Implementation of LTE/WiFi link aggregation with very tight coupling

The tremendous increase of mobile data traffic pushes operators to find quick and efficient solutions in order to avoid an overload on their networks. Using WiFi to offload a part of the traffic is interesting for the operators as they can take advantage of the unlicensed bands and high bit rates. Moreover, thanks to the convergence of fixed and cellular networks, it is possible to connect WiFi access points to the LTE eNodeBs in order to have Very Tight Coupling between LTE and WiFi. Thus, the different flows are merged at the link layer (i.e. PDCP) and share the same IP instance. This allows the terminal to have a unique IP address, ensuring a seamless experience when using WiFi and LTE simultaneously. However, both networks can have different delays. In this paper, we investigate the impact of such differences in the delay by means of a real implementation of very tight coupling on an open test bed. We show that aggregation of LTE and WiFi is beneficial only when the delays are similar.