Level of Fusion in Multimodal Biometrics: a Review

User verification systems that use a single biometric indicator often have to contend with noisy sensor data, restricted degree of freedom, non-universality of the biometric trait and unacceptable error rates. So the need of using multimodal biometric system occurred. A multimodal biometric system combines the different biometric traits and provides better recognition performance as compared to the systems based on single biometric trait or modality. In this paper, studies of different modalities are discussed and also discuss the various techniques used in different level of fusion with the objective of improving performance & robustness at each level of fusion. Keywords— Multimodal Biometrics, level of fusion, rule based methods, estimation based methods, classification based fusion