Coverage and Throughput Analysis for Dual Connectivity in Ultra-Dense Heterogeneous Networks

The requirements of higher data rate and quality-of-service (QoS) enhancement for edge users lead to the densification of the small base stations (SBSs), which shortens the service distance. Due to the low transmission power of the SBSs, the technique of cell range expansion (CRE) is used for offloading macro base station (MBS) users to SBSs, reducing the throughput of the biased user on the other hand. In this paper, a tractable model based on dual connectivity (DC) is proposed in two-tier heterogeneous networks to enhance the SINR of the biased users, and analytical expressions are derived in terms of coverage probability, average throughput and area spectral efficiency (ASE). Taking advantage of DC, the MBS and the SBS serve the biased user simultaneously, which increases the throughput by improving the utilization of radio resources across two BSs. By including the handover cost derived with handover rate in the analysis, the mobility-aware average per-user throughput and ASE for mobile users are obtained. The results show that in the proposed network architecture, the average throughput of the biased user can be improved by 2× and the per-user throughput shows a maximum increase of 15% over the network without DC.