TABLE OF CONTENTS

• How is the radio range of a wireless device defined in NetSim?
• What is the default range of sensor nodes?

How is the radio range of a wireless device defined in NetSim?

There are two different channel model in NetSim which decides the communication range of the device.

Range-based: The propagation loss depends only on the distance (range) between the transmitter and receiver. There is a single Range attribute that determines the path loss. This is not a real-world loss model but a theoretical model useful for experimentation. Please see https://tetcos.com/help/v13.3/Technology-Libraries/Propagation-Models.html#range_based to understand the working of this model.

Receivers at or within Range meters see a 0 dB path loss. Hence received power equals transmit power. Receivers beyond Range see a 1000 dB path loss. Hence received power will be close to -1000 dBm i.e., zero in linear units.

This can be configured by right-clicking on the ad-hoc link going to properties and setting the path loss model to range based

Pathloss model-based: The communication range of sensors in a simulation can be increased/decreased by adjusting the (i) transmitter power of the transmitting sensor nodes, (ii) receiver sensitivity of the receiving sensor nodes, and (iii) the path loss in the network. 

The first image below shows how to modify the (i) transmitter power and receive sensitivity in the interface settings. The second image below shows how to modify the path loss in the ad-hoc link properties. 

Increasing the transmitter power and reducing the path loss will increase the communication range of the sensor nodes while decreasing the transmitter power and increasing the path loss will reduce the communication range.

1. Transmitter power (More Tx power implies a higher range)
2. Path loss (Higher path loss exponent leads to the lower range)
3. Receiver sensitivity (Lower Rx sensitivity leads to a higher range. Rx sensitivity is in negative dB, hence lower means more negative).
4. Distance between the nodes will have an impact on the received signal strength since path loss increases with distance. 

Pathloss from the standard path loss equation is equated to the receiver sensitivity to compute the radio range, viz.,

where TX(power)  is the transmitter Power, 

G(T) is the transmit antenna gain, 

G(R)is the receiver antenna gain,

PL(do) is the reference distance path loss,

η  is the path loss exponent,

d(T) is the transmitter range

d(0) is the reference distance

The reference distance path loss (PL(d0)) is given by,

We now consider an example involving IoT/WSN which uses the 802.15.4 standard. 

In 802.15.4, d(0) the reference distance is 8m, while the operating frequency is 2400MHz. Applying these in the above formula, we get PL(do)  58 dB. 

Given a transmitter power of 1mW or 0dBm, zero gains for the transmit and receive antennas, and, receive sensitivity of -85 dBm, we can compute the transmit range, as follows:

These calculations are explained in some depth in the white paper: https://www.tetcos.com/iot-wsn-white-papers.html

What is the default communication range of sensor nodes?

The default range of sensor nodes in a simulation depends on the path loss model used. For example, if the path loss model is set to "No Path Loss," then the range of the sensor node is unlimited. The default path loss model is set to "Log Distance" with an exponent of 2, which has a range of approximately 177 meters.

There is a common misunderstanding that a range of 177 m implies that transmissions work perfectly till 176 m but suddenly stop at 177 m. This is not so. The error rate gradually increases as the tx-rx distance is increased assuming all other parameters are kept constant. Therefore, the range is defined as the tx-rx distance at which there is a certain packet-error probability.

Simulation environment (grid) Settings: To modify the GUI grid size in proportion to the communication range, you can adjust the physical dimensions of the simulation environment. For example, if you double the communication range of the sensors, you can double the size of the simulation environment to maintain the same proportion of communication range to physical distance. Keep in mind that the environment (grid) size is set at the beginning of the simulation.

Useful Links

1. NetSim IoT/WSN Overview: https://www.tetcos.com/iot-wsn.html