A VR-CELP codec implementation for CDMA mobile communications

This paper focuses on the design, implementation and testing of a variable rate (VR) CELP codec aimed to be used in the testbed of one RACE-II project: CoDiT (code division testbed). The project has been conceived to demonstrate the potentiality of CDMA for the UMTS (universal mobile telecommunications system). Because of the flexibility permitted by CDMA to easily convey the information stream over a VR physical channel, the fixed-rate constraint has been removed from the speech coding algorithm design, in order to exploit the time-varying local character of speech. One major feature of the proposed algorithm is the possibility for the average rate to be either source-controlled or network-controlled. This is particularly appealing for cellular communications in order to cope with areas or cells with a high time-varying congestion