Joe Nielson
Radio Terminology/Basics
 What is “trunked radio”
 TETRA

 Technology
 Standards
 Features
 TETRA today
Base Station – Tower site “repeater”
radio
 Portable Radio – Hand held, lower
power, when compared to Mobile
 Mobile Radio – High power when
compared to portable radio (larger
antenna)
 PMR – Professional Mobile Radio, radio
systems that are used by public safety,
and other organizations that use the
above equipment.

The PMR market requires constant reliable
communication and needs to allow for capacity
increases during major incidents
 This makes it necessary to have tower sites to
increase the range of communication for
portable and mobile radios

Along the
M5
motorway
in England

A radio channel is a single band of
frequency that can successfully deliver
radio communications
 Either voice or data

The size of the channel, or bandwidth
is determined by the channels frequency
tolerance and the type of transmission
 Cannot have channels interfering with each
other
Ex: Center frequency = 150 kHz (f0)
bandwidth allocation = 50 kHz
Then the 150 kHz frequency cannot be modulated above 175
(f2) kHz, or below 125 (f1) kHz
The channel is identified by a distinct
frequency, and has to be modulated in
order to transport a message across the
channel
 Some types are frequency, amplitude,
phase modulation and pi/4 DQPSK
(Differential Quaternary Phase Shift
Keying)
 Due to technology improvements, it is
now possible to have the same amount
of channels with less bandwidth

TETRA in Europe - 380-385/390-395 MHz
Asia Pacific and South America: frequencies 806-824//851-869 MHz
Able to operate between 300 to 1000 MHz
http://ptolemy.eecs.berkeley.edu/eecs20/si
debars/radio/freqchrt.pdf
Digital systems use binary numbers and
have to encode and decode a voice
signal by using a voice codec
 The voice signal is translated in a way
so that it best represents a voice signal
in the codecs reference table
 Since something like background noise
cannot be translated in the reference
table, it makes digital systems good at
filtering background noise

Note: Just for an overall picture, other factors can effect the
voice quality as well
 Security is easier to implement on a digital
system because encryption algorithms are
generally digital themselves
 Non-voice services in an analog system
would need an entirely separate method,
whereas it can be built into digital
 Digital radios are much more expensive
 Really depends on the type of user and what
they need

Only a single channel of frequency is
used for each communication path
 - predetermined
Not very efficient, especially for critical
communications
 A pair of frequencies can be used in the
same way, (one for North, one for south)

 Manual switching
The frequency carrier itself
defines who the message gets
sent out to
Multiple channels are pooled together
and used as a shared resource
 A trunking controller is used to locate an
open channel in the pool of channels
and uses it to repeat the message
across the system

 Unknown what frequency will be used
A talkgroup is used to keep track of who
needs to hear what messages
 Why the name “Trunked”?

1. Fire: Using channel 1, only
Talk Group 1 will hear it
2. Simultaneously Police
sends a message
3. Trunking controller
automatically allocates
another channel for TG 2 to
use
-Could be a different channel
every time
-Each time a user is essentially
sending a request to use the
system, vs. the actual message
The main advantage to trunking is that it
factors in that not everyone will need
channel access at the same time
 Therefore, fewer channels are required
for the same amount of users
 Likewise, with the same number of radio
channels, more users can be brought in

TETRA at 4 channels per 25 kHz bandwidth
Trunking does not increase the amount
of simultaneous conversations per
channel, it only utilizes the channels
more efficiently
 If a channel goes down, it can be
(almost) seamlessly transferred to
another channel

Problems with the channel controller
could mean problems for everyone
 A slightly longer delay for
communication set up
 Trunking radios are more expensive


TETRA is an open standard developed by the
European Telecommunications Standards Institute
It was developed for the PMR market in order to
solve the problems of congestion and a growing
demand for data services

Schengen Agreement

 An agreement to lessen
border controls between
distinct countries (1985)
TETRA is in use throughout the world
and is considered the first truly open
digital private mobile radio standard
 The openness allows different
equipment from different manufacturers
to be able to fully communicate with
each other.
 It is currently not allowed in the US for
multiple reasons, some of which there is
debate over, but will be allowed soon
 Others: P25, DMR

TETRA is currently not fully compliant
with certain FCC rules dealing with
frequency allocation
 The TETRA Association has already
requested that the rules be waived and
the waivers are currently in progress
with some of them already waived
 In the future it is likely that the FCC will
follow the waivers with a rule-making
process to allow TETRA equipment in
the US permanently

Motorola Inc. has many intellectual
property rights on TETRA due to the
companies effort in developing the
standard
 The company claims that it would
support the use of TETRA in the US, if
there is evidence that enough people
have a need for it
 There are many in the industry that
believe Motorola is protecting its P25
business

o
o
o
TETRA uses Time Division Multiple
Access (TDMA) in order to increase the
number of channels on a given
frequency
It can divide one 25 kHz channel into
four separate communication channels
This creates both a cost savings in
frequency needed and the amount of
hardware needed per system
1 time slot = 14.167 ms
 1 TDMA frame = 4 time slots = 56.67 ms
 1 muliframe = 18 TDMA frames = 1.02 s

 Circuit mode compresses the data frames
down to 17 to allow the 18th to be a control
frame
pi/4 DQPSK – pi/4 Differential
Quaternary Phase Shift Keying is what
TETRA uses for its common TETRA
V+D and TEDS control channel
 Phase shift keying relies on shifts of the
phase of the signal to transmit data,
versus shifting the frequency or
amplitude
 In pi/4 there are four possible phase
shifts: -3π/4, +3π/4, +π/4, -π/4

Example, not actually what TETRA uses
Bit value
00
01
10
11
Amount of shift
None
1/4
1/2
3/4
Correct Pattern:
00 00 10 00 10 00
Quadrature Amplitude Modulation
(QAM) is a combination of amplitude
modulation and PSK
 If two different amplitudes are used,
along with 4 different phases, that
equates to a total of 8 different possible
combinations

Bit
value
Amplitude
Phase
shift
000
1
None
001
2
None
010
1
1/4
011
2
1/4
100
1
1/2
101
2
1/2
110
1
3/4
111
2
3/4
Each wave gets shifted from the wave before it
 In general, the higher order modulations provide higher data rates,
but are more prone to error
** The three different levels of 64-QAM refer to the amount
of interference protection against noise used
16-QAM equates to 16 possible bit
values: 0000, 0001 …. 1110, 1111
 64-QAM equates to 64 possible bit
values: 100000, 110000, …
 The higher the amount of possible
values, the more chance there is for
error since the shifts are closer together
 QoS attributes can also be negotiated
such as; throughput, delay, priority and
reliability.

the decision boundaries of lower
order schemes are much larger
 The difference in phase is known
as “phase jitter”


TETRA Release 1:
 The original release of TETRA occurred,
previously known as the TETRA V & D or
voice and data.
 Defined the original functionality such as the
interfaces, voice and basic (slow) data
services
 < 20 k bit/s throughput…
DMO – Direct Mode Operation
 AIR IF – Air Interface
 TEI – Terminal Equipment Interface
 ISI – Inter-System Interface

Also can interface to:
PSTN/ISDN/PABX, WAN/LAN, and internet
Group Call – Not unique to TETRA
 TETRA provides very fast call set-up time of
300 ms
 This would be very difficult to do on a cellular
network, since they were primarily designed
for one-to-one calls
 Pre-Emptive Priority Call (Emergency Call)
 Call Retention – protects users from being
forced off the network

Priority Call – allows 16 different resource
access levels
 Dynamic Group Number Assignment
(DGNA) – creating talkgroups “on the fly”
 Ambience Listening
 Busy Queuing
 Full-Duplex phone calls: Basically anything
that you can do with a regular phone – caller
ID, block call, call forward, call hold…

 Eliminates the need for a cell phone
Data Services :
 Short Data Service – Implemented on the
TETRA control channel, only can support up
to 256 bytes per message
 Packet Data Service – Both connectionoriented and connection-less configurations

Data Rate (bit/s)
No. Time Slots
High Protection*
Protected
Not Protected
1
2400
4800
7200
2
4800
9600
14400
3
7200
14400
21600
4
9600
19200
28800
*Protection – protection against data corruption due to noise, or
other environmental factors
Many organizations are looking at using cellular based services
due to the data rates available
Technology Unit
Narrow
Band
Wide Band
TETRA 1
kbits/s
7.2 to 28.8
TETRA 2
kbits/s
GSM
kbits/s
GPRS
kbits/s
115
EDGE
kbits/s
144 to 384
3G
kbits/s
Broadband
28.8 to 384+
9.6
384 to 2,000
Service
TETRA
GSM 3G
Service
TETRA
GSM 3G
Group call
yes
no
No
Priority call
yes
no
yes
Broadcast call
yes
no
No
yes
no
No
End-to-End
encryption
yes
no
No
Ambience
listening
yes
no
No
DMO
yes
no
No
Multiple key
encryption
Gateways
yes
no
No
Full duplex
telephony
yes
yes
yes
Transmit Inhibit
yes
no
No
yes
yes
yes
Simultaneous V yes
&D
no
No
Over air
encryption
yes
no
No
Receive only
yes
no
No
Long range
capability
Access Priority
yes
no
No
Area selection
yes
no
No
Late Entry
yes
no
No
Discreet
Listening
yes
no
No
TETRA was designed for PMR use, by PMR
users
 Cellular technologies were designed for oneone-communication primarily and therefore do
not offer the services needed by PMR users
 The higher data rates offered are not of interest
to the PMR market
 Other features are more important:

 Call setup time, (6-9 seconds versus 300 ms)
 Reliability, security, must be highly available
Direct Mode Operation – Allowing
TETRA radio terminals to communicate
directly with one another while outside of
the TETRA network
 Allows for local communications when
the entire group does not need to be
notified - “Back-to-Back mode”
 Allows for Trunked Mode Operation
extension or “Gateway mode”, an
extension back to the network to out-ofrange terminals

 “Back-to-Back” – normal DMO
operation (nearby
communications)
 “Gateway Mode” – special
equipment can provide
communications between both
networks
 “Dual Watch” – Also allows
communication between both
networks
TMO
Dual Watch Mode
(Receives from TMO only)
Gateway
Mode
DMO
DMO
FAIL
“Back-to-Back”

Allows a TETRA terminal to access
another TETRA network other than the
one it is registered on
 Assignment of talk groups needs to be
defined
 Billing of telephony calls
 Encryption schemes used must be released
 No need for extra hardware

Only a few systems currently using ISI
Work started around 1999, and was
released at the end of 2005
 High Speed data with rates almost 10
times greater than that of Release 1

 Expected rates of 30 – 400 kbits/s
More voice codecs in order to improve
communications with cellular systems
 Fully compatible with TETRA Release 1
 TMO range extension


3 methods:
 Authentication
○ Used to make sure both the radio is allowed,
and if the network is trusted
 Air Interface Encryption (AIE)
○ Protects against eavesdropping
 End to End encryption

Supports four AIE Algorithms
 TEA1, 2, 3, 4 which each have a specific
area of use

Enabling/Disabling of terminals
Custom Applications can be created for
a TETRA system using SDS, Packet
data service, or TEDS
 No generic “TETRA SDK” – systems
differ on terminal and network side a lot
 The SDS on TETRA primarily would only
be useful for status messaging or
Automatic Vehicle Location, (AVL) due
to the low data rate

The Packet data service allows for
things such as: Database lookup,
imaging, or slow scan video.
 High speed data could be used for
things such as fingerprinting or real time
video.
 The wide variety of data services offered
by TETRA, along with over 350
companies offering solutions, make it an
ideal choice for data applications in the
PMR market


BMW’s plant in Dingolfing, Germany
 Had multiple analog systems replaced by a
single TETRA system
 SDS message is sent whenever there is a
fault on the production line
 If no one accepts, the system re-sends the
message up to three times, and then gets
transferred to a manager
 If more than one person accepts, only one of
them will be given instructions to attend the
fault

2008 Beijing Olympics
 Handled 1.6 million calls a day, Asia's
largest TETRA network
 90,000 users

Petrom S.A. Petrobrazi Oil Refinery
 Around 2,000 employees, using SDS for
tracking of employees
 Doubled the previous systems capacity
using the same amount of spectrum
 New system is also much more scalable

NYC Transit carried out a TETRA pilot in
2011, along with NJ Transit in 2010
 Both pilots confirmed that TETRA meets and
exceeds their requirements for voice and
data communications

TETRA pilot in Wisconsin
 Nielson Communications Inc. Green Bay, WI
is comparing their current analog system to
a TETRA system
Blue = Best
Red = Weak
Black = No signal
Connected the TETRA system to an IPbased phone system for full duplex
phone calls, also had AVL capabilities
 In summary the results of signal
coverage compared to other systems is
about the same as TETRA
 Loud background noise is filtered out
very well on a TETRA system
 Easy radio interface to train and use

As of 2010, total TETRA contracts has
grown to 465
 TETRA is operating in over 125
countries
 Over the next four years, the Compound
Annual Growth Rate of TETRA is
expected to grow by 15%

2010 a record year for terminal shipments
(IMS analysis)
 Deployment of new networks up 6% and
extensions up 8%

Source: TETRA MoU
Source: TETRA MoU
Video Examples
http://www.youtube.com/watch?v=LdKp6
M4pKSo&feature=relmfu
 http://www.youtube.com/watch?feature=
player_embedded&v=LJn2HrJarQM
 http://www.youtube.com/watch?v=PVAK
RQofNoY&feature=endscreen&NR=1


Trunking Benefits
 Spectrum utilization, security, better coverage

TDMA benefits
 less hardware = less cost, concurrent voice and
data
Unique TETRA services; ISI, DMO, security
features, DGNA, full duplex phone calls.. Etc
 Increased competition due to openness
means cheaper products and solutions

Questions
Sources

References

Is TETRA on its way to North America? - Urgent Communications article. (n.d.). Urgent
Communications magazine online | Formerly MRT magazine. Retrieved March 25, 2012, from
http://urgentcomm.com/networks_and_systems/commentary/tetra-north-america-20090617/
Phase Shift Keying. (n.d.). Home - University of Delaware Dept. of Physics & Astronomy.
Retrieved March 27, 2012, from
http://www.physics.udel.edu/~watson/scen103/projects/96s/thosguys/psk.html
Unrequited love | Many in the U.S. are smitten with TETRA, and they don’t understand why they
can’t have it. (n.d.). Urgent Communications magazine online | Formerly MRT magazine.
Retrieved March 25, 2012, from http://urgentcomm.com/mobile_voice/mag/digital-trunkedmobile-tetra-0301/index1.html
Signal Harbor. (2005). Understanding trunking. Retrieved from
http://www.signalharbor.com/sr/05apr/index.html
Hayes, W. (2003, May 29). What is trunking. Retrieved from
http://www.thebriarpatch.org/trunking/
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Sources
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TETRA Association. (n.d.). Tetra. Retrieved from
http://www.tetramou.com/about/page/12027
TETRA Association. (2006, January). Tetra technology advantages & benefits.
Retrieved from http://www.tetramou.com/Library/Documents/Why_TETRA/Technology
Benefits.pdf
Krishna, S. (2012, April 12). Non coherent demodulation of pi/4 dqpsk (tetra). Retrieved
from http://www.dsplog.com/2010/04/12/non-coherent-demodulation-of-pi4-dqpsk-tetra
Barrus, J. (2012, March 5). Fresh ideas in two-way communications. Retrieved from
http://communities.motorola.com/community/two-way_communications/blog
Charan, L. (2006). Complex technology made real. Retrieved from
http://www.complextoreal.com
ETSI. (2007, October). Etsi TR 102 580 v1.1.1. Retrieved from
http://pda.etsi.org/exchangefolder/tr_102580v010101p.pdf
University of California, Berkeley. (Producer). (2000). The radio spectrum. [Print Photo].
Retrieved from http://ptolemy.eecs.berkeley.edu/eecs20/sidebars/radio/spectrum.gif
Ascom. (n.d.). Tetra - terrestrial trunked radio. Retrieved from
http://www.ascom.com/en/tetra-article.pdf