CTRL

Abstract

Femtocell technology has been drawing considerable attention as a cost-effective means of improving cellular coverage and capacity. However, under co-channel deployment, femtocells may incur high uplink interference to existing macrocells, and vice versa. To alleviate this interference, we propose a distributed and self-organizing femtocell management architecture, called CTRL Complementary TRi-control Loops), that consists of three control loops. First, for protection of macrocell users' uplink communications, CTRL controls the maximum TX power of femtocell users based on the fedback macrocell's load margin so as to keep, on average, the macrocell load below a certain threshold. Second, CTRL determines the target SINRs of femtocell users, conditioned on the maximum TX power, to reach a Nash equilibrium based on their utility functions, thus achieving efficient coordination of uplink usage among femtocells. Third, for protection of femtocell users' uplink communications, the instantaneous TX power of each femtocell user is controlled to achieve the target SINR against bursty interference from nearby macrocell or femtocell users. Our in-depth evaluation has shown CTRL to successfully preserve the macrocell users' service quality from femtocells' interference and converge to an optimal point under highly dynamic user TX conditions. CTRL is also shown to limit the effects of the estimation errors of channel gains and feedback delay.