4 Lifetime Analysis of ExScal
In this section, we analyze the lifetime of ExScal. We first discuss some key
assumptions needed in the lifetime analysis, then we derive the parameters
270
needed in the lifetime analysis. Next, we use these parameters to derive the
network lifetime in the fully active mode, when using the LPL feature, and
when using the hierarchical sensing feature. Finally, we analyze the e?®ects of
other fine-grained power management schemes such as varying the frequency
of periodic control messages, performing in-network data aggregation, tuning
the number of wireless reprogrammings, and controlling the amount of
actuations performed in the network, on the lifetime of ExScal.
We define the lifetime of a WSN to be the time period during which the
network continuously satisfies the application requirement. The application
requirement can be stated in various forms. One simple way to express the requirement
of an always-on application is in terms of the degree of coverage and
the notification latency. For example, in ExScal, all intruders were required
to be detected by the network at least five times in their trajectory through
the network (in order to perform detection with a high probability) and the
event notification was required to reach the closest base station in at most
two seconds. We derive a lower bound on the lifetime of ExScal. The purpose
of doing so is to allow some bu?®er so that even if some factors are missed in
the analysis (which almost always are), the network has a high likelihood of
lasting at least as long as predicted by the analysis.
Pages:
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443