Tag Archives: UMTS

Performance of CS Fallback from LTE to UMTS

One of the key challenges for telcos deploying LTE networks is to provide voice services. While many solutions have been proposed, Circuit-Switched Fallback (CSFB) and Voice over LTE (VoLTE) are currently the two most talked about options. A new paper in the IEEE Communications magazine looks at CSFB performance in great detail. Here’s an excerpt from the abstra

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.

Link to the paper

The reader is also referred to an Alcatel-Lucent whitepaper on the same topic.

Options for Providing Voice over LTE and Their Impact  on the GSM/UMTS Network


LTE-WLAN Interworking: 3GPP Release-12 Perspective

This presentation gives an overview of the ongoing  3GPP Study Item on LTE-WiFi interworking.

3GPP-WLAN Interworking – Part II : Requirements and Scenarios

In the previous post, I had written about the scope of the Release 12 Study Item (SI) on 3GPP-WLAN Interworking. As with any other SI, the first step was define the requirements and scenarios for this study. While the focus is on Carrier WiFi deployments only, this includes the case where an independent WLAN provider partners with a 3GPP operator to provide WLAN access to the latter’s subscribers. The requirements for the candidate solutions have been captured in 3GPP TR 37.834 and they are reproduced below:

1.   Solutions should provide improved bi-directional load balancing between WLAN and 3GPP radio access networks in order to provide improved system capacity. 

2.   Solutions should improve performance (WLAN interworking should not result in decreased but preferable in better user experience).

3.   Solutions should improve the utilization of WLAN when it is available and not congested.

4.   Solutions should reduce or maintain battery consumption (e.g. due to WLAN scanning/discovery).

5.   Solutions should be compatible with all existing CN WLAN related functionality, e.g. seamless and non-seamless offload, trusted and non-trusted access, MAPCON and IFOM.

6.   Solutions should be backward compatible with existing 3GPP and WLAN specifications, i.e. work with legacy UEs even though legacy UEs may not benefit from the improvements provided by these solutions.

7.   Solutions should rely on existing WLAN functionality and should avoid changes to IEEE and WFA specifications.

8.   Per target WLAN system distinction (e.g. based on SSID) should be possible.

9.   Per-UE control for traffic steering should be possible.

10. Solutions should ensure that access selection decisions should not lead to ping-ponging between UTRAN/E-UTRAN and WLAN.

The candidate solutions should be based on the understanding that there is no RAN level information exchange between H(e)NBs/eNBs/RNCs  and APs via standardized interface. Based on these requirements and the working assumption, a set of solutions are being currently discussed by 3GPP RAN2. These will be described in the next post.

3GPP-WLAN Interworking – Part I

3GPP-WLAN interworking support at Core Network level is already specified in the standard. As part of Release 12, a study on ‘WLAN/3GPP Radio Interworking’ is in progress to find solutions for RAN-level interworking between 3GPP and WLAN. The aim and scop of this study are defined in document no RP-122038.  The following issues are being addressed during the study:

1.   Under-utilization of operator-deployed WLAN

2.   Sub-optimal user experience when UE connects to an overloaded WLAN

3.   Unnecessary WLAN scanning leading to draining of UE battery resources

The first phase of this study identified the requirements for RAN level interworking and defined the scenarios to be considered in the study. The outcomes are captured in the 3GPP Technical Report TR 37.834.

In the current phase of this study, the focus is on identifying solutions addressing the requirements identified in the first phase and evaluation of the benefits and impacts of identified mechanisms over existing functionality, including core network based WLAN interworking mechanisms (e.g. ANDSF).

This TR is updated after every RAN2 meeting to capture the results of this study. I will summarise the key points in the coming days.