Cost of Increased Bandwidth Efficiency in 5G NR

Abstract

In this paper, subband filtered CP-OFDM and windowed CP-OFDM waveforms proposed for 5G new radio (NR) are compared to LTE-like downlink and uplink waveforms under different power amplifier (PA) models. The effects of subband filtering or windowing are evaluated in terms of out-of-band and inband emissions, average error vector magnitude (EVM) and maximum uplink PA output power when increasing the bandwidth efficiency from 90% to 97.2%. The evaluations include recently proposed PA models by 3GPP TSG-RAN WG1 for downlink and uplink. It is shown that the cost of increased bandwidth efficiency in fullband downlink transmission is mainly complexity increase required by the steeper channelization filter. On the other hand, the increased EVM caused by channel filter induced inter-symbol-interference may limit the usability of modulation 256-QAM and above. In uplink with fullband transmission using 64-QAM modulation, the spectral containment is not an issue because the required backoff with highly non-linear PA model limits the Tx power to a very low level independently of the maximum allocation size. In the 1 PRB uplink, increased bandwidth utilization decreases the maximum PA output power while increased backoff improves the inband ACLR.