Radio Traffic Simulator for Electronic Warfare Applications

Hans Blad

Telub Teknik AB S-351 80 V h J O , Sweden

1. ABSTRACT

A modem electronic warfare system is a very complex system. To be able to, in an effective way, train oper- ating personnel and perform functional tests of the system one needs a simulator for the radio traffic.

Telub Teknik AB has on contract from the Swedish Defence Materiel Administration developed a radio traffic simulator which is used for training and main- tenance purposes. It is a system that is comparatively cheap and is simple, to use, but is still a very quali- fied training and maintenance system. The operational experience is good and the users are very pleased.

2. INTRODUCTION

The simulator can generate radio traffic of either FM, A M or SSB modulation in the frequency range of 20 to 512 MHz. The simulator can simulate a great num- ber of radio nets and radio stations. However, only a few transmitters can be transmitting at one time. The simulator simulates both distance and direction to the transmitter and therefore "locates" it at a specific geographical location.

The information sent by the simulated radio nets is re- corded messages of any kind.

These features make it possible to simulate a war-time signal environment to allow for realistic training con- ditions.

The construction of a simulation scheme is made interactively with a number of menus. The simulation data is stored on diskettes and the traffic on audio casette tapes.

The simulator is designed to work with a Swedish Army electronic warfare system but can easily be adapted to other systems. As the simulator simulates

traffk with real messages it can be used not only to train operating personnel of the electronic warfare system but also any intelligence personnel whose duty is to intercept and listen to radio traffic.

3. FUNCTIONAL DESCRIPTION

The simulator is connected to the antenna inputs of the electronic warfare system instead of the antennas. The radio signals are distributed on coax and therefore no signals are sent "on the air".

A brief block diagram of the traffic simulator is given in Figure 1.

I I m ELECTRONIC

RADIO TRAFFIC SIMULATOR WARFARE SYSTEM

DIRECTON FINDERS

DISTANCE 4 (Anmunora)

I I ' 1

AUDIO DISTANCE INTERCEPT (Tapa mcordo (Anmuaton) RECEIVERS Dlgltal)

JAMMERS PROGRAM DISTANCE CONTROL (AH"Ion) ~ C ~ p u C e r )

Figure 1

The radio signals, which are the physical carriers of the simulated traffic, are generated and modulated under program control of a traffic simulator computer. The computer calculates, in real time, the direction and signal strength for the simulated radio station which is about to transmit. This is the input to the electronic warfare system to locate the radio in the frequency and space domain. The coordinates for both

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the radio station and the receivers of the electronic warfare system are stored as a part of the control information for the simulation. Since the calculation is carried out in real time, the coordinates for the elec- tronic warfare system can be changed with no delay for recalculation etc.

The propagation model used for the signal strength calculation is a spherical earth model. No terrain data base is used, since this would not give any additional training benefits.

The signal can be subjected to simulated fading to simulate the effects of a moving transmitter.

4. USER INTERFACE

The simulator is operated by means of a number of menus. The menus are divided into three main groups, depending of the main purpose of the functions. A graph of the menus is given in Figure 2. To be able to run a simulation one needs to generate the simu- lation data. This is done from the menu Simulation Construction. Running a simulation is done from the menu Simulation Handling. The third main group of menus is used for fault location both in the electronic warfare system and the simulator itself.

Main menu

I See next figure

specific military unit. This process has been called sequenzation of a simulation.

Finally in step three the sequenced data is undertaken a process which has been called compilation, which to a great extent is an unattended operation. This gives as an output the simulation data on two diskettes and a number of audio cassette tapes. The diskettes and the tapes include the complete simulation and can therefore be distributed for use on other simulators besides the one used to generate the simulation.

The menus used for the construction of simulation data are shown in Figure 3.

A I I <,>le Unlt catalogue

Unit mwement -1 Alphabet recardlng

Figure 3

5.1 Recording of messages

The messages that are to be used in the simulation can either be recorded on cassette tape or can be stored digitally in the computer. The tape storage gives higher speech quality but the digital storage gives faster access to the message. The audio input is either a microphone input or a line input if some kind of prerecorded messages are being used.

Besides the two special kinds of digital messages that can be defined. The f i s t kind is data transmission. For these messages the operator only gives the length of the message. This results in a message made up by an, in the system prerecorded, FSK signal of the specified length.

Figure 2

5. GENERATION OF SIMULATION DATA

The process of generating simulation data is carried out in three major steps.

The first step involves recording of messages, defining radio stations, radio nets and military units together with their geographical location. These data are used to generate the simulation scheme, which is done in step two. The same basic messages and data can be used to generate many different simulations.

In step two simulation data is generated by defining which message is to be sent at a certain time by a

digital recorded message there

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The second kind is spelled message. For these mess- ages the operator has recorded the alphabet for dif- ferent languages in advance. When defining a mess- age, the letters that are to be spelled are typed in.

5.2 Defining radio stations

To be able to define radio nets and their properties one has to define the used radio stations. The proper- ties that have to be defined for each type of radio station are frequency range, modulation type, channel spacing, output power and antenna height. Up to 999 different radio stations can be defined.

5.3 Defining military units

The radio net involves different military units. These units have to be defined to the simulator. The data needed by the simulator is the unit code and its geo- graphical coordinates. Since a military unit is normally moving the coordinates change in time. The operator therefore gives the coordinates for different times. The number of moments for which the operator defiies the coordinates depends on how accurately he wants to define the unit’s location. The simulator interpolates the location of the unit between the given coordinates as a function of time.

The operator can also define times at which the unit is radio silent. No transmission of messages from this unit is possible during periods with radio silence.

5.4 Defining radio nets

A military unit can be a part of many different radio nets. Therefore the different radio nets have to be defined. The data needed for each net is which units that use the radio net and what radio station each unit is using. Different units can use different radio sta- tions. The simulator verifies that the different radio stations in the net have common frequencies and are using the same modulation,

In this menu the operator is also informed about the total number of messages sent in this net and how many messages each unit has sent. These numbers are updated during sequenzation of a simulation.

5.5 Coordinates of the electronic warfare system

The operator shall define the coordinates for the elec- tronic warfare system. These coordinates can be changed when running the simulation. The purpose for

giving the coordinates at this point is to give a default location if no change is made while running the simu- lation. This function can also be used to make same basic tests of a connected electronic warfare system. A transmitter can be located at any coordinates and the directions and signal strength to the electronic warfare system are given.

5.6 Sequenzation

During sequenzation the operator defines which mess- age is to be sent from which net and unit at a speci- fic time. When a transmission is specified the coor- dinates for the transmitting unit are calculated and put into the sequenced data.

The menu gives the operator a graphical representation of the transmissions to help place the messages at the correct times.

To any of the transmitted messages, the operator can attach a note. This is a free text of up to 120 lines of text. These messages are marked with an asterisk and the notes can be read when running the simulation. These notes are helpful for the operator running the simulation to give him instructions, data what events that have occurred etc.

5.7 Compilation

The compilation performs an extensive check of the simulation data to verify that no illegal data has been entered. It collects all the necessary information need- ed to run a simulation and puts it onto two diskettes. Also all the transmitted messages are copied onto new cassette tapes, since they need to be in the right order on the tape for running a simulation.

This operation, which takes some time, is all under- taken unattended except when the operator is asked to change cassette tape in any of the tape recorders.

6. RUNNING A SIMULATION

To run a simulation only the diskettes and cassette tapes generated during compilation is needed.

When the operator selects a simulation that is to be run the frequencies for the different nets are random- ized within the frequency range of the net. Two fre- quencies for each net are randomized. One ordinary frequency and one spare frequency. The operator can, whenever he wants, change to the spare frequency for any net. The operator can also choose to use either

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new randomized frequencies or he can use the fre- quencies used last time the simulation was run.

The operator can start the simulation from any point in the simulation data. He can stop the simulation at any time, go back or step forward in simulation time and restart the simulation. If any transmission has a note attached to it, the operator can read the note.

When the simulation is stopped, the operator can change the coordinates for the electronic warfare sys- tem, and restart the simulation with no further delay for recalculation etc.

7. HARDWARE

The simulator is housed in three cases. See Figure 4. One case contains the computer, one case all the audio parts of the simulator and the third case con- tains the radio frequency parts of the simulator. The RF part of the simulator is galvanically isolated from the other two cases and can be placed up to 100 m from the others to allow a convenient connection to the electronic warfare system.

The computer is a standard UNIX workstation, HP 9000 model 330, with 4 MByte main memory. The program which is written in Ada has an object code of about 1 MByte.

The tape recorders are remote controllable. They have two channels. One is used for the audio and the other channel is used for positioning and identification of the tape. The tape recorder is running at a fourth of normal speed, giving 6 hour recording time on a standard C90 cassette tape.

Figure 4

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