CN101075998A - Method for estimating channel based on orthogonal frequency division multiplexing system - Google Patents

Abstract

The method comprises: 1) using the pilot frequency to get the channel estimation value of pilot frequency subcarrier location; 2) determining the pilot frequency point in nearest distance to the point to be interpolated; 3) according to the space distance, making weight value allocation for the pilot frequency point; 4) using the allocated weight value to get the value of the point to be interpolated; 5) getting the estimation value of overall channel.

Description

A kind of channel estimation methods based on ofdm system

Technical field

The present invention relates to the information wireless transmission technology in the field of wireless communications, particularly relate to a kind of OFDM (Orthogonal Frequency Division Multiplexing, OFDM) communication system radio channel estimation method based on pilot tone.

Background technology

The OFDM technology has advantages such as spectral efficient, anti-multipath effect, will be a very promising technology in the radio communication in future therefore, is subjected to people's extensive concern and research.IEEE802.16 working group mainly is responsible to define the standard of wireless MAN, has just adopted the transmission technology of OFDM as it in the air-interface standard 802.16a/802.16d/802.16e of its formulation.Europe digital video broadcast terrestrial (Digital Video Broadcasting-Terrestrial, DVB-T), digital video broadcasting/digital speech broadcasting (Digital Video Broadcasting/Digital Audio Broadcasting, DVB/DAB), Hiper (High Performance Radio, high performance radio) MAN/LAN (Metropolitan AreaNetwork/Local Area Network, metropolitan area network/local area network (LAN)) all used the OFDM transmission technology, and IEEE802.11a has also used the transmission technology of OFDM as WLAN (wireless local area network).

At the receiving terminal of ofdm system, in order to improve the performance of system, adopt coherent demodulation usually, coherent demodulation needs channel parameter information, and it can obtain by channel estimating.The performance of channel estimator directly influences systematic function, is one of key technology of receiver.Channel estimation methods based on pilot tone has obtained using widely.Under multipath fading and Quick-Change channel situation, for example in the High Data Rate OFDM mobile system,, generally adopt comb pilot signal to estimate to obtain the Real-time Channel response for overcoming the adverse effect of channel.

The Comb Pilot channel estimating is made of pilot sub-carrier channel estimation method and interpolation algorithm.Because the channel response value at data subcarrier is to obtain by the channel response value of pilot frequency carrier wave is carried out interpolation, so systematic function depends on the accuracy that the pilot sub-carrier channel response is estimated to a great extent.Have fairly simple LS (Least Square, least square) to estimate based on the channel estimating of pilot tone, more complicated MMSE (Minimum Mean Square Error, least mean-square error) estimates and the time-frequency domain two dimension is united methods such as estimation.

Because the channel response value at data subcarrier is to obtain by the channel response value of pilot frequency carrier wave is carried out interpolation, so illustrate also that on the other hand interpolation algorithm influences the performance of ofdm system to a great extent.Effectively interpolation algorithm must be based upon on the basis to the fading channel accurate description.In ofdm system, interpolation method commonly used has: the first-order linear interpolation method, the second-order linearity interpolation method, spline method and traditional time domain interpolation method, document 2 (" channel estimation technique of arranging based on pilot tone in the ofdm system " sees reference, Sinem Coleri, Mustafa Ergen, IEEE about broadcast communication can report, the 48th 3 phases of volume of September in 2002, Sinem Coleri, Mustafa Ergen, " Channel Estimation TechniqueBased on Pilot Arrangement in OFDM Systems ", IEEE Transaction OnBroadcasting, Vol.48, No.3, September, 2002).These interpolation methods all are that the channel parameter of tentation data section is constant substantially or variation is slow, thereby can use the method match of linear weighted function.

As how lower realization complexity, obtain the channel response of whole channel more accurately, this is the problem that channel estimation methods need be considered.And multipath fading is the non-linear process of a complexity, uses said method to carry out interpolation (comprising interpolation and extrapolation, especially extrapolation) and will have the shortcoming of poor accuracy inevitably.

Summary of the invention

Technical problem to be solved by this invention is to provide a kind of channel estimation methods based on ofdm system, is used for overcoming the shortcoming that prior art is utilized the linear interpolation method poor accuracy, obtains with lower implementation complexity and obtains preferable performance.

To achieve these goals, the invention provides a kind of channel estimation methods, be applicable to ofdm system, it is characterized in that, comprising based on ofdm system:

Step 1 utilizes pilot tone to obtain the channel estimation value of pilot sub-carrier position;

Step 2 is determined the pilot tone point nearest apart from interpolation point, and is calculated the space length that this pilot tone is put this interpolation point;

Step 3 is carried out weights according to described space length to this pilot tone point and is distributed;

Step 4 is asked for the value of described interpolation point by the weights of described distribution;

Step 5 is asked for the estimated value of whole channel.

Described channel estimation methods based on ofdm system wherein, in the described step 1, carries out the channel estimating of described pilot sub-carrier position with least-squares estimation method or the least mean-square error estimation technique or the linear minimum mean-squared error estimation technique.

Described channel estimation methods based on ofdm system, wherein, described space length is the interval of described pilot sub-carrier.

Described channel estimation methods based on ofdm system, wherein, described weights be described space length square.

Described channel estimation methods based on ofdm system, wherein, between described step 4, the step 5, comprise that also one judges whether to ask for the step of the value of all interpolation points, if carry out described step 5, if not, then carry out described step 2 to described step 4.

Described channel estimation methods based on ofdm system, wherein, described step 5 is specially: by ask for the estimated value of whole channel in conjunction with the value of the channel estimation value of described pilot sub-carrier position and described all interpolation points.

Described channel estimation methods based on ofdm system, wherein, described ofdm system is the multi-input multi-output-orthogonal frequency division multiplexing communication system.

Described channel estimation methods based on ofdm system, wherein, described ofdm system is the ofdm system based on the IEEE802.16a/802.16d/802.16e standard.

The channel estimation methods that the present invention proposes is a kind of effective channel estimation methods, this method overcomes the shortcoming of utilizing the linear interpolation method poor accuracy of the prior art, advantage with high-performance and low complex degree obtains preferable performance with lower implementation complexity, and is easy to realize; Be specially adapted to use radio channel estimation based on the communication system of the OFDM of IEEE802.16a/802.16d/802.16e standard or MIMO (Multiple Input MultipleOutput, multiple-input and multiple-output)-OFDM transmission technology (perhaps being similar to the OFDM transmission technology of 802.16a/802.16d/802.16e standard).

Describe the present invention below in conjunction with the drawings and specific embodiments, but not as a limitation of the invention.

Description of drawings

Fig. 1 is the OFDM symbolic construction of Comb Pilot;

Fig. 2 is the flow chart of channel estimation methods of the present invention.

Embodiment

Be described in further detail below in conjunction with the enforcement of accompanying drawing technical scheme.

See also shown in Figure 1ly, be the OFDM symbolic construction of Comb Pilot.Sub-carrier number in the supposing the system is N=256, insert pilot tone P and data D (M=64) with 1: 3 ratio, if l=0, then pilot frequency locations is (0,4, ..., 252), CP (Cyclic Prefix, Cyclic Prefix) length is 32 (calculating with sampled point), maximum delay expands to 10 (calculating with sampled point), sends signal and arrives receiving terminal through behind the multidiameter fading channel.

According to the principle of OFDM, the binary message data are through ovennodulation, and after the insertion pilot tone, (Inverse Fast Fourier Transform IFFT), adds Cyclic Prefix, sends again through invert fast fourier transformation; Receiving terminal removes Cyclic Prefix by after receiving synchronously, and (FastFourier Transform FFT), passes through channel estimating and equilibrium then, demodulates information signal through fast fourier transform.Whole process is specific as follows:

At transmitting terminal, the binary message data are through ovennodulation, modulation back symbol be designated as Λ, N-1}, N are the subcarrier numbers for X (k), k=0, uniformly-spaced insert M pilot tone, and its position is: $l,\frac{N}{M}+l,\mathrm{\Λ},(M-1)\frac{N}{M}+l,$ After the process IFFT conversion is formula (1):

$x\left(n\right)=\mathrm{IFFT}\left\{X\left(k\right)\right\}=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}X\left(k\right)e^{j2\mathrm{\πkn}/N},n=\mathrm{0,1},\mathrm{\Λ},N-1...\left(1\right)$

At last, launch by antenna behind the insertion Cyclic Prefix.

At receiving terminal, received signal can be expressed as circular convolution formula (2):

y(n)＝x(n)h(n)+w(n)，n＝0，1，Λ，N-1 (2)

Wherein, h (n) is a channel impulse response, and w (n) is an additive white Gaussian noise, and h (n) can be expressed as formula (3):

$h\left(h\right)=\underset{i=0}{\overset{r-1}{\mathrm{\Σ}}}{h}_i\exp \left(j\frac{2\mathrm{\π}}{N}{f}_{\mathrm{Di}}\mathrm{Tn}\right)\mathrm{\δ}(\mathrm{\τ}-{\mathrm{\τ}}_i),0\≤n\≤N-1...\left(3\right)$

Wherein, r is the multipath number, h _iBe of the multiple impulse response of i footpath in time domain, f _DiBe Doppler frequency shift, τ _iIt is the time delay of i bar multipath.

Remove Cyclic Prefix synchronously, carry out the FFT conversion again, obtain formula (4):

Y(k)＝FFT{y(n)}＝X(k)H(k)+I(k)+W(k)，k＝0，1，Λ，N-1 (4)

Wherein, H (k) is the channel frequency domain response of k subcarrier correspondence, and I (k) is other subcarrier (Inter Carrier Interference, ICI), W (k) is the Fourier transform of w (n) to the interference of k subcarrier.

See also shown in Figure 2ly, be the flow chart of channel estimation methods of the present invention.The supposing the system ideal synchronisation, the concrete steps of channel estimating are as follows:

Step 210 utilizes pilot tone can obtain the locational channel estimating value sequence of pilot sub-carrier H (k), k=0,4, Λ, 252;

In this step, the preferably LS estimation of method, MMSE estimation or the low order LMMSE (Linear Minimum Mean Square Error, linear minimum mean-squared error) that carry out the channel estimating of pilot sub-carrier estimate to wait other method;

Step 220 determines that M is individual from the nearest pilot tone point of interpolation point k; Interpolation point wherein is meant other sub-carrier positions except that pilot frequency locations (being the pilot sub-carrier position);

Step 230 is calculated this M space length d that puts interpolation point k _Ik, i=1 ..., M;

In this step, space length can be the interval of pilot sub-carrier, and space length can be tried to achieve by following formula (5):

d _ik＝|i-k|，i＝1，...，M (5)

Step 240, the size of distributing M weights according to space length;

In this step, the weights of distribution can be space length square;

Step 250 according to the M that an is assigned to weights, is tried to achieve the value of interpolation point k; Concrete acquiring method is undertaken by following formula (6):

$H_k=\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\frac{H_i}{d_{\mathrm{ik}}^2}/\underset{i=1}{\overset{M}{\mathrm{\Σ}}}\frac{1}{d_{\mathrm{ik}}^2}...\left(6\right)$

H in the following formula _i(i=1 ..., M) M in is the M that is determined by step 220.

Step 260, judge whether to obtain the value of all unknown point (interpolation point): if not, then repeated execution of steps 220 is to step 250; If then execution in step 270;

Step 270, the result of result of integrating step 210 (channel estimation values of pilot frequency positions) and step 260 (values of all interpolation points) can obtain the estimated value of whole channel.

Like this, just obtained the estimated value H of the whole channel of this OFDM symbol correspondence by above step.

Channel estimation methods of the present invention has the advantage of high-performance and low complex degree, is easy to realize.

Certainly; the present invention also can have other various embodiments; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art work as can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.

Claims (8)

1, a kind of channel estimation methods based on ofdm system is applicable to ofdm system, it is characterized in that, comprising:

Step 1 utilizes pilot tone to obtain the channel estimation value of pilot sub-carrier position;

Step 2 is determined the pilot tone point nearest apart from interpolation point, and is calculated the space length that this pilot tone is put this interpolation point;

Step 3 is carried out weights according to described space length to this pilot tone point and is distributed;

Step 4 is asked for the value of described interpolation point by the weights of described distribution;

Step 5 is asked for the estimated value of whole channel.

2, the channel estimation methods based on ofdm system according to claim 1, it is characterized in that, in the described step 1, carry out the channel estimating of described pilot sub-carrier position with least-squares estimation method or the least mean-square error estimation technique or the linear minimum mean-squared error estimation technique.

3, the channel estimation methods based on ofdm system according to claim 1 is characterized in that, described space length is the interval of described pilot sub-carrier.

4, according to claim 1,2 or 3 described channel estimation methods, it is characterized in that based on ofdm system, described weights be described space length square.

5, according to claim 1,2 or 3 described channel estimation methods based on ofdm system, it is characterized in that, between described step 4, the step 5, comprise that also one judges whether to ask for the step of the value of all interpolation points, if, carry out described step 5, if not, then carry out described step 2 to described step 4.

6, the channel estimation methods based on ofdm system according to claim 5, it is characterized in that described step 5 is specially: by ask for the estimated value of whole channel in conjunction with the value of the channel estimation value of described pilot sub-carrier position and described all interpolation points.

7, according to claim 1,2 or 3 described channel estimation methods, it is characterized in that described ofdm system is the multi-input multi-output-orthogonal frequency division multiplexing communication system based on ofdm system.

8, according to claim 1,2 or 3 described channel estimation methods, it is characterized in that described ofdm system is the ofdm system based on the IEEE802.16a/802.16d/802.16e standard based on ofdm system.

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