CN100385835C - OFDM receiver - Google Patents
OFDM receiver Download PDFInfo
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- CN100385835C CN100385835C CNB021468958A CN02146895A CN100385835C CN 100385835 C CN100385835 C CN 100385835C CN B021468958 A CNB021468958 A CN B021468958A CN 02146895 A CN02146895 A CN 02146895A CN 100385835 C CN100385835 C CN 100385835C
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- 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
- H04L27/2649—Demodulators
- H04L27/265—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/01—Equalisers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/015—High-definition television systems
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- Physics & Mathematics (AREA)
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- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
Abstract
An OFDM receiver comprises a splitter used for dividing the OFDM signals isostatic at the time-domain into a plurality of signals; a first discrete DFT unit used for DFT the plurality of divided known signal sequences which is appointed by the transmitter and the receiver; and a frequency domain equilibria unit used for executing frequency domain equilibria of OFDM symbols, wherein the second discrete DFT unit executes a fourier transformation to effective OFDM symbols on the basis of the known sequences for executing a fourier transformation to the first DFT unit. When at least two known sequences used for OFDM signals exist, for the known sequences, a window regulation unit is provided for regulating separated sequences to be suitable for the multi-path environment, and the known sequences after a window regulation is executed a fourier transformation by the first DFT unit. By using the known sequences through a fourier transformation, the fourier transformed OFDM signals can execute frequency domain equilibrium.
Description
Technical field
Present invention relates in general to a kind of OFDM receiver, relate in particular to a kind of OFDM (orthogonal frequency division multiplexing, the OFDM) equalizer of receiver.
Background technology
In general, the broadcasting system of high definition TV (HDTV) can be divided into image encoding unit and image modulation unit roughly.The image encoding unit becomes the digital data compression of the about 1Gbps that imports from the high-definition image source data of 15～18Mbps.The limited frequency band passage of image modulation unit by approximate 6～8MHz sends to receiving terminal with the numerical data of tens Mbps.HDTV has adopted the synchronous broadcasting method in land, and this method is used the very high frequency(VHF)/hyperfrequency (VHF/UHF) that distributes because of the purpose of television broadcasting.Broadcast synchronously in the process of environment on consideration land, the modulator approach that is used for the broadcasting system of HDTV requires to satisfy following condition.
At first, be used for the demanding spectrum efficiency of modulation of the broadcasting system of HDTV, so that send the numerical data of tens Mbps by the limited frequency band passage of 6～8MHz.Secondly, because because of multipath fading takes place often for building or certain facility, the modulator approach that is used for the broadcasting system of HDTV should be able to antidamping.The 3rd, the modulator approach that is used for the broadcasting system of HDTV should be able to resist co-channel (adjective) to disturb, and this interference takes place often because of anolog TV signals.At last, the modulation signal in the broadcasting system of HDTV should be able to reduce to minimum to the interference in the simulated television receiver.
As providing as increasing a modulator approach of transmission rate and pre-anti-tampering advantage, in Europe, OFDM (OFDM) method is adopted the synchronous broadcasting method in the land that is used as follow-on HDTV.
The symbol sebolic addressing that ofdm system is come in serial at a predetermined module unit is converted into parallel data, then these parallel symbol multichannels is distributed on the different subcarrier frequencies.Different with the modulator approach of the single subcarrier of existing use (single sub-carrier), ofdm system uses multi sub-carrier (multi sub-carrier).Mutually orthogonal between these multi sub-carriers.Because orthogonality, the product of two subcarriers are zero, this is to use one of necessary condition of subcarrier.Ofdm system realizes that by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) this can directly obtain by the definition of orthogonality between the subcarrier and fast Fourier transform (FFT).
Simultaneously, the advantage of ofdm system is as follows:
Because TV land sending method has a channels feature: the transmission quality depends critically upon reflected wave and co-channel interference and the adjacent channel interference during signal sends, so the designing requirement of emission system is quite complicated.Yet OFDM is effectively strong in multi-path environment.In other words, because OFDM has used various carrier waves, the symbol transmitting time can be extended.Correspondingly, system becomes to interference signal and has immunity, therefore, even in the long relatively time period echo-signal, the also reduction of rarer quality take place.Ofdm system also is effectively strong for existing signal, and therefore, interference has less influence to co-channel (adjective).Because some features can be set up Single Frequency Network (SFN) like this.Here, ' SFN ' means that single broadcasting mode carries out the broadcasting of nationwide with a frequency.Even when the increase of the interference in certain channel, because ofdm system is effectively strong in this environment, so it is also in receivable scope.As mentioned above, by using Single Frequency Network, a limited number of frequency resources can be effectively utilized.
Simultaneously, ofdm signal is made up of a plurality of carrier waves, and each carrier wave has less relatively bandwidth.Because all frequency spectrums are read to be defined in the rectangle (shape of a square), in fact, frequency efficiency is higher than single carrier wave.Another advantage of ofdm system is, because the waveform of ofdm signal has the feature of white Gaussian noise, with other forms such as the line-by-line inversion (PAL) of the service of broadcasting, order compares its rarer interference with storage color standards such as (SECAM).Because the modulation of each carrier wave is used in the conversion of ofdm system energy, it is possible that classification sends.
Though the ofdm system of Ditital modulation method since as mentioned above advantage in broadcast on the land of HDTV, adopted by Europe, also have some more serious problems.That is,, in sending channel, there is various distorted signals owing to be subjected to the influence of the state of channel, wherein, because the distortion that produced by the influence of multipath has seriously influenced the signal in the digital broadcasting especially.For correcting distortion, provide equalizer to proofread and correct the error of the transmission channel in receiving end signal recovery process.Usually, equalizer compensates the error that sends channel by the error of the adjacent signals of the OFDM input signal of having made Fourier transform is calculated.For example, based on paid-in known array, promptly the ofdm signal that receives is carried out synchronously and channel estimation based on the PN sequence.
In general, the PN sequence length is 2
m-1 (m=integer).For example, correspond to the length of effective OFDM symbol, the PN sequence length is 255 or 511.Then after carrying out Fourier transform, by interpolation method and elimination restore data.Problem is, the length of PN sequence is not that the length by effective OFDM symbol is provided with.Therefore, data can not accurately be recovered.
Summary of the invention
Therefore, the purpose of this invention is to provide a kind of OFDM receiver, it has one and the OFDM symbol that received and carries out the equalizer of channel equalisation, but does not need guiding (pilot) information in the frequency of utilization territory, to improve balanced efficient.
The above purpose can realize that it comprises a time domain equalization unit by OFDM receiver of the present invention, is used for synchronizing information balanced ofdm signal in time domain according to ofdm signal; Splitter is used for an ofdm signal balanced in time domain separately and become a plurality of signals; First discrete Fourier transform (DFT) unit is used for a plurality of known signal sequences that separated are carried out Fourier transform, and this known array is by reflector and receiver agreement; The second discrete Fourier transform unit based on the known array that carried out Fourier transform by a DFT unit, carries out Fourier transform to the OFDM symbol of a plurality of separate signal.
Utilization is expressed as the length of effective OFDM symbol of N, and the known array length T that is input to a DFT can be expressed as
Here, N, T and k are integers.
In addition, when at least two of existence are used for the known array of ofdm signal, provide the window adjustment unit, be used to adjust known array separately and make it to be fit to multi-path environment, then, a DFT unit carries out Fourier transform to the known array through the window adjustment.
Based on the known array that carried out Fourier transform by a DFT unit, frequency-domain balancing unit is carried out equilibrium to effective OFDM symbol, and described known array is assigned to by the 2nd DFT unit and was undertaken on each k subcarrier of effective OFDM symbol of Fourier transform.
According to the present invention, be provided at employed equalization methods in the OFDM receiver, the step that this method comprises is: input has the ofdm signal of known array and gives receiver; The ofdm signal that receives is changed into digital signal; In time domain, the ofdm signal that receives is carried out equilibrium based on known array; Divide and export balanced ofdm signal and become known array, GI and effective OFDM symbol; By oneself known array and effective OFDM symbol are carried out Fourier transform so that periodically distribute known array on each k subcarrier of effective OFDM symbol; The estimated channel distortion information; And the known array that distributes of each the k subcarrier that is based upon effective OFDM symbol, the distortion that sends on the channel at the OFDM symbol is proofreaied and correct.
The method also comprises step: about the known array of two equal lengths, adjust window so that select to be fit to the division that the known array of multi-path environment comes; Selecteed suitable known array and effective OFDM symbol are carried out Fourier transform separately; Based on known array the distortion on the transmission channel of ofdm signal is proofreaied and correct accurately.
According to the present invention,,, under the situation that does not need pilot signal independent in the frequency domain, improve balanced efficient by in frequency domain, effective OFDM symbol of finishing Fourier transform being carried out equilibrium based on known array through Fourier transform.
Description of drawings
Purpose as mentioned above of the present invention and characteristic will be clearer by describing through embodiments of the invention with reference to accompanying drawing, and accompanying drawing is as follows:
Fig. 1 is the principle block diagram of traditional OFDM receiver;
Fig. 2 is the more detailed block diagram that is used for the equalizer of a balanced ofdm signal according to embodiments of the invention;
Fig. 3 A is the view that shows an OFDM frame structure according to Fig. 2;
Fig. 3 B is the known array (kS) and the effective view of OFDM symbol that is presented among Fig. 3 A;
Fig. 4 is the view that shows a frequency spectrum, and it carries out Fourier transform by the N-DFT unit of Fig. 2;
Fig. 5 is the more detailed block diagram that is used for the equalizer of a balanced ofdm signal according to an alternative embodiment of the invention;
Fig. 6 is the view that shows according to the OFDM frame structure of Fig. 5; With
Fig. 7 A and Fig. 7 B are the flow charts that shows according to the equalization methods of the OFDM of being used for receiver of the present invention.
Embodiment
Embodiments of the invention will be described in the back in more detail with reference to accompanying drawing.
Fig. 1 is the principle block diagram of traditional OFDM receiver.
The OFDM receiver comprises analog to digital converter (ADC) 10, time domain equalization unit 20, (N-DFT) unit of leaf transformation in the N point discrete Fourier and forward error recovery device (FEC) 50.
ADC 10 changes into digital signal to paid-in ofdm signal.Time domain equalization unit 20 carries out equilibrium according to the synchronizing information of ofdm signal to ofdm signal in time domain, this synchronizing information is by reflector and receiver agreement.After, synchronizing information will be known as ' known array '.
N-DFT unit 30 is divided into known array carry out balanced ofdm signal according to known array, personal distance GI and effective OFDM symbol, and effective OFDM symbol is carried out Fourier transform at frequency domain.
FEC50 carries out the error-detecting of OFDM data according to predetermined error detection method to ofdm signal, and proofreaies and correct the error that is detected.
Fig. 2 is the more detailed block diagram that is used for the equalizer of a balanced ofdm signal according to embodiments of the invention.
N-DFT unit 30 comprises splitter 31, be used for known array is divided and be output into to the ofdm signal of the 20 quilt equilibriums in the time domain equalization unit, personal distance GI and effective OFDM symbol, the one DFT unit 32, be used for known array is carried out Fourier transform, the 2nd DFT unit 33, be used for effective OFDM symbol is carried out Fourier transform and frequency-domain balancing unit 40, known array based on carried out Fourier transform in the first and second DFT unit 32,33 is used for effective OFDM symbol is carried out equilibrium.
At first, as shown in Figure 3A, the frame of the ofdm signal that is sent out is configured so that in before N effective OFDM symbol, GI and known array are provided.Shown in Fig. 3 B, the N of the length of known array and N-DFT unit 30 relation of counting expressed by following formula 1:
[formula 1]
As implied above, effectively the length of OFDM symbol be known array length T k doubly.
Having as mentioned above, the ofdm signal of frame structure is imported into time domain equalization unit 20 and balanced by use known array quilt in time domain.
After time domain equalization unit 20 carried out time domain equalization, described ofdm signal was imported into the splitter 31 of N-DFT unit 30.This ofdm signal then is divided and is output into known array, personal distance GI and effective OFDM symbol.
Next, in the time domain shown in Fig. 3 B and be carried out Fourier transform by as above formula 1 expressed known array in a DFT unit 32 with length T.Then the 33 pairs of effective OFDM symbols in the 2nd DFT unit carry out Fourier transform and become N subcarrier in frequency domain.
In other words, as shown in Figure 4, periodically distribute known array on each k subcarrier of effective OFDM symbol.Because known array is the sequence by transmitting terminal and receiving terminal agreement, so its effect is the same with insertion pilot signal in frequency domain ofdm signal.
Therefore, periodically distribute on each k subcarrier of effective OFDM symbol based on known array, frequency-domain balancing unit 40 is the estimated channel distortion information very accurately, and the distortion on the transmission channel of this ofdm signal is proofreaied and correct.
As mentioned above, in a single day the ofdm signal that is received carries out equilibrium in time domain, with that known array and effective OFDM symbol is carried out Fourier transform, then based on the known array that generates in each the k subcarrier in frequency domain, proofreaies and correct effective OFDM symbol.As a result, can very accurately carry out the adjustment of data.
Fig. 5 has shown the equalizer that is used for a balanced ofdm signal according to second embodiment of the present invention;
N-DFT unit 300 comprises splitter 310, is used for an ofdm signal of the 20 quilt equilibriums in the time domain equalization unit and divides and be output into known array, personal distance GI and effective OFDM symbol; Window adjustment unit 321 is used for adjusting window that a kind of division adapts with multi-path environment so that select known array; The one DFT unit 323 is used for the known array through the window adjustment is carried out Fourier transform; And the 2nd DFT unit 330, be used for effective OFDM symbol is carried out Fourier transform and frequency-domain balancing unit 400.
At first, as shown in Figure 6, the frame of the ofdm signal that is sent out is configured so that in before N effective OFDM symbol, provides GI and two known arrays with equal length T.Shown in Fig. 3 B, the relation of the length of known array and the points N of this DFT by
(T, k=integer) expression.
With regard to reducing, more effective than the ofdm signal that has only a known array during data send, with regard to the influence of the adjacent symbols of appearance, having two known array kS of equal length T under the multipath conditions.
Ofdm signal with two known array kS of equal length T is imported into the time domain equalization unit 20 in the receiver, carries out equilibrium based on this signal of known array in time domain.
After 20 equilibriums of time domain equalization unit, this ofdm signal is imported into the splitter 310 of N-DFT unit 300.Follow described ofdm signal and be divided and be output into known array, personal distance GI and effective OFDM symbol.
Consider that known array divided by splitter 310, promptly, consider that described two known arrays have the equal length T shown in Fig. 3 B and expressed by formula 1, for the known array of a division selecting to be suitable for multi-path environment, window adjustment unit 321 is adjusted windows.Follow selecteed suitable known array and be carried out Fourier transform in a DFT unit 323.Because the known array through Fourier transform is handled through the window adjustment, so the length that this known array has is T.
Next, in frequency domain, effective OFDM symbol is carried out Fourier transform by the 2nd DFT unit 330 and form N subcarrier.
With reference to Fig. 4 as mentioned above, in each k subcarrier of effective OFDM symbol, periodically distribute known array.Because known array is the sequence by transmitting terminal and receiving terminal agreement, so its effect is the same with insertion pilot signal in frequency domain ofdm signal.
Therefore, periodically distribute on each k subcarrier of effective OFDM symbol based on known array, frequency-domain balancing unit 400 can be estimated the distortion information of each k subcarrier in the frequency domain, like this, frequency-domain balancing unit 400 can be proofreaied and correct the distortion on the transmission channel of this ofdm signal.
In addition, because two known arrays with equal length T are used and situation with ofdm signal of single known array is compared, the influence between intrasystem adjacent-symbol can more effectively be reduced in data transmission procedure.
Fig. 7 A and Fig. 7 B are the flow charts that shows according to the equalization methods of the OFDM of being used for receiver of the present invention.
Fig. 7 A has shown the equalization methods according to the OFDM receiver of first embodiment of the present invention Fig. 2.
At first, the ofdm signal with the known array that satisfies following formula 2 is imported into receiver:
[formula 2]
The ofdm signal that has received is converted to digital signal (step S10) by ADC unit 10, and based on known array, carries out time domain equalization (step S20) by time domain equalization unit 20.
After being carried out time domain equalization by time domain equalization unit 20, ofdm signal is imported into N-DFT unit 30, and is divided into known array by splitter 31, personal distance GI and effective OFDM symbol (step S30).
Known array and effective OFDM symbol carry out Fourier transform (step S40) respectively by the first and second DFT unit 32,33.
In other words, as shown in Figure 4, on each k subcarrier of effective OFDM symbol, periodically distribute known array.
Therefore, periodically distribute on each k subcarrier of effective OFDM symbol based on known array, frequency-domain balancing unit 40 can accurately be estimated the channel distortion information, and (step S50) proofreaied and correct in the distortion on the transmission channel of this ofdm signal.
Fig. 7 B has shown the equalization methods according to the OFDM receiver of second embodiment of the present invention Fig. 5.
At first, as shown in Figure 6 and the ofdm signal with the known array that satisfies formula 2 be imported into receiver.Through S10, steps such as S20 and S30, according to known array, the 20 pairs of ofdm signals that received in time domain equalization unit carry out time domain equalization, and splitter 310 is divided into known array respectively to it, personal distance GI and effective OFDM symbol (step S30).
Consider two known arrays with equal length T, window adjustment unit 321 is adjusted windows so that for the known array (step S410) of a division selecting to be suitable for multi-path environment.Then 323, the 330 pairs of selecteed suitable known arrays in the first and second DFT unit and effective OFDM symbol carry out Fourier transform (step S430).
Therefore, known array periodically is assigned on each k subcarrier of effective OFDM symbol, and based on this known array, the distortion on the transmission channel of this ofdm signal can accurately be proofreaied and correct (step S50).
As mentioned above, the known array that satisfies formula 2 is carried out Fourier transform, and, ofdm signal is carried out frequency domain equalization by using the known array on each the k subcarrier that periodically is assigned to effective OFDM symbol.As a result, balanced efficient is improved.
According to the present invention, after time domain equalization, the known array of crossing based on Fourier transform carries out frequency domain equalization by effective OFDM symbol that Fourier transform is crossed, and under the situation that does not need pilot signal independent in the frequency domain, balanced efficient is improved.
Though embodiments of the invention are described, one skilled in the art should appreciate that the present invention should be not limited to described embodiment, but, can in described spirit and scope of the present invention, do various changes and revision as what in additional claims, define.
Claims (6)
1. OFDM receiver comprises:
A time domain equalization unit is used for synchronizing information balanced ofdm signal in time domain according to ofdm signal;
Splitter is used for ofdm signal balanced in time domain is divided into known array, protection interval and effectively OFDM symbol and output;
The first discrete Fourier transform unit is used for known array is carried out Fourier transform, and this known array is by reflector and receiver agreement;
The second discrete Fourier transform unit, the known array based on carried out Fourier transform by the first discrete Fourier transform unit is used for the OFDM symbol is carried out Fourier transform;
Frequency-domain balancing unit is used for effective OFDM symbol is carried out frequency domain equalization, and described known array is assigned on each k subcarrier of effective OFDM symbol.
2. according to the OFDM receiver of claim 1, wherein, utilize the length of the effective OFDM symbol that is expressed as N, the known array length T that is input to first discrete Fourier transform is expressed as
Here, N, T and k are integers.
3. according to the OFDM receiver of claim 1, also comprise the window adjustment unit, when having at least two known arrays that are used for ofdm signal, the known array that is used to adjust a kind of division makes its suitable multi-path environment,
Wherein, the first discrete Fourier transform unit carries out Fourier transform to the known array through the window adjustment.
4. the equalization methods of an OFDM receiver, this method comprises the steps:
Input has the ofdm signal of known array and gives receiver;
The ofdm signal that receives is changed into digital signal;
In time domain, the ofdm signal that receives is carried out equilibrium based on known array;
Divide and export balanced ofdm signal and become known array, protection interval and effective OFDM symbol;
Respectively known array and effective OFDM symbol are carried out Fourier transform so that periodically distribute known array on each k subcarrier of effective OFDM symbol;
The estimated channel distortion information; With
Be based upon the known array that each k subcarrier of effective OFDM symbol distributes, the distortion that sends on the channel at the OFDM symbol is proofreaied and correct.
5. according to the equalization methods of claim 4, also comprise the steps:
For the known array of two equal lengths, adjust window so that select to be fit to the known array of a kind of division of multi-path environment;
Selecteed suitable known array and effective OFDM symbol are carried out Fourier transform respectively;
Based on known array, the distortion on the transmission channel of ofdm signal is proofreaied and correct accurately.
6. according to the equalization methods of claim 4 or 5, wherein, utilize the length of the effective OFDM symbol that is expressed as N, the length T of carrying out discrete Fourier transform is expressed as
Here, N, T and k are integers.
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| KR33178/2002 | 2002-06-14 | ||
| KR33178/02 | 2002-06-14 | ||
| KR1020020033178A KR20030095665A (en) | 2002-06-14 | 2002-06-14 | OFDM recevier |
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| CNB021468958A Expired - Fee Related CN100385835C (en) | 2002-06-14 | 2002-10-18 | OFDM receiver |
| CNA021468974A Pending CN1469561A (en) | 2002-06-14 | 2002-10-18 | Quadrature frequency division multiplexing receiver with pseudo-random noise generator |
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| KR101108952B1 (en) * | 2005-01-31 | 2012-02-06 | 엘지전자 주식회사 | Method and Apparatus for extracting the output data of frequency domain equalizer |
| KR101111509B1 (en) * | 2005-01-31 | 2012-02-24 | 엘지전자 주식회사 | Method and Apparatus for frequency-domain equalizing |
| KR100755125B1 (en) * | 2006-06-13 | 2007-09-04 | 엘지전자 주식회사 | Equalizer for signal by both single carrier modulation and multi carrier modulation and method thereof |
| CN102959918B (en) * | 2012-08-31 | 2015-02-25 | 华为技术有限公司 | A training sequence generating method, a training sequence generating device, and an optical communication system |
| US9945901B1 (en) * | 2016-10-18 | 2018-04-17 | Analog Devices, Inc. | Measuring and correcting non-idealities of a system |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0897798A (en) * | 1994-09-26 | 1996-04-12 | Nippon Columbia Co Ltd | Ofdm modulator and ofdm demodulator |
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| KR100224864B1 (en) * | 1997-08-20 | 1999-10-15 | 윤종용 | Equalizing method for ofdm receiver and equalizer |
| KR100338733B1 (en) * | 1998-07-30 | 2002-07-18 | 윤종용 | Method for equalizing and equalizer in OFDM receiver |
| KR100290855B1 (en) * | 1999-02-05 | 2001-05-15 | 구자홍 | Appartus for equarizing of digital broadcasting receiver |
| JP4488605B2 (en) * | 1999-07-30 | 2010-06-23 | パナソニック株式会社 | OFDM signal transmission method, transmitter, and receiver |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH0897798A (en) * | 1994-09-26 | 1996-04-12 | Nippon Columbia Co Ltd | Ofdm modulator and ofdm demodulator |
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| KR20030095665A (en) | 2003-12-24 |
| CN1466290A (en) | 2004-01-07 |
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Granted publication date: 20080430 Termination date: 20171018 |