GCD Matrix based PAPR Reduction Technique for OFDM System

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient method of data transmission for high speed communication systems. One of the challenging issues for OFDM system is its high Peak-to-Average Power Ratio (PAPR) which causes inefficient use of the High Power Amplifier (HPA) and could limit transmission efficiency. In this paper we analyze the effects of PAPR on HPA and its reduction technique based on GCD matrix In Selected Mapping (SLM) method. Simulation results shows that the new phase sequence based SLM method has good performance in PAPR reduction. OFDM is a Multi Carrier Modulation (MCM) technique, offers a considerable high spectral efficiency, multipath delay spread tolerance, immunity to the frequency selective fading channels, power efficiency and immune to inter symbol interference (1). These days the OFDM technique is considered as a strong candidate for the Fourth Generation (4G) of mobile communication systems. However, though OFDM has many advantages, still some challenging issues remains unsolved in the design of the system. One of the major problems is high Peak-to-Average Power Ratio (PAPR) of transmitted OFDM signal. These multi carrier systems have a problem that PAPR increases with the increase of the number of sub carriers, which makes the signal peaks moves into the non linear region of the RF power amplifier which causes signal distortion (2). Therefore, the OFDM receiver's detection efficiency is very sensitive to the non linear devices used in its signal processing loop, such as Digital-to- Analog converter (DAC) and high power amplifier, which may severely impair system performance due to induced spectral regrowth and detection efficiency degradation (3). The high peaks of OFDM signal can be reduced in three ways. The fist kind is distribution technique, such as clipping, companding and so on. This kind of technique is simple and intuitionistic, but it's inevitable to cause some performance degradation. The second kind is coding technique. In particular, the use of Golay complementary sequence. In an efficient method to reduce the PAPR for a small number of subcarriers, but it has a drawback that it decreasing the transmission rate significantly for a large number of subcarriers. The third kind is probabilistic technique including selective mapping (SLM) and the partial transmit sequence (PTS)(4).In this paper, firstly, we investigate the effect of PAPR on HPA based on characteristics of the OFDM