This paper presents a wireless network performance study of a modified TCP/IP protocol stack with a network coding layer inserted between the transport and the network layer. The simulation was performed with the OPNET simulation tool and considered a heterogeneous wireless environment where a mobile device could connect to both LTE (Long Term Evolution) and WLAN (wireless LAN) networks. We simulate various user-network association policies in such an environment with the goal of usage cost optimization under a Quality of Service (QoS) constraint. The results show that using a threshold-based online policy the network usage cost can be reduced significantly while remaining within the user’s QoS requirements.