CN102904845A - Channel estimation method and device for orthogonal frequency division multiplexing (OFDM) system - Google Patents

Abstract

The invention relates to the field of wireless communication, and discloses a channel estimation method and a channel estimation device for an orthogonal frequency division multiplexing (OFDM) system. According to P subcarriers included in pilot signals, an OFDM signal matrix XP transmitted by a transmitting end and a P*L constant matrix WP are generated; and minimum mean-square error estimation of a channel is calculated in a time domain, and channel estimation of all the subcarriers is also calculated in a frequency domain. Therefore, the channel characteristics of all the subcarriers can be estimated without interpolation when the pilot signals only contain partial subcarriers in channel estimation, and thus the complexity of the system is simplified.

Description

Channel estimation methods in the orthogonal frequency division multiplex OFDM system and device

Technical field

The present invention relates to wireless communication field, particularly the channel estimation methods in the orthogonal frequency division multiplex OFDM system and device.

Background technology

The orthogonal frequency division multiplex OFDM technology has the advantages such as spectral efficient, anti-multipath effect, is therefore adopted by various wireless standard, such as IEEE 802.11a, 802.16, ETSI HIPERLAN/2 and digital video broadcasting (DVB).Adopt the ofdm system of qam mode to have higher data transfer rate and spectrum efficiency, but must adopt simultaneously coherent demodulation technology to realize the reception of ofdm signal, this just need to carry out parameter Estimation and tracking to wireless channel.The channel that channel estimating in ofdm system relates on each subcarrier in frequency domain and OFDM symbol in time changes.And pilot channel and reference symbol are sparsely launched on time and frequency.Must utilize the channel statistical on time and the frequency and estimate channel in every other position at the channel that pilot frequency locations obtains.

In frequency domain, can be with the ofdm signal Z=[Z that receives ₀, Z ₁..., Z _N-1] ^TBe expressed as:

$Z=X\tilde{H}+n=\mathrm{XW}\tilde{h}+n,---\left(1\right)$

Wherein, the ofdm signal X of transmission is a diagonal matrix, { X ₀, X ₁..., X _N-1It is the diagonal element of diagonal matrix.W is a constant matrices as shown in Equation (2):

$W=\left[\begin{array}{ccccc}1& 1& 1& \·\·\·& 1\\ 1& e^{\frac{-j2\mathrm{\π}}{N}}& e^{\frac{-j4\mathrm{\π}}{N}}& \·\·\·& e^{\frac{-j2\mathrm{\π}(N-1)}{N}}\\ 1& e^{\frac{-j4\mathrm{\π}}{N}}& e^{\frac{-j8\mathrm{\π}}{N}}& \·\·\·& e^{\frac{-j2\mathrm{\π}2(N-1)}{N}}\\ \·& \·& \·& \·& \·\\ \·& \·& \·& \·& \·\\ \·& \·& \·& \·& \·\\ 1& e^{\frac{-j2\mathrm{\π}(N-1)}{N}}& e^{\frac{-j2\mathrm{\π}2(N-1)}{N}}& \·\·\·& e^{\frac{-j2\mathrm{\π}{(N-1)}^2}{N}}\end{array}\right].---\left(2\right)$

A mistake! Do not find Reference source.The channel dispersion pulse excitation response that the sampling of channel continuous impulse exciter response is obtained:

A mistake! Do not find Reference source.(3)

A mistake! Do not find Reference source.In before ε zero represent OFDM frame synchronization error, N _cThe length of channel dispersion pulse excitation response, ε+N _c+ r=N.Each subcarrier amplitude that channel causes and the distortion of phase place are mistakes in frequency domain! Do not find Reference source.Fourier transform be:

A mistake! Do not find Reference source.(4)

To mistake! Do not find Reference source.Carrying out least square (Least Square is called for short " LS ") estimates:

${\tilde{H}}_{\mathrm{LS}}=[\frac{Z_0}{X_0},\frac{Z_1}{X_1},\·\·\·,\frac{Z_{N-1}}{X_{N-1}}].---\left(5\right)$

But there are two subject matters in least-squares estimation; At first, it is subject to noise jamming, and estimated accuracy is lower; Secondly, when pilot signal does not comprise some subcarrier, when namely some diagonal element of X is zero, can't obtain from following formula the mistake of corresponding subcarrier! Do not find Reference source.Value.In order to obtain the channel estimating of these subcarriers, need to carry out interpolation to the result that other sub-carrier channels is estimated.Interpolation calculation has not only increased the precision that system complexity has also reduced channel estimating.

Existing least mean-square error (MMSE) channel estimation technique is mainly based on following formula:

A mistake! Do not find Reference source. ${\tilde{H}}_{\mathrm{MMSE}}=\mathrm{WE}\left[\tilde{h}{Z}^H\right]{\left(E\right[{\mathrm{ZZ}}^H\left]\right)}^{-1}Z$

(6)

A mistake! Do not find Reference source. $E[\tilde{h}{Z}^H=E[\tilde{h}{\tilde{h}}^H]W^H{X}^H$

(7)

A mistake! Do not find Reference source. $E\left[{\mathrm{ZZ}}^H\right]=\mathrm{XWE}\left[\tilde{h}{\tilde{h}}^H\right]W^H{X}^H+{\mathrm{\σ}}^2{I}_N$

(8)

In following formula () ^-1Represent matrix inversion, () ^HRepresent conjugate transpose, σ ²It is noise power.Mainly there are three problems in this channel estimation technique: the first, do not consider the channel estimating when pilot signal does not comprise some subcarrier; The second, need to know in advance mistake! Do not find Reference source.Value, but in practice, mistake! Do not find Reference source.Value change with the variation of channel and OFDM frame synchronization error, make this algorithm be difficult to use in practice; The 3rd, do not take full advantage of N _cThis characteristic of＜N goes to improve the precision of least mean-square error channel estimating.

Summary of the invention

The object of the present invention is to provide channel estimation methods and device in a kind of orthogonal frequency division multiplex OFDM system, so that channel estimating also need not the channel characteristics that interpolation can be estimated all subcarriers when pilot signal only comprises the parton carrier wave, thereby simplified system complexity.

For solving the problems of the technologies described above, embodiments of the present invention provide the channel estimation methods in a kind of orthogonal frequency division multiplex OFDM system, comprise following steps:

Receive pilot signal, wherein, described pilot signal comprises P subcarrier, and P is less than or equal to N, and N is the total number of sub-carriers of pilot signal;

According to the pilot signal of described reception, produce the ofdm signal matrix X that transmitting terminal sends _PWherein, described X _PThe diagonal matrix of a P * P, { X ₀, X ₁..., X _P-1It is the diagonal element of described diagonal matrix;

According to P subcarrier of described pilot signal, the constant matrices W of structure P * L _PWherein, described L is maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum;

According to described X _PWith described W _P, in time-domain calculating the least mean-square error of channel is estimated

According to described

Calculate the channel estimating of all subcarriers in frequency domain

Embodiments of the present invention also provide the channel estimating apparatus in a kind of orthogonal frequency division multiplex OFDM system, comprise:

Receiver module is used for receiving pilot signal, and wherein, described pilot signal comprises P subcarrier, and P is less than or equal to N, and N is the total number of sub-carriers of pilot signal;

The transmitted signal generation module is used for the pilot signal according to described reception, produces the ofdm signal matrix X that transmitting terminal sends _PWherein, described X _PThe diagonal matrix of a P * P, { X ₀, X ₁..., X _P-1It is the diagonal element of described diagonal matrix;

The constant matrices constructing module is used for P subcarrier according to described pilot signal, the constant matrices W of structure P * L _PWherein, described L is maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum;

The time-domain computing module is used for according to described X _PWith described W _P, in time-domain calculating the least mean-square error of channel is estimated

The frequency domain computing module is used for according to described Calculate the channel estimating of all subcarriers in frequency domain

Embodiment of the present invention in terms of existing technologies, P the subcarrier that comprises according to pilot signal produces the ofdm signal matrix X that transmitting terminal sends _PAnd the constant matrices W of P * L _P, and the least mean-square error estimation of calculating channel in time-domain

And then calculate the channel estimating of all subcarriers in frequency domain So that channel estimating of the present invention also need not the channel characteristics that interpolation can be estimated all subcarriers when pilot signal only comprises the parton carrier wave, thereby simplified system complexity.

In addition, described in calculating

The time, first with described

Value be set to

Wherein, described I _LBe unit matrix; Again with described X _PW _PBy the following formula diagonalization:

X _PW _P=U _PS _PV _P

Wherein, U _PAnd V _PUnit matrix, S _PIt is diagonal matrix.

By inciting somebody to action

Be set to fixed value, can need not to know in advance

Changing value with channel and OFDM frame synchronization error change can carry out channel estimating; And with X _PW _PDiagonalization, can with Calculating formula in matrix inversion operation be reduced to the asking down of diagonal element of diagonal matrix, avoided matrix inversion operation, further simplified system complexity.

Description of drawings

Fig. 1 is the flow chart according to the channel estimation methods in the orthogonal frequency division multiplex OFDM system of first embodiment of the invention;

Fig. 2 is the flow chart according to the channel estimation methods in the orthogonal frequency division multiplex OFDM system of second embodiment of the invention;

Fig. 3 is the structural representation according to the channel estimating apparatus in the orthogonal frequency division multiplex OFDM system of third embodiment of the invention.

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing the embodiments of the present invention are explained in detail.Yet, persons of ordinary skill in the art may appreciate that in each execution mode of the present invention, in order to make the reader understand the application better many ins and outs have been proposed.But, even without these ins and outs with based on many variations and the modification of following each execution mode, also can realize each claim of the application technical scheme required for protection.

The first execution mode of the present invention relates to the channel estimation methods in a kind of orthogonal frequency division multiplex OFDM system, when the method does not comprise some subcarrier in pilot signal, need not the channel characteristics that interpolation can be estimated all subcarriers.Below include only P subcarrier with pilot signal, wherein, P is less than or equal to N, N is that the total number of sub-carriers of pilot signal is that example illustrates present embodiment, flow process as shown in Figure 1, concrete steps are as follows:

Step 101 receives pilot signal;

Step 102 according to the pilot signal that receives, produces the ofdm signal matrix X that transmitting terminal sends _PWherein, X _PThe diagonal matrix of a P * P, { X ₀, X ₁..., X _P-1It is the diagonal element of diagonal matrix;

Because pilot signal only comprises P subcarrier, and receiving terminal is known the pilot signal that transmitting terminal can send in advance, therefore only need to receive pilot signal, and definite subcarrier, can be easy to determine transmitted signal.

Step 103, according to P subcarrier of pilot signal, the constant matrices W of structure P * L _PWherein, L is maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum;

Specifically, be formula 2 from the constant matrices W(of N * N) to get P the corresponding P of subcarrier capable, get the matrix that the capable front L row of P form a P * L, obtain W _P

Step 104 is according to X _PAnd W _P, in time-domain calculating the least mean-square error of channel is estimated

According to step 102 and 103 X that produce _PAnd W _P, in frequency domain, can be with the ofdm signal Z that receives _PBe expressed as:

$Z_P=X_P{\tilde{H}}_P+n_P=X_P{W}_P{\tilde{h}}_L+n_P,---\left(9\right)$

Wherein, the ofdm signal Z of reception _PA column vector that has P element, the noise signal n of reception _PIt also is a column vector that has P element.Because maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum is L, therefore,

Rear N-L element be zero entirely, L element before only needing to estimate, namely

From formula 6,7 and 9, can obtain:

$E\left[{\tilde{h}}_L{Z}_P^H\right]=E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]W_P^H{X}_P^H---\left(10\right)$

$E\left[Z_P{Z}_P^H\right]=X_P{W}_{P}E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]W_P^H{X}_P^H+{\mathrm{\σ}}^2{I}_P---\left(11\right)$

Therefore, in time-domain the least mean-square error of channel is estimated and can be calculated by formula 12:

${\tilde{h}}_{\mathrm{MMSE}}=E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]W_P^H{X}_P^H\left\{X_P{W}_{P}E\right[{\tilde{h}}_L{\tilde{h}}_L^H]W_P^H{X}_P^H+{\mathrm{\σ}}^2{I}_P{\}}^{-1}{Z}_P$

Step 105, according to

Calculate the channel estimating of all subcarriers in frequency domain

Can calculate by following formula:

${\tilde{H}}_{\mathrm{MMSE}}=W_L{\tilde{h}}_{\mathrm{MMSE}}---\left(13\right)$

W in the following formula _LBy the front L row of the constant matrices W that gets formula 2 defined N * N the constant matrices of a N * L of formation.

Compared with prior art, P the subcarrier that present embodiment comprises according to pilot signal produces the ofdm signal matrix X that transmitting terminal sends _PAnd the constant matrices W of P * L _P, and the least mean-square error estimation of calculating channel in time-domain And then calculate the channel estimating of all subcarriers in frequency domain

So that channel estimating of the present invention also need not the channel characteristics that interpolation can be estimated all subcarriers when pilot signal only comprises the parton carrier wave, thereby simplified system complexity.

The second execution mode of the present invention relates to the channel estimation methods in a kind of orthogonal frequency division multiplex OFDM system.The second execution mode has been done further improvement on the first execution mode basis, and main improvements are: in second embodiment of the invention, in time-domain calculating the least mean-square error of channel is estimated The time, will

Value be set as fixed value, and with X _PW _PDiagonalization is so that calculating

In time, not only need not to know in advance

Changing value with channel and OFDM frame synchronization error change can carry out channel estimating, and has avoided matrix inversion operation, has simplified system complexity.

See also Fig. 2, calculating

Before, step 201 produces the ofdm signal matrix X that transmitting terminal sends in 203 _PWith the step 101 of the constant matrices WP of P * L and the first execution mode to 103 consistent, do not repeat them here.

Step 204 to 205 in, to calculating

Formula carry out some simplification:

Step 204 will Value be set to

Wherein, I _LBe unit matrix.Specifically, because Value change with the variation of channel and OFDM frame synchronization error, be difficult to know in advance.Without any about The situation of priori under, suppose that signal energy is evenly distributed in

L element on be common Robust estimation method, so the present invention used following Robust estimation, will

Value be fixed as:

$E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]=\frac{1}{L}{I}_L.---\left(13\right)$

Accordingly, in time-domain the least mean-square error of channel is estimated and can be reduced to:

${\tilde{h}}_{\mathrm{MMSE}}=W_P^H{X}_P^H\{X_P{W}_P{W}_P^H{X}_P^H+L{\mathrm{\σ}}^2{I}_P{\}}^{-1}{Z}_P---\left(14\right)$

In order to simplify system complexity, avoid matrix inversion operation, in step 205, with X _PW _PDiagonalization:

X _PW _P=U _PS _PV _P。(15)

U in the following formula _PAnd V _PUnit matrix, S _PIt is diagonal matrix.Therefore, in step 206, the least mean-square error of channel is estimated in time-domain calculating by following formula

${\tilde{h}}_{\mathrm{MMSE}}=V_P^H{S}_P^H\{S_P{S}_P^H+L{\mathrm{\σ}}^2{I}_P{\}}^{-1}{U}_P^H{Z}_P.---\left(16\right)$

Because

Be diagonal matrix, above-mentioned matrix inversion only needs its diagonal element is asked respectively reciprocal, thereby has avoided matrix inversion operation, has further simplified system complexity.

Next, basis in step 207

Calculate the channel estimating of all subcarriers in frequency domain

Similar with the step 105 of the first execution mode, do not repeat them here.

The step of top the whole bag of tricks is divided, and just in order to be described clearly, can to merge into a step during realization or some step is split, and is decomposed into a plurality of steps, as long as comprise identical logical relation, all in the protection range of this patent; To adding inessential modification in the algorithm or in the flow process or introduce inessential design, but the core design that does not change its algorithm and flow process is all in the protection range of this patent.

Third embodiment of the invention relates to the channel estimating apparatus in a kind of orthogonal frequency division multiplex OFDM system, as shown in Figure 3, comprises:

Receiver module is used for receiving pilot signal, and wherein, pilot signal comprises P subcarrier, and P is less than or equal to N, and N is the total number of sub-carriers of pilot signal.

The transmitted signal generation module is used for producing the ofdm signal matrix X that transmitting terminal sends according to the pilot signal that receives _PWherein, X _PThe diagonal matrix of a P * P, { X ₀, X ₁..., X _P-1It is the diagonal element of diagonal matrix.

The constant matrices constructing module is used for P subcarrier according to pilot signal, the constant matrices W of structure P * L _PWherein, L is maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum; Specifically, the constant matrices constructing module is got P the corresponding P of subcarrier from the constant matrices W of N * N capable, gets the matrix that the capable front L row of P form a P * L, obtains WP.

The time-domain computing module is used for according to X _PAnd W _P, in time-domain calculating the least mean-square error of channel is estimated

Specific formula for calculation is:

${\tilde{h}}_{\mathrm{MMSE}}=E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]W_P^H{X}_P^H\left\{X_P{W}_{P}E\right[{\tilde{h}}_L{\tilde{h}}_L^H]W_P^H{X}_P^H+{\mathrm{\σ}}^2{I}_P{\}}^{-1}{Z}_P$

Wherein,

Front L element of channel dispersion pulse excitation response that channel continuous impulse exciter response sampling is obtained,

Be Autocorrelation matrix; σ ²It is noise power; I _PBe unit matrix;

n _PBe noise; Z _PBe the ofdm signal that receives; () ^-1Represent matrix inversion, () ^HRepresent conjugate transpose.

The frequency domain computing module is used for basis

Calculate the channel estimating of all subcarriers in frequency domain

Specific formula for calculation is:

${\tilde{H}}_{\mathrm{MMSE}}=W_L{\tilde{h}}_{\mathrm{MMSE}}$

Wherein, W _LBe listed as the constant matrices of formed N * L for the front L of the constant matrices W that gets N * N.

Be not difficult to find, present embodiment is the system embodiment corresponding with the first execution mode, present embodiment can with the enforcement of working in coordination of the first execution mode.The correlation technique details of mentioning in the first execution mode is still effective in the present embodiment, in order to reduce repetition, repeats no more here.Correspondingly, the correlation technique details of mentioning in the present embodiment also can be applicable in the first execution mode.

It is worth mentioning that, each involved in present embodiment module is logic module, and in actual applications, a logical block can be a physical location, also can be the part of a physical location, can also realize with the combination of a plurality of physical locations.In addition, for outstanding innovation part of the present invention, will not introduce not too close unit with solving technical problem relation proposed by the invention in the present embodiment, but this does not show the unit that does not have other in the present embodiment.

Four embodiment of the invention relates to the channel estimating apparatus in a kind of orthogonal frequency division multiplex OFDM system.The 4th execution mode has been done further improvement on the 3rd execution mode basis, and main improvements are: in four embodiment of the invention, the time-domain computing module calculates in time-domain to be estimated the least mean-square error of channel

The time, will

Value be set as fixed value, and with X _PW _PDiagonalization is so that calculating

In time, not only need not to know in advance

Changing value with channel and OFDM frame synchronization error change can carry out channel estimating, and has avoided matrix inversion operation, has simplified system complexity.

Specifically, the time-domain computing module also comprises auto-correlation submodule and diagonalization submodule, wherein, the auto-correlation submodule, being used for will

Value be set to

Wherein, I _LBe unit matrix; The diagonalization submodule is used for X _PW _PBy the following formula diagonalization:

X _PW _P=U _PS _PV _P

Wherein, U _PAnd V _PUnit matrix, S _PIt is diagonal matrix.

Therefore,

Can be expressed as:

${\tilde{h}}_{\mathrm{MMSE}}=V_P^H{S}_P^H\{S_P{S}_P^H+L{\mathrm{\σ}}^2{I}_P{\}}^{-1}{U}_P^H{Z}_P.$

Because

Be diagonal matrix, above-mentioned matrix inversion only needs its diagonal element is asked respectively reciprocal, thereby has avoided matrix inversion operation, has further simplified system complexity.

Because the second execution mode is mutually corresponding with present embodiment, thus present embodiment can with the enforcement of working in coordination of the second execution mode.The correlation technique details of mentioning in the second execution mode is still effective in the present embodiment, and the technique effect that can reach in the second execution mode can be realized in the present embodiment too, in order to reduce repetition, repeats no more here.Correspondingly, the correlation technique details of mentioning in the present embodiment also can be applicable in the second execution mode.

Persons of ordinary skill in the art may appreciate that the respective embodiments described above are to realize specific embodiments of the invention, and in actual applications, can do various changes to it in the form and details, and without departing from the spirit and scope of the present invention.

Claims (10)

1. the channel estimation methods in the orthogonal frequency division multiplex OFDM system is characterized in that, comprises following steps:

Receive pilot signal, wherein, described pilot signal comprises P subcarrier, and P is less than or equal to N, and N is the total number of sub-carriers of pilot signal;

According to the pilot signal of described reception, produce the ofdm signal matrix X that transmitting terminal sends _PWherein, described X _PThe diagonal matrix of a P * P, { X ₀, X ₁..., X _P-1It is the diagonal element of described diagonal matrix;

According to P subcarrier of described pilot signal, the constant matrices W of structure P * L _PWherein, described L is maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum;

According to described X _PWith described W _P, calculate the least mean-square error of channel in time-domain and estimate

According to described

Calculate the channel estimating of all subcarriers in frequency domain

2. the channel estimation methods in the ofdm system according to claim 1 is characterized in that, at described P subcarrier according to described pilot signal, and the constant matrices W of structure P * L _PStep in, comprise following substep:

From the constant matrices W of N * N, get P the corresponding P of subcarrier capable, get the matrix that the capable front L row of described P form a P * L, obtain described W _P

3. the channel estimation methods in the ofdm system according to claim 1 is characterized in that, described according to described X _PWith described W _P, in time-domain calculating the least mean-square error of channel is estimated

Step in, comprise following substep:

Calculate described by following formula

${\tilde{h}}_{\mathrm{MMSE}}=E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]W_P^H{X}_P^H\left\{X_P{W}_{P}E\right[{\tilde{h}}_L{\tilde{h}}_L^H]W_P^H{X}_P^H+{\mathrm{\σ}}^2{I}_P{\}}^{-1}{Z}_P$

Wherein,

Front L element of channel dispersion pulse excitation response that channel continuous impulse exciter response sampling is obtained,

Described

Autocorrelation matrix; σ ²It is noise power; I _PBe unit matrix; n _PBe noise; Z _PBe the ofdm signal that receives; () ^-1Represent matrix inversion, () ^HRepresent conjugate transpose.

4. the channel estimation methods in the ofdm system according to claim 3 is characterized in that, and is described in calculating

Step in, also comprise following substep:

With described

Value be set to

Wherein, described I _LBe unit matrix;

With described X _PW _PBy the following formula diagonalization:

X _PW _P=U _PS _PV _P

Wherein, U _PAnd V _PUnit matrix, S _PIt is diagonal matrix.

5. the channel estimation methods in the ofdm system according to claim 1 is characterized in that, described according to described

Calculate the channel estimating of all subcarriers in frequency domain

Step in, comprise following substep:

Calculate described by following formula

${\tilde{H}}_{\mathrm{MMSE}}=W_L{\tilde{h}}_{\mathrm{MMSE}}$

Wherein, W _LBe listed as the constant matrices of formed N * L for the front L of the constant matrices W that gets N * N.

6. the channel estimating apparatus in the orthogonal frequency division multiplex OFDM system is characterized in that, comprises:

Receiver module is used for receiving pilot signal, and wherein, described pilot signal comprises P subcarrier, and P is less than or equal to N, and N is the total number of sub-carriers of pilot signal;

The transmitted signal generation module is used for the pilot signal according to described reception, produces the ofdm signal matrix X that transmitting terminal sends _PWherein, described X _PThe diagonal matrix of a P * P, { X ₀, X ₁..., X _P-1It is the diagonal element of described diagonal matrix;

The constant matrices constructing module is used for P subcarrier according to described pilot signal, the constant matrices W of structure P * L _PWherein, described L is maximum channel length N _CmaxWith maximum OFDM frame synchronization error ε _MaxSum;

The time-domain computing module is used for according to described X _PWith described W _P, in time-domain calculating the least mean-square error of channel is estimated

The frequency domain computing module is used for according to described

Calculate the channel estimating of all subcarriers in frequency domain

7. the channel estimating apparatus in the orthogonal frequency division multiplex OFDM system according to claim 6, it is characterized in that, described constant matrices constructing module is got P the corresponding P of subcarrier from the constant matrices W of N * N capable, gets the matrix that the capable front L row of described P form a P * L, obtains described W _P

8. the channel estimating apparatus in the orthogonal frequency division multiplex OFDM system according to claim 6 is characterized in that, described time-domain computing module is described in calculating The following formula of Shi Caiyong:

${\tilde{h}}_{\mathrm{MMSE}}=E\left[{\tilde{h}}_L{\tilde{h}}_L^H\right]W_P^H{X}_P^H\left\{X_P{W}_{P}E\right[{\tilde{h}}_L{\tilde{h}}_L^H]W_P^H{X}_P^H+{\mathrm{\σ}}^2{I}_P{\}}^{-1}{Z}_P$

Wherein,

Front L element of channel dispersion pulse excitation response that channel continuous impulse exciter response sampling is obtained,

Described

Autocorrelation matrix; σ ²It is noise power; I _PBe unit matrix;

n _PBe noise; Z _PBe the ofdm signal that receives; () ^-1Represent matrix inversion, () ^HRepresent conjugate transpose.

9. the channel estimating apparatus in the orthogonal frequency division multiplex OFDM system according to claim 8 is characterized in that, described time-domain computing module also comprises auto-correlation submodule and diagonalization submodule;

Described auto-correlation submodule is used for described Value be set to

Wherein, described I _LBe unit matrix;

Described diagonalization submodule is used for described X _PW _PBy the following formula diagonalization:

X _PW _P=U _PS _PV _P

Wherein, U _PAnd V _PUnit matrix, S _PIt is diagonal matrix.

10. the channel estimating apparatus in the orthogonal frequency division multiplex OFDM system according to claim 6 is characterized in that, described frequency domain computing module is described in calculating

The following formula of Shi Caiyong:

Wherein, W _LBe listed as the constant matrices of formed N * L for the front L of the constant matrices W that gets N * N.

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