Adaptive turbo coded modulation for OFDM transmissions

We propose a fixed-power adaptive turbo coded modulation scheme for orthogonal frequency division multiplexing (OFDM). In this paper, we first observe that turbo coded modulation provides more than 15 dB signal-to-noise-ratio (SNR) gain on uncoded OFDM in fading channels. Then we conclude that when the transmission rate is adapted to the channel adequately, adapting the power as well yields a negligible capacity gain for adaptive OFDM from numerical simulation results. An adaptive OFDM scheme based on subband adaptation is given and mode allocation algorithm based on the capacity evaluation of current subband is presented. Simulation results show that our adaptive OFDM scheme exhibits more than 7.5 dB SNR gain relative to non-adaptive turbo coded modulation. We also discuss the effect of feedback delay and channel estimation error on bit-error-rate (BER) performance of our adaptive scheme.