  We study an uplink multi secondary user (SU) cognitive radio system having
average delay constraints as well as an instantaneous interference constraint
to the primary user (PU). If the interference channels from the SUs to the PU
have independent but not identically distributed fading coefficients, then the
SUs will experience heterogeneous delay performances. This is because SUs
causing low interference to the PU will be scheduled more frequently, and/or
allocated more transmission power than those causing high interference. We
propose a dynamic scheduling-and-power-control algorithm that can provide the
required average delay guarantees to all SUs as well as protecting the PU from
interference. Using the Lyapunov technique, we show that our algorithm is
asymptotically delay optimal while satisfying the delay and interference
constraints. We support our findings by extensive system simulations and show
the robustness of the proposed algorithm against channel estimation errors.
