# Positioning Systems for Unmanned Underwater Vehicles: A Comprehensive Review
## 1 Introduction  
Unmanned Underwater Vehicles (UUVs) have successfully entered various applications, including oceanographic research, underwater archaeology, and rescue operations. These Autonomous or Remotely Operated Vehicles are revolutionizing underwater exploration and monitoring by enabling the collection of data, inspection of submerged structures, and execution of complex missions without direct human involvement [1, 2]. UUVs rely heavily on advanced positioning systems to navigate accurately and perform their tasks efficiently [3, 4, 5]. These systems utilize a combination of technologies, such as GPS (Global Position System) when near the surface, acoustic positioning, inertial navigation, and Doppler velocity logs, to determine the vehicle's precise location and trajectory [4]. Accurate positioning is essential for detailed seabed mapping, effective tracking of marine life, and reliable search and rescue missions. The development and integration of these positioning technologies are critical for optimizing resource utilization, minimizing environmental impact, and enhancing the capabilities of UUVs in scientific, commercial, and rescue applications [5, 6]. However, despite the considerable potential of Unmanned Underwater Vehicles (UUVs) in various applications, numerous questions and challenges remain to be addressed. Traditionally limited by human operational capabilities, underwater exploration and operations have seen a significant transformation in the past decade, evolving into more sophisticated and technology-driven activities. This transformation has been propelled by innovations in UUVs and their advanced positioning systems. These technologies enable researchers, scientists, and operators to make well-informed decisions regarding underwater navigation, marine environment monitoring, and numerous factors affecting mission success and operational efficiency [7]. This enhancement boosts overall productivity andsafety in underwater endeavors. However, these advancements also necessitate specialized knowledge and skills, along with substantial investments in hardware, software, and other infrastructural resources. Moreover, challenges such as extreme underwater conditions, restricted communication capabilities, and the requirement for long-term operational reliability further complicate UUV deployment [8]. While these obstacles add complexity to underwater missions, they simultaneously present opportunities for technological innovation and growth in marine exploration and other operations. Our continuous research about the positioning systems in UUVs progresses with the development of a comprehensive framework for implementing advanced positioning systems in Unmanned Underwater Vehicles (UUVs), emphasizing crucial components essential for their seamless integration. Through a comparative analysis presented in detailed tables, we explore technical nuances and draw significant conclusions concerning the implementation and operational constraints of these systems. While the importance of precise positioning in UUV operations is widely acknowledged, practical applications often encounter challenges such as underwater communication limitations and environmental variables. Despite technological strides, a notable disparity exists between theoretical concepts and real-world deployment, with proposed solutions often reliant on future advancements rather than current practical implementations [9]. This study offers several novel insights and contributions to the field of Unmanned Underwater Vehicle (UUV) positioning systems that address key positioning technologies, including Inertial Navigation Systems (INSs), Doppler Velocity Logs (DVLs), and various acoustic positioning systems. Furthermore, it addresses the following:  
1. Integration of Multiple Technologies: A key contribution is the emphasis on integrating multiple positioning technologies to improve navigation accuracy and reliability, particularly in GPS-denied environments;
2.