KR20180091550A - Apparatus and method for interference cancellation robust to carrier frequency offset in wireless communication system - Google Patents

Abstract

An apparatus and method for interference cancellation robust to a frequency offset in a wireless communication system are provided. The apparatus receives a modulated transmission signal according to a predetermined modulation method in a case of interference cancellation, estimates a carrier frequency offset based on the preamble and the pilot of a transmission signal, detects an optimal filter coefficient matched with an estimated carrier frequency offset among optimal filter coefficients calculated for each of a plurality of carrier frequency offsets stored in advance, filters the detected optimum filter coefficient by using reception filter, demodulates a transmission signal by a demodulation method corresponding to the modulation method, and detects data.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an interference canceling apparatus and method robust to frequency offset in a wireless communication system,

The present invention relates to an apparatus and method for eliminating interference due to a frequency offset at a receiving end of a wireless communication system.

OFDM (Orthogonal Frequency Division Multiplexing) technology has been widely used as a core technology in 4th generation mobile communication and wireless LAN system. However, OFDM systems are very sensitive to synchronization and have a disadvantage of out-of-band channels (OOB). Due to these problems, OFDM technology is not suitable for the machine-to-machine (M2M) and vehicle-to-vehicle (V2V) scenarios of the fifth generation network.

Accordingly, GFDM (Generalized Frequency Division Multiplexing) communication technology that overcomes the disadvantages of OFDM and uses a new waveform suitable for a fifth generation network scenario has been proposed. The GFDM scheme is a block-based filtering multi-carrier scheme, which is suitable for low-delay communication and has a low peak-to-average power ratio (PAPR).

As described above, the GFDM scheme has several advantages over the OFDM scheme. However, since the orthogonality between subcarriers is lost due to the use of a non-orthogonal signal, there is a problem that interference occurs.

In this regard, Korean Patent Laid-Open No. 10-2009-0075730 (entitled " Method and apparatus for interference cancellation in a wireless communication system ") discloses a method and apparatus for interference cancellation in a wireless communication system, Discloses a method for eliminating interference caused by a function and an apparatus for performing the method. The interference canceller includes a receiver device receiving a signal to which a window function is applied, a processing device coupled to the receiver device, the processing device comprising a plurality of coefficients derived from a window function, (E.g., by retrieving from a storage device coupled to the processing device) and applying the coefficients to the received signal to remove at least some of the interference from the received signal.

An embodiment of the present invention relates to an interference cancellation apparatus and a method for eliminating interference using a reception filter robust to a frequency offset in a wireless communication system.

It should be understood, however, that the technical scope of the present invention is not limited to the above-described technical problems, and other technical problems may exist.

According to another aspect of the present invention, there is provided an apparatus for canceling interference based on a frequency offset of a wireless communication system, the apparatus comprising: a demultiplexer for demultiplexing a preamble and a pilot A frequency offset estimator for estimating a carrier frequency offset based on the carrier frequency offset; A filter coefficient detector for storing an optimal filter coefficient calculated for each of a plurality of carrier frequency offsets in advance and detecting an optimum filter coefficient matched to the estimated carrier frequency offset among the preliminarily stored optimum filter coefficients; And a reception filter for demodulating the transmission signal using a demodulation scheme corresponding to the modulation scheme using the detected optimal filter coefficient to detect data.

In another aspect of the present invention, an interference cancellation method based on frequency offset includes: receiving a transmission signal modulated according to a predetermined modulation scheme; Estimating a carrier frequency offset based on the preamble and the pilot of the transmission signal; Detecting an optimal filter coefficient matched with the estimated carrier frequency offset among optimal filter coefficients calculated for each of a plurality of carrier frequency offsets stored in advance; And detecting the data by demodulating the transmission signal using a demodulation scheme corresponding to the modulation scheme using the detected optimal filter coefficient for the reception filter.

According to an embodiment of the present invention, it is possible to effectively remove interference of a reception signal having a frequency offset due to an oscillator and a Doppler effect in a wireless communication system including GFDM and OFDM.

According to the present invention, filter design robust to frequency offset is possible without changing the basic structure of the receiving end of the wireless communication system.

1 is a configuration diagram of a wireless communication system according to an embodiment of the present invention.
2 is a block diagram of a receiving apparatus according to an embodiment of the present invention.
3 is a structural diagram of GFDM data applied to an embodiment of the present invention.
FIG. 4 is a graph comparing performance of a reception filter robust to frequency offset and another conventional reception filter according to an embodiment of the present invention.
5 is a flowchart illustrating an interference cancellation method based on a frequency offset according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description in the drawings are omitted, and like parts are denoted by similar reference numerals throughout the specification. In the following description with reference to the drawings, the same reference numerals will be used to designate the same names, and the reference numerals are merely for convenience of description, and the concepts, features, and functions Or the effect is not limited to interpretation.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between . Also, when a component is referred to as " comprising ", it is understood that it may include other components as well as other components, But do not preclude the presence or addition of a feature, a number, a step, an operation, an element, a component, or a combination thereof.

In this specification, the term " part " means a unit realized by hardware or software, a unit realized by using both, and one unit may be realized by using two or more hardware, The above units may be realized by one hardware.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a reception filter apparatus and method robust to frequency offset in a wireless communication system according to an embodiment of the present invention will be described in detail with reference to the drawings.

1 is a configuration diagram of a wireless communication system according to an embodiment of the present invention. 2 is a block diagram of a receiving apparatus according to an embodiment of the present invention.

Hereinafter, it will be described that the wireless communication system 10 according to an embodiment of the present invention is a GFDM communication system. However, the wireless communication system 10 is not limited to the GFDM communication system, and may be a wireless communication system according to various communication methods such as OFDM communication.

The OFDM communication system 10 includes a transmitting apparatus 100 and a receiving apparatus 200. [

)로서 출력한다.The transmitting apparatus 100 performs GFDM modulation processing on the data d to transmit a GFDM signal. The GFDM signal is transmitted to the receiving apparatus 200 through a noise channel. The receiving apparatus 200 performs GFDM demodulation of the received GFDM signal to generate detection data (

).

Before describing the configuration of the GFDM communication system 10 in detail, the GFDM signal will be described with reference to FIG.

3 is a structural diagram of GFDM data applied to an embodiment of the present invention.

As shown in FIG. 3, the GFDM data is composed of K subcarriers and M subsymbol blocks. At this time, the GFDM communication system 10 uses a filter for each subcarrier in the transmitting end. If the GFDM communication filter 10 passes the GFDM modulation filter, the out-of-band channel OOB can be reduced and the CP (cyclic prefix) The equalization process in the receiving device is simple.

Returning to FIG. 1, the transmitting apparatus 100 converts the data d to be transmitted into parallel data through an S / P encoder (serial to parallel encoder). Then, the transmitting apparatus 100 GFDM-modulates the parallel processed data through a GFDM modulator 110 including a predetermined filter. At this time, the transmitting apparatus 100 allows each subcarrier to pass a predetermined filter. The transmitting apparatus 100 then adds CP to the GFDM-modulated GFDM signal, upconverts it via digital-to-analog conversion (D / A), and sends out.

The GDFM signal (i.e., transmission signal) transmitted from the transmission apparatus 100 can be expressed by the following Equation (1).

&Quot; (1) "

은 서브캐리어마다 통과시키는 필터로서

이다. 즉,

는 k번째 서브캐리어와 m번째 서브심볼로 전송하는 데이터에 곱해지는 필터 계수이다. 그리고

은 k번째 서브캐리어와 m번째 서브심볼로 전송하는 데이터를 의미한다.In Equation (1)

Is a filter that passes through every subcarrier

to be. In other words,

Is a filter coefficient that is multiplied by the data transmitted on the kth subcarrier and the mth subsymbol. And

Denotes data transmitted on the kth subcarrier and the mth subsymbol.

Equation (1) can be expressed in the form of a matrix as shown in Equation (2).

&Quot; (2) "

는

로서

크기의 행렬을 의미하며, N은 업샘플링 계수를 의미한다.At this time,

The

as

Size matrix, and N means up-sampling coefficient.

이고 M=1인 경우를 OFDM 통신 시스템이라고 할 수 있다. 즉, 상기 수학식 2에서의

행렬이 IFFT(Inverse Fast Fourier Transform) 행렬이 되므로 OFDM의 구조와 같아지며, 따라서 GFDM과 OFDM의 차이는 송신단의 행렬

에서

과 M이 얼마인지에 따라 결정될 수 있다.For reference, the GFDM communication system 10 according to an embodiment of the present invention can be applied to an OFDM communication system. Generally, an OFDM communication system is composed of an OFDM transmitter that transmits data symbols by performing Inverse Fast Fourier Transform (IFFT), and a receiver that restores data by performing an FFT (Fast Fourier Transform) on a signal from an OFDM transmitter. The transmitting apparatus 100 according to an embodiment of the present invention may use a raised cosine filter or a square root raised cosine filter,

And M = 1 is referred to as an OFDM communication system. That is, in Equation 2,

Since the matrix is an Inverse Fast Fourier Transform (IFFT) matrix, it is equal to the structure of OFDM, and thus the difference between GFDM and OFDM is the matrix

in

And M can be determined depending on how much.

)를 출력한다. 이때, 필터는 GFDM 신호에 기설정된 최적 계수를 적용하여 간섭을 제거한다.The receiving apparatus 200 receives the GFDM signal (i.e., the transmission signal) modulated in the GFDM manner, and downconverts it through analog-to-digital conversion (A / D). Then, the reception apparatus 200 removes the CP from the digitally converted GFDM signal, removes the interference due to the frequency offset through the GFDM demodulator 210 including the predetermined filter, and performs GFDM demodulation. Next, the receiving apparatus 200 converts the GFDM demodulated signal into serial data through a P / S encoder (Parallel to Serial encoder)

). At this time, the filter removes interference by applying a predetermined optimal coefficient to the GFDM signal.

가 곱해진 전송 신호를 수신하되, 전송 신호에는 반송파 주파수 오프셋(CFO)인

이 발생하고 노이즈가 더해진다. 이처럼, 전송 신호에 대해 주파수 오프셋이 발생하게 되면 성능이 떨어지게 된다.Referring to FIG. 2, the receiving apparatus 200 receives a modulation matrix

(CFO), which is a carrier frequency offset

And noise is added. As such, when the frequency offset occurs with respect to the transmission signal, the performance is degraded.

에 해당하는 필터 계수를 검출한다. 다음으로, GFDM 복조기(210)는 정합필터(즉, 수신 필터)(213)에 상기 검출된 필터 계수를 적용하여 전송신호로부터 간섭을 제거한다.Therefore, the GFDM demodulator 210 of the receiving apparatus 200 firstly estimates the frequency offset generated in the transmission signal based on the preamble and the pilot existing in front of the data through the frequency offset estimation unit 211. The method of predicting the frequency offset can utilize various prediction algorithms proposed in the prior art, and thus a detailed description thereof will be omitted. Then, the GFDM demodulator 210 demodulates the estimated frequency offset of the filter codebook, which has been previously calculated and stored through the filter coefficient detector 212,

Is detected. Next, the GFDM demodulator 210 applies the detected filter coefficients to a matched filter (i. E., A receive filter) 213 to remove interference from the transmitted signal.

Hereinafter, a process of calculating and storing filter coefficients for a plurality of frequency offsets will be described in detail.

The receiving apparatus 200 can detect data through a matched filter or a minimum mean-squared error filter (MMSE) as a demodulation filter.

)는 다음의 수학식 3과 같이 나타낼 수 있다.When the matched filter is used,

) Can be expressed by the following equation (3).

&Quot; (3) "

은

의 파워를 갖는 노이즈를 의미한다.At this time,

silver

Of the noise.

)는 다음의 수학식 4와 같이 나타낼 수 있다.For reference, when the MMSE filter is used,

) Can be expressed by the following equation (4).

&Quot; (4) "

The transmission signal having the frequency offset due to the oscillator and the Doppler effect of the transmission apparatus 100 and the reception apparatus 200 can be expressed by Equation (5).

Equation (5)

는 주파수 오프셋 행렬로서

를 의미한다. 이때,

는 대각행렬(diagonal matrix)을 의미하고,

은 GFDM 반송파의 간격으로서 정규화(normalize)된 주파수 오프셋을 의미한다.here

Is a frequency offset matrix

. At this time,

Denotes a diagonal matrix,

Means a frequency offset normalized as the interval of GFDM carriers.

행렬의 허미션 행렬(Hermition matrix)인

를 곱해줌으로써 데이터를 검출할 수 있었다. When a matched filter is used,

The Hermitian matrix of the matrix

The data can be detected.

을 정합필터로 사용하며, 이를 통해 검출된 데이터는 다음의 수학식 6과 같이 나타낼 수 있다.Meanwhile, in the receiving apparatus 200 according to an embodiment of the present invention,

Is used as a matched filter, and the detected data can be expressed by the following Equation (6).

&Quot; (6) "

는

로서,

크기의 행렬을 의미한다. 또한

으로서,

을 시간과 주파수로 시프트(shift)시킨 필터를 의미한다.At this time,

The

as,

Size matrix. Also

As a result,

Is shifted in time and frequency.

The data detected using a filter stronger to the frequency offset (i.e., data shown in Equation (6)) can be expanded as shown in Equation (7) below.

&Quot; (7) "

In Equation (7), the diagonal component is the signal to be obtained (i.e., actual data) and the remaining portion is the interference signal.

를 구한다.If the frequency offset is removed, the matrix of Equation (7) approaches the identity matrix and interference is reduced, so that a desired signal can be detected. Therefore, it is possible to maximize the signal-to-interference ratio (SIR) with respect to Equation (7) since the desired signal (i.e., actual data) can be detected by minimizing the interference

.

In Equation (7), since the diagonal component is the desired signal and the remaining portion is the interference signal, the power of the diagonal component and the power of the remaining components are calculated to calculate the signal-to-interference ratio.

At this time, the signal-to-interference ratio can be expressed by Equation (8) below.

&Quot; (8) "

의 성질 중 아래 수학식 9와 같은 성질을 이용한다.To simplify the equation (8)

The following equation (9) is used.

&Quot; (9) "

에 시간을 시프트시키는 행렬인

및 주파수를 시프트시키는 행렬인

를 곱함으로써

를 표현할 수 있다.As in Equation 9 above, the time and frequency are not shifted

Lt; RTI ID = 0.0 >

And a frequency shift matrix

By multiplying

Can be expressed.

에 수학식 9를 대입하면, 다음의 수학식 10과 같이 정리할 수 있다.Therefore,

The following equation (10) can be obtained.

&Quot; (10) "

In this case, U is a value related to the reception power of the signal transmitted through the kth subcarrier and the mth subsymbol, V is a value related to the sum of the reception power of data and the interference power generated due to the frequency offset to be.

In Equation (10), U and V can be expressed by the following equations (11) and (12), respectively.

Equation (11)

&Quot; (12) "

를 사용함으로써, 주파수 오프셋이 발생하는 환경에서 간섭을 최소화하고 시스템의 성능을 향상시킬 수 있다.Therefore, a filter capable of maximizing the value of Equation (10)

The interference can be minimized and the performance of the system can be improved in an environment in which frequency offset occurs.

For this purpose, the optimal solution of equation (13) is calculated.

&Quot; (13) "

The optimal solution of Equation (13) can be obtained by the Rayleigh-Ritz theorem as shown in Equation (14). For reference, the Rayleigh-Ritz Theory is a weighted residual method which is a linear combination of a finite number of basis functions satisfying the displacement boundary conditions and is used to represent unknown functions and to obtain solutions by using basis functions as weighting functions

&Quot; (14) "

를 계산한 후, 그 고유치(eigenvalue)를 계산할 수 있다. 고유치 중 최댓값을 찾고 그에 대응하는 고유벡터(eigenvector)를

로 사용한다.

이므로 수학식 14에서 구한 필터 계수를 수신단 필터(즉, 도 2의 도면부호 ‘213’)에 사용한다.In the equations (11) and (12), U and V can be obtained.

And then calculate the eigenvalue thereof. Find the largest value of the eigenvalues and find the corresponding eigenvectors

.

, The filter coefficient obtained from Equation (14) is used for the receiving end filter (i.e., reference numeral 213 in FIG. 2).

As described above, the filter coefficients obtained through Equation (14) are not calculated and used in real time every time the GFDM signal is received. Instead, the filter coefficients are calculated by the filter coefficient detector 212 for each frequency offset, . The filter coefficient detector 212 uses matched filter coefficients among the filter coefficients stored in the codebook according to the frequency offset of the received transmission signal.

FIG. 4 is a graph comparing performance of a reception filter robust to frequency offset and another conventional reception filter according to an embodiment of the present invention.

FIG. 4 shows a case where a zero-forcing is used for a GFDM communication system in which a matched filter is used as a conventional receiving filter, a signal-to-interference ratio in the case of using a receiving filter robust to a frequency offset according to an embodiment of the present invention, (I.e., performance). FIG. 4 shows a reception filter with a frequency offset value optimized to 0.2, and a reception filter according to an exemplary embodiment of the present invention shows excellent performance over a frequency offset of 0.2.

Hereinafter, with reference to FIG. 5, a description will be made of a method of canceling interference through a coarse interference canceller in a frequency offset in a wireless communication system according to an embodiment of the present invention. In the GFDM communication system according to the embodiment of the present invention, the reception apparatus can operate as an interference cancellation apparatus that processes a GFDM signal.

5 is a flowchart illustrating an interference cancellation method based on a frequency offset according to an embodiment of the present invention.

First, when a GFDM-modulated transmission signal is received (S510), a frequency offset for the transmission signal is estimated (S520).

For reference, it is possible to analog-to-digital convert (A / D) the received transmission signal prior to estimating the frequency offset for the transmission signal, and to perform the procedure of removing the CP.

Next, a filter coefficient matched to the estimated frequency offset among the previously calculated filter coefficients for each frequency offset is detected (S530).

At this time, the previously calculated filter coefficients can be generated and stored in the codebook. Since the method of calculating the filter coefficient is expressed by Equations (3) to (14), detailed description thereof will be omitted.

Then, the detected filter coefficient is applied to the reception filter to process the GFDM demodulation, and the data from which the interference is removed from the transmission signal is detected and output (S540).

At this time, the reception filter may be a matched filter or an MMSE filter. In addition, after processing the GFDM demodulation, the signal can be converted into serial data through a P / S encoder (Parallel to Serial encoder) and output as detection data.

The interference cancellation apparatus and method robust to the frequency offset of the wireless communication system according to the above-described embodiments of the present invention can also be implemented in the form of a recording medium including instructions executable by a computer such as a program module executed by a computer Can be implemented. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. The computer readable medium may also include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes any information delivery media, including computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transport mechanism.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

10: Wireless communication system
100: transmitting apparatus
200: Receiver

Claims (11)

An interference cancellation apparatus based on a frequency offset of a wireless communication system,
A frequency offset estimator for estimating a carrier frequency offset based on a preamble and a pilot of the transmission signal when the modulated transmission signal is received according to a predetermined modulation scheme;
A filter coefficient detector for storing an optimal filter coefficient calculated for each of a plurality of carrier frequency offsets in advance and detecting an optimum filter coefficient matched with the estimated carrier frequency offset among the preliminarily stored optimal filter coefficients; And
And a reception filter that demodulates the transmission signal using a demodulation scheme corresponding to the modulation scheme using the detected optimal filter coefficient to detect data.
The method according to claim 1,
Wherein the filter coefficient detector generates and stores an optimal filter coefficient for each carrier frequency offset as a codebook, based on the frequency offset of the wireless communication system.
The method according to claim 1,
Wherein the filter coefficient detecting unit comprises:
A diagonal matrix for the normalized frequency offset, which is a carrier interval applied in the modulation,
A signal-to-interference ratio is calculated on the basis of the power of the diagonal component and the power of the remaining component in the diagonal matrix,
And calculates a filter coefficient that maximizes the signal-to-interference ratio and stores the calculated filter coefficient as the optimal filter coefficient, based on the frequency offset of the wireless communication system.
The method of claim 3,
Wherein the filter coefficient detecting unit comprises:
The transmission signal in which the frequency offset is generated

The signal-to-interference ratio is calculated according to the following equation (1)
Calculating an optimal solution for the Rayleigh-Ritz theorem according to Equation (2) below based on the calculated signal-to-interference ratio,
And the optimal solution is stored as the optimal filter coefficient.
&Quot; (1) "

&Quot; (2) "

(Where C is the frequency offset matrix < RTI ID = 0.0 >

However,

Is a diagonal matrix,

Is the normalized frequency offset, which is the interval of the carrier waves,

Lt; RTI ID = 0.0 >

As a filter shifted in time and frequency

However,

Is a filter coefficient that is not shifted in time and frequency,

And

Are matrices that shift time and frequency,
Time-to-noise ratio

U is a value based on the reception powers of the transmission signals transmitted on the kth subcarrier and the mth subsymbol, V is a value based on the sum of the reception powers for data and the interference power generated due to the frequency offset,

The optimal solution is

It is an eigenvector corresponding to the largest eigenvalue of the matrix.)
The method according to claim 1,
The reception filter includes:
Wherein the interference canceller is one of a matched filter or a minimum mean-squared error filter (MMSE).
The method according to claim 1,
Wherein the modulation scheme is Generalized Frequency Division Multiplexing (GFDM) modulation.
A method of interference cancellation based on frequency offset through an interference canceller for processing a transmission signal of a wireless communication system,
Receiving a modulated transmission signal according to a predetermined modulation scheme;
Estimating a carrier frequency offset based on the preamble and the pilot of the transmission signal;
Detecting an optimal filter coefficient matched with the estimated carrier frequency offset among optimal filter coefficients calculated for each of a plurality of carrier frequency offsets stored in advance; And
And using the detected optimal filter coefficient for a reception filter to demodulate the transmission signal in a demodulation scheme corresponding to the modulation scheme to detect data.
8. The method of claim 7,
Wherein the optimal filter coefficients calculated for each of the plurality of carrier frequency offsets are generated and stored as a codebook.
8. The method of claim 7,
Before the step of detecting the optimal filter coefficient,
Calculating a diagonal matrix with respect to a normalized frequency offset that is a carrier interval applied at the time of modulation, calculating a signal-to-interference ratio based on powers of the diagonal components and powers of the remaining components in the diagonal matrix, And storing the result as the optimal filter coefficient.
8. The method of claim 7,
The reception filter includes:
Wherein the frequency offset is one of a matched filter or a minimum mean-squared error filter (MMSE).
8. The method of claim 7,
Wherein the modulation scheme is Generalized Frequency Division Multiplexing (GFDM) modulation.

Images