A popular question in simulation is how users can simulate the uplink from the low power radio to the high power tower. There are several methods to do this, presented here in order of complexity:

Transpose the power

This is the simplest method and involves taking the radio power output, for example 2 Watts, and using it at the tower location and height. This works because of the link reciprocity between A to B and B to A.

The antenna gains used don’t need to be changed so if the tower has a high gain antenna, leave that there.

Create an uplink/downlink colour key

Both directions can be simulated with a single calculation when you know the difference, in decibels, between the two link budgets. For our example we will use a 50W downlink with a 5W uplink.

Normally the difference is about 10-20dB which is considered a “balanced” repeater. Any higher, and distant radios will not be able to respond to calls.

	Power Watts	Power dBm
Downlink	50	47
Uplink	5	37

With a difference of 10dB, we can make a Signal-to-Noise colour key with a step size matching the difference in dB.

This colour will show the stronger downlink as red and the weaker uplink as amber. The separation between the two matches the computed difference.

Using SNR, an appropriate threshold of at least 5dB should be used along with the local noise floor.

If the noise floor is quiet this could be -110dBm otherwise use -90dBm if you are unsure.

Maximum Acceptable Path Loss

The Maximum Acceptable Path Loss is a more advanced method which considers a technology link budget with a threshold. For example, the uplink threshold may be different to the downlink.

To compute the MAPL. establish the ERP power output in dBm and then add it to the receiver threshold in dBm multiplied by -1 so -100 would be 100.

Using our 50W/5W example from earlier with a -100 receiver threshold would return an uplink MAPL of 147dB and a downlink 10dB lower at 157dB. These values can be used with a custom Path Loss (dB) colour key.