Deutsche Telekom and T-Mobile

CDMA is one form of spread spectrum communications (direct sequence).

Frequency hopping spread spectrum (the other kind) was conceived of by
Heddy Lamarr (no kidding!). She turned over the rights to the Federal
Gov't to assist with the WWII war effort.


Gray



Al Klein wrote:
>
> On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
> <[email protected]> posted to alt.cellular.verizon:
>
> >2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
>
> Pretty much. Jamming is just noise to a CDMA receiver, and it's
> designed to operate in the presence of noise (the other CDMA phones on
> the channel are also noise).

--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
[email protected]

---

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"Isaiah Beard" <[email protected]> wrote in message
news:[email protected]...
> 2. Wasn't CDMA a military invention meant to be *resistant* to jamming?

That and also resistant to detection.


---
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On Sun, 11 Jan 2004 07:22:09 GMT, Gray Frierson Haertig
<[email protected]> posted to alt.cellular.verizon:

>Frequency hopping spread spectrum (the other kind) was conceived of by
>Heddy Lamarr (no kidding!).

Yep. Old, but true, story.

In article <[email protected]>,
Al Klein <[email protected]> wrote:
>On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
><[email protected]> posted to alt.cellular.verizon:
>
>>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
>
>Pretty much. Jamming is just noise to a CDMA receiver, and it's
>designed to operate in the presence of noise (the other CDMA phones on
>the channel are also noise).

The idea is that a CDMA signal is scattered all over a "carrier" (1.25MHz
for cellular/PCS phones), so the jammer has to spread his signal over
the entire carrier with sufficient power to jam the communication. A
strong jamming signal at a particular frequency will cause whatever data
that happened to use that frequency to be lost, but any given data bit
is duplicated in several "chips," and furthermore, voice encoders can
correct for a certain amount of lost data. In fact, if the error rate at
the cell site is too low, the handset will be commanded to reduce its
power until the error rate is *raised* to be within specified bounds.

On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
<[email protected]> chose to add this to the great equation of
life, the universe, and everything:

>David S wrote:
>
>> ... That'd be one way to get the real estate to expand the GSM network --
>> put a mini-cell in every McD's in the country. Failing that, they could
>> just put a CDMA jammer in them.
>
>1. I think McD's wants to stick to (mostly) legal business models.

Uh, yeah, if you say so.

>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?

Okay, a jammer on the frequencies used by the competition in that area. I'm
sure even a resistant mode can be jammed on a localized basis.

--
David Streeter, "an internet god" -- Dave Barry
http://home.att.net/~dwstreeter
Expect a train on ANY track at ANY time.
"Any person who shall in the city of Wichita use or carry concealed or
unconcealed any bean snapper or like article shall, upon conviction, be
fined." - City ordinance 349 of Wichita, Kansas

On 12 Jan 2004 02:10:14 GMT, [email protected]lid (CharlesH) chose to add
this to the great equation of life, the universe, and everything:

>In article <[email protected]>,
>Al Klein <[email protected]> wrote:
>>On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
>><[email protected]> posted to alt.cellular.verizon:
>>
>>>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
>>
>>Pretty much. Jamming is just noise to a CDMA receiver, and it's
>>designed to operate in the presence of noise (the other CDMA phones on
>>the channel are also noise).
>
>The idea is that a CDMA signal is scattered all over a "carrier" (1.25MHz
>for cellular/PCS phones), so the jammer has to spread his signal over
>the entire carrier with sufficient power to jam the communication.

Okay, so how hard is that to do? (Honest question.) It seems to me they
wouldn't need all that much power to block a cellular-strength signal
within the confines of a small building.

--
David Streeter, "an internet god" -- Dave Barry
http://home.att.net/~dwstreeter
Expect a train on ANY track at ANY time.
"I should never have bitten the head off that bat." - Ozzy Osbourne

You are right. Direct sequence spread spectrum (which is what CDMA is)
is vulnerable to HIGH levels of broadband noise in the frequency block
in use. Noise at the power level other users generate can be tolerated
very nearby, but serious power (100 watts) can disrupt cellphone level
signals for hundreds of feet.

In most tactical situations, the enemy can't get close enough with
enough power to disrupt communications. DS spread spectrum is capable
of retrieving signals that are actually a bit below the noise level.


Gray


David S wrote:
>
> On 12 Jan 2004 02:10:14 GMT, [email protected]lid (CharlesH) chose to add
> this to the great equation of life, the universe, and everything:
>
> >In article <[email protected]>,
> >Al Klein <[email protected]> wrote:
> >>On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
> >><[email protected]> posted to alt.cellular.verizon:
> >>
> >>>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
> >>
> >>Pretty much. Jamming is just noise to a CDMA receiver, and it's
> >>designed to operate in the presence of noise (the other CDMA phones on
> >>the channel are also noise).
> >
> >The idea is that a CDMA signal is scattered all over a "carrier" (1.25MHz
> >for cellular/PCS phones), so the jammer has to spread his signal over
> >the entire carrier with sufficient power to jam the communication.
>
> Okay, so how hard is that to do? (Honest question.) It seems to me they
> wouldn't need all that much power to block a cellular-strength signal
> within the confines of a small building.
>
> --
> David Streeter, "an internet god" -- Dave Barry
> http://home.att.net/~dwstreeter
> Expect a train on ANY track at ANY time.
> "I should never have bitten the head off that bat." - Ozzy Osbourne

--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
[email protected]

On Tue, 13 Jan 2004 05:57:01 GMT, David S <[email protected]> posted
in alt.cellular.verizon:

>On 12 Jan 2004 02:10:14 GMT, [email protected]lid (CharlesH) chose to add
>this to the great equation of life, the universe, and everything:

>>The idea is that a CDMA signal is scattered all over a "carrier" (1.25MHz
>>for cellular/PCS phones), so the jammer has to spread his signal over
>>the entire carrier with sufficient power to jam the communication.

>Okay, so how hard is that to do? (Honest question.)

Very.

>It seems to me they
>wouldn't need all that much power to block a cellular-strength signal
>within the confines of a small building.

Getting a signal that wide is the problem. A CDMA signal doesn't
exist at all frequencies in the bandwidth at once - a jammer has to.
Once you have a signal that wide, amplifying it isn't the problem.
You could jam an entire city almost as easily as you could jam one
building. (And remember that it would take at least a few
transmitters to jam an entire building - signals at those frequencies
don't penetrate steel walls well.)

On Tue, 13 Jan 2004 07:35:28 GMT, Gray Frierson Haertig
<[email protected]> posted in alt.cellular.verizon:

>You are right. Direct sequence spread spectrum (which is what CDMA is)
>is vulnerable to HIGH levels of broadband noise in the frequency block
>in use. Noise at the power level other users generate can be tolerated
>very nearby, but serious power (100 watts) can disrupt cellphone level
>signals for hundreds of feet.

>In most tactical situations, the enemy can't get close enough with
>enough power to disrupt communications. DS spread spectrum is capable
>of retrieving signals that are actually a bit below the noise level.

An 800 MHz equivalent of the old Russian buzz-saw might do the job,
but those transmitters were hardly portable.

Maybe a rotary spark gap resonant at 850 MHz?

On Sun, 11 Jan 2004 01:14:47 -0500, Al Klein <[email protected]> chose to add
this to the great equation of life, the universe, and everything:

>On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
><[email protected]> posted to alt.cellular.verizon:
>
>>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
>
>Pretty much. Jamming is just noise to a CDMA receiver, and it's
>designed to operate in the presence of noise (the other CDMA phones on
>the channel are also noise).

Okay, I've thought about this while actually awake now.

I don't think you need to jam the whole carrier. The jammer just needs to
detect the frequency of the control channel from the tower to the phone and
overpower *that*, again just within the confines of a building.

--
David Streeter, "an internet god" -- Dave Barry
http://home.att.net/~dwstreeter
Expect a train on ANY track at ANY time.
"This makes me so angry it gets my dandruff up." - Sam Goldwyn

On Wed, 14 Jan 2004 05:17:24 GMT, Al Klein <[email protected]> chose to add
this to the great equation of life, the universe, and everything:

>On Tue, 13 Jan 2004 05:57:01 GMT, David S <[email protected]> posted
>in alt.cellular.verizon:
>
>>On 12 Jan 2004 02:10:14 GMT, [email protected]lid (CharlesH) chose to add
>>this to the great equation of life, the universe, and everything:
>
>>>The idea is that a CDMA signal is scattered all over a "carrier" (1.25MHz
>>>for cellular/PCS phones), so the jammer has to spread his signal over
>>>the entire carrier with sufficient power to jam the communication.
>
>>Okay, so how hard is that to do? (Honest question.)
>
>Very.
>
>>It seems to me they
>>wouldn't need all that much power to block a cellular-strength signal
>>within the confines of a small building.
>
>Getting a signal that wide is the problem. A CDMA signal doesn't
>exist at all frequencies in the bandwidth at once - a jammer has to.
>Once you have a signal that wide, amplifying it isn't the problem.
>You could jam an entire city almost as easily as you could jam one
>building. (And remember that it would take at least a few
>transmitters to jam an entire building - signals at those frequencies
>don't penetrate steel walls well.)

But we're talking about a McDonald's, which is pretty much all one room.

--
David Streeter, "an internet god" -- Dave Barry
http://home.att.net/~dwstreeter
Expect a train on ANY track at ANY time.
"Lately, when I tell people I work for a newspaper, I've detected the
subtle signs of disapproval -- the dirty looks; the snide remarks; the
severed animal heads in my bed." - Dave Barry

I don't claim to be a wonk on how CDMA cell systems are implemented, but
I believe that the control channel is just another direct sequence
spread spectrum channel, so it is spread across the same block of
spectrum that all the voice channels are spread across. In a direct
sequence spread spectrum system there are no discrete frequencies.

In a frequency hopping spread spectrum system (Heddy Lamar's kind) there
are discrete frequencies but they are constantly changing according to a code.


Gray




David S wrote:
>
> On Sun, 11 Jan 2004 01:14:47 -0500, Al Klein <[email protected]> chose to add
> this to the great equation of life, the universe, and everything:
>
> >On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
> ><[email protected]> posted to alt.cellular.verizon:
> >
> >>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
> >
> >Pretty much. Jamming is just noise to a CDMA receiver, and it's
> >designed to operate in the presence of noise (the other CDMA phones on
> >the channel are also noise).
>
> Okay, I've thought about this while actually awake now.
>
> I don't think you need to jam the whole carrier. The jammer just needs to
> detect the frequency of the control channel from the tower to the phone and
> overpower *that*, again just within the confines of a building.
>
> --
> David Streeter, "an internet god" -- Dave Barry
> http://home.att.net/~dwstreeter
> Expect a train on ANY track at ANY time.
> "This makes me so angry it gets my dandruff up." - Sam Goldwyn

--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
[email protected]

Creating a jamming signal is no more difficult than generating the CDMA
signal. The problem is getting the interfering signal power high enough
AT THE RECEIVER to jam the signal.

Doing this within a building to jam cell phones would not be terribly
difficult. Doing it in a tactical military situation would be.


Gray



Al Klein wrote:
>
> On Tue, 13 Jan 2004 05:57:01 GMT, David S <[email protected]> posted
> in alt.cellular.verizon:
>
> >On 12 Jan 2004 02:10:14 GMT, [email protected]lid (CharlesH) chose to add
> >this to the great equation of life, the universe, and everything:
>
> >>The idea is that a CDMA signal is scattered all over a "carrier" (1.25MHz
> >>for cellular/PCS phones), so the jammer has to spread his signal over
> >>the entire carrier with sufficient power to jam the communication.
>
> >Okay, so how hard is that to do? (Honest question.)
>
> Very.
>
> >It seems to me they
> >wouldn't need all that much power to block a cellular-strength signal
> >within the confines of a small building.
>
> Getting a signal that wide is the problem. A CDMA signal doesn't
> exist at all frequencies in the bandwidth at once - a jammer has to.
> Once you have a signal that wide, amplifying it isn't the problem.
> You could jam an entire city almost as easily as you could jam one
> building. (And remember that it would take at least a few
> transmitters to jam an entire building - signals at those frequencies
> don't penetrate steel walls well.)

--
Telecommunications Engineering
Gray Frierson Haertig & Assoc.
820 North River Street, Suite 100
Portland, Oregon 97227
503-282-2989
503-282-3181 FAX
[email protected]

"Al Klein" <[email protected]> wrote in message
news:[email protected]...
> On Tue, 13 Jan 2004 05:57:01 GMT, David S <[email protected]> posted
> in alt.cellular.verizon:
>
> >On 12 Jan 2004 02:10:14 GMT, [email protected]lid (CharlesH) chose to
add
> >this to the great equation of life, the universe, and everything:
>
> >>The idea is that a CDMA signal is scattered all over a "carrier"
(1.25MHz
> >>for cellular/PCS phones), so the jammer has to spread his signal over
> >>the entire carrier with sufficient power to jam the communication.
>
> >Okay, so how hard is that to do? (Honest question.)
>
> Very.
>
> >It seems to me they
> >wouldn't need all that much power to block a cellular-strength signal
> >within the confines of a small building.
>
> Getting a signal that wide is the problem. A CDMA signal doesn't
> exist at all frequencies in the bandwidth at once - a jammer has to.
> Once you have a signal that wide, amplifying it isn't the problem.
> You could jam an entire city almost as easily as you could jam one
> building. (And remember that it would take at least a few
> transmitters to jam an entire building - signals at those frequencies
> don't penetrate steel walls well.)

Cell towers are how much? 3 watts? (I don't know) so if you had a jamer with
about 500 watts, you should be able to jam a sizable area. The FCC will be
very "angry" with you though.

On Wed, 14 Jan 2004 06:00:40 GMT, David S <[email protected]> posted
in alt.cellular.verizon:

>On Sun, 11 Jan 2004 01:14:47 -0500, Al Klein <[email protected]> chose to add
>this to the great equation of life, the universe, and everything:
>
>>On Thu, 08 Jan 2004 10:11:08 -0500, Isaiah Beard
>><[email protected]> posted to alt.cellular.verizon:
>>
>>>2. Wasn't CDMA a military invention meant to be *resistant* to jamming?
>>
>>Pretty much. Jamming is just noise to a CDMA receiver, and it's
>>designed to operate in the presence of noise (the other CDMA phones on
>>the channel are also noise).
>
>Okay, I've thought about this while actually awake now.
>
>I don't think you need to jam the whole carrier. The jammer just needs to
>detect the frequency of the control channel from the tower to the phone and
>overpower *that*, again just within the confines of a building.

In the event that something goes wrong, there's more than 1 control
channel.