  We analyze the spectral efficiency performance and limits of orthogonal
frequency-division multiple access (OFDMA) cognitive radios (CRs) with an
imperfect availability of cross-link knowledge. In particular, in contrast to
the conventional `average' and `worst' cases of channel estimation error in the
literature, we propose a stochastic approach to mitigate the total imposed
interference on primary users. Channel-adaptive resource allocation algorithms
are incorporated to optimize the cognitive system functionality under transmit
and interference power constraints. An expression for the cumulative density
function (cdf) of the received signal-to-interference-plus-noise ratio (SINR)
is developed to evaluate the average spectral efficiency. Analytical
derivations and results are confirmed through computer simulations.
