Homepage - RF Cafe
Webmaster: Kirt Blattenberger | KB3UON | Sitemap | ©1996-2014
Menu below is just a small sample of what is here!
 
Custom Search
More than 10,000 searchable pages indexed.
•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

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 Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


enricolia
Post subject: WCDMA Back-Off Power Calculation Posted: Mon Jul 07, 2008 8:01 am

Lieutenant

Joined: Mon Jul 07, 2008 7:57 am
Posts: 2
Location: Belgium
Hello All,

I want to know if there is any formula or calculation we can do for back-off power in WCDMA systems.

Supposing I 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 advance.


Top

IR
Post subject: Posted: Mon Jul 07, 2008 4:28 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello Enrico,

The most 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 the P1dB.

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.


Top

enricolia
Post subject: Posted: Mon Jul 07, 2008 7:05 pm

Lieutenant

Joined: Mon Jul 07, 2008 7:57 am
Posts: 2
Location: Belgium
Hi IR,

Thank you for the reply.

You 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 ?

I am 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.


Top

IR
Post subject: Posted: Mon Jul 07, 2008 11:20 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello Enrico,

From my experience you should back off 7-10dB. Then, measure your ACPR and see if this is enough.


Top

FSomma
Post subject: Posted: Fri Jul 11, 2008 8:50 am
Hello Enrico,

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
0.0001% --- 11.24dB



Posted  11/12/2012
A Disruptive Web Presence

Custom Search
Over 10,000 pages indexed! (none duped or pirated)

Read About RF Cafe
Webmaster: Kirt Blattenberger
    KB3UON

RF Cafe Software

RF Cascade Workbook
RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

RF & EE Symbols Word
RF Stencils for Visio

Product & Service Directory
Personally Selected Manufacturers
RF Cafe T-Shirts & Mugs

RF Cafe Software

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel
Your RF Cafe Progenitor & Webmaster
Click here to read about RF CafeKirt Blattenberger... single-handedly redefining what an
                                 engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem! (Seize the Day!)

5CCG (5th MOB): My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website