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10 gigabit Ethernet 80 GHz point-to-point bridges

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Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#61

Post by walrus01 »

wrigby wrote: post #57
walrus01 wrote: post #17

Earlier quoted context omitted.

terrestrial microwave engineer here: "80 GHz" is actually 71-86 GHz FDD. The original FCC band plan allowed for 5000 MHz wide channels each direction and basically OOK or BPSK level modulation. Newer radios use 250, 500 or 1000 MHZ wide FDD channels and QPSK or better. Incredibly wide channels can be used because it falls off in the atmosphere so rapidly after a few km, and the antennas are all very narrow parabolic…

Thanks for jumping in! Sounds like it's really nice for urban small-cell deployments, campus networks, etc. Do you experience a lot of issues with keeping links aligned at those tiny beamwidths?

Not really, 80 GHz is definitely difficult to aim, the very center of the beam is quite small. The mounts for the most popular antennas accommodate this and have very fine adjustments for the azimuth and elevation. Keeping them aligned long term? Not a problem as long as the mounts the radios are on (whether non penetrating or bolted to a wall/structure on a building roof) are done properly.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#62

Post by walrus01 »

Dwolb wrote: post #59
walrus01 wrote: post #20

Earlier quoted context omitted.

Most new licensed band 6, 11, 18, 23 GHz radios these days are 1024QAM capable. For 80 GHz the hot new thing is radios capable of 16/64/256QAM at varying code rates.

What's the limiting factor when designing to a constellation? Otherwise, what's improved about the chip or firmware to be able to move from 256QAM to 512QAM?

signal/noise ratio is a big one and RSL level. There are even 4096QAM radios now but they need a signal like -51 to operate at their full modulation. Otherwise they ACM down to 1024 (around -62), 256 and then 64QAM.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#63

Post by walrus01 »

ArkyBeagle wrote: post #56
walrus01 wrote: post #45

Earlier quoted context omitted.

That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band. It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical…

But it's something of an apparently completely different... phenotype from a small waveguide. The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?

The key part in physics is it's still a wave... And a singlemode fiber is a type of waveguide. A 120GHz signal is a wave, a 171 THz signal is a wave, the latter just has a much shorter wavelength.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#64

Post by nrs »

walrus01 wrote: post #61
wrigby wrote: post #57

Earlier quoted context omitted.

Thanks for jumping in! Sounds like it's really nice for urban small-cell deployments, campus networks, etc. Do you experience a lot of issues with keeping links aligned at those tiny beamwidths?

Not really, 80 GHz is definitely difficult to aim, the very center of the beam is quite small. The mounts for the most popular antennas accommodate this and have very fine adjustments for the azimuth and elevation. Keeping them aligned long term? Not a problem as long as the mounts the radios are on (whether non penetrating or bolted to a wall/structure on a building roof) are done properly.

I'm wondering how the natural motion of some taller buildings affects this kind of deployment.

Lots of buildings swing and twist in the normal course of the day. We found this out with some of the free space optical solutions available.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#68

Post by cm2187 »

wrigby wrote: post #15

It's interesting to see the huge channel bandwidths they're using to attain this. Advances like this are largely driven by higher sample rate ADCs and DACs becoming more viable in recent years. Edit for clarity: channel bandwidths in the datasheet are up to 2 GHz. Need to close the link at 32 QAM to hit 10 gb before error correction overhead at that bandwidth, which is certainly doable. Also, it's interesting to note…

What sort of latency would you expect with a system like this (I mean the link in this submission, not satellites)?

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#69

Post by kardos »

walrus01 wrote: post #9
nixisfun wrote: post #7

This would get really bad rain fade at 80GHz or even on a humid day the speed would back off a lot. You need to run a lower frequency backup link in parallel.

That's the nature of 80 GHz, design the links for your climate and don't try to go more than 2-3km. You can achieve five nines. And yes, run a 5.x GHz backup path in parallel.

> You can achieve five nines.

As long as nobody pilots a drone in the path.

Re: 10 gigabit Ethernet 80 GHz point-to-point bridges

#70

Post by Sanddancer »

ArkyBeagle wrote: post #56
walrus01 wrote: post #45

Earlier quoted context omitted.

That is true. One of the fun things illustrating first-hand how microwave/millimeter wave and fiber are the same thing is if you ever get to handle a 120 GHz band waveguide/feed. Some radar and military stuff operates in the 120 band. It's so incredibly tiny and narrow compared to a 11 or 18 GHz microwave waveguide. Then imagine continuing to make it narrower while increasing the frequency, follow that to its logical…

But it's something of an apparently completely different... phenotype from a small waveguide. The seemingly arbitrary 300Ghz line was probably more cultural than essential; the instrumentation was just very different. What's the analog for a prism for microwave?

300Ghz ends up with a wavelength of 1mm, so it more follows the pattern of bandwidth assignment, which likes nice round numbers given in wavelength.
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