Time-Varying Rician K-factor in Measured Vehicular Channels at cmWave and mmWave Bands

TL;DR

The paper investigates how time-varying Rician $K$-factors behave in vehicle-to-infrastructure channels across cmWave and mmWave bands in an urban street. It conducts synchronized measurements at $f_c = 3.2$, 34.3, and 62.35 GHz with $B = 155.5$ MHz, applying a MoM-based $K$-factor estimator and a DPSS-tapered delay-domain analysis to extract $K$ and the RMS delay spread $\sigma_{\tau}$. The study finds that $K$-factors evolve similarly across bands, with higher values when LOS components dominate and lower values as diffuse components rise, and that $\sigma_{\tau}$ exhibits an inverse relationship with $K$, with the correlation $\rho$ being negative and increasing in magnitude at higher frequencies. The results, including their alignment with 3GPP urban micro benchmarks, provide practical guidance for fading mitigation and adaptive transmission strategies in multi-band vehicular systems, informing design choices for both cmWave and mmWave deployments in dynamic V2I environments.

Abstract

Future vehicular communication systems will integrate millimeter wave (mmWave) technology to enhance data transmission rates. To investigate the propagation effects and small-scale fading differences between mmWave and conventional centimeter wave (cmWave) bands, multi-band channel measurements have to be conducted. One key parameter to characterize small-scale fading is the Rician K-factor. In this paper, we analyze the time-varying K-factor of vehicle-to-infrastructure (V2I) channels across multiple frequency bands, measured in an urban street environment. Specifically, we investigate three frequency bands with center frequencies of 3.2 GHz, 34.3 GHz and 62.35 GHz using measurement data with 155.5 MHz bandwidth and a sounding repetition rate of 31.25 μs. Furthermore, we analyze the relationship between K-factor and root-mean-square (RMS) delay spread. We show that the Ricean K-factor is similar at different frequency bands and that is correlated with the RMS delay spread.

Figures (6)

• Figure 1: Transmit antennas (left) are mounted on the roof of a car (middle). Receive antennas (right) are mounted on a pole of a tripod.
• Figure 2: A car approaches an intersection and stops. The directional receive antennas are pointed towards the intersection.
• Figure 3: The $K$-factor varies over time and exhibits a similar temporal trend for both CMW and MMW bands.
• Figure 4: The RMS delay spread varies over time and shows a clear relationship to the $K$-factor.
• Figure 5: In the three frequency bands, the CDF of the $K$ factor shows similar behavior.