CN101860503B - Method for echo interference cancellation of 3G digital repeater based on blind detection - Google Patents

Abstract

The invention discloses a method for echo interference cancellation of a 3G digital repeater based on blind detection, which comprises the following steps: equalizing channels beside an echo channel and the echo channel as an IIR channel w (n), wherein the echo channel refers to a channel from a repeater transmitter antenna of signals to a repeater receiver antenna; arranging a transverse equalizer in the repeater; making a transmission sequence x (n) pass through the IIR channel and adding Gaussian noise n (n) to obtain an IIR channel output sequence y (n), and connecting the IIR channel output sequence y (n) to the input end of the equalizer; updating the tap coefficient of the equalizer through the constant modulus algorithm CMA, and filtering the repeater received signal. The invention has the advantages that: the channels and the echo channel are equalized as the IIR channel, the equalizer is arranged in the repeater and adopts a transverse filter structure, and the tap coefficient of the equalizer is updated through the constant modulus algorithm. The equalizer output sequence is transmitted out through the repeater transmitter antenna. Therefore, the invention has the beneficial effects of inhibiting the echo interference and reducing the inter-low-symbol interference.

Description

A kind of 3G digital high-frequency amplification station method for echo interference cancellation based on blind Detecting

Technical field

The invention belongs to the signal processing field in the radio communication, relate to a kind of method for echo interference cancellation of the 3G digital high-frequency amplification station based on blind Detecting.This method can be applied to suppress in WCDMA, TD-CDMA, the CDMA2000 standard digital high-frequency amplification station echo and disturb, reduces intersymbol interference.

Background technology

The repeater is a kind of radio transmission transferring equipment that is used for enhancing signal in the wireless communication transmissions process, and basic function is exactly a radiofrequency signal power intensifier.Mainly form by reception antenna, signal handling equipment, transmitting antenna.In order to reduce small product size, dual-mode antenna usually puts together (or close).The difference that only has antenna directional angle; Therefore, possibly there is the echo interference problem in the repeater, and promptly the reception antenna of repeater can receive the process amplifying signal that its forwarding antenna sends; The superposed signal of interference and desired signal can be sent to power amplifier once more; Amplify forwarding again, the intensity of interference signal can add up always, finally makes the repeater can't operate as normal.The echo cancellation scheme that adopts at present has, methods such as the gain of the isolation of adjustment dual-mode antenna, control repeater, echo interference cancellation.Yet can not fundamentally solve the wireless channel time varying characteristic through adjustment isolation between transmitting and receiving antenna, control repeater gain method.The self adaptation method for echo interference cancellation not only wastes system resource, increases hardware cost, and convergence rate is slow, and steady-state error is big.

Summary of the invention

In order to overcome the existing shortcoming that echo disturbs that suppresses; Better suppressing echo disturbs; The invention provides a kind of 3G digital high-frequency amplification station method for echo interference cancellation based on blind Detecting; This method can suppress WCDMA, TD-CDMA, the interference of CDMA2000 standard digital high-frequency amplification station echo, can reduce the intersymbol interference that brings because of the channel finite bandwidth.

The technical solution adopted for the present invention to solve the technical problems.This 3G digital high-frequency amplification station method for echo interference cancellation based on blind Detecting is an IIR channel w (n) with channel, echo channel equivalence except that echo channel; Echo channel is meant that signal repeater transmitting antenna gets back to the channel of repeater reception antenna; One transversal equalizer is set in the repeater; Behind transmitting sequence x (n) process IIR channel, adding Gaussian noise n (n); Obtain IIR channel output sequence y (n),

wherein n is time series; IIR channel output sequence y (n) is linked into the equalizer input; Upgrade equalizer tap coefficient through constant mould CMA algorithm, the repeater is received signal carry out Filtering Processing through equalizer.

As preferably; One transversal equalizer is set in the repeater, and the transversal equalizer exponent number can be realized getting higher value under the prerequisite at the assurance system hardware; Equalizer tap coefficient adopts the centre cap initialization; That is: establishing equalizer h (n) tap exponent number is 2*L+1, and the L tap coefficient is initialized as 1, and all the other tap coefficients are initialized as 0.

As preferably, upgrade equalizer tap coefficient through constant mould CMA algorithm; The repeater is received signal carries out Filtering Processing, may further comprise the steps through equalizer with the constant modulus algorithm updating of tap coefficients:

1) with equalizer input sequences y (n), do filtering operation with equalizer h (n), obtain equalizer output sequence:

$\left(n\right)=\underset{l=-L}{\overset{L}{\mathrm{\Σ}}}(n,l)y(n-l)h^H\left(n\right)y\left(n\right);$

2) error of calculation functional value: e (n)=| z (n) | ²-R ²

3) equalizer tap coefficient is upgraded: h (n+1)=h (n)-μ e (n) y (n) z (n), wherein μ is a step factor;

4) turn back to 1) step repeat.

As preferably, R ²Value adopts this formula, R ²=E{|x ⁴(n) | }/E{|x ²(n) | } x (n) is the information source transmitting sequence.

The effect that the present invention is useful: the present invention is an IIR channel with channel (channel except that echo channel), echo channel (signal repeater transmitting antenna is got back to the channel of repeater reception antenna) equivalence; One equalizer is set in the repeater; Equalizer adopts transverse filter structure, and equalizer tap coefficient upgrades through constant modulus algorithm.Equalizer output sequence is gone out through the repeater transmission antennas transmit.The invention has the beneficial effects as follows, suppress echo and disturb, reduce intersymbol interference.

Description of drawings

Fig. 1: have the repeater channel isoboles that echo disturbs;

Fig. 2: principle of the invention figure;

Fig. 3: embodiment 1 simulation result figure, modulation signal is BPSK, (a): ideal signal figure; (b): equalizer input signal figure; (c): the constant modulus algorithm learning curve; (d) equalizer output signal figure.

Fig. 4: embodiment 2 simulation result figure, modulation signal is QPSK, (a): ideal signal figure; (b): equalizer input signal figure; (c): the constant modulus algorithm learning curve; (d) equalizer output signal figure.

Fig. 5: embodiment 3 simulation result figure, modulation signal is 8PSK, (a): ideal signal figure; (b): equalizer input signal figure; (c): the constant modulus algorithm learning curve; (d) equalizer output signal figure.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is described further:

Transmit through wireless channel; Arrive the repeater; See that from stay of two nights end be the FIR channel with signal flow to the forward channel equivalence of the stay of two nights; Is IIR channel to the back of information source to the channel equivalence with signal flow, and like accompanying drawing 1, we can be an IIR channel with forward channel (channel except that echo channel), echo channel (signal repeater transmitting antenna is got back to the back to channel of repeater reception antenna) equivalence.Shown in accompanying drawing 1.Add channel equalizer in the rear end, repeater,, accomplish IIR channel equalization, and then suppress echo and disturb, reduce intersymbol interference through designing this equalizer.Like accompanying drawing 2.

Transversal filter has stable properties, and equalizer adopts transverse filter structure, because channel adopts the IIR channel model, transversal filter tap exponent number should keep enough height satisfying under the hardware requirement condition.The equalizer tap exponent number is got 2*L+1, and the L tap coefficient is initialized as 1, and all the other tap coefficients are initialized as 0, i.e. centre cap initialization.

Among Fig. 2, { x (n) } is the sequence that transmits; { w (n) } is the impulse response of channel; { n (n) } is the white Gaussian noise sequence; { y (n) } is the list entries of equalizer; { h (n) } is equalizer weight coefficient vector, and length is 2L+1, and L gets positive integer, ' ^*' the expression conjugation; { z (n) } is the output sequence of equalizer; { e (n) } is constant modulus algorithm error term.Make y (n)=[y (n+L) ..., y (n-L)] ^T, h (n)=[h (n-L) ..., h (n+L)] ^T, ' ^T' the expression transposition.The expression convolution with

, export behind the transmission sequence process IIR channel:

$y\left(n\right)=x\left(n\right)\⊗w\left(n\right)+n\left(n\right)$

This signal gets into the input equalizer input, carries out filtering operation with equalizer, obtains:

$z\left(n\right)=\underset{l=-L}{\overset{L}{\mathrm{\Σ}}}h(n,l)y(n-l)=h^H\left(n\right)y\left(n\right),$

For CMA, error function:

e(n)＝|z(n)| ²-R ²

In the formula,

Cost function J=E{ through CMA (| z (n) | ²-R ²) ²Obtain the renewal function of equalizer weight vector among the CMA:

h(n+1)＝h(n)-μe(n)y(n)z ^*(n)

In the formula, μ is an iteration factor, and balanced tap coefficient is brought in constant renewal in through constant modulus algorithm, and equalizer input signal is carried out Filtering Processing, suppresses echo and disturbs, and reduces intersymbol interference, finally recovers useful signal.

The enforcement detailed step is following:

1) be an IIR channel w (n) with channel (channel except that echo channel), echo channel (signal repeater transmitting antenna is got back to the channel of repeater reception antenna) equivalence;

2) equalizer is set in the repeater, equalizer h (n) tap exponent number is got 2*L+1, and equalizer tap adopts the centre cap initialization; That is: the L tap coefficient is initialized as 1, and all the other tap coefficients are initialized as 0, because the channel equivalence is the IIR channel; Satisfying under the hardware condition, L gets higher value;

3) computational constant modulo n arithmetic mould value: R ²=E{|x ⁴(n) | }/E{|x ²(n) | };

4) with behind transmitting sequence x (n) process IIR channel, the adding Gaussian noise n (n); Obtain IIR channel output sequence y (n);

wherein n is time series, down together;

5) IIR channel output sequence y (n) is linked into the equalizer input;

6) with 5) equalizer input sequences y (n), do filtering operation with equalizer h (n), obtain equalizer output sequence:

$z\left(n\right)=\underset{l=-L}{\overset{L}{\mathrm{\Σ}}}h(n,l)y(n-l)=h^H\left(n\right)y\left(n\right);$

7) error of calculation functional value: e (n)=| z (n) | ²-R ²

8) equalizer tap coefficient is upgraded: h (n+1)=h (n)-μ e (n) y (n) z (n), wherein μ is a step factor, the μ value influences the convergence rate and the steady-state error of constant modulus algorithm.When requiring to hang down steady-state error, desirable μ smaller value, when requiring rapid convergence speed, desirable μ higher value; When requiring low steady-state error, rapid convergence speed, desirable μ is function u (the n)=f (e (n)) about error function e (n), and at the convergence initial stage, u (n) is bigger, and later stage u (n) is less;

9) turn back to 5) step repeat.

Exemplifying embodiment 1 modulation signal is BPSK

Transmitting is 3G modulation signal BPSK, and channel adopts the transfer function with ten echo paths

Signal to noise ratio is 25dB, equalizer tap exponent number 41, centre cap initialization; Constant modulus algorithm step size mu=1 * 10 ^-3

Exemplifying embodiment 2 modulation signals are QPSK

Transmitting is 3G modulation signal QPSK, and channel adopts the transfer function with ten echo paths

Signal to noise ratio is 25dB, equalizer tap exponent number 41, centre cap initialization; Constant modulus algorithm step size mu=1 * 10 ^-3

Exemplifying embodiment 3 modulation signals are 8PSK

Transmitting is 3G modulation signal 8PSK, and channel adopts the transfer function with ten echo paths

Signal to noise ratio is 25dB, equalizer tap exponent number 41, centre cap initialization; Constant modulus algorithm step size mu=1 * 10 ^-3

Except that the foregoing description, all employings are equal to the technical scheme of replacement or equivalent transformation formation, all drop on the protection range of requirement of the present invention.

Claims (2)

1. 3G digital high-frequency amplification station method for echo interference cancellation based on blind Detecting, it is characterized in that: with channel, echo channel equivalence except that echo channel is an IIR channel w (n); Echo channel is meant that signal repeater transmitting antenna gets back to the channel of this repeater reception antenna; One transversal equalizer is set in said repeater; Behind transmitting sequence x (n) process IIR channel, adding Gaussian noise n (n); Obtain IIR channel output sequence y (n),

wherein n is time series; IIR channel output sequence y (n) is linked into the equalizer input; Upgrade equalizer tap coefficient through constant mould CMA algorithm, said repeater is received signal carry out Filtering Processing through equalizer;

Upgrade equalizer tap coefficient through constant mould CMA algorithm; Said repeater is received signal carries out Filtering Processing, may further comprise the steps through equalizer with the constant modulus algorithm updating of tap coefficients:

1) with equalizer input sequences y (n), do filtering operation with equalizer h (n), obtain equalizer output sequence: $z\left(n\right)=\underset{l=-L}{\overset{L}{\mathrm{\Σ}}}h(n,l)y(n-l)=h^H\left(n\right)y\left(n\right),$ Wherein equalizer h (n) tap exponent number is 2*L+1;

2) error of calculation functional value: e (n)=| z (n) | ²-R ², R wherein ²=E{|x ⁴(n) | }/E{|x ²(n) | }, x (n) is the information source transmitting sequence;

3) equalizer tap coefficient is upgraded: h (n+1)=h (n)-μ e (n) y (n) z (n), wherein μ is a step factor;

4) turn back to 1) step repeat.

2. according to the 3G digital high-frequency amplification station method for echo interference cancellation based on blind Detecting of claim 1; It is characterized in that: a transversal equalizer is set in the repeater, and the transversal equalizer exponent number can be realized getting higher value under the prerequisite at the assurance system hardware; Equalizer tap coefficient adopts the centre cap initialization; That is: establishing equalizer h (n) tap exponent number is 2*L+1, and the L tap coefficient is initialized as 1, and all the other tap coefficients are initialized as 0.

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