Collisions for secrecy in cooperative cognitive radio networks with time-varying connectivity

We study user cooperation in a cognitive radio network with random connectivity and collision channels, where the primary user has secrecy constraints. We characterize secure stable throughput region for multiple packet-level cooperative transmission protocols that incorporate packet relaying and collision generation. Stable throughput region is derived for each protocol and then compared to other protocols, including non-cooperative protocol. We show that a collision generation protocol can always provide gains over the non-cooperative protocol while it is not the case for the relaying protocol. In addition, we show that collision generation protocol may achieve superior performance compared to a protocol that involves both cooperative relaying and collision generation, even if the performance of the latter protocol is superior to the non-cooperative protocol.