  In the literature, channel estimation and synchronization (CE/SY) algorithms
are classified as blind, and hence spectrally efficient, if they do not require
pilot symbols. However, we show in this letter that such classification is not
accurate and can be misleading. Consequently, this letter presents a more
reliable and accurate approach to evaluate the spectral efficiency of
communications systems with various CE/SY algorithms. The proposed approach
allows fair spectral efficiency comparison between various systems with blind
or non-blind CE/SY algorithms. In particular, we evaluate the spectral
efficiency of communications systems that incorporates blind CE/SY algorithms
and compare it to other blind and pilot-based algorithms. The obtained results
reveal that, on the contrary to what is widely accepted, blind CE/SY algorithms
with modulation-type constrain do not necessarily improve the spectral
efficiency as compared to pilot-based techniques. Consequently, such techniques
are classified as conditionally blind, to distinguish them from fully blind
techniques.
