CN103166878A - Method and device for channel estimation - Google Patents

Abstract

The invention provides a method and a device for channel estimation. The method comprises the following steps: carrying out initial channel estimation on reference signals, estimating the amount theta of phase rotation needed by frequency domain response calculation of a channel on the positions of the reference signals, and carrying out theta phase rotation; according to relevance of each subcarrier, carrying out interpolation and filtering after theta phase rotation; and carrying out theta phase unwrapping rotation on a value after interpolation and filtering, and obtaining a channel estimation value of the reference signals. According to the method and the device for channel estimation, influence of channel tapping energy leakage caused by non-integral-multiple sampling on frequency domain filtering is considered during channel estimation, and therefore frequency domain filtering is accurate. Meanwhile, when a filter coefficient is calculated, influence of receiving in advance is considered, and therefore the filter coefficient is accurate. Thus, estimation results of the reference signals are accurate.

Description

A kind of method and apparatus of channel estimating

Technical field

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

Background technology

In orthogonal frequency division multiplexi (Orthogonal Frequency Division Multiplexing, OFDM) system, usually utilize the reference signal (RS) of the discrete insertion of time-frequency domain to carry out channel estimating.Wherein relatively be typically linear minimum mean-squared error (the Linear Minimum Mean Square Error that adopts two dimension, LMMSE) channel estimating, after namely the RS place being carried out initial channel estimation, carry out least mean-square error (Minimum Mean Square Error in frequency domain, time domain respectively, MMSE) filtering, interpolation are to obtain the channel estimating at Data Position place.

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

When using the MMSE interpolation algorithm; need to utilize the correlation of 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 channel delay power spectrum commonly used can be expressed as:

$\mathrm{\&theta;}\left({\mathrm{\&tau;}}_m\right)=\left\{\begin{array}{cc}1/{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="HDA0000117798260000041.png"\; state="\{\{state\}\}">L</figure-callout>}}_0& {\mathrm{\&tau;}}_m\&Element;[0,L_0]\\ 0& \mathrm{otherwise}\end{array}\right.---\left(2.1\right)$

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

$R_f(k-k^{\&prime;})={\&Integral;}_0^{{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="HDA0000117798260000041.png"\; state="\{\{state\}\}">L</figure-callout>}}_0}\mathrm{\&theta;}\left({\mathrm{\&tau;}}_m\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000117798260000041.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{\mathrm{\&tau;}}_m(k-k^{\&prime;})/K}d{\mathrm{\&tau;}}_m$ $\left(2.2\right)$

$=\sin c(\mathrm{\&pi;}{L}_0(k-k^{\&prime;})/K)e^{-\mathrm{j\&pi;}{L}_0(k-k^{\&prime;})/K}$

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

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

H _LMMSE＝H _LS*R _f (2.3)

R wherein _fBe frequency domain correlation coefficient, through the schematic diagram of frequency domain MMSE filtered channel estimation in frequency domain as shown in Figure 2, in figure, dash area refers to the channel estimating of these subcarriers, can pass through filtering interpolation by the channel estimating at RS place and obtain.。

In the calculating of reality, if each sub-carrier channels impulse response is made phase rotating, namely

The spectrum correlation function after phase rotating becomes:

This moment, coefficient correlation became real number fully, the filtering interpolation coefficient that calculates has accordingly also become real number, thereby can greatly reduce amount of calculation, carries out the phase place derotation again and can obtain final channel estimation results after frequency domain interpolation filtering, this processing procedure comprises as shown in Figure 3:

301, the RS signal is carried out channel estimating;

302, channel estimation results is carried out phase rotating, namely

K is the frequency domain index of each subcarrier;

303, postrotational channel estimating is carried out LMMSE interpolation, filtering, namely

The interpolating matrix of W for calculating according to frequency domain correlation coefficient

304, above-mentioned filtering interpolation result is carried out the phase place derotation, obtain final LMMSE channel estimating, that is:

But there are the following problems at least for channel estimation methods of the prior art:

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

2, in ofdm system, in order to prevent definite time delay (definite time delay can cause the ofdm system performance sharply to descend, and timing advance is little to the ofdm system performance impact), often can receive in advance.Reception meeting is in advance carried out a continuous phase rotating to channel estimating, thereby frequency domain correlation is impacted, and prior art is not considered this point when calculating phase rotating and derotation, can cause the hydraulic performance decline of channel estimating yet.

Summary of the invention

In prior art, channel tap not necessarily at the integral multiple sampled point, can cause the channel tap energy leakage, thereby cause the inaccurate problem of channel estimating in order to solve, and the embodiment of the present invention provides a kind of method and apparatus of channel estimating.

A kind of method of channel estimating comprises:

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

Calculate described Need to carry out the amount θ of phase rotating, and with described

Carry out the 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, obtain the channel estimation value of described reference signal.

A kind of channel estimating apparatus comprises:

The initial channel estimation unit is used for reference signal is carried out initial channel estimation, estimates the frequency domain response of described reference signal place channel

The phase rotating unit is used for calculating described

Need to carry out the amount θ of phase rotating, and with described

Carry out the θ phase rotating;

The filtering interpolation unit is used for according to the correlation between each subcarrier, to after described θ phase rotating

Carry out interpolation and filtering;

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

The apparatus and method that adopt the embodiment of the present invention to provide, considered the impact on frequency domain filtering of the energy leakage of the channel tap that causes due to non-integral multiple sampling when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously at calculating filter coefficient the time, considered the impact that receives in advance, made filter factor more accurate; Make like this result that reference signal is estimated more accurate.

Description of drawings

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

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

Fig. 3 estimates flow process for time-delay uniform power spectrum MMSE;

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,

$\mathrm{\&theta;}\left({\mathrm{\&tau;}}_m\right)=\left\{\begin{array}{cc}1/{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="HDA0000117798260000041.png"\; state="\{\{state\}\}">L</figure-callout>}}_0& {\mathrm{\&tau;}}_m\&Element;[-{\mathrm{\&tau;}}_{\mathrm{leak}},L_0-{\mathrm{\&tau;}}_{\mathrm{leak}}]\\ 0& \mathrm{otherwise}\end{array}\right.$

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

The embodiment of the present invention provides a kind of method of channel estimating, as shown in Figure 4, comprising:

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

S2, calculate described

Need to carry out the amount θ of phase rotating, and with described

Carry out the 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 has been considered the impact on frequency domain filtering of the energy leakage of the channel tap that causes due to non-integral multiple sampling when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously at calculating filter coefficient the time, considered the impact that receives in advance, made filter factor more accurate; Make like this result that reference signal is estimated more accurate.

Embodiment two:

The embodiment of the present invention provides 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 to carry out the amount θ of phase rotating, wherein, the account form of the amount θ of this phase rotating is:

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

In above-mentioned formula, τ _LeakBe the leakage value of the channel tap that causes of non-integral multiple sampling, relevant with the frequency of sampling, concrete value is obtained by emulation; τ _AIt is the sampled point that receives in 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 that last OFDM symbol disturbs the multipath of current OFDM symbol, when shifting to an earlier date quantities received τ _ADuring less than CP length, compare with not receiving in advance, can think receiving sequence through ring shift right, this will cause subcarrier in frequency domain after FFT have one with quantities received τ in advance _ARelevant phase rotating.Therefore, be real number in order to satisfy filter factor, in the process of carrying out phase rotating and derotation, need to take into account the impact that receives in advance.

S3, the value after the reference signal channel estimating is carried out phase rotating, the phase rotating module is output as

Its element value is:

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

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

S4, according to the correlation between each subcarrier, postrotational LS channel estimating is carried out LMMSE interpolation and filtering, this module is output as

Its element value is:

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

Wherein W is Rf.

S5, the LMMSE channel estimating is carried out the phase place derotation, this module is output as

Its element value is:

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

In above-mentioned formula,

The number of sub carrier wave of a RB of expression.

The method that the embodiment of the present invention provides (new model) compare with original method (original) have advantages of outstanding, 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, in the situation that the 16QAM performance has the lifting of very about 0.5dB, in the situation that the 64QAM performance has the lifting of very about 1dB.

Embodiment three:

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

Initial channel estimation unit 801 is used for reference signal is carried out initial channel estimation, estimates the frequency domain response of described reference signal place channel

Phase rotating unit 803 is used for calculating described

Need to carry out the amount θ of phase rotating, and with described

Carry out the θ phase rotating;

Filtering interpolation unit 805 is used for according to the correlation between each subcarrier, to after described θ phase rotating

Carry out interpolation and filtering;

Phase place derotation unit 807 is used 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, considered the impact on frequency domain filtering of the energy leakage of the channel tap that causes due to non-integral multiple sampling when carrying out channel estimating, make frequency domain filtering more accurate, simultaneously at calculating filter coefficient the time, considered the impact that receives in advance, made filter factor more accurate; Make like this result that reference signal is estimated more accurate.

More than some better 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 exceeding under the prerequisite of the technical scope that the present invention relates to, can do various replenishing and modification to the details that the present invention describes.Protection scope of the present invention is not limited to the cited scope of embodiment, and protection scope of the present invention is as the criterion with claim.

Claims (7)

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

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

Calculate described Need to carry out the amount θ of phase rotating, and with described

Carry out the 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, obtain the channel estimation value of described reference signal.

2. method according to claim 1, is characterized in that, calculates described The method that need to carry out the amount θ of phase rotating is:

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

τ wherein _LeakIt is the leakage value of the channel tap that causes of non-integral multiple sampling; τ _ABe the sampled point that receives in 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 be more than or equal to-τ _Leak, less than or equal to L ₀-τ _Leak

4. the method for claim 1, is characterized in that, with described

The computing formula of carrying out the θ phase rotating is:

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

Wherein, Represent described

Carry out the result of θ phase rotating, described

Refer to the number of downlink bandwidth RB in long evolving 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:

Wherein, described Represent described

Carry out the result of θ phase rotating, described

The result after filtering interpolation, the channel interpolating matrix of described W for calculating according to frequency domain correlation coefficient.

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

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

Wherein, described

Be the result after the phase place derotation, described Be the result after filtering interpolation, described

Refer to the number of downlink bandwidth RB in long evolving system, described

The number of sub carrier wave of a RB of expression.

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

The initial channel estimation unit is used for reference signal is carried out initial channel estimation, estimates the frequency domain response of described reference signal place channel

The phase rotating unit is used for calculating described

Need to carry out the amount θ of phase rotating, and with described Carry out the θ phase rotating;

The filtering interpolation unit is used for according to the correlation between each subcarrier, to after described θ phase rotating

Carry out interpolation and filtering;

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

Images