Structural Health Monitoring Using Smart Sensors - ideals ...

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Figure 5.11. Packet loss rate estimation.
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Trial
IDs of the sender and receivers, the number of packets to be sent, and the number of
repetitions. The base station forwards this information to the sender. On reception, the
sender starts broadcasting packets. In this experiment, 100 packets are broadcast. After the
sender completes transmission of the 100 packets, the sender tells the receiver that
transmission is complete and queries each receiver regarding how many packets were
received. This procedure is repeated 10 times.
This experiment is conducted on the lawn in front of Newmark Civil Engineering
Laboratory at the University of Illinois at Urbana-Champaign. The sender and receiver
nodes are held at the height of about 1 m. The distance between the sender and the receiver
is 3.3 m. Figure 5.11 summarizes the results. In this experiment, the packet loss is usually
smaller than 20 percent. There are many rounds of data transfer without any lost packets,
while the maximum packet loss rate reached 86 percent. The packet loss rate does not
show a clear trend among the six nodes. One node without any packet loss in one round of
data transfer may suffer from severe data loss in the subsequent round of communication.
While a loss of no or a few packets is anticipated to take place often in communication,
such a low packet loss rate cannot always be assumed. Smart sensor communication
sometimes experiences a loss of a large number of packets.
A packet loss of 20 percent or 86 percent is apparently much larger than the data loss
level discussed in the previous section and is not acceptable for SHM applications. A
reliable communication protocol suitable for transfer of a large amount of data, as well as
a protocol for short messages, is proposed in the next section.
5.2.3 Reliable communication protocol
Reliable communication protocols for long data records and short messages are
developed in this section. Communication packets range from one-bit acknowledgments
to lengthy acceleration time histories. A communication protocol suitable for long data
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