For the inner-tier iteration, we employ the first-order Taylor expansion and successive convex approximation (SCA) method to solve the DC optimization problem.
For the outer-tier iteration, we first employ the Dinkelbach method to convert the fractional objective function into a polynomial form, and then transform the optimization problem into a difference of concave (DC) programming.
For clarity, the detailed procedure of the two-tier alternative iteration optimization algorithm is listed in Table 3, the first-tier iteration optimization indicates the D2D link optimization problem, and the second-tier iteration optimization indicates the primal optimization problem.
In order to solve the optimization problem, we propose an algorithm that can obtain a near-optimal solution, which consists of outer-tier and inner-tier iterations.
Table 3 Two-tier alternative iteration optimization algorithm.
A new two-tier alternative iteration optimization algorithm is proposed to solve the optimization problem.
Finally, we demonstrate that the proposed two-tier alternative iteration optimization algorithm can converge very quickly.
To overcome this difficulty, a new two-tier alternative iteration optimization algorithm is proposed in this section.
Then, a new two-tier alternative iteration optimization algorithm is proposed to solve the primal optimization problem.
Figures 8 and 9 show the average optimal EE and the average optimal SE versus different residual power of SI under the proposed two-tier alternative iteration optimization algorithm.
Besides, we can find that the results obtained by the proposed optimization algorithm are very close to those obtained by the exclusive searching method, which indicates that the two-tier alternative iteration optimization algorithm can find a suboptimal solution.
