The power of TETRA - Direct Mode Operation Francesco Pasquali Selex Communications
Dec 24, 2015
The power of TETRA - Direct Mode Operation
Francesco Pasquali
Selex Communications
Agenda
• Introduction to Direct Mode Operation (DMO)
• Applications & related benefits
• Services & facilities
• Conclusions
Why Direct Mode in Trunking?
SpectralSpectralEfficiencyEfficiency
Automatic Automatic OperationOperation
Feature RichFeature RichServiceService
Ease of Ease of Data Data ServicesServices
Legacy trunking offered many benefits over conventional communications and was a great success in the market
?It missed a key feature that conventional
communications offered:
direct communication outside network coverage
TETRA offers the best of two worlds
DMO
TRUNKING MODE
BUT ...
DIRECT MODE
What PMR users ask?
Users require to communicate everywhere at anytime, regardless of
– lack of network coverage
– lack of resources
– any type of network failure
and always need
– emergency communications
– security
– voice & data transmission, individual & group calls
TETRA operation modes
DMO adds border or out of coverage area communications
TETRA terminals provide integrated digital trunked (TMO) and direct (DMO) modes of operation
DMO provides communications within coverage at times of capacity limitations or whenever connection with the infrastructure is not needed
What is TETRA Direct Mode ?
There are 4 basic operational modes of TETRA DMO:
• “Back-to-back”– standard terminal to terminal communications
• DM Repeater– extension of DMO terminal coverage
• DM Gateway– relay between DMO and TMO
• Dual Watch– periodic “scanning” of ‘other’ mode
Back-to-back scenario (1/3)
TETRATETRADMODMO
For border or out of coverage area communications...
TRUNKEDTRUNKEDTETRATETRA
Back-to-back scenario (2/3)
TETRATETRADMODMO
… for communications
within coverage at
times of capacity
limitations (e.g. major
incidents)
TRUNKEDTRUNKEDTETRATETRA
FAIL!!
Back-to-back scenario (3/3)
… for communications within
coverage if connection to the
infrastructure is not needed
or wanted (localised activities
or private communications)
Direct
comm
unication
DMO Characteristics
• Normal mode DMO enables 1 communication per carrier (i.e. 1 per 4 timeslots, 2 slots used + 2 free)
• Frequency Efficient Mode DMO enables 2 communications per carrier (i.e. all 4 slots used, 2 slots used per each call)
• Transmitting radio acts as ‘Master’ on a single DMO channel (i.e. pair of alternated time slots)
• Receiving radio is ‘Slave’ on a single DMO channel
• Timeslot 1 is used as “traffic channel” for voice and data transmission by the Master radio
• Timeslot 3 is used for signalling transmission by Master, slave and idle radios (e.g. for pre-emption and PTT request)
‘Back-to-back’ DMO channel usage
‘Frequency Efficient’ mode
can use timeslots 2 and 4 for
another callSpeech Slots
A B C
DMOMaster
TX TX TXDMOSlave
RX RXRX
TETRA DMO Air Interface TDMA frame
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
A B C
Pre-emption request
P
TX
RX
P
Master uses Timeslot 1 for voice/data TX
11 1 1
Slave (& Idle) use Timeslot 3 for pre-emption
33 3 3
Benefits of “Back-to-back” DMO
• Reliability– Local area communications always granted under any kind of
fault of the network (disruption, congestion, interference)
• Cost – Relaxed requirements for coverage in low-traffic areas and
“enclosed” areas (e.g. buildings, tunnels, underground areas, etc.)
– Relaxed requirements for base station channels provisioning
• Special Applications– Local area operations (e.g. “strip-line”)
– Covert operations
TETRA DMO: Repeater
Special radio terminal equipment called DMO repeater, allows enlarging the DMO coverage when needed
FAIL!!
TETRATETRADMODMO
RepeaterRepeaterTETRTETR
AADMODMO
DM Repeater Type 1A & 1B
• Based on usual 4 slot structure– 2 slots for Master Repeater transmissions
– 2 slots for Slave / Idle Repeater transmissions
– Master/slave operation (3 slot delay)
• Single carrier (1A) DM repeater– 1 communications– Single frequency DM for Tx & Rx– Higher spectrum efficiency
Trunked ModeAir Interface
BS RX
DM
BS TX
Preferred Frequency Usage
• Dual carrier (1B) DM repeater– 1 communications– Two frequencies: DM1 for Rx & DM2 Tx– Reduces potential RF interference to TMO
Trunked ModeAir Interface
BS RX
DM2
BS TX
Preferred Frequency Usage
DM1
• Two simultaneous calls per repeater
DM Repeater Type 2
• Based on usual 4 slot structure– Two alternated slots per call on each link
– Master/slave operation (4 slot delay)
• Dual carrier
– 2 communications
– 2 frequencies: DM1 for Rx & DM2 Tx
– Need for RF full duplex Hw platform
– More complex and expensive than Type 1
Trunked ModeAir Interface
BS RX
DM1
BS TX
Preferred Frequency Usage
DM2
Benefits of DM Repeater
• Same benefits as back-to-back DMO in terms of
• BUT … on a wider area and with increased
communication reliability
Reliability
Cost
Special Applications
TETRA DMO: Gateway
TETRATETRADMODMO
Special radio terminal
equipment can operate
as a gateway between
the two worlds
TRUNKEDTRUNKEDTETRATETRA
TETRATETRADMO GatewayDMO Gateway
DM Gateway
• Uses ‘normal’ DMO air interface (single call)
Trunked ModeAir Interface
BS RX
DM1
BS TX
TM1 TM2
Preferred Frequency Usage
• One DMO carrier per call
• Enables DMO terminals to communicate with the trunking system & vice versa
Gateway
DMO User Trunked ModeCell
Direct M
ode
Channel
DM1
Uplink (TM1)
Downlink (TM2)
Benefits of DM Gateway• Reliability:
– Trunked communications through adjacent cells partially supported under fault of one radio base station
• Cost: – More relaxed requirements for coverage in low-traffic areas and
“enclosed” areas (incl. buildings, tunnels, underground areas, etc.)
– Better coverage possibilities during early stages of network roll-out
• Special Applications: – Enable “occasional and immediate coverage” at cost-effective rates
TETRATETRADMODMO
TETRA DMO: Dual watchSpecial radio terminal
equipment can get in touch
with both TMO and DMO
worlds simultaneously
TRUNKEDTRUNKEDTETRATETRA
TETRATETRADual WatchDual Watch
TerminalTerminal
Dual Watch• The Radio is operational in one mode (Direct or Trunked) and
simultaneously monitors the other for incoming communications.
• In particular the Radio Unit whilst idle (Idle Dual Watch) or engaged
in a call (Full Dual Watch) in Direct mode
receives TMO call, status and short messages from TMO users
Benefits of Dual Watch
• Cost:– Enlarge communication support in fringe areas: it allows
further relaxing of coverage requirements
• Special Applications:– Improve local area communications: terminals avoiding to
waste resources can be contacted whenever needed
Managed Direct Mode - MDMO
• Authorisation can be received– directly from the SwMI (for Dual Mode or Dual Watch terminals)
– from a DMO gateway and/or repeater device
– from an authorising device permanently in contact with the system
• MDMO terminal is restricted
from transmitting unless it
receives an authorising signal
O.K.DMO
• Authorisation can be limited both in time and geographically
Benefits of MDMO
• Network Operators maintain better control of their network resource/ revenues
• Removes potential for interference
• Manages roaming
DMO Services and Facilities
• Simplex speech - Individual & Group Call
• Late Entry
• Transmitting Party Identification (TPI), incl. suppression
• Emergency & pre-emptive calls
• Status and Short Data Service (SDS)
• Circuit mode data up to 7.2 kbps (P2P and P2MP)
DMO Security (Encryption)
• Air-interface encryption– Static Key Encryption
– TEA1, TEA2, TEA3 and TEA4 incl. time stamping
• Implicit authentication– Provided by Air Interface Encryption
• End-to-end encryption
DMO Benefits & Applications
• Operation outside the coverage of Trunking Infrastructure
• Gives extra capacity when trunked network is highly loaded
• Operations in poor signal strength areas (allows more relaxed coverage requirements and lower the related expenditure)
• Fall-back operation when the Trunking Infrastructure system is inoperative
• Covert Operations - cannot be monitored by Control
• ‘Stripline’ applications (power, oil, water distribution lines) not
requiring trunked network capacity
Conclusions
• TETRA is a multi-mode standard offering trunking and direct communication in-one
• DMO - a powerful feature thanks to exhaustive set of sub-modes of operation
• Significant commonality with trunked V+D TETRA enables for dual-mode terminals actually available on the market
DMO is a key differentiator between TETRA and
other, public and private, cellular technologies
The power of TETRA - Direct Mode Operation
Francesco Pasquali
OTE
Thank you