Question - 999/112 Emergency Services

[Nickhlx]

...and in response to a comment a page or two back, few areas have cells that are that far (15 miles) apart - I'd be surprised if with the output power of a handset that the signal can go anything like that far, and anyway it is restricted by timing the return signal. So even if they only know which cell you are operating within, and that cell probably knows which sector you are in, your position is known to some accuracy. Add on coverage in one more cell and its already down to tens of metres or better and a third cell will diminish that inaccuracy.

 

It used to be the case that position of the transmitting cellphone was done purely with the cell sites information, nothing to do with GPS - few phones even had a gps receiver in them and many still don't, and I am not persuaded that the current situation uses GPS now, although some phones I know do have the ability to send their postion from the included GPS receiver, and maybe on demand by the operator/authorities when needed.

 

It would be great if someone in the industry could give us the current, up-to-date status on how accurate cellular triangulation is these days, and the method(s) being used...

 

Nick

[Graham Davis]

Why not ask one of the suppliers directly?

 

And some of the cells around here are so big there is NO signal in some areas!!

[mayalld]

...and in response to a comment a page or two back, few areas have cells that are that far (15 miles) apart - I'd be surprised if with the output power of a handset that the signal can go anything like that far, and anyway it is restricted by timing the return signal. So even if they only know which cell you are operating within, and that cell probably knows which sector you are in, your position is known to some accuracy. Add on coverage in one more cell and its already down to tens of metres or better and a third cell will diminish that inaccuracy.

 

It used to be the case that position of the transmitting cellphone was done purely with the cell sites information, nothing to do with GPS - few phones even had a gps receiver in them and many still don't, and I am not persuaded that the current situation uses GPS now, although some phones I know do have the ability to send their postion from the included GPS receiver, and maybe on demand by the operator/authorities when needed.

 

It would be great if someone in the industry could give us the current, up-to-date status on how accurate cellular triangulation is these days, and the method(s) being used...

 

Nick

 

I believe that the usable distance is governed by the time slot overlap, which means a range of around 35 km, although it is possible to extend to 120km.

 

In terms of phone placement, the timing advance slot count on a typical directional mast with 120 degree arc for each cell will place the phone in a 120 degree arc 550m wide.

 

The intersect of alternate signals will allow position to be triangulated.

[Nickhlx]

I believe that the usable distance is governed by the time slot overlap, which means a range of around 35 km, although it is possible to extend to 120km.

 

In terms of phone placement, the timing advance slot count on a typical directional mast with 120 degree arc for each cell will place the phone in a 120 degree arc 550m wide.

 

The intersect of alternate signals will allow position to be triangulated.

 

 

Are the time slots though, not limited for the expected range of handsets with their ? 1 watt max output and their internal ( relatively inefficient) aerials - even with high gain receiver aerials ( which still need to be not too directional) 35kms seems a tall order..

 

Nick

[mayalld]

Are the time slots though, not limited for the expected range of handsets with their ? 1 watt max output and their internal ( relatively inefficient) aerials - even with high gain receiver aerials ( which still need to be not too directional) 35kms seems a tall order..

 

Nick

 

Applying logic to the question...

 

If handsets were out of practical radio range at 35km, it seems unlikely that operators would implement extended range of 120km on any remote BTS by the use of double timeslots (which halve the capacity of the cell)

[Nickhlx]

Applying logic to the question...

 

If handsets were out of practical radio range at 35km, it seems unlikely that operators would implement extended range of 120km on any remote BTS by the use of double timeslots (which halve the capacity of the cell)

 

 

That's for "some services" that have in-vehicle boosters that can reach out of normal coverage of a cell to the next one in case of emergencies / interference, cell failure etc...

 

Nick

[mayalld]

That's for "some services" that have in-vehicle boosters that can reach out of normal coverage of a cell to the next one in case of emergencies / interference, cell failure etc...

 

Nick

 

I understand that tests of the extended range included the use of ordinary handsets.

[JDR]

Timeslots have nothing to do with range.

 

The biggest single factor on range is the frequency of the carrier signal-the higher the freq the shorter the range.

Edited July 13, 2011 by JDR

[mayalld]

Timeslots have nothing to do with range.

 

The biggest single factor on range is the frequency of the carrier signal-the higher the freq the shorter the range.

 

Timeslots have EVERYTHING to do with range!

 

The radio signals used in mobile phones are capable of reception over significantly greater distances than 35km.

 

However, there is a technical limitation in terms of propagation time between base station and mobile device, which means that beyond 35km the response time will be too great.

 

So, whilst signal strength etc falls off on a curve, you reach 35km and there is a hard cut-off. You could boost the signal at both ends to 100 times the normal levels, and it STILL wouldn't work at 36 km

[Nickhlx]

Timeslots have EVERYTHING to do with range!

 

The radio signals used in mobile phones are capable of reception over significantly greater distances than 35km.

 

However, there is a technical limitation in terms of propagation time between base station and mobile device, which means that beyond 35km the response time will be too great.

 

So, whilst signal strength etc falls off on a curve, you reach 35km and there is a hard cut-off. You could boost the signal at both ends to 100 times the normal levels, and it STILL wouldn't work at 36 km

 

 

I am sure that is correct Dave - my point is that I would be more than surprised that the power out from a handset with the inefficient aerial within them would not permit a workable range of 35km in a normal cellphone environment - even if he was line of sight, if his head was in the way the link would not be made... I do not think the engineers would configure the system to allow such circumstances to exist as the dropped call rate ( assuming it were set up in the first place) would be intolerable for the statistics ( and the users).

 

Even at 430 MHz with 1/4 wave aerials and 1 watt would struggle to make that link and the handset aerial is certainly many dB down from a 1/4 wave, regardless of how much gain/power the cell aerial emanates ( around 9 dBd - they can't be too high a gain as they need to cover a reasonable sector) and this is at a quarter of the frequency (approx). Sure, amateurs can do it, but this is a dependable, commercial / reliable / public system, working in average conditions, not a "surfing the edge, at the limits" sort of network.

 

Nick

Edited July 14, 2011 by Nickhlx

[DaveP]

'3' operate on 2100Mhz - so a 1/4 wavelength aerial would be ~3.5cm - easily within the physical constraints of a mobile phone. Most of the rest are on 1800Mhz - makes the aerial only mm longer?

[Nickhlx]

'3' operate on 2100Mhz - so a 1/4 wavelength aerial would be ~3.5cm - easily within the physical constraints of a mobile phone. Most of the rest are on 1800Mhz - makes the aerial only mm longer?

 

Correct - but they aren't whips in free air, but folded up and surrounded by other parts, not least a persons head a few cms away, so many dBs down and shielded...

 

Nick

[JDR]

Timeslots have EVERYTHING to do with range

 

They might do in the case of a theoretical 120km bts but in real life other factors will kick in before you reach the theoretical 35km limit.Another factor is the topography of the land.I wonder if that 35km cutoff still applies if you are firing a signal over water?

[mayalld]

They might do in the case of a theoretical 120km bts but in real life other factors will kick in before you reach the theoretical 35km limit.Another factor is the topography of the land.I wonder if that 35km cutoff still applies if you are firing a signal over water?

 

Yes, the 35km applies. It is an absolute limit that you cannot exceed.

[JDR]

Yes, the 35km applies. It is an absolute limit that you cannot exceed.

 

Thanks Dave food for thought.I know when they first put in 1800 networks they had to use a lot more sites than 900mhz I think interference and signal quality at 1800mhz without decent mast head amps make 35km quite optimistic at 1800mhz anyway.

[Justme]

When it said I was within a 15 mile radius I was in fact less than 6 crow flying miles from the mast.

[OptedOut]

This thread explains why the the police rang me back at Silsden to enquire which part of Worcestershire I was in, but does not explain their disregard for all the previous location info.

 

After reading the latest technical posts I must assume the police were working from an A-Z Atlas (early 90s)The distance from Silsden to Worcs being 190 odd Kilometers.