PAPR Reduction with Pre-chirp Selection for Affine Frequency Division Multiplexing

TL;DR

This paper addresses high $PAPR$ in AFDM, a high-mobility multicarrier scheme based on $DAFT$, by introducing grouped pre-chirp selection ($GPS$). GPS partitions subcarriers into groups, assigns group-specific pre-chirp values from carefully chosen sets, and selects the signal with the lowest $PAPR$ among candidates, with an optimal exhaustive variant and a low-complexity non-enumerated variant. The analysis covers $PAPR$, complexity, spectral efficiency, and BER, showing significant $PAPR$ benefits with modest BER/spectral efficiency trade-offs; GPS can outperform OTFS in $PAPR$ while preserving AFDM’s lower modulation complexity. Practical gains are demonstrated via simulations for 16QAM, revealing near-competitive BER with small SNR loss and high spectral efficiency, validating GPS as a viable method for $PAPR$ reduction in high-mobility communications.

Abstract

Affine frequency division multiplexing (AFDM) is a promising new multicarrier technique for high-mobility communications based on discrete affine Fourier transform (DAFT). By properly tuning two parameters in the DAFT module, the effective channel in the DAFT domain can completely circumvent path overlap, thereby constituting a full representation of delay-Doppler profile. However, AFDM has a crucial problem of high peak-to-average power ratio (PAPR), stemming from randomness of modulated symbols. To reduce the PAPR of AFDM, a novel algorithm named grouped pre-chirp selection (GPS) is proposed in this letter. The GPS varying the pre-chirp parameter across subcarrier groups in a non-enumerated manner and then selects the signal with the smallest PAPR among all candidate signals. We detail the operational procedures of the GPS algorithm, analyzing GPS from four aspects: PAPR performance, computational complexity, spectral efficiency, and bit error rate (BER) performance. Simulations indicate the effectiveness of the proposed GPS in reducing PAPR. At the cost of slight communication performance, AFDM with GPS can achieve better PAPR performance than orthogonal time frequency space (OTFS) while maintaining a lower modulation complexity.

Figures (5)

• Figure 1: AFDM block diagram.
• Figure 2: AFDM with GPS block diagram.
• Figure 3: PAPR performance of 16QAM AFDM with GPS.
• Figure 4: PAPR performance of 16QAM AFDM with GPS, enumerated algorithm, and OTFS.
• Figure 5: BER performance of 16QAM AFDM with GPS.