Impact of Water Vapor and Droplet on PS-LTE Communication in Indoor Fire-Fighting Scenarios

In an indoor fire-fighting environment, water jets from fire hoses generate steam and water droplets due to heat and moisture, potentially affecting firefighters’ wireless communication using Public Safety Long-Term Evolution (PS-LTE). This study examines key environmental factors, including indoor vapor temperature, humidity variations, and water accumulation on wireless terminals, to assess their impact on communication. For the PS-LTE band (700–800 MHz), a dipole antenna (linear polarization) and a spiral antenna (circular polarization) were used, while a horn antenna was employed in the Ka-band (27–40 GHz) to evaluate transmission (S21) under varying vapor temperature and humidity conditions. Results indicate that vapor temperature and humidity have minimal impact on transmission. A key focus is the effect of water droplets accumulating on the antenna housing of wireless terminals. Communication performance under light and heavy rain conditions was analyzed using a monopole antenna from a real PS-LTE terminal (VM65PS). Findings reveal that water accumulation shifts the reflection coefficient slightly to lower frequencies due to water’s permittivity. Antenna efficiency, initially 82% under standard conditions, decreases to 58% in light rain and 21% in heavy rain. This study demonstrates that while water vapor does not significantly impact wireless communication in fire scenarios, water accumulation on wireless terminal surfaces degrades antenna performance and transmission efficiency.