Quality enhancement of coded and corrupted speeches in GSM mobile systems using residual redundancy

There is often residual redundancy remaining in coded speech data, even if a powerful speech codec (e.g. the full rate coder used in GSM mobile communications) is employed. By using such redundancy together with the information provided by the channel decoder, such as soft output (L-value), the number of channel bits inverted by the decoder, or a cyclic redundancy check, the bit error rate can be further reduced and a more graceful degradation of speech quality can be achieved, especially under bad channel conditions. In this paper, we report on the study with regard to this aspect for GSM full rate speech transmission and error concealment. The algorithms developed can be easily implemented with a currently available DSP designed for GSM mobile phones