CN1744590A - Method and device for anti-DC interference for orthogenic frequency-division multiplexing system - Google Patents
Method and device for anti-DC interference for orthogenic frequency-division multiplexing system Download PDFInfo
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- CN1744590A CN1744590A CN 200410074108 CN200410074108A CN1744590A CN 1744590 A CN1744590 A CN 1744590A CN 200410074108 CN200410074108 CN 200410074108 CN 200410074108 A CN200410074108 A CN 200410074108A CN 1744590 A CN1744590 A CN 1744590A
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Abstract
In time of OFDM system simulation, a weighting look table is built to reflect relation between modulation type, frequency offset of system and interference degree of system caused by DC source. In decoding time, based on the look table gives different weighting values for interfered sub carrier waves so that credible signal compensates interfered questionable signal in order to reach purpose of anti-DC interference of OFDM system.
Description
Technical field
The present invention is method and the device thereof that the anti-direct current of a kind of Orthodoxy Frequency Division Multiplex (OFDM) system disturbs.Particularly give the compensation of different weights at the ofdm signal transmission course to different modulation types and frequency offset, to reach the method and the device thereof of the purpose that anti-direct current disturbs about a kind of.
Technical background
Orthodoxy Frequency Division Multiplex (Orthogonal Frequency Division Multiplexing, OFDM) can be considered a kind of modulation technique, also can be considered a kind of multiplexing technique, being the load mode of a kind of multicarrier (Multi-carrier), is that the subcarrier that a data was ganged up low transmission rate is transmitted.One of important key of using OFDM is can increase the opposing frequency to select decay (frequency selective fading) or narrow frequency to disturb the ability of (narrowband interference).Because Digital Signal Processing (DSP) and very lagre scale integrated circuit (VLSIC) (VLSI) development of technology, nowadays OFDM has been widely used in the two-forty digital communication technology, as be applied on digital broadcasting, Digital Television and the WLAN, in the wireless and multimedia communication technology, OFDM will become one of indispensable technology in future.
Orthogonal frequency division multiplexer adopts a discontinuous multi-tone technology, and a large amount of signals in the carrier wave (carrier) of different frequency are merged into single signal, transmits and finish signal.The development of OFDM technology is in order to improve the spectrum of carrier utilance, or in order to improve modulation purpose to multicarrier, be characterized in each subcarrier mutually orthogonal (orthogonal), so the frequency spectrum after the band spectrum modulation can overlap mutually, thereby reduced phase mutual interference between subcarrier, can realize multiple reliable high speed data transfer.
Radio communication is in the process that transmits signal, the transmission end must be transmitted the frequency band that baseband signal is modulated to appointment with carrier wave, and receiving terminal is demodulated to baseband signal with the carrier wave of same frequency with signal again, but because the frequency oscillation device (oscillator) of transmission end and the required synthetic carrier wave of receiving terminal can not be identical, so just have the effect of frequency shift (FS) at receiving terminal.This frequency shift (FS) meeting makes direct current (DC) interference source interfere with the sub-carrier signal of close DC, and makes system effectiveness reduce, so it is quite important to ofdm system to solve the problem of this DC interference.
The configuration diagram of known Orthodoxy Frequency Division Multiplex receiving terminal as shown in Figure 1, ofdm signal is received by the radio-frequency module of receiving terminal, after being transformed into fundamental frequency signal, after the analog-digital converter sampling, through the discrete fourier change-over circuit by time domain (time domain) conversion of signals to frequency domain (frequencydomain) signal, frequency-region signal through etc. the change circuit do channel distortion compensation, at last by output signal behind the decoder decode.
The technology of problems such as known compensating signal interference or frequency shift (FS) is U.S. Patent No. 6 as shown in Figure 1,487, OFDM channel response method of estimation in the 253 described interfering processes (OFDM ChannelEstimation in the presence of Interference), promptly estimate the channel response (channel response) of this ofdm system by a plurality of training signals (training symbol), in this ofdm system running, as shown in the figure, RF module 201 is received from a plurality of RF signals that include training signal (trainingsymbol) that transmitting terminal is sent, after this ofdm signal is delivered to receiving system 202, via filtration, amplify and the analog and digital signal conversion, and transfer the signal of time domain to baseband channel (baseband channel), signal mat one anti-fast fourier conversion (IFFT) unit 203 is transferred to the signal of frequency domain with the pulse condition form of separating.Then obtain unit 206 and receive training signal in the signal by a training signal, channel estimation unit 207 is estimated the interference volume of this signal, the signal data of proofreading and correct in the frequency domain is used in changes computing (equalization) unit 204 that waits after then, and the decoding after being proofreaied and correct by decoding unit 205 is at last exported.
Compensate or proofread and correct though known technology has at the interference in the RF signal, but there is no the effect of considering the direct current interference signal in radio frequency (RF) assembly, the method and apparatus that the present invention carried is to draw corresponding various modulation type (modulation type) when ofdm system emulation, BPSK for example, QPSK, 16-QAM, 64-QAM etc., make weights table look-up (weighting look-uptable) with frequency offset (frequency offset), be subjected to the subcarrier of the interference of DC source to give different weights at ofdm signal, to reach the purpose that the anti-direct current of ofdm system disturbs at decoding unit.
Summary of the invention
The present invention is method and the device thereof that the anti-direct current of a kind of Orthodoxy Frequency Division Multiplex (OFDM) system disturbs, receiving terminal can use high frequency filter to remove filtering direct current interference source, yet high frequency filter also can damage near near the sub-carrier signal the DC source simultaneously.Another method is to eliminate the direct current interference source with the direct current arrester, that is to say to estimate earlier and the direct current interference volume at receiving terminal, remove to eliminate this direct current interference source with this estimated value then, the method can reduce the less number of sub carrier wave of injury, but estimation error is arranged during owing to estimation direct current interference volume, especially when there is frequency shift (FS) in system, the estimation error of direct current interference volume is bigger, so behind direct current arrester elimination direct current, still have remaining DC source and disturb near the sub-carrier signal of DC source.So must seek a more efficient methods again goes could improve the performance of ofdm communication system to the direct current interference source.
Make some subcarrier of ofdm system be subjected to the interference of DC source because of frequency offset, so can corresponding various modulation types (modulation type), for example BPSK, QPSK, 16-QAM, 64-QAM etc., make weights with frequency offset (frequency offset) and table look-up (weighting look-up table) to decoding unit, when decoding, give different weights, reach the purpose that the anti-direct current of ofdm system disturbs at the subcarrier that is disturbed.
The method step that the anti-direct current of the present invention disturbs includes:
Receive ofdm signal by a RF module; With this ofdm signal of demodulator circuit demodulation; Introducing weights tables look-up; Utilize lookup table mode, give different weights at decoding unit for the subcarrier that is disturbed with a frequency offset according to a modulation type.
And wherein weights to table look-up be to make in advance, the step that comprises has:
RF module in the ofdm system produces the test signal of the OFDM of various different frequency side-play amounts; The RF module of receiving terminal receives the test signal of this ofdm system, and the RF module tool direct current interference source of receiving terminal; In order to make receiving terminal have less packet error, it is that modulation type and this frequency offset according to this signal produces that these weights are tabled look-up.
The included device of one embodiment has: a RF module is for receive the device of an ofdm signal through a communication channel; Flow disturbance source estimation unit is to be electrically connected this radio-frequency module, to be received from the DC source that this radio-frequency module produces always; One demodulator circuit is to be electrically connected this RF module; One Frequency offset estimation unit is to be electrically connected this demodulator circuit, to do a frequency offset estimation at this ofdm signal, and deserved weights are tabled look-up according to this frequency offset and a modulation type again; And a decoder, be to be electrically connected this demodulator circuit, and give the output of decoding again of different weights to the subcarrier that is disturbed should weights tabling look-up.
Description of drawings
Figure 1 shows that U.S. Patent No. 6,487, the system architecture schematic diagram of the OFDM channel response method of estimation in the 253 described interfering processes;
Fig. 2 A is baseband signal and frequency shift (FS) schematic diagram;
Fig. 2 B is baseband signal and frequency shift (FS) schematic diagram;
Fig. 2 C is baseband signal and frequency shift (FS) schematic diagram;
Figure 3 shows that the ofdm system configuration diagram of Orthodoxy Frequency Division Multiplex framework of the present invention;
Figure 4 shows that the preceding DC source of ofdm system running of the present invention is estimated and the most preferred embodiment schematic diagram of compensation;
The flow chart of steps that Fig. 5 tables look-up and produces for weights in the anti-direct current interference method of the present invention;
The method step flow chart that Fig. 6 disturbs for the anti-direct current of orthogenic frequency-division multiplexing system of the present invention.
The figure number explanation
201 RF modules, 202 receiving systems
203 anti-fast fourier converting unit 204 arithmetic elements such as grade
205 decoding units, 206 training signals are obtained the unit
207 channel estimating unit
40 transmission ends, 41 communication channels
42 RF modules, 43 demodulator circuits
45 decoders such as 44 circuit such as grade
46 weights, 401 input signals of tabling look-up
402 modulation circuits, 403 digital analog converters
404 RF modules, 47 direct current interference source estimation units
48 Frequency offset estimation unit, 49 analog-digital converters
Embodiment
In the system of Orthodoxy Frequency Division Multiplex (OFDM), because of environment or wherein the factor of assembly cause the signal interference in when transmission, especially as the interference of DC source (DC) in the RF assembly, as Fig. 2 A is the base-band signal spectrum of the ofdm signal of transmission end, if receiving terminal does not have the phenomenon of frequency shift (FS) (frequency offset) when demodulation (demodulate), the base-band signal spectrum that receives should be shown in Fig. 2 B, the direct current interference source can interfere with the DC subcarrier of ofdm system, because the DC subcarrier of ofdm system is the subcarrier of a sky usually, do not carry any signal, so this moment, the direct current interference source did not interfere with ofdm system.But the frequency shift (FS) phenomenon that produces because of frequency of oscillation is different between the transmission end and receiving terminal in the ofdm system is arranged if separate timing; the base-band signal spectrum that receives is shown in Fig. 2 C; the direct current interference source can be because the size of frequency offset; and interfere with ofdm system some the subcarrier that carries signal is arranged; therefore can cause the mistake and the deviation of ofdm system decoding; so the weights that mat of the present invention is set up are in advance tabled look-up (weighting look-up table); according to the different frequency side-play amount; and give different weights; make in decoding end and can protect insecure information, to reach the purpose of anti-direct current interference source with reliable information.
The ofdm system configuration diagram of Orthodoxy Frequency Division Multiplex framework as shown in Figure 3, ofdm system can generally be divided into signal transmission ends, signal receiving end and communication channel therebetween (channel).As shown in the figure, there is an input signal 401 transmission end 40 through modulation circuit 402 filtering, modulation circuit 402 is changed (lnverse Discrete Fourier Transform by anti-discrete fourier thus, IDFT) by frequency domain (frequencydomain) conversion of signals to time domain (time domain) signal, by digital analog converter 403 digital signal is converted to analog signal again.
At this moment, analog signal is transmitted by the RF module 404 of transmission end 40, through communication channel (channel) 41, its medium such as air etc., after radio frequency (RF) module 42 receptions by the OFDM receiver, signal is transferred to the receiving terminal internal circuit, include the conversion of the analog and digital signal transducer 49 of conversion of signals, be discrete fourier conversion (Discrete Fourier Transform by demodulator circuit 43 again, DFT), and then be sent to first-classization circuit 44, each subcarrier is done the compensation of communication channel distortion, after decoder 45 draws output signal.The present invention can use the direct current arrester to eliminate most direct current interference source and compensating frequency side-play amount earlier at receiving terminal, then, cooperate modulation type and frequency offset again, design weights (the weighting look-up table) 46 that table look-up, when decoder 45 is decoded, give different weights at the subcarrier that is disturbed (sub-carrier).The subcarrier that is promptly disturbed gives less weights, reaches the purpose with the insecure information of reliable information protection.
And Figure 4 shows that the ofdm system configuration diagram that anti-direct current disturbs.When an ofdm system is tested, send ofdm signal is sent to near-end via communication channel 41 RF module 42 by transmission end shown in Figure 3 40, again with analog-digital converter 49 switching signals, because the DC source effect that RF module 42 itself produces is disturbed ofdm signal, so the present invention can be provided with a direct current interference source estimation unit 47 that is electrically connected this RF module 42 and make circuit as the reality of cancellation DC source effect, one embodiment can partly be filtered High-frequency Interference through a low pass filter (low-pass filter) by the signal that RF module 42 is received, more interference signals is done a mean value computing by an average calculating operation unit and draws the estimated value that direct current disturbs.After eliminating the direct current interference, with a Frequency offset estimation unit 48, do frequency offset compensation at this signal of receiving, and then according to this frequency offset and this modulation type to deserved weights (the weightinglook-up table) 46 that table look-up, when the subcarrier of this channel through etc. change circuit 44 when entering decoder 45 decodings, promptly corresponding these weights 46 pairs of subcarriers that disturbed of tabling look-up give different weights.
Above-mentioned modulation type (modulation type) is as quadrature amplitude modulation (Quadrant AmplitudeModulation, QAM) etc. transmission means, various signal kenels have different resistivities to environment or the next noise of assembly, its kenel information can be learnt by each ofdm signal file header (header), so when the present invention tables look-up in these weights of design, promptly cooperate frequency offset to give different weights again at different modulation types.When actual ofdm system operates, the different weights of subcarrier that the weights that corresponding this mat emulation in advance (simulation) is made when decoding are tabled look-up and disturbed at different situations.
Fig. 5 is the weights of the anti-direct current interference method of the present invention generation steps flow chart of tabling look-up.The RF module of receiving terminal receives the signal from transmission ends in the ofdm system, in the step that the generation weights are tabled look-up, can produce a plurality of test signals (step S60) by the RF module in this ofdm system, detecting direct current interference source (step S61), and estimate the frequency offset (step S62) of the RF of system module to system; Produce weights table look-up (step S63) according to the frequency shift (FS) of different modulation type and system.Give different weights when decoding at the subcarrier that is disturbed at last, to reach the purpose that the anti-direct current of the present invention disturbs.
See also the method step flow chart that the anti-direct current of orthogenic frequency-division multiplexing system of the present invention shown in Figure 6 disturbs.
During beginning, receiving the ofdm signal that is produced by transmission ends by RF module in the ofdm system, is the signal (multi-carrier) (step S71) of a multicarrier;
Is digital signal (step S72) through a transducer with the analog signal conversion that receives;
Carry out the signal demodulation by the demodulator circuit of realizing with the discrete fourier change-over circuit, wherein the discrete fourier change-over circuit is anti-fast fourier conversion and the real circuit (step S73) of doing of fast fourier conversion;
Distortion phenomenon (step S74) through communication channel such as circuit modifications such as gradeization;
When signal enters decoder, introduce weights of making in advance table look-up (step S75);
Utilize lookup table mode, comply with the different weights (step S76) of subcarrier that different modulation types and frequency offset are disturbed;
Decode the signal (step S77) of weights effect;
Protect the lower unreliable signal of weights via the reliable signal that above-mentioned steps can be higher with weights, to reach purpose of the present invention.
In sum; the present invention is method and its device that the anti-direct current of an orthogenic frequency-division multiplexing system disturbs; be to disturb ofdm signal and propose weights and table look-up at the DC source effect that the RF assembly produces; give different weights to the subcarrier that is subjected to the direct current interference source; reach the purpose that anti-direct current disturbs with the insecure signal of reliable signal protection; be rare invention article in fact; and the practicality on the tool industry; novelty and progressive; meet the application for a patent for invention important document fully; file an application in the whence in accordance with the law; would like to ask detailed survey and grant accurate this case patent, to ensure inventor's rights and interests.
Only the above only is a preferable possible embodiments of the present invention, and non-so promptly inflexible limit claim of the present invention so use specification of the present invention and the equivalent structure variation for it of icon content institute such as, all in like manner is contained in the scope of the present invention, closes and gives Chen Ming.
Claims (10)
1. the method disturbed of the anti-direct current of an orthogenic frequency-division multiplexing system is characterized in that this method comprises the following step at least:
Receive an orthogonal frequency division multiplex signal by a radio-frequency module;
By this orthogonal frequency division multiplex signal of demodulator circuit demodulation;
Introducing weights tables look-up;
Utilize lookup table mode, comply with the different weights of subcarrier that a modulation type and a frequency offset give respectively to be disturbed; And
Decode the signal of weights effect.
2. the method that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 1 disturbs is characterized in that this frequency offset is different with frequency of oscillation between the receiving terminal and produce by a transmission end of this orthogenic frequency-division multiplexing system.
3. the method that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 1 disturbs is characterized in that this demodulator circuit can realize by a discrete fourier change-over circuit.
4. the method that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 1 disturbs is characterized in that this modulation type learnt by the file header information of this orthogenic frequency-division multiplexing system signal.
5. the method for the anti-direct current interference of orthogenic frequency-division multiplexing system as claimed in claim 1 is characterized in that it is tabling look-up of making in advance that these weights are tabled look-up, and the method step of generation comprises:
Produce the test signal of a plurality of multicarriers, produce by this radio-frequency module in this orthogenic frequency-division multiplexing system;
Reception is from the test signal of this orthogenic frequency-division multiplexing system transmission ends, by this radio-frequency module reception of receiving terminal;
Estimate frequency offset; And
Produce these weights and table look-up, according to the modulation type and the generation of this frequency offset of this signal.
6. the method that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 5 disturbs, it is characterized in that after the step of this reception, estimate the direct current interference source that this radio-frequency module produces this orthogenic frequency-division multiplexing system with the source of a flow disturbance always estimation unit that is electrically connected this radio-frequency module from the test signal of this orthogenic frequency-division multiplexing system transmission ends.
7. the method that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 5 disturbs is characterized in that this step that estimates frequency offset is to reach with a Frequency offset estimation unit that is electrically connected this demodulator circuit.
8. the device that disturbs of the anti-direct current of an orthogenic frequency-division multiplexing system is characterized in that this device includes at least:
One radio-frequency module is for receiving the device of an orthogonal frequency division multiplex signal through a communication channel;
Flow disturbance source estimation unit is to be electrically connected this radio-frequency module, to be received from the DC source that this radio-frequency module produces always;
One demodulator circuit is to be electrically connected this radio-frequency module;
One Frequency offset estimation unit is to be electrically connected this demodulator circuit, to do a frequency offset estimation at this DC source, and deserved weights are tabled look-up according to this frequency offset and a modulation type again; And
One decoder is to be electrically connected this demodulator circuit, and gives the output of decoding again of different weights to should weights tabling look-up to the subcarrier that is disturbed.
9. the device that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 8 disturbs is characterized in that this direct current interference source estimation unit connects an average calculating operation unit with a low pass filter and reaches.
10. the device that the anti-direct current of orthogenic frequency-division multiplexing system as claimed in claim 8 disturbs, wherein this demodulator circuit can be realized by a discrete fourier change-over circuit.
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| Application Number | Priority Date | Filing Date | Title |
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| CN 200410074108 CN1744590A (en) | 2004-08-31 | 2004-08-31 | Method and device for anti-DC interference for orthogenic frequency-division multiplexing system |
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| CN 200410074108 CN1744590A (en) | 2004-08-31 | 2004-08-31 | Method and device for anti-DC interference for orthogenic frequency-division multiplexing system |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2459504A (en) * | 2008-04-25 | 2009-10-28 | Ipwireless Inc | Wireless communication unit and method for dc offset estimation and compensation |
| WO2022142817A1 (en) * | 2020-12-30 | 2022-07-07 | 展讯通信（上海）有限公司 | Direct-current interference estimation method and device, and storage medium and terminal |
-
2004
- 2004-08-31 CN CN 200410074108 patent/CN1744590A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2459504A (en) * | 2008-04-25 | 2009-10-28 | Ipwireless Inc | Wireless communication unit and method for dc offset estimation and compensation |
| GB2459504B (en) * | 2008-04-25 | 2010-06-16 | Ipwireless Inc | Wireless communication unit and method for channel estimation |
| US8160164B2 (en) | 2008-04-25 | 2012-04-17 | Wireless Technology Solutions Llc | Wireless communication unit and method for channel estimation |
| US8559565B2 (en) | 2008-04-25 | 2013-10-15 | Nvidia Corporation | Wireless communication unit and method for DC offset estimation |
| US8787472B2 (en) | 2008-04-25 | 2014-07-22 | Nvidia Corporation | Wireless communication unit and method for channel estimation |
| WO2022142817A1 (en) * | 2020-12-30 | 2022-07-07 | 展讯通信（上海）有限公司 | Direct-current interference estimation method and device, and storage medium and terminal |
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