SIMULATION IN SYSTEM DESIGN

3.2.1 General

Simulation is a necessary tool for planning ACDS. The operational concept of ACDS is so large that computer simulation is essential to getting the job done on time in the design, evaluation, checkout and training stages of developing the command data system. There will be many different equipment and system interfaces for ACDS. Management information needs will require that nearly continuous simulation takes place to keep abreast of the evaluations of proposed system improve-ments and changes.

ACDS must also interface with other command data systems. Changes in these systems can radically affect the command data system. To be ready for such changes planners must be able to evaluate their possible effects. Simulation is the only effective tool that can be used to do this.

During the design phase of ACDS, planners will rely heavily on simulation to prevent fruitless investigation and insure maximum use of budgetary allocations. Since data systems in particular, and defense systems in general, continue to grow in complexity, scope, and cost, it becomes increasingly important for planners to be provided with tools that will let them test proposed configurations without buildinghardware.

Simulation is the most powerful tool available to the planner for this purpose.

Before describing the simulation tools of particular importance to the ACDS planner, some background information is appropriate. This information is applicable to all simulation problems. This background is, however, slanted to the particular problems faced by the planner of the advanced command data system.

The obvious feature of all simulations is imitation or modeling. But a simulation is more than just a model; it has an operator and an objective. The operator adds dynamics to the model. For example, the operator of a ship-to-shore trajectory simulation would be a numerical integration method, a computer program, and a

computer, Common objectives of simulation are analysis, checkout, and training.

Command system designers use simulation to analyze the complex operation of contem-plated or existing systems. Large systems are checked out with simulated inputs.

System operators are trained with man-machine simulations. System design, checkout, and training simulations are all important to planners of an effective command data system.

Once a planner has identified a need for simulation to help him solve a specific command control problem, then he has to decide whether or not it is practical and economic to use simulation. If he decides in favor of sinul-ation he next must decide what type of simulation and how it must be implemented.

There are two problems to be faced in deciding if simulation should be used. First the planner must find out if the specific command problem area can be simulated accurately enough for the simulation results to be valid. Next he must determine the trade-offs between simulating part of the system and using part of a real system.

For example, it may be more expensive to simulate a piece of transmission hardware of a tactical data system than it would be to buy the piece of equipment and try it, especially if the equipment is an off-the-shelf item.

If simulation seems appropriate, the next step is to develop a model of the specific command data problem to be solved. Modeling is an art which requires the talent of a specialist. Yet the planner must understand a great deal of this art to plan effectively and wisely. A section of this volume is devoted to modeling.

One point should be emphasized about design of simulations. A simulation should be easy to use. Parameters in the simulation must be easy to vary. Also the simulation should record its results so that they can be readily interpreted.

These, then, are the fundamentals of simulation. Now we will discuss simulation for system design, development. checkout; test and evaluation with particular reference to use in simulation of ACDSo

A system designer does not simulate and model to create system designs but to

test system designs. A system designer can test and examine early forms of his design with simple diagrams and hand calculations. His intuition and experience tell him

that one equipment configuration is more functional than another. However, as the design becomes more advanced, he finds it increasingly difficult to evaluate

de-sign trade-offs. Finally, the dede-sign is too complex. He can no longer see the dynamics and interrelationships of the heavy components.

How can he be sure his design will perform as he expects when subjected to stresses in the real world? One method is to build a prototype system and subject it to a simulated real-world environment. Reasons why this is often an unrealistic approach,

especially for military command and control systems are:

1) Simulated environments, such as military maneuvers, are expensive in time, manpower, and money.

2) It is difficult to reproduce real-world environments for repetitive tests of system prototypes.

3) System prototypes are expensive and may require years of development.

4) .Often, srcarce resources such as shipyards, cannot be used.

Computer simulation is a fast and inexpensive alternative method. Simulation is limited by the ability of the simulation designer to create an accurate model of the system components and their inieraction. System components may be computer programs, people, information channels, sensors, and weapon systems. Each com-ponent and its dynamic relationship with others must be represented accurately for valid system simulation. However, 'The actions of people are relatively unpredictable,

especially when involving evaluation and decisions.

Two general classifications of system simulations are man-machine and all-computer simulation. Application of these two types of simulation to the design of command and control systems are discussed next.

3.2.2 Man-Machine Simulation (General)

Operations simulation simulates operation of a command data system at the interface between command personnel and displays. Figure 3-1 shows a command data

environment and the simulated man-machine interface.

An operations simulation presents simulated information to command personnel and modifies the information to suit their response. An operations simulation consists of command personnel, communication equipment, and information exchange. How

information exchange between command people and communication equipment is controlled depends on information rate and quantity. If small amounts of information are communicated, the information exchange might be done manually with switches or grease pencil displays. Since information rates and quantities are high for command and control systems, operations simulations generally use computers to control informa-tion exchange. A computer also.simulat.es other components of the command and control environment, such as sensing and controlling devices, and external world activities.

Objectives of system designers are to increase the effectiveness and functionality of system design and reduce time and cost of implementation. The operations simulation tool can be used by system designers to achieve these objectives. However, these objectives are too general to be used in planning specific simulation runs. Fach simulation run or series of runs must produce data to form specific conclusions about system design.

System design is arrived at by using past experience, imagination, projection, and intuition. Many system parameters are difficult to evaluate: type of information displayed, frequency of information updating, number of operators required,

per-formance of the operators under peak loading, reaction time of the operators, types of operator errors,. consequences of operator errors, unnecessary control options, and necessary automatic modes of operation. These parameters affect system, design; quantity of communication links, size of computer memory, speed -of the selected computer, computer software, and so on.

A model of the system may contain hundreds of parameters to be examined. Sometimes only one parameter needcbe examined with a series of simulation runs. For instance, the effect of aggregate or lumped radar returns during peak loading on the commander's actions could be tested with a series of simulation runs.

Sometimes a system design contains latent parameters as requirements which are illumi-nated during operations simulation. Simulation stimulates ideas to improve system design.

Operations simulation provides feedback to system designers for improving system design.

This reduces time and cost of implementation by reducing modifications to the pro-duction model of the system.

-I J World \-.

•.• ^t Acrivities ¹ .

Sensing Controlling

Devices Devices

I ,A

Devices

Comomunication devices

*

0

00