# Cross-Layer Methods for Ad Hoc Networks--Review and Classification
## 3 Cross-Layer Method Publications Review
### One Layer
#### 3.1.2 Channel Layer
A novel metric for the probability of successful transmission of a channel is derived by considering channel statistics, sensing periodicity of the secondary users, time-varying channel quality, and a time-varying set of idle channels from the physical layer. Furthermore, the number of available channels and their characteristics are considered for the selection of a next-hop node with an aim to avoid the one-hop neighbors located in the primary user transmission range. The primary user is the user with granted resources, which are not used all the time. Secondary users attempt to use the resources of primary users when resources are free. In their subsequent work, [PERSON] et al. [52] offer a cross-layer approach that minimizes power consumption in UAV networks. The approach uses network and channel layers. The network layer uses the AODV protocol for routing, the cluster head is selected by the GSO (Glow Swarm optimization) protocol, and the Cooperative MAC protocol is used at the channel layer. The network has a cluster head. Using AODV, the cluster head finds routes to all nodes and creates a node tree. The cluster head then assigns TDMA slots \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Publication** & **Year** & **Citations** & **Layers** & **Goal** \\ \hline
[48] & 2005 & 69 & 2, 3 & line throughput \\
[49] & 2006 & 58 & 2, 3 & line throughput \\
[50] & 2007 & 94 & 2, 3 & line throughput \\
[47] & 2018 & 34 & 1, 2, 3 & line throughput, route stability \\
[51] & 2020 & 10 & 1, 2, 3 & line throughput, route latency, route stability \\
[52] & 2022 & 25 & 2, 3 & energy consumption \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Cross-layer methods concentrated on channel layer resource reservation. to other nodes along the node tree in such a way as to minimize packet interference and collisions, which results in lower power consumption, as fewer packets are sent repetitively. _Channel layer (random access)_  
In work focused on optimizing channel random access (Table 4), the channel layer uses data from the physical and network layers. The physical layer evaluates the state of the channel and reports to the channel layer. If the channel state is poor, the data link layer does not transmit the packet, as the packet is likely to be corrupted, further interfering with other users. The channel layer can also indicate the physical layer at what power the packet should be transmitted, making a trade-off between the high probability of successful packet delivery and the high interference for the other users. [PERSON] et al. [53] analyze the mutual influence of power control, queue types, routing protocols, and channel access protocols. The authors found that the effectiveness of the CSMA/CA channel layer protocol is highly dependent on the routing protocol, and the proposed two channel-layer protocols are superior to CSMA/CA. One of the protocols performs joint channel access control and power control, ensuring higher throughput and energy efficiency. The second protocol sacrifices energy efficiency in exchange for more bandwidth. [PERSON] et al. [54] propose a cross-layer approach. The physical layer in that approach shares the channel state with the other layers. If the channel state is bad, the upper layers decide not to transmit a packet, as this will result in energy consumption, interference, and waiting for packet reception confirmation reply. The approach is applicable to the Rayleigh fading channel. The level of future Rayleigh channel fading can be predicted based on previous measurements. The authors developed an attenuation prediction algorithm based on the Markov chains and examined in detail the interaction of the physical and channel layers. The authors derived theoretical formulas for bandwidth, packet processing speed, probability of packet loss and average packet delay in Rayleigh channels. The proposed approach increases network capacity and reduces energy consumption.