  This paper investigates the effect of oscillator phase noise and channel
variations due to fading on the performance of communication systems at
frequency bands higher than 10GHz. Phase noise and channel models are reviewed
and technology-dependent bounds on the phase noise quality of radio oscillators
are presented. Our study shows that, in general, both channel variations and
phase noise can have severe effects on the system performance at high
frequencies. Importantly, their relative severity depends on the application
scenario and system parameters such as center frequency and bandwidth. Channel
variations are seen to be more severe than phase noise when the relative
velocity between the transmitter and receiver is high. On the other hand,
performance degradation due to phase noise can be more severe when the center
frequency is increased and the bandwidth is kept a constant, or when
oscillators based on low power CMOS technology are used, as opposed to high
power GaN HEMT based oscillators.
