Systems and methods for a portable electronic device are provided. A user is validated to use the resource based on data provided in an act by the user. The method further may comprise coupling at least one of the electrodes to a controllable currentvoltage source while the electrodes are deployed in the seawater. The plurality of refinement triangles may include a plurality of sets of triangles, wherein each set is generated for a particular level of refinement. The cell further includes first and second planar electrodes covered with first and second hydrophobic layers. A pilot signal is transmitted concurrently by the transmitters in a plurality of pilot blocks, and a receiver processes the plurality of received pilot blocks to recover a channel estimate for at least one of the transmitters while suppressing the interference due to the pilot signals from the other transmitters.