CN101083650A - Planisphere mapping based signal-noise ratio estimation method and apparatus in multi-carrier system - Google Patents

Abstract

The method includes steps: based on data information after channel equalization to carry out QAM mapping so as to obtain ideal position QAM_out of data information on planisphere; calculating first function value YH_QAM and second function value HH of the point on planisphere corresponding to the data information; first function includes factors of channel information, ideal position QAM_out, and data information before channel equalization; second function includes factor of channel information; first function and second function constitute distance of deviation Dist of the point related to the ideal position; accumulating first functions and second functions of corresponding points; using the accumulated first function value and second function value to calculate SNR.

Description

The signal-noise ratio estimation method and the device that shine upon based on planisphere in the multicarrier system

Technical field

The invention belongs to digital information transmission technical field, be specifically related in a kind of multi-carrier receiver system signal to noise ratio (snr) method of estimation and device based on the planisphere mapping.

Background technology

In the receiver of multicarrier system, often needing to utilize received signal to come the quality to the signal transmission is that signal to noise ratio (snr) is estimated.Traditional method of estimation mainly is divided into following two big classes:

1) utilize the useless subcarrier in the multicarrier frequency spectrum to estimate.

In multicarrier systems such as for example OFDM, for the effectively transmission of the useful subcarrier information of protection, transmitting terminal has inserted the protection subcarrier in the both sides of useful data frequency spectrum, and amplitude is 0; Can utilize the information of these useless subcarriers that receive to carry out SNR at receiving terminal estimates.The document of U.S. Patent number US6 4,566 53 B1 has provided the method for estimating SNR based on useless subcarrier.The estimated accuracy of the method depends on the annoyance level that is subjected to of the useless frequency spectrum of OFDM to a great extent.And this often is difficult under actual conditions guarantee that it is not subjected to the front end simulation or faces the interference of signal frequently.Therefore the precision of estimating can be subjected to restriction to a great extent.

2) utilize the data message of useful subcarrier on the multicarrier frequency spectrum to estimate.

A kind of method is to utilize the pilot frequency information that inserts in the frequency spectrum.Receiving terminal extracts pilot signal from frequency spectrum and the reference pilot value compares, and obtains the pilot tone difference.Utilize this difference just can estimate the SNR value of channel.The patent documentation of Chinese patent application publication number CN1753396A has provided the SNR method of estimation based on pilot tone.The method realizes fairly simple, could use but have only when having pilot signal in the frequency spectrum, and pilot number is generally fewer, and therefore the error ratio of estimating is bigger.

Another kind method is to use the data message in the frequency spectrum.The modulation signal that receives is carried out the judgement of maximum likelihood, the position that obtains transmitting.Then by relatively adjudicating the SNR value that back signal and received signal obtain channel.The patent documentation of U.S. Patent Application Publication No. US2006/0140312 A1 has provided the SNR method of estimation based on the OFDM data message.The method can realize the blind estimation to SNR, and estimated accuracy is than higher under channels such as AWGN.But can't guarantee have the accuracy that SNR estimates under the abominable channel such as multipath delay and Doppler frequency shift.

Summary of the invention

The object of the present invention is to provide a kind of SNR method of estimation of new multicarrier system, improve the SNR estimated accuracy and the channel scope of application greatly.

In order to achieve the above object, one aspect of the present invention provides the signal-noise ratio estimation method that shines upon based on planisphere in the multicarrier system, this method comprises: carry out the QAM mapping according to the data message after the channel equalization, obtain the ideal position of data message on planisphere; First functional value and second functional value of calculating channel balanced data information corresponding points on planisphere; The data message of first function before with channel information, ideal position and channel equalization is the factor, and second function is the factor with the channel information, and first function and second function constitute the offset distance of corresponding points relative ideal position; First functional value and second functional value to described corresponding points add up respectively; First functional value after utilization adds up and second functional value calculate signal to noise ratio.

The present invention provides in second aspect shines upon the device that carries out signal-to-noise ratio (SNR) estimation based on planisphere in the multicarrier system, and it comprises: the QAM mapping block, carry out the QAM mapping according to the data message after the channel equalization, and obtain the ideal position of data message on planisphere; The offset distance parameter calculating module, first functional value and second functional value of calculating channel balanced data information corresponding points on planisphere; The data message of first function before with channel information, ideal position and channel equalization is the factor, and second function is the factor with the channel information, and first function and second function constitute the offset distance of corresponding points relative ideal position; The accumulation process module adds up respectively to first functional value and second functional value of described corresponding points, utilizes first functional value and second functional value after adding up, calculates signal to noise ratio.

SNR of the present invention estimates to introduce the balanced preceding data message and the channel information of channel estimating, effectively reduced the influence of channel by corresponding computing, thereby can guarantee have the accuracy that SNR estimates under the abominable channel such as multipath delay and Doppler frequency shift estimated result.Simultaneously, the present invention can eliminate the division arithmetic that traditional SNR method of estimation need be used, and therefore, it is few to expend hardware resource, and hardware circuit implementation is simple.

Description of drawings

Below with reference to accompanying drawings specific embodiments of the present invention is described in detail, wherein:

Fig. 1 is a DVB-T receiving system flow chart according to an embodiment of the invention;

Fig. 2 is the mapping of the planisphere behind a hard decision schematic diagram under awgn channel;

Fig. 3 is the planisphere mapping schematic diagram behind hard decision under the Rayleigh channel.

Embodiment

Fig. 1 is a DVB-T receiving system flow chart according to an embodiment of the invention.

As shown in Figure 1, comprise that in the DVB-T of one embodiment of the present of invention receiving system RF down conversion module 1, Domain Synchronous module 2, OFDM demodulation module 3, channel equalization module 4, QAM separate mapping block 5, de-interleaving block 6, channel decoder 7, QAM mapping block 8, offset distance parameter calculating module 9, accumulation process module 10.

In the RF of DVB-T down conversion module 1 aerial signal is carried out down-conversion, obtain the intermediate frequency time-domain signal.Then, Domain Synchronous module 2 according to the protection of ofdm signal at interval characteristics obtain the time domain position of windowing synchronously.OFDM demodulation module 3 is removed protection with the time-domain signal of input, and carrying out the FFT computing is transformed into frequency domain, dateout information Y at interval.Channel equalization module 4 utilizes the pilot signal in the frequency domain data to carry out the information H that channel estimating obtains transmission channel, and carries out the influence that channel equalization removes channel and obtain balanced data information

Then, QAM separates mapping block 5 and separates the soft information that mapping obtains corresponding bit according to the data and the channel information of channel equalization.Pass through de-interleaving block 6 deinterleavings afterwards.The information flow that 7 pairs of soft information of channel decoder are deciphered to obtain exporting.

The SNR method of estimation that the present invention proposes utilizes QAM to separate mapping block 5 output soft bit informations, and soft bit information carries out hard decision and QAM mapping and obtains the ideal position QAM_out of data message on planisphere through QAM mapping block 8.The data message Y that draws of the channel information H that obtains of comprehensive channel balance module 4 and OFDM demodulation module 3 then utilizes first functional value and second functional value of offset distance parameter calculating module 9 calculating channel balanced data information corresponding points on planisphere.Respectively first functional value and second functional value are added up through accumulation process module 10 at last, utilize the functional value after adding up, calculate the SNR estimated value in the channel.

Detail to present embodiment is described in detail below.

QAM mapping block 8 carries out the QAM mapping according to the data message after the channel equalization, obtains the ideal position (QAM_out) of data message on planisphere.The QAM of ofdm system separates mapping block and generally selects the output soft bit information for improving decoder performance.In a preferred embodiment, the soft bit information of QAM being separated mapping block 5 output carries out hard decision, shine upon according to the QAM mapping ruler of transmitting terminal then to obtain QAM_out, its corresponding to balanced data information on planisphere ideal position.In another example, the information flow that can utilize channel decoder 7 to export carries out chnnel coding and the QAM mapping obtains QAM_out.

Offset distance parameter calculating module 9 is used for first functional value and second functional value of calculating channel balanced data information corresponding points on planisphere.The data message Y of first function before with channel information H, ideal position QAM_out and channel equalization is the factor, and second function is the factor with the channel information.

Below the derivation of preferred first function of the present invention and second function is described.

Fig. 2 is the mapping of the planisphere behind a hard decision schematic diagram under awgn channel.The balanced data signal is subjected to The noise and has departed from original ideal position QAM_out under awgn channel as can be seen from Figure 2.Therefore only need the deviation value of calculated data and ideal position just can obtain the SNR value of awgn channel, the computing formula of offset distance is shown below:

Dist＝|Equal_out-QAM_out| ²

$\mathrm{Equal}\_\mathrm{out}=\frac{Y}{H}$

This computing formula can accurately obtain offset distance under awgn channel.When having multipath delay and Doppler frequency shift in the channel, above directly utilize in the formula data after balanced to carry out the calculating of distance, will produce bigger error.Fig. 3 has provided the planisphere of the QAM_out after Equal_out under the Rayleigh channel and hard decision mapping.

As can see from Figure 3, because there is bigger difference in the influence of Rayleigh channel under the channel situation such as data constellation figure and AWGN.Wherein a lot of discrete points have been increased at whole ideal constellation periphery, these points mainly are because the distortion of channel equalization causes, the Rayleigh channel is more serious in the position of these somes fading ratio, the amplitude that is H is attenuated to very little, bigger in this channel estimation error, thus the data after balanced will produce bigger deviation with original ideal position.Therefore, if also directly calculate distance according to top formula, error will be very big, can't correctly estimate the value of SNR.At this problem, SNR method of estimation of the present invention is introduced channel information H and is calculated, and utilizes the data Y before the channel equalization to carry out distance calculation, and new computational methods are shown below:

$\mathrm{Dist}={|\frac{Y}{H}-\mathrm{QAM}\_\mathrm{out}|}^2$

$={|\frac{{\mathrm{YH}}^{*}}{{\mathrm{HH}}^{*}}-\mathrm{QAM}\_\mathrm{out}|}^2$

$={\left|\frac{{\mathrm{YH}}^{*}-\mathrm{QAM}\_\mathrm{out}{\left|H\right|}^2}{{\left|H\right|}^2}\right|}^2$

Make YH_QAM=|YH ^*-QAM_out|H| ²|

HH＝|H| ²

$\mathrm{Dist}={\left|\frac{\mathrm{YH}\_\mathrm{QAM}}{\mathrm{HH}}\right|}^2$

First functional value of the offset distance parameter calculating module in the present embodiment is YH_QAM, and second functional value is HH.First function and second function constitute the offset distance Dist of corresponding points relative ideal position.

The accumulation process module is used for first functional value of each corresponding points and second functional value are added up respectively, and utilizes first functional value and second functional value after adding up, calculates signal to noise ratio snr.Can obtain the first functional value YH_QAM and the second functional value HH of each corresponding points according to top new computing formula.In a preferred version, functional value is carried out smothing filtering before adding up, at first functional value is carried out The disposal of gentle filter and reduce the influence of planisphere erroneous judgement or burst error estimated value, and then with these results raising estimated accuracy that adds up.

The process of the Filtering Processing that adds up is shown below:

Sum_YH＝Smooth_filter(YH_QAM)

Sum_HH＝Smooth_filter(HH)

Wherein, the expression formula of Smooth_filter

Y(n)＝Smooth_filter(X(n))Y(n+1)＝(1-α)Y(n)+αX(n)

α is a smoothing factor, α＜1

Because the estimated value of SNR can be expressed as the dB value, therefore in a preferred version, will ask the division arithmetic of Dist to be converted into subtraction.

SNR_dB＝20log10(Sum_YH)-201og10(Sum_HH)

The present invention utilizes the balanced preceding data message Y and the H of channel estimating, avoided effectively because the problem of the SNR distortion estimator that channel equalization causes, hardware circuit implementation is simple simultaneously, only needs the plus-minus multiplying, has eliminated the division arithmetic that some SNR method of estimation kind needs of tradition are used.Just adopted the method in the DVBT system of our design, realized proof, whole SNR estimation module expends hardware resource seldom, can both estimate the SNR value of channel simultaneously under different channel conditions accurately.

Obviously, the present invention described here can have many variations, and this variation can not be thought and departs from the spirit and scope of the present invention.Therefore, the change that all it will be apparent to those skilled in the art all is included within the covering scope of these claims.

Claims (15)

1. signal to noise ratio (snr) method of estimation that is used for multicarrier system comprises step:

Carry out the QAM mapping according to the data message after the channel equalization, obtain the ideal position (QAM_out) of data message on planisphere;

First functional value (YH_QAM) of calculating channel balanced data information corresponding points on planisphere and second functional value (HH); First function is the factor with the data message (Y) before channel information (H), ideal position (QAM_out) and the channel equalization, second function is the factor with channel information (H), and first function and second function constitute the offset distance (Dist) of corresponding points relative ideal position;

First functional value and second functional value to described corresponding points add up respectively;

First functional value after utilization adds up and second functional value calculate signal to noise ratio (snr).

2. the method for claim 1 is characterized in that described QAM mapping steps comprises that the soft bit information that utilizes multicarrier system QAM to separate mapping output carries out the Bit hard decision of maximum likelihood, carries out the QAM mapping based on Bit hard decision result then.

3. the method for claim 1, it is characterized in that the described step that adds up comprises carries out smothing filtering respectively before first functional value and second functional value added up.

4. the method for claim 1 is characterized in that described first function is YH_QAM=|YH ^*-QAM_out|H| ²|, described second function is HH=|H| ², described offset distance $\mathrm{Dist}={\left|\frac{\mathrm{YH}\_\mathrm{QAM}}{\mathrm{HH}}\right|}^2,$ Here H is a channel information, and Y is the data message before the channel equalization, and QAM_out is the ideal position of data message on planisphere after the channel equalization.

5. the method for claim 1 is characterized in that the step of described calculating signal to noise ratio snr comprises the logarithm that the logarithm of first functional value after adding up is subtracted second functional value after adding up.

6. the method for claim 1 is characterized in that described multicarrier system is ofdm system.

7. signal to noise ratio (snr) estimation unit that is used for multicarrier system, described device comprises:

The QAM mapping block carries out the QAM mapping according to the data message after the channel equalization, obtains the ideal position (QAM_out) of data message on planisphere;

The offset distance parameter calculating module, first functional value (YH_QAM) of calculating channel balanced data information corresponding points on planisphere and second functional value (HH); First function is the factor with the data message (Y) before channel information (H), ideal position (QAM_out) and the channel equalization, second function is the factor with channel information (H), and first function and second function constitute the offset distance (Dist) of corresponding points relative ideal position;

The accumulation process module adds up respectively to first functional value and second functional value of described corresponding points, utilizes first functional value and second functional value after adding up, calculates signal to noise ratio (snr).

8. device as claimed in claim 7, it is characterized in that comprising that QAM separates mapping block, be used to export soft bit information, the soft bit information that described QAM mapping block utilizes QAM to separate mapping block output carries out the Bit hard decision of maximum likelihood, carry out the QAM mapping according to the hard-decision bits that obtains then, obtain the ideal position (QAM_out) of data message on planisphere.

9. device as claimed in claim 7 is characterized in that described accumulation process module carries out smothing filtering respectively before first functional value and second functional value are added up.

10. device as claimed in claim 7 is characterized in that comprising the channel equalization module, is used for output channel information (H).

11. device as claimed in claim 7 is characterized in that comprising demodulation module, is used for dateout information (Y).

12. device as claimed in claim 7 is characterized in that described first function is YH_QAM=|YH ^*-QAM_out|H| ²|, described second function is HH=|H| ², described offset distance $\mathrm{Dist}={\left|\frac{\mathrm{YH}\_\mathrm{QAM}}{\mathrm{HH}}\right|}^2,$ Here H is a channel information, and Y is the data message before the channel equalization, and QAM_out is the ideal position of data message on planisphere after the channel equalization.

13. device as claimed in claim 7 is characterized in that described accumulation process module comprises the submodule that the logarithm of first functional value after adding up is subtracted the logarithm of second functional value after adding up.

14. device as claimed in claim 7 is characterized in that described multicarrier system is ofdm system.

15. a multi-carrier receiver comprises signal to noise ratio (snr) estimation unit as claimed in claim 7.

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