# A Hybrid Route Selection Scheme for 5G Network Scenarios: An Experimental Approach
## 2 Related Work
### Routing in 5G
#### 2.1.1 Traffic Offloading  
Traffic offloading allows traffic to be offloaded from highly utilized BSs, particularly MC BSs to other BSs (e.g., in femtocells) in order to improve load balancing and reduce traffic congestion at BSs of the upper-tier (i.e., the macrocell layer). This can be achieved via D2D communication.  
In [34], a distributed channel allocation scheme is proposed to offload traffic to D2D nodes in small cells to avoid (or reduce) interference between licensed and unlicensed users. The scheme addresses network heterogeneity (i.e., small-cell BSs and D2D users) and potential interference from unlicensed users. For channel allocation, channels are allocated to licensed users, and then the available channels are shared among D2D users communicating within the range of a small-cell network called a coalition. Therefore, the priority of spectrum sharing is higher among D2D devices in a coalition. The proposedscheme increases the throughput and network spectrum utilization due to better channel allocation and route selection.  
In [9], a distributed route selection scheme is proposed to offload traffic from highly congested BSs to less congested BSs via D2D communication in order to achieve load balancing. The scheme addresses network heterogeneity (i.e., macrocell and small-cell BSs) and ultra-densification. Traffic can be offloaded from: (a) congested MS BSs to less congested small cells; (b) congested small-cell BSs to less congested small-cell BSs; and (c) from congested small-cell BSs to less congested MC BSs. Deploying a large number of small cells can lead to ultra-densification. [PERSON]'s algorithm [35] is applied to determine the shortest route (which has the least number of nodes and hops) towards a destination node. The proposed scheme increases the throughput due to better traffic distribution among the network cells.  
In [32], a distributed route selection scheme is proposed to offload traffic from nodes with lesser resources (i.e., residual energy and memory) to those with more resources via D2D communication in order to improve network performance. The scheme addresses the dynamicity of channel availability and network heterogeneity, whereby nodes have different amounts of resources. Since routes have different resource requirements, nodes with higher residual energy and memory are selected to establish resource-intensive routes to deliver more traffic; however, once their resources drop below a certain threshold, the nodes are selected for less resource-intensive routes. The proposed scheme is shown to increase the packet delivery rate as nodes with more resources are selected for packet forwarding.  
In [23], a distributed route selection scheme is proposed to offload traffic from nodes with low residual energy to those with higher residual energy yet less traffic load via D2D communication in order to prolong the network lifetime. The scheme addresses the dynamicity of channel availability and network heterogeneity, whereby nodes have different residual energy levels. In other words, nodes with higher residual energy levels are well utilized, while nodes with lower residual energy levels serve the backup role. Rerouting is performed from time to time as the residual energy levels at different nodes reduce at different rates, and the traffic load is dynamic in nature. Among the available routes, the one with higher residual energy and lower end-to-end delay, in terms of the number of hops, is selected to deliver traffic. The proposed scheme is shown to increase the network lifetime and packet delivery rate as load balancing is achieved among nodes with different residual energy levels throughout the network.