CN106169985A - Envelope-tracking amplifier digital pre-distortion method based on improved model - Google Patents

Abstract

The invention provides a kind of envelope-tracking amplifier digital pre-distortion method based on improved model, including: utilize the memory polynomial model improved dynamically to adjust pre-distortion parameters, the input data of predistorter are increased to baseband signal and envelope signal co-controlling by single baseband signal.Method in the present invention overcomes the shortcoming that the conventional memory multinomial model pre-distortion method for fixed bias voltage power amplifier is not suitable for dynamically changing the envelope-tracking amplifier of power amplifier offset voltage, under conditions of identical complexity, reach more preferable linearisation effect, improve the linearity of envelope-tracking amplifier.

Description

Envelope-tracking amplifier digital pre-distortion method based on improved model

Technical field

The present invention relates to wireless communication field, in particular it relates to a kind of envelope based on modified model memory polynomial model Follow the tracks of amplifier digital pre-distortion method.

Background technology

Along with the continuous progress and development of wireless system, the lifting of signal rate brings signal bandwidth and signal peak-to-average ratio Increase, generally for meeting the linearity of communication system, need to be operated in power amplifier back-off region, sternly Heavily reduce the efficiency of power amplifier.In order to solve this contradiction, researcher proposes to be combined envelop following technology with current power amplifier, bag Amplifier (Envelope-tracking Power Amplifier, ETPA) followed the tracks of by network can be according to power amplifier input letter Number " envelope " dynamically adjust direct current power source voltage, make power amplifier be operated in the widest power bracket close to saturation region, improve Power amplification efficiency.

The technological difficulties of envelope tracking power amplifier are, its variable bias voltage makes power amplifier more be operated in saturation region Territory, causes the memory effect of power amplifier to be obviously enhanced, and non-linear distortion is serious.For the contradiction between power amplification efficiency and the linearity, Non-linear distortion can be reduced while improving terminal power amplification efficiency in conjunction with digital pre-distortion technology.And traditional static merit The mathematical model put can not express the characteristic of envelope-tracking amplifier well so that nonlinear improvement is paid no attention to by predistorter Think.

Summary of the invention

For defect of the prior art, it is an object of the invention to provide a kind of envelope-tracking based on improved model and amplify Device digital pre-distortion method.

The envelope-tracking amplifier digital pre-distortion method based on improved model provided according to the present invention, including walking as follows Rapid:

Step A: calculate the corresponding envelope signal V of base-band input signal x (n) of envelope-tracking amplifier_envAnd base band is defeated Enter the input as predistorter of signal and adjusted envelope signal；

Step B: utilize the envelope signal V of input_envDynamically control memory polynomial model parameter, export pre-distorted signals；

Step C: utilize indirect learning method self adaptation to obtain predistorter parameter, by after predistortion signal send into envelope with Track amplifier, it is achieved the improvement of envelope-tracking Amplifier linearity.

Preferably, described step A includes:

Step A1: base-band input signal x (n) of envelope-tracking amplifier is indicated with plural form, and calculate defeated Enter power, order:

P_{in_W}=0.5*real (V_in*conj(V_in/R_in))

Power signal is converted to dBm unit:

P_{in_dBm}=10*log (P_{in_W})+30

In formula: P_{in_W}Represent base-band input signal power, V_inRepresent base-band input signal magnitude of voltage, R_inRepresent power amplifier input Link resistance, real (.) expression takes complex signal real part computing, and conj (.) represents complex signal transposition computing, P_{in_dBm}Represent base band Input signal power, unit: dBm；

Step A2: carry out according to the power amplifier bias voltage scope that input signal power and envelop modulator are controlled Adjust, obtain input signal V needed for predistorter_env:

$V_{env}=\left\{\begin{array}{cc}{P}_{\min },& P_{in\_dBm}\&le;P_{\min }\\ P_{in\_dBm},& P_{\min }<P_{in\_dBm}<P_{\max }\\ P_{\max },& P_{in\_dBm}\&GreaterEqual;P_{\max }\end{array}\right.$

In formula: P_minRepresent the input signal power corresponding to minimum bias voltage in order, P_maxRepresent that maximum bias voltage is corresponding Input signal power.

Preferably, described step B includes:

Step B1: the mathematical formulae providing traditional memory polynomial model is as follows:

$y\left(n\right)=\underset{p=1}{\overset{P}{\&Sigma;}}\underset{m=0}{\overset{M}{\&Sigma;}}{c}_{pm}x(n-m)|x(n-m){|}^{p-1}$

Step B2: step B1 is improved to the functional form with input signal envelope as variable, i.e. dynamically changes memory many Item formula model parameter, concrete mathematical formulae is as follows:

$c_{pm}=f\left(V_{env}\right)=\underset{n=0}{\overset{N}{\&Sigma;}}{b}_{pm}{V}_{env}^n$

In formula: y (n) represents power amplifier output signal, c_pmRepresenting memory polynomial model parameter, n represents the n-th bit digital letter Number, m represents current memory depth, and p represents current polynomial order, and x (n-m) represents power amplifier input signal, maximum order of a polynomial Number P span is P >=1, and the span of maximal memory degree of depth M is M >=1；b_pmRepresent that input signal envelope calculates memory many The polynomial module shape parameter that item formula model parameter uses, N represents this function maximum order.

Preferably, described step C includes:

Step C1: build digital predistorter for core with modified model memory polynomial mathematical model, by base band input letter Number x (n) carries out after pre-distortion, and the predistortion that will obtain signal z (n) as the input signal of envelope-tracking amplifier, Concrete mathematical expression is as follows:

$z\left(n\right)=\underset{p=1}{\overset{P}{\&Sigma;}}\underset{m=0}{\overset{M}{\&Sigma;}}f\left(V_{env}\right)x(n-m)|x(n-m){|}^{p-1}$

Step C2: process with indirect learning structure adaptive, with multinomial model matching memory polynomial parameter expression f (V_env), and by f (V_env) substitute into memory polynomial mathematical model, obtain fitting of a polynomial parameter b with RLS algorithm_pm。

Compared with prior art, the present invention has a following beneficial effect:

Being confirmed by substantial amounts of Computer Simulation and actual experiment, the present invention is by based on modified model memory polynomial mould The envelope-tracking amplifier digital pre-distortion method of type, it is possible to preferably improve the linearity of envelope-tracking amplifier.This number Word pre-distortion method in the application of envelope-tracking amplifier can the effective promotion signal linearity, thus reach to improve can dose-effect The purpose of rate.

Accompanying drawing explanation

By the detailed description non-limiting example made with reference to the following drawings of reading, the further feature of the present invention, Purpose and advantage will become more apparent upon:

Fig. 1 is envelope-tracking amplifier digital pre-distortion system structure chart based on modified model memory polynomial model；

Fig. 2 is modified model memory polynomial modular concept schematic diagram；

Fig. 3 is the output signal power spectrum density result schematic diagram using modified model predistorter.

Detailed description of the invention

Below in conjunction with specific embodiment, the present invention is described in detail.Following example will assist in the technology of this area Personnel are further appreciated by the present invention, but limit the present invention the most in any form.It should be pointed out that, the ordinary skill to this area For personnel, without departing from the inventive concept of the premise, it is also possible to make some changes and improvements.These broadly fall into the present invention Protection domain.

The envelope-tracking amplifier digital pre-distortion method based on improved model provided according to the present invention, including walking as follows Rapid:

Step A: calculate the corresponding envelope signal V of base-band input signal x (n) of envelope-tracking amplifier_envAnd base band is defeated Enter the input as predistorter of signal and adjusted envelope signal；

Step B: improved for the conventional memory multinomial model being applicable to fixed bias power amplifier, utilize defeated The envelope signal V entered_envDynamically control memory polynomial model parameter, export pre-distorted signals；

Step C: utilize brief introduction learning method self adaptation to obtain pre-distortion parameters, sends signal after predistortion into envelope-tracking Amplifier, to improve the linearity of envelope-tracking amplifier.

Described step A calculates the corresponding envelope signal V of baseband signal x (n)_env, and envelope signal is acted upon rear conduct Pre-distorter input signal, specific as follows:

Step A1: base-band input signal x (n) of envelope-tracking amplifier is expressed with plural form, and in terms of this Calculate input power, order:

P_{in_W}=0.5*real (V_in*conj(V_in/R_in))

Power signal is converted to dBm unit:

P_{in_dBm}=10*log (P_{in_W})+30

Step A2: the power amplifier bias voltage scope controlled according to input signal power and envelop modulator is in addition Correspondence, obtains input signal V needed for predistorter_env:

$V_{env}=\left\{\begin{array}{cc}{P}_{\min },& P_{in\_dBm}\&le;P_{\min }\\ P_{in\_dBm},& P_{\min }<P_{in\_dBm}<P_{\max }\\ P_{\max },& P_{in\_dBm}\&GreaterEqual;P_{\max }\end{array}\right.$

Owing to the bias voltage of radio-frequency (RF) power amplification can not be 0, the maximum electricity that envelop modulator can be output by can not be exceeded Pressure value, so the adjustable bias voltage of envelope-tracking amplifier has fixed range, P here_minCorresponding to minimum bias voltage in order Input signal power, P_maxFor maximum bias voltage correspondence input signal power.

Described step B, is improved conventional memory multinomial model, specific as follows:

Step B1: traditional memory polynomial model is applicable to fixed bias voltage power amplifier, for envelope-tracking amplifier The feature of variable bias voltage, can not express power amplifier characteristic very well, and it is mathematically represented as:

$y\left(n\right)=\underset{p=1}{\overset{P}{\&Sigma;}}\underset{m=0}{\overset{M}{\&Sigma;}}{c}_{pm}x(n-m)|x(n-m){|}^{p-1}$

Step B2: be the function shape with input signal envelope as variable by polynomial for above-mentioned conventional memory parameter improvement Formula, dynamically changes memory polynomial model parameter, uses fitting of a polynomial here, and it is mathematically represented as:

$c_{pm}=f\left(V_{env}\right)=\underset{n=0}{\overset{N}{\&Sigma;}}{b}_{pm}{V}_{env}^n$

Described step C, with improve memory polynomial model as core, with indirect learning structural adaptation predistortion Device, specific as follows:

Step C1: build digital predistorter for core, by baseband signal x with modified model memory polynomial mathematical model N () carries out after pre-distortion, and the predistortion that will obtain that signal z (n) is as the input signal of ETPA, it is mathematically represented as:

$z\left(n\right)=\underset{p=1}{\overset{P}{\&Sigma;}}\underset{m=0}{\overset{M}{\&Sigma;}}f\left(V_{env}\right)x(n-m)|x(n-m){|}^{p-1}$

Step C2: process with indirect learning structure adaptive, with multinomial model matching memory polynomial parameter expression f (V_env), and substituted into memory polynomial mathematical model, obtain fitting of a polynomial parameter b with RLS algorithm_pm。

Fig. 1 illustrates envelope-tracking amplifier digital pre-distortion system structure based on modified model memory polynomial model, Envelope-tracking amplifier digital pre-distortion method based on modified model memory polynomial model of the present invention mainly comprises three Individual aspect: first, obtains envelope signal another input parameter as predistorter of input signal, many in order to control memory Item formula model parameter；Secondly, predistortion based on modified model memory polynomial model is built according to the envelope signal size of input Device；Finally, indirect learning structure RLS algorithm self adaptation is utilized to obtain predistorter parameter and realize the line of envelope-tracking amplifier Property degree optimize.

It is illustrated in figure 2 the explanation of modified model memory polynomial model.Modified model memory polynomial model for envelope with Track amplifier feature is using input signal envelope through processing another input signal as mathematical model, many in conjunction with conventional memory Item formula model, overcomes the conventional memory multinomial model pre-distortion method for fixed bias voltage power amplifier not to be suitable for The shortcoming dynamically changing the envelope-tracking amplifier of power amplifier offset voltage.

In experimentation, utilize and illustrate that the envelope-tracking shown in the present invention amplifies based on ADS artificial circuit case Device digital pre-distortion method, shown in Fig. 3 be do not use predistorter, use conventional memory multinomial model predistorter, Use the output signal power spectrum density figure in the case of modified model memory polynomial predistorter three kinds.There is provided according in the present invention Method, in experiment, input signal is 10MHz bandwidth LTE signal, the different predistorter improvement to the linearity of output signal Judging with NMSE Yu ACPR, result is as shown in table 1.As it can be seen from table 1 under two kinds of different pre-distortion, based on changing The pre-distortion system entering type memory polynomial model is best to the nonlinear improvement of output signal, is embodied in device output signal Sideband power leakage has the improvement of 5-6dB than (ACPR) contrast conventional memory polynomial predistorter.

Table 1

More specifically, in a preference of the present invention, the present invention is achieved by the following technical solutions, this Bright comprise the following steps:

The first step: by the corresponding envelope signal V of base band LTE input signal x (n)_envInput as predistorter；

Second step: build modified model memory polynomial model in predistorter；

3rd step: utilize indirect learning structure RLS algorithm self adaptation obtain predistorter parameter and realize envelope-tracking and put The linearity optimization of big device.

Above the specific embodiment of the present invention is described.It is to be appreciated that the invention is not limited in above-mentioned Particular implementation, those skilled in the art can make a variety of changes within the scope of the claims or revise, this not shadow Ring the flesh and blood of the present invention.In the case of not conflicting, the feature in embodiments herein and embodiment can any phase Combination mutually.

Claims (4)

1. an envelope-tracking amplifier digital pre-distortion method based on improved model, it is characterised in that comprise the steps:

Step A: calculate the corresponding envelope signal V of base-band input signal x (n) of envelope-tracking amplifier_envAnd by base band input letter Number with adjusted envelope signal as the input of predistorter；

Step B: utilize the envelope signal V of input_envDynamically control memory polynomial model parameter, export pre-distorted signals；

Step C: utilize indirect learning method self adaptation to obtain predistorter parameter, sends signal after predistortion into envelope-tracking and puts Big device, it is achieved the improvement of envelope-tracking Amplifier linearity.

Envelope-tracking amplifier digital pre-distortion method based on improved model the most according to claim 1, its feature exists In, described step A includes:

Step A1: base-band input signal x (n) of envelope-tracking amplifier is indicated with plural form, and calculates input work Rate, order:

P_{in_W}=0.5*real (V_in*conj(V_in/R_in))

Power signal is converted to dBm unit:

P_{in_dBm}=10*log (P_{in_W})+30

In formula: P_{in_W}Represent base-band input signal power, V_inRepresent base-band input signal magnitude of voltage, R_inRepresent power amplifier input link Resistance, real (.) expression takes complex signal real part computing, and conj (.) represents complex signal transposition computing, P_{in_dBm}Represent base band input Signal power, unit: dBm；

Step A2: adjust according to the power amplifier bias voltage scope that input signal power and envelop modulator are controlled Whole, obtain input signal V needed for predistorter_env:

$V_{env}=\left\{\begin{array}{cc}{P}_{\min },& P_{in\_dBm}\&le;P_{\min }\\ P_{in\_dBm},& P_{\min }<P_{in\_dBm}<P_{\max }\\ P_{\max },& P_{in\_dBm}\&GreaterEqual;P_{\max }\end{array}\right.$

In formula: P_minRepresent the input signal power corresponding to minimum bias voltage in order, P_maxRepresent the input of maximum bias voltage correspondence Signal power.

Envelope-tracking amplifier digital pre-distortion method based on improved model the most according to claim 1, its feature exists In, described step B includes:

Step B1: the mathematical formulae providing traditional memory polynomial model is as follows:

$y\left(n\right)=\underset{p=1}{\overset{P}{\&Sigma;}}\underset{m=0}{\overset{M}{\&Sigma;}}{c}_{pm}x(n-m)|x(n-m){|}^{p-1}$

Step B2: step B1 is improved to the functional form with input signal envelope as variable, the most dynamically changes memory polynomial Model parameter, concrete mathematical formulae is as follows:

$c_{pm}=f\left(V_{env}\right)=\underset{n=0}{\overset{N}{\&Sigma;}}{b}_{pm}{V}_{env}^n$

In formula: y (n) represents power amplifier output signal, c_pmRepresenting memory polynomial model parameter, n represents the n-th position digital signal, m table Showing current memory depth, p represents current polynomial order, and x (n-m) represents power amplifier input signal, maximum polynomial order P value Scope is P >=1, and the span of maximal memory degree of depth M is M >=1；b_pmRepresent that input signal envelope calculates memory polynomial model The polynomial module shape parameter that parameter uses, N represents this function maximum order.

Envelope-tracking amplifier digital pre-distortion method based on improved model the most according to claim 1, its feature exists In, described step C includes:

Step C1: build digital predistorter with modified model memory polynomial mathematical model for core, by base-band input signal x N () carries out after pre-distortion, and the predistortion that will obtain that signal z (n) is as the input signal of envelope-tracking amplifier, specifically Mathematical expression is as follows:

$z\left(n\right)=\underset{p=1}{\overset{P}{\&Sigma;}}\underset{m=0}{\overset{M}{\&Sigma;}}f\left(V_{env}\right)x(n-m)|x(n-m){|}^{p-1}$

Step C2: process with indirect learning structure adaptive, with multinomial model matching memory polynomial parameter expression f (V_env), and by f (V_env) substitute into memory polynomial mathematical model, obtain fitting of a polynomial parameter b with RLS algorithm_pm。