Method and apparatus for speech transmission in a mobile communications system

A transmitter apparatus for a telecommunications system transmitting digital speech on a transmission channel, said apparatus comprising:

• speech means for coding a speech signal by a speech coding method to provide a speech encoded signal,
• channel encoding means for channel-encoding the speech-encoded signal to a signal whose transmission rate is equal to a total transmission rate on the transmission channel,
• the speech encoding means employing two or more speech coding methods, which provide speech-encoded signals have mutually different transmission rates (S1, S2, . . . , SN),
• the channel encoding means being arranged to provide the channel encoding in two steps comprising
• first channel encodings which are specific for each speech encoding method and which, from the encoded speech signals having different transmission rates, generate first channel-encoded signals having a same constant transmission rate (S1) which is independent of the speech coding method, and
• a second channel encoding which is independent of the speech coding method and which, from a selected first channel-encoded signal, generates a second channel-encoded signal having a constant transmission rate (S1+C) which is independent of the speech coding method and which is the same as said total transmission rate.

A receiver apparatus in a telecommunications system transmitting digital speech on a telecommunications channel at a total transmission rate, comprising:

• channel decoding means for decoding a received channel-coded speech signal,
• speech decoding means for speech-decoding a channel-decoded speech signal by a speech decoding method,
• the channel decoding means being arranged to provide channel decoding two steps comprising:
• a second channel decoding which is independent of the speech coding method and which, from said received channel-encoded speech signal, sharing a constant transmission rate (S1+C), which is independent of the speech coding method and is the same as the total transmission rate used in the telecommunications channel, produces a first signal having a lower constant transmission rate (S1) which is independent of the speech coding method, and
• first channel decodings which are specific for each speech coding method and which channel-decode said first signal, producing encoded speech signals which are specific for each speech coding method and which have mutually different transmission rates (S1, S2, . . . , S3), and
• the speech decoding means employ two or more speech decoding methods for decoding said speech-coded speech signals produced by two or more speech encoding methods and having mutually different transmission rates (S1, S2, . . . , SN).