CN102378336A - Low-intermodulation repeater and realization method thereof - Google Patents

Abstract

The invention relates to a low-intermodulation repeater and a realization method thereof. An open-loop DPD (Digital Pre-Distortion) module is added in a downlink transmission link of the repeater; the DPD module is arranged in back of a digital processing module in an FPGA (Field Programmable Gate Array); and the nonlinearity of a power amplifier is improved by using the DPD module to reduce the intermodulation. I/Q (In-phase/Quadrature) signals which are output by the digital processing module are received by the open-loop DPD module; meanwhile, a pre-distortion treatment is completed by affecting a DPD coefficient on the received I/Q signals and a treatment result is used as an input of the power amplifier. A grain regulation module is additionally arranged in the back of the open-loop DPD module and used for tracing a grain variation generated by a temperature variation of the power amplifier. The realization method provided by the invention has the advantages that: the open-loop DPD module is realized in the FPGA without changing a hardware circuit in a cheap and easily-operated manner; an open-loop mode is easily realized and the intermodulation can be improved just by a group of pre-distortion coefficients once for all; and the grain regulation module can be used for compensating the grain variation which is caused by the temperature variation of the power amplifier, therefore, the properties of the open-loop DPD are ensured to be excellent.

Description

A kind of repeater of low intermodulation and its implementation

Technical field

The invention belongs to moving communicating field, mainly is repeater and its implementation of a kind of low intermodulation.

Background technology

In the linear amplifier that constitutes by various active devices,, in amplification process, always produce various distortions because the characteristic of active device is non-linear.Intermodulation distortion is exactly wherein a kind of.

Intermodulation is meant that the two phase inter-modulation will produce many new combination frequency components when the very approaching signal input amplifier of two frequencies.If these combination frequency components just in time drop in the working band of amplifier, then can cause interference to useful signal.This interference is not to be produced by the harmonic wave of two input signals, but is caused by the phase inter-modulation of these two input signals, so be called intermodulation distortion.

The repeater is a kind of multiplying arrangement, is in the wireless communication transmissions process, to play a kind of radio transmission transferring equipment that signal strengthens.The basic function of repeater is exactly a radiofrequency signal power intensifier.In the down link of repeater,, to carrying out fabulous isolation, the signal of filtering is transmitted into after power amplifier amplifies once more treats the overlay area with logical outer signal through band pass filter by donor antenna pickoff signals from existing overlay area.But the repeater also can produce inter-modulated signal when radiofrequency signal is amplified, will produce serious the interference to communication network if inter-modulated signal is excessive, reduces the quality of communication network.The inter-modulated signal of repeater mainly is because the nonlinear characteristic of the radio-frequency power amplifier of repeater produces, and eliminate the inter-modulated signal of repeater and will improve the non-linear of repeater radio-frequency power amplifier.

Improve the power amplifier non-linear method back-off method, feed forward approach and pre-distortion method are generally arranged.The back-off method is simple, does not need any components and parts of extra increase, but can the efficient of power amplifier greatly be reduced, and works as back-off in addition to a certain degree, continues the linearity that rollback will no longer improve amplifier.Feed forward approach can realize more accurate inter-modulated signal elimination, but structure is complicated, mainly contains compositions such as main power amplifier, booster amplifier, coupler, delay unit and power divider.If will use feed forward approach, then must need to revise the radiofrequency signal link.The predistortion ratio juris is to seek the inverse function of the nonlinear characteristic function of power amplifier, and two characterisitic functions are acted on mutually, then can obtain linear characterisitic function.This function can realize that in the fpga chip of repeater cost is lower, and efficient is higher.

General, the variation of power amplifier nonlinear characteristic makes that the effect of adaptive algorithm in pre-distortion system is most important.The Adaptable System of closed loop can be followed the tracks of these variations, changes pre-distortion coefficients, makes adjustment timely.But if the power amplifier characteristic is more stable, DPD (Digital Predistortion) system just can be operated under one group of fixing coefficient so, i.e. open loop mode.Open loop DPD is a kind of like this mode of operation: its based on feedback link is accomplished in PC, and the software that application is relevant obtains one group to be improved after the good coefficient of power amplifier non-linear effect, and what open loop DPD module was just fixing is operated under this group coefficient.Thereupon, based on feedback link also removes from direct discharging station.In the application of reality, open loop DPD has only forward link, no based on feedback link.

Summary of the invention

The object of the invention will overcome the deficiency of above-mentioned technology just, and repeater and its implementation of a kind of low intermodulation are provided, and improves the method that repeater intermodulation suppresses in the moving communicating field.

The present invention solves the technical scheme that its technical problem adopts: the repeater of this low intermodulation; In the downlink link of repeater, increase open loop DPD module; This module is arranged on after the digital signal processing module among the FPGA, thereby adopts the DPD module to improve the non-linear reduction of power amplifier intermodulation.Open loop DPD module receives the i/q signal of digital signal processing module output, simultaneously the DPD coefficient acting is accomplished pre-distortion in the i/q signal that receives, and result is as the input of power amplifier.

The implementation method of the repeater of this low intermodulation of the present invention, concrete steps are following:

(1), in the downlink link of repeater, increase open loop DPD module, this module is arranged on after the digital signal processing module among the FPGA, the DPD mode of operation is an open loop mode;

(2), catch the data of transmitting chain and the data of based on feedback link, and it is kept among the RAM of FPGA through FPGA; Use the DPD adaptive algorithm and handle emission data and feedback data among the RAM, obtain the DPD coefficient;

(3), open loop DPD module receives the i/q signal of digital signal processing module output in system; Receiving software is handled the DPD coefficient (pre-distortion coefficients) that obtains simultaneously; Its internal structure is built according to MP memory multinomial; Effect is thereby that result is as the input of power amplifier with the function of DPD coefficient acting in the i/q signal completion predistortion that receives.

Though the characteristic curve of power amplifier is more stable, along with variation of temperature, the gain of power amplifier also has some variations, and these variations can influence the DPD performance.As preferably, in the downlink link of repeater, add gain regulation module, gain regulation module is arranged on after the open loop DPD module, is used for according to the power amplifier variation of temperature transmitting chain gain being adjusted, and precision is 0.1dB; This adjustment precision is higher, can follow the tracks of link gain timely and effectively and change, and makes open loop DPD keep good effect.

The processing of DPD coefficient further is the processing procedure that software and hardware combines.The function that hardware components is accomplished is: catch the data of transmitting chain and the data of based on feedback link through FPGA software, and it is kept among the RAM of FPGA.The function that software section is accomplished is: use the DPD adaptive algorithm and handle emission data and feedback data among the RAM, obtain the DPD coefficient.Because in open loop DPD, this group DPD coefficient is changeless, need it is backed up in EEPROM, in case behind the something unexpected happened, open loop DPD still can operate as normal.

The effect that the present invention is useful is: open loop DPD module realizes in FPGA, need not change hardware circuit, and cost is low, is prone to row; Open loop mode is realized simple, only needs one group of pre-distortion coefficients just can improve intermodulation, puts things right once and for all; Gain regulation module can compensate because the gain variations that the power amplifier variations in temperature causes guarantees that open loop DPD is functional.

Description of drawings

Fig. 1 is the descending theory diagram in traditional repeater (closed loop DPD);

Fig. 2 is the descending theory diagram in repeater of the present invention (open loop DPD);

Fig. 3 is the data flow block diagram that open loop DPD of the present invention relates to;

Fig. 4 is the theory diagram of gain regulation module of the present invention.

Embodiment

In order to make the object of the invention, technical scheme and advantage clearer, reach for example below in conjunction with accompanying drawing, the present invention is further elaborated.Should be appreciated that described hereinly, and be not used in qualification the present invention for example only in order to explaining the present invention.

Fig. 1 is the repeater down link block diagram of the traditional closed loop DPD pattern that works in, and DPD wherein and DPD training aids are all accomplished in FPGA.

Fig. 2 is a repeater of the present invention down link block diagram, and wherein open loop DPD module and gain regulation module are accomplished in FPGA, and open loop DPD training aids is accomplished in PC, in practical application, only keeps preceding two modules.

One, the realization of open loop DPD module

Among the present invention, the model of DPD adopts MP (Memory Polynomial, memory multinomial) model.

Memory polynomial expression formula is following:

$F\left[x\left(n\right)\right]=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\underset{q=0}{\overset{Q-1}{\mathrm{\Σ}}}{a}_{\mathrm{kq}}x(n-q){\left|x(n-q)\right|}^{k-1}---\left(1\right)$

Wherein: K is a nonlinear factor, and Q is the memory effect factor, a _KqIt is pre-distortion coefficients.

According to the memory multinomial, the form of an accepted way of doing sth (2) is write in the input and output of the open loop DPD module among Fig. 3, as follows:

$z\left(n\right)=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\underset{q=0}{\overset{Q-1}{\mathrm{\Σ}}}{a}_{\mathrm{kq}}x(n-q){\left|x(n-q)\right|}^{k-1}---\left(2\right)$

Open loop DPD module among Fig. 2 is exactly the logical resource that utilizes among the FPGA, the module of building according to formula (2).Pre-distortion coefficients a _KqObtain through the processing of open loop DPD training aids.

Two, the realization of open loop DPD training aids

The function of DPD module and power amplifier characterisitic function are contrafunctional relations.So,, the coefficient a that the relation of an accepted way of doing sth (3) obtains is write in the input and output of power amplifier according to the memory multinomial _KqIt is exactly the DPD coefficient.

$g\left(n\right)=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\underset{q=0}{\overset{Q-1}{\mathrm{\Σ}}}{a}_{\mathrm{kq}}y(n-q){\left|y(n-q)\right|}^{k-1}---\left(3\right)$

Down in the face of pre-distortion coefficients a _KqObtain and elaborate.

At first, obtain the deal with data g (n) and the y (n) of training aids.Y (n) has certain delay with respect to g (n), and can be known by formula (3), and what equation was handled is the data of synchronization.So, when catching data g (n), need add a time-delay adjusting module, make g (n) constantly identical with y (n).

The extracting of g (n) and y (n) can be grasped software and obtain through the data of FPGA software.

Secondly, find the solution a _Kq, promptly separate memory multinomial about g (n) and y (n).

The degree of depth of catching of supposing g (n) and y (n) is N, is all write this N data as memory polynomial form, suc as formula (3), wherein, and n=0,1,2,3 ..., N-1.

Make u _Kq(n)=and y (n-q) | y (n-q) | ^K-1, then following formula can be converted into

Z＝UA (4)

Wherein: Z=[z (0), z (1) ..., z (N-1)], (5)

U＝[u(0)，u(1)，…，u(N-1)]， (6)

A＝[a ₁₀，…，a _K0，a ₁₁，…a _K1，a _1，Q-1，…，a _K，Q-1] ^T， (7)

u(n)＝[u ₁₀(n)，…，u _K0(n)，u ₁₁(n)，…，u _K1(n)，…，u _K，Q-1(n)]。(8)

Find the solution formula (4) and just can obtain pre-distortion coefficients a _Kq

In Matlab, write code solving equation (4), obtain a _KqAfter, this coefficient is configured to open loop DPD module just can realizes predistortion function.

Three, the realization of gain regulation module

The change in gain of power amplifier is caused by variation of temperature.Along with the rising of temperature, the gain of power amplifier can decrease.The temperature compensation principle of taking among the present invention is: on the benchmark of temperature-compensating, and 10 ℃ of the every risings of temperature, gain compensation 0.5dB; Being divided into 5 intervals with these 10 ℃ again, whenever is an interval twice, and interval gain compensation 0.1dB of every variation so just can obtain higher compensation precision.Shown in accompanying drawing 4, behind the corresponding compensating gain of temperature selection, this yield value and input I, Q signal are multiplied each other, just can accomplish the gain compensation function.

Concrete operations are: the assumed temperature standard of compensation is T ₀℃, the power amplifier temperature surpasses this temperature and just carries out gain compensation.Fiducial temperature T ₀Units be b ₀Read the temperature T of power amplifier _PA, get [T _PA+ (10-b ₀)] units note make b ₁, b ₁As shown in the table with the relation of interval selection signal sel:

b 1	sel
		0，1	0

2，3	1
		4，5	2
6，7	3
		8，9	4

The computing formula of gain compensation is suc as formula shown in (9),

10·log(x ²·(I ²+Q ²))-10·log(I ²+Q ²)＝y (9)

Wherein: x representes the ratio of i/q signal value before gain adjustment back and adjustment;

Y representes each interval corresponding yield value that should increase, and unit is dB.

According to following formula (9) and different interval corresponding y, just can obtain different interval x.In FPGA, I, Q signal multiply by this x, just can reach the effect of gain compensation.

The design of satisfying said process can improve the non-linear of power amplifier, thereby reduces the intermodulation distortion of repeater.It is understandable that, for a person skilled in the art, technical scheme of the present invention and inventive concept are equal to replacement or change the protection range that all should belong to the appended claim of the present invention.

Claims (5)

1. the repeater of a low intermodulation is characterized in that: in the downlink link of repeater, increase open loop DPD module, this module is arranged on after the digital signal processing module among the FPGA; Open loop DPD module receives the i/q signal of digital signal processing module output, simultaneously the DPD coefficient acting is accomplished pre-distortion in the i/q signal that receives, and result is as the input of power amplifier.

2. the repeater of low intermodulation according to claim 1; It is characterized in that: in the downlink link of repeater, add gain regulation module; Gain regulation module is arranged on after the open loop DPD module, is used for according to the power amplifier variation of temperature transmitting chain gain being adjusted, and precision is 0.1dB.

3. the implementation method of the repeater of a low intermodulation, it is characterized in that: concrete steps are following:

(1), in the downlink link of repeater, increase open loop DPD module, this module is arranged on after the digital signal processing module among the FPGA;

(2), catch the data of transmitting chain and the data of based on feedback link, and it is kept among the RAM of FPGA through FPGA; Use the DPD adaptive algorithm and handle emission data and feedback data among the RAM, obtain the DPD coefficient;

(3), open loop DPD module receives the i/q signal of digital signal processing module output in system, thereby receive the DPD coefficient simultaneously and the DPD coefficient acting accomplished pre-distortion in the i/q signal that receives, result is as the input of power amplifier.

4. the implementation method of the repeater of low intermodulation according to claim 3; It is characterized in that: in the downlink link of repeater, add gain regulation module; Gain regulation module is arranged on after the open loop DPD module; Gain adjusts to transmitting chain according to the power amplifier variation of temperature, and precision is 0.1dB.

5. the implementation method of the repeater of low intermodulation according to claim 3 is characterized in that: the DPD coefficient is backed up in EEPROM.

Images