A feature required by potential femtocell operators, location lock prevents a femtocell from being moved to a new location without the owning network operator’s awareness and permission. We explain the justification for this feature and technical implementation options.
Why Femtocell Location Lock?
Emergency Call Location: Operators are required to report the location of emergency calls, so that assistance can be dispatched to the correct address. By ensuring that the femtocell only operates when at the specified location, it enforces that any moves to a new address are properly registered and tracked.
Spectrum Use: Femtocells used licensed frequencies and form part of the operator’s live network. They must be used at the correct frequencies for the area they are located, and be disabled when away from licenced territories (e.g. taken abroad on a business trip).
Commercial: Operators may decide they can justify charging an additional fee to process a femtocell relocation, including updating the registered operating address.
How is Femtocell Location Lock implemented?
Femtocells are connected via broadband IP and are associated with an IP address. Where both the wired broadband and the femtocell are provided by the same provider, it may be possible to associate the IP address with a registered physical address. Most domestic customers are allocated dynamic IPv4 addresses rather than static ones, which would restrict the identification to the area served by that pool of IP addresses (for example a DSLAM or Central Office).
Sniffing external 2G and 3G cellsites. Many femtocells can often detect external 2G and 3G cellsites (especially 2G operating at lower frequencies, which penetrate inbuilding better). They can remember the cellsite IDs, which shouldn’t change frequently.
GPS: Although located indoors, femtocells (especially those designed for CDMA), can include a GPS receiver. This is used for both location purposes (and therefore able to lookup what frequencies are licenced for use) and long term frequency clock accuracy. Modern GPS chipsets are remarkably low power and sensitive, so they even work indoors. Although included in CDMA femtocells, its generally thought this approach is unsuitable/undesirable for 3G UMTS femtocells because it requires an antenna (or the femtocell) to be located near a window and increases the product cost.
Exceptions to be considered
Should a femtocell still accept emergency calls, even though it’s disabled because it’s been moved? Arguably not, because the operator doesn’t know where it is (including being abroad).
What if there’s a power outage, and all external macrocells fail but your femtocell still operates using your UPS? Hopefully, the location lock won’t block your calls.
Spotted an omission, error or just have a question?
Comment on this article with your own views on reasons, technical implementation and exceptions.
No need to register, just fill in the comment form below – you can remain anonymous if you prefer.