Power Allocation and Adaptive Modulation for OFDM Systems with Imperfect CSI

The transmit adaptation is a key technique to realize the full potentials of orthogonal frequency-division multiplexing (OFDM) systems. In this paper, we first present a new channel state information (CSI) model in order to save the reverse channel spectrum. By using clustering and interpolation according to the correlation between subcarriers, the estimation of CSI is obtained at the transmitter. Then, the transmit adaptation scheme including power allocation and adaptive modulation is proposed. In this scheme, the transmit power is allocated to the subcarriers by water filling theory, during which a fast search algorithm for the water filling line is presented, and then the adaptive modulation is carried out maintaining a certain system BER. Compared with the existing schemes, the proposed scheme achieves a better performance with the same cost of feedback data.