On Achievability for Downlink Cloud Radio Access Networks with Base Station Cooperation

Abstract

This work investigates the downlink of cloud radio access networks (C-RANs), assuming digital cooperation links among the base stations (BSs). A generalization of the data-sharing scheme is proposed for the case of two BSs and two mobile users. The generalized data-sharing scheme includes a common part and allows full exploitation of correlation among auxiliary codewords. The cooperation links between the BSs are used to exchange and to redirect indices precomputed at the central processor. On the other hand, by simplifying the achievable rate region of the distributed decode-forward (DDF) scheme, it is shown that the DDF scheme for broadcast achieves the capacity region of a downlink $N$-BS $L$-user C- RAN with BS cooperation under the memoryless Gaussian model to within a gap of $\frac{L}{2}#x002B;\frac{\min {N,L\log_2 N\}}{2}$ bits per dimension. Numerical evaluations for the memoryless Gaussian model indicate that the generalized data-sharing scheme 1) outperforms the DDF scheme in the low-power regime and when the channel gain matrix is ill-conditioned and 2) benefits more from BS cooperation.