On spectrum allocation and interference management for WCDMA and OFDMA femtocells

In this paper we analyze how femtocell base stations (FBS) cause interference in the receivers of user terminals connected to macro base stations. A coverage hole around a FBS appears when closed access strategies are used, i.e. when only authorized users can access the FBS, and when the FBS shares the same or a portion of the macrocell frequency channel. At the cell borders of a macrocell the coverage holes can be large, especially for indoor users (10 - 30 m radius for the investigated cases). The coverage holes can be reduced if different frequency channels are allocated for macrocell and femtocell operation, e.g. down to 1 - 2 m for WCDMA femtocells in adjacent channels. When separation in frequency is not feasible, dynamic channel allocation (OFDMA) or adjustment of the FBS transmission power can be used to reduce the coverage holes. However, the different dynamic strategies have drawbacks in the form of reduced FBS performance and increased system complexity. Operators should consider open access schemes when using co-channel operation.