Technical White Paper
Unidata NEON satellite telemetry systems can have integrated Inmarsat and Iridium satellite systems. We have conducted modelling of the data latency and, equally importantly, the costs of these services. We have also modelled the power consumption of these services. It is now clear to us that while these services are all satellite technology there are subtle aspects of each service that need to be considered when choosing an appropriate service for your needs. There are three distinct applications, where some service providers are more suitable than others.
If you have the need for what we call the “alert” function, services such as Iridium Short Burst data or Inmarsat ISAT Data Pro are probably best. However, the data transmission costs escalate greatly for these services when the data rate is anything more than an occasional transmission of a short packet of data.
If you have a need for a traditional logging and reporting function, such as regular hydrographic or industrial measurement data from a measurement site, including water level, flow, and quality, or some Modbus channels, services like Inmarsat are probably best, as the data transmission costs are more reasonable for larger volumes of data.
If you have a need for a low resolution or high resolution, image or perhaps a video capture capability, then Inmarsat would be the best as the bandwidth requirements are higher.
Satellite services are also used for only the most remote locations. Another important consideration for such very remote locations is power consumption. The ability to turn off the satellite modem most of the time to conserve power is critical. Some services allow for this easily. However, some services require establishing a “session” each time the modem is powered on, and the communications overhead in establishing a session is high, increasing the overall monthly cost to sometimes prohibitive levels.
The physical location of the measurement station is another consideration, and there is a clear distinction between Low Earth Orbit Systems and Geostationary Systems. If a geostationary system is chosen, the satellite antenna must be located such that there is a clear view of the Geostationary Satellite’s location in the sky. Sometimes this is impossible, especially in deep valleys. If a Low Earth Orbit System is chosen, these systems transit the sky and satellite antennae, regardless of location, should be able to “see” a satellite most of the time.
Low Earth Orbit systems are different, with Iridium providing the highest satellite numbers today.
The geographical location of your measurement station is another important consideration. For example, Iridium has coverage in the middle of the Pacific Ocean and in Antarctica, whereas Globalstar has coverage mainly over land areas. Inmarsat has worldwide coverage, but you still need to ensure a good view towards the satellite. The antenna elevation in, say northeast Australia maybe 60 degrees elevation and very convenient, however in south-west Australia, the elevation may be only 40 degrees elevation and this may be less convenient.
Finally, it is always prudent to have a mix of services. In a flood alert system, for example, perhaps it is best to have a mix of services from different providers and not put all your eggs in one basket. This concept is commonly referred to in the telecommunications industry as network diversity.
