Abstract: A modulation scheme for use in a digital mobile radio communications system. The modulation scheme uses a four slot time-division multiple access scheme with 12.5 kHz channels. Each 12.5 kHz channel contains plural sub-carriers and each sub-carrier is modulated with a modulation scheme that encodes at least 4 bits per symbol. The modulation scheme can be used in a standalone mobile radio communications system, or in a hybrid mobile radio communications system that also uses standard TETRA modulation schemes.

Abstract: A scheme for indicating the presence of stealing or other information in a digital mobile radio communications system. A sequence of pilot symbols and/or synchronization symbols that can be distinguished from a normal sequence of pilot symbols and/or synchronization symbols is included in a transmission to indicate the presence of stealing. A receiver determines whether a received transmission includes the stealing sequence or the normal sequence and decodes the transmission accordingly.

Abstract: A scheme for indicating the presence of stealing or other information in a digital mobile radio communications system. A sequence of pilot symbols and/or synchronisation symbols that can be distinguished from a normal sequence of pilot symbols and/or synchronisation symbols is included in a transmission to indicate the presence of stealing. A receiver determines whether a received transmission includes the stealing sequence or the normal sequence and decodes the transmission accordingly.

Abstract: A modulation scheme for use in a digital mobile radio communications system. The modulation scheme uses a four slot time-division multiple access scheme with 12.5 kHz channels. Each 12.5 kHz channel contains plural sub-carriers and each sub-carrier is modulated with a modulation scheme that encodes at least 4 bits per symbol. The modulation scheme can be used in a standalone mobile radio communications system, or in a hybrid mobile radio communications system that also uses standard TETRA modulation schemes.

Abstract: A method and system that allows a mobile station of a communications system to request and be granted a fraction (a sub-set) of the overall frequency bandwidth of a communications channel for its transmissions. Thus, for example, in a TETRA system, a mobile station can, instead of having to request and be granted the full frequency bandwidth of an, e.g., 150 kHz QAM channel, request and be granted only a portion or fraction of the 150 kHz bandwidth of the channel, such as a 25 kHz portion of it. This allows the requested and allocated transmission resources to be more readily optimized to the amount of data that a mobile station wishes to transmit.

Abstract: A TETRA gateway apparatus (1) can send and receive call traffic and SDS messages via radio signals with the fixed radio infrastructure (4) on the one hand, and can send and receive call traffic and SDS messages via radio signals with one or more direct mode operating terminals (2 and 3,) etc., on the other hand. The gateway apparatus (1) is also configured to be operable such that when it provides a gateway function to appropriate direct mode operating terminals, such as a TET.RA terminal (2), it can also allow a user (9) of the gateway apparatus 1 to participate in a call, etc., that is proceeding via the gateway apparatus (1). A TETRA direct mode repeater apparatus can similarly be configured to allow a user of the repeater apparatus to participate in a call, etc., that is proceeding via the repeater apparatus.

Abstract: A method and apparatus of providing an audio output to a user in a communications system in which the audio to be output to a user, preferably an audio frame, is assessed before it is broadcast to the user, and then selectively changed on the basis of the assessment. The assessment may be carried out in the audio encoding process, in the audio decoding process and/or after the audio decoding process. The selective changing of the audio output may comprise selectively replacing the audio output and/or re-encoding of the audio output.