Spectrum Sharing between Wireless Networks

TL;DR

This paper analyzes how two wireless networks sharing the same frequency band can reach different equilibrium behaviors based on environmental factors, revealing conditions under which they naturally cooperate or compete.

Contribution

It models spectrum sharing as a game, characterizes Nash equilibria, and identifies environmental conditions influencing cooperative or competitive regimes.

Findings

Three distinct spectrum sharing regimes identified

High pathloss environments promote cooperation

Simulations confirm analytical equilibrium predictions

Abstract

We consider the problem of two wireless networks operating on the same (presumably unlicensed) frequency band. Pairs within a given network cooperate to schedule transmissions, but between networks there is competition for spectrum. To make the problem tractable, we assume transmissions are scheduled according to a random access protocol where each network chooses an access probability for its users. A game between the two networks is defined. We characterize the Nash Equilibrium behavior of the system. Three regimes are identified; one in which both networks simultaneously schedule all transmissions; one in which the denser network schedules all transmissions and the sparser only schedules a fraction; and one in which both networks schedule only a fraction of their transmissions. The regime of operation depends on the pathloss exponent $\alpha$, the latter regime being desirable, but attainable only for $\alpha>4$. This suggests that in certain environments, rival wireless networks may end up naturally cooperating. To substantiate our analytical results, we simulate a system where networks iteratively optimize their access probabilities in a greedy manner. We also discuss a distributed scheduling protocol that employs carrier sensing, and demonstrate via simulations, that again a near cooperative equilibrium exists for sufficiently large $\alpha$.