Continuous Phase Modulation（CPM） is widely used in wireless communications

especially in military communications

due to its high power and spectrum utility

but the complexity of its demodulation exponentially grows with the partial response length and the modulation parameters.This paper proposes a reduced-state noncoherent sequence detection algorithm for CPM

remarkably decreases the number of the matched filters by the orthogonalizing process

reduces the states of viterbi decoding by the state combination and finally detects the signal with decision feedback.