## 6 Conclusions  
Maritime industry has a long tradition of continuously adopting and adapting to new technologies. However, the advancements in information and communication technologies have not been adopted as much, primarily due to the restrictions and constraints of the operating environment. In this paper, we have reviewed the current state and different modalities of maritime communications and proposed a novel unified cross-layer SDN-SDR communications framework for the maritime industry. The proposed framework leverages the robust capabilities and baked-in flexibility of SDRs and SDNs. Our proposed framework integrates the existing SATCOM infrastructure for improved and resilient maritime communications in highly dynamic and resource-constrained environments. We have presented the theoretical underpinnings along with a non-trivial example illustrating the expected performance improvement of the proposed framework over purely SATCOM communications in light of a geo-synchronous satellite. Our work, which includes a detailed real-world use-case justifying the motivation for the proposed framework, presents an analytical approach that indicates the feasibility of our overall framework. As an added benefit, with the proposed SDN-SDR framework, the vast amounts of maritime data that are currently going unused can be effectively analyzed and integrated into decision-making processes at all levels of the organization. By creating a more connected, integrated, and efficient maritime industry--from cargo vessels and cruise ships to Navy fleets--digital transformation will have a profound impact on maritime operations.  
Our future research will take a two-phase approach. Phase-1 will focus on a simulation-based implementation of the proposed unified SDN-SDR cross-layer communications framework. Among other things, we will take into consideration various environmental factors along with different types of satellites (LEO, MEO, GEO) to empirically validate the robustness of the proposed framework in the highly dynamic and resource-constrained maritime environment. Based on the results and lessons learned, Phase-2 will focus on implementing a working prototype testbed with COTS (commercially off the shelf) SDN and SDR hardware.  
The project's inception was marked by the collaborative conceptualization efforts of N.N., A.S. and K.S.G. Methodological decisions were collectively shaped by the entire team. N.N., A.S. and K.S.G. were responsible for the articulate writing of the manuscript, ensuring a cohesive presentation of our findings. The critical review and meticulous editing were conducted by N.N. and J.W. [PERSON] supervision played a pivotal role in guiding the project's trajectory. Importantly, all authors actively engaged in the review process and collectively endorse the final published version, attesting to our unified dedication to the accuracy and credibility of our research. All authors have read and agreed to the published version of the manuscript.  
This research was supported in part by NSF grants CNS 2214940, CPS 2128378, CNS 2107014, CNS 2150152, CNS 1824440, and CNS 1828363.  
Not applicable.  
The authors declare no conflict of interest.