# Deep-Sea Underwater Cooperative Operation of
## 5 Work Efficiency Analysis
### Pure Research Vessel R/V Mode  
The research vessel R/V can only provide communication and positioning services for one HOV and two AUVs simultaneously based on the underwater cooperative operation of the research vessel R/V because of the limitation of underwater acoustic communication bandwidth and underwater positioning time. During underwater cooperative operations, the research vessel R/V can deploy one HOV and two AUVs in sequence to perform underwater operations. After completing the operational task, the submersibles are recovered at regular intervals. Figure 11 shows the elapsed time in the cooperative operational mode. If the operating water depth is 4000 m, the time for diving and ascent is 1.6 h each, and the time required to complete the task is 52 h. However, in the previous distributed mode operations, three steps were required to complete these tasks, that is, after the HOV completed the underwater operation, it was recovered by the research vessel R/V, and then, AUV01 was deployed to conduct the underwater operation. When AUV01 was successfully recovered by the research vessel R/V, and AUV02 was deployed to continue the underwater operation. Figure 11: Elapsed time in cooperative operation mode based on the pure research vessel R/V. After the operation was completed, AUV02 was recovered by the research vessel R/V. Figure 12 shows the elapsed time in a traditional distributed operational mode. Distributed mode takes 110 h to complete the same task. This shows that cooperative operations have a considerable advantage in the execution time needed to complete the unit tasks, which saves the research vessel R/V's time and improves the operational efficiency. Based on the cooperative operation of the pure research vessel R/V, positioning and communication timing allocation mechanisms are also required to ensure the effective operation of submersible communication and positioning. In this study, we propose a positioning and communication timing allocation method for heterogeneous submersible underwater cooperative operations. The timing distribution of positioning and communication is realized by a high-precision atomic clock acting as a synchronous clock module. The synchronous clock module has four trigger pulse outputs for the USBL, and the UACS of the HOV, AUV01, and AUV02. The trigger pulse periods are \(t\), \(6t\), \(6t\), and \(6t\), respectively. The operating mode of UACS needs to be set. After the communication host receives the trigger pulse, it will not transmit the acoustic signal immediately but will transmit it after a delay (\(\tau\)), in order wait for the positioning transponder to transmit the response signal and then transmit the underwater acoustic signal to the research vessel R/V. Each submersible is equipped with a synchronous clock module, which supports the research vessel R/V surface communication system and the USBL, which share a synchronous clock module. Before diving, unified timing synchronization is performed through the precise positioning service of the differential GNSS. The timing allocation diagram of underwater positioning communication is shown in Figure 13.  
To avoid the interference between communication and positioning, the positioning mode of heterogeneous submersibles when operating underwater uniformly uses the external synchronization positioning mode. The synchronization pulse comes from the clock source module that realizes the unified time reference with the submersible and the transponder equipped with the submersible. The trigger pulse signal comes from the synchronous clock source of each submersible, which can ensure the accuracy of the time recorded by the USBL. To determine the identity of the transponder sending the signal, each transponder has a fixed response signal and an identity number (ID number), and the ID number of the transponder corresponds to the different submersibles.