Coding and modulation techniques used are of particular concern to the fixed wireless system. Coding consists of a transformation of the format of the signals in the alphabet to take account of the methods of synchronization, introduction of redundancy in accordance with the error-control and/or correction system (forward error correction), spectrum shaping and to meet the requirements of interfacing with the transmission medium or channel. Modulation consists of transferring information in the baseband signal onto an RF carrier. In general, this is achieved by a single change or combined changes in the phase, frequency or amplitude of the RF carrier for radio-frequency transmission.
