CN1716933B - Method for realizing CDMA signal wave elimination - Google Patents
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Abstract
This invention relates to a method for realizing CDMA signal clipping capable of realizing joint cancel to multiple peak values of input signals characterizing in computing suitable windowed position to carry out jointly windowed process to multiple peak values to realize the cancel to the peak values, among which, the windowed phase and amplitude are determined by those of peak values of the input signals, said windowed phase is determined by the derivate of said windowed function, which effectively reduces PAR of the system and reduces the resource demand for peak value process.
Description
Technical Field
The invention relates to a method for realizing signal clipping in the field of digital mobile communication, in particular to a combined clipping method capable of effectively reducing the peak-to-average ratio of a CDMA signal.
Background
In a wireless transmission system, a certain dynamic range needs to be reserved in order to ensure that signals are transmitted without distortion. The dynamic range may be defined by the peak-to-average ratio. In multi-carrier, the signal dynamic range is compressed due to the need for increased average transmit power. However, the peak-to-average ratio of multiple carriers is not lower than that of single carriers, but higher. In order to satisfy the trade-off between the average transmission power and the maximum transmission power, the signal waveform transmitted by the multi-carrier needs to be subjected to peak clipping to ensure the efficiency of the power amplifier. The methods for peak clipping (clipping) of the waveform of a multicarrier transmitted signal are classified into the following categories:
(1) the amplitude is directly cut off, and the phase is kept unchanged;
this method, also called hard clipping, is the simplest and most straightforward method with minimal impact on EVM, but the most major drawback is that it causes signals to have sharp edges and sharp peaks, and abrupt changes in clipping and short duration of clipping edges can generate significant out-of-band spectral anomalies such as spectral distortion, adjacent band interference, spectral spreading, etc.
(2) Generating corresponding cancellation pulse, and adding the cancellation pulse with the original signal after filtering;
the method adopts a method for canceling pulses, isolates the peak value of an input signal according to a clipping threshold voltage, generates an extreme value signal representing a local extreme value (or an envelope peak value) of a peak isolation signal, sends the extreme value signal to a pulse filter, generates a filter signal, subtracts the filter signal from the input signal (the position needing clipping) delayed for a preset time period to clip, and performs multiple cancellation through multiple levels of thresholds. The main disadvantages of this method are that when there are several extrema in a certain time, it needs to perform cancellation of several positions, which has high requirements for system processing resources and control and buffering, and it is difficult to compensate I, Q band-pass signal.
(3) Carrying out carrier phase staggering treatment;
the method can not only not influence the original spectrum characteristic, but also reduce PAR, adopts the idea of backward push, selects the optimal initial phase configuration of each carrier after a plurality of times of iterative optimization, and reduces the peak value after the combination of a plurality of carriers to the minimum, thereby achieving the purpose of multi-carrier clipping. The method has the main disadvantages that the time delay is long, the implementation is complex, particularly, the optimization is carried out for multiple times, and simultaneously, under the conditions of different time slots and different code channel numbers, the phase of each carrier needs to be readjusted, which is not beneficial to the phase locking of a receiver.
(4) Processing at the symbol level using predictive feedback;
and after the combined multi-carrier signal is subjected to wave cutting, despreading and descrambling are carried out, symbol-level soft information is obtained, and then spread spectrum modulation is carried out again and path combining transmission is carried out. The method has the main defects that the system has longer delay time, needs to carry out up-conversion and down-conversion once at intermediate frequency, and occupies more processing resources.
(5) Processing on a code domain;
the method adopts a series of different standby code channels, and adopts a plurality of different code channels to spread the same code channel information to obtain a group of spread spectrum information of the user, and other code channels are processed similarly to obtain a plurality of groups of spread spectrum information to be combined, and the peak-to-average ratio is selected to be minimum, thereby achieving the aim of clipping. The method has the advantages of less influence on EVM, but is not suitable for a code channel limited system, and the available code channel needs to be modified at any time, so that the receiver cannot perform despreading.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a method for implementing CDMA signal clipping, which can implement joint cancellation of multiple envelope peaks, and effectively reduce the peak-to-average ratio PAR of the system under the condition of meeting a certain spectrum requirement.
In order to achieve the above object, the present invention provides a method for implementing clipping of a CDMA signal, which can implement joint cancellation of multiple peaks of an input signal, wherein the multiple peaks are jointly windowed by calculating an appropriate windowing position to implement the cancellation of the peaks.
The method of (a), wherein the phase and amplitude of the windowing are determined by the position and amplitude of the peak of the input signal.
The method of (1), wherein the windowed phase is determined by calculating a derivative of a windowing function.
The method of (a), wherein the windowed phase is further determined by comparing a slope between peaks of a signal related to the input signal with a derivative of the window function.
The method of (a), wherein the signal related to the input signal is a signal 1-c (n), c (n) is a hard-clipping factor of the input signal,where x (n) is the input signal, a is the clipping threshold, and n is the input signal phase.
The method of the above, further comprising a step of equally dividing the input signal into segments of fixed length, and performing the windowing process separately for each segment of the input signal.
The method of, wherein the determining of the windowed phase further comprises the steps of:
step one, calculating a hard cutting factor c (n) of the input signal, and further calculating 1-c (n), wherein n represents the phase of the input signal;
determining the center position of a signal and the average (center) position of two peak extreme values positioned at two sides of the center of the signal in the step 1-c (n), and calculating the slope of the peak extreme values positioned at two sides of the center position of the signal;
step three, comparing the derivative of the window function with the slope obtained in the step two, and selecting the position value corresponding to the derivative value closest to the slope value as the offset value of the windowed central position relative to the average (central) position of two peak extreme values positioned at two sides of the signal center in the range of 1-c (n);
and step four, offsetting the average (central) position of the extreme values of the 1-c (n) peak values positioned at two sides of the center of the signal, wherein the offset is the offset value obtained in the step three, thereby determining the windowed phase.
In another embodiment, the determining of the windowing phase further comprises the steps of: selecting a window function type and a window length, and storing the window function and the first derivative of the window function after the window function is corrected; equally dividing an input signal into segments with the length being the window length, and calculating the central position of a segment signal; judging the distribution condition of the peak value of the input signal exceeding a preset threshold value relative to the signal center; when there are one or more peaks on only one side of the signal center, the compensation is directly windowed and corrected according to the maximum value.
The method of (a), further comprising a step of calculating a compensation factor b (n), the compensation factor b (n) being determined by a product of the multiplication of 1-c (n) by a corresponding one of the window functions for which the windowed phase is determined; the clipped output signal is the product of a compensation factor b (n) and the input signal.
The method of (a), wherein the window function is one or more of a hamming window, a rectangular window, a Blackman window, or a Caesar (Kaiser) window.
The method of (1), wherein the derivative is a first derivative of a window function.
The method of (a), wherein the slope or derivative may be a modified slope or derivative, the modification comprising a linear or non-linear modification.
The invention provides a combined clipping method, which obtains a windowed phase by a method of calculating slopes of two peaks, and determines the windowed amplitude according to the windowed phase and the positions and powers of the two peaks. The multiple peaks can be compensated by choosing the two peaks where the amplitude is the largest.
The invention utilizes a method of window function at a proper position to process the compensation factor through the window function and carry out compensation cancellation, thereby effectively reducing the PAR of the system under the condition of ensuring the vector error amplitude EVM and the peak code domain error PCDE. Moreover, compared with the prior art, the method and the device realize the combined processing of a plurality of peak values, reduce the requirement of peak value processing resources, ensure that the compensated signals can not generate phase reversal and improve the EVM performance. The phase and amplitude of the windowing are obtained by a derivative calculation method, so that the problem of phase inversion of the compensated signal possibly caused by convolution windowing can be avoided, the EVM is reduced under the condition of the same adjacent channel leakage power ratio ACLR, and the better peak clipping performance can be realized.
The invention is described in detail below with reference to the drawings and specific examples, but the invention is not limited thereto.
Drawings
FIG. 1 is a schematic diagram of a Hamming window waveform;
FIG. 2 is a waveform schematic of a Hamming window derivative;
FIG. 3 is a graph of the time domain power of an input signal;
FIG. 4 is a flow chart of peak processing;
FIG. 5 is a schematic diagram of waveforms 1-c (n);
FIG. 6 is a graph of the correspondence between window functions and positions 1-c (n);
fig. 7 is a schematic diagram of a clipped output signal.
Detailed Description
The phase and amplitude of the windowing of the method of the invention is determined by the position and amplitude of the peak. For the case where there are multiple peaks, the impact of the peak's position and amplitude on the window needs to be compromised. There is a document that proposes windowing using a convolution method. The convolution will act like a low pass filter and will act to sum the amplitude or power. Under the condition that the peak amplitude has no prior knowledge, the windowing amplitude is easily overlarge, so that the ratio of the compensated signal to the input signal is opposite in phase, and the EVM index is rapidly deteriorated.
The method for reducing the peak-to-average power ratio of the CDMA signal comprises the following steps:
the input signal x (n) is equally divided into segments with the length W, and peak value detection and cancellation are respectively carried out on each segment. The length of the windowing is also chosen to be W. When the input signal has only one or no peak exceeding the threshold in a segment of length W, it can be processed by the method of peak detection and cancellation in the general sense (i.e., the prior art method). When a plurality of signal peaks exist in an input signal segment with the length of W, the windowing phase is obtained by solving the slope of two input signal extreme values exceeding a threshold, and the amplitude of the windowing is determined by the windowing phase and the peak power of the signal.
The core algorithm is as follows:
(1) selecting a window function type and a window length W, and storing the window function and the first derivative after the window function is corrected;
(2) the input signal is equally divided into segments of length W, and the central position W/2 of the segment signal is calculated. Performing the operations of the steps (3) to (7) in each section;
(3) selecting independent clipping or combined clipping according to the peak value distribution condition, if only one side (namely one side positioned at the center position of the signal) has a peak value, selecting independent clipping, directly windowing according to the maximum value, correcting and compensating, and jumping to the step (2) to execute next section of data clipping; if the two sides of the signal center position have peak values, selecting combined clipping and continuing the step (4);
(4) calculating the average (center) position of two peaks of the joint clipping located at both sides of the center position of the signal;
(5) calculating a hard cutting factor c (n), and calculating a slope according to the peak extreme position and amplitude of 1-c (n); (6) determining an offset of the windowed position from the mean (center) position of the peak value by looking up a derivative table, and adding the offset to the center position of the peak value obtained in the step (4), thereby determining the absolute position of the windowed center;
(7) calculating a joint clipping compensation factor;
(8) calculating the output signal power;
(9) for complex signals, the real part and the imaginary part are respectively compensated after power evolution according to the input signal.
Let the input signal power x (n), n be the input signal phase. With a clipping threshold a, the hard clipping method without considering spectral dispersion can be expressed as:
y(n)＝c(n)x(n)，(1)
wherein, <math> <mrow> <mi>c</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfenced open='{' close=''> <mtable> <mtr> <mtd> <mn>1</mn> <mo>,</mo> <mo>|</mo> <mi>x</mi> <mo>|</mo> <mo>≤</mo> <mi>A</mi> </mtd> </mtr> <mtr> <mtd> <mfrac> <mi>A</mi> <mrow> <mo>|</mo> <mi>x</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>|</mo> </mrow> </mfrac> <mo>,</mo> <mo>|</mo> <mi>x</mi> <mo>|</mo> <mo>></mo> <mi>A</mi> </mtd> </mtr> </mtable> </mfenced> </mrow></math>
in order to limit the spectrum, hard cutting is not generally used, and c (n) is replaced by b (n), wherein n is the input signal phase.
Where w (n) is a window function. The window function may limit the superimposed spectrum to a certain range. The window function may be in the form of a hamming window (hamming), a rectangular window, a Blackman window, or a Caesar (kaiser) window, etc. Since the actual window length cannot be infinite impulse response, the window length is also chosen to be W so that the subsequent window function is multiplied by the signal to achieve peak cancellation.
In order to satisfy the limitation of the signal power after clipping in A, the requirement is
To satisfy requirement (3), we guarantee by windowing the inequality pair c (n).
There is a method of solving b (n) by convolution, as shown in formula (4),
however, the convolution method can accumulate error signals 1-c (k), and the correction term a is beyond the clipping threshold for the case that the envelopes of adjacent sampling points exceed the clipping thresholdkw (n-k) is much more than necessary, even if b (n) < 0,
when a iskwhen w (n-k) is greater than 1, <math> <mrow> <mi>b</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> <mo>=</mo> <mn>1</mn> <mo>-</mo> <munderover> <mi>Σ</mi> <mrow> <mi>k</mi> <mo>=</mo> <mo>-</mo> <mo>∞</mo> </mrow> <mo>∞</mo> </munderover> <msub> <mi>a</mi> <mi>k</mi> </msub> <mi>w</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>-</mo> <mi>k</mi> <mo>)</mo> </mrow> <mo><</mo> <mn>0</mn> </mrow></math>
b (n) less than 0, the compensated signal is inverted, and the EVM index is greatly deteriorated. The intermediate band pass signal is just a signal with a slowly changing envelope, the low-pass filtering effect of convolution is very serious, and the low-pass accumulation effect of the compensation signal needs to be reduced.
The clipping process of the present invention is described below by way of an example.
The intermediate frequency signal power x (n) is equally divided into segments of windowed length W, and separate peak detection and cancellation are performed for each segment.
The selection of the W length needs to be balanced according to the requirements of the ACLR and the EVM indexes. A longer W may result in better ACLR, but the EVM index will deteriorate. A shorter W may result in better EVM, but the ACLR index will deteriorate.
Taking the window function as a hamming window as an example, assuming that the window length is W ═ 21, the hamming window coefficient is:
[0.0800 0.1025 0.1679 0.2696 0.3979 0.5400 0.68210.8104 0.9121 0.9775 1.0000 0.9775 0.9121 0.81040.6821 0.5400 0.3979 0.2696 0.1679 0.1025 0.0800]
the hamming window function is shown in fig. 1.
The derivative of each point of the hamming window is:
[ 0.02250.06530.10180.12820.14210.14210.12820.10180.06530.0225-0.0225-0.0653-0.1018-0.1282-0.1421-0.1421-0.1282-0.1018-0.0653-0.0225 ], as shown in FIG. 2.
The derivative of the window function is scaled to adapt to the signal variation trend (it may also be unadjusted or non-linearly scaled), for example, the derivative is divided by 3 to obtain a modified derivative:
[0.0075 0.021767 0.033933 0.042733 0.047367 0.0473670.042733 0.033933 0.021767 0.0075 -0.0075 -0.021767 -0.033933-0.042733 -0.047367 -0.047367 -0.042733 -0.033933 -0.021767-0.0075]
in the following, all derivatives mentioned refer to derivatives that have been corrected, if not specified otherwise.
The derivative of points at a distance of m [ -W/4+1.. W/4] [ -5-4-3-2-112345 ] from the center position W/2 ═ 10.5, respectively, is approximately y (m) [ 0.0473670.0427330.0339330.0217670.0075-0.0075-0.021767-0.033933-0.042733-0.047367 ];
suppose there is a segment of input intermediate frequency signal x (n) with time domain power: [ 0121.83.1433.610.90.80.60.60.711.31.41.10.70.60.3 ], where the clipping threshold is 1, as shown in FIG. 3.
Samples beyond threshold 1 are present on both sides of the central position 11. Dividing the signal in the signal segment with width W into the length of
Based on whether the first half and the second half have a value exceeding the threshold a equal to 1, the process proceeds to the flow shown in fig. 4. In fig. 4, it is judged that the input signal has a peak value exceeding a threshold (step 401); further judging the peak value distribution at two sides of the relative center position (step 402), and determining the windowing position directly according to the maximum value when the peak value exists only on one side (if the peak value exists only on the left side or the peak value exists only on the right side) (steps 403 and 405); if there are peaks on both sides of the center position, then a joint peak clipping is performed (step 404).
Since it is relatively simple to have only one side with respect to the center position that exceeds the clipping threshold, windowing methods have been described in the literature. Only the case of performing combined peak clipping when there are peaks on both sides is described below.
For the input signal x (n) (peaks on both sides of the center of the signal), the corresponding hard-clipping factors c (n) ═ 110.50.555560.322580.250.333330.2777811111110.769230.714290.90909111, 1-c (n) ([ 000.50.444440.677420.750.666670.7222200000000.230770.285710.090909000 ], and as shown in fig. 5, the slope of the two local maxima 1-c (6) ═ 0.75 and 1-c (17) ═ 0.28571 at 1-c (n) — 0.75-0.28571)/(17-6) — 0.0422 can be determined.
As previously mentioned, the modified derivative of the hamming window has been stored prior to calculating the slope. Comparing the obtained slope with the stored derivative of the hamming window, the position index corresponding to the derivative closest to the slope is chosen as y (-4) ═ 0.042733, so that the maximum value of 1-c (n) can be determined at the offset-4 of (17+6)/2 ═ 11.5 on average of the two extreme point positions. Namely the center position of the added window is
Wherein,
to round the symbol down. The correspondence between the window function and the positions 1-c (n) is shown in FIG. 6.
The values of the compensation factors b (n) can be obtained by multiplying the values of 1-c (n) and the window function according to the position correspondence described in fig. 6. Finally, the output of the clipped signal is x (n) b (n), and the time domain waveform after clipping is shown in fig. 7.
The method of the invention is suitable for the case that the intermediate frequency CDMA signal is a single carrier or a multi-carrier. And no matter whether low-pass filtering is adopted to realize the detection of the peak envelope so as to synchronously adjust the division mode of the input signal, the invention is applicable as long as the length of the signal before compensation is fixed. Alternatively, the clipping operation may be performed in multiple stages in series according to the method provided by the present invention.
The method reduces the requirement of peak processing resources, improves the EVM performance by realizing the joint processing of a plurality of peaks, and realizes the cancellation of the peaks by calculating the proper peak superposition position and carrying out the joint windowing processing on the plurality of peaks. By combining windowing, the peak-to-average ratio can be reduced under the condition of meeting a certain spectrum requirement.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. A method for realizing CDMA signal clipping, used for realizing the joint cancellation of multiple peak values of the input signal, characterized by, through calculating the suitable windowing position, carry on the joint windowing to multiple peak values in order to realize the cancellation of the peak value; wherein the phase and amplitude of the windowing are determined by the position and amplitude of the peak of the input signal; wherein the windowed phase is determined by calculating a derivative of a window function; wherein the windowed phase is further determined by comparing a slope between peaks of a signal related to the input signal with a derivative of the window function.
2. The method of claim 1, wherein the signal related to the input signal is a signal 1-c (n), c (n) is a hard-cutting factor of the input signal,
where x (n) is the input signal, a is the clipping threshold, and n is the input signal phase.
3. The method of claim 2, further comprising a step of equally dividing said input signal into segments of fixed length, said windowing being performed separately for each segment of input signal.
4. The method of claim 3, wherein the determining of the windowed phase further comprises the steps of:
step one, calculating a hard cutting factor c (n) of the input signal, and further calculating 1-c (n), wherein n represents the phase of the input signal;
determining the center position of a signal and the average position of two peak extreme values of the 1-c (n) position on two sides of the center position of the signal, and calculating the slope of the peak extreme values on two sides of the center position of the signal;
step three, comparing the derivative of the window function with the slope obtained in the step two, and selecting the position value corresponding to the derivative value closest to the slope value as the offset value of the windowed central position relative to the average position of two peak extreme values positioned at two sides of the signal central position in the range of 1-c (n);
and step four, offsetting the average positions of the extreme values of the 1-c (n) peak values positioned at two sides of the center of the signal, wherein the offset is the offset value obtained in the step three, thereby determining the phase of the windowing.
5. The method of claim 3, wherein the determining of the windowed phase further comprises:
selecting a window function type and a window length, and storing the window function and the first derivative of the window function after the window function is corrected;
equally dividing an input signal into segments with the length being the window length, and calculating the central position of a segment signal;
judging the distribution condition of the peak value of the input signal exceeding a preset threshold value relative to the signal center; when there are one or more peaks on only one side of the signal center, the compensation is directly windowed and corrected according to the maximum value.
6. The method of claim 4, further comprising the step of calculating a compensation factor b (n), said compensation factor b (n) being determined by multiplying said 1-c (n) by a corresponding one of the window functions for which the windowed phase is determined; the clipped output signal is the product of a compensation factor b (n) and the input signal.
7. The method of any one of claims 2, 4, 5 or 6, wherein the window function is one or more of a Hamming window, a rectangular window, a Blackman window, or a Caesar window.
8. The method of any of claims 2, 4, 5 or 6, wherein the derivative is a first derivative of a window function.
9. The method of any of claims 2, 4, 5 or 6, wherein the slope or derivative is a modified slope or derivative, the modification comprising a linear or non-linear modification.
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| CN101162924B (en) * | 2006-10-11 | 2011-06-22 | 中兴通讯股份有限公司 | Peak clipping device for implementing self-adaptive control peak window width |
| CN101232483B (en) * | 2007-01-22 | 2011-08-17 | 大唐移动通信设备有限公司 | Processing method and apparatus in the course of cutting peak power |
| CN101237262B (en) * | 2007-01-30 | 2016-07-06 | 世意法（北京）半导体研发有限责任公司 | The active set method of the transformation that peak-to-average power ratio reduces is realized by retaining tone |
| CN102368094B (en) * | 2010-10-22 | 2013-10-16 | 中国石油天然气股份有限公司 | Rectangular window band-pass amplitude-preserving filtering data processing method in geophysical exploration |
| CN102694755B (en) * | 2011-03-23 | 2015-07-01 | 鼎桥通信技术有限公司 | Method for standing wave detection |
| CN107094038B (en) * | 2017-03-06 | 2020-07-24 | 上海华为技术有限公司 | Method, device and system for adjusting power of antenna system |
| CN108009347B (en) * | 2017-11-30 | 2021-06-22 | 南京理工大学 | Time-frequency analysis method based on synchronous compression joint improvement generalized S transformation |
| CN115442200A (en) * | 2022-11-09 | 2022-12-06 | 成都芯通软件有限公司 | Crest factor reduction processing method, crest factor reduction processing device, storage medium and communication equipment |
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|---|---|---|---|---|
| CN1553670A (en) * | 2003-05-30 | 2004-12-08 | 华为技术有限公司 | Signal clipper and its method |
| CN1595855A (en) * | 2003-09-09 | 2005-03-16 | 电子科技大学 | A novel method for decreasing peak-to-average ratio of OFDM signal |
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