CN1972264B - A Method of Reducing the Peak-to-Average Ratio of Multi-carriers - Google Patents

Abstract

The present invention provides a method for reducing the peak-to-average ratio of multi-carriers. The method includes the following steps: generating a hard clipping signal according to the input multi-carrier combination signal and threshold parameters; The signal generates a peak cancellation signal; generates and updates matched filter coefficients; performs matching filtering on the multi-carrier peak cancellation signal; and mixes the filtered peak cancellation signal with the multi-carrier combination signal. The method of the present invention can achieve a better clipping effect under the conditions of the same error vector magnitude, peak code domain error, and adjacent channel power leakage ratio, that is, the clipped multi-carrier combined signal has a lower peak-to-average ratio, thereby improving the efficiency of the power amplifier.

Description

A Method of Reducing the Peak-to-Average Ratio of Multi-carriers

【Technical field】

The invention relates to a communication system, in particular to a method for reducing the peak-to-average ratio of multi-carrier peak signals entering a power amplifier.

【Background technique】

As we all know, a transmitter of a wireless base station in a mobile communication system uses a power amplifier to transmit signals to compensate for signal attenuation caused by propagation distance. The power amplifier has a certain linear region, and the cost of the power amplifier is determined by the size of its linear region. A signal with a peak-to-average ratio will reduce the efficiency of the power amplifier and increase power consumption, which puts high demands on the linearity of the power amplifier. In order to ensure that the power amplifier works in the linear region to improve its efficiency, the peak-to-average ratio of the signal entering the power amplifier is required to be below a certain range.

In mobile communication systems, clipping technology is often used to reduce the peak-to-average ratio of the signal entering the power amplifier, but unfortunately the introduction of clipping technology may bring a certain degree of signal distortion, out-of-band spectrum expansion or adjacent channel interference and other launch performance. For Wideband Code Division Multiple Access (WCDMA) systems, the error vector magnitude and peak code domain error are used to measure the degree of signal distortion, and the adjacent channel power leakage ratio is used to measure the degree of out-of-band spectrum expansion of the base station transmitter.

Generally, clipping technology can be divided into two categories: baseband clipping technology and digital intermediate frequency (DIF) clipping technology. The great advantage of the baseband clipping technique is that its processing occurs at baseband before the pulse shaping filter, so it does not bring any out-of-band spectrum spread or adjacent channel power leakage ratio performance. Its disadvantage is that the peak-to-average ratio of the clipped signal will increase after passing through the DIF multi-stage interpolation filter, which makes the suppression performance of the signal peak-to-average ratio very unsatisfactory. In addition, the baseband clipping causes a large distortion of the signal, which is manifested as a decrease in the emission performance of the error vector magnitude and peak code domain error. Therefore, under the premise of meeting the error vector magnitude and peak code domain error transmission performance indicators, it is difficult for the baseband clipping technology to make the signal peak-to-average ratio after DIF processing meet the requirements.

DIF clipping technology means that the baseband signal is clipped after passing through the DIF multi-stage interpolation filter. Commonly used DIF clipping technologies include hard clipping and matched filter clipping. The advantage of the hard clipping technology of DIF is that the hardware implementation is relatively simple, but the disadvantage is that direct DIF hard clipping processing will lead to serious out-of-band spectrum expansion and adjacent channel power leakage. Under the condition of ensuring that the adjacent channel power leakage ratio performance index is met, at this time, it is difficult for the DIF hard clipping technology to achieve the expected peak-to-average ratio performance.

Another DIF clipping technology is matched filter clipping technology. The technology used in the invention patent of Chinese Patent Application No. 03800497.3 belongs to DIF matched filter clipping technology, which is aimed at multi-carrier signal clipping. If only the scaler is used to adjust the matched filter gain, so that the expected peak-to-average ratio can be obtained under the condition of satisfying the expected transmission performance conditions such as error vector magnitude, peak code domain error and adjacent channel power leakage ratio. However, when the transmit power of each carrier is different, the clipping technology uses the same scaling factor to adjust the matched filter coefficients of each carrier, and the peak cancellation signal of the multi-carrier combined signal after hard clipping is passed through the matched filter This will seriously deteriorate the carrier error magnitude vector and peak code domain error transmission performance at low transmit power levels. Therefore, the peak-to-average ratio of the clipped signal cannot achieve satisfactory results when the requirements of system error vector magnitude, peak code domain error and adjacent channel power leakage ratio are met.

In addition, when designing filter coefficients, this technical solution considers that the gain of each carrier-matched filter coefficient is properly adjusted to achieve better performance than just using a scaler for gain adjustment. Unfortunately, the The technical invention patent does not specify how to adjust the gain of each carrier matched filter coefficient, and how to adjust each carrier matched filter coefficient in real time, especially how to adjust the gain of each matched filter in system implementation.

【Content of invention】

The purpose of the present invention is to provide a method for reducing the peak-to-average ratio of multi-carrier peak signals entering a power amplifier.

The object of the present invention is achieved through the following technical solutions: a method for reducing the peak-to-average ratio of multi-carriers, said method comprising the following steps:

Generate a hard-limited signal according to the input multi-carrier combined signal and threshold parameters;

Generate a peak cancellation signal according to the delayed multi-carrier combined signal and the hard-limited signal;

Generation and update of matched filter coefficients;

performing matched filtering on the multi-carrier peak canceling signal; and

mixing the filtered peak canceling signal with the delayed multi-carrier combining signal;

The step of generating and updating the matched filter coefficients further includes: performing power estimation on the carrier corresponding to the matched filter coefficient of the carrier; performing frequency mixing on the source filter coefficients according to the frequency corresponding to each carrier; performing gain adjustment on the matched filter coefficients of the carrier; and mixing the matched filter coefficients corresponding to each carrier.

Before the method for reducing the peak-to-average ratio of multi-carriers generates hard-limited signals, it further includes generating a linear threshold for hard-limited operations according to multi-carrier signals and threshold parameters.

The method for reducing the peak-to-average ratio of multi-carriers further includes an iterative step of performing multi-stage matched filter processing on the peak cancellation signal.

According to the estimated power value of each carrier, the invention adjusts the gain of the matched filter coefficient of the corresponding carrier, and performs digital intermediate frequency matching filtering and clipping processing on the combined multi-carrier signal, so as to avoid using the same matched filter for different power carriers. Gain introduces additional signal distortion. The present invention can achieve a better clipping effect under the conditions of the same error vector magnitude, peak code domain error and adjacent channel power leakage ratio, that is, the multi-carrier combined signal after clipping has a lower peak-average Ratio, thereby improving the efficiency of the power amplifier.

The present invention can be appropriately modified and tailored according to hardware resources and performance requirements in actual communication system design. For example, when processing digital intermediate frequency, if a higher sampling rate is achieved and hardware resources are saved, a two-stage half-band interpolation filter can be used. If you want to obtain lower peak-to-average ratio performance under the conditions of error vector magnitude, peak code domain error, and adjacent channel power leakage ratio, you can use a multi-stage matched filter processing method to achieve it. In the scheme provided by the present invention, the digital signal processing adopts a sequential processing mode, and does not involve any feedback processing module, so it is very convenient to realize in the actual hardware system.

【Description of drawings】

Fig. 1 is the schematic diagram of the location of multi-carrier signal generating device and multi-carrier peak clipping device in the present invention;

Fig. 2 is a basic structural diagram of a multi-carrier clipping device for reducing the peak-to-average ratio of multi-carrier signals according to the method for realizing the present invention;

Fig. 3 is a kind of specific realization structural diagram of realizing the basic structure of the multi-carrier clipping device shown in Fig. 2;

Fig. 4 is a flowchart of the method of the present invention.

Fig. 5 is a flowchart of the matching filter system generating and updating steps in the method of the present invention.

Fig. 6 is the magnitude-frequency response of the corresponding matched filter coefficient in the specific structure diagram shown in Fig. 3;

FIG. 7 is another specific implementation structure diagram for realizing the basic structure of the multi-carrier clipping device shown in FIG. 2 .

【Detailed ways】

The present invention can be fully explained and understood by the detailed description provided below in conjunction with the accompanying drawings, and the features, properties and advantages of the present invention will become more apparent.

In the wireless transmitter of the wireless communication system, the clipping technique is used to reduce the peak-to-average ratio of multi-carrier signals entering the power amplifier, so as to improve the efficiency of the power amplifier and reduce the cost of the power amplifier.

Please refer to Figure 1. This figure is a schematic diagram of the location of the multi-carrier signal generating device 300 and the multi-carrier clipping device 400 in the present invention. A multi-carrier signal is formed by superimposing multiple single-carrier signals. For each single-carrier signal, its generation process is the same, so only the generation process of one of the single-carrier signals is used for illustration. For each single-carrier signal, its baseband complex signal is shaped and filtered through a pulse-shaping interpolation filter (PSF) 11, passed through a half-band interpolation filter (HBF) 12 to increase the adoption rate of the DIF signal, and then through a stacked integral comb interpolation filter (CIC) 13 to enhance the image rejection of the signal in the frequency domain, and mix with the numerically controlled oscillator (NC0) 14 to form a single-carrier digital intermediate frequency signal output. Finally, the single-carrier digital intermediate frequency signals are combined in the summer 40 to generate a multi-carrier combined output signal. Furthermore, if a higher sampling rate and reduced hardware implementation complexity are required, a two-stage half-band interpolation filter (HBF) can be used in digital IF processing.

Please refer to Figure 2. This figure shows the basic structure of a multi-carrier clipping device 400 for reducing the peak-to-average ratio of multi-carrier signals according to the present invention. As shown in Figure 2, the multi-carrier clipping device 400 includes a threshold generator 110, a hard clipping module 120, two delay modules 130, a matched filter coefficient generator 160, a matched filter processing module 150 and two summing and accumulating modules 140 and 180. The threshold generator 110 calculates a threshold for hard clipping according to preset threshold parameters and the input multi-carrier combined signal. The hard-limiting module 120 performs hard-limiting processing on the input multi-carrier combined signal according to the threshold, so as to generate a hard-limiting signal. At this time, the multi-carrier combined signal after passing through the delay module 130 is subtracted from the hard-limited signal to generate a peak cancellation signal. The matched filter processing module 150 performs matched filter processing on the peak cancellation signal to obtain a filtered peak cancellation signal according to the matched filter coefficient combined signals corresponding to each carrier frequency generated by the matched filter generator. Finally, the original multi-carrier combined signal passed through the delay module 130 is subtracted from the filtered peak cancellation signal to generate a multi-carrier clipped signal.

The multi-carrier clipping device 400 of the present invention can be applied not only to a multi-carrier communication system, but also to a single-carrier communication system. The technical solution of the present invention will be further elaborated below through the application of the device in a multi-carrier communication system.

Please refer to Figure 3. This figure is a specific implementation structure diagram of a three-carrier clipping processing of the basic structure of the multi-carrier clipping device 400 shown in FIG. 2 , and a specific implementation structure diagram of the matched filter coefficient generator 160 is further described in FIG. 3 . Matched filter coefficient generator device 160 among Fig. 3 further comprises: Carrier power estimation device 161 that carries out power estimation to baseband IQ complex signal; Frequency mixing device 163 that carries out frequency modulation process to source filter coefficient according to the frequency corresponding to three carriers, 165, 167; Gain adjustment devices 168, 169, 172 for performing amplitude modulation on frequency-modulated three-carrier matched filter coefficients according to the estimated carrier power level; used for the summation of combined matched filter coefficients corresponding to the three carriers accumulation device 174 .

First consider the mathematical model of the three-carrier communication system. The three-carrier combined signal before entering the three-carrier clipping module can be modeled as:

$\mathrm{the\; y}\left(k\right)=\underset{i=1}{\overset{3}{\mathrm{\Σ}}}{A}_i\left(k\right)\·e^{(2{\mathrm{\πf}}_{i}k+{\mathrm{\φ}}_i)}$ Formula 1

In Equation 1, A _i (k), f _i and φ _i are the complex envelope, NCO frequency and phase offset corresponding to the ith carrier DIF output signal sampled in decibels.

The threshold generator 110 generates a hard-limited linear threshold linear_thr according to the input three-carrier combined signal y(k) and the threshold parameter thr (dB value). The hard clipping module 120 then performs y(k) hard clipping processing according to the linear threshold and obtains the clipped signal clip(k). The processing process can be represented by the following expression:

$\mathrm{clip}\left(k\right)=\left\{\begin{array}{cc}\mathrm{the\; y}\left(k\right),& \left|\mathrm{the\; y}\left(k\right)\right|\≤\mathrm{linear}\_\mathrm{thr}\\ \mathrm{liner}\_\mathrm{thr}*e^{j*\mathrm{the\; angle}\left(\mathrm{the\; y}\left(k\right)\right)},& \left|\mathrm{the\; y}\left(k\right)\right|>\mathrm{linear}\_\mathrm{thr}\end{array}\right.$ Formula 2

The delayed three-carrier combined signal is mixed with the hard-limited signal to generate a peak cancellation signal c(k).

c(k)=y(k)-clip(k) Formula 3

Assuming that the length of the source filter coefficient h(n) is N, each source filter coefficient is mixed with the NCO of the corresponding carrier to obtain the matched filter coefficient matched_h(n) corresponding to the i-th carrier frequency.

$\mathrm{matched}\_h\left(\mathrm{no}\right)=h\left(\mathrm{no}\right)\·e^{(2\mathrm{\π}{f}_{i}k+{\mathrm{\φ}}_i)},$ n=1, 2,..., N Formula 4

The carrier power estimation module 161 periodically performs power estimation on the baseband signals of each carrier to obtain respective power estimation values PE _i , and calculates gain adjustment G _i based on the power estimation and the maximum transmission power P _max (full power).

$G_i={10}^{\frac{{\mathrm{PE}}_i-{\mathrm{<figure-callout\; id="20"\; label="P\; max"\; filenames="H2005101017937E00041.png"\; state="\{\{state\}\}">P</figure-callout>}}_{\max }}{20}}$ Formula 5

Therefore, the matched filter coefficients corresponding to three carriers can be expressed as:

$\mathrm{combiner}\_h\left(\mathrm{no}\right)=\underset{i=1}{\overset{3}{\mathrm{\&Sigma;}}}{G}_i\&Center\; Dot;h\left(\mathrm{no}\right)\&Center\; Dot;e^{(2\mathrm{\&pi;}{f}_{i}k+{\mathrm{\&phi;}}_i)}$ Formula 6

$<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\frac{{\mathrm{<span\; class="notranslate">\; PE</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="20"\; label="P\; max"\; filenames="H2005101017937E00041.png"\; state="\{\{state\}\}">P</figure-callout></span><figure-callout\; id="20"\; label="P\; max"\; filenames="H2005101017937E00041.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 20</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}$

Please refer to Figure 5. This figure is a flow chart of the method 500 for reducing the peak-to-average ratio of multiple carriers according to the present invention. The method 500 includes the following steps:

Step 510, generating a linear threshold for hard clipping operation according to the multi-carrier signal and threshold parameters;

Step 520, generating a hard-limited signal according to the input multi-carrier combined signal and threshold parameters;

Step 530, generating a peak cancellation signal according to the delayed multi-carrier signal and the hard-limited signal;

Step 540, generation and update of matched filter coefficients;

Step 550, performing matched filtering on the multi-carrier peak cancellation signal; and

Step 560, mixing the filtered peak cancellation signal and the multi-carrier combined signal.

The method 500 for reducing the multi-carrier peak-to-average ratio further includes a step 570 of delaying the multi-carrier combined signal, wherein the delayed multi-carrier combined signal is mixed with the filtered peak cancellation signal.

The method 500 for reducing the multi-carrier peak-to-average ratio further includes an iterative step 580 of performing multi-stage matched filter processing on the peak cancellation signal.

Wherein, the step 540 of generating and updating the matched filter coefficients further includes: step 542, for adjusting the carrier power estimation of the corresponding carrier matched filter coefficient; Frequency mixing; step 546, according to the estimated value of the carrier power, the matched filter coefficients of the corresponding carrier are adjusted for gain; and step 548, the matched filter coefficients corresponding to each carrier are mixed.

Please refer to Figure 6. This figure shows the magnitude-frequency response diagram of the matched filter for clipping the three-carrier combined signal. The power of each carrier is normalized, that is, when transmitting at full power, its power is normalized to 0dB. The matched filter coefficient gain corresponding to each carrier is adjusted according to the offset values (-5dB, 0dB and -3dB) of the estimated carrier power relative to the full power. The figure shows the magnitude-frequency response corresponding to the matched filter coefficients when each carrier transmits at -5dB, 0dB and -3dB power (normalized power value) respectively.

Finally, the peak cancellation signal processed by the matched filter is mixed with the delayed three-carrier combined signal, and an output three-carrier clipped signal z(n) is obtained.

z(k)=y(k)-filter(c(k), combiner_h) Formula 7

In the above formula 7, filter(·) represents the operation of processing the peak cancellation signal c(k) through the matched filter combiner_h.

Please refer to Figure 7. This figure is a specific implementation structure diagram of another three-carrier clipping processing of the basic structure of the multi-carrier clipping device 400 shown in FIG. 2 . The specific implementation of Fig. 7 is different from that of Fig. 3 in that during system design, an N-level iterative filtering device 150' composed of matched filtering processing modules can be added to perform multiple matching on the peak cancellation signal according to system performance requirements and hardware resource conditions. The filter processing operation makes better peak-to-average ratio performance under the condition of satisfying the system error vector magnitude, peak code domain error and adjacent channel power leakage ratio, that is, to ensure that the multi-carrier clipping signal has a smaller peak-to-average ratio.

The present invention can be appropriately modified and tailored according to hardware resources and performance requirements in actual communication system design. For example, when processing digital intermediate frequency, if you want to obtain a higher sampling rate and consider saving hardware resources, you can use a two-stage half-band interpolation filter. If you want to obtain lower peak-to-average ratio performance under the conditions of error vector magnitude, peak code domain error, and adjacent channel power leakage ratio, you can use a multi-stage matched filter processing method to achieve it. In the scheme provided by the present invention, the digital signal processing adopts a sequential processing mode, and does not involve any feedback processing module, so it is very convenient to implement in the actual hardware system.

Here, the present invention has been described in detail through specific implementation examples. The description of the above embodiments is provided in order to enable those skilled in the art to make or apply the present invention. Various modifications of these embodiments are easy for those skilled in the art understand. The invention is not limited to these examples, or to certain aspects thereof. The scope of the present invention is specified by the appended claims.

Claims (3)

1. A method for reducing multi-carrier peak-to-average ratio, said method comprising the following steps: Generate a hard-limited signal according to the input multi-carrier combined signal and threshold parameters; Generate a peak cancellation signal according to the delayed multi-carrier combined signal and the hard-limited signal; Generation and update of matched filter coefficients; performing matched filtering on the multi-carrier peak canceling signal; and mixing the filtered peak canceling signal with the delayed multi-carrier combining signal; The step of generating and updating the matched filter coefficients further includes: performing power estimation on a carrier corresponding to a carrier matched filter coefficient; Perform frequency mixing on the source filter coefficients according to the frequency corresponding to each carrier; performing gain adjustments on matched filter coefficients for corresponding carriers based on the carrier power estimates; and The matched filter coefficients corresponding to each carrier are mixed. 2. The method for reducing the peak-to-average ratio of multi-carriers as claimed in claim 1 is characterized in that: the method for reducing the peak-to-average ratio of multi-carriers further includes generating a multi-carrier signal and a threshold value parameter before generating a hard-limited signal. Linear threshold for hard clipping operation. 3. The method for reducing multi-carrier peak-to-average ratio according to claim 1, characterized in that: the method for reducing multi-carrier peak-to-average ratio further comprises an iterative step of performing multi-stage matched filter processing on the peak cancellation signal.

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