# Experimental Measurements of a Joint 5G-VLC Communication for Future Vehicular Networks
## 3 5G Field Trials
### 5G Network
#### 3.2.2 Physical Infrastructure  
In the deployed infrastructure the cloud-radio access network (RAN) approach has been adopted. BSs are composed by several radio frequency elements called (active antenna units--AAU) and the base band unit (BBU) that is the element of processing. The BBU can ben centralized in a single point or virtualized in the cloud and represents the smart-element of the BS while only simple RF equipment are needed at the network edge.  
AAUs are able to work on different frequencies, thus a multimode network is deployed. In particular, a heterogeneous multi-layer 5G cellular architecture is considered where cells of different coverage areas are overlapped and provide services in different frequency bands (e.g., 3.7 GHz and mmWave) and with different access technologies (e.g., 5G-NR, WiFi and VLC). In this case, a dual-connectivity approach is adopted. The 5G-NR AAU operating in low frequency bands provides basic services on a wide area, while small cells operating on mmWave and visible light spectra provide high data-rate services indoor and in hot-spots.  
AAUs and BBU are connected though the fronthaul link that is characterized by low-latency and high-speed thanks to the adoption of the common public radio interface (CPRI) [16]. CPRI is an interface that defines the transmission of digital-radio over fiber and allows a transmission of data with a fixed bit rate over a dedicated channel.  
A single BBU and a single AAU connected to a channel emulator and to a basic User Equipment (UE) were used during the very initial tests. Successively, several BBUs and AAUs, connected to the LTE-CN following the 3 GPP NSA deployment scenario Options 3 and 3a [17], have been deployed in the two cities. In particular, the LTE radio and CN were used as an anchor for mobility management  
Figure 2: Network slicing conceptual architecture.  
and coverage, while adding new 5G carrier. Hence, the LTE-RAN connects the LTE-CN with the 5G NR.  
The FlexE [18] standard was used to manage via software the transport network. This allowed a flexible reconfiguration of the network, making the physical layer transparent to the service layer. 100G Ethernet rings provided connections to BBUs, while optical links provided connections with the core network.  
NSA deployment allows to validate KPIs mainly related to control plane and user plane latency, user and cells peak data rates, and to test network slicing approach [15].  
The SA 5G NR architecture will be deployed during the last part of the roll-out phase. In particular, 3 GPP Option 2 [19], i.e., 5G NR devices are directly connected to the new 5G CN, is considered in the deployment of the network. This solution is independent on 4G network deployments and it provides simpler implementation. Anyway, the above solution requests the 5G end-to-end network to be completely defined before the pre-commercial phase, and substantial investments to provide the service coverage over all the territory. In this phase, KPIs related to mobility and handover will be tested.  
The 5G NR improved air interface is based on:  
* Operations in multiple frequency bands;
* Massive MIMO (mMIMO) techniques;
* Non-orthogonal multiple access (NOMA);
* Dense network deployment.