# Future Is Unlicensed: Private 5G Unlicensed Network for Connecting Industries of Future
## 2 Background
### Nr-U  
The 3 GPP has defined three main industrial deployment scenarios for NR-U: Carrier Aggregation mode, Dual Connectivity mode and Standalone mode. Carrier Aggregation mode is based on LTE-LAA in Release-13 [30]. In LTE-LAA, the unlicensed spectrum is used to augment downlink capacity, whereas the uplink and control plane signals are passed via the license carrier. Dual Connectivity mode is based on the design of LTE-extended LAA (eLAA) in Release-14 [31], which supports both uplink and downlink data-plane traffic over the unlicensed spectrum, whereas the control plane is anchored over the licensed band. Standalone mode is a novel approach in Release-16 [32,33]. In the first two modes, NR-U is anchored to both licensed band. In standalone NR-U, similar to the MulteFire Alliance for standalone operation [11,34], NR-U is expected to work in the unlicensed spectrum without being anchored to any licensed carrier. Thus, NR-U is attracting much interest in industrial networks since it allows removal of the dependency on public networks. In Table 3, we present a taxonomy of the different deployment modes of NR-U, including the standardization body, operational frequencies, the frequency band, the protocol, the maximum supported bandwidth, supported streams, and the underline technology. There are also two main modes of spectrum sharing proposed for NR-U in unlicensed scenarios [33,35] as shown in Table 4. The first is asynchronous shared spectrum mode for NR-U. This is the evolutionary path that works within the existing coexistence rules applied to the unlicensed spectrum, i.e., when deployed, NR-U must follow LBT channel access protocols. Thus, NR-U uses a variety of strategies to boost its reliability and availability performance in these shared spectrum bands. Second is the synchronous shared spectrum for NR-U. The synchronous shared spectrum is a more advanced approach of spectrum sharing technology, which allows overlapping of the contention window (CW) of the node. It offers great potential for more efficient spectrum sharing, with more stable, more consistent performance. However, this approach requires sharing mechanisms  
Figure 1: Evolution of NR-U [16]. eLAA, extended Licensed Assisted Access. \begin{table}
\begin{tabular}{l l l l} \hline \hline  & **Carrier Aggregation Mode** & **Dual Connectivity** & **Standalone Mode** \\ \hline
**Standardization** & LTE Release 13 & LTE Release 14 & LTE Release 16 \\ \hline
**Frequency** & 5 GHz & 5 GHz & 2.4, 3.5, 5, 6, 37, 60 GHz \\ \hline
**Frequency band** & License + unlicensed & License + unlicensed & Unlicensed \\ \hline
**Protocol** & LTE & LTE & NR \\ \hline
**Aggregated bandwidth** & 80 MHz & 80 MHz & 800 MHz \\ \hline
**Streams** & Downlink & Uplink + Downlink & Uplink + Downlink \\ \hline
**Underlying technology** & LAA & eLAA & MulteFire \\ \hline \hline \end{tabular}
\end{table} 
Table 3: A taxonomy of the deployment modes of NR-U. with a common synchronization reference among operators and will need support from regulators. This synchronous method was popular in the U.S. initially, and now, Europe is also interested in this approach due to the following advantages over asynchronous mode:  
* Improves service predictability and user experience via CW overlapping to minimize the latency. * Enables advanced technologies such as coordinated multi-point (CoMP) to enhance spectrum efficiency and reliability. * Facilitates flexible sharing via a reservation slot structure, which ensures that no node is blocked from accessing the medium for an extended period, and channel use is \"guaranteed.\"
* Enables advanced sharing such as spatial domain multiplexing to improve spectrum utilization. The NR-U study item has considered different unlicensed bands or shared bands such as 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz [12; 36] as initial candidates; however, later on, 3.5 GHz and 37 GHz bands were open for shared access in the U.S. The 3 GPP classifies these bands for NR-U as sub-7 GHz and mmWave bands.