Structural Health Monitoring Using Smart Sensors - ideals ...

Sender
Receiver
SendSMsg.bcast()
Pack parameters
(e.g., Destination, message
ID)
post BCBeginTask
BCBeginTask
Inquire of receivers whether
they are ready to receive
data.
if all the receivers
acknowledge,
post BeginTask();
SendNoticeSubTask()
SendNoticeMsg.sendDone()
post BCBeginTask()
ReceiveNoticeMsg.receive()
If the receiver is among the
destination nodes,
receiver stores received
parameters.
Afterward, message ID and
sender’s address will be
used to rejects packets for
other communication
request.
TimerNotice.fired()
if acknowledged,
post SendDataTask()
else
post SendNoticeSubTask()
ReceiveNoticeMsg.receive()
set flag as acknowledged
SendAckMsg()
SendNoticeSubTask()
BeginTask()
Pack parameters and data
(e.g., Destination, message
ID, data, etc. )
SendShortSubTask()
SendShortMsg.sendDone()
call TimerNotice.start()
ReceiveShortMsg.receive()
Receiver stores received
parameters and data.
Acknowledge the sender
Signal received()
TimerShort.fired()
if acknowledged,
signal SendDone()
else
post SendShortSubTask()
ReceiveNoticeMsg.receive()
set flag as acknowledged
SendAckMsg()
SendShortSubTask()
Figure 5.19. Detailed block diagram of the reliable multicast protocol for short messages.
of communication, the receiver keeps the source ID, message ID, and waiting time of the
last 15 rounds of communication (see Figures 5.18 and 5.19).
5.3 Synchronized sensing
Time synchronization error in a smart sensor network can cause inaccuracy in SHM
applications. Time synchronization is a middleware service common to smart sensor
applications and has been widely investigated. Each smart sensor has its own local clock,
which is not synchronized initially with other sensor nodes. By communicating with
surrounding nodes, smart sensors can assess relative differences among their local clocks.
For example, Mica2 motes employing TPSN are reported to synchronize with each other
to an accuracy of 50 sec; different algorithms and hardware resources may result in
different precision. Whereas time synchronization protocols have been intensively
studied, requirements for synchronization from an application perspective have not been
clearly addressed. The effect of time synchronization on SHM applications is first studied.
As stated earlier, spectral density and correlation function estimation are oftentimes
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