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- Published on Friday, 25 January 2008
- Written by David Chambers
What are Femtocells?
Femtocells are fully featured but very low power mobile phone basestations, connected using standard broadband DSL or Cable service into the mobile operator's network. They offer excellent mobile phone coverage at home for both voice and data, but at lower cost than outdoor service.
Standalone or integrated femtocells
Early femtocell products look very much like WiFi broadband modems, needing only two cables - one for power and one internet connection.
Several vendors such as Thomson, Netgear, Pirelli, Cisco and others have integrated the femtocell with other features such as DSL modem, WiFi and even IPTV into a single box. It is expected that in the longer term, most femtocells will be sold in this form.
Locked to a single mobile phone network
Unlike WiFi, these devices use licenced radio spectrum, so must be operated and controlled by a mobile phone company. Thus it will work with only one mobile phone operator, and thus encourages all users in a household to switch to the same network operator.
When in range of the femtocell at home, the mobile phone will automatically detect it and use it in preference to the outdoor cellsites. Calls are made and received in exactly the same way as before, except that the signals are sent encrypted from the femtocell via the broadband IP network to one of the mobile operators main switching centres. Making and receiving calls uses the same procedures and telephone numbers, and all the standard features (call divert, text messaging, web browsing) are available in the same way - indeed data services should operate more quickly and efficiently due to the short range involved.
Low power but high quality
Femtocells operate at very low radio power levels - less than cordless phones, WiFi or many other household equipment. This substantially increases the battery life, both on standby and talktime. Since they are so much closer to the handset or mobile device, call quality is excellent and data devices can operate at full speed. Standard units can handle up to 3 or 4 simultaneous calls from different users depending on the model. Larger femtocell designs intended for business (enterprise) use can handle 8, 16 or even 32 concurrent calls.
Open or restricted access
Restrictions can be applied on who can use the femtocell service. In extreme cases, there may be additional charges for DSL broadband supplier where a quota applies - however this would equate to many long voice calls or data service. Thus, whilst operators will hope that most femtocell users are willing to provide open access to other users, they usually offer the facility to restrict service to a whitelist of up to 50 specified telephone numbers.
Secure and self-managing
The femtocell encrypts all voice and data sent and received from mobile phones and would normally not allow access to the home computer network, so external users cannot break into your computer.
In order to reduce cost, these units are self installing and use a variety of clever tricks to sense which frequency to transmit on and power level to use.
Unlike outdoor mobile phone basestations (masts), femtocells don't require specialist RF planning engineers to design, calibrate or configure themselves - minimising the ongoing cost of maintaining them. They do have remote management from the network operator, who can upgrade the configuration and software as required.
Doesn't require special phones
They are compatible with existing standard mobile phones, although in future some minor enhancements would allow clear indication of when the phone is using the local femtocell (and thus using a free call allowance) - currently this can be provided by tones at the start of each call.
Most of the excitement is based around the new 3G UMTS mobile phone system, which includes the ability for high speed data services. However, vendors have developed femtocells for 2G GSM phones which are the most common globally, and also CDMA systems popular in the US.
So if anyone asks you what femtocells are, you can now confidently reply. Read more about the various femtocell system architectures, vendors and operators on the rest of this site.
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