Monitoring Link 16 Networks for Compliance with National ... - MilCIS

Monitoring Link 16 Networks 

for Compliance with National 

Frequency Clearance 

Agreements

Agenda 

Frequency Usage Background 

Australian Frequency Clearance 

Agreement 

Monitoring Challenges 

Implementation Approaches 

ViaSat Brings Your Network To Life

Frequency Allocations 

The use of the band 960-1215 MHz by the 

aeronautical radionavigation service is 

reserved on a worldwide basis for the 

operation and development of airborne 

electronic aids to air navigation and any 

directly associated ground-based facilities. 

960 – 1164 MHz 

Aeronautical Mobile (R) 5.327A 

Aeronautical RadioNavigation 5.328 

1164 – 1215 MHz 

Aeronautical RadioNavigation 5.328 

Radionavigation-Satellite 5.328B 


Link 16 Frequency Usage 

960 

14 FREQs 

IFF IFF 

1030 

1090 1215 

51 TOTAL CENTER FREQUENCIES SPACED AT 3 MHz INTERVALS 

Spread Spectrum 

5 FREQs 32 FREQs 

Frequency Hopping – 51 Frequencies 

Rate: 1/13 msec or 76,923 hops per second 

Frequency not held constant 

IFF NOTCHES (2) 

Centered on 1030 & 1090 MHz 


Link 16 Radio Limitations 

§ 87.479 

stations. 

Harmful interference to radionavigation land 

Military or other Government stations have been authorized to 

establish wide-band systems using frequency-hopping spread 

spectrum techniques in the 960–1215 MHz band. Authorization 

for a Joint Tactical Information Distribution Systems (JTIDS) has 

been permitted on the basis of non-interference to the 

established aeronautical radionavigation service in this band. In 

order to accommodate the requirements for the system within 

the band, restrictions are imposed. Transmissions will be 

automatically prevented if: 

(1) The frequency-hopping mode fails to distribute the JTIDS 

spectrum uniformly across the band; 

(2) The radiated pulse varies from the specified width of 6.4 

microseconds ±5%; 

(3) The energy radiated within ±7 MHz of 1030 and 1090 MHz 

exceeds a level of 60 dB below the peak of the JTIDS spectrum 

as measured in a 300 kHz bandwidth. The JTIDS will be 

prohibited from transmitting if the time slot duty factor exceeds 

a 20 percent duty factor for any single user and a 40 percent 

composite duty factor for all JTIDS emitters in a geographic 

area. 


The Time Slot 

Link 16 uses the 

principle of Time 

Division Multiple 

Access (TDMA) 

Each JU is assigned a 

set of “time slots” in 

which to transmit 

their data 

Contains: Jitter, 

Synchronization, Time 

Refinement, 

Message Header, 

Data, Propagation 

Jitter & Propagation: 

“Dead Times” 

Message Information 

 

(no pulses Jitter 

transmitted) 

Pulses: Encoded with 

Sync Header Data 1 

258 Pulses 

Data 2 Propagation 

information 

444 Pulses 

ViaSat Brings Your Network To Life 

Link 16 

7.8125 msec 

Time Slot

Link 16 Time Intervals 

1 Day = 24 hours 

1 Day = 112.5 Epochs 

1 Epoch = 12.8 min 

1 Epoch = 64 Frames 

1 Epoch = 98k Timeslots 

1 Frame = 12 seconds 

1 Frame = 1,536 Timeslots 

(3 sets of 512) 

1 Timeslot = 7.8125 msec 


Time Slot Duty Factor 

TSDF is a percentage value representation 

of the number of Link 16 pulses in a 12 

second frame 

100% TSDF = 396,288 pulses in a frame 

100% TSDF is one STD Pack or P2DP 

Transmission (258 pulses) in every slot in 

a frame 

8 Units 

~5% TSDF 


1 Unit 

50% TSDF

Australian Frequency 

Clearance Agreement 

Between The Commonwealth 

of Australia (Department of 

Defence) and Airservices 

Australia 

Applies to all airspace within 

the Australian Flight 

Information Region 

Applies to all Link 16 

operations within sovereign 

Australian airspace 


http://www.airservicesaustralia.com/aboutus/howatcworks/ourairspace.asp

FCA Transmission Limitations 

Multiple Voice Nets Permitted 

Contention Access Allowed 

Time Slot Reallocation Permitted 

Up to 3 separate networks in a single 

geographic area 

200 Watt Maximum Transmit Power 

Packed 2 Double Pulse and Packed 4 

(444 pulse slots) Permitted 

Combat Mode is Prohibited 

50% TSDF Maximum For Any One Radio 

(applies to closely grouped radios too) 

Planned TSDF must be used for 

geographic area (volume) analysis if a 

monitoring system is not available 


“Planned” TSDF 

Worst case TSDF based on network 

design 

Assumes a radio is transmitting in every 

available transmission slot 

Typical per participant values 

Fighter: ~9% (~60% with relay active) 

C2: ~12% 

Ship: ~9% 

Ground Station: ~5% 

Voice nets – 12.55% per net in use 


Required NAVAID Separation 

DME/TACAN 

< 50% TSDF within 0.5 NM (926 m) 

< 20% TSDF within 0.18 NM (333 m) 

< 1% TSDF allowed within 300 feet (92 

m) 

Some specific NAVAIDS have more 

stringent restrictions (no 

transmissions within 2 nm) 


Geographic Area Definition 

100 nm (185 km) Cylinder 

Extends from the ground to the 

altitude of the highest Link 16 

transmitter 

Centered on ‘any’ point – 

maximum allowed TSDF is 150% 

Maximum TSDF for any one radio 

is 50% (applies to closely spaced 

radios too) 


TSDF Volumes 

Planned TSDF – 183% 

Observed TSDF – 16.4% 



Observed TSDF – 25.5% 



200 nm 

radius 

Centered 

around each 

transmitter 

Maximum of 

400% TSDF

TSDF Volumes 






100 nm 

radius 

Centered 

around any 

point – best 

fit algorithms 

Maximum of 

150% TSDF

Monitoring Challenges 

Simultaneous Transmissions 

Multiple Relay Platforms 

Stacked Voice Nets 

Multiple Control and Fighter to Fighter Channels 

Contention Access 

Improper Radio Initialization 

Line of Sight Limitations 

Position Accuracy of all Transmitters 

Overlapping Networks 


Approaches to FCA 

Monitoring 

Multiple ground terminals to form the 

backbone of the network and 

simultaneously monitor its compliance 

Modify Link 16 radios to self report 

transmission usage 

Single point monitoring tool with 

delayed synchronization capability 

Non-JTIDS/MIDS radio frequency 

monitoring system (pulse counter) 


FCA Monitoring – Multiple 

Terminals 

Use multiple ground terminals to form 

the backbone of the network and 

simultaneously monitor its compliance 

Using multiple terminals allows the detection of 

additional transmissions in the Slot Reuse case. 

Each monitoring terminal is capable of listening on 

a separate net for a given timeslot. 

If the monitoring terminals are geographically 

separated, each terminal could also detect a 

different relay platform in the flood relay and 

contention access cases (not all relay platforms will 

necessarily be detected). The more terminals used, 

the more transmitters that can be detected. 

The ground based terminals can be used 

simultaneously for exchange of tactical data. 


FCA Monitoring – Self Reporting 

Terminals 

There are currently several active discussions regarding 

modifications to the MIDS terminal software for each radio 

to periodically report the number of pulses transmitted in a 

given time period. 

Advantages 

Each radio would be able to account for all usage including voice and 

stacked nets 

Disadvantages 

Implementation timeline – MIDS and JTIDS software changes, regression 

testing and subsequent field upgrades to the installed platform base 

Cost (see implementation timeline) 

Monitoring system upgrades – either a new monitoring system would 

need to be fielded or upgrades implemented to existing system to 

process the reports generated by each radio 

Increased TSDF – the reports would need to be transmitted, including 

possible relay of transmission usage reports 

Network design impacts 

Possible host system updates to process own terminal TSDF reports and 

send to monitoring units and/or stations 


FCA Monitoring – Single Point 

with Delayed Synchronization 

Use an LVT-2/11 or ANGR-43 radio with 

a delayed synchronization capable host 

to detect other transmissions 

The delayed synchronization capability of the LVT-2 

can be used to systemically determine the number 

of active relay platforms. With knowledge of the 

network design, duty factor for the relaying 

platforms could be calculated based on a sampling 

of observations. 

There are some line of sight assumptions that 

enter into the assumption of what transmissions a 

given relay platform is actually retransmitting. 

How and if the fielded products realize this is not 

known to us, but in theory it is possible 


FCA Monitoring – 

Pulse Counter 

Use a non-Link 16 radio frequency 

monitoring system 

The non-Link 16 systems, basically RF pulse 

counters, are capable of counting all Link 16 

transmissions. 

There may be some capability based on the 

number of receivers in the system to associate 

transmissions to a given unit if the system is 

integrated with an active tactical system. 

This is an adjunct system to Link 16 and does 

not leverage the data inside the Link 16 

messages. 


Leveraging the PPLI 

Reported position 

Self reported quality values 

Time Quality (TQ) 

Horizontal Position Quality (PQ) 

Vertical Quality (VQ) – Altitude Quality 

(AQ) or Elevation Quality (EQ) 

Active relay indicator 

Voice net 

Control channel 


Evaluating Reported Position 

Time Quality directly 

impacts reported 

position accuracy 


Improperly Configured 

Ground Station 


QUESTIONS? 

Jon Stearn 

Jon.Stearn@viasat.com 

+1.760.795.6312

Monitoring Link 16 Networks for Compliance with National ... - MilCIS

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