Feasibility of DFT-s-OFDM in 6G Downlink: Coverage and Energy-Efficiency Assessment

The future 6G mobile communication systems are expected not only to improve the broadband connectivity and other services but also enhance the network coverage, energy-efficiency and sustainability. In this paper, we address the coverage and energy-efficiency challenges, and study the feasibility of discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) as the potential downlink physical-layer radio access waveform. Building on the prevailing 5G New Radio (NR) downlink transmit signal quality requirements and behavior of contemporary power amplifier (PA) systems, we assess and show the available downlink coverage gain and energy saving potential, compared to ordinary cyclic prefix (CP) OFDM. The obtained results show that DFT-s-OFDM allows improving the downlink coverage by up to 20%, with largest gains available for low modulation orders. The results also show that truly saving energy for a given throughput requirement is more difficult – yet possible, assuming that the PA bias and supply voltages can be properly controlled during the downlink transmission.