Energy allocation optimization for AF multi-hop in a cognitive radio system

In this paper, novel optimal energy allocation schemes for the secondary users in an amplify-and-forward multi-hop underlay cognitive network are proposed. The optimization problem is formulated as a maximization of the instantaneous received signal to noise ratio, under interference power constraints that are imposed to protect the primary network. First, a novel geometrical approach is proposed for the two and three hop cases. Simulations show that the proposed approach combined with adaptive modulation outperforms the cooperative cognitive system with uniform energy distribution. Then, a Lagrange-based analytical approach solution is proposed to the problem for the 2-hop case. Numerical results show that the Lagrangian resolution leads to the same results as the geometrical one. The advantage of the geometrical approach is to get more insight for the 2-hop case and makes the resolution tractable for more hops in the network. 2017 Elsevier B.V.Scopu