Design and Performance of Underlay-Overlay Cellular Networks

We study the design and performance of Underlay-Overlay (U-O) wireless networks, in which the available spectrum is partitioned into two groups - an overlay group with a conservative reuse factor, and an underlay group with a more frequent reuse. A key performance factor is the absorption, i.e., the proportion of traffic in a cell that can be supported on the underlay. To address the two principal problems in U-O networks, namely, (a) Where are the boundaries of the underlay to be placed? (b) How are the channels to be allocated? We propose an optimization problem and a traffic model respectively. Our optimization problem introduces a novel set of interference constraints, and can be effectively approximated using bounds and heuristics. The traffic model, which is a simplified queueing system with a product form solution, effectively captures capacity gains realized from absorption. Numerical results on a simple linear network suggest substantial capacity gains from the U-O design compared to a single layer network.