# QoS-Guaranteed Radio Resource Management in LTE-A Co-Channel Networks with Dual Connectivity
## 1 Introduction  
Due to the rapidly growing mobile data traffic, 4G is not able to meet the current traffic demand. With the limited wireless radio resource, dual connectivity (DC) technology and heterogeneous network (HetNet) architecture can improve the data transfer rate beyond 4G. DC is based on carrier aggregation (CA) and coordinated multi-point (CoMP), allowing user equipment (UE) to connect two different base stations at the same time, which are referred to as Master eNodeB (MeNB) and SecondaryeNodeB (SeNB) [1]. Recently, DC has been further extended to include multiple connectivity in 5G New Radio (NR) [2]. The research studies on DC have attracted quite a lot of attention, e.g., in [3; 4; 5], authors have explored the potential benefits and challenges, including buffer status reporting, power headroom calculation, discontinuous reception, logical channel prioritization, bearer split, and so on. In [6], authors indicated that MeNB and SeNB have different scheduling requirements, proposing the coordination mechanism to prevent the user equipment from using beyond its maximum transmission power. In [7], a study of DC was divided into control plane and user plane issues. Using the channel state information reference signal (CSI-RS), which is unique to the Multi-input Multi-output (MIMO) frame, SeNB no longer deals with handover issues and MeNB can update the Radio Resource Control (RRC) of the user equipment to achieve handover between the different base stations. In summary, DC can effectively improve throughput in HetNet by optimal resource allocation [8]. Thus, in this paper, we focused on DC combined with the radio resource management to integrate resources across base stations and do the best to satisfy the bandwidth requirements of UEs. We explored three research topics in DC, including resource allocation, cell selection, and enhanced inter-cell interference coordination (e-ICIC). In the study of the resource allocation, most commonly adopted resource scheduling mechanisms are Round Robin Scheduler (RR), Best Channel Quality Indicator (CQI) Scheduler (BCQI), and Proportional Fair Scheduler (PF) [9; 10; 11]. RR, which is simple to implement, assigns equal portions of resource blocks (RB) to each UE in a circular order. However, the disadvantage is that this scheduler does not consider channel condition and can lead to low system throughput. In contrast, BCQI assigns resource blocks based on the channel condition. Although the system throughput is increased, it may cause UEs with low CQI suffer starvation. PF is a compromise between throughput and fairness, based on the balance of the competing benefit among the UEs, trying to maintain fairness while maximizing throughput. Therefore, in order to emphasize the system throughput and fairness, most of the literature adopted Proportional Fair scheduling. In [12], the authors use Karush-Kuhn-Tucker optimization conditions to reduce the complexity of Proportional Fair, assuming that the transmission power of the base station is evenly distributed on each subcarrier. In [13], the geometric mean is used to replace the arithmetic mean in the Proportional Fair, which yields quicker convergence and improves throughput and block error rate (BLER). In DC, since a UE could connect to two base stations at the same time, the co-channel interference factors must also be considered. Therefore, the Proportional Fair is not necessarily the best scheduler. We proposed to estimate the channel quality of each subcarrier and assign resource block to the UE with the best CQI while considering how to integrate resources from two stations to enhance QoS as well as data transfer rate of each UE. In the study of the cell selection, the 3 GPP defines that the basic cell selection principle of the user equipment is done according to the received reference signal reception power (RSRP). The higher the transmission power of the base station, the wider the range of signals that can be covered and the more UEs will connect to that base station [14; 15].