Page 392 - From GMS to LTE

378 From GSM to LTE-Advanced Pro and 5G

Service (QoS) for a bearer (in the same way as for VoLTE) or the use of eMBMS
(Multimedia Broadcast Multicast Service) for a group call multicast downlink data flow.
In contrast, current 2G group call implementations for PMR require deep integration
into the radio chipset as pressing the talk button triggers radio‐layer messages to the
circuit‐switched infrastructure in a control channel. Requesting the uplink in LTE PMR
also requires interaction with the PMR application server in the network but this is
performed over an IP connection and is completely transparent to the radio stack on
the device as well as to the radio network.

PMR on the IP Layer and Not Part of the Radio Stack
PMR services are based on the IP protocol with only a few interfaces to the underlying
network for multicast and quality of services. While LTE is gradually exchanged for
something faster or new radio transmission technologies are introduced in 5G, the
PMR application layer can remain the same. This is, again, unlike 2G PMR, where the
network and applications such as group calls were a monolithic block and thus no evo-
lution was possible as the air interface and even the core network did not evolve but
were replaced by something entirely new.

Only Limited Radio Knowledge Required by Software Developers
No deep and specific radio‐layer knowledge is required anymore to implement PMR
services such as group calling and push‐to‐talk on mobile devices. This allows soft-
ware development to be done outside the realm of classic device manufacturer
companies.

Upgradeable Devices in the Field
Performing software upgrades of devices over the air has only become feasible with 3G
and 4G networks. 2G PMR devices used today cannot typically be upgraded over the air,
which makes it very difficult to add new functionality or to fix bugs and security issues
in these devices. Current devices which would be the basis for PMR devices can easily
be upgraded over the air as they are much more powerful and because the LTE network
is capable of supporting large software downloads.

Network Coverage in Remote Places
PMR users might want to have LTE in places that are not normally covered by network
operators because it is not economical. If PMR organizations paid for the extra coverage
and if the network was shared, there could be a positive effect for consumers as well.
Another option, which has also been specified, is to temporarily extend network cover-
age when needed by using relays, e.g. installed in cars.

5.7.3 Challenges of Mission Critical Communication for LTE
While LTE technology doubtlessly offers many advantages over 2G PMR networks a
number of challenges still remain.

Speed of Evolution in PMR Networks
The first and foremost problem PMR imposes on the infrastructure are the very long
decision and implementation time frames in the sector. While many consumers