CDMA takes advantage of quiet times during speech to raise capacity. A variable rate vocoder is used; for the original vocoder the channel is a 9,600 bps when the user is talking. When the user pauses, or is listening, the data rate drops to only 1,200 bps (CDMA Variable Rate Speech Coder). Data rates of … Read more
Closed loop power control is used to allow the power from the mobile unit to deviate from the nominal as set by open loop control. This is done with a form of delta modulator. The base station monitors the power received from each mobile station in reverse link and commands the mobile to either raise … Read more
Voice data at 9600 bps or 14400 bps (full rate) is first passed through a convolutional encoder, which doubles the data rate for the 9600 bps case or increases it by 1.33 times for the 14400 bps case. It is then interleaved, a process that has no effect on the rate, but does introduce time … Read more
Vocoders Convert Voice to/from Analog Using Data Compression There are Three CDMA Vocoders: IS-96A Variable Rate (8 kbps maximum) CDG Variable Rate (13 kbps maximum) EVRC Variable Rate (improved 8 kbps) Each has Different Voice Quality: IS-96A – moderate quality EVCR – near toll quality CDG – toll quality All digital communication systems use various … Read more