The field experiment system is designed for conducting experiment in real environment. The Marina Del Rey testbed consists of 4 nodes numbered from 1 through 4. Node 1 is the special Gateway Node and it does not have an acoustic modem attached to it. Rather, it provides a platform for the user to control nodes 2 through 4 via the RF control channel.
Each of the Marina nodes have a local controller box, containing the three major components essential for node operation - a battery, a Raspberry Pi computer, and an RF modem. The battery is a 14.8V 8Ah (118.4Wh, 8A rate) battery capable of continuous operation for 48 hours for a single charge, it supplies power to everything on the node, including the Raspberry Pi, the RF modem, as well as the acoustic OFDM modem. The Raspberry Pi is the local controller for the node. Loaded with Ubuntu Linux, the Raspberry Pi runs the experiment scripts and the SeaLinx protocol stack that drives the acoustic modem. From the Gateway Node, users may access the Raspberry Pi on nodes 2 through 4 via the attached MicroHardTM n920-ENC modem, which is a spread spectrum modem that operates at 900MHz with wireless link rates up to 230.4kbps, more than enough for terminal accessing each of the experiment nodes. To increase its range, we attach to each of these modems a 900 MHz 8 dBi Omnidirectional Antenna on the outside of the control box. The Gateway Node also has a cellular modem as an additional component, allowing users to access it from the Control Center in the lab.
The whole mooring system is shonw above. For deployment into water, we use a child-sized kayak. The kayak acts both as a buoy from which our acoustic modem can hang and as a storage unit that holds all the necessary equipment for the node. We modify the kayak by mounting on it a wooden frame, which has the roles of supporting the antenna as mentioned in the previous section, stabilizing the kayak, and lodging the controller box in its place. The kayak is anchored in place from both ends to prevent itself from drifting in circles. The acoustic modem hangs from the back of the kayak on a rope tied to the wooden frame so that its cable would not need to support its weight.
The deployment locations at Marina Del Ray is as showing below. The distances between each pair of nodes are 250-350 meters, and the water depth in this area is 10-13 feet. Node 1 which is the master node.