Active Constellation Extension based Trellis shaping for Peak-to-Average-Power-Ratio (PAPR) reduction in SISO-OFDM Systems

Abstract

To accomplish the necessity of high data rate, different research groups have proposed different communication technologies. Orthogonal Frequency Division Multiplexing (OFDM) is one of such technologies that has gained admiration and popularity due to its reliable and error-free transmission. OFDM is spectrally effective multicarrier modulation technique for high speed transmission of data through multipath fading channels. However, a major drawback in OFDM is the high dynamic range of the transmit signal, i.e the transmit signal has sporadic high peaks as compared to the mean transmit power. It is expressed as high peak to average power ratio (PAPR), which can significantly degrade the system performance. As most of the electronic devices are peak power limited, thus, passing such a high amplitude signal through the non-linear devices will drive them to work in its non-linear region, resulting in signal clipping. This results in both in-band distortion and out-of-band radiation which degrades the system performance in terms of Bit Error Rate (BER). Different techniques have been proposed to limit these peak excursions. One of such techniques that has been proved to be very efficient in terms of PAPR reduction is Trellis shaping (TS). Trellis shaping has been found capable in terms of PAPR reduction without any increase in the mean power of the transmit signal for moderate computational complexity. Herein, we propose Active Constellation Extension (ACE) based Trellis shaping for PAPR reduction in single input single output (SISO) OFDM systems to further enhance system efficiency in terms of PAPR reduction. Moreover, it has been found in the lite rapture that shaping gain increases with Trellis depth of the shaping code. Therefore, to further improve the system effectiveness, shaping codes of different depths were used as well. The simulation results show that a sizeable PAPR Reduction can be achieved using ACE based TS technique and a gain of almost 2.5 dB can be achieved using 16-state trellis depth of the shaping code. Besides PAPR reduction, a comparative analysis of our proposed system using ACE based TS is carried out with a system without ACE in terms of FER. Simulation results were obtained using hard decision decoding as well as soft decision decoding with BCJR. The simulation results show that our proposed algorithm slightly performs better than the conventional system both for hard decision decoding as well as soft decision decoding.