KR101565386B1 - PAPR Reduction Method Using Specific PAPR Reduction Signals - Google Patents

Abstract

A method of reducing the PAPR using a specific PAPR (Peak to Average Power Ratio) reduction signal is described.

A PAPR reduction signal having a predetermined signal value at a predetermined number of subcarrier positions and a peak position in a time domain of each predetermined information signal are made coincident with each other in a mobile communication system using an OFDM scheme, The PAPR reduction signal is reduced by decreasing the PAPR reduction signal in the information signal while the peak value is matched. The PAPR reduction signal is a PAPR reduction signal in which the PAPR reduction signal itself has a maximum PAPR reduction signal, And / or that the difference between the largest peak value and the second largest peak value of the PAPR reduction signal among the possible PAPR reduction signals is predetermined as the largest PAPR reduction signal.

PAPR, Tone Reservation

Description

PAPR Reduction Method Using Specific PAPR Reduction Signals [

In the following description, a method of reducing PAPR using a PAPR reduction signal satisfying a specific condition in a mobile communication system using an OFDM scheme, specifically, a method of reducing a PAPR reduction signal and / or a PAPR reduction And a method for reducing the PAPR of an information signal using a PAPR reduction signal set such that the difference between the largest peak value and the second largest peak value of the signal is greatest.

Multicarrier systems have a drawback in that they are effective for high-speed data transmission and have a large Peak to Average Power Ratio (PAPR). An OFDM scheme, a DFT-S-OFDM (DFT Spreading OFDM) scheme, and an OFDMA scheme will be briefly described as an example of a communication method of a multi-carrier system for this purpose.

First, orthogonal frequency division multiplexing (OFDM) will be described. The basic principle of OFDM is to divide a data stream having a high-rate into a plurality of data streams having a slow-rate, and to simultaneously transmit them using a plurality of carriers. Each of the plurality of carriers is referred to as a subcarrier. Since there is orthogonality between the plurality of carriers of the OFDM, even if the frequency components of the carriers overlap each other, detection at the receiving end is possible. The data stream having the high-speed data rate is converted into a data stream having a plurality of low data rates through a serial-to-parallel (S / P) converter, and each of the sub- And then the respective data strings are summed and transmitted to the receiving end.

The parallel data streams generated by the serial-to-parallel conversion unit may be transmitted on a plurality of subcarriers by an inverse discrete Fourier transform (IDFT), and the IDFT may be an Inverse Fast Fourier Transform Fast Fourier Transform).

The symbol duration of a sub-carrier having a low data rate is increased, so that the relative signal dispersion in time caused by multipath delay spreading is reduced. Inter-symbol interference can be reduced by inserting a guard interval longer than the delay spread of a channel between OFDM symbols. Also, if a part of the OFDM signal is copied in the guard interval and placed at the beginning of the symbol, the OFDM symbol can be cyclically extended to protect the symbol.

Next, the DFT-S-OFDM scheme will be described. The DFT-S-OFDM scheme is also referred to as SC-FDMA (Single Carrier-FDMA). In the conventional SC-FDMA scheme, spreading is first applied to a DFT matrix in the frequency domain before OFDM signals are generated, and then the result is modulated by a conventional OFDM scheme and transmitted .

1 is a diagram showing a structure of a transmitter of the DFT-S-OFDM scheme.

Several variables are defined to illustrate the operation of the illustrated DFT-S-OFDM transmitter. N denotes the number of subcarriers for transmitting an OFDM signal, and Nb denotes the number of subcarriers for an arbitrary user. In addition, F denotes a discrete Fourier transform matrix, i.e., a DFT matrix, s denotes a data symbol vector, x denotes a vector in which data is dispersed in the frequency domain, and y denotes an OFDM symbol vector to be transmitted in the time domain do.

In SC-FDMA, the data symbols (s) are distributed using a DFT matrix before transmission. This is expressed by the following equation.

는, 데이터 심볼(s)을 분산시키기 위해서 사용된 Nb 크기의 DFT 행렬이다. 이렇게 분산된 벡터(x)에 대하여 일정한 부 반송파 할당 기법에 의해 부 반송파 매핑(subcarrier mapping)이 수행되고, IDFT 모듈에 의해 시간영역으로 변환되어 수신 측으로 전송하고자 하는 신호가 얻어진다. 상기 수신 측으로 전송되는 전송신호는 아래 식과 같다. In Equation (1)

Is a DFT matrix of Nb size used to distribute the data symbols s. A subcarrier mapping is performed by the constant subcarrier allocation technique on the dispersed vector x, and a signal to be transmitted to the reception side is obtained by converting the time domain by the IDFT module. The transmission signal transmitted to the receiving side is expressed by the following equation.

는 주파수 영역의 신호를 시간 영역의 신호로 변환하기 위해 사용되는 크기 N의 IDFT 행렬이다. 상술한 방법에 의해 생성된 신호 y는, 순환 전치(cyclic prefix)가 삽입되어 전송된다. In Equation (2)

Is an IDFT matrix of size N that is used to transform a frequency domain signal into a time domain signal. The signal y generated by the above method is transmitted by inserting a cyclic prefix.

A method of generating a transmission signal by the above-described method and transmitting the transmission signal to the receiving side is referred to as an SC-FDMA method. The size of the DFT matrix can be variously controlled for a specific purpose.

Next, orthogonal frequency division multiple access (OFDMA) will be described. OFDMA refers to a multiple access method that realizes multiple access by providing each user with a part of a subcarrier available in a modulation system using a plurality of orthogonal subcarriers. OFDMA provides a frequency resource called a sub-carrier to each user, and each frequency resource is provided to a plurality of users independently of one another and does not overlap with each other.

The problem of PAPR is as follows.

2 shows a typical OFDM signal in the time domain.

As can be seen from FIG. 2, when the OFDM signal is examined in the time domain, it can be seen that there is a portion (A, B) having a significantly higher power than the average signal power value. In a practical system, a signal generated as shown in FIG. 2 is transmitted through a nonlinear power amplifier. The nonlinear power amplifier can amplify power linearly within a specific power range (linear section) Is nonlinearly amplified and the received signal receives a distorted signal even in a noisy environment. Such a distortion can be reduced by using a power amplifier having a wide linear section, but the price of the power amplifier having a large linear section is greatly increased.

Accordingly, the present invention proposes a method of efficiently reducing PAPR in a mobile communication system using a multi-carrier.

Particularly, in an embodiment of the present invention, it is proposed to increase the PAPR reduction effect by using the PAPR reduction signal used in the tone reservation scheme as a PAPR reduction signal satisfying a specific condition.

According to an aspect of the present invention, there is provided a method of reducing a Peak to Average Power Ratio (PAPR) in a mobile communication system using an OFDM scheme, the method comprising: receiving a predetermined signal at a predetermined number of subcarrier positions; And a peak position in a time domain of each of the predetermined information signals; And subtracting the PAPR decrease signal from the information signal in a state where the peak value is matched, wherein the PAPR decrease signal is predetermined as a PAPR decrease signal in which the PAPR reduction signal itself has a maximum PAPR reduction signal We propose a PAPR reduction method.

This may mean that the positions of the predetermined number of subcarriers among the total subcarriers in the system band and the predetermined signal value are predetermined so that the PAPR of the PAPR reduction signal itself is maximized.

The peak position matching step may include converting the PAPR reduction signal and the information signal into a time domain signal, respectively; And matching the position having the peak in the time domain of the information signal and the position having the peak in the time domain of the PAPR reduction signal using cyclic shift or phase rotation .

Also, the peak value position matching step and the calculating step can be repeatedly performed until the peak value exceeding the linear interval of the reception filter of the receiving end in the information signal disappears.

According to another aspect of the present invention, there is provided a method of reducing a Peak to Average Power Ratio (PAPR) in a mobile communication system using an OFDM scheme, the method comprising: receiving a PAPR reduction signal having a predetermined signal value at a predetermined number of sub- And matching a peak position in a time domain of each of the predetermined information signals; And subtracting the PAPR reduction signal from the information signal when the peak value is matched, wherein the PAPR reduction signal is a difference between the largest peak value and the second largest peak value of the PAPR reduction signal, And proposes a predetermined PAPR reduction method as the largest PAPR reduction signal.

This means that the positions of the predetermined number of subcarriers in the entire system sub-carriers and the predetermined signal value are predetermined so that the difference between the largest peak value and the second largest peak value of the PAPR reduction signal is largest .

According to the above-described embodiments, PAPR is efficiently reduced in a mobile communication system, signal distortion that may occur when a given nonlinear filter is used is prevented, and a long nonlinear filter having a long linear interval is prevented from being used at the transmitting / receiving end Can be applied.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. In the following description, the base station may be replaced with other terms such as "Node B "," eNode B ", and the terminal may be replaced with terms such as "UE "," have.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

As described above, PAPR in the OFDM system is one of the biggest disadvantages that the OFDM system has to overcome. Therefore, studies for reducing PAPR are actively being conducted. The PAPR reduction technique can be roughly classified into a technique of reducing PAPR through original signal distortion and a technique of reducing PAPR using a specific algorithm without distortion.

Representative methods in each method are described.

First, the clipping technique is described as a representative method of reducing the PAPR through the original signal distortion.

3 and 4 are views for explaining a clipping technique for PAPR reduction.

In Fig. 3, the signal waveform is the same as the signal waveform shown in Fig. According to the clipping technique, as shown in FIG. 3, the power corresponding to the non-linear section of the nonlinear power amplifier is removed by intentionally reducing the power of a portion having a predetermined power P _threshold .

That is, when the clipping technique is applied, the signal shown in FIG. 3 can be changed as shown in FIG. 4, and the changed signal is transmitted. This technique has the advantage that it can be implemented very simply, but it has the disadvantage of distorting the original signal. That is, the clipping technique is effective when the distortion caused by the clipping technique of the original signal is smaller than the distortion caused by the nonlinear power amplifier of the original signal.

Second, the Tone Reservation scheme is described as a PAPR scheme that does not distort the original signal.

5 is a diagram for explaining a tone reservation technique as a PAPR reduction technique.

According to this technique, the subcarriers in the entire system band can be divided into subcarriers for data transmission and subcarriers for generating PAPR reduction signals. In general, a subcarrier for generating a PAPR reducing signal (hereinafter referred to as a "PAPR reducing signal") may insert the same value at a predetermined interval N for all frequency band subcarriers. For example, if the FFT size is 1024 and the modulation scheme is BPSK, 1 can be inserted into 64 subcarriers at intervals of 16 subcarriers.

As shown in FIG. 5, the time domain signals obtained by IFFT processing the data portion in the frequency domain and the PAPR decrease signal portion have orthogonality with each other in the time domain. This is a characteristic of the OFDM system described above, and signals using subcarriers in the frequency domain that are not overlapped with each other maintain orthogonality with each other in the time domain. Therefore, the process of adding or subtracting the PAPR reduction signal to the data signal in the time domain does not distort the original data signal. By using such a characteristic, a point having the greatest power in the PAPR reduction signal at the point having the greatest power in the data signal is matched through cyclic shift and phase rotation, so that the PAPR . Generally, we use a method of iteratively finding the point having the maximum power value described above.

In FIG. 5, although a data signal is shown as a signal including information to be originally transmitted, an information signal to be transmitted may include not only data but also a control signal.

The tone reservation scheme as described above has the advantage of not distorting the present signal but has a disadvantage in that the data rate is reduced because a subcarrier is allocated for the PAPR reduction signal.

In addition, according to the tone reservation method described above, in the process of subtracting the PAPR decrease signal from the information signal in order to remove the peak value of the information signal, for example, the data signal, portions other than the peak value of the information signal change, There may be a problem. Specifically, in the process of subtracting the PAPR reduction signal from the information signal, the power of the portion having the maximum power value of the information signal is lowered, but at the same time, the power value also changes with respect to other portions. That is, other partial power values may be larger or smaller. As a result, a portion having a large power can newly occur.

Therefore, in a preferred embodiment of the present invention, in order to reduce the peak value of the information signal by decreasing the PAPR according to the tone reservation method, the peak value of the information signal and the peak value of the PAPR decrease signal are made to coincide with each other, It is proposed to perform a PAPR reduction procedure by selecting a PAPR reduction signal that minimally affects a portion other than the peak value of the information signal.

As an example of such a PAPR reduction signal, a method of selecting a signal having a large PAPR of the PAPR reduction signal itself will be described. If the PAPR of the PAPR reduction signal itself is large, the difference in power value between the peak value and the peak value of the PAPR reduction signal becomes large. Therefore, when the PAPR reduction signal is subtracted from the information signal in the state where the peak value of the information signal and the peak value of the PAPR reduction signal are matched, the influence of the information signal other than the peak value is reduced. Therefore, in one embodiment of the present invention, it is proposed to perform the PAPR reduction procedure according to the above-mentioned tone reservation scheme using a signal having a large PAPR of the PAPR reduction signal itself.

On the other hand, among the signals having a large PAPR of the PAPR reduction signal itself as in the above-described embodiment, there may be a PAPR reduction signal in which the difference between the largest peak and the second largest peak is not so large. In the case of performing the PAPR reduction procedure as shown in FIG. 5 using the PAPR reduction signal having a peak value which is not significantly different from the largest peak value, the maximum peak of the PAPR reduction signal in order to remove the peak value of the information signal In the process of subtracting the PAPR reduction signal from the information signal, the second largest peak of the PAPR reduction signal may cause an unwanted portion of the information signal to be generated at another peak value, in agreement with the peak to be removed in the information signal.

Therefore, in another embodiment of the present invention, a method of selecting a PAPR reduction signal having the largest difference between the first peak value and the second peak value among the possible PAPR reduction signals to use for the tone reservation method as shown in FIG. 5 I suggest.

Of course, as described above, when the PAPR reduction signal itself has a large PAPR, the PAPR reduction signal having the largest difference between the first peak value and the second peak value of the PAPR reduction signal may have superior performance.

The PAPR of the OFDM signal is affected by the position and data values of subcarriers allocated in the frequency domain. Therefore, in order to generate a PAPR reduction signal satisfying the above-described characteristics, it is possible to generate and compare possible PAPR reduction signals while changing the positions and signal values of subcarriers allocated to the PAPR reduction signals, Carrier position and signal values for the subcarrier.

For example, if four subcarriers among the 128 subcarriers are used as the PAPR reduction signal, the position can be determined by ₁₂₈ C ₄ operations. In the case of BPSK, the signal value to be inserted needs to be calculated ²⁴ times. Such an operation is not required every time the signal is transmitted, but is determined in advance according to the total number of subcarriers, the number of subcarriers allocated to the PAPR reduction signal, and the modulation method, and thus does not affect the amount of computation and complexity in signal transmission and reception in an actual system .

For a concrete example, 128 subcarriers may be used, and in a system in which four subcarriers may be used for a PAPR reduction signal, the position of the most preferred PAPR reduction signal subcarrier and the signal value of the PAPR reduction signal at that location, As a result of simulation by measuring PAPR reduction effect, the following cases showed optimal performance.

PRPR Decreased Signal Subcarrier Location PAPR Decreased Signal Subcarrier Signal Value 2 -One 24 -One 114 -One 116 -One

The PAPR reduction signal according to the example of Table 1 above shows that the PAPR reduction signal itself has a high PAPR and the difference between the largest peak value and the next largest peak value is large.

The subcarrier positions allocated for the PAPR reduction signal and the signal values of the PAPR reduction signals at the corresponding positions as shown in Table 1 are allocated to 1024 subcarriers and 64 subcarriers for the PAPR reduction signals. In the system using BPSK modulation, And the present invention proposes to reduce the PAPR of the signal through the tone reservation scheme as shown in FIG. 5 using the PAPR reduction signal thus obtained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the invention. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims It can be understood that Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the above-described embodiments, the PAPR reduction method efficiently reduces PAPR in various mobile communication systems using a multi-carrier scheme such as OFDM and OFDMA, prevents signal distortion that may occur when a given nonlinear filter is used, Can be applied to prevent expensive linear segments from using long non-linear filters.

1 is a diagram showing a structure of a transmitter of the DFT-S-OFDM scheme.

2 shows a typical OFDM signal in the time domain.

3 and 4 are views for explaining a clipping technique for PAPR reduction.

5 is a diagram for explaining a tone reservation technique as a PAPR reduction technique.

Claims (8)

A method for reducing Peak to Average Power Ratio (PAPR) in a mobile communication system using an OFDM scheme, A PAPR reduction signal having a predetermined signal value at a predetermined position of four subcarriers, and a peak position in a time domain of each of the predetermined information signals; And And subtracting the PAPR reduction signal from the information signal when the peak value is matched, The PAPR reduction signal is previously determined as a PAPR reduction signal that maximizes the PAPR of the PAPR reduction signal itself among possible PAPR reduction signals, The positions of the four subcarriers of the entire subcarriers in the system band and the predetermined signal value are predetermined so that the PAPR of the PAPR reduction signal itself becomes the maximum, The step of matching the peak position comprises: Converting the PAPR reduction signal and the information signal into a time domain signal; And And synchronizing a position having a peak in the time domain of the information signal and a position having a peak in the time domain of the PAPR reduction signal using cyclic shift or phase rotation. PAPR reduction method. delete delete The method according to claim 1, The step of matching the peak position and the calculating step Wherein the information signal is repeatedly performed until a peak value exceeding a linear interval of the reception filter of the reception end disappears. A method for reducing Peak to Average Power Ratio (PAPR) in a mobile communication system using an OFDM scheme, A PAPR reduction signal having a predetermined signal value at a predetermined position of four subcarriers, and a peak position in a time domain of each of the predetermined information signals; And And subtracting the PAPR reduction signal from the information signal when the peak value is matched, The PAPR reduction signal is predetermined as the PAPR reduction signal having the largest difference between the largest peak value and the second largest peak value of the PAPR reduction signal among the possible PAPR reduction signals, The positions of the four subcarriers in the entire system sub-carriers and the predetermined signal value are predetermined so that the difference between the largest peak value and the second largest peak value of the PAPR reduction signal is the largest, The step of matching the peak position comprises: Converting the PAPR reduction signal and the information signal into a time domain signal; And And synchronizing a position having a peak in the time domain of the information signal and a position having a peak in the time domain of the PAPR reduction signal using cyclic shift or phase rotation. PAPR reduction method. delete delete 6. The method of claim 5, The step of matching the peak position and the calculating step Wherein the information signal is repeatedly performed until a peak value exceeding a linear interval of the reception filter of the reception end disappears.

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