In this paper, the authors present a novel grouped OFDM-IDMA based downlink transmission scheme for femtocell networks. To avoid the cross-tier interference, they assign the femto users and marco users into different subcarrier groups for transmission. IDMA is used to mitigate the co-tier interference within the same group of users. They give the detailed system model as well as the transceiver structure of the proposed scheme. With the notion of SNR evolution function, they investigate the performance of the proposed scheme in terms of spectral efficiency and Bit Error Rate (BER).