Depending on utilisation, update rates and payload sizes for the various nodes a full gateway (8 channel vs single/dual/nano versions which struggle with joins and fact GW’s and nodes may be on wrong channels, etc.) should sustain 000’s if not 0’s,000’s of nodes and I suspect that are not too many TTN GW’s yet even close to saturating. Also the nature of radio means co-located or very close proximity GW’s will essentially see the same nodes payloads so having them co located unless using more complex spectrum management with say 2x8channel implementations or more is essentially redundant…unless that is the plan - have redundant GW’s in case on fails or goes off line - poss if on different backhaul solutions etc.
I ,and I know others, occasionally run co-located GW’s for performance comparison etc. and for commissioning/test set up.
Better therefore to have at least some separation…how much will depend on your location and environment, built or rural etc. Personally I tend to recommend at least 200m and pref 500-1500m separation in heavily built environments or 1-3km suburban and 2-5km+ rural depending on terrain. That way you likely get good dual coverage for many nodes (giving some coverage redundancy albeit likely on dissimilar SF’s) and also extend total single coverage by a significant amount. If you know there is good line of site coverage and key target areas well served then even greater separations can be used, again accepting a lot of covered area will be using high SF’s.
LoRa/LoRaWAN performance in general is such that in rural flat environments, using raised sites for antennae/GW’s its not unreasonable to separate the GW’s by 10-20km such that a band for nodes near the middle ground gets to see both but any further out will only be seen by one GW. Are there other GW’s in the Region? perhaps you can try to ‘dovetail’ with them for greater coverage & efficient overlap?
Am sure others will chip in with their own take on deployment…
Addendum/Edit! - if you are into BMS it may be your focus (or at least that of your boss!) may be not so much on how far apart is realistic for ‘area’ coverage but how to best achieve in/through building penetration,especially if looking in from the outside…in that case a ‘build inside/out’ approach may be more realistic for you - place GW deep inside target large buildings that are the focus and then any external area coverage is a ‘bonus’…there are many in the LoRa eco-system taking that approach including some commercial operations taking that route.
in that situation it may be that a large/deep tower block or commercial building is best served by middle floor mounted GW’s or ‘top & bottom/meet in the middle’ deployments with adjacent buildings having similar deployments…in these cases deployments are planned on assumption that through building attenuation to outside may be 10’s, 50+ or even >>100db such that large buildings within even a km or so of each other are largely invisible to each other or only provide mutual coverage in the outer margins of the buildings, and intervening spaces, etc.
You perhaps need to think on what likely deployments best suite your needs (and your boss if he is buying! …good luck…