Joint Resource Allocations in Distributed Antenna Systems with Coherent Transmitter

From the view of radio resource management, many literatures for distributed antenna systems (DAS) focus on the joint precoding design and related optimal power allocation (PA), which is a narrowband case. The joint resource allocation in broadband orthogonal frequency division multiple access DAS (OFDMA-DAS) has not been thoroughly studied, which includes the distributed antenna port selection, subcarrier assignment and PA under the power constraint per antenna port. This paper focuses on the downlink resource allocation in OFDMA-DAS. The coherent transmitter with phase steering is used. The problem to maximize the system spectrum efficiency (SE) is formulated, and solved by the dual decomposition method, where the decomposed subproblems in the dual domain are solved from the perspective of analytic geometry. Next, a suboptimal algorithm is developed. From the analysis of per subcarrier transmission, it is found that a proportional PA (PPA) method can achieve a local SE optimality for an individual subcarrier. By applying the PPA, the original problem is transformed into a new form and can be solved similarly. Numerical results show that the optimal algorithm has good convergence. The suboptimal algorithm can save a considerable part of system power while achieving the SE optimality, thanks to the distributed feature in DAS.