# Interference Management in Femtocells by the Adaptive Network Sensing Power Control Technique
## 1 Introduction  
The exponentially increasing demand for high data rate and capacity in mobile communications has created a real challenge for wireless communication network operators, as a large percentage of indoor users suffer from a poor quality of service (QoS) [1]. The current mobile system should be equipped to cope with these demands. The third-generation partnership project long-term evolution-advance (3 GPP-LTE-A) is a promising technology in this regard, whose objective is to increase spectral efficiency, coverage, capacity and offload traffic from the macrocell. LTE-A is a progressively evolving technology that adapted generic and novel technologies of orthogonal frequency division multiplexing (OFDM) and multiple input, multiple output (MIMO), in order to accomplish future demands [2]. The overlay integration of low-power femtocells over MIMO in a heterogeneous network (HetNet) is widely discussed [3] as a feature that will achieve the expected user-demand in terms of coverage, data rate, capacity and quality. The femtocell is a short-range wireless access point, also called femto access point (FAP), which is linked to broadband Internet backhaul and uses the licensed frequency spectrum. Femtocells are specifically developed for an indoor environment (i.e., home, schools, airports and offices) to increase coverage area and to provide a higher data rate [4]. It has been predicted that, in the near future, the origination of indoor data and voice traffic will be increased by up to 90% and 60% respectively [5]. The two-tier, macro-femto heterogeneous system, where the primary system is the macro base station (MBS also called eNB) and the secondary system, represented by the user-installed femtocell(HeNB), ignore their mutual presence, while both systems work in a frequency reuse fashion [6]. In such an operating scenario, the downlink (DL) transmission of HeNB causes inter-cell interference for the cell-edge macro user. The deployment of the femtocell in HetNets plays a significant part in causing interference in the MUE (Macro User Equipment). The user-deployed, low-power femtocell has no coordination with the macrocell and it is not controlled by the operator. When the deployment of the femtocell is inadequate and in ad-hoc style and users can change the position from one place to another, this can drastically degrade the performance of the whole system and cause interference with the nearby MUE. The interference is crucial in MUE, as the received signal from the macrocell has lower power due to path loss and from shadowing the signal from the femtocell. The interference can lead to errors such as a loss of data packets, a delay in connection and transmission and link failure, which significantly decrease the QoS. The mitigation of interference cannot be accomplished by using the customary resource management and nominal cell planning. Rather, adaptive and cognitive techniques are the advanced solution. The access style of user equipment (UE) has a massive impact on the overall femtocell network, in terms of interference [7]. The deployment of the femtocell depends on three different access modes. Closed access mode is where only authorized UE has access to a femtocell [8]. Open access mode is deployed by the operator to maximize the capacity, where all UE has access. Hybrid access mode is where some UE is prioritized over other UE and it is a user-deployed mode. The different modes serve different mechanisms to network users. The Inter-cell interference (ICI) is much harsher in the closed access mode as compared to the open access mode [9]. Consequently, dynamic management of resources is difficult for operators. The optimization of performance in the femtocell is most reliant on its allocation of resources and position in an indoor environment. It also requires an effective and vigorous approach to sense its adjacent surroundings and has dynamic techniques to diminish any interference [10].