Downlink Performance and Capacity of Distributed Antenna System in Multi-User Scenario

Recent studies show that introducing DAS into the cellular system can reduce the inter-cell interference and achieves a non-trivial capacity increase over the conventional cellular system. On the other hand, base station cooperative processing is explored to address the inter-cell interference mitigation problem in the cellular system. But most of the analytical work is based on the single-user scenario. This paper provides a generalized information theoretic analysis to illuminate the downlink performance limits of DAS in the multi-user cellular system with antenna module cooperative processing. A comparison of several transmit schemes is given: scheduling the best user, scheduling multiple users simultaneously and scheduling multiple best users. It is demonstrated that with simple linear processing at the transmitters scheduling multiple users simultaneously achieves a tremendous system capacity increase over scheduling the best user. This is because antenna module cooperative processing can mitigate the inter-user interference effectively and the spatial degrees of freedom are fully exploited. Furthermore, when the number of users is much larger than the number of remote antenna modules, scheduling multiple best users can attain the multi-user diversity gain which leads to an increase of the sum capacity. These analytical results are verified by Monte Carlo simulations.