Downlink Spectral Efficiency of Distributed Antenna Systems Under a Stochastic Model

This paper studies the downlink spectral efficiency of distributed antenna system (DAS) where antenna ports are distributed as a Poisson point process (PPP), while assuming channel state information is not available at the transmitter and each antenna has an individual power constraint. We first consider the case with a single user per cell and analyze regular DAS with fixed cell boundaries, and study both blanket transmission where the user is served by all the antenna ports within each cell, and selective transmission where only the closest antenna port to the user within each cell is selected. We derive efficiently computable spectral efficiency expressions as a function of the user location, and show the limitation of blanket transmission by establishing that the cell-edge spectral efficiency under blanket transmission is upper bounded by a constant. Further, from a network perspective, we also model users as a PPP and assume a time-division multiple-access (TDMA) scheme, and give analytical expressions for and compare the average spectral efficiencies of regular DAS and user-centric DAS where no fixed cell boundaries exist. We validate our models with simulation, and show that selective transmission outperforms blanket transmission for regular DAS, and user-centric DAS with selective transmission achieves a higher spectral efficiency averaged over the network than regular DAS.