Data Rate–Range Trade-off
At the same transmitter power, lowering the data rate increases range and raising it shortens range. The reason is receiver bandwidth: as the band narrows, the noise power entering it decreases and sensitivity improves. Halving the bandwidth theoretically gains about 3 dB of sensitivity, and that adds directly to the link budget.
The noise power the receiver sees is proportional to bandwidth. When you lower the data rate and narrow the filter, the signal power stays the same but the noise drops, so the signal-to-noise ratio rises. The price is a longer packet duration and a slower response.
- The 3 dB rule: halving the bandwidth gains about 3 dB; once you accumulate 6 dB, the theoretical range doubles.
- The limit: in a very narrow band, the frequency offset between transmitter and receiver and the crystal tolerance start to become a problem.
- On the remote control side: the payload is a few bytes, so no high rate is needed.
Practical outcome: in remote control links the design choice is almost always in favour of range. On the other hand the latency budget must also be preserved; when the operator releases the button, the motion must stop in under a second. In AXI's XRF protocol the latency stated in the dump data is below 1 second.
Context where this term is used: 433 MHz or 2.4 GHz?