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Update of GPS systems technical Update of GPS systems technical specifications and challengesspecifications and challenges
– GPS– Communication– Power
Bjorn JohnsSeptember 7, 2005Polar Technology WorkshopWashington, DC
GPS receiversGPS receiversState-of-the-art in 2005:• Power: ~2W• 1 Gb on-board memory• <$10,000 with DM chokering antenna• Observables: Track all-in-view GNSS satellites, L1, L2, C/A,
P (Y), L2C, GLONASS• Communication protocol: serial and IP• Easy field downloads: removable CF memory or just swap
receivers• Reliability: real-world MTBF > 4 years• Extreme cold environment not a big issue• Mature, commercially available, solid-state, consumer
electronics
Some off the shelf GPS choicesSome off the shelf GPS choices
Topcon
TrimbleNovatel
DM IGS standard chokeringantennas
Dana Caccamise/Eddie Wheeler Tech 2000
SCIGN radome
GPS receiver challengesGPS receiver challenges• All features are not provided in one product – typically
issue a wish-list RFP and make tradeoff decisions• New products are plagued by hardware and firmware
flaws – require rigorous testing, follow-up, and vendor response
• Custom firmware for unique needs of academic community and extreme environment
• Don’t know real MTBF in advance – operational field experience is essential before committing to a particular model in the Antarctic
Communications for GPS summaryCommunications for GPS summary• Why: Data users benefit from low latency data retrieval• Why: Advance knowledge for station maintenance and troubleshooting• Why: Streamlining of downstream data quality control and processing• GPS data volume < 1Mb/day• Adds 1W to power budget• Cost:
– Radio modem $1,500 and no recurring– Iridium modem $1,500 plus recurring airtime cost
• A three-tiered approach for GPS data retrieval:1. Line-of-sight radio links and repeaters proven for IP and serial comms an
Internet node2. Commercial satellite-based connection (e.g., Iridium) if the distance to an
Internet node exceeds the distance capability of radio modems3. Onboard memory will serve as backup in the event of loss of the communication
link, allowing for manual data retrieval during the next maintenance visit or opportunity visits.
Radio communications provenRadio communications proven
• FreeWave radios used by community since mid 1990s
• Transantarctic sites • Mt. Erebus sites• UNAVCO global applications,
EarthScope
Erebus site HOOZ
Iridium communication test at TAMDEF site Iridium communication test at TAMDEF site Fishtail PointFishtail Point
Communications for GPS Communications for GPS challengeschallenges
• Iridium data link reliability – latency, disconnects, and lock-ups
• Custom hardware solutions• Future satellite solutions?• Integrating GPS and seismic state-of-health into
one data link• Keeping on-site “smarts” to a minimum• Managing summer vs. winter comms for power-
saving• System integration: GPS/modems/download
software/delivery to data archive
Autonomous testAutonomous test--bed site built this summer, bed site built this summer, McMurdo deployment planned for October 2005McMurdo deployment planned for October 2005
UNAVCO network monitoring and data archive
On-line data access
Self-contained McMurdo test-bed
Remote site
Remote GPS data collection
Deploy system to field after burn-in
Burn-in and test integrated system, communications link
Radio link GPS data communications flow
Mt. Erebus Repeater
RADARSAT/ Bldg 71 Internet access
UNAVCO network monitoring and data archive
On-line data access
Self-contained McMurdo GPS test-bedVery remote site
Very Remote GPS data collection
Deploy system to field after burn-in
Burn-in and test integrated system, communications link
Iridium link GPS data communications flow
Iridium LEO satellite communications system
Power systems for GPSPower systems for GPS• GPS receiver system total power budget <5W
(GPS, comms, ancillary)• Photovoltaics and sealed lead acid battery
power systems well understood, but heavy and temperature limited– Solar-only “brute force”: 160W PV array, 2700Ah
battery bank for year-round operation, 5W system at 80 deg S ($3500, 2000lb)
• Wind turbines: Promising, used successfully with GPS systems on Erebus and at Mt. Coates
Power systems for GPS Power systems for GPS --challengeschallenges
• Better (and affordable) battery technology: cold performance, energy density
• One-time lithium or air cell batteries for reserve
• Wind turbine reliability, set-up• Power saving measures: near year round
operation, comms only in summer• Insulated enclosures bulk vs. cost vs.
longevity
GPS component matrixGPS component matrix
2,400bps2lb$1,5001W Iridium modem
40lb$200Solar panel frame
40lb$700Enclosure
2 lb$35030APower board
15lb$500GPS antenna mount
56kbps2lb$1,5001WRadio modem
25lb$35080WSolar panel
70lb$120100AhBattery
750kb/day10lb$10,0002.5WReceiver w/chokeData rateWeightCost PowerItem
Key GPS technical points:Key GPS technical points:
• No major “extreme environment” problems for GPS sensors
• GPS systems can be readily deployed for “spring-summer-fall” only operation
• Advanced battery technology and reliable wind systems desired for year-round operation
• Thorough system integration, testing, operation and maintenance is necessary for success
• Challenges well within reach of an organized community effort
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