The power of TETRA - Direct Mode Operation Francesco Pasquali Selex Communications

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


TETRATETRADMODMO

… for communications

within coverage at

times of capacity

limitations (e.g. major

incidents)


FAIL!!


… 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


BS RX

DM2

BS TX


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


BS RX

DM1

BS TX


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


TETRATETRADMO GatewayDMO Gateway

DM Gateway

• Uses ‘normal’ DMO air interface (single call)


BS RX

DM1

BS TX

TM1 TM2


• 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


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

Documents

The power of TETRA - Direct Mode Operation Francesco Pasquali Selex Communications