Signal interference between multiple ROVs


#1

Hi

When we were building and testing 10 OpenROV 2.7 kits in Oslo last weekend we noticed several times that the digital feeds could get mixed up. It sounds absolutely crazy but you could see the video feed from an ROV that you weren't connected to via tether and sometimes even control it after a fashion, for a while. After ruling out wifi shenanigans we think that the tethers might be acting like antennas and the Tenda-adapter cards are finding the weak signal and tuning in on it.

When we were outside testing the completed ROVs the problems reoccurred and disturbed operation.

I think we can neutralize the confusing part of this problem by simply setting the different ROVs to different IP-numbers. That would make the cockpit-webserver-adresses unique for the different ROVs, ensuring that your computer only talks to and listens to the correct ROV. What this solution might NOT solve is that the Tenda-filters could be tuning in on the wrong signal. That could then result in lost contact with your tethered ROV, but at least you would know it! A possible workaround if that part of the problems persists could be trying to use the Pairing function on the Tenda-plugs, according to their manual that adds a encryption to the signal. But that functionality might be lost when we hack the boards. (http://www.tenda.cn/tendacn/DownLoads/show.aspx?downid=1127)

Please let us know if you have had similar experiences or ideas and I'll try to do some experiments with changing the IP next time we have an Oslo OpenROV meetup.

All thoughts are welcome :)

Happy Diving!


[solved] Connecting to wrong OpenROV unit?
#2

Hi Jakob:

Yes, we've seen the same issue here at OpenROV. There is definitely a problem if the tethers of two different ROVs get tangled- the RF signal from one ROV hops over to the other one.

We haven't spent a lot of time working on solutions to this, as we rarely drive multiple ROVs in the same area. Please keep us informed as to whatever solutions you find.

-W


#3

Hi Guys:

I think that if the problem is due, as it looks to be, to RF interference, IP changes will not solve it. Encryptation may allow for receiving the desired ROV only, but not for avoiding signal "noise".

In RF interference, signals are mixed in the tether(antenna), and sent to the receiver that cannot tell one ROV from another.

Standard solution is carrying the signals through a coaxial cable, but it is too heavy and stiff for the ROV.

Has anybody checked the tether data into an Oscilloscope ? Is there anykind of "carrier" signal/wave ? Changing this "carrier" frequency will avoid interference from entering the receiver.

From another point of view....

How far can a ROV interfere another ? :-) Or do tethers have to be in contact ?

Regards


Connecting to a different ROV?
#4

Hey guys,

So the way the homeplug works, it needs to be able to identify all of the adapters on the wire to work right. If two different homeplug networks are close to one another you do get the RF interference.

The way to work with multiple ROVs in the area is to gang all of the tethers to a single top-side box and then plug that in to a router that hands out IP addresses. The ROVs will all get separate IPs and your off to the races. Hint: If you do this, change the hostname on the ROV so that you can distinguish between them when looking at the DHCP assignments from the router.


#5

I think there is a significant risk that we overestimate the noise problem. It could turn out to be so easy that if we switch to different IPs or pair the tenda boards all problems dissappear. I think we are confusing the boards to tune in on the wrong signal by using the exact same setup cloned and in parallel. I hope to test this next oslo openrov meetup but I’ll be as happy if you beat me to it.