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3G performance?

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Mon, 05/01/2017 - 23:45

#1

w6bi

3G performance?

We set up a 7.5 mile link on 3 GHz this weekend. It's line of site between two hill tops. Frequency is 3440 and bandwidth is 20 MHz
Here are the metrics:
LQ/NLQ between 98 & 100% both directions. SNR about 10 dB, both ends.
Because the link was so good, we dropped the power on each end down 3 dB. That did improve the throughput some. But the throughput is significantly lower than a similar 5 GHz link. Using iperf we get 7.5 Mbits/second one direction, 6 Mbits/second the other.
It's possible that there's some interference from 2 and 5 GHz APs on one end. The other has no other emitters nearby.
What can be done to improve the throughput?

Thanks.

Tue, 05/02/2017 - 10:47

#2

AE6XE

AE6XE's picture

If not already, double check

If not already, double check and tune the distance settings. Also, have you tired a 10Mhz channel test to compare throughput? It's been a while, but I found a ~13 mile link on 3Ghz had higher throughput on 10Mhz as compared to both 5Mhz and 20Mhz channels. Larger channel widths receive higher energy from other noise and interfering signals across the larger bandwidth. The xmit power is staying the same applied across the various channel widths.

Lowering the xmit power by 3 dB and receiving higher thoughput seems counter-intuitive. With an SNR of 10dB, was that before or after the 3 db drop in xmit power? With a SNR of 10dB, you probably won't get higher than a MCS3 (26Mbps) or MCS10 (39Mbps) in 20Mhz due to the Rx sensitivity levels. You need higher SNR to get higher rates and thus throughput. Going to 10Mhz will drop the max rates in half, but jump up the SNR proportionally more to get better thoughput (at the distances we are talking about). But going to 5Mhz generatlly limits the max rates so the higher SNR may not help.

Joe AE6XE

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