This paper considers a scenario in which a secondary user makes opportunistic use of a channel allocated to some primary network. The primary network operates in a time-slotted manner and switches between idle and active states according to a stationary Markovian process. At the beginning of each time slot, the secondary user can choose to stay idle or to carry out spectrum sensing to detect if the primary network is idle or active. If the primary network is detected as idle, the secondary user can carry out data transmission. Spectrum sensing consumes time and energy and introduces false alarms and mis-detections. Given the delay cost associated with staying idle, the energy costs associated with spectrum sensing and data transmission, and the throughput gain associated with successful transmissions, the objective is to decide, for each time slot, whether the secondary user should stay idle or carry out sensing, and if so, for how long, to maximize the expected net reward. We formulate this problem as a partially observable Markov decision process (POMDP) and prove several structural properties of the optimal spectrum sensing/accessing policies. Based on these properties, heuristic control policies with low complexity and good performance are proposed. I.

Abstract—The spectrum scarcity has led to rethink in the current frequency spectrum usage and develop a new concept of wireless networking. Opportunistic Spectrum Networks (OSNs) have been considered as a promising solution to the problem of spectrum shortage. In this paper, in order to compensate for the need of complex hardware, a novel and efficient Medium Access Control (MAC) framework that integrates a kind of cooperative spectrum sensing method at the physical layer into a cooperative MAC protocol is developed for distributed OSNs considering the requirements of both the primary and secondary users. For the MAC framework, an innovative deterministic sensing policy called Allocated-group Sensing Policy (ASP) is proposed to identify the spectrum opportunities based on a dynamic ID numbering approach, and its effectiveness is demonstrated by comparison with two random sensing policies. Moreover, a computationally simple but efficient sensing algorithm is developed to assist each sensing user to identify the optimal number of channels to sense and the optimal sensing duration. It is demonstrated that the proposed cooperative MAC framework can efficiently achieve the ultimate goal of the OSNs even with only a small number of sensing users each equipped with a single cognitive radio transceiver.

Abstract—In this paper, the effects of the primary-user (PU) mobility on spectrum sensing in Cognitive Radio (CR) networks are studied. To this aim, first, the spectrum sensing problem is reformulated to account for the PU mobility. Then, the effects of the PU mobility are studied with the objective to determine the parameters that affect the spectrum sensing functionality. For this, two performance metrics are analytically derived: i) the detection capability, whichmeasuresthePUmobilityimpacton the CR user detection probability; ii) the mobility-enabled sensing capacity, anewmetricthatmeasurestheexpectedtransmission capacity achievable by a CR user in the presence of PU mobility. The mathematical analysis is carried out in different scenarios, by using mobility and spectrum occupancy models. The results show that the detection capability is affected by five parameters: the PU protection range, the network region size, the PU mobility model, the CR spatial distribution, and the number of PUs that use the same spectrum band. Moreover, it is shown that the sensing capacity can significantly increase in the presence of PU mobility if the PU protection range is smaller than the network region size. The mathematical results are derived by considering the dynamic PU traffic, and validated through simulations. I.

Abstract—Two objectives of sensing in cognitive radio (CR) are to detect the primary user (PU) accurately and quickly, which are contradicting objectives. Therefore, many papers try to optimize this tradeoff and find the minimum sensing time which protects the PU. The trends are classified in enhancing false alarm probability (

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The electromagnetic radio spectrum is a natural resource. Effective Utilization of this natural resource is a Challenging task in Present Day Wireless Communication. Cognitive Radio is an emerging trend in wireless communication to Combat for spectral scarcity. Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment and uses the methodology of learning, and understanding from the environment and adapting to it. Advanced signal processing techniques are used in Cognitive Radio Network to achieve this intelligence. Spectrum Sensing is one of such a signal processing to identify spectrum holes which can be temporarily used without interfering Primary User. Every cognitive radio receiver is incorporated with Spectrum Sensing. There are various existing techniques to detect the spectrum of which some widely used are presented in this thesis. General Terms Your general terms must be any term which can be used for general classification of the submitted material such as Pattern