Optimizing for VoLTE: overcoming the challenges facing operators

6 JULY 2017

This article was written by Daniel Ramirez, Director of RAN Products at TEOCO and originally appeared on The Mobile Network

The launch of a new service brings new opportunities for operators to generate revenue, boost quality of service, and retain, customers with an exclusive or innovative offering.

With the promise of high quality and high definition voice calls to customers, VoLTE (Voice over LTE) is one service that can provide a fertile ground for operators looking to differentiate. It enables operators to migrate their voice call traffic from current 2G and 3G networks to LTE networks, and to reallocate this finite spectrum to IoT or “regular” LTE instead.

But launching and supporting VoLTE is not always as straightforward for operators as it may seem. As services worldwide gain in popularity, it will place new and never-before-seen demands on operators’ LTE networks. For example, new types of traffic generate new patterns of usage among subscribers, the operator’s network may not have experienced this before, and may not have been optimized to manage this change.

However, as with other new services, the challenges presented by the launch of VoLTE can be very different in developed and developing markets.

Covering the basics
Within developing markets, a vast majority of the challenges associated with VoLTE fall into the category of ‘covering the basics’ of radio access network (RAN) design and optimization.

VoLTE is a data service, and so the RAN design must be optimized to the right levels for it to deliver the right quality. However, whereas a normal data call can be throttled down if the subscriber is in an area of low quality (high interference), a VoLTE call has a guaranteed rate of service. This means that, if the quality of the network is anything less than average, the demands of VoLTE calls can grow exponentially and this can result on a few users rapidly hogging a lot of the capacity available in a cell.

To explain how this happens, we need to understand a metric called “Call Quality Index” (CQI). This is an indication sent from the user device to the network, with CQI 15 representing the best quality and CQI 1 the worst. When the handset reports low conditions the network responds, but it does so differently for data than for VoLTE services. With VoLTE, when a device registers a CQI of 7 or lower, the network responds by sending a disproportionately large amount of cell resources to the device, in the form of Physical Resource Blocks (PRB’s), hogging capacity. This causes the overall quality of the network to decrease.

This puts specific pressure on LTE-only networks, because, without the luxury of a 3G network to fall back on, demand from VoLTE calls creates a massive capacity issue. The continued growth of this problem, from the moment the network dips to ‘below average’, is something that must be kept front of mind by operators when deploying VoLTE services in developing markets. They must get the RAN fundamentals right, as well as ensuring that the network is better than average. Otherwise VoLTE will have a negative effect on overall quality.

Optimizing the core
In developed markets, any challenges inherent in VoLTE deployment are very different because networks have been established for longer, and there is a better overall understanding of LTE. The biggest difference is when the network is of a high quality. In this case any issues around VoLTE tend to be found in the core network, and on the user devices themselves, rather than the RAN.

Specifically, VoLTE issues within developed markets are related primarily to the EPC (Authentication failures, Gateway failures, Network failures, QoS handling failures) and IMS (SIP timeouts, Bearer control issues, diameter failures, service integration issues). Challenges can also arise between domains, where it can be difficult to pin point the root cause of issues – their location and whether it was the device, the RAN, the EPC, or the IMS.

In order for operators to reap the benefits that VoLTE in both developing and developed markets can bring, preparation and planning is key. To successfully launch and support VoLTE, operators need to plan for a range of network performance issues. After all, the right mobile network planning and optimization steps will play a central role in delivering a high-quality VoLTE experience for subscribers.