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.