  Energy efficiency (EE) is a major performance metric for fifth generation
(5G) and beyond 5G (B5G) wireless communication systems, especially for ultra
dense networks. This paper proposes an end-to-end (e2e) power consumption model
and studies the energy efficiency for a heterogeneous B5G cellular architecture
that separates the indoor and outdoor communication scenarios in ultra dense
networks. In this work, massive multiple-input-multiple-output (MIMO)
technologies at conventional sub-6 GHz frequencies are used for long-distance
outdoor communications. Light-Fidelity (LiFi) and millimeter wave (mmWave)
technologies are deployed to provide a high data rate service to indoor users.
Whereas, in the referenced nonseparated system, the indoor users communicate
with the outdoor massive MIMO macro base station directly. The performance of
these two systems are evaluated and compared in terms of the total power
consumption and energy efficiency. The results show that the network
architecture which separates indoor and outdoor communication can support a
higher data rate transmission for less energy consumption, compared to
non-separate communication scenario. In addition, the results show that
deploying LiFi and mmWave IAPs can enable users to transmit at a higher data
rate and further improve the EE.
