Propagation Channel Measurements for Indoor-to-Outdoor Communications for Device-to-Device Public Safety Applications

Recent interest in Device-to-Device (D2D) communication systems, particularly by Public Safety Organizations (PSOs), arises from scenarios where no infrastructure is available. One notable scenario is Indoor-to-Outdoor (I2O), where emergency responders inside buildings communicate with command posts on the street. We aim to understand the propagation channel for designing wireless systems in such contexts. We report findings from a comprehensive measurement campaign in the public safety frequency band near 800 MHz, assessing multiple-input-multiple-output (MIMO) channels between users across five floors of a California office building and a multi-antenna base station at street level. This study provides insights as well as statistical channel models for pathgain, delay spread, angular spreads, and power distribution among Multi-Path Components (MPCs) and their dependence on indoor-user height. In Line-of-Sight (LoS) scenarios, 10 dB pathgain variation was observed between ground and the 5th floor, while Non-Line-Of-Sight (NLoS) cases showed no such variation. Delay spreads exhibited a similar trend in LoS scenarios, with a 10 ns variation based on RX height, while NLoS scenarios remained heightindependent. Angular spreads were consistently large for indoor units, regardless of height. Analysis of the probability density function of the MPC powers using a 5D κ parameter revealed approximately 8 dB for LoS scenarios and −1 dB for NLoS scenarios, assuming beamforming for maximum received power.