  A Cramer-Rao bound (CRB) for semi-blind channel estimators in redundant block
transmission systems is derived. The derived CRB is valid for any system
adopting a full-rank linear redundant precoder, including the popular
cyclic-prefixed orthogonal frequency-division multiplexing system. Simple forms
of CRBs for multiple complex parameters, either unconstrained or constrained by
a holomorphic function, are also derived, which facilitate the CRB derivation
of the problem of interest. The derived CRB is a lower bound on the variance of
any unbiased semi-blind channel estimator, and can serve as a tractable
performance metric for system design.
