The technology behind femtocells is far from trivial. Operators have approached their deployments carefully, ensuring they “cover all bases” to give consumers confidence in the solution. But long before the deployment stage, companies in the femtocell ecosystem were working on overcoming the substantial technological hurdles involved.

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Femtocells actually include far more intelligence than traditional basestations. Because of this change in the way tasks are partitioned in the network, femtocell chips like the picoXcell family from picoChip need to provide enhanced security features for authentication, location detection, and encryption as well as the prevention of denial of service attacks (see the figure).

Conventionally, the basestation (“Node B” in 3GPP jargon) is the radio stage, while the radio network controller (RNC) handles the intelligence and management. The RNC sets up and tears down calls, controls power levels and session parameters, allocates bandwidth to users, and supports handoff between sectors or cells. It is the bridge between the radio access network (RAN) of basestations and the core network. One RNC can control many basestations.

But in a femtocell, all of this intelligence is localized. Managing calls, controlling interference (which is crucial, so femtocells don’t damage the network by transmitting inappropriately), and interfacing the radio with the broadband network securely all are RNC functions. So a femtocell isn’t just a basestation, it also integrates the smarts of the RNC—and a lot more too.

Overcoming Obstacles

The security issue has been solved. Indeed, one of the strengths of femtocells is their very strong security compared to Wi-Fi. To begin with, everything in wireless is secured with strong encryption. There are theoretical attacks. But even GSM, which is an old technology, is still robust against all practical attacks, and 3G is stronger still.

The picoChip PC302 is an integrated baseband system-on-a-chip (SoC) used to implement femtocells for the consumer market. It can be used with LTE, HSPA+, and multiple-input multiple-output (MIMO) and provides 64-state quadrature amplitude modulation (64QAM) that can provide data rates to 21 Mbits/s downlink and 5.7 Mbits/s uplink.

Then there are end-to-end techniques. For example, the core must authenticate the handset, but also vice versa, so it is very hard to intercept. Cellular was designed to be secure in a way that Wi-Fi never was. (There is a value to calls.) Finally, it is hard to eavesdrop or intercept calls if you do not know who to listen to. A perhaps surprising fact is that the phone number is not used. An IMSI number that only maps to the phone number in the core identifies the handset.

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