KR100666689B1 - Real-time Peak-to-Average Power Reduction Method Using Phase Rotation and Selective Mapping Method and Data Transmission System Using the Same - Google Patents

Abstract

Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM) reduces the high peak-to-average power ratio (PAPR) caused by many subcarriers in a communication system. A method for high quality signal transmission and high efficiency power amplification by avoiding nonlinear distortion in a high power amplifier (hereinafter referred to as HPA) is disclosed. The phase rotation signal used in the present invention gives the transmission data various phase rotations from 0 ° to 360 °. Therefore, the present invention has the same complexity of the system and shows superior performance in PAPR reduction compared to the conventional SLM method of giving only two phase rotations of 0 ° or 180 ° to the transmission data. By using the present invention, nonlinear HPA can be used more efficiently, and the influence on nonlinear distortion can be reduced, thereby enabling high quality OFDM signal transmission. In addition, since it is possible to perform real-time processing without information loss due to additional information loss and no calculation time for PAPR reduction, it is more effective than other PAPR reduction techniques, and is suitable for OFDM-based communication and broadcasting system.

Description

Real-time PAPR reduction method by the combination of phase rotation and selective mapping and system for transmitting data using the same}

1 is a block diagram illustrating an OFDM transmitter of a new SLM method according to the present invention.

 <Explanation of symbols for the main parts of the drawings>

110: data mapping unit 120: serial / parallel conversion unit

130: data copy unit 140: multiplier

150: phase rotation signal generator 170: inverse fast Fourier transform unit

180: minimum PAPR selection

The present invention relates to a method for real-time peak-to-average power reduction using a phase rotation and selective mapping method, and a system for performing the same. In particular, the present invention relates to many subcarriers in orthogonal frequency division multiplexing (OFDM) communication system. Reduces the high peak-to-average power ratio (PAPR) that occurs, thereby avoiding nonlinear distortion in high power amplifiers (hereinafter referred to as HPAs) The present invention relates to a method for real-time peak-to-average power reduction using phase rotation and selective mapping for high efficiency power amplification, and a system for performing the same.

In general, the OFDM system is a useful system widely used for communication and broadcasting. In the OFDM system, the spectrums of subchannels overlap each other while maintaining orthogonality, and thus have good spectral efficiency. Transform (IFFT) and Fast Fourier Transform (FFT) enable efficient digital implementation of the modulation and demodulation unit, and robust against frequency selective fading or narrowband interference. It is an effective technology for high speed data transmission that is adopted as a standard for high capacity wireless communication systems such as broadcast transmission and IEEE 802.11a and IEEE 802.16a and b.

OFDM technology with this advantage has the biggest disadvantage with high PAPR. Since OFDM transmits data using a large number of carriers, the final OFDM signal has a large amplitude variation since the amplitude is the sum of the amplitudes of the respective carriers, and if the phases of the respective carriers coincide with each other, they have a very large value.

Therefore, the linear operating range of the high-power amplifier (hereinafter referred to as HPA) is out of range, and the signal passing through the HPA causes distortion. Therefore, to reduce the distortion of these signals, the operating point of the HPA is adjusted downward. This is called back-off. As the back-off value increases, so does the power consumption, resulting in a very poor amplifier efficiency. Therefore, a signal with a high PAPR degrades the efficiency of the linear amplifier, and in the nonlinear amplifier, the operating point is located in the nonlinear region, resulting in nonlinear distortion, causing intermodulation and spectral emission between carriers.

One of the basic techniques to reduce this PAPR is to widen the linear range of the power amplifier so that all signals operate linearly to avoid signal distortion, or back-off in nonlinear amplifiers. In this case, there is a disadvantage in that the power efficiency becomes poor and the implementation cost increases. In this case, a method of reducing PAPR to prevent nonlinear distortion is very important for a high quality and high efficiency OFDM communication system. The solution is being derived.

Typically, there are clipping, block coding, and phase adjustment methods to reduce the PAPR. First, the clipping method is a method of forcibly cutting the size of a signal if it is larger than a predetermined value. It is a simple and effective method of reducing the PAPR, or an in-band distortion occurs due to nonlinear operation, resulting in BER performance. Adjacent channel interference occurs due to missing, out-band clipping noise.

In the block coding method, a coding technique is added to the extra carrier so that the PAPR of the signal is lowered and transmitted. This technique can reduce PAPR without distortion, as well as error correction, but with very poor spectral efficiency and a large look-up table or generation matrix, which is very complex and computational. .

Lastly, there are a partial transmission sequence (hereinafter referred to as PTS) and selective mapping (hereinafter referred to as SLM) as a phase adjusting method. PTS not only has the same advantages as SLM, but is also known as the most effective and flexible way of reducing PAPR without nonlinear distortion. SLM multiplies M statistically independent N-log ₂ M phase rotation signals by the same data of length N-log ₂ M and transmits the sequence having the lowest PAPR among them. While M IFFT processes are required, PAPR can be considerably lowered and can be applied regardless of the number of carriers. These two methods have no spectral distortion, can effectively reduce PAPR, and can be applied regardless of the modulation method.

However, in the conventional selective mapping (SLM), which uses phase rotation, a signal for phase rotation of transmission data is set to 0 or 0 using only two phase rotation signals of 1 or -1 to reduce PAPR. It gives a rotation of ° or 180 ° to increase the calculation time, there is a problem in that real-time processing is difficult and not efficient.

SUMMARY OF THE INVENTION The present invention has been invented to solve the above problems, and in order to effectively reduce peak power to average power ratio (PAPR) without distorting a signal in a communication system using an orthogonal frequency modulation multiplexing (OFDM) method, the phase of transmission data Codes that are pointed out as the biggest weakness of block coding are effectively reduced PAPR by giving various phase rotations from 0 ° to 360 ° to the transmitted data to dramatically reduce the computation time and processing in real time. Real-time peak-to-band using phase rotation and selective mapping to reduce PAPR, which significantly improves code rate or bandwidth efficiency, and at the same time reduces PAPR, which solves the problem of processing time delays at the transmit end of the PTS. It is a first object to provide a method for reducing average power.

It is a second object of the present invention to provide a system for implementing the above real-time peak to average power reduction method.

The present invention for achieving such a first object,

After the data D to be OFDM modulated is mapped according to the modulation level, the mapped signal is serially / parallel transformed to sequentially convert the data D to N-log ₂ M (N is the number of points in an inverse fast Fourier transform, M is the number of branches and N-log ₂ M is a positive number) and outputting the parallel conversion;

Copying the output data by M times, and sequentially multiplying the remaining data except for the first output data D1 among the copied data with a phase rotation signal of various ranges from 0 ° to 360 °;

Including phase rotation signal pattern information in the multiplied data and then performing inverse fast Fourier transform (OFDM); And

Select and transmit an inverse fast Fourier transformed signal, but set a threshold of the peak power to average power ratio (PAPR), and if a PAPR lower than the threshold set in the initial data (D1) occurs, find the PAPR from the remaining data. Ending the search, and transmitting a symbol of the data having the lowest PAPR if no PAPR below the threshold is generated until the last data.

In addition, the present invention for performing the above second object,

A data mapping unit 110 for receiving data to be OFDM modulated and mapping the data according to a modulation level;

N-log ₂ M (N is the number of points during the inverse fast Fourier transform, M is the number of branches and N-log ₂ M is a positive number) sequentially connected to the output data of the data mapping unit 110 and mapped. Serial / parallel conversion unit 120 for outputting the parallel conversion into a dog;

S / is connected to the output side of the parallel converter (120) N-log ₂ data copying section 130 for output to copy the data entered M pieces of predetermined times magnification M;

It is connected in parallel to the output side of the data copying unit 130, a plurality of N-log ₂ to parallel conversion in the serial / parallel conversion unit 120 and outputted through the data copying unit at a constant magnification M times each of the plurality of A plurality of connected multipliers 140a to 140n for multiplying the data and the phase rotation signals in the range from 0 ° to 360 °, respectively;

0 ° to 360 connected to the multipliers 140b to 140n except for the multiplier 140a at the top of the output stages of the multipliers 140a to 140n, respectively, suitable for data input to the multipliers 140b to 140n. Phase rotation signal generators 150a to 150n configured to input phase rotation signals in various ranges up to °;

A plurality of inverse fast Fourier transform units connected to the output side of the plurality of multipliers 140, respectively, for inverse fast Fourier transforming a signal obtained by multiplying information data and a phase rotation signal, and performing parallel / serial conversion to output a waveform in a time domain. (IFFT) 170a-170n; And

It is connected to the output side of a plurality of inverse fast Fourier transform units (IFFTs) 170a to 170n to set a threshold of the PAPR of the inverse Fourier transformed data, and is set in the data input to the multiplier 140a at the highest level at the set threshold. If a PAPR lower than the threshold occurs, the search for searching for a PAPR in the remaining data ends, and if the PAPR lower than the threshold is not generated until the last data, the minimum PAPR for performing control to transmit a symbol of the data having the lowest PAPR is performed. It includes a selection unit 180.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating an OFDM transmitter implemented by a new SLM method according to the present invention.

The present invention is a method to reduce the PAPR by a new SLM method, by multiplying the data transmitted to multiple branches by various phase rotation signals having a phase rotation range of 0 ° to 360 ° generated by different rules for each branch. Fourier transform (IFFT) reduces PAPR in real time.

Further, according to the present invention, when selecting and transmitting a signal whose PAPR is reduced in order to reduce the amount of computation compared to the conventional SLM method, a threshold of PAPR is set in selecting a transmission signal, and a PAPR lower than this threshold is generated. If it does not process the remaining branches, the search process is terminated, the next data symbol is processed, and if the PAPR lower than the threshold of the PAPR set up to the last branch does not come out, the symbol of the branch having the lowest PAPR is transmitted.

FIG. 1 illustrates an OFDM transmitter of a new SLM method, in which N-log ₂ M pieces of input data mapped to an output side of a data mapping unit 110 for receiving data to be OFDM-modulated and mapped to a modulation level are mapped sequentially. The serial / parallel conversion unit 120 for outputting the parallel conversion is connected. Where N is the point at the inverse fast Fourier transform (IFFT), M is the number of branches, and N-log ₂ M is positive.

The data copying unit 130 is connected to the output side of the serial / parallel conversion unit 120 to copy and output the data inputted by N-logs ₂ M at a predetermined magnification M times. The output side of the data copying section 130, serial / parallel converter (120) N-log ₂ M pieces each predetermined ratio of M times the number of data and the phase rotation signal output in parallel is converted by the data copying section 130 in A plurality of multipliers 140a to 140n connected in parallel for multiplying the phase rotation signals of various ranges from 0 ° to 360 ° generated by the generator 150 are formed. In this case, in each of the multipliers 140a to 140n, a plurality of data sequentially output from the data copying unit 130 and phase rotation of various ranges from 0 ° to 360 ° generated by the phase rotation signal generator 150 The signal is multiplied, and the data of the top branch of the entire data input from the data copying unit 130, that is, the data input to the multiplication unit 140a at the uppermost level, is generated by the phase rotation signal generating unit 150. It does not multiply the phase rotation signal and does not multiply, and inputs it to the multipliers 140b to 140n except for the data of the second branch to the data of the last branch, that is, the data input to the multiplier 140a at the top. The data is configured to perform a multiplication operation with each N-log ₂ M phase rotation signal generated by the rules according to each branch in the phase rotation signal generator 150.

That is, the multiplier 140a which receives data of the uppermost branch of the entire data input from the data copying unit 130 among the multipliers 140 is not connected to the phase rotation signal generator 150.

On the output side of the plurality of multipliers 140, a plurality of inverse fast Fourier transform units (IFFTs) for outputting time-domain waveforms by inverse fast Fourier transforming a signal multiplied by information data and a phase rotation signal and performing parallel / serial conversion. (170a to 170n) are connected to each other, and on the output side of the plurality of inverse fast Fourier transform units (IFFTs) 170a to 170n, a threshold value of a PAPR of inverse Fourier transformed data is set, and the control is performed according to the set threshold. The minimum PAPR selector 180 is formed.

FIG. 1 configured as described above describes the detailed operation of an OFDM transmitter implemented by a new SLM method according to the present invention.

The data to be OFDM modulated is input to the mapping unit 110 and mapped according to the modulation level. The mapped signal is sequentially converted into N-log ₂ M pieces of input data D by a serial to parallel converter 120 and output.

A plurality of signals output from the serial / parallel converter 120 are M-folded by the data copying unit 130 and are sequentially connected to a plurality of multipliers 140a to 140n sequentially connected in parallel to receive data for the first time. To the lowest branch (where data is last received). The data input to the multiplier 140a at the highest level is not inversely multiplied with the phase rotation signal generated by the phase rotation signal generator 150, but is inverse fast Fourier transform unit IFFT connected to the output side of the multiplier 140a. It is moved to 170a.

The reason why the phase rotation signal is not multiplied with the uppermost branch of the summation unit 140a is that, in some cases, the signal as it is without multiplying the phase rotation signal by the data has a lower PAPR than the signals obtained by multiplying the phase rotation signal. Because there are cases.

The data of the second branch excluding the uppermost branch, the data of the last branch, that is, the data input to the multipliers 140b to 140n except for the data input to the multiplier 140a at the uppermost level, is a phase rotation signal generator. from 150 to perform each of N-log ₂ M phase of the rotation signal and the multiply operation generated by the rules for each branch.

However, since the phase rotation signal used in the present invention is a phase signal of various ranges from 0 ° to 360 °, there is a better PAPR reduction effect than the conventional SLM compared to the case of using only 0 ° and 180 °.

The pattern for generating the phase rotation signal for each branch in the phase rotation signal generator 150 is as follows.

<식1>

<Equation 1>

는 3번째 브렌치의 2번째 부반송파에 곱해지는 위상회전 신호이다. 위와 같은 패턴으로 발생한 위상회전신호는 0°부터 360°까지의 범위를 가지며 각 브렌치는 브렌치 번호에 의한 고유한 위상회전신호를 사용한다. 본 발명을 적용한 전송데이터 심볼은 기존의 SLM방법을 적용한 전송 데이터 심볼에 비해 평균 2dB가 적은 PAPR을 갖는다.Here, B is the number of each branch, and as described above, since the first branch does not multiply the phase rotation signal, B has a range of (2, 3, ..., M). k is the number of subcarriers and has a range of (1, 2, ..., N). N is the number of subcarriers of the OFDM system. E.g

Is the phase rotation signal multiplied by the second subcarrier of the third branch. The phase rotation signal generated in the above pattern ranges from 0 ° to 360 ° and each branch uses a unique phase rotation signal by branch number. The transmission data symbol to which the present invention is applied has an average of 2 dB less PAPR than the transmission data symbol to which the conventional SLM method is applied.

Each N-log ₂ generated by the rules according to each branch of the data input to the multipliers 140b to 140n and the phase rotation signal generator 150 except for the data input to the multiplier 140a at the uppermost level. Perform multiplication operation with M phase rotation signals.

Then, the length of the data symbol is N by adding a data log ₂ M bit containing the phase rotation signal pattern information (Side information, hereinafter referred to as SI) used to restore the original signal at the receiving side to the multiplied signal. Since the SI is included in the transmission signal and transmitted, the receiver can perform phase restoration of the original signal using the information.

The plurality of inverse fast Fourier transform units 170a to 170n respectively connected to the output sides of the plurality of multipliers 140a to 140n convert the signals obtained by multiplying the information data and the phase rotation signal by inverse fast Fourier transform and parallel / serial conversion. Output the waveform of the time domain. The signals output from the plurality of inverse fast Fourier transform units 170a to 170n are input to the minimum PAPR selector 180. The minimum PAPR selector 180 controls to select a transmission signal that satisfies the threshold PAPR. When selecting a transmission signal, the minimum PAPR selector 180 sets a threshold of the PAPR to calculate the PAPR from the first branch to the Mth branch. .

In the conventional SLM method, once all phases except the first branch are multiplied by a phase rotation signal, the PAPRs of all data symbols from the first branch to the Mth branch are calculated and the data symbols having the lowest PAPR are transmitted. do. However, the method used in the present invention is as follows. The PAPR of the data symbol that is not multiplied by the phase rotation signal of the first branch is calculated, and when it is lower than the threshold, the transmission signal is selected. The copied data from the second branch to the last branch is discarded. If the data symbol of the first branch is higher than the threshold PAPR, the data symbol of the first branch is not selected as the transmission data. The data symbol of the second branch is multiplied by the phase signal, compared with the threshold PAPR, and if it is lower than the threshold PAPR, the data symbol is selected as the transmission data. No PAPR comparison is made for data symbols from the third branch. If the PAPR of the data symbol of the second branch is higher than the threshold PAPR, the PAPR comparison is performed using the data symbol of the third branch as described above. In the worst case, the PAPR of the data symbols is compared up to the Mth branch. If the PAPR of the data symbol of the Mth branch is lower than the threshold PAPR, it can be selected and transmitted as a transmission signal. Otherwise, the first branch to the Mth branch is selected. Among all data symbols up to, the data symbol having the lowest PAPR is selected as the transmission data.

This has the advantage that the amount of calculation is much smaller than the existing SLM method and PTS method. Therefore, it is possible to transmit faster than the OFDM system using the conventional SLM scheme and PTS scheme.

In the OFDM communication system employing the method according to the present invention, a transmission apparatus for reducing PAPR converts sequentially input data into a parallel / parallel conversion unit that converts data in parallel and then converts each branch to parallel data received in multiple branches. Each phase generates a phase rotation signal generated by different rules and multiplies the received parallel data. As the phase rotation signal, various signals having a range of 0 ° to 360 ° are used. Unlike the conventional SLM, which uses only two phase rotation signals, 0 ° and 180 °, various signals having a range of 0 ° to 360 ° are used in the present invention, so that the performance of PAPR reduction can be further improved compared to the existing SLM. have.

Thereafter, the signal multiplied by the phase rotation signal is transmitted to the inverse fast Fourier transform unit 170 to perform OFDM modulation, and then select and transmit a signal. When selecting a transmission signal, a threshold of the PAPR is set, which is lower than this threshold. If a PAPR occurs, the remaining branch is not processed, the search process is terminated, the next data symbol is processed, and if the PAPR lower than the threshold is not reached until the last branch, the symbol having the lowest PAPR is transmitted. This has the advantage that the amount of calculation less than the conventional SLM method.

The improved SLM (selected mapping) method using various phase rotation signals according to the present invention can efficiently reduce the high PAPR, which is the biggest problem due to the use of multiple carriers in an orthogonal frequency division multiplexing (OFDM) communication system, thereby providing a high power amplifier. High power amplifier (HPA) can increase the power efficiency and prevent non-linear distortion, enabling high quality communication. That is, in the present invention, the phase rotation signal is generated in each branch in a specific pattern to reduce the PAPR of the transmission data. In the OFDM communication system, the phase rotation signal generated according to different rules for the data input to each branch like the SLM method. Transmitting by multiplying to reduce the PAPR.

As described above, the improved SLM (selected mapping) method that applies various phase rotation signals according to the present invention effectively reduces high PAPR, which is the biggest problem due to the use of multiple carriers in an orthogonal frequency division multiplexing (OFDM) communication system. In this way, the power efficiency of the high power amplifier (HPA) can be increased, and nonlinear distortion can be prevented, thereby enabling high quality communication. In addition, by using the SLM type, parallel processing of a plurality of pieces of information is performed, so that processing delay time, which is a problem of the PTS (Partial transmit sequences) method, does not occur and requires less computational amount than the conventional SLM method. Therefore, the transmission speed can be faster than the existing SLM method.

Therefore, by using the present invention, nonlinear HPA can be used more efficiently, and the influence on nonlinear distortion can be reduced, thereby enabling high quality OFDM signal transmission. It is more effective than other PAPR reduction techniques because it enables real-time processing without the computation time for PAPR reduction with a small amount of calculation, and is suitable for the communication and broadcasting system based on OFDM.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited thereto and may be improved or modified by those skilled in the art within the scope of the technical idea of the present invention.

Claims (4)

I) After the data D to be OFDM-modulated is mapped to the modulation level, the mapped signal is serially / parallel transformed to sequentially convert the data D to N-log ₂ M (where N is the point at the inverse fast Fourier transform). (M, where N is the number of branches and N-log ₂ M is a positive number) and outputting the parallel conversion; Ii) copying the data output in step ⅰ by M times, and sequentially multiplying the remaining data except for the first output data D1 among the copied data with a phase rotation signal of various ranges from 0 ° to 360 ° step; Iv) including phase rotation signal pattern information in the data multiplied in step ii and then performing inverse fast Fourier transform (OFDM); And Iii) select and transmit an inverse fast Fourier transformed signal in step iv, set a threshold of peak power to average power ratio (PAPR), and have a PAPR lower than the threshold set in the initial data D1 in step ii. If this occurs, the search for the PAPR in the remaining data is terminated, and if there is no PAPR lower than the threshold until the last data, the phase rotation and selective mapping method comprising the step of transmitting a data symbol having the lowest PAPR Real-time peak-to-average power reduction method. The real-time peak-to-average using the phase rotation and selective mapping method of claim 1, wherein the phase rotation signal pattern information of step (v) is data having log ₂ M bits used to recover an original signal at a receiver. Power reduction method. The method of claim 1, wherein the step 는 calculates a PAPR of the first data D1 not multiplied by the phase rotation signal in step ii, selects a transmission signal when a PAPR lower than a threshold is set, and selects the remaining data. Not computing; If the PAPR value of the first data D1 in the step ii is higher than the threshold, the data symbols sequentially input from second to last are multiplied by the phase rotation signal, compared with the threshold, and then the data is lower than the threshold. Selecting a symbol as transmission data and not calculating data after the selected data; And selecting the data symbol having the lowest PAPR among all data symbols from the first data symbol to the Mth data symbol as transmission data when the data symbol inputted to the end in step ii is higher than the threshold. Real-time peak-to-average power reduction using phase rotation and selective mapping. A data mapping unit 110 for receiving data to be OFDM modulated and mapping the data according to a modulation level; N-log ₂ M (N is the number of points during the inverse fast Fourier transform, M is the number of branches, and N-log ₂ M is a positive number). The input data mapped to the output side of the data mapping unit 110 is sequentially mapped. Serial / parallel conversion unit 120 for outputting the parallel conversion into pieces); The serial / parallel converter is connected to the output side of the (120) N-log ₂ data copying section 130 for output to copy the data entered M pieces of predetermined times magnification M; It is connected in parallel to the output side of the data copying unit 130, and converted in parallel to the N-log ₂ M in the serial / parallel conversion unit 120 is outputted at a constant M times through the data copying unit 130, respectively A plurality of connected multipliers 140a to 140n for multiplying a plurality of data and phase rotation signals in a range from 0 ° to 360 °, respectively; 0 ° suitable for data input to the multipliers 140b to 140n, respectively, connected to the multipliers 140b to 140n except for the multiplier 140a at the top of the output terminals of the respective multipliers 140a to 140n. Phase rotation signal generation unit 150a to 150n formed to input various phase rotation signals from 360 ° to 360 °; A plurality of inverse fast Fourier transforms respectively connected to the output side of the multiplier 140 to multiply the signals multiplied by the information data and the phase rotation signal, inverse fast Fourier transform, and parallel / serial conversion to output time-domain waveforms. (IFFT) 170a-170n; And Connected to an output side of the plurality of inverse fast Fourier transform units (IFFTs) 170a to 170n to set a threshold of the PAPR of the inverse Fourier transformed data, and at the data inputted to the multiplier 140a at the highest threshold at the set threshold. If a PAPR lower than the set threshold is generated, the search for searching for the PAPR is terminated in the remaining data, and if a PAPR lower than the threshold is not generated until the last data, performing control of transmitting a symbol of the data having the lowest PAPR. Data transmission system using a real-time peak-to-average power reduction method using a phase rotation and selective mapping method comprising a minimum PAPR selection unit for the.

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