Femtocells: Are They Right for Your Environment?

One of the challenges in the cellular world is coverage.  Sometimes getting a signal when inside the bowels of a large building or even inside a residential structure can be difficult.  One solution is to install some type of distributed antenna system (DAS) or picocells.  However, these can be expensive to install and operate.

Another alternative is a technology called femtocells.  Femtocells are small, limited-range devices that extend the mobile operator’s network using an ISP connection.  These devices are similar to a wireless router that you would find in a typical residence, but instead of a Wi-Fi signal (unlicensed spectrum), femtocells have a cellular radio (licensed spectrum).  A diagram comparing the two technologies is below.

Here are some examples of femtocell products:

As you can see, femtocells are compact and can be easily moved to different locations.  Femtocells have been made predominantly for residential use, but public service (metro and rural) and enterprises are also becoming interested in the technology.

Femtocells can also offload traffic from the mobile operator’s cellular towers, since the traffic is carried over an ISP to the mobile operator.

The Femto Forum, a non-profit organization to promote the use of femtocells, estimates that at the end of 2010 there were 1.7 million femtocells deployed worldwide, with around 350,000 in the US.  An Infonetics Research report in March 2011 on the femtocell market predicts that shipments will exceed 5 million units worldwide by 2012.

While femotcells can be beneficial, there are a number of considerations that you should understand before deploying them.

  • Number of simultaneous users – most femtocells can only accommodate three to six simultaneous devices.
  • Limited to short distances – Typical maximum distance is around 12 meters (40 feet for us Americans).
  • One-way call hand-off – While you can transfer from a femtocell to the mobile operator network, you usually can’t do the reverse.
  • Needs GPS signal – The femtocell needs to be located such that it can receive a GPS signal, which is a requirement to support E911 emergency service in the US.  This could be problematic since the location which needs coverage may be far from any windows, like a basement or storage area.
  • Carrier-specific – The femtocell is usually provided by the mobile operator and will only work with their network.
  • Specific to air interface – Although some femtocells can support multiple air interfaces, most only support either GSM or CDMA.
  • Restricted access – You may need to configure the femtocell with allowable devices (whitelist).
  • May not support all network technologies  – For example, AT&T currently only supports 3G devices.
  • Conflicts with mobile operator cell towers or other femtocells – A strong signal from a nearby tower or another femtocell may affect performance.
  • Billing models – This varies widely among mobile operations, so read the fine print and ask a lot of questions.  Some mobile operators charge for femtocells while others provide them for free. There may be a separate plan required or usage may count toward your monthly minutes.

Enterprise femtocells may offer the following additional features:

  • Simultaneous connections for up to 64 devices.
  • Greater range.
  • Proxy-aware – Many enterprises connect to the Internet through a proxy server, so the femtocell will have to be configurable to support it similar to modern web browsers.
  • Connection hand-offs both from and to the femtocell.
  • Unrestricted access – not having to pre-program devices to be used.  This can also be an issue with having ‘uninvited’ users on your network.

So there you have it.  Hopefully you have enough information to determine if femtocells are right for your environment.

You can use the following resources to find out more about femtocells:

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