KR20180008025A - Method of iteratively estimating and equalizing a channel in a frequency oversampling domain in a fbmc/oqam system and apparatus for the same - Google Patents

Abstract

Disclosed is a method of iteratively estimating and equalizing a channel in a frequency oversampling domain in an FBMC/OQAM system and an apparatus for performing the same. One embodiment incudes the steps of extracting a channel estimation value of a pilot sub-channel position in a sample, calculating a channel estimation value of a sub-carrier unit with respect to the extracted channel estimation value, and equalizing the channel estimation value of the sub-carrier unit.

Description

FIELD OF THE INVENTION This invention relates to a method and apparatus for estimating and equalizing a channel repeatedly in a frequency and table domain of an FBMC / OQAM system, and a device for performing the same. [0002]

The following embodiments relate to a method for estimating and equalizing a channel repeatedly in frequency and table regions of an FBMC / OQAM system and an apparatus for performing the same.

OFDM / QAM (Orthogonal Frequency Division Multiplexing on Quadrature Amplitude Modulation) system is a multicarrier transmission system used in the latest mobile communication and digital broadcasting transmission standards. In this system, complex data corresponding to one QAM constellation is transmitted on a subcarrier, where the subcarrier uses a rectangular function as a prototype filter It can be seen as a signal obtained by multiplying a specific frequency tone in the time domain.

This system can remove Inter-Symbol Interference (ISI) for a multipath channel by using a CP (Cyclic Prefix) as a guard interval. This system eliminates ISI and ICI (Inter-Carrier Interference) Channel estimation is facilitated and a frequency-domain single tap equalizer is employed to easily and easily equalize a channel.

However, since CP is not an essential part of data transmission, it is a part of decreasing data transmission efficiency. In recent years, as the frequency bandwidth used for improving the transmission speed has widened, the sampling period is becoming shorter and shorter. Therefore, the symbol interval of the OFDM / QAM system becomes shorter and the length of the CP is determined by the characteristics of the transmission channel, which causes the ratio of the CP to the symbol interval to increase. In contrast, in the OFDM / QAM system, a prototype filter capable of reducing the ISI and ICI in the time domain and the frequency domain without using the CP can not exist as a complex filter. Therefore, in order to cope with ISI caused by multipath, Depending on the situation, a certain percentage of CP should be used.

Embodiments can perform equalization by repeatedly modifying a channel estimation value for each subcarrier in a frequency oversampling domain based on an FBMC / OQAM system and an auxiliary pilot scheme.

In addition, the embodiments can provide superior performance compared to frequency-domain single tap channels in an existing FBMC / OQAM system and frequency-domain single tap channel equalization systems in an OFDM / QAM system.

A method of equalizing a channel according to an embodiment includes extracting a channel estimation value of a pilot sub-channel position in a sample, performing a sub-carrier estimation on the extracted channel estimation value, Calculating channel estimation values of the subcarrier units, and equalizing channel estimation values of the subcarrier units.

The method includes passing a de-overlapped sample through an extended fast Fourier transform module (FFT module), and transmitting at least one of the samples passed through the extended FFT module and the equalized channel estimate value To the frequency domain.

The filtering may include frequency de-spreading at least one of the samples passed through the extended FFT module and the equalized channel estimate.

The step of calculating the channel estimation value includes a step of time interpolation of the extracted channel estimation value in a time domain and a step of frequency interpolation of a channel estimation value interpolated in the time domain in a frequency domain can do.

The step of calculating the channel estimation value may include repeatedly calculating the channel estimation value by a predetermined number n.

Wherein the step of storing the channel estimation value further comprises the step of correcting the channel estimation value calculated from the previous number of times if the channel estimation value is not repeatedly calculated by the predetermined number of times n And outputting the stored channel estimation value when it is repeatedly calculated by the predetermined number of times n.

The modifying may include multiplying the channel estimate computed at the previous number of times with an equalization value for the pilot subchannel.

The extracting may include extracting the channel estimation value based on the following equation.

[Mathematical Expression]

와

는 각각 파일럿 부 채널의 인덱스(index)를 나타내고,

는 파일럿 부 채널을 통한 채널 추정 값이고,

는 번째 OQAM 심볼의

번째 부 채널에 적용되는 채널의 주파수 응답이고,

는 QAM 심볼의 실수 부분과 허수 부분을 취하여

번째 OQAM 심볼의

번째 부 채널로 전송되는(carry) 데이터(실수 부분)이고,

는 QAM 심볼의 실수 부분과 허수 부분을 취하여

번째 OQAM 심볼의

번째 부 채널에 대한 고유한 간섭(intrinsic interference; 허수 부분)이고,

는

번째 OQAM 심볼의

번째 부 채널의 백색 가우시안 잡음임.here,

Wow

Denotes an index of a pilot subchannel,

Lt; / RTI > is the channel estimate over the pilot subchannel,

The Of the second OQAM symbol

Lt; th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

(Real part) to be transmitted to the i < th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

Lt; th > subchannel is an intrinsic interference (imaginary part)

The

Of the second OQAM symbol

Th subchannel is white Gaussian noise.

The step of equalizing the subcarrier units may include equalizing the subcarrier units on the basis of the following equations.

[Mathematical Expression]

는 n번째 OQAM 심볼의 m번째 부 채널에 포함된 각 부 반송파 위치의 채널 추정 값이고,

는 n번째 OQAM 심볼이 수신단에서 확장 FFT(fast Fourier transform)를 통과한 부 반송파의 값이고,

는 프로토타입 필터의 주파수 영역 계수임.Where K is the overlay factor of the FBMC / OQAM system,

Is a channel estimation value of each sub-carrier position included in the m-th sub-channel of the n-th OQAM symbol,

Is the value of the sub-carrier through which the n-th OQAM symbol passes through the extended FFT (fast Fourier transform) at the receiving end,

Is the frequency domain coefficient of the prototype filter.

The channel equalization apparatus includes an extractor for extracting a channel estimation value of a pilot subchannel position in a sample, a channel calculator for calculating a channel estimation value of a subcarrier unit with respect to the extracted channel estimation value, And an equalizer for equalizing the channel estimation value of the subcarrier unit.

The channel equalizer comprising: an extended fast Fourier transform module for passing de-overlapped samples; and at least one of a sample passed through the extended FFT module and the equalized channel estimate value To the frequency domain.

The frequency filter may inversely convert at least one of a sample passed through the extended FFT module and the equalized channel estimation value.

The channel calculator includes a time domain interpolator for performing time interpolation on the extracted channel estimation value in a time domain and a frequency interpolator for frequency interpolation of a channel estimation value interpolated in the time domain, Region interpolator.

The channel calculator may repeatedly calculate the channel estimation value by a predetermined number n.

And the storage unit stores the channel estimation value. If the storage unit does not repeatedly calculate the predetermined number of times n, it modifies the channel estimation value calculated from the previous number of times of the channel value, and repeats the predetermined number of times n And outputs the stored channel estimation value.

The storage unit may multiply the channel estimation value calculated at the previous number of times by the equalization value for the pilot subchannel to modify the channel estimation value calculated at the previous number, if the calculation is not repeated the predetermined number of times n.

The extractor may extract the channel estimation value based on the following equation.

[Mathematical Expression]

와

는 각각 파일럿 부 채널의 인덱스(index)를 나타내고,

는 파일럿 부 채널을 통한 채널 추정 값이고,

는

번째 OQAM 심볼의

번째 부 채널에 적용되는 채널의 주파수 응답이고,

는 QAM 심볼의 실수 부분과 허수 부분을 취하여

번째 OQAM 심볼의

번째 부 채널로 전송되는(carry) 데이터(실수 부분)이고,

는 QAM 심볼의 실수 부분과 허수 부분을 취하여

번째 OQAM 심볼의

번째 부 채널에 대한 고유한 간섭(intrinsic interference; 허수 부분)이고,

는

번째 OQAM 심볼의

번째 부 채널의 백색 가우시안 잡음임.here,

Wow

Denotes an index of a pilot subchannel,

Lt; / RTI > is the channel estimate over the pilot subchannel,

The

Of the second OQAM symbol

Lt; th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

(Real part) to be transmitted to the i < th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

Lt; th > subchannel is an intrinsic interference (imaginary part)

The

Of the second OQAM symbol

Th subchannel is white Gaussian noise.

The equalizer may include equalizing on the subcarrier units based on the following equation.

[Mathematical Expression]

는 n번째 OQAM 심볼의 m번째 부 채널에 포함된 각 부 반송파 위치의 채널 추정 값이고,

는 n번째 OQAM 심볼이 수신단에서 확장 FFT(fast Fourier transform)를 통과한 부 반송파의 값이고,

는 프로토타입 필터의 주파수 영역 계수임.Where K is the overlay factor of the FBMC / OQAM system,

Is a channel estimation value of each sub-carrier position included in the m-th sub-channel of the n-th OQAM symbol,

Is the value of the sub-carrier through which the n-th OQAM symbol passes through the extended FFT (fast Fourier transform) at the receiving end,

Is the frequency domain coefficient of the prototype filter.

1 is a conceptual diagram for explaining an OFDM / OQAM system.
Figures 2a to 2c show the response of the prototype filter and the frequency response of the filter bang according to the overlap factor K. [
3 shows a process of transmitting symbols of a transmitter through an extended IFFT module.
FIG. 4 shows an example of an offset-QAM technique.
5 shows an example of an operation in which de-overlapped samples in the receiving end pass through the extended FFT module.
6 shows an example of the operation for frequency de-spreading in the receiver.
7 shows an example of the calculation region of the auxiliary pilot and the position of the auxiliary pilot.
8 shows a process of estimating a channel in the frequency and table regions.
FIG. 9 shows a process of equalizing a channel for each subcarrier.
10 shows the structure of an iterative channel estimation and equalizer in frequency and table regions.
11 shows an example of an algorithm of a method of estimating and equalizing a channel.
12 shows an example of a symbol error rate for a Brazil-D channel, which is a frequency selective fixed channel, and a TU (Typical Urban) -6 channel, which models a mobile reception situation.

It is to be understood that the specific structural or functional descriptions of embodiments of the present invention disclosed herein are presented for the purpose of describing embodiments only in accordance with the concepts of the present invention, May be embodied in various forms and are not limited to the embodiments described herein.

Embodiments in accordance with the concepts of the present invention are capable of various modifications and may take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. However, it is not intended to limit the embodiments according to the concepts of the present invention to the specific disclosure forms, but includes changes, equivalents, or alternatives falling within the spirit and scope of the present invention.

The terms first, second, or the like may be used to describe various elements, but the elements should not be limited by the terms. The terms may be named for the purpose of distinguishing one element from another, for example without departing from the scope of the right according to the concept of the present invention, the first element being referred to as the second element, Similarly, the second component may also be referred to as the first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Expressions that describe the relationship between components, for example, "between" and "immediately" or "directly adjacent to" should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms " comprises " or " having ", and the like, are used to specify one or more of the features, numbers, steps, operations, But do not preclude the presence or addition of steps, operations, elements, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning of the context in the relevant art and, unless explicitly defined herein, are to be interpreted as ideal or overly formal Do not.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, the scope of the patent application is not limited or limited by these embodiments. Like reference symbols in the drawings denote like elements.

A module in this specification may mean hardware capable of performing the functions and operations according to the respective names described in this specification and may mean computer program codes capable of performing specific functions and operations , Or an electronic recording medium, e.g., a processor or a microprocessor, equipped with computer program code capable of performing certain functions and operations.

In other words, a module may mean a functional and / or structural combination of hardware for carrying out the technical idea of the present invention and / or software for driving the hardware.

1 is a conceptual diagram for explaining an OFDM / OQAM system.

Referring to FIG. 1, an OFDM / OQAM (OFDM on Offset-Quadrature Amplitude Modulation) system has been introduced as a multicarrier transmission system that can compensate for a decrease in data transmission efficiency due to an increase in the CP ratio of an OFDM / QAM system. This system transmits data through each subchannel using a prototype filter that can reduce ISI and ICI in the time domain and frequency domain without using a CP, thereby improving the data transmission efficiency compared to the OFDM / QAM system There is an advantage that it can be increased.

In the OFDM / OQAM system, one QAM data is separated into a real part and an imaginary part as shown in FIG. The OQAM scheme is a technique of transmitting the subchannels transmitting the real part and the imaginary part over a time difference corresponding to half of the data symbol period. With this technique, the OFDM / OQAM system can achieve the same data transmission efficiency as the OFDM / QAM system without CP.

The OFDM / OQAM system requires an additional hardware complexity in addition to generating a prototype filter in the OFDM / QAM system. To solve this problem, an FBMC / OQAM system has been introduced that can reduce the increase of hardware complexity by using the filter bank theory. (The term OFDM / OQAM can be used with the term FBMC / OQAM).

The prototype filter of the FBMC / OQAM system can increase the length in the time domain compared with the square pulse, which is a prototype filter of the OFDM / QAM system, and can use a finer response in the frequency domain. Due to this characteristic, the subchannels are superimposed on the time domain and the frequency domain. Assuming an ideal channel, the subchannels transmitted to the real number region are orthogonal to each other, and the subchannels transmitted to the imaginary number region are also orthogonal to each other. Therefore, when the received signal is filtered for each sub-channel, the data portion exists as a real value, and the interference due to adjacent sub-channels exists as an imaginary value. This is called Real orthogonality. Therefore, by filtering the received signal for the subchannel and taking the real part, the data can be completely recovered.

From the viewpoint of channel estimation and compensation, the FBMC / OQAM signal passed through the multipath channel can be equalized through a frequency-domain single tap equalization method using an OFDM / QAM system, but further work is required . This is because there is interference due to adjacent subchannels in the FBMC / OQAM system and this interference causes channel estimation through the pilot to be inaccurate. A method of adding an auxiliary pilot (AP) to the imaginary part of the pilot at the transmitting end has been introduced to eliminate such pilot interference. However, even in the case of using the frequency-domain single tap equalizer based on the auxiliary pilot scheme, the reception performance tends to be lower than that in the frequency domain single tap equalizer of the OFDM / QAM system in frequency selective channel conditions. Due to the deterioration of the channel estimation and compensation performance, the data transmission efficiency of the FBMC / OQAM system is superior to that of the OFDM / QAM system.

Hereinafter, the FBMC / OQAM system model will be described.

Before describing the FBMC / OQAM system, the OFDM / QAM system will be described first.

The OFDM / QAM system is a multi-carrier transmission system that carries complex data corresponding to a QAM constellation on each sub-carrier and can be expressed as Equation (1).

은 n번째 OFDM/QAM 심볼의 m번째 부 반송파에 실리는 QAM 데이터,

는 주파수 영역에서 부 반송파 사이의 간격,

는 OFDM/QAM 심볼 구간이며,

는 프로토타입 필터로 사각 펄스를 나타낸다. 수학식 1과 같이 OFDM/QAM 시스템에서 각 부 반송파는 프로토타입 필터에 특정한 주파수 톤을 시간 영역에서 곱한 신호이며 부 반송파들을 모두 중첩시키면 하나의 OFDM/ QAM 심볼을 생성할 수 있다.here

QAM data carried on the m-th subcarrier of the n-th OFDM / QAM symbol,

Is the spacing between subcarriers in the frequency domain,

Is an OFDM / QAM symbol interval,

Represents a square pulse with a prototype filter. As shown in Equation (1), in the OFDM / QAM system, each subcarrier is a signal obtained by multiplying a specific frequency tone in a time domain by a prototype filter, and one OFDM / QAM symbol can be generated by superimposing all subcarriers.

에 영향을 미치지 않는다.Assuming an ideal channel, each subcarrier has orthogonality with respect to time domain and frequency domain, so that data can be completely recovered. If there is an ISI due to a multipath channel, the ISI due to the multipath channel is removed by using a CP that copies the rear part of the n-th OFDM / QAM symbol interval to the guard interval, And the length of the CP is the spacing of subcarriers

Lt; / RTI >

The FBMC / OQAM system uses a prototype filter capable of reducing the ISI due to the multipath channel as shown in Equation (2), unlike the OFDM / QAM system, it does not require a CP.

은 QAM 심볼의 실수 부분과 허수 부분을 취하여 n번째 OQAM 심볼의 m번째 부 채널에 실리는 데이터,

는 프로토타입 필터인

를 이용하여 n번째 OQAM 심볼의 m번째 부 채널을 생성하는 필터로 수학식 3을 통해 생성할 수 있다.Where M is the number of subchannels of the FBMC / OQAM system,

Is the data carried in the m-th subchannel of the n-th OQAM symbol, taking the real and imaginary parts of the QAM symbol,

Is a prototype filter

And the m-th subchannel of the n-th OQAM symbol is generated using Equation (3).

는 주파수 영역에서 부 채널 간의 간격,

는 인접한 OQAM 심볼간의 시간차이다.The subchannel used in the FBMC / OQAM system is obtained by multiplying the impulse response of the prototype filter by a frequency component which increases by 1 / M times. This means that the frequency response of each subchannel in the frequency domain is located 1 / M have.

Is the spacing between subchannels in the frequency domain,

Is the time difference between adjacent OQAM symbols.

The prototype filter used in the present invention can be generated by Equation (4).

Where T is the data transmission period and K is the overlap factor. In order to reduce the ISI and ICI in the time domain and the frequency domain, the prototype filter is longer in the time domain than the square filter, which is a prototype filter of the OFDM / QAM, and has a subdivided response in the frequency domain have.

Figures 2a to 2c show the response of the prototype filter and the frequency response of the filter bang according to the overlap factor K. [

가 표 1에 표시되어 있다.In the present specification, a prototype filter with K = 4 was verified and the coefficient of the sub-divided frequency response of the prototype filter according to K

Are shown in Table 1.

The number of subchannels is 256 using Equation (4), and the impulse response of the prototype filter according to K is shown in FIGS. 2A and 2B. The length L of the impulse response of the prototype filter of the OFDM / QAM system in the time domain is equal to the number of subcarriers, which is the same as in the case of K = 1. In contrast, the length of the impulse response of the prototype filter used in the FBMC / OQAM system is equal to the length of the subchannel multiplied by the overlay factor K, as shown in FIG.

In the frequency domain, the subcarrier of the OFDM / QAM system is composed of one coefficient. However, when the overlay factor of the FBMC / OQAM system is K, the frequency response of the subchannel consists of 2K-1 subcarriers as shown in FIG. Therefore, since there are K subcarriers between subchannels at intervals of 1 / M in the frequency domain, the superposition factor K is used together with the term frequency oversampling rate.

The subcarrier filter used in the OFDM / QAM system can be simply implemented using an IFFT (Inverse-Fast Fourier Transform) module. In order to implement the sub-channels of the FBMC / OQAM system, a separate polyphase network (PPN) Requires an FFT module and uses an extended FFT module in this specification.

In the extended FFT scheme, the transmitter spreads the data symbols to be transmitted to the respective sub-channels in the frequency domain using the frequency domain coefficients of the prototype filters shown in Table 1, as shown in FIG. Adjacent subchannels of the FBMC / OQAM system are located at a 1 / M interval in the frequency domain, so that interference occurs without orthogonality with each other as shown in FIG. 2C.

FIG. 3 shows a process in which symbols of a transmitter are passed through an extended IFFT module, and FIG. 4 shows an example of an offset-QAM technique.

Referring to FIG. 3 to FIG. 4, adjacent subchannels may use the technique of transmitting data to the real number area of the even subcarrier and the imaginary area of the odd subcarrier (or vice versa).

Then, the frequency-spread symbols are passed through an extended IFFT module of K * M size to obtain K * M samples. Therefore, in order to maintain the same data transmission efficiency as that of the OFDM / QAM system not adopting the CP scheme, the FBMC / OQAM transmission symbols in the time domain have time differences corresponding to the M / 2 sampling period which is half of the QAM symbol period as shown in FIG. The technique of superposing transmission symbols is Offset-QAM technique.

과의 상관값을 통해 n번째 OQAM 심볼의 m번째 부채널에 변조된 신호를 수학식 5를 통해 복구할 수 있다.Even if the FBMC / OQAM symbols are superposed and transmitted,

The signal modulated on the m-th subchannel of the n-th OQAM symbol can be recovered through Equation (5).

는 하나의 부 채널에 1이 변조된 경우 주변 부 채널에 미치는 간섭의 크기이며 본 명세서에서 사용된 프로토타입 필터에 대한 간섭의 크기가 표 2에서 표시되어 있다.

Is the magnitude of the interference on the peripheral subchannels when 1 is modulated on one subchannel and the magnitude of the interference to the prototype filter used in this specification is shown in Table 2.

The correlation value obtained through Equation (5) consists of interference due to subchannels adjacent to the data portion transmitted through the subchannel.

Assuming an ideal channel, the subchannels transmitted to the real area are orthogonal to each other, and the subchannels transmitted to the imaginary area are orthogonal to each other. Therefore, when the received signal is filtered for each subchannel through Equation (5), interference exists only in the imaginary region. This is called real orthogonality property, so if you take the real part after filtering for each subchannel, you can recover the data perfectly.

5 shows an example of an operation in which de-overlapped samples in the receiving end pass through the extended FFT module.

Referring to FIG. 5, a receiving unit slides an overlapped FBMC / OQAM symbol in units of M / 2, and restores K * M samples. Thereafter, an extended FFT operation is performed, and an operation of re-summing the data symbols spread from the transmitter to the frequency domain is performed to perform the operation of taking the real value of the even data symbol and the imaginary value of the odd data symbol.

Hereinafter, a channel estimation and equalization technique of the FBMC / OQAM system will be described.

6 shows an example of the operation for frequency de-spreading in the receiver.

As shown in FIGS. 3 and 4, the FBMC / OQAM signal is overlapped in the frequency domain and the time domain with respect to the adjacent subchannels. Therefore, in the FBMC / OQAM system, there is interference between the subchannels, but after the filtering of the receiver, the values are orthogonal to the original subchannel. The vertical axis represents the frequency domain, and the horizontal axis represents the index of the subchannel with respect to the time domain. Each subchannel of the transmitter is generated by alternating between the real and imaginary regions. After the filtering of the receiver, the interference with the original data (parenthesized portion of FIG. 6) exists.

Assuming that the ideal channel is assumed, the data can be completely recovered by taking the real or imaginary part after filtering at the receiving end. However, when the FBMC / OQAM signal passes through the transmission channel, as in the OFDM / QAM system, In channel estimation using a channel, this interference must be resolved to obtain accurate channel estimation.

, 백색 가우시안 잡음을

라고 할 때, 수신된 신호의 기저대역에 대한 표현은 다음 수학식 6과 같다.Assuming that the value of the transmission channel for one subchannel is constant, the frequency response of the channel applied to the m-th subchannel of the n-th OQAM symbol

, White Gaussian noise

, The expression of the baseband of the received signal is expressed by Equation (6).

The received signal obtained through Equation (6) is filtered by the receiving end to obtain the following Equation (7).

)라고 할 때, 파일럿 부 채널을 통한 채널 추정 값은 다음 수학식 8과 같이 표현할 수 있다.Let the index of the pilot subchannel be (m, n =

), The channel estimation value through the pilot subchannel can be expressed as Equation (8).

로 인해 채널 추정에 오차가 발생한다. 이를 해결하기 위해 파일럿 부 채널의 간섭을 제거하는 보조 파일럿 기법이 소개되었다. As can be seen from Equation (8), even excluding the noise item

An error occurs in the channel estimation. In order to solve this problem, an auxiliary pilot technique for eliminating the interference of the pilot subchannels has been introduced.

)하고, 파일럿에 대한 고유한 간섭을 상쇄할 수 있는, 즉

을 만족시키도록 하는 보조 파일럿의 값을 구하는 것이다.

을 구하기 위해서는 하나의 부 채널이 주변 부 채널에 작용하는 간섭의 양을 알아야 하며 이는 프로토타입 필터에 따라 결정된다. 표 2는 본 명세서에서 사용하는 프로토타입 필터로 생성된 하나의 부 채널이 수신단의 필터링 이후 주변 부 채널에 작용하는 간섭의 양을 나타낸 것이다. 이를 이용하여 각 부 채널의 위치에 해당하는 데이터를 곱한 값을 모두 합하면 송신단에서 미리

를 계산할 수 있다. 수학식 9를 통해 보조 파일럿을 계산하여 적절한 위치에 삽입하면 파일럿에 작용하는 간섭을 상쇄할 수 있다.7 shows an example of the calculation region of the auxiliary pilot and the position of the auxiliary pilot. Auxiliary pilot scheme means that the position of auxiliary pilot is selected at the transmitting end (m, n =

) And can cancel out the inherent interference to the pilot, i. E.

Of the auxiliary pilot.

It is necessary to know the amount of interference that a subchannel has on the peripheral subchannel, which is determined by the prototype filter. Table 2 shows the amount of interference that one subchannel generated by the prototype filter used in the present invention affects peripheral subchannels after filtering of the receiving end. By summing up the values obtained by multiplying the data corresponding to the positions of the respective sub-channels by using them,

Can be calculated. Equation (9) can be used to calculate the auxiliary pilot and insert it into the proper position to cancel the interference acting on the pilot.

The position of the sub-carrier used in calculating the interference through Equation (9) is the portion denoted by Neighboring Data in FIG. 7, and the position of the auxiliary pilot is the portion denoted by the Auxiliary Pilot in FIG.

Hereinafter, repetitive channel estimation and equalization techniques in the frequency domain table will be described.

In the case of the channel estimation described above, the frequency domain single tap channel equalization is performed on the assumption that the channel value for one subchannel is constant. However, in the case of a frequency selective channel, the estimated value obtained through Equation (8) may be inaccurate.

In the FBMC / OQAM system, the frequency domain single tap channel equalization may be performed for the subchannel, but channel equalization for the subcarrier or multi-tap channel equalization for one subchannel may be performed.

8 shows a process of estimating a channel in the frequency and table regions.

Referring to FIG. 8, in order to obtain a channel estimation value for each subcarrier, a channel estimation value for a pilot subchannel position obtained through Equation (8) is interpolated through a cubic spline method, The estimated values can be obtained and interpolated on the subcarrier units in the same manner. That is, the channel estimation value of the subcarrier unit can be calculated with respect to the channel estimation value of the subchannel location.

In addition, channel estimation values of subcarrier units can be equalized.

FIG. 9 shows a process of equalizing a channel for each subcarrier.

Referring to FIG. 9, it can be confirmed that the samples passing through the receiver filter are filtered. The samples may be samples that are de-overlapped through the extended fast Fourier transform module (FFT module) and filtered in the frequency domain. At this time, the inversely overlapped samples can perform fast Fourier transform or bypass.

As shown in Equation (10), if channel equalization is performed on each subcarrier and filtering is performed, the channel equalization performance can be improved in a frequency selective situation. The filtering operation may include frequency de-spreading at least one of the samples passed through the extended FFT module and the equalized channel estimate.

는 n번째 OQAM 심볼의 m번째 부 채널에 포함된 각 부 반송파 위치의 채널 추정 값이고,

는 n번째 OQAM 심볼이 수신단에서 확장 FFT(fast Fourier transform)를 통과한 부 반송파의 값이고,

는 프로토타입 필터의 주파수 영역 계수일 수 있다.Where K is the overlay factor of the FBMC / OQAM system,

Is a channel estimation value of each sub-carrier position included in the m-th sub-channel of the n-th OQAM symbol,

Is the value of the sub-carrier through which the n-th OQAM symbol passes through the extended FFT (fast Fourier transform) at the receiving end,

May be a frequency domain coefficient of the prototype filter.

은 수학식 8을 통해 구해졌으므로, 채널 추정 오차가 존재할 수 있다. 이에 대해 본 발명에서 제안된 채널 추정 방식에서는 현재 채널 추정값과 수학식 10을 통해 구해진 등화 값을 이용하여 채널 추정값을 수정할 수 있다. 파일럿 부 채널에 대한 i번째 채널 추정 값을

, 수학식 10을 통해 구해진 i번째 파일럿 부 채널에 대한 등화 값을

라고 할 때, 수학식 11과 같이 채널 추정값을 반복하여 수정할 수 있다.At this time, the channel estimation value < RTI ID = 0.0 >

Is obtained through Equation (8), a channel estimation error may exist. On the other hand, in the channel estimation method proposed in the present invention, the channel estimation value can be modified using the current channel estimation value and the equalization value obtained through Equation (10). The i-th channel estimate for the pilot subchannel is

, The equalization value for the i < th > pilot subchannel obtained through Equation

, The channel estimation value can be repeatedly modified as in Equation (11).

When the channel estimation for the pilot subchannel is completed by performing the predetermined repetition times, the channel is interpolated on a subcarrier-by-subcarrier basis and the final channel equalization is performed through Equation (10). The constant number of iterations may be a predetermined integer value of one or more.

10 shows the structure of an iterative channel estimation and equalizer in frequency and table regions.

Referring to FIG. 10, sub-carriers passing through the extended FFT module may be channel equalized before frequency de-spreading frequency de-spreading. The method of obtaining the sub-carrier unit channel estimation value may be as follows.

And extract a channel estimate value of a pilot sub-channel position in the sample. At this time, the sample may be a signal.

And may be stored in the Channel Store / Modification block if it is the first channel estimation value. The channel estimation value of each sub-carrier unit is obtained through a time interpolation block and a frequency interpolation block, and the sub-carrier channel equalizer block and the frequency de-spreading block are equalized to each other on a sub-carrier basis using Equation (10) . The filtered value is used to modify the channel estimate stored in the Channel Store / Modification block through Equation (11). And performs channel equalization of subcarrier units through Equation (10). The predetermined number of times may be a predetermined integer value of 1 or more.

11 shows an example of an algorithm of a method of estimating and equalizing a channel.

When the number of repetitions of the channel estimation is set to n, the first channel estimation value obtained through Equation (8) is stored. If the number of repetition times is increased, the existing channel estimation value is corrected, . As the channel estimation performance is improved, the reception performance of the FBMC / OQAM system using the proposed channel estimation and equalization scheme in the frequency selective channel condition can be brought close to the reception performance of the single tap equalization system of the OFDM / QAM system .

The results of analyzing the performance of the present invention will be described below.

The reception performance of the channel estimation and equalization method of the FBMC / OQAM system proposed by the present invention is compared with the frequency tap single channel equalization method of the FBMC / OQAM system and the single tap frequency axis tap of the OFDM / QAM system in the frequency selective channel and the mobile channel environment. In order to compare with the channel equalization method, computer simulation parameters are set as shown in Table 3 with reference to the parameters of the current terrestrial digital broadcasting bandwidth and the number of subcarriers used in the DVB-T2 transmission system.

12 shows an example of a symbol error rate for a Brazil-D channel, which is a frequency selective fixed channel, and a TU (Typical Urban) -6 channel, which models a mobile reception situation. 12, when the number of subchannels is 1024 and frequency-axis single-tap channel estimation and equalization are used, the reception performance of the FBMC / OQAM system is significantly degraded as compared with the OFDM / QAM system .

If the channel estimation and equalization are performed for each subcarrier in the frequency domain, the performance is improved compared to the frequency single tap channel equalization method in a frequency selective situation.

If the equalization method is used to further modify the channel estimation value repeatedly in this area, the performance is improved up to the third estimation, and the reception performance is not significantly lower than that of the OFDM / QAM system. It can be seen that the reception performance of the OFDM / QAM system and the FBMC / OQAM system do not differ greatly when the number of subchannels is 4096.

For the TU-6 channel, as shown in the right diagram of FIG. 12, the performance improvement is slightly improved when the number of subchannels is 1024, but the performance improvement is not clear when the number of subchannels is increased. This shows that the proposed scheme can improve reception performance in frequency selective channel conditions.

The apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the apparatus and components described in the embodiments may be implemented within a computer system, such as, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA) , A programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For ease of understanding, the processing apparatus may be described as being used singly, but those skilled in the art will recognize that the processing apparatus may have a plurality of processing elements and / As shown in FIG. For example, the processing unit may comprise a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as a parallel processor.

The software may include a computer program, code, instructions, or a combination of one or more of the foregoing, and may be configured to configure the processing device to operate as desired or to process it collectively or collectively Device can be commanded. The software and / or data may be in the form of any type of machine, component, physical device, virtual equipment, computer storage media, or device , Or may be permanently or temporarily embodied in a transmitted signal wave. The software may be distributed over a networked computer system and stored or executed in a distributed manner. The software and data may be stored on one or more computer readable recording media.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (18)

Extracting a channel estimate value at a pilot sub-channel location in the sample;
Calculating a channel estimation value for a sub-carrier unit with respect to the extracted channel estimation value; And
Equalizing the channel estimation value of the subcarrier unit
≪ / RTI >
The method according to claim 1,
Passing a de-overlapped sample through an extended fast Fourier transform module (FFT module); And
Filtering at least one of the samples passed through the extended FFT module and the equalized channel estimation values in a frequency domain;
≪ / RTI >
3. The method of claim 2,
Wherein the filtering comprises:
Frequency de-spreading at least one of the samples passed through the extended FFT module and the equalized channel estimate value
≪ / RTI >
The method according to claim 1,
The step of calculating the channel estimate value comprises:
Interpolating the extracted channel estimation values in a time domain; And
Interpolating channel estimation values interpolated in the time domain in a frequency domain;
≪ / RTI >
The method according to claim 1,
The step of calculating the channel estimate value comprises:
Repeatedly calculating the channel estimation value by a predetermined number of times n
≪ / RTI >
The method according to claim 1,
Storing the channel estimate value
Further comprising:
Wherein the storing the channel estimate value comprises:
Modifying the channel estimation value calculated from the previous number of times of the channel value if it is not repeatedly calculated by the predetermined number of times n; And
And outputting the stored channel estimation value if it is repeatedly calculated by the predetermined number of times n
≪ / RTI >
The method according to claim 6,
Wherein the modifying comprises:
Multiplying the channel estimation value calculated at the previous number by an equalization value for the pilot subchannel
≪ / RTI >
The method according to claim 1,
Wherein the extracting comprises:
Extracting the channel estimation value based on the following equation
≪ / RTI >
[Mathematical Expression]

here,

Wow

Denotes an index of a pilot subchannel,

Lt; / RTI > is the channel estimate over the pilot subchannel,

The

Of the second OQAM symbol

Lt; th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

(Real part) to be transmitted to the i < th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

Lt; th > subchannel is an intrinsic interference (imaginary part)

The

Of the second OQAM symbol

Th subchannel is white Gaussian noise.
The method according to claim 1,
Wherein the equalizing in units of sub-
Performing equalization on the sub-carrier basis on the basis of the following equation
≪ / RTI >
[Mathematical Expression]

Where K is the overlay factor of the FBMC / OQAM system,

Is a channel estimation value of each sub-carrier position included in the m-th sub-channel of the n-th OQAM symbol,

Is the value of the sub-carrier through which the n-th OQAM symbol passes through the extended FFT (fast Fourier transform) at the receiving end,

Is the frequency domain coefficient of the prototype filter.
An extractor for extracting a channel estimate value of the pilot subchannel location in the sample;
A channel calculation unit for calculating a channel estimation value of a sub-carrier unit with respect to the extracted channel estimation value; And
An equalizer for equalizing the channel estimation value of the subcarrier unit
/ RTI >
11. The method of claim 10,
An extended fast Fourier transform module for passing de-overlapped samples; And
A frequency filter for filtering at least one of the samples passed through the extended FFT module and the equalized channel estimation values in a frequency domain;
Further comprising a channel equalizer.
12. The method of claim 11,
Wherein the frequency filter comprises:
And transforming at least one of the samples passed through the extended FFT module and the equalized channel estimation value.
11. The method of claim 10,
Wherein the channel calculator comprises:
A time domain interpolator for time interpolating the extracted channel estimation values in a time domain; And
A frequency domain interpolator for frequency interpolating channel estimation values interpolated in the time domain in a frequency domain;
/ RTI >
11. The method of claim 10,
Wherein the channel calculator comprises:
And repeatedly calculating the channel estimation value by a predetermined number of times n.
11. The method of claim 10,
A channel estimation value storage unit
Further comprising:
Wherein,
If the channel estimation value is not calculated repeatedly by the predetermined number of times n, the channel estimation value calculated from the previous number of channel values is corrected,
And outputs the stored channel estimation value if it is repeatedly calculated by the predetermined number of times n.
16. The method of claim 15,
Wherein,
Wherein the channel estimation value calculated at the previous time is multiplied by the equalization value for the pilot subchannel so as to correct the channel estimation value calculated at the previous number if the channel estimation value calculated at the previous time is not repeatedly calculated by the predetermined number of times n.
11. The method of claim 10,
The extractor
And the channel estimation value is extracted based on the following equation.
[Mathematical Expression]

here,

Wow

Denotes an index of a pilot subchannel,

Lt; / RTI > is the channel estimate over the pilot subchannel,

The

Of the second OQAM symbol

Lt; th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

(Real part) to be transmitted to the i < th > subchannel,

Takes the real and imaginary parts of the QAM symbol

Of the second OQAM symbol

Lt; th > subchannel is an intrinsic interference (imaginary part)

The

Of the second OQAM symbol

Th subchannel is white Gaussian noise.
11. The method of claim 10,
The equalizer comprises:
Performing equalization on the sub-carrier basis on the basis of the following equation
≪ / RTI >
[Mathematical Expression]

Where K is the overlay factor of the FBMC / OQAM system,

Is a channel estimation value of each sub-carrier position included in the m-th sub-channel of the n-th OQAM symbol,

Is the value of the sub-carrier through which the n-th OQAM symbol passes through the extended FFT (fast Fourier transform) at the receiving end,

Is the frequency domain coefficient of the prototype filter.

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