cell phones and 9-11 (from an engineer)

brad

cell phones and 9-11 (from an engineer)

Mon Jul 31, 2006 00:33

When i first heard about the cell phone calls from planes on september 11, i thought something was funny.
Actually, i figured they meant to say "airphones"
(the seatback phones)
While its true that there are seatback phones, i later found that some of the calls had to come from cell phones.
at least 2 people said they saw their loved ones caller ID,
that cant happen with a seatback phone.

not long after 9-11 i started my research, especially in the details of the cell phone use.

You see, at the time, i was an R/F engineer.
I designed cell phone systems for Sprint, and before that Verizon and other companies.

I recieved an email regarding the use of cell phones and 9-11 a while back.

This is my response.

I also have this article here

http://911review.org/brad.com/sept11_cell-phones/engineer_tech.html

cell phones and 9-11 an engineers view

(and others) at
911review.org

begin
==================

Analysis and technical Discussion on the possibility of cell phone use on September 11
This is a response to an email I recieved, on the question as to
whether it is possible to use cell phones in aircraft as it relates to the attacks on 9/11

first, keep in mind, some of the phone calls were cell phones, some were seat -back phones.
Ted Olson actually said BOTH, in different interviews, also stating she was in the bathroom,
(airphone cords DONT reach the bathroom)
then, she wasnt,
then she didnt have her purse to use a credit card

i have several articles that contradict each other.
the first articles out motly stated that they used cell phones,
later articles mostly stated airphones.

Some of the call HAD to be cell phones though
Ed Felt dialed 911 (emergency operator) and the call went to Verizon -GTE
you cant do that with an airphone

also, some victims families have said...
(I knew it was him i saw the caller ID)

i worked for several communications companies, and have been in the buisiness over 15 years.
first as a bench technician, repairing cell phones, 2 way radios, setting up microwave, 2-way, and paging systems,
troubleshooting base stations (cell sites)
base staation troubleshooting is very complex, and needs a electionic background,
as well, as an understanding of RF (radio Frequency)
The last few years i worked as a design engineer, and senior desing engineer
(although i have been out of the buisiness for about 2-3 years now)
also doing a LOT of "in building testing" and RF design, for places like the superdome,
convention center and a couple of airports.
the in-bulding testing gave me a lot of insight as to what effects a barrier,
such as a wll, metal, concrete, or other had on RF frequencies.

(ever try to use a cell phone in an elevator ?)

as a side note:
CDMA, GSM, and ANALOG are different "technologies"
but, there are also different frequency ranges associated with different carriers.
(SPRINT, NEXTEL, etc...)
so if Sprint owned the airspace frequency range for 1900mhz in pittsburg,
then they had a choice still of which technology they wanted to use (CDMA, GSM etc...)

USUALLY the 1900mhz span was used with CDMA (digital) and 800mhz was used by analog

now by sept 2001 MOST cell phones were working on CDMA at 1900mhz
i am sure there were some GSM used (and still are), and they could have been at 800mhz OR 1900mhz

The reason all this is important is cos the RF signal works a bit differently with different technologies,
and on different frequencies, working differently on barriers, distance etc....

POWER
Analog phones can use more power as allocated by the FCC.
the phones could use a MAX of 3 watts, but ONLY for non-hand-held
so on a plane, i would suspect, they were all handheld phones.
Handheld phones can use a MAX power of .6 watts as per FCC.
but most digital phones actually only go up to a max of .4

So the calls on the flights could have been different technologies, CDMA, or GSM
(analog was allmost ALL phased out by then)
and could have been 800mhz OR 1900mhz

Frequency
800mhz is a longer wavelength than 1900mhz
loger wavelengths travell better THROUGH objects,
shorter ones (like 1900mhz) are more "line of sight"
in laymans terms, 1900mhz is closer to light, easily blocked by a piece an object
even a piece of cardboard, but 1900 can BOUNCE better.

CDMA
- signal strength
a CDMA phone is trained to try and use the strongest signal. (cell site)
and it will change from one, to the next IF it can.
(often, it tries, but the signal strength has changed since it polled the level)

since probabally most of the cell calls were CDMA (most popular) at 1900mhz (again most popular)
you have digital technology at a high Frequency.
the MAIN problem"S" are....
at that height, the (digital) phone would not be able to use the closest signal to it.
The closest signal would be from UNDERNEATH the plane.
at 30,000, there would be very little energy left to ANY signal, and would have nothing to "bounce off of"
so, it (the closest signal) would hit the bottom of the plane and stop.
so , to make a call, the phone would have to use signals from even father away.
which creates a bigger problem.
Handoffs....
the phone (CDMA) uses a handoff list, sent by each cell site it talks too.
if you go from a site from the east side of a plane at 30,000ft, then, the BEST signal, starts to come from a site on the WEST side of the plane,
those sites could be 100 miles from each other.
since each site has a handoff list of only a certian number of sites
(the list -usually- only contains sites that are next to it.)
at 30,000ft, it is VERY doubtfull that the next strongest signal, would be from the next closest site
the phone would be seeing dozens of signals, from dozens of sites, from miles apart of each other.
the signal strengh for each of these would vary GREATLY within milliseconds.

and believe me, its hard to OPTIMIZE these sites correctly for cars going 50mph on the ground.
the sites antennas are OPTIMIZED toward highways, and cities,
and usually DOWNTILTED
at 30,000ft even 1 degree of downtilt would make the RF energy totally useless.
(you can research antenna patterns + downtilt)
even NOT downtilted, there is a natural "roll off"
even if an antenna is pointed straight alaong the horizon,
the farther you go ABOVE the top of the antenna, the power rolls off

different systems - border handoffs...
since different carriers may use different frequencies AND tehcnologies,
when you cross a border, the phone drops. PERIOD.
(border handoffs work in many places NOW, but not in 2001)
the different technologies, phones and fequencies could NOT cross carriers boundreis.
(if bought a phone in New Orleans, and flew to Baton Rouge,
the New Orleans system could NOT handoff to the baton rouge system)
now, you could re-originate the call and be ROAMING, but as soon as you go over the border it drops.
i dont know exactly what the borders for different carriers were in 2001, in Pa
but going 500mph, you are sure to cross one in 1/2 hour at the MOST i would guess.

Now, all that aside, i tried it.
several times. on several flights
(i know your not supposed to, but that is becuase it effects the carrier (SPRINT etc...)
NOT the electronics of the plane.
so rest assured i endangered no-one.
i was able to make a call or 2 before the plane lifted off
(and actually 1 failed right there on the tarmac)
several times i was able to get siganl strength, even over 20,000ft
but never actually connected.
at least not over 2,000ft
many many tries altogether

i have HEARD of people using them on planes, but i never got a clear answer as to the altitude,
except one guy who flew a cesna at 2,000ft (or under ?)
---------------

there are a few different types of phones,
GSM, CDMA, and Analog.
analog is the OLD type, CDMA is digital.
CDMA uses 1 frequency, for everyone to talk on, but each conversation is CODED differently.

here are some more tech details written by me....
(copy and pasted)
http://www.aldeilis.net/aldeilis/content/view/375/107/
I am a senior design RF cell phone engineer ( cellular/CDMA engineer) and have designed systems for Sprint, Verizon and Alltel. I have 2 FCC licenses and have worked in the industry for 13 yrs. That out of the way...
OK all of the new handsets are .6 to 1 watt max.
From what i read several calls were made on flight 93 some were reported to last as long as 20 minuits. NO WAY !
We design these systems to work on the ground, ususally providing "downtilt" to the antenna, so the signal gets pointed downward.
There are calculations to do this. The range for a call site is 5 to 20 miles max, but that is on the ground. The handshaking is now refered to in digital as soft handoff, or hard handoff if you are going between systems, or in an analog mode.
most phones today are now digital, though some can do both. for a handoff to occur( going from one cell to another) the system needs to have a neighbor list setup, telling the phone which cell is next on the list( i have made around 100 of these). at 500mph, the phone would have passed several sites and it would try to handoff to a site already passed. The phone can be in handoff with up to 3 sites at one time, but generally this can make things worse as it will degrade the signal.
Also inside of a metal plane, the signal degrades
( it does in a car, or building by 3 to 6 db or more)
I have done in building testing for years. each 3 db means 1/2 power. inside a metal plane i would guess it would be about the same, if you stick the antenna next to a window, MAYBE only 1 to 2 bd loss, but still a loss. i havent tested it, but i have a lot of experience in this area. Note there is a lot of messaging between the phone and the site, and at that height the signal would be quite low and the phone would get confused as to which site it is on.

I dont know the height the plane was at at that time, but the higher it is, the more signals come in, which degrades the quality and confuses the phone more, not to mention lowering the signal level.
One more thing, in remote areas, where these calls were made i believe, these companies do not build many sites. The sites cost 1/2 million a peice or so.
Just try driving from 1 city to another through a very rural area and see if your phone works, we point the antennas down the highways to get the most out of each site. Planes do not fly along highways.

when i first heard this, it didnt add up in my head.

--------------------

these links (HAD) a very detailed technical discussion on cell phones, mainly by me.
ill have to see if i can get the webmaster to fix them....

physics911.ca/org/modules/xfsection/article.php?articleid=1
physics911.ca/org/modules/xfsection/article.php?articleid=2

UPDATE _article is now archived here...

physics911 technical discussion

physics911 technical discussion Part 2

one call was said to have been recieved by a 911 (emergency phone)operator
in Chicago, hundereds of miles from where the plane was...
http://physics911.ca/org/modules/weblog/details.php?blog_id=65
or here...
http://911review.org/brad.com/sept11_cell-phones/illinois_flight-93.html

http://911review.org/

9/11 LIKE WATERGATE — Camilo H. Tapia, Tue Aug 1 15:01

9/11 LIKE WATERGATE — Camilo H. Tapia, Tue Aug 1 14:44

MOVIE: 9/11 GREATEST LIE EVER SOLD — envax, Mon Jul 31 02:04