CN101895491A - Self-adapting signal detecting method for eliminating frequency offset interference - Google Patents

Abstract

The invention discloses a self-adapting signal detecting method for eliminating frequency offset interference, which comprises the following steps of: S1 adding a pseudo-random code into a frame head of a data frame as a lead code by a sending end, and sending the sampled data frame; S2 multiplying the received data frame by delay thereof in a conjugating way by a receiving end after receiving the data frame to obtain the received signal which eliminates the frequency offset; S3 dividing the received signal into two same signals, respectively computing a statistical decision quantity and setting a self-adapting threshold; and S4 comparing the magnitude of the statistical decision quantity with the magnitude of the self-adapting threshold, and outputting an identification signal which indicates that an effective signal is detected if the statistical decision quantity is larger than the self-adapting threshold. The method eliminates the frequency offset generated during signal transmission by means of conjugate multiplication, reduces the computation quantity, improves the computation speed, improves the detecting precision of the signal, and is stable in performance, simple in structure, and easy in realization.

Description

Eliminate the self-adapting signal detecting method of frequency offset interference

Technical field

The present invention relates to a kind of signal detecting method in burst communication field, specifically, is a kind of self-adapting signal detecting method of eliminating frequency offset interference.

Background technology

Under the burst mode of radio communication, receiver must have reliable input could guarantee to recover exactly the data of transmission.But in the wireless communications environment of reality, because carrier frequency shift that the error of the crystal oscillator of transceiver itself is brought or the Doppler frequency shift that in high-speed mobile environment, produces, will disturb the correlated performance of pseudo random sequence, influence input.Frequency shift (FS) is big more, and correlation peak is more little, and under the bigger situation of frequency shift (FS), the auto-correlation peak value of pseudo random sequence will be submerged, and tangible peak value can not occur, and influence detects performance.In order to guarantee to detect performance, must take the detection scheme of anti-frequency deviation measure.

At present, the signal detecting method of the antagonism frequency offset interference that adopts has PMF-FFT (Partial Matched Filtering-Fast Fourier Transform, fast fourier transform method based on the part matched filtering), frequency compensation method and segmented matched filter method.Wherein, be based on all based on the FFT converter technique of part matched filtering and frequency compensation method that the FFT conversion carries out, the inherent limitation on the FFT property makes above-mentioned two kinds of methods all exist compensate of frequency deviation not exclusively and the big problem of amount of calculation.And the segmented matched filter method is that cost is resisted frequency deviation with the loss signal to noise ratio, and the increase that its Y-PSNR loses with the frequency deviation tolerance increases the weight of.Therefore, the performance of the signal detecting method of elimination frequency offset interference is in urgent need to be improved.

Summary of the invention

At the deficiencies in the prior art, the purpose of this invention is to provide the self-adapting signal detecting method of the little elimination frequency offset interference of a kind of amount of calculation.

To achieve these goals, the invention provides a kind of self-adapting signal detecting method of eliminating frequency offset interference, may further comprise the steps: the S1. transmitting terminal is at initial data frame S _d(m) frame head adds pseudo noise code PN (m) as lead code, makes Frame be

With Frame S (m) carry out the D sampling obtain sampling the back Frame be

Send sampling back Frame S (n); S2. receiving terminal receives receiving data frames r (n)=S (n-θ) e of sampling back Frame S (n) ^{J2 π nfT}Behind+the w (n), wherein, f is frequency shift (FS), comprise carrier frequency shift and Doppler frequency shift, T is the employing cycle, w (n) is a white Gaussian noise, and θ is a transmission delay, receiving data frames r (n) and receiving data frames r (n) is postponed the as a result r (n+D) of data after the cycle carry out be eliminated received signal R (n)=r (n) * r after the frequency offset interference of conjugate multiplication ^*(n+D); The received signal R (n) that S3. will eliminate after the frequency offset interference is divided into two same signals, wherein one the tunnel utilizes coupling correlation computations statistical decision amount u (m), and another road signal calculated power also utilizes the invariable false alerting criterion to set adaptive threshold V _TS4. comparative statistics judgement amount u (m) and adaptive threshold V _TSize, if statistical decision amount u (m) is greater than adaptive threshold V _T, then the output expression detects the marking signal of useful signal, continues to detect useful signal otherwise return step S2.

According to an aspect of the present invention, utilize coupling correlation computations statistical decision amount u (m) to be among the step S3

Wherein, R (mD) is the received signal after the elimination frequency offset interference, and N is the data total length of PN (m), and D is the number of samples of data in the cycle, and local pseudo noise code d (m) is d (m)=PN (m) PN (m+1).

According to another aspect of the present invention, adaptive threshold is set at V among the step S3 _T=CP, wherein, signal power

R (mD) is the received signal after the elimination frequency offset interference, and N is the total length of PN (m); Constant C=1-(P _Fa) ^{1/ (N-1)}, P _FaBe invariable false alerting.Set the accuracy that rational adaptive threshold can effectively improve input.

According to a further aspect of the invention, the self-adapting signal detecting method of this elimination frequency offset interference also is included in and adopts the judgement window that slides to come comparative statistics judgement amount u (m) and adaptive threshold V among the step S4 _TSize, satisfy u (m)＞V if be arranged in the statistical decision amount u (m) of the judgement window that slides _TAnd (during i ≠ m), then the output expression detects the marking signal of useful signal to u (m)＞u (i).Utilize the judgement window that slides to carry out the size judgement, only need the signal of window interior be detected, reduced amount of calculation, improved the accuracy of judgement.

According to a further aspect of the invention, the self-adapting signal detecting method of this elimination frequency offset interference also is included among the step S3 adaptive threshold V _TAdd offset V to constitute new adaptive threshold

The numerical value of suitably adjusting adaptive threshold can adapt to the variation of various channel circumstances, reduces the generation of false-alarm burr.

Compared with prior art, the invention has the beneficial effects as follows: the self-adapting signal detecting method of this elimination frequency offset interference utilizes conjugate multiplication to come the frequency deviation that produces in the erasure signal transmission course, reduce operand, improved arithmetic speed, adopted the judgement window that slides to compare judgement, improved precision of signal detection, and this method does not increase performance loss with the variation of frequency deviation size, can resist the frequency deviation of any size, stable performance, simple in structure, be easy to realize.

Description of drawings

The each side advantage that the present invention is above-mentioned can obviously and easily be understood from following accompanying drawing with to becoming the description of example, wherein:

Fig. 1 is the flow chart of the self-adapting signal detecting method of elimination frequency offset interference of the present invention;

Fig. 2 is the self-adapting signal detecting method of elimination frequency offset interference of the present invention adds lead code at transmitting terminal a principle schematic;

Fig. 3 is the receiving terminal circuit schematic diagram of the self-adapting signal detecting method of elimination frequency offset interference of the present invention;

Fig. 4 is the schematic diagram that window is adjudicated in the slip of the self-adapting signal detecting method of elimination frequency offset interference of the present invention.

Embodiment

Describe embodiments of the invention below in detail, the example of described embodiment is shown in the drawings, and wherein identical from start to finish or similar label is represented identical or similar device or the device with identical or similar functions.Below by the embodiment that is described with reference to the drawings is exemplary, only is used to explain the present invention, and can not be interpreted as limitation of the present invention.

Shown in Fig. 1 is the flow process that the present invention eliminates the self-adapting signal detecting method of frequency offset interference.This method may further comprise the steps:

S1. transmitting terminal is at initial data frame S _d(m) frame head adds PN (the Pseudo Noise of one group of N bit length, pseudo noise) sign indicating number is as lead code, shown in Fig. 2 is the principle of the self-adapting signal detecting method of elimination frequency offset interference of the present invention in transmitting terminal adding lead code, and the Frame after the adding lead code is

$S\left(m\right)=\left\{\begin{array}{cc}\mathrm{PN}\left(m\right)& m\∈[1,N]\\ S_d\left(m\right)& m>N\end{array}\right.---\left(1\right)$

Wherein, N is the data length of pseudo noise code PN (m), with Frame S (m) carry out the D sampling obtain sampling the back Frame be

$S\left(n\right)=\left\{\begin{array}{cc}\mathrm{PN}\left(n\right)& n\∈[1,N\·D]\\ S_d\left(n\right)& n>N\·D\end{array}\right.---\left(2\right)$

Transmitting terminal sends sampling back Frame S (n) then.

S2. after receiving terminal receives the receiving data frames r (n) of sampling back Frame S (n), receiving data frames r (n) and receiving data frames r (n) are postponed the r as a result (n+D) of data after the cycle carry out be eliminated received signal R (n) after the frequency offset interference of conjugate multiplication.The circuit theory of receiving terminal as shown in Figure 3.

Receiving data frames r (n) is

r(n)＝S(n-θ)e ^j2πnfT+w(n) (3)

Wherein, f is frequency shift (FS), comprises carrier frequency shift and Doppler frequency shift, and T is the employing cycle, and w (n) is a white Gaussian noise, and θ is a transmission delay.In eliminating the frequency offset interference module, mainly utilize the lead code part of receiving data frames r (n) and time-delay thereof to carry out conjugate multiplication and calculate received signal R (n) and be

R(n)＝r(n)×r ^*(n+D) (4)

＝[S(n-θ)e ^j2πnfT+w(n)]×[S(n-θ+D)e ^-j2π(n+D)fT+w(n+D)]

＝S(n-θ)S(n-θ+D)e ^-j2πDfT+W(n)

＝PN(n-θ)PN(n-θ+D)e ^-j2πDfT+W(n)n∈[1，N·D]

According to the shifter-adder characteristic of pseudo random sequence, wherein (n-θ+D) still is one and has identical feedback factor, the pseudo random sequence that initial phase is different with transmitting terminal PN sign indicating number result of calculation PN (n-θ) PN of lead code part.Among the following formula received signal R (n), lead code PN (n-θ) length is relatively shorter and only postponed a data cycle backward, therefore can be similar to and think that frequency offseting value f is a fixed value in this short time, so phase place 2 π DfT also are stationary phases, do not change with sampling point, W (n) represents noise.Therefore, R (n) just is expressed as a pseudo random sequence signal and a noise signal sum with fixed phase offsets.

The received signal R (n) that S3. will eliminate after the frequency offset interference is divided into two same signals, wherein one the tunnel utilizes coupling correlation computations statistical decision amount u (m), and another road signal calculated power also utilizes the invariable false alerting criterion to set adaptive threshold V _T

Among the step S3, one road signal enters the coupling correlation module, utilizes coupling correlation computations statistical decision amount u (m) to be

$u\left(m\right)={|\frac{1}{N}\underset{m=1}{\overset{N}{\mathrm{\Σ}}}R\left(\mathrm{mD}\right)\·d\left(m\right)|}^2---\left(5\right)$

Wherein, R (mD) is the received signal after the elimination frequency offset interference, and N is the data total length of PN (m), and D is the number of samples of data in the cycle, at the local pseudo random sequence d of receiving terminal (m) is d (m)=PN (m) PN (m+1), and the PN sign indicating number cyclic shift that is transmitting terminal obtains.During counting statistics judgement amount u (m), only need from each sampling period of received signal R (n), extract data on data and local pseudo noise code d (m) relevant position and multiply each other and get final product, reduce amount of calculation effectively.

Among the step S3, another road signal enters into extraction signal power module extraction signal power and is

Carry out the setting of adaptive threshold then according to signal power P, be specially

$V_T=\mathrm{CP}=\frac{1}{N}[1-{\left(P_{\mathrm{fa}}\right)}^{1/(N-1)}]\underset{m=1}{\overset{N}{\mathrm{\Σ}}}|R\left(\mathrm{mD}\right){|}^2---\left(6\right)$

Wherein, R (mD) is the received signal after the elimination frequency offset interference, and N is the total length of pseudo noise code PN (m); Constant C=1-(P _Fa) ^{1/ (N-1)}, P _FaBe invariable false alerting.Set the accuracy that rational adaptive threshold can effectively improve input.

S4. comparative statistics judgement amount u (m) and adaptive threshold V _TSize, if statistical decision amount u (m) is greater than adaptive threshold V _T, then the output expression detects the marking signal of useful signal, continues to detect useful signal otherwise return step S2.

In comparison judging module shown in Figure 3, compare statistical decision amount u (m) and adaptive threshold V _TBig or small the time, can adopt directly and adaptive threshold V all statistical decision amount u (m) _TCompare, if statistical decision amount u (m) is greater than adaptive threshold V _T, then show to detect match peak, export corresponding marking signal.But this kind judgement mode can not guarantee entirely accurate, because when signal is very little, and the adaptive threshold value V that calculates _TAlso very little, when small peak value occurring in the matching value, just may cause the false-alarm phenomenon.In order to guarantee the laser propagation effect of system; usually can adopt over-sampling; if the over-sampling multiple is D; then the correlation of Dui Ying received signal and local reference sequences has D; and they are all above threshold value; if carry out the synchronous of system according to wherein less sample value, will influence synchronous accuracy, thereby influence the performance of system.

As a kind of improvement, can adopt the judgement window that slides to come comparative statistics judgement amount u (m) and adaptive threshold V in the self-adapting signal detecting method of this elimination frequency offset interference _TSize, the principle of the judgement window that slides is as shown in Figure 4.The relevant statistical decision amount u (m) that obtains of coupling is pushed in the window of the judgement window that slides successively along with the clock cycle, each clock cycle compares the value in the window, have only when the window median greater than other each value and when surpassing the adaptive threshold value of correspondence, u (m)＞V promptly satisfies condition _TAnd u (m)＞u (i) is (during i ≠ m), then Shu Chu court verdict detects the marking signal of useful signal for expression, the expression received signal is really alignd with local pseudo random sequence, obtain the initial border of lead code more accurately, guaranteed the accuracy of input, so that carry out accurate system synchronization.Adopt after the judgement window that slides, only need utilize a bit of statistical decision amount u (m) in the window to participate in relatively, when having improved the judgement accuracy, also can reduce operand, improve arithmetic speed.

If adaptive threshold V _TToo small, just might occur the noise erroneous judgement is useful signal, thereby produce the false-alarm burr.In order to reduce the false-alarm burr, improve the correctness of judgement, the self-adapting signal detecting method of this elimination frequency offset interference also needs adaptive threshold V _TSuitably adjusting, particularly, is at adaptive threshold V _TA small offset V is to constitute new adaptive threshold in last interpolation

Then with new adaptive threshold

Be applied in the relatively judgement.The size of minor shifts amount Δ V is selected and the channel circumstance parameter, especially with channel gain much relations is arranged, and in emulation experiment, when channel gain was 1, minor shifts amount Δ V was set to 0.1 and has the good detection probability.Because statistical decision amount u (m) must be greater than new adaptive threshold

Be only correct capture point, effectively shielded the false-alarm burr.

To adaptive threshold V _TAfter suitably adjusting, can adopt direct and adaptive threshold with all statistical decision amount u (m)

The mode of comparing detects useful signal.Certainly as previously described, if adopt the judgement window that slides to come comparative statistics judgement amount u (m) and adaptive threshold

Big young pathbreaker reduce amount of calculation effectively and improve the accuracy of judgement.

The self-adapting signal detecting method of elimination frequency offset interference of the present invention has adopted the mode that is simple and easy to realize effectively to resist the frequency deviation of size arbitrarily, combining adaptive Threshold detection technology, guarantee in the system of burst communication, when having frequency offset interference, system still can effectively carry out input, guarantees to detect performance.The received signal R (n) that adopts conjugate multiplication to obtain has fixing phase deviation, can not have the advantage of accuracy of detection height and stable performance along with sampling point length increases and the increase calculation cost.

The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (5)

1. self-adapting signal detecting method of eliminating frequency offset interference is characterized in that may further comprise the steps:

S1. transmitting terminal is at initial data frame S _d(m) frame head adds pseudo noise code PN (m) as lead code, makes Frame be

With described Frame S (m) carry out the D sampling obtain sampling the back Frame be

Send described sampling back Frame S (n);

S2. receiving terminal receives receiving data frames r (n)=S (n-θ) e of described sampling back Frame S (n) ^{J2 π nfT}Behind+the w (n), wherein, f is frequency shift (FS), comprise carrier frequency shift and Doppler frequency shift, T is the employing cycle, w (n) is a white Gaussian noise, and θ is a transmission delay, described receiving data frames r (n) and described receiving data frames r (n) is postponed the as a result r (n+D) of data after the cycle carry out be eliminated received signal R (n)=r (n) * r after the frequency offset interference of conjugate multiplication ^*(n+D);

S3. the received signal R (n) after the described elimination frequency offset interference is divided into two same signals, wherein one the tunnel utilizes coupling correlation computations statistical decision amount u (m), another road signal calculated power also utilizes the invariable false alerting criterion to set adaptive threshold V _T

S4. more described statistical decision amount u (m) and described adaptive threshold V _TSize, if described statistical decision amount u (m) is greater than described adaptive threshold V _T, then the output expression detects the marking signal of useful signal, continues to detect useful signal otherwise return step S2.

2. according to the self-adapting signal detecting method of the described elimination frequency offset interference of claim 1, it is characterized in that: utilize coupling correlation computations statistical decision amount u (m) to be described in the step S3

Wherein, R (mD) is the received signal after the elimination frequency offset interference, and N is the data total length of PN (m), and D is the number of samples of data in the cycle, and local pseudo noise code d (m) is d (m)=PN (m) PN (m+1).

3. according to the self-adapting signal detecting method of the described elimination frequency offset interference of claim 1, it is characterized in that: adaptive threshold is set at V described in the step S3 _T=CP,

Wherein, signal power

R (mD) is the received signal after the elimination frequency offset interference, and N is the total length of PN (m); Constant C=1-(P _Fa) ^{1/ (N-1)}, P _FaBe invariable false alerting.

4. according to the self-adapting signal detecting method of the described elimination frequency offset interference of claim 3, it is characterized in that: also be included in and adopt the judgement window that slides to come more described statistical decision amount u (m) and described adaptive threshold V among the step S4 _TSize, satisfy u (m)＞V if be arranged in the statistical decision amount u (m) of described slip judgement window _TAnd (during i ≠ m), then the output expression detects the marking signal of useful signal to u (m)＞u (i).

5. according to the self-adapting signal detecting method of claim 3 or 4 described elimination frequency offset interference, it is characterized in that: also be included among the step S3 described adaptive threshold V _TAdd offset V to constitute new adaptive threshold

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