Optimal and Efficient Bit Loading for OFDM in the Presence of Channel Uncertainty

In practice only imperfect Channel State Information (CSI) is available at the transmitter due to noisy and time-varying channel. In this paper, the authors consider optimal bit loading for Orthogonal Frequency Division Multiplexing (OFDM) with imperfect CSI subject to channel estimation. The frame length comes in as an important control parameter, while soft channel estimation and the Cramer-Rao bound are used to include the effect of channel estimation. They modify the conventional waterfilling to take the maximal allowed rate on each subcarrier into account while considering CSI error.