Since
the design of TPSN is based on a hierarchical methodology similar to NTP,
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Chapter 9 Time-Synchronization Challenges and Techniques
Fig. 4. Illustration of the RBS.
nodes within the hierarchy may fail and cause nodes to be unsynchronized.
In addition, node movements may render the hierarchy useless, because nodes
may move out of their levels. Hence, nodes at level i can not synchronize with
nodes at level i ??’ 1. Thus, synchronization may fail throughout the network.
As for the timing technique of type (2), the RBS provides an instantaneous
time synchronization among a set of receivers that are within the reference
broadcast of the transmitter. The transmitter broadcasts m reference packets.
Each of the receivers that are within the broadcast range records the time-ofarrival
of the reference packets. Afterwards, the receivers communicate with
each other to determine the o?®sets. To provide multi-hop synchronization, it
is proposed to use nodes that are receiving two or more reference broadcasts
from di?®erent transmitters as translation nodes. These translation nodes are
used to translate the time between di?®erent broadcast domains.
As shown in Figure 4, nodes A, B, and C are the transmitter, receiver,
and translation nodes, respectively. The transmitter nodes broadcast their
timing messages, and the receiver nodes receive these messages. Afterwards,
the receiver nodes synchronize with each other.
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