JOURNAL OF TELECOMMUNICATIONS, VOLUME 10, ISSUE 1, AUGUST 2011 1 © 2011 JOT http://sites.google.com/site/journaloftelecommunications/ Modeling of Opportunistic Spectrum Sharing with Sub-banding in Cognitive Radio Networks Samira Homayouni, Seyed Ali Ghorashi Abstract—Cognitive radio is a technology to solve the problem of spectrum under-utilization in some licensed bands. In this paper, we propose a model for opportunistic spectrum sharing in cognitive radio networks for a special case in which, two secondary users are allowed to coexist in a channel (sub-banding). The proposed model is such that, when all the channels are occupied by the primary and secondary users, then the secondary users’ channels can be divided into two sub-bands, and two secondary users may use a sub-band, simultaneously. The state equations of the system are derived based on two-dimensional Markov chain model. Next, the system performance is evaluated by some metrics such as blocking and dropping probability as well as channel utilization. Furthermore, the results for the cases of using and not using sub-banding for the secondary users have been compared. The results demonstrate that in a spectrum sharing system, channel sub-banding significantly reduces the blocking and dropping probabilities of the secondary users, with the cost of lower quality channels in comparison with state without using sub-bands. Index Terms— Dynamic spectrum access, cognitive radio, channel sub-banding, Markov chain, blocking and dropping probabilities.    1 INTRODUCTION                                                                       !                             "        #$% #&%                  #’% #(%       #)%      "        "     *                      +                       "          #,% -                               -                                .           #/% *                "            #0%  #1%   #$2%                     3             4            - #$$%     56  7   #$2%  #$$%              "     #$&%                  #$’%           -    #$&%  #$’%                             8                                               ———————————————— •                 ! !  "#$%#&""%  ’! •  (   ( )            *   ! ! "#$%#&%""%  ’! 9