tunnel radio propagation disadvantages

1, Frequency distortion... EM waves gets distorted as there is in visible 3-d propagation

RF propagation models generally characterize two aspect
s of RF
propagation: large scale and small scale fading


Large Scale propagation models predict the mean signal
strength
for a given transmitter and receiver separation distance
and are
used to predict RF coverage


Friis Free Space Path Loss Model


Two Ray Ground Reflection Model


Log Distance Path Loss Model with Shadowing

2. Node Coverage:
Test under the coal mine shows that when the RF
transmitting power is 100mW (maximal transmitting power of 2.4GHz set by the state), it can cover 100–150 m by using omni-directional antenna. But if using
directional antenna, the cover range’s radius can reach 300m in the straight main
tunnel. IEEE 802.15.4 specifies that each device shall be capable of transmitting
at least 1 mW . Typical devices (1mW) are expected to cover a 10–20 m range. As radio propagation along the coalmine tunnel has a strong waveguide
effect, we can confirm that the cover range is at least 10 – 100 m in the coalmine tunnel.