Impact of intra- and inter-RAT offloading on the spectrum/energy efficiency of HetNets

This paper addresses the problem of simultaneously achieving high spectral efficiency (SE) and energy efficiency (EE) in the heterogeneous radio access technology (RAT) environment via biased intra- and inter-RAT offloading. An analytical framework is developed for investigating the SE and EE performance of a two-RAT heterogeneous network (HetNet), based on which it is shown that the feasibility of increasing the SE and EE via offloading is strongly dependent on the load level and the biased offloading factors. For jointly maximizing the SE and EE, a multi-objective optimization problem subject to quality of service (QoS) constraints is formulated and solved to give the Pareto optimal operational regime in terms of the network parameters. Following this, the constrained Pareto regime is used to quantify the tradeoff between SE and EE as an opportunity cost measure. By opportunistically adapting the small cell BS density and biased offloading factors to the load conditions, we numerically show the range of load values that achieves a good balance in the SE-EE tradeoff while satisfying the specified users´ QoS requirements.