RAN optimisation brings VoLTE benefits for SK Telecom but challenges others

VoLTE optimisation doesn't stop with the IMS, the radio network holds the keys to a good customer experience, and its complexity is delaying rollout, TMN hears.

Radio network optimisation is a critical component in ensuring consumers get the experience they expect with VoLTE, according to speakers at Informa’s LTE Voice conference held this week.

A presentation from SK Telecom demonstrated that even companies that have had VoLTE rolled out for a while can still improve. SK Telecom started VoLTE services in 2012, but saw a steep rise in customer satisfaction with the service from 2014 and 2015, when surveys revealed that 76% of customers were happy with the service quality, compared to just under 60% the year before..

This came about after the company better optimised its radio access network for VoLTE, according to Chloe Lee, Director of IMS and Project Manager for HD Voice at the carrier.

Speaking to TMN after her talk, SKT’s Lee said the operator took steps to identify and monitor important KPIs for VoLTE  and optimise the network around those. The operator also deployed network-based optimisation tools such as TTI bundling, and call prioritisation for VoLTE sessions over other data sessions in congested cells, she said (going beyond the dedicated bearer that VoLTE establishes in any case.)

Petrit Nahi, of VP of Mobile Access at Tektronix Communications, a NETSCOUT company, also has longer experience than most of VoLTE – having supported Metro-PCS with its VoLTE launch. He told TMN that operators needed to build up a “heatmap” of VoLTE QoE, which requires deep knowledge of cell coverage and handovers, as well as where and when call attempts and drops were happening, and the locations of SRVCC and CSFB handovers.

That can be complex in the RAN, where the speed and scale of LTE rollouts have often meant that existing network maps and monitoring are outdated or ineffective, he said.  “LTE operators are often rolling out aggressively and fast and that often means a lot of rehoming – and that affects handovers,” Nahi said. That can lead to reporting of “false positives” for LTE-CS handovers, for example.

The issue for operators is that VoLTE is in many respects a “stand still” service, ending up with offering customers reliable voice. Running too hard just to stand still doesn’t sound too attractive. Operators already have their hands full with understanding the core network and especially IMS implementation for VoLTE. Hearing that they also need to add RAN monitoring and optimisation around VoLTE-specific KPIs is not likely to be welcomed.

Nahi’s view is that it will be worth it because operators should be looking to exceed their current quality thresholds;  he sees VoLTE as a foundational service to be followed by other VxLTE and RCS. “VoLTE sets the foundations,” he said, “and the QoE has to be better if they hope to enable other services.”

The difficulty of lining up the network for VoLTE has lead many operators to jump off first with VoWiFi services. Keith Mumford, VP technology of Taqua Wireless, said that one key reason that operators are leading with VoWiFi services is “because it’s easier”.  Mumford said “tuning” the LTE radio network in terms of coverage and dealing with overlaps  and handovers, plus the complexity of a mass deployment  where the service has to work for everyone from the get go, has proved arduous. That in turn meant that VoWiFi has served as a stepping stone on the road to VoLTE.