We have investigated the noise characteristics in the intensity-modulated and phase-modulated signals and estimated how much the single-page storage density and data transfer rate increase by using the multivalued signals. In our simulation, the diffracted image was calculated considering two important aspects in actual holographic data storage systems. One is the aperture inserted in the signal optical path, and the other is the oblique hologram shape formed in the recording medium. Our numerical simulation revealed that in the case of the intensity-modulated signal, the single-page storage density was almost unchanged even if the number of multivalued signals was increased. In contrast, when an 8-level phase multivalued signal was employed in the system, the single-page storage density was estimated to be increased by a factor of 2.4 -3.0 compared to the intensity binary signal.