CN105827560A - Noise suppression method applied to broadband OFDM power line communication system - Google Patents

Abstract

The invention provides a noise suppression method applied to a broadband OFDM power line communication system. According to the noise suppression method, discrete Fourier transform is carried out on an OFDM signal at a receiving terminal; a protection frequency band signal is extracted from an output result and that is, a useless part distributed between two adjacent channels in the frequency spectrum is extracted; a correlated parameter of a pulse noise is estimated by combining time-domain and frequency-domain methods; and according to the estimated parameter of the pulse noise, a proper envelope window function is constructed to suppress the pulse noise in the time domain. Therefore, the pulse noise can be suppressed effectively; the frequency spectrum leakage can be reduced substantially; and performances of the broadband power line communication system can be improved.

Description

It is applied to the noise suppressing method of wideband OFDM electric line communication system

Technical field

The present invention relates to communication technical field, particularly relate to a kind of noise suppressing method being applied to wideband OFDM electric line communication system.

Background technology

Power-line broadband communication technology utilizes power line network by information fast propagation to each corner.In broadband power line communication environment, there are the various electrical equipments that a large amount of unknown watt level differs.The switch of these equipment and work, and the radio wave that various radio produces, bring various strong time-varying noise jamming all can to broadband power line communication channel.Difference according to noise source can be divided into: background noise and impulsive noise, and the amplitude of the latter is significantly larger than background noise, can impulsive noise be divided into according to the difference of noise model: bernoulli Gauss pulse noise and bunch hair style impulsive noise.The randomness of impulsive noise and high intensity seriously constrain reliability and the handling capacity of broadband power line communication system.

At present in the method for noise suppressed, widely used is zero suppression and limiting technology, especially the simplest effectively with zero suppression technology.But, zero suppression process is carried out for bernoulli Gauss pulse noise, effect is notable, and for bunch hair style impulsive noise, conventional zero suppression technology is equivalent to process in a simple rectangular window function envelope, due to the non-linear behavior of this technology, can bring certain spectral leakage, the problem causing inter-sub-carrier interference, the performance of system will degradation.Need the most in the industry a kind of bunch hair style impulse noise suppression method badly, to reduce the spectral leakage that the limitation of zero suppression technology is brought.

Summary of the invention

(1) to solve the technical problem that

In view of above-mentioned technical problem, the invention provides a kind of noise suppressing method being applied to wideband OFDM electric line communication system.

(2) technical scheme

The present invention is applied to the noise suppressing method of wideband OFDM electric line communication system and includes:

Step A: the ofdm signal received is carried out discrete Fourier transform, extracts guard band signal S from result of variations_g, and calculate its instantaneous mean power P_g；

Step B: according to instantaneous mean power P_gDetermine that ofdm signal, whether by a bunch hair style impulse noise effect, if ofdm signal is by bunch hair style impulse noise effect, performs step C；Otherwise, step F is performed；

Step C: by the sampled value of each ofdm signal and adaptive amplitude-limiting threshold value T based on optimal false-alarm probability and detection probability_clipCarry out, statistical result, determine that bunch hair style impulsive noise bunch sends out territory ψ according to comparative result；

Step D: send out territory ψ according to bunch hair style impulsive noise bunch and determine burst of noise persistent period Φ and burst of noise center n₀；And

Step E: send out territory ψ, burst of noise persistent period Φ and burst center n according to bunch hair style impulsive noise bunch₀Process bunch hair style impulsive noise in ofdm signal, it is achieved noise suppressed；

Step F: perform OFDM demodulation.

(3) beneficial effect

Can be seen that from technique scheme, the present invention is in broadband power line communication environment, estimation is made decisions for bunch hair style impulsive noise on electric lines of force, determine that suitable envelope window function carries out suppression process to noise it is thus possible to impulse noise mitigation effectively according to the impulsive noise relevant parameter estimated, greatly reduce spectral leakage simultaneously, improve the performance of broadband power line communication system.

Accompanying drawing explanation

Fig. 1 is the FB(flow block) of the noise suppressing method being applied to wideband OFDM electric line communication system according to first embodiment of the invention.

Fig. 2 is the detailed process block diagram of step A in noise suppressing method shown in Fig. 1, B；

Fig. 3 is the FB(flow block) determining optimum window function peak A in noise suppressing method shown in Fig. 1.

Detailed description of the invention

Noise suppressing method of the present invention includes: noise monitoring and estimation, the determination of envelope window function and noise suppressed three part.Receiving terminal ofdm signal is carried out discrete Fourier transform; guard band signal is extracted from output result; frequency spectrum namely distributes a part useless between two neighbouring channels; the relevant parameter of impulsive noise is estimated in conjunction with time-domain and frequency-domain method; then according to the estimation parameter of impulsive noise, build a suitable envelope window function impulse noise mitigation in the time domain.

For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with specific embodiment, and referring to the drawings, the present invention is described in more detail.

In one exemplary embodiment of the present invention, it is provided that a kind of noise suppressing method being applied to wideband OFDM electric line communication system.

As it is shown in figure 1, baseband signal produces ofdm signal Symbol by IDFT conversion (InverseDiscreteFourierTransform, inverse discrete Fourier transform)_k.Ofdm signal Symbol_kBroadband power line channel transmits, thus introduces impulsive noise and background noise.Therefore, comprise in the signal that receiving terminal receives: ofdm signal Symbol_k, impulsive noise and background noise.

Continuing referring to Fig. 1, the present embodiment is applied to the noise suppressing method of wideband OFDM electric line communication system and includes:

Step A: the ofdm signal received is carried out discrete Fourier transform (DiscreteFourierTransform is called for short DFT transform), extracts guard band signal S from output result_g, and calculate its instantaneous mean power P_g；

Wherein, guard band signal S is calculated_gInstantaneous mean power P_gIn, guard band signal S_gIn sample point be exactly the subcarrier of guard band signal, obtain the amplitude of each subcarrier, be averaging after the amplitude of each subcarrier being carried out square and obtain guard band signal S_gInstantaneous mean power P_g。

Refer to Fig. 2, this step A farther includes:

Sub-step A1: the ofdm signal received is carried out discrete Fourier transform；

Sub-step A2: extract guard band signal S the signal after carrying out discrete Fourier transform_g；

Sub-step A3: obtain guard band signal S_gIn the amplitude of each subcarrier, be averaging after the amplitude of each subcarrier being carried out square and obtain guard band signal S_gInstantaneous mean power P_g。

Step B: according to instantaneous mean power P_gDetermine that ofdm signal, whether by a bunch hair style impulse noise effect, if ofdm signal is by bunch hair style impulse noise effect, performs step C；Otherwise, step F is performed；

Refer to Fig. 2, this step B farther includes:

Sub-step B1: calculate mean power P of the guard band of background noise AWGN_w；

Sub-step B2: by instantaneous mean power P_gWith mean power P_wCompare, if P_gMore than P_w, illustrate that ofdm signal, by bunch hair style impulse noise effect, performs step C；Otherwise, illustrate that ofdm signal, not by a bunch hair style impulse noise effect, performs step F.

Step C: by the sampled value of each ofdm signal and adaptive amplitude-limiting threshold value T based on optimal false-alarm probability and detection probability_clipCarry out, statistical result, determine that bunch hair style impulsive noise bunch sends out territory ψ according to comparative result；

Specifically, this step C farther includes:

Sub-step C1: by sampled value x of each ofdm signal_nWith adaptive amplitude-limiting threshold value T_clipCompare, if x_nMore than T_clip, record the position of now sampled value；

Wherein, adaptive amplitude-limiting threshold value T_clipIt is defined as follows:

$T_{\mathrm{clip}}=\sqrt{\frac{{2\mathrm{\σ}}_s{\mathrm{\σ}}_w}{{\mathrm{\σ}}_s^2-{\mathrm{\σ}}_w^2}\ln \left(\frac{{\mathrm{\σ}}_s^2+{\mathrm{\σ}}_w^2}{{\mathrm{\σ}}_s^2+(1+\mathrm{\μ}){\mathrm{\σ}}_w^2}\right)}$

Wherein, μ is impulsive noise energy and the energy ratio of background noise AWGN, i.e. It is the variance of white Gaussian noise,It is the variance of impulsive noise,It it is the variance of ofdm signal；

Sub-step C2: definition bunch hair style impulsive noise bunch is sent out territory ψ and is: sampled value x of ofdm signal_nMiddle amplitude is more than the set of the position of adaptive amplitude-limiting threshold value.

Step D: send out territory ψ according to bunch hair style impulsive noise bunch and determine burst of noise persistent period Φ and burst of noise center n₀；

In this step, burst of noise persistent period Φ is that bunch hair style impulsive noise bunch that statistics obtains sends out the element number in the ψ of territory, burst of noise center n₀The central point of territory ψ is sent out for bunch hair style impulsive noise bunch.

Step E: send out territory ψ, burst of noise persistent period Φ and burst center n according to bunch hair style impulsive noise bunch₀Process bunch hair style impulsive noise in ofdm signal, it is achieved noise suppressed；

Wherein, the window function envelope function that the impulsive noise process sent out in the ψ of territory for bunch hair style impulsive noise bunch is used is as follows:

Wherein, n is noise sample point；n₀For a bunch center for hair style impulsive noise；A is window function peak value, and 0≤A≤1；β represents the transformation factor of window function；For the width factor of window function, wherein Φ is the burst of noise persistent period, and N is the sub-carrier number of the size of discrete Fourier transform DFT, i.e. its correspondence, T_sPersistent period for ofdm signal.

Refer to Fig. 3, the determination process of window function peak A is as follows:

(1) impulsive noise average power density P is determined_i',Wherein N_gRepresent guard band signal S_gSub-carriers number, S_gN () represents guard band signal S_gMiddle sample point amplitude；

(2) according to impulsive noise average power density P_i' determine the gross energy E of impulsive noise_total, wherein, E_total=NP_i', N is the sub-carrier number of the size of discrete Fourier transform DFT, i.e. its correspondence；

(3) impulsive noise mean power P in time domain is calculated_i, wherein,

(4) repressed pulse energy E is determined according to envelope window function_i, wherein,

(5) dump energy E of ofdm signal is determined according to envelope window function_res, wherein,Wherein P_nMean power for ofdm signal；

(6) window function transformation factor β takes 0.2,0.1,0.05,0.025 and 0.01 respectively, and A puts an initial value 0；

It should be noted that window function transformation factor β minimum be 4, can in the range of less than 1 value, window function peak A can value in the range of more than or equal to 0.

(7) according to E_total, E_iAnd E_resCalculate the signal to noise ratio after impulse noise mitigation, represent with SNR, whereinAnd

(8) judge that the value of A has completed to change to 1 from 0 the most, if it is not, make A=A+0.01, forward step (7) to and perform；Otherwise, find out during 0 to 1 so that the A that SNR is maximum, be designated as optimum window function peak A_opti, as window function peak A.

It should be noted that in above-mentioned A=A+0.01,0.01 is only a preferred value, and those skilled in the art can carry out value as required, value can in the range of less than 0.1 value, value is the least more accurate, but its computational complexity is the highest.

In this step, process bunch hair style impulsive noise in ofdm signal and comprise following three kinds of situations:

(1) when judging ofdm signal sample point n and burst of noise center n₀Meet (1-2 β) K≤(n-n₀)≤(1+2 β) K time, use following suppressing method:

$x_n=\left\{\begin{array}{c}{x}_n,\left|x_n\right|\≤\frac{A}{2}+A\cos \left(\frac{\mathrm{\πn}-2\mathrm{\βK}}{2\mathrm{\βK}}\right)\\ 0,\left|x_n\right|>\frac{A}{2}+A\cos \left(\frac{\mathrm{\πn}-2\mathrm{\βK}}{2\mathrm{\βK}}\right)\end{array}\right.$

Wherein, x_nSampled value for ofdm signal n " ' sample point；|x_n| represent the amplitude of the sampled signal of ofdm signal n " ' sample point；

(2) when judging ofdm signal sample point n and noise center n₀Meet (-1-2 β) K≤(n-n₀)≤(2 β-1) K time, use following suppressing method:

$x_n=\left\{\begin{array}{c}{x}_n,\left|x_n\right|\≤\frac{A}{2}+A\cos \left(\frac{\mathrm{\πn}-2\mathrm{\βK}}{2\mathrm{\βK}}\right)\\ 0,\left|x_n\right|>\frac{A}{2}+A\cos \left(\frac{\mathrm{\πn}-2\mathrm{\βK}}{2\mathrm{\βK}}\right)\end{array}\right.$

(3) when judging ofdm signal sample point n and noise center n₀Meet (2 β-1) K≤(n-n₀)≤(1-2 β) K time, use following suppressing method:

$x_n=\left\{\begin{array}{c}{x}_n,\left|x_n\right|\≤1-\frac{\mathrm{A\β}}{2}\\ 0,\left|x_n\right|>1-\frac{\mathrm{A\β}}{2}\end{array}\right.$

Through above-mentioned steps, complete the noise suppressed of signal.

Step F: the signal after processing is sent to OFDM demodulation module and is demodulated.

So far, already in connection with accompanying drawing, the embodiment of the present invention has been described in detail.According to above description, those skilled in the art should be applied to the noise suppressing method of wideband OFDM electric line communication system to the present invention have been had and has clearly recognized.

It should be noted that in accompanying drawing or description text, the implementation not illustrating or describing, it is form known to a person of ordinary skill in the art in art, is not described in detail.Additionally, the above-mentioned definition to each element and method is not limited in various concrete structures, shape or the mode mentioned in embodiment, it can be changed or replace by those of ordinary skill in the art simply.

Additionally, can provide the demonstration of the parameter comprising particular value herein, but these parameters are worth equal to corresponding without definite, but can be similar to analog value in acceptable error margin or design constraint.Additionally, unless specifically described or the step that must sequentially occur, the order of above-mentioned steps there is no and is limited to listed above, and can change according to required design or rearrange.

In sum, the present invention, in broadband power line communication environment, makes decisions estimation for bunch hair style impulsive noise on electric lines of force, and the impulsive noise relevant parameter according to estimating determines that suitable envelope window function carries out suppression process to noise.Impulsive noise can effectively be suppressed by this noise suppressing method, greatly reduces spectral leakage simultaneously, improves the performance of broadband power line communication system, has preferable practical value.

Particular embodiments described above; the purpose of the present invention, technical scheme and beneficial effect are further described; it is it should be understood that; the foregoing is only the specific embodiment of the present invention; it is not limited to the present invention; all within the spirit and principles in the present invention, any modification, equivalent substitution and improvement etc. done, should be included within the scope of the present invention.

Claims (10)

1. the noise suppressing method being applied to wideband OFDM electric line communication system, it is characterised in that including:

Step A: the ofdm signal received is carried out discrete Fourier transform, extracts guard band signal S from result of variations_g, and calculate its instantaneous mean power P_g；

Step B: according to instantaneous mean power P_gDetermine that ofdm signal, whether by a bunch hair style impulse noise effect, if ofdm signal is by bunch hair style impulse noise effect, performs step C；Otherwise, step F is performed；

Step C: by the sampled value of each ofdm signal and adaptive amplitude-limiting threshold value T based on optimal false-alarm probability and detection probability_clipCarry out, statistical result, determine that bunch hair style impulsive noise bunch sends out territory ψ according to comparative result；

Step D: send out territory ψ according to bunch hair style impulsive noise bunch and determine burst of noise persistent period Φ and burst of noise center n₀；And

Step E: send out territory ψ, burst of noise persistent period Φ and burst center n according to bunch hair style impulsive noise bunch₀Process bunch hair style impulsive noise in ofdm signal, it is achieved noise suppressed；

Step F: perform OFDM demodulation.

Noise suppressing method the most according to claim 1, it is characterised in that in described step E, bunch hair style impulsive noise according in following three kinds of situations process ofdm signal:

(1) when judging ofdm signal sample point n and burst of noise center n₀Meet (1-2 β) K≤(n-n₀)≤(1+2 β) K time, use following suppressing method:

$x_n=\left\{\begin{array}{c}{x}_n,\left|x_n\right|\≤\frac{A}{2}+Acos\left(\frac{\mathrm{\π}n-2\mathrm{\β}K}{2\mathrm{\β}K}\right)\\ 0,\left|x_n\right|>\frac{A}{2}+Acos\left(\frac{\mathrm{\π}n-2\mathrm{\β}K}{2\mathrm{\β}K}\right)\end{array}\right.$

(2) when judging ofdm signal sample point n and noise center n₀Meet (-1-2 β) K≤(n-n₀)≤(2 β-1) K time, use following suppressing method:

$x_n=\left\{\begin{array}{c}{x}_n,\left|x_n\right|\≤\frac{A}{2}-Acos\left(\frac{\mathrm{\π}n+2\mathrm{\β}K}{2\mathrm{\β}K}\right)\\ 0,\left|x_n\right|>\frac{A}{2}-Acos\left(\frac{\mathrm{\π}n+2\mathrm{\β}K}{2\mathrm{\β}K}\right)\end{array}\right.$

(3) when judging ofdm signal sample point n and noise center n₀Meet (2 β-1) K≤(n-n₀)≤(1-2 β) K time, use following suppressing method:

$x_n=\left\{\begin{array}{c}{x}_n,\left|x_n\right|\≤1-\frac{A\mathrm{\β}}{2}\\ 0,\left|x_n\right|>1-\frac{A\mathrm{\β}}{2}\end{array}\right.$

Wherein, A is window function peak value, and 0≤A≤1；β represents the transformation factor of window function；For the width factor of window function, wherein, N is the sub-carrier number of the size of discrete Fourier transform, i.e. its correspondence, T_sPersistent period for ofdm signal；

Wherein, x_nSampled value for ofdm signal n " ' sample point；|x_n| represent the amplitude of the sampled signal of ofdm signal n " ' sample point.

Noise suppressing method the most according to claim 2, it is characterised in that described window function peak A is obtained by following steps:

(1) impulsive noise average power density P is determined_i',Wherein N_gRepresent guard band signal S_gSub-carriers number, S_gN () represents guard band signal S_gMiddle sample point amplitude；

(2) according to impulsive noise average power density P_i' determine the gross energy E of impulsive noise_total, wherein, E_total=NP_i′；

(3) impulsive noise mean power P in time domain is calculated_i, wherein,

(4) repressed pulse energy E is determined according to envelope window function_i, wherein,

(5) dump energy E of ofdm signal is determined according to envelope window function_res, wherein,Wherein P_nMean power for ofdm signal；

(6) initializing the initial value of window function transformation factor β and window function peak A, wherein, window function transformation factor β at least takes 4 values, and each value is respectively less than 1, window function peak A value in the range of more than or equal to 0；

(7) according to E_total, E_iAnd E_resCalculate the signal to noise ratio after impulse noise mitigation, represent with SNR, whereinAnd

(8) judge that the value of A has completed to change to 1 from 0 the most, if it is not, make A=A+a, forward step (7) to and perform；Otherwise, find out during 0 to 1 so that the A that SNR is maximum_opti, as window function peak A.

Noise suppressing method the most according to claim 3, it is characterised in that in the described step determining repressed pulse energy according to envelope window function:

Noise suppressing method the most according to claim 3, it is characterised in that in the step of the initial value of described initialization window function transformation factor β and window function peak value: described window function transformation factor β takes 0.2 respectively, 0.1,0.05,0.025 and 0.01, described window function peak A initial value is 0.

Noise suppressing method the most according to claim 3, it is characterised in that in the described step making A=A+a, a=0.01.

Noise suppressing method the most according to any one of claim 1 to 6, it is characterised in that in described step A, obtains each guard band signal S_gThe amplitude of subcarrier, calculates guard band signal S according to these amplitudes_gInstantaneous mean power P_g, wherein, described guard band signal S_gThe corresponding described guard band signal S of subcarrier_gIn sample point.

Noise suppressing method the most according to any one of claim 1 to 6, it is characterised in that described step B includes:

Sub-step B1: calculate mean power P of the guard band of background noise_w；And

Sub-step B2: by instantaneous mean power P_gWith mean power P_wCompare, if P_gMore than P_w, illustrate that ofdm signal, by bunch hair style impulse noise effect, performs step C；Otherwise, illustrate that ofdm signal, not by a bunch hair style impulse noise effect, performs step F.

Noise suppressing method the most according to any one of claim 1 to 6, it is characterised in that described step C includes:

Sub-step C1: by sampled value x of each ofdm signal_nWith adaptive amplitude-limiting threshold value T_clipCompare, if x_nMore than T_clip, record the position of now sampled value；And

Sub-step C2: a bunch territory ψ for definition bunch hair style impulsive noise is: sampled value x of ofdm signal_nMiddle amplitude is more than the set of the position of adaptive amplitude-limiting threshold value；

Wherein, described adaptive amplitude-limiting threshold value T_clipIt is defined as follows:

$T_{clip}=\sqrt{\frac{2{\mathrm{\σ}}_s{\mathrm{\σ}}_w}{{\mathrm{\σ}}_s^2-{\mathrm{\σ}}_w^2}ln\left(\frac{{\mathrm{\σ}}_s^2+{\mathrm{\σ}}_w^2}{{\mathrm{\σ}}_s^2+(1+\mathrm{\μ}){\mathrm{\σ}}_w^2}\right)}$

Wherein, μ is the energy ratio of impulsive noise energy and background noise, i.e.It is the variance of white Gaussian noise,It is the variance of impulsive noise,It it is the variance of ofdm signal.

Noise suppressing method the most according to any one of claim 1 to 6, it is characterised in that in described step D, burst of noise persistent period Φ is that bunch hair style impulsive noise bunch that statistics obtains sends out the element number in the ψ of territory, burst of noise center n₀The central point of territory ψ is sent out for bunch hair style impulsive noise bunch.