Received February 2010; accepted April 2010
2. Related Works
3.1 Architecture Design
There are many popular 3GPP radio access technologies in the world, this paper only focuses on the design of the supported system among LTE, LTE-A and UMTS. There are two kinds of approach for LTE domain (E-UTRAN, EPC) to provide connection between UMTS-UE and UMTS domain (UTRAN, UMTS CN) for the Multi-RAT Virtualization DeNB. For air radio interface, Multi-RAT Virtualization DeNB must apply both original LTE-UE and UMTS-UE radio connection. Moreover, if the RN has connected to DeNB as a UMTS-NodeB for UMTS-UEs, the RN is also a repeater device for Virtual NodeB
(Virtual NB) under Virtual UTRAN area. So RN backhaul link Un interface is also a
WCDMA PHY layer tunnel for Virtual NB as shown in the lower left corners of Figure 5 and Figure 6. For wired core network interface, the first one is to add tunnel connectivity between EPC and UMTS domain, which is named as Arch_A. The other one is to add connectivity between E-UTRAN and UMTS domain, which is named as Arch_B.FIGURE 3. Virtualization system architecture
FIGURE 4. Multi-RAT Virtualization DeNB architecture
4. Performance Analysis. The two proposed architectures, Arch_A, and Arch_B, have different advantages and disadvantages. Table 1 shows the qualitative comparison between Arch_A, and Arch_B. There are some differences in criteria UMTS RNC Complexity, DeNB Complexity, LTE/UMTS CN Complexity, UMTS-UE Transmission Efficiency and Security Concern. Arch_A presents less complexity of DeNB at the expense of increased complexity of UMTS RNC in comparison with those in Arch_B. Generally speaking, transmission path for UMTS-UE in Arch_A results increased latency. Arch_B might have higher security concerns among network transmission than Arch_A, since its connectivity is going through an Intranet connection. Table 3 has shown the quantitative comparison in criteria of Handover latency and Number of handover signal. The analysis of handover latency can be identified by formula (1) with several parts such as radio link, wired link and processing time. Moreover, the numerical analysis parameters can be found in Table 2 and the analysis scenario can be illustrated by Figure 7. Based on results of Table 1 and Table 3, our proposed Arch_B has better performance. However, to apply Arch_A for different cases is also an alternative solution for Multi-RAT Virtualization supporting in
LTE-Advanced network.
Handover latency =
TRadio-link ×NRadio-link + TWired-link ×NWired-link+ TBearer configuration ×NBearer configuration + TCP-processing × NDevice (1)
Figure 5. Arch_A architecture
UTRAN
FIGURE 6. Arch_B architecture TABLE 1. Qualitative comparison between two architectures
Metric Arch_A Arch_B
UMTS RNC Complexity Serving UMTS-UE via EPC tunneling Virtual NB with RNC RN Complexity UMTS-Uu (access link) and WCDMA tunnel (backhaul link)
DeNB Complexity Bearer management + NB Virtualization Virtualization (NB and RNC) LTE/UMTS CN Complexity Bearer management S4 btw S-GW and SGSN No impact
UMTS-UE Transmission Efficiency Low High
Security Concern Low Middle
FIGURE 7. Analysis scenario
TABLE 2. Analysis parameters
Parameter Description Value
TRadio-link Transmission time via radio link 2 ms TWired-link Transmission time via wired link 2 ms TBearer configuration Transport bearer setup/release time 5 ms TCP-processing Control-plane processing time 5 ms
TUP-processing User-plane processing time 1 ms
TABLE 3. Quantitative comparison
Handover latency Number of handover signal Metric
Arch_A Arch_B Arch_A Arch_B
Intra-NB handover (ms) 157 5 21 0
Inter-NB handover (ms) 188 118 24 14
5. Conclusions. Both LTE and LTE-Advanced are backward compatible with 3G UMTS and 2G GSM, GPRS cellular networks. Considering wireless coverage and upgrade deployment cost, the LTE-Advanced adds a new entity RN to enlarge service coverage.
This paper has designed two workable Multi-RAT Virtualization architectures by which DeNB with RN is able to provide services for both UMTS UEs and LTE UEs by Virtualization supporting. Thus, analysis results have shown that our proposed structures
can let the UEs’ transition between core networks of UMTS and LTE-Advanced with virtualization support. It is an achievable and novel Multi-RAT Virtualization architecture for future 4G wireless network.
Acknowledgment. This work was supported in part by the National Science Council
(NSC), Taiwan, R.O.C., under the grant no. NSC 102-2221-E-164-007. The authors also gratefully acknowledge the helpful comments and suggestions of the reviewers, which have improved the presentation.REFERENCES
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