A method for improving the stability of shortwave digital predistortion system

Abstract

The present invention relates to the field of adaptive digital predistortion technology, and in particular to a method for improving the stability of a shortwave digital predistortion system. The present invention constrains and verifies a predistortion table calculated by a digital predistortion system, makes a validity judgment on the predistortion table, and finally selects a suitable predistortion table according to demand, thereby reducing the fluctuation of the predistortion index performance of the digital predistortion system and improving the stability of the digital predistortion system.

Description

Technical Field

[0001] The invention relates to the technical field of adaptive digital predistortion, and in particular to a method for improving the stability of a shortwave digital predistortion system. Background Art

[0002] With the development of digital mobile communication technology, higher and higher requirements are placed on the performance of base station power amplifiers, that is, to make the power amplifier have higher efficiency while meeting higher linearity requirements. In order to achieve this requirement, the amplifier must be both linear and efficient, which means that linearization processing is required for the RF amplifier or RF system.

[0003] The most important step in the development of linearization technology is the emergence of pre-distortion technology, which was initially applied to the RF part of analog communication systems. With the development of digital signal processing technology, it can also be implemented in the digital domain to form digital pre-distortion technology.

[0004] For ease of implementation, the digital pre-distortion system adopts a lookup table (LUT) method, in which the pre-distortion table extraction structure is mainly modified through continuous iteration to output the pre-distortion table for use by the digital pre-distortion system.

[0005] However, the power amplifier characteristics of the digital pre-distortion system will change with time or external environment changes, which often leads to fluctuations in pre-distortion index performance and system instability during the iterative update of the pre-distortion table, affecting the application of the entire system. Summary of the invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide a method for improving the stability of a shortwave digital predistortion system, reduce the fluctuation of the predistortion index performance of the digital predistortion system, and improve the stability of the digital predistortion system.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions to achieve it.

[0008] A method for improving the stability of a shortwave digital predistortion system comprises the following steps:

[0009] Step 1, after the digital pre-distortion system calculates the pre-distortion table each time, the pre-distortion table is obtained and recorded as LUT1, and a peak compensation check is performed on the pre-distortion table LUT1;

[0010] If the peak compensation check fails, step 1 is repeated; if the peak compensation check passes, it is determined whether the digital pre-distortion system has a pre-distortion table currently in use. If not, the pre-distortion table LUT1 is used by the digital pre-distortion system, and step 1 is repeated; if it exists, the pre-distortion table currently in use is recorded as LUT0, and step 2 is entered;

[0011] Step 2, obtaining an input signal X and a feedback signal Y of the current digital predistortion system; then obtaining an output signal X′ after the input signal X is input into the predistortion table LUT0 currently in use, an output signal Y′ after the feedback signal Y is input into the predistortion table LUT0 currently in use, and an output signal Y″ after the feedback signal Y is input into the predistortion table LUT1; judging whether the signals Y′ and Y″ can be gain compensated, if not, re-performing step 1; if gain compensation can be performed, performing gain compensation on the signals Y′ and Y″, obtaining signals Y′1 and Y″1, and proceeding to step 3;

[0012] Step 3, using the pre-distortion table verification criterion shown in formula (2) to perform pre-distortion table verification;

[0013] RMS(X′,Y′1) / RMS(X′,Y″1)>ThreshValue (2)

[0014] In formula (2), RMS(X′, Y′1) is the RMS value of signal X′ and signal Y′1 in the time domain; RMS(X′, Y″1) is the RMS value of signal X′ and signal Y″1 in the time domain; ThreshValue is the threshold value;

[0015] If formula (2) is not true, the pre-distortion table check fails, and step 1 is performed again; if formula (2) is true, the pre-distortion table check passes, and the pre-distortion table LUT1 is output to replace the pre-distortion table LUT0 currently in use.

[0016] Further, the peak compensation check of step 1, specifically, obtains the maximum peak value X of the sample of the digital predistortion system peak And enter the pre-distortion table LUT1 to obtain the maximum peak value of the sample after passing through the pre-distortion table LUT1

[0017] Determine the maximum peak value X of the sample peak The maximum peak value of the sample after the pre-distortion table LUT1 Whether it satisfies formula (1);

[0018]

[0019] In formula (1), MaxDPDGain is the maximum predistortion gain.

[0020] Furthermore, in step 2, it is determined whether the signal X′, the signal Y′ and the signal Y″ can be gain compensated. Specifically, it is determined whether the signal X′, the signal Y′ and the signal Y″ satisfy equation (3):

[0021]

[0022] In formula (3), Power() is calculated as Where N is the sample point data length of the signal, n = 1, 2, ..., N; GainThreshValue is the threshold;

[0023] If the formula (3) is not true, gain compensation cannot be performed; if the formula (3) is true, gain compensation can be performed.

[0024] Furthermore, in step 2, gain compensation is performed on the signal Y′ and the signal Y″. Specifically, the gain compensation method is as follows:

[0025] Y′1=Y′×Gain1 Y″1=Y″×Gain2

[0026] Among them, Gain1=Power(X′) / Power(Y′), Gain2=Power(X′) / Power(Y″).

[0027] Furthermore, the calculation method of the RMS value in step 3 is shown in formula (4):

[0028]

[0029] Compared with the prior art, the beneficial effects of the present invention are: reducing the fluctuation of the predistortion index performance of the digital predistortion system and improving the stability of the digital predistortion system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 A flowchart of a method for improving the stability of a shortwave digital predistortion system according to the present invention;

[0032] Figure 2 This is a graph showing the relationship between the predistortion improvement index and the number of iterations with and without adding predistortion table constraints and verification in the simulation experiment. DETAILED DESCRIPTION

[0033] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0034] refer to Figure 1 , is a flowchart of a method for improving the stability of a shortwave digital predistortion system according to the present invention; the method for improving the stability of a shortwave digital predistortion system comprises the following steps:

[0035] A method for improving the stability of a shortwave digital predistortion system comprises the following steps:

[0036] Step 1, after the digital pre-distortion system calculates the pre-distortion table each time, the pre-distortion table is obtained and recorded as LUT1, and a peak compensation check is performed on the pre-distortion table LUT1;

[0037] Specifically, obtain the maximum peak value X of the sampling samples of the digital predistortion system peak And enter the pre-distortion table LUT1 to obtain the maximum peak value of the sample after passing through the pre-distortion table LUT1

[0038] Determine the maximum peak value X of the sample peak The maximum peak value of the sample after the pre-distortion table LUT1 Whether it satisfies formula (1);

[0039]

[0040] In formula (1), MaxDPDGain is the maximum pre-distortion gain, and MaxDPDGain is configured according to requirements.

[0041] If the formula (1) is not true, the peak compensation check fails; if the formula (1) is true, the peak compensation check fails.

[0042] If the peak compensation check fails, step 1 is repeated; if the peak compensation check passes, it is determined whether the digital pre-distortion system has a pre-distortion table currently in use. If not, the pre-distortion table LUT1 is used by the digital pre-distortion system, and step 1 is repeated; if it exists, the pre-distortion table currently in use is recorded as LUT0, and step 2 is entered;

[0043] Step 2, obtaining an input signal X and a feedback signal Y of the current digital predistortion system; then obtaining an output signal X′ after the input signal X is input into the predistortion table LUT0 currently in use, an output signal Y′ after the feedback signal Y is input into the predistortion table LUT0 currently in use, and an output signal Y″ after the feedback signal Y is input into the predistortion table LUT1; determining whether the signal Y′ and the signal Y″ can be gain compensated;

[0044] Specifically, it is determined whether the signal X′, the signal Y′ and the signal Y″ satisfy equation (3):

[0045]

[0046] In formula (3), Power() is calculated as Wherein N is the sample point data length of the signal, n=1, 2, ..., N; GainThreshValue is the threshold, and GainThreshValue is configured according to requirements.

[0047] If the formula (3) is not true, gain compensation cannot be performed; if the formula (3) is true, gain compensation can be performed.

[0048] If gain compensation is not possible, then step 1 is repeated; if gain compensation is possible, then gain compensation is performed on signal Y′ and signal Y″ to obtain signal Y′1 and signal Y″1, and then step 3 is entered;

[0049] Specifically, gain compensation is performed on the signal Y′ and the signal Y″ in the following manner:

[0050] Y′1=Y′×Gain1 Y″1=Y″×Gain2

[0051] Among them, Gain1=Power(X′) / Power(Y′), Gain2=Power(X′) / Power(Y″).

[0052] Step 3, using the pre-distortion table verification criterion shown in formula (2) to perform pre-distortion table verification;

[0053] RMS(X′,Y′1) / RMS(X′,Y″1)>ThreshValue (2)

[0054] In formula (2), RMS(X′, Y′1) is the RMS value of signal X′ and signal Y′1 in the time domain; RMS(X′, Y″1) is the RMS value of signal X′ and signal Y″1 in the time domain; ThreshValue is the threshold value, and ThreshValue is configured according to requirements.

[0055] If formula (2) is not true, the pre-distortion table check fails, and step 1 is performed again; if formula (2) is true, the pre-distortion table check passes, and the pre-distortion table LUT1 is output to replace the pre-distortion table LUT0 currently in use.

[0056] Furthermore, the calculation method of the RMS value in step 3 is shown in formula (4):

[0057]

[0058] The present invention constrains and verifies the predistortion table calculated by the digital predistortion system, judges the validity of the predistortion table, and finally selects a suitable predistortion table according to demand, thereby reducing the fluctuation of the predistortion index performance of the digital predistortion system and improving the stability of the digital predistortion system.

[0059] Through actual simulation and testing, in the process of downloading and updating the pre-distortion table of the digital pre-distortion system more than 10,000 times, the pre-distortion improvement index is recorded every 100 times. Figure 2 It can be seen that after the method of the present invention constrains and verifies the predistortion table, it can ensure that the digital predistortion system has a greatly improved predistortion stability without deteriorating the performance of the digital predistortion system.

[0060] Although the present invention has been described in detail in general terms and in specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements may be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for improving the stability of a shortwave digital predistortion system, characterized in that: The following steps are involved: Step 1, after the digital pre-distortion system calculates the pre-distortion table each time, the pre-distortion table is obtained and recorded as LUT1, and a peak compensation check is performed on the pre-distortion table LUT1; If the peak compensation check fails, repeat step 1; If the peak compensation check passes, it is determined whether the digital pre-distortion system has a pre-distortion table currently in use. If not, the pre-distortion table LUT1 is used by the digital pre-distortion system, and step 1 is repeated; if it exists, the pre-distortion table currently in use is recorded as LUT0, and step 2 is entered; Step 2, obtaining an input signal X and a feedback signal Y of the current digital predistortion system; then obtaining an output signal X′ after the input signal X is input into the predistortion table LUT0 currently in use, an output signal Y′ after the feedback signal Y is input into the predistortion table LUT0 currently in use, and an output signal Y″ after the feedback signal Y is input into the predistortion table LUT1; judging whether the signals Y′ and Y″ can be gain compensated, if not, re-performing step 1; if gain compensation can be performed, performing gain compensation on the signals Y′ and Y″ to obtain signals Y′1 and Y″1, and proceeding to step 3; Step 3, using the pre-distortion table verification criterion shown in formula (2) to perform pre-distortion table verification; RMS(X′,Y′1) / RMS(X′,Y″1)>ThreshValue (2) In formula (2), RMS(X′, Y′1) is the RMS value of signal X′ and signal Y′1 in the time domain; RMS(X′, Y″1) is the RMS value of signal X′ and signal Y1″ in the time domain; ThreshValue is the threshold value; If the formula (2) is not true, the pre-distortion table check fails, and step 1 is performed again; if the formula (2) is true, the pre-distortion table check passes, and the pre-distortion table LUT1 replaces the pre-distortion table LUT0 currently in use.

2. The method for improving the stability of a shortwave digital predistortion system according to claim 1, characterized in that: The peak compensation check in step 1 is to obtain the maximum peak value X of the sample of the digital predistortion system. peak And enter the pre-distortion table LUT1 to obtain the maximum peak value of the sample after passing through the pre-distortion table LUT1 Determine the maximum peak value X of the sample peak The maximum peak value of the sample after the pre-distortion table LUT1 Whether it satisfies formula (1); In formula (1), MaxDPDGain is the maximum predistortion gain.

3. The method for improving the stability of a shortwave digital predistortion system according to claim 1, characterized in that: In step 2, it is determined whether the signal Y′ and the signal Y″ can be gain compensated. Specifically, it is determined whether the signal X′, the signal Y′ and the signal Y″ satisfy equation (3): In formula (3), Power ( ) is calculated as Where N is the sample point data length of the signal, n = 1, 2, ..., N; GainThreshValue is the threshold; If the formula (3) is not true, gain compensation cannot be performed; if the formula (3) is true, gain compensation can be performed.

4. The method for improving the stability of a shortwave digital predistortion system according to claim 1, characterized in that: In step 2, gain compensation is performed on the signal Y′ and the signal Y″. Specifically, the gain compensation method is as follows: Y'1=Y'×Gain1 Y"1=Y"×Gain2 Among them, Gain1=Power(X′) / Power(Y′), Gain2=Power(X′) / Power(Y″).

5. The method for improving the stability of a shortwave digital predistortion system according to claim 1, characterized in that: The calculation method of the RMS value in step 3 is shown in formula (4):

Images