PAPR Reduction In Uplink SCMA

Abstract

Sparse Code Multiple Access (SCMA) is a promising non-orthogonal multiple access (NOMA) technique for 5G and beyond which offers massive connectivity and improved spectral efficiency. However, when deployed with OFDM, uplink SCMA signals suffer from a high Peak-to-Average Power Ratio (PAPR), which reduces power amplifier efficiency and limits practical implementation. Addressing this issue is therefore critical for the energy-efficient deployment of SCMA in future wireless networks. The work in dissertation investigates PAPR reduction methods used for OFDM systems and adapts it into SCMA systems. The study starts with a baseline approach using the constellation permutation method of SCMA codebooks by showing that carefully designed permutation patterns can provide measurable reductions in PAPR across different FFT sizes. Two established multicarrier reduction techniques are then integrated with permutation: Tone Reservation (TR) and Partial Transmit Sequence (PTS). Simulation results demonstrate that TR reduces PAPR significantly in the non-permuted baseline. However, it delivers small additional gain when combined with the permutation method. In contrast, PTS provides meaningful higher reductions rates of up to 2 dB compared to permutation method alone, in particular when FFT sizes are larger, highlighting its suitability as a complementary technique. The main contributions this dissertation has done include: (i) proving the efficiency of permutation as a low-complexity PAPR reduction method for SCMA. (ii) recognising that TR works well with SCMA on its own but offers limited benefit when combined with permutation and (iii) validating PTS as a powerful extension that consistently enhances performance. These achievements provide new insights into how codebook-level and signal-level methods interact, paving the way for future research on hybrid strategies, adaptive phase optimization, and hardware implementation in next-generation uplink SCMA systems.