Long term evolution (LTE) networks have gained global recognition for their ability to achieve high speed data transmission. However, one of the emerging applications of LTE that is witnessing increased deployment is the IP-based voice and video calling solution, called voice over LTE (VoLTE). Operators can deliver high capacity mobile broadband services and launch interoperable communication services using VoLTE. The key VoLTe services are high definition (HD) voice, video calling, HD conferencing, IP messaging and contact management.

VoLTE is also gaining recognition due to its advantages as compared to over-the-top (OTT) applications such as Skype and FaceTime. According to a report by Ericsson, there are currently no quality of service (QoS) measures in place for OTT solutions, no handover mechanism in the circuit switched network and no widespread interoperability of services between different OTT services and devices. Therefore, OTT solutions cannot provide a satisfactory experience. Further, the uptake of OTT services is directly dependent on mobile broadband coverage, which limits its adoption.

Across the globe, operators have started launching commercial services for voice and video calling over LTE. VoLTE was launched in South Korea in August 2012 and since then, the VoLTE ecosystem has evolved and VoLTE-capable devices have gained traction. Currently, there are three commercial networks that offer the service in South Korea and several device vendors offer different models of VoLTE smartphones. During 2014, several operators in Asia and North America launched VoLTE services. According to a recent GSA report, by 2014, 80 operators in 42 countries or over 22 per cent of operators had invested in VoLTE deployments, studies and trials. Meanwhile, 14 operators had launched HD voice services using VoLTE in seven countries. A large number of operators are planning to launch these services in 2015.

Case for India

Although VoLTE has generated limited interest in India so far, both in terms of testing and deployment, a strong potential exists for it. The following are the key benefits that the Indian telecom industry can avail of with VoLTE deployments:

HD voice: HD voice offers improved sound quality over conventional voice calls by utilising a wider range of frequency coverage. This service can be provided on LTE networks apart from wideband code division multiple access and GSM networks. The HD voice feature of VoLTE services creates a strong case for VoLTE deployments in India as voice continues to be the dominant communication medium for users in the country. The improved quality of experience can also help in increasing voice ARPU for telecom operators.

RCS and VoLTE interoperability: VoLTE provides operators with a complete solution to evolve their voice business towards an all-IP communications network. This is achieved by evolving the installed base circuit switched core network to an IP multimedia subsystem (IMS) core network, which supports rich communications suite (RCS) services. RCS has an edge over OTT services. Further, these services allow telecom operators to better serve their enterprise customers. At present, several operators across the globe are undertaking trials for RCS and VoLTE interoperability.

Faster call set-up time: Under VoLTE, the call set-up time can be reduced to 1 second. This is a significant improvement over the typical 4 second target in circuit switched fallback (CSFB) systems on 2G and 3G networks.

Spectrum efficiency: As per industry reports, vendors consider VoLTE to be up to 95 per cent more spectrum efficient than legacy voice technologies as it works in conjunction with the underlying IMS to enable more simultaneous calls per MHz of spectrum. This further enables operators to pack in more voice calls per MHz and free up more spectrum for data users. Spectrum efficiency can also facilitate a reduction in spectrum usage costs that are associated with operators’ adjusted gross revenue.

Phase-out of multiple overlay networks: Once VoLTE has been established on a given network, operators can migrate all 2G and 3G subscribers to an LTE environment. Thereafter, operators can phase out various legacy 2G and 3G data overlays (including GPRS, EDGE and HSPA) to achieve a simplified all-IP network. This can further help reduce the operational expenditure incurred by operators.

Simplified mediation and billing: VoLTE deployed on an IMS-based architecture can help simplify the operations support systems (OSS)/business support systems (BSS) used by operators, particularly the mediation and billing elements. In fact, operators can derive benefits from simplified OSS/BSS solutions, saving them from the issues of complexity of integrating silo systems.

Reduced energy usage and the industry’s carbon footprint: VoLTE obviates the need for connections to switch from the LTE network to a circuit switched network for establishing and terminating voice calls. Such switchovers and switchbacks not only require more network elements to be active but are also a drain on the handset’s battery life. VoLTE implementations help operators to significantly reduce their direct as well as indirect energy usage. Indirect energy reductions would be achieved through other VoLTE benefits such as spectrum efficiency, removal of redundant data access layers and simplified operations. VoLTE would require the network to be IMS based, which would bring in a greater degree of traffic intelligence for conserving energy during idle states.

The greatest roadblock to VoLTE deployment is the lack of IMS in the Indian domain. This deters telecom operators from leveraging their LTE assets. For instance, Bharti Airtel has been unable to offer HD IP voice that is possible on an LTE network. Instead, the company is using CSFB technology, which allows LTE to be only incrementally superior to 3G. With CSFB, LTE becomes a network that supports more bandwidth than 3G and offers voice as well. However, it falls short of achieving the above benefits enlisted for VoLTE.

Another persistent challenge is the poor financial condition of telecom operators. Their high debt burden, owing to large spectrum costs, has restricted investments in developing the LTE ecosystem. In such a scenario, infrastructure sharing agreements will ease the expenditure for establishing the VoLTE infrastructure. Another major hurdle in the large-scale roll-out of VoLTE is the frequency bands in which the broadband wireless access spectrum has been allotted. For India this is in the 2300 MHz band. Signals in this spectrum band have a shorter coverage area and require more cell sites in a given licensed service area. This not only increases network costs, but also makes coverage in sparsely populated rural areas harder to achieve. This can add to the cost of providing VoLTE services. However, refarming of existing spectrum and migrating to LTE in a phased manner can help address this challenge. In addition, telecom operators need to test the viabil-ity of VoLTE deployment in the lower frequency bands.

Paving the way for VoLTE deployment

Although the country has started witnessing initial 4G launches, these services have been oriented towards data. However, India is gradually exploring the posibility of deployment of VoLTE technology with companies like Reliance Jio Infocomm Limited (RJIL) and Tata Communications, which are taking initial steps towards the same. According to analysts, RJIL, as part of its upcoming launch of 4G services in 2015, is likely to launch frequency division duplex VoLTE services by using its spectrum in the 1800 MHz band. The company had acquired this spectrum in 14 circles during the February 2014 spectrum auction. Meanwhile, Tata Communications is planning to introduce solutions that can support telecom operators to offer VoLTE services in the country.

Despite this growing interest in VoLTE, its deployment remains at a nascent stage in India. This is due to the fact that the current focus of 4G telecom operators is on building demand for their 4G data services. Once this is achieved, they will consider foraying into the VoLTE domain. Going forward, as the 4G ecosystem evolves in India, VoLTE will gradually come to the forefront of telecom operations. This will not only help increase operator profits, but also mark the return of voice services as the mainstay of the Indian telecom industry.