# Interference Mitigation Strategies in Beyond 5G Wireless Systems: A Review
## 3 Classification and Evolution of Interference Management Strategies in B5G Networks
### Classification and Analysis of Interference Management Strategies in B5G Networks
#### 3.2.2 Heterogeneous Networks
Furthermore, HetNets are considered an efficient approach for improving coverage and system efficiency for future cellular networks [28; 107; 108]. To achieve the quality of experience (QoE) and QoS, low cost, and high EE, the B5G HetNets must integrate multiple components including wireless fidelity and cellular radio access network (RAN) through the utilization of different radio access technologies over different carrier frequencies [109]. It is also attractive for operators to deploy HetNets, as it will allow them to provide expanded services and also offer new market opportunities. However, the densification of HetNets also faces the issue of usable BW scarcity, considering their potential advantages. To ensure the success of this essential technology, reliable and scalable solutions that allow operators to use the available spectrum are mandatory [90]. In the research and design of future cellular networks, the challenge of HetNet interference is considered one of the most critical topics. ICI analysis has always been a main research problem in homogeneous systems as well. Interference from neighboring cells in the conventional cellular grid has often caused performance degradation for users of the cell edge who have suffered from both slower reception of the signal and increased interference [110]. There are many reasons for the resurgence of HetNets interference. First, due to the number of cells in each tier does not allowing effective resource partitioning schemes, it is almost necessary to think about universal FR deployments. Furthermore, in the past, interference affected only the cell-edge users of the macro-cell, while the de  
Figure 5: Heterogeneous cellular wireless architecture of 5G. ployment of a HetNet and the number of BSs makes any user in the network suffer from or cause interference. Hence, in the HetNet case, the system-level implications of ICI are more relevant. Last but not least, the unplanned and even random nature of a HetNet deployment makes the problem of managing interference more challenging than the case of well-thought homogeneous deployments [111]. Owing to the uncoordinated nature of HetNet, IM is one of the most important challenges [112]. Despite the performance benefits of HetNets, their deployment is often limited by backhaul constraints, especially for SCs in rural or infrastructurally weak areas. Coordinating inter-tier interference is also hindered by the lack of centralized control and variable spectrum licensing conditions across regions. Hardware heterogeneity among macro cell and SC introduces further complexity in unified interference coordination. In regions with limited infrastructure, such as rural or developing areas, HetNet deployment faces challenges in synchronization and coordination [113]. Power- and spectrum-efficient solutions that operate under limited backhaul conditions are vital for viable IM in these contexts [114]. Proper treatment of HetNet interference involves two main tasks: understanding the phenomenon of interference (i.e., modeling and study of interference) and techniques for minimizing it as effectively as possible. Several studies have been carried out in this field. [PERSON] et al. [108] proposed a joint optimization technique combining 3D positioning of non-terrestrial base station (NTBS) and reconfigurable intelligent surface (RIS) reflection control in non-orthogonal multiple access (NOMA) HetNets. Their IMI approach significantly improved DOL coverage and SINR in multi-tier deployments. A deep RL approach for joint RA in 5G HetNets is investigated in [109]. Their method used a multi-agent learning framework to enhance EE while mitigating inter-tier interference, making it particularly suitable for UD B5G networks. Two IM schemes, blind IA and a hybrid topological IM orthogonal multiple access scheme are presented in [115]. It was found that both schemes reach at least twice the rate of time division multiple access.