LTE-Heterogeneous Networks (HetNets) with dense deployment of small cells are expected to effectively meet unprecedented ever increasing data traffic demands and offer improved coverage in indoor environments. However, HetNets are raising major issues to Mobile Network Operators (MNOs) such as complex distributed control plane management and increased energy costs. Hence, MNOs are looking for flexible software defined mobile architectures to reduce their capital expenditure (CAPEX) and operational expenditure (OPEX). In this work, in order to reduce energy costs of the HetNets, we propose an interference and QoS aware cell switch-off strategy (IQ-CSOS) on a software defined LTE Radio Access Network (SD-LTE-RAN) framework. Unlike existing CSOSs, IQ-CSOS investigates both network energy costs and QoS satisfaction of sessions during CSOS decisions. In performance evaluation under various test scenarios, it is found that IQ-CSOS is able to provide 50–80% of network energy savings. Besides, it is able to provide 30% more energy savings compared to existing CSOSs with slight affect on network QoS. © 2018 Elsevier Ltd