# How to Isolate Non-Public Networks in B5G: A Review
## 3 Spectrum Isolation  
Spectrum isolation means that different NPNs share the spectrum in an orthogonal way, and the wireless performance of one NPN does not deteriorate when the dynamic factors of other NPNs, such as wireless traffic and channel conditions, exist. Using spectrum isolation, spectrum resources can be shared among NPNs flexibly; thus, the efficiency of the spectrum resources can be improved greatly. In spite of this, there is a serious challenge, which is that the spectrum isolation performance of NPNs must be expressed quantitatively and meet the requirements. To achieve this, there are two key aspects. One is how to calculate the performance and requirements of spectrum isolation for one NPN quantitatively. The other is assigning spectrum resources among NPNs to meet isolation requirements. For the first aspect, spectrum isolation can be represented by the QoS parameters of one NPN, which is called spectrum isolation based on QoS parameters. Thus, the QoS requirements can be used as the isolation requirements directly or they can be further mapped onto one isolation requirement, which needs to represent all the QoS requirements or the comprehensive requirement of all the QoS requirements. Then, the isolation indicators of one NPN are defined in accordance with the isolation requirements to represent the corresponding isolation performances [17]. For instance, there is one NPN \(g\) with one QoS requirement, \(q_{g}\). Thus, the isolation requirement denoted by \(z_{g}\) equals \(q_{g}\). Then, the index of the isolation performance denoted by \(s_{g}\) is defined to reflect whether \(z_{g}\) is met or not. Thus, if \(z_{g}\) is met, \(s_{g}\) equals 1; otherwise, \(s_{g}\) is smaller than 1. \(s_{g}\) can be calculated by \(\text{E}\big{(}\min\big{(}p_{g}(t),z_{g}\big{)}/z_{g}\big{)}\) if NPN \(g\) requires its performance to be no smaller than \(z_{g}\). Otherwise, \(s_{g}\) can be calculated by \(\text{E}\big{(}z_{g}/\max\big{(}p_{g}(t),z_{g}\big{)}\big{)}\), if NPN \(g\) requires its performance to be no larger than \(z_{g}\), where \(\text{E}(x)\) means to calculate the expectation of \(x\)[17]. \(p_{g}(t)\) is the instantaneous performance corresponding to \(q_{g}\). Besides the QoS parameters, spectrum isolation can also be expressed by the degree of sharing of the spectrum resource among NPNs, which is called spectrum isolation based on resource sharing. This means that each NPN is assigned a part of the spectrum resource, and one NPN can use other NPNs' spectrum resources temporarily [22]. Thus, the isolation requirement and indicator of one NPN can be the amount of time that the NPN uses the wireless resources of other NPNs. For example, there is one NPN \(g\) that has already obtained \(r_{g}\) bits of the spectrum resource. At the same time, in time window \(i\), NPN \(g\) shares its spectrum resource with other NPNs, denoted by \(a_{g,i}\), and it obtains spectrum resources from other NPNs, denoted by \(\beta_{g,i}\), temporarily. \(d_{g,i}\) is the data that \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Deployment Option**} & \multicolumn{6}{c}{**Performance Metrics**} \\ \cline{2-7}  & **Isolation** & **Data Privacy** & **Latency** & **Cost** & \begin{tabular}{c} **Standardized** \\ **or not** \\ \end{tabular} & **Application Scenarios** \\ \hline Isolated S-NPN & High & High & Low & High & Yes & High-speed train \\ \hline Shared spectrum-only & High & High & Low & \
\begin{tabular}{c} Medium \\ high \\ \end{tabular} & Yes & Smart power grid \\ \hline Shared RAN PNI-NPN & Medium & Medium & Low & Medium & Yes & Remote telemedicine \\ \hline Shared RAN and CP & & Medium low & Medium & Medium & Yes & Internet of Vehicles \\ PNI-NPN & & Low & High & Low & Yes &
\begin{tabular}{c} Automation \\ warehousing \\ \end{tabular} \\ \hline N3 LBO NPN & Low & Low & Medium & Low & No & AR/VR \\ \hline F1 LBO NPN & Low & Low & Medium & Low & No & AR/VR \\ \hline \hline \end{tabular}
\end{table}