# Green Communication in IoT for Enabling Next-Generation Wireless Systems
## 2 Related Work
### Approach-Based Routing Protocols (ARP)  
A new routing protocol called State-Aware Link Maintenance Approach (SALMA) has been proposed in [27]. The SALMA protocol is combined of two existing protocols, dynamic-source routing (DSR) and optimized link state routing (OLSR). This novel protocol places emphasis on the activity of sensor nodes in IoT operations, classifying them into three states: black, white, and gray. According to the findings of this study, the SALMA protocol demonstrates improvements in various quality of service (QoS) metrics. It exhibits a lower routing overhead compared to OLSR, shorter delays than DSR, and ensures low energy consumption for all sensor nodes in the network. Sequential Assignment Routing (SAR) was introduced as an innovative routing protocol that tackles the issues encountered in routing protocols, striving to cater to the diverse quality of services. SAR operates as a multi-path routing protocol that assists in determining optimal routing decisions. Its design revolves around three key phases: assessing the quality of service on each path, considering energy resources, and factoring in the priority level of the packet. Nonetheless, SAR faces a number of problems and limitations, including its challenge of maintaining routing tables and the complexity of efficiently monitoring quality of service metrics at each individual sensor node [28]. The Low-Energy Adaptive Clustering Hierarchy (LEACH) routing protocol was introduced in [29]. LEACH is a routing protocol based on clustering, where cluster heads are randomly selected to evenly distribute the power load among sensor nodes in the IoT networks. This protocol uses localized coordination to ensure resilience and scalability in dynamic IoT networks. Furthermore, it implements a data fusion mechanism to reduce the volume of transmitted data to the sink node. In [30], the authors introduced an adaptive threshold-sensitive energy-efficient sensor network protocol (APTEEN). APTEEN was designed for an all-encompassing information retrieval approach. Within this network, the sensor nodes not only react to critical time events but also periodically share comprehensive network details while minimizing energy consumption. In such a system, users have the flexibility to make requests for current, past, and future data using persistent, one-time, or historical queries. The authors in [31] presented a novel routing protocol known as Geographical and Energy-Aware Routing (GEAR) in their paper. GEAR selects the next hop in the path, based on either geographical location proximity or cost. In [32], researchers introduced Geographic Adaptive Fidelity (GAF), a routing protocol primarily designed for MANET networks but also applicable to IoT networks. The main concern of GAF is to address power consumption issues within the network. This is achieved by intelligently turning off unnecessary sensor nodes while maintaining the stability of process fidelity. The GAF protocol divides the sensor node field into grid squares, with each sensor node utilizing location information, either from the GPS or any available location system. Figure 3 depicts the diagram of state transitions for Geographic Adaptive Fidelity, consisting of three states: active, sleeping, and discovery. In the sleeping state, sensor nodes turn off their radios to conserve energy. During discovery mode, sensor nodes send messages to gather information about other nodes within the same grid. Even in active mode, sensor nodes periodically send messages to inform others about their current state. The primary objective of this protocol is to prolong the IoT networks' lifetime by ensuring only one active sensor node exists in each grid [33]. In [34], the authors introduced a Stateless Protocol for Real-Time Communication (SPEED) for IoT networks. This protocol offers backing for three categories of real-time transmission services: real-time area multicast, real-time area anycast, and real-time unicast.