Estimation of wave parameters from accelerometry data to aid AUV-shore communication
A deployed Slocum glider.Note the nose-down posture with the tailelevated to facilitate communication. In this picture, the antenna is locatedapproximately 30 cm above the sea surface.
Gliders use Iridium as their primary means of communicating with the outside world. The accompanying glider software and FreeWave need an on-site server. There is no support for multiple freewave nodes and gliders communicating within the network. We developed our communication system to
- Reduce Iridium costs
- Speeding up data-transfers significantly over Iridium
- Enable data-driven path-planning by leveraging the faster data transfer speeds
During actual field trials, from data we collected using the glider in May 2009, we were able to build a communication map, and use a classifier that could predict (given the location of the glider and the sea-state), whether the glider should attempt to do data-transfer with a base-station (because the communication will be really good), or just send a status packet while deferring data transmission for later (low-reliability communications) or make Iridium calls (poor communication via radio modem).
We had several useful outcomes from this work:
- Developed coastal communication system for glider AUVs
- System tested with single glider over two month-long deployments
- Max data-rate achievable is 5 KB/sec. Practical rate is 2 KB/sec
- With compression 24x faster than Iridium
- File transfers successful up to 14 km
- Individual packets received up to 20km
- Using accelerometer data for wave-parameters we can estimate poor communications fairly well. File transfers can be avoided to prevent bottle- necking communication based on this prediction.
A very interesting next step is to use the accelerometer data to modify the communication protocol in real-time (by adjusting the packet-size and the transmission time) so as to maximize throughput.