Effect of a double-slant (45 degree) antenna offset, on Mimosa B5c
In the presence of rain, vertically polarized waves attenuate less than horizontal polarized waves. Rotating the vertical polarization to be more horizontal would normalize the performance between the two polarizations during rain, but it would also result in lower overall performance because of the additional rain fade.
Mimosa has implemented a software Transmit Power Control (TPC) algorithm that attempts to equalize Rx signal strength across the 4 chains if they are unequal.
For these reasons, Mimosa normally recommends maintaining standard antenna orientation (horizontal polarization parallel with ground, vertical polarization perpendicular to ground) when using the B5/B5c. This especially applies to longer backhaul links in areas that experience heavy precipitation.
Mimosa B5c link examplesSeven-Mile Link in Arizona: Actual throughput (MAC layer): 300-400Mbps: From small town to tower in remote area: April 2015
- Using B5c with 34dBi dishes on both sides
- A lot of interference from operator's own APs on one towers (12 APs on remote tower, 4 on the small-town tower).
- Using 20-40MHz DFS channels
- Not using RFArmor
- This is an actual, working link
- Noise floor: 90.49dBm
- 21km link from a building in the city, out to a suburban or rural location, with one hill or small mountain in the path, but this is not high enough to be in the frenzel zone.
- To make this 21km link, customer will need B5c with 34dBi dual polarity dish (2FT) on each end. B5 with its 25dBi antenna gain is not sufficient.
- Throughput at MAC layer: 200Mbps. For higher throughput, you would need RFArmor.
Optimizing Mimosa backhaul link: B5 and B5cOptimization of the link involves trying different settings of channel sizes and power:
- Long links: For links over 10 miles / 22km: Smaller channel size 20MHz is almost certainly going to work best on a link of this distance. You should try 20MHz and then compare to 40MHz to compare the throughput with each size.
- Short links can use a wider channel size: 40 to 80 MHz, to get more throughput (as long as there is not too much interference). Experiment with the channel size and see which one gives you the most throughput.
- Power level: Adjust the power to see if you get more throughput by adjusting up and down
Posted by George Hardesty on 24th Aug 2022