Autonomous control system for offshore oil exploitation using digital acoustic communication

Underwater acoustic communication systems are the best choice to implement a cableless communication system suitable for the expected setups at subsea oil production systems. The main points at these systems are the communication reliability and the hardware reliability. Usually the control or monitoring systems could operate at a very low data rate. Typically, these acoustic systems need to operate at horizontal distances ranging from 1 to 10 km and at water depths from 100 to 2000 m. To select suitable signaling techniques in these fading multipath channels, it is fundamental to evaluate the distortions introduced in the signal by the channel. Experimental results with some of these configurations, with evaluations of time spreading, frequency spreading, frequency and time coherence and statistical distribution of the fading are presented. The multipath configuration can be evaluated by ray-tracing software. The main difficulties to implement a simple FSK system, even with a low data rate, are the multipath. A modem that can overcome the multipath and intersymbolic interference is proposed; this modem uses a FSK modulation scheme with silence intervals (guard intervals). A special symbol synchronization system is also proposed, based on the use of Williard words. Experimental results with this modem at the Brazilian Campos Basin showed promising results.