6571 ?¤ 0.014)
tlpl
slp + 0.014
, (from (1))
imsg
lpl =
(382) ?¤ (0.02 + tlpl
slp) ?¤ (8 + 16)
3600
, (from (3))
isensor = 0.292 + 0.575 + 6.48 = 7.347, (from Table 2)
ievent
awk = 0.2618mA, (from (4))
and those from Table 4, we obtain a graph of the ?„“hr as a function of tlpl
slp
shown in Figure 4 for the lifetime of ExScal. The lifetime curve is concave
because there is trade-o?® in choosing the wakeup period for the radio in the
LPL mode. The higher the wakeup interval, the lower the energy consumption
when an XSM is sleeping, but the higher the energy consumed in sending a
longer preamble. The optimal value of lifetime occurs at 187.99 hours or 7.83
days. This represents an increase by a factor of 2.6 over that in the fully active
mode.
Fig. 4. ExScal network lifetime in the low power listening mode as a function of
radio sleep period, tlpl
slp.
277 Chapter 11 Maximizing the Lifetime of an Always-On WSN Application
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
120
130
140
150
160
170
180
190
Radio Sleep Period tlpl
slp
(in seconds) ??’??’>
XSM Lifetime l
hr
(in hours) ??’??’>
Santosh Kumar, Anish Arora, and Ten H. Lai
4.5 Lifetime When Using Hierarchical Sensing With LPL
When using a hierarchical sensor with the LPL mode, the network lifetime is
still given by (6), except that now the value of isensor becomes lower because
some other sensors are put to sleep.
In ExScal, the PIR sensor qualifies as a wakeup sensor.
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