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The Wireless Blog from Unwired Insight discusses the latest developments in wireless networks and services, including the new technologies and architectures of LTE-Advanced and 5G. For expert advice on 2G, 3G, 4G and 5G mobile systems and standards, including GSM, UMTS, LTE, LTE-Advanced and 5G-NR, please contact us.

Voice over LTE (VoLTE) faces a technology and marketing battle

Photograph of Alastair BrydonThe latest “Evolution to LTE Report” from the Global mobile Suppliers Association (GSA) includes, among other things, a (very short) list of Voice over LTE (VoLTE) launches around the world. Over two years ago I expressed my concern at the lack of long term solutions for voice over LTE. While the situation is gradually becoming clearer, there is still some way to go before there is wide deployment of a common approach to LTE voice.

Unlike previous mobile systems, such as GSM and UMTS, LTE does not provide a circuit-switched method for carrying voice traffic. However, voice services still generate something like 70% of network operator revenues worldwide. LTE is fundamentally a packet switched system, and therefore voice traffic must be a carried either as Voice over IP (VoIP) or by relying on existing 2G or 3G systems.

It is now generally accepted that the preferred long term solution for voice and messaging over LTE is VoLTE, which has been supported by the GSM Association (GSMA) since 2010. VoLTE is critically important for mobile network operators, by enabling them to integrate telecom grade voice telephony with a range of rich media services over a variety of packet switched networks and devices. However, there are significant challenges to overcome in implementing VoLTE and a number of stop-gap solutions have been put in place in early LTE networks. The longer it takes to implement the ultimate solution, the stronger become third party “over the top” VoIP services such as Skype and Google Talk, which undermine network operator revenues.

VoLTE is underpinned by the IP Multimedia Subsystem (IMS), which provides a framework for basic voice and messaging services and integration with a variety of multimedia applications. The approach offers some important potential benefits:

  • a standard method for carrying voice and messaging, integrated into LTE devices and networks in much the same way as today’s voice services
  • interoperability between different networks and devices
  • economies of scale enabled by a common approach across multiple platforms
  • roaming between networks
  • integration with rich media services including presence, messaging, video telephony, video sharing, file sharing, desktop sharing
  • high quality of service achieved by tight integration with the underlying LTE transmission methods e.g. reserved bandwidth
  • high definition (HD) voice, enabled by wideband codecs and the high data rates of LTE
  • lower battery consumption than previous voice communication methods
  • fast call setup (less than 1 second)
  • automatic fallback to 2G/3G services when outside LTE coverage
  • the facility for third parties to develop applications building on the capabilities of VoLTE

However, there are significant challenges to overcome in delivering VoLTE, including:

  • introduction of an IMS core and its integration with other network systems
  • implementation of radio network features to prioritise VoLTE traffic over other classes of IP data
  • co-ordinated operation of devices, radio network, core network and service platforms to provide an end-to-end path with the quality of service parameters required by voice
  • scheduling of variable packet sizes generated by VoLTE, to maintain system performance
  • management of IMS protocol stacks and registrations to support multiple applications in a device
  • possible routing of VoLTE traffic to dedicated network destinations
  • new approaches to charging for voice

So far only a small number of network operators have launched commercial VoLTE services. In South Korea, KT, LG U+ and SK Telecom are all early adopters of VoLTE. In the USA, metroPCS already offers VoLTE in some of its markets and Verizon Wireless has announced that it will launch services late in 2013 or early in 2014. VoLTE is particularly attractive for CDMA operators, such as metroPCS and Verizon Wireless, because switching between LTE and CDMA to deal with voice traffic is cumbersome and consumes significant power in the mobile device. Therefore, moving to a pure LTE solution will have capacity, performance and battery-life benefits.

Most network operators are taking their time with VoLTE. Recognising the critical importance of voice revenue they know it is crucial that VoLTE delivers on its promises. Rushing to market with immature VoLTE services could be highly damaging. If the quality, reliability or capabilities of VoLTE are perceived as no better than low-cost or free over-the-top services, there is a risk that voice revenues could rapidly evaporate. In many cases LTE network operators have implemented temporary solutions for voice telephony, which either fall back to existing 2G or 3G circuit switched services, or employ power-hungry dual-radio solutions.

Mobile network operators must strike a careful balance. The longer they wait to introduce VoLTE, the more mature the technology will be and the broader the ecosystem of devices, networks and applications will become. However, all the time, over-the-top VoIP services are gaining market traction, customers and usage, while also improving their service capabilities and voice quality. Also, short-term solutions such as circuit-switched fallback will become increasingly entrenched over time and it will become more difficult to phase them out and introduce new solutions.

While over-the-top VoIP services may not be able to meet the reliability of traditional circuit switched voice services, their low cost makes them an attractive option. Downloading a Skype app to a mobile handset (or integrating it into the operating system) will be commonplace and services such as Skype will be embedded in the psyche of many users, particularly the younger generation who have grown up with them as free communication services.

The battle over mobile voice will not be won by technology alone. Recognising this, the GSM Association (GSMA) has launched the joyn initiative as a focal point for the development of an ecosystem that enables mobile network operators to deploy Rich Communication Services (RCS), which exploit VoLTE and the associated IMS architecture to deliver integrated voice, SMS, presence information, instant messaging, video and file sharing across devices and networks.

As the technology and marketing battle heats up, the only thing that is clear is that the future for mobile voice will remain highly uncertain for sometime yet.

Dr Alastair Brydon has worked in digital radio communications for over 25 years. He provides expert advice on 2G, 3G and 4G mobile systems and standards including GSM, UMTS and LTE. He has written over 40 reports on the development of wireless technologies and services and has acted as an expert witness in major patent disputes.

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