Abstract: When multiple primary network (PN) with different interests competes to offer spectrum access opportunities for a single secondary network, a spectrum sharing scheme based on a repeated game model could be adopted to form a colluded monopoly for the licensed spectrum so as to maximize their total transmission utility. However, when a does not value its future transmission utility enough, it might choose to deviate from the present colluded monopoly to obtain a transmission utility larger than its monopoly utility, which then reduces the current and future transmission utilities of all other PN. Two new strategies were thereby proposed to produce a more flexible and credible spectrum sharing monopoly among all PN. Numerical simulation shows that, compared with the existing triggering strategy, the proposed strategies can effectively increase the overall transmission utility of all PN.