Multipath Cluster Fading Statistics and Modeling in Millimeter-Wave Radio Channels

The second-order statistics of indoor directional channels are investigated using millimeter-wave (mmWave) band (30.4–37.1 GHz) ultrawideband (UWB) channel measurements. Considering two main mmWave system assumptions (high bandwidth and high beamforming gain), this paper aims to investigate the validity of the Rayleigh–Rice fading models for the cluster fading envelope. The results from the mmWave band study are compared to an already well-studied lower frequency FCC band (3.4–10.1 GHz). During the measurements, only selective objects (emulated multipath clusters in the propagation channel) are illuminated in a small lecture room. The experiments show that for both UWB channels, the complex received (Rx) signal is a circularly symmetric non-Gaussian random variable with highly correlated inphase (I) and quadrature (Q) components. These properties demonstrate that the intracluster multipath components (MPCs) structure is sparse. Consequently, modeling the cluster fading envelope with Rayleigh–Rice distribution is not realistic. Therefore, the sum-of-cisoids principle is used for intracluster multipath modeling which inherently considers a correlation between I and Q components. It has been established that a reasonably good approximation of the cluster fading envelope can be obtained with $N=3-6$ equal amplitude cisoids. However, we remark that Rayleigh–Rice models may become realistic cluster fading envelopes for narrowband mmWave systems.