# Data-Driven Analysis of Outdoor-to-Indoor Propagation for 5G Mid-Band Operational Networks
## 2 Background, Related Work, and Contributions
### Contributions and Innovation  
The present paper provides an empirical investigation of channel characteristics for 5G systems operating in Band n78, focusing on outdoor-to-indoor propagation. The contributions of this paper can be summarized as follows:  
* An extensive set of measurements collected in an indoor environment in the city of Rome, Italy is analyzed, covering two 5G networks under deployment by two network operators. A passive channel measurement approach was used. The standardized downlink reference signals of a commercial 5G network were collected and used for extracting the channel impulse responses. The channel propagation characterization was performed based on the actual configurations applied in a commercial 5G deployed network, including the carrier frequency, bandwidth, antenna, beam-based transmission, etc. * Channel propagation characterization is presented for two different deployed networks, i.e., single Wide-beam and multiple SSB based 5G networks. Multipath components were extracted from measurements and used to carry out a comprehensive study of time and power-related channel parameters for different measurements locations and operators. The number of paths, interarrival times between paths, RMS delay spread, and mean excess delay are evaluated on the collected channel measurements in order to characterize time-related channel aspects. In contrast, MPC power attenuation, path loss, and Rician K-factor are studied in order to characterize power-related aspects. * The channel parameters' dependencies are also studied. A comprehensive correlation analysis between the aforementioned channel parameters is carried out in order to highlight and quantify the correlation between heterogeneous propagation parameters. Three main innovative elements can be highlighted when comparing the present work with the existing literature reviewed above: (a) Existing studies on channel characterization and analysis at 3.5 GHz were commonly based on measurements executed on dedicated, mostly single-link testbeds. In this paper, channel characterization and analysis are instead performed on measurements executed _in the wild_, i.e., on real 5G network deployments. This allows to derive useful insights on the indoor coverage provided by commercial 5G networks, moving towards the design and implementation of reliable and high-performing 5G systems; (b) Channel propagation characterization is presented for two different beam strategies, i.e., single Wide-beam and multiple SSB-based 5G networks. To the best of our knowledge, this is the first work presenting a comparison of channel propagation properties between a single SSB and multiple SSB-based 5G networks, since it is very hard to replicate a 3 GPP standard-compliant multiple SSB-based network in a laboratory setup; (c) Existing literature did not provide a complete correlation analysis of all channel characterizing parameters. This paper instead presents a comprehensive correlation analysis by considering all channel parameters evaluated on the collected measurements. To summarize, this is the first work characterizing outdoor-to-indoor propagation based on commercial 5G systems, providing a comparison between a single Wide-beam \begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|} \hline \multirow{2}{*}{**Ref.**} & **Propagation** & \multicolumn{5}{c|}{**Characterized Channel Propagation Parameters**} \\ \cline{2-7}  & **Scenario** & & **RMS Delay** & **Mean Excess Delay** & **Pathloss** & **K-Factor** & **Correlation of Parameters** \\ \hline  
*This Work** & **outdoor-to-indoor** & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison between the proposed work and existing literature analyzed in Section 2.3. Note that works in [24; 38] do not address specific analyses of propagation parameters. However, we report them in the table for completeness, since they discuss relevant aspects related to outdoor-to-indoor propagation (e.g., building penetration and channel matrix model).