Femtocells are low-power and low-cost base stations that provide residential cellular services, providing a coverage of roughly 10 m . They can integrate with mobile operator through a broadband connection, typically ADSL. In General, femtocell makes that the traffic from the home cellular system, deviates through the broadband connection, releasing the resource consumption of the macrocell.
The 3GPP has introduced the concept of Closed Subscriber Group (CSG), which essentially identifies a group of subscribers who have access permission to one or more cells. Femtocells basically have three different operating modes: open access, closed access and a combination of both named hybrid access  and , the access methods are:
- Open ccess: In this case, the UE can access the femtocell without any restrictions, this is seen in the Figure # 1 wherein the EU2 has unrestricted access to the femtocell in the building.
- Closed Access: The administrator defines the only femtocell users (CSG) that can access the network. For this mode, emergency calls are exempt.
- Hybrid Access: In this type of access, a limited amount of resources is allocated for access to users who are not part of CSG.
Figure # 1. Example of different femto-cell's access methods : Open access, closed access and hybrid access.