Controlling Spectrum Handoff with a Delay Requirement in Cognitive Radio Networks

In Cognitive Radio Networks, secondary users are required to handoff from a wireless channel to another in order to cope with the dynamic spectrum environment imposed by primary users activity. Spectrum handoff may cause service interruptions or significant delays leading to the degradation of the quality of transmission. In this paper, we propose and study a novel spectrum handoff strategy aiming at reducing the unnecessary handoff operations while considering a delay bound requirement. First, the expected delay of application packets is computed as a function of the queue associated with a channel. This delay reflects the status of the channel and its usability for transmitting packets. Second, and in order to prevent the unnecessary handoffs, we use the expected delays to estimate a delay violation ratio that guides the spectrum handoff and selection decisions. Besides, we study the utility of using additional backup channels at the time of handoff to alleviate the problem of fast successive handoffs. We show through simulations that our strategy controls better the tradeoff between channel handoffs and achieving the delay requirement compared to random handoff and low channel occupancy handoff.