Frame erasure compensation method in a variable rate speech coder

A variable rate speech coder configured to compensate for a frame erasure, comprising:

• means for decoding a pitch lag value and a first delta value for a current frame processed after an erased frame is declared, the first delta value being equal to the difference between the pitch lag value for the current frame and a pitch lag value for a frame immediately preceding the current frame, the current frame being encoded according to a first encoding mode;
• means for decoding at least one delta value for at least one frame prior to the current frame and after the frame erasure, wherein the at least one delta value is equal to the difference between a pitch lag value for the at least one frame and a pitch lag value for a frame immediately preceding the at least one frame, the at least one frame encoded according to a second encoding mode different from the first encoding mode;
• and
• means for subtracting each delta value from the pitch lag value for the current frame to generate a pitch lag value for the erased frame.

A subscriber unit configured to compensate for a frame erasure, comprising:

• a first speech coder configured to decode a pitch lag value and a first delta value for a current frame processed after an erased frame is declared, the first delta value being equal to the difference between the pitch lag value for the current frame and a pitch lag value for a frame immediately preceding the current frame, the current frame encoded according to a first encoding mode;
• a second speech coder configured to decode at least one delta value for at least one frame prior to the current frame and after the frame erasure, wherein the at least one delta value is equal to the difference between a pitch lag value for the at least one frame and a pitch lag value for a frame immediately preceding the at least one frame, the at least one frame encoded according to a second encoding mode different from the first encoding mode;
• and
• a control processor coupled to the first and second speech coders and configured to subtract each delta value from the pitch lag value for the current frame to generate a pitch lag value for the erased frame.

An infrastructure element configured to compensate for a frame erasure, comprising:

• a processor;
• and
• a storage medium coupled to the processor and containing a set of instructions executable by the processor to dequantize a pitch lag value and a first delta value for a current frame processed after an erased frame is declared, the first delta value being equal to the difference between the pitch lag value for the current frame and a pitch lag value for a frame immediately preceding the current frame, dequantize at least one delta value for at least one frame prior to the current frame and after the frame erasure, wherein the at least one delta value is equal to the difference between a pitch lag value for the at least one frame and a pitch lag value for a frame immediately preceding the at least one frame, and subtract each delta value from the pitch lag value for the current frame to generate a pitch lag value for the erased frame,
• wherein the current frame is encoded according to a first encoding mode, and the at least one frame is encoded according to a second encoding mode different from the first encoding mode.

A method of compensating for a frame erasure in a variable rate speech decoder, wherein frames received at the speech decoder include a delta value, each delta value corresponding to a change in pitch lag from an immediately preceding frame, the method comprising:

• declaring an erased frame;
• decoding a first delta value for a first frame, the first frame being received after the erased frame is declared, wherein the first frame is encoded using a first encoding mode;
• decoding a current pitch lag value and a current delta value for a current frame processed after receiving the first frame, wherein the current frame is encoded using a second encoding mode different from the first encoding mode;
• generating a first pitch lag value for the first frame based on the first delta value and the current pitch lag value;
• and
• subtracting the first and current delta values from the current pitch lag value for the current frame to generate a pitch lag value for the erased frame.

An apparatus for compensating for a frame erasure in a speech decoder, wherein frames received at the speech decoder include a delta value, each delta value corresponding to a change in pitch lag from an immediately preceding frame, the apparatus comprising:

• means for declaring an erased frame;
• means for decoding a first delta value for a first frame, the first frame being received after the erased frame is declared, wherein the first frame is encoded using a first encoding mode;
• means for decoding a current pitch lag value and a current delta value for a current frame processed after receiving the first frame, wherein the current frame is encoded using a second encoding mode different from the first encoding mode;
• means for generating a first pitch lag value for the first frame based on the first delta value and the current pitch lag value;
• and
• means for subtracting the first and current delta values from the current pitch lag value for the current frame to generate a pitch lag value for the erased frame.