Adaptive inter-cell coordination for the distributed antenna system with correlated antenna-clusters

In the implementation of distributed antenna systems (DASs), the antenna elements in some cases may only be deployed in the form of distributed antenna-clusters (ACs), due to various practical limitations. Consequently, correlation usually exists among the antenna elements within each AC. In contrast to most of the previous work that focused on the antenna correlation in a single-cell environment, this paper investigates the impact of the antenna correlation in a more general multi-cell scenario, where the inter-cell interference becomes the key challenge. We formulate a joint multi-cell input covariance optimization problem, accounting for the transmit antenna correlation, the propagation path-loss and the shadow fading. We show that the problem is a complicated non-convex problem. Moreover, the objective function, i.e., the ergodic sum capacity, is found difficult to be expressed in a straightforward form. After mathematical simplification, we propose an iterative inter-cell coordination scheme by adopting the successive approximation method. Simulation results demonstrate that, thanks to much more effective adaptation to the antenna correlation, the proposed scheme outperforms the existing ones and can significantly improve the system performance of a DAS with highly-correlated ACs.