There are places where even femtocells can’t reach

DungeonSomeone posed me a question recently relating to poor coverage in their office. Calls and text messages were being missed. Surely a femtocell would be the obvious, quick and low cost answer to the problem? Sadly, I fear this is an unusual case where femtocell technology doesn’t apply.

It’s US based

Unlike other countries, all femtocells in the US are fitted with GPS. This is for several reasons:

  • To synchronise the signal with an accurate timing source, essential where handover to outdoor cellsites is required. This is essential for CDMA mobile networks (such as Verizon or Sprint); other network technologies found elsewhere don’t require this.
  • To provide an accurate location for use when reporting emergency calls
  • To determine if the femtocell is in an area where the network operator owns licensed spectrum and so determine whether to work, and if so at what frequency

In order for the femtocell to work in the US, it needs to receive a GPS signal. The receivers used are very sensitive  so do work indoors in many cases. A stronger signal can either be achieved by locating near to a window or using an antenna cable connected to the device.

In other countries, the GPS receiver is not required. Other methods are used to determine where the femtocell is located (such as sniffing for signals from outside cellsites, deriving this from your internet connection/IP address etc.). They would still be able to be used in this situation.

It’s completely underground

The office in question was a sealed lab, based underground. It had no windows and no easy access to the sky. In these cases, the femtocell wouldn’t be able to work out where it was and would refuse to operate.

Perhaps a cable could be used to run an antenna up to ground level, enabling GPS reception. If this was the case, then service could be provided. For some situations, this may not be as easy as it sounds.

This is a corner case

For most users with a basement that has poor coverage today, a femtocell located at ground level would emit enough signal to penetrate downstairs and throughout the building. So it’s a pretty unusual case.

As stated above, I don’t think this applies for femtocells in other countries

Let me know if you disagree, otherwise it’s back to the traditional wireline phone for this office.

 

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Comments   

#1 David Brady said: 
Perhaps some kind of GPS repeater could be used http://www.gpssource.com/mysql/repeaters.php http://www.tdc.co.uk/marketing/interface_sp02.htm#gpss - specifically designed for lab use and testing of GPS equipment
0 Quote 2010-04-07 12:47
 
#2 Andy Tiller said: 
One option is for the femtocell to be installed first in a location where a GPS fix is available and then moved to the basement. If the femto is started up within a specified time period after the initial installation (e.g. a few minutes), the operator can assume that the femto is still at the same address.

BTW, GPS is typically not used for timing sync. A combination of Network Listen and NTP are the usual methods.
0 Quote 2010-04-15 14:12
 
#3 ThinkFemtocell said: 
@David: I'd not heard of a GPS repeater before... interesting idea.

@Andy: Thanks for the clarification (you should know - ip.access is providing the femtocell technology for AT&T's microcell). It looks like there is a workaround for AT&T customers then.

I'm not sure this would be the case for Sprint/Verizon femtocells, which use CDMA technology. My understanding is that CDMA does require GPS for timing/sync (because CDMA is a synchronous technology with all cellsites being aligned), so I believe my statement would be true for that technology. (I'm happy to be corrected on this if others know better).
0 Quote 2010-04-15 21:10
 
#4 Ed Sanford said: 
Actually, GPS Repeaters are perfect for offices that are in underground sealed labs. We help install this kind of system every day. But, you do have to get to the GPS signal above ground (must be within line of sight of the GPS satellites). This is easily achievable with an outdoor GPS antenna and a cable travelling from the antenna to the GPS repeater located in the underground facility or with fiber optics.
0 Quote 2010-04-30 20:45
 
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