The worldwide implementation of Long Term Evolution (LTE) continues as market requirements for greater data-communications capability grow. In the midst of the excitement over increased available bandwidth, it is easy to overlook one crucial problem: LTE does not support voice communication. In other words, current LTE networks can only handle data. Understandably, the consumers who view voice services as the core function of mobile phones see this issue as a deal breaker.

As a result, states Paul Beaver, Products Director at Anite (see photo; www.anite.com), operators risk being superseded by OTT providers, such as Skype, in the mobile voice market. Beaver notes that the industry is increasingly determined to develop a solution that will allow voice calls to be made over LTE networks. Voice-over-LTE (VoLTE) technology also will enable operators to pioneer new business models, reinstating them as the primary purveyors of premium voice services.

Paul Beaver, Products Director at Anite.

VoLTE trials are now being performed. Device manufacturers, chipset vendors, and operators are all testing VoLTE solutions in the laboratory. With VoLTE still in a state of technological infancy, however, mobile communications network operators have a diverse range of approaches for integrating VoLTE with networks and devices. With such varied interpretations, there can be no “one-size-fits-all” VoLTE solution. Instead, operators will have to rigorously test a diverse range of variable conditions—all of which could potentially impact their ability to deploy and uphold VoLTE.

Beaver believes that mobile subscribers will continue to expect top-quality voice services on their mobile devices. As a result, a “best effort” Voice-over-Internet-Protocol (VoIP) -type service, such as Skype, will not be sufficient. VoLTE must provide a top-quality service or risk gaining a negative perception among consumers. Upon VoLTE’s introduction, network signaling levels will naturally escalate, putting networks under increased strain. Operators will need to prepare for this signaling issue and build this scenario into their testing program.

Of course, VoLTE’s ultimate success will be determined by its ability to deliver top-quality voice services across an all-IP network and on the latest LTE devices. Cooperation within the mobile industry is a necessity if VoLTE is to emerge as a viable commercial possibility.

According to Beaver, a rigorous testing program will be a decisive factor in determining the success of VoLTE’s introduction—especially considering the variety of implementations taking place. This could be a costly and labor-intensive process. By leveraging lab-based testing, however, Beaver asserts that handset manufacturers, chipset vendors, and mobile-communications network operators could utilize a simulated network environment to test both component interoperability and audio quality. Operators could then avoid relying upon live network testing and expensive, time-consuming device field trials.

LTE’s Choices For Voice Support

Voice-over-LTE (VoLTE) is based on the IP Multimedia Subsystem (IMS) network. It has specific profiles for control and media planes of voice service on LTE, which are defined by GSMA in PRD IR.92. This approach results in the voice service being delivered as data flows within the LTE data bearer. As a result, there is no reliance on the legacy circuit-switch voice network, eliminating the need to maintain that network.

LTE supporters preferred and promoted VoLTE from the beginning. Yet the lack of software support in initial LTE and core network devices prompted a number of carriers to promote Voice-over-LTE-Generic-Access (VoLGA) technology as an interim solution. The idea was to use the same principles as the Generic Access Network [GAN, which also is known Unlicensed Mobile Access (UMA)].

GAN defines the protocols through which a mobile handset can perform voice calls over a consumer’s private Internet connection. This approach never gained much support, however, because VoLTE (IMS) promises much more flexible services. Yet it also calls for the entire voice-call infrastructure to be upgraded. In addition, VoLTE will require Single Radio Voice Call Continuity to smoothly perform a handover to a third-generation (3G) network in case of poor LTE signal quality.