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Femtocells to solve network capacity issues

Posted: 01 Dec 2011 ?? ?Print Version ?Bookmark and Share

Keywords:femtocells? network deployments? mobile data?

Interference management
Since femtocells are being deployed in configurations and topologies that were not originally anticipated by 3G standards, one of the challenges that has required additional research and development to overcome is how to minimize downlink and uplink interference to macrocells and neighboring femtocells when femtocell RF frequency channel overlaps with that of macro cellular transmissions.

In this report
??Why femtocells?
??Interference management
??A cellular access point in every home
??Femtocell discovery
??Femtocell power-saving advancements
??One device to rule them all

Femtocells are therefore now being designed to self-configure so that they seamlessly integrate and operate satisfactorily with the existing femtocell-macro network and provide excellent performance irrespective of their location in the residence, enterprise or the macro network. Femto solution providers, Qualcomm included, have developed algorithms for 3G femtocells to enable co-existence with macro network. These advanced interference mitigation technologies minimize the impact of the femtocells on the macro network. They use RF measurements by the femtocell and associated handsets to adapt their operations (e.g. channel of operation, femto transmit power, associated handset transmit power cap) to minimize impact on the macro network.

Femtocell board

A femtocell board designed around one of Qualcomm's chips.

Qualcomm has had an active R&D program in this area for four years, resulting in the UltraSON suite of algorithms that provide for interference as well as mobility management of femtocells. The UltraSON algorithms provide effective downlink power calibration and uplink interference management as well as reliable mobility between macrocells and femtocells. In addition to using mobile handset measurements, femtocells that use UltraSON algorithms require a key additional hardware function, network listen. Network listen is an RF receiver module which resides in the femtocell and "sniffs" the surrounding RF environment, to provide inputs to the UltraSON algorithms which then compute the initial downlink transmit power, frequency channel and scrambling code prior to the femtocell transmitting its RF signal. Subsequent to initialization, the network listen can continuously monitor the RF environment to make dynamic changes as needed to avoid transient interference scenarios.

3G small cell interference management has had to be performed in an isolated cell environment without explicit co-ordination with the macro network, since these small cells were not anticipated as part of the original macro network deployments. LTE, the next-generation mobile air interface network technology, however has incorporated support for interference management of small cells in the Release 10 and Release 11 versions of the LTE standard.

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