Planes & Cell phones

"Greg Copeland" wrote in message
news
[...] I'm not sure how far you could even transmit on 0.6 of watt.

FRS (the 90's answer to walkie-talkies) is limited to 0.5 watts and is
considered usable up to about 2 miles (not counting obstructions). Range is
dependent not just on the transmitted power, but also how sensitive the
receiver is. Pitifully weak signals are received over distances of hundreds
of millions of miles on a regular basis (just ask NASA).

Pete

"Greg Copeland" wrote in message
news
On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

The switching is done in a fraction of a second. The most that would
happen
is a dropped call.

People forget that cell switching is not magical. And it's certainly is
not zero cost. I must admit I do not fully understand everything that
goes on, but I am sure it's not as simple as you imply. Everytime a call
switches cells, it creates lots of work for the cell network to make sure
only a single tower handles that call. So, while it may take a fraction
of a second from a given phone and a given tower, there is lots going on
behind the scenes. Worse, instead of it going on with one, two or maybe
three towers, now it's causing a flurry of on twenty or more (highest
estimates I've read) towers. Let's also not forget that each tower can
only process and multiplex n-number of signals at a given time. DSPs,
just like your CPU, does have finite capacity. During cell switching, as
I understand it, this finite resource is being used on each tower in
contact with the phone. So, to say, "it causes all sorts of problems on
the cell network", does seem like a spot on statement to me.


True. I oversimplified it. A dropped call is all the users would
experience.

Even though it is theoretically possible to overload the processing
capability, I doubt that it is really a significant problem in the real
world.

For example, a group of people standing at the top of the CN Tower using
their phones would be line-of-sight to almost every cell tower in the
Toronto area. The system would select the best tower and lock on.

A better example that includes moving: People on their phones driving
through downtown NYC. A densely populated area would need more towers with
closer spacing. With all the buildings acting as giant reflectors we now
have multipath signals from many towers as well as phones. If the system
can lock onto thousands of phones under these conditions, a couple of 747's
with about half of the people on phones would be minor.

As some pilots who used their phones in the air have reported, they have to
lower their altitude to get a signal. Regardless of what the reports say,
hitting twenty towers with such a low wattage is highly unlikely.

On Tue, 20 Apr 2004 20:59:28 -0500, FUji wrote:

Even though it is theoretically possible to overload the processing
capability, I doubt that it is really a significant problem in the real
world.

It happens on the time. Capacity planning is part of their job. It's
just that proper planning by the various carriers tend to hide this fact.


For example, a group of people standing at the top of the CN Tower using
their phones would be line-of-sight to almost every cell tower in the
Toronto area. The system would select the best tower and lock on.

Right, which means they are not changing towers and are only using the
resources of a single tower.


A better example that includes moving: People on their phones driving
through downtown NYC. A densely populated area would need more towers with
closer spacing. With all the buildings acting as giant reflectors we now
have multipath signals from many towers as well as phones. If the system
can lock onto thousands of phones under these conditions, a couple of 747's
with about half of the people on phones would be minor.

That's really part of a capacity planning issue, IMO. If you were to
figure out the average call density, it would probably be fairly sparse.
After all, only so many cars can fit in a given area. Now then, if you
have a plane with 250 people and half those are using their phone, that's
an extra 125 calls on each tower that is now suddenly passing from tower
to tower. That's a HUGE difference in capacity in a very short period of
time.


As some pilots who used their phones in the air have reported, they have to
lower their altitude to get a signal. Regardless of what the reports say,
hitting twenty towers with such a low wattage is highly unlikely.

If it's reasonable to assume a ground based user can get two to three
towers at any given time, I don't think it's hard to easily imagine two,
three or even four times that since you're in the air with much fewer
obstructions (less scatter, direct, and father los), especially since
there is a much higher chance that your phone is operating at or near its
maximum output. Granted, chances are you not in a rural area if you're
hitting that many towers. But, just for the sake of argument, let's say
it's less. Is using use two or three times your normally alloted capacity
fair on the carriers? With enough phones in use at any given time, I can
easily imagine it playing heck with their capacity planning.

"Greg Copeland" wrote in message
news

Hmm. Everything I've ever read says that maximum output is 5-watts. I'm
not saying that's right, but that has been a constant.

At 5 watts your battery would last about 5 minutes, if that.

I'm not sure how
far you could even transmit on 0.6 of watt.

With my external antenna that I use when hunting I usually see 25-30 miles
without much problem.

In article , Newps wrote:

"Greg Copeland" wrote in message
news

Hmm. Everything I've ever read says that maximum output is 5-watts. I'm
not saying that's right, but that has been a constant.

At 5 watts your battery would last about 5 minutes, if that.

My Nokia 6820 will give 7 hours talk time and 10 days just switched on
off a tiny battery. There's no way it's even 1 watt transmit, let alone
5 (at least under normal circumstances).

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

"Greg Copeland" wrote in message
news
On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the
old
in-car and bag phones going up to 3 watts.
The radius of
interference from 0.6 watt phones transmitting from inside an aluminum
can
would be rather small.

I'm not sure how far you could even transmit on 0.6 of watt.

From London, on the 144MHz band, under the right conditions, I
once talked to a guy in Germany through a repeater in Belgium on
my 1W handheld. I then switched down to 150mW and could still
talk to him clearly. This was from the 12th floor of a building.

It's amazing how far 0.6W will go from a plane...if not for a good
quality phone call, at least to cause some interference.

People forget that cell switching is not magical. And it's certainly is
not zero cost. I must admit I do not fully understand everything that
goes on, but I am sure it's not as simple as you imply. Everytime a call
switches cells, it creates lots of work for the cell network to make sure
only a single tower handles that call. So, while it may take a fraction
of a second from a given phone and a given tower, there is lots going on
behind the scenes. Worse, instead of it going on with one, two or maybe
three towers, now it's causing a flurry of on twenty or more (highest
estimates I've read) towers. Let's also not forget that each tower can
only process and multiplex n-number of signals at a given time. DSPs,
just like your CPU, does have finite capacity. During cell switching, as
I understand it, this finite resource is being used on each tower in
contact with the phone. So, to say, "it causes all sorts of problems on
the cell network", does seem like a spot on statement to me.

Not only does it cause these problems with signalling in the network,
it also causes interference in other ways. With analogue, it will render
the frequency used unusable for the same frequency, repeated through
the 7 or 21 cell re-use pattern over the transmitted area. With TDMA
(D-AMPS or GSM), you'd wipe out that time slot on that frequency.
Greater than about 20 miles away, the time delay on the transmitted
signal would mean you'd also wipe out the adjacent time slot. You could
be decreasing capacity significantly over a wide area.

With CDMA I'm not sure about the interference potential, though it's
bound to increase the noise. I took our test gear up in the plane over
Newbury one day to see what I could receive. I got well over 20
cells and it was adding, deleting and replacing radio links like mad.
Absolute chaos on the network. Note that this network had not yet
been launched to the public (Vodafone UMTS - 3G).

It's not so much the "tower"s processing capacity, but that of the
BSC/MSC (or RNC on CDMA) controlling the base stations, and
also the capacity of the signalling links. All this is finite.

Someone said something (I've heard it said a few times) that the phone
"locks on" to the nearest cell. In laymans terms, yes. In actual terms,
you're transmitting, just like any other transmitter. The cell used for
communication will be the one receiving you the strongest. Note that
the neighbouring cells will be on different frequencies, so your phone
will tune to one of the frequencies used by the strongest cell. There is
then a re-use pattern, and the same frequencies will be re-used somewhere
a certain distance away, depending on the cell size. The cell size depends
on whether you're in an urban or rural environment...in an urban
environment they use a smaller cell size - lower power, more obstructions,
so the next cell using the same frequencies will be closer. They're banking
on the other cells not being able to pick you up due to your low power
and the buildings, hills,. trees and so on blocking the signal. (note that
the frequency thing doesn't apply to CDMA)

If conditions are right (wrong?) you may be picked up by other cells
on the same frequency...this is interference. If this is above a certain
level, this same frequency on the other cell will be rendered unusable.
(or that time slot on that frequency...and maybe the adjacent one, as
mentioned above).

If you use a phone in the air over an urban environment, you will cause
a large amount of interference. If you're down low over a rural area,
you may not cause any at all.

Paul

On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the old
in-car and bag phones going up to 3 watts. It can't output more than it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum can
would be rather small. And it's a little hard to imagine a plane full of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.

Greg Copeland wrote:

On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the old
in-car and bag phones going up to 3 watts. It can't output more than it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum can
would be rather small. And it's a little hard to imagine a plane full of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.

Both of my run-of-the-mill Nokias have a maximum transmit power of 600
mW. They are two different digital/analog models.

On Wed, 21 Apr 2004 00:53:13 +0000, James Robinson wrote:

Greg Copeland wrote:

On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the old
in-car and bag phones going up to 3 watts. It can't output more than it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum can
would be rather small. And it's a little hard to imagine a plane full of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.

Both of my run-of-the-mill Nokias have a maximum transmit power of 600
mW. They are two different digital/analog models.

Well, that's an interesting point. I know if I leave my phone on in the
air, it tends to degrade to analog mode (dual band phone). While I am
aware the digital mode uses far less power (just didn't realize that
little), perhaps the 5-watt maximum number is representative of phones
operating in analog mode? I dunno. That's my best guess.

"Greg Copeland" wrote in message
news
On Tue, 20 Apr 2004 16:35:03 -0500, FUji wrote:

Huh? Maximum output of most handheld cell phones is 0.6 watts with the
old
in-car and bag phones going up to 3 watts. It can't output more than
it's
maximum no matter how far you are away from the tower. The radius of
interference from 0.6 watt phones transmitting from inside an aluminum
can
would be rather small. And it's a little hard to imagine a plane full
of
people with bag phones.

I thought I might just toss this out there. I quickly looked. I did not
have any trouble finding modern, handheld phones, with 2-watts output.
So, I think it's safe to say that we know for sure it's at least 2-watts.


0.7 watts is the maximum that is considered "safe" for handheld use by
medical experts. Any more than that gets your brain frying, so they say.
;-)

I've had cell phones for fifteen years (novatel, motorola, mitsubishi, etc.)
and all the handhelds except the ericssons were 0.6 watts. The ericssons
were only 0.5 watts! Way back then I remember if you complained about bad
reception with a handheld they'd tell you to "upgrade" to a transportable.

Any links or names of the ones you found?