How to calculate the path loss for a point in an UMTS FDD system from the RSCP value?

[vladdd]

Dear Professionals,

My apologies for the uneducated question, but I have not been able to find a straightforward answer to it in any specifications.

Please let me elaborate:

Let's say we have an HNB with 2 Watts of power allocated for the common pilot channel. This would mean that the radiated signal power at the HNB site (with 1dBi antenna attached) should be around 33-34dBm (with only 1 test UE in idle mode attached).
Now, by using the mobile phone to test the reception, we can see that that the RSCP power will be -25dBm on the site and will gradually reduce when increasing the distance between the HNB and UE (as expected).

What I don't understand, is how exactly the radiated CPICH power and measured RSCP values are correlated. My goal is to calculate the exact path loss value in dB by using only these 2 parameters.

I know the RSCP range in UMTS FDD is [-25;-120] by specification, but how does it correspond to standard power measurements performed with an RF power meter (in case we could measure only the CPICH power)?
Experimentally, when only the test UE is attached to the HNB, I can see that the power meter measures ~27 dBm a couple of meters away from it. This will correspond to -36 dBm RSCP on the test phone (the values are not exact, I'm just using them to illustrate my point).

I will be immensely grateful if anyone could explain this relation to me in an understandable way.

Regards,
Vlad

[Amr Harby]

Hi Vlad,

The question is not 100% clear to me ...so I will just advice with the below generic points.
1... The methodology to calculate the path loss is very simple , you calculate the difference between the CPICH value you find in SIB 5, and the RSCP measured atbthe at the idle mode...this is the methodology used by the mobile to calculate the initial RACHing power in the open loop power control.

2... one point need to be verified that the RSCP isn't at the max value of -25 dbm ... as this might indicate a higher values of RSCP while the mobile is not capable to measure due to power amplifier limitation -clipping- ...so if you have the max measured value ...it's adviced to reduce the CPICH in order in order to make sure that you're measuring a practical value not a clipped one.

3...depending on regular power meter instead of idle mode UE measurements isn't accurate , as in such a case you will be measuiring the RSSI. ..not the CPICH RSCP...the RSSI will include all the control channels power ...PCCPCH, PGCH....etc and thus you can't compare it with the CPICH transmetted value

[firstmaxim]

Total Path Loss (dB) = EIRP(dBm) - RSCP (dBm) = 34 - (-25) = 59 dB
Assume receive antenna gain = 0 dBi

[vladdd]

Hi Vlad,

The question is not 100% clear to me ...so I will just advice with the below generic points.
1... The methodology to calculate the path loss is very simple , you calculate the difference between the CPICH value you find in SIB 5, and the RSCP measured atbthe at the idle mode...this is the methodology used by the mobile to calculate the initial RACHing power in the open loop power control.

2... one point need to be verified that the RSCP isn't at the max value of -25 dbm ... as this might indicate a higher values of RSCP while the mobile is not capable to measure due to power amplifier limitation -clipping- ...so if you have the max measured value ...it's adviced to reduce the CPICH in order in order to make sure that you're measuring a practical value not a clipped one.

3...depending on regular power meter instead of idle mode UE measurements isn't accurate , as in such a case you will be measuiring the RSSI. ..not the CPICH RSCP...the RSSI will include all the control channels power ...PCCPCH, PGCH....etc and thus you can't compare it with the CPICH transmetted value

Hello,

Thank you for the response, please find my comments below:

1. Do you mean the PICH power offset parameter?
2. The value only reaches -25 about 10cm from the antenna, so it is not clipped.
3. The setup that I am using does not provide any services to the phone, it is used only for measurement tests. The power reserved for other channels is also capped to ~1dBm in this case.
I know that without decoding I am practically measuring the RSSI, but in my situation this is basically the RSSI of the CPICH, which should be the same as the value that the RSCP is derived from.

[vladdd]

Total Path Loss (dB) = EIRP(dBm) - RSCP (dBm) = 34 - (-25) = 59 dB
Assume receive antenna gain = 0 dBi

Thanks! I am using this to calculate the distance to the mobile, I will post the results soon.

Regards,
Vlad