An Empirical Intracluster Power Factor Model for Sparsity Property Based on New Mid-Band MIMO Channel Measurements

The channel sparsity is crucial for the design and application of new mid-band and multiple-input–multiple-output (MIMO) systems. However, the 3rd Generation Partnership Project (3GPP) model fails to accurately characterize channel sparsity, as indicated by the constant cluster number across 0.5 GHz to 100 GHz, which leads to significant system overhead and increased redundancy. While the intracluster power factor (ICP) can enhance the characterization of sparsity to some extent, existing models treat the ICP as a constant across all clusters. This does not reflect the propagation behavior of dominant rays in real channels, resulting in excessive redundancy or inadequate resource allocation in system design. Therefore, this letter investigates the ICP distribution and proposes an empirical ICP model based on MIMO channel measurements at the new mid-band. First, MIMO ($128\times 64$) channel measurements are conducted at 6 GHz and 13 GHz in an urban macro scenario. Second, channel sparsity and ICP values across different clusters are analyzed, revealing that the ICP values vary in different clusters. Third, the ICP is modeled as a function of cluster delay and delay spread. Incorporating the ICP model into the 3GPP model is found to reduce the error in channel sparsity characterization to 0.01 compared to the existing model, as verified through simulations under the 50$\%$ case at 13 GHz. This letter provides empirical data and sparsity modeling theory for the standardization of 6G channel modeling.