Performance of practical transmit beamforming methods for interference suppression in closed-access femtocells

In femtocellular systems, all active user equipments (UEs) share the same spectrum. Since handover between adjacent femtocells is prohibited when closed subscriber group (CSG) configuration is applied, considerable co-channel interference levels may be generated in reception. To combat this impairment a recently proposed method can be used, whereby each active UE has the chance to maintain a control-only connection to the strongest interfering femto base station (FBS). Based on this feedback information each FBS can apply different transmit beamforming (TBF) methods, trying to alleviate the interference perceived by users in disadvantageous situations. Closed-form expressions for the rate performance of three different TBF methods are presented. Our analysis reveals that even simple TBF techniques are very useful to mitigate co-channel interference effects in CSG femtocells.