Measuring Signal Strength on PLS8-X and PHS8-US using AT^SMONI command | Telit Cinterion IoT Developer Community
July 4, 2017 - 7:41am, 4905 views
Currently I am using AT+CSQ command to measure signal strength on PLS8-X for 3G/4G.
"According to 3GPP TS 27.007 [47], the <rssi> value is not applicable to 3G networks. Yet, with a view to
employing AT+CSQ for all networks the PHS8-P has been designed to show a <rssi> value derived from the
3G specific RSCP parameter shown by AT^SMONI. Nevertheless, please consider that connection quality in 3G
networks is depending on further factors. For example, despite good <rssi> or RSCP values for signal quality,
data throughput may vary depending on the number of subscribers sharing the same cell. It is therefore recom-
mended to use also AT^SMONI which delivers additional information, in particular the values RSCP, EC/n0,
SQual and SRxLev RX level."
So it is advisable to measure signal strength using AT^SMONI command.
Here my query is how to measure signal strength in dB using AT^SMONI command.
Syntax of AT^SMONI is as below for 3G,
^SMONI: ACT,UARFCN,PSC,EC/n0,RSCP,MCC,MNC,LAC,cell,SQual,SRxLev,PhysCh,SF,Slot,EC/
n0,RSCP,ComMod,HSUPA,HSDPA
So here I can get EC/n0, RSCP, SQual, SRxLev, EC/
n0, RSCP. But from these value how I can derive single value for signal strength and what will be acceptable range for the same.
It will be good if someone has equation to derive signal strength from AT^SMONI command.
Hello,
It's more about the network quality than the signal power. Because of the network architecture (many devices use the same frequency) the signal power is not enough to describe the network quality in 3G. That is why the RSCP (Received Signal Code Power) and EC/N0 (Carrier to noise ratio) is advised to be used instead. So to get the network quality indicator you could assign some ranges to integer values.
For example when taken separately you can consider:
RSCP >= -80 => 5
-80 > RSCP >= -90 => 4
-90 > RSCP >= -100 => 3
-100 > RSCP >= -106 => 2
-106 > RSCP >= -125 => 1
Ec/N0 >= -9 => 5
-9 > Ec/N0 >= -11 => 4
-11 > Ec/N0 >= -13 => 3
-13 > Ec/N0 >= -15 => 2
-15 > Ec/N0 >= -19 => 1
Then you can create the two dimensional table with these two values and create the combined indicator.
Regards,
Bartłomiej
Thanks for your reply. If I need to show only one value then can I show RSCP value for 3G and RSRP(Reference Signal Received Power) for 4G?
As RSCP = RSSI + Ec/N0.
Hello,
You can use only RSCP for 3G and RSRP for 4G but using RSCP + Ec/No for 3G and RSRP + RSRQ for 4G would be more accurate. As you have written RSCP is related to RSSI and Ec/N0, so we can imagine the situation when RSSI is strong and Ec/N0 is very poor which could give the acceptable RSCP but there can be problems with connection quality.
So I'd say that it all depends on how accurately you need to measure this.
Regards,
Bartłomiej
From AT^SMONI I am getting below response,
^SMONI: 3G,1007,169,-6.0,-121,310,410,3E29,C593E95,36,21,DPCH,256,2,-13.0,-102,0,11,12
OK
So my signal strength without ec/n0 is -121.
Where at the same time I am getting below response from AT+CSQ,
+CSQ: 10,99
OK
which meand signal strength is -93 (-113 + 2 * 10).
Why both values have so much difference? For stable connection, what will be threshold for signal strength (without ec/n0). Currently I have set -100dBm threshold.
Hello,
Please also notice that in the SMONI response there are RSSI and EC/N0 parameters in two places - for serving cell and dedicated channel which have different values.
Regards,
Bartłomiej
Thanks. So in below example we got two RSCP value -121 and -102 then which will be useful to show signal strength.
^SMONI: 3G,1007,169,-6.0,-121,310,410,3E29,C593E95,36,21,DPCH,256,2,-13.0,-102,0,11,12
If we should use -102dBm for signal strength then how to define signal strength in below response,
^SMONI: 3G,662,190,-7.5,-82,310,410,3E5B,C79529A,33,31,NOCONN
Also when I got NOCONN, UE connection is established. I am able to download over 3G.
For 3G RSSI = RSCP - ec/n0 (This will be negative)
For 4G RSSI = RSRP - RSRQ
Correct?
Hello,
In case of NOCONN the parameters for dedicated channel are not available. If you had a constant downloading of bigger data amount you'd probably be able to see also the dedicated channel parameters also.
Generally for signal quality monitoring it's better to use serving cell parameters.
In the documentation for PLS8 it is written that for AT+CSQ command in case of 3G RSSI value is derived from the 3G specific RSCP parameter shown by AT^SMONI.
Have you tried to issue the commands more ***** in a short time and were the replies consistent?
Generally you don't need RSSI for 3G but both RSCP and EC/N0. For 4G that would be RSRP and RSRQ.
Regards,
Bartłomiej
Currently I am executing AT^SMONI command at every 5 second. And yes for some time it is consistence.
But when I compare received signal strength (RSCP - EC/N0 for 3G and RSRP - RSRQ for 4G) from AT^SMONI with AT+CSQ then there is about 20-30 dBm difference.
Hello,
At the moment I don't know why there is a difference between RSSI calculated by you from RSCP and EC/N0 taken form SMONI reply and the RSSI value returned by CSQ command. Maybe it is calculated by the module in a different way or it's because it's measured separately and in a different way.
I agree that the difference that you have calculated is not small but this module is intended to be a communication device only. It provides some measurements to help the user ***** the network conditions but on the other hand it's not a network diagnostic unit.
Generally for 3G and 4G signal quality *****sment you should not use RSSI but the other parameters discussed here because of the 3G and 4G radio technology specifics.
Regards,
Bartłomiej