  This paper presents a simple and effective method to study the spectral and
energy efficiency (SE-EE) trade-off in cellular networks, an issue that has
attracted significant recent interest in the wireless community. The proposed
theoretical framework is based on an optimal radio resource allocation of
transmit power and bandwidth for the downlink direction, applicable for an
orthogonal cellular network. The analysis is initially focused on a single cell
scenario, for which in addition to the solution of the main SE-EE optimization
problem, it is proved that a traffic repartition scheme can also be adopted as
a way to simplify this approach. By exploiting this interesting result along
with properties of stochastic geometry, this work is extended to a more
challenging multi-cell environment, where interference is shown to play an
essential role and for this reason several interference reduction techniques
are investigated. Special attention is also given to the case of low signal to
noise ratio (SNR) and a way to evaluate the upper bound on EE in this regime is
provided. This methodology leads to tractable analytical results under certain
common channel properties, and thus allows the study of various models without
the need for demanding system-level simulations.
