CN101945060A - Channel estimation method based on pilot frequency signal in 3GPP LTE downlink system - Google Patents

Abstract

The invention provides a channel estimation method based on the pilot frequency signal in a 3GPP LTE downlink system aiming at the 3GPP LTE downlink system, which is the channel estimation method using the frequency two dimension combining Weiner iterative filtering and based on the Linear Minimum Mean-square Error (LMMSE) algorithm. In the invention, the Weiner iterative filtering is performed in the frequency domain based on the LMMSE algorithm firstly, then the value estimated by the frequency domain is used to perform the first Weiner iterative filtering in the frequency domain. The experimental test indicates that the channel estimation method can effectively enhance the property of Bit Error Rate (BER), and is closer to the ideal channel estimation compared with the traditional methods. In addition, the method of the invention reduces the operation complexity of the algorithm through the Singular Value Decomposition (SVD) of the LMMSE algorithm, therefore the channel estimation method provided by the invention can not increase too much operation complexity.

Description

In a kind of 3GPP LTE downlink system based on the channel estimation methods of pilot signal

Technical field

The invention belongs to the channel estimation technique field in the communication system, more specifically say, relate in a kind of 3GPP LTE downlink system channel estimation methods based on pilot signal.

Background technology

LTE (Long Term Evolution) is third generation partner program (3rd GenerationPartnership Project, 3GPP) under " mobile communication broad bandization " trend, in order to resist global inserting of microwave interoperability (World interoperability for Microwave Access, the market challenges of mobile broadband access technology such as WiMAX), in super 3G of more than ten years (Beyond 3rd Generation, " accurate 4G " technology of B3G) developing on Yan Jiu the technological reserve basis.LTE is interface aspect frequency division multiple access (Frequency Division Multiple Access aloft, FDMA) substituted long-term code division multiple access (the Code Division Multiple Access that uses of 3GPP, CDMA) as multiple access technology, and adopted multiple-input and multiple-output (multiple-input multiple-output in a large number, MIMO) technology and adaptive technique improve data rate and systematic function, and the air interface transmittability is reached more than the 100Mbit/s.3GPP LTE has been subjected to the favor of most operators in the world, has been acknowledged as the mobile communication system that can support WorldCom's industry at 2010～the year two thousand twenty.

Because OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology has very high data transmission rate and spectrum efficiency, it can resist advantages such as multidiameter delay expansion effectively simultaneously, and the physical layer of 3GPP LTE downlink system has adopted the OFDM technology.Because the wireless channel in the wide-band mobile communication system has frequency domain selectivity and time variation, so receiver is before carrying out coherent demodulation to ofdm signal at a high speed, and multidiameter fading channel is carried out dynamic estimation and tracking is very important.In the OFDM technology, channel estimating is the most frequently used is based on the auxiliary channel estimation methods of pilot tone.

In the channel estimation method auxiliary based on pilot tone, transmitting terminal inserts transmitting terminal and all known pilot signal of receiving terminal in fixing position, and receiving terminal estimates the channel response of each OFDM symbol by the received signal of handling these positions then.In the 3GPP LTE downlink system based on the channel estimation methods of pilot signal roughly can be divided into least square (Least-Squares, LS) and least mean-square error (Minimum Mean-Square Error, MMSE) two class methods.These two class methods all are on frequency domain each subcarrier to be carried out channel estimating, and wherein, the LS channel estimation methods does not need channel information, realize the simplest; The MMSE channel estimation methods has utilized channel statistical informations such as correlation between subcarrier and signal to noise ratio, and estimated performance is better, is widely used in the channel estimating of OFDM.

Summary of the invention

The object of the invention is to overcome the deficiency of existing channel method of estimation, and the channel estimation methods based on pilot signal is provided in the 3GPP LTE downlink system that a kind of error rate is low, computational complexity is not high.

For achieving the above object, based on the channel estimation methods of pilot signal, it is characterized in that in the 3GPP LTE downlink system of the present invention, may further comprise the steps:

(1), the dimension of frequency domain is received iteration filtering

At first obtain the channel frequency domain response estimation value of reference signal position on the same OFDM symbol:

${\hat{H}}_{P,\mathrm{LMMSE}}^{\left(1\right)}=R_{H_P{H}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LS}}---\left(1\right)$

In the formula (1),

The autocorrelation matrix of representing same OFDM symbol internal reference signals virgin carrier wave, β are that SNR is an average signal-to-noise ratio, I by the constant of signal constellation which decision _PBe unit matrix;

Channel frequency domain response H for the reference signal position _PThe LS estimated value, subscript () _PThe position of expression transmission of reference signals.

Right then Carry out receiving iteration filtering based on the dimension of LMMSE algorithm and reduce noise and disturb influence to the locational channel frequency response estimated value of reference signal, improve bit error rate performance, dimension is received the locational channel frequency response estimated value of the filtered reference signal of iteration

${\hat{H}}_{P,\mathrm{LMMSE}}^{\left(2\right)}=R_{H_P{H}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LMMSE}}^{\left(1\right)}---\left(2\right)$

Utilize at last through dimension and receive the channel frequency domain response estimation value of the filtered reference signal of iteration position

Estimate the channel frequency domain response value at all subcarrier places on the same OFDM symbol

${\hat{H}}_{F,\mathrm{LMMSE}}=R_{{\mathrm{HH}}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LMMSE}}^{\left(2\right)}---\left(3\right)$

In the formula (3),

The cross-correlation matrix of representing the subcarrier at subcarriers all in the same OFDM symbol and reference signal place;

(2), the dimension of time domain is received iteration filtering

To the channel frequency domain response estimation value on n the subcarrier

Carry out receiving iteration filtering based on the dimension of LMMSE algorithm, to reduce relevant residual noise and to improve bit error rate performance:

${\tilde{H}}_{F,\mathrm{LMMSE}}^{\left(n\right)}=R_{H_P{H}_P}^{\left(n\right)}{(R_{H_P{H}_P}^{\left(n\right)}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_L)}^{-1}{\hat{H}}_{F,\mathrm{LMMSE}}^{\left(n\right)}---\left(4\right)$

In the formula (4),

Be that all comprise the autocorrelation matrix between the OFDM symbol of reference signal, I on n subcarrier in the subframe _LBe unit matrix, L represents to comprise in each subframe the OFDM number of symbols of reference signal;

Utilize dimension to receive channel frequency response estimated value after the iteration filtering

Estimate the channel frequency response value at all n subcarrier places of OFDM symbol in each subframe

${\hat{H}}_{T,\mathrm{LMMSE}}^{\left(n\right)}=R_{{\mathrm{HH}}_P}^{\left(n\right)}{(R_{H_P{H}_P}^{\left(n\right)}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_L)}^{-1}{\tilde{H}}_{F,\mathrm{LMMSE}}^{\left(n\right)}---\left(5\right)$

Wherein,

Be all OFDM symbols and comprise cross-correlation matrix between the OFDM symbol of reference signal on n the subcarrier;

To the channel frequency domain response estimation value on all subcarriers

Carry out aforementioned calculation, finally receive iteration filtering and obtained the channel transfer function value at all resource particle places through the dimension of frequency domain and time domain.

In the present invention, in the superincumbent arthmetic statement, no matter be that there all have to be right at frequency domain or in the dimension of time domain is received iteration filtering:

$(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}I)$

Inversion operation, if the number of reference signal is many, this inversion operation will become very complicated so.

In order to lower the computational complexity of the channel estimation methods that the present invention proposes, to autocorrelation matrix

Carry out singular value decomposition, and then calculate inverse matrix

${(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}I)}^{-1};$

Inverse matrix is decomposed into:

${(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}I)}^{-1}=\frac{\mathrm{SNR}}{\mathrm{\β}}(I-\frac{\mathrm{SNR}}{\mathrm{\β}}\×U{({\mathrm{\Λ}}^{-1}+\frac{\mathrm{SNR}}{\mathrm{\β}}I)}^{-1}{U}^H)---\left(6\right)$

Wherein U is an orthogonal moment array, and Λ is a diagonal matrix.

Owing to calculate Do not need can calculate easily matrix inversion, simultaneously in the 3GPP LTE downlink system, each subframe has only 14 OFDM symbols, and the shared OFDM symbol of reference signal has only 4, so autocorrelation matrix

Singular value decomposition also relatively easy, so simplified the computational complexity of algorithm greatly.

Among the present invention, at 3GPP LTE downlink system, channel estimation methods based on pilot signal has been proposed in a kind of 3GPP LTE downlink system, adopt time-frequency two-dimensional to unite dimension and receive the channel estimation methods of iteration filtering, this method is based on linear minimum mean-squared error (Linear Minimum Mean-Square Error, LMMSE) algorithm.In the present invention, at first carry out receiving iteration filtering, and then utilize value that frequency domain estimates once to tie up and receive iteration filtering in time domain based on the dimension of LMMSE algorithm at frequency domain.Show that this signal estimation method can improve bit error rate effectively, and (Bit Error Rate, BER) performance are compared with traditional method and to be approached ideal communication channel more and estimate through experiment test.In addition, (Singular Value Decomposition SVD) reduces the computational complexity of algorithm, so the channel estimation methods that the present invention proposes can not increase too many computational complexity by the LMMSE algorithm being carried out singular value decomposition in the present invention.

Description of drawings

Fig. 1 is a 3GPP LTE downlink system illustraton of model;

Fig. 2 is the distribution schematic diagram of reference signal in Resource Block;

Fig. 3 is the bit error rate performance comparison diagram of different channels method of estimation.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.What need point out especially is that in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these were described in here and will be left in the basket.

Fig. 1 is a 3GPP LTE downlink system illustraton of model, as shown in Figure 1, at transmitting terminal, input bit at first enters channel coding module, coded-bit is modulated into complex modulation symbols again through scrambling then, these complex modulation symbols are mapped on the transport layer of one or more antenna ports, each layer is mapped on the resource particle of each antenna port through after the precoding, insert reference signal simultaneously, at last, these symbols of each antenna port comprise data and reference signal, are modulated into plural time domain OFDM signal and transmit in wireless multipath channel.

At receiving terminal, under the ideal synchronisation situation, receiving end signal Y can be expressed as after the OFDM demodulation:

Y＝XH+W (7)

Wherein H and W represent channel frequency domain response and additive white Gaussian noise respectively, and X and Y represent to send signal and acknowledge(ment) signal respectively.

In order to recover the transmission bit from the signal that receives, channel estimation module need obtain the estimator of Parameter H.For this reason, 3GPP LTE downlink system inserts reference signal on fixing time-frequency two-dimensional position, can be expressed as at these locational receiving end signals:

Y _P＝X _PH _P+W _P (8)

X wherein _P, H _PAnd W _PBe the subclass of correlation matrix in the formula (7), subscript () _PThe position of expression transmission of reference signals.

3GPP LTE standard definition three kinds of downlink reference signals: the reference signal of cell-specific, Multicast Broadcast Single Frequency Network (Multicast Broadcast Single Frequency Network, the MBSFN) reference signal of reference signal and terminal-specific.In the present embodiment, adopt the reference signal of cell-specific to analyze.

Fig. 2 has provided the allocative decision of descending cell special reference on Resource Block that single antenna sends.As seen, reference signal (R ₀) 7 OFDM symbols in interval on same subcarrier on the time domain, 6 subcarriers in interval in the same OFDM symbol on frequency domain.

Existing channel estimation method:

Data Y by the reference signal position that receives _PWith the reference signal X that sends _P, the channel frequency domain response H of reference signal position in the formula (8) _PLS estimate and can be expressed as:

${\hat{H}}_{P,\mathrm{LS}}={X_P}^{-1}{Y}_P---\left(9\right)$

Carry out linear interpolation by estimated value in time domain and frequency domain then, thereby obtain the channel transfer function of all data resource particles among Fig. 2 the channel frequency domain response of reference signal position.Channel estimation method based on the LS criterion is simple in structure, but does not utilize the frequency domain of channel and the correlation properties of time domain in LS estimates, has ignored The noise when estimating, so channel estimation value is relatively more responsive to The noise.

Another kind of channel estimation methods is the MMSE algorithm, is widely used in the OFDM channel estimating, and this method is utilized signal to noise ratio, and (Signal to Noise Ratio, SNR) and other channel statistical characteristic informations, performance is better than the LS algorithm.The expression formula of MMSE frequency domain channel algorithm for estimating is as follows:

$H_{\mathrm{LMMSE}}=R_{{\mathrm{HH}}_P}{(R_{H_P{H}_P}+{\mathrm{\σ}}_W^2{\left({\mathrm{XX}}^H\right)}^{-1})}^{-1}{\hat{H}}_{P,\mathrm{LS}}---\left(10\right)$

Wherein,

H in the representation formula (9) _PThe LS estimated value,

Be the cross-correlation matrix of representing the subcarrier at subcarriers all in the same OFDM symbol and reference signal place,

The autocorrelation matrix of representing same OFDM symbol internal reference signals virgin carrier wave,

Be the variance of additive white Gaussian noise, subscript () ^HThe expression conjugate transpose.If the sign map of transmission arrives same planisphere,

So in the formula (10)

Can be with its expectation

Represent:

${\mathrm{\σ}}_W^2{\left({\mathrm{XX}}^H\right)}^{-1}=E\left\{{\mathrm{\σ}}_W^2{\left({\mathrm{XX}}^H\right)}^{-1}\right\}=\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P---\left(11\right)$

Wherein,

Be a constant by the signal constellation which decision, X _kFor the point on the planisphere, for QPSK, β=1, for 16QAM, β=17/9, SNR is an average signal-to-noise ratio, I _PBe unit matrix.Formula (11) can further be reduced to so:

${\hat{H}}_{\mathrm{LMMSE}}=R_{{\mathrm{HH}}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LS}}---\left(12\right)$

Carry out linear interpolation by channel frequency domain response estimation value in time domain then, obtain the channel transfer function of all data resource particles among Fig. 2 at last frequency domain.

By formula (12) as can be seen, the LMMSE channel estimation method is actually according to the MMSE criterion LS channel estimation results is carried out Filtering Processing one time, can eliminate the influence of partial noise like this.In order further to eliminate noise, improve the error rate of system performance, simultaneously can not increase too many computational complexity again, consider that 3GPP LTE downlink system has inserted reference signal simultaneously on time domain and frequency domain both direction, the time-frequency two-dimensional that has proposed a kind of 3GPP of being applicable to LTE downlink system is in the present invention united dimension and is received iteration filtering channel method of estimation, this channel estimation methods, at first the OFDM symbol that comprises reference signal is tieed up and received iteration filtering, utilize value that frequency domain estimates all subcarriers to be tieed up again and receive iteration filtering in time domain at frequency domain.

In this enforcement, with the single output of the single input of single user (single-user single-input single-output, SUSISO) be example, tested the performance of various channel estimation methods under the VehA of 3GPP LTE downlink system (VehicularA) channel circumstance.Test environment parameter: the 1.4M bandwidth, the QPSK modulation, reference signal adopts sub-district special reference signal, and sample frequency is 1.92MHz, and subcarrier spacing is 15KHz, and number of times is 1000 times.

Fig. 3 is the bit error rate performance comparison diagram of different channels method of estimation.

Fig. 3 has showed the bit error rate performance of different channels method of estimation under the 3GPP LTE downlink system VehA channel, wherein " LS " represents the bit error rate performance of LS channel estimation methods, the bit error rate performance of " MMSE " expression MMSE channel estimation methods, the bit error rate performance curve is followed successively by the bit error rate performance curve of LS, MMSE, the present invention and ideal communication channel method of estimation from top to bottom.As can be seen from Figure 3 the time-frequency two-dimensional that proposes of the present invention is united dimension and is received the bit error rate performance of iteration filtering channel algorithm for estimating and be better than LS and MMSE algorithm, more approachingly estimates with ideal communication channel, can not increase too many computational complexity again simultaneously.

The present invention for 3GPP LTE downlink system proposed a kind of complexity relatively not high time-frequency two-dimensional unite dimension and receive iteration filtering channel method of estimation.The method is received iteration filtering and is reduced noise effect and improve bit error rate performance by tieing up in frequency domain and time domain.Test result shows that the channel estimation methods that the present invention proposes has more performance than LS and MMSE channel estimation methods.The inventive method has significantly reduced the computational complexity of algorithm also by the autocorrelation matrix in the algorithm is carried out singular value decomposition simultaneously.

Although above the illustrative embodiment of the present invention is described; so that the technical staff of present technique neck understands the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various variations appended claim limit and the spirit and scope of the present invention determined in, these variations are conspicuous, all utilize innovation and creation that the present invention conceives all at the row of protection.

Claims (2)

1. In the 3GPP LTE downlink system based on the channel estimation methods of pilot signal, it is characterized in that, may further comprise the steps:

   (1), the dimension of frequency domain is received iteration filtering

   At first obtain the channel frequency domain response estimation value of reference signal position on the same OFDM symbol:

   ${\hat{H}}_{P,\mathrm{LMMSE}}^{\left(1\right)}=R_{H_P{H}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LS}}---\left(1\right)$

   In the formula (1),

   

   The autocorrelation matrix of representing same OFDM symbol internal reference signals virgin carrier wave, β are that SNR is an average signal-to-noise ratio, I by the constant of signal constellation which decision _PBe unit matrix;

   

   Channel frequency domain response H for the reference signal position _PThe LS estimated value, subscript () _PThe position of expression transmission of reference signals.

   Right then

   

   Carry out receiving iteration filtering based on the dimension of LMMSE algorithm and reduce noise and disturb influence to the locational channel frequency response estimated value of reference signal, improve bit error rate performance, dimension is received the locational channel frequency response estimated value of the filtered reference signal of iteration

   

   ${\hat{H}}_{P,\mathrm{LMMSE}}^{\left(2\right)}=R_{H_P{H}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LMMSE}}^{\left(1\right)}---\left(2\right)$

   Utilize at last through dimension and receive the channel frequency domain response estimation value of the filtered reference signal of iteration position

   

   Estimate the channel frequency domain response value at all subcarrier places on the same OFDM symbol

   

   ${\hat{H}}_{F,\mathrm{LMMSE}}=R_{{\mathrm{HH}}_P}{(R_{H_P{H}_P}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_P)}^{-1}{\hat{H}}_{P,\mathrm{LMMSE}}^{\left(2\right)}---\left(3\right)$

   In the formula (3),

   

   The cross-correlation matrix of representing the subcarrier at subcarriers all in the same OFDM symbol and reference signal place;

   (2), the dimension of time domain is received iteration filtering

   To the channel frequency domain response estimation value on n the subcarrier

   

   Carry out receiving iteration filtering based on the dimension of LMMSE algorithm, to reduce relevant residual noise and to improve bit error rate performance:

   ${\tilde{H}}_{F,\mathrm{LMMSE}}^{\left(n\right)}=R_{H_P{H}_P}^{\left(n\right)}{(R_{H_P{H}_P}^{\left(n\right)}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_L)}^{-1}{\hat{H}}_{F,\mathrm{LMMSE}}^{\left(n\right)}---\left(4\right)$

   In the formula (4),

   

   Be that all comprise the autocorrelation matrix between the OFDM symbol of reference signal, I on n subcarrier in the subframe _LBe unit matrix, L represents to comprise in each subframe the OFDM number of symbols of reference signal;

   Utilize dimension to receive channel frequency response estimated value after the iteration filtering Estimate the channel frequency response value at all n subcarrier places of OFDM symbol in each subframe

   

   ${\hat{H}}_{T,\mathrm{LMMSE}}^{\left(n\right)}=R_{{\mathrm{HH}}_P}^{\left(n\right)}{(R_{H_P{H}_P}^{\left(n\right)}+\frac{\mathrm{\β}}{\mathrm{SNR}}{I}_L)}^{-1}{\tilde{H}}_{F,\mathrm{LMMSE}}^{\left(n\right)}---\left(5\right)$

   Wherein,

   

   Be all OFDM symbols and comprise cross-correlation matrix between the OFDM symbol of reference signal on n the subcarrier;

   To the channel frequency domain response estimation value on all subcarriers

   

   Carry out aforementioned calculation, finally receive iteration filtering and obtained the channel transfer function value at all resource particle places through the dimension of frequency domain and time domain.
2. 2. based on the channel estimation methods of pilot signal, it is characterized in that in the 3GPP LTE downlink system according to claim 1, at first to the autocorrelation matrix in step (1) and (2)

   

   Carry out singular value decomposition, and then calculate inverse matrix

   

   Inverse matrix is decomposed into:

   

   Wherein U is an orthogonal moment array, and Λ is a diagonal matrix, and I is the I in step (1) and (2) _pOr I _L

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