KR20120054264A - Apparatus and method for controlling transmission signal in mobile commnication system - Google Patents

Abstract

PURPOSE: A transmission signal control apparatus of a mobile communication system and method thereof are provided to effectively reduce average output ratio by minimizing the degradation of signal quality. CONSTITUTION: Attenuation error generation units(213,217) creates attenuation error signals for input signals which are bigger than attenuation threshold values. Shaping error generation units(221,223,225) creates shaping error signals by filtering the attenuation error signal of a signal band. The shaping error generation units correct the shaping error signals in order to control the peak size of the attenuation error signal. An error attenuation unit(230) attenuates the corrected shaping error signals in the input signals.

Description

Transmission signal control device and method in mobile communication system {APPARATUS AND METHOD FOR CONTROLLING TRANSMISSION SIGNAL IN MOBILE COMMNICATION SYSTEM}

 The present invention relates to an apparatus and method for controlling a transmission signal in a mobile communication system, and more particularly, to an apparatus and method for controlling a peak level of a transmitted RF signal.

In the wireless communication system, since the transmission signals of the base station and the terminal are amplified through the RF transmitter and transmitted to the wireless channel, the RF transmitter is designed to be linearly amplified up to the maximum size of the input signal. Therefore, as the peak-to-average output ratio (PAR) of the input signal is smaller, the maximum output design capacity of the transmitter of the base station and the terminal may be reduced, and the efficiency and linearization performance of the power amplifier in the RF transmitter may be improved at the average output. To help. Therefore, the role of peak-to-average power attenuator (CFR) in the design of communications equipment is essential. Of course, there may be some degradation in the signal quality by attenuating the peak level above a certain level, but the attenuation occurs at the demodulator level at the receiver, and even at the same level of attenuation depending on the performance of the peak-to-average output ratio attenuator. The effect of degradation is different.

 As a representative example of various algorithms used for the operation of the peak-to-average Crest Factor Reduction (CFR), filtering and filtering, peak windowing, and peak cancellation methods Etc. can be mentioned.

First, the clipping and filtering method is a basic model of the peak-to-average output ratio attenuator. The clipping and filtering of the signal above the clamping threshold having a fixed value from the input signal is carried out and then the signal is returned to the adjacent frequency. It is a method of filtering (Shaping Filter) to remove the signal. However, in this case, there is a disadvantage that Peak Re-growth occurs when the Clipped Siganl through the attenuator becomes larger than the initially set attenuation threshold in the filtering process. Therefore, it is attenuated in consideration of the desired peak-to-output ratio. The threshold must be set much lower, and the deterioration of signal quality is also increased.

Second, the peak windowing method is a complementary algorithm for minimizing peak reproduction occurring in the filtering and filtering method. The peak windowing method extracts a signal above the attenuation threshold and then cancels the attenuation error signal. Error, and the attenuation error signal is subtracted from the original input signal by multiplying the Hamming or Hanning window so as to reduce the amount of the signal induced at the adjacent frequency. However, since the induced signal to the adjacent frequency is not completely removed from the windowed attenuation error signal, the attenuation signal obtained by subtracting the windowed attenuation error signal from the original input signal is also induced to the adjacent frequency. Will have To compensate for this, the window length to be multiplied by the attenuation error signal must be increased, which also involves the disadvantage of causing peak attenuation more than necessary to increase the degree of degradation of signal quality. In addition, excessive peak attenuation (Over Clipping), which causes peak attenuation more than necessary for a continuous peak signal, frequently occurs, resulting in deterioration of signal quality.

Third, the peak cancellation method used in a modified form has a separate peak detector to search for peaks and to prepare a peak cancellation signal prepared in advance in the area where the peak is searched. It generates and subtracts it from the input signal. In this case, the peak cancellation signal used is a signal from which components that are induced at adjacent frequencies are removed in advance, that is, a filtered signal. The peak searcher prevents excessive peak attenuation by operating by taking only the maximum peak point for successive peak signals. However, due to the peak search operation, the peak cancellation signal is restricted for adjacent peaks, resulting in peak missing, which does not cancel the peak signal below the attenuation threshold, resulting in similar results to peak regeneration. Has

 An object of the present invention is to provide peak re-growth, over clipping, and peak attenuation in the prior art Crest Factor Reduction (CFR) of an RF transmitter. The present invention proposes an apparatus and a method for remedying a disadvantage such as Missing. To this end, the peak-to-average output ratio attenuator according to the embodiment of the present invention minimizes the deterioration of the signal quality while sufficiently reducing the input signal peak required by the original system without the signal induced by the adjacent frequency as much as the design value, thereby minimizing the deterioration of the signal quality. Maximize the amount of peak attenuation at the deterioration level or minimize signal degradation at the same peak attenuation level.

An apparatus for attenuating the peak level of a transmission signal in a mobile communication system includes an attenuation error generator that generates an attenuation error signal for an input signal that is greater than an attenuation threshold, and filters the attenuation error signal in a signal band to generate a shaping error signal. And a shaping error generator for correcting the peak amplitudes of the shaping error signal and the attenuation error signal, and an error attenuator for attenuating the corrected shaping error signal from the input signal.

In addition, the method for attenuating a peak level of a transmission signal in a mobile communication system according to an embodiment of the present invention includes the steps of generating an attenuation error signal for a peak level of an input signal larger than an attenuation threshold, and attenuation error signal of a signal band. Filtering to generate a shaping error signal, feedback correcting the peak amplitude of the shaping error signal and the attenuation error signal to be the same, and attenuating the corrected shaping error signal from the input signal. .

 In an embodiment of the present invention, by adding a feedback block to an error shaping FIR block of a peak-to-average output ratio attenuator, the adjacent frequency is minimized while minimizing the degradation of signal quality measured by an error vector magnitude (ECM) or a configuration error (CE). It is possible to effectively reduce the peak-to-average output ratio of the transmitted signal without affecting the furnace. This allows the RF transmitters that transmit the same average output to reduce the maximum output design capacity, thereby reducing the manufacturing cost of the RF transmitter and reducing power consumption by operating the RF transmitter internal RF power amplifier with higher efficiency than before. There is this. In addition, even a predesigned RF transmitter can reduce the degradation of signal quality at the same peak attenuation level.

1 is a diagram showing a configuration of a transmitter of a mobile communication system;
FIG. 2 is a diagram showing the configuration of a peak-to-average power ratio attenuator (CFR) according to the embodiment of the present invention in FIG.
3 is a view for explaining the operation characteristics of each part of FIG.
4 is a view for explaining the operation characteristics of each part of FIG.
5 is a view for explaining a procedure for attenuating peak values of a signal transmitted according to an embodiment of the present invention in a mobile communication device;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same configurations of the drawings denote the same reference numerals as possible whenever possible.

The present invention relates to an apparatus and method for improving the performance of the peak-to-average Crest Factor Reduction (CFR) of the RF transmitter in a mobile communication system. The present invention relates to an apparatus and a method for reducing the maximum output design capacity of an RF transmitter and improving linearization performance and efficiency performance. To this end, the peak-to-average Crest Factor Reduction (CFR) of the RF transmitter according to an embodiment of the present invention is sufficient to reduce the input signal peak required by the original system as much as the design value without the signal being induced to the adjacent frequency. By minimizing the deterioration of signal quality, the peak attenuation is maximized at the same signal deterioration level or the signal deterioration is minimized at the same peak attenuation level. In an embodiment of the present invention, by adding a feedback block to an error shaping FIR block of a peak-to-average output ratio attenuator, the adjacent frequency is minimized while minimizing the degradation of signal quality measured by an error vector magnitude (ECM) or a configuration error (CE). In this paper, we propose a technique to effectively reduce the peak-to-average output ratio of a transmitted signal without the effect of the circuit.

1 is a view for explaining the RF transmission and reception operation of the mobile communication system. 1 illustrates an example of a configuration of an RF transceiver of a terminal device of a mobile communication system.

Referring to FIG. 1, the transmission data is modulated by the modulator 10 and input to the RF transmitter 20. The RF transmitter 20 frequency upconverts and power amplifies and outputs the modulated baseband transmission signal. The water separator 30 outputs a transmission signal output from the RF transmitter 20 through an antenna. The water separator 30 may be a duplexer. The RF receiver 430 generates a baseband signal by frequency down converting the signal received through the transmitter / receiver 30. The demodulator 50 demodulates and outputs the converted baseband received signal.

Referring to the operation of the RF transmitter 20, the digital up converter (DUC) 110 performs a function of digitally raising the frequency of the baseband data to be transmitted. That is, the DUC110 controls the sampling rate of the transmission data (ie, increases the sampling rate) to perform up-converting, and performs a signal shaping function to block signals other than the frequency domain signal band. It performs the function. The peak-to-average output ratio attenuator (CFR) 120 attenuates a peak level of a predetermined level or more in the signal output from the DUC110. A digital pre-distortion (DPD) 130 predistorts the signal output from the peak-to-average output ratio attenuator 120 to compensate for the nonlinear characteristics of the power amplifier. The RF up converter (RUC) 140 performs a function of upconverting the frequency output from the signal output from the DPD130 into a signal of an RF transmission band. The power amplifier 150 amplifies and outputs the transmission signal output from the RUC140.

The RF transmitter 20 illustrated in FIG. 1 is a diagram for describing the input / output relationship between the peak-to-average output ratio attenuator 130 according to the embodiment of the present invention. Therefore, some components of the RF transmitter 20 are omitted, and may be configured differently from FIG. 1.

FIG. 2 is a diagram showing the configuration of the peak-to-average output ratio attenuator according to the embodiment of the present invention in FIG.

Referring to FIG. 2, an input signal may be a signal output from the DUC110. The attenuation threshold generated by the reference value generator 211 may be a reference value for detecting whether an input signal exceeds a peak value of a predetermined level or more. The attenuation threshold (reference value) may be set by the user and may be set to an optimized value at the time of manufacturing the terminal device. The peak comparator 213 generates a comparison result signal of the input signal and the attenuation threshold. The peak comparator 213 may be configured as a subtractor. In this case, the peak comparator 213 subtracts and outputs the attenuation threshold value from the input signal. In this case, a positive value is output when the level of the input signal is greater than the attenuation threshold. The peak detector 217 detects a peak level greater than the attenuation threshold set at the output of the peak comparator 213 and outputs the peak level as a clipping error signal (CLP error). In this case, the peak comparator 213 outputs a signal having a negative component when a peak level at which an input signal is larger than a threshold is input. Then, the peak detector 217 compares the output of the peak comparator 213 with a reference value for peak detection (here, ground level, zero level), and detects a smaller signal (that is, a peak level signal larger than the threshold). Output as attenuation error signal (CLP error).

The above configuration may be a decay error generator block that generates an attenuation error signal by comparing an input signal with an attenuation threshold to attenuate a peak signal.

The attenuation error signal (CLP error) output from the peak detector 217 is applied to a shaping filter (Finite Impulse Response) 223 through the compensator 221. Then, the shaping filter 223 may be configured as an FIR filter, and the shaping filter 223 filters and outputs an attenuation error signal corresponding to the baseband of the transmission signal. That is, the shaping filter 223 removes a signal of an adjacent band of the attenuation error signal. Accordingly, the shaping filter 223 performs an error shaping function to minimize interference of the attenuation error signal to an adjacent frequency.

The attenuation control signal CLP error is a value obtained by multiplying -1 by extracting an amount exceeding a threshold from an input signal. The shape CLP error is a signal that passes through the Shaping FIR 233 without feedback correction in the CLP error. When the two signals are compared, the shaping error signal is a minimum attenuation error required for peak attenuation. The peak magnitude of the contrast shaping error becomes relatively large, resulting in excessive peak attenuation below the threshold. In order to prevent this, it is preferable to use the feedback correction function such that the attenuation error signal, which is the minimum attenuation error required for peak attenuation, and the peak magnitude of the shaping error are the same.

The output of the shaping filter 223 is applied to the feedback (225). The feedback unit 225 compares whether the value obtained by subtracting the shaping error from the input signal is equal to the attenuation threshold value that is the minimum attenuation error, and the attenuation error signal and the shaping error that are the minimum attenuation error when the two values are not equal to each other. It may be composed of a compensator for correcting the attenuation error so that the peak size is the same. If the peak magnitudes of the attenuation error signal and the shaping error are not equal to each other (that is, the value obtained by subtracting the shaping error from the input signal is not equal to the attenuation threshold value), the feedback unit 223 sends the corrected shaping error value to the compensator 221. Is authorized. Then, the compensator 221 subtracts the attenuation error value corrected by the feedback unit 225 from the attenuation error signal (SLP error), and the output of the compensator 221 is applied to the shaping filter 223. If the value obtained by subtracting the shaping error from the input signal is equal to the attenuation threshold while repeating the above operation (that is, the peak magnitude of the minimum reduction error value and the sleeping error value is the same), the feedback unit 225 performs the shaping. The error value is applied to the error attenuator 230. Here, the feedback unit 225 and the compensator 221 may be a feedback block for feedback correction by comparing the shaped attenuation error signal with an initially set attenuation error signal. In this case, the feedback used for the shaping correction may be corrected by feeding back all or a part of the impulse response of the shaping FIR. The output of the compensator 221 is transmitted to the input of the shaping filter 223. Therefore, the shaping filter 223 can minimize adjacent frequency interference and optimize peak shaping in in-band.

The above configuration performs error shaping to minimize interference of adjacent attenuation error signals (CLP error) to adjacent frequencies, and performs feedback correction by comparing the shaped error signal with the initially set attenuation error signal. It can be the configuration of the shaping error generator.

The error attenuator 230 receives the input signal and the shaping error signal to attenuate the peak level of the input signal. In FIG. 2, the error attenuator 230 subtracts the shaping error signal from an input signal to attenuate a peak level exceeding an attenuation threshold in the input signal. The error attenuator 230 may be a peak attenuation block that attenuates and outputs a shaped clipping error generated from an input signal.

As described above, the peak-to-average output ratio attenuator 120 according to the embodiment of the present invention generates a clipping error signal by comparing the input signal and the attenuation threshold to attenuate the peak signal. Thereafter, error shaping (Shaping FIR) is performed to minimize interference of the attenuation error signal to the adjacent frequency, and feedback correction is performed by comparing the shaped error signal with an initially set attenuation error signal. The shaping clipping error signal generated as described above is attenuated from the input signal and output. The peak-to-average output ratio attenuator according to the embodiment of the present invention having such a configuration compensates for shortcomings such as peak re-growth, excessive peak attenuation, and peak missing at the attenuator output stage. Can be.

3 is a diagram showing signal characteristics according to the operation of the peak-to-output ratio attenuation apparatus according to the embodiment of the present invention, and FIG. 4 is a diagram showing the frequency spectrum of the signal. In FIG. 3, blue reference numeral 311 is an input signal, apricot color reference number 313 is an output of the peak detector 217, pink reference number 315 is an output of the shaping filter 223, and red reference numeral 317 is an output of the peak attenuator 230. The output is shown. In FIG. 4, blue reference numeral 411 denotes an input signal, pink reference numeral 413 denotes an output of a peak detector 217, an apricot reference numeral 415 denotes an output of a shaping filter 223, and a red reference numeral 417 denotes a peak attenuator 230. The output is shown.

 3 and 4, the attenuation error signal CLP ERROR 313 is a value obtained by extracting an amount exceeding a threshold value from the input signal In 311 and multiplying by −1 to obtain the peak detector 217. Signal output from The attenuation error signal (CLP ERROR) 313 is error-shaped by the shaping filter 223 to minimize interference of adjacent frequencies, and the feedback signal corrects the error signal shaped by the compensator 221 to the attenuation error signal (CLP ERROR) 313. . That is, the feedback corrected and error shaped signal FB Shaped CLP ERROR 315 is a signal completed by the compensator 221 and the shaping filter 223 from the attenuation error signal CLP ERROR 313 to feedback correction and error shaping, and is required for peak attenuation. It can be seen that the peak magnitudes of the attenuation error signal (CLP ERROR) such as 313 which is the minimum attenuation error and the shaped attenuation error signal (FB CLP Shaped CLP error) such as 315 are the same. The attenuation error signal shaped as 315 is attenuated from the input signal such as 311 by the peak attenuator 230 and output as 317. Therefore, as shown in the final output signal FB CFR out as shown in 317 of FIG. Reduces attenuation errors to prevent over peaking, and when small, increases attenuation to prevent peak re-growth or peak missing.

Comparing the two signals (CLP error and BP shaped CLP error) in the frequency domain, the frequency spectrum of the attenuation error signal (CLP ERROR) such as 413 as shown in Figure 4 is the frequency of the input signal (In) 411 While the signal component outside the band is considerably large, the frequency spectrum of the FB Shaped CLP ERROR such as 415 shows that the signal component outside the frequency band of the input signal In is greatly attenuated. . In addition, the final output signal FB CFR Out of the peak-to-average output ratio attenuator such as 417 is attenuated from the input signal In to the peak threshold of the signal above the threshold, and the frequency spectrum is also a signal other than the frequency band of the signal. It can be confirmed that is sufficiently attenuated.

5 is a flowchart illustrating a procedure of performing an operation of a peak-to-average output ratio attenuator according to an embodiment of the present invention in a mobile communication terminal.

Referring to FIG. 5, the attenuator sets an attenuation threshold in step 511. Here, the attenuation threshold may be set by the user as described above or may be set at the product manufacturing stage. The attenuator then controls the peak level of the transmission signal with reference to the attenuation threshold. When the transmission signal is input, the attenuator compares the input signal with an attenuation threshold in step 513. If the input signal is greater than the attenuation threshold, the attenuator ends the input signal as an output signal in step 525.

However, if the input signal is greater than the attenuation threshold in step 513, the attenuator proceeds to step 515 to generate a shaping error signal. In this case, the shaping error signal is a signal obtained by filtering the attenuation error signal of the baseband of the transmission signal, and is a signal from which adjacent frequency interference of the attenuation error signal is removed. Thereafter, the attenuator performs feedback compensation by checking the shaping error signal in steps 519 to 523. That is, the attenuator compares whether the value obtained by subtracting the shaping error signal from the input signal is equal to the attenuation threshold in step 519. If the two values are the same in the comparison process, that is, if the peak magnitudes of the attenuation error signal (CLP error signal) and the shaping error signal (Shape CLP error), which are the minimum attenuation errors required for peak attenuation, are the same, the attenuator may proceed to step 523. Subsequently, the shaping error signal is subtracted from the input signal, that is, the error is attenuated and output as an output signal.

However, if the two values are not the same in the comparison process of step 519, the attenuator returns to step 521 and corrects the shaping error value so that the peak size of the minimum attenuation error and the peak size of the shaping error have the same size. . The correction operation corrects the value obtained by subtracting the shaping error signal from the double attenuation error signal to be the attenuation error value, and shaping filters the corrected attenuation error value. In this case, the shaping filtering is a value for filtering the attenuation error signal of the baseband of the transmission signal as described above. The above process is repeated until the shaping error signal is subtracted from the input signal equal to the attenuation threshold. If the two values are the same, the attenuator detects it in step 519 and performs the step 523 to subtract the shaping error signal from the input signal and output the same.

As described above, the attenuator first determines an appropriate attenuation threshold at the level of demodulation, and then determines whether the attenuation operation is performed by comparing the input signal with the attenuation threshold. Then, the input signal is compared with the attenuation threshold to extract a clipping error signal, and the shaping error signal is minimized by shaping and filtering the extracted attenuation error signal. When the above error shaping is completed, a feedback correction process is performed by determining whether the shaped attenuation error is an appropriate value. That is, the attenuator reduces the attenuation error when the shaped attenuation error is greater than the difference between the input signal and the attenuation threshold, thereby preventing over peak attenuation, and when the attenuation is small, increases the attenuation error, thereby causing peak re-growth. ) Or to prevent peak missing.

Embodiments of the present invention disclosed in the specification and drawings are only specific examples to easily explain the technical contents of the present invention and aid the understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

Claims (10)

In the device for reducing the peak level of the transmission signal in a mobile communication system,
An attenuation error generator for generating an attenuation error signal for an input signal that is greater than an attenuation threshold;
A shaping error generator for generating a shaping error signal by filtering an attenuation error signal of a signal band, and correcting the shaping error signal to have the same peak magnitude of the attenuation error signal;
And an error attenuator configured to attenuate the corrected shaping error signal from the input signal. The method of claim 1, wherein the shaping error generator,
And a compensator for compensating the attenuation error signal by subtracting the attenuation control signal corrected from the attenuation error signal.
A shaping filter for generating a shaping error signal by filtering the attenuation error signal output from the compensator to a baseband of the signal in order to minimize interference to an adjacent frequency;
And comparing the shaping error signal with the attenuation error signal, and correcting the two values to be the same, applying them to the compensator, and outputting the shaping error signal to the error attenuator. Device. The apparatus of claim 2, wherein the shaping filter is a FIR filter, and the feedback unit feedbacks and corrects all or part of an impulse response of the FIR filter. The method of claim 3, wherein the feedback unit
A comparator for comparing the difference between the input signal and the shaping error signal and the attenuation threshold, and outputting the shaping error signal to the error attenuator if the difference is the same;
If the comparator is not the same, the attenuation error signal is a 2 * attenuation error control signal to the shaping error correction value so that the same value, characterized in that it comprises a compensator for feeding back the corrected attenuation error signal to the compensator Device. The method of claim 3, wherein the attenuation error generator,
A peak comparator for comparing the input signal with the attenuation threshold;
And a peak detector configured to input an output of the peak comparator to detect an input signal larger than the attenuation threshold and output the attenuation error signal. The method of claim 5,
The peak comparator is a subtractor which subtracts the attenuation threshold from the input signal.
And the peak detector generates a signal smaller than the ground potential as an attenuation error signal in the comparison signal output from the subtractor. In the method for reducing the peak level of the transmission signal in a mobile communication system,
Generating an attenuation error signal for the peak level of the input signal that is greater than the attenuation threshold;
Generating a shaping error signal by filtering the attenuation error signal of the signal band, and performing feedback correction so that the peak magnitudes of the shaping error signal and the attenuation error signal are the same;
And attenuating the corrected shaping error signal from the input signal. The method of claim 7, wherein the feedback correction process,
Generating a shaping error signal by filtering the attenuation error signal to the baseband of the signal to minimize interference to an adjacent frequency;
Comparing the shaping error signal with the attenuation error signal, correcting the attenuation error signal so that the two values are the same, and feeding back the shaping error signal generation process;
And if the shaping error signal is the same as the attenuation error signal, a step of attenuating and outputting a shaping error signal to the input signal. The method of claim 8,
The generating of the shaping error signal may include FIR filtering the attenuation error signal into a baseband band of the signal.
And correcting the attenuation control signal by feeding back all or part of the FIR filtered impulse response. The method of claim 3, wherein the correcting of the attenuation control signal is performed.
Comparing the difference between the input signal and the shaping error signal and the attenuation threshold value to be the same;
If it is not the same in the comparison process, the attenuation error signal is corrected to be the same value as the shaping error is subtracted from the 2 * attenuation error control signal, and the shaping error signal is repeatedly generated using the corrected attenuation error signal. Characterized by consisting of a process.

Images