# Practical Performance Analyses of 5G Sharing Voice Solution
## 4 Voice Services Based on 5G Sharing
### SA Sharing VoNR Process  
VoNR refers to voice services carried end-to-end by NR, 5 GC, and IMS [37; 38]. When the VoNR feature is mature, only the gNodeB is shared. NR accesses 5 GC to provide the voice service through VoNR. VoNR services are bearing in the 5G network, which can realize the unification of data and voice services in the same network. Compared with EPS fallback, the advantages of VoNR are apparent: firstly, there is no need to fall back, so the call setup delay is shorter; secondly, it supports 5G voice and data services concurrently, as shown in Figure 7.  
The VoNR handover process involves interoperation between 5G and 4G. 5 GC and EPC complete the handover and contextual information interoperation through the N26 interface during the handover process to ensure the continuity of the session. The flow of VoNR is shown in Figure 8.  
In the past network era, networks in high-frequency bands have had a coverage discontinuity problem [25], especially in mobile scenarios, where most users have a short residency time in the band, and 5G is no exception. Due to the discontinuous network coverage caused by the high-frequency band of 5G, by the edge of 5G, VoNR will switch to the respective 4G via N26 when it is unable to provide voice services, similar to the SRVCC scheme in the 4G era [39]. The residency time in this region can be modeled by  
Figure 8: VoNR call setup process.  
Figure 7: Voice over NR (VoNR) architecture under stand-alone (SA) networking.  
a hyper-exponentially distributed random variable. As shown in Equation (6), \(\eta_{w}\) is the average rate, and \(\alpha_{w}\) is the mobility variability parameter.  
\[F_{\text{5G}}(s)=\frac{\alpha_{w}}{\alpha_{w}+1}\frac{\alpha_{w}\eta_{w}}{\alpha_ {w}\eta_{w}+s}+\frac{1}{\alpha_{w}+1}\frac{\frac{1}{\alpha_{w}}\eta_{w}}{\frac {1}{\alpha_{w}}\eta_{w}+s} \tag{6}\]  
The VoNR solution also supports smooth handover between VoNR and VoLTE through the Inter-RAT handover mechanism [38]. Its handover flow is shown in Figure 9.  
The whole handover process can be divided into six steps: firstly, the UE needs to send the measurement report to the gNodeB; secondly, the gNodeB executes the handover judgment and then initiates the handover request to the 5 GC; thirdly, the target eNodeB prepares for the handover and then sends the handover indication; fourthly, the UE initiates random access at the target eNodeB; fifthly, the UE switches to the target cell; finally, the source gNodeB is notified of the handover completion, and the UE context is released.  
Equation (7) is the calculation method of handover delay from VoNR to VoLTE.  
\[T_{\text{VoNR}-\text{VoLTE}-\text{HO}}=T_{Radom.Access}+2\delta+\eta+4\gamma+4 \theta+3\mu \tag{7}\]  
\(T_{Radom.Access}\) is the time delay of the UE to initiate random access in eNodeB. The rest of the parameters are investigated in the same way as in Table 1.  
As can be seen in Figure 9, there are two times of communication between UE and gNodeB; one time of communication between UE and eNodeB; four times of communication between gNodeB and 5 GC; four times of communication between 5 GC and EPC; and three times of communication between EPC and eNodeB.  
Based on theoretical analysis, the access delay of VoLTE's non-back-to-home solution is shorter than the back-to-home solution in the NSA sharing phase, about 2.0 s, which is more recommended. The setup delay of EPS fallback based on handover or redirection is about 3.0-4.0 s in SA-SA calls, which increases compared with VoLTE setup delay. Because of the large time delay introduced, EPS fallback can only be used as a transition solution in the early SA sharing deployment. The theoretical VoNR setup delay is about 1.5-2.0 s, which is the lowest and the ideal solution.