On hybrid access for cognitive radio systems with time-varying connectivity

In this work, we consider a hybrid of interweave and underlay modes of operation for cognitive radio systems with random connectivity and bursty packet arrivals. Under the designed hybrid access policy, the secondary communication system is allowed to operate in the interweave mode only when its transmission has no harm on the primary communication. This is when the primary communication system is idle or the interference link from the secondary source to the primary destination is disconnected. The secondary communication system can optionally operate in the underlay mode, although when it is inevitable to interfere with the primary communication. The underlay mode is activated with some probability, called the hybrid rate. We analyze the stability of the hybrid access policy and show that it is not always beneficial when compared against the interweave-only mode. Thus, the condition for which the hybrid access policy can outperform is specified.