Differential capacity bounds for distributed antenna systems under low SNR conditions

A distributed antenna system (DAS) architecture is believed to be able to enhance capacity performance of Cloud Radio Access Networks (C-RAN), especially for users near the cell boundary who experience low Signal-Noise-Ratio (SNR). However, the problem of finding the analytical bounds on the capacity of DAS with the rising number of antennas in low SNR rigime has not been fully studied. In this paper, we investigate a case in C-RAN of multiple transmitting base stations and a single receiving user under low SNR conditions. We derive closed-form upper and lower bounds in efficiently computable expressions for differential capacity (DCAP) using the moment generating function (MGF) of SNR. Bounds accuracy is evaluated and compared to results in current literature. Numerical results corroborate our analysis and the analytic bounds on DCAP is tight in the low SNR regime. Furthermore, The upper bound approximates better compared with the one obtained in [1] under two different channel models. These lower and upper bounds provide more accurate capacity measures which can be used in the evaluation of DAS performance and C-RAN design.