What's the point of having infill 1800MHz GSM in major cities?

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simon14

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Topic # 56898 27-Jan-2010 22:26

What's the point of having infill 1800MHz GSM in major cities?

Surely if the reason was for more capacity, why couldn't Vodaofne just make additional or higher capacity 900MHz cell towers instead? Why use an entirely different frequency?

Same question goes for XT network using 2100MHz WCDMA as infill over and beyound their 850MHz WCDMA coverage.

nzbnw

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Spark

Reply # 293679 27-Jan-2010 22:31

Likely due to the lack of available 900MHz frequency.

XT is a 100% WCDMA 850 network, while Telecom does employ the use of 2100MHz, it isn't infill, mainly for in bound roamers. Local users can obviously connected to the 2100MHz network where available.

nzbnw

sbiddle

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Reply # 293681 27-Jan-2010 22:34

You can't create more capacity in crowded 900 spectrum - that's exactly why 1800 is used for infill.

GSM is a TDMA based system, there are a fixed number of frequencies that can only be reused so many times within a certain area before you suffer from interference.

Likewise WCDMA based networks suffer from a noise floor, add more sites and your noise levels increase. Using additional 2100MHz spectrum is the simplest and most logical way to add extra capacity.

simon14

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Reply # 293687 27-Jan-2010 22:44

So Vodafone couldn't just put another 900MHz cell tower right next to another if that other one was always congested in order to get extra capacity in that area? The only alternaitve is to add a new tower in a different frewquency range?

In that case, how much data/calls/text simultaneously can one cell tower handle?

johnr

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Reply # 293689 27-Jan-2010 22:49

1800 has smaller coverage foot print so handy when on waters edge and you can see another town across the bay

johnr

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Reply # 293690 27-Jan-2010 22:52

We also add 1800 to existing 900 sites don't need to build a new cell

Blindspot

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Reply # 294000 28-Jan-2010 16:21

There are very few (if any) locations with 1800 equipment installed without co-located 900. As john points out they have slighly different coverage footprints due to the different radio propagation. Like your radio AM travels better then FM. In most cases you will setup your call on 900 and depending on certain criteria being met, you will be pushed to 1800.

wellygary

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Reply # 294006 28-Jan-2010 16:39

simon14: So Vodafone couldn't just put another 900MHz cell tower right next to another if that other one was always congested in order to get extra capacity in that area?

The only alternaitve is to add a new tower in a different frewquency range? In that case, how much data/calls/text simultaneously can one cell tower handle?

No, you cannot simply add a new tower when one is full, vodafone only own a certain amount of spectrum/bandwidth/channels in the 900mhz range, while you can reuse the channels on a different site out of range of the full one, simply adding another site will mean each site is only using half the channels, but the number of users remains the same.

You can lower the power to shrink the cells to squeze in more reuse, but you get to a point where you cannot lower power ratings anymore as they have to penetrate buildings/vehicles.

At that point you need to get more channels from somewhere, and that somewhere is new frequencies i.e. 1800mhz.

sbiddle

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Reply # 294140 28-Jan-2010 21:44

Blindspot: There are very few (if any) locations with 1800 equipment installed without co-located 900. As john points out they have slighly different coverage footprints due to the different radio propagation. Like your radio AM travels better then FM. In most cases you will setup your call on 900 and depending on certain criteria being met, you will be pushed to 1800.

There are plenty of 1800 only sites, primarily scattered throughout the Wgtn and Auckland CBD's. These are actually the bulk of the 1800Mhz sites.

simon14

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Reply # 294145 28-Jan-2010 21:49

So if it got to a point where 900MHz and 1800MHz frequencies were running at capacity and their power had been reduced as much as possible to move in closer towers, in that situation, can nothing be done to add more capacity?

Not taking into account 2100 and 900 HSPDA of course...

wellygary

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Reply # 294155 28-Jan-2010 22:03

simon14: So if it got to a point where 900MHz and 1800MHz frequencies were running at capacity and their power had been reduced as much as possible to move in closer towers, in that situation, can nothing be done to add more capacity?

Not taking into account 2100 and 900 HSPDA of course...

In the short term no, but you have just answered your own question with your second comment.

The solution is to find a more efficient protocol, hence the move to 3G from 2G, its not just about more speed, but better use of the available spectrum.- ( but the cost of shifting is non-trivial for the operator and the customers, hence why you tend to plan these things while you still have surplus capacity)

http://en.wikipedia.org/wiki/Spectral_efficiency#Comparison_table

Blindspot

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Reply # 294223 29-Jan-2010 06:12

sbiddle:
There are plenty of 1800 only sites, primarily scattered throughout the Wgtn and Auckland CBD's. These are actually the bulk of the 1800Mhz sites.

You obviously know the Vodafone 2g Network betther than me