A method for reducing the transmission rate of a channel vocoder by using frame interpolation

A simple coding scheme has been devised for reducing the transmission rate of a channel vocoder from 2400 bits/s to 1200 bits/s. In this scheme alternate frames of vocoder data are transmitted. At the vocoder receiver, the missing frames are regenerated from those transmitted by interpolation or by repeating frames. The method of regeneration for each missing frame is determined at the transmitter and signalled to the receiver using two bits in each transmitted frame. At 1200 bits/s the coding scheme introduces only slight additional degradation, but extending the scheme to lower transmission rates causes further degradation.