Influence of White LO Noise on Wideband Communication

Applying a spectrally efficient modulation to a wideband signal provides an extremely high data rate potential in millimeter-wave communication. In reality, wideband systems, as reported in open literature, typically suffer from insufficient signal-to-noise ratio (SNR) and thus are not able to support high-order modulation. In a recent experimental study, we have identified that a high noise floor from frequency-multiplied local oscillator (LO) sources is a major data rate limitation in wideband systems. In this paper, we present a detailed study with a mathematical model to describe the influence of the LO noise on a communication signal through frequency conversion. Followed by experimental investigations using multigigabit 64-quadrature amplitude modulation signals, measurements are performed at frequency up- and down-conversions. Both cases show SNR degradation on the frequency-converted signals as the corresponding LO noise floor increases. We provide experimental proof that the nature of the LO noise floor is white, with nearly the same amount of phase and amplitude noises. Various ways to reduce the white LO noise floor through the new hardware design are discussed providing design requirements and considerations.