Adaptive modulation for OFDM systems with partial CSI feedback.

Abstract

In this dissertation we treated the adaptive modulation problem for a time-varying and frequency selective channel when the channel state information is imperfect. The imperfections of channel state information are due to errors in channel estimation or in delay caused by the Doppler spread. By using a uniform power allocation of every sub-channel, the non linear problem considered was to maximize the spectral power efficiency and keeping the same targeted instantaneous bit error rate for all subchannels. Furthermore we compared different scenarios such as adaptive and non-adaptive modulation in order to know how to efficiency adapt the modulation. The simulation results show how it is important to underload the system when errors in channel state information are detected. Keywords : OFDM, Channel capacity, Spectral efficiency, Adaptive modulation, Bit allocation.