# Coexistence in Wireless Networks: Challenges and Opportunities
## 5 Interference and Mitigation Techniques  
Interference is a common issue that occurs in various wireless communication systems. It can cause signal distortion or complete signal loss, leading to poor quality of service or even a complete breakdown of the system [92; 93; 94; 95]. However, various interference mitigation techniques are available to address these issues and ensure a reliable and stable communication system [96]. One of the most common interference mitigation techniques is frequency hopping. This technique rapidly switches communication channels to deter interference [97]. Spread spectrum techniques distribute signals across a wider frequency band to minimize the impact of interfering signals. Power control mitigates interference by adjusting transmission power to optimize signal strength without causing disturbances [98]. This technique is particularly effective in cellular communication systems, where multiple devices may transmit simultaneously. Another effective interference mitigation technique is beamforming [99]. This technique involves the use of multiple antennas to create a focused signal in a particular direction, minimizing interference from other directions. Beamforming is particularly useful in outdoor communication systems, where signals may be disrupted by natural obstacles or competing signals. The effect of discrete modulations on three-user interference channel interference mitigation is examined in [100]. The study offers effective and straightforward capacity approximations. It implies that for more generic channels, the Ozarow-Wyner bound needs to be improved, since the current bound might be pessimistic in the event of poor alignment or when an inefficient number of levels (N) is used. Although the findings are primarily theoretical, they point to real-world uses for interference alignment by considering discrete interference as noise once discretely modulated signals have been aligned. The usefulness of relaying in mitigating interference in a communication context with limited interference was examined in [101]. The study optimizes quantization noise covariance to characterize rate scaling with relay link capacity. It links this scaling to the deterministic relay channel by analyzing the spatial DoF gains from MIMO relaying under noise correlation. The study examines a BICM OFDM system using a prediction-error filter (PEF) to minimize the time-domain disturbance [102]. This approach effectively handles interference without weakening distant tones. Simulations show that, without narrowband interference, the system with PEF performs efficiently and matches similar systems [103]. In [104], two spectrum sharing approaches, orthogonal and non-orthogonal, were investigated for integrated satellite-mobile and autonomous terrestrial-mobile systems. An interference management scheme for co-located base stations and indoor small cells was developed, optimizing the number of blank subframes within a pattern period. System-level performance metrics, including the capacity, spectral efficiency, and energy efficiency, were derived. A novel hybrid approach combining Maximum Likelihood Estimation and \begin{table}
\begin{tabular}{l l} \hline
**Coexistence** & **References** \\ \hline Coexistence of 5G system and fixed satellite service & [8; 7; 93; 94; 95; 96; 97; 98; 99; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90] \\ \hline Coexistence of radar and communication systems & [96; 97; 98; 99; 90; 95; 96; 97; 98; 99; 96; 99; 97; 98; 99; 90] \\ \hline Coexistence of terrestrial and satellite services & [75; 76; 77; 91] \\ \hline \end{tabular}
\end{table} 
Table 1: Overview of coexistence with the References. wavelet-based self-cancelation is proposed to enhance BER performance in OFDM systems [105]. Significant improvements in the bit error rate were observed when comparing 64-QAM and differential offsets with the traditional rapid Fourier transform methods.