Digital fingerprinting is a scheme to insert user's own ID information into digital contents in order to identify illegal users who distribute unauthorized copy. One of the important problems is a collusion attack such that several users combine their copies of a same content to modify /delete the embedded fingerprint. In this paper, we propose a collusion-resilient fingerprinting scheme based on the CDMA technique. By combining spread spectrum sequence with orthogonal transform, we allocate the combination of spectrum components to users as their fingerprints. At a detector side, a threshold for the detection of colluded users is determined considering the false positive probability. We then estimate the parameters in the scheme for both optimal embedding and detection, and improve the accuracy of the detection of colluders. Experimental results show the effectiveness of proposed scheme.