Uplink Capacity and Interference Avoidance for Two-Tier Cellular Networks

TLDR: In this article, an uplink capacity analysis and interference avoidance strategy in a two-tier CDMA network with universal frequency reuse is presented. And the authors evaluate a network-wide area spectral efficiency metric called the Operating Contour defined as the combinations of the average macrocell users and femtocell BS per cell-site that meet a target outage constraint.

Abstract: Two-tier femtocell networks-comprising a conventional macrocellular network plus embedded femtocell hotspots- offer an economically viable solution to achieving high cellular user capacity and improved coverage. This paper develops an uplink capacity analysis and interference avoidance strategy in such a two-tier CDMA network with universal frequency reuse. We evaluate a network-wide area spectral efficiency metric called the Operating Contour (OC) defined as the combinations of the average macrocell users and femtocell BS per cell-site that meet a target outage constraint. A contribution of this work is an accurate characterization of the uplink outage probability taking cross-tier power control, path-loss and shadowing into account. Considering worst case interference at a corner femtocell, results reveal that interference avoidance through a time-hopped CDMA physical layer and sectorized antennas allows about a 7x higher femtocell BS density, relative to a split spectrum network with omnidirectional femtocell antennas. These results provide guidelines for the design of robust shared spectrum two-tier networks.