CN102291340B - Channel estimation methods and device in a kind of ofdm system - Google Patents

Channel estimation methods and device in a kind of ofdm system Download PDF

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CN102291340B
CN102291340B CN201010211261.XA CN201010211261A CN102291340B CN 102291340 B CN102291340 B CN 102291340B CN 201010211261 A CN201010211261 A CN 201010211261A CN 102291340 B CN102291340 B CN 102291340B
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signal
user
unit
pilot
afterbody
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CN102291340A (en
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李�杰
耿鹏
马毅华
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ZTE Corp
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ZTE Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only

Abstract

The invention discloses channel estimation methods in a kind of OFDM (OFDM) system, comprise: the pilot signal received carried out eliminating the female code of pilot tone successively, afterbody is connected, inverse discrete Fourier transform (DFT) (IDFT), be separated the process of multi-user, discrete Fourier transform (DFT) (DFT) and frequency domain truncation, obtain the channel estimation Signal of each user.The present invention discloses channel estimating apparatus in a kind of ofdm system, adopt method of the present invention and device, so, effectively can isolate the channel estimation Signal of multiple user, and can channel estimation quality be improved.

Description

Channel estimation methods and device in a kind of ofdm system
Technical field
The present invention relates to OFDM (OFDM) technology, refer to channel estimation methods and device in a kind of ofdm system especially.
Background technology
In OFDM (OFDM) system, available frequency band is divided into multiple little frequency band, also can be described as subcarrier, and data symbol is modulated onto on these subcarriers to be launched.In order to enable receiver demodulating data exactly, known pilot signal must be placed on certain sub-carriers, receiver processes accordingly to pilot signal, obtains the channel estimating at pilot frequency locations place, and is obtained the channel estimating of other position by means such as interpolation.
After user receives pilot signal, common handling procedure is: first transform to time domain and do noise reduction process, and then change back to frequency domain, finally obtains the channel estimating at pilot signal place.In processing procedure, because the pilot signal received is the segment signal intercepted from continuous print channel response, the two ends of frequency domain are discontinuous, therefore, do discrete Fourier transform (DFT) (DFT)/inverse discrete Fourier transform (DFT) (IDFT) when processing, the generation of Gibbs phenomenon can be caused, and then make the deleterious of channel estimating.Described Gibbs phenomenon refers to that shake ripple appears in the channel estimation in frequency domain two ends finally obtained.
Application number is the Chinese patent of 200780039909.6, discloses a kind of channel estimator, respectively after the front and rear of pilot signal adds spread signal, carry out IDFT and DFT process again, so, inhibit Gibbs phenomenon to a certain extent, improve channel estimating effect.
But the pilot signal that above-mentioned patent is only applicable to single user is launched processes, when multiple user simultaneously transmitting pilot signal time, adopt method disclosed in above-mentioned patent then can not for the treatment of the channel estimating of multiple user.
Summary of the invention
In view of this, main purpose of the present invention is to provide channel estimation methods and device in a kind of ofdm system, can improve channel estimation quality, and is applicable to the channel estimating of multi-user.
For achieving the above object, technical scheme of the present invention is achieved in that
The invention provides channel estimation methods in a kind of ofdm system, the method comprises:
The pilot signal received is carried out eliminating successively to the process of the female code of pilot tone, afterbody linking, IDFT, separation multi-user, DFT and frequency domain truncation, obtain the channel estimation Signal of each user.
In such scheme, before carrying out DFT process, the method comprises further:
The time-domain signal obtained after separation multi-user process is carried out to the process of stress release treatment, obtain carrying out the signal needed for DFT process.
In such scheme, before receiving pilot signal, the method comprises further:
Ofdm system retrains the pilot signal that each user terminal is launched;
Describedly to retrain, be specially:
Adopt the female code of identical pilot tone, be multiplied by different phase rotatings respectively, obtain the pilot signal of each user terminal.
In such scheme, described phase rotating is specially:
If there is K user terminal transmitting pilot signal simultaneously, the phase rotating of K user terminal is respectively
In such scheme, the described pilot signal to receiving is carried out afterbody and is connected process, is specially:
The frequency-region signal structure K section after eliminating the female code of pilot tone is adopted to have the curve signal of continuity and differentiability, and K section curve signal is added to the afterbody of the frequency-region signal after the female code of described elimination pilot tone, make the frequency domain two ends of mixed channel response signal keep continuously, described K value is the user terminal number of transmitting pilot signal simultaneously.
In such scheme, the described afterbody constructing K section curve signal, K section curve signal is added to frequency-region signal, is specially:
Take out signal separately from the head position of the frequency-region signal after eliminating the female code process of pilot tone and tail position, construct the curve of one section of continuity and differentiability, K user then constructs K section continually varying curve respectively;
The signal of K section curve is staggeredly placed, is merged into required afterbody and is connected signal;
Described afterbody linking signal is engaged on after the frequency-region signal after the female code of described elimination pilot tone, obtains afterbody and be connected the signal after processing.
In such scheme, described in carry out being separated the process of multi-user, be specially:
Position coordinates in time-domain signal g (n) making a kth user obtain after IDFT process is:
p k = k M + KL K , k = 0,1 , . . . , K - 1 ;
When k ≠ 0, construct the equivalent time domain impulse response signal g of each user kn the method for () is:
From signal g (p k) before take out N findividual signal, takes out N from behind bindividual signal, signal all zero-addings of other position, and carry out time delay processing, then obtain:
g k(n)＝[g(p k)，g(p k+1)，...，g(p k+N B)，0，0，...，0，g(p k-N F)，...，g(p k-1)]；
As k=0, structure g 0n the method for () is:
g 0(n)＝[g(0)，g(1)，...，g(N B)，0，0，...0，g(M+KL-N F)，...，g(M+KL-1)]。
In such scheme, described in carry out the process of stress release treatment, be specially:
Noise threshold is set;
Compare the power of non-zero signal and the size of noise threshold in the signal after being separated multi-user's process successively, if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting.
Present invention also offers channel estimating apparatus in a kind of ofdm system, this device comprises: pilot processing unit, afterbody are connected unit, IDFT unit, multi-user's separative element, DFT unit and frequency domain truncation unit; Wherein,
Pilot processing unit, for carrying out the process eliminating the female code of pilot tone to the pilot signal received, and sends to afterbody to be connected unit the signal after process;
Afterbody is connected unit, for after the signal receiving pilot processing unit transmission, carries out the process of afterbody linking to the received signal, and the signal after process is sent to IDFT unit;
IDFT unit, for after the signal receiving the transmission of afterbody linking unit, carries out the process of IDFT to the received signal, and the signal after process is sent to multi-user's separative element;
Multi-user's separative element, for after the signal receiving the transmission of IDFT unit, carries out the process being separated multi-user to the received signal, and the signal after process is sent to DFT unit;
DFT unit, for after the signal receiving the transmission of multi-user's separative element, carries out the process of DFT to the received signal, and the signal after process is sent to frequency domain truncation unit;
Frequency domain truncation unit, for after the signal receiving the transmission of DFT unit, carries out the process of frequency domain truncation to the received signal, obtains the channel estimation Signal of each user terminal.
In such scheme, this device comprises further: noise canceling unit, for after the signal receiving the transmission of multi-user's separative element, carries out the process of stress release treatment to the received signal, and the signal after process is sent to DFT unit;
Described multi-user's separative element, for after the signal receiving the transmission of IDFT unit, carries out the process being separated multi-user to the received signal, and the signal after process is sent to noise canceling unit;
Described DFT unit, for after the signal receiving the transmission of noise separation unit, carries out the process of DFT to the received signal, and the signal after process is sent to frequency domain truncation unit.
In such scheme, this device comprises further: dispensing unit, for adopting the female code of identical pilot tone, being multiplied by different phase rotatings respectively, obtaining the pilot signal of multiple user terminal.
In such scheme, described afterbody is connected unit, specifically for:
The frequency-region signal structure K section after eliminating the female code of pilot tone is adopted to have the curve signal of continuity and differentiability, and K section curve signal is added to the afterbody of the frequency-region signal after the female code of described elimination pilot tone, make the frequency domain two ends of mixed channel response signal keep continuously, described K value is the user terminal number of transmitting pilot signal simultaneously.
In such scheme, described noise canceling unit comprises further:
Statistical module, for adding up the average power of the residual signal of the signal after IDFT cell processing after the process of multi-user's separative element, and sends to the average power obtained and arranges module;
Module is set, for after the average power receiving statistical module transmission, noise threshold is set;
Processing module, for comparing the power of non-zero signal in the signal that receives and the size of noise threshold, if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting, and the signal after process is sent to DFT unit.
Channel estimation methods and device in ofdm system provided by the invention, the pilot signal received is carried out eliminating successively to the process of the female code of pilot tone, afterbody linking, IDFT, separation multi-user, DFT and frequency domain truncation, obtain the channel estimation Signal of each user, so, effectively can isolate the channel estimation Signal of multiple user, inhibit Gibbs phenomenon, and can channel estimation quality be improved;
In addition, the phase rotating of regulation K user terminal is respectively then the pilot signal of a kth user is: so, the separating effect of the time domain impulse response signal of multiple user terminal can be made best.
Accompanying drawing explanation
Fig. 1 is the method flow schematic diagram of channel estimating in ofdm system of the present invention;
Fig. 2 is the method flow schematic diagram of the channel estimating of embodiment;
Fig. 3 is the signal schematic representation in embodiment after the female code process of pilot signal elimination pilot tone;
Fig. 4 is that in embodiment, afterbody is connected the signal schematic representation after processing;
Fig. 5 is the signal schematic representation in embodiment after IDFT process;
Fig. 6 is the time-domain signal schematic diagram of first user terminal in embodiment;
Fig. 7 is the channel estimating of first user terminal reality and desirable channel estimating real part curve;
Fig. 8 is the apparatus structure schematic diagram of channel estimating in ofdm system of the present invention.
Embodiment
Basic thought of the present invention is: the process pilot signal received being carried out eliminating successively to the female code of pilot tone, afterbody linking, IDFT, separation multi-user, DFT and frequency domain truncation, obtains the channel estimation Signal of each user.
Below in conjunction with drawings and the specific embodiments, the present invention is further described in more detail.
The method of channel estimating in ofdm system of the present invention, as shown in Figure 1, comprises the following steps:
Step 101: after receiving pilot signal, carries out the process eliminating the female code of pilot tone, obtains the first signal;
Here, suppose that pilot signal occupies M subcarrier, accordingly, the sequence length of the female code of pilot tone is M, if the female code of pilot tone is r (n), n=0 ...., M-1, namely comprises a sequence of M signal;
Suppose that the signal in the pilot frequency locations that receives is y (n), the process eliminating the female code of pilot tone is carried out then, be specially: by the signal in the pilot frequency locations that receives divided by female code r (n) of pilot tone, be x (n) by the first signal indication obtained, then have
x(n)＝y(n)/r(n)；
Wherein, signal y (n) comprises the pilot signal of multiple user terminal transmitting and the product of corresponding channel transfer functions and noise signal; Signal x (n) comprises the mixed channel response of multiple user, and the response of this mixed channel is containing noise signal;
Ofdm system retrains the pilot signal that each user terminal is launched, and is specially:
Adopt female code r (n) of pilot tone that identical, be multiplied by different phase rotatings respectively, obtain the pilot signal of each user terminal; Particularly, suppose there is K user terminal transmitting pilot signal simultaneously, the phase rotating of regulation K user terminal is respectively then the pilot signal of a kth user is:
r k ( n ) = r ( n ) · exp ( j 2 π k K n ) , n = 0 , . . . , M - 1 , k = 0 , . . . , K - 1 ;
Wherein, ofdm system retrains the female code of adopted pilot tone and receiving terminal to the pilot signal that each user terminal is launched, and to carry out eliminating the pilot tone mother code that the female code process of pilot tone adopts identical, ofdm system carries out after constraint process completes, notifying the female code of pilot tone that receiving terminal adopts in the pilot signal of launching each user terminal;
It should be noted that: other phase rotating mode specified in the agreement of ofdm system also can use, but only has employing said method, the separating effect of the time domain impulse response signal of multiple user terminal just can be made best.In addition, K user terminal here, is not limited to the terminal number in physical significance.Such as: certain physical terminal 2 antennas transmitting pilot signal simultaneously, this physical terminal is regarded as 2 equivalent user terminals; Wherein, the 4G standard in future has the appearance of this kind of situation.
Step 102: afterbody is carried out to the first signal and is connected process, obtain secondary signal;
Here, because the pilot signal received is the segment signal intercepted from continuous print channel response, therefore, the two ends of frequency domain are discontinuous, carry out afterbody linking process to the first signal to refer to: construct according to adopting the frequency-region signal after eliminating the female code of pilot tone the curve signal that K section has continuity and differentiability, and K section curve signal is added to the afterbody of the first signal, thus make the head and the tail signal of the secondary signal obtained continuous, that is: make the frequency domain two ends of mixed channel response signal keep continuously;
Described to the first signal carry out afterbody be connected process, be specially:
Take out signal separately from the head position of the frequency-region signal after eliminating the female code process of pilot tone and tail position, construct the curve that a section has continuity and differentiability, K user then constructs K section continually varying curve respectively;
The signal of K section curve is staggeredly placed, is merged into required afterbody and is connected signal;
Described afterbody linking signal is engaged on after the frequency-region signal after the female code of described elimination pilot tone, obtains afterbody and be connected the signal after processing;
Particularly, secondary signal is expressed as f (n), arranging length is M+KL; Be z (l) by linking signal indication, length is KL; Wherein, z (l) is by K section curve z kl () is staggered is formed, k=0, and 1 ..., K-1, every section of length of a curve is that the size of L, L value will can arrange by implementation principle according to DFT/IDFT function, that is: length is that the burst of M+KL easily realizes with DFT/IDFT;
At curve construction z ktime (l), need to select some signal to construct at the head position of x (n) and tail position, and require: curve z kl () has continuity and differentiability, but do not ensure that being connected signal z (l) has continuity and differentiability; Particularly, multiple method for designing can be adopted to carry out curve construction z kl (), only needs the curve z ensureing to construct kl the burst of () itself is smooth, continually varying, exists without any breakpoint, that is: the curve z constructed kl () has continuity and differentiability;
A kind of simple design is trade-off curve z kl () is one section of straight line, utilize head signal that a position coordinates is x (k) and position coordinates to be that the tail signal of x (M-K+k) constructs, thus produces the sequence that an amplitude and phase place are all linear change; Certain combined method of x (k) and x (M-K+k) can also be selected to construct z k(l), or, select arbitrary head signal and tail signal to construct z k(l);
Z kafter (l) construction complete, adopt z kl () constructs and is connected signal z kl (), particularly, is connected signal z (l) by z kl () is staggered is formed, that is:
z(l)＝[z 0(1)，z 1(1)，...，z K-1(1)，z 0(2)，z 1(2)，...，z K-1(2)，...，z 0(L)，z 1(L)，...，z K-1(L)]；
Signal x (n) be connected signal z (l) and form secondary signal f (n), then have
f(n)＝[x(n}，z(l)]；
Step 103: carry out IDFT process to secondary signal, obtains the 3rd signal;
Here, the object of secondary signal f (n) being carried out to IDFT process is to obtain time-domain signal g (n), that is: the 3rd signal; If when the length of secondary signal sequence is the integer power of 2, inverse fast fourier transform (IFFT) process is specifically as follows to the IDFT process that secondary signal is carried out; Described secondary signal f (n) is carried out IDFT process and is referred to and carry out IDFT functional operation to secondary signal f (n);
Time-domain signal g (n) is:
g(n)＝[g(0)，g(1)，....，g(M+KL-1)]；
The sequence length of time-domain signal g (n) is: M+KL.
Step 104: the process being separated multi-user is carried out to the 3rd signal, obtains the 4th signal;
Here, described 4th signal comprises the equivalent time domain impulse response signal g of each user k(n), wherein, g kn () is the sample composition extracted from time-domain signal g (n);
The position coordinates of certain user in g (n) is made to be:
p k = k M + KL K , k = 0,1 , . . . , K - 1 ;
When k ≠ 0, structure g kn the method for () is:
From signal g (p k) before take out N findividual signal, takes out N from behind bindividual signal, signal all zero-addings of other position, and carry out time delay processing, then obtain
g k(n)＝[g(p k)，g(p k+1)，...，g(p k+N B)，0，0，...，0，g(p k-N F)，...，g(p k-1)]；
Wherein, g kn the sequence length of () is M+KL, the sequence length of head signal is N b+ 1, the sequence length of tail signal is N f; Wherein, according to characteristic of channel parameter, the length of channel time domain impulse response signal is pre-set, N fwith N bvalue to make the g that constructs kn in (), the length of non-zero signal is greater than default length;
As k=0, g 0n the building method of () is:
g 0(n)＝[g(0)，g(1)，...，g(N B)，0，0，...0，g(M+KL-N F)，...，g(M+KL-1)]。
Step 105: the process the 4th signal being carried out to stress release treatment, obtains the 5th signal;
Here, before the process of stress release treatment is carried out to the 4th signal, need process time-domain signal g (n) being carried out to noise power estimation, particularly, the sample taken out at step 104 by time-domain signal g (n) is all set to zero, that is: comprise K (N f+ N b+ 1) individual zero, the average power of signal remaining in statistics g (n), if average power is P n; In addition, be here all suitable for for the method for statistical noise power in prior art;
The described process 4th signal being carried out to stress release treatment, is specially:
Noise threshold is set;
Particularly, by average power P nthe value of certain multiple be set to noise threshold; In actual application, can get different multiples, carry out emulation experiment, selecting to emulate the channel estimation Signal that obtains and the desirable channel estimation Signal best multiple that coincide is the foundation arranging noise threshold;
Compare g successively kn in the sequence of (n) f+ N bthe power of+1 non-zero signal and the size of noise threshold, if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting; To K g kn () all carries out above-mentioned process respectively, thus obtain the 5th signal, by the 5th signal indication is the signal obtained after the process of stress release treatment is carried out in the equivalent time domain impulse response that 5th signal comprises K user; the length of sequence is still M+KL;
In fact, step 105 can not perform, and the object that this step performs is to obtain better channel estimating effect, if do not perform this step, then the subscriber signal estimated signal quality obtained is poor.
Step 106: carry out DFT process to the 5th signal, obtains the 6th signal;
Here, to the 5th signal the object of carrying out DFT process is to obtain frequency-region signal h k(n), that is: the 6th signal; If five signals when the length of sequence is the integer power of 2, fast fourier transform (FFT) is specifically as follows to the DFT process that the 5th signal carries out, describedly DFT process is carried out to the 5th signal refers to DFT functional operation is carried out to the 5th signal;
Frequency-region signal h kn the sequence length of () is M+KL.
Step 107: the process the 6th signal being carried out to frequency domain truncation, obtains the channel estimation Signal of each user, terminates current handling process;
Particularly, by frequency-region signal h kn in (), the length of afterbody is that KL signal all cuts out, only the length retained above is M signal, obtains the channel estimation Signal of a kth user;
To K h kn () all carries out above-mentioned process respectively, obtain the channel estimation Signal of K user.
Such scheme is not only applicable to the channel estimating of multi-user, is also applicable to the channel estimating of single user, and now, the K in such scheme is 1.
Below in conjunction with embodiment, the solution of the present invention is described in any further.
The application scenarios of the present embodiment is: the sequence length of the female code of pilot tone: M=60, has four user terminal transmitting pilot signals, then these four user terminals phase rotating is separately respectively: k=0,1,2,3.
The method of the present embodiment channel estimating, as shown in Figure 2, comprises the following steps:
Step 201: to the signal in the pilot frequency locations received, is the female code of pilot tone of 60 divided by sequence length, obtains signal x (n);
Signal x (n) obtained after performing this step, as shown in Figure 3; Wherein, abscissa represents the position of each signal, and ordinate represents the intensity of each signal.
Step 202: afterbody is carried out to signal x (n) and is connected process, obtain signal f (n);
Here, according to the convenient rule implemented of IDFT function, select L=10, and construct z kl () is four sections of straight lines, afterbody is become to be connected signal z (l) by the signal decussate structure of four sections of straight lines afterwards, and the afterbody constructed is connected the afterbody that signal z (l) adds signal x (n) to, obtain signal f (n), as shown in Figure 4, the sequence length of signal f (n) is 100, wherein, abscissa represents the position of each signal, and ordinate represents the intensity of each signal.
Step 203: IDFT process is carried out to signal f (n), obtains time-domain signal g (n);
Here, as shown in Figure 5, the sequence length of time-domain signal g (n) is 100 to time-domain signal g (n); Wherein, abscissa represents the position of each signal, and ordinate represents the intensity of each signal;
Time-domain signal g (n) comprises the equivalent time domain impulse response signal of four user terminals.
Step 204: carry out the process being separated multi-user to time-domain signal g (n), obtains the equivalent time domain response g of each user k(n);
Here, the position coordinates of four user terminals in g (n) is respectively: 0,25,50,75; Select N f=9, N b=5, make p kequal 25,50 and 75 respectively, from signal g (p k) before take out 9 signals, from behind take out 5 signals, the signal of other position is all set to zero, and line delay process of going forward side by side, can obtain g respectively 1(n), g 2(n) and g 3(n), and in conjunction with g 0n the building method of (), can obtain the equivalent time domain response g of four user terminals k(n).
Step 205: to the equivalent time domain response g of each user terminal kn () carries out the process of stress release treatment, obtain signal
Particularly, according to characteristic of channel parameter and average power P n, noise threshold is set; Compare g successively kthe power of 15 non-zero signal and the size of noise threshold in the sequence of (n), if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting; To four g kn () all carries out above-mentioned process respectively, obtain respectively: and sequence length be 100, wherein, signal that is: the time-domain signal of first user terminal as shown in Figure 6, and wherein, abscissa represents the position of each signal, and ordinate represents the intensity of each signal;
Before noise threshold is set, needs process time-domain signal g (n) being carried out to noise power estimation, obtain average power;
Particularly, when performing step 204, K (N has been taken out from time-domain signal g (n) f+ N b+ 1), i.e. 4 × (9+1+5)=60 sample, therefore, also remaining 40 samples, calculate the average power P of these 40 samples n.
Step 206: right carry out DFT process, obtain frequency-region signal h k(n);
Here, frequency-region signal h kn the sequence length of () is 100.
Step 207: to frequency-region signal h kn () carries out the process of frequency domain truncation, obtain the channel estimation Signal of each user, terminates current handling process;
Particularly, frequency-region signal h is removed kn 40 signals of () afterbody, only retain 60 signals above, obtain the channel estimation Signal of this user terminal;
To four h kn () all carries out above-mentioned process respectively, obtain the channel estimation Signal of four users;
Fig. 7 illustrates channel estimating real part curve on 60 subcarriers of first user terminal and desirable channel estimating real part curve, and wherein, abscissa represents the position of each signal, and ordinate represents the intensity of each signal; Curve 1 represents desirable channel estimating real part curve, curve 2 represents the channel estimating real part curve adopting the inventive method to obtain, as can be seen from the figure, curve 2 is very large with the degree of agreement of curve 1, illustrate and adopt method of the present invention, the channel estimating of each user terminal can well be obtained.
For realizing said method, present invention also offers channel estimating apparatus in a kind of ofdm system, this device as shown in Figure 8, comprising: pilot processing unit 81, afterbody are connected unit 82, IDFT unit 83, multi-user's separative element 84, DFT unit 85 and frequency domain truncation unit 86; Wherein,
Pilot processing unit 81, for carrying out the process eliminating the female code of pilot tone to the pilot signal received, and sends to afterbody to be connected unit 82 signal after process;
Afterbody is connected unit 82, for after the signal receiving pilot processing unit 81 transmission, carries out the process of afterbody linking to the received signal, and the signal after process is sent to IDFT unit 83;
IDFT unit 83, for after the signal receiving the transmission of afterbody linking unit 82, carries out the process of IDFT to the received signal, and the signal after process is sent to multi-user's separative element 84;
Multi-user's separative element 84, for after the signal receiving IDFT unit 83 transmission, carries out the process being separated multi-user to the received signal, and the signal after process is sent to DFT unit 85;
DFT unit 85, for after the signal receiving multi-user's separative element 84 transmission, carries out the process of DFT to the received signal, and the signal after process is sent to frequency domain truncation unit 86;
Frequency domain truncation unit 86, for after the signal receiving DFT unit 85 transmission, carries out the process of frequency domain truncation to the received signal, obtains the channel estimation Signal of each user terminal.
Wherein, described device can further include:
Noise canceling unit 87, for after the signal receiving multi-user's separative element 84 transmission, carries out the process of stress release treatment to the received signal, and the signal after process is sent to DFT unit 85;
Described multi-user's separative element 84, also for the signal after process is sent to noise canceling unit 87;
Described DFT unit 85, for after the signal receiving noise separation unit 87 transmission, carries out the process of DFT to the received signal, and the signal after process is sent to frequency domain truncation unit 86.
Described device can further include: dispensing unit, for adopting the female code of identical pilot tone, being multiplied by different phase rotatings respectively, obtaining the pilot signal of each user terminal.
Described noise canceling unit 87, can also comprise:
Statistical module, for add up IDFT unit 83 process after the average power of residual signal of signal after multi-user's separative element 84 processes, and the average power obtained is sent to module is set;
Module is set, for after the average power receiving statistical module transmission, noise threshold is set;
Processing module, for comparing the power of non-zero signal in the signal that receives and the size of noise threshold, if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting, and the signal after process is sent to DFT unit 85.
Described afterbody is connected unit, specifically for:
The frequency-region signal structure K section after eliminating the female code of pilot tone is adopted to have the curve signal of continuity and differentiability, and K section curve signal is added to the afterbody of the frequency-region signal after the female code of described elimination pilot tone, make the frequency domain two ends of mixed channel response signal keep continuously, described K value is the user terminal number of transmitting pilot signal simultaneously.
The above, be only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention, and all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (10)

1. a channel estimation methods in OFDM (OFDM) system, it is characterized in that, the method comprises:
The pilot signal received carried out eliminating the female code of pilot tone successively, afterbody is connected, inverse discrete Fourier transform (DFT) (IDFT), be separated the process of multi-user, discrete Fourier transform (DFT) (DFT) and frequency domain truncation, obtain the channel estimation Signal of each user;
The described pilot signal to receiving is carried out afterbody and is connected process, is specially:
The frequency-region signal structure K section after eliminating the female code of pilot tone is adopted to have the curve signal of continuity and differentiability, and K section curve signal is added to the afterbody of the frequency-region signal after the female code of described elimination pilot tone, make the frequency domain two ends of mixed channel response signal keep continuously, described K value is the user terminal number of transmitting pilot signal simultaneously;
The described process carrying out separation multi-user, is specially:
Position coordinates in time-domain signal g (n) making a kth user obtain after IDFT process is:
k=0,1 ..., K-1; Wherein, M is the sequence length of the female code of pilot tone;
When k ≠ 0, construct the equivalent time domain impulse response signal g of each user kn the method for () is:
From signal g (p k) before take out N findividual signal, takes out N from behind bindividual signal, signal all zero-addings of other position, and carry out time delay processing, then obtain:
g k(n)＝[g(p k),g(p k+1),...,g(p k+N B),0,0,...,0,g(p k-N F),...,g(p k-1)]；
As k=0, structure g 0n the method for () is:
g 0(n)＝[g(0),g(1),...,g(N B),0,0,...0,g(M+KL-N F),...,g(M+KL-1)]；
The described process carrying out frequency domain truncation, is specially:
By frequency-region signal h kn in (), the length of afterbody is that KL signal all cuts out, only the length retained above is M signal, obtains the channel estimation Signal of a kth user.
2. method according to claim 1, is characterized in that, before carrying out DFT process, the method comprises further:
The time-domain signal obtained after separation multi-user process is carried out to the process of stress release treatment, obtain carrying out the signal needed for DFT process.
3. method according to claim 1 and 2, is characterized in that, before receiving pilot signal, the method comprises further:
Ofdm system retrains the pilot signal that each user terminal is launched;
Describedly to retrain, be specially:
Adopt the female code of identical pilot tone, be multiplied by different phase rotatings respectively, obtain the pilot signal of each user terminal.
4. method according to claim 3, is characterized in that, described phase rotating is specially:
If there is K user terminal transmitting pilot signal simultaneously, the phase rotating of K user terminal is respectively k=0 ..., K-1, n=0 ...., M-1.
5. method according to claim 1, is characterized in that, the described afterbody constructing K section curve signal, K section curve signal is added to frequency-region signal, is specially:
Take out signal separately from the head position of the frequency-region signal after eliminating the female code process of pilot tone and tail position, construct the curve of one section of continuity and differentiability, K user then constructs K section continually varying curve respectively;
The signal of K section curve is staggeredly placed, is merged into required afterbody and is connected signal;
Described afterbody linking signal is engaged on after the frequency-region signal after the female code of described elimination pilot tone, obtains afterbody and be connected the signal after processing.
6. method according to claim 2, is characterized in that, described in carry out the process of stress release treatment, be specially:
Noise threshold is set;
Compare the power of non-zero signal and the size of noise threshold in the signal after being separated multi-user's process successively, if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting.
7. a channel estimating apparatus in ofdm system, is characterized in that, this device comprises: pilot processing unit, afterbody are connected unit, IDFT unit, multi-user's separative element, DFT unit and frequency domain truncation unit; Wherein,
Pilot processing unit, for carrying out the process eliminating the female code of pilot tone to the pilot signal received, and sends to afterbody to be connected unit the signal after process;
Afterbody is connected unit, for after the signal receiving pilot processing unit transmission, carries out the process of afterbody linking to the received signal, and the signal after process is sent to IDFT unit;
IDFT unit, for after the signal receiving the transmission of afterbody linking unit, carries out the process of IDFT to the received signal, and the signal after process is sent to multi-user's separative element;
Multi-user's separative element, for after the signal receiving the transmission of IDFT unit, carries out the process being separated multi-user to the received signal, and the signal after process is sent to DFT unit;
DFT unit, for after the signal receiving the transmission of multi-user's separative element, carries out the process of DFT to the received signal, and the signal after process is sent to frequency domain truncation unit;
Frequency domain truncation unit, for after the signal receiving the transmission of DFT unit, carries out the process of frequency domain truncation to the received signal, obtains the channel estimation Signal of each user terminal;
Described afterbody is connected unit, specifically for:
The frequency-region signal structure K section after eliminating the female code of pilot tone is adopted to have the curve signal of continuity and differentiability, and K section curve signal is added to the afterbody of the frequency-region signal after the female code of described elimination pilot tone, make the frequency domain two ends of mixed channel response signal keep continuously, described K value is the user terminal number of transmitting pilot signal simultaneously;
The described process carrying out separation multi-user, is specially:
Position coordinates in time-domain signal g (n) making a kth user obtain after IDFT process is:
k=0,1 ..., K-1; Wherein, M is the sequence length of the female code of pilot tone;
When k ≠ 0, construct the equivalent time domain impulse response signal g of each user kn the method for () is:
From signal g (p k) before take out N findividual signal, takes out N from behind bindividual signal, signal all zero-addings of other position, and carry out time delay processing, then obtain:
g k(n)＝[g(p k),g(p k+1),...,g(p k+N B),0,0,...,0,g(p k-N F),...,g(p k-1)]；
As k=0, structure g 0n the method for () is:
g 0(n)＝[g(0),g(1),...,g(N B),0,0,...0,g(M+KL-N F),...,g(M+KL-1)]；
The described process carrying out frequency domain truncation, is specially:
By frequency-region signal h kn in (), the length of afterbody is that KL signal all cuts out, only the length retained above is M signal, obtains the channel estimation Signal of a kth user.
8. device according to claim 7, it is characterized in that, this device comprises further: noise canceling unit, for after the signal receiving the transmission of multi-user's separative element, carry out the process of stress release treatment to the received signal, and the signal after process is sent to DFT unit;
Described multi-user's separative element, for after the signal receiving the transmission of IDFT unit, carries out the process being separated multi-user to the received signal, and the signal after process is sent to noise canceling unit;
Described DFT unit, for after the signal receiving the transmission of noise separation unit, carries out the process of DFT to the received signal, and the signal after process is sent to frequency domain truncation unit.
9. the device according to claim 7 or 8, is characterized in that, this device comprises further: dispensing unit, for adopting the female code of identical pilot tone, being multiplied by different phase rotatings respectively, obtaining the pilot signal of multiple user terminal.
10. device according to claim 8, is characterized in that, described noise canceling unit comprises further:
Statistical module, for adding up the average power of the residual signal of the signal after IDFT cell processing after the process of multi-user's separative element, and sends to the average power obtained and arranges module;
Module is set, for after the average power receiving statistical module transmission, noise threshold is set;
Processing module, for comparing the power of non-zero signal in the signal that receives and the size of noise threshold, if power is greater than noise threshold, then this signal retains, otherwise, be zero by this signal setting, and the signal after process is sent to DFT unit.
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