Femtocell as a Relay: An Outage Analysis

Femtocells promise to increase the number of users served in a given macrocell by creating indoor hotspots through the deployment of home base stations (HBSs) connected to the mobile operator network via cheap backhaul links (i.e., the Internet). However, the interference created by femtocell transmissions may critically impair the performance of the macrocell users. In this paper, a novel approach to the operation of HBSs is proposed, whereby the HBSs act as relays with the aim of improving transmission reliability for femtocell users and, possibly, also macrocell users. The proposed approach enables cooperative strategies between HBS and macrocell base stations (BSs), and is unlike the conventional deployment of femtocells where HBSs operate as isolated encoders and decoders. The performance advantages of the proposed approach are evaluated by studying the transmission reliability of macro and femto users for a quasi-static fading channel in terms of outage probability and diversity-multiplexing trade-off for uplink and, more briefly, for downlink. Overall, the analytical and numerical results lend evidence to the fact that operating femtocells as relays may potentially offset the performance losses associated with the presence of additional active users in the cell due to femtocells and even provide overall performance gains.