Browsing by Author "Wietfeld, Christian"

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Performance of CS Fallback for Long Term Evolution Mobile Network
(2014-10-01)
Liou, Ren-Huang
;
Lin, Yi-Bing
;
Sung, Yingrong Coral
;
Liu, Pang-Cheng
;
Wietfeld, Christian
When a mobile operator migrates its network from the third generation (3G) system to Long Term Evolution (LTE), both 3G and LTE will coexist for a period of time. Since the 3G circuit-switched (CS) voice mechanism is more mature and available than that for the LTE Voice over Internet Protocol (VoIP), the operator may consider CS fallback (CSFB) as a solution for providing reliable voice calls. According to the 3G Partnership Project (3GPP) CSFB procedure, when a mobile user in the LTE network has an incoming or an outgoing call, the user equipment (UE) falls back from LTE to Universal Mobile Telecommunications System (UMTS). When the call is complete and released, the UE immediately returns to LTE. If the next activity for the UE is another voice call, immediately switching from UMTS to LTE may not be efficient. In this case, the UE has to perform another CSFB. To resolve this issue, we suggest delaying the returns to avoid unnecessary CSFBs, which is called delayed return (DR). Based on the measurements from the real UMTS and LTE networks, we develop an analytic model for investigating the performance of the CSFB with DR. This paper indicates that the DR scheme can effectively reduce the CSFB costs by up to 60%.
QoE-Aware LTE Radio Link Control Parameters for Voice over IP in Vehicular Environments
(2014-01-01)
Liou, Ren-Huang
;
Ide, Christoph
;
Dusza, Bjoern
;
Wietfeld, Christian
;
Lin, Yi-Bing
In Long Term Evolution (LTE), Voice over Internet Protocol (VoIP) is used for the delivery of the voice data. One of the major challenges for VoIP over LTE is to guarantee the Quality of Experience (QoE) of the VoIP calls. This paper uses an LTE base station emulator and a radio channel emulator to evaluate the impacts of different User Equipment (UE) velocities and Radio Link Control (RLC) parameter values on the QoE of the calls in the vehicular environment. Our study shows that LTE can provide acceptable VoIP quality in the high-speed scenarios (e.g., high-speed train). This paper provides the guidelines for the telecommunications operators to select the appropriate parameter values when deploying their VoIP services in LTE.