Next-generation satellite system architectures that are vying to provide low-cost, global connectivity fall into two categories:
Many companies are developing architectures targeting Satellite IoT. With one exception these companies use LEO, low-cost satellites. The exception is eSAT Global.
Above is a pictorial overview of the eSAT communications platform. Features include the GEO MSS satellites that eSAT uses. The IoT terminals, be they sensors or actuators or tracking devices, all contain an eSAT communications module which transmits about the same amount of RF power as the key fob that opens a car door – about 10 milliwatts, or 1% of a watt. Very importantly, there are no terrestrial relays or base stations. The eSAT module uses its 10-milliwatt signal to communicate directly to the MSS satellite positioned about 22,000 miles above the Earth. Although intuition might suggest that low-cost LEO satellites would lead to low-cost IoT-type connectivity, the numbers tell a much different story. Quantitative comparison of LEO vs. GEO performance reveals clear and possibly surprising conclusions, as summarized in the chart shown above. That is, in the key areas of cost-per-bit (in both directions), terminal transmit power, capacity, and spectral efficiency, GEO satellites offer a multiple of around 100x better performance.
The average cost of sending a 100-bit command via LEO CubeSat to a remote IoT terminal (“forward link”) is over 200 times higher than sending that same 100-bit command via eSAT technology using a GEO MSS satellite, such as those operated by Inmarsat. Similarly, a 100-bit report sent from a remote terminal (“return link”) will cost about 90 times more via LEO CubeSat than via GEO eSAT. On the other hand, for similar availability and data rate, the average amount of radio transmission power needed at the remote IoT terminal is about 25 times higher for LEO CubeSat systems than for the eSAT architecture, implying more expensive terminal gear with lower battery life.
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