A Multidimensional Structural Channel Similarity Index Measure Across Multiple Frequencies

To meet the required coverage and data rate demands of next-generation mobile communications, the coexistence of multiple radio frequency systems operating in well-separated frequency bands in precisely identified scenarios will be exploited in the long term. In this context, it is necessary to investigate frequency-dependent and environment-dependent channel characteristics by exploring the spatial and temporal correlations of multipath channels across different frequency bands and different environments. Traditional evaluation indexes, such as channel parameters and correlation coefficients, either do not enable direct derivation of the relationship between two channels or can only be evaluated from a certain dimension mathematically. Here, by combining large-scale and small-scale channel characteristics, a channel similarity index measure (CSIM) is proposed. This structural similarity index comprehensively considers several multipath parameters of two different channels, including amplitude, phase, delay, angle of arrival (AoA), and angle of departure (AoD). The results of ray tracing simulations and field measurement campaigns conducted across both centimeter wave (cmWave) and millimeter wave (mmWave) bands in typical indoor and outdoor scenarios verify that the proposed CSIM can effectively measure similarity from specific dimensions. Moreover, the statistical distributions of the CSIM, which reflect the similarities between channels of different frequencies, are also presented.