1 Introduction
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To solve the problem of the relative scarcity of spectrum resources, we use D2D users as a relay to forward data instead of the traditional cellular relay, which undoubtedly makes the spectrum efficiency greatly improved and guarantees transmission performance of cell-edge users.
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Considering the optimal power allocation of UEs and transmission rate of the user, we formulate a mixed-integer non-linear programming (MINLP) problem to maximize the data rate of CEUs. We develop an efficient power allocation algorithm and derive the optimal closed-form solutions based on the Lagrange dual method.
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Theoretical analyses and extensive simulations are provided to reveal the rationale of the proposed algorithms. Simulation results demonstrate that our D2D-relay scheme outperforms the traditional cellular-relay communication scheme.