## 2 Literature Review  
Extensive research in the literature has thoroughly investigated the advantages of utilizing multi-frequency and multi-constellation signals [13; 14; 15; 16]. In [17], the authors carried out several experiments to evaluate the performance of a high-end commercial receiver under diverse jamming conditions, including varying the jamming signal strength and type. They replicated the same trajectories twice: Once with only the GPS signal enabled and once with both GPS and GLONASS constellations enabled. Furthermore, the paper investigated the effects of jamming on both the GPS and GLONASS bands. The findings suggest that employing multi-constellation systems offers a promising solution to mitigate jamming issues, particularly in terms of solution availability and reliability. In [18], additional GNSS constellations and frequencies beyond GPS L1 are usable for automotive applications by including them in an integrated GNSS/INS localization algorithm. The results showed that the main advantages are increased satellite availability, the elimination of ionospheric error, and reduced vulnerability to high-power interference signals. The authors in [19] explored the benefits of the use of multi-constellation on high-dynamic platforms experiencing jamming. Several evaluation metrics were used to evaluate the performance, including satellite availability, carrier-to-noise ratio (C/N0), dilution of precision (DOP), the percentage of solution availability, the minimum number of available satellites, and positioning accuracy. The comparison between using GPS-only and combined GPS/GLONASS revealed that the latter yielded superior results across all evaluation metrics used. In [20], the utilization of multi-constellation receivers in combination with interference mitigation techniques hasdemonstrated enhancements in both position availability and accuracy. The authors in [21] examined the susceptibility of existing maritime receivers to jamming and explored whether enhancing system resilience could be achieved by upgrading to a multi-constellation or multi-frequency receiver. The results showed that single-frequency multi-constellation receivers offered better jamming robustness when compared with multi-frequency (L1 + L2) GPS receivers. Another important finding is that the GLONASS constellation showed better robustness against jamming as compared to the GPS constellation. The results also suggest dependence on GPS L1 signals in the acquisition of GPS L2 signals. With these findings, the authors suggested the use of multi-constellation GPS/GLONASS receivers as the most economical solution for enhancing jamming robustness. The authors in [22] examined the effectiveness of a software-defined GNSS receiver that operates on multi-frequency, multi-constellation signals. They conducted this analysis both in the presence and absence of a commercial L1 jamming signal. They studied the potential advantages associated with utilizing multi-constellation and multi-frequency approaches to enhance their capabilities for mitigating jamming effects. The results showed that the presence of multiple signals and constellations would result in enhanced positioning availability and reliability; however, it would have a minimal effect on positioning accuracy except in challenging signal conditions, such as the presence of a jamming signal. Based on these findings, the authors suggested assessing the satellite signal quality from various GNSS constellations before incorporating them into a combined navigation solution.