Re: Ira's Poetry Break

Eugene Leitl (
Fri, 15 Nov 1996 13:12:56 +0100 (MET)

On Thu, 14 Nov 1996, Ira Brodsky wrote:

> [...]
> However, each of the conversations is digitized (i.e., the voices are sent
> as bit streams) and assigned a unique "code." The base station receiver
> picks up all of the signals at once; a computer is able to distinguish and
> separate the different conversations by "decoding" the composite bit
> stream.

Isn't this the same technology enabling a NAVSTAR GPS receiver to sift
through several simultaneous sat signals? (in contrast to GLONASS, which is
conventional). Where's the novelty of the CDMA approach, can you disclose
a bit more details? Sounds really intriguing, but achieving the same
signal ratio must involve a feedback loop, to dynamically adjust the
sender power. What the highest possible talker load on a single
frequency? Some 10, some 100? 'twould be interesting to learn. The stuff
operates in GHz range, I presume? Individual channel bandwidth???

Lots of questions, I know...

> To the CDMA engineer, this means designing a radio network in which the
> base stations must control the transmit power of every handset to within an
> extremely fine tolerance -- no easy thing to do since signals received from
> mobile handsets naturally vary more than ten thousand-fold due to fading
> and multipath interference (i.e., signals taking different paths and
> recombining at the receiver out-of-phase).

Ah, so they have an autofeedback control loop allright...

> However, if one can make power control work it delivers significant
> advantages to the end-user. Since the handset is continually compensating
> for fading by adjusting its transmit power -- thousands of times each
> second -- the hissing and fluttering sound normally associated with
> cellular telephone completely vanishes. CDMA phones sound very much like

Uh, I thought the cellular stuff was digital? The only artefacts being voice
compression alias?

> desktop phones; some people will refuse to believe you are calling them
> from your car. And there is another beneficial side-effect of granular
> power control: it greatly extends handset battery life.

An vanilla cell phone in Europe has about 5 W peak power. What does CDMA
average about to? Does this result in nondeterministic battery life time,
depending on your movement dynamics and EM environment?

> [...]
> Well, I now have one of these CDMA personal communication phones in hand
> and it does work. Sound quality is excellent. Due to its enhanced battery
> life, you can leave the phone on all day. (Actually, it can be left in

The usual good cell stuff has a standby of max 50 hours, I thought.

> standby for two days, or you can talk for four hours, or some combination

4 hours? It's not too sensational.

> inbetween.) Initial prices are 10% - 15% less than cellular telephone.

Ah. That's an argument. Hardware prices, what about provider prices?

> However, CDMA claims ten times the capacity of conventional cellular, so

Wowie. Ten times 9.6 kBaud???

> prices will probably go much lower as competition heats up. It is also
> easy to provide features like caller ID over an end-to-end digital network,
> so they are part of the standard package. Some of the conspiracy theorists
> are now buying time for themselves by focusing on CDMA's capacity claims,
> saying the technology will blow up in operators' faces *later* -- as they
> bring more subscribers online.

But CDMA must be just cellular, with a (big) plus. They sure modeled
expected user load, this must be a bogus argument.

> In this case, the "conspiracy theory" is really just the predictable
> reaction of the radio communication industry's equivalent of The Flat Earth
> Society. It is peddled mainly by old-guard engineers (plus a couple of
> well-known Stanford professors) who simply can't accept the shift from a
> separate-frequency to a same-frequency paradigm.
> There is also much progress being made toward accessing the Net via
> wireless phones. AT&T is now selling a product called "PocketNet Phone"
> that retrieves intelligently-filtered text from Web pages. Nokia has
> introduced a phone with a somewhat larger screen and built-in Web browser.

Yeah, I've seen it. A flat box looking a plain cellphone, you open it up
like an oyster and see a diminuitive qwerty and a graphical LCD. I think
they're using ARM chips. Btw ARM, have a look at StrongARM (at DEC site),
it will be part of the next Newton, and some other products.

> If there is interest, perhaps I can post more on this later...

Yeah, please do. Most extropians like tech things, methinks ;)

Check out the Motorola website (must be, they've
progressed quite far Iridium-wise (which is just planetwide satellite
cellular), now they're trying to launch a Internet-thru-space project, a
number with direct line-of-sight intersat links (wasn't Billie up to
something similiar?). It will have some ground-located infrastructure as
well, and targeted to cost about 5 G$, or so. I forgot exact details,
check out the site.


> Ira Brodsky
> Datacomm Research Company
> Wilmette, Illinois

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