CN105812296A - Self-adaption frequency domain interpolation method and self-adaption frequency domain interpolation system - Google Patents

Abstract

The invention discloses a self-adaption frequency domain interpolation method and a self-adaption frequency domain interpolation system. The self-adaption frequency domain interpolation method is characterized in that a first threshold value used for selecting frequency domain interpolation (FI) way can be determined; a SNR (Signal to Noise Ratio) value of a current channel can be measured and acquired, and then the SNR value can be compared with the corresponding first threshold value, and according to the comparison result, the corresponding FI way can be selected.

Description

A kind of adaptive frequency domain interpolation method and system

Technical field

The present invention relates to the channel estimation technique of wireless communication field, particularly relate to a kind of adaptive frequency domain interpolation method and system.

Background technology

In wireless communication system, in order to ensure that systematic function is not by the impact of channel multi-path and fading effect, it is necessary to adopt the method for channel estimating to follow the tracks of the change of channel response.The purpose of channel estimating is exactly estimate time domain or the frequency domain response of channel according to pilot signal.

Reference information for channel estimating comes from pilot tone, and pilot tone can not take too many expense in whole resource, otherwise can be substantially reduced the efficiency of whole communication system.Channel estimating, is the channel response value first estimating pilot frequency locations according to pilot signal, is interpolated thus obtaining the channel response value of data (non-overlapping with pilot tone) position again through to the channel response value of pilot tone.

Long Term Evolution (LTE, LongTermEvolution) system can be used for Data Physical DSCH Downlink Shared Channel (PDSCH, PhysicalDownlinkSharedChannel) the primary pilot signal demodulated has cell special reference (CRS, and subscriber equipment (UE Cell-specificReferenceSignal), UserEquipment) DRS (Dedicated Reference Signal) (UERS, UE-specificReferenceSignals) etc..CRS is fixed in full bandwidth and sends, and UERS then only sends in the data bandwidth of this UE.Wherein, the mapping pattern of CRS is as it is shown in figure 1, can directly reflect current channel situation to the estimated result of CRS；The mapping pattern of UERS is as in figure 2 it is shown, owing to UERS have passed through extra pre-coding matrix, what therefore the estimated result of UERS is reflected is the result of product of present channel and pre-coding matrix.

Channel estimating based on UERS mainly includes the steps such as descrambling, time domain interpolation (TI, TimeInterpolation), frequency domain interpolation (FI, FreqInterpolation).TI process signal as it is shown on figure 3, the signal of FI process as shown in Figure 4.The FI of UERS generally has following several ways:

On average (it is called for short FI0) in 1 Resource Block (RB, ResourceBlock)；

On average (it is called for short FI1) in half RB；

First-order linear interpolation (is called for short FI2).

At LTE based in the channel estimating of UERS, conventional method is to fix one FI mode of selection according to modulation system, the relatively low QPSK (QPSK, QuadraturePhaseShiftKeying) in such as operating point selects FI0, and the higher 64QAM in operating point selects FI2.But when the number of plies is higher or channel become middle height relevant time, the operating point of QPSK also can uprise, if being now still fixedly selected FI0 cannot obtain optimal performance.As it is shown in figure 5, transverse axis represents SNR in figure, the longitudinal axis represents throughput；From this QPSK, 4 layers, extension walking model (EPA, ExtendedPedestrianAmodel) example relevant in 5 can be seen that, at low signal-to-noise ratio (SNR, SignalNoiseRatio) under (in Fig. 5, SNR is lower than 9dB), the performance of FI0 is best, under high s/n ratio (in Fig. 5, SNR is higher than 11dB), the performance of FI2 is best, then be fixing selection FI0 or fixing FI2 handling capacity (throughput) performance that all can not obtain optimum.It is to say, the fixing method selecting FI of routine cannot obtain the throughput performance of optimum all the time.

Summary of the invention

For solving the technical problem of existing existence, embodiment of the present invention expectation provides a kind of adaptive frequency domain interpolation method and system.

The invention provides a kind of adaptive frequency domain interpolation method, described method includes:

Determine for the first threshold value that frequency domain interpolation FI mode selects；

Measure the signal to noise ratio snr value obtaining present channel, and described SNR value is compared with corresponding first threshold value, select corresponding FI mode according to comparative result.

It is preferred that described the first threshold value determined for selecting FI mode, including:

The performance simulation data of the different FI mode of traversal, selecting the middle SNR value of intermediate zone in described performance simulation data is described first threshold value R.

The SNR value obtaining present channel is measured it is preferred that described, including:

Measure the Reference Signal Received Power RSRP and noise power N of present channel₀；

Calculate the SNR value obtaining described present channel in the following manner: SNR=10log10 (RSRP/N₀)。

It is preferred that at RSRP and the N measuring present channel₀After, described method also includes:

Respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing；

Accordingly, the SNR value of described calculating present channel includes: according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel.

It is preferred that in the following manner respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing:

RSRP=old_RSRP*(1-alfa)+new_RSRP* alfa,

$N_0={\mathrm{old}}_{N_0}*(1-\mathrm{alfa})+{\mathrm{new}}_{N_0}*\mathrm{alfa};$

Wherein, old_RSRPFor front once forget Filtering Processing after the RSRP value that obtains, new_RSRPThe RSRP value of gained is measured for this,For front once forget Filtering Processing after the N that obtains₀Value,The N of gained is measured for this₀Value, alfa is forgetting factor.

It is preferred that obtain described forgetting factor in the following manner:

The performance simulation data of the different FI mode of traversal, selecting the half length of the SNR value scope of intermediate zone in described performance simulation data is L；

RSRP and N in described performance simulation data₀Do not do when forgeing filtering, the first average of statistical measurement gained SNR value and first variance σ₁；

RSRP and N in described performance simulation data₀Do when forgeing filtering, attempt different forgetting factor values respectively, and corresponding the second average measuring gained SNR value of statistics and second variance σ respectively₂；

Choose in the different forgetting factors value attempted, make the ratio measuring gained SNR value dropping in [R-L, R+L] scope reach the minimum forgetting factor value of predetermined threshold.

Invention further provides a kind of adaptive frequency domain interpolating apparatus, described device includes:

Parameter determination unit, for determining for the first threshold value that frequency domain interpolation FI mode selects；

FI selects unit, for measuring the signal to noise ratio snr value obtaining present channel, and is compared with corresponding first threshold value by described SNR value, selects corresponding FI mode according to comparative result.

It is preferred that described parameter determination unit is further used for, the performance simulation data of the different FI mode of traversal, selecting the middle SNR value of intermediate zone in described performance simulation data is described first threshold value R.

It is preferred that described FI selects unit to be further used for,

Measure the Reference Signal Received Power RSRP and noise power N of present channel₀；

Calculate the SNR value obtaining described present channel in the following manner: SNR=10log10 (RSRP/N₀)。

It is preferred that described FI selects unit to be further used for, at RSRP and the N measuring present channel₀After, respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing；

Accordingly, the SNR value of described calculating present channel includes: according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel.

It is preferred that described FI selects unit to be further used in the following manner respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing:

RSRP=old_RSRP*(1-alfa)+new_RSRP* alfa,

$N_0={\mathrm{old}}_{N_0}*(1-\mathrm{alfa})+{\mathrm{new}}_{N_0}*\mathrm{alfa};$

Wherein, old_RSRPFor front once forget Filtering Processing after the RSRP value that obtains, new_RSRPThe RSRP value of gained is measured for this,For front once forget Filtering Processing after the N that obtains₀Value,The N of gained is measured for this₀Value, alfa is forgetting factor.

It is preferred that described parameter determination unit is further used for obtaining described forgetting factor in the following manner:

The performance simulation data of the different FI mode of traversal, selecting the half length of the SNR value scope of intermediate zone in described performance simulation data is L；

RSRP and N in described performance simulation data₀Do not do when forgeing filtering, the first average of statistical measurement gained SNR value and first variance σ₁；

RSRP and N in described performance simulation data₀Do when forgeing filtering, attempt different forgetting factor values respectively, and corresponding the second average measuring gained SNR value of statistics and second variance σ respectively₂；

Choose in the different forgetting factors value attempted, make the ratio measuring gained SNR value dropping in [R-L, R+L] scope reach the minimum forgetting factor value of predetermined threshold.

A kind of adaptive frequency domain interpolation method of embodiment of the present invention offer and system, SNR value according to measuring selects suitable frequency domain interpolation mode adaptively, solve conventional method with relatively low implementation complexity and can not take into account low signal-to-noise ratio scene and the problem of high s/n ratio scene, make no matter to be under low signal-to-noise ratio scene or under high s/n ratio scene, the throughput performance of optimum can be obtained.

Accompanying drawing explanation

Fig. 1 is the mapping pattern schematic diagram of the CRS of two antenna ports in correlation technique；

Fig. 2 is the mapping pattern schematic diagram of the UERS of two antenna ports in correlation technique；

Fig. 3 is the TI process schematic in correlation technique based on UERS；

Fig. 4 is the FI process schematic in correlation technique based on UERS；

Fig. 5 is the throughput performance schematic diagram of QPSK correlated channels in correlation technique；

Fig. 6 is the flow chart of the adaptive frequency domain interpolation method of the embodiment of the present invention one；

Fig. 7 is the adaptive frequency domain interpolating apparatus composition structural representation of the embodiment of the present invention two；

Fig. 8 is the SNR measured value range schematic diagram forgotten in filtering of the embodiment of the present invention；

Fig. 9 is the performance curve schematic diagram of the embodiment of the present invention.

Detailed description of the invention

Below in conjunction with the drawings and specific embodiments, the technical solution of the present invention is further elaborated.

Embodiment one

A kind of adaptive frequency domain interpolation method that the embodiment of the present invention one provides, as shown in Figure 6, the method specifically includes that

Step 101, it is determined that for the first threshold value that FI mode selects.

Wherein, described the first threshold value determined for selecting FI mode, including:

The performance simulation data of the different FI mode of traversal, selecting the middle SNR value of intermediate zone in described performance simulation data is described first threshold value R.

Step 102, measures signal to noise ratio (SNR) value obtaining present channel, and is compared with corresponding first threshold value by described SNR value, selects corresponding FI mode according to comparative result.

Wherein, the described SNR value measuring acquisition present channel, including:

Measure the Reference Signal Received Power RSRP and noise power N of present channel₀；

Calculate the SNR value obtaining described present channel in the following manner: SNR=10log10 (RSRP/N₀)。

Wherein, at RSRP and the N measuring present channel₀After, described method may also include that

Respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing；

Accordingly, the SNR value of described calculating present channel includes: according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel.

Can in the following manner respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing:

RSRP=old_RSRP*(1-alfa)+new_RSRP* alfa,

$N_0={\mathrm{old}}_{N_0}*(1-\mathrm{alfa})+{\mathrm{new}}_{N_0}*\mathrm{alfa};$

Wherein, old_RSRPFor front once forget Filtering Processing after the RSRP value that obtains, new_RSRPThe RSRP value of gained is measured for this,For front once forget Filtering Processing after the N that obtains₀Value,The N of gained is measured for this₀Value, alfa is forgetting factor.

Wherein it is possible to obtain described forgetting factor in the following manner:

The performance simulation data of the different FI mode of traversal, selecting the half length of the SNR value scope of intermediate zone in described performance simulation data is L；

RSRP and N in described performance simulation data₀Do not do when forgeing filtering, the first average of statistical measurement gained SNR value and first variance σ₁；

RSRP and N in described performance simulation data₀Do when forgeing filtering, attempt different forgetting factor values respectively, and corresponding the second average measuring gained SNR value of statistics and second variance σ respectively₂；

Choose in the different forgetting factors value attempted, make the ratio measuring gained SNR value dropping in [R-L, R+L] scope reach the minimum forgetting factor value of predetermined threshold.

Embodiment two

Corresponding adaptive frequency domain interpolation method described in the embodiment of the present invention one, the embodiment of the present invention two provides a kind of adaptive frequency domain interpolating apparatus, as it is shown in fig. 7, this device includes:

Parameter determination unit 10, for determining for the first threshold value that FI mode selects；

FI selects unit 20, for measuring the SNR value obtaining present channel, and is compared with corresponding first threshold value by described SNR value, selects corresponding FI mode according to comparative result.

Wherein, described parameter determination unit 10 is further used for, and the performance simulation data of the different FI mode of traversal, selecting the middle SNR value of intermediate zone in described performance simulation data is described first threshold value R.

Described FI selects unit 20 to be further used for, and measures the Reference Signal Received Power RSRP and noise power N of present channel₀；

Calculate the SNR value obtaining described present channel in the following manner: SNR=10log10 (RSRP/N₀)。

Described FI selects unit 20 to be further used for, at RSRP and the N measuring present channel₀After, respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing；

Accordingly, the SNR value of described calculating present channel includes: according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel.

Described FI selects unit 20 to be further used in the following manner respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing:

RSRP=old_RSRP*(1-alfa)+new_RSRP* alfa,

$N_0={\mathrm{old}}_{N_0}*(1-\mathrm{alfa})+{\mathrm{new}}_{N_0}*\mathrm{alfa};$

Wherein, old_RSRPFor front once forget Filtering Processing after the RSRP value that obtains, new_RSRPThe RSRP value of gained is measured for this,For front once forget Filtering Processing after the N that obtains₀Value,The N of gained is measured for this₀Value, alfa is forgetting factor.

Described parameter determination unit 10 is further used for obtaining described forgetting factor in the following manner:

The performance simulation data of the different FI mode of traversal, selecting the half length of the SNR value scope of intermediate zone in described performance simulation data is L；

RSRP and N in described performance simulation data₀Do not do when forgeing filtering, the first average of statistical measurement gained SNR value and first variance σ₁；

RSRP and N in described performance simulation data₀Do when forgeing filtering, attempt different forgetting factor values respectively, and corresponding the second average measuring gained SNR value of statistics and second variance σ respectively₂；

Choose in the different forgetting factors value attempted, make the ratio measuring gained SNR value dropping in [R-L, R+L] scope reach the minimum forgetting factor value of predetermined threshold.

The embodiment of the present invention, SNR value according to measuring selects suitable frequency domain interpolation mode adaptively, solve conventional method with relatively low implementation complexity and can not take into account low signal-to-noise ratio scene and the problem of high s/n ratio scene, make no matter to be under low signal-to-noise ratio scene or under high s/n ratio scene, the throughput performance of optimum can be obtained.

In conjunction with concrete example, above-mentioned adaptive frequency domain interpolation method and device are further elaborated on below.

In this example, it is determined that the process of threshold value and forgetting factor is as follows:

The first step, carries out the performance simulation of FI0, FI1, FI2 respectively, and simulation result is as it is shown in figure 5, in the scope of 9-11dB, each bar curve is almost overlap；The intermediate value 10dB selecting intermediate zone 9-11dB is threshold value R, and the half length of intermediate zone is L=(11-9)/2=1dB.

Second step, RSRP and N₀Not doing and forget filtering and when true signal to noise ratio is 10dB, preserve and measure the SNR value obtained in 200,000 subframes, it is 10.02 that statistics obtains average, variances sigma₁For 7.6dB.

3rd step, RSRP and N₀Do and forget filtering and when true signal to noise ratio is 10dB, attempt alfa=0.1/0.01/0.005/0.001 respectively, preserve respectively and 200,000 subframes are measured the SNR value obtained, respectively statistical variance σ₂.Finding 3 σ=1.12dB during alfa=0.001, as shown in Figure 8, at this moment most of measurement SNR value all drops within the scope of the surrounding ± 1dB of 10dB, thus selected 0.001 is forgetting factor.

Travel through different modulation system (QPSK/16QAM/64QAM), the number of plies (v) and various representative channel, QPSK/16QAM/64QAM draws a threshold value respectively, and 16QAM/64QAM determines that threshold value is identical with QPSK above with the process of forgetting factor.The comprehensive various number of plies and representative channel draw final adaptive frequency domain interpolation strategies.

The process of LTEUERS adaptive frequency domain interpolation is as follows:

The first step, measures RSRP and the N of present channel₀。

Second step, respectively to RSRP and the N measuring gained₀Do and forget filtering, forgetting factor alfa=0.001.

3rd step, according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel: SNR=10log10 (RSRP/N₀)。

4th step, selects FI method:

Modulation system is QPSK, if v >=3 and SNR >=10dB, then select FI2, otherwise select FI0；

Modulation system is 16QAM, if v >=3 and SNR >=11.7dB, then select FI1, otherwise select FI0

Modulation system is 64QAM, selects FI2.Wherein, v represents the number of plies.

5th step, performs selected FI.

The performance curve after adaptive frequency domain interpolation method is adopted to see shown in the adaptive curve in Fig. 9, it is seen that after using the adaptive frequency domain interpolation method of the embodiment of the present invention, low signal-to-noise ratio and all obtain the performance of optimum under high s/n ratio.That is, the embodiment of the present invention selects suitable frequency domain interpolation mode adaptively according to the SNR value measured, solve conventional method with relatively low implementation complexity and can not take into account low signal-to-noise ratio scene and the problem of high s/n ratio scene, make no matter to be under low signal-to-noise ratio scene or under high s/n ratio scene, the throughput performance of optimum can be obtained.

Those skilled in the art are it should be appreciated that embodiments of the invention can be provided as method, system or computer program.Therefore, the present invention can adopt the form of hardware embodiment, software implementation or the embodiment in conjunction with software and hardware aspect.And, the present invention can adopt the form at one or more upper computer programs implemented of computer-usable storage medium (including but not limited to disk memory and optical memory etc.) wherein including computer usable program code.

The present invention is that flow chart and/or block diagram with reference to method according to embodiments of the present invention, equipment (system) and computer program describe.It should be understood that can by the combination of the flow process in each flow process in computer program instructions flowchart and/or block diagram and/or square frame and flow chart and/or block diagram and/or square frame.These computer program instructions can be provided to produce a machine to the processor of general purpose computer, special-purpose computer, Embedded Processor or other programmable data processing device so that the instruction performed by the processor of computer or other programmable data processing device is produced for realizing the device of function specified in one flow process of flow chart or multiple flow process and/or one square frame of block diagram or multiple square frame.

These computer program instructions may be alternatively stored in and can guide in the computer-readable memory that computer or other programmable data processing device work in a specific way, the instruction making to be stored in this computer-readable memory produces to include the manufacture of command device, and this command device realizes the function specified in one flow process of flow chart or multiple flow process and/or one square frame of block diagram or multiple square frame.

These computer program instructions also can be loaded in computer or other programmable data processing device, make on computer or other programmable devices, to perform sequence of operations step to produce computer implemented process, thus the instruction performed on computer or other programmable devices provides for realizing the step of function specified in one flow process of flow chart or multiple flow process and/or one square frame of block diagram or multiple square frame.

The above, be only presently preferred embodiments of the present invention, is not intended to limit protection scope of the present invention.

Claims (12)

1. an adaptive frequency domain interpolation method, it is characterised in that described method includes:

Determine for the first threshold value that frequency domain interpolation FI mode selects；

Measure the signal to noise ratio snr value obtaining present channel, and described SNR value is compared with corresponding first threshold value, select corresponding FI mode according to comparative result.

2. adaptive frequency domain interpolation method according to claim 1, it is characterised in that described the first threshold value determined for selecting FI mode, including:

The performance simulation data of the different FI mode of traversal, selecting the middle SNR value of intermediate zone in described performance simulation data is described first threshold value R.

3. adaptive frequency domain interpolation method according to claim 1, it is characterised in that described measurement obtains the SNR value of present channel, including:

Measure the Reference Signal Received Power RSRP and noise power N of present channel₀；

Calculate the SNR value obtaining described present channel in the following manner: SNR=10log10 (RSRP/N₀)。

4. adaptive frequency domain interpolation method according to claim 3, it is characterised in that at RSRP and the N measuring present channel₀After, described method also includes:

Respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing；

Accordingly, the SNR value of described calculating present channel includes: according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel.

5. adaptive frequency domain interpolation method according to claim 4, it is characterised in that in the following manner respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing:

RSRP=old_RSRP*(1-alfa)+new_RSRP* alfa,

$N_0={\mathrm{old}}_{N_0}*(1-\mathrm{alfa})+{\mathrm{new}}_{N_0}*\mathrm{alfa};$

Wherein, old_RSRPFor front once forget Filtering Processing after the RSRP value that obtains, new_RSRPThe RSRP value of gained is measured for this,For front once forget Filtering Processing after the N that obtains₀Value,The N of gained is measured for this₀Value, alfa is forgetting factor.

6. adaptive frequency domain interpolation method according to claim 5, it is characterised in that obtain described forgetting factor in the following manner:

The performance simulation data of the different FI mode of traversal, selecting the half length of the SNR value scope of intermediate zone in described performance simulation data is L；

RSRP and N in described performance simulation data₀Do not do when forgeing filtering, the first average of statistical measurement gained SNR value and first variance σ₁；

RSRP and N in described performance simulation data₀Do when forgeing filtering, attempt different forgetting factor values respectively, and corresponding the second average measuring gained SNR value of statistics and second variance σ respectively₂；

Choose in the different forgetting factors value attempted, make the ratio measuring gained SNR value dropping in [R-L, R+L] scope reach the minimum forgetting factor value of predetermined threshold.

7. an adaptive frequency domain interpolating apparatus, it is characterised in that described device includes:

Parameter determination unit, for determining for the first threshold value that frequency domain interpolation FI mode selects；

FI selects unit, for measuring the signal to noise ratio snr value obtaining present channel, and is compared with corresponding first threshold value by described SNR value, selects corresponding FI mode according to comparative result.

8. adaptive frequency domain interpolating apparatus according to claim 7, it is characterized in that, described parameter determination unit is further used for, and the performance simulation data of the different FI mode of traversal, selecting the middle SNR value of intermediate zone in described performance simulation data is described first threshold value R.

9. adaptive frequency domain interpolating apparatus according to claim 7, it is characterised in that described FI selects unit to be further used for,

Measure the Reference Signal Received Power RSRP and noise power N of present channel₀；

Calculate the SNR value obtaining described present channel in the following manner: SNR=10log10 (RSRP/N₀)。

10. adaptive frequency domain interpolating apparatus according to claim 9, it is characterised in that described FI selects unit to be further used for, at RSRP and the N measuring present channel₀After, respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing；

Accordingly, the SNR value of described calculating present channel includes: according to forgeing RSRP and the N after Filtering Processing₀Calculate the SNR value of described present channel.

11. adaptive frequency domain interpolating apparatus according to claim 10, it is characterised in that described FI selects unit to be further used in the following manner respectively to RSRP and the N measuring gained₀Carry out forgeing Filtering Processing:

RSRP=old_RSRP*(1-alfa)+new_RSRP* alfa,

$N_0={\mathrm{old}}_{N_0}*(1-\mathrm{alfa})+{\mathrm{new}}_{N_0}*\mathrm{alfa};$

Wherein, old_RSRPFor front once forget Filtering Processing after the RSRP value that obtains, new_RSRPThe RSRP value of gained is measured for this,For front once forget Filtering Processing after the N that obtains₀Value,The N of gained is measured for this₀Value, alfa is forgetting factor.

12. adaptive frequency domain interpolating apparatus according to claim 11, it is characterised in that described parameter determination unit is further used for obtaining described forgetting factor in the following manner:

The performance simulation data of the different FI mode of traversal, selecting the half length of the SNR value scope of intermediate zone in described performance simulation data is L；

RSRP and N in described performance simulation data₀Do not do when forgeing filtering, the first average of statistical measurement gained SNR value and first variance σ₁；

RSRP and N in described performance simulation data₀Do when forgeing filtering, attempt different forgetting factor values respectively, and corresponding the second average measuring gained SNR value of statistics and second variance σ respectively₂；

Choose in the different forgetting factors value attempted, make the ratio measuring gained SNR value dropping in [R-L, R+L] scope reach the minimum forgetting factor value of predetermined threshold.