KR100521402B1 - Receiver of orthogonal frequency division multiple access system for carrier frequency offset compensation employing time domain parallel interference cancellation algorithm - Google Patents

Abstract

The present invention relates to a receiver and a compensation method of an orthogonal frequency division multiple access system for compensating carrier frequency offset in a multi-user environment. In particular, by eliminating interference components due to carrier frequency offset difference between users through Time Domain Parallel Interference Cancellation (TDPIC) algorithm, orthogonal frequency division to effectively compensate for carrier frequency offset in a multi-user environment A receiver and a compensation method of a multiple access system.

To this end, the receiving apparatus of the present invention receives the OFDMA signal of the time domain by multiple users from the outside to remove the carrier frequency offset component included in the received signal for each user carrier from the first means and the first means A second means for outputting a signal from which interference components due to carrier frequency offset differences for each user are output by inputting a signal from which the frequency offset component is removed, and fast Fourier transforming a signal from the second means to generate a signal in a frequency domain And third means.

Description

RECEIVER OF ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS SYSTEM FOR CARRIER FREQUENCY OFFSET COMPENSATION EMPLOYING TIME DOMAIN PARALLEL INTERFERENCE CANCELLATION ALGORITHM}

The present invention relates to a receiving apparatus of an orthogonal frequency division multiple access system, and more particularly, to receiving an orthogonal frequency division multiple access system capable of effectively compensating a carrier frequency offset in a multi-user environment. Relates to a device.

In the case of transmitting data at high speed in a wireless communication system using wireless, the bit error probability of transmitted data is increased due to the effects of multipath fading and Doppler spread. The quality will be reduced. Therefore, in recent years, a lot of research has been conducted to overcome the disadvantages of such wireless communication. Among them, orthogonal frequency division multiplexing (hereinafter, referred to as OFDM) is a field that is most actively researched as a method suitable for high-speed data transmission in wired and wireless communication systems.

OFDM uses a fast Fourier transform (FFT) and an inverse fast Fourier transform (IFFT) to convert a signal composed of a plurality of subcarriers orthogonal to each other through a given frequency band. It is a kind of Multi Carrier Modulation (MCM) method for transmitting and receiving. The OFDM scheme uses a plurality of carriers having mutual orthogonality, and thus has an advantage of high frequency utilization efficiency and robustness to multipath fading in a mobile environment. Because of these advantages, the OFDM scheme provides high-speed wireless LAN, broadband wireless access (BWA), digital audio broadcasting (DAB) and digital terrestrial television broadcasting (DTTB), and asymmetric digital (ADSL). It is adopted as a standard method of Subscriber Line and Very High Bit Rate Digital Subscriber Line (VDSL).

On the other hand, when the OFDM method is used for mobile communication, wireless ATM, wireless LAN, etc., which is not for broadcasting, a multiple access method for multiple users is required like a single carrier transmission method. As is well known, multiple access schemes include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA). These may be used in combination with the OFDM scheme, respectively. Among them, the FDMA access scheme is applied to the OFDM scheme as OFDM / FDMA or OFDMA (hereinafter referred to as OFDMA).

Currently, OFDMA is adopted as a standard of IEEE 802.16, an air interface standard for high-speed data transmission in different frequency bands, and it is easy to implement variable data rates, and has a frequency diversity effect and a receiver structure. The advantage is simple.

OFDMA enables multiple access by multiple users by assigning specific subcarriers to each user among multiple subcarriers. In the OFDMA system, the degree of Multiple Access Interference (MAI) due to the multi-user access is different depending on the subcarrier allocation (SA). That is, the degree of performance deterioration by MAI appears to be different. Such subcarrier allocation methods include block subcarrier allocation (BSA), block interleaved subcarrier allocation (BISA), random block and interleaved subcarrier allocation (RBISA), and the like. There is this. Among them, the least degradation of performance for MAI is known as RBISA. However, it is best to change the SA adaptively according to the transport channel environment.

On the other hand, since the OFDM scheme uses a plurality of subcarriers orthogonal to each other, when the orthogonality between these subcarriers is destroyed, carrier interference (ICI) occurs between adjacent users, which greatly increases the bit error rate. In the OFDM scheme, the largest cause of orthogonality between subcarriers is caused by a carrier frequency offset (CFO) caused by the carrier's frequency synchronization being not performed at the receiving end or the uplink (UPLINK). By Synchronization research in a multi-user environment for estimating and compensating for these carrier frequency offsets has been actively conducted until recently.

In the conventional proposed carrier frequency offset compensation method (IEEE COMMUNICATION LETTERS, VOL.4, NO.12, DECEMBER 2000), complex complexes before receiving a fast Fourier transform (FFT) on the received OFDM symbols There are a method of compensating a carrier frequency offset by multiplying a complex exponents value and a method of compensating a carrier frequency offset using a circular convolution after performing a fast Fourier transform.

1 is a block diagram of a transmission module and a channel environment of a mobile terminal using OFDMA. In FIG. 1, it is assumed that there are U users and an OFDMA system using N subcarriers. The N subcarriers include actual subcarriers N _used and virtual subcarriers in a guard band.

Referring to FIG. 1, subcarriers X _{u, 0} , X _{u, 1} , X _{u, 2} , ... assigned to respective users 100-1, 100-2, ..., 100-U. , X _{u, N-1} ) are performed by the inverse fast Fourier transformers 102-1, 102-2, ..., 102-U, respectively, and the operation of Equation 1 below is performed. x _{u, n where} n = 0, 1, 2, ..., N-1).

(Where X _{u, k} is the k th subcarrier of the u th user, = exp (-j2πkn / N))

In addition, Cyclic Prefixes (hereinafter, CP: x _{u, NL} , x _{u, N-L + 1} , ..., x _{u, N)} are inserted into transmission symbols for transmission to prevent interference between adjacent symbols. _-1 ) is also included. Each CP is inserted by copying the last L symbols of the symbols from the inverse fast Fourier transformer.

Transmission symbols including CPs for each user (100-1, 100-2, ..., 100-U) are converted by the parallel-to-serial converters 104-1, 104-2, ..., 104-U. Each transmit symbol vector ( _u ) Equation 2 below shows the transmission symbol vector of the u th user ( _u ).

In Equation 2, a transmission symbol vector ( Definition of each element of _u ) is disclosed in Equation 1 above.

Meanwhile, the transmission symbol vectors transformed by the respective bottle / serial converters 104-1, 104-2, ..., 104-U ( ₁ , ₂ , ..., _U ) is transmitted to a base station (BS) through transmission channels 106-1, 106-2,..., 106 _-U for each user. At this time, each data symbol vector (through the transmission channels 106-1, 106-2, ..., 106-U) ₁ , ₂ , ..., _U ) has an attenuation component value Η _u corresponding to the attenuation characteristic of each transmission channel 106-1, 106-2,..., 106 -U. Equation 3 below shows the data symbol vector of the u-th user including the attenuation component of the transmission channel.

(only, )

In [Equation 3], Η _u is the determinant of the u-th user's channel attenuation component in the form of ((N + L) × (N + L)). Denotes a carrier frequency offset component of the n th symbol of the u th user, Means a Rayleigh fading profile component. F ^u denotes a generalized carrier frequency offset between the u th user and the uplink receiver.)

On the other hand, the signal received from the base station ( ) Is the data symbol vector ( ₁ , ₂ , ..., The sum of _U ) and the noise of the channel (AWGN: Additive White Gaussian Noise) ), Which can be expressed as shown in Equation 4 below.

(only, )

2 is a block diagram of a conventional OFDMA receiver for compensating carrier frequency offset using a complex function value. 2, a conventional OFDMA receiver includes a multiplier (200-1, 200-2, ..., 200-U), a serial / parallel converter (202-1, 202-2, ..., 202-) U), CP removers 204-1. 204-2, ..., 204-U, and fast Fourier transformers 206-1, 206-2, ..., 206-U. Hereinafter, FIG. 2 will be described based on any one user (u-th user) because the block configuration and operation of each user are similar. (Where u is one of 1, 2, ..., U)

In the multiplier 200-u of the u-th user, the signal received through the receiving antenna of the OFDMA receiver ( ) Is multiplied by a complex function (u-complex function) obtained by estimating a carrier frequency offset component to obtain a received signal ( Compensation for the carrier frequency offset component of the u-th user included in the).

The serial-to-parallel converter 202-u converts a signal input from the multiplier 200-u into parallel symbols 203-u and _{u, 0} , _{u, 1} , ..., _{u, N-1} ). Transformed symbols 203-u and _{u, 0} , _{u, 1} , ..., _{u, N-1} ) also includes a CP 203-u component inserted to prevent interference between symbols during initial transmission.

The CP remover 204-u removes only the CP component 203-u of the symbols from the serial / parallel converter 202-u.

The fast Fourier transformer 206-u is a symbol with the CP component 203-u removed. _{u, 0} , _{u, 1} , ..., _{u, N-1} ) using the fast Fourier transform _{u, 0} , _{u, 1} , ..., recovery symbols close to _{u, N-1} ) _{u, 0} , _{u, 1} , ..., _{u, N-1} ).

However, reconstruction symbols obtained by compensating the carrier frequency offset component through the method shown in FIG. _{u, 0} , _{u, 1} , ..., _{u, N-1} ) still has interference components due to carrier frequency offset differences between neighboring users.

3 to 6 are diagrams illustrating interference components caused by carrier frequency offset differences between adjacent users even after compensating carrier frequency offsets through the conventional method as shown in FIG. 2. For convenience of description, only two carriers for each user are shown for two users.

FIG. 3A illustrates a carrier signal of a first user, and FIG. 3B illustrates a carrier signal of a second user. As shown in FIG. 3, each user carrier has a frequency difference of Δf. 4A illustrates a signal including a carrier frequency offset f ¹ due to interference between carriers in the first user, and FIG. 4B illustrates a second user in FIG. FIG. 7 shows a signal including a carrier frequency offset (-f ² ) due to interference between carriers.

5 is a diagram illustrating a signal in which a carrier signal for each user is transmitted through one OFDMA uplink channel. The signal shown in FIG. 5 is restored to the original signal for each user by removing the carrier frequency offset component through the conventional carrier frequency offset compensation method shown in FIG.

FIG. 6 is a diagram illustrating a signal reconstructed for each user by removing a carrier frequency offset component through a conventional frequency offset compensation method as shown in FIG. 2. As shown in FIG. 6A, even after compensating the carrier frequency offset, the recovered signal of the first user still has the interference component (-f ¹ -f ² ) due to the carrier frequency offset difference with the first second user. do. In the case of the second user as well, as shown in FIG. 6B, there is an interference component f ¹ + f ² .

As shown in the above description, even after compensating a carrier frequency offset value for each user by estimating a carrier frequency offset and multiplying a complex function, the interference component due to the difference in the carrier frequency offset value between users still exists. Therefore, this results in performance degradation of the OFDMA receiver.

Disclosure of the Invention An object of the present invention is to provide an orthogonal frequency division multiple access system capable of compensating interference components caused by carrier frequency offset differences between multiple users in the uplink of an orthogonal frequency division multiple access system through a parallel interference cancellation algorithm in the time domain. To provide a receiver.

The OFDMA system receiving apparatus of the present invention receives a first signal of an OFDMA scheme by multiple users from the outside and outputs a second signal by removing a carrier frequency offset component included in the first signal for each user and the second signal. A second means for outputting a third signal from which interference components due to carrier frequency offset differences for each user are input as a signal, and a third means for generating a fourth signal in a frequency domain by fast Fourier transforming the third signal; do.

(Example)

FIG. 7 is a block diagram illustrating a receiver of an orthogonal frequency division multiple access system implemented using a time-domain parallel interference cancellation algorithm according to the present invention. As shown in FIG. 7, the receiver of the OFDMA system includes multipliers 700-1, 700-2, ..., 700-U, and serial / parallel converters 702-1, 702-2, ... for each user. , 702-U), CP cancellers 704-1, 704-2, ..., 704-U, Time Domain Parallel Interference Canceller (TDPIC: Time Domain Parallel Interference Cancellation) and Fast Fourier transformers 1, 708-2, ..., 708-U).

The multipliers 700-1, 700-2,..., 700 -U for each user receive signals received through the reception antenna of the OFDMA receiver. ) Is multiplied by the complex function obtained by estimating the carrier frequency offset component, respectively, Signals from which the carrier frequency offset component included in each user) are removed.

The serial / parallel converters 702-1, 702-2, ..., 702-U parallel the signals input from the respective multipliers 700-1, 700-2, ..., 700-U. In the form of symbols [703-1 and _1,0 , _1,1 , ..., _{1, N-1} ), (703-2 and _2,0 , _2,1 , ..., _{2, N-1} ), ..., (703-U and _{U, 0} , _{U, 1} , ..., _{U, N-1} )] to output. At this time, the converted symbols also include CP components 703-1, 703-2, ..., 703-U inserted to prevent interference between symbols during initial transmission.

CP cancellers 704-1, 704-2, ..., 704-U are CP components of symbols from the serial / parallel converter 702-1, 702-2, ..., 702-U. Only the symbols from which (703-1, 703-2, ..., 703-U) are removed are output. Hereinafter, the symbols output by the CP canceller are referred to as first-order compensation symbols (because these symbols primarily compensate for the carrier frequency offset using a complex function).

On the other hand, the output signal at this time includes an interference component due to the difference in the carrier frequency offset value between each user as mentioned in the prior art. In more detail through the equation, for the u-th user, the symbols (output from the CP remover 704-u ( _{u, 0} , _{u, 1} , ..., _{u, N-1} or less, in the form of a vector Is expressed in a vector form as shown in Equation 5 below.

However, in [Equation 5] Denotes a carrier frequency offset estimation value of the u-th user, and is represented by Equation 6 below.

In [Equation 6] above Is a carrier frequency offset estimation value for the n th symbol of the u th user, as shown in Equation 7 below.

(only, Is the carrier frequency offset synchronization value between the u-th user and the uplink receiver, and n = 0, 1, 2, ..., N-1.)

In [Equation 5], the influence on the nth received symbol of the u-th user is expressed as Equation 8 below, which may be divided into three components as shown in Equation 9 below.

In [Equation 9] Denotes the signal component of the n th received symbol of the u th user, Is a symbol representing an interference component generated by a carrier frequency offset difference between users. Denotes an additive white Gaussian noise (AWGN) component. As shown in Equation 9, the signal input to the TDPIC from the CP cancellers includes interference components that cause performance degradation of the OFDMA receiver. And, using the above Equation 8 and Equation 9, such interference components can be expressed as Equation 10 below.

As mentioned above, interference components such as Equation 10 are generated because carrier frequency offset values of the users are different from each other. If the carrier frequency offset values of all users are the same, the interference component as shown in [Equation 10] will not occur.

The time domain parallel interference canceller 706 uses the first compensation symbols input from the CP cancellers 704-1, 704-2,. The interference components represented by Equation 10 above are removed and output. Meanwhile, the TDPIC 706 removes an interference component (TDPIC) in the time domain, that is, before the fast Fourier transform.

8 is a block diagram illustrating an embodiment of the TDPIC 706 of the present invention. Referring to FIG. 8, the TDPIC 706 includes a signal reproduction block 802, an operation block 804, and an interference cancellation block 806. The symbol shown in FIG. 8 means a vector form.

The signal regeneration block 802 is composed of signal regeneration circuits 802-1, 802-2, ..., 802-U corresponding to each user, and each signal regeneration circuit has 1 from the corresponding CP canceller. The second compensation symbols are input to reproduce the symbols before the compensation. This is possible because not all carriers obtained by fast Fourier transforming the first compensation symbols of a specific user are affected by the carrier of another user. That is, referring to FIG. 6A, one of the carriers 602a and 604a of the first user is not affected by the carriers 602b and 604b of the second user. Hereinafter, the symbol reproduction operation will be described in more detail with the u-th signal reproduction circuit as an example.

9 is a block diagram showing an embodiment of a u-th signal reproducing circuit of the present invention. Referring to FIG. 9, the signal reproducing circuit includes a fast Fourier transform unit 902, a demodulator 904, a decoder 906, an encoder 908, a modulator 910, and an inverse fast Fourier transform 912. Include. The u th signal regeneration circuit 802-u receives the first compensation symbols (i) which are input from the u th CP canceller 704-u. _u ) symbols before the first compensation by using a carrier that is not affected by other carriers among the carriers obtained by fast Fourier transforming _{u, 0} , _{u, 1} , ..., _{u, N-1} : or less, vector Form _{play u} .) The fast Fourier transform, demodulation, decoding, encoding, modulation and inverse fast Fourier transform operations of the signal regeneration circuit for this purpose are well known techniques, and thus detailed descriptions thereof will be omitted.

On the other hand, the symbols before the first compensation through the signal reproduction block 802 ( ₁ , ₂ , ... _{When U} ) is reproduced, the operation block 804 can completely reproduce the interference component due to the difference in the carrier frequency offset value between users included in the first compensation symbols through the calculation using Equation 11 below. only, Is assumed.)

In the interference cancellation block 806, the first compensation symbol input from the CP cancellers using the respective adders 806-1, 806-2, ..., 806-U, as shown in Equation 12 below. field( ₁ , ₂ , ..., Interference components reproduced by arithmetic block 804 in _U ) ₁ , ₂ , ..., _By subtracting _U ), the symbols whose carrier frequency offset is fully compensated ( ₁ , ₂ , ..., _U )

The fast Fourier transformers 706-1, 706-2,..., 706-u receive symbols input from the TDPIC 706 [( _1,0 , _1,1 , ..., _{1, N-1} ), ( _2,0 , _2,1 , ..., _{2, N-1} ), ..., ( _{U, 0} , _{U, 1} , ..., _{U, N-1} )] through the fast Fourier transform _{u, 0} , _{u, 1} , ..., symbols in the frequency domain close to _{u, N-1} ) _{u, 0} , _{u, 1} , ..., _{u, N-1} ).

10 is a performance evaluation graph of a conventional OFDMA receiver using only a complex function and the OFDMA receiver proposed by the present invention. The graph of FIG. 10 is a simulation result through a computer by applying the parameters as shown in Table 1 below.

Parameter Application value Total carrier frequency (N) 256 Number of carriers used (M × U) 200 Max number of users 4 Channel coding Convolution Code K = 5 Bandwidth 10 MHz CP (Cyclic Prefix: L) 64 Modulation method QPSK Carrier Allocation (SA) RBISA Free Carrier Frequency Offset (RCFO) F ^u | ≤v · Δf (v = 1,2,3,4)

(In Table 1, v denotes a range of carrier frequency offset, and Δf denotes a normalized subcarrier spacing.)

Referring to FIG. 10, the portions indicated by dotted lines {P1 (when v = 1), P2 (when v = 2), P3 (when v = 3), and P4 (when v = 4)} are known Is the characteristic curve according to the value of v, and the solid line {(I2 (when v = 2), I3 (when v = 3), I4 (when v = 4)} is applied when the TDPIC compensation method of the present invention is applied. The thick solid line T is a theoretical characteristic curve, as shown in Fig. 10. As shown in Fig. 10, the OFDMA receiver to which the TDPIC algorithm of the present invention is applied has a bit error rate for all v values. It can be seen that there is an excellent performance improvement in both symbol energy vs. noise power spectral density (Es / No), especially when v = 2 (I2), which is almost similar to the theoretical characteristic curve (T), where v < In case of 2, it is completely coincident with the theoretical characteristic curve (T).

In the above, the configuration and operation of the TDPIC algorithm according to the present invention and the OFDMA system receiving apparatus using the same have been described above with reference to the above drawings, but these are merely exemplary and various applications and modifications are made without departing from the technical spirit of the present invention. This is possible.

As described above, the OFDMA receiver of the present invention can effectively compensate for the carrier frequency offset in a multi-user environment by removing not only the carrier frequency offset caused by user interference but also the interference component caused by the carrier frequency offset difference between users. Therefore, an excellent effect can be obtained even at a bit error rate.

1 is a block diagram of a transmission module and a channel environment of a mobile terminal using OFDMA.

2 is a block diagram of a conventional OFDMA receiver for compensating carrier frequency offset using a complex function value.

3 to 6 are diagrams illustrating interference components caused by carrier frequency offset differences between adjacent users even after compensating carrier frequency offsets through the conventional method as shown in FIG. 2.

FIG. 7 is a block diagram illustrating a receiver of an orthogonal frequency division multiple access system implemented using a time-domain parallel interference cancellation algorithm according to the present invention.

8 is a block diagram illustrating an embodiment of a time domain parallel interference canceller of the present invention.

9 is a block diagram showing an embodiment of a u-th signal reproducing circuit of the present invention.

10 is a performance evaluation graph of a conventional OFDMA receiver using only a complex function and the OFDMA receiver proposed by the present invention.

Claims (19)

In the receiving apparatus of an orthogonal frequency division multiple access (OFDMA) system, First means for receiving a first signal of an OFDMA scheme by multiple users from the outside and outputting a second signal for compensating carrier frequency offset components included in the first signal for each user; Second means for outputting a third signal by removing the interference component due to the carrier frequency offset difference for each user as the second signal; And And third means for generating a fourth signal in a frequency domain by performing fast Fourier transform on the third signal. The method of claim 1, And the first signal, the second signal, and the third signal are signals in a time domain. The method of claim 1, And the second signal is represented by symbols in parallel form. The method of claim 1, The first means includes: a multiplier for compensating the carrier frequency offset by multiplying the first signal and a complex function obtained by estimating the carrier frequency offset for each user; and A serial / parallel converter for converting the output signal of the multiplier into parallel signals; And And a CP canceller for removing the CP component signals from the signals from the serial / parallel converter. The method of claim 4, wherein The multiplier, the serial / parallel converter and the CP canceller are configured to correspond to the users, respectively. The method of claim 1, The second means includes a signal reproducing block for reproducing the signals of the first signal by inputting the second signal; and An arithmetic block which performs predetermined arithmetic operation for each user by inputting reproducing signals from the signal reproducing block; And And an interference cancellation block for subtracting the calculation results from the operation block from the second signal for each user. The method of claim 6, And the signal regeneration block is composed of a plurality of signal regeneration circuits corresponding to each user. The method of claim 7, wherein The signal reproducing circuit includes a fast Fourier transform unit for converting the second signal into a signal in a frequency domain through fast Fourier transform; A demodulator for demodulating the fast Fourier transformed signal; A decoding unit for decoding a signal from the demodulation unit; An encoding unit for encoding the signal from the decoding unit; A modulator for modulating a signal from the encoder; And an inverse fast Fourier transform unit for outputting a reproduction signal of the first signal through an inverse fast Fourier transform on the signal from the modulator. The method according to claim 1 or 6, The operation result of the operation block is the reception device of the OFDMA system, characterized in that the same as the interference component included in the second signal for each user. The method of claim 9, The operation block is a reception device of an OFDMA system, characterized in that for each user performs the following operation. (only, Is a signal reproducing the interference component of any u-th user, Is the carrier frequency offset of the i-th user, Is a compensation value for the carrier frequency offset of the u-th user, and Is a reproduction signal of the first signal of the i-th user.) A device for parallel interference cancellation in a time domain for removing interference components caused by carrier frequency offset differences between users in an OFDMA system, A signal reproducing block configured to reproduce signals of the first signal by inputting a second signal that compensates for a carrier frequency offset component between users included in the first signal received from the outside; An arithmetic block for reproducing the interference component by inputting reproduction signals from the signal reproduction block; And And an interference cancellation block for subtracting the interference component from the operation block in the second signal. The method of claim 11, And the signal reproduction block comprises a plurality of signal reproduction circuits corresponding to each user. The method of claim 12, The signal reproducing circuit includes a fast Fourier transform unit for converting the second signal into a signal in a frequency domain through fast Fourier transform; A demodulator for demodulating the fast Fourier transformed signal; A decoding unit for decoding a signal from the demodulation unit; An encoding unit for encoding the signal from the decoding unit; A modulator for modulating a signal from the encoder; And an inverse fast Fourier transform unit configured to generate a reproduction signal of the first signal through an inverse fast Fourier transform of the signal from the modulator. The method of claim 11, And an operation result of the operation block is the same as the interference component included in the second signal for each user. The method of claim 14, And said operation block performs the following operation for each said user. (only, Is a signal reproducing the interference component of any u-th user, Is the carrier frequency offset of the i-th user, Is a compensation value for the carrier frequency offset of the u-th user, and Is a reproduction signal of the first signal of the i-th user.) A method for removing interference components due to carrier frequency offset differences between multiple users in a receiving apparatus of an OFDMA system, A signal reproducing step of reproducing the first signal by using a second signal that compensates carrier frequency offset components between users included in the first signal received from the outside; A calculation step of reproducing the interference component for each user through a predetermined operation using the signal reproduced in the signal reproduction step; And And eliminating the interference component reproduced in the operation step from the second signal for each user. The method of claim 16, The signal reproducing step may include a first step of converting the second signal into a signal in a frequency domain by performing fast Fourier transform; Demodulating the signal in the frequency domain; A third step of decoding the demodulated signal; A fourth step of re-encoding the decoded signal; A fifth step of modulating the encoded signal; And And a sixth step of converting the modulated signal into an inverse fast Fourier transform into a signal in a time domain. The method of claim 17, And in the sixth step, the signal in the time domain is a reproduction signal of the first signal. The method of claim 16, In the calculating step, the interference component removing method, characterized in that for each user performs the following operation. (only, Is a signal reproducing the interference component of any u-th user, Is the carrier frequency offset of the i-th user, Is a compensation value for the carrier frequency offset of the u-th user, and Is a reproduction signal of the first signal of the i-th user.)