How to asses the link quality?

Cellular Modules
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1

It might be useful to map the link quality to a simple scale for instance for a bar indicator.
The approach would depend on the technology. For 2G we can simply use RSSI value. For instance it can be provided by AT+CSQ command.

2G

Below there is an example of approximate mapping RSSI values in dBm to 0-9 scale:

RSSI(dBm) Indicator
>-60 9
>-65 8
>-70 7
>-75 6
>-80 5
>-85 4
>-90 3
>-95 2
>-100 1
<=-105 0

3G

For 3G RSSI would not provide us the reliable link quality due to the different radio technology. For best results we need to use 2 indicators.
Below there is an example of approximate mapping of ECN0 and RSCP (which can be obtained for most modules with AT^SMONI command) to 0-9 scale:

ECN0/RSCP <-112 >-112 >-108 >-104 >-100 >-96 >-92 >-88 >-84 >-80
>-4 0 3 4 7 8 8 9 9 9 9
>-5 0 3 4 6 7 8 8 9 9 9
>-6 0 1 3 4 6 7 8 8 9 9
>-8 0 1 3 4 5 6 7 8 8 9
>-10 0 1 2 3 4 5 6 7 8 8
>-12 0 1 2 2 3 4 5 6 7 8
>-14 0 1 1 2 2 3 4 4 6 7
>-16 0 0 1 1 2 2 3 3 4 4
>=-18 0 0 0 1 1 1 1 1 3 3
<-18 0 0 0 0 0 0 0 0 0 0

4G

For 4G it would be similar as for 3G, but we take RSRQ and RSRP (which can also be obtained for most modules with AT^SMONI command) and map to 0-9 scale:

RSRQ/RSRP <-112 >-112 >-108 >-104 >-100 >-96 >-92 >-88 >-84 >-80
>-4 0 3 4 7 8 8 9 9 9 9
>-5 0 3 4 6 7 8 8 9 9 9
>-6 0 1 3 4 6 7 8 8 9 9
>-8 0 1 3 4 5 6 7 8 8 9
>-10 0 1 2 3 4 5 6 7 8 8
>-12 0 1 2 2 3 4 5 6 7 8
>-14 0 1 1 2 2 3 4 4 6 7
>-16 0 0 1 1 2 2 3 3 4 4
>=-18 0 0 0 1 1 1 1 1 3 3
<-18 0 0 0 0 0 0 0 0 0 0
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Data Transfer Methods