Abstract: A magnetic induction based underwater communication
link is evaluated using an analytical model and a custom
Finite-Difference Time-Domain (FDTD) simulation tool. The
analytical model is based on the Sommerfeld integral, and a full-wave
simulation tool evaluates Maxwell’s equations using the FDTD
method in cylindrical coordinates. The analytical model and FDTD
simulation tool are then compared and used to predict the system
performance for various transmitter depths and optimum frequencies
of operation. To this end, the system bandwidth, signal to noise
ratio, and the magnitude of the induced voltage are used to estimate
the expected channel capacity. The models show that in seawater, a
relatively low-power and small coils may be capable of obtaining a
throughput of 40 to 300 kbps, for the case where a transmitter is at
depths of 1 to 3 m and a receiver is at a height of 1 m.
Abstract: Variable channel conditions in underwater networks,
and variable distances between sensors due to water current, leads to
variable bit error rate (BER). This variability in BER has great
effects on energy efficiency of error correction techniques used. In
this paper an efficient energy adaptive hybrid error correction
technique (AHECT) is proposed. AHECT adaptively changes error
technique from pure retransmission (ARQ) in a low BER case to a
hybrid technique with variable encoding rates (ARQ & FEC) in a
high BER cases. An adaptation algorithm depends on a precalculated
packet acceptance rate (PAR) look-up table, current BER,
packet size and error correction technique used is proposed. Based
on this adaptation algorithm a periodically 3-bit feedback is added to
the acknowledgment packet to state which error correction technique
is suitable for the current channel conditions and distance.
Comparative studies were done between this technique and other
techniques, and the results show that AHECT is more energy
efficient and has high probability of success than all those
techniques.