Voice coding communication system and apparatus therefor

A voice coding apparatus which is provided with a discontinuous transmitter for interrupting transmission during a voice-nonactive period to reduce the transmitting power for transmitting an input voice signal in a coded form, characterized by:

• an LD-CELP encoder for encoding the input voice signal into an LD-CELP code;
• a voice activity detector for detecting the presence or absence of the voice of the input signal;
• A CN flag generator for generating a CN flag indicating the voice-nonactive period;
• a switch for switching mutually the output of the LD-CELP encoder and the output of the CN flag generator;
• a discontinuous transmitter which transmits the output from the switch to a transmission line, and, after a certain elapsed time from the transmitting of the CN flag, interrupts transmission until the transmission of the next CN flag or until a voice-active period begins;
• and
• a control circuit which, upon detecting the start of the voice-nonactive period by a signal from the voice activity detector, controls the switch to send the CN flag and the encoded background noise from the LD-CELP encoder for the predetermined period at the predetermined time intervals during the voice-nonactive period and outputs a reset signal for resetting the LD-CELP encoder at a predetermined point in time.

A voice decoding apparatus which is supplied with, as a received signal, a signal interrupted to be transmitted in a voice-nonactive period after a CN flag indicating a voice-nonactive period of an LD-CELP encoded voice signal and an LD-CELP encoded background noise are sent for a predetermined period of time at predetermined time intervals, characterized by:

• a pseudo-noise generator for generating the pseudo-noise;
• an LD-CELP decoder which decodes the received signal and holds the coefficients of a synthesis filter and the gain of a gain sealing unit at the time of having decoded the LD-CELP encoded background noise, then decodes the generated pseudo-noise inputted next by the use of the held coefficients of the synthesis filter and the held gain of the gain scaling unit;
• a switch for selectively inputting the received signal and the pseudo-noise into the LD-CELP decoder;
• and
• a control circuit which controls the switch for switching to the pseudo-noise generator side upon completion of the decoding of the LD-CELP encoded background noise after the detection of the CN flag from the received signal and for switching to the received signal side upon detecting the CN flag next, controls the LD-CELP decoder to hold or update the coefficients of the synthesis filter and the gain of the gain scaling unit in accordance with the operation of the switch and outputs a reset signal for resetting the LD-CELP decoder at a predetermined point in time.