  In this paper, the potential of extending 5G New Radio physical layer
solutions to support communications in sub-THz frequencies is studied. More
specifically, we introduce the status of third generation partnership project
studies related to operation on frequencies beyond 52.6 GHz and note also the
recent proposal on spectrum horizons provided by federal communications
commission (FCC) related to experimental licenses on 95 GHz - 3 THz frequency
band. Then, we review the power amplifier (PA) efficiency and output power
challenge together with the increased phase noise (PN) distortion effect in
terms of the supported waveforms. As a practical example on the waveform and
numerology design from the perspective of the PN robustness, link performance
results using 90 GHz carrier frequency are provided. The numerical results
demonstrate that new, higher subcarrier spacings are required to support high
throughput, which requires larger changes in the physical layer design. It is
also observed that new phase-tracking reference signal designs are required to
make the system robust against PN. The results illustrate that single-carrier
frequency division multiple access is significantly more robust against PN and
can provide clearly larger PA output power than cyclic-prefix orthogonal
frequency division multiplexing, and is therefore a highly potential waveform
for sub-THz communications.
