KR20100062153A - Papr reduction method using specific papr reduction signals - Google Patents

Abstract

PURPOSE: A PARR reduction method using a specific PARR reduction signal is provided to effectively reduce PARR in a mobile communications system, thereby preventing the distortion of a signal which occurs in case a given nonlinear filter is used. CONSTITUTION: The locations of the peak values of each time domain of a PARR diminishing signal and a set information signal are equalized. The PAPR reduction signal has a preset signal value in the location of a preset number of subcarriers. The PARR reduction signal is reduced from the information signal in a matching state of the peak value. The PARR reduction signal is previously determined as a PARR reduction signal with maximum PARR among the possible PARR diminishing signals. Among all the subcarriers within a system bandwidth, the location and the preset number of subcarriers and the preset signal value are previously determined to have the maximum PARR.

Description

PAPR Reduction Method Using Specific PAPR Reduction Signal {PAPR Reduction Method Using Specific PAPR Reduction Signals}

In the following description, a method for reducing PAPR using a PAPR reduction signal satisfying a specific condition in a mobile communication system using an OFDM scheme, specifically, a PAPR reduction signal and / or PAPR reduction in which the PAPR of the PAPR reduction signal itself is set to be greatest The present invention relates to a method for reducing the PAPR of an information signal by using a PAPR reduction signal set such that a difference between the largest peak of a signal and the second largest peak is greatest.

Multi-carrier systems have an efficient communication method for high speed data transmission but have a large PAPR (Peak to Average Power Ratio). To this end, as an example of a communication method of a multi-carrier system, an OFDM scheme, a DFT-S-OFDM (DFT Spreading OFDM) scheme, and an OFDMA scheme will be briefly described.

First, orthogonal frequency division multiplexing (OFDM) will be described. The basic principle of OFDM is to divide a high-rate data stream into a plurality of low-rate data streams and transmit them simultaneously using multiple carriers. Each of the plurality of carriers is called a subcarrier. Since orthogonality exists between the multiple carriers of the OFDM, the frequency components of the carriers can be detected at the receiving end even if they overlap each other. The high data rate data stream is converted into a plurality of low data rate data streams through a serial to parallel converter, and each subcarrier is included in the parallel data streams. After multiplying, the respective data strings are summed and sent to the receiving end.

A plurality of parallel data streams generated by the serial / parallel transform unit may be transmitted to a plurality of subcarriers by an inverse discrete fourier transform (IDFT), and the IDFT is an inverse fast Fourier transform (IFFT). Fast Fourier Transform can be implemented efficiently.

Since the symbol duration of the low carrier subcarrier is increased, relative signal dispersion in time caused by multipath delay spread is reduced. Inter-symbol interference can be reduced by inserting a guard interval longer than the delay spread of the channel between OFDM symbols. In addition, if a part of the OFDM signal is copied to the guard interval and placed at the beginning of the symbol, the OFDM symbol may be cyclically extended to protect the symbol.

Next, the DFT-S-OFDM method will be described. The DFT-S-OFDM scheme is also called Single Carrier-FDMA (SC-FDMA). Conventional SC-FDMA technique is a technique that is mainly applied to uplink. Before generating an OFDM signal, spreading is first applied to a DFT matrix in a frequency domain, and then the result is modulated by a conventional OFDM scheme and transmitted. .

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

Several variables are defined to describe the operation of the illustrated DFT-S-OFDM transmitter. It is assumed that N represents the number of subcarriers transmitting an OFDM signal, and Nb represents the number of subcarriers for any user. In addition, it is assumed that F denotes a discrete Fourier transform matrix, that is, 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 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 formula.

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 an Nb-sized DFT matrix used to disperse the data symbols s. Subcarrier mapping is performed on the distributed vector x by a constant subcarrier allocation scheme, and a signal to be transmitted to the receiver is obtained by converting to the time domain by the IDFT module. The transmission signal transmitted to the receiving side is as follows.

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 convert a signal in the frequency domain to a signal in the time domain. The signal y generated by the above-described method is transmitted by inserting a cyclic prefix.

The method of generating a transmission signal and transmitting it to the receiving side by the above-described method is called 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 for realizing multiple access by providing each user with a part of subcarriers available in a modulation system using a plurality of orthogonal subcarriers. OFDMA provides each user with a frequency resource called a subcarrier, and each frequency resource is provided to a plurality of users independently of each other so that they do not overlap each other.

The problem of PAPR is as follows.

2 shows a typical OFDM signal in the time domain.

As shown in FIG. 2, when looking at the OFDM signal in the time domain, it can be seen that there are portions A and B having a significantly larger power than the average signal power value. In a real system, a signal generated as shown in FIG. 2 is then transmitted through a nonlinear power amplifier. The nonlinear power amplifier can amplify the power linearly within a specific power range (linear section), but has more power than that. Is non-linearly amplified so that the received signal receives a distorted signal even in a noisy environment. This distortion can be reduced by using a power amplifier with a wide linear section, but the price will be increased significantly for a power amplifier with a wide linear section.

Accordingly, the present invention proposes a method for efficiently reducing PAPR in a mobile communication system using multiple carriers.

In particular, one embodiment of the present invention proposes to increase the PAPR reduction effect by setting and using the PAPR reduction signal used in the tone reservation method as a PAPR reduction signal satisfying a specific condition.

In one embodiment of the present invention for solving the above problems, a method for reducing a peak to average power ratio (PAPR) in a mobile communication system using the OFDM scheme, the predetermined signal at a predetermined number of subcarrier positions Matching a PAPR reduction signal having a value, and a peak position in a time domain of each of the predetermined information signals; And subtracting the PAPR reduction signal from the information signal while the peak value is matched, wherein the PAPR reduction signal is predetermined as a PAPR reduction signal in which the PAPR of the PAPR reduction signal itself is maximized among the possible PAPR reduction signals. We propose a PAPR reduction method.

This may mean that the position of the predetermined number of subcarriers and the predetermined signal value of all subcarriers in the system band are predetermined such that the PAPR of the PAPR reduction signal itself is maximized.

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

In addition, the peak-to-peak position matching step and the calculating step may be repeatedly performed until the peak value beyond the linear section of the reception filter of the receiver in the information signal disappears.

Meanwhile, according to another embodiment of the present invention, in a method for reducing a 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 number of subcarrier positions Matching peak positions in the time domain of each of the predetermined information signals; And subtracting the PAPR reduction signal from the information signal while the peak value is matched, wherein the PAPR reduction signal has a difference between the largest peak value of the PAPR reduction signal and the second largest peak value among the possible PAPR reduction signals. We propose a PAPR reduction method which is predetermined as the largest PAPR reduction signal.

This means that the position of the predetermined number of subcarriers among all subcarriers in the system band, and the predetermined signal value are predetermined such that the difference between the largest peak value and the second largest peak value of the PAPR reduction signal is the largest. Can be.

According to the embodiments described above, the PAPR is effectively reduced in a mobile communication system to prevent signal distortion that may occur when a given nonlinear filter is used, and to prevent the use of an expensive nonlinear filter having a long linear section at the transmitting and receiving end. Can be applied.

Hereinafter, exemplary embodiments of 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 applied by being replaced with other terms such as "Node B" and "eNode B", and the terminal may be applied by being replaced by terms such as "user equipment" (UE) and "mobile station (MS)". have.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates 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, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

As described above, PAPR in an OFDM system is one of the biggest disadvantages that an OFDM system must overcome. Therefore, research to reduce the PAPR is actively conducted. PAPR reduction techniques can be divided into two methods: reducing PAPR through distortion of the original signal and reducing PAPR using a specific algorithm without distortion.

Representative methods are described in each method.

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

3 and 4 are diagrams for describing a clipping technique for reducing PAPR.

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, a signal corresponding to a nonlinear section of a nonlinear power amplifier is removed by intentionally reducing power of a portion having a predetermined power (P _treshold ) or more.

That is, when the clipping technique is applied, the signal shown in FIG. 3 may be changed as shown in FIG. 4, and the changed signal is transmitted. This technique has the advantage of being very simple to implement but has the disadvantage of distorting the original signal. That is, the present 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, a tone reservation technique will be described as a PAPR method that does not distort the original signal.

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

According to this technique, subcarriers within an 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 reduction 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 may be inserted into 64 subcarriers at intervals of 16 subcarriers.

As shown in FIG. 5, time-domain signals obtained by IFFT processing of the data portion and the PAPR reduction signal portion in the frequency domain have orthogonality with each other in the time domain. This is a characteristic of the above-described OFDM system, and signals using subcarriers in the frequency domain not overlapping with each other maintain orthogonality with each other in the time domain. Therefore, adding or subtracting the PAPR reduction signal to the data signal in the time domain does not distort the original data signal. Using this characteristic, PAPR of the data signal is matched by cyclic shift and phase rotation by matching the point with the largest power in the PAPR reduction signal at the point with the largest power in the data signal. It is a way to reduce. In general, a method of repeatedly finding and subtracting a point having the maximum power value described above is used.

Although the data signal is originally shown as a signal including information to be transmitted in FIG. 5, the information signal to be transmitted may include not only data but also a control signal.

The tone reservation scheme 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 must be allocated for the PAPR reduction signal.

In addition, according to the tone reservation method described above, a portion other than the peak value of the information signal may be changed in the process of subtracting the PAPR reduction signal from the information signal in order to remove the peak value of the information signal, for example, the data signal. There may be a problem. In detail, 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 reduced, but at the same time, the power value also changes for other portions. In other words, other partial power values can be large or small. As a result, a portion having a large power can be newly generated.

Accordingly, in a preferred embodiment of the present invention, the PAPR is reduced according to the tone reservation scheme described above, but the PAPR is reduced from the information signal in a state where the peak value of the information signal coincides with the peak value of the PAPR reduction signal in order to reduce the peak value of the information signal. When subtracting the reduction signal, it is proposed to perform a PAPR reduction procedure by selecting a PAPR reduction signal that has a minimal effect on portions other than the peak value of the information signal.

As an example of such a PAPR reduction signal, first, a method of selecting a signal having a large PAPR of the PAPR reduction signal itself will be described. When the PAPR of the PAPR reduction signal itself is large, the difference in power value between the peak value and the portion other than 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 coincident with each other, the influence on the parts other than the peak value of the information signal is small. Accordingly, one embodiment of the present invention proposes to perform a PAPR reduction procedure according to the tone reservation method described above by using a signal having a large PAPR of the PAPR reduction signal itself.

Meanwhile, as in the above-described embodiment, among the signals having a large PAPR of the PAPR reduction signal itself, 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 the peak that does not differ from the largest peak, the largest peak of the PAPR reduction signal is removed to remove the peak of the information signal. In the process of subtracting the PAPR reduction signal from the information signal by matching the value with the peak to be removed in the information signal, an unwanted portion of the information signal may be generated as another peak value due to the second largest peak value of the PAPR reduction signal.

Accordingly, in another embodiment of the present invention, a method of selecting a PAPR reduction signal having the largest difference between the first peak and the second peak among the possible PAPR reduction signals and using the same in the tone reservation scheme as shown in FIG. Suggest.

Of course, when the PAPR of the PAPR reduction signal itself is large as described above, when the PAPR reduction signal having the largest difference between the first and second peak values of the PAPR reduction signal is selected, it may have better performance.

The PAPR of the OFDM signal is affected by the position and data value of the allocated subcarriers in the frequency domain. Therefore, in order to generate a PAPR reduction signal that satisfies the above characteristics, by generating and comparing possible PAPR reduction signals while varying the position and signal value of subcarriers assigned to the PAPR reduction signal, the PAPR reduction signal of the best performance is obtained. A subcarrier position and a signal value for may be obtained.

For example, if four subcarriers are used as the PAPR reduction signal among 128 subcarriers, the position can be determined through ₁₂₈ C ₄ operations, and the signal value to be inserted requires 2 ⁴ operations for BPSK. This operation is not necessary for each signal transmission, but is determined in advance according to the total number of subcarriers, the number of subcarriers assigned to the PAPR reduction signal, and the modulation method, and thus does not affect the amount of computation and complexity in transmitting and receiving signals in a real system. .

For a specific example, 128 subcarriers can be used and 4 subcarriers can be used for a PAPR reduction signal. In this system, the position of the subcarrier for the PAPR reduction signal and the signal value of the PAPR reduction signal at that position are actually measured. As a result of measuring and reducing the effect of PAPR, the following cases showed the best performance.

PRPR Reduction Signal Subcarrier Location PAPR Reduction Signal Subcarrier Signal Values 2 -One 24 -One 114 -One 116 -One

PAPR reduction signal according to the example of Table 1 has a high PAPR of the PAPR reduction signal itself, it can be seen that the difference between the largest peak and the next largest peak.

The subcarrier position allocated for the PAPR reduction signal as shown in Table 1 and the signal value of the PAPR reduction signal at the corresponding position also use 1024 subcarriers and 64 subcarriers are allocated for the PAPR reduction signal, and the system uses BPSK modulation. The same simulation can also be obtained, and the present invention proposes to reduce the PAPR of the signal through the tone reservation technique as shown in FIG. 5 by using the PAPR reduction signal thus obtained.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can. 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 embodiments described above, the PAPR reduction method efficiently reduces PAPR in various mobile communication systems using a multi-carrier scheme such as OFDM and OFDMA, thereby preventing signal distortion that may occur when a given nonlinear filter is used. An expensive linear interval can be applied to prevent the use of long nonlinear filters.

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

2 shows a typical OFDM signal in the time domain.

3 and 4 are diagrams for describing a clipping technique for reducing PAPR.

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

Claims (8)

In a method for reducing a peak to average power ratio (PAPR) in a mobile communication system using an OFDM scheme, Matching a PAPR reduction signal having a predetermined signal value to a predetermined predetermined number of subcarrier positions, 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 while the peak value is matched. And the PAPR reduction signal is predetermined as a PAPR reduction signal in which the PAPR of the PAPR reduction signal itself becomes the maximum among the possible PAPR reduction signals. The method of claim 1, The position of the predetermined number of subcarriers, and the predetermined signal value of the total subcarriers in the system band is predetermined so that the PAPR of the PAPR reduction signal itself is maximized. The method of claim 1, The peak position matching step, Converting the PAPR reduction signal and the information signal into time domain signals, respectively; And Matching a location having a peak in the time domain of the information signal with a location having a peak in the time domain of the PAPR reduction signal using cyclic shift or phase rotation; PAPR reduction method. The method of claim 1, The peak position matching step and the calculating step And repeatedly performing the peak information beyond the linear interval of the reception filter of the receiver in the information signal. In a method for reducing a peak to average power ratio (PAPR) in a mobile communication system using an OFDM scheme, Matching a PAPR reduction signal having a predetermined signal value to a predetermined predetermined number of subcarrier positions, and a peak position in a time domain of each of the predetermined information signals; And Subtracting the PAPR reduction signal from the information signal while the peak value is matched, And wherein the PAPR reduction signal is predetermined as the PAPR reduction signal with the largest difference between the highest and second peak value of the PAPR reduction signal among the possible PAPR reduction signals. The method of claim 5, The position of the predetermined number of subcarriers, and the predetermined signal value among all the subcarriers in the system band 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. Reduction method. The method of claim 5, The peak position matching step, Converting the PAPR reduction signal and the information signal into time domain signals, respectively; And Matching a location having a peak in the time domain of the information signal with a location having a peak in the time domain of the PAPR reduction signal using cyclic shift or phase rotation; PAPR reduction method. The method of claim 5, The peak position matching step and the calculating step And repeatedly performing until there is no peak value beyond the linear interval of the reception filter of the receiver in the information signal.

Images