Femtocells can be lie detectors

Surely not an outlandish claim for this advanced technology? Femtocells know where you are and can tell if you are trying to use them from a different location. For some countries and some networks, this makes a significant difference.

We know where your femtocell is

When you buy and register a femtocell, you usually have to state the address you plan to install it. If you give the wrong information and try to plug it in elsewhere, the system can spot you aren't telling the truth and decide not to enable service.

Femtocells in North America are equipped with GPS receivers to determine the location. This might not be accurate enough to identify a specific apartment in a high-rise block, but should be more than enough to narrow down the building itself and confirm you have given the right address.

If you register the address you plan to use your femtocell and it doesn’t match the GPS location detected, the network operator will know you are lying and may well decide not to activate the device until the information matches correctly.

Why is location so important for femtocells?

There are three main reasons why precise location is important for network operators.

1) Frequency spectrum may differ in some parts of the country

Many (probably most) countries allocate their frequency spectrum on a nationwide basis, so that each network operator has exactly the same for all regions. There’s no need to restrict or configure the frequencies made available to femtocells depending on where they are.

Other countries, such as the United States have auctioned off their frequency spectrum in blocks on a regional and/or state-by-state basis. This means that the nationwide networks don’t own exactly the same frequencies in every state. In some cases, they may not own any at all and rely on roaming partner agreements with local or other networks.

This means that the femtocell must report exactly where it is. This location can be used to lookup a central database to determine which frequencies permitted in that area.

Potentially this could help the femtocell further by restricting the range of frequencies it needs to scan to detect nearby cellsites. The results of this local scan are used by the femtocell to build up a list of nearby cellsites and broadcast to its own mobile phones

2) Emergency call handling

When you dial 911 or 112 (or whatever emergency number for your country), the call is immediately directed to a local emergency call centre. It’s important to be connected to the right one – usually the nearest – so that the most appropriate resources can be provided quickly.

Many mobile phone networks map each cellsite to a specific call centre, usually on a geographic basis. Others – say in smaller countries – may only have one, or may have a special call centre specifically for such calls from mobile networks.

3) National billing

In many countries, calls between mobile phones are charged at the same rate regardless of distance – every call is effectively a long distance call. Some networks have gone a step further and introduced discounted local call rates based on where the call originates and terminates.

In very large countries, local and long distance rates have been applied for mobile phone calls since they were launched. This means that the location where a call originates and/or the customers registered billing address are taken into account when working out the cost of each call. This must be implemented for both prepaid and postpaid billing systems (which are usually independent of each other).

Could networks in other countries be interested in GPS location validation?

GPS hardware adds cost to the femtocell device, so even if this is just a few dollars more there would need to be a good case for it. Any of the three reasons above could be used to make a business case, but my own opinion is that it probably wouldn’t be very strong at this stage outside North America:

Location can be determined by reporting any external cellsite that can be detected. Since the location of every outdoor cellsite is know, reporting the cell identity could be used to lookup a database and get a rough (within say 10-20 miles) estimate – which might be good enough for frequency spectrum purposes. If no other cellsites can be detected, then perhaps location isn't that important where interference is concerned.

Emergency call handling is dealt with on the same basis as VoIP (Voice over IP) services in many countries. Registration of an address is usually required, but the onus is on the customer to ensure it is correct and up to date. Unless legislation is brought in to mandate the stronger requirements of the US, then its unlikely networks in other countries will follow suit.

Special rates for calls using femtocells are still in their infancy. Network providers may take the view that abuse would be relatively limited and that the cost of policing such special cases would outweigh the customer dis-satisfaction. Clearly, it's a factor to be taken into account when determining femtocell charges.

Summary

So while GPS equipped femtocells will continue to be prevalent across North America, I don’t expect to see this being adopted as a required feature in many other parts of the world.

If you agree/disagree or have further insights on this topic, please comment below – you can do so anonymously if you prefer.

Read a separate article about femtocell location lock