What is a Femtocell?

A femtocell is a very low-range, low-power cellular base station, that can be deployed in a home, or office. It is provided by a mobile network operator and operates in licensed frequency bands. Femtocells are used to provide network coverage to cellular devices where operator base stations or macrocells cannot reach or have weak coverage such as inside building complexes, underground structures (train stations, basement levels etc.), trains & buses etc.

The main difference between a femtocell and a base station, microcell or picocell is the range. A base station might have a range of 20-30 km, macro cell a range of 1-2 km, picocell a range of 200-300 meters and femtocell can have a range as low as 10 meters. However, a femtocell uses the same licensed frequency band as the macrocell (base station). A femtocell can coordinate with an operator base station to provide mobile devices with optimum mobile coverage by switching between femtocells and macrocells according to signal strength. For this, the femtocell needs to interface with the operator’s base station via a fixed-line like a cable, fiber-optic or a twisted pair telephone line which is available via broadband (DSL or cable).

Femtocells are usually separately sold or leased by a mobile network operator (MNO) to its customers. It is typically the size of a wireless router and connects to the user's broadband line. Femtocells are plug-and-play devices and require no specific installation or technical knowledge; they can be installed by anyone at home. These devices only allow pre-declared phone numbers to connect to it which is usually done y the user through a webpage or application provided by the MNO. Femtocells also have protection mechanisms that report changes in location to the respective MNO. Whether the MNO allows femtocells to operate in a different location depends on the MNO's policy.

Advantages of Femtocells

• Exceptional coverage as all connected devices are in close proximity to a femtocell, especially in places where there is no existing signal or poor coverage.
• Femtocells offer better voice quality (via HD voice) depending on a number of factors such as operator/network support, customer contract/price plan, phone and operating system support.
• Due to reduced transmitter-receiver distance with a femtocell, mobile devices don’t have to use as much power as when connecting to a macrocell. This improves the battery life of handsets connected to a femtocell and also improves the overall energy efficiency of the network.
• Femtocells may also provide higher mobile data capacity than a macrocell base station as it only serves a much smaller number of users.
• Calls placed and mobile data used under femtocell coverage may have special tariffs depending on the pricing policy of the MNO.

Disadvantages of Femtocells

• As Femtocells use the same frequency bands as the conventional cellular network, they may cause interference in the wider network and also experience interference in the femtocell network themselves. This can have a critical effect on performance and rather than improving the situation it could potentially cause problems. Hence, femtocells must be equipped with capable interference mitigation techniques that detect macrocells, adjust power and scramble codes accordingly.
• When using an Ethernet or ADSL connection via home broadband, the femtocell must either share the backhaul bandwidth with other services, such as Internet browsing, gaming consoles, set-top boxes and triple-play equipment in general or alternatively directly replace these functions within an integrated unit. In shared-bandwidth scenarios, which are the majority of designs currently being developed, femtocells may affect the quality of service for both the broadband connection and the femtocell network.
• There is also the very likely possibility of problems arising when the provider of the broadband service differs from the mobile network provider. In such scenarios, the user may have to switch either one of their connection (broadband or mobile network) to the same company as the other.

Femtocells were initially designed for use in wideband code division multiple access (WCDMA) networks. Later other standards like the Global System for Mobile Communications (GSM), CDMA2000, Time Division Synchronous Code Division Multiple Access (TD-SCDMA), WiMAX, and LTE also started to support it. Many operators worldwide offer a femtocell service, mainly targeted at businesses but also offered to individual customers (often for a one-off fee) to resolve issues regarding poor or non-existent signals at their location. Operators who have launched a femtocell service include SFR, AT&T, C Spire, Sprint Nextel, Verizon, Zain, Mobile TeleSystems, T-Mobile US, Orange, Vodafone, EE, O2, Three etc.

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