An adaptive modulation method is considered for multicarrier systems such as OFDM. The modulation mode is adapted in each sub-channel according to the current channel conditions. To encompass an even wider range of channel SNR, adaptive modulation augmented by adaptive-rate turbo coding is then analysed. Performance is evaluated for the Gaussian channel and extended to fading channels with the addition of a simple retransmission technique. Although adaptation affects transmission capacity, results show that a worthwhile improvement in decoded image quality is obtainable over a useful range of channel SNR.