# Interference Challenges and Management in B5G Network Design: A Comprehensive Review
## 4 Interference in B5G Networks
### Heterogeneous Networks
#### 4.1.4 Related Works in HetNet  
Depending on the cell types and distinct interference discussed above, we will present the most recent solutions conducted to mitigate co-tier interference ([68; 69; 70; 71; 72; 73; 74]), cross-tier interference ([75; 76; 77; 78]), or hybrid interference ([79; 80]) as follows:  
1. Co-tier Interference Solutions  
In [68], the authors investigated the interference management for both uniform small base station deployment (U-SBSD) and non-uniform small base station deployment (NU-SBSD) in a two-tier uplink HetNets scenario. A non-uniform SBS deployment (NU-SBSD) with fractional power control (FPC) and reverse frequency allocation (RFA) in the MBS coverage area was proposed to mitigate uplink ICI and improve uplink coverage performance. Simulation results stated that the proposed method enhances the edge users' coverage and ICI significantly by NU-SBSD with FPC and RFA as compared with U-SBSD. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Cell** & **Scenario** & **Power** & **Radius** \\ \hline Femto & Home, small enterprises & [0.01, 0.2] & [0.01, 0.05] \\ Pico & Office building, underground parking & [0.25, 2] & [0.1, 0.2] \\ Micro & Shopping malls, railway station & [2; 20] & [0.2, 1] \\ Macro & Mountaintop & [20; 160] & [1; 25] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A comparison of several network types [60]. The improvement of maximum uplink coverage was around 39.8% in the macro-outer region by employing NU-SBSD with FPC and RFA, compared with U-SBSD. Similarly, the improvement of maximum uplink coverage was about 18.34% in the macro center region by employing NU-SBSD with FPC and RFA. However, increasing the value of the fractional path loss compensation factor results in a reduction in uplink coverage probability because of high path loss and interference, which causes a degradation in the SINR of the proposed system. In [69], the authors proposed a distributed joint interference management (DJIM) algorithm for various domains in downlink heterogeneous ultra-dense small-cell networks (UDSNs) to mitigate the interference and maximize the total network's throughput. The frequency-domain orthogonal frequency division multiple access (OFDMA) scheduling was implemented to assign the appropriate sub-channels and construct reliable transmission links to mitigate adjacent co-tier interference in a single slot. The proposed algorithm enables each small-cell base station (SCBS) to self-organize and interact into a stable overlapping coalition structure, eventually reducing multi-domain interference and attaining an optimal cost-benefit tradeoff. According to the simulation results, the proposed algorithm delivers a significant improvement in overall performance in terms of total throughput. Nonetheless, the impact of the ICI that minimizes the system's throughput was not considered in this model. In [70], the authors investigated the interference management in heterogeneous small-cell networks in uplink transmissions where interference cancellation strategies based on two sophisticated waveforms universal filtered multi-carrier (UFMC) are proposed to reduce both inter- and intra-cell interference in heterogeneous small-cell networks (HetSC-Nets). The first proposed strategy was the dynamic spectrum allocation strategy based on UFMC, and the second strategy was the precoding strategy based on UFMC. The proposed precoding strategy based on UFMC outperformed the dynamic spectrum allocation strategy based on UFMC in terms of BER performance. Additionally, the precoding strategy based on UFMC achieved a greater data rate than the dynamic spectrum allocation strategy based  
Figure 6: The interference in HetNet. on UFMC. Nevertheless, the non-uniform distribution for both users and BS that affects the system's power consumption was not considered in these strategies.