# From Cyber-Physical Convergence to Digital Twins: A Review on Edge Computing Use Case Designs
## 9 Network Digital Twin for Vehicle-to-Edge Communication
### Edge Computing-Based Digital Twin for Open RAN
#### 9.2.1 Edge-Based Vehicular Communications  
A Primer for Open RAN DT  
Improving computational capabilities to serve latency-intolerant services will present new opportunities for those service providers who will be prepared to embrace it [139]. For instance, most of the existing research contributions in vehicular-to-anything (V2X) communications assume either deterministic or static channel models, which might be unrealistic. Vehicular channels in urban environments are highly dynamic, owing to the influence of high-speed motion and intermittent connections. In line with the enterprise digitization enabled by 5G/6G networks [140], an edge intelligence system that allows a customized functional split to cater for 6G mission-critical services is shown in Figure 10 below.  
Shown in Figure 10 above is a vehicular network with the support of the transportation infrastructure. Here, it is assumed that communication between the RSU and vehicles is based on 6G communications, and the coverage of the RSU determines the service zone. The edge intelligence system on the edge site is based on functional split, which is defined as follows [141]:  
**Definition 1**.: _In the context of open RAN, the functional split determines the number of gNB functions that can be left locally, i.e., closer to the user, in order to relax the bit rate and delay requirements of the fronthaul network. It also determines the number of gNB functions that can be centralized in order to achieve greater processing capabilities._  
According to the open RAN split architecture, the edge computing system consists of (i) a fixed RSU, (ii) a distributed unit (DU), and (iii) a centralized unit (CU), which complete the open architecture defined for edge computing.  
* Distributed Unit: The DU is the lower-layer split of the open RAN protocol stack, while the fixed RSU together with the DU are considered as the edge cloud. According to the logical split 7.2x, the DU can be defined as the logical node that includes a portion of the gNB functions. It is tasked with controlling the operation of a number of RSUs.
* Centralized Unit: The CU is the upper-layer split of the open RAN protocol stack, and it is considered as the central data center. It is the logical node that includes a portion of the gNB functions, i.e., packet data convergence protocol (PDCP) and the radio link controller (RLC) layers of the protocol stack, as defined by logical split 2. The CU can also support a number of DUs. Therefore, by taking advantage of network function virtualization (NFV) techniques and running them at CUs, part of the network functions can be transferred into data centers instead of running them at the RSU.  
In Figure 10 above, it is assumed that the open and flexible edge platform consists of node software that runs on devices at the edge, as well as a management system that runs on the edge-cloud continuum. Since the infrastructure nodes are wire connected via high-speed fronthaul connections, all the infrastructure nodes can be regarded as one giant  
Figure 10: Edge intelligence on an open edge platform capable of handling vehicular communications.  
node together. Both resource availability and resource requirements are quantified with resource units.