Fortunately, this is
also the lowest energy consuming sensor, drawing 20 times less current than
a magnetometer. Figure 5 shows ?„“hr for ExScal as a function of tlpl
slp. Here
?„“hr is given by (6) with isensor = 0.292 mA. We observe that the maximum
lifetime achievable increases to 878.85 hours (or 36.62 days). This represents
an increase by a factor of 4.67 over that achieved by just using the LPL mode
and a factor of 12 over that achieved in the fully active mode.
Fig. 5. ExScal network lifetime in the low power listening mode and hierarchical
sensing with PIR as the wakeup sensor, as a function of radio sleep period, tlpl
slp.
4.6 E?®ect of Periodic Control Messages on the Lifetime
In this section, we analyze the e?®ect of varying the frequency of periodic control
messages on the network lifetime. To study the e?®ect of periodic messages
on the lifetime, we vary the value of mpr. The e?®ect of varying mpr on the
lifetime in the fully active mode is straightforward (derive a new value for
imsg
act in (5)). Analyzing the e?®ect of varying mpr when the network is using
278
the LPL mode is, however, nontrivial, because the optimal lifetime now occurs
at di?®erent values of tlpl
slp depending on the range of values of mpr.
The optimal value of ?„“hr (given by (6)) occurs at tlpl
slp = 0.4 seconds when
mpr ?· 82, at tlpl
slp = 0.2 seconds when 83 ?· mpr ?· 672, and at tlpl
slp = 0.1
seconds when 673 ?· mpr ?· 2580.
Pages:
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454