Personal Experience
Line of Sight
For long range WiFi communication, line of sight should be completely clear.
Must have some idea of features falling on line of sight, it should be clear even from treetops.
Very long range (15 to 50 km) will not work on flat earth
Over 15 km, trees in the middle will block line of sight
Over 20 km, even bushes or undulating ground will break line of sight.
Over 30km earth curvature comes in between even with 30-40m high towers.
Frequency Management
Frequency management becomes a real issue once one originating point links multiple sites through point-to-point WiFi briges. In case of point-to-multipoint, frequency band has to remain essentially same, however due to omni directional antenna long distances can not be spanned.
Such a situation (as illustrated), had following peculiarities:
For long range WiFi communication, line of sight should be completely clear.
Must have some idea of features falling on line of sight, it should be clear even from treetops.
Very long range (15 to 50 km) will not work on flat earth
Over 15 km, trees in the middle will block line of sight
Over 20 km, even bushes or undulating ground will break line of sight.
Over 30km earth curvature comes in between even with 30-40m high towers.
Frequency Management
Frequency management becomes a real issue once one originating point links multiple sites through point-to-point WiFi briges. In case of point-to-multipoint, frequency band has to remain essentially same, however due to omni directional antenna long distances can not be spanned.
Such a situation (as illustrated), had following peculiarities:
- Broadband internet was available at point A.
- It was to be carried at point C, D and E which were 50-60 km from point A.
- Clear line of sight was not available to any of the points.
- I selected a point B on a hill-top, which was in clear line-of-sight with all (point A, C, D and E).
- Distance between A and B was 40, whereas from B to other points it varied from 10-20 km.
2.4 GHz Frequency Chart
Problem
- There were three WiFi routers at location B, all in point-to-point connection.
- Leaving the selection of best frequency on 'auto' did not worked.
- Channels and frequencies are non-overlapping
What I Did?
As you can see that there are only 4 non-overlapping channels in b/g/n (20 MHz) mode and only 2 in case of 40MHz bandwidth. Thus choices in 2.4GHz were very limited.
Workable Option: Link A-B on Channel 1, whereas 5, 9 and 13 for C, D and E respectively (all OFDM 20MHz)
In case C, D and E are on 'b' mode then channel 6, 11 and 14 may be used.