# A Study of MANET Routing Protocols in Heterogeneous Networks: A Review and Performance Comparison
## 2 MANET Routing Protocols: Background and a Review of the Literature  
### MANET Classification  
MANETs have been extensively studied due to their ability to operate in infrastructure-less environments, making them ideal for applications such as disaster recovery, military operations, and IoT deployments. However, the performance of MANETs in heterogeneous environments--where the nodes have varying capabilities in terms of the mobility,transmission rates, and energy consumption--remains a critical challenge. This section reviews recent advancements in MANET routing protocols, focusing on their performance in heterogeneous networks and highlighting unresolved research gaps. MANETs have emerged as a vital networking technology, especially in scenarios where the traditional infrastructure is unavailable. Their flexibility and self-configuring capabilities allow for dynamic networking solutions in diverse environments, such as battlefields and disaster relief operations. As highlighted in [14], the performance of MANETs significantly hinges on the choice of routing protocols, which are crucial for establishing efficient communication paths among mobile nodes. MANET routing protocols can be broadly classified into three categories: reactive (on-demand), proactive (table-driven), and hybrid protocols. Reactive protocols, such as AODV, establish routes only when needed, minimizing the overhead during periods of low network activity [17]. Proactive protocols, such as OLSR, maintain up-to-date routing information for all the nodes, enabling immediate route availability at the cost of increased control overhead [18]. Hybrid protocols, such as DYMO, combine the strengths of both reactive and proactive strategies, offering improved scalability and adaptability in dynamic environments [19]. Recent studies have explored enhancements to these protocols to address the challenges of heterogeneous networks. For instance, [17] proposed modifications to AODV, demonstrating improved performance in terms of the delay and throughput in heterogeneous MANETs. Similarly, [18] conducted a comparative analysis of OLSR and AODV, highlighting the trade-offs between the proactive and reactive approaches in dynamic environments. These studies underscore the importance of protocol design in optimizing the performance in heterogeneous networks. The evaluation of routing protocols in heterogeneous environments remains a crucial area of research. Studies by [20] explored the performance of AODV and DYMO in varying conditions, emphasizing the importance of understanding how different node types influence network performance metrics such as the end-to-end delay and throughput. Furthermore, the BATMAN protocol has been introduced as an innovative approach to address some limitations associated with traditional routing protocols, focusing on maximizing the message delivery probabilities while minimizing the control overhead [21; 22; 23]. Our findings concerning AODV's throughput align with previous studies, such as [19], which also reported lower throughput in high-mobility scenarios. However, the inclusion of heterogeneous nodes in our study introduces additional complexity, leading to slightly lower throughput compared to homogeneous networks. These comparisons highlight the impact of node heterogeneity on protocol performance and underscore the need for adaptive routing strategies. The authors of [24] reviewed recent advancements in routing strategies aimed at minimizing energy consumption in MANETs. They highlighted that energy-efficient protocols are critical to prolonging the operational life of battery-powered devices, which are prevalent in mobile ad hoc networks. Their findings suggest that integrating energy awareness into routing protocols can substantially improve the sustainability of MANETs. The integration of MANETs with emerging technologies, such as 5G and the IoT, has opened up new avenues for research.