Speech communication system and method for handling lost frames

A decoder for a speech communication system, the decoder comprising:

• a receiver that receives a plurality of frames of a speech signal, each frame of the plurality of frames including a pitch lag parameter;
• a control logic coupled to the receiver for resynthesizing the speech signal based in part on the pitch lag parameters;
• a lost frame detector that detects a lost frame;
• and
• a frame recovery logic that, when the lost frame detector detects the lost frame, uses the pitch lag parameters of a plurality of previously received frames to extrapolate a pitch lag parameter for the lost frame.

A decoder for a speech communication system, the decoder comprising:

• a receiver that receives parameters of a speech signal to be decoded, the parameters being received on a frame-by-frame basis where each frame includes a plurality of subframes and the parameters include a gain parameter for each subframe of the plurality of a subframes;
• a control logic coupled to the receiver for decoding the parameters and for resynthesizing the speech signal;
• a lost frame detector that detects a lost frame;
• and
• a frame recovery logic that, when the lost frame detector detects a the lost frame, sets the gain parameter of a subframe of the lost frame in a first manner if the gain parameter of the subframe of the lost frame is an adaptive codebook gain parameter and in a second manner if the gain parameter of the first subframe of the lost frame is a fixed codebook gain parameter.

A decoding method comprising the steps of:

• receiving parameters of a speech signal on a frame-by-frame basis, the parameters including a line spectral frequency (LSF) for each frame;
• decoding the parameters on the frame-by-frame basis to reproduce the speech signal, wherein the decoding step uses a minimum spacing indicative of a minimum difference required between the LSFs of consecutive frames;
• detecting a lost frame;
• and
• setting the minimum spacing for the lost frame to a first value which is greater than the minimum spacing for the previously received frame.