Optimal behaviour of smart wireless users

Abstract

We consider a smart or cognitive user (CU) that operates as a secondary user of a cognitive channel. Before transmission, the CU samples the channel until it estimates that it can be accessed successfully. When the CU transmits a packet, it may nevertheless be unsuccessful because its estimate was wrong. The CU then knows about its failure and stops the ongoing transmission sometime before the transmission ends. Then the CU restarts sensing the channel. In this paper we analyse the total delay experienced by a CU. We derive the first and second moments of the effective transmission time of a packet sent by such a smart user, in view of the fact that the sensing and errors made in transmitting a packet when the channel is actually unavailable, will introduce additional delay. This is similar to a "vacation time" in queues, though it differs from conventional vacation time models because such "sampling vacations" can be beneficial to the future transmission. © 2013 Springer International Publishing.