# Game theory-based Routing for Wireless Sensor Networks: A Comparative Survey
## 5 Future Directions and Challenges
### Future Research Directions  
Although a decade of research has passed in the field of WSNs, there are concerns still to be addressed for future research. The following research directions can be followed to design new routing protocols based on game theory. For a robust and efficient routing, multiple routing metrics should be considered. For example, a routing protocol can be energy efficient but may lead to a lower packet delivery ratio, or a protocol can increase network lifetime but may result in greater end-to-end delay. Therefore, cumulative routing metrics should be considered. Furthermore, some QoS metrics can be combined with these routing metrics, namely link quality, path reliability, and packet loss. The protocols discussed herein hardly include the problem of combining routing metrics along with QoS metrics. Certain protocols consider only one routing metric. Existing protocols can be improved by proving their robustness through a performance comparison with hybrid and cumulative routing metrics. WSNs are prone to many security concerns that have not been dealt with in many of the designed routing protocols. The vulnerability of the network to eavesdropping, unauthorized access, spoofing, and DDoS attacks has increased owing to the wireless communication between sensor nodes [74]. Moreover, resource limitation in WSNs resulted in us considering the effectiveness of the traditional security mechanisms. It is quite easy to make a WSN secure through the implication of game theory-based routing protocols. As these protocols can make sensor nodes in a WSN rational, it is possible to exclude malicious nodes from the routing path. The protocol presented in [43] is an example of this. Few protocols have used game theory to ensure secure routing. This can be a future research subject. As we have already discussed that WSNs are resource-constrained networks, data redundancy can lead to more resource limitations. To prevent this, we must ensure the freshness of data. This implies that the data are recent and ensures that no adversary can replay old messages. Existing works that use game theory-based algorithms to design routing protocols do not cover the problem of data redundancy. If the game is designed in such a way that the pay-off of a sensor node decreases when it causes unnecessary redundant transmissions, the data redundancy concern can be avoided. The energy hole problem is another crucial concern, and it is very important to solve this problem through routing techniques to keep a WSN fully functional. The nodes near the sink region will die sooner because the nodes send their own data as well as forward data from outer subregions to the sink [75]. Only GTEB [40], among the routing protocols discussed here, considers this problem. Certain protocols in the literature have used the cooperative game theory to ensure cooperative routing for the sake of reducing energy consumption. There is a high risk that these protocols would result in an energy hole problem causing harm to the network's functionality. This problem should be carefully handled in the future design of a routing protocol. Game theory is important for WSN routing because the game theory makes the nodes rational. For example, certain protocols involve rational decision making, which incorporates a node's decision on whether to be a CH or not on the basis of residual energy [41, 42]. Furthermore, a protocol may involve the rational decision of the nodes when they transmit the data packet selfishly or cooperatively [43]. Designing these types of strategies to make the nodes rational is a great challenge. Although it varies based on the design and implementation of routing protocols, the main objective is to increase energy efficiency by decreasing delay through the introduction of rationality among nodes. Therefore, game theory-based routing protocols are suitable for applications where energy is a critical resource.