In this paper, we study single cell multi-user downlink distributed antenna systems (DAS) where the antenna ports are geographically separated in a cell. First, we derive an expression of the ergodic sum rate for DAS in the presence of pathloss. Then, we propose a transmission selection scheme based on the derived expressions to maximize the overall ergodic sum rate. Utilizing the knowledge of distance information from a user to each distributed antenna (DA) port, we consider the pairings of each DA port and its supporting user to optimize the system performance. Then, we compute the ergodic sum rate for various transmission mode candidates and adopt a transmission selection scheme which chooses the best mode maximizing the ergodic sum rate among the mode candidates. In our proposed scheme, the number of mode candidates are greatly reduced compared to that of the ideal mode selection. Through Monte Carlo simulations, we will show the accuracy of our derivation for the ergodic sum rate expression. Moreover, simulation results with the pathloss modeling confirm that the proposed transmission selection scheme produces the average sum rate identical to the ideal mode selection with significantly reduced selection candidates.Comment: 6 pages, 5 figures, Submitted to Globecom 201
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