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LTP5901-IPM/LTP5902-IPM

59012ipmf

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Network motes typically route through at least two parents

the traffic destined for the manager. The supply current

graphs shown in Figure 5 include a parameter called de-

scendants. In these graphs the term descendants is short

for traffic-weighted descendants and refers to an amount

of activity equivalent to the number of descendants if all

of the network traffic directed to the mote in question.

Generally the number of descendants of a parent is more,

typically 2x or more, than the number of traffic-weighted

descendants. For example, with reference to Figure 6.

Network Graph mote P1 has 0.75 traffic-weighted de-

scendants. To obtain this value notice that mote D1 routes

half its packets through mote P1 adding 0.5 to the traffic-

weighted descendant value; the other half of D1’s traffic is

routed through its other parent, P2. Mote D2 routes half

its packets through mote D1 (the other half going through

parent P3), which we know routes half its packets to mote

P1,addinganother0.25tothetraffic-weighteddescendant

value for a total traffic-weighted descendant value of 0.75.

As described in the Application Time Synchronization

section, Eterna provides two mechanisms for applications

to maintain a time base across a network. The synchro-

nization performance plots that follow were generated

using the more precise TIMEn input. Publishing rate is

the rate a mote application sends upstream data. Syn-

chronization improves as the publishing rate increases.

Baseline synchronization performance is provided for a

network operating with a publishing rate of zero. Actual

performance for applications in network will improve

as publishing rates increase. All synchronization testing

was performed with the 1-hop mote inside a temperature

chamber. Timing errors due to temperature changes and

temperature differences both between the manager and

this mote and between this mote and its descendents

therefore propagated down through the network. The syn-

chronization of the 3-hop and 5-hop motes to the manager

was then affected by the temperature ramps even though

they were at room temperature. For 2°C/minute testing

the temperature chamber was cycled between –40°C and

85°C at this rate for 24 hours. For 8°C/minute testing, the

temperaturechamberwasrapidlycycledbetween85°Cand

45°C for 8 hours, followed by rapid cycling between –5°C

and 45°C for 8 hours, and lastly, rapid cycling between

–40°C and 15°C for 8 hours.

Figure 6. Example Network Graph

REPORTING INTERVAL (sec)

1.0

1.5

2.0

4.0

58012ipm F05b

0.5

3.0

3.5

2.5

5 HOPS

4 HOPS

3 HOPS

2 HOPS

1 HOP

REPORTING INTERVAL (sec)

100

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200

5 DESCENDANTS

2 DESCENDANTS

1 DESCENDANTS

0 DESCENDANTS

Figure 5

TEMPERATURE (°C)

–60

100

120

140

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–10

2 DESCENDANTS 5sec REPORTING

5 DESCENDANTS 30sec REPORTING

2 DESCENDANTS 30sec REPORTING

0 DESCENDANTS 5sec REPORTING

0 DESCENDANTS 30sec REPORTING

MANAGER

1 HOP

2 HOP

3 HOP

58012ipm F06

Typical perForMance characTerisTics

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