We address the problem of spectrum sharing where competitive operators coexist in the same frequency band. First, we model this
problem as a strategic non-cooperative game where operators simultaneously share the spectrumaccording to theNash Equilibrium
(NE). Given a set of channel realizations, several Nash equilibria exist which renders the outcome of the game unpredictable.
Then, in a cognitive context with the presence of primary and secondary operators, the inter-operator spectrum sharing problem
is reformulated as a Stackelberg game using hierarchy where the primary operator is the leader. The Stackelberg Equilibrium (SE)
is reached where the best response of the secondary operator is taken into account upon maximizing the primary operator’s utility
function. Moreover, an extension to the multiple operators spectrum sharing problem is given. It is shown that the Stackelberg
approach yields better payoffs for operators compared to the classical water-filling approach. Finally, we assess the goodness of the
proposed distributed approach by comparing its performance to the centralized approach.