  In this paper, we study single cell multi-user downlink distributed antenna
systems (DAS) where antenna ports are geographically separated in a cell.
First, we derive an expression of the ergodic sum rate for the DAS in the
presence of pathloss. Then, we propose a transmission selection scheme based on
the derived expressions which does not require channel state information at the
transmitter. Utilizing the knowledge of distance information from a user to
each distributed antenna (DA) port, we consider the optimization of pairings of
DA ports and users to maximize the system performance. Based on the ergodic sum
rate expressions, the proposed scheme chooses the best mode maximizing the
ergodic sum rate among mode candidates. In our proposed scheme, the number of
mode candidates are greatly reduced compared to that of ideal mode selection.
In addition, we analyze the signal to noise ratio cross-over point for
different modes using the sum rate expressions. Through Monte Carlo
simulations, we show the accuracy of our derivations for the ergodic sum rate.
Moreover, simulation results with the pathloss modeling confirm that the
proposed scheme produces the average sum rate identical to the ideal mode
selection with significantly reduced candidates.
