift, insensitive to Doppler frequency shift in the estimation procedure of doppler changing rate;

3), complexity is lower, only needs L-2 plural number to add operation with 3L-2 CM, wherein L is the sampling number of the OFDM symbol cyclic prefix of ofdm system;

4), need not extra pilot tone, improved the spectrum efficiency of system.

Description of drawings

Fig. 1 is the structural representation of OFDM symbol;

Fig. 2 is the flow chart that is used for the doppler changing rate method of estimation of ofdm system according to an embodiment of the invention;

Fig. 3 is the flow chart that calculates the method for correlation sum according to an embodiment of the invention;

Fig. 4 is the flow chart that calculates the method for correlation sum in accordance with another embodiment of the present invention;

Fig. 5 is the precision schematic diagram of the doppler changing rate of employing method estimating OFDM provided by the invention system; And

Fig. 6 adopts the doppler changing rate method of estimation for ofdm system provided by the invention to the sensitiveness schematic diagram of initial Doppler frequency shift.

Embodiment

The present invention is described in detail below in conjunction with the drawings and specific embodiments.

According to one embodiment of present invention, provide a kind of doppler changing rate method of estimation for ofdm system.This method is carried out autocorrelation operation by sampled point and its corresponding sampled point at the OFDM end to Cyclic Prefix, and autocorrelative result is done the secondary autocorrelation operation according to the sampling number certificate in the OFDM symbol, comes the estimating Doppler rate of change.

At first determine to receive the method for expressing of signal, the Doppler frequency shift that becomes when considering under the awgn channel in an OFDM symbol can be with receiving signal indication:

$r_t=s_t\exp \left[j(2\mathrm{\π}{\∫}_0^t{f}_{\mathrm{Doppler}}\left(\mathrm{\τ}\right)\mathrm{d\τ}+{\mathrm{\θ}}_0)\right]+n_t,---\left(1\right)$

Wherein, r _t, s _tAnd n _tBe illustrated respectively in t reception signal, transmission signal and noise signal constantly, f _Doppler(τ) expression τ Doppler frequency shift constantly, j is imaginary symbols, θ ₀It is unknown initial phase.

After continuous signal (referring to formula (1)) the process A/D conversion that obtains, the discrete signal that obtains can be represented with following formula:

$r_k=s_k\exp \left[j(2\mathrm{\π}\underset{p=1}{\overset{k}{\mathrm{\Σ}}}{f}_{\mathrm{Doppler}}\left(p\right)\·T_s+{\mathrm{\θ}}_0)\right]+n_k,---\left(2\right)$

Wherein, duration t=kT _s, T _sIt is the sampling interval.K=0,1 ..., N+L-1, expression sampled point sequence number (sampling number is N+L), L is CP(Cyclic Prefix, Cyclic Prefix) length, N is the length of effective OFDM symbol, r _kBe k and receive signal (or claim, at the reception signal of k sampled point/sampled point k).Fig. 1 shows the intrinsic signal Cyclic Prefix of OFDM symbol, and from Fig. 1 as seen, CP is that a part of sampled point with OFDM symbol end copies to the OFDM head, the intersymbol interference problem that causes with the antagonism multidiameter delay.In one embodiment, N can be the sampling number of effective OFDM symbol, and L is the sampling number of Cyclic Prefix.

Then adopt following formula to the time become Doppler frequency shift and carry out normalized:

${\mathrm{\ϵ}}_p=\frac{f_{\mathrm{Doppler}}\left(p\right)}{{\mathrm{\Δf}}_{\mathrm{subcarrier}}},---\left(3\right)$

Wherein,

The subcarrier spacing of expression ofdm system.Therefore, formula (2) can also be expressed as:

$r_k=s_k\exp \left[j(\frac{2\mathrm{\π}}{N}\underset{p=1}{\overset{k}{\mathrm{\Σ}}}{\mathrm{\ϵ}}_p+{\mathrm{\θ}}_0)\right]+n_k,---\left(4\right)$

Consider that in an OFDM symbol linear Doppler frequency shift changes, namely the interior doppler changing rate of OFDM symbol is fixed, and then normalized Doppler frequency shift can be expressed as:

ε _p=ε ₀+αp （5）

Wherein,

Be illustrated in normalization doppler changing rate fixing in the OFDM symbol, Δ f _DopplerBe to be the doppler changing rate of unit with Hz/s, ε ₀Represent initial Doppler frequency shift, then receive signal and can be written as:

$r_k=s_k\exp \left[j(\frac{2\mathrm{\π}}{N}\underset{p=1}{\overset{k}{\mathrm{\Σ}}}({\mathrm{\ϵ}}_0+\mathrm{\αp})+{\mathrm{\θ}}_0)\right]+n_k,---\left(6\right)$

Receive signal indication based on this, can make up the doppler changing rate estimation function.

In the time-varying field scape, consider sampled point k among the CP and the auto-correlation of the corresponding sampled point k+N of OFDM symbol afterbody, k ∈ [0, L-1] wherein, auto-correlation can be expressed as:

$P_{\mathrm{corr}}\left(k\right)=r_k{r}_{k+N}^{*},---\left(7\right)$

Wherein,

Expression r _K+NConjugation.To receive signal (formula (6)) substitution formula (7) can obtain:

$P_{\mathrm{corr}}\left(k\right)={\left|s_k\right|}^2\exp \{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003407536100021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}[{\mathrm{\&epsiv;}}_0+\frac{1}{2}\mathrm{\&alpha;}(2k+N+1)\left]\right\}.---\left(8\right)$

Similarly, consider these two sampled points of k+1 and k+N+1, can obtain:

$P_{\mathrm{corr}}(k+1)=r_{k+1}{r}_{k+N+1}^{*}$

$={\left|s_{k+1}\right|}^2\exp \{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003407536100021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}[{\mathrm{\&epsiv;}}_0+\frac{1}{2}\mathrm{\&alpha;}(2k+N+3)\left]\right\}---\left(9\right)$

Then, in order to obtain the estimation of normalization doppler changing rate α, formula (8) and (9) are carried out autocorrelation operation, are shown below:

$P_{\mathrm{corr}}^{\&prime;}\left(k\right)=P_{\mathrm{corr}}\left(k\right)P_{\mathrm{corr}}^{*}(k+1)$ （10）

$={\left|s_k\right|}^2{\left|s_{k+1}\right|}^2\exp \left(\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003407536100021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;\&alpha;}\right)$

Make up the estimation function of normalization doppler changing rate α:

$\hat{a}=\frac{1}{2\mathrm{\&pi;}}\arg \left\{P_{\mathrm{corr}}^{\&prime;}\left(k\right)\right\}---\left(11\right)$

Therefore, can use four sampled points to obtain the estimation of a doppler changing rate.In a further embodiment, fall The noise for smooth, can be to all possible P ' _Corr(k) summation obtains P ' _{Corr_sum}:

$P_{\mathrm{corr}\_\mathrm{sum}}^{\&prime;}=\underset{k=0}{\overset{L-2}{\mathrm{\&Sigma;}}}{P}_{\mathrm{corr}}^{\&prime;}\left(k\right)---\left(12\right)$

With reference to formula (12), the estimation of doppler changing rate can be expressed as:

$\hat{a}=\frac{1}{2\mathrm{\&pi;}}\arg \left\{P_{\mathrm{corr}\_\mathrm{sum}}^{\&prime;}\right\}---\left(13\right)$

Formula (12) and (13) are last estimator, and this estimation is one does not have estimation partially.Perhaps said process can be written as of equal valuely:

$\hat{a}=\frac{1}{2\mathrm{\&pi;}}\arg \left\{\underset{k=0,k=k+1}{\overset{L-2}{\mathrm{\&Sigma;}}}\left(r_k{r}_{k+N}^{*}\right){\left(r_{k+1}{r}_{k+N+1}^{*}\right)}^{*}\right\},---\left(14\right)$

After obtaining the normalization doppler changing rate, can be converted into Hz/s is the actual doppler changing rate of unit:

${\mathrm{\&Delta;f}}_{\mathrm{Doppler}}=\frac{{\mathrm{\&Delta;f}}_{\mathrm{subcarrier}}}{T_s}\mathrm{\&alpha;}---\left(15\right)$

Fig. 2 shows an embodiment for the doppler changing rate method of estimation of ofdm system, and this method comprises following step:

The first step: the sampling number certificate that obtains an OFDM symbol at radio-frequency head

In this step, can be according to the sample rate of default Carry out the A/D conversion, thereby obtain digital baseband signal, and an OFDM symbol is carried out buffer memory.

Second step: each sampled point in the OFDM symbol cyclic prefix is carried out autocorrelation operation with its corresponding sampled point at OFDM symbol end, and the result after the autocorrelation operation is carried out the secondary autocorrelation operation obtains correlation, calculate correlation with.

According to formula (12), can be calculated as follows correlation and:

$P_{\mathrm{corr}\_\mathrm{sum}}^{\&prime;}=\underset{k=0}{\overset{L-2}{\mathrm{\&Sigma;}}}{P}_{\mathrm{corr}}^{\&prime;}\left(k\right)$

$=\underset{k=0}{\overset{L-2}{\mathrm{\&Sigma;}}}{P}_{\mathrm{corr}}\left(k\right)P_{\mathrm{corr}}^{*}(k+1)---\left(16\right)$

$=\underset{k=0}{\overset{L-2}{\mathrm{\&Sigma;}}}\left(r_k{r}_{k+N}^{*}\right){\left(r_{k+1}{r}_{k+N+1}^{*}\right)}^{*}$

In one embodiment, in this step, can adopt that as shown in Figure 3 method is calculated correlation and P ' _{Corr_sum}That is, use the method for serial that each sampled point in the Cyclic Prefix and its are carried out autocorrelation operation in OFDM symbol end corresponding sampling points, and the result of this result and previous sampled point autocorrelation operation is carried out autocorrelation operation again, obtain correlation.Whenever obtain a correlation, just this correlation is added to P ' _{Corr_sum}(its initial value is 0) is up to obtaining all correlations.

In another embodiment, consider hard-wired needs, can use parallel method calculate correlation and, as shown in Figure 4.At first, from the OFDM symbol of buffer memory, take out CP, and take out the symbol afterbody relevant with this CP and it is got conjugation, thereby obtain two vectors: (r ₀, r ₁..., r _L-2, r _L-1) with

Secondly, these two vectors are done dot product obtain (P _Corr(0), P _Corr(1) ..., P _Corr(L-2), P _Corr(L-1)); Then, get preceding 0 to the L-2 number, and get back 0 to L-2 number and it is got conjugation, obtain two vector (P _Corr(0), P _Corr(1) ..., P _Corr(L-2)) with $(P_{\mathrm{corr}}^{*}\left(1\right),\&CenterDot;\&CenterDot;\&CenterDot;,P_{\mathrm{corr}}^{*}(L-2),P_{\mathrm{corr}}^{*}(L-1));$ Then, to these two vectors do dot product obtain (P ' _Corr(0), P ' _Corr(1) ..., P ' _Corr(L-2)); To at last, (P ' _Corr(0), P ' _Corr(1) ..., P ' _Corr(L-2)) all elements summation obtains P ' in _{Corr_sum}

The 4th step: calculate the normalization doppler changing rate

On the basis in the 3rd step, according to formula (13)

Can obtain the normalization doppler changing rate.In a further embodiment, can adopt the method for tabling look-up to get phase place.

The 5th step: calculate actual doppler changing rate

According to formula (15)

Can calculate actual doppler changing rate.In one embodiment, can

Calculate in advance, it is standby to be saved as a form, to reduce complexity.

According to one embodiment of the invention, also provide a kind of doppler changing rate estimating system for ofdm system.Comprise:

The device that is used for the sampling number certificate of an OFDM symbol of acquisition;

Be used for the sampled point of OFDM symbol cyclic prefix is carried out the result that autocorrelation operation obtains with its corresponding sampled point at OFDM symbol end, carry out the result that autocorrelation operation obtains with the next sampled point of this sampled point with the corresponding sampled point of this next one sampled point at OFDM symbol end, carry out the device that autocorrelation operation obtains correlation; And

For the device that obtains according to above-mentioned correlation for the doppler changing rate of ofdm system.

For verifying the validity of the doppler changing rate method of estimation for ofdm system provided by the invention, the inventor has carried out repeatedly emulation experiment, and table 1 shows the ofdm system configuration of adopting in the emulation:

Table 1

The precision of emulation experiment one, checking doppler changing rate method of estimation provided by the invention

Normalization doppler changing rate in inventor's ofdm system is set at 0.1 o'clock, estimated accuracy to method of estimation provided by the invention (abbreviating the SOD method as) is tested, Fig. 5 has provided the result, as can be seen from Figure 5, algorithm for estimating provided by the invention can estimate the doppler changing rate in the ofdm system more exactly, and MSE is 10 ^-4To 10 ^-1Between.

Emulation experiment two, checking doppler changing rate method of estimation provided by the invention are to the sensitiveness of Doppler frequency shift

The inventor is 15dB with signal-to-noise ratio settings, and target normalization doppler changing rate is set to 0.1, adopts method provided by the invention that doppler changing rate is estimated under the situation that initial Doppler frequency shift is 0-1.Fig. 6 has provided the estimated result under the situation of the initial Doppler frequency shift of difference, and this result shows that the almost not fluctuation of variation MSE along with initial Doppler frequency shift shows that method of estimation provided by the invention is insensitive to Doppler frequency shift.

Should be noted that and understand, under the situation that does not break away from the desired the spirit and scope of the present invention of accompanying Claim, can make various modifications and improvement to the present invention of foregoing detailed description.Therefore, the scope of claimed technical scheme is not subjected to the restriction of given any specific exemplary teachings.

Claims (10)

1. doppler changing rate method of estimation that is used for ofdm system comprises:

The sampling number certificate of step 1), an OFDM symbol of acquisition;

Step 2), the sampled point in the described OFDM symbol cyclic prefix is carried out the result that autocorrelation operation obtains with its corresponding sampled point at described OFDM symbol end, carry out the result that autocorrelation operation obtains with the next sampled point of this sampled point with the corresponding sampled point of this next one sampled point at described OFDM symbol end, carry out autocorrelation operation and obtain correlation;

Step 3), obtain doppler changing rate for ofdm system according to described correlation.

2. method according to claim 1, wherein, step 2) comprising:

Step 21), according to following formula sampled point is carried out autocorrelation operation with its corresponding sampled point at described OFDM symbol end, obtain P _Corr(k):

$P_{\mathrm{corr}}\left(k\right)=r_k{r}_{k+N}^{*},$

Wherein, k is sampled point sequence number and k ∈ [0, L-2], and L is the sampling number of Cyclic Prefix, and N is the sampling number of effective OFDM symbol, r _kRepresent that k receives signal, Expression r _K+NConjugation;

Step 22), next sampled point is carried out autocorrelation operation with the corresponding sampled point of this next one sampled point at described OFDM symbol end, obtain P _Corr(k+1);

Step 23), according to following formula with step 21) result and the step 22 that obtain) result that obtains carries out autocorrelation operation, obtains correlation P ' _Corr(k):

$P_{\mathrm{corr}}^{\&prime;}\left(k\right)=P_{\mathrm{corr}}\left(k\right)P_{\mathrm{corr}}^{*}(k+1),$

Wherein,

Expression P _Corr(k+1) conjugation.

3. method according to claim 2, wherein, step 3) comprises according to following formula calculates the normalization doppler changing rate:

$\hat{a}=\frac{1}{2\mathrm{\&pi;}}\arg \left\{P_{\mathrm{corr}}^{\&prime;}\left(k\right)\right\}.$

4. method according to claim 3 wherein, also comprises the value of calculating doppler changing rate according to following formula after the step 3):

${\mathrm{\&Delta;f}}_{\mathrm{Doppler}}=\frac{{\mathrm{\&Delta;f}}_{\mathrm{subcarrier}}}{T_s}\mathrm{\&alpha;},$

Wherein, Δ f _SubcarrierBe the subcarrier spacing of described ofdm system, T _sBe the sampling interval, α is the value of normalization doppler changing rate.

5. method according to claim 2, wherein,

$r_k=s_k\exp \left[j(\frac{2\mathrm{\&pi;}}{N}\underset{p=1}{\overset{k}{\mathrm{\&Sigma;}}}({\mathrm{\&epsiv;}}_0+\mathrm{\&alpha;p})+{\mathrm{\&theta;}}_0)\right]+n_k,$

J is imaginary symbols, and k is the sampled point sequence number, s _kAnd n _kRepresent that respectively k sends signal and k noise signal, ε ₀Represent initial Doppler frequency shift, θ ₀It is unknown initial phase.

6. method according to claim 2, wherein, step 23) also comprise afterwards:

Step 24), that calculate correlation according to following formula and P ' _{Corr_sum}:

$P_{\mathrm{corr}\_\mathrm{sum}}^{\&prime;}=\underset{k=0}{\overset{L-2}{\mathrm{\&Sigma;}}}{P}_{\mathrm{corr}}^{\&prime;}\left(k\right),$

Wherein, L is the sampling number of Cyclic Prefix.

7. method according to claim 6, wherein, step 3) comprises according to following formula and obtains the normalization doppler changing rate:

$\hat{a}=\frac{1}{2\mathrm{\&pi;}}\arg \left\{P_{\mathrm{corr}\_\mathrm{sum}}^{\&prime;}\right\},$

Wherein, P ' _{Corr_sum}Be correlation and.

8. method according to claim 7 wherein, also comprises the value of calculating doppler changing rate according to following formula after the step 3):

${\mathrm{\&Delta;f}}_{\mathrm{Doppler}}=\frac{{\mathrm{\&Delta;f}}_{\mathrm{subcarrier}}}{T_s}\mathrm{\&alpha;},$

Wherein, Δ f _SubcarrierBe the subcarrier spacing of described ofdm system, T _sBe the sampling interval, α is the value of normalization doppler changing rate.

9. according to any one described method among the claim 1-8, wherein, also comprise before the step 1):

Step 0), the continuous signal that obtains is changed the acquisition baseband digital signal through A/D.

10. doppler changing rate estimating system that is used for ofdm system comprises:

The device that is used for the sampling number certificate of an OFDM symbol of acquisition;

Be used for the sampled point of described OFDM symbol cyclic prefix is carried out the result that autocorrelation operation obtains with its corresponding sampled point at described OFDM symbol end, carry out the result that autocorrelation operation obtains with the next sampled point of this sampled point with the corresponding sampled point of this next one sampled point at described OFDM symbol end, carry out the device that autocorrelation operation obtains correlation; And

For the device that obtains according to described correlation for the doppler changing rate of ofdm system.

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