Enabling High-Speed Communication between Autonomous Underwater Vehicles

Canada once had a thriving research program in underwater acoustics for the echolocation of enemy vessels led by Defence Research & Development Canada (DRDC) in Halifax but the end of the Cold War in the early '90s brought a sudden interruption to the funding of these programs.Recently there has been an increasing interest in subsea exploration for a variety of applications, such as seaport surveillance, oceanographic behaviour analysis and monitoring of offshore equipment. For example, in the Maritimes, there is significant investment in the deployment of turbines for efficient energy generation in the Bay of Fundy. Monitoring of the wildlife and subsea equipment is crucial to assess environmental and economic impacts. To avoid the burden of cables, acoustic communication is proposed.In the proposed research program, we intend to develop state-of-the-art equipment to communicate acoustically in subsea environments. To extend the lifetime of deployed underwater acoustic equipment, low power techniques shall be considered, but will inherently limit transmission range.To help increase the communication range, we propose to use autonomous underwater vehicles (AUVs). However, communication capabilities to these devices are currently strongly restricted, due to technology limitations. As a result, once an AUV is launched, there is typically no feedback mechanism and the AUVs' mission cannot be monitored and controlled in real-time. A reliable communication link that allows video transmission is needed and would require a high data rate on the order of 100 kbps.Existing underwater acoustic modems have very limited throughput, on the order of 10 kbps and consume significant power, thus limiting the lifetime of the batteries in AUVs. The technical challenges for underwater communication are, in part, due to the low frequency of operation of the equipment used for underwater transmission, but primarily to the unpredictable propagation of sound underwater.In comparison to the well-understood radio-electric propagation channel, the underwater acoustic channel impairments are quite severe. One can imagine that in the ocean where currents and waves create a dynamically varying environment, it is difficult to predict the distortion of the signal. An accurate model of the physical phenomena that govern the signal propagation currently includes frequency dependent absorption, multipath arrival, Doppler shift due to mobility and small-scale fluctuations.The proposed work aims to improve the throughput of underwater communication by at least one order of magnitude using novel algorithms implemented on custom processors. In order to mitigate distortion, the proposed digital algorithms will need to compensate for the underwater propagation extreme impairments. Also, the transmitter and receiver will be equipped with multiple transducers and hydrophones to increase the data rate.Using multiple transducers will require a significant amount of memory and important computation resources. To satisfy these requirements, the signal processing will be programmed on a custom fully integrated platform. Additionally, to allow an analog interface to the processor and consequently minimize the number of off-chip interconnections, the integrated circuit will also hold high-resolution data converters.This research program shall lead to innovative solutions in the fields of communication, signal processing and very large scale integration (VLSI) technology. Canada being surrounded by 3 large bodies of water will benefit greatly from the research developed in this project. This research will be conducted in collaboration with local industry in Halifax for commercial and scientific applications that require sub sea monitoring.