(keitai-l) Re: Multimodal technology

I have avoided the alphabet soup of wireless networking protocols, for the
most part.  I guess it's my past abortive forays into international telecom
standards -- I break out in hives whenever I hear "ITU" even whispered.

I wonder if someone could just point us to some primary sources?  Ericsson
and UMT Forum seem to say little more than "this is the best stuff since
sliced bread and pop-up toasters, you just wait".  WCDMA, as a standard,
must be pretty big -- it covers a lot of stack layers, anyway.  There can't
be any shortage of primacy sources.  Rather than having lengthy descriptions
of the wrong thing, and descriptions of the right thing that admit to not
really being clear, how about just pointing to the original descriptions of
WCDMA?

-michael turner
leap@gol.com



----- Original Message -----
From: "Joran Roslund" <joran_roslund@hotmail.com>
To: <keitai-l@appelsiini.net>
Sent: Sunday, November 11, 2001 1:41 AM
Subject: (keitai-l) Re: Multimodal technology


> Hi,
>
> >
> >On Wednesday, 7 November 2001 11:46 PM Marc Printz wrote:
> >
> > >> Now: that is interesting. How does the call setup work? Tedious?
> > >> Or could you in principle with the press of one link get a voice
> > >> connection to an IVR system up and at the same time an i-mode
> > >> connection? What about i-appli, is it possible to have concurrent
> > >> i-appli running? THIS would be excellent.
> >
> >
> >Without having exact details of FOMA's internal handset and base station
> >architecture (which I am guessing they keep secret) one cant say exactly
> >how it is implimented (anyone that knows specifics please sing out and
> >feel free to correct the figures that I guessed)
>
> You're actually describing GPRS, not WCDMA. :-)
>
> WCDMA is a lot harder to explain than a TDMA system like GPRS. I'll give
it
> a try anyway.
>
> WCDMA is a standard using CDMA. CDMA stands for code-division multiple
> access. It means that a radio resource is divided among users based, not
on
> timeslots (as in TDMA) or on different frequencies (as in FDMA) but, on
> codes. Each user is assigned a specific "code" which is used to encode the
> message. All users then transmit simultaneously using the same
frequencies.
>
> One normally uses the so-called Cocktail Party Analogy to illustrate this.
> Assume that you understand English but not French or Russian. You're at a
> cocktail party and in your vicinity there are three simulatenous
> conversations, in English, French and Russian, respectively. Since you
only
> understand English, you will capture the information in the English
> conversation, but the French and Russian ones will be just like noise to
> you. Similar for a monoglot Frenchman or Russian. On the other hand, a
> person fluent in both French and English will -- at least in theory -- be
> able to follow both conversations. Voila, there's your multimode keitai!
> It's "just" a matter of signal processing to decode several concurrent
> messages in realtime.
>
> That's the thing with CDMA. You can have 10 or 100 channels using the same
> frequency band, but your receiver, decoding with _your_ code will only
hear
> the message intended for you. The other channels will be just background
> noise.
>
> I don't want to go into too many technical details about the encoding, but
> it's actually quite simple. One thing it does, is that it increases the
> bandwidth of the message. Another word for the encoding is therefore
> _spreading_ and CDMA is referred to as a "spread-spectrum radio
technique".
>
> Spread-spectrum techniques have been used by the military for decades. One
> of the more astounding features is that the signal strength of the message
> is allowed to be very weak, since you have to decode it with the proper
> code. For instance, it's possible to send a message with a signal strength
> that lies far below the background noise level! This means that your enemy
> won't even know that you're transmitting something unless he's listening
> with the right code. Spread-spectrum techniques are also very robust
against
> jamming.
>
> Regards,
>
> Joran
>
>
>
> .
>
>
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