# Network Lifetime Improvement through Energy-Efficient Hybrid Routing Protocol for IoT Applications
## 2 Related Work  
Numerous authors have undertaken research with the aim of devising effective routing for WSNs. This section presents some of the prominent results and findings by such researchers in the field. [PERSON], [PERSON], et al. [13] suggested a delay aware and energy-efficient opportunistic node selection in restricted routing (DA-EEORR). The authors claim the suggested model to be novel and suitable for a delay-sensitive environment. The proposed model attains a promising balance between energy consumption and average end-to-end delay by finding an optimal path. The model uses the idea of an opportunistic connection random graph (OCRG) to select the next hop. OCRG is further used to calculate optimal path connectivity, using factors such as transmission frequencies, residual energy, link quality, and so forth. The concept of a restricted research space was also employed in the proposed model to find the minimum distance next-hop node. The simulation findings advocate that the proposed method outperforms the current standards. This outperformance of the suggested approach can be witnessed in terms of the network lifespan, power usage, the overhead of the control packet, and the packet delivery ratio. Most of the findings showed only a marginal improvement since the study was focused more on path correction and the tracking of routes rather than establishing the optimal path in a hierarchical network. Thus, the proposed work achieves great balance between energy consumption and end-to-end delay; however, the work can still be extended further in the direction of incorporating multiple sink nodes to realize realistic delay-sensitive applications. The authors [PERSON], [PERSON], et al. [14] presented research on optimal route selection in wireless body area networks (WBANs). A WBAN is a network of miniaturized wearable sensing and computing devices that communicate the sensed data around a human body, and hence, they have been excessively used in remote patient monitoring, sports activity monitoring, and so on. They may be used to monitor vital physical parameters, such as electro-cardiograph (ECG), electro-encephalography (EEG), and so on. Now, as WBANs are resource constrained, they necessitate efficient and energy-efficient routing mechanisms. The authors of [14] proposed an energy-efficient and reliable routing scheme (ERRS) to increase reliability and resource stability in WBANs. To achieve this, the suggested approach implements two solutions, namely the selection of the forwarder node and the rotation of the forwarder node. EERS employs adaptive static clustering routing to achieve an enhanced stability period and a prolonged network life. During the simulation of the proposed approach, it was observed that the EERS achieved an improvement of 26% over the established protocols. The performance of the EERS is measured in terms of throughput and network stability. Additionally, it achieved an improvement of 17% and 40% in terms of end-to-end delay over the SIMPLE and M-ATTEMPT protocols, respectively, establishing the supremacy of the proposed algorithm. Although the study provided an efficient solution for WBANs during the simulation, motivating the researchers, its scalability and mobility remain challenges that need to be addressed in order for its real-life and widespread deployment. The need for longer network lifetimes and fast data transmissions for unattended time-sensitive nodes was also recognized by [PERSON], [PERSON], et al. [15]. In their study, the authors claimed that most of the routing approaches for such applications rarely consider all related issues at once, such as network traffic, the loss of packets, and energy consumption. Another associated challenge mentioned by the authors is the consideration of a homogeneous sensor network, as real-life deployments need to handle heterogeneous nodes. To address these challenges, the authors of [15] proposed a novel delay-aware energy-efficient reliable routing (DA-EERR) technique that considers heterogeneous nodes.