The Performance of WiFi Offload in LTE Networks

Abstract: Currently, cellular networks are overloaded with mobile data traffic due to the rapid growth of mobile broadband subscriptions. The combination of Smartphones such as iPhones, netbooks and 3G/4G mobile networks are rapidly growing in very large numbers and as a result, this has created an exceptional demand for ubiquitous connectivity and quality of rich digital content and applications. To meet the requirements of future data-rich applications and terminals with improved multimedia, future wireless networks are expected to combine multiple access technologies and as a result mobile broadband operators are including WLANs like WiFi as an alternative access network technology. This enables solutions to offload traffic from the primary access technology to the WiFi access when applicable so as to provide extra capacity and improve overall performance. By offloading, it means that using alternative network technologies for delivering data originally targeted for e.g. cellular networks when it becomes saturated.

The main objective of this thesis work is to address solutions for WiFi offloading in LTE networks when performance needs exceeds the capability of the LTE access. Novel offloading algorithms are proposed and implemented, that decides when to move flow(s) between LTE and WiFi access networks. These offloading algorithms should be evaluated and compared to steer WiFi offloading to increase the combined network performance of LTE and WiFi access technologies connected to the evolved packet core (EPC) with at least the baseline case of having all the traffic in LTE. Understanding how these techniques fit into the existing standards is part of the scope of the work. With the models and assumptions used, our simulation results of LTE and IEEE 802.11a indicates that when we have a smaller LTE Inter Site Distance it is always best to stay connected to LTE. Whereas when we set the LTE Inter Site Distance to a larger value, it is always best to connect to WiFi and in this case users can benefit from being offloaded to the available WiFi access networks. Further, our evaluations have demonstrated that offloading users from LTE to WiFi reduces demand on the LTE network without affecting user performance.

This thesis proposes an optimized SNR-threshold based handover solution and extension to the 3GPP standard for Access Network Discovery and Selection Function (ANDSF) discovery that can be used for WiFi offloading.