Sign in with
Sign up | Sign in
Your question

VZW and modded scanners

Last response: in Network Providers
Share
Anonymous
May 29, 2005 12:44:22 PM

Archived from groups: alt.cellular.verizon (More info?)

Yesterday i was helping my father work on a car up at his garage at his
tenement house. While we were fixing the car one of his tenants came out
with a scanner. He showed me the scanner and showed me it was picking up
the cellular bands. I think he said he said he was tuning in somewhere
in the 900 band (902.xxx) ??? I asked him WHAT carrier was the scanner
picking up. He said all.
I don't beleive he was picking up ALL the carriers . But he was
receiving at LEAST one carrier on this modified scanner. Question: How
protected is VZW against these modified scanners ? I had no way of
knowing what carrier(s) he was possibly receiving. I know its NOT legal
to modify and unblock the cellular bands but i just came across this in
the real world.

More about : vzw modded scanners

Anonymous
May 29, 2005 4:18:18 PM

Archived from groups: alt.cellular.verizon (More info?)

On Sun, 29 May 2005 08:44:22 -0400, Norbert_Rocks@webtv.net
(~Norbert~) wrote:

>Yesterday i was helping my father work on a car up at his garage at his
>tenement house. While we were fixing the car one of his tenants came out
>with a scanner. He showed me the scanner and showed me it was picking up
>the cellular bands. I think he said he said he was tuning in somewhere
>in the 900 band (902.xxx) ??? I asked him WHAT carrier was the scanner
>picking up. He said all.
>I don't beleive he was picking up ALL the carriers . But he was
>receiving at LEAST one carrier on this modified scanner. Question: How
>protected is VZW against these modified scanners ? I had no way of
>knowing what carrier(s) he was possibly receiving. I know its NOT legal
>to modify and unblock the cellular bands but i just came across this in
>the real world.

Early models of some scanners (like the Radio Shack Pro-51) had
certain key press sequences that would allow you to tune in
frequencies out of its assigned bands. With scanners like this, you
can tune in the cellular band and pick up the occasional analog call.
Digital calls cannot be picked up and deciphered using these radios.
He may have also been picking up 900mhz *non-digital* cordless phones.
Anonymous
May 29, 2005 5:15:24 PM

Archived from groups: alt.cellular.verizon (More info?)

It is my understanding that they can only pick up analog cellular.
Related resources
Can't find your answer ? Ask !
Anonymous
May 29, 2005 10:35:22 PM

Archived from groups: alt.cellular.verizon (More info?)

On Sun, 29 May 2005 08:44:22 -0400, Norbert_Rocks@webtv.net (~Norbert~) wrote:

>Yesterday i was helping my father work on a car up at his garage at his
>tenement house. While we were fixing the car one of his tenants came out

>I don't beleive he was picking up ALL the carriers . But he was
>receiving at LEAST one carrier on this modified scanner. Question: How
>protected is VZW against these modified scanners ? I had no way of
>knowing what carrier(s) he was possibly receiving. I know its NOT legal
>to modify and unblock the cellular bands but i just came across this in
>the real world.
More than likely he was receiving a cordless phone not a cellular phone.

Scanners made prior to 1984 could easily receive the OLD ANALOG AMPS cell phone
systems between 861-896/824-851. Scanners made after 1984 had this band locked
out. In some it was as simple as a few keystrokes to restore, others required a
little electronic surgery and were quickly back to scanning this area.

Modern ones have this area locked out in the firmware similar to a PC BIOS in
ROM that can not be modified.

In the US it is ILLEGAL to monitor cellular phone systems, analog (AMPS) or
digital (CDMA, TDMA, iDEN, GSM). Monitoring the more prevalent digital systems
would require a very expensive device called a service monitor, NEW $20,000.00 +
USED $7,000.00 and up.

If this was in the 902-928 band then he was monitoring analog cordless phones,
just like you can do the same for the older model phones in the 46-50MHz region.
Also some 2.4GHz & 5.8GHz phones are analog and can be monitored if the radio
covers these bands, some of the more high end ones do.

If you have a DIGITAL cellular phone your not likely to be monitored by just Joe
Scanner, these can be monitored quite easily with the right equipment.

If you have a cordless phone make sure it says DIGITAL SPREAD SPRECTUM or DSS or
DSSS or FSSSH on it other wise its monitorable


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
Anonymous
May 29, 2005 11:59:05 PM

Archived from groups: alt.cellular.verizon (More info?)

Your dad lives in a tenement house?
Anonymous
May 30, 2005 3:04:30 AM

Archived from groups: alt.cellular.verizon (More info?)

On Sun, 29 May 2005 08:44:22 -0400, Norbert_Rocks@webtv.net (~Norbert~)
wrote:
>He showed me the scanner and showed me it was picking up
>the cellular bands. I think he said he said he was tuning in somewhere
>in the 900 band (902.xxx) ??? I asked him WHAT carrier was the scanner
>picking up. He said all.

If it was 900 MHz, he was picking up analog cordless phones.

If it was 800 MHz, he was picking up analog cell phones. If your phone
is digital-only, or if you can set it to digital-only, a regular scanner
will not be able to monitor your calls.

--
Bob Scheurle | "There's nobody getting
njtbob@X-verizon-X.net | rich writing software."
Remove X's and dashes | -- Bill Gates, March 1980
Anonymous
May 30, 2005 3:36:25 AM

Archived from groups: alt.cellular.verizon (More info?)

xxnonexnonexx@tampascanner.info wrote in
news:rdgk9112bo4fjqa8tleane80tnb0s84n4d@4ax.com:

> Scanners made prior to 1984 could easily receive the OLD ANALOG AMPS
> cell phone systems between 861-896/824-851. Scanners made after 1984
> had this band locked out. In some it was as simple as a few keystrokes
> to restore, others required a little electronic surgery and were
> quickly back to scanning this area.
>

The government scanners (FBI, CIA, IRS) all listen to your CDMA signal.....

They're a LOT more dangerous than Dad would ever be. After 9/11 they don't
even need a judge's permission to listen in the name of "Homeland
Security", the Gestapo's new arm.

Be careful what you say.....
Anonymous
May 30, 2005 6:02:05 AM

Archived from groups: alt.cellular.verizon (More info?)

~Norbert~ wrote:
> Yesterday i was helping my father work on a car up at his garage at his
> tenement house. While we were fixing the car one of his tenants came out
> with a scanner. He showed me the scanner and showed me it was picking up
> the cellular bands. I think he said he said he was tuning in somewhere
> in the 900 band (902.xxx) ??? I asked him WHAT carrier was the scanner
> picking up. He said all.

If it was the 900MHz band, then he probably wasn't picking up ANY
cellular carriers. Instead, he was picking up analog 900Mhz cordless
phones hooked up to the wireline network, the common variety of cordless
landline phones you can buy at wal-mart and radioshack. It's likely
quite a few people have these in the surrounding neighborhood, and their
signal can carry a surprisingly long distance. But, it was highly
unlikely that any of those signals he was picking up were cellular.

> I don't beleive he was picking up ALL the carriers . But he was
> receiving at LEAST one carrier on this modified scanner. Question: How
> protected is VZW against these modified scanners ? I had no way of
> knowing what carrier(s) he was possibly receiving. I know its NOT legal
> to modify and unblock the cellular bands but i just came across this in
> the real world.

Assuming someone actually does have a modified scanner that can pick up
the cellular band, the chances of picking up present-day signals is
becoming more and more slim as time passes. VZW, Cingular, AT&T and
other networks that have licenses in the 800MHz cellular band are
radpily converting to all digital, with a "sunset date" for required
analog capability of January 1, 2007. And carriers in the 1.9GHz band
(Sprint, T-Mobile, and the newer portions of Verizon and Cingular) were
always digital, so there is nothing to worry about there.

In layman's terms: a modified scanner could only pick up analog cellular
transmissions, and those are becoming more and more scarce as time
passes. "Old school" cellular companies that have been around for
awhile usually have one or two channels per cell site on their networks
that are still analog to accomodate roaming and people with older
phones, but the vast majority of cellular traffic nowadays is digital.
Scanners, however, are only capable of picking up the narrowband FM type
of signal that analog service transmits. If you use that same scanner
to pick up a digital signal, all you'll hear is a high frequency hiss or
buzz, instead of conversations. In fact, the newer technology (CDMA
1xRTT, EV-DO, and UMTS) has an analog "sound" that sounds a lot like
plain old static.

So as long as you have a digital cell phone (CDMA, TDMA, iDEN or GSM)
and make calls in digital mode only, you're very safe from the average
Joe eavesdropping with a scanner. If you stick with carriers like
Sprint, T-Mobile or Nextel, then you're virtually guaranteed protection
from such eavesdroppiung, as these carriers never did and never do offer
analog service.

As far as landline cordless phones go (which is what your friend was
probably picking up), you're still safe as long as you avoid the 900Mhz
analog models, and instead use a 2.4GHz or 5.8GHz Digital Spread
Spectrum (DSS) phone. Such phones use an encryption method very similar
to Verizon and Sprint's CDMA digital cellular service, and are just as
difficult to decode and eavesdrop on.

Of course, if you're conducting the type of business that government
agencies might be interested in, then all bets about eavesdropping are
off. But usually they have other, more direct methods for intercepting
phone calls at the cellular switch, rather than using an over-the-air
method for picking up your calls.



--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 30, 2005 6:02:06 AM

Archived from groups: alt.cellular.verizon (More info?)

analog is optional for Cellular providers on Feb 18, 2008

It is against the law today to listen to the Cellular Band

It is very illegal to listen in digital very hard to do on CDMA.
Government like (FCC, FBI, CIA) in my opinion should not monitor your
calls unless you are under an investigation or someone not a US citizen
with a suspicion of committing a crime.

Sometimes a road to hell is paved on good intentions. :flamemad:


--
agentHibby
------------------------------------------------------------------------
Cell Phone Forums: http://cellphoneforums.net
View this thread: http://cellphoneforums.net/t176993.html
Anonymous
May 30, 2005 6:21:49 AM

Archived from groups: alt.cellular.verizon (More info?)

Larry W4CSC wrote:



> The government scanners (FBI, CIA, IRS) all listen to your CDMA signal.....

Actually, listening in on CDMA is harder than you think, and only
getting harder as the vocoders get more diverse (QCELP 8k/13k, EVRC, and
the new packetized vocoders coming out for EVDO Rev a) . But no matter.
The government generally has NO INTEREST in monitoring the *signal*.
They don't have to. It's way easier for them to just tap your line at
the MTSO and get a much more reliable, better quality recording of your
calls that way, and they don't even have to follow you around with an
antenna.

> They're a LOT more dangerous than Dad would ever be. After 9/11 they don't
> even need a judge's permission to listen in the name of "Homeland
> Security", the Gestapo's new arm.
>
> Be careful what you say.....

You keep wearin' your foil hat, Larry. :) 



--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 30, 2005 10:09:39 AM

Archived from groups: alt.cellular.verizon (More info?)

Isaiah Beard <sacredpoet@sacredpoet.com> wrote in
news:119lc80ba2uk1b5@corp.supernews.com:

> You keep wearin' your foil hat, Larry. :) 
>

No....My cell antenna doesn't require a groundplane...(c;
Anonymous
May 30, 2005 11:34:59 AM

Archived from groups: alt.cellular.verizon (More info?)

Larry W4CSC wrote:
>> xxnonexnonexx@tampascanner.info wrote in
>> news:rdgk9112bo4fjqa8tleane80tnb0s84n4d@4ax.com:
>>
>>> Scanners made prior to 1984 could easily receive the OLD ANALOG AMPS
>>> cell phone systems between 861-896/824-851. Scanners made after 1984
>>> had this band locked out. In some it was as simple as a few
>>> keystrokes to restore, others required a little electronic surgery
>>> and were quickly back to scanning this area.
>>>
>>
>> The government scanners (FBI, CIA, IRS) all listen to your CDMA
>> signal.....
>>
>> They're a LOT more dangerous than Dad would ever be. After 9/11
>> they don't even need a judge's permission to listen in the name of
>> "Homeland Security", the Gestapo's new arm.
>>
>> Be careful what you say.....

Not so - court orders are still required to tap phone lines......

"Listening" to CDMA signals is pretty difficult and the "Homeland Security"
people, for whom I do consulting work, don't eavesdrop on everyone. They DO
monitor cellular traffic that is connected with narcotrafficantes in
Colombia and other countries and, with a court order, on suspected criminals
and terrorists in the USA......and that don't make them the "new"
Gestapo.....that's a pretty vicious canard that you can't support with
facts....

PC
Anonymous
May 30, 2005 11:37:07 AM

Archived from groups: alt.cellular.verizon (More info?)

Larry W4CSC wrote:
>> Isaiah Beard <sacredpoet@sacredpoet.com> wrote in
>> news:119lc80ba2uk1b5@corp.supernews.com:
>>
>>> You keep wearin' your foil hat, Larry. :) 
>>>
>>
>> No....My cell antenna doesn't require a groundplane...(c;

Your views in re the actions of the HSD requires more than a
grounplane.....:) 

PC
Anonymous
May 30, 2005 4:13:07 PM

Archived from groups: alt.cellular.verizon (More info?)

On Mon, 30 May 2005 02:02:05 -0400, Isaiah Beard
<sacredpoet@sacredpoet.com> wrote:
>As far as landline cordless phones go (which is what your friend was
>probably picking up), you're still safe as long as you avoid the 900Mhz
>analog models, and instead use a 2.4GHz or 5.8GHz Digital Spread
>Spectrum (DSS) phone.

You make it sound like all 900 MHz phones are analog and all 2.4/5.8 GHz
phones are digital. That's not true. I had a digital 900 MHz phone, and
some 2.4/5.8 GHz phones are analog.

>Such phones use an encryption method very similar
>to Verizon and Sprint's CDMA digital cellular service, and are just as
>difficult to decode and eavesdrop on.

I would not call spread spectrum transmission an "encryption method".

--
Bob Scheurle | "There's nobody getting
njtbob@X-verizon-X.net | rich writing software."
Remove X's and dashes | -- Bill Gates, March 1980
Anonymous
May 30, 2005 4:13:08 PM

Archived from groups: alt.cellular.verizon (More info?)

Bob Scheurle wrote:
> On Mon, 30 May 2005 02:02:05 -0400, Isaiah Beard
> <sacredpoet@sacredpoet.com> wrote:
>
>>As far as landline cordless phones go (which is what your friend was
>>probably picking up), you're still safe as long as you avoid the 900Mhz
>>analog models, and instead use a 2.4GHz or 5.8GHz Digital Spread
>>Spectrum (DSS) phone.
>
>
> You make it sound like all 900 MHz phones are analog and all 2.4/5.8 GHz
> phones are digital.


No, I specifically stated he needs to pick up a *DSS* phone in the 2.4
GHz or 5.8GHz band. I'd appreciate it if you didn't read more into my
posts than is there.


>>Such phones use an encryption method very similar
>>to Verizon and Sprint's CDMA digital cellular service, and are just as
>>difficult to decode and eavesdrop on.
>
>
> I would not call spread spectrum transmission an "encryption method".

Encryption: 1. The use of an algorithmic process to transform data into
a form in which there is a low probability of assigning meaning without
use of a process or key. 2. The process of obscuring information to
make it unreadable without special knowledge.

The primary purpose of spread spectrum technology in cordless phones is
to obscure the transmission to eavesdroppers and ensure a reasonable
level of privacy. That seems to count as a form of encryption.

Now is there anything else about my posts you'd like to misconstrue?


--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 30, 2005 7:13:49 PM

Archived from groups: alt.cellular.verizon (More info?)

I thought the primary purpose of cdma wireless phones was account
security and getting past interference. Lower power and privacy are
added benefits.
Anonymous
May 30, 2005 7:42:09 PM

Archived from groups: alt.cellular.verizon (More info?)

On Mon, 30 May 2005 10:57:06 -0400, Isaiah Beard
<sacredpoet@sacredpoet.com> wrote:
>The primary purpose of spread spectrum technology in cordless phones is
>to obscure the transmission to eavesdroppers and ensure a reasonable
>level of privacy. That seems to count as a form of encryption.

No, the primary purpose is to improve the signal-to-noise ratio.

--
Bob Scheurle | "There's nobody getting
njtbob@X-verizon-X.net | rich writing software."
Remove X's and dashes | -- Bill Gates, March 1980
Anonymous
May 31, 2005 2:10:20 AM

Archived from groups: alt.cellular.verizon (More info?)

Bob Scheurle wrote:
> On Mon, 30 May 2005 10:57:06 -0400, Isaiah Beard
> <sacredpoet@sacredpoet.com> wrote:
>
>>The primary purpose of spread spectrum technology in cordless phones is
>>to obscure the transmission to eavesdroppers and ensure a reasonable
>>level of privacy. That seems to count as a form of encryption.
>
>
> No, the primary purpose is to improve the signal-to-noise ratio.

Bzzt! Sorry. There are a few reasons for the implementation fo CDMA,
but "improving the signal-to-noise ratio" - whatever that's supposed to
mean, as it sounds like you're picking up a random radio-related term
out a hat to make yourself look knowledgeable - is NOT one of them. In
fact, a degrading Ec/Io (or what you call "the signal-to-noise ratio")
is CDMA's biggest WEAKNESS as such a network gets heavily loaded. The
more users you have on a pilot, the higher the noise floor... a
compromise you do NOT have to contend with in analog, IS-136, iDEN or GSM.

And it seems that just about everyone with actual knowledge of spread
spectrum disagrees with you:

"The basic idea behind frequency hopping is simple -- instead of
transmitting on one frequency, a spread spectrum system switches rapidly
from one frequency to the next. The choice of the next frequency is
random, so it is nearly impossible for someone to eavesdrop or jam the
signal." - http://tinyurl.com/7cbag

"Increased privacy is inherent to CDMA technology. CDMA phone calls will
be secure from the casual eavesdropper since, unlike an analog
conversation, a simple radio receiver will not be able to pick
individual digital conversations out of the overall RF radiation in a
frequency band." - http://tinyurl.com/492yv

"With FDMA a signal can be detected simply by using an off-the-shelf
scanner. TDMA detection is more difficult but not impossible for the
expert. Obviously CDMA privacy is much better. It is very difficult to
locate calls in the noise stream let alone crack the code to gain
illegal access to the data you want." - http://tinyurl.com/d7ld2

While privacy isn't the ONLY reason for CDMA deployment (the other major
reason being superior system capacity when properly deployed to
compensate for the above-mentioned noise floor issue), it is indeed a
primary one. Incendence of cloning and eavesdropping were very nearly
eliminated with CDMA deployment, and cellular carriers have a huge
motivation to ensure call privacy when a lack thereof costs them money
in terms of fraud.

--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 31, 2005 2:25:21 AM

Archived from groups: alt.cellular.verizon (More info?)

Isaiah Beard wrote:
>
> You keep wearin' your foil hat, Larry. :) 

Isaiah! and I thought you were devoid of a sense
of humor.

-Quick
Anonymous
May 31, 2005 2:36:21 AM

Archived from groups: alt.cellular.verizon (More info?)

Isaiah Beard wrote:
>
> Bzzt! Sorry. There are a few reasons for the
> implementation fo CDMA, but "improving the
> signal-to-noise ratio" - whatever that's supposed to
> mean, as it sounds like you're picking up a random
> radio-related term out a hat to make yourself look
> knowledgeable - is NOT one of them. In fact, a
> degrading Ec/Io (or what you call "the signal-to-noise ratio")
> is CDMA's biggest WEAKNESS as such a network gets heavily
> loaded. The more users you have on a pilot, the higher
> the noise floor... a compromise you do NOT have to
> contend with in analog, IS-136, iDEN or GSM.

Of course you fail to mention that you can't get that
that many users on comparable analog, IS-136, or
GSM (iDEN I know absolutely nothing about). The
primary reason for CDMA is capacity. Yes, quality
degrades as it gets "crowded" but you can get far
more users on there before the quality is unacceptable.
(I'm suprised. You've always just dryly presented the facts
with no agenda... what happened?)

> "Increased privacy is inherent to CDMA technology. CDMA
> phone calls will be secure from the casual eavesdropper
> since, unlike an analog conversation, a simple radio
> receiver will not be able to pick individual digital conversations
> out of the overall RF radiation in a frequency band."
> - http://tinyurl.com/492yv

"inherent to". Comes with it, comes for free, side benefit, etc.

> While privacy isn't the ONLY reason for CDMA deployment
> (the other major reason being superior system capacity
> when properly deployed to compensate for the
> above-mentioned noise floor issue), it is indeed a
> primary one. Incendence of cloning and eavesdropping
> were very nearly eliminated with CDMA deployment, and
> cellular carriers have a huge motivation to ensure call
> privacy when a lack thereof costs them money
> in terms of fraud.

Yes, I'm sure it was a requirement but the overwhelming
impetus was capacity.

-Quick
Anonymous
May 31, 2005 3:00:12 AM

Archived from groups: alt.cellular.verizon (More info?)

"Proconsul" <nospam@nospam.org> wrote in
news:eLHme.10877$7p.2455@fed1read06:

> and that don't make them the "new"
> Gestapo.....that's a pretty vicious canard that you can't support with
> facts....
>

If I worked for them, I'd be on their side, too.

I never said they were monitoring anyone's phone calls. Noone did. What I
said is the POTENTIAL now exists for them to monitor phone calls in the
interest of "National Security" without bothering to go to the court system
for permission. This has been widely discussed in all the media. Does
your job keep you in a vacuum, too?

Here's a good place to start reading:

http://www.global-teck.com/english/wiretappingnews.php

Scary....very scary.....

George Orwell had the DATE wrong......
Anonymous
May 31, 2005 3:00:13 AM

Archived from groups: alt.cellular.verizon (More info?)

Larry W4CSC wrote:
>> "Proconsul" <nospam@nospam.org> wrote in
>> news:eLHme.10877$7p.2455@fed1read06:
>>
>>> and that don't make them the "new"
>>> Gestapo.....that's a pretty vicious canard that you can't support
>>> with facts....
>>>
>>
>> If I worked for them, I'd be on their side, too.
>>
>> I never said they were monitoring anyone's phone calls. Noone did.
>> What I said is the POTENTIAL now exists for them to monitor phone
>> calls in the interest of "National Security" without bothering to go
>> to the court system for permission. This has been widely discussed
>> in all the media. Does your job keep you in a vacuum, too?

Nonsense - and you can cut the ad hominum stuff.....I've worked in the
security area for more than forty years in order to preserve that security,
not enter into conspiricies for the likes of you to keep braying
about.....like most naysayers, you haven't a clue.....

What you've posted is simply untrue.....

>> Here's a good place to start reading:
>>
>> http://www.global-teck.com/english/wiretappingnews.php

Hardly a credible source.....

>> Scary....very scary.....

Why? What is there to be "scared" about - is the sky falling???

>> George Orwell had the DATE wrong......

Rubbish.....

PC
Anonymous
May 31, 2005 6:54:51 AM

Archived from groups: alt.cellular.verizon (More info?)

With cordless phones, it's DSS that you are looking for to avoid
interception, regardless of the band. I have a 900MHz DSS phone. BTW,
are the higher frequencies only better from a marketing point of view
(more MHz somehow better), or is there some technical advantage of
900MHz vs. 2.4GHz vs 5.8GHz? And as has been pointed out, there are
analog phones the higher frequencies which are easy to intercept.

With CDMA cellular/PCS service, the spreading algorithm for the link
from the phone to the cell site includes the ESN, without which it is
VERY difficult to even detect the particular signal out of all of the
other traffic on the same frequency, even with the appropriate test
equipment.
Anonymous
May 31, 2005 7:07:40 AM

Archived from groups: alt.cellular.verizon (More info?)

On Mon, 30 May 2005 22:10:20 -0400, Isaiah Beard
<sacredpoet@sacredpoet.com> wrote:
>
>Bob Scheurle wrote:
>> On Mon, 30 May 2005 10:57:06 -0400, Isaiah Beard
>> <sacredpoet@sacredpoet.com> wrote:
>>
>>>The primary purpose of spread spectrum technology in cordless phones is
>>>to obscure the transmission to eavesdroppers and ensure a reasonable
>>>level of privacy. That seems to count as a form of encryption.
>>
>> No, the primary purpose is to improve the signal-to-noise ratio.
>
>Bzzt! Sorry. There are a few reasons for the implementation fo CDMA,
>but "improving the signal-to-noise ratio" - whatever that's supposed to
>mean, as it sounds like you're picking up a random radio-related term
>out a hat to make yourself look knowledgeable - is NOT one of them. In
>fact, a degrading Ec/Io (or what you call "the signal-to-noise ratio")
>is CDMA's biggest WEAKNESS as such a network gets heavily loaded. The
>more users you have on a pilot, the higher the noise floor... a
>compromise you do NOT have to contend with in analog, IS-136, iDEN or GSM.
>[remainder snipped]

We're talking about cordless phones, so there's no "pilot". What I was
referring to is that with DSS you can actually pull the signal out from
below the noise floor. i.e., a useable signal can be much weaker than a
non-spread spectrum signal. That's the primary purpose of the use of DSS
in cordless phones - to allow the reception of a signal which is much
weaker than a normal phone's signal.

Of course there are other advantages, and we can argue about them until
the cows come home. e.g., longer battery life (because the signal can be
weaker), less interference (because you can recover the signal from below
the noise), and more security (but not what would rate as "encryption"
unless your standards are so low you'd count ROT13 as encryption).

Cincinnati Microwave, maker of what I believe was the first consumer
spread-spectrum phone, had an excellent white paper on the subject, but
it's no longer online, and is not available via archive.org. I'll see if
I can find it. I think I have it on an old VAX at work somewhere.

--
Bob Scheurle | "There's nobody getting
njtbob@X-verizon-X.net | rich writing software."
Remove X's and dashes | -- Bill Gates, March 1980
Anonymous
May 31, 2005 7:07:41 AM

Archived from groups: alt.cellular.verizon (More info?)

Bob Scheurle wrote:

> We're talking about cordless phones, so there's no "pilot".



Funny, this is alt.cellular.verizon, and the OP was concerned about the
privacy of his cellular phone.


--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 31, 2005 1:54:51 PM

Archived from groups: alt.cellular.verizon (More info?)

On Tue, 31 May 2005 02:54:51 GMT, CharlesH <hoch@exemplary.invalid>
wrote:
>With cordless phones, it's DSS that you are looking for to avoid
>interception, regardless of the band. I have a 900MHz DSS phone. BTW,
>are the higher frequencies only better from a marketing point of view
>(more MHz somehow better), or is there some technical advantage of
>900MHz vs. 2.4GHz vs 5.8GHz? And as has been pointed out, there are
>analog phones the higher frequencies which are easy to intercept.

I would expect that, all other things being equal, _lower_ frequencies
would have greater range and better building penetration. Certainly, 900
MHz would be better than 5.8 GHz in terms of effects on the human body.

Any advantage of the higher frequencies may simply be that they're
"newer", so you're less likely to have a neighbor on the same frequency
causing interference.

--
Bob Scheurle | "There's nobody getting
njtbob@X-verizon-X.net | rich writing software."
Remove X's and dashes | -- Bill Gates, March 1980
Anonymous
May 31, 2005 1:54:52 PM

Archived from groups: alt.cellular.verizon (More info?)

Thankx for the responses . He was picking up old analog carriers and the
cordless land line phones i just wanted to be sure. My main area of
concern was using the cell phone and giving CC info over it. I always
make sure its in DIGITAL mode when making such a call. Im quite sure the
goverment doesn't care about me ordering a pizza over the phone.
Anonymous
May 31, 2005 7:49:53 PM

Archived from groups: alt.cellular.verizon (More info?)

Larry W4CSC wrote:
> Isaiah Beard <sacredpoet@sacredpoet.com> wrote in
> news:119nhsdgovqnm41@corp.supernews.com:
>
>
>>ONLY reason for CDMA deployment
>
>
> Let's all be honest. CDMA has nothing to do with SERVICE.

Actually, it does. You're seriously oversimplifying the issue.

I know you're a huge fan of AMPS, but to be honest, cellular use has
grown to a point where analog won't cut it. If we were to throw out all
the digital gear today and put everyone back on analog, there would be a
TON of network busies and failed call attempts.

The AMPS spectrum layout allocated roughly 660 channels among two
carriers. That gives each carrier an effective ability to handle about
325 or so callers at one time in analog mode only. that used to be fine
back when a mobile phone was a luxury item, but now that carriers are
counting their users in the millions, the number of simultaneous users
on a network in a given metro area can number well into the thousands,
AMPS isn't going to cut it. GSM boasts 6 to 15 times that capacity,
which starts to make the situation look reasonable. CDMA claims 10-20
times capacity, which is even better.


> If you come up with a working scheme that can load each channel up to 512
> simultaneous users, they'll drop CDMA like a hot potatoe and make you
> filthy rich, too.....

I'm certain they would!

--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 31, 2005 7:50:54 PM

Archived from groups: alt.cellular.verizon (More info?)

Quick wrote:
> Isaiah Beard wrote:
>
>>You keep wearin' your foil hat, Larry. :) 
>
>
> Isaiah! and I thought you were devoid of a sense
> of humor.

Don't confuse me with you, Quick. ;) 

--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
May 31, 2005 8:17:05 PM

Archived from groups: alt.cellular.verizon (More info?)

Quick wrote:
> Isaiah Beard wrote:
>
>>Bzzt! Sorry. There are a few reasons for the
>>implementation fo CDMA, but "improving the
>>signal-to-noise ratio" - whatever that's supposed to
>>mean, as it sounds like you're picking up a random
>>radio-related term out a hat to make yourself look
>>knowledgeable - is NOT one of them. In fact, a
>>degrading Ec/Io (or what you call "the signal-to-noise ratio")
>>is CDMA's biggest WEAKNESS as such a network gets heavily
>>loaded. The more users you have on a pilot, the higher
>>the noise floor... a compromise you do NOT have to
>>contend with in analog, IS-136, iDEN or GSM.
>
>
> Of course you fail to mention that you can't get that
> that many users on comparable analog, IS-136, or
> GSM (iDEN I know absolutely nothing about). The
> primary reason for CDMA is capacity. Yes, quality
> degrades as it gets "crowded" but you can get far
> more users on there before the quality is unacceptable.


In theory yes; in practice I'd have to disagree. Qualcomm has a
wonderful marketing machine that espouses the wonders of CDMA and how
exceptionally superior it is in handling excessive call loads. And yes,
a "properly-deployed" network will outperform a GSM, iDEN or IS-136
network. But the fact is, Qualcomm makes light of the fact that the
requirement to "properly deply" are VERY hard-felt when you try to push
CDMA to the marketed extremes. Overcoming the limitations requires
significantly more capital outlay (read: more cell sites spaced closer
together) than GSM or other networks to get the desired results. So,
most CDMA carriers prefer NOT to push the limits as much, and don't
"properly deploy" as Qualcomm would like. They certainly could, if they
had the inclination to throw a few billion more dollars at the problem,
and some more lawyers to handle the NIMBY crowds that will offer
resistance to more cell antennas going up in their neighborhoods. But
you can bet the carrier that does will charge an arm and a leg to let
you use that network.

Meanwhile, new vocoders have been developed for GSM and iDEN that have
improved compression ratios and increased their cpacity somewhat as
well. Of course they don't surpass the ideal theoretical capabilities
of CDMA 1xRTT, but they do keep up quite well with the far-from-ideal
implementations that exist in the real-world. And when UMTS finally
gets off the ground in a larger scale, the point will be moot anyway, as
it's slated to run on W-CDMA.

So, with all things being equal, CDMA in the real world still performs
about the same as GSM and iDEN, perhaps slightly better if you're
willing to give less than toll-quality service. If better vocoders were
implemented on IS-136, the same would probably be true there as well.
But so far, there isn't a carrier I know of that's interested in moving
IS-136 forward.

Bottom line: there's no doubt that CDMA is the best network money can
buy. It's just that no one has actually paid full price for it yet.

> (I'm suprised. You've always just dryly presented the facts
> with no agenda... what happened?)

I'm still presenting the facts as I see them. You on the other hand,
ALWAYS have an agenda. So, what is yours in this thread?



--
E-mail fudged to thwart spammers.
Transpose the c's and a's in my e-mail address to reply.
Anonymous
June 1, 2005 1:04:00 AM

Archived from groups: alt.cellular.verizon (More info?)

On Tue, 31 May 2005 03:07:40 GMT, I wrote:
>Cincinnati Microwave, maker of what I believe was the first consumer
>spread-spectrum phone, had an excellent white paper on the subject, but
>it's no longer online, and is not available via archive.org. I'll see if
>I can find it. I think I have it on an old VAX at work somewhere.

Here it is. The part especially relevant to my comment about
signal-to-noise ratio is: "The increase in signal bandwidth resulting
from the PN signal coding proportionately increases the 'processing gain'
of the telephone. Processing gain increases the signal-to-noise ratio
between the receiver's RF input and its baseband output. This results in
an associated increase in 'jamming immunity.' Jamming immunity is defined
as the amount of interference that a receiver can withstand while
producing an acceptable output signal-to-noise ratio."


SureLink Digital Spread Spectrum Communications and Cincinnati
Microwave Cordless Telephones

September 1995

Introduction

Cincinnati Microwave (CNMW) is a leading designer and manufacturer of
miniature wireless communications devices that operate in the
ultrahigh-frequency radio and microwave spectrum. The company is
dedicated to developing a continuing series of leading-edge electronic
devices for the consumer and commercial wireless communication markets.
A major breakthrough in consumer wireless communications technology is
the company's SureLink cordless telephone technology.

SureLink, first introduced in 1993, is a low-cost adaptation of advanced
military "battlefield" digital spread spectrum technology to a consumer
product. Using SureLink, the company is able to offer cordless
telephones that eliminate the problems that have plagued consumers since
cordless telephones were introduced in the early 1980s, e.g., poor audio
quality, limited range and lack of security.

SureLink telephones achieve their advantage by using superior high
frequency spread spectrum technology with ultrasecure encoding
techniques for digitized voice signals. The combination yields a
superior consumer telephone that fulfills the promise of cordless
telephone technology at a price that consumers can afford.

Cincinnati Microwave Introduced the World's First Consumer Spread
Spectrum Cordless Telephone in 1993

CNMW was the first company to incorporate Spread Spectrum communications
into a cordless telephone. Its SureLink technology provides telephones
with market leading characteristics:

* Total Security
* Excellent Sound Clarity
* Expanded Operating Radius
* High Performance Reliability

To simplify the process of obtaining Federal Communications Commission
(FCC) approval, SureLink cordless telephones are designed to use the
902-928 mHz band designated for industrial, scientific, and medical
devices as well as high frequency cordless telephones. CNMW designed an
integrated circuit (IC) that implements an FCC approved version of
Spread Spectrum communications called 'Direct Sequence.' But even with
IC technology available, the real challenge in creating this kind of
product was its physical design.

The IC contains a very fast dedicated Digital Signal Processor that must
coexist in the telephone with a 900 mHz broadband transceiver. High
frequency digital ICs produce harmonics that can interfere with radio
frequency (RF) circuits. Classic military design methods achieve
isolation between digital and RF sections through exotic and expensive
shielding techniques. CNMW's challenge was to accomplish the design
objectives as well as to produce a product that would not be
prohibitively expensive or unwieldy in size. The objective would require
innovative 'firsts' in IC design and device technologies.

The Allure and Pitfalls of Cordless Telephones

In a world increasingly dominated by high quality personal electronics
products, portable personal communication devices have quickly gone from
novelty to indispensable. Seeking the convenience of a cordless
alternative to the traditional telephone, consumers have flocked to this
new market segment, which now represents about half of all telephones
sold in the U.S. each year. Once acquired, the buyer expects to enjoy
the convenience and pleasure of having telephone conversations as they
move around the room, the house, the yard, and the pool.

Some analysts suggest, however, that many ordinary cordless telephones
actually end up in the closet because of consumer frustration with
performance. Cordless telephones face the tough challenge of being
evaluated against traditional corded telephone features such as:

* private conversations -- ever since "party lines" went out of style,
eavesdropping has required hard-to-obtain equipment
* excellent sound quality -- few Americans can remember telephone service
that did not have "in the same room" sound quality
* reliability -- corded telephones have been reliable products, removed
from service more often because of style than quality

While usage statistics are unavailable, it is undeniable that retail
store return rates for ordinary analog cordless telephones are among the
highest of all consumer electronics products. This may reflect the
limited performance capabilities of ordinary analog telephones, such as:

* lack of security -- eavesdropping requires only another corded or
cordless telephone, baby monitor, radio scanner, stereo remote
headphones or walkie talkie.
* poor sound quality -- substandard audio response capability and
susceptibility to interference from other consumer products and
household electrical devices as well as every other cordless telephone
in the vicinity, a huge problem in high density housing areas
* short range -- the primary appeal of a cordless telephone is the
ability to "move around," when a cordless telephone offers a range
little greater than a telephone cord its appeal is limited
* frequent breakdowns -- compromise between technical capabilities and
price has not been highly successful for cordless telephones

The Next Engineering Steps at Cincinnati Microwave

It is the conflicting results of what has been called the mass market
"cordless telephone experiment" that has lead to the rush to develop
Personal Communication Systems (PCS) wireless communications. These
low-wattage, intended-to-be-low cost implementations of the cellular
phone networks have garnered an unusual level of attention. Frequency
spectrum in the 1.9 gHz range has been assigned and even auctioned to
PCS investors by the FCC. The development of PCS type cordless
communications is several years away, however, due to the difficulties
of creating a new standard, implementation of a new nationwide (if not
worldwide) infrastructure, and the cost and uncertainties inherent to an
emerging marketplace, particularly one that is already being served by
cellular and cordless telephones, as well as pagers, to some extent.

While CNMW is following closely the developments in the PCS arena, at
present, the market is unfocused and fragmented, making it virtually
impossible to identify a specific product need. However, by staying in
touch with the participants, which include AT&T Wireless, Sprint, Bell
Atlantic Personal Communications, U.S. West, Ameritech Wireless
Communications, and Southwestern Bell Mobile Systems, CNMW is positioned
to respond rapidly when specific product needs appear. (The company's
first cordless telephone was brought to market less than 18 months after
the market need was identified.)

On another front, unlike the 0.70 to 0.75 mW narrow band cordless
telephones at 46 - 49 mHz and 902-928 mHz, the FCC allows 902 - 928 mHz
spread spectrum products to operate as much as 1000 mW of power (the
present CNMW cordless telephone transmits only 40 mW of power). This
power advantage has positioned SureLink products to be the technology of
choice for increased range.

SureLink technology can also be used at other points on the spectrum to
address specific market needs. For example, 2.4 gHz is presently
available, virtually worldwide, for consumer electronics. Relying on
Spread Spectrum's inherent interference rejection, this spectrum band is
currently being investigated for a "worldwide" cordless telephone
product.

Technology of the Traditional Cordless Telephone

Classic analog cordless telephone technologies operate in the 46-49 mHz
spectrum. They are limited by the FCC to 0.7 mW (for isotropic
antennas). Despite their low power, they are narrow band products and
exhibit improved signal to noise ratios over spread systems. However, at
0.7 mW these products have limited range, rarely exceeding a 500 foot
operating range. The 46-49 mHz spectrum is also used by baby monitors,
stereo remote headphones, walkie talkies, garage door openers, and child
locators creating additional interference.

Attempts have been made to improve the security of these products
because conversations can be monitored and expensive long distance calls
can be placed on the unprotected radio links of unsuspecting users.
While some of these products have featured the use of security codes
over the radio link between handset and base to prevent fraudulent
calls, most of these "solutions" do not provide voice security once the
call is made. Even today, few classic analog cordless telephones are
available with technology that prevents monitoring or intrusion into the
voice channel.

A few 'analog' and 'digital' cordless telephone products have been
introduced that operate in the same region of the Spectrum as the CNMW
SureLink telephones (902 - 928 mHz). Most are narrow band FM systems
that use Frequency Shift Keying (FSK) modulation. These systems
typically occupy 20 kHz in bandwidth. Some security in the voice channel
is achieved by scrambling the bits before transmitting the signal and
then rearranging them in the receiver. However, since they are narrow
band and not Spread Spectrum, the FCC still limits these products to a
0.75 mW power maximum. As a result, range remains limited.

Due to the lower frequencies involved, the RF section of 46-49 mHz
cordless telephone products could be created with (old style) leaded
components and 'through-hole' printed circuit boards. Cordless telephone
products in the 900 mHz spectrum, regardless of the transmission system
used, can only be realized with the finer geometries (new miniature
sizes) found in surface mount components. CNMW is one of the leading
manufacturers of products containing surface mount technology, having
pioneered high volume surface mount production in a 24 gHz receiver
product in 1984.

A Short History of Spread Spectrum

The concept of Spread Spectrum communications dates back to the 1940s
when Shannon first proposed the idea of transmitting coded wide-band
signals. Spread Signals offered unique advantages over other
transmission categories.

* Secure communications are an inherent property of these systems
* Multiple overlapping signals can occupy the same spectrum
* Spread signals provide inherent interference rejection known as
"jamming immunity"
* Low energy signals are less likely to interfere with other systems

Figure 1. TECHNOLOGY COMPARISON DIAGRAM

As a result of these advantages, Spread Spectrum concepts were quickly
assimilated into the military world. In the late 1940s, Spread Spectrum
systems were created using rooms full of vacuum tubes. By the late
1950s, the military had fielded a variety of portable military
transceivers. These systems also found applications in satellite
communications where security and jamming immunity are most critical.

In more recent years, technology advances in IC designs have enabled the
construction of single chip Spread Spectrum designs. Consumer
applications for Spread Spectrum became practical when these techniques
were declassified and the FCC approved selected regions of the spectrum
for their use.

The properties of Spread Spectrum signals make them ideal for products
requiring security, range, and high signal quality. An endless array of
consumer electronics applications can be envisioned that would take
advantage of these properties. One exciting application for Spread
Spectrum is in voice communications products such as the cordless
telephone.

Spread Spectrum Categories

For a signal to be considered Spread Spectrum, it must meet several
requirements. The central property of all Spread Spectrum signals is
that their bandwidth is substantially higher than the bandwidth of the
signal being transmitted. Four types of Spread Spectrum signals include
the following.

* Direct Sequence
* Frequency Hopping
* Time Hopping
* Pulse-FM or Chirp

Direct Sequence signals are generated by modulating a carrier with a
code sequence meeting various requirements. The Direct Sequence method
was chosen by CNMW and involves the use of 'PN' codes. At the heart of
the CNMW telephone, a voice signal is converted into serial digital data
using a CODEC (COder/DECoder) chip. The CODEC produces 64k bits/second.
Simultaneously, the CODEC receives 64k bits/second from a remote source
(Despite the bandwidth limitation of the typical telephone line, this
data rate is roughly 2.5 times the rate of today's fastest wireline
modems).

The 'spreading' in Direct Sequence systems occurs when each of the bits
from the CODEC is replaced by 'PN' codes. See figure 2. When the CODEC
produces a zero, the code sequence for an 'N' is transmitted. Likewise,
a 'P' is transmitted when the CODEC produces a one. These PN codes
directly modulate the carrier. Typical sequences for P and N are
composed of 32 bits called 'chips' and are chosen to meet a variety of
criterion. But the key to the spreading operation lies in the fact that
the transmitted set is much higher than the actual rate of the voice
data. These signals are generally referred to as CDMA, or Code Division
Multiple Access.

The increase in signal bandwidth resulting from the PN signal coding
proportionately increases the 'processing gain' of the telephone.
Processing gain increases the signal-to-noise ratio between the
receiver's RF input and its baseband output. This results in an
associated increase in 'jamming immunity.' Jamming immunity is defined
as the amount of interference that a receiver can withstand while
producing an acceptable output signal-to-noise ratio.

Figure 2. DIRECT SEQUENCE BLOCK DIAGRAM

Frequency Hopping signals are also generated through the use of code
words. However a carrier would be modulated directly by the 64k
bits/second from a CODEC without the substitution of PN codes. Spreading
is achieved by changing the frequency of the transmitted signal in
'hops' dictated by the code words. The FCC approves systems that hop at
rates as slow as 0.4 seconds per hop. Since the bit rate is low, the
transmitted signal is a narrow band during each hop interval. This would
be a disadvantage if there is a narrow band interfering signal at one of
the hop frequencies. However, frequency hopping systems are often
enhanced by training the 'hop' pattern to avoid noisy frequencies.
Creating significant design challenges, these training algorithms can
become quite complex because they must occur simultaneously with the
communication link itself.

A hopping system using 0.4 seconds per hop will appear as Spread
Spectrum after many seconds due to the use of the entire spectrum
covered by all the hops. The processing gain of a hopping system is
defined as the ratio of the spectrum covered by all of the hops divided
by the information bandwidth of the transmitted signal. However, an
accurate calculation of processing gain is confused by the variation in
hop patterns resulting from the training patterns.

Time Hopping systems achieve spreading through pulse width modulation.
Typical systems transmit very narrow pulses at substantially longer time
intervals. The bandwidth of the transmitted signal is directly related
to the inverse of the pulse width. These systems offer excellent jamming
immunity from other RF sources as well as other Time Hoppers. However
another key parameter, acquisition time, can become substantial if
interfering sources are near a remote receiver. Significant problems are
yet to be solved for these systems when they are to be operated in
proximity to other Time Hoppers.

Pulse-FM or Chirp systems do not employ coding or other modulation but
rather are simple swept frequency pulses. Chirp systems are not well
suited to the communications requirements of the telephone because
chirps do not convert well into the data sets needed by the CODEC. They
do find uses in RADAR systems that must measure the distance and
location of targets such as aircraft.

Cincinnati Microwave is Using Direct Sequence Spread Spectrum

CNMW chose to design SureLink with the Direct Sequence method because it
provides a robust transmission capability that will stand up to
increased "crowding" over the years from all types of 900 mHz products.

The significant technical objectives in cordless telephone design are
security, range, and interference rejection. Of these items,
interference issues present the most significant uncertainty into system
design. Telephones with SureLink technology must be able to operate in
proximity to other 900 mHz products as well as other direct sequence
phones. For greater security, unmatched CNMW phones will not 'link' with
each other.

There are several factors at the root of the interference issues. One is
the choice for the PN codes. The other is the selection of the center
frequency chosen for the communication. SureLink offers a selection of
100 center frequencies or channels. CNMW assigns different PN codes
during the final stages of the manufacturing process to each telephone.
The selection is made from a wide variety of random codes and guarantees
that no two phones can link.

Design Considerations in the CNMW Phone

Cordless telephones with SureLink transmit and receive signals over the
same frequency. Furthermore, the unit never transmits and receives
simultaneously. This not only adds another layer of security but
eliminates the cost of isolating the transmitter and receiver sections.
The telephone alternately transmits and receives 'bursts' of information
in a 'Time Division Multiplexed' arrangement. The incoming signal is
stored in memory called a FIFO or First-in-First-Out buffer. The FIFO is
filled with the incoming data burst. Meanwhile it is emptied at a lower
rate into the receiving end of a CODEC, which converts the data back
into an analog signal.

From a communications point of view, the handset and base are identical.
Each side alternately transmits and receives data. Each operates on the
same frequency using identical transceiver designs. Each uses a CODEC,
and each uses the same PN codes to spread the signal or to de-spread it.
The only differences between the two are in their operation and
synchronization. Operationally, the base is transmitting while the
handset is receiving or vice versa. Synchronization issues require that
either the handset or base be considered the 'master' and that the other
be considered the 'slave.' The master always establishes the 'timing' of
events. The slave receives the signal from the master and synchronizes
its activities to the master. When the telephone rings, the base asserts
itself as the master. When the user initiates a call, the handset
asserts as the master.

The handset is operated from batteries and must conserve battery life in
order to provide adequate 'talk time' (the time during active
communications) and 'standby' time (the time when the handset is waiting
for communication from the base while in a remote location). Significant
operating range is a critical feature in the CNMW telephone. Range is a
direct function of the transmitted power. Naturally, increasing transmit
power reduces battery life. The advantages offered by Spread Spectrum
made it possible for CNMW to operate the telephone at 40 mW and still
reach a half mile line of sight design objective. The product has a
standard 600 mA battery pack and can operate at 40 mW for 4 hours before
the battery must be recharged.

During standby, the handset conserves energy by spending most of its
time asleep. During sleep intervals, the handset powers down most of its
circuits, extending the battery life to seven days between charges.
About once a second, the handset wakes up and turns on its receiver to
determine if its 'base' is trying to make contact. If a transmission is
detected, the handset remains awake and synchronizes itself as a slave
with the base. In a similar way, the handset also checks its keyboard to
see if any buttons have been depressed. If the 'talk' button is
detected, the handset terminates its stand-by state and powers up its
transmitter with a message for the base. Shortly thereafter, the base
synchronizes to the handset and goes 'offhook,' returning a dial tone
over the voice channel.

Each transmitted data burst contains more than just digital voice
information. There are a variety of pieces of information that must be
transferred between the handset and base such as the fact that there is
an incoming call. When the handset wakes up and finds that a data burst
has been received, it triggers the 'ringer' to indicate there is an
incoming call. In the reverse direction, keystrokes on the handset are
transmitted to the base and instruct it to generate DTMF (Touch Tone)
during dialing operations as well as other functions.

Direct Sequence Spread Spectrum Demodulation

As mentioned earlier, the PN codes for a specific phone are assigned
during the final stages of the manufacturing operation. These values are
stored in nonvolatile memory in the base. While the handset is placed in
the base or other charging cradle, it is assigned a PN code via a
default RF data channel at the request of the base. Further
communications between the base and handset are based on the assigned PN
code.

At the heart of a direct sequence receiver is a correlator that compares
the incoming data with expected PN values. Each time a chip is produced
by the receiver, it is clocked into a shift register. After each new
chip is received, the entire contents of the register are compared with
the assigned codes for P and N using two separate correlator circuits.
Each correlator outputs a value corresponding to the number of matching
chips called the Hamming distance. When there are 32 chip sequences,
each correlator will produce an output ranging from 0 to 31. If the 'P's
correlator output is near 31, a P code is declared. Likewise, N is
passed on if the N correlator output is near 31. These decisions are
made each time a new chip is loaded into the correlator. Clearly, it is
possible to miss several chips yet still successfully measure the
presence of P or N. As a result, the analog output signal does not
exhibit more noise as the handset moves further away from the base. This
property is one of the most striking differences between SureLink and
conventional analog cordless telephone technology.

To improve the differentiation of PN codes, they must be chosen so that
they are orthogonal to each other as well as shifted versions of
themselves. To further enhance the decision making process, a digital
phased lock loop synchronizes itself to the boundaries between
successive PN codes, which is the bit rate. If the correlators fail to
produce outputs over a series of inputs, they are permitted to free run
until a new lock is achieved.

A critical design subject is chip synchronization. A variety of
synchronous and asynchronous methods are employed in direct sequence
designs. The CNMW design is based on an asynchronous approach in which
the data is oversampled at twice the chip rate with an asynchronous
clock. This approach increases the gate count in the correlator but
presents a good tradeoff in overall design simplicity.

RF Transceiver Design

The transceiver is designed around a non-synchronous Binary Phase Shift
Keying (BPSK) Modulator. This modulation involves switching the carrier
phase in response to the chip signal. The RF section performs a single
conversion between 900 mHz and base band. CNMW also used its custom chip
design skills to create a single chip RF modulator/demodulator. The
design includes baseband analog filters to shape the 'code' spectrum and
to filter the receive spectrum.

To understand the spectral properties of the Spread Spectrum signal,
start with a 64 kbit/second signal from the CODEC. Each bit is replaced
with a 32 chip PN code. Therefore, chips are generated at the rate of
about 2 million chips/second. The chip signal is passed through a low
pass shaping filter. It then directly modulates the transmitted carrier.
The resulting Average Power Spectrum is essentially the spectrum of the
filtered chip signal convolved with the spectrum of the carrier. The
bandwidth of the composite signal is directly affected by the short-term
Spectral properties of the PN codes themselves. As a result, the PN
codes must be chosen so that they are both random and produce the
flattest possible spectrum.

Since bandwidth of the spread signal is directly proportional to the
chip 'period,' signal spreading can be controlled to virtually any
degree. To qualify as a spread signal, the FCC requires that the minimum
6 dB bandwidth of the signal be at least 500 kHz. At 2 million
chips/second, the CNMW telephone has a bandwidth of nearly 5 mHz.

Internal Computer

Both the handset and the base are managed by an embedded microprocessor.
It decides when to sleep, when to test for keystrokes and RF input, and
when to notify of a low battery condition. The base microprocessor tests
for RF input from the handset as well as monitor the telephone line for
a ring detection. Both base and handset microprocessors manage
fundamentals such as the dissemination of PN codes, channel selection,
radio control, and the decision to become master or slave. They also
handle complexities that occur when the handset is near the edge of the
detection range or in proximity to interfering RF sources.

While Spread Spectrum technology opens the door for a new age in RF
communication, the embedded microprocessors manage the practical
application of this technology.

References

1 Papers edited by Robert C. Dixon. Spread Spectrum Techniques, IEEE
Press, 1965.
2 Ferrel G. Stremler, Communications Systems, Addison-Wesley
3 Bernard Sklar, Digital Communications Fundamentals and Applications,
Prentice Hall, 1988

------------------------------------------------------------------------
Anonymous
June 16, 2005 9:03:46 PM

Archived from groups: alt.cellular.verizon (More info?)

On Mon, 30 May 2005 10:57:06 -0400, Isaiah Beard
<sacredpoet@sacredpoet.com> chose to add this to the great equation of
life, the universe, and everything:

>Bob Scheurle wrote:
>> On Mon, 30 May 2005 02:02:05 -0400, Isaiah Beard
>> <sacredpoet@sacredpoet.com> wrote:
>>
>>>As far as landline cordless phones go (which is what your friend was
>>>probably picking up), you're still safe as long as you avoid the 900Mhz
>>>analog models, and instead use a 2.4GHz or 5.8GHz Digital Spread
>>>Spectrum (DSS) phone.
>>
>> You make it sound like all 900 MHz phones are analog and all 2.4/5.8 GHz
>> phones are digital.
>
>No, I specifically stated he needs to pick up a *DSS* phone in the 2.4
>GHz or 5.8GHz band. I'd appreciate it if you didn't read more into my
>posts than is there.

Sorry, but he's right. Someone who didn't know phone technology (like you
and Bob and I do) could read your statement and get the impression that all
900s are analog and all 2.4s and 5.8s are DSS. This person would then think
that all he needed to look for was the frequency and not pay attention to
all the other gobbledygook on the boxes. He could easily go to the store
and say "That's 900 MHz, I don't want it" even though it was DSS, or,
worse, could say "This one's 2.4 GHz (or 5.8 GHz), I'll take it" and end up
with analog.

Let me ask you this: Why did you specify 900 MHz when you said to avoid
analog, and why did you specify 2.4/5.8 GHz when you said to get DSS? The
point is that analog phones can be monitored by older or modified scanners,
regardless of frequency, and that DSS phones cannot, also regardless of
frequency.

If you had JUST said "avoid analog and instead use Digital Spread Spectrum
(DSS)," then my theoretical dumbshit from above would be forced to look at
the information that was really important.

--
David Streeter, "an internet god" -- Dave Barry
http://home.att.net/~dwstreeter
Remove the naughty bit from my address to reply
Expect a train on ANY track at ANY time.
"Oh, sure, we still teach our children some Halloween traditions. We teach
them that this is a time when we buy pumpkins and carve faces into them.
But we don't teach them the underlying spiritual reason WHY we do this,
which is that each fall, the average American pumpkin farmer produces 17
trillion of these things, and if he doesn't get rid of them, they will rot,
and everything the farmer owns, including his smaller children, will
disappear under a gigantic cloud of flies. THAT is why we buy pumpkins and
carve faces into them." - Dave Barry
!