  Heterogeneous networks have emerged as a popular solution for accommodating
the growing number of connected devices and increasing traffic demands in
cellular networks. While offering broader coverage, higher capacity, and lower
latency, the escalating energy consumption poses sustainability challenges. In
this paper a novel optimization approach for OFDMA heterogeneous networks is
proposed to minimize transmission power while respecting individual users
throughput constraints. The problem is formulated as a mixed integer geometric
program, and optimizes at once multiple system variables such as user
association, working bandwidth, and base stations transmission powers.
Crucially, the proposed approach becomes a convex optimization problem when
user-base station associations are provided. Evaluations in multiple realistic
scenarios from the production mobile network of a major European operator and
based on precise channel gains and throughput requirements from measured data
validate the effectiveness of the proposed approach. Overall, our original
solution paves the road for greener connectivity by reducing the energy
footprint of heterogeneous mobile networks, hence fostering more sustainable
communication systems.
