We'll explain the details for a 3G UMTS mobile phone system here, because this is the most common technology being used for femtocells today. Other mobile phone systems would operate in a very similar way.

The femtocell appears to the standard 3G phone as just another cellsite from the host mobile operator, and can be used by almost any 3G phone including roamers visiting from other countries.

The mobile operators telephone switch (MSC) and data switch (SGSN) also communicate to the femtocell gateway in the same way as for other mobile calls. Therefore, all services including phone numbers, call diversion, voicemail etc. all operate in exactly the same way and appear the same to the end user.

The connection between the femtocell and the femtocell controller uses secure IP encryption (IPsec), which avoids interception and there is also authentication of the femtocell itself to ensure it is a valid access point.

The figure below illustrates the system architecture and context for femtocell operation.

Inside the femtocell are the complete workings of a mobile phone basestation. Additional functions are also included such as some of the RNC (Radio Network Controller) processing, which would normally reside at the mobile switching centre. Some femtocells also include core network element so that data sessions can be managed locally without needing to flow back through the operators switching centres.

The key functions are integrated onto a single chip, such as the PC302 from picoChip or the PRC6500 from Percello. These and other chip manufacturers document the different components in more detail in their reference designs. In addition to these highly integrated chips, a radio frontend (such as from Bitwave) and a highly accurate frequency reference crystal oscillator are also required.

The extra capabilities of a femtocell demand it to be self-installing and self-configuring. This requires considerable extra software which scans the environment to determine the available frequencies, power level and/or scrambling codes to be used. This is a continuous process to adapt to changing radio conditions, for example if the french windows are opened in a room containing the femtocell.

Within the operators network, femtocell gateways aggregate large numbers of femtocell connections (typically 100,000 to 300,000) which are first securely connected through high capacity IP security firewalls.

Read further to learn about which radio technologies are used for femtocells.

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Comments (10)

Anurag said:

	... how handover happens to the 3G network from the femto cell when people go out from home to the road while talking...
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April 10, 2011
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ThinkFemtocell said:

... @Anurag: Handover when leaving a femtocell works almost exactly as when moving between outdoor cellsites. First, the femtocell sniffs the environment to identify what other outdoor cellsites are available and what frequencies they are using. This is broadcast to all mobile phones by the femtocell, so that they can measure the signal strength and quality of nearby cellsites. When this is much better than the signal from the femtocell (such as when you walk outdoors), the system then co-ordinates a hard handover between the femtocell to the RNC, with the connection anchored in the central voice (MSC) or data (GSN) switch. Most of the functionality which controls the handover exists in the RNC (for outdoor cellsites) and in the femtocell - these both communicate with each other using standard messages/signalling protocols. Handover from 3G to 2G GSM when moving outdoors is also possible using the same mechanisms.

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April 13, 2011
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SAMET YILDIRIM said:

	... hi,? wonder that what the most significial harm of FEMTOCELL..
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May 01, 2011
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ThinkFemtocell said:

... @Samet: Why should they be harmful? They emit less RF power than many Wi-Fi hotspots, and mean that your own mobile phone whispers at very low RF levels across a few metres, rather than needing to power up and penetrate walls/several miles to the nearest outdoor basestation. If many femtocells are deployed in densely populated areas, the transmissions all add up to a much lower total. So I'd argue that these should reduce concerns about harm than increase them. This viewpoint is validated by a report commissioned by the Femto Forum into the subject (available from the website), and I've not seen any studies that refute it.

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May 03, 2011
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samet said:

	... In fact,FEMTOCELL is perfect technology for people to connect to each other at fast and qualitied... THANK you for replay.
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May 10, 2011
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Mahin said:

	... this is really an interesting technology.. but i dint understand the concept of femto gateway..i mean where it is located n is it necessary to have a gateway in the city where we want to use femto cell...???
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June 09, 2011
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rahi said:

	... i'm telecomm student doing final yr project on femtocells and its tech benefits. does any one know how to throughput analysis and outage probability using matlab?
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June 27, 2011
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ThinkFemtocell said:

	... @rahi: I haven't come across this analysis being made public yet. It should make for an interesting research project. At last week's conference, operators made it clear that femtocells had to provide at least as good performance as the macro network and (if correctly engineered) that this was certainly achievable.
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June 27, 2011
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CASTRO said:

	private gsm network Can I use the femtocell to build a private gsm network ??
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January 08, 2012 | url
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ThinkFemtocell said:

... @CASTRO Yes, you could do this - provided you had legal rights to use the frequencies. For example, many cruise and commercial ships have installed their own. Calls made to others onboard are directly connected, whilst international calls are sent via satellite. Another example is for smaller/remote islands. ip.access has plenty of experience in providing systems for these applications, with companies like Quortus (a ThinkFemtocell Sponsor) providing small core network to support it. You can also look at open source projects, like OpenBTS project, which I've described here http://www.thinkfemtocell.com/Technology/build-your-own-opensource-femtocell.html

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January 11, 2012
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