How to create a network

The US Institute for Telecommunications Science (ITS) has published a well-known model for radio propagation commonly referred to as the Longley-Rice model. The original code in FORTRAN has been translated into a dynamic link library for Windows. The input of the model includes environmental, system, and statistical parameters. The output is the predicted path loss between units.

There are some technical parameters in addition to those of the ITS model that must be selected to compute the received signal knowing the path loss. The program supports 25 different configurations that are related to the radio installation in use.

The program does more than evaluate the quality of communication between units. If you have selected a network topology where rebroadcast is allowed, the program will initiate as much iteration as necessary to find the shortest successful path between units. If no path is found after the maximum number of rebroadcasts is reached, the link will be shown in red.

Each unit entered in a net has a role and a radio system.

The net name can be up to 30 characters long.

For a frequency hopping net, these entries correspond to the lower and upper limits of the hopping set. The program computes the mean frequency as the entry for the propagation model.

Either horizontal or vertical (in accordance with the system in use).

The Spot mode is for a one-try message. The Accidental mode is for interference evaluation. The Mobile mode is for units that are moving while communicating. The Broadcast mode is for stationary units. The effect of percentage of time, locations, and situations depends on the mode selected.

The terrain surface refractivity is a measure of the air refractivity above/near the ground. In general, the average refractivity would decrease with altitude, being a maximum at sea level. In the absence of any specific data, the default value should be used.

These properties determine together the nature of the radio wave reflection on the ground in a Line-Of-Sight radio link. In general, the more conductive the terrain is, the greater is the risk to have important attenuation or fluctuations of the radio signal. The worst case is the “picket fence” type. In the absence of any specific data, default values should be used.

This option is used to select the type of climate mostly encountered in the selected deployment area.

        Equatorial

        Continental Subtropical

        Maritime Sub-Tropical

        Desert

        Continental Temperate

        Maritime Temperate Over Land

        Maritime Temperate Over Sea

These options set some of the calculation parameters in the ITS algorithm used in the program. The atmospheric conditions like climate and weather vary in the different areas of the world, and affect both the refractive index of free air and play an important role in determining the strength and fading properties of radio signals. For instance, the refractive index gradient of air near the surface of the earth determines the way a radio ray is bent or refracted as it passes through the atmosphere. The Continental Temperate climate is common to large landmasses in the Temperate Zone.

Restores all net properties to their initial value, when the form was opened.

Sets the propagation model parameters of a network to their defaults.

Example:

        VHF Name of the first installation

        50 Power in Watts

        0.25 Receiver threshold in microVolt

        0.5 Line loss in dB

        0.8 Antenna gain in dBi

        2 Antenna height in meters

        UHF Name of the second installation

        20 Power in Watts

        0.5 Receiver threshold in microVolt

        1.5 Line loss in dB

        4 Antenna gain in dBi

        2.5 Antenna height in meters

        ...

Transmit power in Watts - manual entry.

Receiver threshold in microVolt into 50 Ohms - manual entry.

Line loss in dB - manual entry.

Antenna gain in dBi (gain relative to an isotropic antenna) - manual entry. To translate from dipole to isotropic just add 2.2 dB.

Antenna height in meters - manual entry.

Use this check box to show or hide a net on the map picture.

Use this option for a net where needlines from command posts to subordinate units are required, but not between subordinates. Rebroadcast units can be used to increase the communication range.

Use this option for a data net where a master unit polls slave units, with no links between slave units.

Use this option for a data net with nodes that can retransmit datagrams (rebroadcast, digipeating).

If set to zero, this parameter will inhibit retransmission.

Otherwise:

(Maximum number of rebroadcasts) = (Time to live) - 1

Since many units in a net may share some technical parameters, these parameters were regrouped under a same system definition to reduce memory usage. As soon as a unit has a parameter that differs from the other units, a new system must be defined for that unit. The only exception is the antenna height, which can be overwritten.

User can select colour and threshold for network drawing.

4. Edit the network name and all radio propagation parameters

10. Check units to be in the network. For each unit select a role and a system.