Spectrum sharing has been considered as a most promising solution to improve the spectrum efficiency of next-generation wireless networks. In particular, non orthogonal spectrum sharing allows the multiple operators to simultaneously use the available frequency bands, which leads to degradation of signal to interference ratio (SIR) at the intended receivers. To improve the SIR, we have proposed fractional frequency reuse (FFR) based structure for non-orthogonal spectrum shared (NOSS) systems. The coverage probability and average rate expressions are obtained for the proposed FFR based NOSS systems, and it is revealed that the proposed spectrum shared system ensures higher sum rate in comparison to no spectrum shared system, without any significant degradation in coverage probability. In particular, our analysis shows that FFR based NOSS system achieves 33% higher rate as compared to the case of no spectrum shared systems, however only 7% decrement is seen in coverage probability.