In terms of subscriber growth, LTE is proving to be the most successful mobile communications standard ever. According to the latest figures produced by Ovum for the GSA1, LTE and LTE-Advanced subscriptions worldwide reached over a billion by the end of 2015—a total of 1.068 billion, more than half of which had been added during the last year, representing a staggering 107% annual growth rate.
While data is now the dominant service, voice remains a crucial part of the subscriber offering. Voice over LTE (VoLTE) holds the promise of providing users with crystal-clear, high-definition (HD) call quality combined with much greater spectral efficiency and capacity compared with conventional circuit-switched calls over legacy 2G and 3G networks. This means that it is easier for a caller not only to hear clearly what the person at the other end of the line is saying, but also to detect their tone of voice, giving a much richer overall experience. For operators VoLTE offers much lower OPEX and CAPEX for voice calls by including them as part of their data packages.
So why have less than 10% of the 480 operators who have so far launched LTE or LTE-Advanced networks started offering VoLTE services commercially? At least part of the answer can be found in the results of preliminary VoLTE trials and commercial deployment worldwide, which indicate that poor VoLTE call quality is being reported, defeating one of the prime motivators for the service. This degradation can manifest itself as poor audio reception, digitization, and waterfall noise, as well as dropped calls. A recent industry report states that the frequency of call drops on VoLTE is 4 – 5 times higher than for 2G and 3G calls, a huge number in total given the higher density of calls that it is able to handle. Some of these dropped calls may be due to a failure in handover between LTE cells, or a failure to correctly implement fallback to a legacy circuit-switched network using SRVCC (Single Radio Voice Call Continuity) where LTE coverage becomes unavailable.
These issues largely go unnoticed by conventional network monitoring and optimization systems, which only detect the integrity of the radio access network and not the actual user experience. Methods used to measure the quality of experience of circuit-switched 2G and 3G voice services are not applicable for evaluating VoLTE performance in an all-IP network. At the same time LTE validation techniques based on patterns of data usage alone cannot adequately predict the effect of network impairments on VoLTE subscribers. Dropped packets that may have minimal effect on a data transmission can seriously impair a voice call being carried over the same data network.
Using SON for LTE (Self-Organizing Networks) to identify usage patterns and improve network performance through user-centric KPIs will play a large part helping operators pave the way to a reliable VoLTE service, with the capability to give users the quality voice experience they expect. Issues that impair quality need to be detected and pinpointed in terms of both the specific network issues that are the root cause and the types of subscribers that are being affected. A system that processes this data against KPIs via big data analytics can inform the SON decisions and actions that will automatically keep the network in a state of optimal performance.
The ability to identify which LTE cells are giving the best and worst performance, and whether any specific device models give poorer performance—or are even incompatible with the VoLTE service—will allow the operator the insight to improve the service. Also where VoLTE calls are being dropped, it is instructive to know in which direction this is happening, and whether the problem lies within the operator’s network or the one that the third party is using.
LTE operators should not take the risk that poor quality could undermine their VoLTE launch, thus defeating their main objectives and compromising customer loyalty and satisfaction. Using a customer-experience based SON solution can assist RF planning teams in deploying and trialing with VoLTE on their existing LTE infrastructure. With the right choice of SON solution, detecting and mitigating low quality VoLTE calls requires no additional effort and can be an integral part of the network optimization process.
1 GSA data announced on January 25, 2016
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