说明：  This Paper is concerned with the study of the performance of DPSK (differential phase shift keying) Modulation Technique using AWGN(Additive white gaussian noise) channel. The DPSK has remarkable features such as limited bandwidth and constant envelope, which are of importance for mobile communication systems for providing the output according to our needs and requirement. In this study we evaluated the Bit error rate performance of the CDMA system by designing the CDMA system using SIMULINK Tool of the MATLAB software and study the performance characteristics of DPSK modulated CDMA system which are helpful for raising the level of present day communication systems, In order to design our DPSK modulated CDMA system we varied only modulation blocks of simple CDMA transmitter and receiver sections.