Signalling-free detection of adaptive modulation in multicarrier systems

Adaptive modulation, i.e. subcarrier-specific selection of the modulation scheme, is a well-known technique for enhancing the performance of multi-carrier systems. The adaptation to the frequency selective characteristics of the channel leads to considerable SNR gains for transmission over non-line-of-sight multipath channels. The actual assignment of modulation schemes to the individual subcarriers must be known to both the transmitter and the receiver. Conventionally this is achieved by exchanging information about the assignment over the communication link. i.e. a certain amount of signalling overhead is introduced. In this paper a signalling-free approach for reconstructing the assignment of modulation schemes in the receiver is presented. The decision about the modulation scheme used on each individual subcarrier is incorporated into the process of channel decoding.