Optimized LDPC code concatenated with Trellis shaping for PAPR reduction in OFDM systems

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) systems are time and again incorporated in modern high-speed communication networks due to an increase in demand of reliable and error-free data transmission. OFDM is a propitious technique for efficient and reliable data transmission. Having said that,one major issue in OFDM systems is its signal’s high dynamic range expressed as the peak to average power ratio (PAPR). In case the signal peaks are found higher than the linear operating range of the non-linear device they are passing through, these peaks are clipped off resulting both in-band distortion and out-of-band radiation. Clipping and Filtering, Tone Reservation (TR), Selected Mapping (SLM), Partial Transmit Sequences (PTS), Tone Injection (TI), Active Constellation Expansion (ACE) and Trellis Shaping (TS) are some of the procedures used for PAPR reduction, everyone with their own pros and cons. However, TS has been found efficient in terms of PAPR reduction without any increase in the mean power of the transmit signal for moderate computational complexity. To further improve the system performance, herein, we propose TS using shaping codes of higher depths. Using shaping codes of higher depths improve the PAPR reduction as well the BER of the system. Moreover, we concatenate an optimized LDPC code with Trellis shaping. For the LDPC code, the variable node degree distribution is optimized based on the error probabilities of the individual bits inside a QAM constellation along with the error probabilities of the shaping code used. Simulation results show that the proposed technique has better PAPR reduction as well better BER as compared to the already existing systems using Trellis shaping with a shaping code of 4 states concatenated with an optimized LDPC code.