Stochastic Analysis of Two-Tier HetNets Employing LTE and WiFi

In order to increase the capacity of mobile networks, operators are investigating the use of unlicensed spectrum in addition to their licensed spectrum. Already today it is possible to integrate WiFi networks into the core networks and perform offloading of traffic to a WiFi network. In future releases of 3GPP a tighter interaction of WiFi and LTE is foreseen that will even enable the aggregation of these two technologies. The design and performance analysis of different offloading and aggregation strategies is a difficult task, because of the different radio access technologies (RAT) involved. One widely used tool for the analysis of such systems is stochastic geometry, but most existing works do not take the heterogeneity of the different RATs into account. This work models the LTE and WiFi networks as well as the users using a probabilistic approach based on stochastic geometry and takes the particular physical layer properties of the two RATs into account. The proposed model allows for the performance analysis of those different networks using closed form expressions. Using these newly developed tools, we show that the max-throughput criterion, which takes the different characteristics of the two RATs into account, performs better than simple offloading and max-SINR association criteria.