Most internet of things (IoT) devices and systems are limited to transmitting data to the cloud at a rate of one or more measurements per second (1 Hz). That rate is fine for sensor measurements where the values don't change frequently, but many mechanical systems change more frequently. Nearly all mechanical systems occur with events in the 100 Hz or less range. To properly measure 100 Hz signals, you need to sample that data at 1 kHz or a sample period of 1 millisecond per measurement. But you will never be able to continuously send data from a sensor to a distant wired/wireless location at that 1 kHz rate.
Real time transmission of 1 kHz sampled data is limited to close proximity applications only. It takes 10 ms for light to travel in a vacuum 1860 miles. Light waves transmitted in a fiber cable between San Francisco and NYC could at best achieve 24 ms latency, or 24x longer than the time needed to transmit 1 kHz data with a 1 ms sample period. New York City to London would take 28 ms, and half way around the world 102 ms. Time-Sensitive Networking (TSN) has a goal of 2 ms latency, but that is for close proximity transmission between the nodes. Radio waves in a vacuum are limited to the speed of light. The propagation delay in copper (wire) is approximately 2/3 the speed of light, and then you need to add serialization delay.
The table below provides a realistic expectation for the continuous transmission of IoT data by various methods. A very wide range of mechanical events that occur between 5 Hz and 100 Hz cannot be serviced by the available long distance data transmission technologies. For anything with a event frequency of 5 Hz or more, the best option is to process the data locally using Edge Computing or Computational Storage technologies.
| Type | Latency | Sample Rate | Maximum Measurable Event Frequency |
|---|---|---|---|
| Satellite | 800 ms | 1.3 Hz | 0.13 Hz |
| 4G Cellular (< 28000 mi) |
150 ms | 7 Hz | 0.7 Hz |
| 5G Cellular (< 4000 mi) |
20 ms | 50 Hz | 5.0 Hz |
| Copper Wire(Ethernet limited to 100 m) | 24 ms | 42 Hz | 4.2 Hz |
| Fiber Cable(across USA) | 24 ms | 42 Hz | 4.2 Hz |
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