KR20010069611A - PAPR Reduction Method by Delay Circiuts in Multi-carrier Communication System - Google Patents

Abstract

PURPOSE: A method for reducing peak to average power ratio(PAPR) using a delay circuit is provided to reduce a complex circuit technique and an additional calculation and to reduce the PAPR without changing information transfer efficiency. CONSTITUTION: An input signal is converted into a quadriphase-shift keying(QPSK) signal through a signal mapping unit(1) and the converted signal is spread by a pseudo noise sequence(2). Before the spread signals are transferred to an inverse fast fourier transform(IFFT) unit(4), the spread signals are delayed by corresponding delay circuits(12) so as to have constellation variation, according to sub carrier waves. The delay circuits(12) change a phase while not changing a signal amplitude.

Description

PAPR Reduction Method Using Delay Circuit in Multicarrier Communication System {PAPR Reduction Method by Delay Circiuts in Multi-carrier Communication System}

The present invention is a peak-to-average that is an important problem caused by using multiple carriers, such as orthogonal frequency division multiplexing (OFDM) or multicarrier code division multiple access (MC-CDMA), used in digital broadcasting systems and high-speed wireless data networks. The present invention relates to a method for reducing the power ratio (PAPR). Typical communication systems use nonlinear amplifiers, such as high power amplifiers (HPAs) 7, which operate in the saturation region for high efficiency output. Multicarrier Because many subcarriers are used, the amplitude change is large due to the high peak-to-average power ratio (PAPR), resulting in large performance degradation due to operation in the nonlinear region, and intermodulation between subcarriers or radiation to adjacent channels. Therefore, there is a prior art for reducing the peak-to-average power ratio (PAPR) of a multicarrier signal. First, a matrix consisting of codewords is used for signal input into a subcarrier. The basic idea of this method is to avoid using code words with high peak-to-average power ratios (PAPRs). Therefore, many calculations are required to find a codeword having a low peak value, and the demand for additional bandwidth caused by the codeword lowers the spectral efficiency. It is also very inefficient in systems with a large number of subcarriers. The second method is to use clipping before passing through the amplifier.

This method also reduces the peak-to-average power ratio (PAPR), but clipping causes in-band distortion and out-of-band noise. Similar to the first method, there is a method of reducing peak-to-average power ratio (PAPR) by using redundancy in block coding for error correction. It is a method of changing to a block code having a low peak-to-average power ratio (PAPR) to reduce the peak-to-average power ratio (PAPR) and correcting errors. However, many operations are required to find the optimal code, and information transmission efficiency is greatly reduced.

The present invention relates to conventional complex design techniques and methods to reduce additional circuitry, eliminate computation, and reduce peak-to-average power ratio (PAPR) without any change in information transmission efficiency.

The proposed scheme is to reduce the peak size by arranging phases differently by applying a delay circuit 12 so that each subcarrier branch has a different delay for each subcarrier branch.

Only the delay circuit 12 is used, the structure is simple, and no operation is necessary.

1 is a general block diagram of a general embodiment of the present invention.

2 is a block diagram of a delay circuit method of the present invention.

※ Explanation of codes for main parts of drawing

(1) Signal Mapper (9) A / D Converter

(2) Pseudo-Noise Sequence (10) Fast Fourier Transform (FFT)

(Pseudo Noise Sequence) (11) Signal Demapper

(3) Subcarrier specific data (12) Delay circuit

(4) Inverse Fast Fourier Transform (IFFT)

(5) adder

(6) D / A converter

(7) High Power Amplifier (HPA)

(8) transmission channel

1 is a typical multi-carrier code division multiple access (MC-CDMA) system. The serial data is converted into a quadrature-shift keying (QPSK) signal via a signal mapper (1), and by an Inverse Fast Fourier Transform (IFFT) (4). Multicarrier modulated. In this case, N is the number of subcarriers, and each branch data (3) X = [ X ₀ , X ₁ ,.. , X _N-1 ] means the Quaternary-Phase Phase Modulation (QPSK) signal. The peak-to-average power ratio (PAPR) is defined as in equation (1).

In the multicarrier system thus transmitted, the same data is sent to each subcarrier at the same time, and the same phase occurs at the same time. Therefore, in this case, as the number of subcarriers increases, the peak-to-average power ratio (PAPR) increases proportionally. Therefore, nonlinear distortion occurs. Thus, in the method of the present invention, a delay 12 for each subcarrier is passed to the inverse fast Fourier transform (IFFT) 4 after passing through a signal mapper 1 to provide a different phase for the data. Let's have

The input signal is converted into a quaternary-phase modulation (QPSK) signal through a signal mapper 1 and spread by a user-specific pseudo noise sequence C (2). As shown in FIG. 2, the spread signal passes through different delay circuits 12 before the inverse fast Fourier transform (IFFT) 4 processes the incoming signal for each subcarrier, unlike a general multicarrier system. The delay circuit 12 does not change the amplitude of the signal but causes a phase change. Accordingly, the signals input to the inverse fast Fourier transform (IFFT) 4 through the delay circuit 12 are signals having the same magnitude but different constellations with different phases. This means that multicarrier modulation of signals input in different phases during the inverse fast Fourier transform (IFFT) process in which the subcarriers have the same initial phase means that the signals of the respective carriers can be avoided to have the same phase at the same time. do. Therefore, it is possible to reduce the peak-to-average power ratio (PAPR) by reducing the sum of the sum vector by preventing each subcarrier vector from being in phase.

In the reduction system configured with the peak-to-average power ratio (PAPR) as shown in FIG. 2, computer simulations were carried out with increasing the number of subcarriers from 4 to 128 to obtain the results of Table 1.

As shown in the results, doubling the subcarriers in a typical multicarrier system increases the peak-to-average power ratio (PAPR) by 3 [dB]. However, in the case of the present invention, it has an increase of 1 dB or less. In order to cope with frequency selective fading and to use high-speed data transmission, 512 or 1024 subcarriers are usually used. Therefore, as the subcarriers increase, compared to the conventional MC-CDMA system and the orthogonal frequency division multiplexing (OFDM) scheme, the peak-to-average power ratio (PAPR) is significantly reduced. When the delay is changed by one chip unit or two chip units by varying the degree of delay, it is a difference between the result of Table 1 and a small value within 1 [dB].

In the present invention, a delay circuit may be used as a peak-to-average power ratio (PAPR) reduction technique in a multicarrier code division multiple access (MC-CDMA) system or a multicarrier modulation system using an orthogonal frequency division multiplexing (OFDM) scheme. 12) was invented. The method of reducing the peak-to-average power ratio (PAPR) of the proposed invention has a simple structure, and it is advantageous that better performance can be obtained as the number of subcarriers increases without calculation. In addition, it can be used in all stages of the previous peak-to-average power ratio (PAPR) reduction scheme, and when used in combination, it has a sufficient peak-to-average power ratio (PAPR) reduction effect with less computation and less complexity.

Claims (1)

As a peak-to-average power ratio (PAPR) reduction technique in a multi-carrier code division multiple access (MC-CDMA) system or a multi-carrier modulation system of orthogonal frequency division multiplexing (OFDM), A) reducing the peak-to-average power ratio (PAPR) by using a delay circuit or delay operation before inverse fast Fourier transform (IFFT) or before multi-carrier modulation; B) a method of using a delay process as a conventional preprocessing step.