Impact of limited backhaul capacity on user scheduling in heterogeneous networks

In this paper, we investigate the impact of limited backhaul capacity on user scheduling in the context of a heterogeneous network comprising a macro base station overlaid with small-cells. Under a global proportional fairness (PF) criteria, we show that this limited capacity has a fundamental impact on user scheduling. When user association and channel allocation are given, like in the infinite-capacity backhaul case, the global PF user scheduling problem can be decomposed into a set of independent local PF user scheduling problems. However, unlike the case with infinite backhaul where the local PF scheme is equivalent to giving equal time to each user, a local PF scheme with finite backhaul can be of one of three types. We completely characterize these three types and the conditions under which to use them. The results show that a backhaul-aware scheduling scheme is simple to implement and necessary to obtain the best performance.