Transmission-Capacity Trade-Off for Coexisting Cellular and Mobile Ad Hoc Networks

In practice, radio spectrums allocated to cellular networks are usually underutilized. To increase the spectrum usage efficiency, we studied spectrum sharing between a cellular uplink and a mobile ad hoc networks. These networks use either all uplink frequency sub-channels or their disjoint sub-sets, called spectrum underlay and spectrum overlay, respectively. Given these methods, the capacity trade-off between the coexisting networks is analyzed based on the transmission capacity of a network with Poisson distributed transmitters. This metric is defined as the maximum density of transmitters subject to an outage constraint for a given signal-to-interference ratio (SIR). Using stochastic geometry, the transmission-capacity trade-off between the coexisting networks is derived, where both spectrum overlay and underlay as well as successive interference cancelation (SIC) are considered. In particular, for small target outage probability, the transmission capacities of the coexisting networks are proved to satisfy a linear equation. Its coefficients depend on the spectrum sharing method and whether SIC is applied. This linear equation shows that spectrum overlay is more efficient than spectrum underlay.