Method and apparatus for transmitting messages in a telecommunication system

A method for receiving a message of short duration in a digital telecommunication system, said method comprising receiving speech frames, some of which contain a message, wherein:

• a corresponding predetermined bit group is defined per each possible message;
• and
• identification of speech frames containing messages is based only on examination of the contents of the speech frames;
• and
• identification of a speech frame as a message requires at least that said speech frame contains a bit group which corresponds to one of said messages, wherein the speech frames are interpreted as messages when the speech frame contains a bit group which differs from a predetermined bit group associated with a message by no more than a predetermined threshold value the bit group including less than all bits of the speech frame.

A transmitter of a digital telecommunication system, comprising a speech encoder for encoding speech to speech frames consisting of bits, and a message encoder for encoding messages to a signal of a transmission channel common to the speech and messages;

• said transmitter being arranged to make at least one change in the signal of the transmission channel in order to transmit each message simultaneously with speech;
• wherein the transmitter is further arranged to:
• transmit messages for short periods at a time relative to the time associated with a speech frame;
• code each message to a corresponding predetermined bit group;
• restrict said change in the signal of the transmission channel in time to the transmission moment of the speech frame corresponding to said message;
• and
• replace less than all of the bits of the speech frame corresponding to said message with the corresponding predetermined bit group associated with said message;
• whereby no other indication of the transmission moment of the message is required.

A receiver of a digital telecommunication system, comprising a speech decoder for generating speech from speech frames, and a message decoder for decoding messages wherein a corresponding predetermined bit group is defined per each possible message;

• and the receiver is arranged to:
• receive a signal comprising speech frames, some of which contain a message;
• identify the speech frames containing messages only on the basis of the contents of the speech frames;
• and
• monitor at least whether a speech frame contains a bit group which corresponds to one of said messages, and when it does, to interpret said speech frame as a message, the bit group including less than all bits of the speech frame.