I'm trying to use a low power wifi connection to move about 20MB/sec of data between a instrument mounted on a rotating steel barrel about 20 inches in diameter and a stationary wifi unit. A low power solution would be nice but not critical. I'm looking to either buy a TP-Link - Archer AX20 AX1800 Dual-Band Wi-Fi 6 Router (https://www.bestbuy.com/site/tp-link-archer-ax20-ax1800-dual-band-wi-fi-6-router-black/6442841.p?skuId=6442841) on the stationary side with the 4 antenna spaced equally arounds the drum (the equipment is enclosed in a steel box) and a ESP32 or similar on the rotating part. It occurred to me that it may be better to have one receiver input and a 4 way splitter. Any advice would be appreciated.
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3$\begingroup$ Honestly, it sounds like just about anything would work fine. Have you tried something and run into problems with it, or are you asking before building? $\endgroup$– hobbs - KC2GMar 31 at 21:01
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1$\begingroup$ "low power wifi connection" and "about 20MB/sec" are not compatible, it won't be an ESP32! For that data rate you need a 400 Mbps PHY which means WiFi-5 or 6. Maybe a Mikrotik board with GbE and 2x2 MIMO. Antenna problems are the least of your worries, to test this just tape your phone to the rotating machine, turn it slowly and use an app like WiFiMan to plot signal strength, its probably fine all the way around. $\endgroup$– tomnexusApr 1 at 19:38
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$\begingroup$ @tomnexus Perhaps they mean only 20Mbps, iiuc that should be more easily doable? $\endgroup$– natevw - AF7TBApr 1 at 22:45
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2$\begingroup$ Note that the signal strength being good enough at every point during a slow rotation doesn't mean communication can work at high rotational speed, @tomnexus. After all, the channel that your WiFi device needs to equalize changes during a rotation - and considering the mechanical size of 50 cm, probably quite substantially. Wifi isn't optimized for dealing with Doppler nor with other kinds of rapidly changing channels, such as this strongly cyclostationary channel. Whether or not wifi is at all feasible for this hence depends on the rotational speed. $\endgroup$– Marcus MüllerApr 3 at 14:34
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1$\begingroup$ Thank you all, I'm trying to anticipate problems. I'll be building this in the next couple of weeks and will report back what worked. $\endgroup$– user3842718Apr 3 at 19:56
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1 Answer
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You definitely don't want to feed all 4 antennas to a single receiver input, since WiFi 6 is MIMO - Multiple Input Multiple Output. Each antenna actually carries a different signal so that the over all transmission is multiplexed in both code and space.
You are probably fine leaving the router just the way it is. At 5 GHz the signal is almost completely spread by multipath so that there is already little correlation from one antenna port to another. If you were to disconnect the antennas from the router and cable them to some other location, most likely all that you would be doing would be adding attenuation loss to the antenna-router path and lowering your available bit rate even further.
