Abstarct: Many attempts has been done to improve and developing the communication systems. Among these researches, using speech coders as a coder of special signal that has human speech production features has been interested by some scientists and companies. In this thesis firstly a brief review of speech coders is given. Then some conventional speech coders are explained briefly. After that the CELP coder as one of the famous speech coders has been investigated and its related standard FS1016 has been implemented. Finally a novel CELP coder baxsed on PLP algorithm, which is commonly used in automatic speech recognition systems, has been introduced. The experiments show results show better results in some cases in compared to general CELP.