KR100637710B1 - Method for reducing peak to average power ratio and calculating complexity in orthogonal frequency division multiplexing system - Google Patents

Abstract

A method for reducing peak to average power ratio(PAPR) and/or calculating complexity in orthogonal frequency division multiplexing(OFDM) carrier communication system is provided to decrease inverse fast Fourier transform(IFFT) operation complexity while maintaining the same PAPR reducing performance in comparison with the selective mapping of partial tones. In a method for reducing peak to average power ratio(PAPR) and/or calculating complexity in orthogonal frequency division multiplexing carrier communication system, an input symbol sequence is multiplied with the U number of circulation Hadamard phase sequence and generates the U number of symbol sequence which are independent of each other. The U number of symbol sequence is performed by IFFT and the OFDM signals are generated. The signal having the lowest PAPR is selected among the OFDM signals and transmits the signal.

Description

METHODO FOR REDUCING PEAK TO AVERAGE POWER RATIO AND CALCULATING COMPLEXITY IN ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM}

1 is a block diagram schematically illustrating a data processing process in a general selective projection method.

FIG. 2 is a diagram for explaining a method of generating an N × N cyclic Hadamard matrix H _N using m-sequence used in the present invention.

FIG. 3 is a diagram comparing PAPR reduction performance according to each phase sequence in the selective projection method.

FIG. 4 is a block diagram schematically illustrating a data processing procedure of the selective thinking method newly proposed in the present invention to reduce the amount of IFFT computation.

FIG. 5 is a view for explaining a process of multiplying a phase sequence with a signal in an intermediate step in the new selection method according to the present invention.

6 is a view comparing the performance of the selection method and the conventional selection method proposed in the present invention.

The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) system, and more particularly, to an OFDM communication method employing an improved selection technique for reducing the maximum power to average power ratio.

With the emphasis on the need for high-speed data transmission systems of 100 Mbps or more to enable real-time transmission of multimedia data in wireless mobile communication environments, orthogonal frequency division multiplexing (OFDM) systems have emerged as the focus of attention. have.

The OFDM system is a standard for digital audio broadcasting (DAB), digital video broadcasting (DVB), IEEE 802.11 local area network (LAN), and IEEE 802.16 wireless metropolitan area network (W-MAN) system. Adopted and widely used now. In particular, in Korea, the OFDM system is expected to be adopted as a standard transmission method for the portable Internet, which will be implemented in the future.

The basic principle of an OFDM system is to divide a frequency band to be used into a plurality of sub-channels, and then load and transmit data in parallel on sub-carriers corresponding to each channel. For signal processing using multiple subchannels, the transmitter uses inverse fast Fourier transform (IFFT) and the receiver uses fast Fourier transform (FFT). Implement a data transfer system.

The OFDM system maintains orthogonality between subcarriers such that the spacing between subcarriers is an integer multiple of the inverse value of the symbol period T so as not to cause interference between subcarriers. In addition, since subcarriers are orthogonal, frequency efficiency can be maximized. In an OFDM system, a transmission period of a signal increases in proportion to the number of subchannels, and a frequency spectrum is represented as a sum of respective subcarriers.

The OFDM system transmits a signal using a plurality of subcarriers, thereby making each subchannel a flat fading channel and showing good performance in a frequency selective fading environment, and guard interval (GI). To remove inter symbol interference (ISI).

The transmission signal of the OFDM system consists of the sum of the respective subchannel signals, and there is a concern that the instantaneous power may be very large when the subchannel signals have in-phase. The maximum instantaneous power-to-average power ratio (hereinafter referred to as PAPR) of the OFDM signal a _t and 0 ≦ t < T is defined as Equation 1 below.

[Equation 1]

In Equation 1, E [x] means an expected value of x, and T is a period of a symbol. An OFDM system may have a PAPR up to N times larger than a single carrier modulation scheme. If the PAPR is large, nonlinear distortion occurs in a high power amplifier (HPA).

In order to reduce such nonlinear distortion, when using a high-quality HPA that maintains linearity even at high power, there is a problem that the production cost of the base station equipment and the terminal increases and the efficiency of the system is lowered.

Therefore, in order to solve the PAPR problem in the OFDM system, block coding (coding), clipping (clipping), scrambling (scrambling), etc. have been proposed. The block coding method is a method of encoding input data with a codeword having a small PAPR, and the clipping method is a method of reducing PAPR by limiting the maximum output to a threshold set in advance before the input of the HPA.

The clipping technique adds distortion to the OFDM signal, thereby increasing power out of the assigned frequency band and causing distortion of the power spectrum within the frequency band. Increasing the power outside the frequency band interferes with adjacent channels, and if the power spectrum within the frequency band is distorted, the bit error rate (BER) performance deteriorates.

The block coding technique maintains the PAPR below a certain value without adding distortion to the signal, but has a disadvantage of lowering a coding rate.

The scrambling technique includes a selective mapping technique and a partial transmit sequence technique (hereinafter, referred to as 'PTS'). The selective thinking method and the PTS are proposed to solve the disadvantages of the block coding method and the clipping method. The method is a method of reducing PAPR without distorting a transmission signal while minimizing additional symbols.

In the PTS, as shown in Equation 2, the input symbol sequence A is divided into non-overlapping V sub-symbol sequences A _v and 1 ≦ v ≦ V.

[Equation 2]

IFFT each subsymbol sequence to generate a signal, multiply each signal by its phase factor r _v (rotating factor), and then add all the signals together. The OFDM signal a transmitted using the PTS is represented by Equation 3 below.

[Equation 3]

이다.In this case, the PAPR of the OFDM signal a is minimized while changing the phase factor r _v . The phase factor r _v generally uses ± 1 and ± j values to make complex calculations easier when multiplying. here

to be.

The transmitter transmits an index of the phase factor a that of a PAPR is minimized. The receiver uses the received index to find the input symbol sequence A. PTS has the advantage that the amount of IFFT operation is smaller than that of the selection method, but it has a disadvantage of using more symbols than the selection method for index transmission.

The selective thinking method multiplies the input symbol sequence with each of the phase sequences to generate a statistically independent symbol sequence, and selects and transmits the lowest PAPR sequence among the symbol sequences. Here, the PAPR of a symbol sequence means a PAPR of an OFDM signal generated by IFFTing a symbol sequence. It is known that the PAPR reduction performance in the selective phase method varies greatly depending on the generation method of the phase sequence.

To date, no clear criteria are known regarding the conditions that an optimal phase sequence should have, but a randomly generated phase sequence with uniform distribution from the simulation results has the best PAPR reduction performance. Known. However, since the irregularly formed phase sequence is literally random, there is a problem that it is difficult to clearly define it. That is, the phase sequence must be defined in a certain format to enable coding and decoding of signals using the transmitting and receiving terminals so that the phase sequence can be used in an actual communication system.

In addition, another disadvantage of the selective thinking method is that the IFFT must be performed by the number of phase sequences. Since the amount of IFFT computations increases in proportion to N log N as the number of carriers increases, it is very important to find a way to further reduce the amount of IFFT computations in order to apply the selective thinking method to an OFDM system having a large number of carriers.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the first object of the present invention is to present a clear reference that an optimal phase sequence should have in the selective phase method, and to construct and select a phase sequence satisfying the criterion structurally and simply. By applying the mapping technique, the PAPR reduction performance is reached to reach the theoretical limit.

A second object of the present invention is to propose a new selective thinking method that can reduce the amount of IFFT calculations while maintaining the same PAPR reduction performance as compared to the existing selective thinking method.

In order to achieve the above object, the OFDM communication method according to the first aspect of the present invention comprises the steps of: (a) generating U symbol sequences statistically independent of each other by multiplying an input symbol sequence with each of U cyclic Hadamard phase sequences; ; (b) IFFT each of the U symbol sequences to generate OFDM signals; And (c) selecting and transmitting a signal having the lowest PAPR among the OFDM signals.

에 U개의 위상 시퀀스 P ^u , 1≤u≤U를 각각 곱하여 U개의 신호

를 생성하는 단계; (c) 상기 U개의 신호

에 대하여, 나머지 n-k단계의 IFFT 연산을 각각 수행 하여 OFDM 신호들을 생성하는 단계; 및 (d) 상기 OFDM 신호들 중에서 가장 낮은 PAPR을 갖는 신호를 선택하여 전송하는 단계를 포함하는 것을 특징으로 한다.According to an aspect of the present invention, there is provided an OFDM communication method comprising: (a) performing an IFFT of steps 1 to k (k &lt; n) on an input symbol sequence during an IFFT process from steps 1 to n; (b) output signal performed up to step k

U signals by multiplying U phase sequences P ^u and 1≤ u ≤ U , respectively

Generating a; (c) the U signals

For each of the remaining n - k steps of IFFT operation to generate OFDM signals; And (d) selecting and transmitting a signal having the lowest PAPR among the OFDM signals.

을 전송하기 위해서,

의 IFFT 신호

를 메모리에 저장해 두고, 상기 메모리에 저장된 색인 신호

를 상기 입력 데이터 심볼 시퀀스

를 IFFT한 신호에 더해서 보내는 단계를 더 포함하도록 하여 부가 계산량 증가를 피할 수 있다.Here, preferably, before the step of selecting and transmitting the signal having the lowest PAPR among the OFDM signals, the index of the phase sequence

In order to send

IFFT signal

Is stored in the memory, the index signal stored in the memory

The input data symbol sequence

In addition to the IFFT signal, the step of sending an additional calculation can be avoided.

Further, the above, the step (b), if necessary U of the phase sequence P ^u is the phase sequence of length N 2 ^{n -} divided into ^k blocks, the length in order to have the same values as elements in the same block the 2 ^{n -} is preferred for the sequence ^k R ^u, 1≤ ^u ≤ generate U and using the generated repeat elements of R ^u 2 ^k times the PAPR reducing effect.

In the above, when generating the sequence R ^u using the cyclic Hadamard sequence, it is possible to further improve the PAPR reduction effect.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment according to the present invention.

1 is a schematic diagram showing a process of data processing in a general selective thinking method. As shown in FIG. 1, in the selective thinking method, an input symbol sequence is multiplied by a predetermined U phase sequence P ¹ , P ² ,..., And P ^U , respectively, and U sequences (A, A ² , ..., A ^U ) Then, each symbol sequence is IFFT to generate OFDM signals a ¹ , a ² ,..., A ^U , and then the signal having the lowest PAPR is selected and transmitted.

The elements of the phase sequence typically use ± 1 and ± j values to conserve transmission power and to facilitate complex calculations when multiplying the input symbol sequence with the phase sequence.

The receiver performs FFT transform on the received signal to generate a sequence of multiplying the input symbol sequence and the phase sequence. At this time, if the receiver knows the phase sequence information used by the transmitter, it can find the input symbol sequence (input symbol sequence originally intended to be transmitted) before the phase sequence is multiplied. In general, the phase sequences to be used in the transmitter are predetermined, so if the contents of the phase sequence are known to the receiver, the transmitter may transmit an index of the phase sequence. Since the index of the phase sequence is very important information, it is encoded to detect or correct an error.

In the selection method, the number of phase sequences decreases as well as the PAPR, but there is a saturation effect in which the decrease of the PAPR decreases gradually compared to the increase in the phase sequence. The IFFT computational complexity and the amount of additional information in the transceiver increase in proportion to the number of phase sequences.

As described above, when the same number of phase sequences are used in the selection method, the PAPR reduction performance shows a large difference depending on the generation method of the phase sequence. The present inventors propose a phase sequence generation method as follows to enable a clear definition when applied to a communication system and to obtain an effective PAPR reduction performance more efficiently.

When the phase sequence satisfies the following two conditions, the PAPR reduction performance in the selection method approach is close to the theoretical limit value. First, the phase sequences should be orthogonal to each other. The second condition is that there should be no periodicity in each phase sequence. Hereinafter, a method of generating a phase sequence proposed by the present inventor to satisfy such a condition will be described.

을 만족하는 N×N 정방 행렬이다. 여기서 I _N 은 크기가 N×N인 항등 행렬을 말한다. 순환 Hadamard 행렬은 첫 행과 첫 열을 제외 하고, 나머지 (N-1)×(N-1) 행렬의 행들이 서로 순환 이동으로 얻어지는 행렬이다.2 exemplarily shows a cyclic Hadamard matrix used for generating a phase sequence proposed in the present invention. The illustrated Hadamard matrix H _N of size N × N has +1 and -1 as elements of the matrix,

Is an N × N square matrix that satisfies. Where I _N is an identity matrix of size N × N. The cyclic Hadamard matrix is a matrix obtained by cyclic movement of the rows of the remaining ( N- 1) × ( N- 1) matrices except the first row and the first column.

Here, a method of generating the cyclic Hadamard matrix illustrated in FIG. 2 will be described. For example, the first row and the column are 1, and the remaining ( N -1) × ( N -1) matrices have a length of N -1. Phosphorus m-sequences can be generated by circular movement.

Here, the m-sequence is generated by using a shift register, and the m-sequence has a property of being cyclically shifted to another m-sequence. Since m-sequences have pseudo-irregular properties and ideal autocorrelation values, the N -1 rows of a cyclic Hadamard matrix created by adding 1 to the front after circularly moving the m-sequence are orthogonal to each other. . The m-sequence is also balanced, so it is orthogonal to the first row where all elements have a value of 1.

Using this property, the present inventors observed that when a row of a cyclic Hadamard matrix is used as a phase sequence, an excellent PAPR reduction effect can be obtained while defining a cyclic Hadamard phase sequence.

When selecting the U rows to be used as the phase sequence in the N × N cyclic Hadamard matrix, the first row is always selected first, and the remaining U −1 are selected from the N −1 rows. When selecting U rows in a cyclic Hadamard matrix, there is no difference in performance depending on the N- 1 selection methods. Therefore, the first to U rows are generally selected.

In addition to the cyclic Hadamard matrix, the Hadamard matrix also has a Sylvester Hadamard matrix. The inventors investigated the possibility of applying the same to the phase sequence for the Sylvester Hadamard matrix as follows.

Sylvester Hadamard matrix H _N of size N × N can be generated as follows using Equation 4.

[Equation 4]

Using the equation (4) it is possible to generate H ₄ by using H _2, it is possible to generate H ₈ using H _4. This can be done repeatedly to generate H _N. The 2 × 2 Sylvester Hadamard matrix is given by Equation 5.

[Equation 5]

The inventor defined the case of using the Sylvester Hadamard matrix as a phase sequence as a 'Sylvester Hadamard phase sequence'. When selecting U rows for use as a phase sequence in the Sylvester Hadamard matrix, the first row with all elements of 1 is always selected, and the remaining U -1s are selected from N -1 rows.

According to the test results of the present inventors, since the Sylvester Hadamard matrix has a different period for each row, there was a difference in the reduction performance of the PAPR according to the U- 1 row selection method. Also, in all cases it was observed that the reduction performance of the PAPR is worse than the cyclic Hadamard matrix.

3 compares the test results for the PAPR reduction performance according to various phase sequence selection methods in the selection method. In FIG. 3, an irregular (binary random and quaternary random phase sequence in FIG. 3) refers to a randomly generated sequence having an equal probability distribution as proposed in the related art. The elements of the binary random phase sequence have values of ± 1 and the elements of the binary random phase sequence have values of ± 1 and ± j .

The test results of FIG. 3 compare the cases in which the first to U rows are selected when U rows are selected for the Sylvester Hadamard matrix and the cyclic Hadamard matrix. Theoretical limit is the optimal value that can be theoretically obtained when the selective thinking method is applied.

As shown, when using the Binary Irregular Sequence, the Quaternary Irregular Sequence, and the Cyclic Hadamard Sequence as the Phase Sequence, the PAPR reduction can be achieved within 0.1 dB, which is almost equivalent to the theoretical limit. Achieve effect. However, when the Sylvester Hadamard sequence is used as the phase sequence, the PAPR reduction performance is remarkably degraded because the orthogonality between the phase sequences is satisfactory, but the periodicity is observed in the Sylvester Hadamard phase sequence.

Therefore, the cyclic Hadamard phase sequence proposed in the present invention can be clearly defined, can be generated by a structural and relatively simple method, and the PAPR reduction performance is close to the theoretical limit. .

In addition, hereinafter, a description will be given of the selective thinker method that can reduce the amount of IFFT calculation, which is the second object of the present invention.

4 is a schematic diagram for explaining a data processing process of the selective thinking method proposed by the present invention. Looking at the IFFT process for data of length N = 2 ⁿ , it can be seen that there are n steps. In general, each step performs N addition operations and N / 2 multiplication operations, and then proceeds to the next step.

As shown in Fig. 1, in the prior art selective projection method, IFFT is performed on each result after multiplying a phase sequence. However, in the selective thinking method proposed in the present invention, the IFFT is divided into two parts. The first part is from the first to kth stages of the IFFT. The second part corresponds to the k th to n th steps of the IFFT. Unlike the prior art, in the selective thinking method of the present invention, as shown in FIG. 4, the IFFT calculation amount is reduced by multiplying a phase sequence with respect to the data having undergone the IFFT process up to the k-th step.

에 U개의 위상 시퀀스 P ^u , 1≤u≤U를 곱한 후 나머지 n-k단계의 IFFT연산을 수행한다.Figure 5 illustrates in more detail the IFFT process of the present invention. As shown, in the selective projection method proposed in the present invention, the signal of the k- th step

The remainder multiplied by the phase sequence of U ^{P u, 1≤ u ≤ U n} - performs an IFFT operation in step k.

와 색인 심볼 시퀀스

의 합으로 표시 될 수 있다.In the general selection method, when the receiver knows the phase sequence used by the transmitter, the original input symbol sequence can be found. If the contents of the predetermined U phase sequence are known to the receiver, the transmitter may transmit an index of the phase sequence. Part of the input symbol is used as an index symbol for index transmission. Therefore, the input symbol sequence A is the input data symbol sequence as shown in Equation (6).

And index symbol sequences

Can be represented as the sum of

[Equation 6]

개의 심볼이 색인 전송을 위해서 필요하다. 따라서 입력 데이터 심볼 시퀀스

의 원소 중

개의 값은 0이고, 색인 심볼 시퀀스

의 원소 중

개의 값은 0이다. In an OFDM system using M -PSK (phase shift keying) or M -QAM (quadrature amplitude modulation) signal constellations, using U phase sequences and encoding the index at code rate R

Symbols are needed for index transmission. Thus the input data symbol sequence

Of elements in

Values are 0, index symbol sequence

Of elements in

Values are 0.

의 IFFT 신호

를 메모리에 저장해 두면 색인 전송을 위한 부가적인 계산량이 늘어나는 것을 방지 할 수 있다. 메모리에 저장된 색인 신호

는 입력 데이터 심볼 시퀀스

를 IFFT 한 신호에 더해서 보내진다. 이와 같은 색인 신호를 감안하면, 본 발명에서 제안된 선택사상기법은 수학식 7과 같이 표현할 수 있다.Index symbol sequence

IFFT signal

Can be stored in memory to avoid additional computation for index transfer. Index signal stored in memory

Input data symbol sequence

Is sent in addition to the IFFT signal. In view of such an index signal, the selective thinking method proposed in the present invention can be expressed as Equation (7).

[Equation 7]

는 i번째 단계에서 j번째 단계까지의 IFFT 행렬을 나타내고

는 대각 성분이 P ^u 인 대각 행렬을 나타낸다.In equation (7)

Represents the IFFT matrix from step i to j

Denotes a diagonal matrix whose diagonal component is P ^u .

Hereinafter, the IFFT calculation amount of the selective thinking method proposed in the present invention and the selective thinking method of the related art are compared. Selected mapping scheme proposed in the present invention by using the operation results by the k-th stage and a common n - may reduce the IFFT computation amount than prior art methods since you perform a new operation only in k steps. The IFFT calculation amount of the conventional selective thinking method is expressed by Equation 8.

[Equation 8]

Where N = 2 ⁿ is the size of the IFFT, U is the number of phase sequences, n _mul is the number of complex multiplication operations, and n _add is the number of complex addition operations.

In contrast, when U phase sequences are used in the newly proposed selection method, the IFFT calculation amount is expressed by Equation (9).

[Equation 9]

Therefore, the IFFT computational complexity reduction gain (CCRG) of the proposed method is expressed by Equation 10.

[Equation 10]

Using the equation (10) to calculate the IFFT calculation gain reduction is shown in Table 1.

TABLE 1

From Table 1, it can be seen that the IFFT calculation amount reduction gain in the selective thinking method of the present invention increases as n - k decreases as N and U increase.

The newly proposed method increases the IFFT computation reduction gain as the phase sequence multiplication step k approaches n (i.e., n - k becomes smaller), but at this time, the deterioration performance of the PAPR decreases. It is very important to choose.

For example, in the proposed selection method, when the size of the IFFT is 256, n - k is 6, and when the size of the IFFT is 2048, when n - k is 5, Almost identical PAPR reduction performance.

When performing an IFFT size of N = 2 ^n, the size N of the IFFT size of N / 2 of the two is calculated using the IFFT of size N / 2 of the IFFT are again size N / 4 in Calculate using two IFFTs. If this form is repeated, the IFFT transform is divided into 2 ^{n - k} blocks in the k- th step, where each block corresponds to an IFFT of N / 2 ^{n - k} = 2 ^k .

In consideration of this, in order to maximize the PAPR reduction performance in the proposed selection method, it is preferable to divide the length N phase sequence into 2 ^{n - k} blocks and to make the elements of the phase sequence within the same block have the same value. . To this end, an element of a sequence R ^u having a length of 2 ^{n - k} and 1 ≦ u ≦ U is repeated 2 ^k times to generate a phase sequence P ^u as shown in Equation (11).

[Equation 11]

For example, if n = 6, k = 3, and R ^u = {+ 1-1 + 1 + 1-1 + 1-1-1}, then P ^u is {+ 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1-1-1-1-1-1-1-1-1L-1-1-1-1-1-1-1-1}. In the proposed selection method, when R ^u is the cyclic Hadamard sequence described above, the PAPR reduction performance can be maximized.

6 is a view comparing the performance of the selection idea technique proposed in the present invention and the conventional selection technique. The result shown in FIG. 6 is a test result for the case of the OFDM system using the 16-QAM modulation where the size of the IFFT is N = 2048, and is proposed in the present invention (denoted as 'New SLM OFDM'). Compared to the conventional selective thinking method (denoted 'Conventional SLM OFDM'), it shows almost the same level of PAPR reduction performance.

The graph of FIG. 6 shows the probability that the PAPR of the OFDM system is greater than the reference value PAPR0. For example, in the original OFDM system without the selection method, the probability of PAPR exceeding 12.2 dB is 10 ^-4 , and when the selection method is applied using four phase sequences (U = 4), the PAPR The probability of exceeding this 10 dB is 10 ^-4 , and a PAPR reduction effect of 2.2 dB is obtained at 10 ^-4 .

On the other hand, from Table 1, as the number of phase sequences is increased from 4 (U = 4) to 16 (U = 16), the amount of IFFT computation of the newly proposed selective thinking method is 40.9% higher than that of the existing selective thinking method. It can be seen that the decrease is up to 51.1%.

Orthogonal frequency division multiple carrier communication method and apparatus according to the present invention can be modified and applied in various forms within the scope of the technical idea of the present invention and is not limited to the above preferred embodiment. In addition, the embodiments and drawings are merely for the purpose of describing the contents of the invention in detail, and are not intended to limit the scope of the technical idea of the invention, the present invention described above is common knowledge in the technical field to which the present invention belongs As those skilled in the art can have various substitutions, modifications, and changes without departing from the spirit and scope of the present invention, it is not limited to the embodiments and the accompanying drawings. And should be judged to include equality.

Orthogonal Frequency Division Multicarrier Communication Method and Apparatus Using the Selective Decision Method Using Cyclic Hadamard Sequence Proposed in the Present Invention, Maximizing PAPR Reduction and Obtaining a Phase Sequence in a More Structured and Simpler Way It is possible to implement.

In addition, the present invention enables the implementation of a new selective quadrature method with a very small IFFT calculation amount compared to the conventional selective quadrature method while maintaining the PAPR reduction performance as it is, and thus is widely used in an OFDM system having a large number of carriers such as the portable Internet. You can use it.

Claims (5)

(a) multiplying the input symbol sequence with each of the U circular Hadamard phase sequences to produce U symbol sequences that are statistically independent of each other; (b) IFFT each of the U symbol sequences to generate OFDM signals; And (c) selecting and transmitting a signal having the lowest PAPR among the OFDM signals. (a) performing an IFFT from steps 1 to k (k &lt; n) on an input symbol sequence in an IFFT process from steps 1 to n; (b) output signal performed up to step k

U signals by multiplying U phase sequences P ^u and 1≤ u ≤ U , respectively

Generating a; (c) the U signals

For each of the remaining n - k steps of IFFT operation to generate OFDM signals; And (d) selecting and transmitting a signal having the lowest PAPR among the OFDM signals. The method according to claim 1 or 2, Before selecting and transmitting the signal having the lowest PAPR among the OFDM signals, The index of the phase sequence

In order to send

IFFT signal

Is stored in the memory, the index signal stored in the memory

The input data symbol sequence

And transmitting the signal to the IFFT signal. The method of claim 2, The U phase sequence P ^u of step (b) is A length of a phase sequence N 2 ^n-divided into ^k blocks, the elements in the same block has a length of 2 ⁿ to have the same value, ^- generating a sequence of ^k R ^u, 1≤ ^u ≤ ^U, and the ^u R OFDM communication method characterized in that the generated by repeating the element 2 ^k times. The method of claim 4, wherein And generate the sequence R ^u using a cyclic Hadamard sequence.

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