Effective Utilization of Licensed and Unlicensed Spectrum in Large Scale Ad Hoc Networks

This paper studies the improvement in network throughput of an ad hoc network from using both licensed and unlicensed spectra compared to the case where only unlicensed spectrum is used. We address the problem of how the nodes of the network, or secondary users (SUs), should spread their transmissions on both licensed and unlicensed spectra to maximize network throughput, and characterize `sharing gain' achievable in such spectrum sharing systems. The gain obtained can be significant and is increasing with the density of the SUs. The primary and secondary users are modeled as two independent Poisson point processes and their performance is evaluated using techniques from stochastic geometry. A co-operative case is considered where the channel selection strategy of the nodes is centrally controlled. Then, a non-cooperative channel selection game where the SUs selfishly select the channels is analyzed. A pricing scheme is proposed to drive the decisions of SUs to a favorable point. Specifically, by setting an `appropriate' price, global optimal performance is attainable at equilibrium in some cases. Finally, the analysis is extended to the case where a network shares spectrum with a cellular network.