Delay-Oriented QoS-Aware User Association and Resource Allocation in Heterogeneous Cellular Networks

To meet ever-growing mobile data traffic, network spatial densification with various low-power nodes in addition to the conventional high-power macro base stations, also known as heterogeneous network (HetNet), is regarded as one key enabling solution. Due to the unplanned nature, HetNets are very irregular and severe interference can happen without judicious designs of the user association rules. Most prior works assumed best-effort traffic and sought the optimal association to maximize metrics, such as the sum of log-rates. In the case of bursty traffic with quality-of-service (QoS) requirements, existing association schemes cannot fully release the traffic offloading capabilities of HetNets. In this paper, we model the downlink traffic to individual mobile station explicitly. Aiming to minimize the network-wide packet delay, we investigate the optimal user association scheme and the corresponding resource allocation algorithm. We then propose the QoS-aware user association (QoSA) strategies of different flavors enjoying low complexity and guaranteed convergence. Furthermore, the proposed QoSA algorithms are readily implemented in distributed manners. Extensive network simulations are carried out to corroborate our designs.