CN1921463A - Communication channel estimation method and realizing device for crossing frequency division multiplexing mobile communication system - Google Patents
Communication channel estimation method and realizing device for crossing frequency division multiplexing mobile communication system Download PDFInfo
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Abstract
The invention relates to a signal channel estimate method of orthogonal frequency division multiplexing mobile communication system and relative device. Wherein, it comprises: based on prefix or judgment feedback information, or the impact response message of last OFDM mark to obtain the impact response rough estimation of relative mark signal channel; generating structural matrix; based on local reference signal and received pilot signal, calculating correlative vector; using recurrence formula to obtain the fine estimation result of signal channel impact response; judging if said fine estimation result is constricted; obtaining the signal channel estimation results of all carrier waves; selecting available data carrier wave signal channel to output. The invention can be used in quick decrease and slow decrease signal channels, with less calculation and small memory space demand, without threshold value selection.
Description
Technical field
The present invention relates to the channel estimation methods in the mobile radio system, be specifically related to the channel estimation methods and the implement device of OFDM mobile communication system, particularly channel estimation methods and the implement device that carries out in conjunction with prefix and pilot tone.
Background technology
As a kind of multi-carrier transmission pattern, OFDM (OFDM) is converted to one group of low-speed parallel data flow transmitted by the data flow with a high-speed transfer, system is reduced greatly to the susceptibility of multidiameter fading channel frequency selectivity, and the introducing of Cyclic Prefix has further strengthened the ability of the anti-intersymbol interference of system (ISI) again.In addition bandwidth availability ratio height, realize that characteristics such as simple make OFDM more and more wider in the application in radio communication basin, and channel estimating also becomes the focus of communications field research as the key technology of ofdm system, receives increasing concern.
The training sequence infix form of ofdm system has two kinds, block pilot tone and Comb Pilot.Existing channel estimation methods is based on mostly that wherein a certain pilot tone arrangement mode (block pilot tone or Comb Pilot) carries out.
This channel estimation methods of two types respectively has characteristics: is not very sensitive based on the channel estimation methods of block pilot tone to the frequency selectivity of channel, but only is applicable to that fading ratio is more slowly in the wireless channel; For channel estimation methods based on Comb Pilot, go for fading ratio wireless channel faster, but but relatively more responsive to the frequency selectivity of channel.And in conjunction with the advantage of these two kinds of channel estimating, it is still rare that channel is carried out estimation approach.
For 802.16 systems based on the OFDMA standard, its existing block pilot tone (below be called prefix) also has dressing pilot tone (the following pilot tone that directly is called).If only utilize prefix to carry out channel estimating,, when channel is fast fading channel, only utilize prefix can't accurately follow the tracks of the variation of channel, thereby influence the demodulation performance of system because prefix sign one frame only sends once.Carry out channel estimating if only utilize pilot tone, when the frequency selectivity of channel is relatively more remarkable, accuracy based on the channel estimation methods of pilot tone also can descend thereupon, even produces " floor effect ", and promptly the bit error rate of system does not improve along with the raising of signal to noise ratio.
With 802.16 systems based on the OFDMA standard is example, and under the FUSC pattern, pilot frequency carrier wave is spaced apart 66kHz., and is the channel of SUI-5 (Stanford University of correction interim channel model-5) for channel model, and the coherence bandwidth of channel is 70kHz; For channel model is the channel of SUI-6 (Stanford University of correction interim channel model-6), and the coherence bandwidth of channel is 38kHz.The coherence bandwidth of pilot frequency carrier wave interval and SUI-5 channel is approaching, greater than the coherence bandwidth of SUI-6 channel, at this moment, just is very easy to take place floor effect.Therefore, in conjunction with prefix and pilot signal, come wireless channel is estimated to be very important.
Publication number is CN1505293A, the open date is " channel estimation methods in the ofdm system and the estimator " on June 16th, 2004, a kind of method that prefix and pilot tone are carried out channel estimating that fully utilizes is proposed, this method promptly can be applied to fast fading channel, also can be applied to the relatively more significant channel of selectivity of channel frequency, comprise the situation of pilot frequency carrier wave interval less than correlation bandwidth.
But in order to implement this method, this method requires the judgement of channel type and the selection of predominating path.If the channel type system of selection is improper, can not accurately judge the type of channel, the performance meeting rapid deterioration of this method, and this patent does not provide the determination methods of channel type yet; Select for main propagation path, predominating path is selected in this patent utilization prefix impulse response, wherein relates to the selection of thresholding, channel estimating performance is also very sensitive to the selection of this thresholding, emulation shows that improper if this thresholding is selected, channel estimating performance can sharply descend.
Summary of the invention
One of purpose of the present invention provides a channel estimation methods that OFDM mobile communication system is carried out in conjunction with prefix and pilot tone, the method of the invention function admirable realizes simply, and can adapt to various channel types, as frequency-selective channel, fast fading channel etc.
The present invention also provides the device of realizing said method.
Be to realize that goal of the invention, the present invention propose a kind ofly to carry out channel estimation methods and device in conjunction with prefix and pilot tone.Produce the used pilot signal of channel estimating by system transmitter, comprise that pilot tone inserted mode and pilot value choose two parts content; The pilot signal that produces becomes time-domain pilot signal through inverse Fourier transform; This time-domain pilot signal of emission on the wireless multipath fading channel; By system receiver time-domain pilot signal is obtained the pilot tone signal through Fourier transform.
The present invention is such specific implementation:
A kind of channel estimation methods of OFDM mobile communication system comprises following processing:
First step is according to the impulse response rough estimate of the impulse response information acquisition respective symbol channel of prefix or a decision-feedback information or a last OFDM symbol;
Second step produces structural matrix according to the channel impulse response rough estimate information that obtains;
Third step calculates cross-correlation vector according to reference signal of this locality and the pilot signal that receives;
The 4th step according to structural matrix, cross-correlation vector, obtains the thin estimated result of channel impulse response by recursive equation;
The 5th step judges whether the thin estimated result that obtains according to recursive equation restrains, and is, exports the thin estimated result of this impulse response, not, proceeds the calculating of recursive equation;
The 6th step is carried out the fast Fourier transform of all carrier numbers of system to the thin estimated result of exporting impulse response, obtains the channel estimation results of all carrier numbers;
The 7th step is selected useful data carrier channel estimation results and output from the channel estimation results of all carrier numbers of system.
Whether the result of described the 5th step by judging double recursive operation mean square deviation is less than a fixed constant, if, the thin estimated result of output impulse response, otherwise, the result of this recursive calculation as the input of recursive calculation next time, is continued recursive calculation.
Described the 5th step is the recurrence number of times fixedly, carry out the recursive calculation of corresponding number of times after, the thin estimated result of output impulse response, and as the impulse response information of next OFDM symbol.
Described structural matrix is the square formation that satisfies conjugate transpose;
The length of described impulse response rough estimate equals the dimension of structural matrix.
The length of described cross-correlation vector equals the dimension of described structural matrix.
The length of the thin estimated result of described channel impulse response equals the dimension of described structural matrix.
A kind of device of realizing the channel estimation methods of OFDM mobile communication system is characterized in that comprising:
Channel impulse response rough estimate gauge is according to the impulse response rough estimate of the impulse response information acquisition channel of prefix, decision-feedback or a last OFDM symbol;
The structural matrix generator produces structural matrix according to channel impulse response rough estimate gauge;
The cross-correlation vector generator calculates the generation cross-correlation vector according to reference signal of this locality and the pilot signal that receives;
Data selector, the rough estimate of selective channel impulse response or the result of recursive equation are as an input of multiplier;
Multiplier calculates the product of structural matrix and data selector output and also exports;
Adder, calculate cross-correlation vector generator, multiplier and data selector output and, and output;
The end condition determinant judges whether recursive equation restrains, if restrain, stops recursive equation and calculates, and the delivery channel impulse response calculates otherwise proceed recursive equation;
Fast Fourier transformer is carried out the fast Fourier transform of system carrier number to the output of end condition determinant;
The channel estimation results selector is selected useful data carrier channel estimating and output from the channel estimation results of all carrier numbers.
Whether described end condition determinant, result's the mean square deviation of judging double recursive operation less than a fixed constant, if, the thin estimated result of output impulse response, otherwise, the result of this recursive calculation as the input of recursive calculation next time, is continued recursive calculation.
Described end condition determinant is the recurrence number of times fixedly, carry out the recursive calculation of corresponding number of times after, the thin estimated result of output impulse response, and as the impulse response information of next OFDM symbol.
Compare with the existing channel method of estimation, this method adapts to fast fading channel and slow fading channel, comprise the situation of the density of pilot tone less than correlation bandwidth, do not need to judge the type of channel and the main selection of transmission paths of channel, it is little to have amount of calculation, the requirement memory space is little, need not carry out thresholding and select, and realizes characteristics such as easy.
Description of drawings
Fig. 1 comprises receiver structure schematic diagram of the present invention;
Fig. 2 is the inner schematic diagram of realizing of channel estimator that the present invention proposes;
Fig. 3 is the inner flow chart of realizing the schematic diagram correspondence of channel estimator that the present invention proposes.
Embodiment
Below in conjunction with accompanying drawing the present invention is elaborated:
For realizing first goal of the invention, the method that the present invention proposes mainly may further comprise the steps:
1, according to the impulse response rough estimate H of the channel of m the symbol of impulse response information acquisition of prefix or a decision-feedback information or a last OFDM symbol
M, 0
2, produce structural matrix T according to formula (1), the dimension of T equals the length of impulse response rough estimate.Structural matrix T is one and satisfies T=T
HThe square formation of relation, T here
HThe conjugate transpose of expression structural matrix T, when the dimension of structural matrix T was L, its form was as follows:
Wherein,
K represents the biasing of carrier wave;
P represents the set of pilot frequency carrier wave biasing;
A is a convergence factor, satisfies 0＜a＜1;
The local reference pilot signal of X (k) expression;
It is the inverse Fourier transform factor.
3, calculate cross-correlation vector R, the length of R equals the dimension L of matrix T, and the form of cross-correlation vector R is as follows:
R＝[r(0)，......r(L-1)]
T； (3)
Wherein,
The pilot signal that Y (k) expression receives;
The a implication is the same.
4, obtain the thin estimated result of channel impulse response according to formula (5).
H
m，n+1＝H
m，n+R-TH
m，n (5)
Wherein,
H
M, nThe thin estimated result of representing m OFDM symbol n secondary channel impulse response in a certain frame, n=0,1,2... ...During n=0, H
M, 0Be the rough estimate of channel impulse response, H
1,0=H
0,0, H
0,0It is the channel impulse response estimation result of prefix.H
M, nBe a vector, length equals the dimension of structural matrix T.
5, to H
M, n+1Carry out N point FFT, can obtain the channel estimation results of all N carrier wave, N refers to the number of all carrier waves of system.
6, from the channel estimation results of N carrier wave, select useful data carrier channel estimation results and output.
Comprise as lower module with the channel estimating apparatus of above-mentioned steps correspondence:
1, cross-correlation vector generator, its effect are to produce the cross-correlation vector R shown in the formula (3).
2, structural matrix generator, its effect are to produce structural matrix T according to channel impulse response rough estimate gauge, and the dimension of matrix T is L.
3, channel impulse response rough estimate gauge is according to the impulse response rough estimate of the impulse response information calculations channel of prefix, decision-feedback or a last OFDM symbol.
4, data selector, its effect are the input of the result of the rough estimate of selective channel impulse response or recursive equation (5) as multiplier.
5, multiplier, its effect are the product and the output of calculating the output of structural matrix T and data selector.
6, adder, calculate cross-correlation vector generator, multiplier and data selector output and, and output.
7, end condition determinant, its effect are to judge whether recursion equation formula (5) restrains, if restrain, stop recursive calculation, delivery channel impulse response H
M, n+1, otherwise proceed recursive calculation.
8, FFT converter, its effect are the output H to the end condition determinant
M, n+1Carry out N point FFT, N refers to the number of all carrier waves of system.
9, channel estimation results selector is selected useful data carrier channel estimating and output from the channel estimation results of N carrier wave.
In the receiver among Fig. 1, front-end processing module 101 is by the reception antenna received RF signal, carries out down-conversion, analog-to-digital conversion then to received signal, goes processing such as Cyclic Prefix, and last, data are output to FFT module 102.
The data of 102 pairs of inputs of FFT module are carried out fast fourier transform, like this data by spatial transform to frequency domain.FFT module 102 outputs to channel compensation block 104 to the data from data carrier, outputs to channel estimation module 103 from the data of pilot frequency carrier wave.
At last, data are output to demodulating and decoding module 105 and carry out subsequent treatment.
Fig. 2 is that schematic diagram is realized in the inside of the channel estimator that proposes of the present invention.
Channel impulse response rough estimate gauge 201 is according to the impulse response rough estimate of the impulse response information acquisition channel of prefix, decision-feedback or a last OFDM symbol.
Structural matrix generator 202 produces the structural matrix T of corresponding dimension according to formula (1) according to the dimension of the definite matrix of channel impulse response rough estimate gauge.
Cross-correlation vector generator 203 produces the cross-correlation vector R shown in the formula (3) according to the reference pilot signal of this locality and the pilot signal of receiving terminal.
Data selector 204 is the initial values that are used for selecting the each recurrence of each symbol, if first symbol, initial value H for the first time
1,0Equal prefix impulse response H
0,0, otherwise each initial value H
M, 0All be the impulse response H of a last OFDM symbol
M-1, n
Multiplier 205 is the product and the output of calculating the output of structural matrix generator and data selector.
Adder 206 be calculate cross-correlation vector generator, multiplier and data selector output and, and output.
End condition determinant 207 is the end that are used for judging recursive calculation.
Fast Fourier transformer 208 is the channel estimating H to the output of end condition determinant
M, n+1The Fourier transform of asking N to order, N refers to the number of all carrier waves of system here.
Channel estimation results selector 209 is channel estimating and the output of selecting the useful data carrier wave from the channel estimation results of N carrier wave.
Fig. 3 correspondence the flow chart that channel estimating realizes schematic diagram.
Step 301 is according to the impulse response rough estimate of the information calculations channels such as impulse response of prefix, decision-feedback or a last OFDM symbol, and this rough estimate is equivalent to the initial value H of each recursive calculation
M, 0, if first OFDM symbol of a certain frame, the initial value H of recursive calculation
1,0Select the impulse response of prefix to estimate H
0,0, otherwise select the impulse response of a symbol to estimate H
M-1, nDetermine the dimension of matrix T according to the length of channel impulse response rough estimate.
Step 302 is determined the dimension of matrix T according to the channel impulse response information of pilot tone, prefix or a last OFDM symbol, produces structural matrix T according to formula (1).With the OFDMA system based on 802.16 agreements is example, can obtain the length of channel impulse response rough estimate according to prefix information, and the dimension of structural matrix T equals this length.The present invention does not limit the method that the channel impulse response information of utilizing pilot tone, prefix or a last OFDM symbol is determined the matrix T dimension.Emulation shows that the present invention is insensitive to the accuracy of channel impulse response length.
Step 303 is according to the cross-correlation r (p) of the pilot signal of the reference pilot signal of this locality and receiving terminal, and according to producing cross-correlation vector R shown in the formula (3), the length of vector R equals the dimension of matrix T.
Step 304 is calculated recursive equation (5) according to structural matrix T and cross-correlation vector R.
Step 305 judges according to each recursive operation result whether recursive calculation finishes, and the judgement of end condition can have two kinds:
Whether a kind of be to differ from less than a fixed constant, such as 0.01 the dividing equally of result of judging double recursive operation.Be output impulse response H
M, n+1, step 306 is the recurrence of last time H as a result
M, n+1As the input H of recurrence next time
M, n, continue recursive calculation.
Another kind is fixing recurrence frequency n, and recursive calculation equation (5) n time is exported impulse response H then
M, n+1
Step 307 is H
M, n+1Recursive calculation initial value H as next OFDM symbol
M+1,0
Step 308 is the impulse response H to channel
M, n+1Be N point FFT, the result is the channel estimating of all N carrier waves, and N refers to the number of all carrier waves of system.
Step 309 is to select useful data carrier channel estimating and output from the channel estimating of N carrier wave, and N refers to the number of all carrier waves of system.
Be the description to one embodiment of the present of invention above, those skilled in the art that should be understood that the various corrections of embodiments of the invention and change and drop in design of the present invention and the claims limited range.
Claims (9)
1, a kind of channel estimation methods of OFDM mobile communication system is characterized in that, comprises following processing:
First step is according to the impulse response rough estimate of the impulse response information acquisition respective symbol channel of prefix or a decision-feedback information or a last OFDM symbol;
Second step produces structural matrix according to the channel impulse response rough estimate information that obtains;
Third step calculates cross-correlation vector according to reference signal of this locality and the pilot signal that receives;
The 4th step according to structural matrix, cross-correlation vector, obtains the thin estimated result of channel impulse response by recursive equation;
The 5th step judges whether the thin estimated result that obtains according to recursive equation restrains, and is, exports the thin estimated result of this impulse response, not, proceeds the calculating of recursive equation;
The 6th step is carried out the fast Fourier transform of all carrier numbers of system to the thin estimated result of exporting impulse response, obtains the channel estimation results of all carrier numbers;
The 7th step is selected useful data carrier channel estimation results and output from the channel estimation results of all carrier numbers of system.
2, the channel estimation methods of OFDM mobile communication system according to claim 1 is characterized in that:
Whether the mean square deviation of described the 5th step by twice recursive equation result calculated less than a fixed constant, if, the thin estimated result of output impulse response, otherwise, with the result of this recursive calculation as the input of recursive calculation next time, the continuation recursive calculation.
3, the channel estimation methods of OFDM mobile communication system according to claim 1 is characterized in that:
Described the 5th step is the recurrence number of times fixedly, carry out the recursive calculation of corresponding number of times after, the thin estimated result of output impulse response, and as the impulse response information of next OFDM symbol.
4, as the channel estimation methods of OFDM mobile communication system as described in claim 1 or 2 or 3, it is characterized in that:
Described structural matrix is the square formation that satisfies conjugate transpose;
The length of described impulse response rough estimate equals the dimension of structural matrix.
5, as the channel estimation methods of OFDM mobile communication system as described in claim 1 or 2 or 3, it is characterized in that:
The length of described cross-correlation vector equals the dimension of described structural matrix.
6, as the channel estimation methods of OFDM mobile communication system as described in claim 1 or 2 or 3, it is characterized in that:
The length of the thin estimated result of described channel impulse response equals the dimension of described structural matrix.
7, a kind of device of realizing the channel estimation methods of OFDM mobile communication system is characterized in that comprising:
Channel impulse response rough estimate gauge is according to the impulse response rough estimate of the impulse response information acquisition channel of prefix, decision-feedback or a last OFDM symbol;
The structural matrix generator produces structural matrix according to channel impulse response rough estimate gauge;
The cross-correlation vector generator calculates the generation cross-correlation vector according to reference signal of this locality and the pilot signal that receives;
Data selector, the rough estimate of selective channel impulse response or the result of recursive equation are as an input of multiplier;
Multiplier calculates the product of structural matrix and data selector output and also exports;
Adder, calculate cross-correlation vector generator, multiplier and data selector output and, and output;
The end condition determinant judges whether recursive equation restrains, if restrain, stops recursive equation and calculates, and the delivery channel impulse response calculates otherwise proceed recursive equation;
Fast Fourier transformer is carried out the fast Fourier transform of system carrier number to the output of end condition determinant;
The channel estimation results selector is selected useful data carrier channel estimating and output from the channel estimation results of all carrier numbers.
8, as the device of the channel estimation methods of realization OFDM mobile communication system as described in the claim 7, it is characterized in that:
Whether described end condition determinant, result's the mean square deviation of judging double recursive operation less than a fixed constant, if, the thin estimated result of output impulse response, otherwise, the result of this recursive calculation as the input of recursive calculation next time, is continued recursive calculation.
9, as the device of the channel estimation methods of realization OFDM mobile communication system as described in the claim 7, it is characterized in that:
Described end condition determinant is the recurrence number of times fixedly, carry out the recursive calculation of corresponding number of times after, the thin estimated result of output impulse response, and as the impulse response information of next OFDM symbol.
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