Choosing protocol for a low power mesh network

[Jonathan E]

Hi!

I am working on creating a Low Power mesh network and am trying to decide which communication protocol I should use with the NRF52840. There are no nodes in the network that have the capacity to have the radio powered on all the time, except one gateway. I have read the other topics on choosing the protocol for mesh networks, but they don't match my exact use case.

Description of the sensor network:

 - There can be hundreds of nodes

 - The nodes can be spread across a big area (Let's say there is a maximum hop distance of 5 nodes from the gateway)

 - The sensory data is simple and is only required to be transmitted once every hour. (Although even lower rates can be accepted, like once every day)

 - The nodes battery capacity is equivalent to roughly 3000 mWh but should last for an extended period (i.e. 5 years).

 - there is one central gateway used to connect the nodes to the internet with unlimited power

 - I plan on using the NRF52840 for the nodes and a Thingy:91 as the gateway for now

 - The nodes should be easy to commission

 - It should be compatible with the nrf connect sdk

Does any communication protocol matching this use case exist? Energy harvesting methods can also be considered if it is required to create this mesh network.

Thanks for your help in advance!

[Joakim Jakobsen]

Hi. 

Thank you for your question. 

In general the Mesh protocols are depending on having a mains powered core network. Where the nodes are able to stay in RX mode for longer periods of time, relaying messages throughout the network. 

There is not problem adding low power end nodes that will have some parent/friend feature with a connected node. 
It's not possible at all for your solution to have more than the central gateway not operating on battery power?

Br, 
Joakim

[Jonathan E]

Joakim Jakobsen said:

central

Unfortunately, it is hard to have nodes that don't operate without a battery as it is intended to be used for an outdoor application... However, it is possible to increase the battery capacity on the nodes.

As a last resort, I am thinking of implementing my own type of mesh network based on BLE where the nodes synchronize when they should wake up and transmit/receive data. I am guessing that the battery capacity is large enough to let the radio stay on for at least some minutes each day. This can possibly be done with the existing mesh protocols as well, but they might require too much time to create the network each time they are turned on.

Another option might be to have a few nodes with extra large capacity and large solar panels, but this is also not optimal as it increases the complexity of the system.

[Joakim Jakobsen]

Thanks. 

Jonathan E said:

As a last resort, I am thinking of implementing my own type of mesh network

This might be a way to go here. 

_________

BLE Mesh was mainly designed for networks without the concern of power consumption (light control etc.). You can add low power nodes and battery operated devices, but they will need a friend to cache messages for the LPN etc. And it still have to follow given "rules" in order to adhere to the security features like key refresh procedures etc.
So low power devices will rely on having a "main network" that can stay in RX mode most of the time. As BLE mesh uses managed flooding for the communication it needs some devices that can stay in RX mode, listening for packets and relaying them further through the network. 

I'm not too familiar with Zigbee or Thread, if that is something you could be interested in? If so, I can ask someone with more experience on those protocols and check wether there are some more suitable solutions?

Br, 
Joakim

[Jonathan E]

It would be very helpful to get some input on Zigbee and Thread!

The nodes are static (Will not change location) once they have been set up, so the network will not change between each wakeup. Maybe it is possible to save the network state so that the time it takes to build the network at each wakeup is reduced?

[Joakim Jakobsen]

Thanks. 

I'll do some research on Thread/Zigbee.

I might not be able to get back to you until early next week. Hopefully that is ok. 

Br, 
Joakim