Joint Downlink and Uplink Aware Cell Association in HetNets With QoS Provisioning

This paper addresses a joint downlink and uplink aware cell association problem in a multi-tier heterogeneous network in which base stations (BSs) have finite number of resource blocks (RBs) to distribute among the users. An optimization problem is defined to maximize the sum of weighted utility of long term data rate in downlink and uplink through cell association and RB distribution while maintaining quality of service (QoS). Separate outage requirements are considered as QoS constraints for downlink and uplink of a user. Using outage QoS constraints renders the problem suitable for fast fading environments. We propose a distributed scheme for the cell association problem. As users cannot measure the uplink attributes by listening to the reference signals of BSs, a limited amount of feedback is added to the reference signals of the BSs to inform the users of the uplink interference and make the distributed algorithm design possible. Moreover, by assigning different weights to the downlink and uplink data rates, the proposed scheme can be downlink oriented, uplink oriented, or both downlink and uplink aware. Comparing the proposed scheme with the downlink oriented maximum signal to interference plus noise ratio (SINR) scheme, significant uplink rate gains are observed in the simulations as well as for the downlink rates.