In October 2015, 3GPP has decided to refer to LTE Release 13 and beyond as LTE-Advanced Pro to point out that LTE specifications have been enhanced to address new markets with special requirements such as Public Safety Services. This has been quite long in the making because a number of functionalities were required that go beyond just delivery of IP packets from point A to point B. A Nokia paper published at the end of 2014 gives a good introduction to the features required by Public Safety Services such as the police, fire departments and medical emergency services:
- Group Communication and Push To Talk features (referred to as “Mission Critical Push To Talk” (MCPPT) in the specs, perhaps for the dramatic effect or to perhaps to distinguish them from previous specifications on the topic).
- Priority and Quality of Service.
- Device to Device communication and relaying of communication when the network is not available.
- Local communication when the backhaul link of an LTE base station is not working but the base station itself is still operational.
Group Communication and Mission Critical Push to Talk have been specified as IP Multimedia Subsystem (IMS) services just like Voice over LTE (VoLTE) that is being introduced in commercial LTE networks these days and can use the eMBMS (evolved Mobile Broadcast Multicast Service) extension in case many group participants are present in the same cell to only send a voice stream in the downlink once instead of separately to each individual device.
In a previous job I’ve worked on the GSM group call and push to talk service and other safety related features for railways for a number of years so all of this sounds very familiar. In fact I haven’t come across a single topic that wasn’t already discussed at that time for GSM and most of them were implemented and are being used by railway companies across Europe and Asia today. While the services are pretty similar, the GSM implementation is, as you can probably imagine, quite different from what has now been specified for LTE.
There is lots to discover in the LTE-A Pro specifications on these topics and I will go into more details both from a theoretical and practical point of view in a couple of follow up posts.