# QoS-Aware Downlink Traffic Scheduling for Cellular Networks with Dual Connectivity
## 2 Related Works
### MAC Scheduling for eNBs  
In a 3 GPP cellular network, the eNB's MAC layer determines RB allocations every TTI, and there are many QoS MAC scheduling methods in the literature. The authors in [8] \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Reference** & **Perform Dispatch** & **Consider QoS** &
\begin{tabular}{c} **Consider SeNB** \\ **Capability** \\ \end{tabular} \\ \hline Ref. [4] & ✓ & ✓ & \\ \hline Ref. [5] & ✓ & ✓ & \\ \hline Ref. [10] & & ✓ & \\ \hline Ref. [17] & ✓ & & \\ \hline Ref. [16] & ✓ & ✓ & \\ \hline Ref. [15] & ✓ & ✓ & \\ \hline Ref. [12] & ✓ & & \\ \hline Ref. [18] & ✓ & & \\ \hline Ref. [13] & ✓ & ✓ & \\ \hline Ref. [14] & ✓ & ✓ & \\ \hline Ref. [11] & & ✓ & \\ \hline QDD & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of prior works with QDD. propose a QoS scheduling method to allow data flows with higher priorities and better signal quality to earn additional radio resources. In [19], the proposed scheme divides data flows into two categories. The category that contains real-time traffic will be scheduled earlier. The schemes in [8; 19] can increase throughput of QoS data, but do not consider the remaining transmission time of packets when scheduling. In [20], the proposed scheme sorts head-of-line delays of downlink packets in ascending order and then decides RB assignments to the corresponding data flows based on the sorted result. The authors in [9] discuss QoS scheduling in small cell networks. The proposed method dynamically adjusts UEs' priorities to ensure that high-priority data can obtain more resources. In [21], a two-stage scheduling method is introduced. The first stage schedules based on packets' remaining transmission times, and the second stage schedules low-priority data flows based on the proportional fair (PF) concept. In [7], the authors propose a two-level scheduling structure. The first level applies game theory to achieve fairness between data flows. The second level then utilizes the knapsack algorithm to assign radio resources. Moreover, in [22], the authors propose a linear programming formulation to make downlink scheduling decisions. The proposed formulation includes jitter, queuing delay, and priority as constraints, and the goal is to satisfy QoS demands of data flows. The authors in [23] consider the scheduling of real-time and non-real-time traffics. The proposed scheme can adapt to various constraints (e.g., head-of-line delay, queue length, channel quality) and try to balance the transmissions between these two traffic types. In [24], the authors propose a scheduling method that aims to minimize packet delay violations. The proposed formulation considers packet arrival rates, packet loss ratio, and head-of-line delays when making scheduling decisions. However, the proposed scheme uses static settings to differentiate traffics. In reference [25], the authors propose a downlink scheduling method for the existence of device-to-device (D2D) links. The proposed scheme can help increase network throughput, but QoS requirements are not addressed. The authors in [6] consider downlink resource scheduling in the network scenario with hybrid beamforming support. The proposed heuristic algorithm can increase network throughput by finding suitable beams to disseminate downlink data. In the proposed scheme, packets that are going to expire can be scheduled earlier, but channel qualities and remaining transmission times are not considered when scheduling. The authors in reference [26] design a scheduling method that considers the QoS requirements and fairness between data flows. When scheduling, the proposed scheme estimates possible packet drops of GBR traffic flows, and then attempts to borrow resources allocated to other flows. However, it is possible that the other flows' resources cannot be borrowed, and thus, the GBR packets will still be dropped. In this work, when allocating resources to packets that are going to expire, the proposed scheme will evaluate the status of buffered data and then allocate resources.