# A Cross-Layer Optimized Opportunistic Routing Scheme for Loss-and-Delay Sensitive WSNs
## 7 Conclusions and Future Work  
Guaranteeing the reliability of communication links and reducing the delay of data transmission is crucial to the application of wireless sensor networks. Opportunistic routing guarantees the reliability of data transmission at the expense of a small delay. The main innovation of this paper is based on the traditional opportunistic routing, and proposes a cross-layer optimization routing method, which improves the performance of the network significantly. The COOR scheme proposed in this paper makes full use of the residual energy of nodes to increase the transmission power, which can effectively improve the reliability of data transmission and reduce the delay. In addition, this scheme includes two types of methods, the COOR(R) method and COOR(P) method. In the COOR(R) method, after the transmission power is increased, the transmission distance is maintained so as to improve the one-hop reliability of transmissions, while the COOR(P) method increases the transmission distance with the one-hop reliability remaining unchanged. After theoretical analysis and experimental results, it is shown that the COOR scheme can significantly improve the reliability of transmissions by 36.62%, with a delay decrease rate of 21.09%.  
The work of this paper aims at the network model where nodes are continuously in working state. Actually, in order to save energy, many wireless sensor networks use a duty cycle-based mode, in which nodes are periodically rotated between awake and sleep states. At the same time, nodes consume relatively less energy in sleep state, so the network life can be effectively improved in this way. However, the disadvantage of this approach is that it will lead to an increase in delay. We will further study the delay optimization of duty cycle-based WSNs in the future.  
[PERSON] performed the experiment, analyzed the experiment results, and wrote the manuscript. [PERSON], [PERSON] comment on the manuscript. [PERSON] conceived of the work and wrote part of the manuscript. [PERSON], [PERSON] and [PERSON] comment on the manuscript.  
This research was funded by the National Natural Science Foundation of China (61772554, 61572528, 61572526), the Open Research Project of the State Key Laboratory of Industrial Control Technology, Zhejiang University, China (No. ICT1800391). The National Basic Research Program of China (973 Program) (2014 CB046305).  
**Conflicts of Interest:** The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c l l} \hline \hline
**Application** & \multicolumn{3}{c}{**Characteristics and Requirements**} & **Appropriate Choice** \\ \hline \multirow{3}{*}{Natural environment monitoring} & 1. & Data should be accurately recorded & \multirow{3}{*}{COOR(R) method} \\  & 2. & Long transmission cycle with high delay tolerance & \\  & 3. & Sensors are often evenly distributed & \\ \hline \multirow{3}{*}{Wildlife tracking records} & 1. & Emphasizes accurate records & \multirow{3}{*}{COOR(R) method} \\  & 2. & No need for fast transmission & \\  & 3. & Small amount of data & \\ \hline \multirow{3}{*}{Border monitoring of military installations} & 1. & Any intrusion requires accurate reporting & \multirow{3}{*}{COOR(R) method} \\  & 2. & Tolerate minor delays & \\ \hline \multirow{3}{*}{Real-time video surveillance} & 1. & Requires real-time data & \multirow{3}{*}{COOR(P) method} \\  & 2. & Obsolete data is useless & \\ \hline \multirow{3}{*}{Human health monitoring} & 1. & Uneven distribution of sensors & \multirow{3}{*}{COOR(P) method} \\  & 2. & Obsolete data is useless & \\ \cline{1-1}  & 3. & Monitoring data can be merged & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Practical applications and method recommendation.