Based on the concept of optimal signal subspace, SC-FDE system could utilize the partial channel state information at the transmitter, so that system bit error rate performance can be improved considerably. However the dimension of the optimal signal subspace is a critical parameter that links system spectral and power efficiency. In this paper, we propose a new criterion called capacity criterion that can balance spectral and power efficiency, by which more information can be transmitted than by a former criterion called Gaussian criterion, though system bit error rate performance degrades.
