  Cognitive radio (CR) technology is regarded as a promising solution to the
spectrum scarcity problem. Due to the spectrum varying nature of CR networks,
unlicensed users are required to perform spectrum handoffs when licensed users
reuse the spectrum. In this paper, we study the performance of the spectrum
handoff process in a CR ad hoc network under homogeneous primary traffic. We
propose a novel three dimensional discrete-time Markov chain to characterize
the process of spectrum handoffs and analyze the performance of unlicensed
users. Since in real CR networks, a dedicated common control channel is not
practical, in our model, we implement a network coordination scheme where no
dedicated common control channel is needed. Moreover, in wireless
communications, collisions among simultaneous transmissions cannot be
immediately detected and the whole collided packets need to be retransmitted,
which greatly affects the network performance. With this observation, we also
consider the retransmissions of the collided packets in our proposed
discrete-time Markov chain. In addition, besides the random channel selection
scheme, we study the impact of different channel selection schemes on the
performance of the spectrum handoff process. Furthermore, we also consider the
spectrum sensing delay in our proposed Markov model and investigate its effect
on the network performance. We validate the numerical results obtained from our
proposed Markov model against simulation and investigate other parameters of
interest in the spectrum handoff scenario. Our proposed analytical model can be
applied to various practical network scenarios. It also provides new insights
on the process of spectrum handoffs. Currently, no existing analysis has
considered the comprehensive aspects of spectrum handoff as what we consider in
this paper.
