TETRA - Direct Mode Operation

Doug GrayMotorola

AGENDA

• Introduction & explanation of Direct Mode

Operation (DMO)

• Services & Facilities

• Benefits & Applications

• Conclusions

WHY DIRECT MODE IN TRUNKING?

SpectralSpectralEfficiencyEfficiency

Automatic Automatic OperationOperation

Feature Rich Feature Rich ServiceService

Ease of Ease of Data ServicesData Services

• 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’s multi-mode capability offers the best of both worlds - Trunking and Direct Communications in a single terminal.

DMO

WHAT IS TETRA DIRECT MODE ? • There are 4 basic operational modes of TETRA DMO, viz.

1 “Back-to-back”“Back-to-back” (standard DMO terminal coverage)

2 DMO RepeaterDMO Repeater (extended DMO terminal coverage)

3 Dual Watch Dual Watch (periodic “scanning” of ‘other’ mode)

4 DMO GatewayDMO Gateway (continuous relay between modes)

• Communication between Direct Mode terminals• Communication between trunked and DMO terminals

• Further permutations are possible, e.g. Gateway/Repeater

TRUNKEDTRUNKEDTETRATETRA

A1A1

A3A3A2A2

B1B1

B2B2

B3B3

TETRATETRADMODMO

CCTETRATETRADMODMO

TETRA DMO - BACK-TO-BACK

TRUNKEDTRUNKEDTETRATETRA

A1A1

A3A3

A2A2

B1B1

B2B2

B3B3TETRATETRADMODMO

CC

TETRATETRADMODMODMO RepeaterDMO Repeater

DMO RepeaterDMO Repeater

TETRA DMO REPEATER

TRUNKEDTRUNKEDTETRATETRA

B1B1

B2B2

B3B3

TETRATETRADMODMO

CC

A1A1

A3A3A2A2

TETRATETRADMODMO

Dual-WatchDual-Watch

Dual-WatchDual-Watch

TETRA DMO-DUAL WATCH

TETRA DMO - GATEWAY

TRUNKEDTRUNKEDTETRATETRA

B1B1

B3B3

TETRATETRADMODMO

CC

A1A1

A3A3

TETRATETRADMODMO

GatewayGateway

GatewayGateway

‘BACK-TO-BACK’ DMO

DMOMaster

DMOSlave

1 2 3 4

Slot Structure

Speech Slot

Pre-emption

1 2 3 4DMO Air Interface ‘Frequency Efficient’

mode can use these timeslots for another call

DMO CHARACTERISTICS

• Normal DMO enables 1 conversation per carrier(i.e. 1 per 4 timeslots)

• Transmitting radio acts as ‘Master’ on a single timeslot

• Receiving radio is ‘Slave’ on a single timeslot• In normal mode, two time slots are used, two are

free• In Frequency Efficient Mode, all four timeslots are

used (2x2) enabling two conversations per carrier

DMO REPEATER TYPE 1A & 1B• Only one call per repeater • Uses a 4 slot structure

•2 slot uplink •2 slot downlink•Master/slave operation (3 slot delay)

• Single carrier (1A)•Simple RF•1 conversation, 1 DM channel•Single carrier

MS RX

DM1

MS TX

TYPE 1A

• Dual carrier (1B) •More complex RF•1 conversation, 2 DM channels•Supports multiple repeaters•Reduces potential for RF interference

MS RX

DM1

MS TX

TYPE 1B

DM2

DMO REPEATER TYPE 1A

Type 1A Repeater

DM1

Frequency Usage

MS RX

Direct ModeChannelDM1

SPEECH DOWNSLOT

Direct Mode

Channel

DM1DMOMaster

SPEECH UPSLOT

1 2 3 4 1 2 3 4

1 2 3 4 1 2 3 4

Master Slot

1 2 3 4

Slave Slot

DMO Air Interface

DMOSlave

Pre-EmptionUpslot

(Slave slot pattern moved for diagram clarity)

• Two simultaneous calls per repeater

• Uses a 4 slot structure•4 slot uplink

•4 slot downlink

•Master/slave operation (4 slot delay)

• Dual carrier•More complex RF but supports multiple repeaters

• Uses power control and addressing

DMO REPEATER TYPE 2

RPT RX

DM1

RPT TX

TYPE 2

DM2

DMOMaster

SPEECH UPSLOT

DMOSlave

Direct Mode

Channel

DM1

SPEECH DOWNSLOT

Direct ModeChannelDM2

Type 2 Repeater

1 2 3 4 1 2 3 4

Uplink Carrier

1 2 3 4

Downlink Carrier

1 2 3 4 1 2 3 4

DMO Air Interface

DMO REPEATER TYPE 2

‘B’ channel can use other slots

Pre-EmptionUpslot

(Slave slot pattern omitted for diagram clarity)

DUAL WATCH

• Radio is operational in one system mode (Direct or Trunked) and simultaneously monitors signalling on the other system.

Mobile Unit whilst engaged in a call in Trunking mode

is alerted of a DMO call/request from a DMO terminal.

DMO GATEWAY• Enables DMO terminal

to communicate with the trunking system & vice versa

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

Gateway

Direct M

ode

Channel

DM1

DMO User

Uplink (TM1)

Downlink (TM2)

'Normal' DMO AirInterface

(One simultaneous call)

Trunked ModeCell

Trunked ModeAir Interface

GW RX

DM1

GW TX

TM1 TM2

Frequency Usage

• One DMO carrier per call

DMO REPEATER/GATEWAY

• Combines the functionality of a repeater and a

gateway (similar to a VHF-UHF talk-through

repeater)

• Interconnects direct mode to trunked mode

• Uses ‘normal’ DMO air interface

(single call)

• Can be manned or stand alone (i.e. free running

or manned by an operator)

Trunked ModeAir Interface

GW RX

DM1

GW TX

TM1 TM2

Frequency Usage

BENEFITS of DMO GATEWAY

• Extends range of Trunking Mode Operation

• Reduces Infrastructure costs

• Enables remote ‘occasional users’ to have

communication at cost effective rates

• Gives Network Operators better coverage

possibilities during early stages of network roll-

out

MANAGED DIRECT MODE - MDMO

• Generated by authorising device which is in permanent contact with system, or…..

• …. generated by modified DMO Gateway or Repeater/Gateway device

• Validity time encoded in authorising signal

• MDMO terminal is restricted from transmitting unlessit receives an authorising signal O.K.

DMO

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 or Group Call• Circuit mode data up to 7.2 kbps, incl. point-to-point & point-to-multipoint

• Status and short data service (SDS)• Late Entry• Emergency call• Talking Party Identification (TPI) , incl. concealment

DMO SECURITY (ENCRYPTION)

• Air-interface encryption - TEA1, TEA2 &

TEA3, incl. time stamping• Implicit authentication• Key management incl. Over The Air Rekeying

(OTAR)• “Zapping” (enabling/ disabling) terminals• End-to-end encryption mechanism

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• Fall-back operation when the Trunking Infrastructure

system is inoperative• Covert Operations - cannot be monitored by Contol• ‘Stripline’ applications (power, oil, water distribution

lines) not requiring trunked network capacity

CONCLUSIONS

• TETRA is a multi-mode standard offering trunking and

conventional operation in-one

• DMO - a powerful feature in the total TETRA offering, as

it comprises of several sub-modes of operation

• Significant commonality with trunked V+D TETRA

enables for multi-mode terminals (DMO & V+D)

• DMO is a significant differentiator between TETRA and

other cellular services

TETRA - Direct Mode Operation

Thank You

Doug GrayMotorola