In this paper,we propose a cooperative spectrum sharing strategy based on the Nash bargaining solution.Specifically,the primary system leases a fraction of its transmission time to the secondary system in exchange for cooperation to improve its transmission performance.To gain access to the spectrum of the primary system,the secondary system needs to split a fraction of its transmission bandwidth to help to forward the primary signal.As a reward,the secondary system can use the remaining bandwidth to transmit its own signal.We find a unique solution for this time and bandwidth allocation using the Nash bargaining solution.Simulation results demonstrate that the performance of the primary and secondary systems can both be improved by the proposed spectrum sharing strategy. In this paper, we propose a cooperative spectrum sharing strategy based on the Nash bargaining solution. Specifically, the primary system leases a fraction of its transmission time to the secondary system in exchange for cooperation to improve its transmission performance. To gain access to the spectrum of the primary system, the secondary system needs to split a fraction of its transmission bandwidth to help to forward the primary signal. As a reward, the secondary system can use the remaining bandwidth to transmit its own signal. We find a unique solution for this time and bandwidth allocation using the Nash bargaining solution. Simulation results demonstrate that the performance of the primary and secondary systems can both be improved by the proposed spectrum sharing strategy.