Cell Phone Pinging Cell Towers?

I read in backpacker last month that even though a person making a cellphone call for help can't get the call through the signal pings cell towers and rescuers know the person they are looking for is still alive.

If that is true then trying to make a call is still a smart thing.

I wonder how this pinging thing works?

Little Rickie said:

I read in backpacker last month that even though a person making a cellphone call for help can't get the call through the signal pings cell towers and rescuers know the person they are looking for is still alive.

If that is true then trying to make a call is still a smart thing.

I wonder how this pinging thing works?

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I can't tell you the technical details, but I do know that sometimes a TXT will get thru when a call will not. AFAIK, you can not TXT 911 but you could TXT someone else to call for you...

Little Rickie said:

I read in backpacker last month that even though a person making a cellphone call for help can't get the call through the signal pings cell towers and rescuers know the person they are looking for is still alive.

If that is true then trying to make a call is still a smart thing.

I wonder how this pinging thing works?

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In order for you to be able to receive an incoming call, the phone has to occasionally send an "I am here" message to a nearby cell tower. This is presumably what is being referred to as a ping. Of course, anytime one attempts to make an outgoing call, the phone also contacts a nearby tower.

If the phone only reaches one tower, then rescuers can only determine that you are somewhere within the range of the tower. (Speculation: some cellphone protocols require precise timing--if it is possible to get an approximate range from this timing you would be on a circle centered on the tower.)

If the phone only reaches two towers, the relative timing at the towers gives your location as being on a parabola. (Speculation con't: in the precise timing case, you would be at the intersection of two circles or at either of two points.)

If the phone reaches three towers, the relative timing between pairs of towers would put you at the intersection of two parabolas, ie at either of two points. (Speculation con't: in the precise timing case, you could be located at one point.) This technique was used by Loran.

If the phone reaches four or more towers, then you could be located at one point.

Sending a text message requires far less energy and less time than sending voice (and the phone will keep trying until it succeeds or the battery dies). Thus a momentary successful contact may suffice to send a text message while being inadequate for voice.

BTW, a ping or text message being received from a cellphone only means that it is alive--you may not be...

Doug

DougPaul said:

In order for you to be able to receive an incoming call, the phone has to occasionally send an "I am here" message to a nearby cell tower. This is presumably what is being referred to as a ping.

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Yes, and if the phone doesn't hit a cell (as is the case in much of the High Peaks region) it keeps pinging away repeatedly, trying to find a tower, draining the battery even though the phone's owner hasn't made or received a single call!

Ask me how I know this...

J.Dub said:

Yes, and if the phone doesn't hit a cell (as is the case in much of the High Peaks region) it keeps pinging away repeatedly, trying to find a tower, draining the battery even though the phone's owner hasn't made or received a single call!

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Even worse:
Cell phones adjust their transmitter power level to use only the minimum necessary for a good contact. Thus when trying to find a tower when none are within range, the pings are at maximum power...

Doug

I think that could be managed by only turning the phone on every couple of hours for 15 min just so rescuers know you're OK or can possibly locate you?

Little Rickie said:

I think that could be managed by only turning the phone on every couple of hours for 15 min just so rescuers know you're OK or can possibly locate you?

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That would conserve the batteries. However, good spots to turn it on may not be entirely predictable...

Doug

DougPaul said:

That would conserve the batteries. However, good spots to turn it on may not be entirely predictable...

Doug

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If you are immobilized, the spot you are at is all you have. Sound familiar?

Tim

I wouldn't know a good spot from a bad spot but I'd still try.

Little Rickie said:

I wouldn't know a good spot from a bad spot but I'd still try.

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General guidelines:
Cellphone towers tend to be located near population centers and along major roadways (ie anywhere there are enough customers...). A single cellphone tower can only handle so many simultaneous calls so in dense population zones, they would tend to be fairly low (for small area coverage) and in less dense population zones they would tend to be higher (for larger area coverage).

Cellphone signals are pretty much line of sight, so you would need a line of sight (or near line of sight) to a tower. In general high places are more likely to have reception, but if you are in too high a place (eg high on Mt Rainier*) you may connect to too many towers which can confuse the system** (try to use a terrain feature to block some of the towers). In general remote locations in deep valleys have a poor chance of connecting, but I have seen a connection from deep in a valley in the WMNF where the end of the valley pointed at a population center. Foliage can also attenuate the signal--so try to find a location that is open toward the towers.

* I tried once to get a contact from the summit of Mt Hight (WMNF) which has line-of-sight to several population centers with no luck. I don't know if this was due to weak signals or too many signals...

** This is one reason that cellphones are not allowed to be used in aircraft.

Your phone protocol (TDMA, CDMA, GSM, or analog) may also be a factor--I have read that GSM has a range limitation in its protocol. Don't have any info on the others.

bikehikeskifish said:

If you are immobilized, the spot you are at is all you have.

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If you are immobilized, obviously you do the best you can from where you are. You may still be able to increase your probability of getting a contact (including voice, text, or ping) by keeping your phone off part of the time because the signal propagation can be affected by temperature and humidity profiles--signals tend to go farther at night than during the day, particularly during the summer.

Doug

J.Dub said:

Yes, and if the phone doesn't hit a cell (as is the case in much of the High Peaks region) it keeps pinging away repeatedly, trying to find a tower, draining the battery even though the phone's owner hasn't made or received a single call!

Ask me how I know this...

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Umm, not any phone that I have used...in fact some go into a deeper sleep when they do not have service.

Before the cell phone can make even a little peep, it has to get synchronized to a tower for various technical reasons, so I think your misfortune was due to some other factor.

J.Dub said:

Yes, and if the phone doesn't hit a cell (as is the case in much of the High Peaks region) it keeps pinging away repeatedly, trying to find a tower, draining the battery even though the phone's owner hasn't made or received a single call!

Ask me how I know this...

Click to expand...

Remix said:

Umm, not any phone that I have used...in fact some go into a deeper sleep when they do not have service.

Before the cell phone can make even a little peep, it has to get synchronized to a tower for various technical reasons, so I think your misfortune was due to some other factor.

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There are four different major protocols: TDMA, CDMA, GSM, and analog and there may be variants on each. It is likely that you are comparing different model phones and it is possible that your phones use different protocols which consume different amounts of power when out of range.

A key issue is who initiates the "I am here" handshake: if the tower initiates it (ie the phone must have the receiver listening much of the time) then the receiver must be powered up. If the phone initiates, then it must periodically transmit and listen for the "pings", but both the receiver and transmitter can be turned off the rest of the time. (One strategy might be to transmit a low power ping and then successively higher power pings until max power or until a reply is received.)

Phones are designed to maximize the standby time, but under what conditions? Maximum standby time when in contact with towers or maximum standby time when out of contact? Or both? The best strategies could also depend on such assumptions made by the designers. (I would guess that most phones would be designed to maximize the standby time when in contact with towers because that is where most users will tend to be.)

I don't know the details of the "I am here" handshakes, but the out-of-range battery lifetime would be a function of the details of the protocol, the design of the individual phones, and the battery size.

Doug

Doug Everything you said is true but the bottom line is that it is the cell towers which constantly transmit to make their presence known to phones. Even the oldest standard, AMPS, worked this way.

I could see a scenario where the OP's phone kept hearing a tower and losing it over and over. Or the OP was up high and phone kept handshaking to many different towers all over the northeast.

But if the phone cannot hear a tower, it does not waste any energy to try and "wake a tower up". In fact many stop listening closely and go even more dormant.

The bottom line is that being in a no-service area should put less of burden on the battery. So no need to worry about extremely fast battery drain or getting butt pocket cancer if you are out-of-range alot.

Doug You can convince yourself of this if you put various phones into a good GTEM cell and see what happens. I did.

Remix said:

The bottom line is that being in a no-service area should put less of burden on the battery. So no need to worry about extremely fast battery drain or getting butt pocket cancer if you are out-of-range alot.

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All the phones I've owned (4 or 5) died much more quickly when there is limited or no service.

Remix said:

Doug Everything you said is true but the bottom line is that it is the cell towers which constantly transmit to make their presence known to phones. Even the oldest standard, AMPS, worked this way.

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OK. I haven't studied the protocols in any detail. However, some aspects are obvious from the nature of the system. Having the towers advertise their presence would be my first guess at how the system should be designed.

I could see a scenario where the OP's phone kept hearing a tower and losing it over and over. Or the OP was up high and phone kept handshaking to many different towers all over the northeast.

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I presume that a cellphone does not answer every ping it hears (to save energy and reduce interference). Once it has registered its presence with a tower, it shouldn't need to re-register for some period of time unless it detects that it has moved to another cell.

But if the phone cannot hear a tower, it does not waste any energy to try and "wake a tower up". In fact many stop listening closely and go even more dormant.

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Reasonable strategies, IMO. But off course, it cannot go totally dormant because it needs to be able to discover when it comes within range of a tower. This dormant state would likely be implemented by turning the receiver off for some period followed by listening for another period. (FWIW, my 2-meter HT has such a mode (manually controlled).)

The bottom line is that being in a no-service area should put less of burden on the battery. So no need to worry about extremely fast battery drain or getting butt pocket cancer if you are out-of-range alot.

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Ideally true, but a weak service area could increase the drain because the replies would require more power than a strong service area.

Tom's observations, however, suggest that at least under some poor-to-no service condition the power drain is relatively high. A possible scenario might be that the phone (at least occasionally) hears the tower, but the tower cannot hear the phone so the phone drains its battery by trying to answer (at maximum transmit power).

Doug You can convince yourself of this if you put various phones into a good GTEM cell and see what happens. I did.

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Don't have access to one and I'm not in the cellphone design business so I don't really need one...

Doug

BTW, a ping or text message being received from a cellphone only means that it is alive--you may not be...

Doug[/QUOTE]

I love that.

Tom Rankin said:

All the phones I've owned (4 or 5) died much more quickly when there is limited or no service.

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Well if you are in a limited service area, the phone must use much more power to communicate with cell, so that is one scenario I mentioned.

In retrospect I could see a scenario where the phone indicates no service because it keeps hearing a weak tower and tries complete a transaction with tower using maximum power, repeating this over and over and over.


But phones do not waste energy by trying to "wake up" or "ping towers" Rather it is the opposite away around.

Once it has registered its presence with a tower, it shouldn't need to re-register for some period of time unless it detects that it has moved to another cell.

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]

Actually, idle cell phones are designed to continually pick the tower with the best signal-to-noise ratio and then register with the that tower---so that the network knows where to send incoming calls. When you are up high, with 30-40 towers in view and interfering with each other, the signal-to-noise ratio can change alot...resulting in high battery drain just to attempt and complete the registrations.

In fact, the network may become quite upset with your phone trying to communicate with 10 towers which are 50 miles apart in a short span of time. The network may simply shut the phone off. This happened to me on Lincoln--the phone displayed "Security Error" and froze until I turned it off.

Tom Rankin said:

All the phones I've owned (4 or 5) died much more quickly when there is limited or no service.

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I absolutely agree with Tom. My battery lasts for several days when I am in a populated area with lots of cell service. When I am in certain locations in the Adirondacks or elsewhere with no service, the battery will drain within a few hours. Every time.

Further evidence of this is when I have to leave my phone in a metal lock box before entering certain facilities. If I forget to turn it off first, it will be severely drained within a couple of hours.

Would there be another explanation?

Remix said:

Actually, idle cell phones are designed to continually pick the tower with the best signal-to-noise ratio and then register with the that tower---so that the network knows where to send incoming calls. When you are up high, with 30-40 towers in view and interfering with each other, the signal-to-noise ratio can change alot...resulting in high battery drain just to attempt and complete the registrations.

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Short-term s/n can change significantly over very short time intervals (fractions of a second), particularly if the phone is moving. It would be poor system design to change towers too often--it would be much better to base a change tower decision based upon the average s/n over some time interval such as 10-30 seconds and to limit the rate of tower changes unless the current tower is lost.

In fact, the network may become quite upset with your phone trying to communicate with 10 towers which are 50 miles apart in a short span of time. The network may simply shut the phone off. This happened to me on Lincoln--the phone displayed "Security Error" and froze until I turned it off.

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The system is designed with the assumption that a phone can only connect to a few nearby towers which must be able to cooperate to hand off a phone as it moves from one cell to the next. The cooperation mechanisms are not designed to handle phones that can connect to towers that are too far apart (ie have too many towers between them) and therefore the system does not work under these conditions. As I noted earlier, this has been observed on Rainier and the user fix is to move to a location with more terrain blocking.

Doug

Nessmuk said:

Further evidence of this is when I have to leave my phone in a metal lock box before entering certain facilities. If I forget to turn it off first, it will be severely drained within a couple of hours.

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A metal box may not actually be all that good a shield. RF leakage of a crack (or joint) in a metal box is more related its length rather than its area. Cellphone signals are UHF--unless the box is designed to be an RF shield it is most likely quite leaky. (You could try calling the phone in the box--if it rings, the box is clearly leaky.) A shielded box is sometimes called a Faraday cage.

Would there be another explanation?

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I don't have an explanation, but a couple of hours is similar to the maximum contact time which suggests that the transmitter is active.

There may be design tradeoffs of battery life with no contact vs battery life with contact. Since most phones are in contact with a tower, a designer might choose to favor low power drain when in contact than low power drain when disconnected.

Doug