- ... important.1
- Note that as sensor devices become more
integrated, it is expected that the ratio of communication to computation costs
will get more important over time as
silicon efficiency increases while the physical costs of
pushing radio waves over the air remain constant.
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- ... network.2
- Note that, as an optimization, it may be useful for the
routing layer to limit the extent to which queries are propagated based on properties
of the query - for example, a short-lived query over constrained geographic
area need not be sent to motes far away from that area. We reserve such optimizations for
future work.
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- ... below.3
- We omit a detailed
discussion of how new aggregate functions are registered with motes. For now,
aggregates are pre-compiled into motes. Virtual-machine
languages recently proposed for TinyOS-style (16)
motes could also be used for this purpose.
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- ... DISTINCT4
- The HISTOGRAM aggregate sorts sensor readings into fixed-width buckets and returns
the size of each bucket; it is content-sensitive because the number of buckets varies depending on how
widely spaced sensor readings are.
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- ... HISTOGRAM5
- COUNT DISTINCT returns the number of
distinct values reported across all motes.
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- ....
6
- Although independent failures are not always
a valid assumption, they will occur when local interference is the cause of loss. For
example, a hidden node may garble communication
to P1 but not P2, or one parent may be in the process of using the
radio when the message arrives.
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