CN102231620A - Power amplifier linearization method and device based on baseband digital predistortion technology - Google Patents
Power amplifier linearization method and device based on baseband digital predistortion technology Download PDFInfo
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Abstract
The invention discloses a power amplifier linearization method based on a baseband digital predistortion technology, comprising the following steps of: calculating an instantaneous amplitude Ai and an instantaneous phase theta i of an input baseband signal; respectively searching out a pre-distorted signal amplitude Bi and a pre-distorted phase offset phi i by regarding the instantaneous amplitude Ai as an indexed address of a predistortion lookup table; calculating a pre-distorted signal and then outputting the pre-distorted signal for up-conversion treatment and analogue-to-digital conversion; and finally sending the signal to a power amplifier. During the predistortion, an output signal of the power amplifier is obtained and converted into a baseband feedback signal via a feedback path; and the predistortion lookup table is self-adaptively updated by using the baseband feedback signal and a desired signal. The invention also discloses a predistortion lookup table initialization method matched with the linearization method disclosed by the invention and a linearization device based on the linearization method. The method disclosed in the invention directly adopts signal amplitude as the indexed address of a predistortion lookup table to obtain predistortion signal simply, which not only reduces the treatment relay of the system and the system load, but also reduces the device complexity and the control complexity of the system.
Description
Technical field
The present invention relates to signal of communication and handle, relate in particular to a kind of linearization technique and device in the communication equipment for power amplifier (PA, Power Amplifier).
Background technology
In Modern Communication System, for effectively utilizing the radio spectrum bandwidth and guaranteeing the lower error rate, adopt linearity modulation technique more, as QAM, QPSK, OQPSK and π/4DQPSK etc.Yet, adopt the envelope of the signal of these linearity modulation techniques to change, and the envelope that changes is for power amplifier, especially high power amplifier (HPA, High Power Amplifier) is non-linear very sensitive, can cause nonlinear distortion.Nonlinear distortion can cause two kinds of serious results: the one, and the distortion of receiver signal; Another kind is an out-of-band power.The distortion of received signal will cause the decline of systematic function, not reach the purpose of signal transmission; Out-of-band power and intermodulation component will produce the neighboring trace of transmitter carrier frequency and disturb, and influence other user's normal transmission signal.
The transmitter intermediate power amplifier is carried out linearisation five kinds of common methods is arranged: feed-forward technique, negative-feedback technology, envelope eliminate and restoration methods (EER), based on Linear magnifying technology in high (LINC), the pre-distortion technology of nonlinear device.
In these technology, pre-distortion technology is used as one of compensated amplifier nonlinear distortion best techniques and has obtained extensively adopting, and this draws from bandwidth, linearity raising index, third order intermodulation raising index, efficient, the lateral comparison of complexity Several Factors.Pre-distortion technology is exactly to modulate nonlinear block of insertion between later input signal and the main power amplifier level, this nonlinear block accurately produces the opposite distortion product of distortion that produces with power amplifier, transmission feature after making both make up presents the linearisation characteristic, thereby offsets the nonlinear distortion of power amplifier.If the variation that this predistortion module of design can the follower amplifier nonlinear characteristic, the decline of this method systematic function of just can real-Time Compensation drawing by factors such as temperature, supply voltage, pipe wear out so.
A kind of common implementation method of pre-distortion technology is based on look-up table (LUT, Look-Up Table) method, in advance pre-distortion parameters is stored among the LUT, the power that utilizes input signal is as index address, index suitable pre-distortion parameters from LUT, again input signal is carried out pre-distortion.
In above-mentioned pre-distortion technology, because the implementation complexity of pre-distortion technology and the size of LUT and the highway width of signal variable have direct relation.In the method for traditional generation X and Y index, adopted signal power as measuring means, with utilize signal amplitude and compare as the tolerance means, signal power is the square value of signal amplitude, adopt signal power many greatly as the metric signal bus width that metric needs more than the employing signal amplitude as metric, this has directly influenced the implementation complexity of system.
In addition, the size of the performance of pre-distortion system and predistortion LUT exists direct relation.Theoretically, LUT is big more, and the resolution of the pre-distortion parameters of LUT storage inside is also just high more, just can reflect the variations in detail of input signal more, thereby make the effect of predistortion good more, and the system linearity degree is high more; Otherwise the performance of system is just poor more.But the size of LUT can not be infinitely great; Must system be under the energy perhaps, just require under the certain situation of LUT reflected signal precision, because the span of power measurement value is much larger than the span of amplitude metric, so the complexity that power method requires will be higher requiring.
According to above-mentioned analysis, traditional pre-distortion technology has poor-performing, the higher shortcoming of complexity.Especially when hardware is realized, for example adopt DSP (Digital Signal Processor, digital signal processor) or FPGA (Field Programmable Gate Array, field programmable gate array) when realizing, the span of signal also will directly influence the complexity of system.
Summary of the invention
The technical problem to be solved in the present invention is to provide a kind of pre-distortion method and device, can reduce operand, the raising accuracy of predistortion process, and the complexity that the reduction system realizes can be eliminated power amplification distortion fast and effectively.
The technical scheme that realizes the object of the invention is as follows:
A kind of power amplifier linearization method comprises the steps:
A, calculating obtain I, the instantaneous amplitude A of Q format base band signal of input pre-distortion unit
iWith instantaneous phase θ
i, with the instantaneous amplitude A of baseband signal
iIndex address as the predistortion look-up table;
B, from the amplitude look-up table, find the instantaneous amplitude B of signal after the pre-distortion according to index address again
i, from the phase deviation look-up table, read phase deviation φ
i
C, with phase deviation φ
iInstantaneous phase θ with the input baseband signal
iAddition obtains the instantaneous phase of signal after the predistortion
Promptly
Again with signal after the predistortion that obtains
Be converted to the signal output of complex field I, Q form, carry out upconversion process and digital-to-analogue conversion then, export the power amplifier input at last to.
D, when carrying out pre-distortion, obtain the output signal of power amplifier and convert baseband feedback signal to by feedback path, utilize this signal the predistortion look-up table to be carried out adaptive updates with corresponding base-band input signal through delay process.
Described method further comprises: start at first in system, begin real Business Processing before, utilize two-tone signal to catch the nonlinear characteristic of power amplifier as training signal, utilize initialization algorithm to come initialization predistortion look-up table.Before initialization, the default value in the predistortion look-up table all think 1,1 ... 1}.
In described method, described predistortion look-up table comprises: amplitude look-up table and phase deviation look-up table, be 1 * N dimension look-up table, and all adopt the instantaneous amplitude A of input baseband signal
iAs index address.
Further, in described method, the concrete steps that obtain baseband signal instantaneous amplitude and instantaneous phase in the described steps A are:
Instantaneous amplitude A
i: suppose that current input I, Q form baseband signal are I
iAnd Q
i, at first two paths of signals earlier respectively square again summation obtain I
i 2+ Q
i 2, then with I
i 2+ Q
i 2Integer part x
iWith fractional part y
iSeparately, handle respectively.Integer part is at first carried out difference processing
Multiply each other with fractional part then and obtain
At last will
Extraction of square root with integer part
Addition obtain input signal instantaneous amplitude
This computational process obtains in fact
But Billy uses
The amplitude information that obtains is accurately a lot, because the amplitude of signal is the index address as the predistortion look-up table, amplitude information is accurate more, and the effect of predistortion is just good more, and the performance of system is just good more.
Instantaneous phase θ
i: the instantaneous amplitude A that obtains signal
iAfter, in conjunction with I
iAnd Q
i, utilize arctan function to draw instantaneous phase θ
i
Owing to direct relation is arranged based on the implementation complexity of the pre-distortion technology of look-up table and the size of look-up table and the highway width of signal variable.Base band predistortion processing method based on look-up table of the present invention, the instantaneous amplitude that adopts signal is directly as the index value of look-up table, needed signal bus width is compared and is adopted signal power as index in traditional non-linear predistortion processing method, and implementation complexity obviously reduces.On the other hand, under certain systematic function, just require under the certain situation of LUT reflected signal resolution, because the span of signal power index value is much larger than the span of amplitude index value, therefore adopt signal amplitude to carry out pre-distortion, then desired complexity will be lower.
The invention also discloses a kind of power amplifier linearization device, comprising: pre-distortion unit, up-conversion unit and feedback receiving element based on base band digital predistortion technology; Pre-distortion unit is used for that the input baseband digital signal is carried out pre-distortion and makes it have the characteristic opposite with the power amplifier nonlinear distortion characteristics; Utilize the baseband feedback signal and the desired signal of the output of feedback receiving element that the predistortion look-up table is carried out adaptive updates simultaneously; The up-conversion unit is used for the pre-distorted signals of pre-distortion unit output is up-converted to radiofrequency signal, as the input signal of power amplifier; The feedback receiving element is used to obtain the output signal of power amplifier and converts baseband feedback signal to.
Further, pre-distortion unit adopts digital signal processor as its core processor, be used for receiving the input baseband digital signal, on the one hand, calculate the instantaneous amplitude that obtains the input baseband signal, as the index address of predistortion look-up table, utilize look-up table that the amplitude and the phase place of input baseband signal are carried out pre-distortion; In addition, baseband signal is stored as desired signal, and utilize baseband feedback signal and its corresponding desired signal adaptive updates predistortion look-up table.
Further, the predistortion look-up table stores is in lookup table memories, and lookup table memories is except being used to store the predistortion look-up table, and also storage and other data look-up table make things convenient for the digital signal processor real-time calling.
Description of drawings
Fig. 1 is the schematic flow sheet of power amplifier linearization method in the embodiment of the invention;
Fig. 2 is the system principle diagram that realizes power amplifier linearization method in the embodiment of the invention;
Embodiment
Below in conjunction with accompanying drawing and example technical scheme of the present invention is described in detail.
The present invention proposes a kind of power amplifier linearization method based on base band digital predistortion, this method is a kind of adaptive power amplifier linearization method.Main innovate point is to have proposed in this method a kind of simple pre-distortion method, it is simple at first to generate the look-up table index address, adopt signal power different with other as the tolerance means, the present invention directly adopts the index address of the amplitude of input signal as the predistortion look-up table, secondly, amplitude and the phase deviation that directly can from look-up table, find pre-distorted signals by index address, and just can obtain pre-distorted signals through simple process.It is convenient that this processing method is calculated simple operations, simplified the pre-distortion process effectively, not only reduced the processing delay and the system loading of system, also reduced the equipment complexity and the control complexity of system.
As shown in Figure 1, provided the schematic flow sheet of the power amplifier linearization method among the present invention, comprised the steps:
Step 101 is calculated the I, the instantaneous amplitude A of Q format base band signal that obtain the input pre-distortion unit
iWith instantaneous phase θ
i, with the instantaneous amplitude A of baseband signal
iIndex address as the predistortion look-up table;
Step 102 reads the instantaneous amplitude B of signal after the predistortion again from the amplitude look-up table according to index address
i, from the phase deviation look-up table, read phase deviation φ
i
Step 103 is with phase deviation φ
iInstantaneous phase θ with the input baseband signal
iAddition obtains the instantaneous phase of signal after the predistortion
Promptly
Again with signal after the predistortion that obtains
Be converted to the signal output of complex field I, Q form, carry out upconversion process and digital-to-analogue conversion then, export the power amplifier input at last to.
Step 104 when carrying out pre-distortion, is obtained the output signal of power amplifier and is converted baseband feedback signal to by feedback path, utilizes this signal with the corresponding base-band input signal through delay process the predistortion look-up table to be carried out adaptive updates
As shown in Figure 2, the system principle diagram that realizes the power amplifier linearization method in the embodiment of the invention has been described.This system mainly comprises three big units: pre-distortion unit, up-conversion unit and feedback receiving element etc.The system works flow process is as follows:
Forward path: pre-distortion unit is carried out pre-distortion to the baseband digital signal of importing this unit, obtain pre-distorted signals with power amplifier nonlinear distortion opposite characteristic, this signal is again through the up-conversion cell processing, after up-converting to radiofrequency signal and converting analog signal to, the ingoing power amplifier carries out signal and amplifies, and by antenna signal is launched at last again.
Feedback path: when carrying out pre-distortion, system also will carry out the adaptive updates adjustment to the predistortion look-up table, and it is consistent with the distorted characteristic of power amplifier that predistortion look-up table parameter is remained.Carrying out look-up table upgrades when adjusting, the feedback receiving element obtains the output signal of power amplifier by coupler from the transmitting antenna end, after carrying out analog-to-digital conversion and Digital Down Convert and handling, convert baseband feedback signal at last to and send to the preceding base-band input signal of pre-distortion unit and corresponding pre-distortion the predistortion look-up table is carried out adaptive updates through delay process.
The invention also discloses the initialized method of a kind of predistortion look-up table, the predistortion look-up table that this method makes up is divided into amplitude look-up table and phase deviation look-up table, is 1 * N dimension look-up table, all adopts the instantaneous amplitude A of input baseband signal
iAs index address.The amplitude look-up table has been represented pre-distortion unit input baseband signal amplitude A
iWith output pre-distorted signals amplitude B
iMapping relations, the phase deviation look-up table has been represented predistorter input baseband signal amplitude A
iWith phase deviation φ
iMapping relations.When system started at first, the default value in the predistortion look-up table all was { 1,1,1} before the real Business Processing of beginning, at first will carry out initialization process to the predistortion look-up table, this builds table method and utilizes two-tone signal to be training signal, and it is as follows specifically to build the table process prescription:
The two-tone signal that a, pre-distortion unit will not passed through pre-distortion sends through forward path, receives the baseband feedback signal of feedback receiving element output simultaneously;
B, baseband feedback signal is carried out FFT handle, obtain feeding back this moment the receiving element output signal spectrum, because there is nonlinear distortion in power amplifier, except that former two-tone signal, also have high-order intermodulation components such as three rank, five rank, seven rank in the feedback receiving element output signal spectrum;
C, be example, suppose that the third-order intermodulation product signal that power amplifier produces and the relative amplitude of former two-tone signal are A with the third-order intermodulation product
1, phase difference is φ
1If being superimposed with one for former two-tone signal is φ with its phase difference
2, relative amplitude also is A
1The third-order intermodulation product signal, this signal is sent through forward path, receive the baseband feedback signal of feedback receiving element output simultaneously, baseband feedback signal is carried out FFT to be handled, obtain power amplifier output signal amplitude-frequency characteristic this moment, the third order distortion intermodulation component of power amplifier output this moment is that its amplitude is because of the stack of third-order intermodulation product in the former third order distortion intermodulation component of the non-linear generation of power amplifier and the input signal:
In like manner, be φ if be superimposed with one for former two-tone signal with its phase difference
3, relative amplitude also is A
1The third-order intermodulation product signal, the third-order intermodulation product amplitude of analog channel output this moment is
Because φ
2And φ
3To know, can obtain φ
1
D, each rank distortion intermodulation component of obtaining according to step c and the phase difference and the relative amplitude of former two-tone signal, structure is identical with each rank intermodulation component frequency, amplitude, the signal that phase place is opposite, with former two-tone signal stack, obtain signal after the predistortion of former two-tone signal, according to signal configuration LUT after original signal and the predistortion, for example: the Ae that is that supposes to work as original input signal
J θThe time, signal is after the predistortion
Then when input signal amplitude was A, predistortion amplitude look-up table was B in the content of the pairing address location of amplitude A, and the phase deviation look-up table in the content of the pairing address location of amplitude A is
By the time the predistortion look-up table is set up, and just can begin normal Business Processing.
Further each functional unit in the system shown in Figure 2 is elaborated respectively below.
(1) pre-distortion unit
As shown in Figure 2, pre-distortion unit mainly comprises digital signal processor and lookup table memories.Wherein digital signal processor is used for receiving the input baseband signal, on the one hand, the input baseband signal is carried out pre-distortion; On the other hand, baseband signal is stored as desired signal, and utilize baseband feedback signal and corresponding desired signal adaptive updates predistortion look-up table.Lookup table memories is used to store predistortion look-up table and other data look-up table, makes things convenient for the digital signal processor real-time calling.
The signal that pre-distortion unit receives is I, Q form baseband signal, and the pre-distortion method based on look-up table that adopts is that the amplitude and the phase place of input baseband signal are carried out predistortion correction respectively, therefore I, Q form Data Format Transform need be become polar form, obtain the amplitude and the phase information of input signal, this process is finished as A201 data conversion module as shown in Figure 2, obtains input signal instantaneous amplitude A
iWith instantaneous phase θ
iDetailed process as follows:
Instantaneous amplitude A
i: suppose that current input I, Q form baseband signal are I
iAnd Q
i, at first two paths of signals earlier respectively square again summation obtain I
i 2+ Q
i 2, then with I
i 2+ Q
i 2Integer part x
iWith fractional part y
iSeparately, handle respectively.Integer part is at first carried out difference processing
Multiply each other with fractional part then and obtain
At last will
Extraction of square root with integer part
Addition obtain input signal instantaneous amplitude
This computational process obtains in fact
But Billy uses
The amplitude information that obtains is accurately a lot, because the amplitude of signal is the index address as the predistortion look-up table, amplitude information is accurate more, and the effect of predistortion is just good more, and the performance of system is just good more.
Instantaneous phase θ
i: the instantaneous amplitude A that obtains signal
iAfter, in conjunction with I
iAnd Q
i, utilize arctan function to draw instantaneous phase θ
i.
Obtain the instantaneous amplitude A of input signal
iWith instantaneous phase θ
iAfter, next step will carry out pre-distortion, and concrete steps are as follows: with the instantaneous amplitude A of input signal
iAs the index address of predistortion look-up table, from the amplitude look-up table, read the instantaneous amplitude B of signal after the pre-distortion according to index address
i, from the phase deviation look-up table, read phase deviation φ
iWith phase deviation φ
iInstantaneous phase θ with the input baseband signal
iAddition obtains the instantaneous phase of signal after the pre-distortion
So just finished pre-distortion.
Before pre-distortion unit sends to the up-conversion unit with pre-distorted signals, pass through A202 data conversion module shown in Figure 2, convert the pre-distorted signals of polar form the pre-distorted signals of I, Q form to, promptly
When carrying out pre-distortion, system also will carry out the adaptive updates adjustment to the predistortion look-up table, and it is consistent with the distorted characteristic of power amplifier that predistortion look-up table parameter is remained.The self adaptation adjustment process of predistortion look-up table is to obtain the output signal of power amplifier and convert baseband feedback signal to by feedback network, utilizes this signal with corresponding desired signal the predistortion look-up table to be carried out adaptive updates again.Concrete renewal process is as follows:
(b1) the calculation expectation signal lag time (A203 time-delay is as shown in Figure 2 estimated)
The base band desired signal of the signal v (i) of input baseband signal s (i) after time-delay τ sampling time as adaptive updates predistortion look-up table, delay time τ=τ
1+ τ
2+ τ
3, τ
1Be the processing time of pre-distortion unit to the input baseband signal, τ
2Be comprise power amplifier analog channel to predistortion after processing time of baseband signal, τ
3For feedback path to the Signal Processing time, need accurately estimate τ.The employing cycle is that (the Gold sequence PN (i) of T＞τ) is test signal to T, utilizes the autocorrelation performance of Gold sequence and high-energy accumulative total characteristic that τ is carried out initialization and obtains τ
IntPN (i) is sent into follow-up forward path after pre-distortion, receiving feedback baseband signal u (i) and PN (i) cross-correlation of delaying time, τ this moment
IntDetermine that by formula (1) K is an integer.
The radio frequency part of system is an analog channel, and analog channel has slow time variation, and its slow time variation is embodied in passband amplitude-frequency characteristic, the nonlinear characteristic of whole analog channel, the variation of delay time, at first should be according to τ
IntVariation to delay time τ estimates that algorithm is as follows:
τ in the following formula
0Be the maximum possible variable quantity of delay time, τ
NewBe the current delay time of determining, Δ φ is the fixed skew of analog channel and feedback path, then base band desired signal v (i)=s (i-τ
New), baseband feedback signal u (i)=u (i) e
-j Δ φ, utilize v (i) and u (i) that the predistortion look-up table is carried out adaptive updates,
(b2) the predistortion look-up table upgrades by desired signal v (i) according to signal v after the current predistortion look-up table pre-distortion
d(i) and baseband feedback signal u (i) according to signal u after the current predistortion look-up table pre-distortion
d(i) finish jointly, because the predistortion look-up table is equivalent to the inversion model of power amplifier nonlinear characteristic, if the inversion model of the nonlinear characteristic of current predistortion look-up table and current power amplifier fits like a glove, v then
d(i)=u
dOtherwise tackle current predistortion look-up table and upgrade (i):
f
a(||) and f
φ(||) is respectively the AM-AM characteristic and the AM-PM characteristic of pre-distortion unit, and be opposite with the nonlinear characteristic of power amplifier.
Because power amplifier nonlinear amplitude characteristic and phase characteristic are separate, its range error and phase error can be expressed as respectively:
e
gain(i)＝|v
d(i)|-f
a(|u(i)|)|u(i)|
e
phase(i)＝∠v
d(i)-∠u(i)-f
φ(|u(i)|)
According to steepest descent method, can obtain f
a(| u (i) |) and f
φThe iterative formula of (| u (i) |) is:
Wherein, μ
GainAnd μ
PhaseBe iteration step length, ▽
Gain(i) and ▽
Phase(i) be slope vector, can be expressed as:
Utilize above algorithm to finish real-time update to the predistortion look-up table.
(2) up-conversion unit
As shown in Figure 2, the up-conversion unit mainly comprises digital up converter and digital to analog converter.Wherein digital up converter is used for the predistortion baseband signal of pre-distortion unit output is up-converted to radiofrequency signal; Digital to analog converter is used for the digital radio signal of digital up converter output is converted to analog radio-frequency signal;
(3) feedback receiving element
As shown in Figure 2, the feedback receiving element mainly comprises analog to digital converter and digital down converter.Wherein analog to digital converter is used for the radio frequency analog signal of power amplifier output is converted to rf digital signal; Digital down converter is used for rf digital signal is down-converted to baseband signal, and this signal is carried out low-pass filtering, and the filtering out of band signal extracts baseband feedback signal.
Claims (17)
1. power amplifier linearization method based on base band digital predistortion technology, this method comprises the steps:
A, calculating obtain I, the instantaneous amplitude A of Q format base band signal of input pre-distortion unit
iWith instantaneous phase θ
i, with the instantaneous amplitude A of baseband signal
iIndex address as the predistortion look-up table;
B, from the amplitude look-up table, read the instantaneous amplitude B of signal after the predistortion according to index address again
i, from the phase deviation look-up table, read phase deviation φ
i
C, with phase deviation φ
iInstantaneous phase θ with the input baseband signal
iAddition obtains the instantaneous phase of signal after the predistortion
Promptly
Again with signal after the predistortion that obtains
Be converted to the signal output of complex field I, Q form, carry out upconversion process and digital-to-analogue conversion then, export the power amplifier input at last to.
2. the described power amplifier linearization method of claim 1 also comprises:
D, when carrying out pre-distortion, obtain the output signal of power amplifier and convert baseband feedback signal to by feedback path, utilize this signal the predistortion look-up table to be carried out adaptive updates with corresponding base-band input signal through delay process.
3. power amplifier linearization method as claimed in claim 1 is characterized in that, according to I, the Q format base band signal of current input pre-distortion unit, it is carried out data transaction in the described steps A, obtains importing the instantaneous phase θ of baseband signal
iIndex address A with the predistortion look-up table
i
4. power amplifier linearization method as claimed in claim 1, it is characterized in that, described pre-distortion method based on look-up table is that signal amplitude and phase place are proofreaied and correct respectively, therefore comprise two kinds of predistortion look-up tables: amplitude look-up table and phase deviation look-up table, be 1 * N dimension look-up table, all adopt input signal amplitude as index address.
5. method as claimed in claim 4, wherein the amplitude look-up table has been represented pre-distortion unit input baseband signal amplitude A
iWith output pre-distorted signals amplitude B
iMapping relations, the amplitude look-up table has been listed the combination of all input baseband signal amplitudes and corresponding output pre-distorted signals amplitude.
6. method as claimed in claim 4, wherein the phase deviation look-up table has been represented pre-distortion unit input baseband signal amplitude A
iWith phase deviation φ
iMapping relations, the phase deviation look-up table has been listed the combination of all input baseband signal amplitudes and corresponding phase deviation.
7. method as claimed in claim 6, wherein phase deviation φ
iRepresented pre-distortion unit output pre-distorted signals phase place
With input baseband signal phase theta
iDifference, promptly
8. method as claimed in claim 4, wherein look-up table is 1 * N dimension, and N has represented the resolution of predistortion look-up table, and N is big more, and the precision of predistortion look-up table is high more, and the pre-distorted signals of finding is accurate more, and the linearisation degree of power amplifier is good more.
9. predistortion look-up table initial method, this method comprises the steps:
The two-tone signal that a, pre-distortion unit will not passed through pre-distortion sends through forward path, receives the baseband feedback signal of feedback receiving element output simultaneously;
B, baseband feedback signal is carried out FFT handle, obtain feeding back this moment the receiving element output signal spectrum, because there is nonlinear distortion in power amplifier, except that former two-tone signal, also have high-order intermodulation components such as three rank, five rank, seven rank in the feedback receiving element output signal spectrum;
C, be example, suppose that the third-order intermodulation product signal that power amplifier produces and the relative amplitude of former two-tone signal are A with the third-order intermodulation product
1, phase difference is φ
1If being superimposed with one for former two-tone signal is φ with its phase difference
2, relative amplitude also is A
1The third-order intermodulation product signal, this signal is sent through forward path, receive the baseband feedback signal of feedback receiving element output simultaneously, baseband feedback signal is carried out FFT to be handled, obtain power amplifier output signal amplitude-frequency characteristic this moment, the third order distortion intermodulation component of power amplifier output this moment is that its amplitude is because of the stack of third-order intermodulation product in the former third order distortion intermodulation component of the non-linear generation of power amplifier and the input signal:
In like manner, be φ if be superimposed with one for former two-tone signal with its phase difference
3, relative amplitude also is A
1The third-order intermodulation product signal, the third-order intermodulation product amplitude of analog channel output this moment is
Because φ
2And φ
3To know, can obtain φ
1
D, each rank distortion intermodulation component of obtaining according to step c and the phase difference and the relative amplitude of former two-tone signal, structure is identical with each rank intermodulation component frequency, amplitude, the signal that phase place is opposite, with former two-tone signal stack, obtain signal after the predistortion of former two-tone signal, according to signal configuration LUT after original signal and the predistortion, for example: the Ae that is that supposes to work as original input signal
J θThe time, signal is after the predistortion
Then when input signal amplitude was A, predistortion amplitude look-up table was B in the content of the pairing address location of amplitude A, and the phase deviation look-up table in the content of the pairing address location of amplitude A is
10. look-up table initial method as claimed in claim 9 is characterized in that the method is to start at first in system, begin real Business Processing before, be used for initialization predistortion look-up table.Before initialization, the default value in the predistortion look-up table all think 1,1 ... 1}.
11. the power amplifier linearization device based on base band digital predistortion technology comprises pre-distortion unit, up-conversion unit and feedback receiving element.
Pre-distortion unit is used for that the input baseband digital signal is carried out pre-distortion and makes it have the characteristic opposite with the power amplifier nonlinear distortion characteristics; Utilize the baseband feedback signal and the preceding base-band input signal of corresponding pre-distortion that receive simultaneously, adopt adaptive algorithm that the predistortion look-up table is upgraded through delay process;
The up-conversion unit is used for the pre-distorted signals of pre-distortion unit output is up-converted to radiofrequency signal and is converted to analog signal, as the input signal of power amplifier;
The feedback receiving element is used to obtain the output signal of power amplifier and converts baseband feedback signal to.
12. device according to claim 11 is characterized in that, described pre-distortion unit comprises:
Digital signal processor is used for receiving the input baseband digital signal, on the one hand, calculates the instantaneous amplitude that obtains input signal, as the index address of predistortion look-up table, utilizes look-up table that the amplitude and the phase place of input baseband signal are carried out pre-distortion; On the other hand, baseband signal is stored as desired signal, and utilize baseband feedback signal and corresponding desired signal adaptive updates predistortion look-up table.
Lookup table memories is used to store predistortion look-up table and other data look-up table, makes things convenient for the digital signal processor real-time calling.
13. device according to claim 11 is characterized in that, described up-conversion unit comprises:
Digital up converter, the predistortion baseband signal Digital Up Convert that is used for pre-distortion unit output is a radiofrequency signal;
Digital to analog converter is used for the output signal of digital up converter is converted to analog signal.
14. device according to claim 11 is characterized in that, described feedback receiving element comprises:
Analog to digital converter is used for the radio frequency analog signal of power amplifier output is converted to rf digital signal;
Digital down converter is used for rf digital signal is down-converted to baseband signal, and this signal is carried out low-pass filtering, and the filtering out of band signal extracts baseband feedback signal.
15. device according to claim 12 is characterized in that, described digital signal processor job step comprises:
Initial phase:
The initialization digital signal processor reads predistortion look-up table and other data look-up table to the ram in slice of digital signal processor from lookup table memories; To the feedback path estimation of delaying time.
The circular treatment stage:
The baseband feedback signal of A01, reception input baseband digital signal and feedback path input; And store the desired signal that current baseband digital signal upgrades as follow-up look-up table;
A02, to the input baseband digital signal utilize the predistortion look-up table to carry out pre-distortion;
A03, utilize baseband feedback signal and corresponding desired signal adaptive updates predistortion look-up table.
16. step according to claim 15 is characterized in that, described steps A 02 further comprises:
Calculate the instantaneous amplitude and the instantaneous phase that obtain the current baseband signal of input;
Utilize the index address of instantaneous amplitude, baseband signal is carried out pre-distortion as the predistortion look-up table.Pre-distorted signals is sent to the up-conversion unit.
17. step according to claim 15 is characterized in that, described steps A 03 further comprises: utilize feedback baseband signal and corresponding desired signal that the predistortion look-up table is carried out adaptive updates.Utilize the predistortion look-up table after upgrading to replace old look-up table in the digital signal processor ram in slice.
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