VoLTE Optimization Challenges

MNOs need to monitor QoE and make network adjustments in real-time

Today’s smartphones are incredible feats of engineering. Packing the processing power of a mid-1980s supercomputer into a sleek, pocket-size slab, they can take photographs, play music and videos, and stream tens of megabits of data to the palm of your hand every second.

But try ringing your boss in rush-hour traffic to say you’re running late, and there’s a good chance your call won’t get through. “Mobile companies have rather lost the focus on a smartphone also being a telephone,” says Jeremy Green, a tech-industry analyst at Machina Research, in Reading, England.

Laboratory tests by Broadcom confirm that even in the best conditions, with a low signal to interference and noise ratio (SINR), users consistently rate voice quality lower on a cellphone than on a landline. Weaken the cellular link or increase interference or noise, and callers’ opinions of the experience drop dramatically because of garbled voice, dropped words, silence and dropped calls.

Interference and noise at the cell edge of the Radio Access Network (RAN) causes service quality degradation and significantly affects VoLTE quality. Noise, interference and network coverage are the leading causes of the following VoLTE quality errors:

  • Packet error – When a packet is lost or incorrectly received, it needs to be retransmitted causing delay, transmission speed reduction and may severely degrade voice quality.
  • Packet delay (latency) – The round trip time (RTT) of a packet can be delayed from network queuing, retransmission, or other issues that delay packet delivery to levels which VoLTE cannot tolerate as the quality of calls become unacceptable.
  • Jitter – Packets which experience a variation in delay of transmission over time due to network queuing, etc., causing timing gaps that result in call quality degradation when the variation is too wide.

The above errors, occurring predominately at the cell edge of the eNodeB, are the root cause of a significant number of VoLTE quality issues.

LTE incorporates end-to-end Quality of Service (QoS) that defines priorities for different services, ensuring appropriate bandwidth for different QoS Class Identifier (QCI) bearers. QoS tries to provide optimal voice quality by guaranteeing bandwidth and if required, reduces network admissions if packet errors or packet delay exceed the thresholds for the bearer.

While QoS is effective in ensuring bandwidth, it doesn’t solve the cell edge noise, interference and coverage problems, which require real-time detection and network adjustments. Mobile Network Operators (MNOs) need a centralized VoLTE optimization platform which has the ability to monitor Quality of Experience (QoE) affecting cell edge performance issues in real-time and to make network changes which result in an enhanced VoLTE service. VoLTE optimization resolves the cell edge quality errors that negatively affect voice quality, the most valuable service offering for MNOs.

How to solve VoLTE quality problems

Users expect high-quality voice from VoLTE.
Users expect high-quality voice from VoLTE.

Welcome to the Mobile Voice Optimization blog, which will be published monthly.

OTT VoIP may be the mobile network operators’ (MNOs) biggest challenge ever, threatening to change the landscape of the mobile industry forever. Voice services have been the cash cow of the industry, not only generating over half the revenue but more importantly the lion’s share of earnings. In addition, since voice quality and coverage are the leading causes of churn, VoLTE quality will impact churn.

Another major MNO challenge is the requirement to offer high enough service quality to VoLTE early adopters to gain acceptance and convince these early adopters to recommend VoLTE to their friends and colleagues. Therefore, if VoLTE is going to succeed and be used by MNOs to combat the threat of OTT VoIP these VoLTE early adopters need to be treated as VIPs.

LTE is significantly more efficient than previous technologies, but since it’s based on an all-IP network, it requires voice calls to traverse the network utilizing VoIP. As everyone knows, VoIP calls struggle to guarantee service levels, but that’s exactly what’s required if MNOs are going to match the service quality level of existing circuit switched calls. VoLTE quality problems fall into 3 categories as follows:

  1. Call set-up failures – VoLTE utilizes IMS (to set-up the VoIP sessions), which is extremely complex.
  2. End to End QoS – Congested cells cause havoc with VoIP calls; therefore, the dedicated bearer to deliver guaranteed bandwidth even when the rest of the cell is congested must be monitored.
  3. Cell Edge Issues – LTE networks are still wireless networks and have the same RF issues as other wireless networks. Therefore when a VoLTE user is on the edge of the cell interference and noise increases often times above acceptable thresholds.

MNOs have automated LTE call trace and bandwidth verification tools to manage the first two categories above, but RF optimization is still very much a manual task. Today, VoLTE is optimized in the same manner voice calls have been optimized for years, but VoIP calls are much more susceptible to higher levels of bit errors caused by noise and interference that change constantly on the edge of LTE cells. Existing optimization methods such as drive testing and walk arounds are just not sufficient to meet the quality threshold required for VoLTE calls. The problem is VoLTE users on the edge of the cell can experience a worse user experience than VoLTE users in the rest of the cell.

A new optimization solution is required in order to automatically monitor VoLTE call quality for every user in real time. The platform needs to provide real-time incremental network adjustments to resolve these issues with a real-time feedback mechanism that verifies results.

Only with such a platform will MNOs resolve the problems associated with the third and most challenging VoLTE quality problem category and harness its ability to combat the OTT VoIP and churn challenge. At Optulink, we’re working to make sure MNOs get what they need to be successful in the VoLTE transition.