## 2 Related Work  
Researchers have proposed numerous research articles that discuss the routing problem in multi-sink WSNs [5; 6; 15; 23; 24; 25; 26; 27; 28; 29; 30]. This section discusses the most related research to our proposed approach.  
Sustainable multipath routing protocol for multi-sink WSNs in harsh environments (SMRP) is presented in [15]. A mixed potential field is utilized in such a protocol to make routing decisions. The mixed field is constructed according to the environment information of sensor nodes, nodes' energy, and depth. The environmental field utilizes sensor node environmental data to prevent data packets from being transmitted on unsafe paths to lower the influence of environmental factors on network data transmission. The potential energy field is used to avoid nodes with insufficient energy in order to improve network energy balance. Using the depth potential field, data packets are directed toward the sink.  
However, from the previous study of SMRP algorithm, it is clear that it has some limitations, since they do not consider some critical issues. First, it overlooks the reliability of data transmission. WSNs depend on reliable data transfer. Ignoring such concerns might increase packet loss, waste energy, and delay packet retransmission. This clearly impacts network efficiency. The second issue is that it misses real-time data transmission. Real-time delivery of data is difficult in WSNs. Transmission of crucial real-time data within a predetermined deadline enables prompt action, whereas late delivery reduces the efficacy of the action done. Ignoring this problem might increase missed deadlines and packet drops.  
Energy efficient multi-sink routing protocol (EERP) for multi-sink WSNs is presented in [23]. Such an algorithm attempted to find the optimal path for data routing using multiple parameters. The nodes' energy, energy consumption rate, and hop count are parameters. The nodes' energy and energy consumption rates balance energy consumption and prevent nodes with low energy from being a part of the routing process. The hop count parameter ensures that data is sent closer to the sink and avoids a loop.  
Energy optimized routing algorithm (EORA) for multi-sink wireless sensor networks is proposed in [24]. This routing algorithm uses a hybrid virtual potential field to construct routing paths. The potential hybrid field is constructed according to the nodes' hop and energy. The nodes' energy virtual potential field is used to balance energy utilization so as the nodes with low energy are prevented from being a part of the routing decision. Hop virtual potential field guarantees the data flow towards the sink and eliminates routing loops.  
Nevertheless, despite the authors of EERP and EORA algorithms [23; 24] suggesting trustworthy techniques and effective energy, they do not consider some critical issues. First, they ignore environmental consequences. Neglecting this challenge might make them unable to adapt to environmental changes such as wildfires and rainstorms, as well as impairing network performance. Secondly, they don't account for lossy links caused by fading and interference. As described previously, ignoring such a problem might increase data loss, retransmission delay, and energy waste. Finally, they can not achieve real-time communications; therefore, they can not send data packets before the deadline. As has been said, timely data supply ensures relevant actions are made, whereas late data delivery reduces the efficacy of such activities.