  We study an uplink multi secondary user (SU) cognitive radio system suffering
statistical heterogeneity among SUs' channels. This heterogeneity may result in
differentiated delay performances to these SUs and result in harmful
interference to the PU. We first derive an explicit closed-form expression for
the average delay in terms of an arbitrary power-control policy. Then, we
propose a delay-optimal closed-form scheduling and power-control policy that
can provide the required average delay guarantees to all SUs besides protecting
the PU from harmful interference. We support our findings by extensive system
simulations and show that it outperforms existing policies substantially.
