In cognitive radio networks (CRNs), secondary networks (SNs) are regulated in order to prevent them from accessing a channel if primary networks (PNs) are currently occupying the channel. However, there not exists any regulation how to coordinate the channel access among multiple heterogeneous SNs. In this paper, we consider a centralized approach to explicitly coordinate the channel accesses among SNs coexisting in the same CRN; these SNs can exchange channel information through a coexistence manager (CM). We propose a channel access scheduling scheme that differentiates the quality-of-service (QoS) by assigning priority values and provides a certain level of fairness by taking the queue waiting time into consideration. Through various simulations, we show that the proposed scheme achieves the QoS differentiation among contending SNs while improving both the throughput and fairness performance in CRNs.