# Practical Performance Analyses of 5G Sharing Voice Solution
## 4 Voice Services Based on 5G Sharing  
5G voice continues the VoLTE feature IP-based solution. However, considering the complexity and authentication security issues of interoperability with other network standards, 3 GPP defines 5G to only interoperate with 4G and no longer interact with 2G/3G. IMS is the foundation for 5G users to use voice communication services.  
On the other hand, as mentioned above, compared to the 4G network scenario, 3 GPP Release 15 defines two deployment options for 5G NR, SA, and NSA modes. Accordingly, the voice solution also needs to be selected based on the existing network architecture, and  
Figure 1: Access network sharing architecture.  
a suitable voice network construction plan needs to be developed based on the network scenario and network construction rhythm. Therefore, the paper gives an achievable evolutionary path, as shown in Figure 2.  
At the beginning of 5G, the voice and data networks are separated. Voice is provided through EPC + LTE with VoLTE. With the adoption of 5 GC, voice services continue to be provided through EPC + LTE, with EPS fallback as the voice solution. Finally, after the 5G network is deeply optimized, the VoNR feature is gradually implemented.  
Handover is involved regardless of the voice solutions. The process of handover based on service type is shown in Figure 3.  
In the process of handover, there will be a handover delay, which is the delay of the radio resource control (RRC) process plus the interrupt delay. The equation is:  
\[D_{Handover}=T_{RRC}+T_{\rm interrupt} \tag{1}\]  
The \(T_{RRC}\) is the RRC process delay, defined in Section 12 of TS 38.331 [8], while the interrupt delay \(T_{\rm interrupt}\) is calculated as follows:  
\[T_{\rm interrupt}=T_{search}+T_{IU}+T_{processing}+T_{\Delta}+T_{margin} \tag{2}\]  
\(T_{search}\) is the time required to search the target cell when the target cell is not already known when the handover command is received by the UE. If the target cell is known, then \(T_{search}\) = 0 ms. If the target cell is an unknown intra-frequency cell, and the target cell Es/Iot \(\geq-\)2 dB, then \(T_{search}\) = Trs ms. If the target cell is an unknown inter-frequency cell, and the target cell Es/Iot \(\geq-\)2 dB, then \(T_{search}\) = 3 * Trs ms. Regardless of whether  
Figure 3: Based on service type handover process.  
Figure 2: 5G voice service evolution.  
DRX is in use by the UE, \(T_{search}\) shall still be based on non-DRX target cell search times. \(T_{IU}\) is the interruption uncertainty in acquiring the first available physical random access channel (PRACH) occasion in the new cell. \(T_{IU}\) can be up to the summation of static shared beam (SSB) to PRACH-occasion association period and 10 ms. SSB to PRACH occasion-associated period is defined in Table 8.1-1 of TS 38.213 [34]. \(T_{processing}\) is time for UE processing. \(T_{processing}\) can be up to 20 ms. \(T_{\Delta}\) is time for fine time tracking and acquiring full timing information of the target cell. \(T_{\Delta}\) = Trs. \(T_{margin}\) is time for SSB post-processing. \(T_{margin}\) can be up to 2 ms. Trs is the SSB measurement timing configuration (SMTC) periodicity of the target NR cell if the UE has been provided with an SMTC configuration for the target cell in the handover command; otherwise, Trs is the SMTC configured in the measObjectNR having the same SSB frequency and subcarrier spacing. If the UE is not provided SMTC configuration or measurement object on this frequency, the requirement in this clause is applied with Trs = 5 ms, assuming the SSB transmission periodicity is 5 ms. There is no requirement if the SSB transmission periodicity is not 5 ms. In the interrupt requirement, a cell is known if it meets the relevant cell identification requirements within the last 5 s; otherwise, it is unknown [35].