## 2 Related Works  
Nowadays, most of the communication between the UE and BS is directly through single-path communication [23] (see Case 1 in Figure 1). This means that the UE will transmit repeatedly to the BS if the UE is far away from the BS. Different from current traditional cellular communication, UE can transmit information to the cooperation node at first, and then the cooperation node transmits the information to the BS or another cooperation node after receiving the UE message, such as a relay system [24] or NR UE-to-Network relay in 5G R16 [25]. This kind of communication extends the coverage of the whole system. It is widely used in smart devices, which are connected to multi-hop networks through Bluetooth low-energy (BLE) devices [26]. Some researchers proposed Dual-Ring Tree for hybrid single-hop/multi-hop instances, which is a reliable formation protocol [27]. A dual-ring subnet was designed for dense areas in a single-hop solution, and a tree-shaped subnet was designed for sparse areas in a multi-hop solution. The performance of this scheme is better than the conventional BlueHRT in terms of routing efficiency and network reliability [27]. Moreover, it is important to select a better cooperation node for performance optimization. An appropriate cooperation node will improve the reliability of the whole system and decrease the latency, which provides a better experience for the UE. The authors of in [28] proposed a cooperation node path selection scheme based on a convolutional neural network (CNN), and the authors of [29] proposed supervised machine learning techniques and a prototype framework for further investigation. These schemes can dynamically select the optimal cooperation node according to the real-time situation of the network, thereby improving the reliability and latency performance of the network. Another piece of research [30] is about a cooperation node selection scheme based on mobile edge computing (MEC), which can use edge computing resources to optimize the selection of cooperation nodes. One of the sink nodes is static and another is mobile in this study. In addition, URLLC technology based on multi-path selection and scheduling can choose the optimal path for data transmission according to the load and bandwidth of the network [31]. In this \begin{table}
\begin{tabular}{l l} \hline \hline
**Notation** & **Explanation** \\ \hline \(d_{\text{UC},ij}\) & Distance between \(i\)th UE and \(j\)th cooperation node \\ \(d_{\text{CB},j}\) & Distance between \(j\)th cooperation node and BS \\ \(T_{\text{UB},i}\) & Transmission number of \(i\)th UE transmitting to BS without cooperation \\  & node assisted \\ \(T_{\text{UC},ij}\) & Transmission number of \(i\)th UE data successfully decoded at \(j\)th cooperation node \\ \(T_{\text{CB},ij}\) & Transmission number of \(j\)th cooperation node assisting \(i\)th UE to BS \\ \(N_{\text{C}}\) & Total cooperation node number within a cell \\ \(\Delta M_{k}\) & Increased cooperation node number for assisting a specified UE at \(k\)th \\  & time unit \\ \(N_{\text{U}}\) & User equipment number in the cell \\ \(E_{i}\) & The overall energy consumption of \(i\)th UE data successfully decoded at BS \\ \(T_{i}\) & The overall latency consumption of \(i\)th UE data successfully decoded \\  & at BS \\ \(\theta_{k}\) & The angle between the UE and the farthest cooperation node that successfully decodes the UE data in the direction of the BS at \(k\)th time unit \\ \(\eta_{k}\) & The ratio of cooperation node decoding successfully at \(k\)th time unit \\ \(\lceil\cdot\rceil\) & Round-up of the value \\ \(\arccos(\cdot)\) & The inverse trigonometric function of cosine \\ \(\min(\cdot)\) & The minimum value of the function \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._work, a linear packet-level coding scheme is used for protecting data packets. The optimal packet distribution follows a special \"delay-equalized\" structure, and this paper proposes a fast bisection scheme to find the optimal packet allocation and code rate.