WO2011130994A1

WO2011130994A1 - Multi-user channel estimation method and device

Info

Publication number: WO2011130994A1
Application number: PCT/CN2010/077714
Authority: WO
Inventors: 李萍
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-04-23
Filing date: 2010-10-13
Publication date: 2011-10-27
Also published as: CN102238110A; CN102238110B

Abstract

A multi-user channel estimation method and device are disclosed in the present invention. The method includes: by a receiver, obtaining M frequency domain channel estimation values of target users at pilot locations by using a received frequency domain pilot demodulation reference signal and a local frequency domain pilot demodulation reference signal; extracting R values from the M frequency domain channel estimation values, and spreading the M frequency domain channel estimation values by using the extracted R values to obtain M+R frequency domain channel estimation values; transforming the M+R frequency domain channel estimation values to the time domain to obtain M+R time domain channel estimation values; performing noise reduction processing on the M+R time domain channel estimation values by using a channel estimation window of the target users to obtain noise-reduced M+R time domain channel estimation values; and transforming the noise-reduced M+R time domain channel estimation values to the frequency domain, and extracting channel estimation values of effective sub-carriers from them. Use of the present invention can improve the demodulation performance of the receiver.

Description

TECHNICAL FIELD The present invention relates to the field of communications, and in particular to a multi-user channel estimation method and apparatus. BACKGROUND Long Term Evolution (LTE) improves and enhances the air access technology of the third generation mobile communication system (referred to as 3G). Compared with 3G, LTE has more technical advantages, mainly in higher user data rate, packet transmission, system delay, system capacity and coverage improvement, and lower operating costs. In the related art, the LTE uplink transmission scheme uses a single-carrier frequency division multiplexing multiple access system (referred to as SC-FDMA) with a cyclic prefix (CP), and the uplink users can mutually interact in the frequency domain. Orthogonal, and effective frequency domain equalization can be obtained on the receiver side, thereby reducing the peak-to-average power ratio of the transmitting terminal and reducing the size and cost of the terminal. In wireless communication systems, because the propagation path between the transmitter and the receiver is very complex and variable, the wireless channel can cause distortion of the received signal, including amplitude, phase, and frequency. In order to correctly resolve the start-end signal, the receiver must perform channel estimation. At present, in the uplink-using SC-FDMA transmission scheme with cyclic prefix, when performing channel estimation, DFT is used to obtain the frequency domain signal, and then the zero symbol is inserted for spectrum shifting, and the shifted signal is then passed through IFFT (hence, SC- The FDMA system is also called DFT-S-OFDM system, and a demodulation reference signal is designed for channel estimation in the transmitted signal. In the actual channel, the delay may not always be an integer multiple of the interval, which will result in leakage. Therefore, when the channel is post-processed to remove noise, excessive introduction of noise paths can degrade the receiver demodulation performance, and improper deletion of the useful signal path also degrades the demodulation performance of the receiver and loses system capacity. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a multi-user channel estimation method and apparatus to solve at least one of the above problems. According to an aspect of the present invention, a multi-user channel estimation method is provided, including: a receiver uses a received frequency domain pilot demodulation reference signal and a local frequency domain pilot demodulation reference signal to obtain Taking M frequency domain channel estimation values of the target user at the pilot position, M is the total number of pilot subcarriers; extracting R values from the M frequency domain channel estimation values, and using the extracted R values to M frequency The domain channel estimation value is extended to obtain a frequency domain channel estimation value, where W is an integer multiple of the number of users er carried on the same time-frequency resource block, W is less than or equal to M; when the frequency domain channel estimation value is converted to Domain, obtains a time domain channel estimation value; uses the channel estimation window of the target user to perform noise reduction processing on the time domain channel estimation values, and obtains the M+R time domain channel estimation values after noise reduction; The +R time domain channel estimates are transformed into the frequency domain from which channel estimates on the effective subcarriers are extracted. According to another aspect of the present invention, a multi-user channel estimation apparatus is provided, including: a receiving module, configured to receive a frequency domain pilot demodulation reference signal; and a frequency domain estimation module, configured to use a frequency domain received by the receiving module The pilot demodulation reference signal and the local frequency domain pilot demodulation reference signal obtain M frequency domain channel estimation values of the target user at the pilot position, where M is the total number of pilot subcarriers; and the spread spectrum module is used to R values are extracted from the M frequency-domain channel estimation values, and the M frequency-domain channel estimates are extended by using the extracted R values to obtain M+R frequency-domain channel estimates, where W is the same time-frequency resource block. The frequency-time transform module is configured to transform the M+R frequency-domain channel estimates obtained by the spread spectrum module into the time domain to obtain M+R time-domain channel estimates; the noise cancellation module, The method uses the channel estimation window of the target user to perform noise reduction processing on the M+R time domain channel estimation values, and obtains the noise-reduced time domain channel estimation values; the time-frequency transform module is configured to reduce the noise after the M+ R time domain channel estimates are transformed to In the frequency domain, the M+R frequency domain channel estimation values after noise reduction are obtained; the extraction module is configured to extract channel estimation values on the effective subcarriers from the frequency domain channel estimation values after the noise reduction, and obtain a time domain drop. Channel estimation of the frequency domain pilot position of the noise. According to the present invention, by estimating the frequency domain of the demodulation reference symbol, the pilot channel estimation in the frequency domain is spread in the frequency domain according to the user number, and then transformed into the time domain, and the time domain channel estimation is performed. Elimination, then transform back to the frequency domain, extract the channel estimation value on the effective subcarrier, thereby realizing the channel estimation of the target user, especially the channel estimation of multiple users, the scheme can improve the detection probability of the signal path, and effectively reduce the false deletion signal The performance loss caused by the path improves the receiver demodulation performance. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are set to illustrate,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, In the drawings: FIG. 1 is a schematic structural diagram of a multi-user channel estimating apparatus according to Embodiment 1 of the present invention; 2 is a flowchart of a multi-user channel estimation method according to Embodiment 1 of the present invention; FIG. 3 is a schematic structural diagram of a multi-user channel estimation apparatus according to Embodiment 2 of the present invention; FIG. 4 is a multi-user according to Embodiment 2 of the present invention; Flow chart of the channel estimation method. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. Embodiment 1 FIG. 1 is a schematic structural diagram of a multi-user channel estimation apparatus according to an embodiment of the present invention. The apparatus is located at a receiver side for performing channel estimation on a signal of a target user received by a receiver. The device mainly includes: a receiving module 10, a frequency domain estimating module 20, a spreading module 30, a time-frequency transform module 40, a noise canceling module 50, a time-frequency transform module 60, and an extracting module 70. The receiving module 10 is configured to receive a frequency domain pilot demodulation reference signal, and the frequency domain estimation module 20 is configured to use the frequency domain pilot demodulation reference signal received by the receiving module 10 and the local frequency domain pilot demodulation signal. The reference signal obtains M frequency domain channel estimation values H^^) of the target user at the pilot position, where k = 0, ..., M - 1 , M is the total number of pilot subcarriers; the spreading module 30 , for extracting R values from M H^ih), and using the extracted R values to extend the frequency domain channel estimation value H^ik) to obtain M+R frequency domain channel estimation values H^^ / ), where W is an integer multiple of the number of users ^er uploaded by the same time-frequency resource block, I = 0, ..., M + R - 7; the frequency-time transform module 40 is configured to obtain the spread spectrum module 30变换^Γ) transforms into the time domain, and obtains the time domain sequence h _RS (nn = Q, ''', M + R _ \ ; the noise cancellation module 50 is configured to utilize the channel estimation window of the target user to the time domain sequence /j ^sf^ performs noise reduction processing to obtain M+R time domain channel estimation values JiRsin) after noise reduction; time-frequency transform module 60 is configured to transform time domain channel estimation values ^ «0 into the frequency domain, and obtain a drop M+R after noise The frequency domain channel estimation value is used by the extraction module 70, for extracting the channel estimation value on the effective subcarrier from the M+R frequency domain channel estimation values obtained by the time-frequency transform module 60, and obtaining the frequency domain after time domain noise reduction. Channel estimation of the pilot position. Preferably, R is less than or equal to. With the above-described multi-user channel estimation apparatus of the present embodiment, the frequency-domain channel estimation value H^ik) of the pilot position is expanded by the spreading factor module 20 using the W values of the M H^ik), thereby realizing The user's channel estimation can effectively reduce the performance loss caused by the erroneous deletion of the signal path, thereby improving the demodulation performance of the receiver. 2 is a flowchart of a multi-user channel estimation method according to Embodiment 1 of the present invention. The method mainly includes the following steps: step 4: S4 - Step 4: S208: Step S200, the frequency domain estimation module 20 uses a receiving module. 10: receiving the frequency domain pilot demodulation reference signal and the local frequency domain pilot demodulation reference signal, and obtaining a frequency domain channel estimation value H^ of the target user at the pilot position, where k=0, ..., M - 1 , M is the total number of pilot subcarriers; in practical applications, when receiving the signal sent by the target user, the receiving module 10 can obtain the frequency domain pilot demodulation reference signal from the pilot position, and the receiver side The same local frequency domain pilot demodulation reference signal used for transmission by the target user will be generated, so that the frequency domain channel estimation value of the target user at the pilot position can be calculated. For example, the frequency domain estimation module 20 may generate the frequency domain pilot demodulation reference signal Y^ik and the receiving end to generate the same local frequency domain pilot demodulation reference signal X _RS (k) as the transmitting end, and calculate the frequency domain uplink. The channel estimation value H^CA:) of the frequency position is:

X _RS (k) ^ 0≤k≤M - \ where M represents the total number of subcarriers of the system; A represents the number in the frequency domain, taking an integer. Step 202: The spreading module 30 extracts R values from the M Hj k), and uses the extracted R values to extend the frequency domain channel estimation value H^i^) to obtain M+R frequency domain channel estimation values. ^ _χρ {1) , where W is an integer multiple of the number of users f-^er on the same time-frequency resource block, I = 0, ..., M +R - 7 ; for example, if the number of users is K user If it is 2, then W can be 48. Step S204, the frequency-time transform module 40 converts M+R frequency-domain channel estimation values Η^ _ρ (/) when i or, obtains M+R times i or channel estimation value w = 0, "., M + R For example, the time-frequency transform module 40 can transform the Η^ _χν (/) to the time using the inverse discrete Fourier transform.

Step S206, the noise cancellation module 50 performs noise reduction processing on the time domain channel estimation values/^f^ by using the channel estimation window of the target user, and obtains the M+R time domain channel estimation values h _RS (n) after noise reduction. The window length J _{w of the} channel estimation window of the target user may be:

L _w =(\ + Y)\ (M + R)x where γ≥ο

2048 Using the window length, the noise cancellation module 50 filters out the noise outside the window, that is:

Step S208, the time-frequency transform module 60 transforms the noise-reduced M+R time-domain channel estimation values ^{hRs n} into the frequency domain, and obtains the frequency- ^reduced frequency domain estimation values t = o, ---, + Rl Extracting module 70 extracts channel estimates on valid subcarriers therefrom

For example, a discrete Fourier transform can be used to transform ^ «) into the frequency domain. With the above-described multi-user channel estimation method of the present embodiment, the spreading module 30 uses the W values in the H^ik to spread the frequency domain channel estimation value H^C of the pilot position, and the frequency-time conversion module 40 then The extended sequence is transformed into the time domain by the noise cancellation module 50 for noise reduction processing, and the time-frequency transform module 60 converts the channel estimation after the noise reduction into the frequency domain to obtain a noise reduction signal in the frequency domain. In the channel estimation, the extraction module 70 selects the channel estimation value on the effective subcarrier, thereby realizing multi-user channel estimation, which can effectively reduce the performance loss caused by the erroneous deletion signal path, thereby improving the demodulation performance of the receiver. Embodiment 2 FIG. 3 is a schematic structural diagram of a multi-user channel estimation apparatus according to the embodiment. As shown in FIG. 3, the multi-user channel estimation apparatus of this embodiment is different from the first embodiment in that, in this embodiment, The spread spectrum module 30 is composed of a grouping module 300, an extracting module 302, a flipping module 304, and a spread spectrum computing module 306. The grouping module 300 is configured to divide the M H^^) into M/K-user groups; the extracting module 302 extracts W ^/ ^{-M r} groups from the dry ^M/K user groups to obtain a total of R values H _RS ) , where t =0, ..., R -1 flip module 304, and the extracted H _RSCTi (t) is flipped according to the following formula to obtain H^ _CTi2 W:

H _RS ^(txK _user: txK _user + K _user -V)

= H _{RS ext} ((R/K_ user -t -Y)xK _user + l:(R/ K _user -t)xK _ user) where t =0, ..., RIK user -7; spread spectrum calculation The module 306 is configured to perform frequency domain expansion on H^CA:) according to the following formula to obtain H'

-\. With the above-described multi-user channel estimation apparatus of the present embodiment, the spread spectrum module 30 groups the M H^ks according to the number of users when spreading the frequency domain pilot estimation values, and then from the M/K_er The RIK user group is extracted from the group, so that the Hj k) for the spread spectrum can be guaranteed to be more in line with the actual situation, thereby improving the accuracy of the channel estimation. It should be noted that, in the above embodiment, although the spread spectrum calculation module 306 expands the M frequency domain channel estimation values into M+R frequency domain channel estimation values in a backward spread manner, it is not limited to Therefore, in practical applications, the M carrier channel estimates may be forward-expanded to obtain M+R frequency i or channel estimation values by using the extracted R values, or may be extended forward and backward to obtain M+R frequency. i or channel estimate. 4 is a flowchart of a multi-user channel estimation method according to Embodiment 2 of the present invention. As shown in FIG. 4, in the embodiment, channel estimation is performed mainly by the following steps: Step S401, the frequency domain estimation module 20 is configured according to the receiving module 10 The received frequency domain pilot demodulation reference signal _s and the receiver generate the same local frequency domain pilot demodulation reference signal as the transmitting end

X _RS (k) , calculated the frequency domain channel estimate of the pilot position in the frequency domain H^ A:):

H _RS (k)=^^-, ≤k≤Ml

X _RS (k) where M represents the total number of subcarriers, in this embodiment, M = 192;

A represents the number in the frequency domain, taking an integer. In step S402, R is determined according to the number of users. In this embodiment, if the number of users K user is 2, the extension sub-length R=48 may be taken. In practical applications, the specific value of R may be obtained through simulation; step S403; The grouping module 300 groups the 192 pilot subcarriers according to the length 2 and divides them into 96 groups. In step S404, the extraction module 302 extracts the groups of the 96 groups of H^k) into the smallest unit, and extracts 24 The extraction module 302 can be extracted in any manner, for example, can be extracted in equal intervals, a total of 48 values, U, t = 0, ---, 47,

K2t') = ^(^ (96/24)")

^J , t =0,···,23 , k =0,···,95

H^ _ext (2t +1) = Η^ ([2k' /(96 / 24)" + 1) Step S405, the flipping module 304 flips the extracted _ext (t) to obtain _∞n (t)

Η^ _α2 (2t : 2t + \) = H^ _ext (48 - 2t - 1 : 48 - 2t) , t =0, ..., 23; Step S406, the spread spectrum calculation module 306 _obtains according to _∞ί2 (0 Spreading sequence

Step S407, the frequency-time transform module 40 converts ^(/) into a time domain h^n), «= 0,····, 192 + 47, using a discrete Fourier transform to perform noise cancellation; step S408 , calculating the effective channel impulse response window length of the target user (ie, the window length of the channel estimation window) J _W , the number of ring shifts

The sample estimation window of the target user is obtained, wherein the different values of the "high-level configuration parameters, through" can identify the starting point of the channel estimation window of different target users, and the _CP is the length of the cyclic prefix (CP). For a regular CP, /^ takes 144, and for an extended CP, /^ takes 512. In practical applications, the parameters related to the effective channel impulse response window length can be obtained through simulation or field actual environmental testing. Step S409, the noise cancellation module 50 filters out the window interference and noise h _RS (ri) n<t,

0 n ≥ L. Step S410, the time-frequency transform module 60 transforms the channel estimation value after noise reduction into a frequency domain _RS by using a discrete Fourier transform (kt = 0, ---, + R1; step S411, the extraction module 70 extracts Channel estimation value on valid subcarriers Channel estimation of frequency domain pilot locations for domain noise reduction:

% _RS {k) =

k = 0, ' -, M _ \. In this embodiment, the length of the spread spectrum is determined by the number of users, and M ^H ^ ( ^k ) is grouped and extracted by the number of users, thereby further ensuring the accuracy of channel estimation. Embodiment 3 In this embodiment, M + R is a power of 2, which is different from Embodiment 1 or Embodiment 2 in that, in this embodiment, the frequency-time transform module 40 uses an inverse fast Fourier. The transformation will ^ (/) ,

1 = 0 , ..., - is transformed into ( '":^,..., + ^^ - and the time-frequency transform module 60 transforms ^^ ") into the frequency domain by fast Fourier transform to obtain ^(^>' = 0,"', + R - 1. With the present embodiment, the fast Fourier transform can be used for channel estimation, which greatly reduces the computational complexity of the implementation, and therefore reduces the hardware cost. The communication system to which the foregoing technical solutions provided by the embodiments of the present invention are applicable includes, but is not limited to, an SC-FDMA system and an OFDM system. From the above description, it can be seen that, in the embodiment of the present invention, the frequency of the reference symbol is demodulated. Domain channel estimation, the pilot channel estimation in the frequency domain is spread in the frequency domain, and then transformed into the time domain, and the interference and noise are eliminated in the time domain channel estimation, and then converted back to the frequency domain to extract the effective subcarriers. The channel estimation value is used to realize multi-user channel estimation, which reduces the interference and noise impact on the target user. Moreover, since the channel estimation is performed by the signal-based extension method, the performance of the erroneous deletion signal path is effectively reduced. loss Therefore, the demodulation performance of the receiver is improved. In addition, the technical solution provided by the embodiment of the invention increases the system capacity and provides a reliable guarantee for the communication service quality. The method can implement channel estimation simply and efficiently, and expands the manner. Simple, operability, no increase in performance due to performance improvement, and the computational complexity of the implementation is increased. Since the fast Fourier transform can also be used for calculation in channel estimation, the computational complexity of the implementation is greatly reduced. Reducing hardware costs. Obviously, those skilled in the art will appreciate that the various modules or steps of the present invention described above can be implemented with a general purpose computing device, which can be centralized on a single computing device or distributed across multiple computing devices. On the network formed, optionally, they can be executed by a computing device The program code is implemented so that they can be stored in the storage device by the computing device, and in some cases, the steps shown or described can be performed in a different order than here, or they can be separately produced. The individual integrated circuit modules are implemented, or a plurality of modules or steps thereof are fabricated into a single integrated circuit module. Thus, the invention is not limited to any specific combination of hardware and software. The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the scope of the present invention are intended to be included within the scope of the present invention.

Claims

A multi-user channel estimation method, characterized in that it comprises:

The receiver uses the received frequency domain pilot demodulation reference signal and the local frequency domain pilot demodulation reference signal to obtain M frequency domain channel estimation values of the target user at the pilot position, where M is the total number of pilot subcarriers. ;

Extracting R values from the M frequency domain channel estimation values, and expanding the M frequency domain channel estimation values by using the extracted R values to obtain M+R frequency domain channel estimation values, where R The integer number of users f_^er uploaded for the same time-frequency resource block, R is less than or equal to M;

Transforming the frequency domain channel estimation values into a time domain to obtain M+R time domain channel estimation values;

And using the channel estimation window of the target user to perform noise reduction processing on the M+R time domain channel estimation values, to obtain the M+R time domain channel estimation values after noise reduction;

The M+R time domain channel estimation values after noise reduction are transformed into a frequency domain, and channel estimation values on the effective subcarriers are extracted therefrom. The method according to claim 1, wherein extracting W values from the M frequency domain channel estimation values comprises: dividing the M frequency domain channel estimation values H^ik) into M/K— User group, where k = 0, ..., M - 1;

Extracting R/K user groups from the M/K-user group, obtaining a total of R values U, where t = 0, ..., R - 1. The method according to claim 2, The method further comprises: expanding the M frequency domain channel estimation values by using the extracted R values, and obtaining the M+R frequency domain channel estimation values, comprising: performing the extracted H _{RS CTi} (t) according to the following Flip to get u : e _xt2 (^K _ user: txK _ user + K _ user - 1)

=

_ user + 1 : (Rl K _ user - t)xK _ user) ', medium, t = 0, ..., R / K user - 7 ; The frequency domain extension of ^^(^) is performed according to the following formula to obtain the frequency domain channel estimation value ^( ):

4. The method according to claim 2, wherein extracting the RIK user groups from the M/K user groups comprises: extracting the i groups from the M groups in an equally spaced manner. ^R / K user groups.

5. The method of claim 1 wherein

Transforming the frequency domain channel estimation values into the time domain comprises: transforming the M+R frequency domain channel estimation values into a time domain by using an inverse discrete Fourier transform to obtain the M+R time domain channels estimated value;

Transforming the noise-reduced time domain channel estimate to the frequency domain comprises: transforming the noise-reduced M+R time-domain channel estimates into the frequency domain using an discrete Fourier transform.

6. The method of claim 1 wherein

The sum of M and R is a power of 2;

Transforming the frequency domain channel estimation values into the time domain comprises: transforming the M+R frequency domain channel estimation values into a time domain by using an inverse fast Fourier transform to obtain the M+R time domain channels estimated value;

Transforming the noise-reduced said time domain channel estimate to the frequency domain comprises: transforming the noise-reduced M+R time-domain channel estimates into the frequency domain using a fast Fourier transform.

7. The method according to claim 1, wherein the channel estimation window of the target user is obtained by:

Calculate the window length J _{w of the} channel estimation window according to the following formula:

L _W = (\ + Y)\\ (M + R)x

2048

Where r ≥ o is the length of the cyclic prefix; forwards the number of cyclic shifts of the target user relative to the mother code as a reference point

2π

/Cj (M + R) x and the backward (M + R) x ¹ ' point, get the package of the target user

2048 2048 The channel estimation window containing _w samples, where "is a pre-configured parameter, taking different values for different target users. A multi-user channel estimation apparatus, comprising:

a receiving module, configured to receive a frequency domain pilot demodulation reference signal;

a frequency domain estimation module, configured to use the frequency domain pilot demodulation reference signal received by the receiving module and a local frequency domain pilot demodulation reference signal to obtain a target user at a pilot position

M frequency domain channel estimation values, M is the total number of pilot subcarriers;

a spreading module, configured to extract R values from the M frequency domain channel estimation values, and expand the M frequency domain channel estimates by using the extracted R values to obtain M+R frequency domain channel estimations. Where R is an integer multiple of the number of users uploaded by the same time-frequency resource block, R is less than or equal to M;

a time-frequency transform module, configured to transform the frequency domain channel estimates obtained by the spreading module into a time domain, to obtain M+R time domain channel estimates;

a noise cancellation module, configured to perform noise reduction processing on the M+R time domain channel estimation values by using a channel estimation window of the target user, to obtain a M+R time domain channel estimation value after noise reduction;

a time-frequency transform module, configured to transform the M+R time-domain channel estimation values after noise reduction into a frequency domain, to obtain M+R frequency-domain channel estimation values after noise reduction;

And an extracting module, configured to extract a channel estimation value on the effective subcarrier from the frequency domain channel estimation values after the noise reduction, to obtain a channel estimation of the frequency domain pilot position after the time domain noise reduction. The apparatus according to claim 8, wherein the spread spectrum module comprises:

a grouping module, configured to divide the M frequency domain channel estimation values H^i^) into M/K_user groups;

An extracting module, configured to extract RIK user groups from the M/K-user group, and obtain a total of W values H _{RS CTi} (t), where t = 0, ..., R - l ; And extracting the extracted H _{RS CTi} (t) according to the following formula to obtain

H RS exti x K—user: txK _ user + K _ user - 1)

=

_ user -t-\)xK _ user + 1 : (Rl K _ user -t)xK _ user) ', medium, t =0, ..., R/K user -7; spread spectrum calculation module, The frequency domain extension is performed on the ^^) according to the following formula to obtain the frequency domain channel estimation value H^^o:

The apparatus according to claim 8 or 9, wherein the sum of M and R is a number of screens of 2; and the frequency-time transform module uses the inverse fast Fourier transform to set the frequency domains The channel estimate is transformed into a time domain; the time-frequency transform module uses a fast Fourier transform to transform the noise-reduced time domain channel estimates into a frequency domain.