how many nRF24L01+ RF tranceivers in a network

[Jasper]

A friend of mine asked me to help with thinking about a solution to create a RF communication between 8 robots and 1 access point. Not a lot of traffic, just to signal that the robot is (almost) at the end of his track and get some control information. once per few minutes. This is not very complicated and I was thinking about the nRF24L01+ chip with external antenna. We need a range of approx. 100 - 150 meter. LOS

the complex part is the following: it is used in a field with solar panels, and we need about 4000 robots and 4000/8 = 500 access points.

So each access point with 8 robots is actually a small network. But because all of these networks are in the same field (not all of them are discoverable) I need to have multiple network ID's and unique ID's for each RF tranceiver, right?

Is this feasible with this amount of tranceivers?

Best regards,

Jasper

[Øyvind Karlsen]

Hi Jasper,

Are you concerned about noise between the different centrals? If you have a configuration that is something like this:(* is a robot and C is an access point)

* * * * * *
* C * * C *
* * * * * *
* * * * * *
* C * * C *
* * * * * *

Then the distance between robots that are transmitting different network ids and the closest access point with a different network id would be 200-300m based on the way I am reading your post.

To get a range of 100-150m reliably with the nRF24L01+ you will need to use a power amplifier(PA) or a low noise amplifier(LNA). Since you are able to control the effect that you transmit you will be able to tune your system so that you can "hear" a robot/access point that is within your 100-150m range, but not within the 200-300m range, i.e. the loss is so high for ranges over 200m that the robots appear to be invisible.

I might be interpreting your question incorrectly, please elaborate if so.

Best regards,

Øyvind

[Øyvind Karlsen]

I'm not sure that it would be a max of 24 robots, potentially you could suddenly see a lot longer range than expected and be able to see all 8 adjacent squares, however this is not necessarily a problem as the robots in your square will always have a higher RSSI than the ones from adjacent squares.

While the modules have a range of 100m described, this is almost always best-case scenario. You want an application that is robust to changing atmospheric conditions and other things that might cause path loss. What is going to happen to your robots if the range suddenly drops to 80m?

Another option is to look at antennas that have higher gain than a regular dipole, for instance since your robots are moving along a track you can have some mechanical contraption that moves a yagi antenna in a way so that it points towards the correct access point.