I’m running into a puzzling issue with gateways on our large college campus. When gateways are installed indoors, they work fine. I can often get 1/2 mile of coverage and they can access multiple floors. However, when I move the gateways outdoors—even using the same models, antennas, and mounting positions—performance drops significantly. The gateway is using a 4g SIM card so it isn’t dependent on any other local network.
Here’s what I’ve tried so far:
Multiple gateway suppliers and models (5 and counting - 3 indoor 2 outdoor models)
Different dB antennas
Trying indoor models outdoors and outdoor models indoors. Outdoor models with higher db antennas don’t work indoors or outdoors. But the indoor models don’t seem to work well outdoors either.
The pattern seems clear: indoors = good reception, outdoors = unreliable.
I suspect this might be related to RF interference. There may be other departments or campus systems operating in the same frequency band, possibly creating noise.
My questions are:
Has anyone experienced a similar issue with outdoor gateways?
Are there practical steps for identifying interference sources on unlicensed bands like this? Like low cost devices I can buy or a service provider/consultant who can help me identify issues.
If interference is confirmed, is there any recourse—e.g., involving the FCC—or is it just part of using unlicensed spectrum?
What devices are you using to assess the ‘performance’ of the GW’s? Are they indoors - in same environment as the GW’s or outdoors? What distances, and with what intervening built environment and screening? Have you analysed the metadata of the received signals at the GW’s to see how the RSSI’s and SNR’s associated with the target devices you are using for the assement? Individual values may not tell you much but analysis of volumes of info and trends may tell you a lot. Remember that whilst RF can be a bit of a black art there are some fundamentals that will likely apply. e.g. RF noise floor is aggregated and is additive……the more sources of interference and the louder they shout the higher the noise floor and consequenty the low the SNR for a given signal. It may be that moving the GW’s outside - especially if moving them higher - exposes them to more sources & higher intereferer levels. When moved inside those external interferers will see higher attenuation from the building materials and therefore the noise floor may fall. If the sensors are reasonably close then from the GW’s perspective it may appear that the sensors signal gains headroom, even if the sensors signal itself is also seeing some additional attenuation. If the sensors signal drops from say -95dbm to -105dbm from a LoRa signal processing perspective that is still a good and very usable signal level, if the noise floor is similarly attenuated by ~10dbm that will improve the SNR and may make the received signal far more useable. Remember that for any given SF there is a limit to how low/high the SNR can be for reliable demodulation, if signal is marginal or occationally droping out at a given SNR then improving the SNR by filtering/attenuating the extenal noise sources can have a remarkable impact on improving the signal capture. e.g. a SF7 signal with SNR @ -10 might not be detected reliably, if at all, but improve that to 0 or even -3 say by improving the noise floor and suddenly you have a very reliable and stable signal for the same RSSI
LoRa’s response and mitigation in the face of other RF sources as interferers, even other LoRa devices will vary by the type of modulation of those sources, or in the case of a LoRa device will depend on the relative SF of the desired target device vs the SF of the interferer(s) (There is information avalable and marketing/research info published on this TL:DR for here - GIYF)
A SDR/spectrum analyser may also be useful in helping you identify the type and relative strength of any interferers or the state of the local noise floor…..
Your ref to FCC suggests you are US based? Sadly whilst there is the positive of higher available Tx power and no duty cycle limits when compared to some other territories, there is also the negative of interferers also having option of higher Tx power and no enforced duty cycle! (Though the latter somewhat mitigated by dwell time limits and associated RF channel hopping, however, poor broadband vs narrow band antennas and limited/cheap RF filtering and device matching may limit the effectiveness of that mitigation)
