The
expriment purpose was to first, measure the Channel Impulse Response (CIR) of
the lake. Second, test the performance of underwater network MAC protocol
UW-Aloha with newly added back off scheme.
Deployment
location
elow
is the overview of Aloha Protocol plus modifications made for this experiment.
Receiver and
Transmitter Algorithm
The new back-off algorithm has shown better performance in compared to pure
Aloha. Plot ,below, shows throughput improvement of back-off in compared to
prior field experiment based on pure UW Aloha.
Throughput comparison between pure Aloha
with no back-off and the new back-off scheme
Table 2 shows
improved packet loss rate in the new algorithm.
TX_Rate |
Back-off (%) |
Pure Aloha(%) |
0.05 |
31 |
48 |
0.08 |
44 |
47 |
0.10 |
39 |
60 |
0.15 |
44 |
84 |
AquaSent modems have four channel hydrophone receivers. Plot below
depicts CIR waveform received by each channel prior to the 0.05 tx-rate trial.
All ten CIR results consistently show maximum delay spread of less than 50ms.
This means for future lake experiments, we can set time guard to 50ms, which
increases transmission rate to 1.38 Kbps.
CIR taken before 0.05
tx-rate trial