Recommendation for LORA mesh network for a flood alarm system

[suyash93]

Hi Guys,

I am currently working on a flood alarm system with sensors that are spread across 7 kms along the river. One option I have is to connect the sensors with a GSM modem with 2G connection but the drawback is the reliability of a network provider since it is in a rural area.

I do not have any experience with pycom devices and hoping for recommendations to solve this issue using LORA mesh network with pymesh and lopy device.

[jcaron]

@suyash93 what region/country are you in? That dictates rules such as duty cycles, dwell times and so on, which in turn has a big influence over whether retransmissions are possible or not.

Another factor that comes into play if you are in a region with low airtime limits is the data rate/spread factor, but it’s probably difficult to estimate in advance whether you’ll be able to use the faster data rates (which mean less air time per transmission and thus less problems with retransmits) or if you have to use the slower ones (which have in theory better range, but the very long air time means hitting the limits quickly).

How far apart are the nodes? Do they have like of sight to each other? What kind of antenna are you planning to use? Are the nodes elevated above ground?

Also, in a mesh scenario, some nodes will have not only their own data but also their “children’s” data to send, which can quickly multiply.

Note that in some regions such as EU868, if you have to go down to SF12 (the slowest data rate), even just sending every 5 minutes without retransmits may quickly become an issue.

As far the reliability of PyMesh, I haven’t used it myself, others may have more to say.

[suyash93]

@jcaron Thank you for your suggestion.
All the nodes will be powered externally with a battery backup and solar chargers so I guess that would not be a problem.

The sensor & alarm nodes will be placed along side the river and ideally two router nodes will placed in reach of sensor nodes. The boarder router will be placed in the control room which will only be in reach of 2/3 router nodes. The sensors will send its status data at 5 min intervals and if any upstream sensor is triggered alarm data is sent and all the downstream alarms will turn on.

Can we guarantee delivery with this configuration of network or is it something inherent property that we cannot rely upon for emergency situation?

[jcaron]

@suyash93 the problem with mesh networks (and as far as I know Pymesh works like this) is that nodes acting as relays/routers/repeaters need to be constantly listening (like gateways), and this in turn means a relatively high power consumption, which means that devices solely battery operated will have a pretty short lifetime.

If you can bring external power (with batteries serving just as a backup if that goes down, though batteries would need to be carefully sized and regularly checked), then that could work.

You could also rely on a local power source such as solar panels, wind turbines, or even water-powered turbines, again coupled with batteries for the times there’s no sun/wind/current. Here again, appropriate sizing of the batteries for the worst case scenario is important.

Alternatively, depending on the layout, you could have all nodes transmitting directly to a single gateway (or a few of them).

Remember however that LoRa is really a best effort protocol on a shared ISM band with no guaranteed delivery. In some regions, there can be strong restrictions on how much data is sent and how often, which may limit or delay retransmits.

If the setup you are considering is life-critical, you need to take all of those into account.