# Survey on Power-Aware Optimization Solutions for MANETs
## 5 Challenges and Future Research Directions
### Challenges  
Hereafter, we present the main research challenges, as shown in Table 6, in energy-efficient optimization for MANETs. (1) Design of Cooperative MAC protocols for MANETs: Using cooperative transmission, the performance of an ad hoc network can be improved [225]. Cooperative Communication (CC) [226] is a capable method that utilizes close terminals to relay the overhearing information to obtain a variety of gains. Traditionally, a wireless transmission among a couple of terminals is considered as interference in other (third) terminals. In CC, third terminals can receive and process this wireless transmission for performance gains. The broadcast nature of the wireless channel is also exploited cooperatively. However, to cope with the complex medium access interactions made by relaying and influencing the advantages of such cooperation, we must design capable Cooperative MAC (CMAC) protocols. The CMAC protocols must consider the medium access layer interactions and signaling overhead due to cooperation. Otherwise, the performance gain through the PHY layer cooperation may not improve end-to-end performance. [PERSON] and [PERSON] [225] suggested a cross-layer distributed energy-adaptive location-based CMAC protocol (DEL-CMAC) for MANETs. DEL-CMAC improves the performance of MANETs in terms of network \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Challenges in the Development of Energy-Aware Optimization Solutions/Goal** & **Solution** & **Reasons** \\ \hline \hline A wireless transmission among a couple of terminals is considered as interference in other terminals. Close terminals relay the overhearing information without gains. & Design of Cooperative MAC protocols for MANETs & \(\bullet\) Cooperative transmission can utilize close terminals to relay the overhearing information and obtain a variety of gains. & Cooperative transmission can utilize close terminals to relay the overhearing information and obtain a variety of gains. \\
**Goal:** To improve the performance of MANETs in the MAC layer. & & \(\bullet\) A CMAC protocol exploits the medium access layer interactions and signaling overhead due to cooperation. \\ \hline \hline Conventional prediction methods are based only on the past locations of the node and they are ineffective for setting up a routing path with longevity. & & \(\bullet\) New hybrid methods are based on the temporal and spatial characteristics concerning its node’s neighborhood. & \(\bullet\) New hybrid methods are based on the temporal and spatial characteristics concerning its node’s neighborhood. \\
**Goal:** To set up a routing path with much longevity. This goal requires the prediction of the location of nodes based on the temporal and spatial characteristics (about its node’s neighborhood). & & \(\bullet\) Such a routing protocol is based on predicted node positions. Heuristic methods can use soft computing approaches, such as ML algorithms, to predict the future location of nodes. \\ \hline \hline In a multicast on-demand routing protocol, a method to select optimal multiple routes to a set of destinations is required. & & \(\bullet\) A fuzzy set of rules can be used for selecting optimal multiple routes to a set of destinations. Such rules can be based on available network bandwidth, route stability, and node-to-node delay. \\
**Goal:** To improve the performance of multicast routing protocols. & & \(\bullet\) Fuzzy-logic support can be adopted in a cross-layer design. \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Challenges in the development of energy-efficient optimization solutions for MANETs and their solutions. lifetime and energy efficiency. [PERSON] and [PERSON] [227] proposed another CMAC protocol for MANETs called network Lifetime Extension-Aware CMAC (LEA-CMAC). The LEA-CMAC protocol enhances network performance through cooperative transmission to complete a multi-objective target orientation.