WCDMA Back-Off Power Calculation - RF Cafe Forums
Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: WCDMA Back-Off Power Calculation Posted: Mon Jul 07, 2008 8:01 am
Joined: Mon Jul 07, 2008 7:57 am
to know if there is any formula or calculation we can do for back-off power in WCDMA systems.
have the transistor datasheet with P1dB, so how much power I must back off from that value for one WCDMA carrier
(considering WCDMA is a spread signal and P1dB normally is measured with CW signal).
Furthermore if there
is any calculation involving WDCMA composite power and power per carrier. I heard that Pcomp = Pcarrier + 20 Log
(n), where n is the number of users on that radio sector. Others say that this calculation follows exponential
rule and not logarithmic.
Please let me know what you can do for help me.
Thank you in
Post subject: Posted: Mon Jul 07, 2008 4:28 pm
Joined: Mon Jun 27, 2005 2:02 pm
important thing to know is the PAR (Peak to Average Ratio) of the signal, which is affected by the modulation
scheme, filter involved, clipping etc. Once you know this value you can derive the average power in your system.
When you find the peak value (PEP), check if this value exceeds the P1dB of the transistor. It should not exceed
Usually the PA is working up to P1dB in order to allow reasonable efficiency (Linearity and
efficiency are opposite to each other). You have to see if at P1dB, the ACPR level still meets the specification.
Post subject: Posted: Mon Jul 07, 2008 7:05 pm
Mon Jul 07, 2008 7:57 am
Thank you for the reply.
are absolutely right for the generic question. Let's try to relate some specific numbers.
For UMTS (WCDMA)
single carrier, QPSK Modulation, Channel Bandwidth 3.84 MHz, the PAR is 7 to 10 dB depending on clippling.
Question is : How much back-off in power is necessary from the P1dB using a multicarrier system ?
not sure if I should back-off 7 to 10 dB from the P1dB of transistor datasheet subtracting for more carriers (n)
10 or 20 Log rule.
Post subject: Posted: Mon Jul 07, 2008 11:20 pm
Joined: Mon Jun 27, 2005 2:02 pm
From my experience you should back off 7-10dB. Then, measure your ACPR and see if this is enough.
Post subject: Posted: Fri Jul 11, 2008 8:50 am
The 3GPP for WCDMA
HSDP defines different Tests Models. Each test model has a special configuration definition that makes the Test
Model proper to an specific measurement. For ex, Test Model 1 is defined, so that the signal has the specific
characteristics to measure ACLR, Spurious Emission, IMD; Test Model 2 is for output power dynamics, TM3 for Peak
code demain power, TM4 for EVM...etc.
The most peaking model is the TM2 w/ 32 DPCH and the CCDF is as follow:
10% --- 3.77dB
1% --- 7.27dB
0.1% --- 9.81dB
0.01% --- 10.71dB
0.001% --- 11.2dB