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2012 - 20142
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Yazar: Kaya, Onur × Konu: Cognitive radio ×

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  • Küçük Resim
    Yayın
    Cognitive cooperative MAC with one primary and two secondary users: achievable rates and optimal power control
    (IEEE-INST Electrical Electronics Engineers Inc, 2014-11) Edemen, Çağatay; Kaya, Onur
    We consider a three-user fading cognitive cooperative multiple access channel (MAC) with one primary and two secondary transmitters. We propose two encoding/decoding strategies with varying levels of cooperation, based on block Markov superposition encoding and backward decoding. The first is an overlay model, where the secondary users (SUs) aid the transmission of the primary user (PU) by causally decoding the PU message and forwarding it while also cooperating among each other. The second is an underlay model, where the SUs cooperate by decoding and forwarding each other's messages while treating the signal received from the PU as noise. In either case, the PU is guaranteed to operate at its maximum achievable single user rate. We characterize the achievable SU rate region for both models and maximize this region as a function of the transmit powers. The simulation results show that the SU rate region can be significantly enlarged, particularly using the overlay model.
  • Küçük Resim
    Yayın
    Power control in the cognitive cooperative multiple access channel
    (IEEE, 2012) Kaya, Onur; İşleyen, Murat
    We extend several encoding and decoding techniques from cooperative communications framework, to a cognitive radio system consisting of a primary user (PU) and a secondary user (SU), sending their messages to a common receiver. Assuming that the transmitters and the receiver have full channel state information (CSI) collected and distributed by the common receiver, and that the SU knows the PU's codebook, the cooperation is obtained by block Markov superposition coding, and backwards decoding, which yield a causal overlay scenario. We formulate two rate optimization problems with the aim of, (i) maximizing the sum rate of the system, and (ii) maximizing the rate of the secondary user. We obtain the optimal power allocations for both cases, and the resulting rate regions. The power controlled cooperation turns out to be especially useful when maximizing the sum rate of the system, as it gives the PU significant rate rewards for allowing the cognitive transmitter to access its resources.