# Cross-Layer Methods for Ad Hoc Networks--Review and Classification
## 3 Cross-Layer Method Publications Review
### One Layer
#### 3.1.2 Channel Layer  
Cross-layer methods concentrated on the channel layer consist of resource reservation, random access, and cooperative transmission methods. _Channel layer (resource reservation)_  
In the works focused on the resource reservation at the channel layer (Table 3), the channel layer rarely uses physical layer data, using mainly network layer data [47]. The network layer reports on the data streams passing through the nodes. On the basis of this data, the channel layer makes the decision to reserve resources. When splitting the network into clusters, route data helps to maximize the number of dedicated channels for intra-cluster communication, and in the case of a tree-like network, where nodes transmit data to a single data collector node, the route tree allows the allocation of disjoint channel resources between the previous and next link. The resource reservation by a channel layer based on the information from the network layer allows for increased network capacity, route stability, and reduced power consumption. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Publication** & **Year** & **Citations** & **Layers** & **Goal** \\ \hline
[45] & 2006 & 98 & \(1,2\) & line throughput, interference \\
[46] & 2007 & 45 & \(1,2,3\) & line throughput \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cross-layer methods concentrated on the physical layer. [PERSON] et al. [48] propose the allocation of node channels using a routing protocol in such a way as to minimize interference of nodes along the route. The proposed method for allocating channels increases the bandwidth in comparison with the allocation of channels based on local node information. In their subsequent work, [PERSON] et al. [49] suggest reserving channels using information about network layer routes. The proposed protocol uses fewer service messages and provides more bandwidth than using only channel layer information. [PERSON] et al. [50] suggest that the channel layer should use the network layer information about the routes passing through the node and, on the basis of this information, pre-reserve bandwidth, minimizing the probability of packet collision. The network layer, in turn, searches for routes based on available reserved bandwidth. [PERSON] et al. [47] divide ad hoc networks into clusters; clusters are formed by the nodes themselves using a distributed algorithm. The access time in each cluster is represented as a synchronized sequence of super-frames. The superframe consists of four periods: the beacon period, the spectrum sensing period, the period of detection of adjacent nodes, and the period of data transmission. The cluster head in the beacon period sends information about synchronization and allocated cluster resources. In this work, the clustering is carried out in such a way as to simultaneously minimize the number of clusters and allocate the maximum number of free frequency channels for intra-cluster communication. For the formation of clusters and allocation of channels, joint work of the physical and channel layers is used. The routing algorithm, on the other hand, prefers the nodes that are the heads of the clusters to be included in the route when routes are selected, as the links with them are more stable. In the ad hoc network in question, there are the main users behind whom a certain channel resource is assigned and secondary users who, having found that the resource is not in use, can use it. When secondary users discover that the primary user has started using their resource, the secondary user must switch to another free resource; the switching takes time. The routing protocol looks for paths with the least delay. The delay is evaluated based on data from the link layer. The delay consists of a delay in the queue, a delay in switching to a new channel resource, and a delay in waiting time for the recharge of the resource. [PERSON] et al. [51] proposed a cross-layer channel assignment and routing algorithm for a cognitive radio ad hoc network that provides stable paths.