Cognitive users with useful vacations

A cognitive user (CU) operates as a secondary user of a cognitive channel. Before transmission CU samples the channel until it estimates that the channel can be accessed successfully. When CU transmits a packet, it may nevertheless be unsuccessful because its estimate was wrong; CU knows about its failure and stops the ongoing transmission sometime before the transmission ends. Then CU restarts sensing the channel. In this paper we derive the first and second moments of the effective transmission time of a packet which experiences additional delay which is similar to a “vacation time” in queues, though it differs from conventional vacation time models because such “sampling vacations” are beneficial to the future transmission. Using an on-off model of channel occupancy, our analysis shows that the duration of the sensing and the packet´s length can both be tuned to optimize for throughput, energy, interference, quality of service (QoS) and average response time of CUs.