WLAN has proven itself as the most economical wireless access technology over the time. Its widespread deployment encouraged 3GPP (3rd Generation Partnership Project) to standardize the integration of such non-3GPP access technologies into the existing 3GPP access networks. This opened the door of numerous opportunities for network operators to make use of the economical bandwidth from WLAN in enhancing the end user Quality of Experience (QoE). 3GPP leaves it up to the network operators to do their own research and devise their individual algorithms for this purpose. This raises the need for a proper simulation environment supporting a heterogeneous network of access technologies interconnected according to 3GPP specifications. The goal of this work is to develop a network simulator where 4G LTE (Long Term Evolution) and WLAN co-exist. In addition to standard 3GPP network entities and protocols the simulator also provides other features like multi-homing support, user QoE optimization algorithm as well as network bandwidth resource management techniques.