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by Graham Woods
School of Engineering, James Cook University
[email protected]
Contents
• Why do we need communications on
the GBR?
• How do we implement communications
on the GBR?
• Results from first EVER
link.
• Conclusion
Introduction
• What is the problem?
– The GBR is a large, remote and complex system.
Would like to monitor;
•
•
•
•
•
Coastal Runoff (fresh water, silt, fertilizer)
Coral Bleaching (temperatures, light)
Human Impact (fishing, shipping, security)
Pests (Crown of thorns)
Science (24-7 video footage)
LOTS OF DATA eg 260Gb for 1month of video!
Introduction cont.
• How do we monitor now?
– Fixed weather stations (HF
radio links)
BOM Link
– Data loggers
• How will we monitor in the
future?
AIMS Automatic Weather Station (AWS) at
Myrmidon Reef approximately 120km NNE
of the City of Townsville, North Queensland
(Australian Institute of Marine Science)
Proposed Network
Short Range Sensor Networks on Individual Reefs
communicating with each other and the mainland via high
speed links.
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Base Node
• Central “hub” for sensor monitoring
system
• Sensor nodes deployed around hub
• Nodes form wireless ad-hoc network.
How do we get data to mainland?
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?
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10 – 100km link
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Reef Sensor Network
Mainland Station
Communication Options
Options
Speed
(bps)
Max. Range
(km)
Running
Cost
($/day)
Purchase
Cost
($)
Availability
(%)
Comments
HF Radio
600
1000s
<1
<10,000
95+
Slow
G3 phone
4k (up)
200
<2
<1,000
99+
Slowish
Satellite
9600
200
100-1000s
<3,000
99+
Speed/ cost
Microwave
Link
10M+?
200?
<1
<50,000
90+?
Purchase
Cost
Microwave Link ?
• Would provide high speed data
transfer needed.
• BUT how could we achieve a range of
100km plus!
• Novel method “communications via the
evaporation duct”
Conventional radio link – Standard
Atmosphere
Need 100m high towers!
Evaporation Duct
Recall:
dN
dp
dT
de
 0.27  1.3  4.5
dh
dh
dh
dh
Decreasing moisture content
above the ocean surface 
trapping layer.
“Evaporation duct height” –
reflects the strength of the duct.
Ray Path Over Ocean
Note : Signal trapping above ocean
Field predictions
2.5GHz
5.5GHz
10.5GHz
Optimum Frequency and
Antenna Height
Height -vs- Path Loss for 80km link
20
2.4 GHz
5 GHz
10.5 GHz
18 GHz
24 GHz
18
Receiver Antenna Height (m)
16
14
Optimum point:
Freq = 10.5 GHz
Height = 3.7 m
12
10
8
6
4
2
0
-220
-210
-200
-190
-180
-170
Path Loss (dB)
-160
-150
-140
-130
Proposed Microwave Link
• Location : Davies Reef to
Australian Institute of Marine
Science (AIMS)
• Operating Frequency :
10.5GHz !
• Power : 1/2 W !
• Range : 78 km!
• Height ASL : 5 m!
• Data rate : 10Mbps!
Predicted Link Operation
Pt
Gt
Path Loss
Gr
A
Pr
Pr
Link:
Transmitter
Transmitter
Antenna
Receiver
Antenna
Amplifier
Commercial System : emSolutions Ethermux
F=10.6GHz, Pt = 27dBm, Gt=Gr=40dB,
Estimated Path Loss 140dB,
Signal Power:
Pr(dBm) = Pt(dBm) +Gt(dB) – PathLoss(dB) + Gr(dB)
Pr(dBm) = 27 + 40 -140 + 40 = -33dBm
Bw = 20MHz, Ta = 300 kelvin.
Noise Power:
Noise = k × Ta × Bw
= -110dBm
Signal to Noise Ratio = 77dB
Trial Davies to AIMS Link
Tx
Signal Level 3pm to 10am 21/22 Dec.
-30
Amplitude (dBm)
-40
-50
-60
-70
-80
Rx
-90
-100
0
10000
20000
30000
40000
50000
60000
70000
Time
Avg 170dB path loss, 15dB diurnal variation
Actual Link
Davies Reef
AIMS pump house
Measured Performance
20/21th August 2007
16:30 to 16:30
30/31st August, 2007
16:30 to 16:30
Min Path Loss = 167dB
Real Demonstration
• Web Camera on Davies Reef
• Realtime video feed, 10
frames/second.
Web Cam
Practical Considerations
Practical Considerations
Fouling from sea birds is a major
problem.
Conclusion
☺ Worlds first high speed over ocean link
to Great Barrier Reef.
☺ Enabling technology for reef monitoring.
 Path Loss more than predicted.
 Availability less than predicted
Questions?
See www.ReefGrid.org