Signalling in a digital mobile communications system

A transmitter for transmitting user information and messages in a digital telecommunications system, the transmitter comprising:

• a user information encoder in which the user information to be transmitted is encoded into frames, each of which has one of two states, the states being a good state and a bad state;
• a message encoder for converting each different message to a corresponding unique bit pattern;
• transmitting means for transmitting the encoded user information and the messages via a transmission channel, wherein the transmitter is adapted to transmit each message by marking as the message at least one transmission frame which is assigned to the user information and restrict the number of consecutive frames marked as messages to a sufficiently low number so as not to substantially impair the quality of the user information and wherein the marking includes inserting the bit pattern corresponding to the message into the at least one transmission frame and setting the state of the transmission frame to bad.

A receiver for receiving information and messages in a digital telecommunications system, the receiver comprising:

• receiving means for receiving a signal via a transmission channel in frames wherein each frame has one of two states, the states being a good state and a bad state;
• a user information decoder operationally coupled to the receiving means for generating decoded user information, and replacing means for replacing a bad frame at least partly with a preceding good frame;
• a message decoder operationally coupled to the receiving means for decoding the messages, wherein for each different message, a corresponding unique bit pattern has been defined, wherein the receiver is adapted to detect a frame which contains a message and that the detecting is based only on identifying a bad frame which additionally contains a bit pattern which deviates from a bit pattern corresponding to a message at most by a predetermined threshold value.

Use of a bad frame indicator as the only indicator in a digital telecommunications system, for indicating that a frame containing a bit pattern which deviates from a bit pattern corresponding to a message at most by a predetermined threshold value, contains a message instead of user information.

A transmission signal in a digital telecommunications system wherein user information is transmitted in frames each of which has one of two states, the states being a good state and a bad state, wherein a bad frame is at least partly replaced by a preceding good frame, and for each different message, there is a corresponding unique bit pattern, wherein, during the time of transmitting the message, the transmission signal has predetermined differences from a transmission signal with similar user information but without the message, and the predetermined differences are substantially restricted to the corresponding frame which has a bad state and contains a bit pattern which deviates from a bit pattern corresponding to a message at most by a predetermined threshold value.