| 摘要 |
<p>The invention relates to a transcoder (TRCU1, TRCU2) having means for preventing tandem coding of speech in a mobile to mobile (MS1, MS2) call within a mobile communication system which employs a speech coding method for reducing transmission rate on the radio path. The transcoder (TRCU1, TRCU2) comprises a speech coder (52, 73) which encodes the speech signal into speech parameters for transmission to a mobile station, and decodes the speech parameters received from the mobile station into a speech signal according to said speech coding method, as well as a PCM coder (54, 72) for transmitting an uplink speech signal to and for receiving a downlink speech signal from a PCM interface in the form of PCM speech samples. In addition to the normal operation, the transcoder transmits and receives speech parameters through a PCM interface in a subchannel formed by least significant bit of the PCM speech samples. Thus, it is possible to prevent tandem coding but at the same time maintain the standard PCM interface and the signallings and services associated thereto. <IMAGE></p> |
