KR100943179B1 - Method of tranmitting/receiving data and constructing pilot for Orthogonal Frequency Division Multiplexing/Offset Quadrature Amplitude Modulation Communication - Google Patents

Abstract

The present invention relates to a pilot signal structure for effective channel estimation capable of eliminating interference inherent to an IOTA function, a configuration method thereof, and a data transmission / reception method.

According to the present invention, adjacent subcarriers around a pilot subcarrier in a frequency and time domain can be disposed relative to each other to cancel the amount of interference to the pilot subcarriers.

Description

Method of transmitting / receiving data and constructing pilot for Orthogonal Frequency Division Multiplexing / Offset Quadrature Amplitude Modulation Communication}

The present invention relates to a pilot signal structure for effective channel estimation that can eliminate interference inherent to an isotropic orthogonal transform algorithm (IOTA) function, a method for configuring the same, and a method for transmitting and receiving data. In particular, the present invention uses an Orthogonal Frequency Division Multiplexing (OFDM) Offset QAM scheme and relates to a pilot structure suitable for this system.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development (National Research Project: Development of cognitive radio technology for improving spectrum use efficiency).

In future mobile communication systems, high speed data transmission is essential for various services such as video, high quality audio, and mobile internet.

Orthogonal Frequency Division Multiplexing (OFDM) reduces the spectral efficiency of an OFDM system because it requires the insertion of guard intervals to overcome inter-symbol interference (ISI) and inter-carrier interference (ICI).

On the other hand, OFDM / OQAM-IOTA (OFDM / Offset Quadrature Amplitude Modulation-Istropic Orthogonal Transform Algorithm) method uses IOTA function which has superior localization characteristics in time and frequency domain without using guard interval compared to conventional OFDM / QAM method. Because it has high spectral efficiency and strong in multipath fading environment, it is suitable for high speed data transmission system.

However, in order to reduce the influence on the multipath channel, the OFDM / OQAM-IOTA method uses the IOTA function instead of the guard interval, so that the inherent interference of the IOTA function is generated. Since the side cannot accurately estimate the channel due to interference due to subcarriers around the pilot, data demodulation is impossible.

A block type signal structure has been proposed to solve this problem, but when the channel estimation is performed using the preamble, a null signal must be transmitted before and after the preamble symbol. Therefore, the data rate is reduced. The problem arises that the length of the frame must not be long.

The present invention provides a pilot structure and a data transmission / reception method for reducing channel estimation errors due to IOTA-specific interference in an OFDM / OQAM-IOTA communication system.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a data transmission method for OFDM / OQAM communication, comprising: outputting a data subcarrier to which a real part or an imaginary part of complex bit data separated at half-symbol intervals is allocated; Outputting an additional data subcarrier to which the binary phase shift modulated additional information data is assigned; And inserting a pilot subcarrier between the output data subcarriers, an interference cancellation subcarrier having a polarity opposite to that of the additional data subcarrier and the additional data subcarrier adjacent to the pilot subcarrier.

A data receiving method for OFDM / OQAM communication of the present invention comprises the steps of: extracting pilot subcarriers inserted between data subcarriers to which real or imaginary parts of complex bit data are allocated; Calculating a channel frequency response from the extracted pilot subcarriers, the interference of which is canceled by an additional data subcarrier inserted adjacent to the pilot subcarrier and an interference cancellation subcarrier having a polarity opposite to that of the additional data subcarrier; And interpolating the channel frequency response.

A pilot configuration method for OFDM / OQAM communication of the present invention comprises the steps of: inserting a pilot subcarrier between data subcarriers assigned real or imaginary parts of complex bit data separated at half-symbol intervals; And inserting a neighboring subcarrier pair of an interference cancellation subcarrier having a polarity opposite to the polarity of the additional data subcarrier and the additional data subcarrier to which additional information data is allocated to cancel interference on a pilot subcarrier based on the pilot subcarrier. can do.

The present invention for achieving the above technical problem can provide a computer-readable recording medium recording a program for executing a data transmission and reception method and a pilot configuration method for OFDM / OQAM communication in a computer.

In the OFDM / OQAM-IOTA system, due to the inherent intersymbol interference by the IOTA function, it is impossible to accurately estimate the channel value at the receiving end. In order to eliminate such interference, adjacent subcarriers around the pilot subcarriers in the frequency and time domains may be disposed relative to each other to cancel the amount of interference given to the pilot subcarriers.

The interference cancellation reduces the channel estimation error caused by the interference at the receiving end, resulting in high channel estimation performance.

In this case, since the location of the adjacent subcarriers is disposed according to the data information bits, additional information can be transmitted, thereby effectively transmitting the data without reducing the data rate.

Performance can also be maintained in high-speed mobile environments of multipath fading channels.

The pilot structure according to the present invention can be applied to various systems using OFDM / OQAM-IOTA.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the same elements among the drawings are denoted by the same reference numerals and symbols as much as possible even though they are shown in different drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

In the OFDM / OQAM-IOTA system, due to the inherent intersymbol interference by the IOTA function, it is impossible to accurately estimate the channel value at the receiving end. That is, the pilot subcarriers transmitted by the transmitter for channel estimation are interfered by adjacent subcarriers. Therefore, it is difficult for the receiver to estimate the correct channel from the pilot subcarrier.

In the present invention, in order to remove the interference on the pilot subcarriers, adjacent subcarriers around the pilot subcarriers are disposed relative to each other in the frequency and time domain so as to cancel the amount of interference given to the pilot subcarriers. In this case, since the location of the adjacent subcarriers is disposed according to the data information bits, additional information can be transmitted, thereby effectively transmitting the data without reducing the data rate.

1 illustrates a frequency and time domain structure in an OFDM / QAM system and an OFDM / OQAM-IOTA communication system.

Referring to FIG. 1, the time domain is represented by a plurality of OFDM symbols, and the frequency domain is represented by a plurality of subcarriers constituting an OFDM symbol. The symbol and each subcarrier constituting the symbol may be assigned an index to distinguish the positions of the subcarriers.

In FIG. 1, ν ₀ represents a subcarrier spacing, T _u represents a symbol period of an existing OFDM / QAM system, and τ ₀ (= T _u / 2) represents a symbol period of an OFDM / OQAM system.

In conventional OFDM / QAM, both the real part and the imaginary part of QAM-modulated complex data are transmitted in symbol period T _u . On the other hand, in an OFDM / OQAM system, a half symbol period τ ₀ , which is half of the symbol interval of OFDM / QAM, is transmitted.

The IOTA filter, an optimal prototype function with orthogonality in both domains of frequency and time, can maintain orthogonality only in real terms. Therefore, by using the OQAM scheme, the IOTA filter can be used by moving the real part or the imaginary part by half-symbol period τ ₀ .

The OFDM signal of the OFDM / OQAM system follows Equation 1.

In Equation 1, a _{m and n} are real values which are OQAM data carried on the m th subcarrier of the n th symbol, and M means the number of subcarriers. Unlike the signals of the conventional OFDM / QAM system, the input data a _{m and n} have only real values, and have multiplication with i ^{m + n} to have only one real or imaginary value rather than a complex value in one subcarrier.

Equation 1 is an input value of the IOTA filter function, and the output value of the IOTA filter function follows Equation 2.

는 IOTA 함수를 나타낸다. In Equation 2,

Represents the IOTA function.

2 is a block type signal structure diagram.

Referring to FIG. 2, a block type signal structure 200 includes an initial preamble symbol 201 and a data symbol 203.

The block type structure is a method in which an entire symbol, that is, a preamble is used for channel estimation, and a channel value of a subsequent data symbol is compensated by using a channel value obtained by using an initial preamble. In this method, there is a problem that performance is degraded as the moving body speed is higher.

3 is a signal structure diagram for an existing OFDM / OQAM-IOTA system.

Referring to FIG. 3, the signal structure 300 of the existing OFDM / OQAM-IOTA system includes a null subcarrier 301, a pilot subcarrier 303, and a data subcarrier 305.

In order to reduce the IOTA filter interference in the time domain, that is, to reduce the amount of interference by the IOTA filter affecting the pilot subcarrier 303 at the receiving end, the null subcarrier 301 is transmitted before and after the preamble symbol for channel estimation. Done. At this time, in order to reduce interference in the frequency domain, two adjacent subcarriers of the pilot for channel estimation have opposite signs to each other, so that the influences of the adjacent pilots cancel each other out. However, in this structure, since three symbols are sent in time to transmit a preamble symbol, the transmission rate is reduced. In addition, since the channel values of all symbols in one frame are compensated for using the channel values estimated in the preamble, a large channel estimation error occurs when the moving body speed is high.

4 illustrates neighboring subcarriers around the subcarrier.

Referring to FIG. 4, the subcarrier spacing in the time domain is τ ₀ (= T _u / 2), which is half of the symbol period T _u of the conventional OFDM / QAM system, and the subcarrier spacing is ν ₀ in the frequency domain. Therefore, S _{m , n} is a subcarrier located at a distance of mτ ₀ from the subcarrier S _0,0 in the time domain and nυ ₀ from the subcarrier S _{0 , 0} in the frequency domain.

The subcarriers S _0,0 are interfered by not only adjacent one-tier subcarriers but also two-tier subcarriers.

FIG. 5A is a diagram illustrating an impulse response of an IOTA function with respect to the subcarrier S ₀ and ₀ of FIG. 4, and FIG. 5B is a diagram illustrating a direction of an impulse response.

의 길이는 4×M(M은 FFT 크기)이 된다. 수직축은 임펄스 응답 G_{i ,j}의 진폭, 수평축은 임펄스 응답의 방향을 정의하는 각 축 l_n에 따라 부반송파 간 거리를 나타낸다.5A and 5B, for convenience of analysis, the IOTA function is limited to the interval [−L · τ ₀ , L · τ ₀ ], and L = 4 is selected. Thus IOTA function

The length of is 4 x M (M is the FFT size). The vertical axis is the amplitude of the impulse response G _{i , j} and the horizontal axis is the axis defining the direction of the impulse response. It shows the distance between subcarriers according to l _n .

Since the impulse response in each direction has bilateral symmetry with respect to the reference response, the interference between the two subcarriers is the same. Also, the interference of l ₂ and l _{4 and} the interference of l ¹ and l ₅ are not symmetric about l ₃ . Thus, the interference of the IOTA function is different on the time axis and frequency axis for the same subcarrier spacing.

Considering only the interference (I) of the IOTA function for the sub-carrier (S _0,0), and then the interference of the reference sub-carrier (S _0,0) as shown in equation (3) is expressed by the sum of the interference from the neighboring sub-carriers. Here, only interference from neighboring subcarriers up to the second layer, which is the main interference source, is considered, but subcarrier interference of more layers may be considered according to design and channel environment.

를 0으로 하는 다음 수학식 4의 조건을 만족한다.For accurate CFR estimation at the receiving side, the pilot structure of the present invention

Satisfies the condition of the following equation (4).

6A to 6C are signal structure diagrams according to an embodiment of the present invention.

The present invention is an additional data transmission based on signal interference cancellation. In the signal of the present invention, pilot structures 610 and 660 are inserted in which an additional data subcarrier and an interference canceling subcarrier pair are inserted adjacent to the pilot subcarrier based on the pilot subcarrier.

6A and 6B, data signal structures 600 and 650 according to the present invention include data subcarriers, pilot subcarriers, additional data subcarriers, and interference cancellation subcarriers.

In the data signal structures 600 and 650 of the present invention, the symbol interval in the time domain is a half-symbol period τ _{0 which} is half of the symbol period T _u of the conventional OFDM / QAM, and the subcarrier interval in the frequency domain is conventional OFDM / It is equal to the frequency interval υ ₀ of QAM.

The data subcarrier is a signal that transmits OQAM modulated data bits. The data subcarrier transmits a real part or an imaginary part from a real part and an imaginary part of complex data separated by half-symbol intervals as shown in FIG. 1.

The pilot subcarrier is a signal modulated by binary phase shift keying (BPSK), and a receiver estimates a channel value using the signal. The position at which the pilot is inserted is predefined. The interval of the pilot subcarriers in the time and frequency domain may be changed and applied according to the channel environment.

The additional data subcarrier is a 1-bit (bit) data signal that is BPSK modulated to transmit additional data bits. The additional data subcarrier is located adjacent to the pilot subcarrier.

The interference cancellation subcarrier has a polarity opposite to that of the 1-bit additional data subcarrier in order to offset the amount of IOTA filter interference given to the pilot subcarrier by the 1-bit additional data subcarrier.

In the pilot structure of FIG. 6A, pilot subcarriers are inserted between data subcarriers, and neighboring subcarrier pairs having opposite polarities are inserted to cancel interference of pilot subcarriers based on the pilot subcarriers. The data subcarriers are allocated real or imaginary parts of complex bit data separated by half-symbol intervals. The neighbor subcarrier pair is an interference cancellation subcarrier having a polarity opposite to that of the additional data subcarrier to which additional information data is allocated and the additional data subcarrier, as shown in Equation 5 below. Eight neighboring subcarriers S _{i , j} (i = 0,1, j = 0,1) around the pilot subcarriers are arranged in a one-tier at one half-symbol and one subcarrier distance from the pilot subcarriers, and 4 Four data subcarriers may be additionally transmitted by the additional data subcarriers and the four interference cancellation subcarriers.

S _{i , 1} = -S _{-i, -1} (if j = 1)

S _{i , 0} = -S _{-i, 0} (if j = 0)

The pilot structure of FIG. 6B is constructed by adding a neighboring subcarrier pair of one half-symbol and one subcarrier distance from a pilot subcarrier and a neighboring subcarrier pair of two half-symbol and one subcarrier distance to a neighboring subcarrier pair of one layer of FIG. -tier). Therefore, by further canceling the interference of neighboring subcarriers S- _2,1 , S- _{2, -1 , S2,1} , S2 _{, -1} with respect to the pilot subcarriers, the receiver can improve the channel estimation.

6C shows a data signal structure in which the pilot structure of the present invention is repeated.

Referring to FIG. 6C, the pilot structure of the present invention is repeatedly inserted at predetermined intervals in the time and frequency domains, and the pilot subcarrier spacing in the time and frequency domains may be changed according to channel environments.

7 is a block diagram schematically illustrating an internal configuration of a data transmission apparatus according to an embodiment of the present invention.

Referring to FIG. 7, the data transmission apparatus 700 according to the present invention includes a data generator 701, a serial-parallel converter 703, a data modulator 705, a 1-bit data modulator 707, and a T. FIG. / 2-time delay unit 709, pilot insertion unit 711, IFFT operation unit 713, IOTA filter unit 715, parallel-to-serial conversion unit 717 and data transmission unit 719. In the data transmission apparatus 600 according to the present invention, a detailed description of the same / similar operation of the same components as the transmission apparatus of the conventional OFDM / OQAM-IOTA system will be omitted.

The data generator 701 generates data consisting of a plurality of bits, and the serial-parallel converter 703 converts the generated data into a parallel signal.

The data modulator 705 modulates the data bits output from the serial-parallel converter 703 into complex bit data by QAM modulation. The T / 2-time delay unit 709 delays and outputs the real part or imaginary part (Q value or I value) of the complex bit data by T _U / 2 which is half of the symbol period of the conventional OFDM / QAM system according to the index. do. For example, the data modulator 705 divides the real part and the imaginary part Q ₁ , I ₁ of the complex bit data of the first index and outputs I ₁ directly, and Q ₁ is a T / 2-time delay part 709. Outputs by delaying by T _U / 2. The real part of the complex bit data of the second index and the imaginary part Q ₂ , I ₂ are divided and Q ₂ is immediately output, and I ₂ is delayed by T _U / 2 and output. Therefore, the real part and the imaginary part are alternately output at half-symbol intervals.

The 1-bit data modulator 707 outputs additional data subcarriers by BPSK-modulating a plurality of 1-bit data including additional transmission information. The output additional 1-bit data subcarrier is then inserted around the pilot.

The pilot inserter 711 inserts an interference cancellation subcarrier corresponding to the 1-bit data subcarrier and the 1-bit data subcarrier generated by the pilot subcarrier and the second data modulator. The interference cancellation subcarrier has a polarity opposite to that of the 1-bit data subcarrier to cancel the interference that the 1-bit data subcarrier imposes on the pilot subcarrier. The 1-bit data subcarrier and the interference cancellation subcarrier pair are inserted to have a symmetrical structure with respect to the time or frequency axis based on the pilot subcarrier.

The IFFT calculator 713 receives a plurality of signals and performs inverse fast fourier tramsform (IFFT) on a plurality of sequence applied signals to output a plurality of OFDM symbols. In this case, the plurality of OFDM symbols corresponds to a baseband OFDM signal.

에 의한 필터링을 수행한다. The IOTA filter unit 715 inputs the output of the IFFT converter 713 to output an IOTA function.

Perform filtering by

The parallel-serial converter 717 receives the OFDM signals input from the IOTA filter 715 in parallel and outputs them in series.

The data transmitter 719 receives a frame output from the parallel-serial converter 717 and transmits the input frame to the data receiving apparatus through a wireless channel.

The transmission signal coefficient transmitted through the data transmission unit 719 follows the following equation (6).

In Equation 6, M is half the FFT size, that is, the size of the IOTA buffer input in parallel, C is the output value of IFFT, Cm, n is the output value at the m-th subcarrier position of the nth symbol, L is the IOTA filter The lengths, k and i, are the transmission coefficient indexes.

For convenience, the pilot inserter, the IFFT unit, and the parallel-to-serial converter are separately shown for signals passing through the time delay unit and signals not passing through the time delay unit, but a single configuration is also possible.

8 is a block diagram schematically illustrating an internal configuration of a data receiving apparatus according to an embodiment of the present invention.

Referring to FIG. 8, the data receiving apparatus 800 according to the present invention includes a data receiver 801, a serial-parallel converter 803, a T / 2-time delay unit 805, an IOTA filter unit 807, FFT calculator 809, pilot extractor 811, channel response calculator 813, interpolator 815, 1-bit information demodulator 817, complex signal demodulator 819, and parallel-serial converter 821. In the data receiving apparatus 800 according to the present invention, a detailed description of the same / similar operation of the same components as the receiving apparatus of the conventional OFDM / OQAM-IOTA system will be omitted.

The data receiver 801 receives a frame transmitted through a wireless channel and outputs a plurality of data symbols.

The serial-parallel converter 803 receives a plurality of data symbols in series from the receiver 801 and outputs them in parallel.

The T / 2-time delay unit 805 delays half of a real or imaginary symbol by T _U / 2, which is half of the symbol length of the conventional OFDM / QAM system.

The IOTA filter unit 807 receives and outputs symbols output from the serial-parallel conversion unit 803 and the T / 2-time delay unit 805.

The received signal passing through the IOTA filter unit 807 follows the equation (7).

In Equation 7, M is half the FFT size, that is, the size of the IOTA buffer input in parallel, L is the length of the IOTA filter, k and i is the transmission coefficient index.

The fast fourier transform (FFT) calculator 809 receives a plurality of data symbols from the IOTA filter unit 807, performs an FFT on the plurality of data symbols, and outputs a plurality of Fourier transform symbols.

The received OFDM / OQAM-IOTA signal through the channel follows Equation 8.

In Equation 8, H _{m , n} represents the m-th subcarrier channel gain of the n-th symbol, M represents the half of the FFT size, that is, the size of the IOTA buffer input in parallel.

The pilot extractor 811 receives a plurality of Fourier transform symbols from the FFT calculator 809, extracts pilots from the plurality of Fourier transform symbols, and outputs a plurality of pilot subcarriers.

The channel response calculator 813 receives the pilot subcarrier from the pilot extractor 811, calculates a channel frequency response (CFR), and outputs a CFR. The channel response calculator 813 calculates a CFR from an additional data carrier inserted adjacent to the pilot subcarrier and a pilot subcarrier whose interference due to a neighboring carrier is canceled by an interference cancellation subcarrier having a polarity opposite to that of the additional data subcarrier.

The interpolator 815 receives a plurality of channel frequency responses from the channel response calculator 813, and linearly interpolates the plurality of channel frequency responses to output a plurality of interpolated channel frequency responses.

The 1-bit data demodulator 817 demodulates 1-bit information through the interpolated signal from the interpolator 815. As shown in Equation 9, demodulation of 1-bit data is performed using a difference between a 1-bit data subcarrier and an interference cancellation data subcarrier in consideration of polarity. For example, the noise variance can be reduced by dividing the difference (+1-(-1)) between the data signal +1 and the interference cancellation signal -1 in half.

The complex signal demodulator 819 selects a real part or an imaginary part of the complex signal according to each index, demodulates a plurality of symbols, and outputs data composed of a plurality of bits.

The parallel-serial converter 821 receives the demodulated signal from the demodulated signal demodulator 819 and outputs a plurality of data bits in series.

For convenience, the serial-parallel converter and the FFT unit are separately shown for signals passing through the time delay unit and signals not passing through the time delay unit, but a single configuration is also possible.

9 is a flowchart illustrating a data transmission method for OFDM / OQAM communication according to an embodiment of the present invention. In the following, detailed descriptions of contents overlapping with the above description will be omitted.

The real or imaginary parts of the complex bit data separated at half-symbol intervals are allocated with the data subcarriers assigned thereto (S901). The multiple bit data input in parallel is QAM modulated with complex bit data, and the real part or imaginary part of the complex bit data is delayed by half-symbol according to the subcarrier index.

The additional data subcarrier, which is a 1-bit data subcarrier to which the binary phase shift modulated additional information data is allocated, is output (S903).

An interference cancellation subcarrier having a polarity opposite to that of the pilot subcarrier, the additional data subcarrier, and the additional data subcarrier is inserted between the output data subcarriers (S905). In detail, in order to cancel interference of the pilot subcarriers based on the pilot subcarriers, neighboring subcarrier pairs having opposite polarities are inserted into one or two layers. The neighboring subcarrier pairs are interference cancellation subcarriers having polarities opposite to those of the additional data subcarriers to which additional information data is allocated and the additional data subcarriers, and are located symmetrically with respect to the frequency axis or the time axis. Neighbor subcarrier pairs include neighboring subcarrier pairs of one half-symbol and one subcarrier distance from the pilot subcarrier, or neighbor subcarrier pairs of one half-symbol and one subcarrier distance and two sub-symbols and one subcarrier distance from the pilot subcarrier. It can include a pair. That is, the additional data subcarrier and the interference cancellation subcarrier are symmetrically inserted in the time axis or the frequency axis with respect to the pilot subcarrier to generate the pilot structure of the present invention. Half of the subcarriers around the pilot place the BPSK modulated data subcarriers, and subcarriers having opposite polarities are placed in the other half to cancel the interference of the pilot subcarriers.

The IFFT is applied to the data symbol in which the pilot subcarriers are inserted (S907).

The IOTA filter function is applied to the IFFT data symbol (S909).

The frame obtained by converting the filtered data symbol to serial is transmitted (S911).

10 is a flowchart illustrating a data receiving method for OFDM / OQAM communication according to an embodiment of the present invention. In the following, detailed descriptions of contents overlapping with the above description will be omitted.

Data symbols of the input frame are output in parallel (S1001).

Half of the data symbols composed of the real part or the imaginary part of the complex bit data are immediately IOTA filtered, and half of the data symbols allocated to the real part or the imaginary part of the complex bit data are IOTA filtered after being delayed by a half-symbol interval (S1003).

FFT the filtered data symbol (S1005).

The pilot subcarriers inserted between the data subcarriers of the FFT symbol are extracted (S1007).

The channel frequency response is calculated from the extracted pilot subcarriers and linearly interpolated (S1009). The interference from the neighboring subcarriers of the pilot subcarriers is canceled by the additional data subcarriers inserted adjacent to the pilot subcarriers and the interference cancellation subcarriers having polarities opposite to those of the additional data subcarriers.

The 1-bit information is demodulated from the additional data subcarrier using the interpolated channel frequency response, and the multi-bit information is demodulated from the data subcarrier (S1011). The additional information data is output by using the difference between the additional data subcarrier and the interference cancellation subcarrier.

FIG. 11 compares the transmission rate of the existing block type pilot structure according to the pilot subcarrier spacing N _pt in the time domain with the pilot structure proposed by the present invention based on QPSK. Case 1 is a pilot structure of one layer shown in FIG. 6A, and case 2 is a pilot structure of two layers shown in FIG. 6B. N _pf is the spacing of pilot subcarriers in the frequency domain.

Referring to FIG. 11, when the interval between pilot subcarriers is narrow, the data rate of the existing block type pilot structure is lower than that of the pilot structure proposed by the present invention. Case 1's pilot structure has the highest data rate and N _pf Regardless of N and _pt , the pilot structure of case2 has a higher data rate than the conventional pilot structure.

FIG. 12 is a diagram illustrating Mean Square Error (MSE) for CFR estimated from pilot subcarriers according to an embodiment of the present invention under an ITU Indoor Channel environment.

Referring to FIG. 12, it can be seen that the best performance is obtained when the two-layer pilot structure of case2 is used under the multipath fading channel environment (ITU Indoor Channel) without considering the channel coding method. In addition, it can be seen that the pilot structure proposed in the present invention exhibits particularly good performance at low E _b / N ₀ (bit signal to noise ratio).

The invention can also be embodied as computer readable code on a computer readable recording medium. Computer-readable recording media include all types of recording devices that store data that can be read by a computer system. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, and may also be implemented in the form of a carrier wave (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, functional programs, codes, and code segments for implementing the present invention can be easily inferred by programmers in the art to which the present invention belongs.

So far, the present invention has been described with reference to preferred embodiments. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims.

Therefore, it will be understood by those skilled in the art that the present invention may be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a frequency and time domain structure in an OFDM / QAM system and an OFDM / OQAM-IOTA communication system.

2 is a block type signal structure diagram.

3 is a signal structure diagram for an existing OFDM / OQAM-IOTA system.

4 is a diagram illustrating neighboring subcarriers around a pilot subcarrier.

FIG. 5A is a diagram illustrating an impulse response of an IOTA function with respect to the subcarrier S ₀ and ₀ of FIG. 4, and FIG. 5B is a diagram illustrating a direction of an impulse response.

6A to 6C are signal structure diagrams according to an embodiment of the present invention.

7 is a block diagram schematically illustrating an internal configuration of a data transmission apparatus according to an embodiment of the present invention.

8 is a block diagram schematically illustrating an internal configuration of a data receiving apparatus according to an embodiment of the present invention.

9 is a flowchart illustrating a data transmission method for OFDM / OQAM communication according to an embodiment of the present invention.

10 is a flowchart illustrating a data receiving method for OFDM / OQAM communication according to an embodiment of the present invention.

FIG. 11 is a graph comparing a transmission rate of a conventional block type pilot structure according to the pilot subcarrier spacing N _pt in the time domain with a pilot structure proposed by the present invention based on QPSK.

FIG. 12 is a graph illustrating Mean Square Error (MSE) for CFR estimated from pilot subcarriers according to an embodiment of the present invention under an ITU Indoor Channel environment.

Claims (10)

Outputting a data subcarrier to which a real part or an imaginary part of complex bit data separated at half-symbol intervals is allocated; Outputting an allocated additional data subcarrier by modulating 1-bit information data additionally transmitted separately from the complex bit data; And And inserting a pilot subcarrier between the data subcarriers and symmetrically inserting an interference cancellation subcarrier having a polarity opposite to that of the additional data subcarrier and the additional data subcarrier adjacent to the pilot subcarrier. A data transmission method for OFDM / OQAM communication. The method of claim 1, The additional data subcarrier and the interference cancellation subcarrier are positioned symmetrically with respect to each other in a vertical direction, a horizontal direction and a diagonal direction with respect to a pilot subcarrier. The method of claim 1, wherein the data subcarrier output step, QAM modulating the plurality of bit data into complex bit data; And And delaying the real part or the imaginary part of the complex bit data by half-symbols. Extracting pilot subcarriers inserted between data subcarriers to which real or imaginary parts of complex bit data are allocated; Calculating a channel frequency response from the extracted pilot subcarriers; And Interpolating the channel frequency response; The pilot subcarrier may be configured such that the 1-bit information data additionally transmitted separately from the complex bit data adjacent to the pilot subcarrier is modulated so that the allocated additional data subcarrier and the interference cancellation subcarrier having a polarity opposite to the polarity of the additional data subcarrier are symmetrical. The data reception method for OFDM / OQAM communication characterized in that the interference is canceled inserted. The method of claim 4, wherein The additional data subcarrier and the interference cancellation subcarrier are located symmetrically with respect to each other in the up, down, left and right directions and the diagonal direction with respect to a pilot subcarrier. The method of claim 4, wherein Demodulating the additional data subcarrier to output additional information data; And Demodulating the data subcarriers and outputting a plurality of bits of data; and receiving data for OFDM / OQAM communication. The method of claim 6, And demodulating the additional data subcarrier by using a difference between the additional data subcarrier and an interference canceling subcarrier. Inserting pilot subcarriers between data subcarriers to which real or imaginary parts of complex bit data separated at half-symbol intervals are allocated; And In order to cancel the interference on the pilot subcarrier, the 1-bit information data additionally transmitted separately from the complex bit data adjacent to the pilot subcarrier is modulated to have an opposite polarity to that of the allocated additional data subcarrier and the additional data subcarrier. And symmetrically inserting the removal subcarriers. The method of claim 8, The additional data subcarrier and the interference cancellation subcarrier are positioned symmetrically with respect to each other in a vertical direction, a horizontal direction and a diagonal direction with respect to the pilot subcarrier. The method of claim 8, wherein the additional data subcarrier and the interference cancellation subcarrier, Symmetrically located at one half-symbol and one subcarrier distance from the pilot subcarrier, And symmetrically positioned at one half-symbol and one subcarrier distance and two half-symbol and one subcarrier distances from the pilot subcarrier.

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