CN1385975A - Method for inhibiting peak-to-average ratio in orthogonal frequency division complex communication system - Google Patents
Method for inhibiting peak-to-average ratio in orthogonal frequency division complex communication system Download PDFInfo
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Abstract
A peak flat specific suppression method of OFDM communication system contains a subcarrier baseband signal modulated by OFDM is sent to a predict device to calculate the amplitude value of the baseband signal points, and predict the peak value after top sampling to judge the deducted signal power value during clipping operation then to clip the baseband signal. The clipped signal then is sent to the top sampling and profiling filter unit to get to the RF terminal via analog orthogonal modulation to finish the transmission of communication system. This invention can be used in monocarrier, multi-carrier OFDM communication system radio local area network and very clear digit TV and broadcast.
Description
Technical field:
The present invention relates to a kind of method for inhibiting peak-to-average ratio of orthogonal FDM communication system, is a kind of method that suppresses signal peak power in communication system, reduce peak-to-average ratio, belongs to digital communication technology field.
Background technology:
(Orthogonal Frequency Division Multiplexing is the very high modulation system of a kind of channel utilization OFDM), has good anti-fading ability, and can realize the parallel convey of data in the OFDM modulation.Along with the extensive use of digital signal processing technology rapid development and large scale integrated circuit, OFDM is subjected to paying close attention to widely day by day, especially in the high-speed digital communication field.
In ofdm communication system, use has synchronized relation on frequency a plurality of carrier waves come modulation signal, because the envelope value of each carrier wave statistics is independent, increase along with carrier number, the peak power of stack back signal and the ratio of average power, be that (peak-to-average power ratio, numerical value PAPR) is bigger for peak-to-average ratio.Therefore, the dynamic range of modulation signal is quite big, this has higher linear amplification scope with regard to requiring the power amplifier in the system, with frequency spectrum diffusion and the nonlinear distortion of avoiding transmission signals, simultaneously also require follow-up D/A converter to have bigger transition width, so just increased system cost and realized difficulty.
At present, reduce the ofdm communication system signal peak-to-average than following several method is generally arranged: direct slicing, windowing, partial transmission sequence etc.Directly slicing is promptly directly pruned the peak power that is higher than thresholding, and it is the most simple and practical method, but it has introduced new noise to system, and bigger to the influence of spectral characteristic, makes the band outdiffusion serious, influences the signal of adjacent channel.The method of windowing limits signal peak power with a window function, for in order to be effective, need under the later higher rate of up-sampling, handle signal, therefore implement the comparison difficulty, and it also can influence the spectral characteristic of signal, and this method is proposed in civilian Reducing the Peak-to-Average Power Ratioof OFDM (IEEE VTC ' 98) by Richard van and Arnout de Wild.The method of partial transmission sequence is, if one group of time-domain signal amplitude that sends symbol is higher than desired threshold value, then this group code is carried out conversion by the known conversion of a kind of receiving end, till its time domain signal amplitude meets the demands, simultaneously the parameter of conversion is sent to the other side with very little cost, though it is relatively good that this method reduces the effect of peak-to-average ratio, but it is difficult in realization, and all need add-on module at the modulation end, this method by Leonard J.Cimini and Nelson R.Sollenberger at civilian Peak-to-Average Power Ratio Reduction of anOFDM Signal Using Partial Transmit Sequences (IEEE COMMUNICATIONS LETTERS, VOL.4 NO.3, MARCH 2000) the middle proposition.
Summary of the invention:
The objective of the invention is to above-mentioned deficiency at prior art, a kind of new method for inhibiting peak-to-average ratio that is applicable to orthogonal FDM communication system is provided, can handle accordingly low power speed signal according to the signal peak envelope behind the up-sampling being carried out prediction result, guarantee that the signal behind up-sampling and the molding filtration has lower peak-to-average ratio, and realization is easy, cost is lower, can be the extent of damage of signal being reduced to minimum.
For realizing such purpose, in the technical scheme of the present invention, adopt the method for prediction slicing to reduce system's peak-to-average ratio, at first the subcarrier baseband signal of OFDM modulation is sent into fallout predictor, calculate the amplitude of baseband signal point earlier, peak value to the point behind the ofdm communication system up-sampling is predicted, judge the signal power value that needs reduce in the slicing operation according to prediction result, according to these parameters baseband signal is carried out the slicing operation again, signal after the slicing is delivered to up-sampling and molding filtration unit, reach radio-frequency head by analog quadrature modulation then, finish the transmission work of ofdm communication system.Concrete operations of the present invention are carried out as follows:
1, the peak value of the point behind the up-sampling is predicted.
The method of prediction slicing at first needs the peak value of the point behind the ofdm communication system up-sampling is predicted, specific practice is, the later baseband signal of modulation is sent into predicting unit, when the rate of adopting on the ofdm system is n, to insert (n-1) individual zero point in per two adjacent signaling points of input, then the coefficient of signal amplitude and formed filter is lacked convolution, promptly current demand signal point i before one times of fast signaling point and the influence of the individual one times of fast signaling point of j afterwards to current point are only taken into account in the calculating of each signaling point, the result who obtains like this is the predicted value M of the corresponding upsampled signal point of this point.Why can predict in this way, be because up-sampling and molding filtration together, can equivalence be the FIR filter of certain exponent number, the linearity that the final output result of FIR can regard the unit impact response of individual data in the list entries as add with.One times of speed input base band amplitude data formation impulse response separately, on output point after adopting actual be the linear weighted function of the impulse responses of adjacent numerous one times of speed point, therefore we can go out the amplitude of high power speed point by the amplitude of adjacent several low power speed points with higher accuracy prediction.I above-mentioned and j are for before the last current point of one times of speed that participates in prediction and number afterwards.Obviously, increase i and j and can improve accuracy of predicting, but will increase the complexity of prediction algorithm, this depends on the required precision that system realizes, generally gets i=j=5.The coefficient of FIR filter calculates and preserves according to 45 rank root raised cosine filters, directly calls in the implementation procedure.
2, judge and in the slicing operation, to need the signal power value that reduces
After prediction, need judge the parameter of the slicing operation that will carry out the back according to prediction result, promptly in slicing operation, need the signal power value that reduces, specific practice is, dope the amplitude M of some A1 on four times of speed after, according to the threshold T h that reserves in advance, value to M is judged, if it is greater than Th, then its consecutive points is carried out the slicing operation, otherwise then be left intact.In slicing operation, the amplitude of A1 need be by the M-Th that prunes, promptly behind the slicing with slicing before the ratio of A1 amplitude be:
Needing in the slicing operation so just to have obtained the signal power ratio η that reduces, be i.e. will have multiply by coefficient η to the amplitude of some consecutive points before and after the A1 in the slicing operation, how many required precision decisions in realizing according to system of specifically counting, generally get at preceding 1 after 2 points.
3, according to prediction result baseband signal is carried out the slicing operation.
Behind the signal power ratio that obtains to carry out the point of slicing operation in front in the operation of two steps and need to reduce, to carry out the slicing operation to baseband signal according to these parameters, because what occur in the forecasting process all is the amplitude amount of signal, therefore but what face when slicing is operated is the data on I, Q road, will be mapped to I to the slicing operating process, get in the Q road.
The method that I, Q two paths of signals are handled is, I, the corresponding numerical value of Q two-way are reduced in proportion, just multiply by coefficient η, implements fairly simplely like this, can guarantee that also the resultant vector phase angle of I, Q two-way is constant.In the concrete operations, after obtaining to carry out one times of speed point of slicing operation, I, the Q way value of these signaling points all be multiply by the η value synchronously.
4, deliver to up-sampling and molding filtration through the signal after the processing of prediction slicing
Signal after handling through the prediction slicing, the peak-to-average ratio after up-sampling and molding filtration can reach requirement substantially, and can change threshold value as required in operating process, and the effect that can guarantee to reduce peak-to-average ratio reaches the target of system design.Predict that the signal after the slicing will deliver to up-sampling and molding filtration unit, reach radio-frequency head by analog quadrature modulation then, thereby finish the transmission work of ofdm communication system.
More than be the method that the prediction slicing reduces peak-to-average ratio in the single carrier ofdm communication system, when ofdm communication system was multicarrier, this method also can be used.In the multicarrier system, the phase place of different carrier signal is not quite similar, therefore the vector that closes transmission signals behind the road and be each carrier signal is synthetic, the peak value of signal will be reduced to Th by M behind the road if will close, by the relation of geometric similarity, the signal phasor of each carrier wave is as long as amplitude becomes original under former phase place situation
Doubly, just can reach the purpose of accurate reduction system peak-to-average ratio, and the signal phase that closes behind the road is constant.
The present invention in the up-sampling of OFDM modulated process and the speed stage of the low power before the formed filter signal peak envelope after to up-sampling predict, according to prediction result low power speed signal is handled accordingly then, thereby guaranteed that the signal behind up-sampling and the molding filtration has lower peak-to-average ratio.This method is implemented on before the formed filter, therefore the almost not influence of spectral performance to modulating the back signal; And owing to be to handle on low power speed, therefore difficulty and the cost that implements is also lower; While therefore can be the extent of damage of signal being reduced to minimum because relevant processing is to carry out after the signal envelope behind the molding filtration is predicted more accurately.
Verify that through in the ofdm communication system link simulation, adding prediction slicing unit the result who obtains shows that the present invention predicts that the method for slicing is significantly to the effect that reduces system's peak-to-average ratio, and smaller to the damage of signal.Compare with the method for direct slicing, method of the present invention is to the damage of signal, and is especially much smaller to the damage of frequency domain performance, but effect is basic identical; Compare with methods such as windowing, partial transmission sequence, encoding compression, method of the present invention not only reduces the effective of peak-to-average ratio, and realizes that difficulty is much lower, and therefore, the prediction slicing is a more satisfactory method that reduces the ofdm communication system peak-to-average ratio.
The present invention can be used for single carrier ofdm communication system, multi-carrier OFDM communication system, also can be applied to WLAN (wireless local area network) as in the 802.11 serial protocols implementation procedures, and in realizing HD digital television broadcasting such as DVB protocol procedures.
Description of drawings:
Fig. 1 predicts the clipping method functional block diagram for the present invention.
As shown in the figure, the present invention asks amplitude to I, Q two-way baseband signal earlier, lack convolution with the coefficient of filter then, calculate the parameter of slicing operation according to the result who obtains, parameter is delivered to the slicing operating unit, respectively this parameter and I, Q two paths of signals are multiplied each other, pass the signal along to up-sampling and molding filtration unit then.
Fig. 2 is applied to single carrier ofdm communication system functional block diagram for the present invention predicts clipping method.
As shown in the figure, the present invention predicts and the slicing operation that with I, Q two-way baseband signal that OFDM modulates gained the signal that obtains carries out up-sampling and molding filtration, delivers to radio-frequency head by analog quadrature modulation then.
Fig. 3 is applied to multicarrier (is example with two carrier waves) ofdm communication system functional block diagram for the present invention predicts clipping method.
As shown in the figure, the present invention sends the baseband signal of each carrier wave into fallout predictor earlier, predict the peak power of each carrier wave after stack on the high power speed, carrying out relevant parameters according to the result calculates, then the baseband signal of the parameter that obtains and each road carrier wave is multiplied each other respectively, the signal of each carrier wave of the above processing of process carries out up-sampling and molding filtration respectively, delivers to radio-frequency head by analog quadrature modulation then.
Embodiment:
Below by specific embodiment technical scheme of the present invention is further described.Embodiment is for having used WLAN (wireless local area network) 802.11a protocol system of the present invention.This system has adopted the modulation system of 16QAM, 3 times of speed samplings on the baseband signal, and formed filter is 45 rank root raised cosine filters, and filter impulse response peak value is 8192, and the threshold T h in the prediction slicing is decided to be 1700.In order to estimate the degree of injury of prediction slicing to signal, vector error mean value commonly used on the engineering, promptly EVM (Error Vector Mean) is as evaluation standard.The concrete steps that the present invention is applied to the 802.11a protocol system are:
1, the peak value of the point behind the up-sampling is predicted.
To insert 2 zero points in per two adjacent signaling points of input, then the coefficient of signal amplitude and formed filter is lacked convolution, promptly 5 one times of fast signaling points and the influence to current point of afterwards 5 one times of fast signaling points before the current demand signal point are only taken into account in the calculating of each signaling point, obtained the predicted value M of the upsampled signal point of this point correspondence like this.
2, judge and in the slicing operation, to need the signal power value that reduces
After doping the amplitude M of some A1 on 3 times of speed,, the value of M is judged,, then its consecutive points are carried out the slicing operation, otherwise then be left intact if it is greater than 1700 according to the threshold T h=1700 that reserves in advance.In slicing operation, the amplitude of A1 need be by the M-1700 that prunes, promptly behind the slicing with slicing before the ratio of A1 amplitude be:
Needing in the slicing operation so just to obtain the signal power ratio η that reduces, in the slicing operation, the amplitude of 1 point in A1 front and 2 points in back multiply by coefficient η.
3, according to prediction result baseband signal is carried out the slicing operation.
After obtaining to carry out 1 times of speed point of slicing operation, I, the Q way value of these signaling points all be multiply by η value synchronously, operate thereby finish slicing.
4, deliver to up-sampling and molding filtration through the signal after the processing of prediction slicing
Predict that the signal after the slicing delivers to up-sampling and molding filtration unit, reach radio-frequency head by analog quadrature modulation then, thereby finish the transmission work of ofdm communication system.
When predicting slicing, the peak-to-average ratio of 802.11a wireless local area network (WLAN) system is about 10dB, after above-mentioned prediction slicing operation, system's peak-to-average ratio is reduced to 7dB, the EVM value of simultaneity factor is-22.6, and the highest EVM value of regulation is-19 in the 802.11a agreement, considers that reserving surplus for modules such as back radio frequencies is 3, be that the EVM value will be lower than-22, therefore, after having used the present invention, under the prerequisite that guarantees systematic function, reduce peak-to-average ratio and reach 3dB, obtained good effect.
Claims (4)
1, a kind of method for inhibiting peak-to-average ratio of orthogonal FDM communication system is characterized in that comprising the steps:
1) the speed stage of the low power before up-sampling and formed filter, signal peak envelope behind the up-sampling is predicted, the later baseband signal of modulation is sent into predicting unit, the coefficient of signal amplitude and formed filter is lacked convolution, promptly current demand signal point i before one times of fast signaling point and the influence of the individual one times of fast signaling point of j afterwards to current point are only taken into account in the calculating of each signaling point, obtained the predicted value M of the corresponding upsampled signal point of this point;
2) if predicted value M greater than the threshold T h that reserves in advance, then carries out the slicing operation to its consecutive points, the signal power ratio that needs to reduce in the slicing operation is η=Th/M;
3) according to the slicing requirement of amplitude, I, the corresponding numerical value of Q two-way of signaling point be multiply by coefficient η, guarantee that the resultant vector phase angle of I, Q two-way is constant;
4) will deliver to up-sampling and molding filtration unit through the signal after the processing of prediction slicing, reach radio-frequency head by analog quadrature modulation then, finish the transmission work of ofdm communication system.
2, as the method for inhibiting peak-to-average ratio of the said orthogonal FDM communication system of claim 1, the signaling point i=5 that is got in it is characterized in that predicting, j=5 to the required precision higher system, can increase the value of i and j.
3, as the application of the method for inhibiting peak-to-average ratio of the said orthogonal FDM communication system of claim 1, it is characterized in that being used for single carrier or multi-carrier OFDM communication system.
4,, it is characterized in that being used for WLAN (wireless local area network) 802.11 serial protocols or realize HD digital television broadcasting DVB protocol procedures as the application of the method for inhibiting peak-to-average ratio of the said orthogonal FDM communication system of claim 1.
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| WO2007009361A1 (en) * | 2005-07-15 | 2007-01-25 | Huawei Technologies Co., Ltd. | A method and system for inhibiting peak-to-average power ratio in orthogonal frequency division multiplexing system |
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| CN100364302C (en) * | 2005-01-28 | 2008-01-23 | 北京北广科数字广播电视技术有限公司 | Digital audio frequency processing method for analog amplitude modulation medium wave broadcasting transmitter digital improvement |
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