# A Hybrid Route Selection Scheme for 5G Network Scenarios: An Experimental Approach
###### Abstract  
With the significant rise in demand for network utilization, such as data transmission and device-to-device (D2D) communication, fifth-generation (5G) networks have been proposed to fill the demand. Deploying 5G enhances the utilization of network channels and allows users to exploit licensed channels in the absence of primary users (PUs). In this paper, a hybrid route selection mechanism is proposed, and it allows the central controller (CC) to evaluate the route map proactively in a centralized manner for source nodes. In contrast, source nodes are enabled to make their own decisions reactively and select a route in a distributed manner. D2D communication is preferred, which helps networks to offload traffic from the control plane to the data plane. In addition to the theoretical analysis, a real testbed was set up for the proof of concept; it was composed of eleven nodes with independent processing units. Experiment results showed improvements in traffic offloading, higher utilization of network channels, and a lower interference level between primary and secondary users. Packet delivery ratio and end-to-end delay were affected due to a higher number of intermediate nodes and the dynamicity of PU activities. hybrid route selection; 5G; reinforcement learning; USRP/GNU radio; Raspberry Pi; centralized route selection; distributed route selection; cognitive radio; D2D communication; femtocell node and base station  
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femtocells \(fc_{1},fc_{2},...,fc_{8}\) are scattered within the transmission range of a macrocell base station (MC BS). The BSs of the macrocell and femtocells can communicate with each other either directly or via multiple hops. Small cells deployed outside the transmission range of macrocells can help to improve network coverage. Due to the different characteristics of the network cells, the network can be segregated into two main layers, as shown in Figure 2. The _macrocell layer_ uses lower frequency bands with a higher transmission power to provide a longer transmission range; however, the channel capacity is lower at lower frequency bands. The small-cell layer (i.e., the _femtocell layer_) uses higher frequency bands (e.g., millimeter wave (mm-wave) or above 30 GHz [14]) with a lower transmission power to provide a higher channel capacity; however, the transmission range is shorter at higher frequency bands. In terms of the dynamicity of channel availability, the macrocell layer may use channels with a higher number of white spaces, given a limited number of available licensed channels. In terms of heterogeneity and ultra-densification, these characteristics are more prevalent in small cells as a large number of small cells must be deployed to provide connections to heterogeneous nodes (or user equipment). Some of the main characteristics of 5G architecture are _control plane_ and _data plane_ separation as shown in Figure 2. The _control plane_, which includes the macrocell layer, contains a central controller (CC) that (a) collects network-wide information (e.g., network topology comprised of nodes, links, and channel availability) from all nodes in the network and maintains the information (e.g., in a routing table); (b) performs global-level tasks (e.g., determines routes); and c) disseminates information (e.g., prioritizes routes) to nodes in the network (i.e., source node \(fc_{s}\)). The _data plane_, which includes the small-cell layer, performs local-level tasks (e.g., selects a route based on a set of available and prioritized routes, and the availability of _device-to-device (D2D)_ communication) [15; 16]. Figure 1: A multi-tiered 5G network. The source node \(fc_{s}\) establishes a route to the destination node \(fc_{d}\). The optional routes are also shown. Figure 2: Control and data plane separation in a multi-tiered 5G network.