Adaptive Bit Loading for OFDM Systems with Imperfect Channel State Information

We consider an orthogonal frequency division multiplexing system employing bit-interleaved coded modulation and pilot aided channel estimation (PACE) at both transmitter and receiver. A low complexity adaptive bit loading scheme in combination with transmit diversity is proposed. The loading procedure minimizes the bit-error rate at the decoder output, and the transmit diversity schemes mitigate channel correlations. Transmit channel state information is obtained by PACE, where a limited feedback channel returns outdated pilot symbols. Since transmit diversity causes the feedback to be outdated more rapidly, we propose a novel transmit channel estimation scheme exploiting the knowledge of the transmit diversity.