CN103929212A - Broadband receiver nonlinear blind recognition and compensation method - Google Patents

Abstract

The invention relates to the field of wireless monitoring, in particular to a broadband receiver nonlinear blind recognition and compensation method. In the method, a distorted signal is compensated for to obtain a mixed signal, a cost function of short-time energy information of distortion components in the mixed signal is worked out, the compensation parameter corresponding to the minimum distortion compensation is worked out, compensation parameters in the compensation model are updated, the steps are carried out repeatedly until the distortion components are well inhibited, and therefore the spurious-free dynamic range of the receiver is expanded, and the weak-signal extraction ability is improved as well.

Description

A kind of broadband receiver nonlinear blind identification and compensation method

Technical field

The invention belongs to radio monitoring field, particularly relate to the identification of broadband receiver nonlinear blind and compensation method.

Background technology

The strong nonlinearity that may exist with respect to transmitter system, the nonlinear characteristic of receiver a little less than.Receiver is received after signal, the analogue devices such as process amplifier, filter, frequency mixer, and signal can produce nonlinear distortion through these analogue devices.ADC(analog to digital converter) as a kind of mixed processing device, be also the nonlinear important sources of receiver link, signal can produce distortion in time domain by ADC, and frequency domain produces harmonic distortion, intermodulation distortion etc.Reducing nonlinear one of them method of receiver is to select speed, and conversion accuracy is higher, the ADC that Spurious Free Dynamic Range is larger.But the price of high performance ADC is very expensive.Now, the research of the linearization technique to receiver is less both at home and abroad.In engineering, in order to ensure the linearity of receiver, the one, can adopt the thought of back-off, power limited below 1dB compression point by input signal, only utilizes the linear gain region of receiver.The shortcoming of Power back is the dynamic range of receiving that has had a strong impact on receiver, has sacrificed efficiency of transmission simultaneously.The 2nd, use feedback technique, distortion component in nonlinear output signal is extracted, feed back to input, thereby and then carry out the anti-phase acquisition that disappears mutually with input signal and suppress the output signal after nonlinear component, but the method exists the stability problem of reponse system, and the signal lag simultaneously existing in transmission system has limited the maximum bandwidth that allows signal transmission.The 3rd, use pre-distortion technology, be in advance input signal to be carried out to certain conversion, make its conversion characteristics just in time reciprocal with the nonlinear characteristic of receiver, thus the non-linearity of cancellation receiver.But before radio-frequency front-end, carry out self-adapted pre-distortion, the actual larger difficulty of upper existence that realizes.

A kind of comparatively common modeling compensation method is at present loop up table.The method is to use specific input signal to encourage system to be compensated, by all possible output code value and it with respect to the Difference Storage of desirable input code in look-up table, in the linearizing process of reality, using the instantaneous amplitude value of output signal as index, search and obtain the corresponding margin of error, again it is deducted from output signal, reach the object of bucking-out system error.But because frequency and the amplitude of input signal have larger scope, simultaneously compensation system may there is memory effect, institute think ensure compensate precision, the look-up table that need to generate multidimensional carrys out the various possible input conditions of index.So like this, if will ensure precision, must need great memory capacity, need addressing faster and processing speed simultaneously, the real-time of guarantee compensation.Therefore, the hardware implementation complexity of the method has limited its application greatly.

Summary of the invention

The object of the invention is just the weak point of background technology to be improved and designed the identification of a kind of broadband receiver nonlinear blind and compensation method, thereby reach the Spurious Free Dynamic Range that improves receiver and the object of extracting the ability of weak signal.

Solution of the present invention is the identification of a kind of broadband receiver nonlinear blind and compensation method, and the method comprises:

Step 1: receiver is received analog signal, this signal is processed distortion is occurred through receiver, obtains distorted signal, and distorted signal is made up of linear component and distortion component;

Step 2: build compensation model according to distorted signal, and default compensating parameter, compensation model output compensating signal compensates distorted signal, obtains mixed signal;

Step 3: use FFT (fast Fourier transform) to ask for the power spectral density function of mixed signal, in power spectral density function, judge frequency and the bandwidth of linear component and distortion component according to default received signal power thresholding;

Step 4: according to the frequency and the bandwidth that receive signal and distortion component, build the spectral response of comb filter, carry out again contrary FFT and obtain filter coefficient, to after filter coefficient windowing and compensating signal carry out filtering, calculate harmonic term and the intermodulation item of linear component;

Step 5: harmonic term and intermodulation item by linear component calculate the short-time energy of distortion component, then construct cost function, obtain the compensating parameter in the time that cost function is obtained minimum value;

Step 6: adopt adaptive algorithm compensating parameter default in step 2 to be replaced with to the compensating parameter of obtaining in step 5, repeat above-mentioned steps, until this adaptive algorithm convergence in computational process reaches the effect that suppresses distortion component.

The compensation model wherein building in step 2 is Volterra compensation model.

A kind of broadband receiver nonlinear blind identification of the present invention and compensation method, by distorted signal is compensated, obtain mixed signal, calculate again the short-time energy cost function of distortion component in mixed signal, calculate the compensating parameter that makes distortion component minimum, then upgrade the compensating parameter in compensation model, repeat this step until distortion component is suppressed preferably, thereby there is the Spurious Free Dynamic Range that improves receiver and the effect of extracting the ability of weak signal.

Brief description of the drawings

Fig. 1 is the flow chart of the method for receiver blind discrimination compensation of the present invention;

Fig. 2 is that the power threshold of linear component is judged schematic diagram.

Embodiment

Step 1: receiver is received analog signal, there is distortion in this signal, obtain distorted signal after the processing of receiver radio frequency front end and AD sampling, and distorted signal is made up of linear component and distortion component.

Step 2: structure Volterra compensation model, the initial value ω of preset model compensating parameter ω ₀, establish the exponent number D=3 of Volterra model, compensation model output compensating signal is p (k)=v (k) ω ₀,

Wherein v (k)=[y ²(k), y (k) y (k-1) ..., y ³(k), y ²(k) y (k-1) ... y ³(k-1)], ω ₀=[ω ₁, ω ₂, ω ₃, ω ₄, ω ₅, ω ₆, ω ₇] ^t=[1,0,0,0,0,0,0] ^tfor the initial value of model parameter, that is:

p(k)=ω ₁y ²(k)+ω ₂y(k)y(k-1)+ω ₃y ²(k-1)+ω ₄y ³(k)+ω ₅y ²(k)y(k-1)+ω ₆y(k)y ²(k-1)+ω ₇y ³(k-1)

Then obtain mixed signal s (k)=y (k)-p (k), wherein y (k) is distorted signal, and p (k) is compensating signal.

Step 3: ask for the power spectral density of mixed signal s (k), and judge frequency and the bandwidth of linear component and distortion component:

Mixed signal s (k) is done to FFT computing, be compensated the power spectral density function of signal s (k), the power threshold P of judgement linear component given in advance _threshold, according to linear component judgment criterion P>P _threshold, can obtain the frequency f of linear component in frequency spectrum ₁, f ₂f _nwith bandwidth l ₁, l ₂l _n, then obtain harmonic component 2f according to the frequency of linear component and bandwidth ₁, 3f ₁... 2f _n, 3f _nand intermodulation component f ₁+ f ₂... 2f _n-1+ f _n... frequency and bandwidth, as shown in Figure 2.

Step 4: according to the frequency of distortion component and bandwidth, structure comb filter calculates distortion component:

According to the spectral response of the frequency of harmonic wave and intermodulation component and bandwidth structure comb filter, spectral response is obtained to filter coefficient as IFFT, to carrying out filtering with mixed signal employing FIR filter after filter coefficient windowing, calculate harmonic term and the intermodulation item of linear component, establishing FIR filter vector is g=[g ₀, g ₁g _b-1] ^t, dimension is B × 1, the nonlinear component of the mixed signal finally extracting is expressed as:

s _f(k,ω)=g ^Ts(k)=g ^T[y(k)-V ^T(k)ω]

Wherein y (k) representative is the distorted signal after broadband receiver AD sampling, and V (k) is the matrix that characterizes bucking-out system nonlinear memory part.ω is the compensating parameter that the present invention wants identification,

y(k)=[y(k-B+1),y(k-B+2)…y(k)] ^T，V(k)=[v(k-B+1),v(k-B+2)…v(k)]，v(k)=[y ²(k),y(k)y(k-1)…,y ³(k),y ²(k)y(k-1)…y ³(k-1)] ^T。

Step 5: construct cost function J (ω) according to the harmonic term of linear component and intermodulation item, utilize adaptive algorithm to upgrade compensation model parameter.

Core of the present invention is in the situation that ensureing linear component constant in energy, makes nonlinear component energy minimum, due at s _f(k, ω)=g ^tin s (k), do not comprise linear component part, therefore make cost function and be:

J(ω)=E[s ² _f(k,ω)]

Recycling LMS adaptive algorithm (conventional is LMS or RLS algorithm) is upgraded compensation model parameter ω, makes the value minimum of cost function.

LMS adaptive approach:

Cost function J (ω) is launched and asks gradient, can obtain:

$\▿J\left(\mathrm{\ω}\left(n\right)\right)=-2E\left[V\left(n\right){\mathrm{gg}}^{T}y\left(n\right)\right]+2E\left[V\left(n\right){\mathrm{gg}}^T{V}^T\left(n\right)\right]\mathrm{\ω}\left(n\right)$

According to Wiener filtering steepest descent method thought: $\mathrm{\ω}(n+1)=\mathrm{\ω}\left(n\right)-\frac{1}{2}\mathrm{\μ}\▿J\left(\mathrm{\ω}\left(n\right)\right)$ Can obtain:

ω(n+1)=ω(n)-μ{E[V(n)gg ^TV ^T(n)]ω(n)-E[V(n)gg ^Ty(n)]}

Utilize instantaneous estimation value to approach assembly average, can obtain the LMS Adaptive Identification algorithm in blind discrimination bucking-out system:

ω(n+1)=ω(n)-μ{V(n)gg ^TV ^T(n)ω(n)-V(n)gg ^Ty(n)}。

Step 6: the ω substitution compensation model that adaptive algorithm is tried to achieve, thereby the mixed signal s after being compensated (k):

By in the ω substitution step 2 of trying to achieve after adaptive algorithm convergence, be compensated model output signal p (k), thereby obtain mixed signal s (k)=y (k)-p (k).

After blind discrimination compensation output, the distortion component in signal is effectively suppressed, and weak signal can be separated from distortion component, has improved the dynamic range of receiver, has improved the nonlinear characteristic of its front end.

Claims (2)

1. the identification of broadband receiver nonlinear blind and a compensation method, the method comprises:

Step 1: receiver is received analog signal, this signal is processed distortion is occurred through receiver, obtains distorted signal, and distorted signal is made up of linear component and distortion component;

Step 2: build compensation model according to distorted signal, and default compensating parameter, compensation model output compensating signal compensates distorted signal, obtains mixed signal;

Step 3: use fast Fourier transform to ask for the power spectral density function of mixed signal, in power spectral density function, judge frequency and the bandwidth of linear component and distortion component according to default received signal power thresholding;

Step 4: according to the frequency and the bandwidth that receive signal and distortion component, build the spectral response of comb filter, carry out again contrary FFT and obtain filter coefficient, to after filter coefficient windowing and mixed signal carry out filtering, calculate harmonic term and the intermodulation item of linear component;

Step 5: harmonic term and intermodulation item by linear component calculate the short-time energy of distortion component, then construct cost function, obtain the compensating parameter in the time that cost function is obtained minimum value;

Step 6: adopt adaptive algorithm compensating parameter default in step 2 to be replaced with to the compensating parameter of obtaining in step 5, repeat above-mentioned steps, until this adaptive algorithm convergence in computational process reaches the effect that suppresses distortion component.

2. a kind of broadband receiver nonlinear blind as claimed in claim 1 identification and compensation method, is characterized in that the compensation model building in step 2 is Volterra compensation model.