Earlier this week I ran a post on voice handover from LTE to GSM (or UMTS) and received an interesting comment from a reader who was of the opinion that there is not much benefit coming from such a handover. He said that instead, the industry should make LTE phones in the future that use GSM for voice and LTE for data.
At first I thought, yes, that's what CS fallback is all about, which nobody, me included, really wants. Personally, I don't like the approach because it significantly increases the already long call setup times and falling back to a legacy network for your bread and butter service is not how wireless technology should advance. But then I read the comment again and realized that the author suggested a devcie that could do GSM and LTE simultaneously. An interesting idea!
And it might even be possible as something similar already exists today! Multi SIM phones that have two transceiver units so both SIM cards can be active in different networks and on different frequency bands simultaneously. This shows that devices with two independent transceivers are practical. In the case of the dual transceiver LTE phone there could be one LTE/UMTS/GSM chain and one independent GSM chain that is only used for voice telephony. Both could work with the same SIM card as long as the GSM chain only communicates with the circuit switched GSM network. Should the LTE/UMTS/GSM chain have to fall back to UMTS or GSM, the GSM only chain could be deactivated in favor of a combined treatment of CS and PS. It would make things a lot easier for the network people.
But we are moving towards an IP only world both in the fixed and the wireless telecommunication domain and this approach doesn't fit into this picture. So I keep preferring an IP based voice solution for LTE which has a handover option to GSM and a single transceiver chain in the mobile device. However, I can very well accept that there are other opinions out there concerning this matter so thanks for the comment, it got me thinking!