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Qualcomm today announced a LTE to WCDMA call using one of its MSM8960 Snapdragon S4 chipsets, and a VoIP-over-LTE connection. Voice-over-LTE (VoLTE) is a 3GPP specified feature that enables seamless switching between a 4G network and a 3G network.

Up until this point, the main use of LTE has been for mobile data traffic. The LTE standard only supports packet switching with its all-IP network. Voice calls in GSM, UMTS and CDMA2000 are circuit switched, so with the adoption of LTE, carriers will have to re-engineer their voice call network.

Voice-over-LTE enables new globally interoperable multimedia services on LTE smartphones with handover of a voice call from LTE to WCDMA. The lack of software support in initial LTE devices as well as core network devices however led to a number of carriers promoting VoLGA (Voice over LTE Generic Access) as an interim solution.

MetroPCS may deploy VoLTE in the first quarter of this year, making it the first operator worldwide to commercially launch VoLTE, the GSMA-backed standard for delivering voice calls over LTE networks. MetroPCS uses CDMA technology to offer service in addition to its 4G network using LTE technology. AT&T Mobility uses UMTS for their voice service and offers LTE on 700 MHz.

Verizon Wireless does not plan to let LTE voice calls roam on to its CDMA network, says Wireless Week, when it introduces voice over LTE (VoLTE) smartphones later this year.

“VoLTE will not hand down to 1X,” Verizon Wireless product development executive Marjorie Hsu told Wireless Week, referring to Verizon’s CDMA 1X Advanced network.

Supporters of VoLTE include nearly all of the major operators as well as equipment vendors such as Alcatel-Lucent, Ericsson and more. Infonetics Research predicts that 78 percent of the operators that participated in its study said that they will have VoLTE, RCS (rich communication service) and/or VoIP over 3G deployed by 2013.

Last month, Microsoft demonstrate pre-release Windows 8 on Snapdragon S4 processors with LTE support. Demonstrations of pre-release Windows 8 on the Snapdragon S4 MSM8960 reference hardware tablet with LTE were held during Dr. Paul E. Jacobs’ opening keynote address at CES in Las Vegas.

The handover mechanism is supported on Ericsson’s carrier products, including LTE/WCDMA/GSM RAN, Evolved Packet Core, MSC and IMS to work towards VoLTE enabled LTE smartphones.

Two options for carriers have momentum: Circuit Switched Fall Back (CSFB) and LTE VoIP-based Single Radio Voice Call Continuity (SRVCC). The latter is widely supported in the industry and has been recommended by the LTE OneVoice Initiative, which has the support of some of the world’s largest operators and network equipment providers and has been endorsed by the GSM Association (GSMA).

The first operators are expected to begin deploying Single Radio Voice Call Continuity (SRVCC) during 2012, followed by more global commercial launches in 2013.

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