Multifunctional Information Distribution System
Multifunctional Information Distribution System ( MIDS, dt: Multi- Functional Information Distribution System) is a military radio system according to the time division multiple access ( TDMA) in the frequency range 890 - 1215 MHz can work.
Use
Originally developed for the armed forces of the United States, today the system is inter alia used in the general area of the NATO air defense. It operates in the frequency range 960 - 1215 MHz, which is allocated in accordance with the Radio Regulation aeronautical radionavigation service worldwide as primary users. Moreover, this frequency range is reserved on a worldwide basis to the use and development of electronic aids to air navigation on board of aircraft and the use and development of related facilities on board. Therefore, the overall system MIDS / JTIDS has in NATO Europe just over a frequency availability with restrictions and conditions.
Features
MIDS is the improved version developed by the U.S. JTIDS and with this largely compatible.
MIDS terminals are used in the Air Force, the Navy and the Army. The technical characteristics of the MIDS terminals are in Standardization Agreement ( STANAG ) 4175 specified.
A variant of MIDS cross section used is the MIDS LVT ( MIDS Low Volume Terminal), which is funded by the U.S., France, Germany, Italy and Spain and MIDSCO, a joint venture between Thomson CSF, GEC, Siemens, Italtel and Enosa has been developed. After production engineering, production was transferred to ViaSat and Data Link Solutions EuroMIDS. EuroMIDS joint venture of the European defense company EADS (DEU), SELEX (ITA ), THALES (FRA) and Indra (ESP ) represents MIDS LVT primarily produce for European MIDS users. As the successor of the MIDS LVT is currently being developed under American leadership, the MIDS JTRS - ( MIDS Joint Tactical Radio System). In Germany, the MIDS - LVT is used by all military Orgisationsbereichen. The use of control has cross-section for this organization areas the weapon system command of the Air Force Department VI 1 - ( 1 WaSysKdoLw VI ) held.
Technical Principle
MIDS uses, for information transfer, a time division multiplexing ( Time Division Multiple Access, TDMA ) in the frequency band 890-1215 MHz. The MIDS terminal sends this in very quick succession on 51 different operating frequencies ( FHSS, selection in the pseudo-random method ) to send its information, or to receive. Base is a periodically repeated 12s - the period of the frame; the smallest, a particular terminal associated information unit is called timeslot. Within the time slot, the frequency is also changed nor in pulse. The sequence in which the individual operating frequencies are run is defined by a key algorithm. The carrier is also modulated with a pseudo-random noise pattern (DSSS), which can only be removed by a crypto key that exists only Confederate forces. This key is also used to determine the transmitting and receiving frequency and the encryption of the data stream. By spreading the signal in conjunction with redundant transmission and additional error correction data according to the Reed-Solomon method, MIDS provides a reliable, secure and difficult störbare radio data link ready. Depending on the complexity in the error correction can be achieved data rates between 57 kbps and 114 kbps in practice.
Usually sends in each time slot is always only one terminal (dedicated access), but there are also network optimization procedure to be used where certain timeslots from any terminal when necessary ( contention access). This is particularly true for information which is not important because of a high repetition rate to the reliable transmission at a given time, in particular for digital voice transmission.
As more terminals to receive the on only one of the available frequencies at all times, creating different, mutually independent sub-networks is made possible by an intelligent nesting / allocation of time slots that do not interfere with each other. In practice, however, this is highly limited, as is increased with the use of multi- netting of the energy input into the frequency band ( time slot duty factor ) so that there is a risk that settled in the same frequency band frequencies of the civil air navigation (DME, IFF) disturbing. The permissible limits are laid down in national frequency clearances, each for a particular air traffic control area ( Flight Information Region, FIR) apply.
The assignment of time slots to certain terminals is performed by the MIDS network design, this determines when a MIDS terminal on which time slot is listening or is allowed to send. The MIDS network is loaded into digital form in the terminal and configured the jump frequency transmitter in accordance with the design specifications.
So do not overlap the individual data packets, MIDS terminals to identify the correct timing of the transmission need a time standard, the net time reference ( NTR ). One of the terminals in the network works as NTR, the sent of him time characters are by definition be correct, and the other terminals adjust their internal clocks after. Depending on the progress of the synchronization process are the terminals in the states
- Starting net entry ( synchronization starts )
- Coarse sync ( achieved coarse synchronization, data reception is possible from here )
- ( achieved fine synchronization, only here a transmission is possible ) fine sync
The NTR itself gets its time usually consists of a binding time standard, eg GPS time.
Offer in order to avoid the dependence on the local time reference NTR MIDS terminals now also have the option of External Time Reference ( ETR ). But this is on each MIDS platform a highly accurate time standard, eg GPS mandatory.
The mixture of ETR and ETR- based networks is possible if an ETR terminal as NTR is selected for those network users who can not use the ETR method.
Services of the MIDS
The communication services listed below can be performed by MIDS at the same time, bearing in mind that, of course, a common bandwidth of the communication channel must be shared:
Data Link
Tactical information is acc. Transferred Link 16 standard in "fixed format messages". The transferred here information is sent to the guidance system, in which the MIDS is integrated.
Secure Voice
MIDS provides two encoded digital radio channels that can be used in different virtual channels 127. Depending on the available bandwidth modulation rates up to 16 kbit / s are used. Audio information is transmitted in "free-format messages".
TACAN
MIDS as a hardware module contains a full TACAN cards set; the terminal is mounting compatible ( in fit form & function) with many military TACAN receivers.
Relative navigation
MIDS uses complex algorithms to evaluate and Kalman filtering of received other MIDS signals. The resulting calculated, corrected proprietary position is again broadcast via the Link 16 PPLI message.
Relative navigation should especially help aircraft to an improved position accuracy. By now widespread use of GPS device which is, however, no longer as important as before.