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Pros and cons of using femtocells

Scott Reeves takes a look some of the advantages and disadvantages of femtocells.

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What exactly is a femtocell? The short answer is that a femtocell is a very low-range, low-power base station, able to be deployed in a home, home office or office. It is usually provided by a mobile network operator, and operates in licensed frequency bands.  

A small amount of terminology may be of use before we proceed further into the world of femtocells. A macrocell defines the cell controlled by the base station of a mobile network operator. A femtocell is the cell controlled by the femto base station. The main difference between a femtocell and a base station is the range. A base station might have a radius of 20-30 km, whereas a femtocell has a radius up to10 metres. However, a femtocell uses the same licensed frequency band as the macrocell. Femtocells can operate with various types of mobile systems such as UMTS and CDMA2000. In future, LTE and WiMax capable femtocells are expected to be deployed.

For backhaul, the femtocell requires a connection to the mobile network operator. This is typically via a fixed line, be it cable, fibre-optic or a twisted pair telephone line. This connection enables the femtocell to interface with the operator’s base station, and provides a way for the two to coordinate when (for example) to handover your mobile device to the femtocell or back to the main base station.

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 Photo: Vodafone
 The femtocell needs to co-exist peacefully with neighbouring users and possibly neighbouring femtocells. This is not too difficult; a femtocell can sniff the spectrum and detect other femtocells. A femtocell will only use the frequency bands it has been allotted. Its short range and inbuilt intelligence means that it can adjust transmission power up or down, according to where its users are and whether neighbouring users are using the spectrum.

Advantages and disadvantages

There are a few controversies around the deployment of femtocells. One of them was pointed out by an erstwhile colleague when he was trying to sort out his home phone issues. He got somewhat irate when the company suggested a femtocell. His gripe was that the Telco company was making him fix their black spots.

Of course, there are advantages to having a femtocell. One of these is that the coverage is likely to remain consistent wherever you are located in the office/home, due to the femtocell. This has the flow-on effect that your mobile terminal/phone won’t use as much power, hence giving more battery time. A further advantage is that a mobile phone can be used as the main phone(s). Femtocells have the capacity to limit how many people are permitted to log on. This is a mechanism to restrict coverage. It makes using a femtocell in a small office attractive.

There are drawbacks. Femtocells utilise the broadband connection, which may also be used for other applications such as video streaming. There can be problems when the provider of the broadband service differs from the mobile network provider. These relate to Quality of Service guarantees. A further issue relates to interference. Although the deployment of femtocells suggests that interference with other femtocells is not a huge issue, there is still some controversy over whether this will continue to be the case.

The use of femtocells is part of a more general trend in mobile communications toward smaller cell sizes. Whilst there are some drawbacks to femtocells, the advantages of using them could be seen in homes and in small offices or home offices.

About

Scott Reeves has worked for Hewlett Packard on HP-UX servers and SANs, and has worked in similar areas in the past at IBM. Currently he works as an independent IT consultant, specializing in Wi-Fi networks and SANs.

3 comments
weinrich.kevin
weinrich.kevin

I bought one of these on eBay for my Mom, who lives in the N.GA mountains.  We've never had cell signal there.  AT&T said there had to be some minimum signal for the femtocell to work.  They were able to check ahead of time, and there was enough signal.  We hooked it up, and presto, she has great signal strength.  She ditched her landline, and has had smooth sailing for months.

laurent.gil
laurent.gil

 @speesd You may want to check on signal boosters - the new generation all-digital smart signal boosters should solve your problem, and they do not need GPS.

speesd
speesd

Just thought I'd toss in one other thing to be aware of.  We attempted to deploy one of these devices from a major mobile provider.  Our intent was to improve coverage in a basement area of our building that had historically poor coverage.  When working through the install requirements we were perplexed by a step that required that the device pick up a GPS signal.  We intended to use it in a location where cell coverage was non-existent.  Picking up a GPS signal was equally impossible.  We thought about initiating the device on a higher floor to obtain the GPS signal, then moving it down to the intended location in the basement.  However, we discovered that the device will want to establish that GPS connection every time it boots up.

After a while we finally reached a support tech who explained that in order to satisfy e911 requirements, they (the provider) had to be able to tell where the device was.  They were using the GPS ping to do that.  Without the GPS ping they couldn't confirm the location of the device.  Without knowing the location of the device they couldn't provide e911 information should someone call 911 from their cell phone connect to the device.  Without being able to provide location information for 911 callers we would not be able to deploy the device.

We were told there was no way around this requirement.  So... no device for us for now.