Enhanced Uplink Coverage for 5G NR: Frequency-Domain Spectral Shaping with Spectral Extension

Abstract

This paper describes and investigates a novel concept of frequency-domain spectral shaping (FDSS) with spectral extension for the uplink (UL) coverage enhancement in 5G New Radio (NR), building on discrete Fourier transform spread orthogonal frequency-domain multiplexing (DFT-s-OFDM). The considered FDSS concept is shown to have large potential for reducing the peak-to-average-power ratio (PAPR) of the signal, which directly impacts the feasible maximum transmit power under practical nonlinear power amplifiers (PAs) while still meeting the radio frequency (RF) emission requirements imposed by the regulations. To this end, the FDSS scheme with spectral extension is formulated, defining filter windows that fit to the 5G NR spectral flatness requirements. The PAPR reduction capabilities and the corresponding maximum achievable transmit powers are evaluated for a variety of bandwidth allocations in the supported 5G NR frequency ranges 1 and 2 (FR1 and FR2) and compared to those of the currently supported waveforms in 5G NR, particularly π/2-BPSK with FDSS without spectral extension and QPSK without FDSS. Furthermore, an efficient receiver structure capable of reducing the noise enhancement in the equalization phase is proposed. Finally, by evaluating the link-level performance, together with the transmit power gain, the overall coverage enhancement gains of the method are analyzed and provided. The obtained results show that the spectrally-extended FDSS method is a very efficient solution to improve the 5G NR UL coverage clearly outperforming the state-of-the-art, while being also simple in terms of computational complexity such that the method is implementation feasible in practical 5G NR terminals.