CN1567762A  A channel estimation method adapted for OFDMA system  Google Patents
A channel estimation method adapted for OFDMA system Download PDFInfo
 Publication number
 CN1567762A CN1567762A CN 03142513 CN03142513A CN1567762A CN 1567762 A CN1567762 A CN 1567762A CN 03142513 CN03142513 CN 03142513 CN 03142513 A CN03142513 A CN 03142513A CN 1567762 A CN1567762 A CN 1567762A
 Authority
 CN
 China
 Prior art keywords
 channel
 channel estimation
 sequence
 pilot
 frequency
 Prior art date
Links
 229950008597 drug INN Drugs 0.000 claims description 10
 238000001914 filtration Methods 0.000 claims description 7
 239000000284 extracts Substances 0.000 claims description 2
 238000005516 engineering processes Methods 0.000 description 5
 239000000969 carriers Substances 0.000 description 4
 238000004891 communication Methods 0.000 description 3
 238000001228 spectrum Methods 0.000 description 3
 230000037010 Beta Effects 0.000 description 2
 230000005540 biological transmission Effects 0.000 description 2
 238000006243 chemical reactions Methods 0.000 description 2
 230000001427 coherent Effects 0.000 description 2
 238000010586 diagrams Methods 0.000 description 2
 230000003044 adaptive Effects 0.000 description 1
 230000000996 additive Effects 0.000 description 1
 239000000654 additives Substances 0.000 description 1
 238000004458 analytical methods Methods 0.000 description 1
 230000000875 corresponding Effects 0.000 description 1
 239000010410 layers Substances 0.000 description 1
 239000011159 matrix materials Substances 0.000 description 1
 238000000034 methods Methods 0.000 description 1
 230000000051 modifying Effects 0.000 description 1
 238000004088 simulation Methods 0.000 description 1
Abstract
Description
Technical field
The present invention relates to the channel estimation methods of a kind of OFDM (OFDMA) system.
Background technology
Can predict multimedia services such as audio frequency, video, image and the Internet will become the dominant traffic of future mobile communications, and these business obviously improve (requiring peak traffic speed greater than 20Mbps) for the requirement of transmission of radio links ability.In this case, OFDM (OFDM) technology is shown up prominently.The OFDM technology is that a plurality of parallel low rate data streams that frequency spectrum overlaps sends with data stream modulates at a high speed.Because the OFDM symbol period significantly increases; therefore improved the ability of OFDM symbol antimultipath time delay; and by increasing at the front end of OFDM symbol greater than the protection of maximum multipath time delay (GI) at interval; then can eliminate the intersymbol interference (ISI) that causes by multidiameter delay fully, simplify the burden of receiving terminal equalizer.OFDM is also adopted by a plurality of standards at present, and is acknowledged as one of physical layer basic fundamental of B3G substantially.Different sub carrier is distributed to different user, and the OFDM technology has then naturally and understandably been distinguished the user by the FDMA mode, just the OFDMA system.The OFDMA system distributes to different users neatly by the subcarrier that quadrature is adjacent, has reduced the interference in the subdistrict, has improved power system capacity.And OFDMA changes by user's subcarrier number purpose, is easy to provide the message transmission of variable Rate, so OFDMA is one of multiple access scheme of very likely adopting of B3G system.
Because coherent detection is compared the raising of the performance that 2.33dB is arranged with incoherent detection, so generally adopt coherent detection technology at receiving terminal.If how the employing detection technique so just must send signal to channel and estimate, promptly channel is estimated.For the channel estimation method in the OFDMA system, roughly can be divided into auxiliary and blind Channel Estimation two classes of pilot signal.Because the channel estimation method superior performance that frequency pilot sign is auxiliary, therefore present most B3G system has adopted the auxiliary channel estimation scheme of frequency pilot sign.For the auxiliary channel estimation method of frequency pilot sign, the algorithm of simple possible is young waiter in a wineshop or an inn (LS) algorithm, and for example channel estimating is asked average method after just having adopted the young waiter in a wineshop or an inn of two pilot frequency sequences to estimate in the WLAN (wireless local area network) Hiperlan2 standard.But, this algorithm is subjected to the influence of Gaussian noise obvious, this algorithm performance worsens significantly when low signaltonoise ratio, especially for the OFDMA system, each user has only the subcarrier of part, the pilot frequency sequence yardstick is far smaller than the yardstick of inverseFourier transform (IFFT), thereby this algorithm can not be applicable to the OFDMA system.
Because the impulse response of wireless channel can equivalence be the filter of limited tap, and the maximum multipath time delay of channel is far smaller than the OFDM symbol period, therefore can think the impulse response of wireless channel equivalent be low pass filter.Pilot frequency sequence channel after can estimating young waiter in a wineshop or an inn like this adopts further algorithm to improve the precision of its estimation.The scholar's suggestion that for example has is carried out the IFFT conversion to known array, adopts the method for filtering to eliminate the adjacent intercarrier interference that time varying channel causes then, improves precision of channel estimation.Some scholar's suggestion is carried out the IFFT processing to signal in addition, utilizes the correlation matrix of sequence then, carries out filtering, improves precision of channel estimation etc.But, because the complexity of these algorithms in filtering limited its possibility of its application.The proposition of especially abovementioned algorithm all is at ofdm system, and does not consider multiuser's problem, therefore also has suitable distance from being applied to the B3G system.
Summary of the invention
At problems of the prior art, the invention provides a kind of pilot frequency sequence that in the OFDMA system, utilizes and provide the method for accurate channel estimating for the multiuser, the method comprising the steps of:
(1) from the multiuser information that receives, extracts a certain user's the pilot frequency sequence that comprises channel information at receiving terminal, utilize young waiter in a wineshop or an inn to estimate to obtain the channel estimation value of pilot portion;
(2) utilize Fourier transform, obtain the frequency domain sequence of initial channel estimation;
(3) described frequency domain sequence is carried out amplitude limit, ZF operation;
(4) utilize inverseFourier transform to obtain the accurate channel estimation value of described pilot frequency sequence;
(5) channel estimation value of pilot portion is applied to the channel characteristic estimation of nonpilot portion, thereby carries out channel compensation and Data Detection.
In the present invention, utilize the FFT conversion, obtained the frequency domain characteristic of each user's initial channel characteristic sequence, by amplitude limit and ZF to frequency domain channel characteristic sequence, reduce the influence of white Gaussian noise effectively, thereby obtained every accurate user channel estimation value.The present invention not only implementation complexity is lower, does not increase system's time delay, and has improved the performance of system significantly.
Description of drawings
Further describe the present invention with reference to the accompanying drawings and in conjunction with example.Wherein:
Fig. 1 shows a kind of timefrequency structure of the OFDMA system of hypothesis;
Fig. 2 shows according to receiver principle figure of the present invention;
Fig. 3 shows the more detailed block diagram according to channel estimation methods of the present invention;
When Fig. 4 showed signal to noise ratio and is 5dB, the characteristic of channel that the characteristic of channel of ideal communication channel pilot frequency locations is the result after the Fourier transform and is done the pilot frequency locations after the young waiter in a wineshop or an inn was the result after the Fourier transform;
Bit error rate was along with the curve of amplitude limit factor variations when Fig. 5 showed high speed and low speed;
Fig. 6 (a) and Fig. 6 (b) show channel estimation methods according to the present invention and the existing channel estimation methods performance curve of system's bit error rate under the different signal to noise ratio conditions at a high speed with low speed the time respectively.
Specific implementation
Fig. 1 shows a kind of timefrequency structure of OFDMA system of our hypothesis.Total subcarrier number is 1024 in the supposing the system, wherein is used for 768 subcarriers that have of transfer of data; And insert a pilot frequency sequence every 3 OFDM symbols, form a data block, encode and detect by 13 OFDM symbols.Supposed to have simultaneously 3 users in the system, promptly each user has 256 subcarriers.A certain user's pilot tone, data mark out with oblique line among Fig. 1.
Fig. 2 is the schematic diagram of receiver.At first, from the data block that receives, solve each user's pilot frequency information respectively, carry out channel estimating then according to shown in Figure 1.Be without loss of generality, we are example with one of them user only in the following analysis.If the pilot frequency sequence that on n OFDM symbol, sends a certain user of transmitting terminal be P (n)=[p[n, 0), p (n, 1) ... p (n, K1)] ^{T}, wherein (n k) is k frequency pilot sign to p, and total number of pilot symbols is K=256.At receiving terminal, can be expressed as so through the received signal behind the FFT demodulating unit:
r(n，k)＝p(n，k)H(n，k)+w(n，k) k＝0，1...，K1(1)
Wherein (n is the white Gaussian noise on k frequency pilot sign on n the OFDM symbol k) to w, and its average is zero, and variance is σ ^{2}(n k) is channel value on n OFDM symbol, the k frequency pilot sign to H, and it is the Fourier transform of time domain channel impulse response.
Usually, can utilize young waiter in a wineshop or an inn's algorithm to estimate channel, promptly
The mean square error of this algorithm for estimating is:
Wherein β is the ratio of frequency pilot sign power and data symbol power, and SNR is the signal to noise ratio of current system.Although we can promptly increase β value by improving the transmitted power of frequency pilot sign, improve the precision of system channel estimation to a certain extent, this method can be brought problems such as peaktoaverage ratio increase, so the increase β that we can not be simply.The precision of therefore young waiter in a wineshop or an inn's algorithm for estimating depends primarily on the white Gaussian noise size that system is subjected to, and promptly white Gaussian noise is more little, and the SNR value is high more, and channel estimation errors is just more little, otherwise then evaluated error is big more.Below we will propose a kind of channel estimation scheme of DFT base, this channel estimation scheme can improve channel estimated accuracy significantly.
At first, use The channel estimating value sequence of representing certain user.Then this sequence is carried out Fourier transform, the frequency domain value that obtains channel estimation value is:
Wherein
Because the impulse response of wireless channel can equivalence be the filter of limited tap, and the maximum multipath time delay of channel is far smaller than the OFDM symbol period, therefore can equivalence think that the impulse response of wireless channel is low pass filter, (n is slowly to change k) can to observe channel value H in emulation.Therefore after channel estimation sequence is carried out Fourier transform, the tap of the characteristic of channel will appear at low frequency part (two of frequency spectrum), and the fluctuating of HFS mainly is because (middle part of frequency spectrum) that additive white Gaussian noise causes.Fig. 4 (a) and Fig. 4 (b) show ideal respectively, and young waiter in a wineshop or an inn estimates that the characteristic of channel is the result after the Fourier transform, and we select for use in the emulation is the channel parameter of table three A M.1225.Obviously, it is the main tap of channel that the range value behind the channel estimation sequence Fourier transform has only the part tap, and all the other mainly are noises.Therefore we have adopted the method for ZF method to come the noise of filtering HFS, promptly
ZF thresholding α wherein _{1}, α _{2}Selection mainly choose according to channel condition.For effective filtering noise, keep the feature of channel simultaneously again, the α that we select in Fig. 4 (a) _{1}, α _{2}Parameter value be 1 and 216.
Further, we can also carry out filtering to the noise of low frequency part.Main operation is to set thresholding β _{1}, β _{2}(β _{1}＜β _{2}), for greater than β _{2}Perhaps less than β _{1}H _{2}(n l), keeps it as effectively tap, otherwise thinks the signal fluctuation that Gaussian noise causes, it is compeled value is zero, can be expressed as
Thresholding β
_{1}, β
_{2}Value can be changeless, also can be (numerical value of current noise power can utilize synchronizing sequence to estimate to obtain) that the variation with signal to noise ratio changes, simulation result shows the better performances of the adaptive threshold value that changes with signal to noise ratio.The β that we select for use in emulation
_{1}, β
_{2}Value be
At last, to H _{3}(n) do corresponding inverseFourier transform, just obtained the accurate estimated value of the characteristic of channel, promptly
After having obtained the channel estimation value of pilot portion, the method by average method or single order, second order interpolation can calculate the characteristic of channel of whole data block, carries out channel compensation and Data Detection then.
Bit error rate was along with the change curve of signal to noise ratio (snr) when Fig. 6 showed high speed and low speed, as can be seen from the figure, this patent is than young waiter in a wineshop or an inn's algorithm for estimating, performance during low speed and ideal communication channel estimated performance almost overlap, about performance during high speed and ideal communication channel estimation performance difference 2dB.Therefore no matter this patent is when high speed and low speed, has all improved channel estimated accuracy significantly, thereby has improved the performance of system.
Claims (5)
Priority Applications (1)
Application Number  Priority Date  Filing Date  Title 

CNB031425135A CN100505596C (en)  20030610  20030610  A channel estimation method adapted for OFDMA system 
Applications Claiming Priority (1)
Application Number  Priority Date  Filing Date  Title 

CNB031425135A CN100505596C (en)  20030610  20030610  A channel estimation method adapted for OFDMA system 
Publications (2)
Publication Number  Publication Date 

CN1567762A true CN1567762A (en)  20050119 
CN100505596C CN100505596C (en)  20090624 
Family
ID=34471120
Family Applications (1)
Application Number  Title  Priority Date  Filing Date 

CNB031425135A CN100505596C (en)  20030610  20030610  A channel estimation method adapted for OFDMA system 
Country Status (1)
Country  Link 

CN (1)  CN100505596C (en) 
Cited By (9)
Publication number  Priority date  Publication date  Assignee  Title 

CN100464543C (en) *  20060127  20090225  东南大学  Compatible singlecarrier OFDMA signal transmitting method 
CN1829206B (en) *  20051219  20100609  北京邮电大学  A channel estimation method for TDSCDMA system 
CN102075466A (en) *  20091123  20110525  电信科学技术研究院  Method for estimating received interference power and receiver 
WO2011157210A1 (en) *  20100618  20111222  中兴通讯股份有限公司  Method and device for channel estimating in orthogonal frequency division multiplexing system 
US8121216B2 (en)  20060124  20120221  Nec Corporation  Channel estimation device, equalization device, and radio system 
CN101729465B (en) *  20081015  20140226  电信科学技术研究院  Method and device for measuring signal to noise ratio and application thereof 
CN104125185A (en) *  20130428  20141029  华为技术有限公司  Signal processing method and apparatus thereof 
CN104426817A (en) *  20130819  20150318  联芯科技有限公司  Channel estimation method and device 
CN107846260A (en) *  20160919  20180327  深圳超级数据链技术有限公司  Modulationdemodemodulation method, device and system based on overlapping multiplexing 
Family Cites Families (4)
Publication number  Priority date  Publication date  Assignee  Title 

KR100224864B1 (en) *  19970820  19991015  윤종용  Equalizing method for ofdm receiver and equalizer 
EP1170916B1 (en) *  20000705  20061227  Sony Deutschland GmbH  Channel estimator for OFDM system 
EP1178640B1 (en) *  20000801  20060524  Sony Deutschland GmbH  Device and method for channel estimating an OFDM system 
US7230911B2 (en) *  20010510  20070612  Intel Corporation  Sparse channel estimation for orthogonal frequency division multiplexed signals 

2003
 20030610 CN CNB031425135A patent/CN100505596C/en not_active IP Right Cessation
Cited By (13)
Publication number  Priority date  Publication date  Assignee  Title 

CN1829206B (en) *  20051219  20100609  北京邮电大学  A channel estimation method for TDSCDMA system 
US8121216B2 (en)  20060124  20120221  Nec Corporation  Channel estimation device, equalization device, and radio system 
CN101375521B (en) *  20060124  20130327  日本电气株式会社  Transmission path estimation device, equalisation device, and radio system 
CN100464543C (en) *  20060127  20090225  东南大学  Compatible singlecarrier OFDMA signal transmitting method 
CN101729465B (en) *  20081015  20140226  电信科学技术研究院  Method and device for measuring signal to noise ratio and application thereof 
CN102075466A (en) *  20091123  20110525  电信科学技术研究院  Method for estimating received interference power and receiver 
CN102075466B (en) *  20091123  20131127  电信科学技术研究院  Method for estimating received interference power and receiver 
WO2011157210A1 (en) *  20100618  20111222  中兴通讯股份有限公司  Method and device for channel estimating in orthogonal frequency division multiplexing system 
CN104125185A (en) *  20130428  20141029  华为技术有限公司  Signal processing method and apparatus thereof 
CN104125185B (en) *  20130428  20170714  华为技术有限公司  The method and apparatus of signal transacting 
CN104426817A (en) *  20130819  20150318  联芯科技有限公司  Channel estimation method and device 
CN104426817B (en) *  20130819  20171110  联芯科技有限公司  A kind of channel estimation methods and its device 
CN107846260A (en) *  20160919  20180327  深圳超级数据链技术有限公司  Modulationdemodemodulation method, device and system based on overlapping multiplexing 
Also Published As
Publication number  Publication date 

CN100505596C (en)  20090624 
Similar Documents
Publication  Publication Date  Title 

Zhou et al.  Finitealphabet based channel estimation for OFDM and related multicarrier systems  
US8537908B2 (en)  Pilot transmission and channel estimation for an OFDM system with excess delay spread  
JP5201421B2 (en)  Channel estimator for OFDM systems  
EP1745618B1 (en)  Staggered pilot transmission for channel estimation and time tracking  
Gupta et al.  Performance evaluation of conventional and wavelet based OFDM system  
US7418046B2 (en)  Pilot transmission and channel estimation for multiple transmitters  
KR100630196B1 (en)  Apparatus and method for acquiring synchronization in a mobile communication system using an orthogonal frequency division multiplexing scheme  
US6327314B1 (en)  Method and apparatus for channel estimation for multicarrier systems  
US7554902B2 (en)  Preamble design for frequency offset estimation and channel equalization in burst OFDM transmission system  
Zhao et al.  A novel channel estimation method for OFDM mobile communication systems based on pilot signals and transformdomain processing  
US8553822B2 (en)  Time filtering for excess delay mitigation in OFDM systems  
US8045633B2 (en)  Estimation of length of channel impulse response  
JP4419957B2 (en)  WIRELESS COMMUNICATION SYSTEM, RECEIVING APPARATUS AND RECEIVING METHOD FOR Performing Multicarrier Transmission  
Yang et al.  Windowed DFT based pilotsymbolaided channel estimation for OFDM systems in multipath fading channels  
JP4046515B2 (en)  Iterative maximum likelihood channel estimation and signal detection system and method for OFDM systems  
KR100635534B1 (en)  Hybrid type chnnel estimation method and system for mobile environment  
KR101643419B1 (en)  Method and apparatus for estimating a channel using phase compensation in a wireless communication system  
TWI407719B (en)  A symbol time synchronization method for ofdm systems  
US7092436B2 (en)  Expectationmaximizationbased channel estimation and signal detection for wireless communications systems  
JP4832261B2 (en)  Channel estimation device  
US7082159B2 (en)  Methods and arrangements in a telecommunications system  
US7961806B2 (en)  Power adaptive channel estimation for a multipath receiving  
US20020181389A1 (en)  Channel estimation for wireless OFDM systems  
US20040066773A1 (en)  Decision feedback channel estimation and pilot tracking for OFDM systems  
JP4472771B2 (en)  Receiver for receiving a multicarrier signal 
Legal Events
Date  Code  Title  Description 

C06  Publication  
PB01  Publication  
C10  Entry into substantive examination  
SE01  Entry into force of request for substantive examination  
C14  Grant of patent or utility model  
GR01  Patent grant  
EXPY  Termination of patent right or utility model  
CF01  Termination of patent right due to nonpayment of annual fee 
Granted publication date: 20090624 Termination date: 20140610 