Project 25
LTE portable radio for some time
and it has been very successful,”
reports Elder. “It shows that there
is a market for an agnostic device.”
At IWCE 2019 in March, Harris
unveiled the XL-185 Mobile, which
it claims is the first vehicular P25-
LTE mobile radio.
“I think it is proven now that
converged or hybrid devices are what
is needed – at least today – and that
is where we have driven our strategy,”
says Teel. “The XL-200P is in the
traditional two-way radio form factor
that public safety users trust, with
LTE baked in as well.”
Florida-based BK Technologies
clearly thinks so too, as it is
launching a hybrid device in the
shape of its BKR 9000 Multi-band
Radio this year, supporting P25 VHF
and UHF bands and LTE 700MHz,
800MHz and 900MHz.
Motorola Solutions has so far
chosen to develop P25 and LTE
terminals, such as the LEX L11 rugged
smartphone, separately. Lonnett says:
“Critical communications users like
the traditional radio form factor, but
administrators and covert operatives
use cellular commercial devices as
standard,” he says. “It’s about the right
form factor for the job role.”
It is also about routing the right
traffic over the right network. A case
in point being Motorola’s decision to
team up with Sierra Wireless to offer
the latter’s AirLink LTE in-vehicle
routers, so first-responders can send
broadband data packets on the move.
Its MC-Edge Intelligent Gateway
provides a hub for P25, LTE and LoRa
IoT data to be transmitted over already
available and reliable P25 networks.
P25 standard
While manufacturers explore these
avenues, the US Telecommunications
Industry Association (TIA)’s TR-8
(Mobile and Personal Private Radio
Standards) Engineering Committee
continues to improve and augment
the P25 standard. Key work items at
present include Group Regrouping,
do,” acknowledges Davis. “It has
taken time, but we should see some
publication later this year.”
P25-LTE Interworking
TIA is also working with ATIS
(Alliance for Telecommunications
Industry Solutions) to deliver a
standard to enable interoperability
and interworking between P25 and
3GPP LTE. The two organisations
are creating a study document for
the interworking function (IWF) to
define behaviours for services that are
common to both technologies, such
as group, individual, broadcast calling,
encryption and emergency calling.
“3GPP has already defined an
IWF,” points out Davis. “You could
describe it as a black box with the
standard 3GPP interfaces on one side
and the standard P25 interfaces on the
other side. If you take the example of
group calling, a call can be initiated
by either technology, so what we are
looking to define is the sequence of
messages necessary to enable that
voice service. You have a standard
message coming in one side and a
standard message coming out the other
side, but in between those messages
need translating.”
The study work is divided into
two phases. Phase 1 covers P25
conventional and trunking call types.
Joint LMR-LTE and analogue FM
interworking will be addressed as part
of Phase 2. Phase 2 will also tackle
individual voice calls and control
Key Fill Interface extensions beyond
Key Fill Device, Link Layer Security
Services and interworking between
P25 and LTE.
Group Regrouping allows a
dispatcher to group multiple talk
groups on different channels onto the
same channel rather than patching
them across to each other. Andy Davis,
chair of TIA TR-8, reports that the
current focus is on the procedures for
exchanging the necessary supporting
messaging for group regrouping.
A second review of Key Fill
Interface, which enables encryption
and encryption key management, has
been completed and another revision
is being drafted to include comment
resolutions. The revised document is
expected later this year.
“Link Layer Encryption has seen
the most activity over the last few
months,” says Davis. “This is a fairly
large effort as it is designed to
encrypt the whole air interface. It
impacts on FDMA and TDMA voice
and data services for trunking and
conventional systems.”
The air interface encryption will
complement the already standardised
voice and data payload encryption.
The new work will also now protect
the control signalling and caller
identities, while applying a second
layer of encryption for the encrypted
voice and data payload. Various
aspects of link layer encryption
key management services are still
under discussion. “There is a lot to
While handheld
devices still
have their place,
police cars are
increasingly
becoming
connectivity hubs
for a range of
wireless protocols
Critical communications
users like the traditional
radio form factor, but
administrators and covert
operatives use cellular
commercial devices
July 2019 @CritCommsToday 17