Abstract: It can not make decision by multi-objective optimization over the multipath channel for Single Carrier Frequency Domain Equalization (SC-FDE) cognitive systems. In order to solve the issue, a novel cognitive radio decision engine is proposed based on channel classification and Adaptive Modulation and Coding (AMC). Firstly, the channel is classified to determine the current channel state by the proposed engine. Then, the optimal Modulation and Coding Scheme (MCS) is selected in the MCS switching table according to the current channel state, and its Modulation and Coding Scheme Duration (MCSD) is calculated. Once the current MCS lasts longer than its MCSD, the cognitive radio decision engine will update the optimal MCS. The simulation results show that the proposed cognitive radio decision engine can provide the optimal transmission strategy to improve the spectral efficiency for SC-FDE cognitive systems. Therefore, the engine makes SC-FDE cognitive systems adapt to the complex electromagnetic environment better.