KR100484447B1 - Transmitting/receiving apparatus and method for improving peak-to-average power ratio in an orthogonal frequency division multiplexing system - Google Patents

Abstract

An apparatus and method are disclosed for improving the characteristics of peak power to average power ratio (PAPR) in an orthogonal frequency division multiplex (OFDM) communication system. According to the "DFA OFDM scheme" according to an embodiment of the present invention, the transmitting end multiplies the signal in the frequency domain by a phase matrix having a delta autocorrelation characteristic, and the receiving end transmits the received signal using the Hermithian matrix of the phase matrix. Demodulate Since the present invention has no redundancy in the transmission signal, there is no loss of data transmission rate, and the delta autocorrelation characteristic in the frequency domain has a constant envelope in the time domain, resulting in an improvement in the PAPR characteristic.

Description

Transmitting and Receiving Device and Method of Orthogonal Frequency Division Multiple Communication System for Improvement of Peak-to-Average Power Ratio Characteristics

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to orthogonal frequency division multiplexing communication systems, and more particularly, to an apparatus and method for improving the peak power to average power ratio (PAPR) characteristics of a transmission signal.

As information utilization increases, information and communication technology is rapidly developing. For example, multimedia services of various video information including existing voice services are becoming more common and popular in general homes as well as large businesses, and the desire for new services is being accelerated and diversified. Orthogonal frequency division multiplexing (hereinafter referred to as " OFDM ") has been proposed as a transmission technology suitable for high-speed data communication to satisfy the needs of consumers.

The OFDM scheme is a communication scheme that enables high-speed data transmission using a plurality of sub-carriers in a given frequency band, and includes a Fast Fourier Transform (FFT) and an Inverse Fast Fourier Transform (IFFT). Modulation and demodulation are performed by Inverse Fast Fourier Transform. Since the OFDM scheme has the advantage of high bandwidth-efficiency and strong characteristics of multipath fading, digital television and wireless local area network (LAN) are used. Has been adopted.

However, the OFDM scheme has a disadvantage in that a peak-to-average-power ratio (hereinafter referred to as "PAPR") of a transmission signal is very large. This is because signals having a limited size in the frequency domain are IFFT and thus a signal having a high maximum value such as an impulse is generated in the time domain. Therefore, when a transmission signal according to the OFDM scheme passes through a nonlinear device such as a power amplifier, a high PAPR causes distortion of the signal. In particular, PAPR is very high when signals input for transmission have the same magnitude and the same phase.

Therefore, various researches for improving the PAPR characteristics in the communication system using the OFDM scheme are in progress. For example, in a communication system using an OFDM scheme, a PAPR is reduced to a selected mapping method (hereinafter, referred to as "SLM"), a tone reduction method, and a Hadamard Transform method. , Carrier Interferometry (hereinafter referred to as "CI") and the like have been proposed. Here, since the tone reduction method and the Hadamard transformation method are less related to the present invention, the present invention will be briefly described. The SLM method and the CI method are related to the present invention, and thus, the present invention will be described in more detail. For example, the SLM scheme is described in ADS Jayalah, C. Tellambura and H. Wu, "Reduced complexity PTS and new phase sequences for SLM to reduce PAP of an OFDM signal", VTC 2000, and the CI scheme is DA Wiegandt. , CA Nassar and Z. Wu, "Overcoming peak-to-average power ratio issues in OFDM via carrier-interferometry codes", IEEE Proc. Described in 2001.

The tone reduction method is a method of generating a pseudo impulse using a predetermined number of subcarriers and using this to cancel the value of the point having the highest peak value in the time domain to reduce the PAPR. Although this method is less than the SLM method in terms of computational amount, the data rate is reduced by the number of subcarriers used to generate the pseudo impulse. The closer the pseudo impulse is to the actual impulse, the better the characteristics, and thus there is a trade-off between the data rate and the improvement of the PAPR characteristic.

The Hadamard transformation method is a method of multiplying a Hadamard matrix by a signal in the frequency domain and transmitting a demodulated signal using an inverse Hadamard matrix. This method has no loss of data rate, but has the disadvantage that the improvement of PAPR is not so large compared to the calculation amount.

The SLM method is a method of multiplying a plurality of phase vectors by an input signal to find a signal having the lowest PAPR among the multiplied signals, and transmitting the same. That is, according to the SLM scheme, one piece of information is multiplied by different U phase vectors and IFFT, and then a signal having the lowest PAPR is selected and transmitted. Therefore, in the SLM scheme, as the number of phase vectors increases, the performance will also be proportionally improved. However, each increase of the phase vector increases the IFFT operation and additionally increases the time-domain PAPR calculation. Therefore, since infinitely many phase vectors cannot be used, it should be limited to the number of phase vectors suitable for the desired performance.

In addition, since the SLM scheme transmits a signal multiplied by an arbitrary phase vector, it is impossible for the receiver to extract the original signal without any information. Therefore, in order to inform the receiver that a phase vector has been multiplied at the transmitter, information about the phase vector must be inserted between signals transmitted from the transmitter. Several subcarriers must be used to transmit the phase vector information. The subcarriers used to transmit the phase vector information cause data to be transmitted at a lower rate than the original data rate. This data rate is also one of the reasons why infinitely large number of phase vectors cannot be used. In other words, the use of a large number of phase vectors increases the number of subcarriers used to inform phase vector information, thereby reducing the data transmission rate.

The CI method allocates each of the N input signals in the frequency domain to all subcarriers and transmits them. The method of allocating an input signal to all subcarriers is accomplished by multiplying the input signal with vectors having orthogonal phases and assigning the vectors to each subcarrier. Since the CI method does not generate redundancy such as phase vector information, a signal in a time domain having a constant envelope without a decrease in data transmission rate can be generated. The generated time domain signal is transmitted after being filtered by a low pass filter. However, even though a signal having a constant envelope, passing through the low pass filter has a problem that the PAPR characteristic is significantly reduced, that is, the PAPR is significantly increased.

Accordingly, an object of the present invention is to provide a transmission apparatus and method for providing an improved PAPR characteristic compared to the above-described conventional techniques in a communication system using an OFDM scheme.

Another object of the present invention is to provide a transmission apparatus and method for providing an improved PAPR characteristic without degrading a data transmission rate in a communication system using an OFDM scheme.

Another object of the present invention is to provide a transmission apparatus and method for providing an improved PAPR characteristic by simple calculation in a communication system using an OFDM scheme.

It is still another object of the present invention to provide a transmission apparatus and method for providing an excellent data transmission rate, a bit error rate (BER) characteristic, and a PAPR characteristic in a communication system using an OFDM scheme as compared to the above-described conventional techniques. have.

Another object of the present invention is to provide a transmission apparatus and method for reducing a zero crossing of a time domain signal in a time domain signal having a constant envelope in a communication system using an OFDM scheme.

It is still another object of the present invention to provide a receiving apparatus corresponding to a transmitting apparatus providing improved PAPR characteristics in a communication system using an OFDM scheme and a signal receiving method by the receiving apparatus.

The present invention for achieving the above object is to provide an IFFT unit for performing an inverse fast Fourier transform (IFFT) for the input signal having a vector size of (1 × K), and a low pass filter for low-pass filtering the output of the IFFT unit A transmission apparatus of an orthogonal frequency division multiplexing (OFDM) communication system is included.

The first matrix generator of the transmitting apparatus generates a first matrix having a size of M × K and M rows are orthogonal to each other. The second matrix generator has a size (M × K) and a second matrix for replacing the (i) th row of the first matrix, and a (K × K) size (j) column of the first matrix. To generate a third matrix to substitute for. The matrix converter generates (M × K) transform matrices by replacing each row and each column of the first matrix by the second matrix and the third matrix. The signal processor converts the input signal by the respective transform matrices to output a plurality of transform signals, and IFFT and low pass filter the plurality of transform signals, respectively. The peak power to average power ratio (PAPR) measuring unit measures the PAPR of each of the output signals of the signal processor. The selector selects a transform matrix corresponding to a signal having the smallest PAPR among the output signals of the signal processor. The signal converter converts the input signal by the selected transformation matrix and provides the converted input signal to the IFFT unit for transmission.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that those skilled in the art may better understand the detailed description of the invention that follows.

Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. Those skilled in the art should recognize that the disclosed concepts and specific embodiments of the invention may be readily used as a basis for modifying or designing other structures for achieving the same purposes of the present invention. Those skilled in the art should also recognize that structures equivalent to the invention do not depart from the spirit and scope of the broadest form of the invention.

DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be noted that reference numerals and like 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.

As mentioned above, conventional techniques for improving PAPR have been proposed in an OFDM communication system (hereinafter, referred to as an "OFDM system"), but there are various problems, such as a decrease in data transmission rate and an increase in calculation amount. The present invention for solving the problems of the prior art is an OFDM transmitting device and a corresponding receiving device and a signal transmission / reception method by the devices so that a good PAPR characteristic is obtained without loss of data transmission rate and simple calculation. Present them. Hereinafter, this embodiment of the present invention will be referred to as "DFA (Delta Frequency Autocorrelation) OFDM scheme".

According to the DFA OFDM scheme, a transmitter multiplies a signal in a frequency domain by multiplying a phase matrix having a delta autocorrelation characteristic, and a receiver uses a Hermitian matrix of the phase matrix. Demodulate the received signal. In the DFA OFDM scheme, since there is no redundancy in the transmission signal, there is no loss of data transmission rate. Since the DFA OFDM scheme has a delta autocorrelation characteristic in the frequency domain, it has a constant envelope in the time domain. Has the effect of improving. Particularly, when a large number of zero crossings occur due to the structure of DFA OFDM having a constant envelope in the time domain, the PAPR characteristic of the transmitting end of the OFDM system to be described later may be deteriorated. Higher PAPR improvement can be achieved by converting the input signal to reduce zero crossings and then using the DFA OFDM scheme.

1 is a diagram illustrating a configuration of a transmitting end of an OFDM system to which the present invention is applied.

Referring to FIG. 1, the transmitting end includes an Inverse Fast Fourier Transform (IFFT) unit 101 (hereinafter referred to as “IFFT”) 101 and Low Pass Filters (LPFs) 102-1 and 102-. 2, multipliers 103-1 and 103-2, phase delay 104 and adder 105.

Complex Input Data applied to IFFT 101 Is composed of N vectors as shown in Equation 1 below. Each vector is assigned to each of N subcarriers in the frequency domain. The input signal Is a signal modulated by a predetermined modulation scheme. The input signal 1 bit per subcarrier for binary phase shift keying (BPSK), 2 bits per subcarrier for quadrature phase shift keying (QPSK), 4 bits per subcarrier for 16 quadrature amplitude modulation (16QAM), and 64 QAM (64 quadrature amplitude modulation) is 6 bits per subcarrier. The input signal According to the modulation scheme of the data rate difference occurs.

IFFT 101 is the input signal By performing an N-point IFFT on the transformed signal, the signal in the frequency domain is converted into a signal in the time domain that can be actually transmitted. This conversion process can be represented by Equation 2 below.

As IFFT is performed by the IFFT 101, a signal having a high PAPR is generated. The low pass filters 102-1 and 102-2 perform low pass filtering on the time domain signal output from the IFFT 101. The low pass filter 102-1 performs low pass filtering on the real component of the time domain signal output from the IFFT 101, and the low pass filter 102-2 performs an imaginary component of the time domain signal output from the IFFT 101. Filter lowpass. The low pass filtering operation is represented by Equation 3 below.

Since the signals output from the low pass filters 102-1 and 102-2 have complex values, they cannot be transmitted in the time domain. Therefore, it is necessary to transmit a portion having a real value and a portion having an imaginary value on a carrier having a phase difference of 90 degrees. The components for this are multipliers 103-1, 103-2, 90 ° phase delay 104 and adder 105. The phase delay 104 is a carrier wave Delays the carrier by 90 ° Outputs The multiplier 103-1 is a carrier wave at the output of the low pass filter 102-1. Multiply and output The multiplier 103-2 is a carrier wave at the output of the low pass filter 102-2. Multiply and output The adder 105 adds the outputs of the multipliers 103-1 and 103-2 and transmits a signal s (t) as shown in Equation 5 below. The signal from the adder 105 may be an intermediate frequency (IF) converted signal or a radio frequency (RF) converted signal. If the signal from the adder 105 is an IF signal, it is then RF-converted and then sent out into the air through the antenna, and if it is an RF signal, it is sent out into the air through the antenna.

A. Principles of the Invention

The delta frequency autocorrelation orthogonal frequency division multiplexing (DFA OFDM) scheme proposed by the present invention multiplies an input signal by using a phase matrix, or "U matrix," having orthogonal vectors in the frequency domain. The autocorrelation of the signal is a delta function, thereby generating a signal having a constant envelope in the time domain. In order to generate a low PAPR signal in the time domain, first, a method in which the signal in the time domain has a constant envelope, and second, a method in which a zero crossing of the time domain signal occurs is small. have. The U matrix used in the present invention allows the autocorrelation of the frequency domain signal to be a delta function so as to have a constant envelope in the time domain. Therefore, the PAPR improvement can be further improved by applying a U matrix which reduces the zero crossing of the time domain signal among these U matrices. In addition, in the DFA OFDM scheme, redundancy does not occur in a transmission signal, and data transmission rate, BER characteristics, and PAPR improvement are superior to conventional methods.

B. Examples

2 is a diagram illustrating a configuration of a transmitting end of an OFDM system including a DFA converter according to an embodiment of the present invention. Here, the low pass filters 102-1 and 102-2 of FIG. 1 are shown to be included in the IFFT 203, and the multipliers 103-1 and 103-2, the phase delayer 104, and the adder 105 of FIG. 1 are omitted. It should be noted that Therefore, although not shown in the drawings, it is well understood that the multipliers 103-1, 103-2, the phase delay 104, and the adder 105 of FIG. 1 are connected between the IFFT 203 and the P / S converter 204. FIG. Will be done. The output signal of the transmitter is shown to be s (t) in the same manner as the configuration of the transmitter shown in FIG.

Referring to FIG. 2, the transmitter has a serial-to-parallel (S / P) converter 201, a DFA converter 202, an IFFT 203, and a parallel / to-parallel (P / S). -Serial) conversion unit 204 is included. The S / P converter 201 inputs a serial input signal d (j) in parallel. Convert to and print it out. The input signal Is Input signal in vector size Is converted to Here, K is the vector size of the input signal, T means transpose (transpose).

The DFA converter 202 is the input signal The DFA transform is performed by using a given U matrix, and a signal vector b is output. The U matrix has a M × K size and is a DFA transform matrix with M rows being orthogonal vectors. Where M is the size of the rows of the U matrix. The U matrix is a matrix consisting of M rows and K columns, as shown in Equation 5 below, and may be an example as shown in Equation 6 in which each row is orthogonal to each other.

In Equation 6 above to be.

The input signal vector If DFA is transformed into the U matrix given by the DFA conversion unit 202, the resulting signal vector is expressed by Equation 7 below. Is obtained.

The IFFT 203 is the signal vector And IFFT and lowpass filtering and output a signal c as shown in Equation (8).

The signal c is converted into an IF or RF band by the multipliers 103-1, 103-2 and the adder 105 shown in FIG. 1 and then applied to the P / S converter 204. The P / S converter 204 converts the applied signal in parallel / serial and outputs the signal s (t) for transmission. In this case, a guard inserter for processing suitable for transmission may be further connected to the rear end of the P / S converter 204, but the configuration thereof will be omitted.

3 is a diagram illustrating a configuration of a receiver of an OFDM system according to an embodiment of the present invention, which corresponds to the configuration of the transmitter illustrated in FIG. 2 and restores an original signal through a process opposite to that of the transmitter. .

Referring to FIG. 3, the receiver includes a serial / parallel (S / P) converter 301, an FFT 302, an inverse DFA converter 303, and a parallel / serial (P / S) converter 304. The S / P converter 301 inputs and receives a received signal r (t) and converts the received signal in parallel. Output as. The FFT 302 is the received signal Taking an FFT for, and taking the FFT Outputs The inverse DFA converter 303 transmits the signal. Inverse DFA converted signal by multiplying by Hermitian matrix Outputs Here, the hermithian matrix means a matrix U ^H satisfying the characteristics of UU ^H = I, and is a value given in advance. The P / S converter 304 converts the inverse DFA signal Serial restore signal Output as.

4 is a diagram illustrating a configuration of blocks for generating a U matrix provided to the DFA converter 202 illustrated in FIG. 2. These blocks are components for the operation of generating a U matrix such that the PAPR of the time domain signal is minimized.

Referring to FIG. 4, the U matrix generator 401 generates a U matrix having a size of (M × K) consisting of M rows and K columns. Each row of the generated U matrix is orthogonal to each other, and a matrix as shown in Equation 6 below may be used. The permutation matrix generator 402 generates a (M × M) substitution matrix P (i) and a (K × K) substitution matrix P (j) for the generated U matrix. As the substitution matrix P (i), a matrix as shown in Equation 10 may be used, and as the substitution matrix P (j), a matrix as shown in Equation 11 may be used. Here, (i) is a variable representing the rows of the matrix and has a value from 0 to (M-1), and (j) is a variable representing the columns of the matrix and has a value from 0 to (K-1). The matrix converter 403 inputs the generated U matrix and the substitution matrices P (i) and P (j), and multiplies them by Equation (12) below to obtain the (i) th row and the (j) th Create a transformed matrix that corresponds to the column. Since the substitution matrix generator 402 generates M substitution matrices P (i) and K substitution matrices P (j), the matrix converter 403 generates (M × K) conversion matrices U (i, j). Will be created.

The signal processor 404 inputs the transform matrices generated by the matrix transform unit 403, and outputs the filtered matrices by DFA transform, IFFT, and low pass filtering. In this case, if the IFFT is taken after the DFA transformation on the input transformation matrix, a signal in a time domain having a constant envelope is generated. This is represented by Equations 15 and 16 below. The PAPR measuring unit 405 measures the PAPR (i, j) of the signal output from the signal processing unit 404. This is represented by Equation 17 below. The Umin selector 406 selects the U matrix that is the minimum among the PAPRs (i, j) measured by the PAPR measuring unit 405 and outputs the U matrix as the Umin matrix. This is represented by Equation 18 below.

5 is a flowchart illustrating a processing flow of an Umin matrix generation operation according to an embodiment of the present invention. This processing flow is performed by the components as shown in FIG. 4 as an operation of selecting a U matrix such that the PAPR of the time domain signal is minimized and generating this selected U matrix as a Umin matrix.

Referring to FIG. 5, in operation 501, an operation of generating a U matrix is performed. That is, in step 501, as shown in Equation 9 below. The substitution matrix P (i) is obtained, and a K × 1 column vector a which is an input signal vector as shown in Equation 10 below is determined. In addition, in step 501, as shown in Equation 11 and Equation 12, or The cyclic correlation or auto-correlation value of the delta function M × K unitary matrix U to be obtained. Here, the substitution matrix P (i) is a matrix for replacing the (i) th row of the U matrix.

In step 502, the variables (i) and (j) are initialized to '0'. In step 503, the substitution matrix P (i) as shown in Equation 13 below is multiplied by the substitution matrix P (i) to the U matrix generated in step 501 as shown in Equation 14 below (i) The transformation matrix U (i, j) corresponding to the first row and the (j) th column is output. Here, the substitution matrix P (j) is a matrix for replacing the (j) th row of the U matrix. In step 503, the output signal vector b is obtained by multiplying the transform matrix U (i, j) by the input signal vector a as shown in Equation 15 below.

In step 504, an IFFT is taken on the output signal vector b . This is shown in Equation 16 below, and the signal vector in which the IFFT is taken is a signal in a time domain having a constant envelope. In operation 505, low pass filtering is performed on the signal in the time domain having the constant envelope. This is shown in Equation 17 below, and as a result The signal is output.

In operation 506, the signal is expressed as in Equation 18. PAPR is measured and the variable j is increased by one. If it is determined in step 507 that the increased variable j is K, the process proceeds to step 508. Otherwise, the process returns to step 503 and the operations of steps 503 to 506 are repeated. In step 508, the variable i is incremented by 1 and the variable j is initialized to 0. If it is determined in step 509 that the increased variable i is M, the process proceeds to step 510. Otherwise, the process returns to step 503 and the operations of steps 503 to 508 are repeated.

If variables (i) and (j) increase during the repetitive operation, the shape of the substitution matrix is changed. For example, if the variable (i) is 1, the substitution matrix represented by Equation (9) is changed to the form in which the rows are increased by one, and if the variable (i) is 2, the substitution matrix represented by the formula (9) is changed to the form in which the rows are increased by two. . That is, if the variable (i) is 1, the second row of the substitution matrix P (i) moves to the third row, the third row moves to the fourth row, the Mth row moves to the first row, The first row moves to the second row. Similarly, if the variable (j) is 1, the substitution matrix represented by Equation 13 is changed to a form in which the column is increased by one, and when the variable (j) is 1, the substitution matrix represented by Equation 13 is changed to the form in which the column is increased by two. That is, if the variable (j) is 1, the second column of the substitution matrix P (j) moves to the third column, the third column moves to the fourth column, the K column moves to the first column, and the first column Moves to the second column.

In operation 510, among the U matrices generated by the repetitive operation, a U matrix having a minimum PAPR (i, j) is selected as shown in Equation 19 below, and the selected U matrix is output as Umin. The output matrix Umin is provided to the DFA conversion unit 202 shown in FIG. 2 and used for the DFA conversion operation on the actual input signal vector a .

A brief summary of the above-described process of FIG. 5 is as follows. First, a U matrix is generated. At this time, the U matrix as described in step 501 or Autocorrelation of Delta Function Where M × K is the unitary matrix U. Subsequently, the generated U matrix is multiplied by the substitution matrices P (i), P (j) to find the U matrix having the lowest PAPR by reducing the zero crossing after the LPF passage in the time domain. Then, DFA transform, IFFT and low pass filtering are performed on the multiplication result. Then, the PAPR is measured on the performance result signal. After the above processes are repeated until i = M, j = K, a U matrix Umin having a minimum PAPR is generated. The generated U matrix Umin is provided to the DFA conversion unit 202 shown in FIG. 2.

Referring back to FIG. 2, the DFA converter 202 of the transmitter according to the embodiment of the present invention is provided with K input signal vectors a as shown in Equation 20 below.

The DFA conversion unit 202 performs DFA conversion on the input signal vector a using a previously generated U matrix Umin, and outputs an output signal vector b . This is represented by Equation 21 below.

IFFT 203 is the output signal vector After taking IFFT with respect to Equation 22, the time domain signal c is expressed as shown in Equation 22 below. The generated time domain signal has a constant envelope and minimizes the increase of the PAPR even if it passes through the low pass filter.

FIG. 6 is a diagram illustrating a detailed configuration of the DFA converter 202 shown in FIG. 2. This figure shows an example in which the DFA converter 202 is implemented with a transversal filter structure.

Referring to FIG. 6, the DFA converter 202 includes a plurality of buffers 610, a plurality of multipliers 620, and an adder 630. The plurality of buffers 610 are u (i, 0), u (i, 1), ... u (i, K-2), u (i, K) of the columns of the (i) th row of the U matrix Umin. Enter -1) to save. Each of the multipliers of the plurality of multipliers 620 inputs each vector of the input signal a as a (0), a (1), ..., a (K-2), a (K-1) as a first input. And each of the columns u (i, 0), u (i, 1) of the (i) th row of the U matrix Umin stored in the buffers of the plurality of buffers 610 as a second input. After inputting (i, K-2) and u (i, K-1) , these first and second inputs are multiplied and output. The adder 630 inputs and adds outputs of the plurality of multipliers 620 and outputs the addition result as b (i) . As such, the DFA transform according to the embodiment of the present invention can be implemented simply by a transversal filter structure. Input signal Acts like a tap of the filter, and b (i) is obtained according to row i of the U matrix.

FIG. 7 is a diagram illustrating a configuration of an apparatus for generating an element u (i, k) of the U matrix provided to the transverse filter shown in FIG. 6. This figure shows an example in which an apparatus for generating an element u (i, k) of the U matrix is implemented by hardware according to a Cordinate Rotation Digital Computer (CORDIC) conversion algorithm. The CORDIC transform algorithm is a type of shift-add algorithms for rotating vectors on a plane, as is well known to those skilled in the art. Therefore, detailed description thereof will be omitted.

Referring to FIG. 7, Is converted to CORDIC as shown in Equation 23 below. It can be expressed as a combination of In Equation 23 below, to be.

C. Simulation Results

The inventors of the present application have simulated in two aspects the embodiments of the present invention as described above. The first simulation demonstrates that the time domain signal output from IFFT 203 in FIG. 2 has a constant envelope. This can be seen from the simulation results shown in FIGS. 8A and 8B below. The second simulation proves that the PAPR is minimized even if the signal in the time domain passes through the low pass filter by the transmitting apparatus according to the embodiment of the present invention. This can be seen from the simulation results shown in FIGS. 9A to 9D and 10A to 10D below. In the following, OFDM denotes a scheme according to the prior art, and DFA-OFDM denotes a scheme according to an embodiment of the present invention. The simulation results are for M = K = N = 64, where M is the row size of the U matrix, K is the input signal vector size, and N is the FFT-point. It is a number.

8A and 8B are contrast diagrams showing waveforms of time-domain signals according to the prior art and the embodiment of the present invention before passing through the low pass filter (LPF) 102-1 and 102-2 shown in FIG. In other words, the contrast of the waveforms of time-domain signals in which IFFT is taken by IFFT is shown. The time domain signals are QPSK modulated signals.

FIG. 8A illustrates a waveform of a time domain signal according to the prior art before passing through the low pass filter (LPF) 102-1 and 102-2 shown in FIG. 1, and FIG. 8B illustrates the low pass illustrated in FIG. 1. Is a diagram showing waveforms of time domain signals according to an embodiment of the present invention prior to passing through filters (LPF) 102-1, 102-2. When passing through the DFA OFDM transmission apparatus according to an embodiment of the present invention, as shown in FIG. 8B, a signal having a constant envelope in the time domain may be output. However, even if the signal has a constant envelope, passing the low pass filter 102-1, 102-2, the PAPR is significantly increased.

9A to 9D illustrate PAPR characteristics according to an embodiment of the present invention before and after the low pass filter (LPF) 102-1 and 102-2 shown in FIG. 1.

Before the low pass filter 102-1, 102-2, the signal was 0dB for BPSK and QPSK, respectively, and the PAPR was 0dB (see FIGS. 9A and 9B), and for 16QAM and 64QAM, about 2.5dB and 3.8dB, respectively. 9C, 9D). However, it can be seen that the signal after passing through the low pass filters 102-1 and 102-2 increases the PAPR rapidly by about 7 to 8 dB (see FIGS. 9A to 9D). This is because the signal has a constant envelope in the time domain, but the PAPR characteristic deteriorates after passing through the low pass filter. This problem is a problem that also existed in the OFDM of the CI method according to the prior art. An embodiment of the present invention is characterized by reducing the number of zero crossings of the time domain signal in order to reduce the PAPR increase after passing the low pass filter. That is, in DFA OFDM, since the zero crossing of the time-domain signal is small, that is, the embodiment of the present invention finds Umin, which is a U matrix enabling the generation of a low PAPR signal, so that the PAPR improvement is superior to the CI method. .

10A to 10D are diagrams showing that the PAPR characteristic according to an embodiment of the present invention changes as the rows and columns of the U matrix are replaced.

10A to 10D, according to an embodiment of the present invention, when i = j = 0, the PAPR characteristic is the same as the PAPR characteristic in the CI method according to the prior art. As shown in the simulation results, the PAPR improvement of DFA OFDM in BPSK and QPSK is considerably superior to the CI OFDM scheme (i = j = 0) or the OFDM scheme. However, in the case of 16QAM and 64QAM, the PAPR improvement is significantly higher than that of the OFDM scheme, but the PAPR performance is improved by about 0.5 dB compared to the CI OFDM scheme.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, according to the present invention, according to the DFA OFDM scheme, a transmitter multiplies and transmits a signal in a frequency domain with a phase matrix having a delta autocorrelation property, and a receiver demodulates a received signal using a Hermithian matrix of the phase matrix. .

Since the DFA OFDM scheme of the present invention has no redundancy in the transmission signal, there is no loss of data transmission rate. Since the DFA OFDM scheme has a delta autocorrelation characteristic in the frequency domain, the DFA OFDM scheme has a constant envelope in the time domain, thereby improving the PAPR characteristic. Has In particular, considering the case where many zero crossings occur due to the structure of DFA OFDM having a constant envelope in the time domain, when the input signal is converted to reduce the zero crossing in the time domain, There is an effect to obtain a PAPR improvement.

1 is a block diagram of a transmitting end of an orthogonal frequency division multiplex (OFDM) communication system to which the present invention is applied.

2 is a block diagram of a transmitter including a DFA converter according to an embodiment of the present invention.

3 is a block diagram of a receiving end according to an embodiment of the present invention.

4 is a block diagram of blocks for generating a U matrix provided to the DFA conversion unit shown in FIG.

5 is a process flow diagram of a U matrix generation operation in accordance with an embodiment of the present invention.

FIG. 6 is a detailed configuration diagram of the DFA conversion unit illustrated in FIG. 2. FIG.

7 is a schematic diagram of a CORDIC converter for generating an element of a U matrix provided to the transversal filter shown in FIG.

8A and 8B show contrasts of waveforms of time domain signals according to the prior art and embodiments of the invention prior to passing through the low pass filter (LPF) shown in FIG.

9A to 9D are diagrams showing PAPR characteristics according to an embodiment of the present invention before and after passing a low pass filter (LPF) shown in FIG.

10A to 10D are diagrams illustrating that the PAPR characteristics change according to the substitution of rows and columns of a U matrix according to an embodiment of the present invention.

Claims (13)

Orthogonal Frequency Division Multiplexing (OFDM) including an IFFT unit for performing an inverse fast Fourier transform (IFFT) on an input signal having a vector size of (1 x K) and a low pass filter for low pass filtering the output of the IFFT unit. In the transmission apparatus of the system communication system, A first matrix generator having a (M × K) size and generating a first matrix in which M rows are orthogonal to each other; A second matrix for substituting the (i) th row of the first matrix with a size of (M × M) and a second substituting for the (j) th column of the first matrix with a size of (K × K) A second matrix generator for generating a third matrix, A matrix transform unit which generates (M × K) transform matrices by substituting each row and each column of the first matrix by the second matrix and the third matrix; A signal processor for converting the input signal by the respective transformation matrices to output a plurality of transformed signals, and IFFT and low pass filtering the plurality of transformed signals, respectively; A PAPR measuring unit measuring a peak power to average power ratio (PAPR) of each of the output signals of the signal processor; A selection unit for selecting a conversion matrix corresponding to a signal having the smallest PAPR among the output signals of the signal processing unit; And a signal converter which converts the input signal by the selected transformation matrix and provides the converted input signal to the IFFT unit for transmission. The apparatus of claim 1, wherein the first matrix is as follows. The apparatus of claim 1, wherein the second matrix is as follows. The transmitting device as claimed in claim 1, wherein the third matrix is as follows. The apparatus of claim 1, wherein the signal converter is a transversal filter. Orthogonal Frequency Division Multiplexing (OFDM) including an IFFT unit for performing an inverse fast Fourier transform (IFFT) on an input signal having a vector size of (1 × K) and a low pass filter for low pass filtering the output of the IFFT unit. In the signal transmission method of the system communication system, (A) generating a first matrix having a size of (M × K) and M rows are orthogonal to each other; A second matrix for substituting (i) rows of the first matrix with a size of (M × M) and a second matrix for substituting (j) columns of the first matrix with a size of (K × K) (B) creating a matrix, (C) replacing each row and each column of the first matrix by the second matrix and the third matrix to generate (M × K) transform matrices; (D) converting the input signal by the respective transformation matrices to output a plurality of transform signals, and filtering the plurality of transform signals by IFFT and low pass, respectively; (E) measuring a peak power-to-average power ratio (PAPR) of each of the signals processed in step (d); (F) selecting a transform matrix corresponding to a signal having the smallest PAPR among the signals processed in step (d); And (g) converting the input signal by the selected transformation matrix and providing the converted input signal to the IFFT unit for transmission. The transmission method as claimed in claim 6, wherein the first matrix is as follows. The transmission method as claimed in claim 6, wherein the second matrix is as follows. The transmission method as claimed in claim 6, wherein the third matrix is as follows. Orthogonal Frequency Division Multiplexing (OFDM) including an IFFT unit for performing an inverse fast Fourier transform (IFFT) on an input signal having a vector size of (1 x K) and a low pass filter for low pass filtering the output of the IFFT unit. An apparatus for receiving a signal from a transmitter of a system communication system, the apparatus comprising: A first matrix generator having a (M × K) size and generating a first matrix in which M rows are orthogonal to each other; A second matrix for substituting the (i) th row of the first matrix with a size of (M × M) and a second substituting for the (j) th column of the first matrix with a size of (K × K) A second matrix generator for generating a third matrix, A matrix transform unit which generates (M × K) transform matrices by substituting each row and each column of the first matrix by the second matrix and the third matrix; A signal processor for converting the input signal by the respective transformation matrices to output a plurality of transformed signals, and IFFT and low pass filtering the plurality of transformed signals, respectively; A PAPR measuring unit measuring a peak power to average power ratio (PAPR) of each of the output signals of the signal processor; A selection unit for selecting a conversion matrix corresponding to a signal having the smallest PAPR among the output signals of the signal processing unit; An FFT unit performing fast Fourier transform (FFT) on the received signal; And a signal converter for converting the FFT received signal by a Hermithian matrix of the selected transform matrix. The receiving apparatus as claimed in claim 10, wherein the first matrix is as follows. The receiving device as claimed in claim 10, wherein the second matrix is as follows. The receiving device as claimed in claim 10, wherein the third matrix is as follows.