• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.8
• /
• pp.1847-1853
• /
• 2014

The PAPR of the input signal is increased due to OFDMA signal in a mobile communication system. High efficiency of a power amplifier, which accounts for power consumption, is a very important key technology. Digital Pre-Distortion techniques were used to improve the linearity of the power amplifier. The Asymmetric Doherty scheme was used to improve the efficiency of the power amplifier. In this paper, we propose a new structure of Asymmetric Doherty. Drive power amplifier part is separated as main path and peak path, and phase shifter is employed to improve power combine characteristics of the Doherty Amplifier. Also, envelope tracking technology for drive gate bais in drive peak amplifier is used to improve efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.12A
• /
• pp.1319-1332
• /
• 2004

Multicarrier direct sequence code-division multiple access CDMA(MC DS-CDMA) is an attractive technique for achieving high data rate transmission even if the potentially large peak-to-average power ratio(PAPR) is an important factor for its application. On the other hand, code select CDMA(CS-CDMA) is an attractive technique with constant amplitude transmission of multicode signal irregardless of subchannels by introducing code selection method. In this paper we propose a new multiple access scheme based on the combination of MC DS-CDMA and CS-CDMA. Proposed scheme, which we called MC CS-CDMA, includes the sutclasses of MC DS-CDMA and CS-CDMA as special cases. The performance of this system is investigated for multipath Sequency selective fading channel and maximal ratio combining with rake receiver. In addition the PAPR of proposed system is compare with that of both MC BS-CDMA and CS-CDMA. Simulation results show that proposed system improves PAPR reduction than MC DS-CDMA at the expense of the complexity of receiver and the number of available non. Also, the numerical result shows that the proposed system is better performance than MC DS-CDMA due to the increasing processing gain and the number of time diversity gain.

• Journal of Satellite, Information and Communications
• /
• v.3 no.2
• /
• pp.18-25
• /
• 2008

A major drawback of Orthogonal Frequency Division Multiplexing (OFDM) system is high peak-to-average power ratio (PAPR) of the transmitted signal which introduces inevitable non-linear distortion in the transmission due to the amplifier non-linear property. This causes both in-band distortion and out of band spectrum re-growth. A polynomial based pre-distortion is estimated using the non-linear and inverse non-linear polynomial achieved through the Least Square Error (LSE) method. A new technique of PAPR reduction called 'Phase Realignment' (PR) is proposed which has a optimal effect in improving the BER performance as well as considerable reduction in the PAPR. In this paper we used the PR method along with the 'Peak Clipping' (PC) method is used before the pre-distortion to remove the high peak present in the non constant amplitude of the OFDM signal responsible to drive the amplifier in near saturation region for better performance of the system.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2001.11b
• /
• pp.71-76
• /
• 2001

OFDM(Orthogonal Frequency Division Multiplexing)의 단점인 높은 PAPR(Peak-to-Average Power Ratio)을 개선하기 위한 방법 중에서 SDT(Signal Distortion Technique)는 전송시스템의 규격 및 수신기의 변경 없이도 적용 가능한 이점이 있다. 본 논문에서는 SDT에 속하는 clipping과 peak windowing 기법을 Eureka 147 DAB(Digital Audio Broadcasting) 시스템에 적용하여 얻은 BER 및 PSD 성능결과를 토대로 PAPR 개선 정도에 따른 시스템의 요구 $Es/N_0$ 및 out-of-band의 PSD 열화 정도를 분석하였다. Hamming windowing을 적용한 경우, PAPR 4㏈에서 clipping에 비해 요구 $Es/N_0$는 비슷한 열화정도가 나타났으나, out-of-band의 PSD는 5dB 정도 개선되는 성능을 보였다.

• ETRI Journal
• /
• v.36 no.1
• /
• pp.42-50
• /
• 2014

Orthogonal frequency division multiplexing (OFDM) is a modulation technique that allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing the data into several narrowband and flat fading channels. OFDM has high spectral efficiency and channel robustness. However, a major drawback of OFDM is that the peak-to-average power ratio (PAPR) of the transmitted signals is high, which causes nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in the transmitter. The most straightforward method to solve this problem is to use a nonlinear mapping algorithm to transform the signal into a new signal that has a smaller PAPR. One of the latest nonlinear methods proposed to reduce the PAPR is the $L_2$-by-3 algorithm, which is based on the discrete sliding norm transform. In this paper, a new algorithm based on the $L_2$-by-3 method is proposed. The proposed method is very simple and has a low complexity analysis. Simulation results show that the proposed method performs better, has better power spectral density, and is less sensitive to the modulation type and number of subcarriers than $L_2$-by-3.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2003.10a
• /
• pp.516-519
• /
• 2003

본 논문은 OFDM 시스템에서 PAPR (peak-to-average power ratio) 저감을 위해 심볼 그룹핑 후 그룹별로 같은 스크램블 코드를 이용하였다. 기존의 SLM 기법은 IFFT단에 들어가는 부반송파 벡터를 여러개의 스크램블 코드에 의해 랜덤화 시켜 PAPR중 작은 값을 선택하여 전송한다. 그러므로 SLM 기법은 스크램블의 코드 갯수만큼 부가 정보를 전송함으로 대역의 손실이 발생한다. 본 논문에서는 부반송파들을 M개로 그룹화 하여 동일한 스크램블 코드를 사용함으로써 그룹화한 OFDM 심볼의 갯수만큼 정보 데이터를 줄일 수 있다. 또한 SLM 기법에서 사용한 숫자만큼 스크램블 코드를 사용한다면 기존의 SLM 기법보다 PAPR 성능을 개선할 수 있다.

• The Journal of the Korea Contents Association
• /
• v.8 no.3
• /
• pp.41-46
• /
• 2008

Many methods have been developed to overcome the PAPR(peak-to-average power ratio) problem. Selective mapping(SLM), partial transmit sequence(PTS), subblock phase weighting(SPW) and gradient descent(GD) are used widely to reduce the PAPR. In this paper, we present an effective PAPR reduction method that decreases the number of calculations through Radix-2 DIF IFFT procedure and GD method that transmits selected data sequence. The data sequence is constructed by choosing elements that satisfy threshold value as one part of the sequence and the rest elements of each sequence are chosen to have the lower papr operating, which yields performance improvement.

• Journal of Satellite, Information and Communications
• /
• v.7 no.3
• /
• pp.26-29
• /
• 2012

In this paper, we propose a Single Carrier Frequency Division Multiple Access(SC-FDMA) scheme with greatly enhanced tolerance of timing offset among the users. The type of the proposed scheme is similar to code spread Multiple Carrier Direct Spread Code Division Multiple Access(MC DS CDMA). The proposed scheme performs partial Discrete Fourier Transform(DFT) in order to solve high Peak to Average Power Ratio(PAPR) of the MC DS CDMA before Inverse Fast Fourier Transform(IFFT). Exploiting the property Properly Scrambled Walsh-Hadamard(PSW) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed scheme achieves Multiple Access Interference free performance with the timing offset up to ${\pm}1$ OFDM symbol duration with low PAPR. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset in multipath fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.42 no.4
• /
• pp.739-746
• /
• 2017

Orthogonal frequency division multiplexing(OFDM) systems have many advantages. However, OFDM systems are much affected by a nonlinear distortion because those systems have a high peak to average power ratio(PAPR) value. A selected mapping technology was suggested to reduce a PAPR value. The technology does not have data loss but receivers need side information to know modified phase sequence. Therefore, side information causes decreased a transmission efficiency. In this paper, we suggest a blind SLM receiver using a cross correlation technology. This receiver does not require side information. The proposed blind SLM receiver calculates sums of cross-correlation between transmitted pilot signals multiplied by each phase sequence and received pilot signals. So, this receiver detects side information which has a maximum sum cross-correlation value. We compared our proposed SLM receiver to a conventional blind SLM receiver through bit error rate(BER) and side information error rate(SIER) performances. Simulation results show that the proposed SLM receiver has improved BER and SIER performances than the conventional SLM receiver.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.26 no.12B
• /
• pp.1637-1647
• /
• 2001

Multi-Code CDMA (MC-CDMA) can not only be integrated easily with a conventional system, but also achieve good spectral efficiency and high processing gain. However, it suffers from high value of peak-to-average power ratio (PAPR). In this paper, we propose the Multi-Phase CDMA (MP-CDMA) system that can provide variable rate service and is not susceptible to the non-linear characteristics of amplifier. The clipping is introduced between at the output of multi-code modulator and at the input of MPSK modulator in order to improve the performance of MPSK chip demodulator and reduce the system complexity, The system performances are compared for the different Number of codes and different clipping levels, respectively. The optimum clipping level is also evaluated for the different number of codes in both, AWGN and frequency flat fading channel.