Adaptive Interference Management of OFDMA Femtocells for Co-Channel Deployment

Femtocell technology has been drawing considerable attention as a cost-effective means of extending cellular coverage and enhancing capacity as well as realizing its potential, when combined with orthogonal frequency-division multiple access (OFDMA), for improved indoor broadband wireless services. However, under the expected co-channel deployment of femto- and macro-cells, femtocells may incur high uplink interference to macrocells, and vice versa. To mitigate this interference, we propose a distributed and self-organizing femtocell management architecture, called the Complementary TRi-control Loops (CTRL), that consists of three control loops to determine (1) maximum transmit power of femtocell users based on the fed-back macrocell load margin for protection of the macrocell uplink communications; (2) target signal to interference plus noise ratios (SINRs) of femtocell users to reach a Nash equilibrium; and (3) instantaneous transmit power of femtocell users to achieve the target SINRs against bursty interference from other nearby users. CTRL requires neither special hardware nor change to the radio resource management (RRM) of existing macrocells, thus facilitating non-disruptive (hence seamless) penetration of femtocells. Also, CTRL guarantees convergence in the presence of environmental changes and delayed feedback. Our evaluation has shown CTRL to successfully preserve the macrocell users' service quality under highly dynamic user transmission conditions and be able to make a tradeoff between macrocell and femtocell capacities.