Broadband access by satellite in Ka band is currently constrained by spectrum availability. In this context, the EU FP7 project CoRaSat is examining the possible ways in which improved frequency utilization could be possible in Ka band via the use of cognitive mechanisms. A database approach utilizing spectrum scenarios between Fixed Satellite Services (FSS), Fixed Services (FS) and Broadcast Satellite Service (BSS) feeder links are considered. Interference in the downlink from BSS and FS are evaluated using real data bases and propagation models. Data base statistics for several EU countries are also evaluated. The importance of using correct terrain profiles and accurate propagation models is shown. For the case of the BSS interference to the FSS downlink it is demonstrated that for the UK an area of less than 2% is affected and thus the additional 400 MHz spectrum band (17.3 to 17.7 GHz) can be used by FSS over the majority of the country. The operational challenges of the database approach across the EU are also discussed.
In cognitive radio networks, the licensed frequency bands of the primary users (PUs) are available to the secondary user (SU) provided that they do not cause significant interference to the PUs. In this paper, we analyzed the normalized throughput of the SU with multiple PUs coexisting under any Frequency Division Multiple Access (FDMA) communication protocol. We consider a cognitive radio transmission where the frame structure consists of sensing and data transmission slots. In order to achieve the maximum normalized throughput of the SU and control the interference level to the legal PUs, the optimal frame length of the SU is found via simulation. In this context, a new analytical formula has been expressed for the achievable normalized throughput of SU with multiple PUs under prefect and imperfect spectrum sensing scenarios. Moreover, the impact of imperfect sensing, variable frame length of SU and the variable PU traffic loads, on the normalized throughput has been critically investigated. It has been shown that the analytical and simulation results are in perfect agreement. Our analytical results are much useful to determine how to select the frame duration length subject to the parameters of cognitive radio network such as network traffic load, achievable sensing accuracy and number of coexisting PUs.
Abstract-During the last years, spectrum scarcity has become one of the major issues for the development of new communication systems. Cognitive Radio (CR) approaches have gained an ever increasing attention from system designers and operators, as they promise a more efficient utilization of the available spectral resources. In this context, while the application of CRs in terrestrial scenarios has been widely considered from both theoretical and practical viewpoints, their exploitation in satellite communications is still a rather unexplored area. In this paper, we address the definition of several satellite communications scenarios, where cognitive radio techniques promise to introduce significant benefits, and we discuss the major enablers and the associated challenges.
Abstract-The satellite communication data traffic is increasing dramatically over the coming years. High throughput multibeam satellite networks in Ka band are potentially able to accommodate the upcoming high data rate demands. However, there is only 500 MHz of exclusive band for download and the same amount for upload. This spectrum shortage impose a barrier in order to satisfy the increasing demands. Cognitive satellite communication in Ka band is considered in this paper in order to potentially provide an additional 4.4 GHz bandwidth for downlink and uplink fixed-satellite-services. In this way, it is expected that the problem of spectrum scarcity for future generation of satellite networks is alleviated to a great extent. The underlying scenarios and enabling techniques are discussed in detail, and finally we investigate the implementation issues related to the considered techniques.
Abstract-In future heterogeneous cellular networks (HCN), cognitive radio (CR) compatible with device to device communication (D2D) technique can be an aid to further enhance system spectral and energy efficiency. The unlicensed smart devices (SDs) are allowed to detect the available licensed spectrum and utilise the spectrum resource which is detected as not being used by the licensed users (LUs). In this work, we propose such a system and provide comprehensive analysis of the effect of selection of SDs' frame structure on the energy efficiency, throughput and interference. Moreover, uplink power control strategy is also considered where the LUs and SDs adapt the transmit power based on the distance from their reference receivers. The optimal frame structure with power control is investigated under high SNR and low SNR network environments. The impact of power control and optimal sensing time and frame length, on the achievable energy efficiency, throughput and interference are illustrated and analysed by simulation results. It has been also shown that the optimal sensing time and frame length which maximizes the energy efficiency of SDs strictly depends on the power control factor employed in the underlying network such that the considered power control strategy may decrease the energy efficiency of SDs under very low SNR regime.Index Terms-Cognitive radio; energy efficiency; device to device Communications; heterogeneous cellular network; optimal frame structure and uplink power control.
Abstract-Detection based on eigenvalues of received signal covariance matrix is currently one of the most effective solution for spectrum sensing problem in cognitive radios. However, the results of these schemes always depend on asymptotic assumptions since the close-formed expression of exact eigenvalues ratio distribution is exceptionally complex to compute in practice. In this paper, non-asymptotic spectrum sensing approach to approximate the extreme eigenvalues is introduced. In this context, the Gaussian approximation approach based on exact analytical moments of extreme eigenvalues is presented. In this approach, the extreme eigenvalues are considered as dependent Gaussian random variables such that the joint probability density function (PDF) is approximated by bivariate Gaussian distribution function for any number of cooperating secondary users and received samples. In this context, the definition of Copula is cited to analyze the extent of the dependency between the extreme eigenvalues. Later, the decision threshold based on the ratio of dependent Gaussian extreme eigenvalues is derived. The performance analysis of our newly proposed approach is compared with the already published asymptotic Tracy-Widom approximation approach.
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