CN103607363A - Blind estimation method of signal to noise ratio - Google Patents

Abstract

The invention discloses a blind estimation method of signal to noise ratio. The method comprises the steps that Hilbert transform is carried out on received original band pass signals to obtain corresponding duplexing baseband signals; lowpass filtering is carried out on the duplexing baseband signals through the preset bandwidth to obtain corresponding band limited signals; M times of upsampling and N times of downsampling are carried out on the band limited signals in sequence, and then the signal to noise ratio is estimated through the singular value decomposition algorithm. The blind estimation method improves stability and accuracy of estimation of the signal to noise ratio, and the application range of the method is widened.

Description

The method of the blind estimation of a kind of signal to noise ratio

Technical field

The present invention relates to wireless technical field, relate in particular to the method for the blind estimation of a kind of signal to noise ratio.

Background technology

Signal to noise ratio is a key character parameter of modulation signal, and estimated snr is controlled significant for the adaptive power of understanding in the characteristic of channel and communication exactly.

All the time, forefathers have proposed a lot of effectively signal-to-noise ratio estimation algorithms, be broadly divided into blind estimation and non-blind estimation, such as maximal possibility estimation, SSME(segmentation symbol square are estimated), SNV(square signal to noise ratio variance ratio estimates), Eigenvalues Decomposition method etc.But use these algorithms often to have a lot of constraints, the especially non-blind estimation based on priori, has limited the range of application of algorithm greatly.

In many practical application scenes, during signal-to-noise ratio (SNR) estimation, lack the prior information of signal, must carry out blind estimation.Eigenvalues Decomposition method is exactly the Typical Representative of Algorithm for Blind Estimation of SNR, and its estimated accuracy, apparently higher than other algorithms, still requires noise should within the scope of whole frequency domain, keep smooth power spectral density.But in actual satellite communication system, modulation signal is often without molding filtration, just before receiver front end digitlization, passed through a band pass filter, because band-pass filtering property is undesirable, actual sample frequency and band pass filter bandwidth is not integral multiple relation conventionally simultaneously, cause the noise after sampling no longer to have white power spectrum characteristic, now Eigenvalues Decomposition method cannot be proved effective.

Summary of the invention

The method that the object of this invention is to provide the blind estimation of a kind of signal to noise ratio, has improved stability and accuracy, has expanded the scope of application.

The object of the invention is to be achieved through the following technical solutions:

A method for the blind estimation of signal to noise ratio, the method comprises:

The grandfather tape messenger receiving is carried out to Hilbert transform, obtain corresponding complex baseband signal;

Utilize predetermined bandwidth to carry out low-pass filtering to described complex baseband signal, obtain corresponding band-limited signal;

Described band-limited signal is carried out after M times of up-sampling and N times of down-sampling successively, adopt singular value decomposition algorithm estimated snr.

As seen from the above technical solution provided by the invention, by signal being carried out to multiple baseband conversion, low-pass filtering and the conversion of upper down-sampling, realized the albefaction completing noise component(s) processed before signal-to-noise ratio (SNR) estimation.By above-mentioned processing, improved robustness and the accuracy of singular value decomposition algorithm, expanded the scope of application of this algorithm.

Accompanying drawing explanation

In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, below the accompanying drawing of required use during embodiment is described is briefly described, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, do not paying under the prerequisite of creative work, can also obtain other accompanying drawings according to these accompanying drawings.

The schematic diagram of a kind of BPSK modulating system that Fig. 1 provides for the embodiment of the present invention one;

The flow chart of the method for the blind estimation of a kind of signal to noise ratio that Fig. 2 provides for the embodiment of the present invention one;

The curve synoptic diagram that utilizes the signal-to-noise ratio (SNR) estimation average that the inventive method obtains that Fig. 3 provides for the embodiment of the present invention one;

The curve synoptic diagram that utilizes the signal to noise ratio relative error that the inventive method obtains that Fig. 4 provides for the embodiment of the present invention one;

The curve synoptic diagram of the signal-to-noise ratio (SNR) estimation average that the method for utilizing prior art that Fig. 5 provides for the embodiment of the present invention one obtains;

The curve synoptic diagram of the signal to noise ratio relative error that the method for utilizing prior art that Fig. 6 provides for the embodiment of the present invention one obtains.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, rather than whole embodiment.Based on embodiments of the invention, those of ordinary skills, not making the every other embodiment obtaining under creative work prerequisite, belong to protection scope of the present invention.

Embodiment mono-

The schematic diagram of a kind of digital signal modulation mode that Fig. 1 provides for the embodiment of the present invention, be illustrated as BPSK(two-phase PSK) modulation, under actual conditions, also can adopt other digital modulation mode, for example, QPSK(Quadrature Phase Shift Keying), 8PSK(eight phase phase shift keyings) etc.

The flow chart of the method that Fig. 2 is the blind estimation of a kind of signal to noise ratio that provides for the embodiment of the present invention one.As shown in Figure 2, the method mainly comprises the steps:

Step 21, the grandfather tape messenger receiving is carried out to Hilbert transform, obtain corresponding complex baseband signal.

In the embodiment of the present invention, can adopt following formula to calculate:

$r_L\left(n\right)=\mathrm{hilbert}\left(r\left(n\right)\right)\&CenterDot;e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000429797800000021.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_{c}n/f_s};$

Wherein, r _l(n) complex baseband signal for obtaining, the grandfather tape messenger of r (n) for receiving, f _sfor sample frequency, hibert represents Hilbert transform, f _cfor signal carrier frequency, the sequence number of the grandfather tape messenger that n receives described in being, j is imaginary unit.

Step 22, utilize predetermined bandwidth to carry out low-pass filtering to described complex baseband signal, obtain corresponding band-limited signal.

In the embodiment of the present invention, adopt the low pass filter of a high-order to be with limit filtering to complex baseband signal, its exponent number should guarantee that the transition band of filter is enough narrow, can be approximately ideal low-pass filter.

The bandwidth W of low pass filter should, a little less than 1/2nd of former band pass filter bandwidth, keep integer ratio relation with 1/2nd of sample frequency, simultaneously

m and N are positive integer, concrete value can be according to the actual requirements or experience determine.

Step 23, described band-limited signal is carried out after M times of up-sampling and N times of down-sampling successively, adopt singular value decomposition algorithm estimated snr.

By the band-limited signal obtaining after filtering, first carry out M times of up-sampling, then carry out N times of down-sampling; Its objective is in order to be full of whole frequency range meeting the signal spectrum making under the prerequisite of Nyquist's theorem after conversion, now by realizing, the albefaction of noise in whole frequency range is processed.

Then, this signal is carried out to autocorrelation matrix singular value decomposition estimated snr.

On the other hand, in order to further illustrate technical scheme of the present invention, have good accuracy and reliability, the technical scheme based on the embodiment of the present invention has been carried out emulation experiment below, and design parameter is as shown in table 1.

System parameters	Value
		Signal carrier frequency	15MHz
Sample frequency	60MHz
		Character rate	3M?Baud
Modulation system	BPSK/QPSK/8PSK
		Signal to noise ratio scope	[0dB,40dB]
Band pass filter bandwidth	22MHz
		Sampling multiple M/N	1/3
Low pass filter bandwidth	10MHz
		Autocorrelation matrix dimension	300
Cycle-index	100

Table 1 emulation experiment parameter list

In this emulation experiment, setting signal source is random 0,1 sequence producing, and noise is white Gaussian noise, and low pass filter is selected chebyII(Chebyshev II) type, exponent number is 20 rank, stopband attenuation is 50dB.

In emulation experiment, [0,40] within the scope of dB, selecting stepping is 2.5, for each signal to noise ratio (snr), carry out respectively 100 independently emulation, calculate estimation average and the relative error average of these 100 simulation results, by the performance of the inventive method with do not have the estimated performance before albefaction to make comparisons, draw corresponding curve and observe.

Its result is as shown in Fig. 3-Fig. 6, and wherein, Fig. 3-Fig. 4 is respectively signal-to-noise ratio (SNR) estimation average and the relative error curve that adopts method of the present invention to obtain; Fig. 5-Fig. 6 is respectively signal-to-noise ratio (SNR) estimation average and the relative error curve that adopts the method acquisition of not carrying out albefaction processing in prior art.Simulation result shows, in [0,30] dB in a big way, for various modulation systems, the improved method signal-to-noise ratio (SNR) estimation of the present invention value is comparatively accurate, and error is less than 2dB, and in [0,20] dB, error is less than 1dB, has good accuracy and reliability; Review and do not do the performance that albefaction is processed, a thousand li of estimated value and actual value difference, mistake completely, the reason that causes this result be exactly noise be not albefaction.

Through the above description of the embodiments, those skilled in the art can be well understood to above-described embodiment and can realize by software, and the mode that also can add necessary general hardware platform by software realizes.Understanding based on such, the technical scheme of above-described embodiment can embody with the form of software product, it (can be CD-ROM that this software product can be stored in a non-volatile memory medium, USB flash disk, portable hard drive etc.) in, comprise some instructions with so that computer equipment (can be personal computer, server, or the network equipment etc.) carry out the method described in each embodiment of the present invention.

The above; be only the present invention's embodiment preferably, but protection scope of the present invention is not limited to this, is anyly familiar with in technical scope that those skilled in the art disclose in the present invention; the variation that can expect easily or replacement, within all should being encompassed in protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.

Claims (3)

1. a method for the blind estimation of signal to noise ratio, is characterized in that, the method comprises:

The grandfather tape messenger receiving is carried out to Hilbert transform, obtain corresponding complex baseband signal;

Utilize predetermined bandwidth to carry out low-pass filtering to described complex baseband signal, obtain corresponding band-limited signal;

Described band-limited signal is carried out after M times of up-sampling and N times of down-sampling successively, adopt singular value decomposition algorithm estimated snr.

2. method according to claim 1, is characterized in that, the described formula that carries out to the received signal Hilbert transform is:

$r_L\left(n\right)=\mathrm{hilbert}\left(r\left(n\right)\right)\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{c}n/f_s};$

Wherein, r _l(n) complex baseband signal for obtaining, the grandfather tape messenger of r (n) for receiving, f _sfor sample frequency, hibert represents Hilbert transform, f _cfor signal carrier frequency, the sequence number of the grandfather tape messenger that n receives described in being, j is imaginary unit.

3. method according to claim 1, is characterized in that, the predetermined bandwidth of described utilization is carried out low-pass filtering to described complex baseband signal and comprised:

The bandwidth W of described low pass filter is:

$W=\frac{M\&CenterDot;f_s}{2N}.$

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