CN101150357A - Method for eliminating peak power - Google Patents
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- CN101150357A CN101150357A CNA2006101132501A CN200610113250A CN101150357A CN 101150357 A CN101150357 A CN 101150357A CN A2006101132501 A CNA2006101132501 A CN A2006101132501A CN 200610113250 A CN200610113250 A CN 200610113250A CN 101150357 A CN101150357 A CN 101150357A
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Abstract
This invention relates to a method for eliminating power of peak values including: 1, carrying out interpolation filter to each channle signals after modulation and spread to change them to signals of different frequency points, 2, making linear overlapping all the frequency point signals on the time domain, 3, carrying out cancel of peaks to signals needing clipping according to the clipping sequence regulated according to the change of amplitude, which can adaptively regulate peak-clipping sequencies of 1 path and Q to adaptively eliminating power of peak values and the loss of phase information of original signals is the least.
Description
Technical Field
The present invention relates to the field of communications, and in particular, to a method for eliminating peak power in a TDD (time division duplex) multi-frequency point communication system and a communication terminal for implementing the same.
Background
In a cell of a TDD communication system (such as a TD-SCDMA time division synchronous code division multiple access communication system and an OFDM _ TDD orthogonal frequency division multiplexing time division duplex communication system), since multiple frequency point signals to be transmitted are combined at a digital intermediate frequency so as to be transmitted by using one set of transmitter in a subsequent radio frequency channel, a strong signal to average power ratio (PAPR) generated by peak-to-peak superposition occurs at an antenna transmitting end. The peak power is too large, which easily causes the transmission of the radio frequency to the non-linear region, thereby generating a strong ACLR (Adjacent Channel Leakage power Ratio of the transmitter), and further reducing the system performance. If non-linear distortion is not wanted, the power of the transmitted signal must be less than 1dB compression point, which requires the average power of the signal to be reduced, but in this case, the efficiency of the power amplifier is reduced, and the power of the rf transmitted signal cannot reach the dB required by the physical layer, so that the coverage of the base station is reduced and the signal power of the user is damaged. Moreover, a high peak-to-average ratio results in a smaller dynamic range of the D/a converter, which greatly increases the cost if a D/a converter with a higher order is used, and increases the quantization noise if a D/a converter with a lower order is used.
Three methods for reducing the peak-to-average ratio are proposed in the prior art: clipping, sequence selection and phase-amplitude transformation. In TDD multi-frequency point systems, the sequence selection method is complex to implement and is not usually adopted. The clipping method is to clip a peak having an excessively high power, and is likely to generate nonlinear distortion. In one of the time domain peak clipping frequency domain filtering methods, a hard decision method is used to perform hard clipping on data exceeding a threshold power, and then a filter is used to clip nonlinear distortion caused by the hard clipping. However, this method does not completely remove the nonlinear distortion, and still results in a large spectral leakage.
Although the phase-amplitude transformation method does not generate nonlinear distortion, if the peak ratio is optimized after each rotation, a large amount of calculation is needed, sideband information needs to be transmitted, the time delay is large, the processing is complex, and the transmission of the sideband information is easy to generate error diffusion.
To this end, the applicant disclosed a method of peak power in application No. 200610007411.9, 8.2.2006, combining two methods of peak-to-average ratio reduction. In the method, the applicant performs peak clipping processing on N/2 data symbols before and after a peak power point and a peak clipping sequence with the same length. The peak clipping operation is only simple addition and subtraction operation, and does not use multiplication operation, so the processing speed of peak clipping is high and the peak clipping is easy to realize. Through the peak clipping processing of the invention, the peak-to-average ratio is reduced.
The TDD system adopts the intelligent antenna, the base station needs to send a plurality of sets of data each time when sending DL (downlink) data, each set of data is sent by using one antenna, each set of data has different beam weighting factors for beam forming, and the beam weighting factors are obtained by carrying out channel estimation on UL (uplink) data. The peak clipping process is to perform peak clipping on each path of data independently, and the prior art generally adopts a digital interpolation method, i.e., peak data detected in a time domain is added or subtracted with a preset peak clipping pulse coefficient, so that a peak clipping sequence is inserted compared with an input digital signal. If the peak clipping process corrupts the phase of the data, the beamforming effect of the smart antenna will suffer. In addition, even if a single antenna system (such as a micro base station of TD-SCDMA) is used, if the phase relation of signals is damaged, the demodulation at the receiving end may cause a large error.
In addition, although the peak-to-average ratio is relatively large at some time, the average power of the signal is relatively small, and the peak power at this time is still lower than the 1dB compression point of the power amplifier, but the conventional scheme usually performs peak clipping processing, so that the processing time and the processing difficulty of the whole signal transmission processing process are increased by the peak clipping processing mode, and most importantly, the problem of signal distortion exists when the carrier data is subjected to peak clipping processing. That is, the prior art only considers the peak-to-average ratio of the carrier data to determine peak clipping, which not only increases the processing difficulty, but also has the problem of information distortion.
In addition, in the prior art, the peak power is usually adjusted to a preset threshold power during the peak clipping process. When the threshold power is set, the probability of occurrence of a peak value is not considered, so that the peak power point is set to be too large or too small, and further, the data is distorted more greatly. For example, for a power amplifier, if the probability of a certain peak power occurring is very small, for example, the probability of exceeding the signal peak to average power ratio PAR (PAR =15 dB) is only one ten thousandth, the peak clipping may not be considered.
Disclosure of Invention
An object of the present invention is to provide a method for eliminating peak power in a TDD multi-frequency point communication system and a communication terminal for realizing the elimination of peak power, so as to solve the problem of data phase corruption caused by the fixed peak-eliminating sequence in the prior art.
In order to achieve the present invention, the present invention provides a method of cutting peak power, comprising: (1) Carrying out interpolation filtering on each path of signals after modulation and spread spectrum, and carrying out frequency conversion to obtain different frequency point signals; (2) linearly superposing all frequency point signals on a time domain; (3) And performing opposite clipping on the signal which needs to be subjected to peak clipping after the superposition according to the peak clipping sequence adjusted according to the amplitude change.
The step (3) of adjusting the peak clipping sequence according to the amplitude variation comprises the following steps of calculating the path I peak clipping sequence h of the time i : a1: using formulasCalculating the maximum value h of the amplitude adjustment of the I path imax Wherein pow _ max 0 Is a target power, I max_m Is pow _ max 0 The corresponding number of the I-way is,
Q max_m is pow _ max 0 Corresponding Q way values; a2: by using
Calculating the peak clipping of this timeI path amplitude adjusting factor scaling _ I; a3: by usingh i ＝scaling_i·hCalculating the peak clipping sequence h of this path I i Wherein h is a preset I-path peak clipping sequence.
The step (3) of adjusting the peak clipping sequence according to the amplitude variation comprises the following steps of calculating the Q-path peak clipping sequence: b1: using formulas
Calculating the maximum value h of the Q-path amplitude adjustment qmax Wherein pow _ max 0 Is a target power, Q max_m Is pow _ max 0 Corresponding number of Q pathsValue of,
I max_m is pow _ max 0 Corresponding Q way values; b2: by usingCalculating a Q-path amplitude adjusting factor scaling _ Q of the peak clipping; b3: by usingh q ＝scaling_q·hAnd calculating the peak clipping sequence of the Q path at this time, wherein h is a preset peak clipping sequence of the Q path.
The paring treatment in the step (3) comprises the following steps: if the way I data corresponding to the peak power is larger than zero, the way I data of the frequency point data symbol and the way I peak clipping sequence h are preserved in advance i Subtracting corresponding bits, otherwise, pre-storing the I path data of the data symbol of the frequency point and the current I path peak clipping sequence h i Adding corresponding bits; if the Q path data corresponding to the peak power is larger than zero, the pre-stored Q path data of the frequency point data symbol and the Q path peak clipping sequence h of the time are stored q Subtracting corresponding bits, otherwise, pre-storing Q-path data of the data symbol of the frequency point and the peak clipping sequence h of the Q-path q The corresponding bits are added.
The pre-stored data symbol of the frequency point is a data symbol with power exceeding threshold power.
The signals needing peak clipping in the step (3) are as follows: the sum of the peak-to-average power dB number and the mean power dB number of the signal is greater than or equal to a preset detection power dB number, and the detection power is less than or equal to 1dB compression point input power value.
The detected power P in，max Comprises the following steps: p in，max ＝P in，1dB X0. Ltoreq. X.ltoreq.3 dB, where P in，1dB Is the 1dB compression point input power value and X is the 1dB back-off value. The 1dB back-off value X is set according to the adjacent channel leakage power ratio ACLR required by the system, and the higher the ACLR required by the system, the larger the X setting.
The method also comprises the following steps before the step (3): setting a reverse cumulative probability distribution function (CCDF) value corresponding to the service according to the requirement on the error rate, and obtaining a parameter peak-to-average ratio corresponding to the CCDF value; the signals needing peak clipping in the step (3) also comprise signals with the peak-to-average ratio more than or equal to the parameter peak-to-average ratio.
A communications end implementing peak power clipping, comprising: a number of interpolation filters: the system is used for carrying out L-time interpolation filtering on one path of data after modulation and spread spectrum; a plurality of converters: the frequency converter is used for converting the interpolated data into a corresponding frequency point data; an adder: all frequency conversion units are connected and used for linearly superposing all frequency point data after frequency conversion on a time domain; the interpolation peak clipper comprises: amplitude adjustment maximum value calculation subunit: the method comprises the steps of calculating the maximum value of the amplitude adjustment of the I path and the maximum value of the amplitude adjustment of the Q path; amplitude adjustment factor calculation subunit: the method is used for calculating the I road amplitude adjustment factor and the Q road amplitude adjustment factor; a peak clipping sequence calculation subunit: used for calculating the peak clipping sequence of the path I and the peak clipping sequence of the path Q; an adder: and the operation unit is used for performing addition and subtraction operation on the pre-stored data symbol of the frequency point and the peak clipping sequence.
The peak clipping signal selection unit is also included: and the peak clipping processing is carried out on the signal which is used for clipping the peak of the sum of the peak-to-average ratio and the average power and is greater than or equal to the preset detection power, wherein the detection power is less than or equal to the input power value of the 1dB compression point.
Compared with the prior art, the peak clipping sequence can be adaptively adjusted each time in the peak clipping process, and phase distortion and amplitude distortion are reduced. The loss of amplitude and phase due to quantization clipping mainly looks at EVM. EVM (Vector Magnitude Error) is defined in TS 25.101V3.2.2 as: the difference between the measured waveform and the theoretical value of the modulated waveform. EVM is the square root of the ratio of the energy of the average error vector to the average reference signal energy and is given in a%. EVM is an important measure of modulation quality in digital communication systems. The modulation accuracy specified by the third generation mobile communication system (WCDMA, CDMA2000, TD-SCDMA) protocol is measured by EVM. Is a mandatory index of the equipment network access test. The invention can improve the deterioration of EVM by adaptively adjusting the peak clipping sequence.
The invention only carries out peak clipping processing on the signals of which the sum of the peak-to-average ratio dB number and the average power dB number is greater than or equal to the preset detection power dB number, and does not carry out peak clipping processing on the signals which do not meet the conditions. The invention reduces the processing amount of the signal transmitting terminal, reduces the processing difficulty and simultaneously reduces the information distortion. And, the threshold power is set according to the system requirement on ACPR, and the setting is more reasonable.
The invention sets corresponding CCDF according to the requirements of different services on bit error rate, obtains the corresponding parameter peak-to-average ratio according to the CCDF value, and performs peak clipping by an interpolation method when the peak-to-average ratio of the signal is more than or equal to the parameter peak-to-average ratio, thereby reducing signal distortion.
Drawings
FIG. 1 is a flow chart of a method of eliminating peak power according to the present invention;
FIG. 2 is a diagram illustrating a case where the average power is low and the peak-to-average ratio conversion range is large;
FIG. 3 is a diagram illustrating a case where the average power is high and the peak-to-average ratio transformation range is small;
FIG. 4 is a diagram illustrating a compression point of a high performance ACPR with a detection power less than 1 dB;
FIG. 5 is a CCDF profile of a data signal for TDD;
fig. 6 is a power map before and after the peak clipping processing by using the peak clipping sequence of the adaptive adjustment;
FIG. 7 is a comparison diagram before and after the amplitude clipping of the I-path data;
FIG. 8 is a comparison diagram before and after Q-way data amplitude peak clipping;
FIG. 9 is a diagram illustrating an example of peak power reduction according to the present invention;
FIG. 10 is a schematic diagram of a method of testing an adaptive peak clipping sequence;
FIG. 11 is a schematic diagram showing the effects of different peak clipping target values on EVM;
FIG. 12 is a diagram illustrating the improvement of the fixed total power test ACPR;
fig. 13 is a diagram illustrating the improvement of the power viewing total power consumption of the fixed output signal.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
Please refer to fig. 1, which is a flowchart illustrating a method for peak power reduction according to the present invention. It includes:
s110: and carrying out interpolation filtering on each path of signals after modulation and spread spectrum, and carrying out frequency conversion on the signals into signals with different frequency points.
Before the interpolation filtering is performed on the signal, a training sequence code may be inserted into each time slot of each path of data after modulation and spreading, and the training sequence codes of different frequency points perform related phase deflection.
According to the existing TDD multi-frequency point scheme, there are the following conventions for multiple frequency points supported by the same cell: the main frequency point and the auxiliary frequency point use the same scrambling code and basic midamble (training sequence) code, so the basic midamble code position of each frequency point is completely aligned, and the basic midamble code of each frequency point is the same binary sequence vector. The basic midamble code part at the transmitting end generates larger peak power due to peak-peak superposition, which is far larger than the data power in the time slot.
If the Midamble codes of different frequency points are subjected to relevant phase rotation, the power of the middle Midamble code is close to the power of data in the time slot, and the peak-to-average ratio of one time slot is reduced to be lower during subsequent peak clipping, and the Midamble codes are damaged less.
Therefore, only different phase deflection is needed to be carried out on the Midamble codes at different frequency points: the Midamble code data is multiplied by exp (j (n-1) × pi), j is an imaginary symbol, n is a carrier number, n:1 to N General assembly ，N General assembly The total number of carriers per cell in the TDD multi-carrier communication system. Correspondingly, only the Midamble data needs to be multiplied by exp (-j (n-1) × pi) at each frequency point of the receiving end.
For example, in a TDD communication system supporting three frequency points, the Midamble code of the second frequency point can be deflected by 180 degrees, and the Midamble codes of the first frequency point and the third frequency point are rotated by 0 degree and 360 degrees, as if there is no deflection, so the phase rotation method is the most simple and easy to implement, and the effect is obvious.
For another example, in a TDD communication system supporting six frequency points, the Midamble codes of the second frequency point, the fourth frequency point, and the sixth frequency point are deflected by 180 degrees.
By analogy, for the multi-frequency point TDD communication system, the Midamble data with the number of the even frequency point is deflected for 180 degrees, and the Midamble data with the number of the odd frequency point is not rotated. Corresponding processing is also performed at the receiving end.
There are many methods for different phase deflection of Midamble codes of different frequency points, which are not illustrated herein, and since the method of phase deflection used by a physical layer is inherited, the following peak clipping processing can have more power for a service data part, and the peak fluctuation of the Midamble codes is close, which can be more accurate when channel estimation is performed, and the Midamble codes are less damaged, so that the channel estimation is more accurate.
S120: and all frequency point signals are linearly superposed on the time domain.
Physical layer data of a TDD communication system is modulated, spread spectrum and scrambled to form frame data, and the transmission rate is 1.28Mps. At the digital intermediate frequency, an L-fold interpolation (L-interpolation multiple) is performed to make it high-speed data. For example, L is 60, and the interpolated rate reaches 76.8Mps. And simultaneously carrying out frequency point shifting on the interpolated multipath physical layer data in a frequency domain and carrying out linear superposition in a time domain. The mathematical expression of the multi-frequency point communication system signal before entering peak clipping is:
n＝1…N，q＝1…Q
in the formula s p (m，k) Is a spreading code specific to frequency point m: spreading code c (k) The combination with the cell scrambling code v can be regarded as a spreading code specific to a user and a cell, and different scrambling codes are used at different frequency points:
q is the length of the normalized spreading code, for TD-SCDMA, the length is 16, N is the symbol amount occupied by one code channel after channel coding modulation, the normalized length is 22, lambda k Is an amplitude adjustment factor, which is obtained from power conversion. Cr (chromium) component 0 (t) is the cosine filter coefficient at time t. Omega 0 Is the central frequency point of the intermediate frequency, omega 1 The frequency band bandwidth occupied by each frequency point.
Here, the peak-to-average ratio is defined as the ratio of the peak power to the average power over a period of time, according to the definition:
L m is that the length of midamble data is 144chip TS Is involved in PAPR calculation for the number of slots, N interpolate is a factor of interpolation at intermediate frequency, in this embodiment, the TDD communication system performs L (L = 60) times interpolation at intermediate frequency, so N interpolate ＝L。
As can be seen from the formula 4-1, the peak power of the data symbol is related to the modulation mode, the number of logical users, and the number of frequency points, and as the number of frequency points and the number of users increase, the peak-to-average ratio will be larger.
S130: and performing opposite cutting on the signal which needs to be subjected to peak cutting after the superposition according to the peak cutting sequence adjusted according to the amplitude change.
The signal needing peak clipping can be a signal with the sum of the peak-to-average ratio dB number and the average power dB number being greater than or equal to the preset detection power dB number, and the detection power is less than or equal to the value of the input power of the 1dB compression point.
Sometimes, although the peak-to-average ratio is relatively large, the average power of the signal is relatively small, and if the peak power at this time is still lower than the preset detection power, for example, the peak power is lower than a 1dB compression point of the power amplifier, the peak power of the signal is preferably not to be eliminated.
Please refer to fig. 2, which is a diagram illustrating a situation where the average power is low and the peak-to-average ratio conversion range is large. Please refer to fig. 3, which is a schematic diagram of a case where the average power is high and the peak-to-average ratio transformation range is small. At a certain moment, for the power amplifier, it is important that the maximum power point (mean + peak-to-average ratio = peak value) at this moment, i.e. neither the mean power nor the peak-to-average ratio, and as long as the peak power is not greater than the preset detection power, the signal distortion is small. If the power of the signal input signal has exceeded the 1dB compression point of the power amplifier and the power of the input signal continues to increase, the ACPR of the signal can deteriorate drastically, e.g., if the input signal exceeds the 1dB compression point, the indication of ACPR in the system may deteriorate by 3dB for every 1dB increase if the signal continues to increase. The signal is already distorted by 1dB by the time the input signal reaches the 1dB compression point. At this time, the ACPR has already deteriorated, so that if the ACPR index required by the system is high, the input signal is still only smaller than the 1dB compression point, and the ACPR of the system can only achieve good results.
Therefore, the invention provides that the sum of the peak-to-average power (PARP) and the average power of the signal is greater than or equal to the preset detection power P in，max Then peak clipping is performed. That is to say that the first and second electrodes,
PARP(dB)+10log 10 pow_mean＞P in，max (4-4)
or
PARP(dB)+10log 10 pow_mean≥P in，max (4-5)
Detecting power P in，max Is composed of
P in，max ＝P m，1dB -X 0≤X≤3dB (4-6)
Wherein, P in，1dB Is the 1dB compression point input power value and X is the 1dB back-off value. The 1dB back-off value X is set according to the adjacent channel leakage power ratio ACLR required by the system, and the higher the ACLR required by the system, the larger the X setting.
Because the input signal is not linear gain when entering the 1dB compression point, the system with high ACPR requirement will not or generate little distortion when working in the linear region of the power amplifier, and the performance of the ACPR will be good, so the detection power should be less than or equal to the input power of the 1dB compression point. Please refer to fig. 4, which is a diagram illustrating a compression point of less than 1dB of detected power under high performance ACPR. The detection power should be less than P in，max Namely:
PARP(dB)+10log 10 pow_mean＞P in,max (4-7)
wherein pow mean = mean { | x [ m ]]| 2 }，0≤m≤(2NQ+L m )·N TS ·N interpolate (4-8)
At this time, the maximum power of the input power amplifier signal is set to pow _ max 0 Obtained according to equations 4-7:
pow_max 0 (dB)＝P in，max ＝P in，1dB -X (4-9)
if X =0dB, then the maximum input power is equal to the input power at the 1dB compression point, and a larger X indicates a higher ACPR required by the system.
The maximum power of the input power amplifier signal is pow _ max 0 The maximum power of the signal input to the power amplifier is also referred to as the target power. During the peak clipping process, the power of the signal needs to be clipped below the target power. The invention provides a threshold power detect _ threshold, the input data symbols to the peak clipping processor are all serial data symbols, a timing period inputs a data, if the sampling clock period is 76.8MSPS, the period of the input data symbols is 1/76.8 microsecond, therefore, only the input signal needs to be judgedAs long as the power is greater than the threshold power detect _ threshold, the power of the signal needs to be cut off to pow _ max 0 Hereinafter, detect _ threshold and pow _ max are used in many cases 0 The values are close or equal, and the target power and the threshold power are set to be equal by the method.
The invention can only carry out peak clipping processing on the signals of which the sum of the peak-to-average ratio dB number and the average power dB number is greater than or equal to the preset detection power dB number, and does not carry out peak clipping processing on the signals which do not meet the conditions. The invention reduces the processing amount of the signal transmitting terminal, reduces the processing difficulty and simultaneously reduces the information distortion. And the threshold power is set according to the ACPR requirement of the system, and the setting is more reasonable.
Because the observation time is different in length, the obtained peak value may be different, so that it has no great significance to consider the PAR simply, and it is more concerned that the statistical information of the peak-to-average ratio, that is, the PAPR needs to be described from the perspective of probability, and usually, the distribution of the PAPR of the TDD system can be expressed visually by using a CCDF (Complementary cumulative distribution function) curve. In the present invention, if the peak occurs with a probability less than a certain probability (e.g., ten-thousandth), the peak point is not considered.
The CCDF is a probability distribution, for a power amplifier, if the probability of a certain peak power is very small, for example, the probability exceeding PAR =40dB is only one ten thousandth, the peak power point with small probability has little distortion and deterioration caused by a system, and the peak power point at the moment can be ignored or not considered, so that the peak value under a certain probability is set by the CCDF to be considered, and the peak value under a certain probability can be ignored, so that the threshold power is set more reasonably.
Setting a threshold peak-to-average ratio (PAPR) 0 Is composed of
The PAPR at any one time is:
then the inverse cumulative probability distribution function CCDF:
CCDF＝Prob[PAPR＞PAPR 0 ](4-12)
according to the CCDF distribution function, the invention provides a method for selecting a proper PARP according to actual needs 0 As the variation range of the transmission power instead of the theoretical maximum PAPR, for example, for a speech signal with low requirement of bit error rate, CCDF =10 may be selected -3 Corresponding one of the PAPRs 0 The value of (A) is used as the requirement for radio frequency power amplification, and for data transmission with high requirement on bit error rate, a higher PAPR corresponding to CCDF can be selected 0 As a desired amplifier linearity range. Please refer to fig. 5, which is a CCDF distribution diagram of a data signal of TDD. The maximum PAR before peak clipping reaches 8.59dB, the probability of a signal reaching the PAR is less than one thousandth, and the influence of the signal can be ignored during power amplification. At CCDF =10 -3 PAR (PAR = PAPR) corresponding to this point 0 ) Is 7.98dB, the peak-to-average ratio must be considered, so the purpose of peak clipping is well defined, i.e. to put the input signal CCDF =10 -3 The corresponding peak power is clipped.
Namely, before peak clipping, the method further comprises the following steps: setting a reverse cumulative probability distribution function (CCDF) value corresponding to the service according to the requirement on the error rate, and obtaining a parameter peak-to-average ratio corresponding to the CCDF value;
the peak clipping treatment comprises the following steps: finding out the signal with the peak-to-average ratio more than or equal to the parameter peak-to-average ratio, and eliminating the peak value by an interpolation method if the peak power is more than the preset threshold power.
Still referring to fig. 5, CCDF =10 before peak clipping -3 Corresponding PAR =7.98, CCDF =10 after peak clipping -3 The corresponding PAR =5.8 shows that the peak-to-average ratio is improved by about 7.98-5.8=2.18db at the thousandth probability point.
In order to minimize the phase loss before and after peak clipping, the phase correspondence needs to be considered most in setting the peak clipping sequence, and the invention adaptively adjusts the peak clipping sequence according to the following steps.
The power of a maximum power point in a certain period of time in the input signal is larger than the threshold power (the peak detection circuit detects the peak power point):
pow_max m ＞detect_threshold(4-13)
where pow _ max m ：pow_max m ＝max(pow m )＝I max 2 +Q max 2 (4-14)
Then, digital interpolation is used to perform digital peak clipping, the peak clipping process is to subtract interpolation filter coefficients from the I-path data and the Q-path data, and the phases of peak power points can be obtained according to the Q-path and the I-path of the input signal, note that at this time, the input peak clipping sequence signals are all complex, the real part is the I-path, and the imaginary part is the Q-path, so that the phase of the complex symbol can be obtained every time a complex symbol is input:
the phase of the peak point of the input signal is also the phase of the peak clipping sequence of the I path and the Q path, and the phase of the maximum power point of the peak clipping sequence is equal to the signal of the peak power point. Meanwhile, after each path of data and the respective peak clipping sequence are clipped, the peak power point of each path of data and the respective peak clipping sequence must be equal to the target power point, so that the method can deduce
The maximum value of amplitude adjustment of each path (I path and Q path) can be obtained
The phase loss can be minimized using the present invention, as evidenced by the following simulation results. Since the peak clipping sequence is essentially a linear phase FIR filter coefficient, the value is fixed. However, the peak power point of the input signal may be different each time, so that the power value to be subtracted by each secondary path is different, that is, the amplitude to be subtracted by each path is different each time, and after the amplitude value to be subtracted by each path is obtained, the amplitude adjustment factor for each path can be obtained:
the amplitude of each peak clipping sequence can be adaptively adjusted according to each obtained amplitude adjustment factor, wherein the amplitude comprises the corresponding relation of the phase.
h i ＝scaling_i·h(4-21)
h q ＝scaling_q·h(4-22)
That is to say that the temperature of the molten steel,
(1) Adjusting the peak clipping sequence according to the amplitude variation includes calculating the peak clipping sequence h of this path I by the following steps i ：
a1: using formulasCalculating the maximum value h of the I-way amplitude adjustment imax Wherein pow _ max 0 Is a target power, I max_m Is pow _ max 0 The corresponding value of the way I is set,Q max_m is pow _ max 0 Corresponding Q way numerical values;
a2: by using
Calculating an I-path amplitude adjusting factor scaling _ I of the peak clipping;
a3: by usingh i ＝scaling_i·hCalculating the peak clipping sequence h of this path I i Wherein h is a preset I path peak clipping sequence.
(2) Adjusting the peak clipping sequence according to the amplitude variation comprises calculating the peak clipping sequence of the Q path according to the following steps:
b1: using formulas
Calculating the maximum value h of the Q-path amplitude adjustment qmax Wherein pow _ max 0 Is a target power, Q max_m Is pow _ max 0 The corresponding value of the Q-way is,
I max_m is pow _ max 0 Corresponding Q way values;
b2: by using
Calculating a Q-path amplitude adjusting factor scaling _ Q of the peak clipping;
b3: by usingh q ＝scaling_q·hCalculating the peak clipping sequence of this Q pathAnd h is a preset Q-path peak clipping sequence.
(3) The paring process in step S130 is:
if the path I data corresponding to the peak power is larger than zero, the pre-stored path I data of the frequency point data symbol and the path I peak clipping sequence h of the time are stored i Subtracting corresponding bits, otherwise, pre-storing the I path data of the data symbol of the frequency point and the current I path peak clipping sequence h i Adding corresponding bits;
if the Q path data corresponding to the peak power is larger than zero, the pre-stored Q path data of the frequency point data symbol and the Q path peak clipping sequence h of the time are stored q Subtracting corresponding bits, otherwise, pre-storing Q-path data of the symbol of the data of the frequency point and the peak clipping sequence h of the Q-path q The corresponding bits are added.
The pre-stored data symbol of the frequency point is a data symbol with power exceeding threshold power.
The function of amplitude adaptive adjustment of the peak clipping sequence (interpolation filter coefficients) is realized according to the above series of processes. The following is a simulation of the above method, when a peak power point is detected, its power is clipped to the target power while the trend of the surrounding waveform fluctuations remains unchanged.
Please refer to fig. 6, which is a power comparison chart before and after the peak clipping processing by the peak clipping sequence of the adaptive adjustment. As can be seen from the figure, consistency before and after peak clipping is satisfied from the power comparison before and after peak clipping processing. Please refer to fig. 7, which is a schematic diagram illustrating comparison before and after peak clipping of the I-path data amplitude. Please refer to fig. 8, which is a comparison diagram of Q-path data before and after amplitude peak clipping. As can be seen from fig. 7 and 8, each amplitude can also be adaptively adjusted according to the respective ratio.
The self-adaptive adjusting peak clipping device not only embodies the self-adaptive adjustment of the amplitude, but also has the minimum damage to the phase of an input signal. If the amplitude of the I-path data is much larger than that of the Q-path data, if the same amplitude is removed from the I-path data and the Q-path data, the phase of the input signal will be greatly damaged even if the peak power point can be removed to the power threshold, but if the method for adaptively adjusting the peak-removing sequence is adopted, the amplitude of the I-path data and the Q-path data is removed with different amplitudes according to the proportional relationship before peak-removing, and the phase damage after peak-removing is relatively less, thereby further improving the peak-to-average ratio.
By improving the peak-to-average ratio, the following technical effects can be achieved:
1) The transmitting power of the multi-carrier signal is improved, and the efficiency of the power amplifier is improved under the condition that the total consumed power is basically unchanged; 2) The efficiency of the power amplifier is improved, when high-power output is needed, the supply power of the power supply can be greatly reduced, so that the hardware cost is saved, the heat dissipation problem of the base station is relieved to a certain extent, and the cost of operation and maintenance is saved.
Please refer to fig. 9, which is a diagram illustrating a method for peak clipping according to an embodiment of the present invention. The linearly superposed signals are respectively cached in I-path data and Q-path data to obtain peak power (S21), whether the peak power is larger than or equal to a detection threshold is judged (S22), if so, a peak clipping sequence is adaptively adjusted, the signals are subjected to peak clipping to obtain the I-path data and the Q-path data after peak clipping, and otherwise, the I-path data and the Q-path data are directly output. The invention can set the threshold power through the requirements of the ACPR. The invention can also judge whether to carry out peak clipping processing or not when the sum of the peak-to-average power dB number and the average power dB number of the signal is more than or equal to the preset detection power dB number, or can further consider whether the peak-to-average power dB number of the signal is more than or equal to the parameter peak-to-average power dB set according to the CCDF value, and carry out peak clipping processing if the peak-to-average power dB number of the signal is more than or equal to the parameter peak-to-average power dB number.
The peak clipping treatment comprises two processes: the first process is to obtain the peak clipping sequence of this I path and the peak clipping sequence of this Q path, and the second process is to use the peak clipping sequence of this I path and the peak clipping sequence of this Q path to carry out the paring process to the saved data symbol of this time.
The first process includes: firstly obtaining the amplitude of the I path and the Q path of the peak power pointAmplitude, i.e. obtaining the peak power pow _ max 0 Corresponding way I value I max_m And obtaining the peak power pow _ max 0 Corresponding Q-way value Q max_m After-use
Calculating the phase thereof; (S23);
then, generating filter coefficient adjustment factors of the I path (formulas 4 to 19) and filter coefficient adjustment factors of the Q path (formulas 4 to 20) respectively (S24);
then, respectively calculating the peak clipping sequence of the path I (formula 4-21) and the peak clipping sequence of the path Q (formula 4-22) (S25);
the second process includes: finishing the clipping processing of the peak power signal by the clipping sequence by utilizing the obtained I path clipping sequence and the Q path clipping sequence (S26):
for way I
if I max_m ＞0
I-h i
else
I+h i
end
The same judgment is also made for the Q path
if Q max_m ＞0
Q-h q
else
Q+h q
end
In order to verify the effectiveness of the adaptive peak clipping sequence adjusting method, the applicant verifies the method. Please refer to fig. 10, which is a diagram illustrating a method for testing an adaptive peak clipping sequence. After all frequency point signals are linearly superposed on a time domain, the method carries out testing according to the following conditions. The first is that the signal is sent to the D/a converter for D/a conversion without peak clipping (i.e. 9dB indicated in the figure), the second is that the target power value for peak clipping is 6dB, the third is that the target power value for peak clipping is 7dB, and the fourth is that the target power value for peak clipping is 8dB.
In order to compare the effectiveness of the test indexes, the indexes are compared and tested, and data without peak clipping and peak clipping data of different target values are compared and tested. Please refer to fig. 11, which shows the influence of different peak clipping target values on EVM. As can be seen from the figure, although the EVM is deteriorated after peak clipping, the EVM still satisfies the requirement of 3GPP, which is less than 12%.
The goal of peak clipping according to the introduction above is to increase the total transmitted power, increase the operating efficiency of the power amplifier and improve ACPR, for which several tests were also performed: the improvement of ACPR is fixed for the total power test (see fig. 12), and the improvement of total power consumption is checked for the power of the fixed output signal (see fig. 13).
The interpolation filter coefficient can be adjusted adaptively according to user requirements, the peak power point can be accurately removed each time, and meanwhile, after the peak power point is removed, the phase damage of the signal is minimum, the phase amplitude damage after demodulation is reduced, and the EVM index deterioration is improved. The automatic peak clipping sequence adjusting device is simple and easy to implement. Meanwhile, the test shows the improvement condition of the power amplifier and the radio frequency device before and after peak clipping.
A communications end that implements peak power clipping, comprising: a number of interpolation filters: the system is used for carrying out L-time interpolation filtering on one path of data after modulation and spread spectrum;
a plurality of converters: the frequency converter is used for converting the interpolated data into a corresponding frequency point data;
an adder: all frequency conversion units are connected and used for linearly superposing all frequency point data after frequency conversion on a time domain;
the interpolation peak clipping device comprises:
amplitude adjustment maximum value operator unit: the amplitude adjustment device is used for calculating the maximum value of the I path of amplitude adjustment and the maximum value of the Q path of amplitude adjustment;
an amplitude adjustment factor calculation subunit: the method is used for calculating the I road amplitude adjustment factor and the Q road amplitude adjustment factor;
a peak clipping sequence calculation subunit: used for calculating the peak clipping sequence of the path I and the peak clipping sequence of the path Q;
an adder: and the operation module is used for performing addition and subtraction operation on the pre-stored data symbol of the frequency point and the peak clipping sequence.
The invention also comprises a peak clipping judging unit: and storing the signal for clipping the peak, wherein the sum of the peak-to-average ratio and the average power is greater than or equal to a preset detection power, and the detection power is less than or equal to the input power value of the 1dB compression point.
The interpolation peak clipper described above may be implemented by a programmable logic device FGPA.
The above disclosure is only for the specific embodiments of the present invention, but the present invention is not limited thereto, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.
Claims (13)
1. A method of clipping peak power, comprising:
(1) Carrying out interpolation filtering on each path of signals after modulation and spread spectrum, and carrying out frequency conversion to obtain different frequency point signals;
(2) All frequency point signals are linearly superposed on a time domain;
(3) And performing opposite cutting on the signal which needs to be subjected to peak cutting after the superposition according to the peak cutting sequence adjusted according to the amplitude change.
2. The method of claim 1, wherein the step (3) of adjusting the peak clipping sequence in accordance with the amplitude variation comprises calculating the present way I peak clipping sequence h by i ：
a1: using formulas
Calculating the maximum of the I-way amplitude adjustmentNumber h imax Wherein pow _ max 0 Is a target power, I max_m Is pow _ max 0 The corresponding value of the way I is set,，Q max_m is pow _ max 0 Corresponding Q way values;
a2: by using
Calculating an I-path amplitude adjusting factor scaling _ I of the peak clipping;
a3: by using h i Calculating the peak clipping sequence h of the path I at this time by = scaling _ I · h i Wherein h is a preset I path peak clipping sequence.
3. The method of claim 1 or 2, wherein the step (3) of adjusting the peak clipping sequence according to the amplitude variation comprises calculating the Q-way peak clipping sequence of this time by:
b1: using formulas
Calculating the maximum value h of the Q-path amplitude adjustment qmax Wherein pow _ max 0 Is a target power, Q max_m Is pow _ max 0 The corresponding value of the Q-way is,
，I max_m is pow _ max 0 Corresponding Q way values;
b2: by using
Calculating a Q-path amplitude adjusting factor scaling _ Q of the peak clipping;
b3: by using h q And computing the current Q-path peak clipping sequence by using the = scaling _ Q · h, wherein h is a preset Q-path peak clipping sequence.
4. The method of claim 3, wherein the paring in step (3) is:
if the corresponding I-way data of the peak powerIf the frequency point data symbol is larger than zero, pre-stored I-path data of the frequency point data symbol and the current I-path peak clipping sequence h i Subtracting corresponding bits, otherwise, pre-storing the I path data of the data symbol of the frequency point and the current I path peak clipping sequence h i Adding corresponding bits;
if the Q path data corresponding to the peak power is larger than zero, the pre-stored Q path data of the frequency point data symbol and the Q path peak clipping sequence h of the time are stored q Subtracting corresponding bits, otherwise, pre-storing Q-path data of the symbol of the data of the frequency point and the peak clipping sequence h of the Q-path q The corresponding bits are added.
5. The method as claimed in claim 4, wherein the pre-stored data symbols of the local frequency point are data symbols whose power exceeds the threshold power.
6. The method of claim 1 or 4, wherein the signal to be peak-clipped in step (3) is: the sum of the peak-to-average power dB number and the mean power dB number of the signal is greater than or equal to a preset detection power dB number, and the detection power is less than or equal to 1dB compression point input power value.
7. The method of claim 6, wherein the detected power P in，max Comprises the following steps: p in，max ＝P in，1dB X0. Ltoreq. X.ltoreq.3 dB, wherein P in，1dB Is the 1dB compression point input power value and X is the 1dB back-off value.
8. The method of claim 6, wherein the 1dB backoff value X is set according to a system required adjacent channel leakage power ratio ACLR, and the higher the system required ACLR, the larger the X setting.
9. The method of claim 1,
the method also comprises the following steps before the step (3): setting a reverse cumulative probability distribution function (CCDF) value corresponding to the service according to the requirement on the error rate, and obtaining a parameter peak-to-average ratio corresponding to the CCDF value;
the signals needing peak clipping in the step (3) also comprise signals with peak-to-average ratio more than or equal to the parameter peak-to-average ratio.
10. The method of claim 6,
the method also comprises the following steps before the step (3): setting a reverse cumulative probability distribution function (CCDF) value corresponding to the service according to the requirement on the error rate, and obtaining a parameter peak-to-average ratio corresponding to the CCDF value;
the signals needing peak clipping in the step (3) also comprise signals with peak-to-average ratio more than or equal to the parameter peak-to-average ratio.
11. A communications terminal that implements peak power clipping, comprising: a number of interpolation filters: the system is used for carrying out L-time interpolation filtering on one path of data after modulation and spread spectrum;
a plurality of converters: the frequency converter is used for converting the interpolated data into a corresponding frequency point data;
an adder: all frequency conversion units are connected and used for linearly superposing all frequency point data after frequency conversion on a time domain;
the interpolation peak clipper comprises:
amplitude adjustment maximum value operator unit: the amplitude adjustment device is used for calculating the maximum value of the I path of amplitude adjustment and the maximum value of the Q path of amplitude adjustment;
an amplitude adjustment factor calculation subunit: the method is used for calculating the amplitude adjustment factor of the I road and the amplitude adjustment factor of the Q road;
a peak clipping sequence calculation subunit: used for calculating the peak clipping sequence of the path I and the peak clipping sequence of the path Q;
an adder: and the operation module is used for performing addition and subtraction operation on the pre-stored data symbol of the frequency point and the peak clipping sequence.
12. The communications end of claim 11, further comprising a peak clipping signal selection unit: and storing the signal for clipping the peak, wherein the sum of the peak-to-average ratio and the average power is greater than or equal to a preset detection power, and the detection power is less than or equal to the input power value of the 1dB compression point.
13. The communication terminal according to claim 11 or 12, wherein the interpolation peak clipper is a programmable logic device FGPA.
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Effective date of registration: 20151026 Address after: 100083 Haidian District, Xueyuan Road, No. 29, Patentee after: Datang Mobile Communication Equipment Co., Ltd. Patentee after: Datang Mobile Communication Equipment Co., Ltd., Shanghai Address before: 100083 Haidian District, Xueyuan Road, No. 29, Patentee before: Datang Mobile Communication Equipment Co., Ltd. |