Global Coordination for Hypersonic Missile Defense
The Department of Defense created SDA in 2019 to build a constellation of missile transport and tracking satellites in low Earth orbit on a rapid timeline, augmenting large spacecraft constellations with hundreds of relatively inexpensive small satellites. These spacecraft constitute what SDA calls its Proliferated Warfighter space architecture and will serve as the foundation for joint and multi-domain command and control capabilities.
Being able to tie the SDA PWSA in with air, ground, and naval tactical assets is important to the SDA concept to track hypersonic missiles from orbit, and coordinate interception using all existing assets. Since most of these assets are already tied in to a Link 16 JTIDS network, this would be the most obvious path. Link 16 has been implemented by most units using a frequency hopping, TDMA architecture, sometimes with stacked nets using CDMA, over tactical areas roughly 2000 NMi square. Even Taiwan, using the PoSheng program, has been using Link 16 compatible radios. Up until this time, satellite gateways have been used to route data beyond the tactical areas.
Why is this a Problem
FAA and FCC regulation of Link 16 in CONUS
The FAA and FCC regulations regarding Link 16 usage within the continental US (CONUS) focus on ensuring compatibility and minimizing interference with civilian aviation systems due to the different purposes and frequencies used. Here's a breakdown of their roles:
Federal Aviation Administration (FAA):
- Spectrum Management: The FAA allocates radio spectrum for civilian aviation use, including ADS-B and air traffic control radars. They have a vested interest in ensuring military operations using Link 16 don't create undue interference with these systems.
- Compatibility Testing: The FAA works with the Department of Defense (DoD) to ensure Link 16 equipment used within CONUS is tested and certified to meet National Telecommunication and Information Administration (NTIA) standards. This certification minimizes the risk of Link 16 transmissions interfering with civilian aviation systems.
- Frequency Coordination: While Link 16 typically operates outside of FAA-controlled spectrum, the FAA might be involved in coordinating with the DoD to identify potential areas of overlap or concern, especially in areas with high concentrations of civilian air traffic.
Federal Communications Commission (FCC):
- Spectrum Allocation: The FCC plays a broader role in managing the electromagnetic spectrum across various sectors, including civilian aviation and the military. While they don't directly regulate Link 16 usage, they establish the overall spectrum allocation framework that the DoD must adhere to when operating within CONUS.
- Enforcement: The FCC enforces regulations regarding spectrum usage to prevent unauthorized transmissions or interference with licensed services. While Link 16 is a military system, the FCC might be involved if there were any reports of Link 16 transmissions causing significant disruptions to civilian aviation communication.
Challenges and Solutions:
- Limited Spectrum Availability: As the demand for radio spectrum increases, ensuring compatibility between military and civilian systems becomes more complex. The FAA and DoD are constantly working on solutions like frequency hopping techniques within Link 16 to minimize the chance of interference.
- Network Evolution: The military is exploring ways to adapt Link 16 for use with smaller, low-power radios. This could potentially lead to a wider range of Link 16 operations within CONUS, requiring continued collaboration between the FAA and DoD to address potential compatibility issues.
Overall, the FAA and FCC play crucial roles in regulating Link 16 usage within CONUS to ensure it coexists peacefully with civilian aviation communication systems. It's an ongoing effort requiring cooperation and technical solutions from both military and civilian stakeholders.
Spectrum Users
The primary radio service operating in the 960 to 1215 MHz frequency range is the aeronautical radionavigation service (ARNS)
. This service is used for ground-based and airborne systems that control civilian and military aircraft in the National Airspace (NAS).Here's a breakdown of the key systems using this band:
- Distance Measuring Equipment (DME): Provides aircraft with precise information about their slant range from a ground station.
- Tactical Air Navigation (TACAN): The military version of DME, offering similar functionality.
- Secondary Surveillance Radar (SSR): Also known as Mode S, a ground-based radar system that interrogates aircraft transponders to identify and track their position.
- Identification Friend or Foe (IFF): A military system that helps identify friendly aircraft using transponders.
Additional Allocations:
While ARNS is the primary service, there are a couple of additional allocations in this band:
-
Aeronautical Mobile (Route) Service (AM(R)S): This service allows for communication between aircraft and ground stations, including:
- Automatic Dependent Surveillance-Broadcast (ADS-B): Aircraft broadcast their position and other data for improved air traffic awareness.
- Universal Access Transceiver (UAT): Used for short-range communication between small aircraft.
-
Limited DoD Use: The Department of Defense (DoD) might operate some communication systems, like the Joint Tactical Information Distribution System (JTIDS), on a coordinated basis within this band.
Regulatory Body:
The International Telecommunication Union (ITU) allocates radio spectrum frequencies for various services globally. In the case of the 960-1215 MHz band, the ITU designates it for worldwide use by the aeronautical radionavigation service.
FCC title 47, up to date as of 3/06/2024. Title 47 was last amended 3/05/2024.
§ 87.479 Harmful interference to radionavigation land stations.
(a) 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.
(b) If radionavigation systems operating in the 960–1215 MHz band experience interference or unexplained loss of equipment performance, the situation must be reported immediately to the nearest office of the FAA, the National Telecommunications and Information Administration, Washington, DC 20504, or the nearest Federal Communications Commission field office. The following information must be provided to the extent available:
(1) Name, call sign and category of station experiencing the interference;
(2) Date and time of occurrence;
(3) Geographical location at time of occurrence;
(4) Frequency interfered with;
(5) Nature of interference; and
(6) Other particulars.
Space Development Agency aims to test Link 16 over the United States this year - ExBulletin
The head of the Space Development Agency said he plans to begin demonstrating Link 16 space-to-ground connectivity over the United States by the end of the year, provided the agency obtains the long-awaited approval from the Federal Aviation Administration.
Link 16 is a military signal commonly used by SDA satellites to connect to ground radios. U.S. forces, NATO, and their international allies rely on the capability of real-time data exchange.
The agency worked with the FAA to obtain permission to test Link 16 over national airspace, but the process took longer than expected.
Primarily, the FAA wants to make sure we have tested compatibility features on our satellites so we can't interfere with any radio navigation aids, SDA Director Derek Tournear said during a Space webinar. News on March 6. This makes sense and we are working with the FAA to put a plan in place to do so.
The Department of Defense created SDA in 2019 to build a constellation of missile transport and tracking satellites in low Earth orbit on a rapid timeline, augmenting large spacecraft constellations with hundreds of relatively inexpensive small satellites. These spacecraft constitute what SDA calls its Proliferated Warfighter space architecture and will serve as the foundation for joint and multi-domain command and control capabilities.
After launching its first satellites last April, the SDA hoped to be able to quickly validate this capability and integrate it into large-scale Department of Defense exercises, such as Northern Edge, a joint training exercise conducted in the Gulf of 'Alaska.
Instead, the agency opted to conduct initial testing in international waters starting in November. In the initial demonstration, three satellites built by Denver-based York Space Systems transmitted signals from low Earth orbit about 1,200 miles above Earth to an international test site.
The Air Force's 46th Test Squadron supported the mission from the ground.
SDA now has 27 satellites in orbit. These spacecraft are not only equipped to communicate via Link 16, but also have what are called inter-satellite optical links that allow them to share data with each other.
SDA first tested these inter-satellite links in 2021 during a demonstration mission with the Defense Advanced Research Projects Agency called Mandrake. Tournear said the agency began testing this capability with the first batch of satellites it launched and plans to expand it to the entire constellation later this summer.
As the agency works to test and demonstrate the capabilities of its first tranche of satellites, it is also preparing for its next launches, which are expected to begin in September. This mission will kick off a nearly year-long campaign to launch approximately 161 satellites from Vandenberg Space Station in California.
“We plan to have at least one of these launches by the end of this calendar year, and then the rest will be done basically as fast as we can get them through the payload processing facilities,” Tournear said .
Courtney Albon is C4ISRNET's space and emerging technologies reporter. She has covered the U.S. military since 2012, focusing on the Air Force and Space Force. She reported on some of the Department of Defense's most significant acquisition, budget and policy challenges.
Sources
2/ https://www.c4isrnet.com/battlefield-tech/space/2024/03/07/space-development-agency-aims-to-test-link-16-over-us-this-year/
Space Development Agency completes first space-to-ground Link 16 transmission
For the first time ever, the Space Development Agency has demonstrated the ability to connect satellites in low-Earth orbit (LEO) to ground-based radios using Link 16 tactical data links — a key step to operationalizing the agency’s future constellation of data transport satellites.
During a series of three demonstrations held Nov. 21-27, SDA connected three satellites equipped with Link 16 payloads to terrestrial radios stationed inside the territory of one of the United States’ Five Eyes allies, the agency announced Tuesday. Operators conducted passive and active network entry, acquired fine frequency synchronization and broadcasted several tactical messages, according to a press release.
The satellites used for the demonstration were made by York Space Systems and launched by SDA earlier this year as part of its Tranche 0 transport layer. The constellation of data relay systems is considered the demonstration tranche for SDA’s Proliferated Warfighter Space Architecture (PWSA) — a planned multi-layer configuration of hundreds of LEO satellites that will enable new and augmented capabilities for the military.
“I can’t underscore enough the significance of this technical achievement as we demonstrate the feasibility of the Proliferated Warfighter Space Architecture and its ability to deliver space-based capabilities to the warfighter over existing tactical data links,” SDA Director Derek Tournear said in a statement.
The PWSA is considered the backbone to the Pentagon-wide effort known as Joint All-Domain Command and Control (JADC2). The idea is to connect all of the U.S. military’s sensors and shooters under a single network, and SDA’s satellites will play a key role in enabling the rapid collection and dissemination of critical decision-making data.
Link 16 has been an integral part of realizing JADC2, as it is the only common tactical data link used across the United States’ military branches, the NATO alliance and other international allies. By deploying satellites equipped with Link 16 payloads into space, SDA aims to offer beyond-line-of-sight connectivity for warfighters.
“This is not only the first time Link 16 has been broadcast from space, but the beginning of turning the world’s finest warfighting force into a truly connected beyond line-of-sight joint force” Tournear said.
SDA began work on the tests “within 10 hours” of being cleared by the National Telecommunications Administration (NTIA) to do so, according to a press release.
In October, the agency announced it had received a waiver from NTIA via the International Telecommunication Union (ITU) — the United Nations body responsible for coordinating shared global use of the electromagnetic spectrum — to begin conducting experimental Link 16 demonstrations in international territories.
The agency sought the waiver in order to bypass regulations from the Federal Aviation Administration that prohibits transmitting space-based Link 16 over U.S. territory in order to prevent interference with radios used for the commercial aviation industry. Tournear has acknowledged in the past that the restrictions have delayed testing some of the Tranche 0 transport layer satellites since they were launched earlier this year.
“While the U.S. military and allied partners have used Link 16 aboard aircraft for years, a fully operational PWSA will require the ability to establish bi-directional communication from space to ground,” a Space Development Agency press release stated. “Testing Link 16 from space, first with an international partner and then over international water, represents a compromise position and SDA’s requirement remains to test over U.S. airspace to demonstrate the feasibility of the PWSA and its ability to deliver fire control information to the warfighter over existing tactical data networks.”
The waiver also allows SDA to conduct future demonstrations in international territories, such as those of the Five Eyes alliance that includes the United States, United Kingdom, Canada, Australia and New Zealand. The agency did not disclose the Five Eyes ally that was involved with this month’s demonstrations.
The successful Link 16 demo lays the groundwork for SDA’s first operational tranche of data transport satellites, known as Tranche 1. The agency plans to begin a monthly launch campaign of the birds — which includes 126 data relay satellites, 35 missile warning and missile-tracking satellites and 12 experimental satellites — at the end of 2024.
Space Development Agency Successfully Completes Space to Ground Transmission from Link 16 Tactical Data Network – Space Development Agency
Demonstration included active and passive Link 16 network entry, transmitting messages to and from low Earth orbit to terrestrial radios
Date: Nov. 28, 2023
WASHINGTON, D.C. – The Space Development Agency (SDA) today announced it successfully demonstrated the first-ever Link 16 network entry through space to ground connection from low Earth orbit (LEO) to a series of receivers using terrestrial radios during three demonstrations held Nov. 21-27, 2023.
Operators working with SDA conducted both passive and active network entry, obtained fine synchronization, and transmitted multiple tactical messages from satellites using L-band radios aboard Tranche 0 (T0) Transport Layer satellites to a ground test site located within the territory of a Five Eyes partner nation.
This success represents a major milestone for T0 of the Proliferated Warfighter Space Architecture (PWSA) and demonstration of a significant new capability for the warfighter. This accomplishment also reflects a leap ahead in the Department of Defense-wide Joint All Domain Command and Control (JADC2) effort, connecting available sensors to available warfighting platforms globally. The PWSA Transport Layer is the backbone of JADC2 in space and will enable delivery of tactical messages, including beyond-line-of-sight scenarios, using Link 16 radios aboard space vehicles.
“I can’t underscore enough the significance of this technical achievement as we demonstrate the feasibility of the Proliferated Warfighter Space Architecture and its ability to deliver space-based capabilities to the warfighter over existing tactical data links,” said SDA’s director, Derek Tournear. “This is not only the first time Link 16 has been broadcast from space, but the beginning of turning the world’s finest warfighting force into a truly connected beyond line-of-sight joint force.”
Link 16 is a tactical datalink communication system used by the United States, NATO, and coalition forces to transmit and exchange real-time situational awareness data among all network participants.
For the initial Link 16 demonstration, SDA used three T0 Transport Layer satellites provided by York Space Systems, Denver, from both of the 2023 T0 launches. The 46th Test Squadron, 96th Test Wing, headquartered at Eglin Air Force Base, Florida, served as the lead developmental test organization for ground operations. The demonstration leveraged prior fixed-site risk reduction testing at the 46th Test Squadron Datalinks Test Lab and with York Space Systems.
The tests began within 10 hours of receiving approval from an allied nation after the National Telecommunications and Information Administration issued a waiver, in accordance with the International Telecommunication Union process, to transmit from space to ground. The waiver also includes permission to conduct future tests over international waters.
Due to current Federal Aviation Administration restrictions that prevent broadcasting Link 16 from space into the U.S. National Airspace System, SDA coordinated with the NTIA to obtain a waiver to transmit to a Five Eyes nation and over international water to meet established PWSA mission criteria.
While the U.S. military and allied partners have used Link 16 aboard aircraft for years, a fully operational PWSA will require the ability to establish bi-directional communication from space to ground. Testing Link 16 from space, first with an international partner and then over international water, represents a compromise position and SDA’s requirement remains to test over U.S. air space to demonstrate the feasibility of the PWSA and its ability to deliver fire control information to the warfighter over existing tactical data networks.
Tranche 0, the warfighter immersion tranche, demonstrates the feasibility of a proliferated architecture in cost, schedule, and scalability toward necessary performance for beyond-line-of-sight targeting and advanced missile detection and tracking. SDA launched the first 10 satellites in April 2023 and the next 13 in September 2023. A third launch carrying the final T0 space vehicles is scheduled for the near future. Once completed, the Tranche 0 constellation will consist of 28 satellites – 19 Transport and eight Tracking satellites, plus one ground-based testbed satellite – forming a resilient constellation in LEO.
SDA plans to field the first operational generation of the PWSA, Tranche 1, beginning in late 2024. Tranche 1 will include 126 Transport Layer satellites, 35 Tracking satellites, and 12 tactical demonstration satellites (called T1DES). Tranche 1 will be operated by SDA’s groundbreaking space operations centers based heavily on commercial space operations models.
About the Space Development Agency. As part of the U.S. Space Force, SDA is recognized as DOD’s constructive disruptor for space acquisition. SDA will accelerate delivery of needed space-based capabilities to the joint warfighter to support terrestrial missions through development, fielding, and operation of the Proliferated Warfighter Space Architecture. For more information on SDA, contact OSD.SDA.Outreach@mail.mil or visit https://www.sda.mil.
-End-
SDA Demonstrates Link 16 in Space With York Space Systems
York Space Systems announces the first-ever demonstration of Link 16 technology from space on its Tranche 0 (T0) satellites. Photo: York Space Systems
The Space Development Agency (SDA) has successfully demonstrated what it claims is the first-ever Link 16 demonstration in space. The demonstrations took place over the last two weeks with three Tranche 0 Transport Layer satellites provided by York Space Systems, demonstrating network entry through space to ground connection from Low-Earth Orbit (LEO) to a series of receivers using terrestrial radios.
Link 16 is a tactical datalink communication system used by the U.S., NATO, and coalition forces to transmit and exchange real-time situational awareness data.
The SDA said in a Nov. 28 release that operators working with the Agency conducted both passive and active network entry, obtained fine synchronization, and transmitted multiple tactical messages from satellites using L-band radios aboard Tranche 0 Transport Layer satellites to a ground test site located within the territory of a Five Eyes partner nation.
“I can’t underscore enough the significance of this technical achievement as we demonstrate the feasibility of the Proliferated Warfighter Space Architecture and its ability to deliver space-based capabilities to the warfighter over existing tactical data links,” said SDA director Derek Tournear. “This is not only the first time Link 16 has been broadcast from space, but the beginning of turning the world’s finest warfighting force into a truly connected beyond line-of-sight joint force.”
The SDA does not have approval from the Federal Aviation Administration (FAA) to broadcast Link 16 from space into U.S. airspace, so SDA received a waiver from the National Telecommunications and Information Administration (NTIA) to transmit to a Five Eyes nation. The SDA said this is a “compromise position” and the Agency still has a requirement to test over U.S. air space.
The SDA said this accomplishment is also a “leap ahead” in the Department of Defense-wide Joint All Domain Command and Control (JADC2) effort, connecting available sensors to available warfighting platforms globally. The SDA’s PWSA Transport Layer is the backbone of JADC2 in space.
York Space Systems delivered the satellites used in this demonstration, as part of a contract for nine satellites awarded in August 2020. Eight satellites were launched in March 2023 by SpaceX, and one was on a SpaceX launch in September.
“We are proud to maintain our role as the most agile prime contractor to SDA as it revolutionizes rapid, dedicated space support to the combatant commands by deploying the most innovative solutions of state-of-the-art technology,” said Dirk Wallinger, CEO of York. “This accomplishment not only cements our commitment to advancing space technology but also underscores our dedication to providing cutting-edge solutions for the evolving needs of global security.”
York has a number of SDA contracts and is also developing 42 satellites for SDA’s Tranche 1 Transport Layer; 12 experimental satellites as part of the Tranche 1 Demonstration and Experimentation System (T1DES) program; and 62 satellites for Tranche 2 Alpha.
SDA gets OK to begin limited testing of data satellites Link 16 nodes – Space Development Agency
Date: October 26, 2023 | Outlet: Breaking Defense | By: Theresa Hitchens
WASHINGTON — The Space Development Agency (SDA) finally can begin testing Link-16 signals from its Transport Layer of data relay satellites in low Earth orbit, having just received approval from a key international regulatory body — although the agency remains caught up in a long-running Defense Department spat with the Federal Aviation Administration that is preventing use of the venerable military data/communications link over US territory.
“I’m glad to report SDA received approval from the International Telecommunication Union (ITU) for experimental use of Link 16 from space from the radios being flown on the York Tranche 0 Transport satellites. This approval allows SDA to test over international water and over the territory of a Five Eyes ally,” SDA Director told Breaking Defense in an email today.
He did not, however, reveal which of those allies — Australia, Canada, New Zealand and the United Kingdom — are involved.
The ITU, headquartered in Geneva, manages electromagnetic spectrum usage that crosses borders to prevent interference. Individual nations, however, are responsible for allocating frequencies for various domestic uses and ensuring against interference inside their own borders. In the case of the United States, the semi-independent Federal Communications Commission is the chief regulatory body, but coordination of spectrum use among federal agencies is managed by the National Telecommunications and Information Administration.
SDA has already launched 19 Tranche 0 Transport Layer satellites, as the first test birds for its planned mesh network constellation to provide high volume, low latency communications between sensors and shooters across all domains — with the Transport Layer deemed by the Defense Department as the backbone of its planned Joint All Domain Command and Control (JADC2) network-of-networks. York Space Systems and Lockheed Martin won contracts in 2020 to each build 10, but one of the York birds is staying on the ground as a test vehicle.
Tournear explained that “testing Link 16 from space first over international waters and with an international partner, while important, represents a compromise position for SDA and our requirement remains to test over U.S. air space in order to demonstrate the feasibility of the Proliferated Warfighter Space Architecture and its ability to deliver space-based capabilities to the warfighter over existing tactical data links.
“This testing is absolutely critical to SDA’s on-time delivery,” he stressed.
For SDA, schedule is everything — after all its motto is Semper Citius, or always faster. The agency has ambitious plans to put some 400 of its Transport Layer satellites up by the end of 2028, developing and launching new variants, or Tranches, every two years. Further, the SDA acquisition model has been embraced by the Space Force and the Pentagon as the way of the future to keep ahead of China.
To allow testing over national airspace, SDA needs to resolve its dispute with the FAA, which comes under the Department of Transportation and is responsible for commercial aviation safety, over concerns that Link 16 signals being broadcast through space could interfere with the ability of civil aircraft radios to receive air traffic control radar signals. While the Link 16 line-of-sight communications network long has been used by US military forces and NATO allies for communications among air-, sea- and ground-based platforms, it has never been used by satellites.
Moreover, sources from both organizations told Breaking Defense that Link 16 has been a subject of bitter contention between DoD and the FAA for several years. Ubiquitous military Link 16 terminals, such as the Joint Tactical Information Distribution System (JTIDS) and the Multifunctional Information Distribution System (MIDS), use the 960 – 1215 MHz frequency band, as do civil radio-navigation systems. Thus, DoD is required, under a decades-old agreement with FAA, to ensure that all radio equipment using Link 16 has been tested and certified to meet NTIA standards against frequency interference.
And both FAA and DoD sources say the Pentagon has been lackadaisical about doing so. Indeed, a senior FAA official in September 2021 — an excerpt of which was provided to Breaking Defense — called DoD officials on the carpet for allowing “hundreds” of uncertified aircraft to participate in exercises in national airspace. And as Aviation Week first reported, the FAA last January moved to limit DoD access to the Link 16 frequency bands for all military air, sea and land systems.
Tournear, on Oct. 19 during the MilSat Symposium in Mountain View, Calif., admitted that part of the Link 16 stalemate is “on DoD” for being slow to certify the SDA satellite links.
To that end, he said in today’s email, SDA “continues to pursue” a temporary frequency assignment from the FAA, that would allow it to “begin testing with the support of military partners with battle-ready DOD instrumentation and personnel trained in such testing.”
Tournear added that the agency is “actively pursuing” what is called “Electromagnetic Compatibility Features (EMCF) validation” within DoD, required to prove that its Link 16 terminals to meet non-interference standards.
“We have done and will continue to do all that is within our agency’s power to prioritize the completion of the requested testing. In the meantime, SDA has provided significant data to FAA outlining the safety of Link16 during its long history of military use,” he said.
Several government and industry sources close to SDA-FAA discussions have indicated to Breaking Defense that senior Defense and Transportation officials now have weighed in to speed a deal. One government official elaborated that there are two proposed SDA demos on the table, one of which is probably more doable than the other.
“I suspect that SDA will get some relief after they do the full testing and have some mitigations they can use over the US,” said another government source.
Link 16
From Wikipedia, the free encyclopedia
Link 16 is a military tactical data link network used by NATO members and other nations, as allowed by the MIDS International Program Office (IPO). Its specification is part of the family of Tactical Data Links.
Link 16 enables military aircraft, ships, and ground forces to exchange their tactical picture in near-real time; it also supports the exchange of text messages, imagery, and voice (the latter on two digital channels: 2.4 kbit/s or 16 kbit/s in any combination). It is one of the digital services of the JTIDS / MIDS in NATO's Standardization Agreement STANAG 5516. MIL-STD-6016 is the related United States Department of Defense Link 16 MIL-STD.
Technical characteristics
Link 16 is a TDMA-based secure, jam-resistant, high-speed digital data link that operates in the radio frequency band 960–1,215 MHz, allocated in line with the International Telecommunication Union (ITU) Radio regulations to the aeronautical radionavigation service and to the radionavigation satellite service.
This frequency range limits the exchange of information to users within line-of-sight of one another, although with satellite capabilities and ad hoc protocols, it is nowadays possible to pass Link 16 data over long-haul protocols such as TCP/IP using MIL-STD 3011 (JREAP) or STANAG 5602 (SIMPLE).
It uses the transmission characteristics and protocols, conventions, and fixed-length or variable length message formats defined by MIL-STD 6016 and STANAG 5516 (formerly the JTIDS technical interface design plan). Information is typically passed at one of three data rates: 31.6, 57.6, or 115.2 kilobits per second (kbits/s), although the radios and frequency-hopping spread spectrum (FHSS) waveform itself can support throughput values well over 1 Mbit/s.[1]
Link 16 information is primarily coded in J-series messages which are binary data words with well-defined meanings. These data words are grouped in functional areas, and allocated to network participation groups (NPG) (virtual networks), most importantly:
- PPLI, or Precise Participant Location and Identification (network participation groups 5 and 6),
- Surveillance (network participation group 7),
- Command (Mission Management/Weapons Coordination) (network participation group 8),
- (Aircraft) Control (network participation group 9),
- Electronic Warfare & Coordination (network participation group 10).
Development
Link 16 is intended to advance Tactical Data Links (TDLs) as the NATO standard for data link information exchange. Link 16 equipment is located in ground, airborne, and sea-based air defense platforms and selected fighter aircraft. The U.S. industry is now developing a new Link 16 SCA compliant radio MIDS-JTRS which currently is projected to implement nine various tactical waveforms, including Link 16.[citation needed]
The MIDS program, which manage the development of the communication component for Link 16, is managed by the International Program Office located in San Diego, California. In the United States, the lead Air Force command for the MIL-STD-6016 standard, plans, and requirements is the Air Force Global Cyberspace Integration Center at Langley AFB, with JTIDS program execution managed by the 653d Electronic Systems Wing at Hanscom Air Force Base near Boston, Massachusetts. The MIL-STD-6016 Standard configuration management custodian is the Defense Information Systems Agency.
What is Link 16? - everything RF
Link 16 is an encrypted, jam-resistant Tactical Data Link (TDL) network used by U.S. and NATO Allies to create situational awareness among dispersed battle elements by sharing information, over a common communication link. This enables the command and control centers to create Common Operating Pictures (COP), which allows friendly forces to electronically observe the battlespace, identify threats, and acquire targets.
Link 16 communications are used to transfer real-time combat data, voice communications, imagery, and relative navigation information in the battlefield. This network uses JTIDS-compatible communication terminals to transmit and receive data messages. Via Link 16 network, messages can be broadcasted simultaneously to as many users as needed. Link 16 is a nodeless network i.e., it does not depend on any one terminal to act as a node, instead all Link 16-capable terminals act as nodes.
This Tactical Data Link (TDL) network was developed by ViaSat Inc. and Data Link Solutions (DLS) LLC to improve interoperability and support joint operations of land, sea, and air forces.
The main application of Link 16 is as an air and missile defense command and control system. This network is being used by various countries for national air defense, linking their sea- and land-based vessels, ground-based sensors, and surface-to-air missile systems. This helps them to protect their airspace by identifying threats and neutralizing them. This link network has been credited by the US Air Force as a key factor for saving lives in multiple contested environments, owing to the high degree of situational awareness the network provides.
Link 16 uses Time Division Multiple Access (TDMA) techniques to provide multiple, simultaneous communication paths through different networks by assigning each user with a unique time duration slot. The network can be used to broadcast messages between two users or from a single user to multiple users at a time. It is referred to as a nodeless network i.e. a single Link 16 terminal does not act as the node for other terminals and thus, every terminal act as a node in the network.
Link 16 data links operate in the radio frequency (RF) band from 960 to 1215 MHz as allocated by the International Telecommunications Union (ITU) radio regulations. It supports data exchange by supporting any of the three data rates: 31.6, 57.6, or 115.2 Kbps. However, by incorporating more advanced high-performance radio architectures along with physical layer techniques such as frequency hopping spread spectrum (FHSS), Link 16 network can deliver data rates of more than 1 Mbps. It supports up to 128 time slots per second, 127 networks, and is appropriately assigned among the JTIDS radio units.
The information exchanged within the Link 16 network is typically coded based on J-series messages, a set of message formats that use binary data words with well-defined meanings. The J-series messages include network management-related information such as communication control, time slot reallocation, radio relay control, connection status, network time update, acknowledgement, and route establishment. Depending on the situational scenario, the data words are grouped under different functional areas and allocated to different network participation groups (NPGs) that include:
- Precise Participant Location and Identification
- Real-Time Surveillance
- Airborne Communications Control
- Mission Management, and
- Electronic Warfare and Coordination
The Link 16 network consists of multiple terminals that are located in various ground, marine, and air defense vehicles. These terminals are military-grade radio equipment designed according to the IPO office in San Diego, California. Different governing bodies formulate policies, standards, plans, and requirements for radio equipment to be used by land, sea, or airborne platforms. For instance, in the US, the lead Air Force command for the MIL-STD-6016 military standard is the Air Force Global Cyberspace Integration Center located in Boston, Massachusetts.
Types of Link 16 Network
A Link 16 network consists of three types of communication modes that determine which network type is suitable for the intended network member. All members of the network should select the same mode so that all the nodes can communicate with each other. Mode 1 refers to the normal mode of Link 16 where the network nodes or members use FHSS technique to hop between different frequencies within the 960-1215 MHz band to transmit and receive tactical messages. This hopping mechanism allows multiple Link 16 networks to transmit and receive over the channel. This type of network is called a Multi-Net. In Modes 2 and 4, members can exchange messages without using frequency hopping scheme. Modes 2 and 4 allow only a single network to share messages at a time. This type of network is called a Single-Net. Mode 3 exists and is a valid mode, but not used in practical applications.
Single Net: A Single Net indicates that each network member in a network has the same net number, security scheme, and the same frequency. Each network member is allocated a single time slot during which the messages can be sent and received. In this network, the nodes cannot perform frequency hopping as only a single frequency is used by the nodes of this network. A typical Single Net Link 16 network is shown in the figure given below.
Single Net Link 16 Network, Image Credit: Link 16 Model Architecture for Multiple Nets Simulation, IEEE
Multi Net: In a multi-net, different networks are available for different cluster platforms and each network contain its unique security authentication scheme, frequency band, and frequency hopping patterns (as there are multiple bands). This topology is used to isolate several NPGs that share the time slot across different networks, thereby eliminating or significantly reducing interference among multiple users. Frequency hopping pattern technique along with other signal processing techniques together improve the network performance of Link 16. A multi net design of Link 16 is shown in the figure given below.
Multi Net Link 16 Network, Image Credit: Link 16 Model Architecture for Multiple Nets Simulation, IEEE
Architecture of the Link 16 Network
The architecture of Link 16 defines the protocol stack that combines different network layers, algorithms used to organize the messages, encode, decode and perform various other operations to transmit and receive the messages over the tactical link effectively.
Components of Link 16 Network, Image Credit: Link 16 Model Architecture for Multiple Nets Simulation, IEEE
The protocol stack architecture for Link 16 is similar to other networking protocols (for example, OSI model) that are developed for computer networking applications. Initially, the application layer present is responsible for generating the desired tactical messages along with added security authentication schemes. The network layer receives these messages and simultaneously checks the optimal routes for the packets, and also determines whether other nodes in the network are active. The packets are accordingly addressed in this layer and then sent to the data link layer – which encodes, decodes and organizes the data as frames. It is also responsible for handling the messages to and from the physical layer and determines how nodes recover from potential interference that may occur during communication. The physical layer is the final layer of the Link 16 network and performs other signal processing-related functionalities such as channel coding and modulation of the message. The propagation delay is nothing but the wireless channel via which the message signals propagate to and from multiple nodes in the network. When the node/nodes on the other end receive the packet, they perform the reverse operation of decoding and organizing the message as shown in the above figure.
Applications of Link 16
Airborne Platforms: Link 16 network is currently used in several defense platforms in the land, sea, and air. For airborne purposes, popular aircrafts and fighter airplanes such as the B-2 Spirit, F/A-18 Hornet, F-22 Raptor, and F-35 Lightning II use Link 16 terminals on-board to communicate between them and with other gateways that extend the network to friendly forces beyond the contested region.
Maritime: Link 16 is being used in various US carrier ships, French carrier, Royal Navy ships, Japan maritime, MILGEM project class, and Swedish authorities.
Ground-based Platforms: VESTA (verification, evaluation, simulation, training, and analysis) is a minivan that mounts a radio station on top of it. This radio station supports Link 16 capabilities, which allows it to communicate with military platforms in the battlefield.
Implementation of Link-16 based Tactical Data Link System Using Software-Defined Radio
Introduction
Link-16 is a tactical data link used by military to secure their communication. It provides two levels of security, information security and transmission security. Information security, Link-16 uses Reed-Solomon coding, matrix interleaver, and CCSK, while in transmission security, Link-16 uses the FHSS technique, which is a spread spectrum technique that is widely used in several fields, such as bluetooth and CDMA. Software-defined radio (SDR) provides some or all function embedded in hardware move into software. Therefore, SDR now is widely used because it's flexibility.
The ability of Link-16 to prevent jamming and the flexibility of SDR have become the backround of this research. The objective of this research areto design both of transmitter and receiver of Link-16 secure communication system and implement by take some of text to transmit on it. LabVIEW is used to design this system. The system includes reed solomon coding, interleaver, cyclic code-shift keying (CCSK), MSK modulation/demodulation, and frequency-hopping.
Secure Communication of Link-16
A. Link-16
Link-16 is a tactical data link currently used by the United States Navy, the Joint Services, and the forces of North Atlantic Treaty Organization (NATO). Link-16 provides tactical communication that is safe and resilient to interference both on land, sea, and air. Link-16 uses Joint Tactical Information Distribution System (JTIDS) as the communication terminal to form the desired radio frequency (RF) signal [1]. Link-16 is the overall name of the data link system, whereas JTIDS is the communication component of the data link [2]. Or in other words, JTIDS is part of Link-16.
![Fig. 1 - Link-16 and JTIDS [3]](https://ieeexplore.ieee.org/mediastore_new/IEEE/content/media/8966551/8988782/8988856/101_154-fig-1-source-large.gif)
JTIDS provides two types of security: Message security (MSEC) and transmission security (TSEC). MSEC, or message data encryption, is applied to Link-16 in the link layer, while TSEC is applied to all transmissions on the physical layer. TSEC includes random jitter messages, symbol interleaving, spreading chips, and random frequency-hopping [4].
![Table 1- Security type in JTIDS [3]](https://ieeexplore.ieee.org/mediastore_new/IEEE/content/media/8966551/8988782/8988856/101_154-table-1-source-large.gif)
JTIDS signals are spread spectrum signals and use Direct Sequences Spread Spectrum (DSSS) and Frequency-Hopping [5] combination methods. JTIDS uses 32 pseudo-random sequences chips to modulate carrier signals, thus making the modulated signal bandwidth wider 6.4 fold as well as enhancing anti-jamming capabilities. By using frequency-hopping, it will reduce the interference because the frequency used will keep changing [6] [7].
B. JTIDS Design of Link-16
JTIDS consists of several components: RS coding, interleaver, CCSK for M-ary baseband symbol modulation, MSK chip modulation for transmission, dual-pulse diversity, and a combination of frequency-hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS) for secure transmission.
The RS code has good ability for burst error correction. Link-16 uses RS (31.15) which has error correction capability of 8 symbols of each code word to encode messages. Each code word has 31 symbols including 15 message symbols and 16 additional symbols for error detection [8].
Interleaving and de-interleaving techniques are used on Link-16 to transform burst channels with memory into random, non-memory channels. And Link-16 uses the matrix interleaving technique in its application [8].
CCSK is a type of M-ary direct sequence spread spectrum (DSSS) technique. Link-16 uses CCSK which is one of two modulations other than MSK, for baseband and spreading spectrum modulation, by transforming 5 bits into 32 chips. 32 sequences of CCSK are derived from 32 bits rotated to the left 31 times. To create a unique sequence for each 5-bit input combination. In the CCSK demodulator, cross-correlation between 32 chips will be received with all 32 possible sequences. We will look for the largest cross-correlation value to determine the 5-bit output of the 32 possibilities. Crosscorrelation is used because CCSK is non-orthogonal. By using this cross-correlation, CCSK not only serves as a spreading spectrum, but also as an error correction [8].
Continuous phase of MSK can mitigate interference beyond the frequency bands derived from process constraints in the satellite repeater. Therefore, MSK is a good modulation scheme when the use of efficient amplitude-saturating transmitters is required [2]. MSK signal is [9]
Where
Where
Spread Spectrum
There are some techniques of spread spectrum, but mostly used are direct sequence spread spectrum (DSSS) and frequency-hopping spread spectrum (FHSS). Both of them are used in Link-16 for secure communication.
A. Direct Sequence Spread Spectrum
![Fig. 3 - DSSS diagram block [10]](https://ieeexplore.ieee.org/mediastore_new/IEEE/content/media/8966551/8988782/8988856/101_154-fig-3-source-large.gif)
In DSSS, baseband signals are obtained by performing XOR operations between the PN sequence input signal to produce a signal with a dispersed spectrum. Once dispersed, the signal is modulated to be transmitted, the most widely used modulation is BPSK modulation. The DSSS signal is represented by equation (3) [11]
Where:
is the data sequence, | |
is the duration of data symbols, | |
is a PN spreading sequence, | |
is the carrier signal frequency, | |
is the carrier signal phase angle at |
For demodulating the DSSS signal, a low pass filter is used and then de-spread by performing an XOR operation between the filtered signal with the PN sequence to recover the initial data. The data signal can be recovered using equation (4) [11].
B. Frequency-Hopping Spread Spectrum
Frequency-hopping spread spectrum (FHSS) is a data transmission technique whose carrier signal moves from one frequency to another. Information is sent on a radio channel that regularly changes frequency according to predefined code. FHSS techniques are useful for suppressing interference, accommodating fading and multipath channels, and providing multiple access capabilities. FHSS is used in the military world because transmission signals using frequency hopping are difficult to detect and monitor [12].
There are two types of FHSS seen from the speed hopping frequency, which is slow FH and fast FH. Slow FH FHSS signal frequency change speed is slower than its symbol rate, while fast FH is FHSS signal frequency transfer speed faster than its symbol rate.
In the modulator, the baseband signal is combined with the hop frequency or carrier signal generated by the frequency hopping block. The carrier frequency will be generated randomly as it is controlled by PN sequence generator [13]. The output of the modulated signal will be summed from both signals, which are scattered throughout the frequency band. In the receiver, the demodulator gets the code signal back from the spread spectrum signal. For this purpose the demodulator requires the same sequence used at the end of the transmission. Therefore, random sequence pattern generators on both sender and receiver must work synchronously with each other. The decoder on the receiver then gets the binary data back. The received data and original input data are inserted into the error calculation block to calculate the error rate of the channel and displayed using the BER display. The block diagram of FHSS can be seen in Figure II.8 [14].
Simulation and Implementation Results
The intact design of the frequency-hopping system transceiver on Link-16 has been created in the LabVIEW according to the figure 2. The carrier frequency in this simulation is defined at 5 MHz, with the number of frequency jumps of 51 frequencies. The adjacent inter-frequency interval is 500 kHz. The frequency jump when simulated can be seen in figure IV.6, IV.7, and IV.8. These three images are samples of most possible hops.
This simulation shows there are two radar. Radar A is on the surface of the earth, while radar B is a plane that is flying in the air. Radar A sends information that contains the identity of radar A and radar position B against radar A. Using the system that has been created, this is the simulation results of data transmission between radar A (sender) and radar B (receiver).
It consists of 600 bits of data sent or there are 120 symbols (5 bits per symbol), then when entering RS Encoder, it turns into 1240 bits, because every 15 symbols (75 bits) is converted to 31 symbols (155 bits). In the interleaver is still the same as 1240 bits And after entering CCSK changed to 7936 bits, because every 5 bits converted into 32 bits. Then spreading with 32 PN sequences chips so that it becomes 253952 bits. These total bits will be modulated and transmitted over the AWGN channel.
In the receiver, the modulated MSK signal is demodulated to produce 253952 bits like the signal before it is modulated. The bits are despreading in the same sequence PN sequence as in the transmitter to produce 7936 bits. Next, enter the de-CCSK block to create a signal that was 7936 bits to 1240 bits or every 32 bits into 5 bits. Then enter de-interleaver to set its position back and enter RS decoder so get 600 bit back.
For the implementation of this system, simulated block diagram is inserted into the block of USRP hardware diagrams in LabVIEW, either transmitter or receiver. To perform the implementation, it takes some hardware, such as USRP, antenna, gigabit ethernet switch. The data sent as 6 text arrays with the composition of one element consists of a maximum of 75 bits or 9 characters. Each element is sent alternately one by one and the receiver will receive every single character continuously during looping. Here is the result of text submission implementation.
Conclusion
The Based on the simulation and implementation it can be concluded as follows:
Designing of frequency-hopping system has been successfully modeled in Matlab/Simulink. In transmitter used RS encoder, interleaver, CCSK, and MSK modulator. While on the receiver, MSK demodulator, de-CCSK, de-interleaver, and RS decoder are used. For transmission of MSK modulated signal, 51 randomly generated frequencies are used.
Delivery text of frequency-hopping system Link-16 successfully simulated in LabVIEW. The data sent in the form of text that shows the identity of the sender radar and the position of the receiver radar against the sender radar with a variable carrier frequency. As a result, the receiver's radar is capable of accurately receiving such information.
Implementation of text submission using USRP successfully done. The text consists of 6 arrays of text with each array consisting of a maximum of 9 characters. The text was sent and successfully received with the same result by the receiver.
Modeling and Simulation of Link-16 System in Network Simulator 2
Z. -x. He and X. Liu, "Modeling and Simulation of Link-16 System in Network Simulator 2," 2010 International Conference on Multimedia Information Networking and Security, Nanjing, China, 2010, pp. 154-158, doi: 10.1109/MINES.2010.41.Abstract: Research on the modeling and simulation of Link-16 has been got much attention nowadays. The common wireless network models are not suitable for Link-16. This paper proposes a Link-16 communication protocol architecture model with 5 layers. An extension of NS-2 (Network Simulator version 2) framework by modifying the original data structure and adding new network module is presented. Validations of delays and throughputs are proposed for further system design and evaluation.
Tactical Data Link is a communication system of combining the battlefield command center, combat forces and weapons platforms, which processes, exchanges and distributes information with wireless network communication and application protocols. It can exchange tactical data among the airborne, land and naval vessels, thereby maximize the fighting effectiveness.
Link-16 is an advanced communications, navigation and identification system that uses TADIL (Tactical Digital Information Link) J-series data format, which is developed by the U.S. to fulfill the needs of future war, and give full play to the Joint Tactical Information Distribution System (Joint Tactical Information Distribution, JTIDS), with the feature of fast, mobile, wireless, multi-user, and etc. It has become the major tactical data link within the military systems of the United States Joint Services, and forces of the North Atlantic Treaty Organization (NATO).
To complete the exchange of information between the weapon and C2 (Command and Control) platforms, verify the interoperability within the data link, and to ensure the data link system and building a steady coordinated development, the simulation of data link is needed. Simulation technology is widely used in many fields because of its advantages of effectiveness, reproducibility, economy and security. The simulation of data link can study its network performance and provide strong authentication for test programs.
A variety of network simulation tools are being used, such as NS-2, OPNET, GlomoSim, OMNeT++ and QualNet. They have strong network simulation capabilities, and corresponding wireless network simulation modules. NS-2 has a good opening feature and expansibility because of its open structure. Ns-2 provides very similar results compared to OPNET Modeler [1], enjoys a high international academic reputation, so it is widely used by many researchers around the world [2] [3]. Among the above wireless network simulation software, NS-2 is one of the most commonly used, occupied 44% of the rate [4].
This article begins with an overview of Link-16 and NS-2 simulation framework. And then according to the distinctive feature of Link-16 compared to the common wireless communication networks, the system protocol architecture is established, including the application layer for distributing tactical information, the network layer for relay with stack-net flooding, data link layer for dedicated slot allocation TDMA and physical layer of wireless network. We conclude with a section to illustrate a NS-2 environment Link-16 data link system simulation and a final section to analysis its network performance.
Related Work
U.S. attaches great importance to Link-16 modeling and simulation research. Many research institutions and companies (MITRE, SAIC, SRI, MIL3) have developed a variety of data link system used in simulation and comprehensive application system, which includes: NETWARS [5] [6], TIMS, SIMNET, EAMLSS and etc.
In contrast, the development of China's military communication network in the simulation area is slow. Although there are not developed products, but some research have been made by now. LI Kun-ming [7] and ZHAO Chun-fang [8] simulate the Link-16 network data link layer in QualNet platform. SHEN Zhen-ning etc. [9] use Matlab software to complete a physical simulation of JTIDS system. CHEN Chun-ming etc. [10], YANG Cai-yan [11] and CUI Hao etc. [12] implement the basic functions of Link-16 in the OPNET environment. YU Xiao-gang etc. [13] use OPNET to design Link-16 simulation platform and provide a variety of communication services for JTIDS functionality.
The Structure of NS-2
NS-2 starts up from Cornell University's Network Emulator REAL. Subsequently in 1995, the research and development of NS has been fund by the U.S. Defense Advanced Research Projects Agency (DARPA) for the virtual network test program (VINT). It has now become powerful network simulation software, which provides a very convenient experimental platform for the simulation of network technology. Its current version is 2, naming NS-2.
Fig. 1 is the NS-2 directory structure, which is installed by allinone way. NS-2's own source code is in the “ns-2.34” directory, which uses the tcl language to write the code in the “tcl” subdirectory, C++ code in other subdirectory. The dashed boxes in Fig. 1 represent the Link-16 simulation code directory, which will be mentioned below.
The Layer Protocol Model of Link-16
The key factor of Link-16 simulation platform is to build the network communications protocols. Therefore, the simulation of data link communications protocols is of great significance to the whole system.
Compared with other wireless communication networks in general, Link-16 has the following notable features, no-nodes, TDMA, multiple network participating groups (NPG), stack-net and flooding relay.
This paper analyzes the technical characteristics of Link-16, and designs a model for the Link-16. Compared with the OSI layers model, the model can be divided into five modules, respectively from top to down, application layer, transport layer, network layer, data link layer and physical layer. As shown in Fig. 2, the left part of the figure indicates the NS-2 wireless node model; the middle part of the figure is a comparison of the OSI/RM layered protocol and Link-16 layer protocol; the right part of the figure illustrates the NS-2 extension for Link-16 data link system model.
A. Application Layer
The application layer of Link-16 is divided into different network participant group according to different tactical application. Each combat unit can be added to one or more NPG to support a variety of tactical mission requirements.
NS-2 itself has achieved a considerable amount of information packet generation models. This paper uses diffusion/diff_sink.cc as a template, and makes data source to set intervals with uniform, Poisson or exponential distribution according to the generating of Link-16 message, so that tactical information message can be packed and sent to network layer by the timing function, timeout(). Reversely the receiver Sink receives package from network layer and unpack it.
B. Transport Layer
The Transport Layer of Link-16 provides transmission medium. Packages of each NPG are sent in a particular set of time slots by broadcasting. These packages do not contain the destination address but the source address. Any receiver in the same network with the same NPG can receives them. For the applications of Link-16 in this paper, the transport layer can be simplified and omitted. Its core function of broadcasting message packages can be implemented in the application layer, so that the program can be made systematization and modularity.
C. Network Layer
The packages of Link-16 generally do not carry the destination address information. They are sent in a block of time slots which is assigned to a specific NPG by broadcasting. Receivers select the corresponding time slots according to the NPG they belong to and receive these packages.
About the routing management, Link-16 mainly uses the flooding algorithm to find neighbors, and send packets from the source through other nodes to the receivers. In diffusion/flooding.cc we modify the original algorithm according to the features of Link-16. By adding the function of switching flooding, network units of Link-16 can relay packages alternatively. It means that all units can involve in the relay packages or certain specific units involve in relaying packages, and relay all messages or only certain message packages.
D. Data Link Layer
In data link layer, packages of Link-16 are classified by their NPGs and enter the queues, get ready to be sent at appropriate time slot. Thus, the data link layer of Link-16 can be divided into 2 sub-modules, As shown in Fig. 2, interface queues (IFqs) and media control access (MAC).
1) IFqs
As shown in Fig. 3, when receiving the packages from the upper layer, the data link layer analysis them, classify them by their message type and send them to the corresponding queue according to their NPGs. Each package in the queue is pushed in accordance with the FIFO principle at the proper blockof time slots.
The NS-2 has achieved a multi-queue model in queue/srr.cc. According to Link-16, the life-time and the priority of packages are added. Because of the real-time property of tactical messages, packages in the queues have their own life-time. If a certain package has been waited in the queue too long to exceed its life-time, it has to be removed from the queue as it does not have any meanings to be sent out. In addition, different packages may have different priorities. Imaging a message which has to be sent urgently, when the package enter a queue, it must be inserted in front of the packages with lower priority in order to be sent as soon as possible.
2) MAC
Link-16 system access is controlled by the TDMA protocol. The basic recurring unit of time for Link-16 is the frame. It is 12 seconds in length and is composed of 1536 individual access/transmit units call time slots. The time slot is the basic unit of access to Link-16. There are 1536 time slots per 12-second frame, each time slot is 7.8125msec in length. Each platform operating in a Link-16 network is assigned to either transmit or receive in each of the 1536 time slots.
In NS-2, mac/mac-tdma.cc has achieved a single-node-single-slot TDMA module with preamble slot, which can assign one slot for one network unit. Based on this file, some changes are made in this paper. An external file is used to set up the time slots plan for each network unit, which can flexibly configure every network unit with several time slots, to meet the needs of a variety of operations task in Link-16.
E. Physical Layer
Link-16 can expand its network capacity by the multi-network structure. It uses different hybrid spread spectrum pattern to separate different nets. Each NPG in which each network unit involved belongs to different net. And each net represents one in a number of mutual interference of the radio channel, which makes a number of different network units can work at the same time in the different net.
In order to improve transmission of anti-interference, Link-16 uses a frequency-hopping technology. In each single net (or a single wireless channel), the message packets are sent with one of the 51 discrete frequencies, which are in the Lx waveform band 960MHz~1215MHz. This allows multiple transmitters to be within Ling-of-Sight of each other without mutual interference.
The physical layer in NS-2, contains network interface (or antenna model), the signal propagation model and wireless channel model. Wireless channel model (mac/channel.cc) is a wireless communication medium, a virtual pipeline, connecting the two ends of communication. Network Interface (mac/wireless-phy.cc) is used to control the channel access, count the SNR of antenna and judging the signal reception. Also it calculates the transition delay and predicts the propagation weaken by the signal propagation model (mobile/propagation.cc).
NS-2 only supports single-antenna single-channel wireless network simulation. Link-16 network units working on different channels (or Link-16 multi-nets) can not communicate with each other, that is, the signals the source unit emits in a channel, can not be detected and received by other units working in another channel. Therefore, the paper added a cognitive radio module [14] [15]. The radio can be dynamically adjusted depending on the environment and the transmitting frequency to support multi-channel [16] and frequency hopping physical layer modeling.
The Experiment and Results
One of the main operational tasks for Tactical data link is real-time battlefield surveillance [17]. It mainly detects and tracks all hostile targets in its monitoring region, surveys the movement and the position of the objects, and transfers the situation information to combat units in real-time to form an effective blow against the enemy targets.
A. The Methodology
A typical surveillance mission tactical data link operational scenario is shown in Fig. 4. In Fig. 4, the blue hexagonal node, No.8, at the corner of the upper right, is the reconnaissance aircraft of the blue force. It attempts to scout the important military area of red force. The red square nodes in the middle of the figure, No.0–3, are the radars of red force. The red circle nodes, No.4–7, at the corner of the lower left, are the fighters of red force. When the blue plane flying from the direction of flight to the red side within a distance of radar surveillance, the radar node (No.3), first detects the blue force and tracks it. The radar node sends the tracking information packets, which are relayed by the other radar nodes (No.0–2), to the fighter nodes (No.4–7) in the assigned time slots in Link-16. Then the radar nodes guide the red fighters to intercept and pursue. It is the typical application of Link-16 to transfer the information of blue force from sensors to shooters of red force in the simulation scenario.
Let's make the following assumptions. Link-16 in the simulation scenario has already been well done functioning at the beginning of the already. The radar node of No. 3 does not exceed the line of sight distance (300 miles) with the nodes of No.1 and 2, can directly communicate. But it is beyond the line of sight distance with the node of No.0. So its packets have to be relayed by the node of No.1 and 2 to be received by the node of No.0. At the same time the node of No.1 and 2 are over the sight distance with the fighter nodes (No.4–7), so packets from them to the fighters have to be relayed by the node of No.0.
B. The Processing
As Fig. 5 shows, when the blue aircraft (No.8) flies into the radar surveillance area, the radar node (No.3) tracks it and broadcast the information in Link-16.
And then the radar node number from 0 to 2 in turn relay the message to the node number 4 to 7 fighter, red fighters immediately take off into battle mode in Fig. 6.
Just as seen in Fig. 7, when the blue aircraft (No.8) goes further to the military area of red force, the radar nodes (No.1–3) detect it also. The four fighter nodes (No.4–7) receive the tactical information and separate into 2 groups (No.4 and 5 for a group and No.6 and 7 for the other group) to intercept and pursue.
Fig. 8 shows that the blue aircraft (No.8) is found and quickly flees. As the same time the 4 fighters of red force (No.4–7) chase and expel it from the battlefield.
Fig. 5–8 are the animation of the simulation in Link-16. The red circle represents the transmission of the packets broadcasted in Link-16.
C. The Results
According to this design in this paper, the system end to end network delay and throughput were measured in NS-2.34.
Fig. 9 shows the delay which the red force transmits the position and other moving parameters of the blue force to the fighter (No.7). At 56s, the radar (No.3) of red force detects the target aircraft of blue force and starts to transmits the message to the fighter (No.7) through the relay by the radars (No.0 and 1) in turn. It counts 2 hops. With the two sides continuing to close each other at 172s, the surveillance messages just have to be relayed only 1 hop to be received by the fighter (No.7), so the delay has been reduced. At 440s when the two sides go closer, the radar on the fighter of its own can detect the target aircraft, so the end to end delay is almost 0.
Fig. 10 shows system throughput of the simulation in Link-16. At the beginning of the simulation there is few packets transferring to maintain the normal operation in Link-16, so the number of packets is almost as 0. At 56s when the radar of red force detects the target aircraft of blue force, packets are broadcasted in Link-16, the network throughput immediately straight up. It lasts for seconds for the network throughput stables at around 15,000bps. At 350s the fighters of red force divide into two groups to pursue and intercept separately, so they begin to exchange packets to work together which increase the fighter-fighter type messages. This leads to further increase network throughput. At the same time the number of packets which need to relay are decrease because of both sides' approaching. Counting this above the network throughput curve does not rise up linearly but rather to increase than the smoothly. Finally it stabilizes at 20,000bps around, which is just like the normal data rate (26,000bps) in Link-16.
Conclusion
This paper analyzes the technical characteristics of Link-16 and designs the protocol system model for Link-16. NS-2 is suitable for simulating the wireless military networks as its features and benefits. So the function of NS-2 is extended by modifying its original data structure and adding new network modules, and a typical simulation scenario is designed to simulate Link-16. Also the simulation results analyzed statistically. As can be seen from the simulation results, the communication protocol architecture model of Link-16 can meet the need of simulation of Link-16.
Open References:
- Demystifying Tactical Data Links.pdf
- Military Data Link Integration Application (MDLIA) James T. Sturdy
- TADIL J: Introduction To Tactical Digital Information Link J and Quick Reference Guide - ADA404334.pdf
- DoD 4650.1-R-1, LINK 16 ELECTROMAGNETIC COMPATIBILITY (EMC) FEATURES CERTIFICATION PROCESS AND REQUIREMENTS April 26, 2005 - 465001r1p.pdf
- NTIA aeronautical radionavigation service (ARNS)0960.00-1164.00_01MAR14.pdf
- Spectrum 101: An Introduction to Spectrum Management - ADA458175.pdf
No comments:
Post a Comment