  A Heterogeneous Network (HetNet) comprises of multiple Radio Access
Technologies (RATs) allowing a user to associate with a specific RAT and steer
to other RATs in a seamless manner. To cope up with the unprecedented growth of
data traffic, mobile data can be offloaded to Wireless Fidelity (WiFi) in a
Long Term Evolution (LTE) based HetNet. In this paper, an optimal RAT selection
problem is considered to maximize the total system throughput in an LTE-WiFi
system with offload capability. Another formulation is also developed where
maximizing the total system throughput is subject to a constraint on the voice
user blocking probability. It is proved that the optimal policies for the
association and offloading of voice/data users contain threshold structures.
Based on the threshold structures, we propose algorithms for the association
and offloading of users in LTE-WiFi HetNet. Simulation results are presented to
demonstrate the voice user blocking probability and the total system throughput
performance of the proposed algorithms in comparison to another benchmark
algorithm.
