What is the fastest, reliable baud rate that can be used using radio modems?

Question

I need to communicate with 30+ devices, via serial data over radio modems (Using C). Each cycle of messages should be done as quick as possible. (< 500ms)

Basic setup would be a master sending out a broadcast, then each slave replying within their allotted time slot with their status, all synchronised nicely.

We'll be using a frequency of around 870Mhz (license free), but I'm wondering what the physical limitation is, and what this would equate to in terms of maximum reliable (95%+) baud rates?

Does anyone have any experience in this field that knows a ball park figure?

Answer 1

You can use the Shannon-Hartley theorem to determine an upper bound on the data rate. You will need to know the bandwidth and the signal-to-noise ratio. Plug these numbers into the formula and you will then have an upper bound on data rate:

C == channel capacity (bits per second)
B == bandwidth of the channel (Hz)
S/N == signal-to-noise ratio (NB: linear power ratio, not dB)