We're making an open-source $30 GPS/mesh radio, would like advice

Re:We're making an open-source $30 GPS/mesh radio, would lik... by rapjr9 on Tuesday March 10, 2020 @08:31PM (#22541630)

Note that there are limits to how large a mesh network can scale, it's likely to start running into problems with several hundred users. You can scale larger by limiting data to short text messages, but you'll probably never be able to handle more than 10,000 users, unless you can find a way to create high bandwidth backbone links between clusters of users. There has been a lot of research on this in the wireless sensor network research community and in the WiFi mesh network research community also. A concert going crowd could easily cause a mesh network to become un-useably slow if everyone was trying to use it at the same time.

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by keithwinstein on Tuesday March 10, 2020 @09:24PM (#22542003)

That's true in practice with current radios, but it was a beautiful discovery in 2006 that it's not true in theory! In a world where radios are perfect and nodes cooperate to do decentralized beamforming, the capacity-per-node of a random mesh network scales as the number of nodes increases. See Ozgur, Leveque, and Tse, "Hierarchical Cooperation Achieves Optimal Capacity Scaling in Ad Hoc Networks," IEEE Trans. Info. Theory (2007) (https://arxiv.org/abs/cs/0611070).

(Also worth reading: Tim Shepard's Ph.D. dissertation from 1995 (http://groups.csail.mit.edu/ana/Publications/PubPDFs/Timothy...), which predates a lot of the "information theory" interest in this subject.)

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by rapjr9 on Wednesday March 11, 2020 @01:44AM (#22543321)

Interesting. I wonder how well it would work in practice though. They assume uniform randomly distributed nodes, whereas people don't tend to distribute themselves randomly. They don't address practical concerns either, like how narrow the MIMO beamwidths need to be and how easy that is to achieve. Still a nice theoretical result.

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by foobarian on Wednesday March 11, 2020 @11:01AM (#22546379)

This seems like it requires point-to-point communication; and with accurate MIMO configuration my intuition for the endpoints is that it's like they are communicating with laser-like narrow beams but in RF. But AFAIK multihop communication is still stuck at sqrt(n) scaling, i.e. not viable.

This is all pretty theoretical though, for a small number of nodes like up to 100 it should work pretty well like in the OP application.

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by deepnotderp on Tuesday March 10, 2020 @11:23PM (#22542678)

Is that paper using cooperative beamforming like pcells?

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by punkgeek on Tuesday March 10, 2020 @08:59PM (#22541861)

yes, this is targeted at hikers etc... so typical max mesh size of about 20 and I bet it would dying by the time a channel had 100 people.

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by sliken on Wednesday March 11, 2020 @05:07AM (#22544265)

Why? Even 200 in a small area, say a ski resort, mountain bike race, or similar seems perfectly reasonable. Sure not 200 people typing as fast as they can, but plenty for the normal chatter I hear over sms. Especially if you keep the messages short and have a latency of a few minutes be acceptable.

Using the family radios (often $30 ish) on hiking trails, parks, amusement parks, etc. I usually hear minimal chatter, just things like "Anyone seen Bob?", "meet at lift #4", "Lunch in 30m?", "Linda stopped to retie her shoes", etc.

Check out js8call if you want to see how to handle 100s of people with very little bandwidth. Sure it's designed for ham radio frequencies and covers 1000s of miles instead of 1000s of feet, but still man portable

A phone, bluetooth sound card, a HF transceiver, and an antenna is all you need. Generally hams are proud when they get better than 1000 miles per watt.

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by punkgeek on Wednesday March 11, 2020 @01:06PM (#22547506)

a channel in this case is a set of friends who are on one common preshared key (and a hopping set of frequencies). So each mesh only cares about (or even sees) packets on that mesh.

Lora is quite a slow bitrate protocol (but it has _great_ range and super low power needs). So we are focusing on our smaller use-case at first (in the interest of speed of development and stability for users)

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Re:We're making an open-source $30 GPS/mesh radio, would lik... by airbreather on Friday March 13, 2020 @01:55AM (#22565083)

I have looked into this in some detail doing deployment studies for wireless HART instruments (industrial processing plant gear) which can talk to a base station or store and forward for a friend.

So depending whether you want broadcast or point to point, or in between, performance is dominated by "pinch points" which is such an obvious term that I wont describe it.

This means that a groups situation in this context could be dramatically improved by a unit or two in a balloon or drone above the group or similar.

I suspect in practice when deployed and medium sized groups use these that a "signals master" or two will have primary responsibiliy to maintain such nodes to keep effective comms up and might use kites, balloons, drones, terrain, whatever and a particular set of skills and equipment would develop.

Also, if any given unit can impose a "cost" relative to business, amount of battery used etc then self levelling and incentive to be terser with messaging can occur. Lets face it, when you are down to 3 bits a second the use of emoticons will drop off pretty quickly.

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