GSM celltower coverage

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richgamer

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#23515 1-Jul-2008 15:33

what is the radius that a cellphone tower can reach in kilometres? like will all cellphones within a 2km radius of a cellphone tower work etc.

wellygary

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#141927 1-Jul-2008 15:41

Cellular coverage like all radio reception is a tricky beast, It is all about line of sight, if you can see the tower, then it is dollars to donuts it will work at that range

On the other hand if you cannot see the transmitter, then all bets are off, it comes down to what is betwen you and the tower, (heavy concrete is a well known absorber ofthings like cellular and wifi signals), but roofs, steel beams etc all provide blaocking properties.

It also depends on the power of the specific cell ( what are it is expected to cover), along with the handset, (modern phones tend to have lower power than some earlier handsets)

If you have a specific concern, the more details you can provide the more likely ppl will be able to give you a good answer.

sbiddle

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#141935 1-Jul-2008 16:26

A standard GSM signal will work up to 35km.

Having said that if you stand 500m away with a big piece of lead between you and the phone you will get no signal.

Coverage is very much dependant on terrain, buildings and trees.

johnr

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#141963 1-Jul-2008 17:55

900mhz umts has a bigger coverage foot print than gsm 2g 900mhz

DjShadow

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#141977 1-Jul-2008 18:36

When you say GSM has a reach of 35kms, do you mean where a 2 way signal is possible?
e.g my parents used to live in Riverton in South just up a hill slightly, when i was there once my phone would pick up winton which is 33kms in a straight line according to google earth, got around 3 or so bars but my phone couldn't send a signal back so would have to wait until it found the riverton site again before I had 2 way again. The terrain in that area of southland is generally flat.

sbiddle

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#141981 1-Jul-2008 18:49

DjShadow: When you say GSM has a reach of 35kms, do you mean where a 2 way signal is possible?
e.g my parents used to live in Riverton in South just up a hill slightly, when i was there once my phone would pick up winton which is 33kms in a straight line according to google earth, got around 3 or so bars but my phone couldn't send a signal back so would have to wait until it found the riverton site again before I had 2 way again. The terrain in that area of southland is generally flat.

The 35km is a limit of the TDMA based system - because calls are divided into timeslots and RF signals travel at a fixed speed it's not possible for the signal to travel either from the BTS->phone or phone->BTS within that time. This results in the phone being unable to make a call but it may still have a signal present and show that it has service. Such issues used to be a pain on plaes like Mt Ruapehu - I remember a few years ago trying to make a call from Turoa while skiing and my phone was showing a CellID of Otaki!

Vodafone do have some rural sites that have double this range but the downide is the capacity of the site is halved.

tonyhughes

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#141997 1-Jul-2008 19:17

johnr: 900mhz umts has a bigger coverage foot print than gsm 2g 900mhz

Hey John,

Is that to do with power levels, or the ability of the handset or something?

I would have assumed (using my rather limited RF knowledge), that a 900MHz signal is a 900MHz signal, and it could be emitted by Teddy Bears for all it matters - as long as the transmitter transmits the same power surely the signal goes as far?

i.e. 900MHz UMTS could only be transmitting further than 900MHz 2G if it was transmitting at a higher power?

Not being contrary - just seeking to be educated!

P.S. Long time no talk, except for that big email today demanding we delete the Vodafone thread

^^^^^^^^ IM JUST KIDDING ^^^^^^^^^^

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johnr

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#141998 1-Jul-2008 19:18

Vodafone do have some rural sites that have double this range but the downide is the capacity of the site is halved.

And no 2G packet switch (GPRS)

johnr

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#142013 1-Jul-2008 19:54

richgamer:
what is the radius that a cellphone tower can reach in kilometres? like will all cellphones within a 2km radius of a cellphone tower work etc.

Also the tilt on the aeriasl have alot to do with the foot print of coverage.

sbiddle

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#142018 1-Jul-2008 20:12

tonyhughes:
I would have assumed (using my rather limited RF knowledge), that a 900MHz signal is a 900MHz signal, and it could be emitted by Teddy Bears for all it matters - as long as the transmitter transmits the same power surely the signal goes as far?

i.e. 900MHz UMTS could only be transmitting further than 900MHz 2G if it was transmitting at a higher power?

Remember that UMTS uses a CDMA air interface and it is not TDMA based therefore you are not facing the same issues with timeslots. I recall reading that Telstra bragged about sustained speeds of 2Mbps 200km from a 850MHz Next G WCDMA cellsite.

That is very damn impressive!

Edit: Now that I googled it I found it was actually 2.3Mbps

February 13, 2007
TELSTRA and its network partner Ericsson have claimed a new record for mobile data coverage, saying a cell in Telstra's 850MHz Next G mobile network can now stretch to 200km.
Telstra said "extended range" Ericsson software had been installed in several mountain-top sites around Australia, saying the upgrade was the first time a range of 200km had been achieved in a commercial mobile network.
Typical range for a cell in the network was about 50km. Telstra said data rates of 2.3Mbps at 200km had been recorded during testing.

johnr

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#142026 1-Jul-2008 20:36

tonyhughes:
johnr: 900mhz umts has a bigger coverage foot print than gsm 2g 900mhz

Hey John,

Is that to do with power levels, or the ability of the handset or something?

I would have assumed (using my rather limited RF knowledge), that a 900MHz signal is a 900MHz signal, and it could be emitted by Teddy Bears for all it matters - as long as the transmitter transmits the same power surely the signal goes as far?

i.e. 900MHz UMTS could only be transmitting further than 900MHz 2G if it was transmitting at a higher power?

Not being contrary - just seeking to be educated!

P.S. Long time no talk, except for that big email today demanding we delete the Vodafone thread

^^^^^^^^ IM JUST KIDDING ^^^^^^^^^^

(Completely O.T. > Watching Simpsons - that classic line "They were the suckiest bunch of sucks that ever sucked - made me literally laugh out loud!)

(PS) The money should dropped of by the red helicopter tomorrow!

Same power very different as Biddle has pointed out!

GSM (2G) 8 time slots per channel time slot 0 for signaling and the other 7 channels for Voice and packet data!

When a call is setup you get allocated a time slot from 1 - 7 you use that same time slot for the entire time you are on the serving cell for your call.

Think of a wheel spinning and it has 8 slots (time slots) to insert voice/data so the further away you get from the serving cell the more time it takes for the bits of information to get into that slot before it comes around again to make up speech and data! 35km

If this does not make sense it might be easier over beer.

John

richgamer

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#142194 2-Jul-2008 12:50

so 35km aye. wow that is a long way. i cannot see a cellphone tower from my house but i still get full coverage so obviously you don't have to have line of sight.

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SaltyNZ

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#142250 2-Jul-2008 15:27

Yes, the standard limit is about 35km due to timeslotting. There is a guard period between each timeslot, and the BTS measures the lag in timing due to propagation delay. It can pre-adjust the downlink signal by up to the guard band interval, and commands the handset to do the same. This result (up to 35km) in the timing still being correct at each end.

The rural extended range sites essentially throw away every second timeslot, giving a much larger guard band available. Hence half the capacity.

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richms

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#143090 4-Jul-2008 21:30

I have seen the signal but no calls thing several times when driving around the north island - Quite annoying, you will have full or close to it signal and cant make a call.

Richard rich.ms

paradoxsm

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#143094 4-Jul-2008 21:53

There are so many factors than can change the outcome, the old GSM 35km limit due to the timeslots crashing or losing synch due to simple distance physics, (each frequency wideband (which is similar to FM broadcast) signal is divided into 8 users all allocated each one of the 8 segments of a time base) rural slots it in to 4 using the other 4 as guards I think so they cannot crash in the same way,

CDMA can suffer from "breathing" which is where one or many handset are outputting too much rf, though this is regulated by the base station via "power control" on the fly very dynamically. Also if there are a lot of users close to the station, the furtherest users may experience degradation in service

The higher 2100MHz frequencies have a much harder job going through physical objects like montains and buildings.

that's it in english anyway! RLC block diagram anyone?

inquisitor

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#143126 4-Jul-2008 23:57

There is a guard period between each timeslot, and the BTS measures the lag in timing due to propagation delay. It can pre-adjust the downlink signal by up to the guard band interval, and commands the handset to do the same. This result (up to 35km) in the timing still being correct at each end.

That's called Timing advance. As explained above the 35km-range is not limited due to the physical signal range, but by the fact the GSM standard has a maximum timing-advance-value of 63, which corresponds to?233?s.
Ericsson (and I suppose others, too) offer a BTS-based solution, halving the number of timeslots per channel in order to extend GSM range to 72km (complete explication at http://www.mrvfone.com.au/vfone/ExtRange.pdf). Afaik this solution has been implemented in Australian GSM networks and recently at Lake Victorika, since when Ericsson praise themselves as live safers (http://www.ericsson.com/ericsson/press/releases/20080313-1200448.shtml). However the actual operability of such range extension is highly dependant on topographic conditions and also on the handset's maximum TX-power. Ten years ago handsets reached up to 2W, but today most phones don't exceed 1W in order to save energy and to provide a small SAR-value, after European and American legislations have ruled limits.
Here you see a?diagram explaining timeslots:

(source: http://www.rfcafe.com/references/electrical/gsm_specs.htm)

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