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Optimum Resource Allocation in Underlay Hybrid Cognitive Gaussian Relay System

Cognitive radio is hailed as the best possible solution for the problem of spectrum under-utilization. Pure Cognitive Radio Networks are unreliable in nature, hence a Hybrid Cognitive Radio Network using both Cognitive and licensed radio resources is more useful in practical. This paper analyses the performance of Hybrid Cognitive Gaussian Relay Channel (HCGRC) for underlay condition, considering the interference constraint at the nearest primary user. The performance metrics such as Capacity, Energy Efficiency and Spectral Efficiency are formulated and computed using numerical simulations with and without Rayleigh fading. These results are helpful in determining optimum power and bandwidth allocation within allowed interference to achieve full Capacity. The study of HCGRC for underlay approach leads to two key observations. First, for given primary user's location, the upper limit of power allocation for Cognitive relay can be determined. Second, Spectral Efficiency can be maximized by allocating optimum bandwidth to achieve peak capacity. The numerical results predict the optimal value of resources for achieving maximum Capacity, Energy Efficiency and Spectral Efficiency.