## 3 Collaborative AUVs
### Communication
Authors implemented a decentralized model predictive control algorithm--centralized schemes are typical for swarms of AUVs--to control teams of AUVs that optimizes vehicle control inputs to account for the limitations of operating in an underwater environment. They simulate their proposal and showed the effectiveness of their approach in a Mine/Countermine mission. Other way to deal with acoustic communication issues was presented by [PERSON] et al. [114]. They proposed that enabling the AUVs to anticipate acoustic messages would improve their ability to successfully complete missions. They outlined an approach to AUV message anticipation in AUVish-BBM (BBM suffix includes the initials of the researchers directly involved in dialect development: [PERSON], [PERSON] and [PERSON] [115]), an acoustic communications language for AUVs [116], based on a University of Idaho-developed paradigm called Language-Centered Intelligence (LCI). They demonstrated a new application of LCI in the field of cooperative AUV operations and argued that message anticipation can be effectively deployed to correct message errors. The structure, content, and context of individual messages of AUVish-BBM, together with its associated communication protocol, supply a systematic framework that can be utilized to anticipate messages expressed by AUVs performing collaborative missions. The absence of an underwater communication standard has been a problem for collaborative teams of AUVs. In 2014, [PERSON] et al. presented the JANUS underwater communication standard [117], a basic and robust tool for collaborative underwater communications designed and tested by the NATO Centre for Maritime Research and Experimentation. This opened the possibilities for simple integration of different robots using this standard [118; 119; 120; 121] for collaborative tasks as underwater surveillance. To improve the performance of underwater communication, optical technologies have been tested either stand-alone [122; 123] or as a complement for an acoustic system [100]. Laser submarine communication has some advantages such as a high bit rate, higher security and broad bandwidth. Blue-green light (whose wavelength is 470-580 nm) penetrates water better and its energy attenuation is less than any other wavelength light [124]. Thus, researchers have explored optical underwater communication systems based in blue-green light, to allow an underwater vehicle to receive a message from an aerial/spatial system at any depth despite its actual speed, course and distance from the transmitter. [PERSON] et al. [122] were seeking for a system to deliver a message from a satellite to a submarine, avoiding the need for the submarine to navigate close to the surface for retrieving the message as happened with the radio-frequency systems used at the time. Authors stated that blue light has the potential to accomplish the result expected in the future. However, their research was only a brief representation of what could be expected when working in such a difficult environment. [PERSON] et al. [123] performed the first demonstration of a two-way laser communication between a submarine vehicle and an aircraft; and concluded that a blue-green laser communication system could, someday, reach operational requirements. [PERSON] et al. [125] made experiments to study the optical communication between an underwater body and a space platform using a red laser with a 635 nm wavelength. Results showed that the performance of the red-light system was lower than the expected for a blue-light system in terms of the attenuation coefficient observed. [PERSON] et al. [126] worked on an optical wireless communication system where both, transmitter and receiver, where at underwater. The optical signal with a 470 nm wavelength was obtained modulating two LED arrays and received by an avalanche photodiode module. Error free transmission was achieved in the three configurations under test (6.25 Mbit/s, 12.5 Mbit/s, and 58 Mbit/s) through 2.5 m clean water.