CN1968030A - Channel estimation method of frequency-domain receiver - Google Patents

Abstract

The invention relates to a signal channel evaluating method of frequency-domain receiver, wherein it converts receiving signal to frequency domain to obtain frequency receiving signal; via iterate method, repeatedly processes spread-spectrum factor removing, signal channel removing, constant-gain combination, to obtain signal evaluation. The invention can improve the accuracy of signal channel evaluation.

Description

A kind of channel estimation methods of frequency-domain receiver

Technical field

The present invention relates to moving communicating field, relate in particular to the channel estimation methods of DS-CDMA (Direct Sequence CodeDivision Multiple Access direct sequence CDMA) signal frequency domain receiver.

Background technology

In second generation radio honeycomb communication system IS-95 and the present systems such as third generation radio honeycomb communication system CDMA2000, WCDMA that developing, all adopted the mode of direct sequence CDMA DS-CDMA.In the DS-CDMA system, each user's low speed signal and one are multiplied each other as this user's transmission signal with high speed signal user-dependent, that be referred to as spread-spectrum signal; And all users in the system use same bandwidth and frequency, and can launch simultaneously.Each user has the spread-spectrum signal of oneself, with other user's spread-spectrum signal maintenance quadrature.In receiver, transmitting of specific user carried out related operation, and estimate the current wireless channel, then the result after relevant is proofreaied and correct, recover this user's information.

Usually, in the DS-CDMA receiver, known pilot signal carries out by inserting in time in transmitting often in the estimation of channel, and correspondingly, channel estimating is carried out on time domain.If the time delay ratio of wireless channel is bigger, and spread-spectrum signal will be subjected to certain infringement through orthogonal property behind the wireless multipath transmisstion, and this will cause the appearance of extra interference, influence the accuracy of channel estimating.

Usually, in a symbol (Symbol), the time domain expression formula that transmits is:

$s=\left[\begin{array}{c}{s}_1\\ ...\\ s_N\end{array}\right]=\sqrt{E_s}\left[\begin{array}{c}{c}_1^d\\ ...\\ c_N^d\end{array}\right]b+\sqrt{E_p}\left[\begin{array}{c}{c}_1^p\\ ...\\ c_N^p\end{array}\right]---\left(1\right)$

Wherein, E _sBe user data energy, E _pBe pilot energy, Be user's spreading code of dedicated channel,

Be the pilot tone spreading code; B is for sending symbol, and N represents the spread spectrum code length, and P represents pilot tone, and d represents dedicated channel.

The FFT conversion that transmits and order through M, M＞=N wherein, frequency domain FFT is expressed as accordingly:

$S=\left[\begin{array}{c}{S}_1\\ ...\\ S_M\end{array}\right]=\sqrt{E_s}\left[\begin{array}{c}{C}_1^d\\ ...\\ C_M^d\end{array}\right]b+\sqrt{E_p}\left[\begin{array}{c}{C}_1^p\\ ...\\ C_M^P\end{array}\right]---\left(2\right)$

Wherein, Be the FFT conversion of user's spreading code,

FFT conversion for the pilot tone spreading code.

So, the FFT of received signal can be expressed as:

$R=\left[\begin{array}{c}{R}_1\\ ...\\ R_M\end{array}\right]=\left[\begin{array}{c}{H}_1(\sqrt{E_s}{C}_1^{d}b+\sqrt{E_p}{C}_1^p)\\ ...\\ H_M(\sqrt{E_s}{C}_M^{d}b+\sqrt{E_p}{C}_M^P)\end{array}\right]+\left[\begin{array}{c}{O}_1\\ ...\\ O_M\end{array}\right]---\left(3\right)$

Wherein, H ₁H _MThe expression channel impulse response is through the value behind the FFT, i.e. channel spectrum, O ₁O _MBe meant that noise is through the value behind the FFT, i.e. noise spectrum.If M＞N, can adopt methods such as over-sampling, common zero padding or interpolation this moment to input signal, makes that carrying out the required input signal of FFT conversion counts and increase to M from N.

Below be the demodulating process of R to received signal:

A. remove the spreading factor influence:

$R1=\left[\begin{array}{c}{R}_1{C}_1^{d^{*}}\\ ...\\ R_N{C}_N^{d^{*}}\end{array}\right]=\left[\begin{array}{c}(H_1(\sqrt{E_s}{C}_1^{d}b+\sqrt{E_p}{C}_1^p)+O_1)C_1^{d^{*}}\\ ...\\ (H_N(\sqrt{E_s}{C}_N^{d}b+\sqrt{E_p}{C}_N^p)+O_N)C_N^{d^{*}}\end{array}\right]---\left(4\right)$

B. remove channel effect:

$Y=\left[\begin{array}{c}{Y}_1\\ ...\\ Y_N\end{array}\right]=\left[\begin{array}{c}{R}_1{C}_1^{d^{*}}{H}_1^{*}\\ ...\\ R_N{C}_N^{d^{*}}{H}_N^{*}\end{array}\right]=\left[\begin{array}{c}(H_1(\sqrt{E_s}{C}_1^{d}b+\sqrt{E_p}{C}_1^p)+O_1)C_1^{d^{*}}{H}_1^{*}\\ ...\\ (H_N(\sqrt{E_S}{C}_N^{d}b+\sqrt{E_p}{C}_N^p)+O_N)H_N^{*}\end{array}\right]$

$=\left[\begin{array}{c}\sqrt{E_s}{\left|H_1\right|}^2{\left|C_1^d\right|}^{2}b+{\left|H_1\right|}^2\sqrt{E_p}{C}_1^p{C}_1^{d^{*}}+O_1{C}_1^{d^{*}}{H}_1^{*}\\ ...\\ \sqrt{E_s}{\left|H_N\right|}^2{\left|C_N^d\right|}^{2}b+{\left|H_N\right|}^2\sqrt{E_p}{C}_N^p{C}_N^{d^{*}}+O_N{C}_N^{d^{*}}{H}_N^{*}\end{array}\right]---\left(5\right)$

C. the row summation obtains judgment variables (equal gain combining):

$Z=\underset{i}{\mathrm{\Σ}}\sqrt{E_s}{\left|H_i\right|}^2{\left|C_i^d\right|}^{2}b+{\left|H_i\right|}^2\sqrt{E_p}{C}_i^p{C}_i^{d^{*}}+O_i{C}_i^{d^{*}}{H}_i^{*}$

$=\left(\sqrt{E_s}\mathrm{\Σ}{\left|H_i{C}_i^d\right|}^2\right)b+\left(\sqrt{E_p}\underset{i}{\mathrm{\Σ}}{\left|H_i\right|}^2{C}_i^p{C}_i^{d^{*}}\right)+\underset{i}{\mathrm{\Σ}}{O}_i{C}_i^{d^{*}}{H}_i^{*}---\left(6\right)$

First representation signal power in the above-mentioned formula (6), the 3rd relevant with noise, and second interference that causes for pilot tone, though pilot tone spreading code and user data spreading code quadrature in time domain, and through after the FFT conversion in frequency domain also quadrature, but owing to there is the weighting of channel, above-mentioned second is not 0, therefore, need carry out Interference Cancellation.Disclose the frequency-domain receiver of a kind of DS-CDMA in the prior art, wherein, under downlink scenario, carried out pilot cancellation before despreading, this method adopts simple average method to obtain the estimated value of channel.Yet, adopt this method to carry out channel estimating, owing to there be nonopiate, the accuracy of estimating is lower, make channel estimating become very difficult, adopt time averaging method just can carry out simple channel estimating can not resembling fully in time domain, therefore need seek a kind of more effective channel estimation methods.

Summary of the invention

The purpose of this invention is to provide a kind of channel estimation methods that can improve accuracy of channel estimation in the frequency-domain receiver.

For achieving the above object, the invention provides a kind of channel estimation methods of frequency-domain receiver, its received signal to frequency-domain receiver is carried out channel estimating, received signal is transformed into obtains the frequency domain received signal on the frequency domain; By alternative manner, repeat repeatedly channel frequency domain received signal to be removed spreading factor influence, removal channel effect, equal gain combining processing, obtain channel estimating.

In said method of the present invention, in t symbol, carry out following operation, wherein t 〉=1:

1) channel is carried out initial estimation, obtain initial channel estimating;

2) utilize current channel estimating, the frequency domain received signal in the step 1) is removed the spreading factor influence successively, removed channel effect, equal gain combining, obtain initially judgement;

3), upgrade channel estimating according to the judgement that obtains;

4) utilize the channel estimating of upgrading, the frequency domain received signal is removed the spreading factor influence, removes channel effect, carried out equal gain combining, adjudicate then, obtain the new judgement of this symbol;

5) repeat above-mentioned steps 3), 4), carry out repeatedly iteration, obtain final channel estimating.

In said method of the present invention, in t symbol, before carrying out step 1), also carry out following steps:

1A) carry out the FFT computing to received signal, obtain the frequency domain received signal on the frequency domain;

1B) to user data power in the frequency domain received signal and pilot power ratio $Q=\frac{\sqrt{E_s}}{\sqrt{E_p}}$ In time domain, estimate;

In described step 3),, upgrade channel estimating according to judgement that obtains and Q parameter.

In said method of the present invention, in described step 1), according to the frequency domain received signal, and the M of local user's spreading code point FFT transformed value, channel is made initial estimation, wherein M is the sub-hop count of entire spectrum; In described step 3), according to the M point FFT changing value of the M point FFT changing value of local user's spreading code, local pilot tone spreading code, at step 1B) in resulting Q parameter, the current judgement that obtains and step 1A) in the frequency domain received signal that obtains, upgrade channel estimating.

In said method of the present invention, at described step 1B) in, the estimation recently of the signal interference ratio SIR of dedicated channel and common signal channel of described Q parameter.

In said method of the present invention, also comprise step 6): the result of above-mentioned iteration is adopted the method for rolling average in time, carry out smoothing processing, obtain the current channel estimating that finally is used for the user data demodulation.

Utilize the present invention, smoothly can improve accuracy of channel estimation in the frequency-domain receiver greatly by iteration, the present invention can be used for DS-CDMA system or MC-CDMA (multicarrier code divisionmultiple access) system.

Description of drawings

Fig. 1 has provided the schematic flow sheet of the channel estimation methods of frequency-domain receiver of the present invention.

Embodiment

Describe the specific embodiment of the present invention in detail below in conjunction with accompanying drawing.But need to prove that given the drawings and the specific embodiments only are used to illustrate the present invention, the present invention is not limited to this.

The channel estimation methods of frequency-domain receiver of the present invention is used for the received signal of frequency-domain receiver is carried out channel estimating, received signal is transformed into obtains the frequency domain received signal on the frequency domain; By alternative manner, repeat repeatedly channel frequency domain received signal to be removed spreading factor influence, removal channel effect, equal gain combining processing, obtain channel estimating.

Particularly, in said method of the present invention, in t symbol, carry out following operation, wherein t 〉=1:

1) channel is carried out initial estimation, obtain initial channel estimating;

2) utilize current channel estimating, the frequency domain received signal in the step 1) is removed the spreading factor influence successively, removed channel effect, equal gain combining, obtain initially judgement;

3), upgrade channel estimating according to the judgement that obtains;

4) utilize the channel estimating of upgrading, the frequency domain received signal is removed the spreading factor influence, removes channel effect, carried out equal gain combining, adjudicate then, obtain the new judgement of this symbol;

5) repeat above-mentioned steps 3), 4), carry out repeatedly iteration, obtain final channel estimating.

Wherein, in t symbol, before carrying out step 1), can also carry out following steps:

1A) carry out the FFT computing to received signal, obtain the frequency domain received signal on the frequency domain;

1B) to user data power in the frequency domain received signal and pilot power ratio $Q=\frac{\sqrt{E_s}}{\sqrt{E_p}}$ Estimate that in time domain wherein the Q parameter here can be used the estimation recently of the signal interference ratio SIR of dedicated channel and common signal channel.

In described step 3),, upgrade channel estimating according to judgement that obtains and Q parameter.

In addition, in said method of the present invention, can also comprise step 6): the result of above-mentioned iteration is adopted the method for rolling average in time, carry out smoothing processing, obtain the current channel estimating that finally is used for the user data demodulation.

More specifically, in said method, in described step 1), according to the frequency domain received signal, and the M of local user's spreading code point FFT transformed value, channel is made initial estimation, wherein M is the sub-hop count of entire spectrum; In described step 3), according to the M point FFT changing value of the M point FFT changing value of local user's spreading code, local pilot tone spreading code, at step 1B) in resulting Q parameter, the current judgement that obtains and step 1A) in the frequency domain received signal that obtains, upgrade channel estimating.

Below, for the purpose of convenient the description, be without loss of generality, make the following assumptions:

● pilot tone is identical with user data spreading code length, is N, and following description and derivation are equally applicable to the unequal situation of spreading code length, only needs to revise corresponding mark;

● scrambled code not, can more perfect descrambling under the receiving and transmitting signal synchronous situation;

● frequency pilot sign is complete 1, because frequency pilot sign is known, is assumed to be entirely 1, is without loss of generality, simultaneously can be so that formula is succinct;

● other users disturb equivalence to be noise, perhaps single user situation.

Fig. 1 has provided under above-mentioned assumed condition, adopts the channel estimation methods of the communication system frequency-domain receiver of DS-CDMA spread spectrum.

According to formula (3), the FFT conversion that the received signal of k frequency sub-band is ordered through M (M＞=N), can be expressed as :-

$R_k=H_k(\sqrt{E_S}{C}_k^{d}b+\sqrt{E_p}{C}_k^p)+O_k$

$=\sqrt{E_p}{H}_k(\frac{\sqrt{E_s}}{\sqrt{E_p}}{C}_k^{d}b+C_k^p)+O_k---\left(7\right)$

Wherein, C _k ^dBe the M point FFT conversion of local user's spreading code, C _k ^pBe the M point FFT conversion of local pilot tone spreading code, H _MThe value of expression channel impulse response after through M point FFT, i.e. channel spectrum, O _MBe meant the value after noise is through M point FFT, i.e. noise spectrum, k=1 ..., M represents the sequence number of these frequency spectrums sections, and M is a FFT length, and the expression entire spectrum has been divided into M sub section.Because of pilot transmit power does not change in time, therefore, can

As by estimator Hk represents the frequency domain response of k frequency sub-band frequency spectrum, the spectral characteristic of expression channel.

The present invention is based on above-mentioned formula (7) and carry out channel estimating, the channel estimation method that is adopted is as follows:

1) according to formula (4), R to received signal _kThe influence of removal spreading factor promptly, makes R _kMultiply by the FFT conversion C of local user's spreading code _k ^dConjugation C _k ^D*, obtain R1.

2) in time domain, carry out user data power and pilot power ratio $Q=\frac{\sqrt{E_s}}{\sqrt{E_p}}$ Estimation.For example, can use the estimation recently of the SIR of dedicated channel and common signal channel.

3) in t symbol (Symbol), carry out following operation:

A. carry out the channel initial estimation according to following formula:

${\hat{H}}_k^{\left(0\right)}=\frac{1}{C_k^p}{R}_k$

This formula is to ignore b and O by formula (7) _kIn time, obtain, wherein The initial estimation of representing the frequency domain response of k frequency sub-band, k=1 ..., M.

B. according to formula (5) R to received signal _kRemove channel effect, that is, make above-mentioned steps 1) in the R1 that obtains multiply by

C. carry out the equal gain combining first time according to formula (6), obtain Z ⁽⁰⁾, channel H wherein _iWith the estimated value among the step a

Replace, adjudicate, adjudicate b the first time that obtains t symbol Symbol _t ⁽⁰⁾

D. carry out the channel estimating second time according to following formula:

${\hat{H}}_k^{\left(1\right)}=\frac{1}{\hat{Q}{C}_k^d{b}_t^{\left(0\right)}+C_k^p}{R}_k$

E. carry out removing the second time channel effect according to formula (5), wherein channel spectrum response H _iWith the estimated value H in the steps d _k ⁽¹⁾Replace;

F. carry out the equal gain combining second time according to formula (6), wherein channel spectrum response H _iWith the estimated value H in the steps d _k ⁽¹⁾Replace, adjudicate, adjudicate b the second time that obtains t symbol Symbol _t ⁽¹⁾:

$Z^{\left(1\right)}=\mathrm{\Σ}\sqrt{E_s}{\left|{\hat{H}}_k^{\left(1\right)}\right|}^2{\left|C_i^d\right|}^{2}b+{\left|{\hat{H}}_k^{\left(1\right)}\right|}^2\sqrt{E_p}{C}_i^p{C}_i^{d^{*}}+O_i{C}_i^{d^{*}}{\hat{H}}_k^{{\left(1\right)}^{*}}$

$=\left(\sqrt{E_s}\mathrm{\Σ}{\left|{\hat{H}}_k^{\left(1\right)}{C}_i^d\right|}^2\right)b+\left(\sqrt{E_p}\underset{i}{\mathrm{\Σ}}{{|\hat{H}}_k^{\left(1\right)}|}^2{C}_i^p{C}_i^{d^{*}}\right)+\underset{i}{\mathrm{\Σ}}{O}_i{C}_i^{d^{*}}{\hat{H}}_k^{{\left(1\right)}^{*}}$

G. repeating step b to f carries out iterating for W time, obtains the W time estimation of channel

${\hat{H}}_k^{\left(W\right)}=\frac{1}{\hat{Q}{C}_k^d{b}_t^{(W-1)}+C_k^p}{R}_k$

(3) result of above-mentioned iteration is adopted in time the method for rolling average, carry out smoothing processing, obtain the current channel estimation value that finally is used for the user data demodulation.

Said method is not only applicable to single carrier DS-CDMA signal frequency-domain and receives, and is applicable in the MC-CDMA receiver.

Above specific embodiment has illustrated the present invention, but these embodiment are exemplary, the invention is not restricted to specific embodiment.Those of ordinary skill in the art can make amendment, change the present invention or substitute under the situation that does not break away from the spirit and scope of the present invention.

Claims (7)

1. the channel estimation methods of a frequency-domain receiver, its received signal to frequency-domain receiver is carried out channel estimating, it is characterized in that,

Received signal is transformed into obtains the frequency domain received signal on the frequency domain; By alternative manner, repeat repeatedly channel frequency domain received signal to be removed spreading factor influence, removal channel effect, equal gain combining processing, obtain channel estimating.

2. method according to claim 1 is characterized in that,

In t symbol, carry out following operation, wherein t 〉=1:

1) channel is carried out initial estimation, obtain initial channel estimating;

2) utilize current channel estimating, the frequency domain received signal in the step 1) is removed the spreading factor influence successively, removed channel effect, equal gain combining, obtain initially judgement;

3), upgrade channel estimating according to the judgement that obtains;

4) utilize the channel estimating of upgrading, the frequency domain received signal is removed the spreading factor influence, removes channel effect, carried out equal gain combining, adjudicate then, obtain the new judgement of this symbol;

5) repeat above-mentioned steps 3), 4), carry out repeatedly iteration, obtain final channel estimating.

3. method according to claim 2 is characterized in that,

In t symbol, before carrying out step 1), also carry out following steps:

1A) carry out the FFT computing to received signal, obtain the frequency domain received signal on the frequency domain;

1B) to user data power in the frequency domain received signal and pilot power ratio $Q=\frac{\sqrt{E_s}}{\sqrt{E_p}}$ In time domain, estimate;

In described step 3),, upgrade channel estimating according to judgement that obtains and Q parameter.

4. method according to claim 3 is characterized in that,

In described step 1), according to the frequency domain received signal, and the M of local user's spreading code point FFT transformed value, channel is made initial estimation, wherein M is the sub-hop count of entire spectrum;

In described step 3), according to the M point FFT changing value of the M point FFT changing value of local user's spreading code, local pilot tone spreading code, at step 1B) in resulting Q parameter, the current judgement that obtains and step 1A) in the frequency domain received signal that obtains, upgrade channel estimating.

5. method according to claim 3 is characterized in that,

At described step 1B) in, the estimation recently of the signal interference ratio SIR of dedicated channel and common signal channel of described Q parameter.

6. according to described method one of among the claim 2-5, it is characterized in that,

Also comprise step 6): the result of above-mentioned iteration is adopted the method for rolling average in time, carry out smoothing processing, obtain the current channel estimation value that finally is used for the user data demodulation.

7. according to described method one of among the claim 2-5, it is characterized in that, be used for DS-CDMA system or MC-CDMA system.

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