KR20030097040A - OFDM receiver capable of recovering symbol timing correspond to channel status and a method recovering symbol timing - Google Patents

Abstract

PURPOSE: An OFDM receiver restoring symbol timing in corresponding to a channel state and a method for restoring symbol timing thereof are provided to realize stable symbol timing restoration in any channel environment by restoring symbol timing based on the current channel state. CONSTITUTION: An offset detecting unit detects a symbol timing offset value from a fast fourier transformed orthogonal frequency division multiplexing(OFDM) signal. A channel state judging unit(400) judges the current channel state according to change in time of the OFDM signal. A print operating unit estimates a predetermined symbol timing offset value to the symbol timing offset value sequentially inputted based on the judged channel state information. An offset compensating unit(200) compensates symbol timing of the OFDM signal based on the estimated symbol timing offset.

Description

FM receiver capable of recovering symbol timing corresponding to channel status and a method recovering symbol timing

The present invention relates to an apparatus for recovering symbol timing of an Orthogonal Frequency Division Multiplexing (OFDM) receiver, and more particularly, to compensate for an offset generated in the process of recovering a received OFM signal. The present invention relates to a symbol timing recovery apparatus of a DM receiver.

In general, a broadcasting system of a digital television (DTV) can be roughly divided into an image encoder and a modulator. The video encoding unit compresses digital data of about 1 Gbps obtained from a video source into data of 15 to 18 Mbps. The modulator transmits several tens of Mbps of digital data to the receiver through a limited band channel of 6 to 8 MHz.

In general, digital television broadcasting adopts a terrestrial simultaneous broadcasting method using a channel of a Very High Frequency (VHF) / Ultra High Frequency (UHF) band allocated for conventional television broadcasting. Therefore, the modulation method used in the television broadcasting system must satisfy the following conditions due to the environment of terrestrial simultaneous broadcasting.

First, the modulation scheme used in the digital television broadcasting system requires high spectrum efficiency in order to transmit digital data of several tens of Mbps to a receiver through a limited band channel of 6 to 8 MHz. Second, the modulation scheme used in the digital television broadcasting system has multipath fading due to the surrounding buildings or structures, and therefore has a strong characteristic against fading. Third, the modulation scheme used in the digital television broadcasting system inevitably causes co-channel interference due to the existing analog television signal, and thus has to have strong characteristics against co-channel interference. In addition, the digitally modulated signal of a digital television system should be able to minimize interference with existing analog television receivers.

Therefore, in order to solve this problem, the Orthogonal Frequency Division Multiplexing (OFDM) method of digital modulation, which can achieve the double effect of the transmission speed per bandwidth and the interference prevention, is adopted as the digital television terrestrial broadcasting method. have.

The OMD method converts a symbol string input in a serial form into parallel data of a predetermined block unit and then multiplexes the parallelized symbols with different subcarrier frequencies. The OMD system uses a multi-carrier, and has a considerable difference from the conventional single carrier. Multiple carriers have orthogonality with each other. Orthogonality means a property in which the product of two carriers becomes '0', which is a requirement for using multiple carriers. The implementation of the UFDM method is accomplished by the Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT), which are simply determined by the definition of orthogonality and fast Fourier transform between carriers. .

As a method of restoring the symbol timing in the European DTV using the modulation scheme of the FM, by inserting a reference signal called a distributed pilot to the subcarrier of the OFM DM symbol, the symbol timing is adjusted using the phase difference between the distributed pilots. Restore

Errors in the time domain, such as the FFT window timing sync offset or the sampling clock, appear in the form of phase rotation in the frequency domain after FFT conversion. Since the phase rotation increases in proportion to the degree of symbol timing offset and the index of the subcarrier, the phase rotation is proportional to the index of the subcarrier within a symbol having the same FFT window timing and almost the same influence of the sampling clock offset. Therefore, if the difference between the phase rotations of two neighboring distributed pilots in the frequency domain is known, it is easy to estimate the degree of offset of the symbol timing.

1 is a block diagram showing an example of a conventional OMD receiver. The OMD receiver includes an analog to digital converter (ADC) 10, an offset compensator 20, a fast fourier transform (FFT) unit 30, an error detector 40, an equalizer 50, and an FEC unit. (forward error corrector) 60.

The ADC 10 converts the received OMD signal into a digital signal through sampling and quantization. The offset compensator 20 compensates for a symbol timing offset of the OMD signal. The FFT unit 30 performs a Fast Fourier Transform (FFT) of the OMD signal compensated for by the symbol timing offset. The error detector 40 detects a symbol timing offset of the OFM signal generated during sampling to convert the OFM signal to the digital signal in the ADC 10. At this time, the symbol timing offset value detected by the error detector 40 is provided to the offset compensator 20. The equalizer 50 compensates for the distortion generated on the transmission channel with respect to the fast Fourier transformed OMD signal output from the FFT unit 30. At this time, the equalizer 50 compensates for the distortion on the transmission channel of the OFM signal by calculating the timing and frequency error values for the symbols of the OFM signal through the pilot signal. The FEC 60 detects an error by an error detection method set for the data of the OMD signal and corrects the detected error.

2 is a detailed block diagram of the error detector 40 of FIG. 1. The error detection unit 40 has a pilot extraction unit 41, an offset detection unit 43, and an offset estimation unit 45.

The pilot extractor 41 extracts a scatter pilot in the OSDM symbol.

The offset detector 43 calculates a phase value of the extracted distributed pilot, estimates a phase difference value from a neighboring distributed pilot SP, takes an average value of these phase difference values in units of symbols, and calculates a symbol timing offset value. Detect.

The offset estimator 45 estimates an average value for a predetermined number of symbol timing offset values detected by the offset detector 43 to determine a symbol timing offset value.

Thereafter, the symbol timing offset value is input to the offset compensator 20 to restore the symbol timing.

As such, the offset estimator 45 for estimating the average value of the symbol timing offset values of the symbols of the error detector 40 adjusts the symbol timing offset values by a sliding window method and a pocketing algorithm method. Decide

First, in the sliding window method, a symbol timing offset value is determined by the sliding operation unit 45a as illustrated in FIG. 3. The sliding calculator 45a has an adder 451a and a divider 453a. The adder 451a performs, for example, four addition operations on the symbol timing offsets detected by the offset detector 43. The divider 453a performs a division operation of dividing the symbol timing offsets that are added by four by the adder 451a by '4'.

That is, the average value obtained by the sliding calculation unit 45a is described as in the following [Equation 1].

That is, as shown in Equation 1, the average value is taken for the symbol timing offset value corresponding to the sliding window sizes (x ₀ , x ₁ , ... x _n-1 ). Such a method has a problem in that an operation is complicated and a bit length increases according to an addition operation. In addition, in a dynamic channel environment, there is a problem in that the difference between the average values becomes larger, so that the compensation of the symbol timing offset is not properly performed.

In order to solve this problem, a forgetting algorithm is used.

As shown in FIG. 4, the forgetting algorithm scheme describes a case in which a symbol timing offset value is determined by the factor calculator 45b. The print operator 45b has a first multiplier 451b, a switching unit 453b, a register 455b, a second multiplier 457b, and an adder 459b.

The first multiplier 451b multiplies the symbol timing offset detected by the offset detector 43 with the weighting factor 'σ'. The switching unit 453b outputs the symbol timing offset detected by the initial offset detector 43 to the outside and bypasses the register 455b to the outside according to the input control signal C. FIG. The register 455b stores the symbol timing offset output by bypassing the switching unit 453b. The second multiplier 457b multiplies the symbol timing offset stored in the register 455b by the weighting factor '1-σ'. The adder 459b performs an addition operation on the value calculated according to the multiplication operation of the first multiplier 451b and the second multiplier 457b, and outputs a result value m according to the addition operation.

For the symbol timing offset values x ₀ , x ₁ , x ₂ , x ₃ ,... X _n detected by the offset detection unit 43, the output values of the factor calculation unit 45b are m ₀ , m ₁ , m ₂ , m _3. M _n becomes. Estimation of the symbol timing offset value by the factor calculator 45b using the forgetting algorithm shown in FIG. 4 may be expressed as in Equation 2 below.

In this way, the weighting factor 'σ' set in the symbol timing offset newly input to the factor calculation unit 45b is multiplied, and the weighting factor '1-σ' set in the output value of the previously input symbol timing offset is multiplied. By reducing the weight of the newly input symbol timing offset in the result of the operation, it is possible to stably perform symbol timing recovery of the OMD signal.

However, the conventional symbol timing recovery method does not satisfy a static channel and a dynamic channel environment at the same time. Of course, the forgetting algorithm determines the optimal weighting factor 'σ' to satisfy both the static and dynamic channel environments at the same time, but does not take the optimal value to satisfy each channel environment.

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide an OMD receiver and a symbol timing recovery method thereof capable of stably performing symbol timing recovery in response to each of a static channel and a dynamic channel. It is.

1 is a schematic block diagram of a typical OPM receiver;

2 is a detailed block diagram of the error detector 40 of FIG. 1;

3 is a view illustrating a case in which the offset estimation unit 45 of FIG. 2 uses a sliding window method.

4 is a diagram illustrating a case in which the offset estimation unit 45 of FIG.

5 is a schematic block diagram of an OMD receiver according to an embodiment of the present invention;

6A to 6C are diagrams for describing a process of determining a channel state in the channel state determination unit 400 of FIG. 5.

FIG. 7 is a detailed block diagram of a part performing symbol timing recovery in the OS receiver of FIG. 5.

FIG. 8 is a detailed block diagram of the print operator 550 of FIG. 5, and

FIG. 9 is a flowchart illustrating a symbol timing recovery method corresponding to a channel state according to the OS receiver of FIG. 5.

Explanation of symbols on the main parts of the drawings

200: offset compensation unit 300: FFT unit

400: channel status determination unit 500: error detection unit

550: printing operation unit 552: selection unit

551: first multiplier 553: switching unit

555: Register 557: second multiplier

559: Adder 600: Equalizer

The OMD receiver according to the present invention for achieving the above object, the offset detection unit for detecting the symbol timing offset value from the fast Fourier transform OFM signal and the degree of variation with respect to the time of the equalized OFM signal A factor calculation unit for estimating a predetermined symbol timing offset value based on the channel state determination unit which determines the current channel state and the channel state information determined by the channel state determination unit with respect to symbol timing offset values sequentially input from the offset detection unit. And an offset compensator for compensating symbol timing of the OMD signal on the basis of the predetermined symbol timing offset value estimated by the factor calculator.

Here, the printing operation unit is a selection unit for selecting a weighting factor corresponding to the channel state based on the channel state information, and a second symbol timing offset successive to the first symbol timing offset inputted to the first symbol timing offset; A first multiplier for multiplying a register for storing and outputting a predetermined time until a predetermined time is obtained, a first weighted person that is a weighted person selected by the selection unit to a second symbol timing offset, and a first symbol timing offset outputted from the register. The second multiplier multiplying the second weighted person corresponding to the weighted person and the value calculated according to the multiplication operation of the first multiplier and the second multiplier are added to calculate an output value, and the output value is output to the outside and It has an adder that bypasses the register.

In addition, the print operator further includes a switching unit for bypassing the first input symbol timing offset to an output and a register according to a control signal.

For example, when the channel state is static, the weighting factor is 0.1 to 0.15, and when the channel state is dynamic, the weighting factor is 0.2 to 0.3, and the sum of the first and second weights is '1'. It is characterized by that.

On the other hand, according to the present invention, a method for recovering a symbol timing corresponding to a channel state comprises: detecting a symbol timing offset value from a fast Fourier transformed OMD signal; Determining a current channel state according to a variation in time of the equalized OMD signal; Estimating a predetermined symbol timing offset value based on the channel state information determined in the channel state determination step with respect to the symbol timing offset value; Compensating for the symbol timing of the OMD signal based on the estimated predetermined symbol timing offset value.

Therefore, by determining the current channel state and performing symbol timing restoration based on the channel information, it is possible to perform stable symbol timing restoration in any channel environment.

Hereinafter, an OMD receiver capable of restoring symbol timing according to a channel state according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 illustrates an OPM receiver according to the present invention, comprising: an analog to digital converter (ADC) unit 100, an offset compensator 200, a fast fourier transform (FFT) unit 300, and a channel state determination unit 400. , An error detector 500, an equalizer 600, and a forward error corrector (FEC) 700.

The analog to digital converter (ADC) unit 100 converts the received OMD signal into a digital signal through sampling and quantization.

The offset compensator 200 compensates for a symbol timing offset value detected by the error detector 500 described below of the OMD signal.

The FFT unit 300 performs a Fast Fourier Transform (FFT) on the OPM signal compensated for by the symbol timing offset.

The error detector 500 detects the symbol timing offset value of the OMD signal generated at the time of sampling in order to convert the OFM signal to the digital signal by the ADC unit 100, and the symbol timing offset value detected here is the channel state. Is an estimated value corresponding to.

The equalizer 600 compensates for the distortion generated on the transmission channel with respect to the fast Fourier transformed OMD signal output from the FFT unit 300. The equalizer 600 predicts a transmission channel of the OMD signal by calculating a timing and frequency error value of a symbol of the OMD signal through the pilot signal.

At this time, the channel state determination unit 400 detects the current channel state according to the magnitude of the channel prediction values predicted by the equalizer 600. Information about the detected current channel state is provided to the error detector 500 to set a symbol timing offset value corresponding to the channel state.

The FEC unit 700 detects an error by the error detection method set for the data of the OMD signal, and corrects the detected error.

On the other hand, with respect to the OPM receiver that the symbol timing is restored through the channel state determining unit 400 and the error detector 500 for estimating the symbol timing offset value in response to the detected channel state information in detail with reference to the drawings below. Explain.

First, the process of determining the current channel state in the channel state determination unit 400 is as follows.

In general, in a static channel environment, the size of a signal viewed in the frequency domain is kept constant regardless of time, as shown in FIG. 6A. However, in a dynamic channel environment, the size of the signal seen in the frequency domain varies with time. Therefore, the current channel state can be detected by changing the magnitude of the signal viewed in the frequency domain.

As described above, in order to observe the signal in the frequency domain, the signal Fourier transformed by the FFT unit 300 may be observed. That is, the signals flowing into the equalizer 600 detect the current channel state according to the variation in the magnitude of the channel prediction values predicted through the equalizer 600.

As shown in FIG. 6C, the channel prediction column A = {a ₁ , a ₂ , a ₃ , ... a ₁₇₀₅ } when time t1, and the channel prediction column B = {b ₁ , b ₂ , b ₃ , ... b ₁₇₀₅ }, the change information of the channel prediction value between time t1 and time t2 Is represented by the following [Equation 3].

,

In other words, the degree of change in the channel prediction value If the value exceeds a certain threshold value, the current channel state is determined to be a dynamic channel state, and as mentioned above, if there is little variation in the channel prediction value, it is determined to be a static channel state.

The appropriate threshold value is determined through simulation, and then the threshold value and the variation The current channel status is determined by comparing the values.

In this way, the information determining the current channel state is provided to the factor calculator 550 for estimating the symbol timing offset value of the error detector 500, as shown in FIG. Since the pilot detector 510 and the offset detector 530 of the error detector 500 are the same as the pilot detector 41 and the offset detector 43 described with reference to FIG. 2, detailed descriptions thereof will be omitted.

FIG. 8 is a detailed diagram for explaining a process of estimating a symbol timing offset value by applying a weighting factor according to a channel state by the factor calculating unit 550.

The print operator 550 includes a selector 552, a first multiplier 551, a switching unit 553, a register 555, a second multiplier 557, and an adder 559.

The selector 552 selects a weighting party in response to the current channel state information determined by the channel state determination unit 400. For example, in static channel state, 'α' is used as the weighting agent, and in dynamic channel state, 'α' is used as the weighting agent. Here, the weighting factors 'α' and 'β' are determined to be optimal values for each channel state through simulation.

For example, when it is determined that the static channel state, the selector 552 selects the weighting factor 'α', and the first multiplier 551 adds the weighting factor 'α to the symbol timing offset detected by the offset detection unit 530. Multiply by The switching unit 553 outputs the symbol timing offset detected by the initial offset detection unit 530 to the outside and bypasses the register 555 according to the input control signal C. The register 555 stores the symbol timing offset output by bypassing the switching unit 553. The second multiplier 557 multiplies the symbol timing offset stored in the register 555 by the weighting factor '1-α'. The adder 559 performs an addition operation on the value calculated according to the multiplication operation of the first multiplier 551 and the second multiplier 557, and outputs a result value m according to the addition operation.

When the first output value is 'x ₀ ' and the second output value is 'x ₁ ' among the symbol timing offsets detected by the offset detector 530, the output value of the factor calculator 550 is expressed by Equation 4 below. Can be represented.

Here, 'm ₀ ' is a value at which the symbol timing offset x ₀ first output from the offset detector 530 is output by the switching unit 553. That is, 'm ₀ ' is the same value as 'x ₀ '. 'x ₁ ' is the symbol timing offset output by the offset detector 530 for the second time. 'm ₁ ' is an output value calculated as 'x ₁ ' is input to the argument calculator 550. That is, the output value m ₁ of the factor calculator 550 according to the input of 'x ₁ ' is a value obtained by multiplying the first output value m ₀ by the weighting factor '1-α' and the second input value ( x ₁ ) is the sum of the weights multiplied by α. At this time, the calculated value m ₁ is bypassed to the register 555.

Equation 5 below shows an operation result value of the factor calculator 550 according to the third symbol timing offset (x ₂ ) output from the offset detector 530.

Here, 'm ₁ ' is an output value of the factor calculator 550 according to input of the second symbol timing offset x ₁ output from the offset detector 530. 'x ₂ ' is the symbol timing offset output from the offset detector 530 for the third time. 'm ₂ ' is an output value calculated as 'x ₂ ' is input to the argument calculator 550. That is, the output value m ₂ of the print operator 550 according to the input of 'x ₂ ' is a weighting factor '1-α' to the second output value m ₁ of the print operator 550 stored in the register 555. It is a value obtained by multiplying a value obtained by multiplying the value multiplied by the weighting factor 'α' by the third input value (x ₂ ) to the factor calculating unit 550. At this time, the calculated value m ₂ is bypassed to the register 555. The factor calculator 550 may output an output value m such as [Equation 4] and [Equation 5] with respect to the input symbol timing offset (x = x ₀ , x ₁ , x ₂ , x ₃ ,... X _n ). performs _{= m 0, m 1, m} 2, m 3, repeat the arithmetic operation for calculating the ··· _n m).

Accordingly, the weight of 'x ₀ ' with respect to the output values m = m ₀ , m ₁ , m ₂ , m ₃ ,... M _n decreases, and the weight of the newly input symbol timing offset increases. However, the weight of the newly input symbol timing offset is relatively reduced compared to the output values (m = m ₀ , m ₁ , m ₂ , m ₃ ,... M _n-1 ) bypassed to the register 555.

Accordingly, the multiplication operation is performed on the weight factor 'α' set in the symbol timing offset newly input to the factor calculator 550, and the addition operation is performed by multiplying the weight factor '1-α' set in the output value of the previously input symbol timing offset. In the result of, the weight of the newly input symbol timing offset is reduced.

That is, in the static channel state, since the channel state is almost fixed, there is almost no change in symbol timing. At this time, the weighting factor α can estimate a symbol timing offset value having a relatively good value of about 0.1 to 0.15. For example, if the weight is 0.1, only about 10% of the input value is accumulated, and only 90% of the accumulated value is updated so that the accumulated value is maintained as it is. Even if is included, the abrupt change in the symbol timing offset value can be prevented, resulting in a phase noise elimination effect.

On the other hand, in the dynamic channel state, in order to quickly track the constantly changing channel state, it is necessary to track the channel state more quickly with the weighting factor β is about 0.2 ~ 0.3. That is, if the weighting factor is 0.3, about 30% of the input value is accumulated, and since only 70% of the accumulated value is updated, the channel state is rapidly increased by applying a relatively large amount of continuously changing input value rather than the accumulated value up to now. To be tracked.

In this way, the symbol timing recovery can be more stably performed by determining the current channel state and selecting an optimal weighter for the current channel environment based on information on whether the channel is static or dynamic.

9 is a flowchart illustrating a method of restoring symbol timing in response to a channel state by an OMD receiver according to the present invention.

The FFT unit 300 performs a Fast Fourier Transform (FFT) on the OFM signal compensated for by the symbol timing offset (S100). The offset detector 530 of the error detector 500 detects a symbol timing offset value from the fast Fourier transformed OMD signal (S200).

The equalizer 600 compensates for the distortion generated on the transmission channel with respect to the fast Fourier transformed OMD signal output from the FFT unit 300. The equalizer 600 predicts a transmission channel of the OMD signal by calculating a timing and frequency error value of a symbol of the OMD signal through the pilot signal. Here, the channel state determination unit 400 determines the current channel state according to the variation of the time of the OMD signal equalized by the equalizer 600 with respect to time (S300).

That is, the degree of change in the variation of the OFM signal in time in the frequency domain If is over a certain threshold, the current channel state is determined to be a dynamic channel state, and if there is little change, it is determined to be a static channel state.

Based on the information on the current channel state, the factor calculating unit 550 of the error detector 500 estimates a predetermined symbol timing offset value (S400). The print operator 550 selects the weighting factors 'α' and 'β' in the selection unit 552 in response to the channel state information. In response to the selected weights 'α' and 'β', the factor calculator 550 estimates a symbol timing offset value.

Thereafter, the offset compensator 200 compensates for the symbol timing of the OSDM signal based on the predetermined symbol timing offset value estimated by the factor calculator 550.

In this way, the symbol timing recovery can be more stably performed by determining the current channel state and selecting an optimal weighter for the current channel environment based on information on whether the channel is static or dynamic.

According to the present invention, by determining the current channel state and performing symbol timing restoration based on the channel information, stable symbol timing restoration can be performed in any channel environment.

In the above described and illustrated with respect to the preferred embodiment of the present invention, the present invention is not limited to the specific preferred embodiment described above, without departing from the gist of the invention claimed in the claims in the art Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

Claims (9)

An offset detector for detecting a symbol timing offset value from the fast Fourier transformed OMD signal; A channel state determination unit determining a current channel state according to a variation in time of the equalized FM signal; A factor calculating unit estimating a predetermined symbol timing offset value based on the channel state information determined by the channel state determining unit with respect to the symbol timing offset values sequentially input from the offset detection unit; And an offset compensator for compensating symbol timing of the OMD signal based on the predetermined symbol timing offset value estimated by the factor calculating unit. The method of claim 1, The printing operation unit, A selection unit for selecting a weighted person corresponding to the channel state based on the channel state information; A register for storing and inputting the first symbol timing offset for a predetermined time until a second symbol timing offset continuous to the first symbol timing offset is input; A first multiplier for multiplying the second symbol timing offset by a first weighted person that is the weighted person selected by the selection unit; A second multiplier for multiplying the first symbol timing offset output from the register by a second weighted party corresponding to the first weighted party; And And an adder configured to add the value calculated according to the multiplication operation of the first multiplier and the second multiplier to calculate the output value, and to output the output value to the outside and to bypass the register. UF DM receiver. The method of claim 1, When the channel state is a static state, the weighting factor is 0.1 to 0.15, And the weighting factor is 0.2 to 0.3 when the channel state is a dynamic state. The method of claim 2, And the switching part for outputting the symbol timing offset initially input to the outside and bypassing the register according to a control signal. The method of claim 2, And the sum of the first and second weighted members is '1'. Detecting a symbol timing offset value from the fast Fourier transformed OMD signal; Determining a current channel state according to a variation in time of the equalized FM signal; Estimating a predetermined symbol timing offset value with respect to the symbol timing offset value based on the channel state information determined in the channel state determination step; Compensating for the symbol timing of the OPM signal based on the estimated symbol timing offset value. The method of claim 6, The symbol timing offset value estimating step, Selecting a weighted party corresponding to the channel state based on the channel state information; A storage step of storing a first input timing timing offset by a predetermined time delay until a second output timing timing continuous to the first timing timing offset is input; A first multiplication operation of multiplying a first weighted person, the weighted person selected by the second symbol timing offset; A second multiplication step of multiplying the outputted first symbol timing offset by a second weighted person corresponding to the first weighted person; And And calculating the output value by adding a value calculated according to the multiplication operation of the first multiplication step and the second multiplication step, and outputting the output value to the outside and bypassing the storage step. A method of restoring a symbol timing of an OS receiver. The method of claim 6, When the channel state is a static state, the weighting factor is 0.1 to 0.15, And if the channel state is a dynamic state, the weighting factor is 0.2 to 0.3. The method of claim 7, wherein And a sum of the first weighted member and the second weighted weight is '1'.