SLM-PTS 결합기법을 적용한 OFDM 시스템의 PAPR 성능개선에 관한 연구

Abstract

In recent years, there has been a need for high-speed and high-quality services including voice, image, and other various multimedia signals applied to wireless communication systems. It is well-known that OFDM scheme has better characteristics in transmission rate, power efficiency, bandwidth efficiency, impulse-noise immunity, and narrow band interference immunity etc. in comparison with other conventional schemes. OFDM scheme, with great efficiency splits data into orthogonal narrow band sub-carriers to overcome ISI caused by multipath fading in wireless broadband high-speed transmission environments.

However, various interferences between sub-channels and higher PAPR can easily occur when data is transmitted via parallel means via many sub-carriers. High PAPR causes some serious non-linear distortion and degrades performance of the communication system.

Therefore, various methods reducing PAPR of OFDM scheme such as the clipping method, block coding method, and phase rotation method etc. have been proposed. However, these methods cause in-band interference and degrade the signal quality. Moreover, the amount of calculation is exponentially increased according to the number of sub-carriers and additional error with time-delay can occur because of side information. As a result of these defects, it is difficult to apply these conventional methods to real-time high-speed transmission systems.

In this dissertation, we propose a high-speed adaptive PTS method which eliminates high PAPR and we compare the proposed method with other conventional methods. In addition, we have designed a combined type SLM-PTS scheme to reduce PAPR and evaluate the performance. The system used for evaluating PAPR performance can be constructed as COFDM applying ETD-Turbo coding scheme and adaptive interleaver.

All the analyses in this dissertation are focused on the system characteristics according to IFFT's point and modulation method and the performance evaluation are based on the PAPR reduction rates. As a result, the SLM-PTS combination method reveals good PAPR reduction rate and remarkable reduction in the amount of calculations. Especially, in the case of combine-3 scheme, we can achieve approximately 3.7~3.9 [dB] PAPR reduction on a basis of 10-5 BER level. Moreover, we can eliminate the side information in COFDM system because of its adaptive characteristics in evaluating PAPR reduction rate, so that the additional errors can be omitted.

The result of performance evaluation applying the modulation methods shows that M-ary QAM method reveals good quality, and the 16-QAM gives the best performance.

Based on the results of these performance evaluations, the proposed method does not increase the amount of calculation when it is applied to OFDM system. On the other hand, it reveals a high PAPR reduction efficiency with improving the transmission efficiency of OFDM system. In addition, it improves a processing rate because it does not use the side information. It is expected that the proposed scheme can be used in the next generation high-speed digital transmission systems.