# On the Design of a Network Digital Twin for the Radio Access Network in 5G and Beyond
## 4 Results
### RAN NDT Instance
#### 4.2.1 Basic Models  
The implemented NDT has approached the basic models as follows:  
1. _Scenario topology_ model: corresponds with an urban scenario of 700 \(\times\) 700 m in Barcelona city shown in Figure 3, which encompasses different streets, avenues, a park, and different seven-floor buildings with 3.5 m floor height.
2. _gNB_ model: includes the gNBs deployed in the area. Each one is modelled as an outdoor microcell and is specified by the following parameters: gNB position, height, operating frequency, total transmitted power, total bandwidth, subcarrier separation, total number of Physical Resource Blocks (PRBs), duplex mode and the gNB antenna gain and noise figure. Only the downlink (DL) direction is considered. The positions of the gNBs in the NDT are shown in Figure 3. To avoid border effects, it is assumed that the study of the capacity sharing algorithm is performed only in the five central gNBs that are numbered and highlighted in yellow in the figure.
3. _UE_ model: is specified by the user density in the area (users/km\({}^{2}\)), the UE type, which can be either stationary, pedestrian or vehicular, as well as by the UE position that changes dynamically, the UE height, antenna gain, noise figure and required bit rate \(R_{b}\).
4. _Channel_ model: provides the Signal-to-Interference and Noise (SINR) ratio for each UE by considering the UE and gNB parameters and obtaining the path loss according to the UE position and the propagation model of the NDT. Moreover, the channel model provides the spectral efficiency \(S_{\mathit{eff}}\) in b/s/Hz to each UE according to the SINR and assuming that the maximum achievable \(S_{\mathit{eff}}\) is 7.4063 b/s/Hz as established in [20], and that UE is in outage if \(S_{\mathit{eff}}\) is lower than 1 b/s/Hz. Additionally, inefficiency factors due to cyclic prefix of 5G transmission and overheads (see [22]) have been considered, taking values 14/15 and 0.8, respectively.
5. _Network slice_ model: is specified by the associated SLA to be guaranteed to the different network slices (i.e., the \(SAGBR_{k}\) and \(MCBR_{k}\) parameters in the DQN-MARL capacity sharing algorithm), the bit rate requirement of UEs belonging to the network slice \(R_{b}\), the traffic generation parameters for the network slice and the percentage of users of the different types in the network slice. In addition, the resource quota of the network slice in the different gNBs during the current time step is also configured here.  
The specific values of the parameters considered for the different basic models in the NDT are listed in Table 1.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline  & \(g\)NB \\ \hline Number of gNBs & 5 \\ gNB height & 10 m \\ Operating frequency & 3.5 GHz \\ Total transmitted power & 35 dBm \\ Total bandwidth & 100 MHz \\ Subcarrier separation & 30 kHz \\ Duplex mode & Time Division Duplex (75\% of symbols allocated to DL) \\ Number of PRBs per gNB & 273 \\ Antenna gain & 20 dB \\ Noise Figure & 9 dB \\ \hline  & \(\text{UE}\) \\ \hline UE height & 1.5 m \\ UE antenna gain & 0 dB \\ Noise Figure & 9 dB \\ \hline  & _Channel_ \\ \hline  & gNB 1 & 3.71 \\ Average Spectral & gNB 2 & 3.73 \\ efficiency (bits/s/Hz) & gNB 3 & 3.59 \\  & gNB 4 & 3.66 \\  & gNB 5 & 3.59 \\ \hline  & _Network slice_ \\ \hline Number of tenants & 2 \\ Required user & Tenant 1 & 8 Mb/s \\ bit rate (\(R_{b}\)) & Tenant 2 & 4 Mb/s \\ \(SAGBR_{k}\) & Tenant 1 & 50\% of the capacity in the system \\ \(MCBR_{k}\) & Tenant 2 & 25\% of the capacity in the system \\ \(MCBR_{k}\) & Tenant 1 and 2 & 90\% of the cell capacity \\ \hline \hline \end{tabular}
\end{table}
Table 1: Configuration of the implemented RAN NDT.  
Figure 3: Map included in the scenario topology model of the implemented RAN NDT. The positions of the considered gNBs correspond to the yellow dots on the map.