Patent ID: 7177320

Claim:
A telecommunications system for connecting to a network and for routing data messages between the network and subscriber terminals of the telecommunications system, the subscriber terminals being connectable to a central terminal of the telecommunications system via a transmission medium, the telecommunications system providing a number of communication channels arranged to utilise the transmission medium for transmission of data between the central terminal and the subscriber terminals, the telecommunications system comprising: a transmitter within the central terminal for sending a data message destined for a particular subscriber terminal over at least one of the communication channels as a number of data blocks; and a frame generator within the central terminal for generating a number of frames to represent each data block, each frame having a header portion and a data portion, the header portion being arranged to be transmitted in a fixed format chosen to facilitate reception of the header portion by each subscriber terminal and being arranged to include a number of control fields for providing information about the data portion, said information comprising at least an indication of the subscriber terminal for which the corresponding data portion of the frame is destined, the data portion being arranged to be transmitted in a variable format selected based on predetermined criteria relevant to the particular subscriber terminal to which the data portion is destined; wherein the predetermined criteria comprises an indication of the signal-to-noise ratio (SNR) of signals received by the destination subscriber terminal from the central terminal, and if there are a plurality of formats selectable as the variable format given the indicated signal-to-noise ratio and the amount of data to be sent in the data block, then the frame generator is arranged to select from those plurality of formats the format requiring lowest transmission power.