This industry research brief explains why underground GPS and radio coverage is a signal-distribution problem rather than a signal-strength issue, primarily due to line-of-sight limitations. It details how RF-over-fiber (RFoF) solutions solve this, and provides evaluation criteria such as matching frequency bands (2.5, 4, and 6 GHz), managing noise figures (down to 10 dB) and dynamic range, and implementing remote monitoring from the surface.