Voice over LTE:Data Voice Tango

A smartphone user often faces the issue of simultaneous unavailability of both data and voice services on the same network, making it non-realistic for him to view content online, while on a call.

Voice over LTE (VoLTE) solves this critical issue by adding voice communications over the LTE network. The technology was first introduced in February 2010, by the GSM Association (GSMA), and has been calibrated with 3rd Generation Partnership Project (3GPP standard).

It was innovated keeping in mind the troublesome process of the LTE operators to return to 2G/3G systems, for enabling voice communication. The technology terminates the current limitations of LTE, for just being used for mobile broadband over internet protocol (IP) framework, and the operators have to return to 2G/ 3G network for enabling voice communications.

VoLTE is a result of realization of operators to have a viable and standardized scheme for voice and SMS traffic since 80% of the revenue of the service providers comes from these 2 services.

At present, the delivery of VoLTE is conducted by the following 4 methods: Circuit Switched Fallback (CSFB) to 2G/3G CS; IMS based, such as 3GPP IP Multimedia Subsystem (IMS) Multimedia Telephony (MMTel) over LTE; Over-the-top (OTT) like Skype; and Circuit Switched over Packet Switched (CS over PS). Among them, CSFB is the most preferred option of the operators, as it will help the users to roam outside 4G coverage.

The US based telecom players like Verizon, MetroPCS, and AT&T are delivering voice on LTE smartphones using the CSFB technology, as the device have multiple radio support but only one radio band functioning at a time, so still when the user makes a call, the device is forced off from the LTE network, and switches to 2G/3G network for calls.

Prevailing Bumps

LTE, unlike the regular cellular telecommunications standard like GSM, lacks dedicated channels for circuit switched telephony. It is an all internet protocol (IP) system, enabling IP connection from the mobile equipment, to the main network, and then out again.

Therefore in order to provide some form of voice connection over a standard LTE bearer, some form of VoIP must be used. But achieving a full VoIP offering on LTE possess some significant problems which the operators are trying to control.

Also, the LTE spectrum exists in more than 40 bands globally, and to make an LTE chip supporting all bands for worldwide roaming is a daunting task. Simultaneously, high speed data and rapid switching from LTE/3G(EVDO & HSPA) to 2G(GSM/GPRS/EDGE & 1X) makes the battery backup unstable, compared to HSPA/EVDO phones.

Defining Interfaces

The industry is defining 3 interfaces to deliver the VoLTE service including User Network Interface (UNI), which is located between the user's equipment and the operator's network.

Roaming Network Network Interface (R-NNI) is located between the home and the visited network and is used for a user who is on roaming. And, Interconnect Network Network Interface (I-NNI) is located between the networks of the 2 parties making a call.

For deploying VoLTE, the handset or phone needs to have a software to provide the VoLTE functionality (it could be in the form of an application), and the network needs to be IMS supportive.

Operationalizing LTE in India

Since India still awaits for the arrival of LTE services, so from the Indian perspective the global condition of LTE is similar to CDMA technology, and is mostly used for data services via dongles, while the voice services on LTE are still in their very initial stage.

Though global operators like LGU+, a South Korean operator, AT&T, and Verizon are already running trials of the technology and intend to officially launch it by the year 2013, it still has a long way to go to become operational in India.

In India BWA operators like airtel and Aircel may adopt CSFB technology to offer voice over LTE devices. While providers like Tikona and Augere may continue to focus on data services.