Voice Over LTE

LTE being a packet based technology; there have been ongoing discussions about Voice implementation over LTE. This is going to be crucial as operators would want just one network to be maintained to reduce their CAPEX and OPEX. There have been quite a few solutions being pondered upon in the 3GPP community.

One way is the CS fallback mechanism to address this. By CS fallback they mean that for voice LTE will handover the call to 2G/3G networks. This is done by MME registering the device with the 2G/3G networks and acting as SGSN communicating with MSC for voice signaling. This will ensure that the voice quality is maintained as of today, but this would also mean that if an existing packet data call is in progress, then it might get suspended or handed over to 2G/3G networks. I am not sure is this will be good idea since earlier generation networks will not have the bandwidth and the capacity to support LTE multi-media applications.

I read a paper about CSoHS (Circuit Switched over HSPA+) . This explains about how HSPA+ radio bearers will be used to carry voice traffic but core used will be CS core.
This can be done via software upgrade on UE as well as RNC. This would add de-jitter and time warping mechanism to ensure smooth voice quality. I hope this can be further extended to LTE, which is approach pursued by VoLGA which stands for Voice over LTE via Generic Access (Thanks to Steve for clarifying this!!). The difference between 2 approaches is avoiding the fallback to legacy networks and also using high capacity radio bearers. Also user not be required to suspend/handoff his data call.

Though these above approaches sound good for now, they would still require different networks to be maintained. Going further, IMS will have an important role to play as it can support end-to-end voice over IP services with call signaling and switching functionality required for voice. It also supports Voice Call Continuity (VCC) that can enable gradual deployment of VoIP.