In this paper, we study cooperative cognitive radio networks consisting of aprimary user and multiple secondary users. Secondary users transmit only whenprimary user is sensed as silent and may interfere with primary transmissiondue to imperfect sensing. When primary activity is sensed correctly, secondaryusers cooperate with primary user by assisting retransmission of failed packetsof primary user. We analyze packet throughput of primary and secondary usersfor three variations of proposed cooperation method. Signal flow graph (SFG)based approach is employed to obtain closed form expressions of packetthroughput. The analysis is done for two cases; individual sensing andcooperative sensing. Further, we characterize optimal transmission probabilityof secondary users that maximizes individual secondary packet throughputkeeping all queues in the system stable. Results present a comparison ofthroughput performance of proposed cooperation methods under differentscenarios and show their benefits for both primary as well as secondary userthroughput.
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