Femtocell Access Control in the TDMA/OFDMA Uplink

This paper investigates open vs. closed access in the uplink of femtocell networks, for the particular case of orthogonal multiple access protocols like TDMA or OFDMA. Open access reduces near-far interference and provides an inexpensive way to expand the capacity of the operator´s network. Additionally, with a cap on the amount of resources allocated to the cellular users, open access ensures the femtocell owner still monopolizes a large portion of the femtocell´s capacity and backhaul. Seemingly open access is the appropriate approach for both two parties. We show mathematically and through simulations that the reality is more complicated and depends heavily on cellular user density: for example, closed access is typically preferable at high user densities in orthogonal multiple access. The results of this paper suggest that OFDMA or TDMA femtocells should adapt their access mechanism to the average cellular user density, which changes slowly.