METHOD AND APPARATUS FOR CLASSIFYING IMPORTANCE OF ENCODED FRAMES IN A DIGITAL COMMUNICATIONS SYSTEM

摘要

Classifying, the importance of encoded frames in a digital communications system by calculating an energy difference between outputs of a frame decoding with an error detection and said frame decoding without said error detection. Said frames are encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP). Said method comprises the following steps: first decoding (106) a frame in an ACELP decoder with a Bad Frame Indication (BFI) function enabled; second decoding (112) said frame in said ACELP decoder with said BFI function disabled; calculating (116) an energy difference between said first and said second decoding output. Said calculated energy difference is a measure of said importance, and may be determined using VAD. The system is decribed with reference to determing which frames may be replaced by encryption synchronisation information in a TETRA network.