Low Earth Orbit vs. Geosynchronous Earth Orbit

Next-generation satellite system architectures that are vying to provide low-cost, global connectivity fall into two categories:

• LEO (Low Earth Orbit) low cost satellites: This category centers around the use of small LEO satellites, typically CubeSats. Many companies are pursuing this approach, with varying configurations in terms of altitude, one-way or two-way transmission, satellite size, frequency band, and means for connecting to gateway stations.
• GEO (Geosynchronous Earth Orbit) conventional MSS (Mobile Satellite System) satellites: This category uses a class of satellites that has provided ubiquitous connectivity over several decades for applications ranging from voice calls to internet access to video transmission.

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 Figure 1. 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.