We propose a spectrum sharing policy based on signal-to-interference-noise ratio (SINR) at a primary receiver. Contrast to the conventional spectrum sharing policy based on full channel state information (CSI) feedback, in our spectrum sharing policy, a secondary link can share the primary user's spectrum only using a binary state feedback for the interference link between a secondary transmitter and a primary receiver. In this paper, the maximized throughput of the proposed spectrum sharing policy is analyzed. The maximized throughput is determined by the ratio of the distance between the secondary transmitter and the primary receiver to the distance between the secondary transmitter and receiver. A secondary link with large distance ratio value can support high data rate applications only using simple binary state feedback as long as the SINR constraint of the primary user is guaranteed.