Moving a Femtocell

Moving a Femtocell If I’ve paid for a femtocell, I might reasonably think I could take it with me on my travels and use it to get great coverage, performance (not to mention low rates), wherever I go.

Imagine sitting in your hotel room in some foreign country. Signup for the hotel’s broadband internet (which is being included in standard rates more often now), plug in your femtocell and use your phone, blackberry (and even laptop dongle) as if at home. The minor hassle of taking an extra box with you would be offset by the convenience of using your own device (with up to date address book), excellent call quality. You could also benefit from using your inclusive minutes, avoiding almost any further charges.

Other popular scenarios for taking a femtocell with you include:
- using the femtocell at your second home if you have one
- using the femtocell on business in your hotel
- using the femtocell in a hired meeting room, conference facility to keep SMS and Blackberry/Email connections

Unfortunately, some of these scenarios are very unlikely for several reasons:

Regulatory/Legal issues: Femtocells use licensed spectrum. In many cases, operators have paid substantial sums to be allowed to use it exclusively and regulators will enforce transgressions. The use of femtocells in a different area would interfere with the visted operators network, sending conflicting signals about who's network uses that frequency. This could affect other legitamate users in the neighbourhood, such as in the room next door.

Commercial issues: Roaming traffic is very profitable (although becoming less so particularly in the European Union due to regulatory pressure). Its particularly beneficial to the serving network (i.e. where you are visiting), who capture perhaps 80% of the revenue for delivering services at premium prices.

Technical Issues: Spectrum allocations can vary in different areas – even for the same operator. In the US, operators with nationwide coverage may have been allocated different frequencies in different states, so must alter the frequency used by their femtocells in each geographic area to match.

Operational Issues: This could affect how operators manage the effects of these changes, including unexpected impacts on their radio planning, femtocell configuration and network traffic.

But how can operators enforce restrictions on moving femtocells (or not)?

1) By sensing any other cellsites in the vicinity. Every cellsite broadcasts its identity, which includes that of the country and mobile network it belongs to. Many femtocells can monitor (but not transmit) both 2G and 3G frequencies. Femtos can “fingerprint” their neighbourhood by building up a list of cellsite ID’s which can include other operator’s signals.

If a femtocell is then restarted and discovers a substantially different neighbourhood, it knows it has been moved. If the cellsite identities are from another country, it knows it’s abroad.

2) Built-in GPS receiver. Some CDMA femtocells have built-in high performance GPS receivers, which give two benefits. One is for emergency calls, the location can be immediately known. The other is for clock synchronisation, which is very important in CDMA networks – the transmitter clock is derived from the GPS signal. An additional benefit is that the GPS would immediately know if the location of the femtocell had been moved between being powered off.

3) IP address: It’s possible to map IP addresses to their originating country. Whilst its not foolproof, this would give a strong indication of where a femtocell was attempting a connection from abroad.

Once a location move has been identified, the femtocell can then take action such as:
a) Stop working – giving a warning signal with the reason (e.g. flashing LED).
b) Send an alarm to the network operator – who can then take action, such as calling the customer and/or disabling the device.
c) Adapt to the new environment – including reselecting frequency/codes to use. These may need to be downloaded from a central server.

What’s likely not to be allowed.

For regulatory reasons, operators cannot permit transmissions in spectrum they don’t own and control. Clearly, when operating abroad, outside the licensed territories, then operators will automatically disable femtocells in this case.

Whilst it can be argued that some of the large operator groups (Vodafone, T-Mobile, Orange) have operations in multiple countries, and thus licenced spectrum, there are operational reasons why femtocells wouldn’t be allowed to be used remotely. For one thing, the spectrum allocated may differ between countries. Another point is that the femtocell would broadcast its original identity (i.e. that of the home network country and operator), and would connect back to the home network. This would confuse any legitimate mobile phones from the visited country that pickup the signal.

What may be allowed and supported.

Moving a femtocell to a new location within the same country. Some designs can take 10-15 minutes to “warm up”, during which they scan around the environment, register with  the operators and configure themselves. This would be required each time the femtocells moves.

Some operators are considering whether to charge a fee each time the femtocell is moved. I can’t see that being popular, and may be more trouble to administer than its worth.

Multiple Femtocells

We’ve previously discussed the scenario where you might have more than one femtocell at home in order to support different mobile networks. For example, a work and personal phone subscription on different networks; multiple household members on different networks.

A business traveller could take a femtocell with them on their travels, but would they need to leave one at home for the rest of the family? (You wouldn’t take your wireline broadband modem with you, would you?).

This may introduce an unusual case where individual customers may be provided with more than one femtocell from the same network operator.

If the cost of femtocells is low, then second homes or other permanent locations, may be equipped with additional devices on the same subscription. This will introduce some additional complexity in the billing, customer care and configuration administration by the network operator.

Conclusion

I would expect to see some tolerance for moving femtocells to different locations within the same network coverage area, but a complete ban on using them abroad.

 

 

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