Tero, I realize this is long but you should read it all and think about it. Do a little investigative work as well.
As an engineer interested in the technological claims of both sides I have to take exception to your claim that W-CDMA has been under development for 7-9 years. I'm going to quote from the ETSI UTRA W-CDMA proposal as submitted to ITU for consideration last June of 1998. I will submit the page numbers so you can read this yourself if you like. I also suggest that you pass it on to your engineer friends so that they too can evaluate what I am saying.
Before I do I want to tell you that my reading of the UTRA document is that it was thrown together by some knowledgeable individuals. Knowledgeable in certain aspects of CDMA... but not all. I can give you many examples of this apparent lack of knowledge but I will give you just one for now. The companies who wrote this specification, although they have done some reading, do not currently manufacture CDMA equipment. Their lack of experience with this technology is self evident. There is much they don't seem to understand.
Here goes.... This is a quote from page 110 of the ETSI UTRA W-CDMA submission available at the ITU website:
Linearity:
Mobile Station:
For 2 equal power signals being separated by 200 kHz leading to an output level of 21 dBm each the resulting intermodulation spectrum shall not exceed relative to peak spectrum: -38 dB at 200 kHz to -90 dB at 800 kHz offset from higher/lower frequency signal (linear decrease)
<=-95 dB at 1 MHz from higher/lower frequency signal and above
This is known as a two tone test. The idea here is that these two tones, if passed through a non-linear amplifier (like a cell phone power amp maybe) will generate intermodulation products. These products will be tones at spacings of 200khz(as above) and depending on the non-linearity...there can be quite a few...theoretically an infinite number. Their powers tend to taper off as you get farther from the two original tones. Note above how the specification calls attention to offsets of 800KHz and 1MHz above and below the original two tones.
Listen carefully... in 1998 I can't think of anyone, who does CDMA and understands it, who would specify linearity this way.
Now consider the following: From the December 1998(this month) issue of Microwave Journal, The featured technical article: "Measuring ACPR in CDMA Amplifiers" by Mark Slovic, Hewlett-Packard Co. Santa Rosa, CA USA. As you know Hewlett-Packard makes test equipment and should be up on what is going on so they can sell test equipment to companies making stuff...like CDMA equipment. Pg 74, Quote" Adjacent-channel power ratio (ACPR) testing is commonly used in the wire-less communications industry to characterize the distortion performance of CDMA amplifiers."
Did you get that? "commmonly used in the wire-less communications industry ....". Wow I'm stunned aren't you? The companies who wrote the ETSI UTRA W-CDMA specification aren't using the "commonly used" method!! BTW, the two tone test goes way way back 20's, 30's??. ACPR(adjacent channel power rejection) is something relatively new (1990's?) and found around systems doing digital noise like signals (spread spectrum...CDMA?? Cool huh??).
Now, read on because it gets even more interesting... from the same issue of Microwave Journal pg. 24 "Linear RF Power Amplifier Design for CDMA Signals: A Spectrum Analysis Approach" by Qiang Wu Intel Corp., Network Product Division, Aloha, OR and Heng Xiao and Fu Li, Portland State University, Deptartment of Electrical Engineering, Portland, OR.
Quote:"Traditionally, the nonlinearity of an RF amplifier is described by IP3 or, equivalently, by the 1dB compression point."
What this means Tero is that traditionally a 1 or 2 tone test has been used to measure the nonlinear characteristics of an amplifier.
But they continue:"In experiments and analysis it was discovered that, in some situations, using IP3(two tone test<my words>) only is not enough to describe the spectrum regrowth(or ACP...adjacent channel power<my words>), especially when the fifth-order intermodulation is relatively high compared to the third-order intermodulation".
Now, get this quote: "Quatitatively, no clear relationship or expression exists to date between the out-of-band emission level and the traditional amplifier nonlinearity description. The lack of such a relationship poses difficulties for RF designers choosing components. This problem is generic in the design of RF power amplifiers for non-constant envelope digital modulations(like CDMA<my words>)".
In other words, if you are going to specify amplifier performance and the signal to be amplified is CDMA than you can't use the traditional or two-tone description. According to Hewlett-Packard, A guy from Intel and two college researchers, this is widely known. As someone who is familiar with this technology I can assure you that this is widely known, at least amongst folks who work with CDMA.
Now, here is what really gets me about the UTRA specification, some might argue that a two-tone test will give you some idea of the amplifier performance. Yes, thats a stretch for CDMA but when you first start out and you're learning about CDMA you might be familiar with the old two tone test and feel comfortable starting with what you know but...spacing the tones 200KHz??????????? Here is what you should ask your engineer friends Tero. If the W-CDMA chip rate is 4.096MCPS and the expected 3rd and 5th order intermodulation products are going to fall say 2MHz and 4MHz away from the center of this spectrum....how in the world is a 200KHz spaced two-tone test going to shed any light on the amplifiers performance?? The 3rd and 5th order products won't fall anywhere near areas of interest!!
Tero, find some qualified engineers and ask them that question. The answer is it doesn't shed any light, it's lousy. It doesn't make any sense. The guys who wrote this spec had to answer a specific question from the ITU. They gave a standard textbook answer for linearity but even screwed up the specifics of that. But the big problem I have is that they didn't even know enough to at least specify it as an ACPR test.
You can get the ETSI UTRA W-CDMA proposal from the ITU Website at itu.int
You can also get the ARIB(Japan) W-CDMA and CDMA-2000 and all the rest there as well.
You may contact Microwave Journal at Horizon House Publications Inc., 685 Canton St., Norwood, MA 02062 and they can put you in touch with the respective authors. Of course, it should be relatively easy to contact them at HP Santa Rosa or Portland State University.
Tero, If you read the various proposals and if you weigh what is in them you will know one thing for sure. ETSI UTRA W-CDMA has not been under development for 7 -9 years with millions of dollars spent on it. The authors didn't even know how to specify amplifier linearity performance correctly for CDMA! This document is the current(according to the website as of June 1998) ETSI submission at the ITU regarding W-CDMA for 3G. Years of development? Cutting edge technology? State of the art proposal? From people who are familiar with and understand CDMA? No...not even close.
Regards
Walt |
