CN101129007A - Channel estimation method for TDD-CDMA system - Google Patents
Channel estimation method for TDD-CDMA system Download PDFInfo
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- CN101129007A CN101129007A CNA2005800486485A CN200580048648A CN101129007A CN 101129007 A CN101129007 A CN 101129007A CN A2005800486485 A CNA2005800486485 A CN A2005800486485A CN 200580048648 A CN200580048648 A CN 200580048648A CN 101129007 A CN101129007 A CN 101129007A
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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
- H04L25/0212—Channel estimation of impulse response
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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
- H04L25/024—Channel estimation channel estimation algorithms
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
Abstract
The present invention relates to a kind of channel estimation methods of TDD-SCDMA system,Include the following steps: estimation while the channel impulse response for a time slot for completing each user using Steiner estimator,The original time domain discrete channel impulse response h n of all users is obtained,K=[hn,K,1,Hn,K,2,.. hn,K,W],K=1,2,..,K; Each tap decision metric tn of time slot n is calculated each user,K,I=α tn-1,K,I+ (1- α) | hn,K,I | 2,K=1,2,..,K,All taps obtain tn,K=[tn,K,1,Tn,K,2,.. tn,K,W]; Elongated degree multi-slot sliding average is carried out to each tap of the time slot n of each user k,Obtain average value
, i=1,2.., W, all taps obtain
, k=1,2.., K; The time slot n of each user is carried out to filter out noise tap processing, obtains hn, k, i '; It exports a user k and believes the road n estimated value hn, k ' in time slot; It repeats the above steps, until obtaining the channel estimation value of all users.
Description
The channel estimation methods technical field of TDD-CDMA systems
The present invention relates to a kind of TDD-CDMA (Time Division Duplex-Code Division Multiple Access, time division duplexing-CDMA）The channel estimation methods of system, more particularly to a kind of use training sequence carries out the channel estimation methods of the TDD- CDMA systems of channel estimation, TD-SCDMA the and WCDMA TDD systems in all systems of channel estimation, especially suitable 3-G (Generation Three mobile communication system) are carried out using training sequence suitable for TDMA/CDMA.Background technology
By taking TD-SCDMA (Time Division-Synchronous Code Division Multiple Access) system as an example, as a kind of cell mobile communication systems, there is following several interference and noise in TD-SCDMA system：1st, due to may be simultaneously present multiple Code Channel transmission in same time slot, under the conditions of mobile channel, orthogonality between Code Channel is by partial destruction, multi-access inference, i.e. MAI (Multiple Access Interference) can be formed between receiving terminal Code Channel;2nd, due to the multipath transmisstion of signal, intersymbol interference, i.e. ISI (Inter-Symbol Interference) can be formed in receiving terminal;3rd, the thermal noise of receiver；4th, thousand from other cells disturb；5th, other interference.
The demodulation performance of TD-SCDMA system is general by meeting certain QOS (Quality of Service, service quality）When receiver required for SIR (Signal to Interference Ratio, signal interference ratio）Or SNR (Signal to Noise Ratio, signal to noise ratio）Is represented, due to honeycomb CDMA (Code Division Multiple Access, CDMA）In system, statistical property of the interference with similar white noise, therefore do not distinguish interference and noise strictly typically.In order to obtain good demodulation performance, it is desirable to which demodulating algorithm has good interference rejection capability.Stronger to the rejection ability of interference, systematic function is better, can carry
The utilization ratio of the frequency spectrum of confession is higher.Therefore, interference mitigation technology turns into the key factor for improving TD- SCDMA performances.
Code design, frame structure, spreading rate of TD-SCDMA system etc. provide feasibility for interference mitigation technology.Associated detection technique is one of TD- SCDMA key technology, associated detection technique is applied in TD- SCDMA systems, MAI and ISI can effectively be suppressed, associated detection technique is built upon on the basis of channel estimation, the effect of channel estimation has particularly important influence to combined detection performance, and good channel estimation technique turns into the necessary condition for determining joint-detection.Generally, wireless mobile environment is modeled as finite length impulse response model, and the task of channel estimation is exactly the amplitude and phase for estimating each time delay tap.Requirement of the multipath transmisstion of signal to channel estimation is very high under wireless mobile environment, and accurate channel estimation how is obtained under complicated channel propagation conditions turns into the key of TD-SCDMA technology.
The method of estimation of existing TD-SCDMA system mainly has following several：
1st, stainer（Steiner) method of estimation
In existing TD-SCDMA systems, the training sequence of all users of same cell is all by a basic, training sequence midamble that the cycle is P, produced by way of cyclic shift, and corresponding channel impulse method of estimation is typically all to use Steiner methods of estimation.Channel estimation methods in this way are commonly referred to as Steiner estimators, and its estimation principle is the channel impulse response for once calculating all users by solving system of linear equations using least square method.Because the training sequence of TD-SCDMA system has cyclic shift characteristic, therefore a correlator can be used when calculating the channel impulse response of each user, efficient, quick implementation method such as FFT (Fas t Fourier Transfer, Fast Fourier Transform (FFT) can be used when implementing）With IFFT (Inverse Fas t Four ier Transfer, inverse fast Fourier transform）, complicated linear convolution is converted into simple cyclic convolution, the algorithm complex and cost of channel estimation can be reduced.But, the performance of Steiner estimators is influenceed by receiving terminal additive noise, and its obtained channel impulse response is compared with ideal communication channel impulse response, comprising noise component(s), this
Namely channel estimation errors Producing reason；Noise power can be expanded simultaneously, cause output end signal to noise ratio relative input end to have a certain amount of loss so that channel impulse response estimation hydraulic performance decline.What Ste iner estimators were calculated is the subscriber channel impulse response estimate of a time slot.Limited by transport overhead, training sequence in one time slot can not be oversize, its performance is influenceed by receiving terminal additive noise and causes precision of channel estimation to be lost, if the decline without any processing that systematic function is directly inevitably resulted in using its estimated result.
2nd, the processing method of the noise reduction of threshold judgement is crossed
Referring to document《Impact of Channel Est imat ion on the 3GPP- TD - CDMA》, Ol iver Prator etc. write, GLOBECOM ' Ol IEEE:The Hes of 3365-3369 vol. 6《The improvement of low-cost channel estimation methods in TD-SCDMA systems》Kang Shaoli, attacks the work such as positive definite,《Communicate journal》, 2002,23 (10)： 125-130.Its basic thought is first to estimate original channel impulse response with Steiner methods of estimation, then with a thresholding, filter out there is no signal in the obtained channel impulse response tap of estimation and be entirely noise contribution tap.The amount of calculation of very little is merely add in this way, and channel estimating performance can be made to obtain certain improvement.
This method on the basis of the Ste iner estimators by there is no signal in channel impulse response tap that the threshold filter Steiner estimators of setting are obtained and be entirely noise contribution tap.It is each multipath composition when receiver is reached after signal is propagated by mobile radio channel that each tap for the channel impulse response that Steiner estimators are obtained is corresponding, if in tap without signal only noise, the merging that then this tap should be just filtered out without participating in multipath, otherwise what is be merged is noise, and the detection to useful signal will produce interference.But this method still do not overcome existing method 1 used a time slot instantaneous estimation defect, therefore there are two shortcomings：First, the noise in channel impulse response in the tap containing signal is not inhibited, and the noise being superimposed upon on signal causes the deterioration of signal detection performance；Second, the filtering method of noise tap is excessively simple, invalid to instantaneous very noisy, and what is be not filtered out strong makes an uproar
Sound can be mistaken for signal, so that interferer signal detection, causes penalty.
3rd, zero correlation window code method
The method that this method is proposed is used as training sequence using midamble codes as defined in the existing TD- SCDMA standards of zero correlation window code substitution, the code character of different zero correlation length how much is used according to the number of user in system, a small amount of shifting function can be carried out to the pilot tone in user's time slot, if using smart antenna, can also be according to the position of user, the angle of arrival configuration of signal, make angle of arrival neighboring user configuration cross-correlation have wider zero correlation window code sequence, reduce system in channel estimation interference.
Because this method employs the zero correlation window code different from existing TD-SCDMA standards as training sequence, the influence that the cross correlation existed between user's training sequence is caused to channel estimation is reduced, so as to reach the purpose for improving channel estimating performance.But this method have two shortcomings ' first is, it is necessary to which complicated training sequence allocation algorithm, multiple parallel correlators, cost is very high, and efficient, quick algorithm can not be used to realize；Second, this technical scheme and existing TD- SCDMA standards are incompatible.The content of the invention
It is an object of the invention to provide a kind of channel estimation methods of TDD- cdma systems, interference of the noise to signal in TDD-cdma system can be reduced, the interference of instantaneous very noisy can effectively be suppressed, can be efficient, quick and inexpensive realize the high performance channel estimators of TDD-CDMA, and strengthen the suppression deviation capability of TDD- CDMA systems, and it is compatible with current standard, without changing existing standard.
To achieve the above object, the invention provides a kind of channel estimation methods of TDD-SCDMA systems, it is characterised in that comprises the following steps：
Estimate while step 1, the channel impulse response for a time slot for completing using Ste iner estimators each user, obtain the original time domain discrete channel impulse response H of all users, H], k-, 2, K, " it is time-gap number, is Customs Assigned Number, be user
Number, is channel impulse response length；
Step 2, each user is calculated time slot n each tap decision metric=-+(1-) | f, k=, 2 ..., K, all taps obtain tnk^,. nt WStep 3, each tap to each user k time slot n carry out becoming length multi-slot moving average, obtain average value
K=l, 2 ,-, K. steps 4, the time slot n of each user is carried out to filter out noise tap processing, obtain/step 5, one user k of output is in time slot letter n road estimate h' ";Step 6, repeat step 1-5, the channel estimation value until obtaining all users.
In the step 3
, J is the number of time slots for being weighted moving average,
J value between 1-16,.〈 ^.When static or walking communication, value is 0.2 ~ 0.5;During high-speed mobile communications, value is 0.5 0.9.
The step 4 is specially：
Step 4.1, calculating noise gate Γ;Step 4.2, the time slot to each user carry out filtering out noise tap processing, and the tap is set to 0 if noise gate is less than after the channel estimation modulus of a tap is squared, otherwise retains tap ni AWork(of making an uproar is
Boltzmann constant, is absolute temperature, and S is signal bandwidth, is receiver noise factor.
Therefore, the present invention has advantages below：
1st, ^ interference of the noise to signal is dropped, can effectively suppress the interference of instantaneous very noisy.
2nd, efficient, quick, inexpensive method can be used to realize high performance channel estimator.
3rd, deviation capability is suppressed strong.
4th, compatible current standard, without changing existing standard.
With reference to the accompanying drawings and examples, technical scheme is described in further detail.Brief description of the drawings
Fig. 1 is the method flow diagram of the channel estimation methods of TDD-SCDMA systems of the present invention.
Fig. 2 for the channel estimation methods of TDD-SCDMA systems of the present invention user in time slot " original channel impulse response each tap calculation decision metric handle schematic diagram.
Fig. 3 for the channel estimation methods of TDD- SCDMA systems of the present invention user * in time slot " the estimation of original transient channel carry out becoming the schematic diagram that length multi-slot average is handled.
Fig. 4 for TDD-SCDMA systems of the present invention channel estimation methods calculating user in time slot " channel impulse response flow chart.Embodiment
The invention thought of the present invention is to provide a kind of new TDD-CDMA channel estimation methods, from reception from multiple mobile stations or base station be superimposed with the digital spread spectrum signal of multiple subscriber signals and noise and interference in extract training sequence symbols, utilize the training sequence symbols of each locally generated user of base station receiver or mobile station receiver, estimate channel impulse response of each user in a time slot, then the channel impulse response of the multiple time slots of same user is handled, to reduce the influence of noise, improve the precision of channel impulse response estimation.
As shown in figure 1, be flow chart of the method for the present invention, channel impulse response estimation of the present invention
Method is as follows:Estimate while step 1, the channel impulse response for a time slot for completing each user using S t e i ne r estimators, obtain the original time domain discrete channel impulse response of Κ user：
Formula（1) in, " it is time-gap number, is Customs Assigned Number, be number of users, be channel impulse response length, depending on the multi-path delay spread of mobile radio channel, such as TD- SCDMA systems, W typical value scope is 4 ~ 32 chips.
Step 2, to each user calculate time slot " each tap decision metric：
T, * 2 " ", ^], k=l, in 2 ..., K (2) formula (2),
,,=<^"— +G— i=\,2,...,W ? k=\,2,...,K (3)
(4)
Formula（3) " it is forgetting factor, 0 in<"<1 ,-as value be 0.1 ~ 0.95.Because this step employs the processing method of noncoherent accumulation, it is possible to increase the ability of the anti-frequency deviation of channel estimation.
Shown in Figure 2, be the user * of channel estimation methods of present system in time slot " original channel impulse response each tap calculation decision metric processing schematic diagram.Including：Individual modulus and squared arithmetic unit 202-1 ~ 202- W;1 ~ 203- of individual multiplier 203- W;Individual multiplier 204-1 ~ 204-W;The individual 205-W of adder 205- 1;Individual delayer 206-1 ~ 206- W, the output of delayer is than one time slot of input time delay.Input 201-1 ~ 201- WΑ" ",Α" ", Α, ^ is the user * that is obtained by Steiner estimators in time slot " original channel impulse response.Containing an identical processing procedure in this figure, its processing procedure is described by taking first processing procedure as an example, other processes are identical therewith.Modulus and squared arithmetic unit 202-1 is to time slot " original channel estimation first tap carry out modulus
And squared computing obtains l wl2, multiplier 203-1 obtains α to multiplying a coefficient) and .*, ι |, on the other hand, 204-1 pairs of the multiplier of the previous time slot of delayer 206-1 outputswMultiply a coefficient " obtain, adder 205-1 multiplier 203-1 output is added with multiplier 204-1 output obtain user * in time slot " first tap decision metric
^·1=α^·' + (1"α) ·*·1Ι, finally, above-mentioned identical processing procedure export user in time slot " channel impulse response individual tap decision metric=[ί", ", ^.2, ^]。
Step 3, each tap to each user * time slot η carry out becoming length multi-slot moving average： (5)
hn-j,k,i = 0^ "~j≤0 , i = \,2,...,W ? k = \,2,...,K (6)
L;*
, k=, 2 ..., K (7) formula（5) in, moving average length is the number of time slots for being weighted moving average, is plus the religion of wooden fork system.Moving average length J contains two kinds of possible situations：Single time slot services and multislot services.For single time slot services, ■ is equal to participate in moving average number of sub-frames, and for multislot services, J is relevant in the timeslot number that a sub- frame in is distributed with moving average number of sub-frames and multislot services.Depending on speed of the J value according to channel variation, the user moved for low speed communicates, value is larger can to obtain good suppression noise immune during for example static or walking；For the user of high-speed mobile, such as the communication in the vehicle of traveling, J values are smaller to obtain the satisfied quick change of adaptive channel while suppressing noise immune.Span can be with unrestricted, but its value is 1 ~ 16 under normal circumstances.Value it is also graceful relevant with the fast ^ of channel variation, such as a kind of possible value is as follows：
Formula（8) in, O ^, the user moved for low speed communicates during for example static or walking, P
Value is 0. 2 ~ 0. 5;For the user of high-speed mobile, such as the communication in high speed row ^ vehicles, value is 0. 5 ~ 0. 9.
Shown in Figure 3, be user * of the present invention in time slot " the estimation of original transient channel become the schematic diagram of length multi-slot average processing.To user in time slot " the estimation of original transient channel carry out becoming the processing of length multi-slot average, including：Individual multiplier 302-0 ~ 302-J;J delayer 303-1 ~ 303-J, the output of delayer is than one time slot of input time delay；1 adder 304.Input 101=[the original channel estimation that ^, ^2, ^ are each users for being obtained by ste iner estimators in a time slot " original channel impulse response, to time slot "h" .* all tap ^^, " " ..., multiplier 302-0 ~ 302- J each tap ζ (= 1'2'-' ^) channel estimation .' and the original channel of preceding J time slot of tap of individual delayer 303-1 ~ 303-J output estimate A-W, " A-w is multiplied with corresponding weight coefficient, obtains Cj-j, 7'=1,2, " ', J, then adder 304
, i=U 2 ..., W ^ it is final user * in time slot " multi-slot average after channel estimation 305 h, k
k = l, 2, ..., K。
Step 4, the time slot n to each user carry out filtering out noise tap processing
Formula（9) in,：Γ is noise filtering thresholding, is set according to actual working environment, for example it is a kind of can obtaining value method it is as follows：
T = \0logl0(Pnoise)+offset formulas（10) in, ".- it is that bottom is made an uproar power, by measuring receiver, when not receiving signal, measurement is obtained, can also be according to following formula（11) calculate and obtain.Ρ--- through determining typically adjust.^ is the offset of power of being made an uproar the bottom of relative to, and its span is unrestricted, generally can by Computer Simulation or
Person's experiment obtains optimal value.
Pnoise = KTB + NF (1 1)
Formula（11) it is Boltzmann constant in,
, Γ is absolute temperature, is signal bandwidth, is receiver noise factor.Unit be it is burnt/open（ J/K ), ：Γ unit is out（Κ), unit is hertz（), Hz unit is decibel（dB ).
Step 5, output user are in time slot " channel estimation valueh'".* :
h'",t =[ w'A,* 〗 （12)
It is shown in Figure 4, be the present invention calculate user in time slot " channel impulse response flow chart.According to formula（8) calculate noise filtering thresholding, from tap=1, judge user in time slot " channel impulse response each tap!' whether meet1QlDgl。(U> :rIf it is determined that setting up, then retain the channel estimation of the tap, i.e.=, otherwise tap is set to 0, tap counts device is incremented by after a tap is disposed, until all taps are disposed, finally output user is in time slot, and " channel estimation value step 6, above step are the operations to a user, repeat the secondary channel estimation for obtaining all users.
The present invention is a kind of efficient, quick, inexpensive combination channel estimating method for being applicable TDD-SCDMA standards, on the basis of Steiner estimators, employ the processing method that a kind of multi-slot processing is combined with noncoherent accumulation, overcome the defect of prior art, reduce interference of the noise to signal, the interference of instantaneous very noisy can effectively be suppressed, while also having good anti-frequency deviation performance.The channel estimation methods of the present invention add the amount of calculation of very little on the basis of S teiner estimators, and efficient, quick, inexpensive method can be used to realize high performance channel estimator.
Therefore this method has the following advantages：First, noise is reduced to the interference of signal and can effectively suppress the interference of instantaneous very noisy；Second, with good anti-frequency deviation performance；3rd, height can be used
Effect, quick, low cost method realize high performance channel estimator.4th, compatible current standard, without changing existing standard.
It is suitable for all systems of channel estimation are carried out in TDMA/CDMA using training sequence, it is especially adapted for use in TD-SCDMA the and WCDMA TDD systems in 3-G (Generation Three mobile communication system), although technical scheme is mainly for TDD-SCDMA wireless communication system, but it is applied equally to CDMA, TDMA system using similar transmission structure, base station receiver is not only suitable for, mobile station receiver is also applied for.With reference to the measurement of correlation process of receiver, present aspect can be adaptively just blunt according to working environment dynamically-adjusting parameter.
It should be noted last that, the above embodiments are merely illustrative of the technical solutions of the present invention and it is unrestricted, although the present invention is described in detail with reference to preferred embodiment, it will be understood by those within the art that, technical scheme can be modified or equivalent substitution, without departing from the spirit and scope of technical solution of the present invention, it all should cover among scope of the presently claimed invention.
Claims (1)
- Claim1st, a kind of channel estimation methods of TDD-SCDMA systems, it is characterised in that comprise the following steps：Estimate while step 1, the channel impulse response for a time slot for completing using Steiner estimators each user, obtain the original time domain discrete channel impulse response of all users, k L, 2, K " is time-gap number, A:It is Customs Assigned Number, is number of users, is channel impulse response length；Step 2, each tap decision metric t for calculating each user time slot nn, i, k=, 2 ..., K, all taps obtain tn,k *,2,...υ ;Step 3, each tap to each user k time slot η carry out becoming length multi-slot moving average, obtain average value Ι ,=^ Α-w ,=1,2 ..., all taps are obtained！^^, ^ ... ^],7=0 ' , k = \,2,...,K\Step 4, the time slot n to each user carry out filtering out noise tap processing, obtain4；Step 5, one user k of output believe n road estimate h' in time slot,t;Step 6, repeat step 1-5, the channel estimation value until obtaining all users.2nd, the channel estimation methods of TDD-SCDMA systems according to claim 1, it is characterised in that in the step 3C/=..., J, J is the number of time slots for being weighted moving average,Value between 1-16,0<^<1o3rd, the channel estimation methods of TDD-SCDMA systems according to claim 2, it is characterised in that：When static or walking communication, value is 0.2 ~ 0.5;During high-speed mobile communications, value is 0.5-0.9. 4th, the channel estimation methods of TDD-SCDMA systems according to claim 1, it is characterised in that the step 4 is specially：Step 4. 1, calculating noise gate Γ;Step 4. 2, the time slot to each user carry out filtering out noise tap processing, and the tap is set to 0 if noise gate is less than after the channel estimation modulus of a tap is squared, otherwise retains the tap5th, the channel estimation methods of TDD-SCDMA systems according to claim 4, it is characterised in that：The noise gate^^^^ ^^+^^ ", P.,.reIt is that bottom is made an uproar power, o is the offset of power of being made an uproar the bottom of relative to.6th, the channel estimation methods of TD-SCDMA system according to claim 5, it is characterised in that：The power P of making an uproar being confused.ise=KTB+NF, are Boltzmann constants,：Γ is absolute temperature, is signal bandwidth, and NF is receiver noise factor.
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| PCT/CN2005/000404 WO2006102792A1 (en) | 2005-03-29 | 2005-03-29 | A method of channel estimate in tdd-cdma system |
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| CN106789769A (en) * | 2016-12-14 | 2017-05-31 | 北京邮电大学 | Channel prediction method and device |
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| DE19917334A1 (en) * | 1999-04-16 | 2000-10-26 | Siemens Ag | Channel estimation method for TD-CDMA mobile radio system |
| US7042926B2 (en) * | 2001-11-21 | 2006-05-09 | Intel Corporation | Low complexity multiuser detector |
| US20040203812A1 (en) * | 2003-02-18 | 2004-10-14 | Malladi Durga Prasad | Communication receiver with an adaptive equalizer that uses channel estimation |
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| CN106789769A (en) * | 2016-12-14 | 2017-05-31 | 北京邮电大学 | Channel prediction method and device |
| CN106789769B (en) * | 2016-12-14 | 2020-04-21 | 北京邮电大学 | Channel prediction method and device |
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