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A feedback-based access scheme for cognitive radio systems

A feedback-based access scheme for cognitive radio systems,10.1109/SPAWC.2011.5990486,Karim G. Seddik,Ahmed K. Sultan,Amr A. El-Sherif,Ahmed M. Arafa

A feedback-based access scheme for cognitive radio systems  
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In this paper, we consider the design of access schemes for secondary users in cognitive radio systems based on the primary user feedback information. We consider a secondary user employing a random access scheme with an access proba- bility that depends on the primary user feedback state. We show that the proposed scheme can enhance the system performance in terms of the secondary throughput and/or primary user delay while guaranteeing a certain quality of service (QoS) for the primary user; this is due to the fact that the proposed scheme avoids sure collisions between the primary and secondary users. The proposed scheme can be deployed with any other random access based scheme and it always results in a performance gain using the extra piece of information coming from the primary user feedback. Cognitive radio technology is a transmission paradigm mak- ing use of the underutilized radio spectrum in order to solve the problem of spectrum scarcity and enhance the overall wireless transmission efficiency and throughput. In cognitive radio networks, secondary users coexist with licensed, primary users in such a way that a minimum quality of service represented by certain performance metrics is guaranteed. In a typical cognitive radio setting, the cognitive transmitter senses primary activity and decides on accessing the channel on the basis of the sensing outcome. This approach is prob- lematic because sensing does not inform the cognitive terminal about its impact on primary receiver. This problem has induced interest in leveraging the feedback from the primary receiver to the primary transmitter to optimize the secondary transmission strategies taking into account the effect it has on the primary receiver. For instance, in (1), the secondary user observes the automatic repeat request (ARQ) feedback from the primary receiver. The ARQs reflect the primary user achieved packet rate. The cognitive radio's objective is to maximize secondary throughput under the constraint of guaranteeing a certain packet rate for primary user. In (2), the authors use a partially observable Markov decision process (POMDP) to optimize the secondary action on the basis of sensing and primary ARQ feedback. Secondary power control on the basis of primary link control feedback is investigated in (3). In (4), the optimal transmission policy for the secondary user when the primary user adopts a retransmission based error control scheme is investigated. The policy of the secondary user determines how often it transmits according to the retransmission state of the packet being served by the primary user. The resulting optimal strategy of the secondary user is proven to have a unique structure. In particular, the optimal throughput is achieved by the secondary user by concentrating its interference to the primary user in the first transmission of a packet. In this paper, we consider a secondary network that em- ploys a random access scheme where the access probability is adjusted based on the primary user feedback state while guaranteeing a certain QoS for the primary network. In this paper, we make the following contributions. We analyze the primary user's queue in the presence of a secondary terminal which changes its transmission strategy based on the primary feedback. In contrast with (4), the primary user can have new packet arrivals during the retransmission phase of the packets delivered unsuccessfully. Based on the queueing analysis, we provide an expression for the secondary throughput and find the access probability that maximizes it. The rest of the paper is organized as follows. The system model is presented in Section II. The performance of the proposed scheme is investigated in Section III. We provide numerical results in Section IV and conclude the paper in Section V.
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