CN103344945A - Direct wave and method for inhibiting multi-path interference of direct wave - Google Patents

Abstract

The invention relates to a direct wave and a method for inhibiting multi-path interference of the direct wave, and belongs to the technical field of radar target acquisition. According to the method, sub-bands adapt to RLS plus NLMS filtering by itself. The method comprises the steps that (1) the sub-bands are decomposed, (2) signals of all the sub-bands respectively pass through the RLS plus NLMS filtering, and (3) the sub-bands are integrated. The method improves the consistency of frequency characteristics between passages of the direct wave and an echo, improves the offset performance of a system, largely reduces the calculation amount of a self-adaptation offset algorithm under wideband signals, and has a high convergence rate and good tracking capacity when an antenna carries out scanning work.

Description

The inhibition method that a kind of direct wave and multipath thereof disturb

Technical field

The present invention relates to the inhibition method that a kind of direct wave and multipath thereof disturb, this method adopts sub-band adaptive RLS to add the method for NLMS filtering, belong to the radar target acquisition technical field, be particularly related to when utilizing digital television signal as irradiation source, external radiation source radar system direct wave and multipath thereof disturb the method that suppresses.

Background technology

External radiation source radar itself does not transmit, but the civilian broadcasting equipment (TV, broadcasting etc.) that utilization extensively distributes is irradiation source, handle by the electromagnetic signal of the receiving target reflection line correlation of going forward side by side, realize detection and location to target, its system configuration as shown in Figure 1.The echo antenna is except the signal that receives the target reflection, direct wave and multipath thereof disturb and also will enter from its secondary lobe and main lobe, the power of these undesired signals generally is higher than more than the target echo signal power 30dB, if these interference are not suppressed, just can't detect target.Therefore a key issue that realizes external radiation source radar system detection performance is exactly that the direct wave and the multipath thereof that suppress in the echo channel disturb.

Adaptive cancellation is to disturb a kind of effective ways that suppress, and adaptive cancellation algorithm commonly used has normalization minimum mean-square (NLMS) wave filter, recursive least-squares (RLS) wave filter etc. in the radar of external radiation source.Its characteristics are more as shown in table 1, and N is filter order in the table.

Table 1NLMS and RLS wave filter characteristics are relatively

During antenna scanning, direct wave and multipath thereof disturb fluctuations very big, do not satisfy smooth conditions, and the NLMS performance of filter will descend this moment; Simultaneously because the broader bandwidth (7.56MHz) of digital television signal, same clutter is apart from the filter order of needs very high (filter order is about 2000), therefore adopt RLS algorithm operation quantity huge (with square being directly proportional of filter order, as shown in table 1), be difficult to real-time implementation.

In addition, the cancellation performance of external radiation source radar system is directly proportional with the frequency invariance of direct wave, two passages of echo, and the more good then cancellation performance of consistance is more high.Under the narrower situation of emitter Signals bandwidth, less than 200KHz, the frequency characteristic consistance of echo receiving antenna and direct wave receiving antenna is better as the fm broadcast signal bandwidth outside; And outside under the emitter Signals broader bandwidth situation, be 7.56MHz as digital TV signal bandwidth, the frequency characteristic consistance variation of echo receiving antenna and direct wave receiving antenna is shown in Fig. 2 (a) and (b), have a strong impact on cancellation performance, need take corresponding signal treatment measures.

Summary of the invention

The objective of the invention is in order to propose the inhibition method that a kind of direct wave and multipath thereof disturb, be applicable to Digital Television external radiation source radar, the purpose of this method is in order to solve under the broadband signal, and direct wave passage, echo channel frequency characteristic consistance variation influence the problem of cancellation performance; And under the broadband signal, high-order sef-adapting filter operand is big, in real time the problem of difficult treatment.

The objective of the invention is to be achieved through the following technical solutions.

The inhibition method that a kind of direct wave of the present invention and multipath thereof disturb, the filtering method that this method adopts the RLS algorithm to combine with the NLMS algorithm in each subband, concrete steps are:

1) sub-band division

Direct wave, echoed signal are decomposed into L subband by analysis filterbank respectively, and relevant mathematical description is as follows:

(1) formula is to be the mathematic(al) representation of L subband with the direct wave signal decomposition; (2) formula is the mathematic(al) representation that target echo signal is decomposed into L subband; (3) formula is the mathematical description of sub-band division bank of filters:

x _m(n)=x(n)*h _m(n) （1）

d _m(n)=d(n)*h _m(n) （2）

h _m(n)=h(n)e ^-j2πmn/M （3）

M=0 in the formula, 1 ..., L-1; The prototype filter that h (n) adopts for the sub-band division wave filter;

2) signal of each subband respectively by RLS in conjunction with NLMS filtering

Under the antenna scanning situation, the method that adopts RLS to be combined with NLMS is established the direct wave signal vector that the signal of m subband carries out after M doubly extracts and is

X _m(n)=[x _m(Mn) x _m(M(n-1)) … x _m(M(n-M+1))] ^T

The filter coefficient update formula is as follows:

$w(n-1)={\left[\begin{array}{cc}{w}_{\mathrm{RLS}}^T(n-1)& w_{\mathrm{NLMS}}^T(n-1)\end{array}\right]}^T---\left(4\right)$

In (4) formula,

$w_{\mathrm{RLS}}\left(n\right)=w_{\mathrm{RLS}}(n-1)+k\left(n\right)e_m^{*}\left(\mathrm{Mn}\right)---\left(5\right)$

$w_{\mathrm{NLMS}}\left(n\right)=w_{\mathrm{NLMS}}(n-1)+\mathrm{\μ}\frac{e_m^{*}\left(\mathrm{Mn}\right)X_m\left(n\right)}{\mathrm{\δ}+{X_m}^H\left(n\right)X_m\left(n\right)}---\left(6\right)$

In (5), (6) formula,

e _m(Mn)=d _m(Mn)-w ^H(n-1)X _m(Mn) （7）

$k\left(n\right)=\frac{{\mathrm{\λ}}^{-1}P(n-1)X_m\left(n\right)}{1+{\mathrm{\λ}}^{-1}{X_m}^H\left(n\right)P(n-1)X_m\left(n\right)}---\left(8\right)$

P(n)=λ ^-1P(n-1)-λ ^-1k(n)X _m ^H(n)P(n-1) （9）

3) subband is comprehensive

The signal cancellation result of each subband is carried out interpolation, and by the synthetic final output signal of sub-band synthesis filter, its mathematical description is shown in (10) formula then; (11) formula is the mathematic(al) representation of sub-band synthesis filter:

$y\left(n\right)=\underset{m=0}{\overset{M-1}{\mathrm{\Σ}}}{f}_m\left(n\right)\⊗e_m\left(n\right)---\left(10\right)$

f _m(n)=f(n)e ^j2πmn/M，m=0,1,…,L-1 （11）

F in the formula _m(n) be m synthesis filter coefficient, f=[f (0) ..., f (N-1)] ^TPrototype filter for the sub-band synthesis filter that adopts;

X (n): direct wave signal;

D (n): echoed signal;

h _m(n): m Subband Analysis Filter;

x _m(n): the signal of m the subband that direct wave signal process sub-band division obtains;

x _m(Mn): x _m(n) take out the signal that M doubly obtains under;

d _m(n): the signal of m the subband that echoed signal process sub-band division obtains;

d _m(Mn): d _m(n) take out the signal that M doubly obtains under;

W (n): RLS+NLMS filter coefficient;

w _RLS(n): the RLS filter coefficient;

w _NLMS(n): the NLMS filter coefficient;

e _m(Mn): m subband offset the result;

e _m(n): e _m(Mn) result that obtains after doubly of interpolation M;

λ: the forgetting factor of RLS wave filter;

K (n): time-varying gain vector in the RLS algorithm;

P (n): the intermediate variable that calculates k (n) in the RLS algorithm

δ: little positive constant, prevent that division from overflowing, δ gets 0.001 here;

μ: the renewal step-length of NLMS algorithm;

f _m(n): m sub-band synthesis filter;

Y (n): offset the back output signal;

M: extract down and the interpolation multiple.

Beneficial effect

1) improves the consistance of frequency characteristic between direct wave and echo channel, improved the cancellation performance of system;

2) greatly reduce the operand of adaptive cancellation algorithm under the broadband signal, when antenna scanning is worked, have speed of convergence and tracking power faster preferably.

Description of drawings

Fig. 1 is external radiation source radar system configuration schematic diagram;

Fig. 2 is that the consistent type of passage improves synoptic diagram after the deterioration of wideband scenarios lower channel consistance and the sub-band division;

Fig. 3 is the synoptic diagram of inhibition method of the present invention;

Fig. 4 is RLS+NLMS filtering algorithm structured flowchart;

Fig. 5 is that RLS, subband RLS+NLMS algorithm cancellation performance compare;

Fig. 6 is that RLS, subband RLS+NLMS algorithm operation quantity compare.

Embodiment

Below in conjunction with accompanying drawing and the experiment analysis of data collected the present invention will be further described.

The inhibition method that a kind of direct wave and multipath thereof disturb, the filtering method that this method adopts the RLS algorithm to combine with the NLMS algorithm in each subband, as shown in Figure 3, concrete steps are:

1) sub-band division

Direct wave, echoed signal are decomposed into L subband by analysis filterbank respectively, and (L can be 8,16,32,64,, concrete condition is chosen as required) because each subband narrow bandwidth, therefore the frequency characteristic consistance between direct wave passage and echo channel improves, shown in Fig. 2 (c), (d); Simultaneously each subband is carried out M and doubly extract down, the exponent number that offsets that each subband is required so just is reduced to original 1/M, has reduced the operand of adaptive cancellation;

Relevant mathematical description is as follows, and (1) formula is to be the mathematic(al) representation of L subband with the direct wave signal decomposition; (2) formula is the mathematic(al) representation that target echo signal is decomposed into L subband; (3) formula is the mathematical description of sub-band division bank of filters

x _m(n)=x(n)*h _m(n) （1）

d _m(n)=d(n)*h _m(n) （2）

h _m(n)=h(n)e ^-j2πmn/M （3）

M=0 in the formula, 1 ..., L-1; The prototype filter that h (n) adopts for the sub-band division wave filter;

2) signal of each subband respectively by RLS in conjunction with NLMS filtering

Under the antenna scanning situation, offset and adopt RLS algorithm performance the best, though take out through under the sub-band division, but the operand of RLS algorithm is still very big, at this moment can adopt method that RLS is combined with NLMS as shown in Figure 4, because direct wave and noise jamming nearby are more intense, so employing RLS wave filter is to reach the reasonable effect that offsets, and a little less than the noise jamming relatively at a distance, can adopt the smaller NLMS wave filter of operand or variable step NLMS wave filter.With both combinations, obtain a kind of new adaptive cancellation wave filter, the method for preceding a part of coefficients by using RLS is upgraded, and then the method for a part of coefficients by using NLMS or variable step NLMS is upgraded.When satisfying very fast speed of convergence and tracking power, reduce operand, establish the direct wave signal vector that the signal of m subband carries out after M doubly extracts and be

X _m(n)=[x _m(Mn) x _m(M(n-1)) … x _m(M(n-M+1))] ^T

The filter coefficient update formula is as follows:

$w(n-1)={\left[\begin{array}{cc}{w}_{\mathrm{RLS}}^T(n-1)& w_{\mathrm{NLMS}}^T(n-1)\end{array}\right]}^T---\left(4\right)$

In (4) formula,

$w_{\mathrm{RLS}}\left(n\right)=w_{\mathrm{RLS}}(n-1)+k\left(n\right)e_m^{*}\left(\mathrm{Mn}\right)---\left(5\right)$

$w_{\mathrm{NLMS}}\left(n\right)=w_{\mathrm{NLMS}}(n-1)+\mathrm{\μ}\frac{e_m^{*}\left(\mathrm{Mn}\right)X_m\left(n\right)}{\mathrm{\δ}+{X_m}^H\left(n\right)X_m\left(n\right)}---\left(6\right)$

In (5), (6) formula,

e _m(Mn)=d _m(Mn)-w ^H(n-1)X _m(Mn) （7）

$k\left(n\right)=\frac{{\mathrm{\λ}}^{-1}P(n-1)X_m\left(n\right)}{1+{\mathrm{\λ}}^{-1}{X_m}^H\left(n\right)P(n-1)X_m\left(n\right)}---\left(8\right)$

P(n)=λ ^-1P(n-1)-λ ^-1k(n)X _m ^H(n)P(n-1) （9）

3) subband is comprehensive

The signal cancellation result of each subband is carried out interpolation, and by the synthetic final output signal of sub-band synthesis filter, its mathematical description is shown in (10) formula then.(11) formula is the mathematic(al) representation of sub-band synthesis filter.

$y\left(n\right)=\underset{m=0}{\overset{M-1}{\mathrm{\Σ}}}{f}_m\left(n\right)\⊗e_m\left(n\right)---\left(10\right)$

f _m(n)=f(n)e ^j2πmn/M，m=0,1,…,L-1 （11）

F in the formula _m(n) be m synthesis filter coefficient, f=[f (0) ..., f (N-1)] ^TPrototype filter for the sub-band synthesis filter that adopts;

X (n): direct wave signal;

D (n): echoed signal;

h _m(n): m Subband Analysis Filter;

x _m(n): the signal of m the subband that direct wave signal process sub-band division obtains;

x _m(Mn): x _m(n) take out the signal that M doubly obtains under;

d _m(n): the signal of m the subband that echoed signal process sub-band division obtains;

d _m(Mn): d _m(n) take out the signal that M doubly obtains under;

W (n): RLS+NLMS filter coefficient;

w _RLS(n): the RLS filter coefficient;

w _NLMS(n): the NLMS filter coefficient;

e _m(Mn): m subband offset the result;

e _m(n): e _m(Mn) result that obtains after doubly of interpolation M;

λ: the forgetting factor of RLS wave filter;

K (n): time-varying gain vector in the RLS algorithm;

P (n): the intermediate variable that calculates k (n) in the RLS algorithm

δ: little positive constant, prevent that division from overflowing, δ gets 0.001 here;

μ: the renewal step-length of NLMS algorithm;

f _m(n): m sub-band synthesis filter;

Y (n): offset the back output signal;

M: extract down and the interpolation multiple.

Embodiment

Adopt digital television signal, its radiation source radar system configuration schematic diagram as shown in Figure 1, the cell site is non-cooperation irradiation source (external radiation source), there are two receiving antennas in receiving station, a direct wave antenna direction radiation source receives the signal of its emission, and another echo receiving antenna points to the signal of searching sector receiving target reflection.The echo receiving antenna is when receiving the moving target reflection echo, its secondary lobe also receives the tetanic wave interference that reaches that directly launches from the external radiation source, also has the multipath that is caused by scatterings such as the external radiation source transmit through a plurality of high-lager buildings, mountain range that enters from main lobe to disturb in addition.

Adopt digital television signal, bandwidth 7.56MHz, base band data sampling rate 9MHz:

1) sub-band division

The sub band number that sub-band division adopts is L=128, the sub-filter exponent number is 1024, and the bandwidth of then decomposing each subband signal of back is 1/128 of original signal, then each subband signal is descended to extract, following extracting multiple is M=128, and data transfer rate becomes 1/128 of raw data.

2) each subband is done RLS+NLMS filtering

Direct wave, each corresponding subband of echoed signal are done respectively and offseted processing, and after the following extraction, each subband RLS filter order is 2 rank, and NLMS filter order 16 rank have reduced operand greatly.

3) subband is comprehensive

128 times of reduction of each subband output signal elder generation interpolation original data rate is finally exported by the sub-band synthesis filter group and is offseted the result.

As shown in Figure 5, adopt the RLS algorithm, system offsets gain (input signal energy before offseting/output signal energy after offseting) and is 35.0818dB, adopts subband RLS+NLMS filtering algorithm to offset gain and is 39.0306dB, than the about 4dB of RLS algorithm raising; And filter order is that 1024 o'clock subband RLS+NLMS algorithms reduce about 9 times than RLS algorithm operation quantity as can be seen from Figure 6, and filter order is to reduce about 37 times at 2048 o'clock.Therefore adopt subband RLS+NLMS algorithm not only to improve and offset gain, and can reduce operand greatly.

Method of the present invention has improved the consistance of frequency characteristic between direct wave and echo channel, has improved the cancellation performance of system, as shown in Figure 5; And greatly reduce the operand of adaptive cancellation algorithm under the broadband signal, as shown in Figure 6, when antenna scanning is worked, have speed of convergence and tracking power faster preferably.

Above-described specific descriptions; the above is specific embodiments of the invention only, and is not intended to limit the scope of the invention, and is within the spirit and principles in the present invention all; any modification of making, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (1)

1. the inhibition method disturbed of a direct wave and multipath thereof is characterized in that: the filtering method that this method adopts the RLS algorithm to combine with the NLMS algorithm in each subband, and concrete steps are:

1) sub-band division

Direct wave, echoed signal are decomposed into L subband by analysis filterbank respectively, and relevant mathematical description is as follows:

(1) formula is to be the mathematic(al) representation of L subband with the direct wave signal decomposition; (2) formula is the mathematic(al) representation that target echo signal is decomposed into L subband; (3) formula is the mathematical description of sub-band division bank of filters:

x _m(n)=x(n)*h _m(n) （1）

d _m(n)=d(n)*h _m(n) （2）

h _m(n)=h(n)e ^-j2πmn/M （3）

M=0 in the formula, 1 ..., L-1; The prototype filter that h (n) adopts for the sub-band division wave filter;

2) signal of each subband respectively by RLS in conjunction with NLMS filtering

Under the antenna scanning situation, the method that adopts RLS to be combined with NLMS is established the direct wave signal vector that the signal of m subband carries out after M doubly extracts and is

X _m(n)=[x _m(Mn) x _m(M(n-1)) … x _m(M(n-M+1))] ^T

The filter coefficient update formula is as follows:

$w(n-1)={\left[\begin{array}{cc}{w}_{\mathrm{RLS}}^T(n-1)& w_{\mathrm{NLMS}}^T(n-1)\end{array}\right]}^T---\left(4\right)$

In (4) formula,

$w_{\mathrm{RLS}}\left(n\right)=w_{\mathrm{RLS}}(n-1)+k\left(n\right)e_m^{*}\left(\mathrm{Mn}\right)---\left(5\right)$

$w_{\mathrm{NLMS}}\left(n\right)=w_{\mathrm{NLMS}}(n-1)+\mathrm{\μ}\frac{e_m^{*}\left(\mathrm{Mn}\right)X_m\left(n\right)}{\mathrm{\δ}+{X_m}^H\left(n\right)X_m\left(n\right)}---\left(6\right)$

In (5), (6) formula,

e _m(Mn)=d _m(Mn)-w ^H(n-1)X _m(Mn) （7）

$k\left(n\right)=\frac{{\mathrm{\λ}}^{-1}P(n-1)X_m\left(n\right)}{1+{\mathrm{\λ}}^{-1}{X_m}^H\left(n\right)P(n-1)X_m\left(n\right)}---\left(8\right)$

P(n)=λ ^-1P(n-1)-λ ^-1k(n)X _m ^H(n)P(n-1) （9）

3) subband is comprehensive

The signal cancellation result of each subband is carried out interpolation, and by the synthetic final output signal of sub-band synthesis filter, its mathematical description is shown in (10) formula then; (11) formula is the mathematic(al) representation of sub-band synthesis filter:

$y\left(n\right)=\underset{m=0}{\overset{M-1}{\mathrm{\Σ}}}{f}_m\left(n\right)\⊗e_m\left(n\right)---\left(10\right)$

f _m(n)=f(n)e ^j2πmn/M，m=0,1,…,L-1 （11）

F in the formula _m(n) be m synthesis filter coefficient, f=[f (0) ..., f (N-1)] ^TPrototype filter for the sub-band synthesis filter that adopts;

X (n): direct wave signal;

D (n): echoed signal;

h _m(n): m Subband Analysis Filter;

x _m(n): the signal of m the subband that direct wave signal process sub-band division obtains;

x _m(Mn): x _m(n) take out the signal that M doubly obtains under;

d _m(n): the signal of m the subband that echoed signal process sub-band division obtains;

d _m(Mn): d _m(n) take out the signal that M doubly obtains under;

W (n): RLS+NLMS filter coefficient;

w _RLS(n): the RLS filter coefficient;

w _NLMS(n): the NLMS filter coefficient;

e _m(Mn): m subband offset the result;

e _m(n): e _m(Mn) result that obtains after doubly of interpolation M;

λ: the forgetting factor of RLS wave filter;

K (n): time-varying gain vector in the RLS algorithm;

P (n): the intermediate variable that calculates k (n) in the RLS algorithm

δ: little positive constant, prevent that division from overflowing, δ gets 0.001 here;

μ: the renewal step-length of NLMS algorithm;

f _m(n): m sub-band synthesis filter;

Y (n): offset the back output signal;

M: extract down and the interpolation multiple.

Images