KR20030040330A - Apparatus and method for the effective papr(peak-to-average power ratio) reduction of ofdm(orthogonal frequency division multiplexing) communication signal by the specified dummy sequence insertion - Google Patents

Abstract

PURPOSE: A method and a device for effectively reducing a PAPR(Peak-to-Average Power Ratio) of OFDM(Orthogonal Frequency Division Multiplexing) communication signals by additionally using a specific dummy sequence are provided to adopt DSI(Dummy Sequence Insertion), so as to efficiently reduce a high PAPR caused by the use of multiple carriers. Accordingly, power efficiency of an HPA(High-Power Amplifier) is enhanced and nonlinear distortion is prevented. CONSTITUTION: Parallel data delivered from a serial-to-parallel converter that converts sequentially inputted data into the parallel data are stored and a dummy sequence is inserted thereto, then the parallel data are delivered to an IFFT(Inverse Fast Fourier Transform) part. If a signal for reducing a PAPR is delivered from a PAPR comparator, a DSI part selects another dummy sequence in the parallel data and delivers the selected dummy sequence to the IFFT part. The DSI part inserts a dummy sequence in data according to sequence types. The data delivered from the DSI part are IFFTed by receiving annexed information and divided data as inputs. The data delivered from the IFFT part are converted into serial data. A PAPR for the data delivered from a parallel-to-serial converter is measured and compared with a PAPR threshold. According to compared results, the data are transmitted to a receiver or feedback to the DSI part is performed to apply another sequence and deliver a signal for reducing the PAPR.

Description

APPARATUS AND METHOD FOR THE EFFECTIVE PAPR (PEAK-TO) APPARATUS AND METHOD FOR THE EFFECTIVE PAPR (PEAK-TO) -AVERAGE POWER RATIO) REDUCTION OF OFDM (ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING) COMMUNICATION SIGNAL BY THE SPECIFIED DUMMY SEQUENCE INSERTION}

The present invention reduces the peak-to-average power ratio (PAPR), which is a problem in Orthogonal Frequency Division Multiplexing (OFDM) communication system. It is about. In addition to the data input in parallel, a dummy sequence generated by a constant complementary sequence, a correlation sequence related to the characteristics of the data, or a sequence of all 1s or 0s, or by flipping add a dummy sequence to reduce the PAPR of the OFDM signal. This dummy sequence is input to a redundant subcarrier. This method will be referred to as a dummy sequence insertion (DSI) method.

OFDM has good spectral efficiency because the spectrums of subchannels overlap each other while maintaining mutual orthogonality. FFT (hereinafter referred to as FFT) enables efficient digital implementation of the modulation and demodulation unit, and is robust against frequency-selective fading or narrowband interference. It is an effective technology for high speed data transmission, which is adopted as a standard for high capacity wireless communication systems.

Despite these advantages, OFDM 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 because the amplitude is the sum of the amplitudes of the respective carriers, and if the phases of the carriers coincide, they have a very large value. Therefore, the linear operating range of a 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 HPA is adjusted downward. This is called back-off. The higher the back-off value, the greater 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.

The basic technique of lowering the PAPR is to widen the linear range of the power amplifier so that all signals operate linearly, or back-off the nonlinear amplifier to operate in the linear region to avoid signal distortion. In this case, the power efficiency is low and the price is high. Therefore, PAPR reduction to prevent nonlinear distortion is very important in the research of OFDM communication system, and various methods and methods have been studied.

Typically, there are clipping, block coding, and phase adjustment methods to reduce the PAPR.

Clipping method is a method of forcibly cutting the size to a fixed value when the signal size is larger than the predetermined value. It is a simple and effective method to reduce the PAPR or in-band distortion due to nonlinear operation. It worsens and generates out-band clipping noise, resulting in adjacent channel interference.

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, large look-up tables and generation matrices, which are very complex and computational. .

There are a partial transmission sequence (hereinafter referred to as PTS) and selective mapping (hereinafter referred to as SLM) in a phase rotation 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 length sequences by the same data of length N 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.

The above two methods have no spectral distortion, can effectively reduce the PAPR, and can be applied regardless of the modulation method. However, there is a problem in that additional information on rotation factors must be transmitted to the receiver in order to recover data. Sending this additional information to a separate channel complicates the communication scheme, and if an error occurs, all of the information of the OFDM symbol at that time may cause an error and be damaged.

The present invention relates to an apparatus and method for effectively reducing peak-to-average power ratio (PAPR) without distorting a signal in a communication system using an orthogonal frequency modulation multiplexing (OFDM) scheme. The present invention is to 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 as a dummy sequence insertion (DSI) technique. Lowering the PAPR increases the power efficiency of the HPA and prevents nonlinear distortion, resulting in high quality communications. This method can be applied regardless of the type of modulation scheme and the number of subcarriers without distortion of the signal.

It is another object of the present invention to provide an apparatus and method for reducing PAPR that significantly improves code rate or bandwidth efficiency, which is pointed out as the biggest weakness of block coding.

The present invention provides an apparatus and method for reducing a PAPR by inserting a dummy sequence, using a complementary sequence, a correlation value, or using 0 and 1 as a dummy sequence. This dummy sequence is only used to reduce the PAPR at the transmitter and is removed at the receiver. Since it is not used as additional information like PTS or SLM, an error may occur.

Another object of the present invention is to apply a PAPR reduction technique for all input signals, to transmit a signal having most low PAPR directly, and to adaptively apply a PAPR reduction technique only to a signal having more than one high PAPR. The present invention relates to an apparatus and a method using a threshold technique applied.

In order to achieve the above object, in the OFDM communication system, a dummy sequence of a predetermined type is inserted in a dummy sequence insertion unit, transferred to an IFFT unit, and then modulated by OFDM. On the contrary, if it is still a high PAPR, feedback information is transmitted to insert another dummy sequence prepared to reduce the PAPR. In this case, when a complementary sequence is used as a dummy sequence, another predetermined complementary sequence is inserted by the dummy sequence inserting unit. Next, the dummy sequence includes a correlation sequence that uses association with input data, a sequence of all zeros, and a sequence of all ones. The method of inserting a dummy sequence of the complementary sequence uses a method of replacing different complementary sequences prepared in order to lower the PAPR. In the other case, the dummy sequence is inserted by a flipping method in which the upper bits of the dummy sequence are inverted one by one to check whether the PAPR is lowered and determine the dummy sequence bits in the lower direction.

In an apparatus for receiving a signal transmitted by reducing the peak-to-average power ratio (PAPR) in an Orthogonal Frequency Division Multiplexing (OFDM) communication system, the data received from the transmitter is converted in parallel. A fast Fourier transform unit for fast Fourier transforming the parallel data received from the serial / parallel converter as an input, and a dummy sequence removal unit for removing the dummy sequence transmitted to the redundant subcarrier with the data received from the fast Fourier transform unit as an input And a dummy sequence remover for transferring the data from which the dummy sequence has been removed to a parallel / serial converter for serially converting the data restored by the data restorer.

1 is a block diagram of an OFDM transmitter block of a dummy sequence insertion (DSI) method.

2 is a data diagram of a DSI method when a dummy sequence is a complementary sequence.

3 is a schematic diagram of a DSI method when the dummy sequence is a correlation sequence.

4 is a CCDF performance analysis diagram when L = 56 and M = 8, with and without DSI method.

5 is a CCDF performance analysis diagram when L = 48 and M = 16 with and without DSI method.

FIG. 6 shows CCDF performance analysis according to threshold values when L = 48, M = 16 and complementary sequences.

7 is L = 48, H = 16, and the number of repetitive searches according to a PAPR threshold when using a complementary sequence.

8 shows BER performance in Additive White Gaussian Noise (AWGN) channel.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention efficiently reduces the high PAPR, which is the biggest problem due to the use of multiple carriers in an Orthogonal Frequency Division Multiplexing (OFDM) communication system by using a dummy sequence insertion (DSI) technique. Lowering PAPR can increase HPA's power efficiency and prevent non-linear distortions, enabling high quality communications. This method can be applied regardless of the type of modulation scheme and the number of subcarriers without distortion of the signal. In an OFDM communication system, peak power is reduced by adding and transmitting a constant complementary sequence, a correlation sequence related to characteristics of the data, or a sequence of all 1s or 0s to data input in parallel. .

In order to achieve the above object, in the transmission apparatus for reducing the PAPR in the OFDM communication system, in addition to the parallel data received from the serial / parallel conversion unit for converting sequentially input data in parallel, the dummy sequence insertion unit ( In the dummy sequence insertion, a dummy sequence of a predetermined type is inserted and transmitted to the IFFT unit for OFDM modulation. Then, the PAPR comparator checks the PAPR and transmits the low PAPR OFDM signal. Reduce the PAPR by inserting another prepared dummy sequence. In this case, when a complementary sequence is used as a dummy sequence, another predetermined complementary sequence is inserted by the dummy sequence inserting unit. Next, the dummy sequence includes a correlation sequence that uses association with input data, a sequence of all zeros, and a sequence of all ones. The method of inserting a dummy sequence of the complementary sequence uses a method of replacing different complementary sequences prepared in order to lower the PAPR. In the other case, the dummy sequence is inserted by a flipping method in which the upper bits of the dummy sequence are inverted one by one to check whether the PAPR is lowered and the dummy sequence bits are determined in the lower direction.

1 is a block diagram illustrating a transmitter block of a dummy sequence insertion (DSI) technique in an OFDM system according to an embodiment of the present invention. The DSI transmitter includes a serial / parallel converter, a dummy sequence inserter, an inverse fast Fourier transform (IFFT), a parallel / serial converter, and a PAPR comparator. In the signal output from the serial / parallel converter, a dummy sequence having a length corresponding to the number of redundant subcarriers determined by the dummy sequence inserter is inserted into the transmission data.

In the present invention, in addition to the data input in parallel, the OFDM signal by adding a constant complementary sequence, or a correlation sequence related to the characteristics of the data, or a sequence of all 1s or 0s as an initial dummy sequence Decreases the PAPR. In addition, by using the PAPR threshold comparator, the Inverse Fast Fourier Transform (IFFT) is used to measure the PAPR of the output signal of the transformer and transmit it immediately when it is lower than the threshold of the PAPR set in the system. The amount of computation can be reduced by feedback to the dummy sequence inserter to insert and transmit a sequence having a low PAPR. In this method, when the PAPR comparator is higher than the reference PAPR, it is fed back to the dummy sequence inserter to insert another dummy sequence. The method used at this time is divided into two types. The first is divided into Method 1 of inserting and using a predetermined sequence in sequence and Method 2 of generating a new sequence using a flipping method.

2 and 3 are block diagrams of the transmission data after the dummy sequence insertion unit. In FIG. 2, a complementary sequence of length M is inserted into a data block diagram when a complementary sequence is used. 3 is a data block diagram when a correlation value is used. As shown in Figure 3, it is a data block diagram when using correlation values. The correlation value is to divide the data by the number of dummy sequences into blocks and then use the inverse of the first value of each block as the first dummy sequence.

The present invention does not transmit additional information unlike the conventional PTS and SLM schemes. That is, the information added to the dummy sequence is used only for PAPR reduction.

For conventional block coding, the code rate is 1 + log ₂ N of possible phase k. Therefore, the code rate is

[Equation 1]

The transmission efficiency of the present invention is always a fixed value as shown in Equation 1 below.

[Equation 2]

L is the number of transmitted data, M is the size of the dummy sequence for PAPR reduction. Therefore, transmission efficiency is increased compared to transmission of block coding. In addition, the PTS transmits when the PTS has the smallest PAPR through repetitive calculation of 2 ^V-1 when the PTS is divided into ^V subblocks. However, the present invention refers to FIG. The maximum number of iterations is M, which shows that the amount of computation is significantly reduced.

Therefore, the structure of the receiver of the present invention is much simpler since the structure of the receiver is not used to recover the original information by demodulating the additional information as in the conventional PTS, SLM, and block coding. In addition, it is possible to prevent the transmission data error caused by the additional information error.

4 is a diagram illustrating CCDF performance analysis when PAPR is reduced according to the present invention by inserting a dummy sequence when L = 56 and M = 8, and when not.

FIG. 5 is a diagram illustrating CCDF performance analysis when a dummy sequence is inserted or not when L = 48 and M = 16.

FIG. 6 is a diagram of CCDF performance analysis according to a threshold value when L = 48 and M = 16 and complementary sequences are used.

7 shows L = 48 and M = 16, and shows the number of repetitive searches according to the PAPR threshold when using a complementary sequence.

8 shows the BER performance in the AWGN channel.

As described above, the present invention is to 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 by a dummy sequence insertion (DSI) technique. Lowering the PAPR increases the power efficiency of the HPA and prevents nonlinear distortion, resulting in high quality communications. This method can be applied regardless of the type of modulation scheme and the number of subcarriers without distortion of the signal. In part, the PAPR reduction efficiency is lowered, but the transmission efficiency is superior to block coding. By inserting the dummy sequence without simply zero padding the untransmitted lower bands, an effective PAPR reduction performance can be obtained. By applying a threshold technique, a signal having a low PAPR is transmitted immediately and a PAPR reduction technique is applied to a signal having a high PAPR, thereby reducing processing time. Finally, since additional information is not added and transmitted, the receiver can prevent performance degradation due to additional information error.

Claims (2)

In the transmission and reception method and apparatus for reducing the peak-to-average power ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) communication system, A) Stores parallel data received from serial / parallel converter that converts sequentially input data in parallel, inserts dummy sequence, transfers it to inverse fast Fourier transform, and transmits signal to reduce PAPR from PAPR comparator Receiving a dummy sequence from the dummy sequence inserter and transferring the dummy sequence to the inverse fast Fourier transform unit; B) The dummy sequence inserting unit inserts a dummy sequence into the data according to the sequence type, converts the data received from the dummy sequence inserting unit into the inverse fast Fourier using the additional information and the divided data as inputs, and the inverse fast Fourier. Convert the data received from the converter to serial, measure the PAPR with the data received from the parallel / serial converter and compare it with the PAPR threshold, and transmit the data to the receiver or the dummy sequence inserter according to the comparison result. And transmitting a signal to reduce the PAPR by applying another sequence by feedback. C) A device for receiving a signal transmitted by reducing the peak-to-average power ratio (PAPR) in an orthogonal frequency division multiplexing (OFDM) communication system, wherein the data received from the transmitter is parallel A fast Fourier transform unit for fast Fourier transforming the parallel data received from the serial / parallel converting unit as an input, and a dummy sequence removal unit for removing a portion where a dummy sequence is inserted as the input of the data received from the fast Fourier transform unit; And removing the data transmitted in the dummy sequence and transferring the restored data to a parallel / serial conversion unit for serially converting the restored data. The method of claim 1, wherein the dummy sequence inserter has a buffer, and when the parallel data received from the serial / parallel converter is stored in the buffer and a signal for reducing the PAPR is received from the PAPR comparator, In the method and apparatus characterized in that for inserting the dummy sequence to the parallel data stored in the buffer A) The method and apparatus of the dummy sequence inserting unit, wherein the serial / parallel transformed portion is allocated to a dummy sequence. B) the dummy sequence is a complementary sequence to have a low PAPR. C) The dummy sequence is characterized in that the sequence having a value of '0' to have a low PAPR. D) the dummy sequence is characterized by a sequence having a correlation value such that it has a low PAPR.