Circuit Switched Fallback Research Articles

Optimal Guard Channel Reservation and its Comparison with Fractional Channel Policies in Mobile Cellular Network

In the current communication era, 2G voice services coexist with higher generation mobile network voice services like Voice over Long Term Evolution (VoLTE) in 4G and Voice over New Radio (VoNR) in 5G. Subscribers registered in the 5G network, but their voice option is in 4G so voice calls can be handled through the Evolved Packet System (EPS) Fallback or Radio access technology (RAT) Fallback. Similarly, subscribers register in a 4G network, but their voice option is in 3G or 2G so voice calls can be handled through Circuit Switched Fallback (CSFB). To provide uninterrupted voice service in such wireless networks usually handoff calls (HCs) receive higher priority than new calls (NCs). So, some guard radio resources (i.e., channels in 2G or RBs in 4G or 5G) may be reserved in each cell to handle this type of HCs. If more channels are reserved for HCs, then the handoff call-dropping probability (HCDP) will be decreased and at that time the new call-blocking probability (NCBP) will be increased. So, by considering the target HCDP if channels are reserved for HC, then HCDP will remain below the target and NCBP will be minimum. In this paper first, we proposed an optimal channel reservation (OCR) policy that reserves guard channels according to the given target HCDP. Second, we compared our OCR policy with fractional channel (FC), limited fractional channel (LFC), and uniform fractional channel (UFC) policies. Finally, we observed the performance of all these policies considering the Global System for the Mobile Communication (GSM) network.

Peeking Over the Cellular Walled Gardens - A Method for Closed Network Diagnosis -

A cellular network is a closed system, and each network operator has built a unique “walled garden” for their network by combining different operation policies, network configurations, and implementation optimizations. Unfortunately, some of these combinations can induce performance degradation due to misconfiguration or unnecessary procedures. To detect such degradation, a thorough understanding of even the minor details of the standards and operator-specific implementations is important. However, it is difficult to detect such problems, as the control plane is complicated by numerous procedures. This paper introduces a simple yet powerful method that diagnoses these problems by exploiting the operator-specific implementations of cellular networks. We develop a signaling collection and analysis tool that collects control plane messages from operators and finds problems through comparative analysis. The analysis process consists of three different control plane comparison procedures that can find such problems effectively. These individual procedures use a time threshold, control flow sequence, and signaling failure as the basis for comparison. To this end, we collect approximately 3.1 million control-plane messages from 13 major cellular operators worldwide. As a case study, we analyze the circuit-switched fallback technology that triggers generation crossover between third generation and long-term evolution technologies.

Practical Performance Analyses of Circuit-Switched Fallback and Voice Over LTE

The Internet Protocol (IP) Multimedia Subsystem (IMS) is a framework for delivering all-IP-based services. Voice via IMS has been defined as a possible solution from Third-Generation Partnership Project (3GPP) Release 5, prior to long-term evolution (LTE). However, the cost and immediate need for IMS services prevented operators from migration to IMS-based services, particularly with the wide presence of circuit-switched (CS) services offered in Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) networks. CS fallback (CSFB), which was introduced in 3GPP Release 8, enables the support of voice service without IMS. This is the common deployed scenario for many exiting LTE networks. Voice over LTE (VoLTE) is compulsory to offer rich communication services (RCS) via IMS, in addition to improving the performance of the already deployed CSFB voice solution. However, CSFB and VoLTE are still deployed concurrently, where operators can gradually roll out an LTE/IMS system, while still supporting 2G/3G fallback mechanism. It is, therefore, important to benchmark the performance of both solutions, highlight the deployment challenges, and study the impacts on the end-user experience. This paper provides performance analysis, deployment challenges, and comparisons between these voice solutions. This paper presents practical performance analysis, including end-to-end assessment of call setup delay under different radio conditions, main challenges impacting the in-call performance, as well as performance aspects of Single Radio Voice Call Continuity (SRVCC) and its evolution releases.

Solution to Reduce Voice Interruption Time during Handover of VoLTE Call in Enhanced Single Radio Voice Call Continuity

LTE network is a packet switched based network, which does not support circuit switched network feature like voice call. Operators have been trying to deploy LTE network in phases and in parallel they are supporting legacy networks too. It is necessary to support voice call. There are many approaches for supporting voice call to serve customer. Circuit Switched Fall Back (CSFB), Simultaneous Voice & LTE (SVLTE), Over The Top solution (OTT), Voice over LTE via Generic Access (VoLGA) and IMS based Voice over LTE (VoLTE). SRVCC is a voice call handover process for an LTE user, while it is in active IMS based voice session. In case of SRVCC, control is performed by the home network which causes voice interruption & call drops. To overcome these issues ATCF and ATGW entities have been introduced. This paper explains about the issues, causes and solution in SRVCC.

Performance of CS Fallback for Long Term Evolution Mobile Network

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%.

Cloud voice service as over-the-top solution for seamless voice call continuity in a heterogeneous network environment

Despite the current introduction of the 4G mobile network technology Long Term Evolution (LTE) and the existing heterogeneous network infrastructure, hardly any service provider supports seamless cloud voice service owing to the high integration cost.In order to address this challenging issue, we present a cost-effective Virtual Room based vertical handoff (VOOH) as an Over-the-top (OTT) solution, which is network provider independent and only uses existing wireless access technologies (e.g., LTE, 2G/3G, WiFi) for connectivity purposes. That means no changes in the underlying network technologies are required that result in lower integration effort. Besides providing handoff of ongoing Voice over IP (VoIP) calls seamlessly between WiFi and LTE, unlike related solutions (e.g., Circuit-Switched Fall Back (CSFB)) VOOH presents a cost-effective OTT solution to support voice call continuity between LTE and the circuit-switched channel of 2G/3G networks. In the long term, VOOH also enables data-offloading (e.g., via WiFi) to lower the traffic load of cellular base stations.While our previous work has mainly focused on proof of concepts and experimental performance evaluations, this manuscript proposes a novel analytical and simulation model to analyze the scalability of the VOOH solution that is discussed for specific use case examples. Moreover, the impact of an enhanced VOOH (eVOOH) approach is presented to improve the system performance in terms of blocking probability. Based on the validated models, the results illustrate that eVOOH outperforms the original solution that is shown by lower call blocking probabilities.

ISDN User Part Traffic Optimization in the SS7 Network

The state of the art Long Term Evolution (LTE) mobile core networks predominantly use Session Initiation Protocol (SIP) and Real-time Transport Protocol (RTP) for transporting voice across networks. Voice-over-LTE (VoLTE) designed for LTE network based on an IP Multimedia System (IMS)) framework is the key to enriched voice communication services for the next generation networks. Emerging technologies like Rich Communication Suite, Web Real-Time Communication (WebRTC) will impart a new dimension to voice communications and harmonise voice and value added services. Many of the mobile networks and voice carriers evolved their network from traditional Time-Division Multiplexing (TDM) / Asynchronous Transfer Mode (ATM) to Internet Protocol (IP). Several interworking protocols have appeared for interexchange of Voice traffic between TDM and IP. SIP to ISDN User Part (ISUP) interoperability mechanisms have been devised. But, in spite of all the endeavours of the mobile networks move to the next generation, it will probably take some time for the networks to completely migrate from UMTS to LTE. As both the technologies will coexist, Circuit Switched Fallback (CSFB) and Single Radio Voice Call Continuity (SRVCC) are two of the most preferred options in the interim to switch from 4G to 3G when the coverage is lost. 3G networks rely still on circuit switching. It can be inferred that circuit switched networks piggybacking on ISUP for voice communication will continue. In this paper, we examine the ISUP signalling aspects to optimize the load sharing and streamline the performance of the traditional voice core networks. We will study the dependencies of the Circuit Identification Code (CIC) selection process on ISUP load sharing to derive our conclusions.

Performance of CS Fallback from LTE to UMTS

Circuit Switched Fallback (CSFB) is the most commonly used method to support voice services over Long Term Evolution (LTE) networks today, as the deployment of IP Multimedia Subsystem (IMS) is still in its infancy. In this article, we discuss the performance of CSFB voice traffic redirection from LTE to UMTS using data from live commercial networks. The key factors impacting CSFB call setup delay are highlighted. Data from multiple cell geometries including stationary and mobility conditions are presented for Mobile Originated (MO) calls towards landlines, Mobile Terminated (MT) calls from landlines and Mobile-to-Mobile (M2M) CSFB calls. Analysis results in well optimized deployments show that on an average, MO/MT call-setup time for CSFB from LTE to UMTS is around 1 sec greater than legacy UMTS. However, the results can vary depending on the network configuration and the conditions of the measurement. To illustrate the optimization of CSFB performance in real networks, we also highlight the principal call set up optimization and implementation factors impacting CSFB call setup delay and success rates. This article demonstrates that in well optimized networks, CSFB to UMTS call setup success rates can be very close to those achieved in the legacy UMTS systems.

CDMA2000 Past, Present and Future

The article looked into the possible future of 3GPP2s CDMA2000 1X and CDMA2000 1xEV-DO networks. The 3G CDMA2000 family of standards including EV-DO (Evolution Data Optimized) is in the daily use of more than 600 million customers across the globe. During the last few years the development efforts around CDMA2000 had been declined and its importance had been overshadowed by more advanced 3GPP LTE and IEEE WiMAX mobile broadband technologies. Due to these reasons, CDMA2000 operators are looking for alternative migration paths. The article investigated multiple facets for the future of CDMA2000 industry and these aspects were covered both from research and operational perspectives. The article first focused on the short term interoperability challenges to LTE and WiMAX and provided some antidotes for addressing these hurdles. The key challenges that were investigated include spectrum planning, authentication and security, end-to-end QoS (Quality of Service), voice enablement and data service continuity. The investigation revealed that a new QoS mapping mechanism between EV-DO and WiMAX similar to the one shown in the article is required for smooth operation. The analysis further indicated that CSFB (Circuit Switched Fallback) and SVLTE (Simultaneous Voice and LTE) were two techniques which could be used to support CS voice on an LTE/CDMA network; however they had different inter-radio access technology interworking requirements. In the following section performance aspects of both WiMAX and EV-DO were highlighted indicating a deep dip in throughput values once the users switches from WiMAX to EV-DO. The article concluded by discussing the future roadmap of CDMA2000 from 1X Advanced and DO Advanced perspectives. A performance comparison between 1X and 1X Advanced and EV-DO and DO Advanced was also presented.