CN1791077A - Time-domain and frequency-domain combined channel estimating method - Google Patents

Time-domain and frequency-domain combined channel estimating method Download PDF

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CN1791077A
CN1791077A CN 200510112247 CN200510112247A CN1791077A CN 1791077 A CN1791077 A CN 1791077A CN 200510112247 CN200510112247 CN 200510112247 CN 200510112247 A CN200510112247 A CN 200510112247A CN 1791077 A CN1791077 A CN 1791077A
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channel
frequency
domain
time domain
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蔡凌云
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BEIHAO COMMUNICATION ELECTRONIC Co Ltd SHANGHAI
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BEIHAO COMMUNICATION ELECTRONIC Co Ltd SHANGHAI
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Abstract

The invention relates to an estimation method for time and frequency domain joint channel, which comprises: adding some pilot frequency between OFDM symbols with quantity related with channel variation feature; using known 144chip in every conventional time slot of TD-SCDMA system as pilot frequency to insert into opposite carrier by one-dimension interpolation; on receiver end, obtaining need channel response on every symbol time and every sub-carrier according to two inserted pilot frequencies, taking weighted-mean to estimated results to obtain final need channel response. This invention can improves channel reliability in TD-SCDMA system effectively.

Description

The method of a kind of time domain and frequency-domain combined channel estimating
[technical field]
The present invention relates to communication technique field, particularly compatible OFDM (Orthogonal Frequency Division Multiplexing, OFDM) method of time domain and frequency-domain combined channel estimating in the TD-SCDMA system of technology.
[background technology]
The TD-SCDMA standard recommendation is adopted as one of four standards of 3G (Third Generation) Moblie by ITU, is the important breakthrough of China at moving communicating field.The standard recommendation of TDD class is integrated into various advanced technologies easily, and as intelligent antenna technology, synchronization CDMA technology and software and radio technique etc., so TD-SCDMA technology has more advantage with respect to the standard of other 3G (Third Generation) Moblie.
The TD-SCDMA system of compatibility to OFDM tech adopts the OFDM technology in transmission course.OFDM (OFDM) technology is a kind of of multi-carrier transmission technology, it is divided into parallel convey on a plurality of quadrature carriers with information, because the orthogonality between the subcarrier in frequency domain, ofdm signal can be on the orthogonal sub-carriers of these overlappings parallel convey and not interfering with each other.If in subcarrier allocation, guarantee the amount of bandwidth of the width of each subcarrier less than the frequency selection, just can think on this subcarrier it is smooth, thereby can adopt better simply balancing technique.But channel estimating is indispensable, and is crucial, and it directly has influence on the demodulation performance of back level system.
In the mobile wireless environment, the response of the time-domain and frequency-domain of channel becomes when being; The frequency domain selectivity decline that multipath causes shows the inconsistency of decline on different subcarriers, make the inhomogeneities that occurs distortion on each data subcarrier of OFDM symbol.The purpose of channel estimating is exactly the response that estimates channel, and the data that receive are proofreaied and correct and recover.The noise of the maximum multipath time delay of channel, user's translational speed, receiver and the density of pilot tone all are the factors that influences the channel estimation method performance.
Mobile communication system utilizes signal processing technology to improve link performance in the abominable radio propagation environment.Because the influence of multipath fading and Doppler frequency shift, mobile radio channel are extremely variable.These influences all can produce very strong negative effect for any modulation technique.In addition, compare with additive Gaussian noise (AWGN) channel, mobile radio channel is bigger in the infringement that aspect distortion and the decline channel is caused, and is more obvious.In order to eliminate the influence of channel to whole communication system, with regard to the situation that must use channel estimation technique to follow the tracks of wireless channel, thereby eliminate the influence of channel to the transmission data at receiving terminal, the ability of raising system antagonism channel disturbance, reduce the generation of error code, receiving terminal just can recover needed data exactly.
OFDM is because of quite high one of the key technology of two-forty mobile communication system that becomes of its utilance to frequency spectrum resource.In order to reach the transfer of data of two-forty, just need in ofdm system, use the modulation system of several degree, leggy, simultaneously, be not subjected to the influence of communication channel multipath and fading effect for the performance that guarantees system, also to adopt the method for channel estimating to follow the tracks of the variation of channel response, and eliminate the influence of channel fading systematic function.This shows, in ofdm system channel estimation technique be related to system can operate as normal and influence one of deciding factor of systematic function.
For the OFDM mobile communication system, the data that system transmitted all will be subjected to the influence of channel multi-path fading effect, thereby influence the correctness of system in receiving terminal judgement data.If can follow the tracks of the characteristic of time domain channel well, just can eliminate the influence of channel at receiving terminal so to data.Channel impulse response can show the effects such as multipath fading of time domain channel better, and can be used for the overall performance of the synchronous scheduling algorithm of ofdm system with the raising system.So in the mobile communication system that adopts the OFDM technology, can utilize the impulse response of time domain estimation channel to eliminate the influence of multipath channel better to data.Simultaneously, in ofdm system, because the data of transmitting terminal and receiving terminal all are frequency domain datas, so the frequency characteristic of channel will produce more directly influence to data.The frequency response of channel can reflect characteristics such as the decline of channel and frequency selectivity well, so estimate that at frequency domain channel response can eliminate the direct influence of channel frequency domain characteristic to data.
Therefore, in general, characterize mobile telecommunication channel and can also can use the frequency response of channel with the impulse response of channel.Estimate the impulse response of channel and estimate that at frequency domain the frequency response of channel has characteristics separately in time domain.Channel impulse response estimation can reflect the influence of multipath effect better, and estimated frequency response can more directly be applied to the system that utilizes the OFDM technology.If time domain channel estimation and frequency domain channel are estimated to combine, so not only can reflect the effects such as multipath of channel, and can eliminate the direct influence of frequency domain channel to data.
The OFDM technology being applied in the TD-SCDMA system, how effectively utilizing the characteristics of the information of TD-SCDMA system and OFDM technology to design the method for channel estimating, improving the reliability of channel estimating, is to need the problem that solves.
[summary of the invention]
The technical problem to be solved in the present invention is to provide the method for channel estimating in a kind of mobile communication system, with channel reliability in the TD-SCDMA system that improves compatibility to OFDM tech, eliminates the influence of channel to whole communication system.
For solving the problems of the technologies described above, the present invention is achieved in that
TD-SCDMA system configuration characteristics according to compatibility to OFDM tech, some information characteristics of TD-SCDMA system are applied in the middle of the OFDM channel estimating, utilize two parts information of time domain and frequency domain to unite the realization channel estimating, promptly adopt time-frequency combination channel estimating method, it may further comprise the steps:
Add the pilot tone of some between the OFDM symbol, concrete pilot number is relevant with the variation characteristic of channel; Be channel variation when fast, it is many that pilot tone adds, and channel variation is when slow, and it is fewer that pilot tone adds.Pilot tone can be selected the reasonable sequence of orthogonality;
Simultaneously, utilize in the TD-SCDMA system each conventional time slot to have that training is long to be 144chip, this part information is known, therefore, can utilize it to be inserted on the corresponding subcarrier as the pilot tone of frequency domain, and the mode that adopts one dimension to insert.
Obtain the required channel response on each each subcarrier of symbol moment in pilot tone that receiving terminal inserts by time domain at first respectively and the pilot tone that inserts again and again;
Again time domain and frequency domain results estimated are drawn the final required channel response on each each subcarrier of symbol moment by a weighted average.
Compared to prior art, the present invention has the following advantages:
Can obtain the characteristic of time domain channel by the pilot tone of time domain;
Can obtain the characteristic of frequency domain channel by the pilot tone of frequency domain;
Utilize channel estimation methods that time-frequency domain combines can be better in conjunction with utilizing time domain channel and frequency domain channel to the influence that frequency domain data produced, thereby help improving the performance of the TD-SCDMA system of compatibility to OFDM tech;
Can make full use of the training sequence information in the conventional time slot in the TD-SCDMA system;
The channel estimating that combines by time domain and frequency domain can effectively suppress additive white Gaussian noise;
Can by add Cyclic Prefix (Cyclic Prefix, CP), the channel estimation methods that time domain and frequency domain combine can also effectively be subdued intersymbol interference (ISI);
Under abominable multipath Rayleigh decline mobile channel, the channel estimation methods that time-frequency domain combines still can keep good estimated performance;
The channel estimating that time domain and frequency domain combine can provide certain gain for decoding module.
[description of drawings]
Fig. 1 is the conventional structure of time slot schematic diagram in the TD-SCDMA of the present invention system.
Fig. 2 is an one dimension pilot signal distribution map.
Fig. 3 is a channel estimation process schematic diagram of the present invention.
[embodiment]
Channel estimation methods is the characteristics according to OFDM technology and TD-SCDMA system in the TD-SCDMA system of the compatibility to OFDM tech that the present invention proposes, combine the advantage that time domain is estimated and frequency domain is estimated, adopt the TD-SCDMA system of the very suitable compatibility to OFDM tech of the method for sending out of time domain and frequency domain combined channel estimating can improve the reliability of system greatly.
The FB(flow block) of the channel estimation methods that the present invention proposes as shown in Figure 1.
Add the pilot tone of some between the OFDM symbol, concrete pilot number is relevant with the variation characteristic of channel; Be channel variation when fast, it is many that pilot tone adds, and channel variation is when slow, and it is fewer that pilot tone adds.Pilot tone can be selected the reasonable sequence of orthogonality.Owing to adopt the OFDM transmission, can transmit more speed by bearing ratio TD-SCDMA, therefore,, for the OFDM transmission, the regular hour redundancy is just arranged in order to guarantee identical speed, this part just is used for adding pilot tone.Time domain pilot inserts to be needed to satisfy
f D max · T s · N k ≤ 1 / 2 . . . ( 1 )
F wherein DmaxBe maximum doppler frequency, T sBe symbol lengths, N kBe pilot signal interval in time.
Can obtain n the pairing time domain channel response of symbol by estimation to time domain channel,
h n = Σ l = 1 L α ( l ) h [ l - d ( l ) ] ( n = - ∞ , + ∞ ) . . . ( 2 )
Wherein α (l) is the amplitude of l root multipath, and d (l) is the time-delay of l root multipath, and L is the quantity of multipath.
Then can obtain the channel response of frequency domain through Fourier transform for the time domain channel response of estimating by time domain to obtain
H n ( k ) = Σ l = 1 N h n e - j 2 πlk N
= Σ l = 1 N Σ l = 1 L α ( l ) h [ l - d ( l ) ] e - j 2 πlk N , ( k = 1 , L , N ) . . . ( 3 )
H wherein n(k), k=1, L, N is n the frequency domain response of different sub carrier constantly.
As shown in Figures 2 and 3, among Fig. 2, each conventional time slot has a long 144chip of being of training in the TD-SCDMA system, and this part information is that the TD-SCDMA system is used for channel estimating, and this part information is known, and it is added on each subcarrier of OFDM transmission now, therefore, can utilize the pilot tone as frequency domain to be inserted on the corresponding subcarrier, the method for insertion can be according to shown in Figure 2, the mode that adopts one dimension to insert will satisfy simultaneously
τ max·ΔF·N L≤1/2 (4)
τ wherein MaxBe maximum delay, Δ F is the carrier spacing, N LBe the interval on the pilot signal frequency.
For the pilot signal of inserting, can adopt and equally spacedly also can adopt dynamic compartment of terrain to be inserted in institute's data flow transmitted, the response that so just can utilize the signal that receives and pilot signal to estimate pilot frequency locations place channel, concrete response can calculate with following formula:
H ^ k , l = Y k , l X k , l . . . ( 5 )
In the formula (5) Be the channel response of k subcarrier of l symbol, Y K, lBe k the value that subcarrier is received of l symbol receiving, X K, lPilot value for k subcarrier of l symbol sending.
The channel response that can utilize those to estimate for the estimation of the channel response of whole subcarrier by pilot tone
Figure A20051011224700123
Obtain, estimation approach can adopt interpolation or filtering level and smooth etc.Wherein interpolating method can be selected linear interpolation, Gauss's interpolation, Cubic interpolation or the like.If channel be become slowly and also change enough slowly, also can not make interpolation, think that the channel response of a Frame is constant, so just the channel response of frame header can be used as the response of entire frame.
Know by last surface analysis,, transform to through FFT then and carry out Filtering Processing in the frequency domain, finally obtain the required channel response on each each subcarrier of symbol moment at the time-domain pulse response of receiving terminal elder generation detection channel on time domain; Simultaneously, the pilot tone that utilization is inserted on again and again estimates also can estimate the channel response on the corresponding subcarrier, also can obtain the required channel response on each each subcarrier of symbol moment by interpolation.
For the channel response that different channel estimating obtains, sue for peace after multiply by different weights, it is as follows to obtain new frequency domain response value:
α is a weighted factor in the formula (6), Be the channel response of k subcarrier of l symbol,
Figure A20051011224700132
Correspond to the channel response of k subcarrier of l the symbol that obtains that utilizes the time domain pilot estimation,
Figure A20051011224700133
Estimate the channel response of k subcarrier of l symbol obtaining for pilot tone.
In the above-mentioned formula (6), weighted factor can be according to the situation change of table 1, so that obtain best choice.
Table 1 weighted factor correction α
Figure A20051011224700134
By the scheme that proposes, clearly can fully improve the reliability of channel estimating.And utilization to the weighted factor correction, can be followed the tracks of the conversion of channel under different channel situation.
As mentioned above, the present invention makes full use of the long 144chip of being of the training of in the conventional time slot in the TD-SCDMA system, and this part information is known for this part information, therefore, can utilize it to be inserted on the corresponding subcarrier as the pilot tone of frequency domain.The characteristic of time domain channel can be obtained by the pilot tone of time domain, the characteristic of frequency domain channel can be obtained by the pilot tone of frequency domain.Adopt channel estimation methods that time-frequency domain combines can be better in conjunction with utilizing time domain channel and frequency domain channel to influence that frequency domain data produced, effectively suppress additive white Gaussian noise, by adding Cyclic Prefix (CyclicPrefix, CP) can also effectively subdue intersymbol interference (ISI), can provide certain gain for decoding module, under this external abominable multipath Rayleigh decline mobile channel, the channel estimation methods that time-frequency domain combines still can keep good estimated performance, thereby helps improving the performance of the TD-SCDMA system of compatibility to OFDM tech.
Being preferred embodiment of the present invention only in sum, is not to be used for limiting practical range of the present invention.Be that all equivalences of doing according to the content of the present patent application claim change and modification, all should be technology category of the present invention.

Claims (14)

1, the method for a kind of time domain and frequency-domain combined channel estimating is applied in the TD-SCDMA system of compatibility to OFDM tech,, its feature is in may further comprise the steps:
The pilot tone that between the OFDM symbol, adds some;
At receiving terminal, on time domain, detect the time-domain pulse response of channel, and in frequency domain, carry out Filtering Processing, to obtain the required channel response on each each subcarrier of symbol moment through Fourier transform;
On frequency domain, calculate the channel response on each subcarrier of each symbol according to the pilot signal of signal that receives and insertion;
Channel estimation results to above-mentioned time domain and frequency domain is weighted processing, obtains the final required channel response value on each each subcarrier of symbol moment.
2, the method for time domain according to claim 1 and frequency-domain combined channel estimating, it is characterized in that: in the described pilot tone step that between the OFDM symbol, adds some, the pilot number that adds is relevant with the variation characteristic of channel, when channel variation is fast, the pilot number that adds is more, and channel variation is when slow, and the pilot number of adding is less.
3, the method for time domain according to claim 2 and frequency-domain combined channel estimating is characterized in that: described pilot tone is selected the reasonable sequence of orthogonality.
4, the method for time domain according to claim 1 and frequency-domain combined channel estimating is characterized in that: time domain pilot need satisfy when inserting f D max · T s · N k ≤ 1 / 2 , f DmaxBe maximum doppler frequency, T sBe symbol lengths, N kBe pilot signal interval in time.
5, the method for time domain according to claim 1 and frequency-domain combined channel estimating is characterized in that: utilize in the TD-SCDMA system information of training sequence in the conventional time slot to be inserted on the corresponding subcarrier as the pilot signal of frequency domain.
6, the method for time domain according to claim 5 and frequency-domain combined channel estimating is characterized in that: on frequency domain, the method that pilot signal is inserted adopts the one dimension inserted mode, and satisfies τ MaxΔ FN L≤ 1/2, τ wherein MaxBe maximum delay, Δ F is the carrier spacing, N LBe the interval on the pilot signal frequency.
7, the method for time domain according to claim 6 and frequency-domain combined channel estimating is characterized in that: the pilot signal of described insertion is inserted in institute's data flow transmitted in equally spaced mode.
8, the method for time domain according to claim 6 and frequency-domain combined channel estimating is characterized in that: the pilot signal of described insertion is inserted in institute's data flow transmitted in the mode at dynamic interval.
9, according to the method for each described time domain and frequency-domain combined channel estimating in the claim 1 to 8, it is characterized in that: utilize those channel responses that estimate by pilot tone to estimate the channel response of whole subcarrier by interpolating method.
10, the method for time domain according to claim 9 and frequency-domain combined channel estimating is characterized in that: described interpolating method comprises linear interpolation, Gauss's interpolation method, Cubic interpolation method.
11, according to the method for each described time domain and frequency-domain combined channel estimating in the claim 1 to 8, it is characterized in that: utilize those channel responses that estimate by pilot tone to estimate the channel response of whole subcarrier by the filtering smoothing method.
12, according to the method for each described time domain and frequency-domain combined channel estimating in the claim 1 to 8, it is characterized in that: if channel be become slowly and also change enough slowly, the channel response of frame header is used as the response of entire frame, thereby draws the channel response of whole subcarrier.
13, the method for time domain according to claim 1 and frequency-domain combined channel estimating is characterized in that: in the described weighted step, to the channel response that different channel estimating obtains, sue for peace after multiply by different weights, the response that obtains new frequency domain is: α≤1, wherein, α is a weighted factor,
Figure A2005101122470004C2
Be the channel response of k subcarrier of l symbol, Correspond to the channel response of k subcarrier of l the symbol that obtains that utilizes the time domain pilot estimation, Estimate the channel response of k subcarrier of l symbol obtaining for pilot tone.
14, the method for time domain according to claim 13 and frequency-domain combined channel estimating is characterized in that: described weighted factor can be according to the variation of Doppler frequency shift and multipath length, by H ^ k , l = Y k , l / X k , l α comes weighted factor is revised, wherein
Figure A2005101122470004C6
Be the channel response of k subcarrier of l symbol, Y K, lBe k the value that subcarrier is received of l symbol receiving, X K, lPilot value for k subcarrier of l symbol sending.
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WO2008119223A1 (en) * 2007-03-30 2008-10-09 Hong Kong Applied Science & Technology Research Institute Co., Ltd. Ofdm/ofdma channel estimation
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CN102007746A (en) * 2008-04-09 2011-04-06 诺基亚西门子通信公司 Permuting slots to logical distributed resource units
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CN102023963A (en) * 2010-12-13 2011-04-20 西安电子科技大学 High-speed multi-mode time domain and frequency domain transform method
WO2012037705A1 (en) * 2010-09-24 2012-03-29 Intel Corporation Uplink channel estimation for a software defined radio
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WO2008119223A1 (en) * 2007-03-30 2008-10-09 Hong Kong Applied Science & Technology Research Institute Co., Ltd. Ofdm/ofdma channel estimation
CN102007746A (en) * 2008-04-09 2011-04-06 诺基亚西门子通信公司 Permuting slots to logical distributed resource units
CN102007746B (en) * 2008-04-09 2015-03-25 诺基亚通信公司 Permuting slots to logical distributed resource units
CN101547180B (en) * 2009-04-28 2012-04-25 北京大学 Distributed channel estimation method
CN102014094A (en) * 2009-09-07 2011-04-13 大唐移动通信设备有限公司 Intelligent calibration method of antenna transmitting channel and antenna receiving channel and relevant device
CN102014094B (en) * 2009-09-07 2013-04-03 电信科学技术研究院 Intelligent calibration method of antenna transmitting channel and antenna receiving channel and relevant device
CN101707574A (en) * 2009-11-27 2010-05-12 北京邮电大学 Channel estimation method and device
US9136882B2 (en) 2010-09-24 2015-09-15 Intel Corporation Uplink channel estimation for a software defined radio
WO2012037705A1 (en) * 2010-09-24 2012-03-29 Intel Corporation Uplink channel estimation for a software defined radio
CN102023963A (en) * 2010-12-13 2011-04-20 西安电子科技大学 High-speed multi-mode time domain and frequency domain transform method
CN102023963B (en) * 2010-12-13 2013-10-16 西安电子科技大学 High-speed multi-mode time domain and frequency domain transform method
CN104580037A (en) * 2014-12-29 2015-04-29 江苏中兴微通信息科技有限公司 Single-carrier communication system noise variance estimation method and device adopting time-domain pilot frequency
CN104580037B (en) * 2014-12-29 2017-12-01 江苏中兴微通信息科技有限公司 Utilize the carrier wave communication system noise variance estimation method and device of time domain pilot
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CN106656441B (en) * 2015-10-28 2020-03-27 上海诺基亚贝尔股份有限公司 Method and apparatus for improving reliability of vehicle-to-vehicle communication
CN105743629A (en) * 2016-03-03 2016-07-06 华为技术有限公司 Signal sending method and device
WO2017148190A1 (en) * 2016-03-03 2017-09-08 华为技术有限公司 Method and apparatus for sending signals
CN105743629B (en) * 2016-03-03 2019-07-19 华为技术有限公司 Signaling method and device
US10505764B2 (en) 2016-03-03 2019-12-10 Huawei Technologies Co., Ltd. Signal sending method and apparatus
CN107171987A (en) * 2017-07-10 2017-09-15 东南大学 A kind of algorithm for estimating suitable for time-varying condition of sparse channel
CN107171987B (en) * 2017-07-10 2020-02-18 东南大学 Estimation method suitable for time-varying sparse channel
CN107391439A (en) * 2017-07-11 2017-11-24 创达特（苏州）科技有限责任公司 A kind of processing method of configurable Fast Fourier Transform (FFT)
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