# Positioning Systems for Unmanned Underwater Vehicles: A Comprehensive Review
## 1 Introduction
Comparison of Operational Capabilities: It offers a detailed comparison of positioning systems based on operational factors such as accuracy, cost, depth limitations, and maintenance requirements, highlighting the trade-offs for different applications;
3. Focus on Maintenance Costs: The study addresses an often-overlooked issue--maintenance costs and recalibration needs of positioning systems--offering a practical perspective that fills a gap in the existing literature;
4. Critical Analysis of Challenges: The paper identifies and analyzes key challenges, such as communication limitations and environmental variability, providing valuable insights for the advancement of UUV positioning technologies;
5. Future Research Directions: It highlights opportunities for future research and technological advancements, suggesting areas of improvement for enhanced UUV positioning performance. This work offers a unique contribution by combining practical, technical, and economic perspectives, advancing the understanding of UUV positioning systems in both scientific and commercial contexts. The structure of this research unfolds as follows: In Section 2, we initially explored the fundamental concepts of Unmanned Underwater Vehicles (UUVs), providing detailed definitions and classifications that encapsulate their full scope. We also categorize the various positioning systems employed by UUVs to enhance our understanding of the technologies used for navigation in both shallow waters and deeper ocean environments. In Section 3, we delve deeper into these positioning systems, analyzing their capabilities through tables to better illustrate their specific uses. Section 4 focuses on the practical applications of these positioning systems, organized in a table that summarizes key information such as the number of references reviewed, the type of research papers analyzed, and the specific applications and technologies associated with each system. Section 5 provides a thorough discussion of the data presented in Section 4, offering critical insights into the research papers and their broader implications. Finally, Section 6 emphasizes future research directions and technological advancements in UUV positioning systems, suggesting potential areas for further exploration based on the findings of this study. Exploring the Definition and Categories of Unmanned Underwater Vehicles and Their Respective Positioning Systems  
Although the development of Unmanned Underwater Vehicles (UUVs) has seen significant growth in recent years [10], the associated hardware and software technologies still appear to be in relatively early stages when compared to the theoretical models and their potential capabilities. In companies that specialize in developing underwater rescue systems, progress has been more advanced and promising compared to those focusing on commercial applications, such as underwater exploration and photography, due to the urgent need for reliable, efficient technology in life-saving operations, greater investment in safety-critical solutions, and the push for innovation driven by the potential to operate in challenging, high-risk environments where human intervention is limited. However, this disparity is not necessarily a setback, as technological advancements tend to occur in a \"chain reaction\". As certain companies make breakthroughs, these discoveries contribute to the overall progress of the industry, accelerating development across the board. With this in mind, it is crucial to delve deeper into the definition of UUVs, examining the positioning systems they employ, the methods by which they are utilized, and the reasons behind their use. UUVs can generally be divided into two main categories, each with distinct characteristics and applications [8; 11; 12; 13; 14; 15]:  
1. Autonomous Underwater Vehicles;
2. Remotely Operated Underwater Vehicles. A common misconception is that Underwater Gliders and Hybrid ROV/AUVs are often mistaken for separate categories of underwater vehicles.