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LTP5901-WHM/LTP5902-WHM

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Typical perForMance cHaracTerisTics

Network motes typically route through at least two par-

ents the traffic destined for the manager. The supply

current graphs shown below include a parameter called

traffic-weighted descendants. In these graphs the term

traffic-weighted descendants refers to an amount of

activity equivalent to the number of descendants if all of

the network traffic was 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 mote

P1 has 0.75 traffic-weighted descendants. 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, adding another

0.25 to the traffic-weighted descendant 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

1-HOP

2-HOP

3-HOP

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MANAGER

Figure 6. Example Network Graph

Figure 5

TEMPERATURE (°C)

–40

100

120

–20

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0 TWD 30s REPORTING

0 TWD 5s REPORTING

2 TWD 30s REPORTING

2 TWD 5s REPORTING

5 TWD 30s REPORTING

TWD=TRAFFIC-WEIGHTED DESCENDANTS

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.

REPORTING INTERVAL (s)

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1 HOPS

2 HOPS

3 HOPS

4 HOPS

5 HOPS

REPORTING INTERVAL (s)

200

150

100

250

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0 TWD

1 TWD

2 TWD

5 TWD

TWD=TRAFFIC WEIGHTED

DESCENDANTS

Supply Current vs Temperature

Packet Latency vs Reporting Interval

Supply Current vs Reporting Interval

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