Re: DA4000 (CDMA Boost for 800MHz)

"Larry W4CSC" <nospam@home.com> wrote in message =
news:3f99a84f.34352418@news.knology.net...
> On Fri, 24 Oct 2003 02:50:59 GMT, "John R. Copeland"
> <jcopelan@columbus.rr.com> wrote:
>=20
> >Larry:
> >Perfectly correct on your power and noise remarks.
> >Off target for your reflection and multipath remarks.
> >
> >CDMA uses RAKE receivers with correlators which adjust for the
> >time differences of the multipath signals, and they combine the =
decoded
> >signals in a diversity-reception manner to improve the net S/N ratio.
> >
> Hmm...thanks for the info. How do they get that to work in
> microseconds?
>=20
>=20
>=20
> Larry W4CSC
>=20

Pretty easily, really.
The chipping rate of the CDMA2000-1x spreading code is 1.2288 MHz.
(For CDMA2000-3x, it'll be equivalent to 3.6864, but that's future =
stuff.)

At the -1x rate, each chip time is equivalent to about 800 feet of =
propagation.
The correlator in each tine of the Rake Receiver slides its matching =
code
forward or backward for best alignment with the received code,
so that it matches any signal delay within plus-or-minus 400 feet.

There's a hard limit on how far the correlator dares to shift, but I =
forget the number.
I think it corresponds to something like 20 miles in the U.S.,
and several times that distance in Australia, where they need to cover
vast areas of low population density in the outback.
---JRC---

Easy. GSM was there first, and the Europeans passed laws
forbidding anything else at the time.
Remember, this was during the era when the government ministries
of Posts and Telecommunications controlled with an iron fist.

If the U.S. had followed the same government-mandated approach,
there simply wouldn't be any CDMA today.

As you know, though, GSM plans to abandon their TDMA-style RF,
and switch over to a wide-bandwidth version of CDMA,
as soon as they can get it working satisfactorily.

Since the GSM world has no prior CDMA equipment to keep compatible,
they felt free to invent WCDMA, in hopes of avoiding at least a few of
Qualcomm's patents.
WCDMA is very complicated.

In areas of the world already using CDMA, the triple-bandwidth (3x)
version will keep backward compatibility with the already deployed -1x.
---JRC---

"Larry W4CSC" <nospam@home.com> wrote in message =
news:3f99a883.34404820@news.knology.net...
> If CDMA is so much better than all the other schemes.....the question
> arises as to WHY does the rest of the world use GSM??
>=20
> Seems like everybody everywhere would want it.....instead of just
> Alltel, Verizon and Sprint.....
>=20
>

"John R. Copeland" <jcopelan@columbus.rr.com> wrote

> In areas of the world already using CDMA, the triple-bandwidth (3x)
> version will keep backward compatibility with the already deployed -1x.

That last sentence says a lot. GSM and TDMA will have to flip a switch
and everybody and everything will have to switch at the same time?

-Quick

"Quick" <dhorwitz@NOSPAMcisco.com> wrote in message =
news:1067039116.872052@sj-nntpcache-3...
>=20
> "John R. Copeland" <jcopelan@columbus.rr.com> wrote
>=20
> > In areas of the world already using CDMA, the triple-bandwidth (3x)
> > version will keep backward compatibility with the already deployed =
-1x.
>=20
> That last sentence says a lot. GSM and TDMA will have to flip a switch
> and everybody and everything will have to switch at the same time?
>=20
> -Quick
>=20
>=20

That is correct.
Perhaps by the time they get WCDMA deployed, there will be handsets
capable of both modes, and maybe those units will handle the switchover.
That's only my speculation, however.
I have absolutely no facts to support that.
But regardless, all GSM/TDMA handsets now in service
will be useless after the full cutover.

Basically that's the reason I advise caution to anyone thinking of =
signing on
to a GSM or TDMA network at the present time.
I'm pessimistic enough to think those networks will experience some
rough spots during their transition to WCDMA.
We'll all be happier if I'm wrong.
---JRC---

In article <Niimb.66936$KJ5.16198@fe2.columbus.rr.com>,
John R. Copeland <jcopelan@columbus.rr.com> wrote:
>
>"Larry W4CSC" <nospam@home.com> wrote in message
>news:3f99a84f.34352418@news.knology.net...
>> On Fri, 24 Oct 2003 02:50:59 GMT, "John R. Copeland"
>> <jcopelan@columbus.rr.com> wrote:
>>
>> >Larry:
>> >Perfectly correct on your power and noise remarks.
>> >Off target for your reflection and multipath remarks.
>> >
>> >CDMA uses RAKE receivers with correlators which adjust for the
>> >time differences of the multipath signals, and they combine the decoded
>> >signals in a diversity-reception manner to improve the net S/N ratio.
>> >
>> Hmm...thanks for the info. How do they get that to work in
>> microseconds?
>>
>>
>>
>> Larry W4CSC
>>
>
>Pretty easily, really.
>The chipping rate of the CDMA2000-1x spreading code is 1.2288 MHz.
>(For CDMA2000-3x, it'll be equivalent to 3.6864, but that's future stuff.)
>
>At the -1x rate, each chip time is equivalent to about 800 feet of propagation.
>The correlator in each tine of the Rake Receiver slides its matching code
>forward or backward for best alignment with the received code,
>so that it matches any signal delay within plus-or-minus 400 feet.
>
>There's a hard limit on how far the correlator dares to shift, but I
>forget the number.
>I think it corresponds to something like 20 miles in the U.S.,
>and several times that distance in Australia, where they need to cover
>vast areas of low population density in the outback.
>---JRC---

What is neat is that the limit is only enforced at the BTS end.
Distance-shifted signals look like they are at a different offset, and
it is up to the BTS to decide how much variance (how many P/N offset
units) from the nominal P/N offset to allow. In Australia, they just
raise the limit. This has the effect of impacting P/N offset re-use
between different cells, but that is generally not their problem in
the Outback. The handsets are oblivious to this. At the Grand Canyon
north rim (the higher side), I could hear a VZW tower 60 miles to the
south on a StarTac 7868, but the timing offset was just too much.
Falling back to AMPS worked fine (with the 600ma power), even using
only the built-in antenna.

On 26 Oct 2003 23:49:31 GMT, hoch@exemplary.invalid (CharlesH) wrote:



>the Outback. The handsets are oblivious to this. At the Grand Canyon
>north rim (the higher side), I could hear a VZW tower 60 miles to the
>south on a StarTac 7868, but the timing offset was just too much.
>Falling back to AMPS worked fine (with the 600ma power), even using
>only the built-in antenna.
>
I sail offshore from Florida to South Carolina near 80W at times, if
you're following along on your chart. Nothing compares with AMPS at
sea, especially with the 3W bagphone running off the house battery
monsters into a 12 dB gain beam antenna hauled up the 56' mainmast
pointed "towards shore" as best I can. Just like your experience at
altitude there, I'm simply amazed at the range and clarity of 20W ERP
at 50' across open water. The only time it drops out and is unusable
is when the waves get over 20' high causing the antenna to point into
the sea too often...(c;

Of course, this is a convenience to crew, not a lifesaving comm
system, which we also carry. Families sure like to hear from us and
how we're doing at regular intervals.



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

"Larry W4CSC"
> I'd buy one of cellantenna's beam antennas to go with it so you can
> put it up on top of the house......and point it at ONE celltower on
> ONE system.

One of the cellular antenna web sites states that an onmi-directional
antenna often outperforms a yagi. I was suprised to read that--especially an
the ad for yagi's!

-Paul-

That would be news to the communications industry, too...(c;



On Mon, 27 Oct 2003 09:36:47 GMT, "Real Estate Agent"
<spamblockCaryRealtor@nc.rr.com> wrote:

>
>"Larry W4CSC"
>> I'd buy one of cellantenna's beam antennas to go with it so you can
>> put it up on top of the house......and point it at ONE celltower on
>> ONE system.
>
>One of the cellular antenna web sites states that an onmi-directional
>antenna often outperforms a yagi. I was suprised to read that--especially an
>the ad for yagi's!
>
>-Paul-
>
>


Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

There's a simple explanation...
You can't point the Omni in the wrong direction:-)

-
David

nospam@home.com (Larry W4CSC) wrote in message news:<3f9d6fc8.197183986@news.knology.net>...
> That would be news to the communications industry, too...(c;
>
>
> >
> >One of the cellular antenna web sites states that an onmi-directional
> >antenna often outperforms a yagi. I was suprised to read that--especially an
> >the ad for yagi's!
> >
> >-Paul-