On the co-channel femtocells exclusion region in fractional frequency reuse macrocells

Femtocells are capable of achieving high capacity and improving indoor coverage due to a shorter distance between the transmitter and receiver, while fractional frequency reuse (FFR) has been proposed to improve spectral efficiency in emerging OFDMA networks. Due to spectrum limitations, FFR macrocell and femtocells are likely to share the same licensed spectrum, thereby inadvertently creating a possible dead-spot problem due to huge two-tier co-channel interferences. Using outage probability analysis, we derive the femtocell exclusion region (FER) or the minimum distance required for the co-channel femtocell to be able to reuse the same channels as the FFR networks. We show that a minimum of one FER could exist in FFR and at different combination of channel parameters and power ratio, two FER could exist; one in the cell-centre region and the other in the cell-edge region. A new static femtocell resource allocation strategy to improve the system performance is proposed.