CN103166878B - A kind of method and apparatus of channel estimating - Google Patents

Abstract

Embodiments provide a kind of method and apparatus of channel estimating, wherein the method comprises and carries out initial channel estimation to reference signal, estimates the frequency domain response of described reference signal place channel described in calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carry out θ phase rotating; According to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering; Described interpolation and filtered value are carried out θ phase place derotation, obtains the channel estimation value of described reference signal.The method and apparatus that the embodiment of the present invention provides, the impact on frequency domain filtering of the energy leakage of the channel tap caused due to non-integral multiple sampling is considered when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously when calculating filter coefficient, consider the impact of receive advance, make filter factor more accurate; Make the result estimated reference signal more accurate like this.

Description

A kind of method and apparatus of channel estimating

Technical field

The present invention relates to the communications field, particularly relate to a kind of method and apparatus of channel estimating.

Background technology

In orthogonal frequency division multiplexi (OrthogonalFrequencyDivisionMultiplexing, OFDM) system, the reference signal (RS) of the discrete insertion of time-frequency domain is usually utilized to carry out channel estimating.Wherein more typically adopt the linear minimum mean-squared error (LinearMinimumMeanSquareError of two dimension, LMMSE) channel estimating, namely after initial channel estimation being carried out to RS place, least mean-square error (MinimumMeanSquareError is carried out respectively in frequency domain, time domain, MMSE) filtering, interpolation, to obtain the channel estimating at Data Position place.

For Long Term Evolution (LongTermEvolution, LTE) system, reference signal time-frequency domain distribution as shown in Figure 1, wherein, the square of shaded background and corresponding RS signal.

When using MMSE interpolation algorithm; need the correlation utilizing channel; the correlation of channel on frequency domain can be expressed as the Fourier transform of the time delay power spectrum of channel; in actual applications; the time delay power spectrum of channel obtains based on some supposition are approximate usually, and conventional channel delay power spectrum can be expressed as:

$\mathrm{\θ}\left({\mathrm{\τ}}_m\right)=\left\{\begin{array}{cc}1/L_0& {\mathrm{\τ}}_m\∈[0,L_0]\\ 0& \mathrm{otherwise}\end{array}\right.---\left(2.1\right)$

Wherein, L ₀for maximum multipath time delay, general L ₀≤ L, L are cyclic prefix CP length, then frequency domain correlation coefficient is obtained by the Fourier transform of (2.1):

$R_f(k-k^{\′})={\∫}_0^{L_0}\mathrm{\θ}\left({\mathrm{\τ}}_m\right)e^{-j2\mathrm{\π}{\mathrm{\τ}}_m(k-k^{\′})/K}d{\mathrm{\τ}}_m$ $\left(2.2\right)$

$=\sin c(\mathrm{\π}{L}_0(k-k^{\′})/K)e^{-\mathrm{j\π}{L}_0(k-k^{\′})/K}$

Wherein, exist $\sin c(\mathrm{\π}{L}_0(k-k^{\′})/K)=\frac{\sin (\mathrm{\π}{L}_0(k-k^{\′})/K)}{\mathrm{\π}{L}_0(k-k^{\′})/K}$ In, (k-k ') is the interval of two sub-intercarriers, and K is FFT transform length, k and k ' represents subcarrier respectively, and π is circumference ratio.

The initial channel estimation of RS position is H _lS, then through the channel estimating H at the filtered Data Position place of frequency domain LMMSE _lMMSEcan be expressed as:

H _LMMSE＝H _LS*R _f(2.3)

Wherein R _ffor frequency domain correlation coefficient, through the filtered channel estimation in frequency domain of frequency domain MMSE schematic diagram as shown in Figure 2, in figure, dash area refers to the channel estimating of these subcarriers, can be obtained by the channel estimating of RS through filtering interpolation.。

In the calculating of reality, if make phase rotating to each sub-carrier channels impulse response, namely frequency domain correlation function then after phase rotating becomes:

Now coefficient correlation becomes real number completely, the filtering interpolation coefficient calculated accordingly also becomes real number, thus greatly can reduce amount of calculation, carries out phase place derotation again and can obtain final channel estimation results after frequency domain interpolation filtering, this processing procedure as shown in Figure 3, comprising:

301, channel estimating is carried out to RS signal;

302, channel estimation results is carried out phase rotating, namely k is the frequency domain index of each subcarrier;

303, LMMSE interpolation, filtering are carried out to postrotational channel estimating, namely w is the interpolating matrix calculated according to frequency domain correlation coefficient

304, phase place derotation is carried out to above-mentioned filtering interpolation result, obtain final LMMSE channel estimating, that is: but at least there are the following problems for channel estimation methods of the prior art:

When 1, adopting this formula (2.1) to calculate channel delay power spectrum, it is generally acknowledged that the time delay power of channel is at 0 ~ L ₀between obey and be uniformly distributed.But in the realization of reality, because some tap of channel may not be on the integral multiple in sampling interval, the energy leakage of the tap of these channels will be caused like this on the sampling interval of integral multiple near it, thus cause the expansion of channel delay.The energy leakage of these channel tap can make previous OFDM symbol produce serious intersymbol interference to previous OFDM symbol simultaneously, therefore in order to prevent the intersymbol interference because energy leakage causes, usually can avoid by receive advance.And, due to this energy leakage, Multipath distribution may be caused no longer to meet [0, L ₀] being uniformly distributed in scope, but being uniformly distributed within the scope of another one.

2, in an ofdm system, in order to prevent definite time delay (definite time delay can cause ofdm system performance sharply to decline, and timing advance is then little to ofdm system performance impact), often receive advance is understood.Receive advance can carry out a continuous print phase rotating to channel estimating, thus impacts frequency domain correlation, and prior art is when calculating phase rotating and derotation, does not consider this point, also can cause the hydraulic performance decline of channel estimating.

Summary of the invention

Not necessarily at integral multiple sampled point for solving channel tap in prior art, channel tap energies can be caused to reveal, thus cause the inaccurate problem of channel estimating, embodiments provide a kind of method and apparatus of channel estimating.

A method for channel estimating, comprising:

Initial channel estimation is carried out to reference signal, estimates the frequency domain response of described reference signal place channel

Described in calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carry out θ phase rotating;

According to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering;

Described interpolation and filtered value are carried out θ phase place derotation, obtains the channel estimation value of described reference signal.

A kind of channel estimating apparatus, comprising:

Initial channel estimation unit, for carrying out initial channel estimation to reference signal, estimates the frequency domain response of described reference signal place channel

Phase rotation units, described in calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carry out θ phase rotating;

Filtering interpolation unit, for according to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering;

Phase place derotation unit, for described interpolation and filtered value are carried out θ phase place derotation, obtains the channel estimation value of described reference signal.

Adopt the apparatus and method that the embodiment of the present invention provides, the impact on frequency domain filtering of the energy leakage of the channel tap caused due to non-integral multiple sampling is considered when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously when at calculating filter coefficient, consider the impact of receive advance, make filter factor more accurate; Make the result estimated reference signal more accurate like this.

Accompanying drawing explanation

Fig. 1 is RS place initial channel estimation schematic diagram in LTE system;

Fig. 2 is channel estimating schematic diagram after frequency domain filtering;

Fig. 3 is that time delay uniform power spectrum MMSE estimates flow process;

Fig. 4 is the first pass figure of embodiment of the present invention channel estimating; ;

Fig. 5 is the second flow chart of embodiment of the present invention channel estimating;

Fig. 6 is channel estimation methods and original channel estimation methods performance comparison schematic diagram one in the embodiment of the present invention;

Fig. 7 is channel estimation methods and original channel estimation methods performance comparison schematic diagram two in the embodiment of the present invention;

Fig. 8 is the structure chart of channel estimating apparatus in the embodiment of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the method and apparatus that the embodiment of the present invention provides is described in detail.

Embodiment one:

Before introducing the embodiment of the present invention, first introduce the new channel delay power spectrum that the embodiment of the present invention proposes,

$\mathrm{\θ}\left({\mathrm{\τ}}_m\right)=\left\{\begin{array}{cc}1/L_0& {\mathrm{\τ}}_m\∈[-{\mathrm{\τ}}_{\mathrm{leak}},L_0-{\mathrm{\τ}}_{\mathrm{leak}}]\\ 0& \mathrm{otherwise}\end{array}\right.$

Wherein, L ₀for maximum multipath time delay, general L ₀≤ L, L are CP length, τ _leakbe the leakage value of the channel tap caused due to non-integral multiple sampling, concrete value is relevant with sample frequency, is determined by emulation.

Embodiments provide a kind of method of channel estimating, as shown in Figure 4, comprising:

S1, initial channel estimation is carried out to reference signal, estimate the frequency domain response of described reference signal place channel

Described in S2, calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carry out θ phase rotating;

S3, according to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering;

S4, described interpolation and filtered value are carried out θ phase place derotation, obtain the channel estimation value of described reference signal.

The method that the embodiment of the present invention provides considers the impact on frequency domain filtering of the energy leakage of the channel tap caused due to non-integral multiple sampling when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously when at calculating filter coefficient, consider the impact of receive advance, make filter factor more accurate; Make the result estimated reference signal more accurate like this.

Embodiment two:

Embodiments provide a kind of method of channel estimating, as shown in Figure 5, comprising:

S1, carry out initial channel estimation LS according to reference signal RS, estimate the frequency domain response of this reference signal place channel

S2, calculate this frequency domain response need the amount θ carrying out phase rotating, wherein, the account form of the amount θ of this phase rotating is:

$\mathrm{\θ}={\mathrm{\τ}}_A+\frac{{\mathrm{\τ}}_{\max }}{2}-{\mathrm{\τ}}_{\mathrm{leak}},$

In above-mentioned formula, τ _leakbe the leakage value of the channel tap that non-integral multiple sampling causes, relevant with the frequency of carrying out sampling, concrete value is obtained by emulation; τ _ait is the sampled point of receive advance; τ _maxthe estimated value of the maximum delay expansion of channel, τ _maxvalue be-τ _leakto L0-τ _leak.

In concrete application, if do not consider the multi-path jamming of last OFDM symbol to previous OFDM symbol, as receive advance amount τ _awhen being less than CP length, compared with not receive advance, can think that receiving sequence is through ring shift right, this subcarrier in frequency domain after causing FFT is had one with receive advance amount τ _arelevant phase rotating.Therefore, being real number to meet filter factor, in the process of carrying out phase rotating and derotation, needing the impact of receive advance to take into account.

S3, carry out phase rotating to the value after reference signal channel estimating, the output of phase rotation module is its element value is:

$0\&le;k^{\&prime;}<2N_{\mathrm{RB}}^{\mathrm{DL}};$

In this formula, refer to bandwidth RB number descending in LTE system; it is the computing formula of phase rotating.

S4, according to the correlation between each subcarrier, carry out LMMSE interpolation and filtering to postrotational LS channel estimating, the output of this module is its element value is:

Wherein W is the channel interpolating matrix calculated according to frequency domain correlation coefficient, is specially:

Wherein W is Rf.

S5, carry out phase place derotation to LMMSE channel estimating, the output of this module is its element value is:

$0\&le;k<N_{\mathrm{RB}}^{\mathrm{DL}}\&CenterDot;N_{\mathrm{sc}}^{\mathrm{RB}}$

In above-mentioned formula, represent the number of sub carrier wave of a RB.

The method (newmodel) that the embodiment of the present invention provides is compared with original method (original) has outstanding advantage, as shown in Figure 6 and Figure 7, under typical EPA channel, when single transmit antenna sends out that under two reception antennas, bandwidth is 10MHz, performance has the lifting of very about 0.5dB in the case of 16 qam, and performance has the lifting of very about 1dB in the case of 64 qam.

Embodiment three:

The embodiment of the present invention additionally provides a kind of channel estimating apparatus, as shown in Figure 8, comprising:

Initial channel estimation unit 801, for carrying out initial channel estimation to reference signal, estimates the frequency domain response of described reference signal place channel

Phase rotation units 803, described in calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carry out θ phase rotating;

Filtering interpolation unit 805, for according to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering;

Phase place derotation unit 807, for described interpolation and filtered value are carried out θ phase place derotation, obtains the channel estimation value of described reference signal.

The channel estimating apparatus that the embodiment of the present invention provides, the impact on frequency domain filtering of the energy leakage of the channel tap caused due to non-integral multiple sampling is considered when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously when at calculating filter coefficient, consider the impact of receive advance, make filter factor more accurate; Make the result estimated reference signal more accurate like this.

More than some preferably execution modes of the embodiment of the present invention, anyone is under the prerequisite of skilled, do not deviate from spirit of the present invention and do not exceed the technical scope that the present invention relates to prerequisite under, can to the present invention describe details do various supplement and amendment.Protection scope of the present invention is not limited to the scope cited by embodiment, and protection scope of the present invention is as the criterion with claim.

Claims (7)

1. a method for channel estimating, is characterized in that, comprising:

Initial channel estimation is carried out to reference signal, estimates the frequency domain response of described reference signal place channel

Described in calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carrying out θ phase rotating, wherein considering that the energy leakage value of the channel tap that non-integral multiple sampling causes is on the impact of frequency domain filtering when calculating described θ;

According to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering;

Described interpolation and filtered value are carried out θ phase place derotation, obtains the channel estimation value of described reference signal;

Wherein, in the process of carrying out phase rotating and derotation, consider the impact of receive advance.

2. method according to claim 1, is characterized in that, described in calculating the method of the amount θ carrying out phase rotating is needed to be:

$\mathrm{\&theta;}={\mathrm{\&tau;}}_A+\frac{{\mathrm{\&tau;}}_{max}}{2}-{\mathrm{\&tau;}}_{leak},$

Wherein τ _leakit is the leakage value of the channel tap that non-integral multiple sampling causes; τ _afor the sampled point of receive advance; τ _maxit is the estimated value of the maximum delay expansion of channel.

3. method as claimed in claim 2, is characterized in that, described τ _maxvalue for being more than or equal to-τ _leak, be less than or equal to L ₀-τ _leak; Wherein, L ₀signal maximum delay length.

4. the method for claim 1, is characterized in that, described in inciting somebody to action the computing formula of carrying out θ phase rotating is:

${\tilde{h}}_{LS,k^{\&prime;}}={\hat{h}}_{LS,k^{\&prime;}}\&CenterDot;e^{j2\mathrm{\&pi;}\&CenterDot;\frac{k^{\&prime;}\mathrm{\&theta;}}{N}},0\&le;k^{\&prime;}<2N_{RB}^{DL};$

Wherein, described in expression carry out the result of θ phase rotating, described in refer to the number of downlink bandwidth RB in long evolving system; be the channel estimation results that LS channel estimation algorithm obtains, j represents imaginary number, and N is the FFT length in ofdm system.

5. the method for claim 1, is characterized in that, described according to the correlation between each subcarrier, to after described θ phase rotating the computing formula of carrying out interpolation and filtering is:

${\tilde{h}}_{LMMSE,k^{\&prime;}}=W{\tilde{h}}_{LS,k^{\&prime;}}$

Wherein, described in described in expression carry out the result of θ phase rotating, described in be the result after filtering interpolation, described W is the channel interpolating matrix calculated according to frequency domain correlation coefficient.

6. the method for claim 1, is characterized in that, by the computing formula that described interpolation and filtered value carry out θ phase place derotation is:

${\hat{h}}_{FD,k}={\tilde{h}}_{LMSSE,k}\&CenterDot;e^{-j2\mathrm{\&pi;}\&CenterDot;\frac{k\mathrm{\&theta;}}{N}},0\&le;k<N_{RB}^{DL}\&CenterDot;N_{sc}^{RB}$

Wherein, described in the result after phase place derotation, described in the result after filtering interpolation, described in refer to the number of downlink bandwidth RB in long evolving system, described in represent the number of sub carrier wave of a RB, j represents imaginary number, and N is the FFT length in ofdm system.

7. a channel estimating apparatus, is characterized in that, comprising:

Initial channel estimation unit, for carrying out initial channel estimation to reference signal, estimates the frequency domain response of described reference signal place channel

Phase rotation units, described in calculating need the amount θ carrying out phase rotating, and described in inciting somebody to action carrying out θ phase rotating, wherein considering that the energy leakage value of the channel tap that non-integral multiple sampling causes is on the impact of frequency domain filtering when calculating described θ;

Filtering interpolation unit, for according to the correlation between each subcarrier, to after described θ phase rotating carry out interpolation and filtering;

Phase place derotation unit, for described interpolation and filtered value are carried out θ phase place derotation, obtains the channel estimation value of described reference signal;

Wherein, in the process of carrying out phase rotating and derotation, consider the impact of receive advance.