  For unforeseen natural disasters, such as earthquakes, hurricanes, and
floods, etc., the traditional communication infrastructure is unavailable or
seriously disrupted along with persistent secondary disasters. Under such
circumstances, it is highly demanded to deploy emergency wireless communication
(EWC) networks to restore connectivity in accident/incident areas. The emerging
fifth-generation (5G)/beyond-5G (B5G) wireless communication system, like
unmanned aerial vehicle (UAV) assisted networks and intelligent reflecting
surface (IRS) based communication systems, are expected to be designed or
re-farmed for supporting temporary high quality communications in post-disaster
areas. However, the channel characteristics of post-disaster areas quickly
change as the secondary disaster resulted topographical changes, imposing new
but critical challenges for EWC networks. In this paper, we propose a novel
heterogeneous $\mathcal{F}$ composite fading channel model for EWC networks
which accurately models and characterizes the composite fading channel with
reflectors, path-loss exponent, fading, and shadowing parameters in 5G-UAV
based EWC networks. Based on the model, we develop the optimal power allocation
scheme with the simple closed-form expression and the numerical results based
optimal joint bandwidth-power allocation scheme. We derive the corresponding
capacities and compare the energy efficiency between IRS and traditional relay
based 5G-UAVs. Numerical results show that the new heterogeneous
Fisher-Snedecor $\mathcal{F}$ composite fading channel adapted resource
allocation schemes can achieve higher capacity and energy efficiency than those
of traditional channel model adapted resource allocation schemes, thus
providing better communications service for post-disaster areas.
