New paradigms for underwater communication
Underwater surveying by swarms of autonomous underwater vehicles presents problems in communication among the robots. Traditional underwater communication uses acoustic transmission. Problems with such communication include low throughput and poor communication robustness. We describe new methods to solve well-known problems associated with high throughput and robust communication in underwater environments. We define robust, to mean simultaneous increases in enabled underwater communication data rates, range, and reliability. Our methods borrow concepts from advanced multi-carrier modulation using Orthogonal Frequency Division Multiplexing (OFDM), multiple input multiple output (MIMO) space time codes (e.g. Alamouti diversity), and zero carrier frequency ultra wideband (UWB) wireless. We present results using low frequency RF signaling in underwater channels using zero-carrier frequency signaling. The aim is to increase the data rates and range of communications in underwater ocean environments. We note that many underwater systems currently rely upon low-rate acoustic communication which cannot propagate behind objects or utilize very short range optical methods. We investigated turbo code algorithms and multi-carrier modulation to enable low packet error rates and high throughput. We address the channel modeling, link budget analysis, and use empirical data in our analysis. In addition, we apply iterative message passing turbo codes for robust decoding in low signal-to-noise ratio (SNR) environments common in undersea scenarios. Our approach aims to increase the data rates and range of underwater communications and the increase in bandwidth allows for error correcting codes to increase reliability. We also discuss prototyping methods for real time communication analysis.