Performance evaluation of OFDMA femtocells link-layers in uncontrolled deployments

The rapidly increasing use of smart phones with Internet access or data connectivity solutions for laptops is putting the infrastructure of cellular operators under stress. Both the number of devices and the bandwidth requirement are increasing. Indoor usage is also becoming prominent. One envisioned solution is the use of so-called femtocells. Femtocells are portable and low-cost base-stations for in-home usage. They are deployed by end-users and are connected to the operator network by a digital subscriber line (DSL), cable modem or optical fiber connection. The femtocells are operated along with the macrocell in a typical two-tier network structure. The regular base stations operate in one tier and the femtocells operate in the other tier. In a shared spectrum configuration, the uncontrolled deployment and loose control of the femtocells generate challenging interference management scenarios. With extensive simulations, we perform an evaluation of several femtocell to femtocell interference scenarios and one macrocell to femtocell scenario. We focus on typical 4G cases, with an orthogonal frequency-division multiple access (OFDMA) physical layer and full frequency reuse. Our results show that without any interference management, system performance is significantly degraded and that complete outages occur in specific cases.