| 摘要 |
PROBLEM TO BE SOLVED: To apply a CS-ACELP (one of the highly efficient coding methods) to PHS (a simple mobile communication system) and to reduce the quality deterioration caused by transmission line errors. SOLUTION: Coded voice 8 kbit/s of CS-ACELP are inserted for every two frames or every four frames of PHS and errors are detected at a receiving side by CRC checks made at every frame (S1). If there exists no error, a normal decoding process is conducted (S3). If there is an error, an error rate Pg is computed back at 100ms by the number of errors and a transmission line error rate PL back at 300ms is computed by the number of errors. If the conditions are met in which PL>th1, th2<PE<th3 and an error is also detected in a previous frame (S5), a frame loss process is conducted (S6). If an error is detected, but the above conditions are not met, a normal decoding process is executed. |
