thumb|320px|Joint Tactical Information Distribution System Users, 1990

The Joint Tactical Information Distribution System (JTIDS) is an L band Distributed Time Division Multiple Access (DTDMA) network radio system used by the United States Department of Defense and their allies to provide secure Integrated Communications, Navigation, and Identification (ICNI) by data communications needs, principally in the air and missile defense community.

JTIDS radiates 6.4 μs long pulses (measured at the 90% amplitude points) followed by a 6.6 μs long pause. Each pulse conveys five bits of data, each represented by a 32-chip cyclic code shift keying pattern obtained from a cyclic permutations of a fixed 32-bit pattern. The 32-chip sequence are encrypted in secure modes of operation, and is then modulated with Continuous Phase Shift Modulation (CPSM) at 5 megabit-per-second (Mbps), also referred to as Minimum Frequency Shift Keying (MFSK). The band is today divided in two bands which are additionally assigned to the Aeronautical Mobile (R) Service (AM(R)S) between 960 MHz to 1164 MHz band and the Radio Navigation Satellite Service (RNSS) between 1164 MHz to 1215 MHz. while a Comparison of National Link 16 (JTIDS/MIDS) Frequency Clearance Agreement, Geographic Area Limits and EMC Test Program Equipment Environments for Europe can be found in.

A JTIDS/MIDS network employs Time Division Multiple Access (TDMA) (similar to cell phone technology) combined with frequency hopping by selecting more or less randomly a frequency for transmission of each pulse among the maximum defined 51 center-frequencies. To reduce the Radio Frequency Interference (RFI) impact of JTIDS/MIDS pulses onto the primary systems, consecutive pulses shall not be a closely adjacent center-frequency to the previously used center-frequency.

Time slots are assigned to a single user (e.g. AWACS) or a group of users (e.g. fighter jets) subscribed to the same JTIDS/MIDS network. This is accomplished by definition of a period called an epoch with a duration of 12.8 minutes consisting of 98304 time slots, before repeating the sequence. Each epoch is divided into 64 individual, 12 second (s) long time frames. Each time frame is divided into 1536 time slots, having a duration of 7.8125 milliseconds (ms) in duration, providing 128 time slots per second for the transmission or reception of data. A time slot is defined by a duration of 7,8125 ms. A time slot can consist of 72 pulses, 258 pulses or 444 pulses, which depends on the message format employed. Each pulse in a time slot is defined by an on time of 6.4 μs (measured at the 90% amplitude points) and followed by a 6.6 μs long pause. Each pulse is transmitted at a more or less randomly selected different carrier frequencies sequentially. Within each slot, the phase angle of the transmission burst is varied to provide PSK. and since no international allocation for the use of JTIDS/MIDS was made, operation of JTIDS/MIDS is limited to Non Interference base use to the Primary Services to which the frequency band between 960 MHz to 1215 MHz has been allocated on a worldwide basis. Operation within a state is subject to limitations and restrictions, which have to be defined in a JTIDS/MIDS Frequency Clearance Agreement (FCA) by each state before JTIDS/MIDS can be operated in that state. While FCA are similar in most states, the can significantly differ depending on local systems in use and density of equipment, and differ e.g. in maximum TSDF or EIRP.

To minimize the impact of JTIDS/MIDS signals during operation on the systems and equipment of the primary systems in the frequency range 960 MHz to 1215 MHz to an acceptable level the ElectroMagnetic Compatibility (EMC) had to be proven in extensive bench and flight tests to the Federal Aviation Administration (FAA) and the ministries supervising aviation safety in the partner states that took part in the JTIDS/MIDS program.

The following Aeronautical Radio Navigation Service (ARNS) systems are in operation in this band:

  • Distance Measuring Equipment (DME/ and DME/P) and ICAO compliant use of
  • TACtical Air Navigation (TACAN)
  • Secondary Surveillance Radar (SSR) - Mode A and Mode C that has in the US the designation ATCRBS (Air Traffic Control Radar Beacon System) - Mode S (Mode Selective)

Systems that are based on the functionality of SSR Mode A, Mode C and Mode S, which are

  • Airborne Collision Avoidance System (Global Positioning System) with a center frequency for the L5-signal of 1176.45 MHz
  • Gallileo E5A und E5B

The specifications to achieve Electromagnetic Compatibility between JTIDS/MIDS and the ICAO systems operating in the frequency range between 1164 MHz bis 1215 MHz are defined in the US in DoD 4650.1-R, Link 16 Electromagnetic Compatibility (EMC) Features Certification Process and Requirements, 2005-04-26

The spreading of the pulses of the radiated power over the frequency range between 960 MHz to 1215 MHz has the benefit that it reduces the interference impact on a few channels of the primary systems, while reducing susceptibility to jamming and interference for JTIDS. Each type of data to be transmitted is assigned a slot or block of slots (channel) to manage information exchanges among user participation groups. In traditional TDMA, the slot frequencies remain fixed from second to second (frame to frame). In JTIDS TDMA, the slot frequencies and/or slot assignments for each channel do not remain fixed from frame to frame but are varied in a pseudo-random manner. The slot assignments, frequencies, and information for each JTIDS/MIDS network are all encrypted to provide computer-to-computer connectivity in support of every type of military platform to include U.S. Air Force fighter aircraft and United States Navy submarines.

The full development of JTIDS commenced in 1981 when a contract was placed with Singer-Kearfott (later GEC-Marconi Electronic Systems, now BAE Systems E&IS). Fielding proceeded slowly throughout the late 1980s and early 1990s with rapid expansion (following the September 11 attacks in 2001) in preparation for Operation Enduring Freedom (Afghanistan) and Operation Iraqi Freedom. Development is now carried out by Data Link Solutions, a joint BAE/Rockwell Collins company, ViaSat, and the MIDS International consortium.

See also

  • List of established military terms
  • Glossary of military abbreviations
  • Air Defense Control Center
  • Combat Information Center
  • Tactical communications
  • Naval Tactical Data System
  • Mission Control Center
  • Electronics Technician

References

  • Collins Aerospace MIDS page
  • Viasat MIDS page