Architecture

The femtocell is a simple concept that can make a major impact: initially conceived as a box similar to a WiFi access point connected to broadband, its scope has now expanded to encompass small-cell solutions for home, metropolitan, rural, enterprise and hot-spot applications.

Femtocells are now deployed around the world, by many of the largest wireless operators. Indeed, there are now more femtocells than traditional 3G basestations - the majority powered by Picochip SoCs.

It has long been evident that the combination of high frequencies, high data rates, large cell size and attenuation from walls represents a challenge for 3G when it comes to indoor coverage. Next-generation technologies such as LTE use even higher frequencies, more aggressive coding and modulation schemes.

Femtocells solve those problems.

Users also get a better deal. When they are at home, their mobile handset uses the femtocell to make and receive calls, backhauled via a broadband connection, even if there had previously been no coverage. On the move, they connect via the operator network. So a standard handset can work anywhere.

There are equally dramatic implications for pricing: operators can offer attractive calling packages to entire households; and it becomes easier to offer differential pricing for connections made at home or on the move.

Installing femtocells has beneficial effects outdoors, too. With femtocell coverage indoors, adjacent basestations need to use less output power, because they don’t have to blast signals through walls. There is therefore less noise for other users outdoors, and hence better service.

Deploying femtocells is not without its challenges. With so many basestations to install, it becomes essential that the hardware should offer a degree of self-configuration in order to ease the operator’s provisioning tasks. No less important are parallel self-optimization technologies that ease on-going maintenance tasks.

Picochip’s network monitor (“sniffer”) products are key enablers for such functions, serving as the femtocell’s “eyes and ears” and allowing it to configure and optimize its behavior.

Just as important are the techniques for integrating many femtocells into the operators’ core networks. 3GPP has defined a new concentrator type network element, the Home NodeB Gateway (HNB-GW). This can aggregate traffic from thousands of basestations into the core network. Communication between femtocell and HNB-GW is via a standard interface, Iuh, that implements security functions, control signaling and a new application protocol (HNBAP) designed to ease basestation deployment.

This approach fits seamlessly into current mobile network operators’ radio access networks (RANs) by supplementing or replacing their current RNCs with the concentrator element. The femtocell itself must handle the radio resource management functions formerly residing in the RNC.

Even though the femtocell extends the carrier network into the home, these standards (TS33.320) ensure that this is done with complete security and integrity. Picochip femtocell SoC integrate hardware based security, together with ARM's TrustZone® technology for a complete solution.