1. TETRA - Direct Mode Operation
Doug Gray
Motorola

2. AGENDA Introduction & explanation of Direct Mode Operation (DMO)
Services & Facilities
Benefits & Applications
Conclusions

3. WHY DIRECT MODE IN TRUNKING?
Trunking offered many benefits over conventional communications and was a great success in the market
DMO
It missed a key feature that conventional communications offered - direct communication outside network coverage
Spectral
Efficiency
Automatic Operation ?
TETRA’s multi-mode capability offers the best of both worlds - Trunking and Direct Communications in a single terminal.
Ease of
Data Services
Feature Rich
Service

4. WHAT IS TETRA DIRECT MODE ?
There are 4 basic operational modes of TETRA DMO, viz.
1 “Back-to-back” (standard DMO terminal coverage)
2 DMO Repeater (extended DMO terminal coverage)
3 Dual Watch (periodic “scanning” of ‘other’ mode)
4 DMO Gateway (continuous relay between modes)
Communication between Direct Mode terminals
Communication between trunked and DMO terminals
Further permutations are possible, e.g. Gateway/Repeater

5. TETRA DMO - BACK-TO-BACK
TRUNKED
TETRA C
TETRA
DMO A1
TETRA
DMO B1 A3 A2 B2 B3

6. TETRA DMO REPEATER TRUNKED TETRA TETRA DMO A1 C A3 DMO Repeater B1

7. TETRA DMO-DUAL WATCH TRUNKED TETRA TETRA DMO TETRA DMO A2 B2 A1 C A3

8. TETRA DMO - GATEWAY TRUNKED TETRA TETRA DMO TETRA DMO A1 C A3 GatewayB1
Gateway B3

9. ‘Frequency Efficient’ mode can use these timeslots for another call
‘BACK-TO-BACK’ DMO 1 2 3 4
DMO Air Interface
‘Frequency Efficient’ mode can use these timeslots for another call 1 2 3 4
Speech Slot
Slot Structure
Pre-emption
DMO
DMO
Master
Slave

10. 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
Slide shows a list of characteristics

11. DMO REPEATER TYPE 1A & 1B Single carrier (1A) Dual carrier (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

12. DMO REPEATER TYPE 1A DMO DMO Master Slave Frequency Usage DM1 MS RX2 3 4
Master Slot
Slave Slot
DMO Air Interface
DM1
Frequency Usage
MS RX
SPEECH
UPSLOT
Direct Mode
Channel
DM1
Direct Mode
Channel
DM1
SPEECH
DOWNSLOT
Pre-Emption
Upslot
(Slave slot pattern moved for diagram clarity)
Type 1A Repeater
DMO
Slave
DMO
Master

13. DMO REPEATER TYPE 2 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
RPT RX
DM1
RPT TX
TYPE 2
DM2

14. DMO REPEATER TYPE 2 ‘B’ channel can use other slots DMO DMO Master1 2 3 4
DMO Air Interface
‘B’ channel can
use other slots 1 2 3 4
Uplink Carrier
Pre-Emption
Upslot
(Slave slot pattern omitted for diagram clarity) 1 2 3 4
Downlink Carrier
SPEECH
UPSLOT
Direct Mode
Channel
DM1
SPEECH
DOWNSLOT
Direct Mode
Channel
DM2
Type 2 Repeater
DMO
Master
DMO
Slave

15. 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.

16. DMO GATEWAY
Trunked Mode
Air Interface
GW RX
DM1
GW TX
TM1
TM2
Frequency Usage
Enables DMO terminal to communicate with the trunking system & vice versa
Uses ‘normal’ DMO air interface (single call)
'Normal' DMO Air
Interface
(One simultaneous call)
Uplink (TM1)
DMO User
Gateway
Downlink (TM2)
Direct Mode
Channel
DM1
One DMO carrier per call
Trunked Mode
Cell

17. 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 Mode
Air Interface
GW RX
DM1
GW TX
TM1
TM2
Frequency Usage

18. 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

19. MANAGED DIRECT MODE - MDMO
MDMO terminal is restricted from transmitting unless it receives an authorising signal
O.K.
DMO
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

20. BENEFITS OF MDMO
Network Operators maintain better control of their network resource/ revenues
Removes potential for interference
Manages roaming

21. 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

22. 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

23. 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

24. 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

25. TETRA - Direct Mode Operation
Thank You
Doug Gray
Motorola