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Asked 14th May, 2019

How the GPS devices send messages on internet without internet connection ??

For Hikers/riders, they carry a GPS device which is connected to satellite and they can send messages to their family and friends ..
If I want to build a system to host all kinds of these devices and receive data from them related to their position.
WHAT kind of information or identification I need to know about these devices??
for example, for wireless or ethernet connection TCP/IP is the way to address .. what about the satellite devices ?
15th May, 2019
Pavel Petrov
University of Economics - Varna
Hi Akram,
My knowledge about GPS satellite tracking is based only on my personal experience. About 7 years ago (in the summer of 2012) me and around 10 my friends (scientists, journalists and crew members) were lost in the Chukchi Sea during an Arctic expedition. We were on the high-speed inflatable boat far away from the mother vessel (ESPY, GP). The main way of communication between the boat and the vessel was VHF marine radio. But it was completely useless, because we were around 30 miles away and the communication could not be established (the VHF capabilities is good for up to 10-15-20 miles depending on both antennas altitude). So the big problem was that we knew our GPS coordinates, but we didn't know the actual vessel coordinates in order to calculate our course and distance to salvation. We didn't even know the general direction where the vessel could be - is it North, South, East or West. The nearest land was about 80 miles to the East, but the fuel was not enough. We were desperately, completely lost in the middle of nowhere and some people started to get crazy...
And then a small device called "Yellow Brick" saves us (I believe it was some pre-version of this one: This small device has GPS receiver but also was capable to send and receive short emails (like SMS) to/from Inmarsat or Iridium satellites. So we on the lost boat could send email to the radio officer on the vessel and he could respond to us. This device could also periodically sent the GPS coordinates by email to someone so he could constantly track your location.
In conclusion - depending on the desired geographic coverage and the application needs you should subscribe to a Satellite Communication Service. The major global providers are Inmarsat, Iridium and VSAT. If you don't need a global coverage then satellites on geostationary orbit could be used and may be the expenditure will be lower.
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