# Collaborative Unmanned Vehicles for Inspection, Maintenance, and Repairs of Offshore Wind Turbines
## 3 Implementing Collaborative UVs for the OWT IMR Operations
### Collaborative Communication Strategies  
Although a commercial unmanned solution for offshore operations already exists [63], however, a communication issue is believed to be the main factor that prevents it from being implemented for most OWT farms. With a maximum range of just 5 km, a communication system based on a Wi-Fi connection, although superior for real-time control and data transmission, cannot be used for most offshore wind farms due to non-existent coverage. For OWT inspection, currently crewed vessels are still being used to transport UAVs near offshore assets [130]. To switch to full unmanned operations, a USV will normally be deployed to carry UAVs without any human operator. Within this arrangement, human operators can be kept in a loop at the GCS, either to monitor a fully autonomous unmanned system or to remotely control the UVs. Using cellular 4G or 5G networks, communication between the GCS with all UVs can be established. However, as wind farms have rapidly been located even further to sea, the probability of zero coverage for 4G or 5G networks is high. UAVs operating within the IMR operations will rely heavily on a reliable and uninterrupted data transmission system. Without sound communication infrastructures, the transmission of IMR data to a GCS will be problematic. Unless proper structure for a cellular network is made available for offshore wind farms, the IMR operations will have to rely on the next best communication solution, which is through satellite networks. Globally, the average distance to shore for offshore wind farms is 18.8 km [131]. Hence, most wind farms rely on a satellite communication system for monitoring purposes. However, a normal satellite communication system has a significant transmission lag in the order of a few minutes to hours due to the high latency issue [132]. Due to this limitation, it is impossible to control a UAV remotely from the GCS, as real-time communication is not available. However, recent advancement in BVLOS satellite communication which utilizes Inmarsat SwiftBroadband satellite service has enabled real-time navigation and control with live video transmission [133]. With a data transmission speed of 432 Kbps and weighing just 1.45 kg in a compact 24 \(\times\) 16 \(\times\) 6 cm\({}^{3}\) enclosing, it is a desirable embedded solution for offshore drones. However, like any other satellite-based communication system, operating near a tall WT structure may affect data transmission due to the loss of signals. To overcome this issue, a collaborative approach between a UAV and a USV can be devised. A USV may be stationed near an OWT while taking into consideration a safe distance for receiving optimized satellite signals. To establish a collaborative communication system, a UAV and a USV equipped with a satellite communication device can be linked with a GCS through a distributed dynamic network topology within an ad hoc network [46]. Utilizing this network, data from the UAV can initially be transmitted to the USV using wireless communication modules (2.4 GHz Wi-Fi module), which are then further transmitted from the USV to the GCS through satellite communication. Vice versa, commands to control the operation of the UAV can be transmitted from the GCS through satellite communication via the USV. The distributed dynamic network can be further expanded for underwater communication involving the UVs. Similar to the UAV, the UUV may also be controlled from a GCS through the satellite communication system via the USV. However, instead of using wireless radio frequency for data transmission, UUVs mostly rely on an acoustic underwater communication system. Unfortunately, data transmission using acoustic transmission for the purpose of IMR operations cannot be performed in real time due to the slow transmission rate of the acoustic signals. Nevertheless, this can be achieved via short-range wireless transmission using underwater radio frequency communication or optical communication at data transmission rates ranging from a few Mbps to Gbps [134].