Abstract: In cognitive radio network, the underlay coexistence problem of the OFDMA based Secondary System (SS) with LTE-A systems is more and more important. This paper focuses on the resource allocation and interference mitigation issues in the aforementioned scenario. The dif?culty lies in the fact that even the subproblem, or power allocation with interference, is NP-Hard. Therefore, this paper proposes a two-phase Resource Allocation algorithm using maximum weighted Matching in the subcarrier allocation phase and interference Quantizing in the power allocation phase, referred to as the MQRA algorithm. As presented in this paper, the proposed MQRA algorithm has a good balance in performance and complexity, which ful?lls the stringent delay requirement of LTE-A systems.