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In this paper, we first introduce the bidirectional distributed antenna systems (DAS) and exploit the choosing algorithm to take user-centric virtual cells into this system. Then, we discuss different power allocation optimization problems with interferences in bidirectional DAS with and without user-centric virtual cells, respectively. The first objective problem is maximizing spectral efficiency (SE) of bidirectional DAS satisfying the requirements of the minimum SE of each user equipment and maximum transmit power of each remote access unit. First, we convert this non-convex objective function into a difference of convex functions (D.C.) problem, and then, we obtain the optimal power allocation by using the concave&#x2013;convex procedure (CCCP) algorithm. The second objective problem is maximizing energy efficiency (EE) of bidirectional DAS under the same constraints as the first problem. First, we exploit fractional programming theory to transform the second problem into an equivalent objective function with subtractive form, and then convert it into a D.C. problem and obtain the optimal solutions by using the CCCP algorithm. In each part, we propose the corresponding optimal power allocation algorithm and also use a similar method to obtain optimal solutions of the same optimization problems in bidirectional DAS with user-centric virtual cells. Simulation results showed the effectiveness of the proposed power allocation algorithms and demonstrate the SE and EE of the bidirectional DAS with user-centric virtual cells which are much better than bidirectional DAS.

Spectral Efficiency and Energy Efficiency of Bidirectional Distributed Antenna Systems With User Centric Virtual Cells