KR20040080366A - Estimating apparatus and method of mobile station speed in a mobile communication system - Google Patents

Abstract

PURPOSE: A device for estimating a velocity of a mobile terminal in a mobile communication system and a method therefor are provided to use a previously normalized correction term to prevent a receiving performance from deteriorating owing to a mobile velocity change, thereby improving performance of a channel estimator. CONSTITUTION: A channel estimator(101) performs a channel estimation by using a signal received from a mobile terminal. The channel estimator(101) estimates a channel by using channel estimator coefficients received from a velocity estimator(110). The channel estimator coefficients are optimized channel estimator coefficients outputted to remove a Doppler shift frequency from the channel-estimated signal. The channel estimated signal is inputted to the velocity estimator(110). The velocity estimator(110) estimates a velocity based on the channel-estimated signal.

Description

TECHNICAL APPARATUS AND METHOD FOR SPECIFIC SPEED OF A MOBILE TERMINAL IN A MOBILE COMMUNICATION SYSTEM {ESTIMATING APPARATUS AND METHOD OF MOBILE STATION SPEED IN A MOBILE COMMUNICATION SYSTEM}

The present invention relates to an apparatus and method for estimating the speed of a mobile terminal, and more particularly, to an apparatus and method for estimating the speed of a mobile terminal in a mobile communication system.

In general, a mobile communication system has been developed to provide mobility of a terminal. As such, the mobile communication system forms a channel between the base station and the terminal through a wireless channel and performs voice and data communication through the formed channel in order to secure the mobility of the terminal. In addition, since the mobile communication terminal provides mobility as described above, the wireless signal output from the terminal is not always transmitted in a fixed position. That is, it is always possible to transmit a radio signal from another location. Therefore, the environment and path of the wireless channel may change from time to time. In addition, since the mobile communication terminal moves with the user, the mobile terminal may stop and transmit a radio signal, but may also transmit a radio signal while moving at a low speed or a high speed.

As described above, in the mobile communication system, the environment of the channel is changed, and the transmission path of the radio signal due to the position shift is changed. Therefore, the base station of the mobile communication system should receive data in consideration of the speed of the mobile terminal. That is, the mobile communication system estimates a transmission channel of the mobile terminal in consideration of the above cases, and extracts data according to the estimated result. Therefore, if the channel estimation of the mobile station is not accurate, it is impossible to extract the correct data. That is, when the channel cannot be accurately estimated in the mobile communication system, data cannot be extracted.

Then, channel estimation in the mobile communication system will be described. The mobile communication system transmits data to the mobile terminal through a forward link transmitted from the base station to the mobile terminal. At this time, in order to enable the mobile station to estimate the channel, transmission is performed including the pilot signal together with the traffic channel. That is, the mobile station transmits data to the base station through the reverse link. At this time, as described above, the base station transmits a reverse pilot signal to estimate the reverse channel. When the base station receives the pilot signal transmitted by the mobile station in the reverse direction, the base station estimates a channel based on this. The base station decodes the traffic received from the mobile station based on the channel estimated value. In this way, the data reception performance is improved by decoding.

However, a Doppler shift occurs between the reverse pilot channel and the reverse traffic channel according to the moving speed of the mobile station. This Doppler transition effect can lead to performance degradation in actual channel estimation. The performance degradation of the channel estimation means that the phase of the traffic has a different value depending on how much the received signal has transitioned. Also, the Doppler transition always has a different value depending on the speed of the mobile terminal. Therefore, in order to completely remove the Doppler transition effect at the base station, the Doppler transition effect should be removed at every speed that the terminal can move. Therefore, since the base station needs to remove the Doppler transition effect and channel estimation according to all speeds of the mobile station, a channel estimator is required for each speed in order to perform both.

Therefore, the method used to estimate the speed of the mobile terminal in the mobile communication system actually installed is as follows. In a real system, a channel estimator for dividing a moving speed of a terminal into several regions and providing an optimal channel estimation performance in a corresponding speed region is designed in advance. Since there are several predesigned channel estimators according to the moving speed of the terminal, it is necessary to determine which channel estimator to use. As such, in order to select a channel estimator, a velocity estimator for estimating a moving speed of the terminal based on the received signal is necessary. Methods of implementing a speed estimator include a method of using an autocorrelation function of a received signal in a time domain and a method of using a discrete fourier transform (DFT) in a frequency domain.

Which of these two methods is used is a matter of how to design. The speed estimator according to the method calculated as described above is generally located in front of the channel estimator and configured to select an estimation coefficient of the channel estimator after estimating the moving speed of the terminal. However, when the speed estimator is located in front of the channel estimator, the received signal signal-to-noise ratio improvement by the channel estimator cannot be taken. That is, the speed estimator exhibits unsatisfactory performance in the time domain or the frequency domain in a low signal-to-noise ratio. In addition, when the speed estimator is located in front of the channel estimator, there is a problem in that there is no proper input of the speed estimator in the gated mode transmission of the CDMA2000.

Accordingly, an object of the present invention is to provide an apparatus and method for accurately estimating the speed of a terminal without being affected by the signal-to-noise ratio and the intermittent mode transmission of CDMA2000 in a mobile communication system.

Another object of the present invention is to provide an apparatus and a method for efficiently performing data demodulation and decoding through accurate channel estimation regardless of a moving speed of a terminal in a mobile communication system.

An apparatus of the present invention for achieving the above objects is a base station apparatus for estimating the speed of a mobile terminal in a mobile communication system, a base station apparatus for estimating the speed of a mobile terminal in a mobile communication system, which is received from a mobile terminal. A channel estimator for receiving a signal of a wireless channel and performing channel estimation; detecting a power spectrum value of the channel estimator; and according to a Doppler transition frequency value of power estimated from the mobile terminal while the speed of the mobile terminal is not changed. And a speed estimator for outputting channel estimation coefficients to be used for channel estimation to the channel estimator.

In addition, the speed estimator,

When the speed of the mobile terminal is changed, the power is corrected for a predetermined time, and the channel estimating coefficient to be used for channel estimation is output to the channel estimator based on the Doppler frequency value according to the speed from the corrected power.

A method of the present invention for achieving the above objects is a method for estimating the speed of a mobile terminal in a base station apparatus of a mobile communication system, the channel estimation for receiving a signal of a radio channel received from the mobile terminal to perform channel estimation And a speed estimating process for detecting the channeled power spectrum value and outputting a channel estimation coefficient to be used for channel estimation according to the Doppler transition frequency value of the power estimated from the mobile terminal while the speed of the mobile terminal is not changed. Include.

In addition, during the channel estimation process,

The method further includes performing power correction for a predetermined time when changing the speed of the mobile terminal and outputting a channel estimation coefficient to be used for channel estimation according to the Doppler frequency value according to the speed from the corrected power.

1 is a block diagram of a speed estimator provided in a base station according to a preferred embodiment of the present invention;

2 is a diagram illustrating a power spectrum of a channel estimator transfer function optimized for each band by dividing the total speed band into four bands;

3 is a diagram illustrating an example of measuring a power spectrum according to a predetermined number of speed bands;

4 is a diagram illustrating a spectrum of a transfer function in two channel estimators having different speed bands;

FIG. 5 is a diagram illustrating a graph according to a correction term when obtaining a channel estimator power spectrum in the same manner as in Equation 2;

6 is a diagram illustrating a graph according to a correction term when obtaining a channel estimator power spectrum in the same manner as in Equation 3;

7 is a transient correction term spectrum graph for correcting a Doppler spectrum estimated from a mobile terminal when the speed is changed from a low speed to a high speed or from a high speed to a low speed;

8 is a control flowchart performed in a speed meter using a transient correction term and a steady state correction term;

9 is a flowchart for reservation of rate estimation update of a transmission rate according to a preferred embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings.

In addition, in the following description, many specific details such as specific index values, etc., are provided to help a more general understanding of the present invention, and it is common in the art that the present invention may be practiced without these specific details. It is self-evident to those who have knowledge of the world. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a block diagram of a speed estimator provided in a base station according to a preferred embodiment of the present invention. Hereinafter, a block configuration and operation of a speed estimator according to the present invention will be described in detail with reference to FIG. 1.

In FIG. 1, a channel estimator 101 and a velocity estimator 110 are included, and the velocity estimator 110 is located at a rear end of the channel estimator 101. The channel estimator 101 performs channel estimation using a signal received from a mobile terminal. In this case, the channel estimator 101 estimates a channel using the channel estimator coefficient received from the speed estimator 110. The channel estimator coefficients are optimized channel estimator coefficients output by the velocity estimator 110 according to the present invention for the removal of the Doppler transition frequency from the channel estimated signal. In addition, the signal estimated by the channel estimator 101 is input to the speed estimator 110. Since the speed estimator 110 estimates the speed based on the channel estimated signal, the signal having the channel compensation is a signal having a channel compensation, so the signal to noise ratio is improved. That is, the speed estimator 110 detects the Doppler transition in the frequency domain by the DFT method using the output of the channel estimator 101, which can have a continuous value even in a transmitted mode.

The channel estimator 101 is distinguished according to the speed band. That is, a plurality of channel estimators may be provided according to speed bands, and may operate differently according to speed bands. In the present embodiment, a method of operating differently according to each speed band will be described. The channel speed estimator 101 estimates a channel by receiving an estimated coefficient optimized for each speed band. The channel estimation coefficient distinguishes the Doppler frequency band for each speed required for channel estimation in the total speed band. And it can be designed to have an optimized value in the band divided by each speed. The optimized speed estimation coefficients in this speed band can be designed off-line. FIG. 2 shows the power spectrum of the channel estimator transfer function optimized for four total speed bands and optimized for Doppler frequency bands of 0 Hz to 100 Hz, 100 Hz to 200 Hz, and 200 Hz to 300 Hz and 300 Hz as an example. 2 is a transfer function for each frequency index, that is, for each Doppler frequency band.

The signal output from the channel estimator 101 and input to the speed estimator 110 is first input to the power spectrum measurer 111. The power spectrum meter 111 measures the power spectrum of the input signal using the DFT. The power spectrum measurer 111 stores a predetermined number of channel estimation output samples among values of power spectrum detection using a DFT. The power spectrum measurer 111 measures the power spectrum with respect to the frequency index of the minimum number q that can distinguish the Doppler bands from the stored samples. 3 shows an example in which the power spectrum is measured.

3 is a diagram illustrating an example of measuring a power spectrum at four frequency indices. Referring to FIG. 3, an example of measuring spectra for four speed bands is illustrated. In the four frequency indexes, reference numeral 301 located on the left side of the frequency side may be the lowest speed, reference numeral 302 becomes the next lowest speed, reference numeral 304 becomes the highest speed, and reference numeral 303 is the highest speed. The lower speed. Therefore, when the frequency index of the speed band is nh, ni, nj, nk, the h, i, j, k is greater than or equal to 1, less than the minimum number (q) that can divide the Doppler band Have the same value. As described above, the power spectrum is measured and the output power spectrum value is input to the power compensator 112.

The power compensator 112 compensates the power level for the estimated power spectrum for each frequency index. Power compensation for the power spectrum performed by the power compensator 112 is due to the spectral shape of the transfer function as shown in FIG. 2. As the Doppler frequency shift occurs according to the moving speed of the terminal, the attenuation of the power spectrum is different for each frequency band while passing through the channel estimator 101. Therefore, the estimated power spectra for each frequency index have different amounts of attenuation. In this way, since the attenuation amount is different from each other, the attenuation amount generated at each frequency index ni must be compensated for. The signal having the power compensation as described above is input to the short term averager 113. The short-term averager 113 calculates and outputs an average value for a predetermined short period with respect to the input signal. Then, the Doppler frequency detection logic 114 detects the Doppler frequency according to the moving speed of the mobile terminal, sets a correction coefficient thereof, and outputs the correction coefficient to the channel estimator 101.

Next, the power compensation method will be described with reference to FIGS. 4 to 7. 4 is a diagram illustrating a spectrum of a transfer function in two channel estimators having different speed bands. When the graph of reference numeral 410 in the speed band of FIG. 4 is referred to as the velocity of v, and the graph of reference numeral 420 is referred to as the velocity of v-1, the channel estimator 101 estimates each frequency index ni and nj. The compensation value for compensating for the distortion in the power spectrum meter 111 may be obtained by multiplying the inverse of the normalized value of the power spectrum. As such, the correction term W _inv (n), which is an inverse value of the normalized value of the power spectrum, may be expressed as in Equation 1 below.

In Equation 1, C (n) | _{vIndx = v} is the power spectrum of the channel estimator 101 for reference 410, wherein C (n) | _{vIndx = v-1} is the power spectrum of channel estimator 101 for reference 420. In Equation 1, the power spectrum of the channel estimator 101 is converted into the corrected power spectrum P _w (n) by multiplying the correction term W _inv (n), which is a normalized reciprocal value, by a weight. In addition, the maximum value C _max of the normalization constant or the channel estimator power spectrum in Equation 1 may be obtained by two methods as shown in Equation 2 or Equation 3 below.

Equation 2 is a method for obtaining the maximum value of the power spectrum for each speed band, and Equation 3 is a method for obtaining the maximum value of all the speed band power spectrum and applying it uniformly. When using Equations 2 and 3, the correction term W _inv (n) for the channel estimator power spectrum of FIG. 4 may be obtained as shown in FIGS. 5 and 6, respectively. 5 and 6, reference numeral 510 and reference numeral 610 are correction terms for the speed v, respectively, and reference numeral 520 and 620 are correction terms when the speed is v-1.

If the speed band is changed in the state where the correction term W _inv (n) is obtained using Equation 2, noise may be introduced into the power spectrum measurement and the corrected result due to the sudden change of the correction term. Is needed. That is, the mobile terminal does not always maintain the same speed, but the speed may change continuously. Therefore, if the case of changing from the speed of v-1 to the speed of v will be described with reference to FIG.

In FIG. 5, considering that the speed of the mobile terminal is v-1 and the speed of the mobile terminal is changed to v, the correction term W _inv (n) | _{vIndx = v-1} has the same graph as reference numeral 510 of FIG. In this case, when the frequency index is i, the correction term has a value of W _inv (ni) = 1, and when the frequency index is j, the correction term has a value of W _inv (nj) = w2. Therefore, the power corrected at time i has a relationship of P _w (ni) = P (ni), and the power corrected at time j has a relationship of P _w (nj) = w 2 ㅧ P (nj). At this time, in order for the speed of the mobile terminal to change to v, the relationship of P _w (ni) < P _w (nj), that is, P _w (ni) / P _w (nj) <

When the speed of the mobile terminal is changed to v when the above relationship is satisfied, the correction term W _inv (n) | _{vIndx = v} is changed into a graph as shown by reference numeral 520 shown in FIG. 5, and the correction power spectrums observed at the moment when the graph is changed are P _w (ni) = P (ni) and P _w (nj). = w1 ㅧ P (nj) is changed suddenly. In the case of the example of FIG. 5, since w1 <w2, the speed estimator 110 repeats the process of detecting the speed which is reversed by vIndx = v-1. On the contrary, considering the case where vIndx = v changes to vIndx = v-1 in FIG. 5, the correction term W _inv (n) | _{vIndx = v} becomes a graph at 520. At this point, W _inv (ni) = 1 and W _inv (nj) = w1, so the corrected power is P _w (ni) = P (ni) and P _w (nj) = w1 ㅧ P (nj). In order to change vIndx = v-1, the relationship of P _w (ni)> P _w (nj), that is, P _w (ni) / P _w (nj)> _w 1 must be satisfied. When this relationship is satisfied and vIndx = v-1, the correction term W _inv (n) | _{vIndx = v-1} is replaced with a graph of 510, causing the momentarily observed correction power spectrum to change abruptly as P _w (ni) = P (ni), P _w (nj) = w2 ㅧ P (nj) do. In the case of the example of FIG. 5, since w1 < w2, the speed estimator repeats the process of detecting the speed which is reversed by vIndx = v. Therefore, two kinds of correction terms W _inv (n) may be introduced as shown in FIG. 7 to eliminate the effect of the sudden size change of the correction term W _inv (n) at the time when the channel estimator coefficient is changed. 7 is a Doppler graph for correcting the speed of a mobile terminal when the speed is changed from low speed to high speed or from high speed to low speed.

When vIndx = v-1 to vIndx = v, the correction term is a graph of reference numeral 730 at vIndx = v-1, and P _w (ni) increases by "w1 / w2" for a period of time at vIndx = v. Use the same graph as 720 in the reduced transient correction term. After a certain time, the transient correction term is changed to the graph of the steady state correction term reference numeral 710 to perform power correction. Conversely, if vIndx = v to vIndx = v-1, the correction term is plotted with a graph of 710 at vIndx = v, and P _w (nj) is equal to "w1 / w2" for a period of time at vIndx = v-1. Use the graph of transient correction term reference 740 with reduced size. After a certain time, the transient correction term is changed to the steady state correction term reference 730 to perform power correction.

8 is a diagram illustrating a control flow performed in a speed meter using a transient correction term and a steady state correction term. Hereinafter, the process of the control flow performed in the speed meter using the transient correction term and the steady state correction term will be described in detail with reference to FIG. 8.

In step 800, the speed estimator 110 measures the power spectrum value P (n). In this way, after measuring the power spectrum value, the process proceeds to step 802 and the speed estimator 110 performs the processing in the steady state. Here, the steady state refers to a state in which the estimated speed band does not change. If the estimated speed of the mobile terminal does not change as described above, Winv = SSinvTable value is used. In other words, the correction term in the steady state is used. After the calculation is performed using the steady state correction term in step 802, the process proceeds to step 804 to determine whether the speed of the currently estimated mobile terminal is the same as the speed of the previous mobile terminal. If a new speed band is detected from the signal received from the mobile terminal as a result of step 804, that is, if the previous speed and the current speed are different, the process proceeds to step 806. However, if the new speed band is not detected as a result of the check of step 804, step 808 is performed.

If the speed estimator 110 proceeds to step 806, it uses a transient correction term according to the newly measured speed to prevent a sudden change in speed. This speed correction term is calculated using the above-described Equation 3 to calculate the correction term W _inv (n). When the correction term is calculated as shown in Equation 3, since the correction term is calculated after normalizing all speed bands, noise generated due to the sudden change of the correction term is not introduced. In this case only, a transient response is generated in the power spectrum measurement due to the system memory reverberation response of the channel estimator due to the change of the estimation coefficient of the channel estimator 101. Therefore, the speed estimator 110 operates to suspend the speed estimation update by simply using a transmission counter (transCount) as shown in FIG. 9 for a predetermined time at the time when the speed is changed.

When the correction term is not used, that is, when the process proceeds from step 804 to step 808, the speed estimator 110 performs power compensation in step 808. Such power compensation is performed in the power compensator 112 of FIG. In operation 810, the short-term averager 113 of the speed estimator 110 takes an average of power-compensated values for a predetermined short period. In this short period of averaging, smoothed power spectra P _a (n) and (n = n1 to nq) are obtained. In operation 812, the Doppler frequency is detected with respect to the average power of the Doppler frequency detector 114 of the speed estimator 110. That is, the Doppler frequency detector 114 finally performs size comparison for each frequency index of P _a (n) and (n = n1 to nq). When the frequency index position having the largest power spectrum is detected, the Doppler frequency detector 114 determines the moving speed of the terminal in the Doppler frequency band to which the frequency index position belongs, that is, the speed band corresponding thereto. When the Doppler frequency is detected as described above, the detected Doppler frequency value is output to the channel estimator 101 so as to be updated and used as a channel estimation coefficient according to the detected Doppler frequency at the time of channel estimation.

9 is a flowchart for reservation of a rate estimation update of a transmission rate according to a preferred embodiment of the present invention. Hereinafter, the flow will be described in detail when the rate estimation update of the transmission rate is reserved with reference to FIG. 9. In the following description, it is assumed that a timer value required when the speed estimation update is reserved is set.

In step 900, the speed estimator 110 measures the power spectrum value P (n). Thus, the power spectrum value is measured. 9 is a control process at the time when the speed estimation update is withheld according to the speed, so the process proceeds directly to step 902 after performing step 900. Accordingly, the power compensator 112 of the speed estimator 110 performs power compensation on the measured power spectrum. Compensation for the measured power spectrum is performed, and the flow proceeds to step 904 where the short term averager 113 averages the compensated power. In other words, the velocity value is obtained from the emulsified power spectrum P _a (n) and (n = n1 to nq). After calculating the emulsified power spectrum value as described above, the process proceeds to step 906 to determine whether the value of the transmission counter has a value of "0". The check whether the value of the transmission counter has a value of "0" is a process of checking whether the time to use the correction term has elapsed according to the change of the speed. When the usage time of the correction term expires, that is, when the correction term is no longer needed, the process proceeds to step 908 to detect the Doppler frequency and applies the value to the channel estimator 101 to estimate the channel. To lose.

However, if it is necessary to continue using the correction term, that is, if the time has not elapsed as determined by the correction term usage time, the flow proceeds to step 914 to decrease the transmission counter value. Thereafter, the speed estimator 110 proceeds to step 900. That is, the speed of the mobile terminal is changed so that the correction term can be used continuously during the time when the correction term is to be used.

As described above, in order to prevent the deterioration of reception performance according to the change of the moving speed of the mobile terminal, a previously normalized correction term is used for a predetermined time, thereby improving the performance of the channel estimator.

Claims (12)

A base station apparatus for estimating the speed of a mobile terminal in a mobile communication system, A channel estimator receiving a signal of a wireless channel received from a mobile station and performing channel estimation; A speed estimator for detecting a power spectrum value of the channel estimator and outputting a channel estimation coefficient to the channel estimator for channel estimation according to a Doppler transition frequency value of power estimated from the mobile terminal while the speed of the mobile terminal is not changed The device characterized in that it comprises a. The method of claim 1, wherein the speed estimator, And correcting the power for a predetermined time when the speed of the mobile terminal is changed, and outputting a channel estimation coefficient to the channel estimator for use in channel estimation according to the Doppler frequency value according to the speed from the corrected power. The method of claim 1, wherein the speed estimator, A power spectrum meter for measuring a power spectrum according to an output value of the channel estimator; A power compensator for outputting power by compensating an output value of the power spectrum measuring device to a correction value or a steady state value according to whether the moving speed of the mobile terminal is changed; An averager for averaging the power output from the power compensator for a predetermined time; And a Doppler frequency detector for detecting a Doppler frequency according to the output of the averager and outputting a correction value for use in channel estimation according to the detected Doppler frequency. 4. The apparatus of claim 3, wherein the value compensated for in the power compensator uses a correction value normalized by the maximum value of the channel estimator transfer function as shown in Equation 4 below. The method of claim 3, wherein the Doppler frequency detector, The method of claim 1, wherein the inverse correction value of the channel estimator transfer function is obtained for each speed band in order to correct the Doppler power spectrum based on the channel estimation coefficient used for channel estimation according to the Doppler frequency. The method of claim 1, wherein the speed estimator, The apparatus as claimed in claim 1, wherein the calculation is performed using a Discrete Fourier Transform (DFT) only for a frequency index according to a predetermined number of frequency bands. A method for estimating the speed of a mobile terminal in a base station apparatus of a mobile communication system, A channel estimation process of performing channel estimation by receiving a signal of a wireless channel received from a mobile terminal; Detecting the channeled power spectrum value and outputting a channel estimation coefficient to be used for channel estimation according to the Doppler transition frequency value of the power estimated from the mobile terminal while the speed of the mobile terminal is not changed. Characterized in that the method. The method of claim 7, wherein in the channel estimation process, And performing a power correction for a predetermined time when changing the speed of the mobile terminal and outputting a channel estimation coefficient to be used for channel estimation according to the Doppler frequency value according to the speed from the corrected power. The method of claim 7, wherein the speed estimation process, Measuring a power spectrum of the channeled power; Outputting power by compensating the output value of the measured power spectrum meter to a correction value or a steady state value according to whether the moving speed of the mobile terminal is changed; Receiving and averaging the power compensated value for a predetermined predetermined time; Detecting a Doppler frequency according to the averaged value and outputting a correction value for use in channel estimation according to the detected Doppler frequency. The method as claimed in claim 8, wherein the value compensated for during power compensation uses a correction value normalized by a maximum value of a channel estimator transfer function as in Equation 5 below. 8. The method of claim 7, wherein an inverse correction value of the channel estimator transfer function is obtained for each speed band in order to correct the Doppler power spectrum based on a channel estimation coefficient to be used for channel estimation according to the Doppler frequency. The method of claim 7, wherein the speed estimation process, The method as claimed in claim 1, wherein the calculation is performed using a Discrete Fourier Transform (DFT) only for a frequency index according to a predetermined number of frequency bands.