Bridging FR1 to FR3: Urban Channel Parameterization Anchored at 4.85 GHz and Literature-Referenced Cross-Band Trends

The transition from 5G to 6G requires frequency-dependent, physically consistent radio channel models across the FR1--FR3 span, particularly in the under-explored $4$--$8$~GHz region targeted in the current WRC-$27$ studies, where outdoor urban channel measurements and parameterizations remain scarce. This paper presents a $4.85$~GHz measurement-anchored study of urban channels and a literature-referenced cross-band analysis. Double-directional measurements were conducted at $4.85$~GHz in urban macrocell (UMa) and urban microcell (UMi) routes in Yokohama, Japan, from which path loss, delay spread (DS), azimuth spread of arrival/departure (ASA/ASD), $K$-factor, and route-dependent spatial-consistency statistics were extracted. To align these results in a broader cross-band context, the measured $4.85$~GHz large-scale parameter (LSP) means were combined with scenario-matched literature anchors to derive log-log trends for DS, ASA, and ASD over an approximately $4$--$28$~GHz range that spans the $7.125$~GHz FR1--FR3 boundary. The resulting trends were compared with 3GPP UMa/UMi reference parameterizations over the same interval. Because the cross-band analysis relies on a single in-house measurement band and a limited number of heterogeneous literature anchors, it is presented as measurement-informed and indicative, rather than as a definitive multi-band model. The paper therefore contributes both a detailed, parameterized $4.85$~GHz urban measurement reference and a bounded literature-referenced cross-band view of channel behavior near the FR1--FR3 transition.